JP2008042096A - Optical amplifier and light transmission system - Google Patents

Abstract

[PROBLEMS] To eliminate the gain tilt due to stimulated Raman scattering or suppress the occurrence of such a gain tilt according to the number of multiplexed wavelengths of signal light while realizing a reduction in manufacturing cost and an increase in processing speed. To do.
An input based on first transmission signal light intensity information, which is information of transmission light intensity to an input transmission path 3 of an upstream device 2a, and input signal light intensity detected by a first detection unit 13. A gain tilt calculation unit 20a that calculates the gain tilt of the signal light due to stimulated Raman scattering in the transmission line 3, an optical amplification unit 40 that amplifies the input signal light, and a control that controls the output intensity based on the calculated gain tilt. A part 30a is provided.
[Selection] Figure 1

Description

  The present invention relates to an optical amplifier and an optical transmission system suitable for use in a wavelength division multiplexing (WDM) transmission system, and further to an optical amplifier and an optical suitable for use in performing relay amplification in a wavelength multiplexing transmission system. It relates to a transmission system.

In recent years, information demand has increased dramatically, and trunk-system optical transmission systems that gather information capacity are required to have a larger capacity and to form a flexible network.
A wavelength division multiplexing (WDM) transmission scheme (wavelength multiplexing transmission system) is one of the most effective schemes for such demands on the trunk optical transmission system.

In wavelength division multiplexing, an amplifier that performs optical amplification with an optical fiber doped with rare earth elements, such as an erbium-doped fiber amplifier (EDFA), wavelength-multiplexed using a wide gain band. It is a key component for realizing a wavelength division multiplexing transmission system because it can amplify light collectively.
By the way, in the wavelength multiplexing transmission system, when signal light wavelength-multiplexed in a wide band propagates through a transmission line (optical fiber), the intensity (power) of the signal light is input (output) to the transmission line as shown in FIG. ) Is the same for all wavelengths, as shown in FIG. 22, the signal light output from the transmission line has a gain slope (SRS (Stimulated Raman Scattering) slope due to stimulated Raman scattering) according to the wavelength; Occurs). This SRS tilt is generated when a short wavelength signal behaves as excitation light of a long wavelength signal due to the SRS effect generated in the transmission path, and as a result, the gain increases toward the long wavelength side. Note that a two-dot chain line Y in FIG. 22 indicates the output intensity of the signal light when no SRS inclination occurs.

  This SRS inclination changes with a change in the number of signal wavelengths of the signal light. For example, when the signal light having 44 waves in the C-band is only one wave having the shortest wavelength, FIG. When 44 waves exist as shown in a), the SRS slope is generated in the output from the transmission line, but when the signal light is only one wave of the shortest wavelength as shown in FIG. Since the SRS inclination is eliminated, the output intensity (output level) of the one wave is substantially the same as the transmission intensity to the transmission line. That is, the output intensity of one wave increases rapidly from the intensity Z1 when the SRS inclination occurs as shown in FIG. 23 (a) to the intensity Z2 when the SRS inclination does not occur as shown in FIG. 23 (b) according to the SRS inclination. To do.

  On the other hand, when the signal light having 44 waves in the C-band is only one wave having the longest wavelength, when 44 waves are present as shown in FIG. Although the SRS inclination has occurred, as shown in FIG. 24B, when the signal light is only one wave of the longest wavelength, the SRS inclination disappears, so that the output intensity (output level) of the one wave is reduced to the transmission line. It is almost the same as the sending intensity. That is, the output intensity of one wave sharply decreases according to the SRS inclination from the intensity Z3 when the SRS inclination shown in FIG. 24 (a) to the intensity Z4 when the SRS inclination does not occur shown in FIG. 24 (b). To do.

Such a level deviation between wavelengths or an OSNR (Optical Signal Noise Ratio) deviation due to SRS tilt, or a level change or OSNR change due to an SRS change causes waveform distortion or a reception error in the receiver. In order to perform this, it should be suppressed so as not to generate an SRS slope.
Therefore, conventionally, the SRS tilt amount to be corrected is determined by directly observing the spectrum of the signal light using a spectrum analyzer, and the output intensity to the transmission line is changed based on the determined SRS tilt amount. There is a technique for suppressing the occurrence of SRS inclination (see, for example, Patent Document 1 below).
JP 2000-277834 A

However, since the spectrum analyzer directly observes the spectrum of the signal light, it cannot expect high processing speed. Furthermore, since a spectrum analyzer is very expensive, the use of a spectrum analyzer increases the manufacturing cost of the optical amplifier.
It should be noted that in determining the SRS inclination amount, in order to realize a reduction in manufacturing cost and an increase in processing speed, it is conceivable to set an SRS inclination amount according to the transmission path in advance. It is conceivable to set the SRS inclination amount when the number of multiplexed wavelengths of light is the maximum wave number.

However, if the SRS tilt amount is set in advance when the number of multiplexed wavelengths is a predetermined number (here, the maximum number of waves), it is not possible to cope with a case where the SRS tilt changes with a change in the number of multiplexed wavelengths of signal light. .
In particular, in a transmission system having a long transmission distance and performing multi-stage relay amplification, when the number of multiplexed wavelengths of signal light changes and an error occurs between the actual SRS tilt amount and the preset SRS tilt amount, The effect will be large, and accurate and high-quality transmission will not be realized.

  The present invention has been devised in view of such a problem, and realizes gain tilt (SRS) due to stimulated Raman scattering according to the number of multiplexed wavelengths of signal light while realizing low manufacturing cost and high processing speed. It is an object of the present invention to provide an optical amplifier and an optical transmission system that can eliminate (tilt) or suppress the occurrence of such gain tilt.

  In order to achieve the above object, an optical amplifier according to the present invention includes a first detector that detects the intensity of input signal light input from an upstream device through an input transmission path, and the input transmission path of the upstream device. A gain tilt calculation unit that calculates a gain tilt of signal light due to stimulated Raman scattering in the input transmission path based on the first send signal light intensity information that is information on the send light intensity of the input signal and the input signal light intensity; An optical amplification unit that amplifies the input signal light and a control unit that controls output intensity based on the calculated gain gradient are provided (claim 1).

  In order to achieve the above object, an optical amplifier according to the present invention includes a first detector that detects an input signal light intensity input from an upstream device through an input transmission line, and the input transmission line of the upstream device. A gain tilt calculation unit for calculating a gain tilt of the signal light due to stimulated Raman scattering in the input transmission line based on the first send signal light intensity information which is information of the send light intensity to the light source and the input signal light intensity; And a controller that controls the output intensity by adjusting the excitation light intensity for Raman amplification to the input transmission line based on the calculated gain slope. (Claim 2).

  In order to achieve the above object, an optical amplifier according to the present invention is connected to an upstream device via an input transmission line and connected to a downstream device via an output transmission line, An optical amplifying unit that amplifies and outputs the signal light input through the input transmission path, and an intensity of light transmitted to the output transmission path of the signal light output from the optical amplifying section (hereinafter referred to as a second transmission signal). A third detector that detects the light intensity), signal light output intensity information that is information on the output intensity of the signal light output from the output transmission path, and the second detected by the third detector. Based on the transmitted signal light intensity, a gain tilt calculation unit that calculates a gain tilt of the signal light due to stimulated Raman scattering in the output transmission line, and based on the gain tilt calculated by the gain tilt calculation unit, the light Output from the amplifier It is characterized by being configured to include a control unit for controlling the second sending signal light intensity of the signal light (claim 3).

  In order to achieve the above object, an optical amplifier according to the present invention is connected to an upstream device via an input transmission line and connected to a downstream device via an output transmission line, A signal that is information on the output intensity of the signal light output from the output transmission path, and a third detection unit that detects the intensity of light transmitted to the output transmission path (hereinafter referred to as second transmission signal light intensity). A gain tilt calculation unit that calculates a gain tilt of signal light due to stimulated Raman scattering in the output transmission path based on light output intensity information and the second transmission signal light intensity detected by the third detection unit; Based on the gain slope calculated by the gain slope calculating section, the intensity of the pumping light for Raman amplification to the output transmission path is adjusted, whereby the signal light output from the output transmission path is adjusted. 2 sending It is characterized in that and a control unit for controlling the issue light intensity (claim 4).

  In order to achieve the above object, an optical transmission system according to the present invention is connected to an optical amplifier interposed between an input transmission path and an output transmission path, and to the optical amplifier via the input transmission path. An upstream device, and the upstream device transmits a signal light to the optical amplifier via the input transmission path, and at least the signal to the optical amplifier via the input transmission path. A first OSC optical transmission unit that transmits first OSC (Optical Supervisory Channel) light including first transmission signal light intensity information, which is information on the intensity of light transmitted to the input transmission path, and the optical amplifier includes: A first detector that detects the intensity of the input signal light input from the upstream device through the input transmission path; and a first transmission signal light intensity that is information of the transmitted light intensity of the upstream apparatus to the input transmission path. Information and the input signal light Based on the degree of gain, a gain tilt calculation unit that calculates the gain tilt of the signal light due to stimulated Raman scattering in the input transmission line, an optical amplification unit that amplifies the input signal light, and the calculated gain tilt And a control unit for controlling the output intensity of the signal light output to the output transmission path (Claim 5).

  As described above, according to the present invention, the gain tilt calculation unit is configured to generate a signal due to stimulated Raman scattering in the input transmission line based on the first transmission signal light intensity information and the input signal light intensity detected by the first detection unit. The controller calculates the gain slope of the light, and the control unit controls the output intensity of the signal light output to the output transmission path based on the gain slope calculated by the gain tilt calculator. Thus, the output intensity of the signal light can be controlled to be the same (substantially equivalent) intensity at all wavelengths, so that the stimulated Raman according to the number of multiplexed wavelengths of the signal light generated in the input transmission path can be achieved. The gain inclination due to scattering can be eliminated (claims 1, 2, 5).

At this time, unlike the prior art, the gain inclination calculation unit calculates the gain inclination by calculation without newly adding expensive parts such as a spectrum analyzer, so that the manufacturing cost can be reduced ( Claims 1, 2, 5).
In addition, since the gain tilt calculation unit calculates the gain tilt by calculation without directly observing the spectrum of the signal light like a spectrum analyzer, the gain tilt of the signal light input via the input transmission path is extremely short. It can be acquired in time, and the processing speed can be increased (claims 1, 2, 5).

  Further, according to the present invention, the gain tilt calculation unit is configured to generate the signal light due to stimulated Raman scattering in the output transmission line based on the signal light output intensity information and the second transmission signal light intensity detected by the third detection unit. The control unit calculates the gain tilt, and the control unit controls the second transmission signal light intensity of the signal light output to the output transmission path based on the gain tilt calculated by the gain tilt calculation unit. Stimulated Raman scattering according to the number of multiplexed wavelengths of signal light in the output transmission path is controlled by controlling the intensity of the second transmission signal light to have an inverse gain tilt so that no gain tilt occurs in the signal light output from the path. It is possible to artificially suppress the occurrence of the gain tilt due to (Claims 3 and 4).

At this time, unlike the prior art, the gain inclination calculation unit calculates the gain inclination by calculation without newly adding expensive parts such as a spectrum analyzer, so that the manufacturing cost can be reduced ( Claims 3 and 4).
In addition, the gain tilt calculation unit calculates the gain tilt by calculation without directly observing the spectrum of the signal light like a spectrum analyzer, so the gain tilt of the signal light output from the output transmission path can be reduced in a very short time. Can be obtained, and the processing speed can be increased (claims 3 and 4).

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[1] First Embodiment of the Present Invention First, the configuration of an optical transmission system 1a as a first embodiment of the present invention will be described with reference to the block diagram shown in FIG.
As shown in FIG. 1, the present optical transmission system (wavelength division multiplexing (WDM) transmission system) 1a includes a front-stage apparatus (upstream apparatus) 2a, an input transmission path 3, an output transmission path 4, and a rear-stage apparatus ( Downstream apparatus) 5a and an optical amplifier 10a. Note that the block arrows 6 and 7 in FIG. 1 indicate the traveling directions of the wavelength-multiplexed signal light, respectively.

The pre-stage device 2a is, for example, an optical amplifier as a transmitter that is the starting end of the optical transmission system 1a or a relay device similar to the optical amplifier 10a, and is upstream of the optical amplifier 10a (that is, the optical propagation direction with respect to the optical amplifier 10a). The signal light is transmitted to the optical amplifier 10 a through the input transmission path 3.
The pre-stage device 2a includes a signal light transmitter (first signal light transmitter) 2a-1 that transmits the signal light to the optical amplifier 10a via the input transmission path 3, and an OSC (Optical) different from the signal light. An OSC optical transmission unit (first OSC optical transmission unit) 2a-2 that transmits supervisory channel (first OSC light) to the optical amplifier 10a via the input transmission path 3 is provided.

When the upstream device 2a is a transmitter, the signal light transmitter 2a-1 generates wavelength-multiplexed signal light (for example, C-band 44 waves) and outputs the signal light to the input transmission path 3.
Also, the OSC optical transmission unit (first OSC optical transmission unit) 2a-2 transmits the transmission intensity of the signal light to the input transmission path 3 via the input transmission path 3 (transmission power, first transmission signal light intensity information; The OSC light including the transmission signal light intensity) is transmitted to the optical amplifier 10a.

Further, the OSC light transmission unit 2a-2 adds the transmission intensity of the OSC light itself to the input transmission path 3 in addition to the transmission signal light intensity (first OSC light transmission intensity information; hereinafter simply referred to as OSC light). The output intensity is also included as information and output to the optical amplifier 10a.
As described above, the upstream device 2a transmits the transmission signal light intensity and the OSC light transmission intensity to the optical amplifier 10a via the OSC.

The input transmission path 3 is a transmission path (optical fiber) for transmitting the signal light and the OSC light transmitted from the pre-stage device 2a to the optical amplifier 10a.
The output transmission path 4 is a transmission path (optical fiber) for transmitting the signal light output from the optical amplifier 10a to the downstream apparatus 5a on the downstream side.
The post-stage device 5a is disposed on the downstream side of the optical amplifier 10a (that is, downstream in the light propagation direction with respect to the optical amplifier 10a), and receives the signal light transmitted from the optical amplifier 10a through the output transmission path 4. For example, it is an optical amplifier as a receiver that is the terminal of the optical transmission system 1a or a relay device similar to the optical amplifier 10a.

  The optical amplifier 10a is interposed between the input transmission path 3 and the output transmission path 4, receives the signal light and the OSC light from the upstream device 2a via the input transmission path 3, and amplifies the received signal light. The first coupler 11, the second coupler 12, the monitor (first detection unit) 13, the SRS (Stimulated Raman Scattering) slope calculation unit (gain slope calculation unit). 20a, a reverse tilt control unit (control unit) 30a, and an optical amplification unit 40.

The first coupler 11 branches the OSC light out of the signal light and the OSC light input via the input transmission path 3 and inputs them to the SRS inclination calculation unit 20a.
The second coupler 12 is partly branched to a monitor 13 for signal light input via the input transmission path 3.
The monitor 13 detects the input intensity of the signal light input through the input transmission path 3 (hereinafter referred to as input signal light intensity) and notifies the detected input signal light intensity to the SRS inclination calculation unit 20a. Yes, for example, a photodiode (PD: PhotoDiode) is provided.

  Based on the OSC light received from the front-stage apparatus 2a via the input transmission path 3, the SRS inclination calculation unit 20a transmits the signal light received from the front-stage apparatus 2a via the input transmission path 3 to the input transmission path 3 as well. The light intensity (send signal light intensity) is acquired, and based on the acquired send signal light intensity and the input signal light intensity detected by the monitor 13, the signal light due to stimulated Raman scattering (SRS) in the input transmission line 3 is obtained. The gain inclination (SRS inclination; SRS inclination amount) is calculated, and specifically includes an OSC light detection unit 21a, a loss coefficient calculation unit 24a, and an inclination amount calculation unit 25a.

The OSC light detection unit 21a detects the OSC light input via the input transmission path 3 and branched by the first coupler 11, and includes an acquisition unit (first acquisition unit) 22a and an OSC light input intensity detection unit. (Second detection unit) 23a is provided.
When the acquisition unit 22a receives the OSC light input via the input transmission path 3 and branched by the first coupler 11, the acquisition unit 22a acquires the transmission signal light intensity included in the OSC light as information based on the received OSC light. In addition, the OSC light transmission intensity related to the OSC light included as information in the OSC light is acquired.

When the OSC light input intensity detector 23a receives the OSC light input via the input transmission path 3 and branched by the first coupler 11, the input intensity of the received OSC light (first OSC light input intensity; hereinafter simply referred to as “OSC light input intensity”). OSC light input intensity), for example, comprising a photodiode.
The loss coefficient calculation unit 24a calculates a loss coefficient (transmission path loss coefficient) applied to the signal light of the input transmission path 3, and when the distance of the input transmission path 3 is unknown (for example, at the time of initial setting). Calculates the distance L (km) of the input transmission path 3 based on the formula (1) described later, and based on the calculated distance L, the loss coefficient αsig ( dB / km) is calculated.

Further, when the distance L of the input transmission path 3 is known (for example, during normal operation after the initial setting), the loss coefficient calculation unit 24a directly calculates the loss coefficient αsig based on Expression (2) described later. To do.
Specifically, the loss coefficient calculation unit 24a determines the difference between the input signal light intensity detected by the monitor 13 and the transmission signal light intensity acquired by the acquisition unit 22a, that is, the input transmission line loss Lsig ( dB), and the difference between the OSC light transmission intensity acquired by the acquisition unit 22a and the OSC light input intensity detected by the OSC light input intensity detection unit 23a, that is, the transmission path in the OSC light input transmission path 3 Loss (hereinafter simply referred to as input transmission line loss) Losc (dB) is obtained.

If there are optical components (here, the first coupler 11 and the second coupler 12) between the front-stage apparatus 2a and the optical amplifier 10a or between the front-stage apparatus 2a and the SRS inclination calculating unit 20a, It is preferable to subtract the loss of the optical component in advance.
Then, the loss coefficient calculation unit 24a, together with the input transmission line loss Lsig (dB) of the signal light and the input transmission line loss Losc (dB) of the OSC light, the difference Ldif (dB / km) of the loss coefficient of the OSC light and the signal light ) To calculate the loss factor.

Here, the loss coefficient wavelength characteristics of the transmission path (input transmission path 3 and output transmission path 4) are as shown in FIGS. 2A and 2B, the fiber type of the transmission path (here, FIG. 2A). Is translated according to the transmission path distance while maintaining a predetermined shape determined by SMF (Single Mode Fiber) and FIG. 2B by DSF (Dispersion Shifted Fiber).
As shown in FIG. 2A, the loss coefficients at the same signal wavelength of the fibers 3a, 3b, and 3c of which the fiber type is SMF are different, but the loss coefficient wavelength characteristic (curve 3a) corresponding to the change of the signal wavelength. ', 3b', 3c ') indicate the same shape.

Further, as shown in FIG. 2B, the loss coefficients at the same signal wavelength of the fibers 3d, 3e, and 3f of which the fiber type is DSF are different, but the loss coefficient wavelength characteristic (curve) according to the change of the signal wavelength. 3d ′, 3e ′, 3f ′) indicate the same shape.
Therefore, the loss factor calculation unit 24a holds the loss factor wavelength characteristic profile of the fiber type corresponding to the input transmission path 3 in a storage area (not shown), and the loss factor calculation unit 24a has the loss factor wavelength characteristic profile. Based on the above, the difference Ldif of the loss coefficient between the OSC light and the signal light according to the wavelength of the signal light and the wavelength of the OSC light is calculated.

Then, the loss coefficient calculation unit 24a calculates the transmission path distance L of the input transmission path 3 based on the following formula (1).
L = | Losc−Lsig | / Ldif (1)
Here, the reason why the transmission path distance L is calculated by the above equation (1) will be described. First, as shown in FIG. 3, the loss Losc of the OSC light in the transmission path is the loss coefficient (slope) αosc of the OSC light and The transmission path distance L can be expressed by the following formula (1a).

Losc = αosc × L (1a)
Further, as shown in FIG. 3, the loss Lsig of the signal light in the transmission path can be expressed by the following formula (1b) by the loss factor (slope) αsig of the signal light and the transmission path distance L.
Lsig = αsig × L (1b)
As shown in FIG. 3, the difference between the loss Losc of the OSC light and the loss Lsig of the signal light (see the double arrow V in the figure) is expressed by the following equation (1c) according to the loss coefficient difference Ldif and the transmission path distance L: Can be expressed as

Losc−Lsig = (αosc−αsig) × L = Ldif × L (1c)
Then, the equation (1) can be obtained by solving the equation (1c) for the transmission line distance L.
Here, since the difference Ldif of the loss coefficient between the OSC light and the signal light is a constant determined according to the fiber type as described above with reference to FIG. 2, the loss coefficient calculation unit 24 a The transmission line distance L can be calculated based on the above formula (1) by determining the difference Ldif of the loss coefficient in accordance with the loss coefficient wavelength characteristic profile held in advance.

Finally, the loss coefficient calculation unit 24a calculates the loss coefficient αsig applied to the signal light of the input transmission path 3 based on the following equation (2).
αsig = Lsig / L (2)
When the transmission line distance L of the input transmission line 3 is known, the loss coefficient calculation unit 24a, for example, during normal operation after obtaining the transmission line distance L at the initial setting, the transmission calculated at the initial setting. Based on the path distance L and the difference between the input signal light intensity detected by the monitor 13 and the transmission signal light intensity acquired by the acquisition unit 22a (that is, the input transmission line loss Lsig of the signal light), the above formula ( 2), the loss coefficient αsig applied to the signal light of the input transmission path 3 is calculated.

Based on the loss coefficient αsig of the input transmission path 3 calculated by the loss coefficient calculation unit 24a, the tilt amount calculation unit 25a calculates a tilt amount (SRS tilt amount) Stilt as a gain tilt according to Equation (4) described later. .
By the way, the SRS inclination amount increases in accordance with the total intensity of light input to the transmission path (here, the input transmission path 3). For example, as shown in FIG. 4, three SMFs 8a to 8c having different loss coefficients αsig when the input C-band 44 wave signal light is 1550 (nm) will be described as an example. When the signal light of C-band 44 waves is 1550 (nm), the loss coefficient αsig of the transmission line 8a (see the solid line 8a ′ in the figure) is 0.195 (dB), and the transmission line 8b (in the figure) The loss coefficient αsig of the broken line 8b ′) is 0.24 (dB), and the loss coefficient αsig of the transmission line 8c (see the dotted line 8c ′ in the drawing) is 0.33 (dB).

Here, as shown by straight lines 8a 'to 8c' in FIG. 4, when the input intensity (transmission path input total intensity (mW)) changes, the SRS slope in each of the transmission paths 8a to 8c in the C-band band. Each quantity (SRS slope αsig band (dB)) increases linearly with respect to the input intensity.
The slope a (dB / km) varies depending on the loss coefficient αsig and can be expressed by a quadratic expression of the loss coefficient αsig as shown in the following expression (3).

a = A * αsig ^ 2 + B * αsig + C (3)
However, A, B, and C are constants. In the input transmission path 3, A is “1.305E-1”, B is “1.041E-1”, and C is “2.744E-2”. Become.
These constants A, B, and C change according to the fiber type, and are determined according to the fiber type.

Therefore, the inclination amount calculation unit 25a holds constants A to C in advance in a storage area (not shown) according to the fiber type of the input transmission path 3, and the constants A to C and the loss coefficient calculation unit 24a Based on the calculated loss coefficient αsig, the slope a is first calculated by the above equation (3).
As described above, the inclination amount calculation unit 25a pays attention to the proportional relationship between the total input intensity to the transmission line and the SRS inclination amount, and the SRS inclination amount from the input total intensity to the transmission line regardless of the number of multiplexed wavelengths of signal light. Is calculated.

Then, the inclination amount calculation unit 25a uses the inclination a obtained by the above equation (3) and the transmission signal light intensity Pin (mW) detected by the acquisition unit 22a of the OSC light detection unit 21a of the SRS inclination calculation unit 20a. Based on the following equation (4), the SRS inclination amount Still is calculated.
Still = a * Pin (4)
In addition, the inclination amount calculation unit 25a calculates the SRS inclination amount Still based on the above equation (4) particularly during the initial setting of the optical transmission system 1a. However, during normal operation after the initial setting, the equation (5) described later is used. ) To calculate the SRS inclination amount Still ′.

  That is, in this optical transmission system 1a, the increase or decrease of the number of signal wavelengths (the number of multiplexed wavelengths) in operation (during normal operation) is not necessarily executed with a notice (for example, from the previous apparatus 2a). In most cases, the OSC light is used (without being notified of changes in the number of wavelengths). At this time, although the SRS inclination amount also changes with the change in the number of signal wavelengths, in order to quickly determine the changed SRS inclination amount Still ′, by the acquisition unit 22a of the OSC light detection unit 21a of the SRS inclination calculation unit 20a. A change (difference) in the input signal light intensity monitored by the monitor 13 at its own stage without waiting for the acquisition of the transmission signal light intensity Pin ′ notified late using the OSC light is changed in the transmission signal light intensity. (Difference) By considering it as dPin, the SRS inclination amount Still ′ after the change is calculated by the following equation (5).

Still '= a * Pin' = a * (Pin + dPin) (5)
The reverse inclination control unit 30a controls the output intensity of the signal light output to the output transmission path 4 based on the gain inclination calculated by the SRS inclination calculation unit 20a, and is calculated by the SRS inclination calculation unit 20a. A reverse slope calculation unit 31 for calculating a reverse gain slope with respect to the gain slope is provided. Note that the reverse gain tilt refers to the tilt of the wavelength characteristic of the gain to be given in order to flatten the gain wavelength characteristic of the signal light having the gain tilt as calculated by the SRS tilt calculating unit 20a.

As shown in FIG. 5, when the SRS inclination of the signal light input via the input transmission path 3, that is, the SRS inclination of the signal light calculated by the SRS inclination calculating unit 20a is indicated by a solid line x, The reverse slope calculation unit 31 calculates a reverse gain slope (reverse SRS slope) indicated by a broken line y that is inversely proportional to the solid line x.
Then, the reverse tilt control unit 30a controls the optical amplification unit 40 that amplifies the output intensity of the signal light to the output transmission path 4 (hereinafter referred to as signal light output intensity), and is output from the optical amplifier 10a for output transmission. The signal light output intensity sent to the path 4 is adjusted based on the inverse gain slope indicated by the broken line y.

Thus, even if the signal light amplified by the optical amplifier 10a and transmitted (output) to the output transmission path 4 is received via the input transmission path 3, it has two points in FIG. As indicated by the chain line z, the signal can be amplified so that the intensity is substantially equalized at all wavelengths.
As described above, the optical amplifying unit 40 amplifies the intensity (power) of the signal light to be output (transmitted), is controlled by the reverse inclination control unit 30a, and is calculated by the SRS inclination calculation unit 20a. In this case, a reverse inclination of the above is generated.

Here, a more specific configuration of the reverse tilt control unit 30a and the optical amplification unit 40 will be described. In the present invention (the first embodiment and the second embodiment described later), the reverse tilt control unit 30a and the optical amplification unit are provided. The specific configuration of 40 is not limited to a specific configuration, and can be configured as shown in the following (1) to (3), for example.
(1) First, as shown in FIG. 6, as indicated by reference numeral 30-1, the reverse tilt control unit 30 a includes a first coupler 43 a, a second coupler 43 b, a third coupler 43 c, a fourth coupler 43 d, a first PD 44 a, and a second PD 44 b. , Third PD 44c, fourth PD 44d, first excitation light source (denoted as first LD (Laser Diode) in the figure) 45a, second excitation light source (denoted as second LD in the figure) 45b, first beam splitter 46a, second beam The optical amplifier 40 includes a splitter 46b and a controller 48a. As indicated by reference numeral 40-1, the optical amplifier 40 includes a first EDF (Erbium-Doped Fiber) 41a, a second EDF 41b, and a VOA (Variable Optical Attenuator). ) 42 and a gain equalizer (indicated as GEQ (Gain EQualizer) in the figure) 47 will be described.

At this time, in the optical amplification unit 40-1, the VOA 42 is interposed between the first EDF 41a and the second EDF 41b, and the inverse gain inclination control unit 30-1 adjusts the gain of the first EDF 41a and the second EDF 41b and the attenuation amount of the VOA 42. By doing so, the gain inclination of the output intensity of the signal light is adjusted.
The control unit 48a of the reverse gain tilt control unit 30-1 calculates the reverse gain tilt amount described above as the reverse tilt calculation unit 31, and holds it as a total gain (denoted as “Total Gain” in the figure). .

As shown by solid lines m1 to m3 in FIGS. 7A to 7C, the reverse tilt control unit 30-1 is configured to realize a flat output while ensuring an amplifier gain in the optical amplification unit 40-1. The VOA 42 is further controlled to adjust the gain of the light that has been gain equalized by the gain equalizer 47 while controlling the gain of the first EDF 41a and the second EDF 41b to be constant.
Here, in the reverse inclination control unit 30-1, the gain of the optical amplification unit 40-1 as a whole becomes a target value while appropriately increasing or decreasing the gains of the first EDF 41a and the second EDF 41b that are kept constant in the control unit 48a. , Control the loss of the VOA 42. As a result, as shown by broken lines n1 to n3 in FIGS. 7A to 7C, a right-sloped inclination (that is, the gain on the short wavelength side becomes higher) is created, or in FIGS. 7A to 7C. As shown by the two-dot chain lines o1 to o3, it is possible to create a slope that rises to the right (that is, the gain on the long wavelength side increases).

  As described above, the inverse tilt control unit 30-1 adjusts the gain slope of the signal light from the optical amplifying unit 40-1 by adjusting the two-stage EDF gain of the first EDF 41a and the second EDF 41b and the attenuation amount of the VOA 42. It can be amplified to a desired value.

  (2) Next, as shown in FIG. 8, the reverse inclination control unit 30a is configured as indicated by reference numeral 30-2, and at least one (here, two) as the optical amplifying part 40 is indicated by reference numeral 40-2. The first EDF 41a and the second EDF 41b and a variable gain equalizer 47 'are provided, and the gain gradient of the output intensity of the signal light is adjusted by the variable gain equalizer 47'.

That is, the optical amplifying unit 40-2 is configured not to include the gain equalizer 47 as compared with the optical amplifying unit 40-1 shown in FIG. 6 but includes a variable gain equalizer 47 ′ instead of the VOA 42. Yes.
In FIG. 8, the same reference numerals as those already described indicate the same or substantially the same parts, and detailed description thereof is omitted here.
Then, the reverse tilt control unit 30-2 calculates the above-described reverse gain tilt as the reverse tilt calculation unit 31, and has the reverse gain tilt calculated by the variable gain equalizer 47 'in the optical amplification unit 40-2. By controlling as described above, as described with reference to FIGS. 7A to 7C, the gain inclination is realized in the same manner as the optical amplifying unit 40-1.

  (3) Subsequently, as shown in FIG. 9, the reverse tilt control unit 30a and the optical amplifying unit 40-3 are configured to realize a so-called lumped-constant Raman amplifier. Specifically, the reverse tilt control is performed. As indicated by reference numeral 30-3 in the unit 30a, a plurality of pumping light sources (here, a first pumping light source (denoted as the first LD in the figure) 45a, a second pumping light source (in the figure, the second LD) (Notation) 45b and a third excitation light source (denoted as the third LD in the figure) 45c), and the gain inclination is adjusted by changing the excitation light intensity of each of the excitation light sources 45a to 45c.

More specifically, the reverse tilt control unit 30-3 includes the first coupler 43a, the fourth coupler 43d, the first PD 44a, the fourth PD 44d, the first beam splitter 46c, and the second beam splitter in addition to the excitation light sources 45a to 45c. 46d, the third beam splitter 46e, and the control unit 48b, and the optical fiber 41a functions as the optical amplification unit 40-3.
In FIG. 9, the same reference numerals as those already described indicate the same or substantially the same parts, and detailed description thereof will be omitted here.

  And the control part 48b of the reverse inclination control part 30-3 calculates the output gain of the excitation light sources 45a-45c so that the calculated reverse gain inclination may be obtained, calculating the above-mentioned reverse gain inclination as the reverse inclination calculation part 31. Control. That is, the control unit 48b stores in advance the gain characteristics of the respective excitation light sources 45a to 45c, and the difference between the intensity detected by the fourth PD 44d and the intensity detected by the first PD 44a for the output of each excitation light source 45a to 45c. By controlling based on the above, a desired gain inclination is realized in the optical fiber 41a as the optical amplifying unit.

  That is, as shown in FIG. 10 (a1), the flat gain realized by equalizing the Raman gain obtained by outputting the same intensity from each of the excitation light sources 45a to 45c as shown in FIG. 10 (a2) is used as a reference. Then, as shown in FIG. 10 (b1), the output intensity of each of the excitation light sources 45a to 45c is controlled to a ratio that increases as the wavelength increases, so that the output increases to the right as shown in FIG. 10 (b2). Can create a slope.

Also, as shown in FIG. 10 (c1), by controlling the output intensity of each of the excitation light sources 45a to 45c so as to become smaller as the wavelength becomes longer, the gain slope that decreases to the right as shown in FIG. 10 (c2) is obtained. Can be produced.
Next, an optical amplification method at the time of initial setting (operation procedure when starting up the optical amplifier 10a) as the first embodiment of the present invention will be described with reference to the flowchart shown in FIG. 11 (steps S1 to S14). .

  First, the fiber type of the input transmission path 3 is set in the SRS inclination calculation unit 20a (step S1). The setting of the fiber type of the input transmission path 3 is set based on, for example, an input by an operator using an input interface (not shown). In addition, the SRS inclination calculation unit 20a may hold the fiber type in advance, and in this case, the process of step S1 is unnecessary.

Then, the OSC light input intensity detector 23a of the OSC light detector 21a detects the OSC light input intensity input via the input transmission path 3 (step S2).
Further, the OSC light transmission intensity is acquired from the OSC light received by the acquisition unit 22a of the OSC light detection unit 21a (step S3).
Next, the loss factor calculation unit 24a calculates the transmission line loss in the input transmission path 3 of the OSC light by calculating the difference between the OSC light input intensity and the OSC light transmission intensity (step S4).

Subsequently, the monitor 13 detects the input signal light intensity of the signal light input via the input transmission path 3 (step S5).
Further, the transmission signal light intensity is acquired from the OSC light received by the acquisition unit 22a of the OSC light detection unit 21a (step S6).
Then, the loss coefficient calculation unit 24a calculates the transmission line loss in the input transmission path 3 of the signal light by calculating the difference between the input signal light intensity and the transmission signal light intensity (step S7).

In the optical amplification method of the present invention, the order of calculation of the OSC light transmission line loss (steps S2 to S4) and calculation of the signal light transmission line loss (steps S5 to S7) is not limited. Either may be calculated first.
Next, the loss coefficient calculation unit 24a calculates the transmission path loss of the OSC light calculated in step S4, the transmission path loss of the signal light calculated in step S7, and the difference between the loss coefficients of the OSC light and the signal light. Based on the above, the transmission line distance L of the input transmission line 3 is calculated by the above-described equation (1) (step S8; transmission line distance calculation step).

Then, the loss coefficient calculation unit 24a performs the loss on the signal light of the input transmission path 3 based on the transmission path loss of the signal light calculated in step S7 and the distance L of the input transmission path 3 calculated in step S8. The coefficient αsig is calculated based on the above-described equation (2) (step S9; loss coefficient calculating step).
Subsequently, the tilt amount calculation unit 25a monitors the input signal light intensity of the signal light (step S10). Here, the inclination amount calculation unit 25a acquires the input signal light intensity detected by the monitor 13 in step S5.

  Then, the inclination amount calculating unit 25a calculates the inclination a of the SRS inclination in accordance with the fiber type of the input transmission path 3 set in step S1, and the transmitted signal light acquired in step S6 and the calculated inclination a. Based on the intensity, the SRS inclination amount Still is calculated by the above-described equation (4) (step S11; inclination amount calculating step), and the calculated SRS inclination amount Still is sent to the reverse inclination control unit 30a (step S12). Note that the processing from the above steps S2 to S11 functions as a gain tilt calculation step in the optical amplification method of the present invention.

  Next, the reverse tilt calculation unit 31 of the reverse tilt control unit 30a calculates the reverse SRS tilt (step S13), and the reverse tilt control unit 30a controls the light amplification by the light amplification unit 40 based on the reverse SRS tilt, The output intensity of the signal light from the optical amplifier 10a to the output transmission line 4 is amplified so as to be an optical signal having the same intensity at all wavelengths without gain inclination (step S14; control step), and the process is terminated.

Next, with reference to the flowchart shown in FIG. 12 (steps S15 to S19), an optical amplification method during normal operation (operation) as the first embodiment of the present invention (operation procedure during normal operation of the optical amplifier 10a). Will be described. FIG. 12 shows only the operation of the SRS inclination calculation unit 20a of the optical amplifier 10a.
During normal operation, the SRS inclination calculation unit 20a monitors the input signal light intensity detected by the monitor 13 (step S15), and whether there is any change in the input signal light intensity (that is, the number of multiplexed wavelengths of signal light changes). Whether or not there is (step S16).

Here, if there is no change in the input signal light intensity (No route in step S16), the SRS inclination calculation unit 20a calculates the current SRS inclination amount (that is, calculated when the input signal light intensity is detected for the first time). Then, it transmits to the reverse inclination control part 30a (step S17).
Although not shown in FIG. 12, when the reverse tilt control unit 30a receives the same SRS tilt as the previous time from the SRS tilt calculation unit 20a, the reverse tilt control unit 30a performs the same control before the reception without calculating the reverse SRS tilt. Continue as it is.

On the other hand, when the input signal light intensity changes (Yes route in step S16), the SRS inclination calculation unit 20a calculates a new SRS inclination based on the changed input signal light intensity detected by the monitor 13 (step S18). .
Specifically, the inclination amount calculation unit 25a of the SRS inclination calculation unit 20a calculates a new SRS inclination by the above-described equation (5) based on the change (difference) in the input signal light intensity. At this time, the OSC light detection unit 21a and the loss coefficient calculation unit 24a do not perform any particular processing.

Then, the SRS inclination calculation unit 20a sends the new SRS inclination calculated by the inclination amount calculation unit 25a in step S18 to the reverse inclination control unit 30a (step S19), and the SRS inclination calculation unit 20a ends the process.
In addition, the reverse inclination control part 30a which received the new SRS inclination from the SRS inclination calculation part 20a in the said step S19 is reverse SRS based on a new SRS inclination similarly to the process in step S13 and step S14 of the said FIG. The inclination is calculated, and the output intensity of the signal light by the optical amplifying unit 40 is controlled based on the calculated inverse SRS inclination.

  As described above, according to the optical communication system 1a (the optical amplifier 10a and the optical amplification method) as the first embodiment of the present invention, the acquisition unit 22a of the SRS slope calculation unit 20a of the optical amplifier 10a acquires the transmission signal light intensity. Then, based on the transmitted signal light intensity acquired by the acquisition unit 22a by the SRS inclination calculation unit 20a and the input signal light intensity detected by the monitor 13, the SRS inclination of the signal light due to stimulated Raman scattering in the input transmission path 3 is calculated. The inverse inclination control unit 30a calculates the output intensity of the signal light output to the output transmission path 4 based on the SRS inclination calculated by the SRS inclination calculation unit 20a (control step). Therefore, by controlling the output intensity of the signal light output to the output transmission path 4 by the reverse tilt control unit 30a so as to be the same intensity at all wavelengths, Generated in the power transmission line 3, it is possible to eliminate the SRS tilt due to stimulated Raman scattering in accordance with the number of multiplexed wavelengths of the signal light.

At this time, unlike the conventional technique, the SRS inclination calculation unit 20a performs the calculation (using the above formulas (1) to (4) or the above formula (5) without newly adding expensive parts such as a spectrum analyzer. The SRS slope is calculated by calculation), so that the manufacturing cost of the optical transmission system 1a (optical amplifier 10a) can be reduced.
In addition, since the SRS inclination calculation unit 20a calculates the SRS inclination by calculation without directly observing the spectrum of the signal light as in the spectrum analyzer, the SRS inclination of the signal light input via the input transmission path 3 is extremely reduced. Can be acquired in a short time, and the processing speed can be increased.

  Moreover, the reverse inclination calculation part 31 of the reverse inclination control part 30a calculates the reverse SRS inclination with respect to the SRS inclination calculated by the SRS inclination calculation part 20a, and outputs according to the reverse SRS inclination calculated by the reverse inclination control part 30a. Since the output intensity of the signal light output to the transmission path 4 is controlled, the SRS inclination generated in the input transmission path 3 can be more reliably eliminated, and a wavelength multiplexed signal with uniform intensity at all wavelengths can be output. it can.

  Further, the SRS inclination calculating unit 20a calculates the loss coefficient of the input transmission path 3 based on the difference between the input signal light intensity detected by the monitor 13 and the transmission signal light intensity acquired based on the OSC light. Since the calculation unit 24a and the inclination amount calculation unit 25a for calculating the SRS inclination amount based on the loss coefficient of the input transmission path 3 calculated by the loss coefficient calculation unit 24a are configured, Thus, without directly measuring the spectrum of the signal light, the SRS inclination amount can be reliably calculated based on the intensity loss of the signal light in the input transmission path 3, and a higher speed processing becomes possible.

  Furthermore, the SRS inclination calculating unit 20a acquires the transmission signal light intensity by the OSC light input via the input transmission path 3, and acquires the OSC light transmission intensity of the OSC light to the input transmission path 3. Unit 22a and an OSC light input intensity detection unit 23a that detects the OSC light input intensity of the OSC light input via the input transmission path 3, and the loss coefficient calculation unit 24a receives the OSC acquired by the acquisition unit 22a. Since the loss coefficient is calculated based on the difference between the light transmission intensity and the OSC light input intensity detected by the OSC light input intensity detector 23a, the SRS slope can be calculated more reliably as a result. In addition, since the OSC light is transmitted using the input transmission path 3 by effectively using the input transmission path 3 that has been conventionally used only for signal light transmission, it is possible to contribute to a reduction in manufacturing cost.

  Further, the loss factor calculation unit 24a of the SRS inclination calculation unit 20a acquires the difference between the loss factors of the signal light and the OSC light based on the wavelength characteristic of the transmission line loss applied to the input transmission line 3 set in advance. Since the loss factor is calculated using the difference between the loss factor of the signal light and the OSC light, the loss factor can be calculated more reliably and at high speed. As a result, the SRS inclination calculation unit 20a can further increase the SRS inclination. It is possible to calculate reliably and at high speed.

Furthermore, since the loss coefficient calculation unit 24a of the SRS inclination calculation unit 20a calculates the loss coefficient based on the preset transmission path distance of the input transmission path 3, the distance of the input transmission path 3 is known. Can greatly reduce the calculation time of the loss factor, and can further speed up the calculation process of the SRS slope.
Furthermore, when the input signal light intensity detected by the monitor 13 changes, the inclination amount calculation unit 25a of the SRS inclination calculation unit 20a calculates the SRS inclination based on the changed input signal light intensity, and the reverse inclination Since the control unit 30a performs control based on the SRS inclination, after the initial setting, that is, after calculating the distance and loss factor of the input transmission path 3, a change (difference) in the input signal light intensity is transmitted. By considering the change (difference) in the signal light intensity, the SRS inclination calculating unit 20a can calculate the SRS inclination after the change at high speed, and the number of multiplexed wavelengths of the signal light changes during normal operation. Moreover, the reverse inclination control part 30a can eliminate the SRS inclination after a change reliably and rapidly.

[2] Modification of First Embodiment of the Present Invention As a modification of the first embodiment of the present invention described above, a distributed constant type Raman amplifier may be used as an optical amplification mechanism. That is, as shown in FIG. 13, the reverse tilt control unit 30a ′ of the optical amplifier 10a ′ of the optical transmission system 1a ′ adjusts the excitation light intensity to the input transmission path 3 that functions as the optical amplification unit 40 ′. You may comprise so that the output intensity of the signal light output to the output transmission path 4 may be controlled. Other configurations are the same as those of the optical transmission system 1a of the first embodiment described above.

  In this case, as shown in FIG. 14, the reverse tilt control unit 30a ′ includes the excitation light sources 45a to 45c, the fourth coupler 43d, the fourth PD 44d, the first beam splitter 46c, the second beam splitter 46d, the third beam splitter 46e, and the control. The input transmission path 3 functions as the optical amplifying unit 40 '.

That is, the reverse inclination control unit 30a ′ adjusts the gain inclination by changing the excitation light intensity of each of the excitation light sources 45a to 45c, similarly to the reverse inclination control unit 40-3. The control unit 48c The gain characteristics of the light sources 45a to 45c are stored in advance, and the outputs of the respective excitation light sources 45a to 45c are controlled based on the intensity detected by the fourth PD 44d, whereby the above-described FIGS. 10 (b1), (b2), ( As shown in c1) and (c2), the gain inclination is realized.
Therefore, the optical transmission system 1a ′ (optical amplifier 10a ′) as a modification of the first embodiment of the present invention can provide the same operational effects as those of the first embodiment described above.

[3] Second Embodiment of the Present Invention Next, the configuration of an optical transmission system 1b as a second embodiment of the present invention will be described with reference to the block diagram shown in FIG.
As shown in FIG. 15, this optical transmission system 1b includes a front-stage apparatus (upstream apparatus) 2b, an input transmission path 3, an output transmission path 4, a rear-stage apparatus (downstream apparatus) 5b, a counter transmission path 9, and an optical transmission line. An amplifier 10b is provided. In FIG. 15, the same reference numerals as those described above indicate the same or substantially the same parts, and thus detailed description thereof is omitted here.
In the optical transmission system 1a according to the first embodiment of the present invention described above, the optical amplifier 10a calculates the SRS slope generated in the input transmission path 3 based on the transmission signal light intensity, the OSC light transmission intensity, etc. from the pre-stage device 2a. In the signal light output from the optical amplifier 10a to the output transmission path 4, the SRS inclination generated in the input transmission path 3 is eliminated, and so-called feedforward control is performed in the optical amplifier 10a.

  In contrast, in the optical transmission system 1b according to the second embodiment of the present invention, the optical amplifier 10b has an SRS inclination generated in the output transmission line 4 based on the signal light output intensity, the OSC light output intensity, and the like from the subsequent apparatus 5b. And the intensity of the signal light output to the output transmission path 4 is controlled to suppress the occurrence of SRS tilt in the output transmission path 4, and so-called feedback control is performed in the optical amplifier 10b.

Therefore, in the following description, a portion common to the optical transmission system 1b of the second embodiment and the optical transmission system 1a of the first embodiment described above (particularly, portions having the same or substantially the same reference numerals in FIGS. 15 and 1). Will not be described in detail.
The upstream device 2b is a relay device similar to the transmitter or the optical amplifier 10b, and outputs signal light to the optical amplifier 10b via the input transmission path 3.

The post-stage device 5b is a receiver or a repeater similar to the optical amplifier 10b, and receives the signal light amplified by the optical amplifier 10b (specifically, the optical amplifier 40) and output via the output transmission path 4. To do.
The rear-stage apparatus 5b includes an optical amplification unit 50, a first coupler 51, a first monitor (fifth detection unit) 52, a second coupler 53, a second monitor (sixth detection unit) 54, and an OSC optical transmission unit ( The second OSC optical transmission unit) 55 is provided.

The optical amplifying unit 50 amplifies the signal light input from the optical amplifier 10b via the output transmission path 4. In addition, when the back | latter stage apparatus 5b functions as a receiver, this optical amplification part 50 becomes a receiving part.
The first coupler 51 splits the signal light of the signal light and the first OSC light (third OSC light) input via the output transmission path 4 and inputs them to the first monitor 52. The first OSC light input via the output transmission path 4 is output from an OSC light output unit 60 described later of the optical amplifier 10b.

The first monitor 52 detects the output intensity (hereinafter referred to as signal light output intensity) of the signal light input via the output transmission path 4 and the first coupler 51, for example, A photodiode (PD: PhotoDiode) is provided.
The second coupler 53 divides the first OSC light of the signal light and the first OSC light input via the output transmission path 4 and inputs them to the second monitor 54.

The second monitor 54 outputs the output intensity of the first OSC light input from the output transmission path 4 and the second coupler 53 from the output transmission path 4 (third OSC light output intensity; hereinafter, simply referred to as OSC light output intensity). For example, it is configured to include a photodiode.
The OSC light transmission unit 55 obtains information (signal light output intensity information and OSC light output intensity) of the signal light output intensity detected by the first monitor 52 and the OSC light output intensity of the first OSC light detected by the second monitor 54. The second OSC light included as (information) is transmitted to the optical amplifier 10b (more specifically, the OSC optical receiver 21b described later) via the counter transmission path 9.

Here, the counter transmission path 9 is provided separately from the output transmission path 4, connects at least the rear stage device 5 b and the optical amplifier 10 b, and transmits the signal light and the first OSC light in the output transmission path 4. (Refer to block arrow 7) is for transmitting the second OSC light in the opposite reverse direction (see block arrow 9 ').
The optical amplifier 10 b is interposed between the input transmission path 3 and the output transmission path 4, amplifies the signal light input from the previous stage device 2 b via the input transmission path 3, and passes through the output transmission path 4. The first coupler 14, the first monitor (third detection unit) 15, the second coupler 16, the second monitor (fourth detection unit) 17, the SRS inclination calculation unit (gain inclination calculation). Part) 20b, reverse tilt control part 30b, optical amplification part 40, and OSC light output part 60.

The first coupler 14 branches the signal light output from the output transmission path 4 and the first OSC light, and inputs the branched signal light to the first monitor 15.
Here, the signal light is obtained by amplifying the signal light input via the input transmission path 3 by the optical amplifying unit 40.
The first monitor 15 transmits the signal light input via the first coupler 14 to the output transmission path 4, that is, the transmission light intensity of the signal light output from the optical amplifier 40 to the output transmission path 4. (Second transmission signal light intensity; hereinafter referred to as transmission signal light intensity) is detected, and for example, includes a photodiode.

The second coupler 16 branches the first OSC light out of the signal light and the first OSC light output via the output transmission path 4 and inputs them to the second monitor 17.
The second monitor 17 transmits the first OSC light input via the second coupler 16 to the output transmission path 4, that is, the first OSC light output from the OSC light output unit 60 to the output transmission path 4. The transmission light intensity (third OSC light transmission intensity; hereinafter referred to as OSC light transmission intensity) is detected.

  The SRS inclination calculating unit 20b acquires the signal light output intensity of the signal light output to the subsequent stage device 5b via the output transmission path 4 based on the second OSC light received from the subsequent stage apparatus 5b via the opposite transmission path 9. Based on the acquired signal light output intensity and the transmitted signal light intensity detected by the first monitor 15, the SRS inclination (gain inclination) of the signal light due to stimulated Raman scattering (SRS) in the output transmission path 4 is calculated. Specifically, it comprises an OSC optical receiver 21b, a loss coefficient calculator 24b, and a tilt amount calculator 25b.

The OSC light reception unit 21b receives the second OSC light transmitted from the OSC light transmission unit 55 of the rear-stage apparatus 5b via the opposite transmission path 9, and includes an acquisition unit (second acquisition unit) 22b. Has been.
The acquisition unit 22b acquires the signal light output intensity and the OSC light output intensity included as information in the second OSC light based on the second OSC light received from the OSC light transmission unit 55 via the opposite transmission path 9. It is.

The loss factor calculation unit 24b is configured to output the transmission signal light intensity detected by the first monitor 15, the OSC light transmission intensity detected by the second monitor 17, the signal light output intensity acquired by the acquisition unit 22, and the acquisition unit 22. Based on the acquired OSC light output intensity, the loss coefficient for the signal light of the output transmission path 4 is calculated.
Specifically, the loss coefficient calculation unit 24b obtains the difference between the signal light output intensity and the transmission signal light intensity, that is, the output transmission line loss Lsig '(dB) of the signal light, and further calculates the OSC light transmission intensity and the OSC. The difference from the optical output intensity, that is, the output transmission line loss Losc ′ (dB) of the first OSC light is obtained.

Note that optical components (here, the first coupler 14, the first monitor 15, the second coupler 16, and the optical amplifier 10b and the post-stage device 5b, or between the optical amplifying unit 40 and the SRS inclination calculating unit 20b) If there is a second monitor 17), it is preferable to subtract the loss of this optical component in advance.
Then, the loss coefficient calculation unit 24b, together with the input transmission line loss Lsig '(dB) of the signal light and the input transmission line loss Losc' (dB) of the OSC light, the difference Ldif 'of the first OSC light and the signal light A loss factor is calculated based on (dB / km).

The loss factor calculation unit 24b holds a loss factor wavelength characteristic profile of the fiber type corresponding to the output transmission path 4 in a storage area (not shown), and the loss factor calculation unit 24b has the loss factor wavelength characteristic profile. Based on the above, the difference Ldif ′ of the loss coefficient between the first OSC light and the signal light according to the wavelength of the signal light and the wavelength of the first OSC light is calculated.
That is, the loss coefficient calculation unit 24b calculates the transmission path distance L ′ of the output transmission path 4 based on the following formula (6).

L ′ = | Losc′−Lsig ′ | / Ldif ′ (6)
Next, the loss coefficient calculation unit 24b calculates a loss coefficient αsig ′ applied to the signal light of the output transmission path 4 based on the following formula (7).
αsig ′ = Lsig ′ / L ′ (7)
The tilt amount calculation unit 25b calculates a tilt amount (SRS tilt amount) Still ″ as a gain tilt based on the loss coefficient αsig ′ of the output transmission path 4 calculated by the loss coefficient calculation unit 24b. First, the slope a ′ (dB / km) of the SRS slope is calculated based on the following formula (8).

a ′ = A ′ * αsig ′ ^ 2 + B ′ * αsig ′ + C ′ (8)
Here, since the constants A ′ to C ′ are determined in advance according to the fiber type of the output transmission path 4, the inclination amount calculation unit 25 b stores these constants A ′ to C ′ in a storage area (not shown). Pre-held.
Then, the inclination amount calculation unit 25b calculates the SRS inclination amount Stil ″ by the following equation (9) based on the inclination a ′ and the transmission signal light intensity Pin ″ (mW) detected by the first monitor 15. calculate.

Still ″ = a ′ * Pin ″ (9)
Note that when the transmission signal light intensity detected by the first monitor 15 changes during normal operation after the initial setting, the inclination amount calculation unit 25b uses the above formula ( 9) Calculate the SRS slope.
The reverse tilt control unit 30b controls the output intensity of the signal light output from the optical amplification unit 40 (that is, the transmitted signal light intensity) based on the SRS tilt calculated by the SRS tilt calculation unit 20b. The apparatus includes a reverse inclination calculation unit 31 that calculates an inverse SRS inclination of the SRS inclination calculated by the SRS inclination calculation unit 20b.

  Here, more specific control contents of the reverse tilt control unit 30b will be described with reference to FIG. 16. The reverse tilt control unit 30b is configured to detect the SRS tilt in the output transmission path 4 (that is, the signal light input to the subsequent stage device 5b). ) Is calculated as indicated by the solid line x, and when the inverse SRS inclination is calculated as indicated by the broken line y by the inverse inclination calculating unit 31, for example, as indicated by the broken line z ′, it is output from the optical amplifying unit 40. Control is performed so that the intensity of the transmitted signal light has the same characteristic as the inverse SRS slope (y).

As a result, the signal light output from the output transmission path 4 and input to the post-stage device 5b can have the same intensity at all wavelengths with no SRS inclination as indicated by the two-dot chain line w.
As described above, the reverse tilt control unit 30b has the reverse SRS tilt in the output signal light intensity input to the output transmission path 4 in order to cancel out the intensity difference between the wavelengths by the SRS tilt generated in the output transmission path 4. Thus, the generation of the SRS inclination in the output transmission path 4 is pseudo-suppressed.

  Next, with reference to the flowchart shown in FIG. 17 (steps S21 to S34), the optical amplification method during the initial operation (operation procedure when starting up the optical amplifier 10b) as the second embodiment of the present invention will be described. As shown in FIG. 17, the processing of steps S21 to S34 in FIG. 17 and the processing of steps S1 to S14 in FIG. 11 showing the optical amplification method during the initial operation of the first embodiment of the present invention described above are as follows. Each corresponds. Therefore, here, processing different from the optical amplification method of the first embodiment described above will be described in detail, and a part of the description of common processing will be omitted.

That is, in the optical amplification method of the second embodiment, after setting the fiber type of the output transmission path 4 (step S21), the second monitor 17 acquires the OSC light transmission intensity (step S22), and the acquisition unit 22b acquires the OSC light. The output intensity is acquired (step S23), and the loss coefficient calculation unit 24b calculates the transmission line loss in the output transmission line 4 of the OSC light (step S24).
On the other hand, the first monitor 15 acquires the transmission signal light intensity (step S25), the acquisition unit 22b acquires the signal light output intensity (step S26), and the loss coefficient calculation unit 24b transmits the signal light on the output transmission path 4. A road loss is calculated (step S27).

Then, the loss coefficient calculation unit 24b calculates the transmission line distance L ′ of the output transmission line 4 based on the above equation (6) (step S28), and the loss coefficient calculation unit 24b outputs based on the above equation (7). The loss coefficient αsig ′ of the transmission line 4 is calculated (step S29).
Next, the first monitor 15 monitors the intensity of the transmitted signal light (step S30), and the loss coefficient calculation unit 24b calculates the SRS inclination amount Still ″ based on the above formulas (8) and (9) (step S31). ).

Thereafter, the SRS tilt amount Still ″ is transmitted from the SRS tilt calculating unit 20b to the reverse tilt control unit 30b (step S32), and the reverse SRS tilt is calculated by the reverse tilt calculating unit 31 (step S33).
Finally, the reverse inclination control unit 30b controls the optical amplification unit 40 based on the reverse SRS inclination, so that the intensity at the time of signal light output from the optical amplification unit 40 has the same inclination characteristic as the reverse SRS inclination. (Step S34), and the process ends.

Next, with reference to the flowchart shown in FIG. 18 (steps S35 to S39), an optical amplification method during normal operation (operation) as the second embodiment of the present invention (operation procedure during normal operation of the optical amplifier 10b). Will be described. FIG. 18 shows only the operation of the SRS inclination calculating unit 20b of the optical amplifier 10b.
Also for the optical amplification method during normal operation, the processes in steps S35 to S39 shown in FIG. 18 correspond to the processes in steps S15 to S19 in FIG. Therefore, here, processing different from the optical amplification method of the first embodiment described above will be described in detail, and a part of the description of common processing will be omitted.

That is, in the optical amplifier 10b, the SRS inclination calculating unit 20b monitors the signal light output intensity detected by the first monitor 15 (step S35), and whether there is a change in the transmitted signal light intensity (that is, the signal light intensity) It is determined whether or not there is a change in the number of multiplexed wavelengths (step S36).
Here, if there is no change in the transmitted signal light intensity (No route in step S36), the SRS inclination calculation unit 20b transmits the current SRS inclination amount to the reverse inclination control unit 30b (step S37).

On the other hand, when the transmission signal light intensity changes (Yes route in step S36), the SRS inclination calculation unit 20b calculates a new SRS inclination using the above equation (9) based on the changed transmission signal light intensity. (Step S38), this new SRS inclination is sent to the reverse inclination control unit 30b (Step S39), and the SRS inclination calculation unit 20b ends the process.
In addition, the reverse inclination control part 30b which received the new SRS inclination from the SRS inclination calculation part 20b in the said step S39 is reverse SRS based on a new SRS inclination similarly to the process in the step S23 and step S24 of the said FIG. The inclination is calculated, and the output (output) intensity of the signal light by the optical amplifying unit 40 is controlled based on the calculated inverse SRS inclination.

  Thus, according to the optical communication system 1b (the optical amplifier 10b and the optical amplification method) as the second embodiment of the present invention, the first signal light intensity of the signal light output from the optical amplification unit 40 is detected. The monitor 15, the acquisition unit 22 b that acquires the signal light output intensity of the signal light output from the output transmission path 4, the signal light output intensity acquired by the acquisition unit 22 b and the transmission signal detected by the first monitor 15 Based on the light intensity, the SRS inclination calculating unit 20b that calculates the SRS inclination of the signal light due to stimulated Raman scattering in the output transmission path 4, and the signal light output from the optical amplifying unit 40 based on the calculated SRS inclination Since the reverse tilt control unit 30b for controlling the intensity of the transmitted signal light of the SRS tilt is generated in the signal light output from the output transmission path 4 by the reverse tilt control unit 30b. By controlling so that the signal light output intensity has an inverse SRS inclination so as not to occur, the generation of SRS inclination due to stimulated Raman scattering according to the number of multiplexed wavelengths of the signal light in the output transmission path 4 can be artificially suppressed. it can.

At this time, the SRS inclination calculation unit 20b performs the calculation (calculation using the above formulas (6) to (9)) without adding an expensive part such as a spectrum analyzer as in the prior art. Therefore, the manufacturing cost of the optical transmission system 1b (optical amplifier 10b) can be reduced.
In addition, since the SRS inclination calculation unit 20b calculates the SRS inclination by calculation without directly observing the spectrum of the signal light like a spectrum analyzer, the SRS inclination of the signal light output from the output transmission path 4 is extremely short. It can be acquired in time, and the processing speed can be increased.

  Moreover, the reverse inclination calculation part 31 of the reverse inclination control part 30b calculates the reverse SRS inclination with respect to the SRS inclination calculated by the SRS inclination calculation part 20b, and outputs according to the reverse SRS inclination calculated by the reverse inclination control part 30b. Since the transmission light intensity of the signal light output to the transmission path 4 is controlled, the SRS inclination generated in the output transmission path 4 can be more reliably suppressed, and the wavelength multiplexing with uniform intensity at all wavelengths from the output end of the output transmission path 4 A signal can be output.

  Further, the SRS inclination calculating unit 20b calculates a loss coefficient of the output transmission path 4 based on the difference between the transmission signal light intensity detected by the first monitor 15 and the signal light output intensity, and the calculation Since it is configured to include an inclination amount calculation unit 25b for calculating an inclination amount as an SRS inclination based on the loss coefficient of the output transmission path 4 thus measured, the spectrum of the signal light is directly measured like a spectrum analyzer. In addition, the SRS inclination amount can be reliably calculated based on the intensity loss of the signal light in the output transmission path 4, and higher-speed processing becomes possible.

Furthermore, since the acquisition unit 22b acquires the signal light output intensity based on the second OSC light input via the opposite transmission path 9, the signal light output intensity can be acquired reliably and at high speed.
In addition, the OSC light output unit 60 that outputs the first OSC light via the output transmission path 4 and the light intensity transmitted to the output transmission path 4 of the first OSC light output from the OSC light output section 60 (first OSC light transmission intensity) ) To detect the first OSC light output of the first OSC light output from the output transmission path 4 based on the second OSC light input via the opposite transmission path 9. The loss factor calculation unit 24b of the SRS inclination calculation unit 20b calculates the loss coefficient of the output transmission path 4 based on the difference between the first OSC light transmission intensity and the first OSC light output intensity. As a result, the SRS slope can be calculated more reliably. In addition, since the OSC light is transmitted using the output transmission path 4 by effectively using the output transmission path 4 that has been conventionally used only for transmitting the signal light, it is possible to contribute to a reduction in manufacturing cost.

  Further, the loss coefficient calculation unit 24b of the SRS inclination calculation unit 20b acquires the difference between the loss coefficients of the signal light and the first OSC light based on the wavelength characteristic of the transmission line loss applied to the preset output transmission line 4. Since the loss factor is calculated using the difference between the acquired loss factors, the loss factor can be calculated more reliably and at a high speed. As a result, the SRS inclination calculating unit 20b can increase the SRS inclination more reliably and at a high speed. Can be calculated.

Furthermore, since the loss coefficient calculation unit 24b of the SRS inclination calculation unit 20b calculates the loss coefficient based on the preset transmission line distance of the output transmission line 4, when the distance of the output transmission line 4 is known Can greatly reduce the calculation time of the loss factor, and can further speed up the calculation process of the SRS slope.
Furthermore, when the transmission signal light intensity detected by the first monitor 15 changes, the SRS inclination calculation unit 20b calculates the SRS inclination based on the changed transmission signal light intensity, and the reverse inclination control unit 30b Since the control is executed based on the SRS inclination, after the initial setting, that is, after calculating the distance and the loss coefficient of the output transmission path 4, the SRS inclination calculating unit 20b is simply monitored directly by the output signal light intensity. The SRS slope after the change can be calculated at high speed, and even if the number of multiplexed wavelengths of signal light changes during normal operation, the reverse slope control unit 30b reliably and promptly changes the SRS slope after the change. Can be suppressed.

[4] Modification of Second Embodiment of the Invention In the second embodiment of the present invention described above, as in the first embodiment described above, the optical amplifying unit 40 (40-1 to 40-3) 6, 8, and 9, as a modification of the second embodiment, a distributed constant Raman amplifier may be used as the optical amplification mechanism. That is, as shown in FIG. 19, the reverse tilt control unit 30b ′ of the optical amplifier 10b ′ of the optical transmission system 1b ′ adjusts the excitation light intensity to the output transmission path 4 that functions as the optical amplification unit 40 ′. The gain of the signal light propagating through the output transmission path 4 may be controlled. This also makes it possible to make the intensity for each wavelength uniform at the output end of the output transmission line 4. Other configurations are the same as those of the optical transmission system 1b of the second embodiment described above.

In this case, the reverse inclination control unit 30b ′ is configured as shown in FIG. 20, and the reverse inclination control unit 30b ′ adjusts the gain inclination by changing the excitation light intensity of each of the excitation light sources 45a to 45c. The control unit 48c stores the gain characteristics of the respective excitation light sources 45a to 45c in advance, and controls the gain of the signal light propagating through the output transmission path 4 by controlling the outputs of the respective excitation light sources 45a to 45c. A gain tilt similar to that of the reverse tilt control unit 30b is realized.
Therefore, the optical transmission system 1b ′ (optical amplifier 10b ′) as a modification of the second embodiment of the present invention can provide the same effects as those of the second embodiment described above.

[5] Others The present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention.
For example, in the first embodiment described above, an example in which the SRS inclination calculation unit 20a of the optical amplifier 10a is configured to include the OSC light detection unit 21a (the acquisition unit 22a and the OSC light input intensity detection unit 23a) has been described. However, the present invention is not limited to this, and it is not necessary for the SRS inclination calculation unit 20a to include the OSC light detection unit 21a, and the OSC light detection unit 21a is provided separately from the SRS inclination calculation unit 20a. Also good. Similarly, in the second embodiment described above, the SRS inclination calculation unit 20b does not need to include the OSC light reception unit 21b (acquisition unit 22b), and the OSC light reception unit 21b is provided separately from the SRS inclination 20b. May be.

  In the above-described first embodiment, the example of calculating the transmission line loss Losc in the input transmission path 3 of the OSC light at the time of initial setting has been described. However, the present invention is not limited to this, and the OSC light loss The invariable parameter such as the transmission line loss Losc in the input transmission line 3 is measured and calculated in advance in the design stage or the like, and the value is held in the holding unit (not shown) in advance by the SRS inclination calculating unit 20a. As a result, the SRS inclination calculating unit 20a can calculate the SRS inclination by obtaining at least the transmission signal light intensity and the input signal light intensity. That is, the SRS inclination calculating unit 20a does not need to calculate the transmission path loss Losc, and the OSC optical transmission unit 2a-2 does not need to include the OSC optical transmission intensity in the OSC light as information, and the configuration of the optical transmission system 1a Can be further simplified. Note that, as an invariable parameter other than the transmission line loss Losc, the distance L of the input transmission line 3 may also be configured to be held in advance by the SRS inclination calculation unit 20a.

  Further, similarly in the second embodiment described above, the transmission line loss Losc ′ in the output transmission line 4 of the OSC light is measured and calculated in advance in the design stage or the like, and the value is stored in the holding unit ( The SRS inclination calculating unit 20b can calculate the SRS inclination by obtaining at least the transmission signal light intensity and the signal light output intensity. That is, the SRS inclination calculating unit 20b does not need to calculate the transmission line loss Losc ′, and thus it is not necessary to provide the second coupler 16 and the second monitor 17 of the optical amplifier 10b, and the second coupler 53 of the rear-stage apparatus 5b. It is not necessary to provide the second monitor 54, and the configuration of the optical transmission system 1b can be further simplified. At this time, the OSC light transmitter 55 does not need to include the OSC light output intensity as information in the OSC light. Further, as an invariable parameter other than the transmission path loss Losc ′, the distance L ′ of the output transmission path 4 may also be configured to be held in advance by the SRS slope calculation unit 20b.

  In the first embodiment described above, an example in which only the upstream device 2a is configured to include the OSC optical transmission unit 2a-2, that is, an example in which the optical transmission system 1a includes only one optical amplifier 10a. However, the present invention is not limited to this, and the optical transmission system 1a may be configured to transmit signal light through a plurality of optical amplifiers 10a. Each of the plurality of optical amplifiers 10a is configured to include an OSC optical transmission unit 2a-2 at a downstream portion in the transmission direction of the signal light, and the SRS tilt of the input transmission path 3 is connected to the subsequent optical amplifier 10a as in the preceding apparatus 2a. Is calculated, the OSC light including the transmission signal light intensity and the OSC light transmission intensity as information is transmitted to the optical amplifier 10a at the subsequent stage.

As a result, no matter how long the transmission distance of the optical transmission system 1a becomes, the SRS inclination is eliminated at each relay point (optical amplifier 10a), so that very high quality and high-speed signal light transmission is realized. Can do.
Similarly, in the second embodiment described above, an example in which only the post-stage device 5b is configured to include the first coupler 51, the first monitor 52, the second coupler 53, the second monitor 54, and the OSC optical transmitter 55. However, the present invention is not limited to this, and the optical transmission system 1b may be configured to transmit signal light through the plurality of optical amplifiers 10b. Each of the plurality of optical amplifiers 10 b includes a first coupler 51, a first monitor 52, a second coupler 53, a second monitor 54, and an OSC optical transmitter 55 in the upstream portion in the signal light transmission direction. In order to cause the optical amplifier 10b in the previous stage to calculate the SRS slope of the output transmission path 4 as in the subsequent apparatus 5b, the second OS including the signal light output intensity and the OSC light output intensity as information in the previous optical amplifier 10b. To send the light. As a result, no matter how long the transmission distance of the optical transmission system 1b becomes, the occurrence of SRS tilt is suppressed at each relay point (optical amplifier 10b), thereby realizing very high quality and high-speed signal light transmission. can do.

[6] Appendix (Appendix 1)
A first detector that detects the intensity of input signal light input from the upstream device through the input transmission path;
The gain of the signal light due to stimulated Raman scattering in the input transmission path based on the first transmission signal light intensity information which is information of the transmission light intensity to the input transmission path of the upstream device and the input signal light intensity. A gain slope calculator for calculating the slope;
An optical amplifier for amplifying the input signal light;
An optical amplifier comprising: a control unit that controls output intensity based on the calculated gain gradient.

(Appendix 2)
A first detector that detects the intensity of the input signal light input from the upstream device through the input transmission path;
The gain of the signal light due to stimulated Raman scattering in the input transmission path based on the first transmission signal light intensity information which is information of the transmission light intensity to the input transmission path of the upstream device and the input signal light intensity. A gain slope calculator for calculating the slope;
A control unit that controls output intensity by adjusting excitation light intensity for Raman amplification to the input transmission line based on the calculated gain slope is provided. An optical amplifier.

(Appendix 3)
The control unit calculates an inverse gain tilt with respect to the gain tilt calculated by the gain tilt calculating unit, and the output intensity is equalized with the intensity of each wavelength component according to the calculated reverse gain tilt. The optical amplifier according to appendix 1 or appendix 2, wherein the optical amplifier is controlled as follows.
(Appendix 4)
The gain slope calculation unit is
A loss factor calculation unit that calculates a loss factor of the input transmission path based on a difference between the input signal light intensity detected by the first detection unit and the first transmission signal light intensity information;
The apparatus further comprises an inclination amount calculation unit that calculates an inclination amount as the gain inclination based on the loss coefficient of the input transmission path calculated by the loss coefficient calculation unit. The optical amplifier according to any one of 1 to 3.

(Appendix 5)
The gain gradient calculating unit acquires the first transmission signal light intensity information from a first OSC (Optical Supervisory Channel) light input from the upstream device via the input transmission path. The optical amplifier according to any one of?
(Appendix 6)
A second detector for detecting an input intensity of the first OSC light input from the upstream device via the input transmission path (hereinafter referred to as a first OSC light input intensity);
The gain slope calculating unit is configured to obtain first OSC light transmission intensity information from the first OSC light;
The loss factor calculation unit of the gain tilt calculation unit calculates the loss factor based on a difference between the first OSC light transmission intensity information and the first OSC light input intensity detected by the second detection unit. The optical amplifier according to appendix 4, wherein

(Appendix 7)
A holding unit that holds in advance a transmission line loss in the input transmission path of the first OSC light input from the upstream device via the input transmission path;
The optical amplifier according to appendix 4, wherein the loss factor calculation unit of the gain slope calculation unit calculates the loss coefficient based on the transmission line loss held in advance in the holding unit.

(Appendix 8)
The loss factor calculation unit of the gain slope calculation unit obtains a difference in loss factor between the signal light and the first OSC light based on a wavelength characteristic of a transmission line loss applied to the input transmission line set in advance, The optical amplifier according to appendix 6 or appendix 7, wherein the loss factor is calculated using a difference in loss factor between the acquired signal light and the first OSC light.

(Appendix 9)
The optical amplifier according to appendix 4, wherein the loss factor calculation unit of the gain slope calculation unit calculates the loss factor based on a preset transmission line distance of the input transmission line.
(Appendix 10)
When the input signal light intensity detected by the first detection unit changes, the gain inclination calculation unit calculates the gain inclination based on the input signal light intensity after the change, and the control unit The optical amplifier according to any one of appendix 1 to appendix 9, wherein the control is executed based on a gain slope.

(Appendix 11)
An optical transmission system comprising an optical amplifier interposed between an input transmission path and an output transmission path, and an upstream device connected to the optical amplifier via the input transmission path,
The upstream device comprises:
A signal light transmitter that transmits signal light to the optical amplifier via the input transmission path;
A first OSC (Optical Supervisory Channel) light including first transmission signal light intensity information, which is at least information of the transmission light intensity of the signal light to the input transmission path, is transmitted to the optical amplifier via the input transmission path. With 1OSC optical transmitter
The optical amplifier is
A first detector that detects the intensity of the input signal light input from the upstream device through the input transmission path;
The gain of the signal light due to stimulated Raman scattering in the input transmission path based on the first transmission signal light intensity information which is information of the transmission light intensity to the input transmission path of the upstream device and the input signal light intensity. A gain slope calculator for calculating the slope;
An optical amplifier for amplifying the input signal light;
An optical transmission system comprising: a control unit that controls an output intensity of signal light output to the output transmission path based on the calculated gain slope.

(Appendix 12)
An optical transmission system comprising an optical amplifier interposed between an input transmission path and an output transmission path, and an upstream device connected to the optical amplifier via the input transmission path,
The upstream device comprises:
A signal light transmitter that transmits signal light to the optical amplifier via the input transmission path;
A first OSC (Optical Supervisory Channel) light including first transmission signal light intensity information, which is at least information of the transmission light intensity of the signal light to the input transmission path, is transmitted to the optical amplifier via the input transmission path. With 1OSC optical transmitter
The optical amplifier is
A first detector that detects input signal light intensity input from the upstream device through the input transmission path;
The gain of the signal light due to stimulated Raman scattering in the input transmission path based on the first transmission signal light intensity information which is information of the transmission light intensity to the input transmission path of the upstream device and the input signal light intensity. A gain slope calculator for calculating the slope;
A controller that controls the output intensity of the signal light output to the output transmission path by adjusting the excitation light intensity for Raman amplification to the input transmission path based on the calculated gain slope; An optical transmission system characterized by being configured.

(Appendix 13)
The OSC optical transmission unit of the upstream device is configured to transmit the first OSC light including the first OSC optical transmission intensity information that is information on the optical transmission intensity of the first OSC light to the input transmission path. ,
The gain tilt calculation unit of the optical amplifier acquires the first OSC light transmission intensity information from the first OSC light, and the acquired first OSC light transmission intensity information and the first OSC detected by the second detection unit. 13. The optical transmission system according to appendix 11 or appendix 12, wherein the gain slope is calculated based on a difference from the optical input intensity.

(Appendix 14)
An optical amplifier connected to the upstream device via an input transmission path and connected to the downstream device via an output transmission path,
An optical amplifying unit for amplifying and outputting the signal light input via the input transmission path;
A third detector for detecting the intensity of the signal light output from the optical amplifier to the output transmission path (hereinafter referred to as second output signal light intensity);
Based on the signal light output intensity information, which is information on the output intensity of the signal light output from the output transmission path, and the second transmission signal light intensity detected by the third detection unit, the output transmission path A gain tilt calculation unit for calculating the gain tilt of the signal light due to stimulated Raman scattering in
And a control unit that controls the second transmission signal light intensity of the signal light output from the optical amplification unit based on the gain inclination calculated by the gain inclination calculation unit. A characteristic optical amplifier.

(Appendix 15)
An optical amplifier connected to the upstream device via an input transmission path and connected to the downstream device via an output transmission path,
A third detector for detecting the intensity of the transmitted light of the signal light to the output transmission path (hereinafter referred to as the second transmitted signal light intensity);
Based on the signal light output intensity information, which is information on the output intensity of the signal light output from the output transmission path, and the second transmission signal light intensity detected by the third detection unit, the output transmission path A gain tilt calculation unit for calculating the gain tilt of the signal light due to stimulated Raman scattering in
Based on the gain inclination calculated by the gain inclination calculation unit, the intensity of the pumping light for Raman amplification to the output transmission line is adjusted, whereby the signal light output from the output transmission line is adjusted. 2. An optical amplifier comprising a control unit for controlling the intensity of the transmitted signal light.

(Appendix 16)
The control unit calculates an inverse gain inclination with respect to the gain inclination calculated by the gain inclination calculating unit, and the intensity of each wavelength component is equal to the second transmission signal light intensity according to the calculated inverse gain inclination. 15. The optical amplifier according to appendix 14 or appendix 15, wherein the optical amplifier is controlled so as to be

(Appendix 17)
The gain slope calculation unit is
A loss factor calculation unit that calculates a loss factor of the output transmission path based on a difference between the second transmission signal light intensity detected by the third detection unit and the signal light output intensity information;
The apparatus further comprises an inclination amount calculation unit that calculates an inclination amount as the gain inclination based on the loss coefficient of the output transmission path calculated by the loss coefficient calculation unit. The optical amplifier according to any one of 14 to appendix 16.

(Appendix 18)
The gain slope calculation unit obtains the second signal light output intensity information based on second OSC (Optical Supervisory Channel) light input from the downstream device via a counter transmission line, The optical amplifier according to any one of appendix 14 to appendix 17.
(Appendix 19)
An OSC light output unit that outputs a third OSC light via the output transmission path;
A fourth detection unit for detecting a transmission light intensity of the third OSC light output from the OSC light output unit to the output transmission path (hereinafter referred to as a third OSC light transmission intensity);
The gain tilt control unit is a third OSC that is information on the output intensity of the third OSC light output from the output transmission path based on the second OSC light input from the downstream device via the opposite transmission path. Configured to obtain light output intensity information;
The loss factor calculation unit of the gain tilt calculation unit calculates the loss factor based on a difference between the third OSC light transmission intensity detected by the fourth detection unit and the third OSC light output intensity information. The optical amplifier according to appendix 18, characterized in that.

(Appendix 20)
A holding unit that holds in advance the transmission path loss of the third OSC light in the output transmission path;
The light according to claim 18, wherein the loss factor calculation unit of the gain tilt calculation unit calculates the loss factor based on the transmission line loss of the third OSC light held in advance in the holding unit. amplifier.

(Appendix 21)
The loss factor calculation unit of the gain slope calculation unit obtains a difference in loss factor between the signal light and the third OSC light based on a wavelength characteristic of a transmission line loss applied to the output transmission line set in advance. The optical amplifier according to appendix 19 or appendix 20, wherein the loss factor is calculated using a difference in loss factor between the acquired signal light and the third OSC light.

(Appendix 22)
18. The optical amplifier according to appendix 17, wherein the loss factor calculation unit of the gain slope calculation unit calculates the loss factor based on a preset transmission line distance of the output transmission line.
(Appendix 23)
When the second transmission signal light intensity detected by the third detection unit has changed, the gain gradient calculation unit calculates the gain gradient based on the second transmission signal light intensity after the change, The optical amplifier according to any one of Appendix 14 to Appendix 22, wherein the control unit executes the control based on the gain inclination.

(Appendix 24)
An optical transmission system comprising: an optical amplifier interposed between an input transmission path and an output transmission path; and a downstream device connected to the optical amplifier via each of the output transmission path and the opposite transmission path. There,
The downstream device comprises:
A fifth detector for detecting an output intensity of the signal light input from the optical amplifier via the output transmission path from the output transmission path (hereinafter referred to as signal light output intensity information);
A second OSC optical transmission unit that transmits second optical supervisory channel (OSC) light including at least the signal light output intensity information detected by the fifth detection unit as information to the optical amplifier via the opposite transmission path; ,
The optical amplifier is
An optical amplifying unit for amplifying and outputting the signal light input via the input transmission path;
A third detector for detecting the intensity of the signal light output from the optical amplifier to the output transmission path (hereinafter referred to as second output signal light intensity);
The signal light output intensity information is acquired from the second OSC light input via the opposite transmission path, and the acquired signal light output intensity information and the second transmission signal light detected by the third detection unit A gain tilt calculation unit that calculates a gain tilt of signal light due to stimulated Raman scattering in the output transmission path based on the intensity;
And a control unit that controls the second transmission signal light intensity of the signal light output from the optical amplification unit based on the gain inclination calculated by the gain inclination calculation unit. A characteristic optical transmission system.

(Appendix 25)
An optical transmission system comprising: an optical amplifier interposed between an input transmission path and an output transmission path; and a downstream device connected to the optical amplifier via each of the output transmission path and the opposite transmission path. There,
The downstream device comprises:
A fifth detector for detecting an output intensity of the signal light input from the optical amplifier via the output transmission path from the output transmission path (hereinafter referred to as signal light output intensity information);
A second OSC optical transmission unit that transmits second optical supervisory channel (OSC) light including at least the signal light output intensity information detected by the fifth detection unit as information to the optical amplifier via the opposite transmission path; ,
The optical amplifier is
A third detector for detecting the intensity of the transmitted light of the signal light to the output transmission path (hereinafter referred to as the second transmitted signal light intensity);
The signal light output intensity information is acquired from the second OSC light input via the opposite transmission path, and the acquired signal light output intensity information and the second transmission signal light detected by the third detection unit A gain tilt calculation unit that calculates a gain tilt of signal light due to stimulated Raman scattering in the output transmission path based on the intensity;
Based on the gain inclination calculated by the gain inclination calculation unit, the intensity of the pumping light for Raman amplification to the output transmission line is adjusted, whereby the signal light output from the output transmission line is adjusted. 2. An optical transmission system comprising a control unit for controlling the intensity of a transmitted signal light.

(Appendix 26)
The optical amplifier is
An OSC light output unit that outputs a third OSC light via the output transmission path;
A fourth detection unit for detecting a transmission light intensity of the third OSC light output from the OSC light output unit to the output transmission path (hereinafter referred to as a third OSC light transmission intensity);
The downstream device comprises:
A sixth detector for detecting an output intensity of the third OSC light input through the output transmission path from the output transmission path (hereinafter referred to as third OSC light output intensity information);
The second OSC light transmitter of the downstream device is configured to transmit the second OSC light including the third OSC light output intensity information detected by the sixth detector as information,
The gain slope calculation unit of the optical amplifier is configured to acquire the third OSC light output intensity information based on the second OSC light input from the downstream device via the counter transmission line,
The loss factor calculation unit of the gain slope calculation unit calculates the loss factor based on a difference between the third OSC light transmission intensity detected by the fourth detection unit and the third OSC light output intensity information. The optical transmission system according to appendix 24 or appendix 25.

1 is a block diagram showing a configuration of an optical transmission system as a first embodiment of the present invention. It is a figure for demonstrating the loss coefficient wavelength characteristic of a transmission line (optical fiber), (a) is a figure for demonstrating the loss coefficient wavelength characteristic of SMF (Single Mode Fiber), (b) is DSF ( It is a figure for demonstrating the loss coefficient wavelength characteristic of Dispersion Shifted Fiber). It is a figure which shows the relationship between the loss of signal light and the transmission line distance in the input transmission line of the optical transmission system as 1st Embodiment of this invention, and the relationship between the loss of OSC light, and a transmission line distance. It is a figure for demonstrating the relationship between the transmission line input total intensity | strength of the signal light in the input transmission line of the optical transmission system as 1st Embodiment of this invention, and SRS inclination amount. The SRS inclination calculated by the SRS inclination calculation unit of the optical amplifier of the optical transmission system as the first embodiment of the present invention, the inverse SRS inclination calculated by the inverse inclination calculation unit, and the intensity of the signal light output from the optical amplifier It is a figure for demonstrating. It is a block diagram which shows the structural example of the optical amplification part of the optical amplifier of the optical transmission system as 1st Embodiment of this invention. FIGS. 7A and 7B are diagrams for explaining a method of realizing gain tilt by the optical amplifying unit illustrated in FIG. 6, where FIG. 7A is a diagram illustrating input characteristics, and FIG. 7B is a diagram illustrating an output after gain equalization in FIG. (C) is a figure which shows the output after VOA adjustment of (b). It is a block diagram which shows the structural example of the optical amplification part of the optical amplifier of the optical transmission system as 1st Embodiment of this invention. It is a block diagram which shows the structural example of the optical amplification part of the optical amplifier of the optical transmission system as 1st Embodiment of this invention. It is a figure for demonstrating the realization method of the gain inclination by the optical amplifier shown in FIG. 9, (a1) is a figure for demonstrating the Raman characteristic obtained by outputting the same intensity | strength with each excitation light source, ( (a2) is a diagram for explaining a flat output realized after gain equivalence of (a1), and (b1) shows a Raman characteristic obtained by controlling the output intensity of each excitation light source so as to increase as the wavelength increases. It is a figure for demonstrating, (b2) is a figure for demonstrating the gain inclination which goes up to the right implement | achieved after the gain equivalence of (b1), (c1) is the output intensity of each excitation light source about a long wavelength. It is a figure for demonstrating the Raman characteristic obtained by controlling so that it may become small, and c2) is a figure for demonstrating the right-falling gain inclination implement | achieved after the gain equivalence of (c1). It is a flowchart for demonstrating the operation | movement procedure at the time of the initial setting of the optical amplification method as 1st Embodiment of this invention. It is a flowchart for demonstrating the operation | movement procedure at the time of normal driving | operation of the optical amplification method as 1st Embodiment of this invention. It is a block diagram which shows the structure of the optical transmission system as a modification of 1st Embodiment of this invention. It is a block diagram which shows the structural example of the optical amplification part of the optical amplifier of the optical transmission system as a modification of 1st Embodiment of this invention. It is a block diagram which shows the structure of the optical transmission system as 2nd Embodiment of this invention. It is a figure for demonstrating the control content of the reverse inclination control part of the optical amplifier of the optical transmission system as 2nd Embodiment of this invention. It is a flowchart for demonstrating the operation | movement procedure at the time of the initial setting of the optical amplification method as 2nd Embodiment of this invention. It is a flowchart for demonstrating the operation | movement procedure at the time of normal driving | operation of the optical amplification method as 2nd Embodiment of this invention. It is a block diagram which shows the structure of the optical transmission system as a modification of 2nd Embodiment of this invention. It is a block diagram which shows the structural example of the optical amplifier of the optical amplifier of the optical transmission system as a modification of 2nd Embodiment of this invention. It is a figure which shows the case where the intensity | strength at the time of the input to the transmission line of the wavelength multiplexed signal light is the same at all the wavelengths. It is a figure for demonstrating the gain inclination generate | occur | produced in the signal beam | light output from the transmission line in the case shown in FIG. (A) It is a figure which shows the gain inclination generate | occur | produced in the signal light by which 44 waves were wavelength-multiplexed, (b) shows the output intensity when the signal light shown to (a) becomes only one wave of the shortest wavelength. FIG. (A) It is a figure which shows the gain inclination which generate | occur | produces in the signal light by which 44 waves were wavelength-multiplexed, (b) shows the output intensity when the signal light shown to (a) becomes only one wave of the longest wavelength. FIG.

Explanation of symbols

1a, 1a ', 1b, 1b' Optical transmission system 2a, 2b Previous device (upstream device)
2a-1 Signal Light Transmitter 2a-2 OSC (Optical Supervisory Channel) Optical Transmitter (First OSC Optical Transmitter)
3 Input transmission line 4 Output transmission line 5a, 5b Subsequent device (downstream device)
9 Opposite transmission lines 10a, 10a ', 10b, 10b' Optical amplifiers 11, 14, 43a, 51 First coupler 12, 16, 43b, 53 Second coupler 13 Monitor (first detector)
15 1st monitor (3rd detection part)
17 Second monitor (fourth detector)
20a, 20b SRS (Stimulated Raman Scattering) slope calculator (gain slope calculator)
21a OSC light detection unit 21b OSC light reception unit 22a acquisition unit (first acquisition unit)
22b Acquisition unit (second acquisition unit)
23a OSC light input intensity detector (second detector)
24a, 24b Loss coefficient calculation unit 25a, 25b Inclination amount calculation unit 30a, 30a ′, 30b, 30b ′, 30-1 to 30-3 Inverse inclination control unit (control unit)
31 Reverse inclination calculation part 40, 40 ', 40-1 to 40-3, 50 Optical amplification part 41a 1st EDF (Erbium-Doped Fiber)
41b 2nd EDF
42 VOA (Variable Optical Attenuator)
43c 3rd coupler 43d 4th coupler 44a 1st PD (PhotoDiode)
44b 2nd PD
44c 3rd PD
44d 4th PD
45a First excitation light source (first LD (Laser Diode))
45b Second excitation light source (second LD)
45c Third excitation light source (third LD)
46a, 46c 1st beam splitter 46b, 46d 2nd beam splitter 46e 3rd beam splitter 47 Gain equalizer (GEQ: Gain EQualizer)
48a-48c control part 52 1st monitor (5th detection part)
54 Second monitor (sixth detector)
55 OSC optical transmitter (second OSC optical transmitter)
60 OSC light output unit

Claims (5)

A first detector that detects the intensity of input signal light input from the upstream device through the input transmission path;
The gain of the signal light due to stimulated Raman scattering in the input transmission path based on the first transmission signal light intensity information which is information of the transmission light intensity to the input transmission path of the upstream device and the input signal light intensity. A gain slope calculator for calculating the slope;
An optical amplifier for amplifying the input signal light;
An optical amplifier comprising: a control unit that controls output intensity based on the calculated gain gradient. A first detector that detects the intensity of the input signal light input from the upstream device through the input transmission path;
The gain of the signal light due to stimulated Raman scattering in the input transmission path based on the first transmission signal light intensity information which is information of the transmission light intensity to the input transmission path of the upstream device and the input signal light intensity. A gain slope calculator for calculating the slope;
A control unit that controls output intensity by adjusting excitation light intensity for Raman amplification to the input transmission line based on the calculated gain slope is provided. An optical amplifier. An optical amplifier connected to the upstream device via an input transmission path and connected to the downstream device via an output transmission path,
An optical amplifying unit for amplifying and outputting the signal light input via the input transmission path;
A third detector for detecting the intensity of the signal light output from the optical amplifier to the output transmission path (hereinafter referred to as second output signal light intensity);
Based on the signal light output intensity information, which is information on the output intensity of the signal light output from the output transmission path, and the second transmission signal light intensity detected by the third detection unit, the output transmission path A gain tilt calculation unit for calculating the gain tilt of the signal light due to stimulated Raman scattering in
And a control unit that controls the second transmission signal light intensity of the signal light output from the optical amplification unit based on the gain inclination calculated by the gain inclination calculation unit. A characteristic optical amplifier. An optical amplifier connected to the upstream device via an input transmission path and connected to the downstream device via an output transmission path,
A third detector for detecting the intensity of the transmitted light of the signal light to the output transmission path (hereinafter referred to as the second transmitted signal light intensity);
Based on the signal light output intensity information, which is information on the output intensity of the signal light output from the output transmission path, and the second transmission signal light intensity detected by the third detection unit, the output transmission path A gain tilt calculation unit for calculating the gain tilt of the signal light due to stimulated Raman scattering in
Based on the gain inclination calculated by the gain inclination calculation unit, the intensity of the pumping light for Raman amplification to the output transmission line is adjusted, whereby the signal light output from the output transmission line is adjusted. 2. An optical amplifier comprising a control unit for controlling the intensity of the transmitted signal light. An optical transmission system comprising an optical amplifier interposed between an input transmission path and an output transmission path, and an upstream device connected to the optical amplifier via the input transmission path,
The upstream device comprises:
A signal light transmitter that transmits signal light to the optical amplifier via the input transmission path;
A first OSC (Optical Supervisory Channel) light including first transmission signal light intensity information, which is at least information of the transmission light intensity of the signal light to the input transmission path, is transmitted to the optical amplifier via the input transmission path. With 1OSC optical transmitter
The optical amplifier is
A first detector that detects the intensity of the input signal light input from the upstream device through the input transmission path;
The gain of the signal light due to stimulated Raman scattering in the input transmission path based on the first transmission signal light intensity information which is information of the transmission light intensity to the input transmission path of the upstream device and the input signal light intensity. A gain slope calculator for calculating the slope;
An optical amplifier for amplifying the input signal light;
An optical transmission system comprising: a control unit that controls an output intensity of signal light output to the output transmission path based on the calculated gain slope.

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