JP2003043429A - Method for setting operating condition and method for detecting operating condition of cross phase modulation type entire optical wavelength transducer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To set an optimum operating condition of a driving current, power of signal light and power of continuous light of a cross phase modulation type entire optical wavelength transducer. SOLUTION: In this cross phase modulation type entire optical wavelength transducer, a Mach-Zehnder type optical interference circuit is constituted by mounting SOAs(semiconductor optical amplifier) 7, 8 on a PLC(plane light wave circuit) 10. Then, when signal light and continuous light are inputted to this transducer, output light having the same wavelength as that of the continuous light is outputted. Moreover, driving currents Imod, Ipc are supplied respectively to the SOA 7 and the SOA 8. At this time, current to be supplied can be reduced by optimally setting values of the power of the signal light, the power of the continuous light and driving currents Imod, Ipc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an operating condition setting method and an operating condition detecting method for a cross-phase modulation type all-optical wavelength converter. The present invention relates to a method for setting and detecting the optimum operating conditions of operating light power (input signal light power and output continuous light power).

[0002]

2. Description of the Related Art In order to increase the capacity of optical communication networks,
In recent years, WDM (Wavelength Division Multipl)
exing) The development of communication methods is progressing. For example, it is possible to transmit signals of 32 different wavelengths with one optical fiber,
In this case, the total transmission capacity can be 32 times the signal bit rate. When the type of optical fiber used for constructing such a WDM network is different, the wavelength group used there is also different. For example, the wavelength groups used in a general single mode fiber have equal wavelength intervals, but in the dispersion shift fiber, the wavelength intervals are unequal intervals in order to avoid deterioration of the signal waveform due to interference between wavelengths. Therefore, at the connection point of interconnection between different WDM networks, wavelength conversion from the wavelength group used in one network to the wavelength group used in the other network is essential.

There is the following method as a conversion method of the all-optical wavelength converter that converts the wavelength of the signal light as it is without photoelectric conversion. (1) Cross Phase Modulatio (XPM)
n) (2) Cross Gain Modulation (XGM) (3) Four Wave Mixing (FWM)

Of the above wavelength conversion systems, four-wave mixing is capable of high-speed response, but its conversion efficiency is low. In the mutual gain modulation, the output extinction ratio is a gain variation, that is, a carrier variation itself, and therefore waveform distortion due to chirping is likely to occur during transmission. On the other hand, the cross-phase modulation method has an advantage that a high output extinction ratio can be obtained with a relatively small gain variation of 3 to 4 dB, and therefore waveform distortion during transmission is suppressed.

The operating principle of the above-mentioned cross-phase modulation type wavelength converter will be described by taking the hybrid integrated circuit of FIG. 1 as an example. A monolithic integrated type in which a semiconductor optical amplifier and a passive or active waveguide are integrally integrated on the same substrate with the same configuration also operates on the same principle.

In FIG. 1, 1 is a continuous light (CW) input port, 2 is an output port, 3 is a signal light input port, 4, 5 and 6 are optical multiplexer / demultiplexers, and 7 and 8 are A semiconductor optical amplifier (semiconductor optical) interposed in an arm waveguide.
amplifier: SOA), 9 is an optical filter, and 10 is a planar lightwave circuit (PLC) platform.

In FIG. 1, a semiconductor optical amplifier (semico
nductor optical amplifier (SOA) 7 and 8 are mounted on a planar lightwave circuit (PLC) platform 10 to form a Mach-Zehnder type optical interference circuit. CW light (continuous light) of wavelength λc is input from the port 1, is branched into two by the first optical multiplexer / demultiplexer 4, and is incident on the two arm waveguides.
The CW light entering the arm waveguides is the semiconductor optical amplifier 7,
Enter in 8. The output light from the semiconductor optical amplifiers 7 and 8 is multiplexed by the second optical multiplexer / demultiplexer 5, and the interference output light is output from the port 2.

On the other hand, a signal light of wavelength λs is input from the port 3 and is passed through the optical multiplexer / demultiplexer 6 to the semiconductor amplifier 7 (S
OA mod). Then, the carrier density decreases due to the saturation phenomenon of the semiconductor optical amplifier 7, which causes a change in the refractive index and causes the phase modulation of the CW light passing through the semiconductor optical amplifier 7. This is a CW that has passed through the other semiconductor optical amplifier 8 (SOApc) and has not undergone phase modulation.
By interfering with the light, the optical filter 9 from the port 2
Intensity modulation of the light of wavelength λc is output. As a result, the wavelength λs of the input signal light is transferred to the wavelength λc of the CW light and wavelength conversion is performed. At this time, the semiconductor optical amplifier 7 on the signal light incident side is SOAmod, and its drive current is Imo.
d, the other semiconductor optical amplifier 8 is SOApc, and its drive current is Ipc.

As shown in FIG. 1, generally, a cross-phase modulation type optical wavelength conversion circuit has at least two SOAs, and the input CW optical power Pc- with respect to the input signal optical power Ps-in.
It has three operation parameters of in, Imod, and Ipc.
Normally, when the transmission bit rate is about 10 Gb / s, the drive current Imod of the semiconductor optical amplifier on the signal light incident side is 200
With a high injection constant value of approximately mA, the remaining two operating parameters, Ipc and Pc-in, are determined as follows.

FIG. 2A shows the CW optical output Pc- with respect to the change of Ipc in the inverting output mode when Imod is constant.
Indicates a change in out. When the signal light is not incident (solid line), the output amplitude increases while Pc-out repeats the maximum and minimum with respect to the increase of Ipc. At the point where Ipc is almost equal to Imod, the amplitude becomes maximum and the maximum output is obtained. This point is defined as an operating point a (Ipc = a). When the signal light is incident in such a state, the Pc-out curve is gradually shifted and changes to a curve shown by a dotted line at a certain input power Ps-in (s). At this time, Pc-out at Ipc = a is the minimum value Pc-
out (min).

FIG. 2B shows a change in Pc-out with respect to the input signal light power Ps-in when Ipc = a. P
Pc-out changes from the maximum value to the minimum value as s-in increases, and the maximum output extinction ratio ER (max) is obtained at the operating point a.

[0012]

However, the above wavelength converter has the following problems in practical use. FIG. 3 shows a configuration example of the collective wavelength conversion device. The wavelength-division-multiplexed signal light enters the wavelength multiplexer / demultiplexer 32 from the port 31 and the demultiplexed signal light of each wavelength is input to the wavelength converter array 33, each wavelength is converted, and the wavelength multiplexer / demultiplexer 34 is again used. The signal light that is incident on and combined with is output to the port 35. Thereby, the wavelength groups λ1 to λ
A collective wavelength conversion from n to wavelength groups λ1 ′ to λn ′ is performed.

As described above, in the case of performing collective wavelength conversion, it is necessary to make the number of wavelength converters equal to the number of used wavelengths. Therefore, it is desired to reduce the power consumption per channel, that is, the injection current to the semiconductor optical amplifier.
Further, from the viewpoint of cost reduction, it is desirable that the CW light source is shared by several collective wavelength conversion devices, and thus the CW light power incident on one channel is reduced.
As a matter of course, the signal light power incident on the wavelength conversion circuit also decreases due to the loss during transmission and inside the node.
That is, along with the increase in the number of channels, both the reduction of the power consumption of the wavelength converter and the reduction of the required operating light power become important issues for practical use.

However, at the conventional operating point a, Imod
However, the following problems occur. FIG. 4 shows fixed pattern signals (“1 continuous”, “0 continuous”, “10 continuous”,
2) schematically shows the output fixed pattern and the eye pattern at that time when there is no pattern effect (a) and when there is a pattern effect (b).

When Imod is sufficiently high (Imod is 2
A good output waveform without the pattern effect as in (a) is observed. At this time, the output amplitude A for the low frequency input of the "1 continuous" signal and the "0 continuous" signal
And the ratio of the high frequency response amplitude B to the "10 continuous" signal appears in the eye pattern as the eye opening B / A.

In the case of the wavelength conversion output, the carrier life becomes longer as Imod decreases, and the high frequency input such as "10 continuous" cannot be followed. As a result, the output amplitude B becomes smaller than the output amplitude A, and the eye opening degree of the output eye pattern deteriorates (FIG. 4B). Such deterioration of the eye opening is observed as a power penalty in measuring the bit error rate.

In order to solve this, it is usually necessary to increase Imod, and it is usually necessary to increase it to near 200 mA. As a result, the total current amount including Ipc is 300.
It becomes a large value of 400 mA. Therefore, it was not easy to realize the low injection current operation to the SOA at the operating point a.

[0018]

In order to solve the above problems, in the present invention, attention is paid to the relationship between the eye opening degree of the output signal light and the phase adjusting current Ipc, and an output signal light without a pattern effect is realized. Therefore, Ipc is shifted from the operating point a where the maximum output extinction ratio is obtained to the operating point (referred to as b) where the maximum output eye opening is obtained. As the transition process, while monitoring the eye opening, (1) Ps-in is constant and Ipc is decreased from Ipc = a in a certain step width, and at the same time, the input CW optical power Pc-in is decreased. Or (2) P
c-in is constant, Ipc is decreased from Ipc = a in a certain step width, and at the same time, the input signal light power Ps-in is increased. Detect points.

Further, the output signal light power Ps-out having the same wavelength as the input signal light is measured under the optimum operating condition once set. When the input operation optical power (Pc-in, Ps-in) changes, the operation optical power is increased / decreased while the other is increased / decreased so that this Ps-out is maintained. .

Furthermore, in the process of reducing the operating light power with a certain step size in order to detect the minimum operating light power, it is also confirmed that the eye opening degree is maintained together with the above Ps-out constant condition. When the eye opening degree deteriorates even with a constant value, an optical power higher than the input operating optical power condition is detected as the minimum operating optical power.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 5 shows the Ipc dependence of the output eye opening and the output power. Imod and Ps-in are constant. In FIG. 5, when Ipc = a, the output power is maximized, but a sufficient eye opening is not obtained.
It can be seen that when c is decreased from a, the output power decreases but there is an operating point b (Ipc = b) that maximizes the eye opening.

As the first embodiment of the present invention, the procedure for shifting from the operating point a to the operating point b will be specifically described with reference to FIG. FIG. 6 is a flow chart showing the current setting procedure of Imod and Ipc. As a second embodiment of the present invention, referring to FIG. 7, the operating light power (Ps-in, Pc-in) is reduced with respect to the input condition set in FIG. 6, and the minimum operating light power is reduced. Ps-in (min), Pc-in
A procedure for detecting (min) will be shown.

First, the current condition setting procedure will be described with reference to FIG. However, the input wavelength condition is constant. (1) ~
The operation (6) is for explaining the operation state of FIG.

First, (1) input CW light of about 0 dBm,
(2) Input any Imod. However, the current value is set to sufficiently generate the SOA chip gain with respect to the input light. (3) Ip
Input c and measure Pc-out. (4) Increase Ipc until Pc-out becomes maximum. Ipc = Ipc (ma
x), enter (5) Ps-in (CW) and enter Pc
-out is measured. Here, Ipc (max) is the above-mentioned operating point a (Ipc = a). (6) Pc-out (mi
When n) is detected, (7) Next, Ps-in (sig) is input. Ps-in (sig) is an EA modulator (Electr
o Absorption modulator) is used for modulation and generation. The input electric signal to the EA modulator is PG (Pattern Gene).
sine wave signal (5 GHz for 10 Gb / s random signal). The optimum Ps-in (si
g) Average power is from Pc-out (max) to Pc-out
The input light power Ps-in (s) required to change (min) is set to half.

(8) Output amplitude ratio B / A (see FIG. 4)
If the B / A is 0.9 or more, return to (2) so that Imod decreases. This operation is performed to set Imod to the minimum operable current value. If the output amplitude ratio B / A is smaller than 0.9 in (8), lower (9) Ipc,
Repeat (10) ((5) → (6) → (7)).

If B / A is maximized in (11) and (12) the value is 0.9 or more, then Ipc at that time is Ipc
(Opt) and other operation parameters Imod, P
Extract s-in and Pc-in. Here, Ipc (opt) is the above-mentioned operating point b of Ipc. In (11), Ipc is decreased until B / A becomes maximum. Further, if B / A is 0.9 or less in (12), the process returns to (2) so that Imod increases. This operation increases Imod and shortens the carrier life of the SOA when the pattern effect of the output eye pattern is not sufficiently suppressed even when Ipc = Ipc (opt) (that is, when B / A <0.9 in (12)). However, it is necessary to improve the response speed. Imod is (8) and (12)
It becomes the minimum value by the feedback operation of.

Further, instead of the processing (10), (10) 'may be used. In (10) ′, the optimum Ps-in (CW extracted in (5) to (7)
or signal) remains constant, Pc-in is lowered while Pc-in is lowered.
Measure t (CW or signal). The equivalence of the processes (10) and (10) 'can be explained by using the auxiliary diagram (10).

The auxiliary diagram (10) shows the optimum CW optical power with respect to the input signal optical power Ps-in with Ipc as a parameter. The solid line is Ipc = Ipc (max), the dotted line is Ipc
= Ipc (opt). As a process of transition from Ipc (max) to Ipc (opt), Pc-in is kept constant and Ps-in is increased (process (10)), Ps-in is kept constant and Pc-in is decreased (process (10)). It can be seen that there are two types of processing (10) ′).

In the flowchart of FIG. 6, Imo
Optimize Ipc (opt) to use d at the minimum current value. Since there are many combinations of Ps-in and Pc-in as shown in the auxiliary diagram (10), the procedure shown in the flowchart of FIG. Will be needed.

In FIG. 7 (a), first, as a preparation, for one optimum operating condition (Ipc, Imod, Ps-in (sig), Pc-in) extracted in the current condition setting procedure of FIG. -out (sig) (output signal light power of the same wavelength as the input signal light) is measured and designated as C. Below, P
s-in represents the modulated signal light Ps-in (sig).

Then, Pc- shown in the inset (10) of FIG.
Decrease Pc-in (or P according to the increasing / decreasing relationship between in and Ps-in
Lower s-in), then lower Ps-in (or lower Pc-in). At this time, monitor Ps-out (sig),
If Ps-out (sig) <C, the process returns.
When Ps-out (sig) = C and the eye opening is not deteriorated by the pattern effect (for example, 0.8 or more), the process is returned to.

The operating light power is divided into steps (for example, Ps-in
Is about 0.5 dB, and Pc-in is about 0.1 dB), the loop exits when the eye opening starts to deteriorate at the n-th operating light power Ps-in (n). , Minimum operating light power Ps-in (min) = Ps-in
(N-1), Pc-in (min) = Pc-in (n-1).

An auxiliary diagram of this flowchart is shown in FIG. In FIG. 7B, Pc-in is used as a parameter, and P on the horizontal axis is used.
The vertical axis represents Ps-out with respect to changes in s-in. It can be seen that as Pc-in increases, Ps-in required to obtain the same Ps-out increases. Ps-out Pc- on a constant line
The optimum combination of in and Ps-in. The processing of and is started from one of the lines on which Ps-out is constant, and there are two ways of decreasing the operating light power, as shown by the arrows in the figure.

FIG. 8 shows output eye patterns at operating points a and b when the operating conditions are optimized according to the procedure of the present invention. At the operating point a, the eye opening was not sufficient, but at the operating point b, a good output with an eye opening of 0.9 or more was obtained.

Further, in FIG. 9, Ipc shows the change in the power penalty when the operating light power Ps-in is decreased.
pc (max) (operating point a in the figure) and Ipc (opt)
(In the figure, operating point b) is shown in each case. When the operating light power is -6 dBm or less, the power penalty does not become 1 dB or less at the operating point (a), while at the operating point (b), the power penalty is 0.5 up to Ps-in = -10 dBm.
It holds about dB. At this time, Pc-in is -10dB
m, the total current amount was 215 mA, which was low.

As described above, according to the procedure for optimizing the operating conditions of the present invention, it is possible to realize the phase modulation type wavelength conversion operation capable of low power consumption driving and low power operation suitable for multi-channel operation.

[0037]

As described above in detail with the embodiments, in the present invention, first, the driving current value Ipc of the semiconductor optical amplifier on the non-incident side of the signal light is set to the operating point at which the output extinction ratio becomes maximum. From the operating point where the output eye opening degree becomes maximum, the output eye opening is measured while following the procedure of decreasing Ipc and increasing the input signal light power or decreasing the input CW light power, The procedure for performing optimization is shown. As a result, it is possible to set the current value Imod of the other semiconductor optical amplifier on the signal light input side to the minimum value, and thus it is possible to reduce the total power consumption.

Under the optimum operating conditions, the output signal light power Ps-out (sig) having the same wavelength as that of the input signal light is measured, and the operation light power (CW light power, signal light power) is held so as to hold it. The desired operating light power can be set by adjusting the increase / decrease. When detecting the minimum operating light power, the above adjustment is performed while reducing the operating light power, and the operating light power is reduced until the waveform deterioration of Ps-out (sig) (confirmed by the eye opening and the Q value) occurs. By this procedure, the minimum operating light power can be detected.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a cross phase modulation (XPM) optical wavelength conversion circuit.

FIG. 2 is an explanatory diagram showing a conventional operating point determination method.

FIG. 3 is a configuration diagram showing a collective optical wavelength conversion device using a multi-channel XPM circuit.

FIG. 4 is a schematic diagram showing an output waveform depending on the presence or absence of a pattern effect.

FIG. 5 is a schematic diagram showing Ipc dependence of output power and eye opening degree.

FIG. 6 is a flowchart showing a current condition setting procedure in the first embodiment of the present invention.

7A and 7B are explanatory diagrams showing a minimum operating light power detection procedure in the second embodiment of the invention, FIG. 7A is a flowchart, and FIG. 7B is an auxiliary diagram.

FIG. 8 is an explanatory diagram showing an eye pattern as a result of implementing the present invention.

FIG. 9 is an explanatory diagram showing the results of implementation of the present invention.

[Explanation of symbols]

1, 2, 3 ports 4, 5, 6 Optical multiplexer / demultiplexer 7,8 Semiconductor optical amplifier 9 Optical filter 10 Planar lightwave circuit 31 ports 32 wavelength multiplexer / demultiplexer 33 Wavelength converter array 34 Wavelength multiplexer / demultiplexer 35 ports

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuaki             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Yasuhiro Suzuki             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation (72) Inventor Ikuo Ogawa             2-3-1, Otemachi, Chiyoda-ku, Tokyo             Inside Telegraph and Telephone Corporation F-term (reference) 2H079 AA05 AA12 BA01 CA04 EA05                       EA07 HA16 KA20                 2K002 AA02 AB12 BA02 DA11 EA30                       GA07                 5F073 AB25 BA01 EA29 GA25

Claims (3)

[Claims] 1. A method for setting an operating condition of a cross phase modulation type all-optical wavelength converter which has two semiconductor optical amplifiers and converts the wavelength of input signal light into the wavelength of input continuous light to obtain output signal light. By decreasing the drive current value of the semiconductor optical amplifier on the non-incident side of the input signal light among the two semiconductor optical amplifiers and increasing the power of the input signal light or decreasing the power of the input continuous light. , The cross-phase modulation type all characterized in that the drive current value of the semiconductor optical amplifier on the non-incident side of the input signal light is changed from the operating condition where the output extinction ratio becomes maximum to the operating condition where the output eye opening becomes maximum. Optical wavelength converter operating condition setting method. 2. A method for setting operating conditions of a cross-phase modulation type all-optical wavelength converter having two semiconductor optical amplifiers, which converts the wavelength of input signal light into the wavelength of input continuous light to produce output signal light. By decreasing the drive current value of the semiconductor optical amplifier on the non-incident side of the input signal light among the two semiconductor optical amplifiers and increasing the power of the input signal light or decreasing the power of the input continuous light. , The value of the drive current of the semiconductor optical amplifier on the non-incident side of the input signal light is changed from the operating condition in which the output extinction ratio is maximum to the operating condition in which the output eye opening is maximized, and further, the output eye opening is maximized. Under the following operating conditions, measure the power of the output signal light of the same wavelength as the input signal light, and measure the power of the input signal light so that the power of the output signal light of the same wavelength as the input signal light is always kept constant. Input continuous light power If either is reduced, cross-phase modulation operation condition setting method of the all-optical wavelength converter and sets the power and the power of the input continuous light of the input signal light by decreasing the other. 3. A method of detecting an operating condition of a cross-phase modulation type all-optical wavelength converter having two semiconductor optical amplifiers, which converts the wavelength of input signal light into the wavelength of input continuous light to produce output signal light. Hold the power of the output signal light of the same wavelength as the input signal light at all times, and confirm that the waveform of the output signal light of the same wavelength as the input signal light is held, until the waveform of the output signal light deteriorates. By repeating the operation of claim 2, the minimum power of the input signal light and the minimum power of the input continuous light under the conditions where the output eye opening is maximized are detected, and the cross-phase modulation type all-optical wavelength is characterized. Method of detecting operating condition of converter.