JPH0779176B2 - Method and apparatus for stabilizing optical output power of semiconductor optical amplifier - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for stabilizing the optical output power of a semiconductor optical amplifier used for optical communication, optical switching and the like.

[0002]

2. Description of the Related Art In an optical communication system, a semiconductor optical amplifier is indispensable for compensating for a loss. However, when applied to an actual system, the optical output power of the semiconductor optical amplifier is kept constant. Things (Auto-P
power-Control; hereinafter abbreviated as APC) is required.

In order to keep the optical output power of the semiconductor optical amplifier constant, the optical output power is detected and the gain of the semiconductor optical amplifier is controlled accordingly by the current value of the semiconductor optical amplifier. . At that time, as a method of detecting the optical output power, 1) a method of optically detecting a part of the output of the semiconductor optical amplifier, and 2) the optical output power of the constant-current-driven semiconductor optical amplifier is the terminal of the semiconductor optical amplifier. A detection method using the fact that it is proportional to the product of voltage change and current value (Marion et al., Electronics Letters (El
electronics Letters), 1989,
25 volumes, 235 pages). The block diagram is shown in FIG.
Of these, the method 2) is a useful method because it does not require optical branching and a photodetector, has no optical loss due to optical branching, and can be constructed on a small scale.

[0004]

In applying the prior art, the premise is that the product of the terminal voltage change of the semiconductor optical amplifier driven by the constant current, the product of the current values, the product of the current values, and the optical output power are proportional or monotonic. In addition to that, there is a need for the relationship to have no current value dependency.

FIG. 2 shows an example of measurement results of the relationship between the product of the terminal voltage change and the current value of the semiconductor optical amplifier and the optical output power. The relationship between the product of the terminal voltage change of the semiconductor optical amplifier and the current value and the optical output power has current dependency. Therefore, the APC operation does not occur in the configuration of the conventional technique shown in FIG. 4, which is considered that the product of the terminal voltage change and the current value is proportional to the optical output power.

An object of the present invention is to eliminate such a factor and perform a stable APC operation without using an extra photodetector or optical branch.

[0007]

In order to solve the above-mentioned problems, the following means are provided.

(1) A method for stabilizing the optical output power of a semiconductor optical amplifier according to the present invention comprises a semiconductor optical amplifier driven by a constant current, the amount of which is proportional to the magnitude of a specific frequency component of the terminal voltage, and the semiconductor optical amplifier. A signal that correctly corresponds to the optical output power by compensating the product signal with the value of the current flowing through the semiconductor optical amplifier on the basis of the relationship between the product signal and the optical output power measured in advance according to the current flowing through the semiconductor optical amplifier. Is produced, and thereby control is performed to make the optical output power constant.

(2) A device for stabilizing the optical output power of a semiconductor optical amplifier according to the present invention comprises a semiconductor optical amplifier for amplifying an optical signal, a constant current source for driving the semiconductor optical amplifier, and a current flowing through the semiconductor optical amplifier. Of the output signal of the first and second detection means, the second detection means for detecting the magnitude of a specific frequency component of the terminal voltage signal of the semiconductor optical amplifier Means for producing a product signal, the output of the first detection means and the product signal as an input, based on the relationship between the product signal and the semiconductor optical amplifier optical output power at various previously measured currents, The semiconductor optical amplifier comprises a processor that outputs a signal corresponding to the optical output power, and a control unit that controls the magnitude of the output current of the constant current source so that the processor output becomes equal to a reference signal. It features the door.

(3) Another method of stabilizing the optical output power of a semiconductor optical amplifier according to the present invention is that in the direction in which an optical signal propagates,
A method for controlling constant optical output power of a semiconductor optical amplifier having a plurality of current injection regions capable of independently controlling an injection current, wherein a first current injection region of the plurality of current injection regions of the semiconductor optical amplifier is provided. A constant current is injected into the semiconductor optical amplifier, the magnitude of the signal proportional to the magnitude of the specific frequency component of the terminal voltage is detected, and a plurality of currents of the semiconductor optical amplifier are detected so that the signal has a predetermined magnitude. It is characterized in that an injection current is controlled in a region other than the first current injection region in the injection region.

(4) Another device for stabilizing the optical output power of a semiconductor optical amplifier according to the present invention is:
A semiconductor optical amplifier having a plurality of current injection regions capable of controlling the injection current independently of each other, and means for injecting a constant current into a first current injection region of the plurality of current injection regions of the semiconductor optical amplifier, Means for extracting a signal proportional to the magnitude of a specific frequency component from the terminal voltage in the current injection region for injecting the constant current, means for generating a reference voltage corresponding to the optical output power value to be made constant, and the magnitude of the signal And a control circuit for controlling an injection current into a region other than the first current injection region of the plurality of current injection regions of the semiconductor optical amplifier so that the height becomes a predetermined value.

[0012]

The principle of the first and second inventions of the present invention will be described.

As shown in FIG. 2, the relationship between the optical output power of the semiconductor optical amplifier, the terminal voltage change, and the product signal of the drive current is as follows.
It can be measured for each current value. Therefore, if such a relationship is measured in advance, it is stored in the memory and the product signal is corrected based on it, a signal corresponding to the optical output power can be created regardless of the magnitude of the drive current. You can In the present invention, APC is performed based on this signal.

The principles of the third and fourth inventions of the present invention will be described.

As shown in FIG. 2, the relationship between the optical output power of the semiconductor optical amplifier, the terminal voltage change, and the product signal of the drive current has current dependency, but when the injection current is kept constant, the optical output There is a one-to-one correspondence between power and terminal voltage change. In the semiconductor optical amplifier, by dividing the electrodes, it is possible to provide a plurality of current injection regions capable of independently injecting current. Therefore, if one of the plurality of injection regions is driven with a constant current, the optical output power is monitored by the change in the terminal voltage, and feedback control is performed to the current in the remaining current injection region, the above-mentioned problem can be solved.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The first and second embodiments of the present invention will be described with reference to FIG.

FIG. 1 is a block diagram showing an embodiment.
Here, a case will be described in which a low-frequency sine wave signal called a tone is superimposed on the optical transmission signal and control is performed so that the magnitude of the frequency component is constant. The optical output power of the semiconductor optical amplifier is obtained by compensating the product of the tone frequency component of the terminal voltage of the semiconductor optical amplifier 1 and the current value flowing in the semiconductor optical amplifier 1 by reading the current value flowing in the semiconductor optical amplifier 1. To be Digital signal processor (hereinafter abbreviated as DSP) for compensation of current value dependence
8 is used. In advance, the DSP 8 stores the current value dependency of the relationship between the product of the tone frequency component of the terminal voltage of the semiconductor optical amplifier and the current value and the optical output power. To compensate.

The embodiment shown in FIG. 1 will be described in detail below. In the transmission light source, modulation is performed with a data signal, and at the same time, modulation of several percent is applied with a low frequency (here, -10 KHz) tone. The light is output through the optical semiconductor amplifier 1.
The signal corresponding to the optical output power is the semiconductor optical amplifier 1
It is obtained by reading the product of the tone frequency component of the terminal voltage and the value of the current flowing through the semiconductor optical amplifier 1 and the value of the current flowing through the semiconductor optical amplifier 1 by the DSP 8 for compensation.
The value of the current flowing through the semiconductor optical amplifier 1 is obtained by detecting the voltage across the resistor 13 with the differential amplifier 7. Regarding the product of the tone frequency component of the terminal voltage of the semiconductor optical amplifier 1 and the value of the current flowing through the semiconductor optical amplifier 1, only the AC portion of the terminal voltage is first taken out by the capacitor 2, amplified by the low noise amplifier 3, and then the differential amplifier The current value detected in 7 is multiplied by the multiplier 4, and the obtained value is passed through a band pass filter 5 whose center frequency is the tone frequency, and the rectifier 6
It is obtained by converting to direct current at. The obtained voltage is DSP8
The DSP 8 also reads the current value flowing from the differential amplifier 7 into the semiconductor optical amplifier 1 to obtain the tone frequency component of the terminal voltage of the semiconductor optical amplifier 1 and the current value flowing into the semiconductor optical amplifier 1. And the current value dependence of the relationship between the product of and and the optical output power of the semiconductor optical amplifier 1 are compensated. The obtained voltage is compared with the reference voltage 9 by the differential amplifier 10 to generate an error signal, which is passed through the proportional integrator 11 and the current supplied to the optical semiconductor amplifier 1 by the current source 12, and thus the gain of the optical semiconductor amplifier 1. The optical output power is changed to be constant. Although the present invention has been described in detail with reference to the embodiment, the present invention is not limited to this embodiment. For example, although the embodiments have been described by taking the case of using a band pass filter as an example, it is obvious that the present invention can be applied to other configurations such as synchronous detection. Further, it will be apparent that the present invention can be applied to a case where a DSP or the like performs the multiplication part. Further, as a method of compensating the current value dependency of the terminal voltage change due to the input signal of the semiconductor optical amplifier, it is not necessary to adopt the configuration using the DSP used in the embodiment, and another processor is used. The present invention can be implemented without any trouble by other methods such as realizing the compensation relationship by an analog electronic circuit. Further, in this embodiment, the low-frequency tone is superimposed on the optical transmission signal and the magnitude of the component is detected. However, the average value of the optical transmission signal itself and the magnitude of the clock component extracted from the optical transmission signal are detected. Good.

Next, embodiments of the third and fourth inventions of the present invention will be described with reference to FIG.

FIG. 3 is a block diagram of an output stabilizing device using the method for stabilizing the output power of a semiconductor optical amplifier according to the present invention. Here, a case will be described in which a low-frequency sine wave signal called a tone is superimposed on the optical transmission signal and control is performed so that the magnitude of the frequency component is constant. Here, the semiconductor optical amplifier 1 has a structure in which the p-side electrode is divided and has two current injection regions 1a and 1b in the traveling direction of the optical signal, and the region 1b on the output side is driven by a constant current to monitor the optical power. Area 1a is used for current control. The optical output power of the semiconductor optical amplifier 1 is proportional to the product of the tone frequency component of the terminal voltage of the semiconductor optical amplifier 1 and the current value flowing in the semiconductor optical amplifier 1. However, here, since the region 1a for monitoring the optical power is driven by a constant current, control is possible using only the terminal voltage change.

The embodiment shown in FIG. 3 will be described in detail below. In the transmission light source, modulation is performed with a data signal, and at the same time, modulation of several percent is applied with a low frequency (here, -10 KHz) tone. The light is output through the optical semiconductor amplifier 1. The current injection region 1b of the semiconductor optical amplifier 1 is a choke coil 1
It is driven by a current source 12b through 4. The signal corresponding to the magnitude of the tone frequency component of the terminal voltage in the region 1b of the semiconductor optical amplifier 1 is first taken out by the capacitor 2 only the AC portion of the terminal voltage, amplified by the low noise amplifier 3, and then the center frequency becomes the tone frequency. Certain band pass filter 5
It is obtained by converting the current into a direct current with the rectifier 6 through the rectifier 6. The obtained voltage is compared with the reference voltage 9 by the differential amplifier 10 to generate an error signal, which is passed through the proportional integrator 11 and the current source 12a.
Then, the current flowing in the region 1a of the optical semiconductor amplifier 1 and thus the gain of the optical semiconductor amplifier 1 are changed to make the optical output power constant.

Although the present invention has been described in detail with reference to the embodiment, the present invention is not limited to this embodiment. For example, although the embodiments have been described by taking the case of using a band pass filter as an example, it is obvious that the present invention can be applied to other configurations such as synchronous detection. In this embodiment, a low frequency tone is superimposed on the optical transmission signal,
Although the magnitude of the component is detected, the average value of the optical transmission signal itself or the magnitude of the clock component extracted from the optical transmission signal may be detected.

[0023]

As described above, if the present invention is applied, the relationship between the product of the terminal voltage change of the semiconductor optical amplifier and the current value and the optical output power does not depend on the current value. Can be accurately detected. as a result,
It is possible to stably control the optical output power without using an extra photodetector and an optical branch.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram for explaining a problem to be solved by the present invention.

FIG. 3 is a block diagram for explaining an embodiment of the present invention.

FIG. 4 is a diagram for explaining a conventional technique.

[Explanation of symbols]

 1 Semiconductor Optical Amplifier 2 Capacitor 3 Low Noise Amplifier 4 Multiplier 5 Narrow Band Band Pass Filter 6 Rectifier 7,10 Differential Amplifier 8 Digital Signal Processor 9 Reference Voltage 11 Proportional Integrator 12 Current Source 13 Resistor 14 Coil 15 Ground 16 Input light 17 Output light

Claims (4)

[Claims] 1. A semiconductor optical amplifier detecting a current value, and generating a signal of a product of an amount proportional to a magnitude of a specific frequency component of a terminal voltage of the semiconductor optical amplifier and the current value, the semiconductor optical amplifier. Of the characteristics relating to the correlation between the optical output power of the optical amplifier and the product signal, paying attention to the previously measured dependence on the current value, creating a compensation signal that compensates the product signal based on the dependence, A method for stabilizing the optical output power of a semiconductor optical amplifier, which is characterized in that the compensation signal is controlled to be a constant value. 2. A semiconductor optical amplifier for amplifying an optical signal, a constant current source for driving the semiconductor optical amplifier, first detecting means for detecting a current flowing through the semiconductor optical amplifier, and a terminal of the semiconductor optical amplifier. Second detection means for detecting the magnitude of a specific frequency component of the voltage signal, means for producing a product signal of the output signals of the first and second detection means, and the output of the first detection means A processor that receives the product signal as an input and outputs a signal corresponding to the semiconductor optical amplifier optical output power based on the relationship between the product signal and the semiconductor optical amplifier optical output power at various currents measured in advance. And a control means for controlling the magnitude of the output current of the constant current source so that the processor output becomes equal to a reference signal. 3. A method for stabilizing the optical output power of a semiconductor optical amplifier having a plurality of current injection regions capable of independently controlling an injection current as a method for propagating an optical signal, the method comprising: A constant current is injected into the first current injection region of the current injection region, and the magnitude of the signal relative to the magnitude of the specific frequency component of the terminal voltage is detected,
A semiconductor optical amplifier characterized by controlling an injection current into a region other than the first current injection region among a plurality of current injection regions of the semiconductor optical amplifier so that the signal has a predetermined magnitude. A method for making the optical output power constant. 4. A semiconductor optical amplifier having a plurality of current injection regions capable of independently controlling an injection current in a propagation direction of an optical signal, and a first current of the plurality of current injection regions of the semiconductor optical amplifier. Means for injecting a constant current into the injection region, means for extracting a signal proportional to the magnitude of a specific frequency component from the terminal voltage of the current injection region for injecting the constant current, and the optical output power value to be made constant A corresponding reference voltage generating means and an injection current to a region other than the first current injection region of the plurality of current injection regions of the semiconductor optical amplifier so that the magnitude of the signal becomes a predetermined value. A device for stabilizing the optical output power of a semiconductor optical amplifier, which comprises a control circuit for controlling.