JP2003322888A - Mutual phase modulation type wavelength converter with stability control function and method for controlling stability of mutual phase modulation type wavelength converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably perform a wavelength converting operation even when power of signal light to be inputted in a mutual phase modulation type wavelength converter is fluctuated. <P>SOLUTION: When signal light Ps-in with wavelength of λs and control light Pc-in being a continuous light and with wavelength of λc are inputted in an XPM type wavelength converter 1, wavelength conversion signal light Pc-out with the wavelength of λc and having the same piece of signal information as that of the signal light Ps-in is outputted via an optical filter 30 and outputted signal light Pc-out with the wavelength of λs is outputted via an optical filter 101. Intensity of the control light Pc-in to be inputted in a port 12 is adjusted by operating an optical power level controller 104 by a control system 103 so that the average intensity of the outputted signal light Pc-out becomes a predetermined value. Thus, the wave converting operation is stably performed even when the intensity of the signal light Ps-in is changed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cross phase modulation type wavelength converter with a stability control function and a stability control method for a cross phase modulation type wavelength converter. More specifically,
Wavelength Division Multiplexing (WDM)
g) In a cross phase modulation wavelength converter used for the purpose of avoiding collision of signal wavelengths, wavelength path routing (path determination by wavelength), etc. Even if the power of the input signal light fluctuates, the wavelength conversion operation can be stably performed.

[0002]

2. Description of the Related Art Optical communication networks are required to have high speed, large capacity, and long distance transmission in order to improve the amount of information transmission. Of these, wavelength division multiplexing (WDM: Wavelength Division) is a technique for dramatically increasing the capacity.
Multiplexing) communication system was developed. In this WDM communication system, a large number of lights (n beams) having different wavelengths are multiplexed by a wavelength multiplexer, coupled into one optical fiber, and transmitted over a long distance, and then a wavelength demultiplexer is used for each wavelength. This is a method of separating and extracting a signal. In this way, by passing n beams having different wavelengths through the same optical fiber, the total transmission capacity per optical fiber can be increased by n times. For example, assuming that the transmission bit rate of each wavelength is 10 Gb / s and the number of wavelengths used is 32, an extremely large transmission capacity of 320 Gb / s can be obtained with one optical fiber.

There are various WDM networks using the WDM communication system, and the wavelengths used in the respective networks are different. Therefore, when connecting the networks, the wavelength used in one network is changed to the wavelength used in the other network. A wavelength converter that converts the signal light to the wavelength used in is required.

Of these wavelength converters, the following four types are known as the modulation methods of the all-optical wavelength converter that converts the wavelength of signal light as light without photoelectric conversion. (1) Cross Phase Modulatio (XPM)
n) (2) Cross Gain Modulation (XGM) (3) Transmission suppression type (4) Four Wave Mixing (FWM)

Among the above wavelength converters, cross phase modulation (X
A conventional cross phase modulation type wavelength converter using PM (Cross Phase Modulation) will be described with reference to FIG.

Cross-phase modulation type wavelength converter 1 shown in FIG.
Is a hybrid integrated circuit.
In this cross phase modulation type wavelength converter 1, a planar lightwave circuit (PLC: Planar Ligation Circuit) formed on the surface of the platform 2 is used.
htwave Circuit) and the semiconductor optical amplifier array 3 arranged on the surface of the platform 2
A Mach-Zehnder interferometer is formed. This Mach-Zehnder interferometer circuit has input ports 11 and 12
, Output ports 13 and 14, and optical multiplexers / demultiplexers 21, 22 and 22.
It has 23 and 24. Further, the optical filter 30 is provided in a state of being connected to the output port 13.

The semiconductor optical amplifier array 3 has two semiconductor optical amplifiers 3a and 3b.
Reference numerals a and 3b are SS-SOA elements in which an SOA portion (active layer portion) and a spot size conversion portion (SS portion) formed on the input end face and the output end face are monolithically integrated. Moreover, the semiconductor optical amplifier array 3 is mounted with the semiconductor optical amplifier 3a interposed in the first arm waveguide of the Mach-Zehnder interferometer and the semiconductor optical amplifier 3b interposed in the second arm waveguide. Has been done.

In the cross phase modulation type wavelength converter 1 having such a configuration, for example, the signal light Ps having a wavelength of λs is input to the input port 11 and the control light Pc which is a continuous light having a wavelength of λc is supplied. Input to the input port 12.

Then, the control light Pc input to the input port 12 is split into two by the optical multiplexer / demultiplexer 21 and is incident on the semiconductor optical amplifiers 3a and 3b.
After passing through a and 3b, they are multiplexed again by the optical multiplexer / demultiplexer 24 and output from the output port 13 or the output port 14.

Further, the signal light Ps enters only one semiconductor optical amplifier 3a through the optical multiplexer / demultiplexer 22 and does not enter the other semiconductor optical amplifier 3b. Then, the gain saturation of the semiconductor optical amplifier 3a reduces the carrier density, which causes a change in the refractive index. As a result, the control light that has passed through both semiconductor optical amplifiers 3a and 3b
When Pc is multiplexed by the optical multiplexer / demultiplexer 24, the phase change due to the refractive index change appears as an intensity change.

Therefore, the output port 13 outputs the converted signal light P having the wavelength components of λs and λc and having the intensity inverted with respect to the data waveform of the signal light Ps. Further, from the output port 14, the converted signal light P 1 whose wavelength components are λs and λc and whose intensity is not inverted with respect to the data waveform of the signal light Ps is output.

Optical filter 3 connected to output port 13
0 has a filtering characteristic of passing only wavelength component light having a wavelength of λc. Therefore, the converted signal light P
Through the optical filter 30, the wavelength is λc,
The wavelength-converted signal light Pc-out whose intensity is inverted with respect to the data waveform of the signal light Ps is obtained. If the optical filter 30 is connected to the output port 14, the converted signal light P 2 output from the output port 14 passes through the optical filter 30 so that the wavelength is λc and the data waveform of the signal light Ps is The wavelength-converted signal light Pc-out whose intensity is non-inverted can be obtained.

[0013]

The stable operation control technique in such a cross phase modulation type wavelength converter is a practically important subject. Up to now, some circuits have been proposed for expanding the tolerance of the input signal light power, but in order to actually confirm stable operation, the eye pattern of the output wavelength-converted signal light Pc-out is directly observed. There was no real proposal.

Generally, the cross phase modulation type wavelength converter has various power level fluctuations of input light (signal light, control light (= continuous light)), gain fluctuations of a semiconductor optical amplifier, fluctuations of fiber loss and the like. The operation becomes unstable depending on the factor. This is because the power distribution of the input light to the semiconductor optical amplifier deviates from the optimum condition. Therefore, it is necessary to have a monitoring function for confirming that the stable operation condition is not deviated and, if deviated, performing feedback control so that the operation is stable.

FIG. 7 shows the power penalty when the optical power of the signal light Ps input without stable control is changed in the cross phase modulation type wavelength converter having the structure shown in FIG. Show changes. From FIG. 7, it can be seen that the range of the input signal light power that can secure the power penalty within 1 dB is only 2 to 3 dB at most, and the operation becomes unstable with respect to the fluctuation of the input signal light power.

In view of the above-mentioned prior art, the present invention is a cross-phase modulation type with a stability control function, which enables stable wavelength conversion operation even if the power of the signal light input to the cross-phase modulation type wavelength converter changes. An object of the present invention is to provide a wavelength converter and a stable control method for a cross phase modulation type wavelength converter.

[0017]

The structure of the cross-phase modulation type wavelength converter with a stable control function of the present invention which achieves the above object has two semiconductor optical amplifiers and is a signal light and a continuous light. When the control light is input, a cross phase modulation type wavelength converter that outputs the wavelength-converted signal light having the same signal information as the signal light of the signal light and having the same wavelength as the wavelength of the control light, Of the light output from the cross-phase modulation type wavelength converter that has passed through the semiconductor optical amplifier, a light receiver for detecting the average light intensity of the output signal light made of light having the same wavelength component as the signal light, The optical power level controller for controlling the light intensity of the continuous light input to the cross phase modulation type wavelength converter and the average light intensity of the output signal light detected by the light receiver have a preset setting value. To
And a control system for controlling the light intensity of the continuous light by the optical power level controller.

A stable control method for a cross phase modulation type wavelength converter according to the present invention, which solves the above problems, has two semiconductor optical amplifiers and receives signal light and control light which is continuous light. A stable control method of a cross phase modulation type wavelength converter that outputs the wavelength-converted signal light having the same signal information as the signal information of the signal light and the same wavelength as the wavelength of the control light, Of the light output from the cross phase modulation type wavelength converter that has passed through the semiconductor optical amplifier, the average light intensity of the output signal light composed of light having the same wavelength component as the signal light is a preset value. So that
It is characterized in that the intensity of continuous light input to the cross phase modulation type wavelength converter is controlled.

Further, the set value is a value obtained by subtracting a certain value X from the value of the saturated output intensity of the optical amplifier, or the value X is 1.5 to 4.5 (dB). Characterize.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a first embodiment of the present invention.
1 shows a cross phase modulation type wavelength converter with a stable control function. In the present embodiment, in addition to the cross phase modulation type wavelength converter 1 and the optical filter 30, an optical filter 101 and a light receiver 102 are provided.
A control system 103, an optical power level controller 104,
The light source 105 is provided.

The cross phase modulation type wavelength converter 1 is composed of a hybrid integrated circuit. In this cross phase modulation type wavelength converter 1, a planar lightwave circuit (PLC) formed on the surface of the platform 2 is used.
The Mach-Zehnder type optical interference circuit is formed by the optical waveguide formed by it) and the semiconductor optical amplifier array 3 arranged on the surface of the platform 2. This Mach-Zehnder interferometer has ports 11, 12, 13, 14 and optical multiplexers / demultiplexers 21, 22, 23, 24. Further, the optical filter 30 is provided in a state of being connected to the port 13.

The semiconductor optical amplifier array 3 has two semiconductor optical amplifiers 3a and 3b.
Reference numerals a and 3b are SS-SOA elements in which an SOA portion (active layer portion) and a spot size conversion portion (SS portion) formed on the input end face and the output end face are monolithically integrated. Moreover, the semiconductor optical amplifier array 3 is mounted with the semiconductor optical amplifier 3a interposed in the first arm waveguide of the Mach-Zehnder interferometer and the semiconductor optical amplifier 3b interposed in the second arm waveguide. Has been done.

In the cross phase modulation type wavelength converter 1 having such a configuration, for example, the signal light having a wavelength of λs is used.
The Ps-in is input to the port 11, and the control light Pc-in that is continuous light having a wavelength of λc is input to the port 12. Although the details will be described later, the control light Pc-in input to the port 12 is
The intensity of continuous light generated from the light source 105 is optimized by the optical power level controller 104.

Control light Pc-in input to the input port 12
Is split into two by the optical multiplexer / demultiplexer 21 and is incident on the semiconductor optical amplifiers 3a and 3b.
After passing through, the light is multiplexed again by the optical multiplexer / demultiplexer 24 and output from the port 13 or the port 14.

Further, the signal light Ps-in enters only one semiconductor optical amplifier 3a through the optical multiplexer / demultiplexer 22 and does not enter the other semiconductor optical amplifier 3b. Then, the gain saturation of the semiconductor optical amplifier 3a reduces the carrier density, which causes a change in the refractive index. As a result, when the control light Pc-in that has passed through both the semiconductor optical amplifiers 3a and 3b is combined by the optical multiplexer / demultiplexer 24, the phase change due to the refractive index change appears as an intensity change.

Therefore, the port 13 outputs the converted signal light P1 whose wavelength components are λs and λc and whose intensity is inverted with respect to the data waveform of the signal light Ps-in. Further, from the port 14, the converted signal light P2 whose wavelength components are λs and λc and whose intensity is not inverted with respect to the data waveform of the signal light Ps-in is output. Therefore, the converted signal light P1 output from the port 13 is passed through an optical filter 30 that passes only the wavelength component light of wavelength λc, so that the intensity of the signal waveform of the signal light Ps-in is λc. The wavelength-converted signal light Pc-out with the inverted wavelength is obtained. That is, the wavelength-converted signal light Pc-out having the wavelength λc and having the same signal information as the signal information of the signal light Ps-in can be obtained.

Further, in this embodiment, the optical filter 101 is connected to the port 14. This optical filter 101 is
It has a filtering characteristic of passing only the wavelength component light having a wavelength of λs, that is, the wavelength component light of the signal light Ps-in. Therefore, the wavelength component output from the port 14 is λ
When the converted signal light P2 having s and λc passes through the optical filter 101, the optical filter 101 outputs the output signal light Ps-out having a wavelength component of only λs.

The output signal light Ps-out output from the optical filter 101 is received by the light receiver 102. Light receiver 10
2 detects the average power (average light intensity) of the output signal light Ps-out, and outputs the detection signal K indicating this average power to the control system 10.
Send to 3.

The control system 103 adjusts the optical power level control amount by the optical power level controller 104 so that the average power of the output signal light Ps-out represented by the detection signal K becomes a preset set value. To do. That is, the output signal light Ps
If the average power of -out is smaller than the preset value, increase the optical power level (optical intensity) of the control light Pc-in input to the port 12, and vice versa.
When the average power of ut becomes larger than the preset value, the optical power level control by the level adjuster 104 is adjusted so as to lower the optical power level of the control light Pc-in input to the port 12. .

The "preset value" set in the control system 103 is, for example, a value obtained by subtracting a certain value (1.5 to 4.5 dB) from the saturation output intensity of the semiconductor optical amplifiers 3a and 3b. . The reason for doing this will be described later.

Here, the output signal light Ps-out is monitored, and feedback control is performed on the input control light Pc-in so that the optical power level of the output signal light Ps-out becomes a set value. The reason why a stable wavelength conversion operation can be performed will be described.

FIG. 2A shows the wavelength conversion input / output static characteristic (inverted output). Control light with constant intensity (continuous light) Pc-in
When the power of the input signal light Ps-in is increased, the power of the wavelength-converted signal light Pc-out that is output becomes the minimum. Ps-i
Let n (conv). The dotted line shows the output when the SOA current on one side is set to 0 mA, and in this case, the output intensity change due to the cross gain modulation (XGM) is shown. At this time, Pc-in (constant) + Gc
(Gain for continuous light) = Pc-out = ΔPc-out =
ΔGc.

FIG. 2B shows the reduction gain ΔGc for each operating light power Ps-in (conv) obtained by optimizing the control light Pc-in. From the figure, it can be seen that ΔGc is always approximately 4 dB. This indicates that from the relationship of ΔGc ∝ΔN (carrier density) ∝Δn (refractive index), if the reduction gain ΔGc is constant, a constant refractive index change Δn occurs in the semiconductor optical amplifier. This condition of constant reduction gain can also be applied to the other wavelength converted signal light Pc-out itself, which is another output light.

FIG. 3 shows the gain Gs (left axis) and the power of the output signal light Ps-out (right axis) with respect to the power of the input signal light Ps-in of the semiconductor optical amplifier (3a in FIG. 1). The dotted line shows the characteristics when the continuous light is not incident (w / o), and the solid line shows the characteristics when the continuous light power is 5 dBm (Pc5). The following relations hold here. Ps-out (w / o) = Ps-in + Gs (w / o) (1) Ps-out (Pc5) = Ps-in + Gs (Pc5) (2) From (1)-(2), Ps-out (w / o) -Ps-out (Pc5) = Gs (w / o) -Gs (Pc5) (3).

Here, under the wavelength conversion optimum condition, the decreasing gain ΔGs (= Gs (w / o) -Gs (Pc5) is constant, and Ps-out (w / o) = constant in the saturation region. In (3), Ps-out (Pc5) = constant.
This relationship does not change even if the value of the control light Pc-in changes.
That is, if the power of the output signal light Ps-out is constant, the optimum operating condition can be monitored.

FIG. 4 shows the optimum power of the control light Pc-in with respect to each operating light power Ps-in (conv), and the power and penalty deterioration amount of the output signal light Ps-out at that time. Output power is increased by increasing the control light Pc-in power as the operating light power Ps-in (conv) increases and decreasing the control light Pc-in power as the operating light power Ps-in (conv) decreases. Signal light Ps
The power penalty was 0.5 dB or less, provided that the -out power was constant. That is, the optimum operation tuning becomes possible by controlling the power of the control light Pc-in while monitoring the output signal light Ps-out. Output signal light
As the value of Ps-out, from the formula (3), measure the saturation output intensity Ps-out (w / o) of the semiconductor optical amplifier, and subtract a certain value ΔGs (1.5-4.5 dB) from this value. It will be a value.

FIG. 5 shows a second embodiment of the present invention.
In the second embodiment, the control light Pc-in generated from the light source 105 and having the optical power optimized by the optical power level controller 104 is input from the port 13. That is, the control light Pc-in is input so that the traveling direction of the control light Pc-in is opposite to the traveling direction of the signal light Ps-in.
Therefore, the wavelength-converted signal light Pc-out is output from the port 12, and the output signal light Ps-out is output from the port 14.

In the second embodiment, since the traveling directions of the signal light Ps-in and the control light Pc-in are opposite, the port 1
The optical wavelength component of the wavelength-converted signal light Pc-out output from 2 is only λc, and the optical wavelength component of wavelength λs is not mixed. Also, the output signal light Ps-o output from the port 14
The wavelength component of ut is only λs, and the light wavelength component of wavelength λc is not mixed. Therefore, the optical filter 30 and the optical filter 101 used in the first embodiment are unnecessary.

The structure of the other parts is similar to that of the first embodiment shown in FIG. Also in the second embodiment, the optical power of the control light Pc-in is controlled by controlling the optical power of the control light Pc-in so that the average power of the output signal light Ps-out becomes a preset setting value. The wavelength conversion operation can be stably performed even if the optical power of 1 changes.

[0041]

As described above in detail with the embodiments, in the present invention, the average power (average light intensity) of the output signal light Ps-out during the optimum operation of the cross phase modulation type wavelength converter is Use as a monitor. If the power level of the input signal light fluctuates for some reason, the output signal light Ps
-out deviates from some optimum constant value. By feeding back the power of the input continuous light (control light) so as to restore this, it is possible to maintain stable operation without penalty deterioration. Further, if the method of the present invention,
The stable operation can be confirmed by measuring the power of the output signal light output from another port without looking at the output wavelength-converted signal light, and the configuration is more suitable for practical use.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a cross phase modulation type wavelength converter with a stability control function according to a first embodiment of the present invention.

FIG. 2 (a) is a characteristic diagram showing wavelength conversion input / output static characteristics, and FIG. 2 (b) is a characteristic diagram showing changes in the reduction gain ΔGc with respect to each operating optical power Ps-in (conv). is there.

FIG. 3 is a characteristic diagram showing signal light input / output characteristics and gain changes thereof.

FIG. 4 is a characteristic diagram showing changes in optimum continuous light power Pc-in, output signal light power Ps-out, and penalty deterioration amount with respect to each operation light power Ps-in (conv).

FIG. 5 is a configuration diagram showing a cross phase modulation type wavelength converter with a stability control function according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram showing a conventional mutual phase modulation type wavelength conversion circuit.

FIG. 7 is a characteristic diagram showing input light power tolerance in a conventional cross phase modulation type wavelength conversion circuit (without stability control).

[Explanation of symbols] 1 Mutual phase modulation type wavelength converter 2 platforms 11-14 ports 21-24 Optical multiplexer / demultiplexer 30 optical filters 101 Optical filter 102 light receiver 103 control system 104 Optical power controller 105 light source

   ─────────────────────────────────────────────────── ─── 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 F term (reference) 2K002 AA02 AB12 BA02 CA13 DA07                       DA08 EB15 GA05 HA16

Claims (6)

[Claims] 1. Having two semiconductor optical amplifiers, when signal light and control light that is continuous light are input, they have the same signal information as the signal information of the signal light and the wavelength of the control light. A cross phase modulation type wavelength converter that outputs a wavelength conversion signal light having the same wavelength as the above, and the signal light among the lights that have passed through the semiconductor optical amplifier and are output from the cross phase modulation type wavelength converter. And a light receiver for detecting the average light intensity of the output signal light consisting of light having only the same wavelength component, and an optical power level controller for controlling the light intensity of continuous light input to the cross phase modulation type wavelength converter, A control system for controlling the light intensity of the continuous light by the optical power level controller so that the average light intensity of the output signal light detected by the light receiver becomes a preset setting value. Characteristic stability controller Mutual phase modulation type wavelength converter with function. 2. The cross-phase modulation type wavelength conversion device with a stable control function according to claim 1, wherein the set value is a value obtained by subtracting a certain value X from the value of the saturated output intensity of the semiconductor optical amplifier. vessel. 3. The value X according to claim 2, wherein the value X is 1.5 to 4.
A cross phase modulation type wavelength converter with a stable control function, which is 5 (dB). 4. Having two semiconductor optical amplifiers, when the signal light and the control light that is continuous light are input, they have the same signal information as the signal information of the signal light and the wavelength of the control light. A method for stabilizing a cross-phase modulation type wavelength converter that outputs a wavelength-converted signal light having the same wavelength as that of the light output from the cross-phase modulation type wavelength converter after passing through the semiconductor optical amplifier. Among them, the average light intensity of the output signal light composed of only light having the same wavelength component as the signal light is a continuous light light input to the cross phase modulation type wavelength converter so that it becomes a preset setting value. A stable control method of a cross phase modulation type wavelength converter characterized by controlling intensity. 5. The stable control method for a cross phase modulation wavelength converter according to claim 4, wherein the set value is a value obtained by subtracting a certain value X from the value of the saturated output intensity of the optical amplifier. . 6. The value X according to claim 5, wherein the value X is 1.5 to 4.
A stable control method for a cross phase modulation type wavelength converter, which is 5 (dB).