JPH0621582A - Optical amplifier - Google Patents

Abstract

PURPOSE:To effectively use signal optical power, by controlling the gain of an optical amplifier, on the basis of spontaneous radiation light generated in the optical amplifier. CONSTITUTION:Optical power of a wavelength which is in the gain bandwidth of an optical amplifier 1 and different from the amplication signal light wavelength is detected with an optical branching filter 2 and a photo detector 3. At this time, the spontaneous radiation light power of the optical amplifier 1 is detected, which power is changed by the excited state of the amplifier 1. The spontaneous radiation light power is large in the high excited state and becomes small in the low excited state. Control is performed in the following manner; when the spontaneous radiation light power is smaller than a specified d value, the excited state is increased, and when the power is large, the excited state is decresed. Thereby the spontaneous radiation light power can be kept constant. The spontaneous radiation light power is in the one-to-one relation to the signal gain of the optical amplifier 1, so that the signal gain is kept constant by keeping the spontaneous radiation light power constant. Thereby the signal light power can be effectively used.

Description

Detailed Description of the Invention

[0001]

The present invention is used in optical communication. In particular, it relates to gain control of an optical amplifier that directly amplifies signal light without converting it into an electric signal.

[0002]

2. Description of the Related Art As an optical amplifier for directly converting signal light, an optical fiber amplifier in which a rare earth element is added to an optical fiber and a semiconductor optical amplifier using a structure equivalent to a semiconductor laser device have been known. There is. The gain of each of these optical amplifiers can be adjusted by adjusting the pumping state, and the pumping light power is adjusted in the case of an optical fiber amplifier and the injection current is adjusted in the case of a semiconductor optical amplifier.

As a method of keeping the gain of the optical amplifier constant, a part of the input / output power of the signal light is detected and the pumping state of the optical amplifier is adjusted so that the ratio is kept constant. Is common. FIG. 3 is a block diagram showing an example of a conventional optical amplification device that performs such control.

In the conventional example shown in FIG. 3, the signal light is input to the optical amplifier 11 via the optical coupler 15 and output via the optical coupler 12. The optical coupler 12 splits a part of the output signal light and couples the split light to the photodetector 13. On the other hand, the optical coupler 15 splits a part of the input signal light and couples the split light to the photodetector 16. The detection outputs of the photodetectors 13 and 16 are supplied to the control circuit 14.
The control circuit 14 obtains the ratio of the detection outputs of the two photodetectors 13 and 16, that is, the ratio of the output power to the input power (output / input), and controls the pumping state of the optical amplifier based on the value. That is, when the output / input value is smaller than a predetermined value, the pumping state of the optical amplifier is strengthened, and when it is large, the pumping state is weakened. This keeps the signal gain of the optical amplifier substantially constant.

[0005]

However, in the conventional optical amplifier, since a part of the signal light is branched to perform the gain control, the loss of the signal light is caused accordingly. This is not desirable in an optical transmission system that wants to maximize the signal light power.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide an optical amplifying device capable of performing gain control without causing a loss of signal light.

[0007]

The optical amplifying device of the present invention comprises:
An optical demultiplexer that branches spontaneous emission light in a wavelength range different from the signal light wavelength from the output light of the optical amplifier, a photodetector that detects the spontaneous emission light that is branched by the optical demultiplexer, and this photodetector And a control circuit for controlling the excited state of the optical amplifier based on the output of

When spontaneous emission light may enter the input of the optical amplifier, for example, when another optical amplifier is connected in the preceding stage, the spontaneous emission light included in the input light of the optical amplifier is It is possible to provide an input light detecting means for detecting and a means for subtracting the output of the input light detecting means from the output of the photodetector on the output side and supplying it to the control circuit.

[0009]

[Function] Instead of branching a part of the signal light, the spontaneous emission light generated in the optical amplifier is extracted from the output light, and the signal gain of the optical amplifier is controlled so that the spontaneous emission light power becomes constant. .

Previous patent application by the applicant of the present application, Japanese Patent Application No. 3
Japanese Patent Application No. 131326 (filed on June 3, 1991, unpublished at the time of filing this application) discloses a technique for detecting spontaneous emission light emitted from the side surface of the optical amplifier and controlling the optical amplifier. On the other hand, the present invention is characterized in that spontaneous emission light is extracted from the output light of the optical amplifier.

[0011]

FIG. 1 is a block diagram showing the first embodiment of the present invention.

This optical amplifying apparatus comprises an optical amplifier 1 for directly amplifying the signal light, and as a control means for controlling the signal gain of the optical amplifier 1, a wavelength band different from the signal light wavelength from the output light of the optical amplifier 1 is used. Demultiplexer 2 that splits spontaneous emission light
And a photodetector 3 for detecting the spontaneous emission light branched by the optical demultiplexer 2, and a control circuit 4 for controlling the excitation state of the optical amplifier 1 based on the output of the photodetector 3.

For example, an erbium-doped optical fiber amplifier is used as the optical amplifier 1, and a signal light having a wavelength of 1.55 μm is amplified. At this time, in the optical demultiplexer 2, the wavelength is 1.535 μm.
Demultiplexes the light of. The optical power of this wavelength of 1.535 μm is detected by the photodetector 3, and the detection signal is sent to the control circuit 4. The control circuit 4 controls so that the excited state of the optical amplifier 1 is strengthened when the detected optical power is smaller than a predetermined value, and weakened when the detected optical power is larger.

In this configuration, the optical demultiplexer 2 and the photodetector 3 detect the optical power within the gain band of the optical amplifier 1 and at a wavelength different from the amplified signal light wavelength. At this time, the spontaneous emission light power of the optical amplifier 1 is detected.
This spontaneous emission light power increases or decreases depending on the excitation state of the optical amplifier 1. That is, the spontaneous emission power increases in the high excitation state and decreases in the low excitation state. Therefore, when the spontaneous emission light power generated by the optical amplifier 1 is controlled to be stronger than the predetermined value and the excited state is strengthened when the power is larger than the predetermined value, the spontaneous emission light power generated in the optical amplifier 1 is made constant. Will keep. The spontaneous emission light power has a one-to-one relationship with the signal gain of the optical amplifier 1, and if the spontaneous emission light power is kept constant, the signal gain is also kept constant.

Further, in this configuration, since the optical demultiplexer 2 demultiplexes only the spontaneous emission light, the signal light is substantially lossless. Therefore, the gain control can be performed without damaging the signal light power.

FIG. 2 is a block diagram showing the second embodiment of the present invention.

In addition to the configuration of the first embodiment, this embodiment
An optical demultiplexer 5 and a photodetector 6 as input light detecting means for detecting spontaneous emission light included in the input light of the optical amplifier 1,
It further includes a difference circuit 7 that subtracts the output of the photodetector 6 from the output of the photodetector 3 on the output side and supplies the subtracted output to the control circuit 4.

In the above-mentioned first embodiment, only the signal light is incident on the input of the optical amplifier 1. But,
For example, when the optical amplifiers are connected in multiple stages, spontaneous emission light from the previous stage may enter. For this reason,
In order to correctly detect the spontaneous emission light power generated by the optical amplifier 1, it is necessary to consider the spontaneous emission light on the input side.

Therefore, in this embodiment, by the optical demultiplexer 5,
Demultiplexes light of the same wavelength as the demultiplexing wavelength in the optical demultiplexer 2,
The optical power is detected by the photodetector 6. In the differential circuit 7, it is assumed that a part of the light of that wavelength has passed through the optical demultiplexer 5 and is incident on the optical amplifier 1, and the ratio and the gain of the optical amplifier 1 relative to it are used as the output value of the photodetector 6. Multiply and subtract the value from the output value of the photodetector 3. The control circuit 4 uses the value obtained by the difference circuit 7 to perform the same control as in the first embodiment.

Also in this case, the optical demultiplexers 2 and 5 demultiplex only the spontaneous emission light, and the signal light is substantially lossless.

In the above embodiments, the case where the erbium-doped optical fiber amplifier is used has been described as an example, but the present invention can be similarly implemented by using other rare earth-doped optical fiber amplifiers and semiconductor optical amplifiers.

[0022]

As described above, the optical amplifying device of the present invention controls the gain of the optical amplifier based on the spontaneous emission light generated by the optical amplifier. Therefore, there is almost no loss of the amplified signal light, and the signal light power can be effectively used.

[Brief description of drawings]

FIG. 1 is a block diagram showing the first embodiment of the present invention.

FIG. 2 is a block diagram showing a second embodiment of the present invention.

FIG. 3 is a block diagram showing a conventional example.

[Explanation of symbols]

 1, 11 Optical amplifier 2, 5 Optical demultiplexer 3, 6, 13, 16 Photodetector 4, 14 Control circuit 7 Difference circuit 12, 15 Optical coupler

Claims (2)

[Claims] 1. An optical amplifier comprising an optical amplifier that directly amplifies signal light and a control means that controls the signal gain of the optical amplifier, wherein the control means changes the output light of the optical amplifier from the signal light wavelength. An optical demultiplexer that branches spontaneous emission light in a wavelength range different from that of the optical demultiplexer, a photodetector that detects the spontaneous emission light branched by the optical demultiplexer, and an optical amplifier based on the output of this photodetector An optical amplifying device comprising a control circuit for controlling an excited state. 2. The control means includes an input light detection means for detecting spontaneous emission light included in the input light of the optical amplifier, and the control by subtracting an output of the input light detection means from an output of the photodetector. Means for supplying to a circuit.
The optical amplification device described.