JP7535915B2 - Optical Transmission Equipment - Google Patents

Description

This disclosure relates to an optical transmission device.

In wavelength division multiplexing optical transmission equipment that transmits wavelength division multiplexed (WDM) optical signals over long distances, an erbium-doped fiber amplifier (EDFA) is generally used to compensate for the level drop that occurs during propagation along the transmission path. On the other hand, the optical signal to noise ratio (OSNR) of the signal light deteriorates due to amplified spontaneous emission (ASE) light emitted from the EDFA during optical amplification. If the OSNR falls below a specified value, the receiver cannot regenerate the signal, which limits the transmission distance. In addition, as the transmission speed per wavelength increases, the OSNR required for regeneration becomes higher, which results in a greater limitation of the transmission distance.

By increasing the output optical level to the transmission line and increasing the input optical level to the receiving optical amplifier, it is possible to suppress deterioration of the OSNR in the receiving optical amplifier.
However, as the output light level to the transmission line increases, the deterioration of the waveform due to nonlinear optical effects increases, so there is a limit to the improvement in OSNR that can be achieved with this method.

For this reason, a Raman amplifier is used which amplifies the signal light in the transmission line and improves the OSNR by increasing the input light level to the receiving optical amplifier.
However, Raman amplifiers require a dedicated pumping light source, which increases the cost of initial installation. In addition, when adding a Raman amplifier to optical transmission equipment that does not have one, a Raman amplifier must be inserted between the transmission line and the receiving optical amplifier, which requires line detouring and places a burden on maintenance and operation personnel.

In light of the above situation, Patent Document 1 shows an optical transmission device that uses only EDFAs at the initial installation to keep installation costs down, while allowing the addition of Raman amplification functionality later.

JP 2006-279610 A

However, with conventional technology, components for adding Raman amplification functionality must be installed in advance, which increases the initial implementation costs.

Therefore, one or more aspects of the present disclosure aim to make it possible to easily add Raman amplification functionality to optical transmission equipment that does not have Raman amplification functionality, without requiring special components to add Raman amplification functionality and without affecting the main signal light during operation.

The optical transmission device according to a first aspect of the present disclosure is an optical transmission device comprising a receiving optical amplifier that separates supervisory light and main signal light including OSC (Optical Supervisory Channel) light from a signal light and amplifies the main signal light, and an OSC optical receiver that has at least an input connection port that receives the OSC light, wherein the receiving optical amplifier is connected to a transmission path and comprises a first connection port that receives the signal light, a first wavelength separation filter that separates the signal light into the supervisory light and the main signal light, an optical amplifier that amplifies the main signal light, and a second connection port that outputs the supervisory light, and the optical transmission device is configured to connect the input connection port and the second connection port with an optical fiber, thereby providing an initial state in which the supervisory light is sent from the receiving optical amplifier to the OSC optical receiver, and an output state in which an optical fiber is used between the input connection port and the second connection port. and a Raman amplification function added state in which a Raman control unit is connected to the third connection port, the Raman control unit includes a third connection port that receives the monitoring light, a second wavelength separation filter that separates the monitoring light into the OSC light and the pumping light, an OSC light level measurement unit that measures the optical level, which is the level of the OSC light, a pumping light source that amplifies the signal light in the transmission path, a light source control unit that controls the pumping light source according to the optical level, and a fourth connection port that outputs the OSC light. In the Raman amplification function added state, the second connection port and the third connection port are connected by optical fiber, and the fourth connection port and the input connection port are connected by optical fiber.

An optical transmission device according to a second aspect of the present disclosure is an optical transmission device comprising: a receiving optical amplifier that separates a supervisory light including OSC (Optical Supervisory Channel) light and a main signal light from a signal light and amplifies the main signal light; and an OSC optical receiver that has at least an input connection port that receives the OSC light, wherein the receiving optical amplifier is connected to a transmission path and comprises: a first connection port that receives the signal light; a first wavelength separation filter that separates the signal light into the supervisory light and the main signal light; a wavelength-by-wavelength optical level measurement unit that measures the optical level for each band of the main signal light; an optical amplifier that amplifies the main signal light; a second connection port that outputs the supervisory light; and an output interface that outputs an optical level signal indicating the optical level. The optical transmission device is in an initial state in which the supervisory light is sent from the receiving optical amplifier to the OSC optical receiver by connecting the input connection port and the second connection port with an optical fiber. , and a Raman amplification function added state in which a Raman control unit is connected between the input connection port and the second connection port using optical fiber, the Raman control unit is provided with a third connection port that receives the monitoring light, a second wavelength separation filter that separates the monitoring light into the OSC light and the pumping light, an input interface that receives an optical level signal indicating the optical level, a pumping light source that amplifies the signal light in the transmission path, a light source control unit that controls the pumping light source according to the optical level, and a fourth connection port that outputs the OSC light, and in the Raman amplification function added state, the second connection port and the third connection port are connected by optical fiber, and the fourth connection port and the input connection port are connected by optical fiber.

According to one or more aspects of the present disclosure, it is possible to easily add Raman amplification functionality to optical transmission equipment that does not have Raman amplification functionality, without requiring special components to add Raman amplification functionality and without affecting the main signal light during operation.

2 is a block diagram showing an example of a main configuration of an optical transmission device according to a first embodiment at the time of initial introduction; 2 is a block diagram showing an example of a main configuration of an optical transmission device to which a Raman amplification function is added in the first embodiment; FIG. 2 is a block diagram showing an example of a hardware configuration. 4 is a graph showing an example of setting a wavelength allocation of signal light and separation wavelengths of a wavelength separation filter in the first embodiment. 1 is a flowchart showing a procedure for adding a Raman amplification function to an optical transmission device. 11A to 11D are graphs illustrating the effects of the first embodiment. 11 is a block diagram showing an example of a main configuration of an optical transmission device according to a second embodiment at the time of initial introduction; FIG. FIG. 11 is a block diagram illustrating an example of a configuration of a main part of an optical transmission device to which a Raman amplification function is added in a second embodiment. 1 is a flowchart showing a procedure for adding a Raman amplification function to an optical transmission device. 13A to 13D are graphs illustrating the effects of the second embodiment.

Embodiment 1.
FIG. 1 is a block diagram showing an example of a main configuration of an optical transmission device 100 according to a first embodiment at the time of initial installation.
As shown in FIG. 1, the optical transmission device 100 includes a receiving optical amplifier section 110 and an OSC (Optical Supervisory Channel) optical receiving section 130 in the initial state.

The receiving optical amplifier 110 separates the optical supervisory light including the OSC light and the optical main signal from the optical signal received from the transmission path 101, and amplifies the optical main signal. The receiving optical amplifier 110 then outputs the output optical signal, which is the optical main signal after processing, to a downstream device such as a transmitting optical amplifier or an optical multiplexing/demultiplexing unit (not shown).
Moreover, the received light amplifier 110 outputs the separated supervisory light to the OSC light receiver 130 .
The OSC optical receiving unit 130 includes an optical connector 131 which is an input connection port for receiving at least the OSC light contained in the supervisory light.

The receiving optical amplifier 110 includes optical connectors 111, 112, and 113, a wavelength separation filter 114, an optical amplifier 115, a variable attenuator 116, a splitter 117, an optical level measurement unit 118, and a variable attenuator control unit 119.

The optical connector 111 is a connection port connected to the transmission line 101, which is an optical transmission line. The optical connector 111 is also referred to as a first connection port. The optical connector 111 receives signal light from the transmission line 101.
The wavelength separation filter 114 is a filter that separates the received signal light into supervisory light including OSC light and main signal light. Here, it is assumed that the OSC light is set to a shorter wavelength side than the band of the main signal light. The wavelength separation filter 114 separates the light in the long wave band including the band of the main signal light toward the optical amplifier 115 and the light in the short wave band including the band of the OSC light toward the optical connector 112. The wavelength separation filter 114 is also called a first wavelength separation filter.

The optical connector 112 is a connection port that outputs the supervisory light and is also referred to as a second connection port.
The optical amplifier 115 amplifies the main signal light and outputs it as an amplified main signal light.

The variable attenuator 116 attenuates the output level of the amplified main signal light. For example, the variable attenuator 116 is an attenuator that can change the amount of attenuation of the amplified main signal light to an arbitrary value to produce an output signal light.
The splitter 117 splits the output signal light into two systems and outputs them.

The optical level measuring unit 118 measures the output optical level, which is the optical level of the output signal light, which is the amplified main signal light processed by the variable attenuator 116. Here, the optical level measuring unit 118 measures the total optical level of the output signal light. The optical level measuring unit 118 can be realized, for example, using a PD (Photo Diode) or the like.

The variable attenuator control unit 119 controls the variable attenuator 116 in accordance with the measurement result of the optical level measuring unit 118. In other words, the variable attenuator control unit 119 controls the variable attenuator 116 in accordance with the output optical level measured by the optical level measuring unit 118.
For example, the variable attenuator control unit 119 controls the variable attenuator 116 so that the difference between the output light level measured by the optical level measuring unit 118 when the excitation light source 147 is stopped and the output light level measured by the optical level measuring unit 118 when the excitation light source 147 is operating is less than a predetermined threshold value.
The optical connector 113 is a connection port for connecting to a subsequent device.

FIG. 2 is a block diagram showing an example of a configuration of a main part of an optical transmission device 100# to which a Raman amplification function is added in the first embodiment.
The optical transmission device 100# shown in FIG. 2 is the same as the optical transmission device 100 shown in FIG. 1 except that a Raman control unit 140 is added.

The Raman control unit 140 includes optical connectors 141 and 142, a wavelength separation filter 143, a splitter 144, an OSC light level measurement unit 145, a light source control unit 146, and an excitation light source 147.

The optical connector 141 is a connection port that is connected to the receiving optical amplifier unit 110 and receives the monitoring light. The optical connector 141 is also called the third connection port.

The wavelength separation filter 143 is a filter that separates the long-wavelength band light including the OSC light band toward the optical connector 142 and the short-wavelength band light including the band of the Raman pumping light, which is the pumping light, toward the pumping light source 147. It separates the reflected components of the OSC light and Raman pumping light contained in the received monitoring light, and also separates the Raman pumping light output from the pumping light source 147 toward the connector 141 and outputs it to the transmission path 101. Here, the OSC light is set to a longer wavelength side than the wavelength band of the Raman pumping light. The wavelength separation filter 143 is also called a second wavelength separation filter.

The splitter 144 splits the OSC light into two systems and outputs them.
The optical connector 142 is a connection port that is connected to the OSC optical receiving unit 130 and outputs the OSC light. The optical connector 142 is also referred to as a fourth connection port.
The OSC light level measuring unit 145 measures the light level of the OSC light. Here, the OSC light level measuring unit 145 measures the total light level of the OSC light. The OSC light level measuring unit 145 can be realized using, for example, a PD or the like. The light level measured by the OSC light level measuring unit 145 is also referred to as the OSC light level.

The light source control unit 146 controls the pump light source 147 in accordance with the measurement result of the OSC light level measurement unit 145 .
For example, the light source control unit 146 controls the Raman amplification gain of the pumping light source 147 so that the difference between the optical level measured by the OSC optical level measuring unit 145 when the pumping light source 147 is stopped and the optical level measured by the OSC optical level measuring unit 145 when the pumping light source 147 is operating is within a control target range.

The pump light source 147 amplifies the signal light in the transmission path 101. For example, the pump light source 147 performs amplification by generating pump light and outputting the pump light to the transmission path 101.

When the Raman control unit 140 is connected, the optical connector 112 and the optical connector 141 are connected by the optical fiber 103, and the optical connector 142 and the optical connector 131 are connected by the optical fiber 104.

As described above, the optical transmission device 100 according to the first embodiment operates in one connection state selected from two connection states: an initial state in which the monitoring light is sent from the receiving light amplifier 110 to the OSC optical receiver 130 by connecting the optical connector 112 and the optical connector 131 with the optical fiber 102, and a Raman amplification function added state in which the Raman control unit 140 is connected between the optical connector 112 and the optical connector 131 using the optical fibers 103 and 104.

As shown in FIG. 3, each of the variable attenuator control unit 119 and the light source control unit 146 can be realized by a processor 10 such as a CPU (Central Processing Unit) or a system LSI (Large Scale Integration), and a memory 11 configured by a RAM (Random Access Memory) or a ROM (Read Only Memory), for example.
The processor 10 executes a program stored in the memory 11 to function as the variable attenuator control unit 119 or the light source control unit 146 .

FIG. 4 is a graph showing an example of the wavelength allocation of signal light and the separation wavelengths of the wavelength separation filter according to the first embodiment.
4 is a separation wavelength of the wavelength separation filter 114. Moreover, a wavelength λ2 is a separation wavelength of the wavelength separation filter 143.
As shown in FIG. 4, the wavelength band of the OSC light is set to the shorter wavelength side than the wavelength band of the main signal light, and the wavelength band of the pump light is set to the shorter wavelength side than the wavelength band of the OSC light.

FIG. 5 is a flowchart showing a procedure for adding a Raman amplification function to the optical transmission device 100.
Here, it is assumed that there is a signal light in operation.
First, the user of the optical transmission device 100 removes the optical fiber 102 (see FIG. 1) between the optical connector 112 of the reception optical amplifier unit 110 and the optical connector 131 of the OSC optical receiver unit 130 (S10).

Next, the user connects the optical fiber 103 between the optical connector 112 of the receiving optical amplifier 110 and the optical connector 141 of the Raman control unit 140, as shown in FIG. 2 (S11).

Next, the user connects the optical connector 142 of the Raman control unit 140 to the optical connector 131 of the OSC optical receiving unit 130 with the optical fiber 104 (S12). Here, it is assumed that the pump light source 147 has stopped outputting pump light.

Next, the optical level measurement unit 118 measures the main signal optical level Pout (OFF) when the excitation light is stopped (S13).

Next, the OSC light level measurement unit 145 measures the OSC light level Posc (OFF) when the excitation light is stopped (S14).

Next, the light source control unit 146 increases the intensity of the pump light source 147 by a predetermined value (S15). Here, it is desirable to make the increase in the intensity of the pump light source 147 as small as possible so as not to affect the main signal light level.

Next, the optical level measurement unit 118 measures the main signal optical level Pout (ON) (S16).

Next, the variable attenuator control unit 119 calculates the difference X (dB) between the main signal light level Pout (ON) measured in step S16 and the main signal light level Pout (OFF) measured in step S13, and determines whether the difference X (dB) is less than a predetermined threshold (S17). If the difference X (dB) is less than the threshold (Yes in S17), the process proceeds to step S19, and if the difference X (dB) is equal to or greater than the threshold (No in S17), the process proceeds to step S18. Here, the threshold is set to a level fluctuation amount that does not affect the main signal light.

In step S18, the variable attenuator control unit 119 increases the attenuation of the variable attenuator 116 by X (dB). Then, the process proceeds to step S19.

In step S19, the OSC light level measurement unit 145 measures the OSC light level Posc (ON).

Next, the light source control unit 146 calculates the difference Y (dB) between the OSC light level Posc (ON) measured in step S19 and the OSC light level Posc (OFF) measured in step S14, and determines whether the difference Y (dB) is within the control target range (S20). If the difference Y (dB) is within the control target range (Yes in S20), the process ends, and if the difference Y (dB) is outside the control target range (No in S20), the process returns to step S15.

Next, the reason why this embodiment makes it possible to add a Raman amplification function and improve the OSNR without affecting the main signal light in operation will be described.
Fig. 6(A) is a graph showing the change over time in the excitation light intensity of the excitation light source 147. Fig. 6(B) is a graph showing the change over time in the main signal light level Pout(ON) in the optical level measuring unit 118. Fig. 6(C) is a graph showing the change over time in the OSC light level Posc(ON) in the OSC light level measuring unit 145. Fig. 6(D) is a graph showing the change over time in the OSNR of the output signal light from the receiving optical amplifier 110.

As shown in FIG. 6(A), as the pump light intensity increases, the Raman amplification effect occurs in the transmission line 101, Pout(ON) increases as shown in FIG. 6(B), and Posc(ON) increases as shown in FIG. 6(C). In addition, as the main signal light input level to the optical amplifier 115 increases, the OSNR improves as shown in FIG. 6(D).

Also, as shown in FIG. 6(B), when the difference X (dB) between Pout (ON) and the main signal light level Pout (OFF) when the pump light is stopped becomes equal to or greater than a threshold value, the variable attenuator control unit 119 controls the variable attenuator 116 to prevent the change in the optical level from affecting the main signal light.

In step S10 of FIG. 5, the user removes the optical fiber 102 between the optical connector 112 of the receiving optical amplifier 110 and the optical connector 131 of the OSC optical receiver 130, temporarily preventing reception of the OSC light. However, by using a ring configuration, for example, the reception of the OSC light can be maintained on a separate path, preventing any impact on monitoring.

As described above, according to the first embodiment, the Raman control unit 140 is connected between the optical connector 112 of the receiving optical amplifier unit 110 and the optical connector 131 of the OSC optical receiver unit 130, and the intensity of the pump light source 147 is increased by a specified value while the main signal light level (Pout) is controlled by the variable attenuator 116 and the OSC light level (Posc) is controlled to a predetermined value. This makes it possible to add a Raman amplification function without requiring any dedicated parts and without affecting the main signal light during operation.

Note that, although the explanation here is given on the assumption that there is an operating signal light, the Raman control unit 140 may be connected when there is no operating signal light. In that case, there is no need for the optical level measurement unit 118 to measure the main signal light levels Pout(ON) and Pout(OFF), and for the variable attenuator 116 to be controlled.

Note that, although an example is described here in which the excitation light intensity is increased by a constant value, the amount of increase in the excitation light intensity may be changed depending on the measurement results.

Note that, although an example in which only one pump light source 147 is provided is described here, two or more pump light sources may be provided. In that case, the wavelengths of all the pump lights are set to be shorter than the wavelength of the OSC light.

The accuracy of the control of the main signal light level Pout (ON) by the variable attenuator 116 may be improved by correcting the ASE light level generated by Raman amplification from the measurement result of the main signal light level Pout (ON) by the optical level measurement unit 118. In this case, since the ASE light level generated by Raman amplification is proportional to the Raman amplification gain value, for example, by measuring the relationship between the Raman amplification gain and the ASE light level in advance, the ASE light level generated from the set Raman amplification gain value can be obtained.

Embodiment 2.
In the first embodiment, the Raman amplification gain is adjusted using the OSC optical level. Meanwhile, in recent optical transmission devices, a configuration that can monitor the optical level of each wavelength of the received light from the transmission line using an OCM (Optical Channel Monitor) or the like is becoming common. In such a configuration, the Raman amplification gain may be adjusted using the ASE optical level of an arbitrary band within the band of the main signal light measured in a part that amplifies the received light.

FIG. 7 is a block diagram illustrating an example of a main configuration of an optical transmission device 200 according to the second embodiment at the time of initial installation.
As shown in FIG. 7, the optical transmission device 200 includes a received optical amplifier 210, an OSC optical receiver 130, and a monitor and control unit 250 in the initial state.
In embodiment 2, a method is described in which the ASE light level of any band within the band of the main signal light measured by the receiving optical amplifier unit 210 is used to add a Raman amplification function without requiring any dedicated components and without affecting the main signal light during operation.

The receiving optical amplifier 210 includes optical connectors 111, 112, and 113, a wavelength separation filter 114, an optical amplifier 115, a variable attenuator 116, a splitter 117, an optical level measurement unit 118, a variable attenuator control unit 119, a splitter 220, an optical level measurement unit for each wavelength 221, and a connection interface (hereinafter referred to as a connection I/F) 222.

The optical connectors 111, 112, 113, wavelength separation filter 114, optical amplifier 115, variable attenuator 116, splitter 117, optical level measurement unit 118, and variable attenuator control unit 119 of the receiving optical amplifier 210 in the second embodiment are the same as the optical connectors 111, 112, 113, wavelength separation filter 114, optical amplifier 115, variable attenuator 116, splitter 117, optical level measurement unit 118, and variable attenuator control unit 119 of the receiving optical amplifier 110 in the first embodiment.

The splitter 220 splits the main signal light separated by the wavelength separation filter 114 into two systems and outputs them.
The wavelength-specific optical level measuring unit 221 measures the optical level of each band of the main signal light. The wavelength-specific optical level measuring unit 221 can be realized by using, for example, an OCM. Here, the wavelength-specific optical level measuring unit 221 measures the optical level of the ASE light within the band of the main signal light.

The connection I/F 222 is an interface for connecting to the monitoring control unit 250. The monitoring control unit 250 and the connection I/F 222 are connected by a communication line such as a LAN (Local Area Network) cable. The connection I/F 222 is an output interface that outputs an optical level signal indicating the optical level measured by the wavelength-specific optical level measurement unit 221.
The wavelength-specific optical level measuring unit 221 provides the measured optical level for each band to the monitor and control unit 250 via the connection I/F 222 .

FIG. 8 is a block diagram showing an example of a main configuration of an optical transmission device 200# to which a Raman amplification function is added in the second embodiment.
The optical transmission device 200# shown in FIG. 8 is configured by adding a Raman controller 240 to the optical transmission device 200 shown in FIG.

The Raman control unit 240 includes optical connectors 141 and 142, a wavelength separation filter 143, a light source control unit 246, an excitation light source 147, and a connection I/F 248.

The optical connectors 141, 142, wavelength separation filter 143 and pumping light source 147 of the Raman control unit 240 in the second embodiment are similar to the optical connectors 141, 142, wavelength separation filter 143 and pumping light source 147 of the Raman control unit 140 in the first embodiment.
It should be noted that the Raman control unit 240 in the second embodiment does not include the splitter 144 and the OSC light level measuring unit 145 in the Raman control unit 140 in the first embodiment.

The connection I/F 248 is an interface for connecting to the monitoring control unit 250. The monitoring control unit 250 and the connection I/F 248 are connected by a communication line such as a LAN cable. The connection I/F 248 is an input interface that receives an optical level signal indicating the optical level measured by the wavelength-specific optical level measurement unit 221.

The light source control unit 246 acquires the measurement result of the wavelength-specific light level measurement unit 221 via the connection I/F 248, and controls the pump light source 147 in accordance with the measurement result.
For example, the light source control unit 246 controls the Raman amplification gain of the pumping light source 147 so that the difference between the optical level measured by the wavelength-specific optical level measuring unit 221 when the pumping light source 147 is stopped and the optical level measured by the wavelength-specific optical level measuring unit 221 when the pumping light source 147 is operating is within a control target range.

The monitor and control unit 250 is a control unit that controls the entire processing in the optical transmission device 200. Here, the monitor and control unit 250 provides the measurement result of the wavelength-specific optical level measuring unit 221 in the received light amplifier unit 210 to the light source control unit 246 in the Raman control unit 240.
The monitoring control unit 250 can also be realized by, for example, the processor 10 and the memory 11, as shown in FIG.

FIG. 9 is a flowchart showing a procedure for adding a Raman amplification function to the optical transmission device 200.
Here, it is assumed that there is a signal light in operation.

First, the user of the optical transmission device 200 removes the optical fiber 102 (see FIG. 7) between the optical connector 112 of the receiving optical amplifier 210 and the optical connector 131 of the OSC optical receiver 130 (S30).

Next, the user connects the optical fiber 103 between the optical connector 112 of the receiving optical amplifier 210 and the optical connector 141 of the Raman control unit 240, as shown in FIG. 8 (S31).

Next, the user connects the optical connector 142 of the Raman control unit 240 and the optical connector 131 of the OSC optical receiving unit 130 with the optical fiber 104 (S32).
At this time, the user connects the communication line 105 for communicating with the monitor and control unit 250 to the connection I/F 248 .
It is assumed here that the pump light source 147 stops outputting the pump light.

Next, the optical level measurement unit 118 measures the main signal optical level Pout (OFF) when the excitation light is stopped (S33).

Next, the wavelength-specific optical level measurement unit 221 measures the ASE optical level Pase (OFF) of any band within the band of the main signal light when the excitation light is stopped (S34). Here, the wavelength-specific optical level measurement unit 211 transmits the measurement result to the monitoring control unit 250 via the connection I/F 222.

Next, the light source control unit 246 increases the intensity of the pumping light source 147 by a predetermined value (S35). Here, it is desirable to make the increase in the intensity of the pumping light source 147 as small as possible so as not to affect the main signal light level.

Next, the optical level measurement unit 118 measures the main signal optical level Pout (ON) (S36).

Next, the variable attenuator control unit 119 calculates the difference X (dB) between the main signal light level Pout (ON) measured in step S36 and the main signal light level Pout (OFF) measured in step S33, and determines whether the difference X (dB) is less than a predetermined threshold (S37). If the difference X (dB) is less than the threshold (Yes in S37), the process proceeds to step S39, and if the difference X (dB) is equal to or greater than the threshold (No in S37), the process proceeds to step S38. Here, the threshold is set to a level fluctuation amount that does not affect the main signal light.

In step S38, the variable attenuator control unit 119 increases the attenuation of the variable attenuator 116 by X (dB). Then, the process proceeds to step S39.

In step S39, the wavelength-specific optical level measurement unit 221 measures the ASE optical level Pase (ON) of any band within the band of the main signal light (S39). Here, the wavelength-specific optical level measurement unit 211 transmits the measurement result to the monitoring control unit 250 via the connection I/F 222.

Next, the light source control unit 246 acquires the ASE light level Pase (ON) measured in step S39 and the ASE light level Pase (OFF) measured in step S34 from the monitoring control unit 250 via the connection I/F 248, calculates the difference Z (dB) between the ASE light level Pase (ON) and the ASE light level Pase (OFF), and determines whether the difference Z (dB) is within the control target range (S40). If the difference Z (dB) is within the control target range (Yes in S40), the process ends, and if the difference Z (dB) is outside the control target range (No in S40), the process returns to step S35.

Next, the basis for the present embodiment being able to add a Raman amplification function and improve signal quality without affecting the main signal light in operation will be described.
Fig. 10(A) is a graph showing the time change in the excitation light intensity of the excitation light source 147. Fig. 10(B) is a graph showing the time change in the main signal light level Pout(ON) in the optical level measuring unit 118. Fig. 10(C) is a graph showing the time change in the ASE light level Pase(ON). Fig. 10(D) is a graph showing the time change in the OSNR of the output signal light from the receiving optical amplifier 210.

As shown in FIG. 10(A), as the pump light intensity increases, the Raman amplification effect occurs in the transmission line 101, Pout(ON) increases as shown in FIG. 10(B), and Pase(ON) increases as shown in FIG. 10(C). In addition, as the main signal light input level to the optical amplifier 115 increases, the OSNR improves as shown in FIG. 10(D).

Also, as shown in FIG. 10(B), when the difference X (dB) between Pout (ON) and the main signal light level Pout (OFF) when the pump light is stopped becomes a value higher than a threshold value, the variable attenuator control unit 119 controls the variable attenuator 116 to prevent the main signal light from being affected by changes in the optical level of the main signal light.

As described above, according to the second embodiment, the Raman control unit 240 is connected between the optical connector 112 of the receiving optical amplifier 210 and the optical connector 131 of the OSC optical receiver 130, and the intensity of the pump light source 147 is increased by a predetermined value while the main signal light level (Pout) is controlled by the variable attenuator 116, and the ASE light level (Pase) is controlled to a predetermined value. This makes it possible to add a Raman amplification function without requiring any dedicated parts and without affecting the main signal light during operation.

In the second embodiment, an example is described assuming that the band in which ASE light is monitored includes ASE light emitted from an optical amplifier in a previous node (not shown), but a band that does not include ASE light emitted from an optical amplifier in a previous node and includes only ASE light generated by Raman amplification may be monitored. In that case, it is not necessary to measure the ASE light level (Pase) without pump light, and the Raman amplification gain can be adjusted by only measuring the ASE light level when pump light is output.

100, 200 Optical transmission device, 101 Transmission path, 102, 103, 104 Optical fiber, 105 Communication line, 110, 110#, 210, 210# Received optical amplifier, 111, 112, 113 Optical connector, 114 Wavelength separation filter, 115 Optical amplifier, 116 Variable attenuator, 117 Branching device, 118 Optical level measurement device, 119 Variable attenuator control device, 220 Branching device, 221 Wavelength-specific optical level measurement device, 222 Connection I/F, 130 OSC optical receiver, 131 Optical connector, 140, 240 Raman control device, 141, 142 Optical connector, 143 Wavelength separation filter, 144 Branching device, 145 OSC optical level measurement device, 146, 246 Light source control unit, 147 Excitation light source, 248 Connection I/F, 250 Monitoring control unit.

Claims (5)

a receiving optical amplifier that separates a supervisory light including an OSC (Optical Supervisory Channel) light and a main signal light from the signal light and amplifies the main signal light;
an OSC light receiving unit having an input connection port for receiving at least the OSC light,
The receiving optical amplifier unit includes:
a first connection port connected to a transmission line and configured to receive the signal light;
a first wavelength separation filter that separates the signal light into the supervisory light and the main signal light;
an optical amplifier for amplifying the main signal light;
a second connection port that outputs the supervisory light,
the optical transmission device operates in one connection state selected from two connection states: an initial state in which the monitor light is sent from the receiving light amplifier unit to the OSC optical receiver unit by connecting the input connection port and the second connection port with an optical fiber, and a Raman amplification function added state in which a Raman control unit is connected between the input connection port and the second connection port using an optical fiber;
The Raman control unit is
a third connection port for receiving the monitor light;
a second wavelength separation filter that separates the supervisory light into the OSC light and the pump light;
an OSC light level measurement unit for measuring an optical level that is a level of the OSC light;
a pumping light source that amplifies the signal light in the transmission line;
a light source control unit that controls the excitation light source in response to the light level;
a fourth connection port for outputting the OSC light;
the second connection port and the third connection port are connected by an optical fiber, and the fourth connection port and the input connection port are connected by an optical fiber in the Raman amplification function added state. a wavelength band of the OSC light is set to a shorter wavelength side than a wavelength band of the main signal light,
2. The optical transmission device according to claim 1, wherein the wavelength band of the pumping light is set to a shorter wavelength side than the wavelength band of the OSC light. 3. The optical transmission device according to claim 1, wherein the light source control unit controls the Raman amplification gain of the pumping light source so that a difference between an optical level measured by the OSC optical level measuring unit when the pumping light source is stopped and an optical level measured by the OSC optical level measuring unit when the pumping light source is operating is within a control target range. The receiving optical amplifier unit includes:
a variable attenuator that attenuates an output level of the amplified main signal light, which is the main signal light amplified by the optical amplifier;
an optical level measuring unit for measuring an output optical level, which is an optical level of the amplified main signal light processed by the variable attenuator;
4. The optical transmission device according to claim 1, further comprising a variable attenuator control unit that controls the variable attenuator in response to the output optical level. 5. The optical transmission device according to claim 4, wherein the variable attenuator control unit controls the variable attenuator so that a difference between an output optical level measured by the optical level measuring unit when the pumping light source is stopped and an output optical level measured by the optical level measuring unit when the pumping light source is operating is less than a predetermined threshold.

Images