JP2000183434A - Highly accurate light output monitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical amplifier output monitoring circuit, capable of accurately receiving output signal light from an optical amplifier and highly accurately controlling the optical output level of the amplifier. SOLUTION: An optical branch 2 transmits an output signal light L2 outputted from an optical amplifier 1 and gives transmitted light to a fiber grating(FBG) 4. The FBG 4 makes the output signal light L2 to be incident from the amplifier 1, reflects signal light L3 which is a part of the signal light L2, and returns the light L3 to the branch 2. At this time, the FBG 4 transmits the residual of the output signal light L2, including spontaneous emission light (ASE). The branch 2 bifurcates the reflected signal light L3 and applies the bifurcated signal to a light receiver 3. The light receiver 3 converts the bifurcated signal light into an electrical signal and gives the electrical signal to a control circuit 5. The circuit 5 controls the optical output level of the amplifier 1, based on the electrical signal inputted from the receiver 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output monitor circuit of an optical amplifier for amplifying an optical signal in a communication system using an optical fiber transmission line, and more particularly, to accurately receiving the level of the output signal light of the optical amplifier. The present invention also relates to a high-precision optical output monitor capable of controlling the level of the output signal light with high accuracy and constant.

[0002]

2. Description of the Related Art Conventionally, output signal light of an optical amplifier is received by an output monitor circuit, and the output level of the optical amplifier is controlled to be constant. FIG. 3 shows a configuration of such a conventional output monitor circuit 200. As shown in the figure, the output monitor circuit 200 includes an optical splitter 20 that splits the output signal light of the optical amplifier 1, a light receiver 30 that receives the split light split by the optical splitter 20, And a control circuit 50 for controlling the optical amplifier 1 based on the electric signal from the light receiver 30.

Here, the optical amplifier 1 has an optical fiber doped with a rare earth element as an amplification medium, and outputs a laser diode (LD) (not shown) by changing a bias current of a laser diode (LD) for inputting excitation light into the optical fiber. The power (light output level) is configured to be controllable.

According to the output monitor circuit 200, the output signal light output from the optical amplifier 1 is split by the optical splitter 20, and a part of the output light of the optical amplifier 1 is received by the light receiver 30. The light receiver 30 outputs an electric signal corresponding to the light receiving level to the control circuit 50. The control circuit 50 controls the bias current of the laser diode included in the optical amplifier 1 based on the electric signal, and controls the output level of the optical amplifier 1 to be constant. As described above, the conventional output monitor circuit 200
In, the output signal light of the optical amplifier 1 is branched, and the optical amplifier 1 is controlled based on the output level of the branched light.

[0005]

However, according to the conventional output monitor circuit 200 described above, the output signal light of the optical amplifier 1 includes not only the signal light having information but also the spontaneous emission light (ASE; Amplified Spontaneous Emission). ) Is also included, so that the light receiving device 30 also receives this ASE.
For this reason, there is a problem that the output signal light of the optical amplifier 1 cannot be accurately received, and the level of the output signal light (light output level) cannot be controlled to be accurately constant.

[0006] For example, Japanese Patent Application Laid-Open No. Hei 10-51388 discloses a high-precision method in which the output light of an optical amplifier and ASE are received by a photodetector and the optical output level of the optical amplifier is controlled according to the difference between the light and the ASE. Discloses a technique for maintaining an optical output level. However, according to this method, since two optical splitters and two light receivers are required, there is a problem that the number of components increases. Moreover, since the control circuit subtracts the ASE signal component included in the output light to obtain the optical level of the output signal, there is a problem that the configuration of the control circuit becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and accurately converts an output signal light of an optical amplifier without complicating a configuration of a control circuit for controlling a bias current of an LD included in the optical amplifier. It is an object of the present invention to provide a high-precision optical output monitor capable of receiving light and controlling the optical output level of an optical amplifier accurately and constantly.

[0008]

In order to achieve the above object, the present invention has the following arrangement. That is, according to the first aspect of the present invention, the output signal light (e.g., corresponding to the output signal light L2) of the optical amplifier is made incident, a part of the output signal light (e.g., corresponding to the signal light L3) is extracted, and the natural light is emitted A signal light extraction unit (e.g., corresponding to the optical splitter 2 and the FBG 4) that transmits the rest of the output signal light including light, and a light reception unit (e.g., a light receiver) that receives the extracted signal light and converts it into an electric signal 3), and a control unit (corresponding to, for example, the control circuit 5) for controlling the optical output level of the optical amplifier based on the electric signal.

According to the present invention, the signal light extractor receives the output signal light of the optical amplifier and extracts a part of the output signal light. At this time, the spontaneous emission light and the rest of the output signal light are transmitted. The extracted output signal light is received by the light receiving unit and converted into an electric signal. The control unit controls the optical output level of the optical amplifier based on the electric signal, and keeps the optical output level constant. Therefore, it is possible to eliminate the influence of spontaneous emission light and control the optical output level of the optical amplifier with high accuracy based on the output signal light.

According to a second aspect of the present invention, the signal light extracting section reflects a part of the output signal light of the optical amplifier and transmits the rest of the output signal light including spontaneous emission light. (E.g., equivalent to FBG4), and provided on an optical transmission path between the optical amplifier and the signal light reflection unit,
A signal light splitter (corresponding to, for example, the optical splitter 2) for transmitting the output signal light of the amplifier and splitting the signal light reflected by the signal light reflector.

According to the present invention, a part of the output signal light having the signal light wavelength is reflected by the light reflecting portion. The reflected output signal light is split by the optical splitter and is incident on the light receiver. Therefore, the output signal light can be extracted,
The light-receiving unit outputs spontaneous emission light (ASE;
Amplified Spontaneous Emission is not received, and the output signal light level can be accurately received.

According to a third aspect of the present invention, the light receiving section is
The controller outputs a current signal corresponding to the amount of light received by the signal light branching unit, and the control unit converts the current signal into a voltage signal (for example, a current / voltage conversion circuit 5A). ), An error amplifying circuit (e.g., corresponding to the error amplifying circuit 5B) for amplifying an error between a predetermined reference voltage and a voltage signal obtained by the conversion circuit, and the error amplifying circuit based on an output signal of the error amplifying circuit. Drive circuit for driving a laser diode built in the optical amplifier in a direction to reduce (for example, equivalent to LD drive circuit 5C)
And characterized in that:

According to a fourth aspect of the present invention, the signal light reflecting portion is a fiber Bragg (FBG).
Gratings). This makes it possible to reflect and extract a part of the output signal light.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. In each figure, the same reference numerals are given to elements common to the elements shown in FIG. In FIG.
Output monitor circuit 1 of optical amplifier 1 according to this embodiment
00 shows the configuration. As shown in FIG. 1, the output monitor circuit 100 includes an optical splitter 2 as a signal light splitter and a fiber grating (FB) as a signal light reflector.
G; Fiber Bragg Gratings) 4, a light receiver 3 as a light receiving unit, and a control circuit 5 as a control unit. The signal light reflecting section and the signal light branching section constitute a signal light extracting section.

The optical amplifier 1 amplifies the input signal light L1 to obtain an output signal light L2. The optical fiber is doped with a rare earth element as an amplifying medium, and the pumping light is incident on the optical fiber (not shown). A laser diode (LD), and the level (power) of the output light L2 can be controlled by changing the bias current of the laser diode.

Here, the FBG 4 is a signal component having a signal light wavelength (hereinafter, referred to as a signal component) of the output signal light L 2 of the optical amplifier 1.
A part of the signal light (hereinafter simply referred to as "signal light") (signal light L3) is reflected, and the remaining signal light and ASE having a wavelength different from the wavelength of this signal light are transmitted therethrough. Is formed.

The optical splitter 2 is provided on an optical transmission line between the optical amplifier 1 and the FBG 4, and splits the signal light L3 reflected by the FBG 4 from the optical transmission line and takes it out. The light receiver 3 receives the split light (signal light L3) split by the optical splitter 2, and converts the split light into a current signal having a current value corresponding to the light receiving level.

The control circuit 5 controls the degree of amplification of the optical amplifier 1 and changes the bias current of the laser diode (LD) of the optical amplifier 1 based on the current signal input from the light receiver 3. The optical output level of the output signal light L2 is controlled to be constant.

FIG. 2 shows a detailed configuration of the control circuit 5. As shown in the figure, the control circuit 5 includes a current / conversion circuit for converting a current signal from the light receiver 3 into a voltage signal.
A voltage conversion circuit 5A, an error amplification circuit 5B for amplifying an error between a reference voltage (predetermined reference voltage) RV and a voltage signal obtained by the current / voltage conversion circuit 5A, and an output signal from the error amplification circuit 5B An LD drive circuit 5C as a drive circuit for driving a laser diode included in the optical amplifier in a direction to reduce the error.

The operation of the output monitor circuit 100 according to this embodiment will be described below. First, the optical amplifier 1 receives an input signal light L1 via an optical fiber connected to an input side, amplifies the input signal light L1, and outputs an output signal light L2. This output signal light L2 passes through the optical splitter 2 and is incident on the FBG 4.

The FBG 4 reflects a part of the output signal light L2 and returns it to the optical splitter 2. At this time, F
The BG4 transmits the remaining signal light and the ASE included in the output signal light L2 as the output signal light L4. FBG4
The signal light L <b> 3 reflected by is split by the optical splitter 2 and enters the light receiver 3. The light receiver 3 receives the signal light L3 and converts it into a current signal. Therefore, the level of the signal light included in the output signal light L2 is accurately received by the light receiver 3 and converted into an electric signal (current signal).

The control circuit 5 controls the amplification degree of the optical amplifier 1 based on the current signal output from the light receiver 3 so as to keep the level of the output signal light L2 constant. That is, the current / voltage conversion circuit 5A constituting the control circuit 5 converts the current signal input from the light receiver 3 into a voltage signal and outputs the voltage signal to the error amplifier circuit 5B.

The error amplifier circuit 5B compares the voltage signal input from the current / voltage conversion circuit 5A with the reference voltage VR and outputs a difference value (error). The LD drive circuit 5C drives the laser diode and changes the bias current of the laser diode included in the optical amplification circuit 1 in a direction in which the difference value decreases.

Here, the reference voltage VR applied to the error amplifier circuit 5B gives the level (light output level) of the output signal light to be output from the optical amplifier 1.
The difference value output from the error amplifier circuit 5B indicates an error in the level of the output light L2 with respect to this light output level. Therefore, if the amplification degree of the optical amplifier 1 is controlled so as to reduce the difference value, the level of the output light L2 is maintained at a constant level corresponding to the reference voltage VR. At this time, since the ASE included in the output signal light L2 is ignored, the output signal light is accurately monitored (received), and the level of the output signal light L2 of the optical amplifier 1 is controlled with high accuracy.

According to the above-described embodiment, the ASE output from the optical amplifier 1 passes through the FBG 4 and reflects only a part of the output signal light having the signal light wavelength. It is possible to accurately receive the light level. In addition, in order to eliminate the influence of ASE contained in the output signal light L2 output from the optical amplifier, it is possible to control the output level of the optical amplifier 1 to be exactly constant. further,
Since the ASE is optically removed by the FBG 4 as an optical component, the configuration of the control circuit 5 can be simplified.

Although the embodiment of the present invention has been described above, the present invention is not limited to this embodiment, and the present invention is applicable to any design change or the like without departing from the gist of the present invention. included. For example, in the above-described embodiment, the light receiver 3 outputs a current signal according to the amount of received signal light L3, but may output a voltage signal. In this case, the control circuit 5 may be configured to control the optical amplifier 1 by inputting a voltage signal.

[0027]

As described above, according to the present invention, the following effects can be obtained. That is, the output signal light of the optical amplifier is incident, a part of the output signal light is extracted and the rest of the output signal light including the spontaneous emission light is transmitted, and the extracted signal light is received and converted into an electric signal. After the conversion, the optical output level of the optical amplifier is controlled based on the electric signal. Therefore, the output of the optical amplifier can be controlled without complicating the configuration of the control circuit for controlling the bias current of the LD of the optical amplifier. By accurately receiving the level of the signal light included in the light, the optical output level of the optical amplifier can be accurately and constantly controlled.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an output monitor circuit of an optical amplifier according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a control circuit according to the embodiment of the present invention.

FIG. 3 is a block diagram illustrating a configuration of an output monitor circuit according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical amplifier, 2 ... Optical splitter, 3 ... Light receiver, 4 ... Fiber grating (FBG), 5 ... Control circuit, 5A ... Current / voltage conversion circuit, 5B ... Error amplifier circuit, 5C ... LD drive circuit.

Claims (4)

[Claims] A signal light extraction unit that receives an output signal light of an optical amplifier, extracts a part of the output signal light, and transmits the rest of the output signal light including spontaneous emission light; A high-precision optical output monitor, comprising: a light receiving unit that receives a signal light and converts the signal light into an electric signal; and a control unit that controls an optical output level of the optical amplifier based on the electric signal. 2. The signal light extraction unit, comprising: a signal light reflection unit that reflects a part of output signal light of the optical amplifier and transmits the rest of the output signal light including spontaneous emission light; A signal light branching unit provided on an optical transmission line between the signal light reflecting unit and transmitting the output signal light of the amplifier and branching the signal light reflected by the signal light reflecting unit. A high-precision optical output monitor characterized by the following. 3. The light receiving section outputs a current signal according to an amount of received signal light branched by the signal light branching section, and the control section converts the current signal into a voltage signal. A conversion circuit; an error amplification circuit that amplifies an error between a predetermined reference voltage and a voltage signal obtained by the conversion circuit; and a built-in optical amplifier in a direction to reduce the error based on an output signal of the error amplification circuit. 3. A high-precision optical output monitor according to claim 1, further comprising: a driving circuit for driving the laser diode. 4. The high-precision optical output monitor according to claim 2, wherein said signal light reflecting section is made of a fiber grating (FBG).