JPH07281219A - Optical fiber amplifier - Google Patents

Abstract

PURPOSE:To attain optical signal amplification with decreased distortion components by adjusting a variable optical attenuator according to an input signal light power and inputting the input signal light power to minimize the distortion to an erbium-doped fiber. CONSTITUTION:The variable optical attenuator 2, an optical coupler 3, a first optical isolator 5, a first WDM 6, the erbium-doped fiber 7, a second WDM 8, a second optical isolator 9 and a connector 10 for output are cascade connected by optical fibers in succession to a connector 1 for input. A first exciting light source 11 and a second exciting light source 12 are electrically connected to a first APC/ATC circuit 13 and second APC/ATC circuit 14 for controlling the light outputs so as attain the specified light outputs. The output light rays of the first exciting light source 11 and the second exciting light source 12 are respectively inputted through the first WDM 6 and the second WDM 8 by the optical fibers to the erbium-doped fiber 7 from before and behind to excite erbium ions, by which the amplification of the signal light is executed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber amplifier used in an optical communication system.

[0002]

2. Description of the Related Art A conventional optical fiber amplifier will be described with reference to FIG. FIG. 3 is a block diagram showing the configuration of a conventional optical fiber amplifier. In FIG. 3, reference numeral 1 is an input connector. A first optical isolator 5 has a small loss in the direction from the point A on the input light side to the point B on the opposite side, and has a large loss in the direction from the point B to the point A. Light is allowed to pass in the direction toward the point B, and light in the direction from the point B to the point A is blocked.
Reference numeral 6 denotes a first wavelength combiner (hereinafter referred to as WDM), which has a small loss of signal light and a large loss of pumping light between point B on the first optical isolator 5 side and point C on the opposite side. , B that passes only the signal light and intersects the BC point
Between points G, the loss with respect to the signal light is large and the loss with respect to the pump light is small, so that only the pump light is passed. Reference numeral 7 is an erbium-doped fiber in which erbium ions are mixed in the optical fiber, which amplifies signal light in the wavelength band of 1.55 μm by injecting pumping light in the wavelength of 1.48 μm. Reference numeral 8 denotes a second WDM, which passes only the signal light between the point D on the erbium-doped fiber 7 side and the point E on the opposite side, and passes only the pumping light between the points D and H. Reference numeral 9 denotes a second optical isolator that allows only light in the direction from the point E on the second WDM 8 side to the point F on the opposite side to pass therethrough. 1
Reference numeral 0 is an output connector. 11 is a first excitation light source,
Light having a wavelength of 1.48 μm is output from the laser diode, and the erbium-doped fiber 7 is excited from the point C side through the first WDM 6. Reference numeral 12 denotes a second pumping light source, which outputs light having a wavelength of 1.48 μm from the laser diode and pumps the erbium-doped fiber 7 from the point D side through the second WDM 8. Reference numeral 13 is a first control circuit (hereinafter referred to as an APC / ATC circuit), which is used to keep the optical output of the first pumping light source 11 constant.
Drive current is passed to 1. Reference numeral 14 denotes a second APC / ATC circuit, which supplies a drive current to the second pumping light source 12 so as to keep the optical output of the second pumping light source 12 constant.

After the input connector 1, the first optical isolator 5, the first WDM 6, the erbium-doped fiber 7, the second WDM 8, the second optical isolator 9, and the output connector 10 are subordinated to each other by an optical fiber. It is connected. The point G of the first WDM 6 is the first pumping light source 11
The point H of the second WDM 8 is connected to the second pumping light source 12 by an optical fiber. The point I of the first pumping light source 11 is the first APC / ATC circuit 13
The point J of the second pumping light source 12 is the second APC / ATC.
Each is electrically connected to the circuit 14.

The operation of the optical fiber amplifier configured as described above will be described below.

Signal light is input to the erbium-doped fiber 7 from the input connector 1 through the first optical isolator 5 and the first WDM 6 in this order. Pumping light from the first pumping light source 11 is input to the erbium-doped fiber 7 from the point C side via the first WDM 6, and the second pumping light source 12
From the point D side to the erbium-doped fiber 7 via the second WDM 8 to excite the erbium ions to amplify the signal light. The amplified signal light is the second
The signal is output from the output connector 10 through the WDM 8 and the second optical isolator 9. Here, the first optical isolator 5 and the second optical isolator 9 are inserted in order to prevent oscillation that occurs when reflected light returns to the erbium-doped fiber 7 again. The distortion generated in the optical fiber amplifier is dominated by the gain tilt characteristic of the erbium-doped fiber 7, and the gain tilt characteristic depends on the power of the signal light input to the erbium-doped fiber 7. Therefore, in order to reduce the distortion in an optical communication system in which the signal light power input to the optical fiber amplifier and the output light power are specified, a gain tilt characteristic in which the distortion is minimized in advance in the specified input signal light power and pump light source power Erbium-doped fiber 7 with

As described above, even in the above conventional optical fiber amplifier, distortion can be suppressed to a small level by selecting an appropriate erbium-doped fiber in advance.

[0007]

However, in the above-mentioned conventional optical fiber amplifier, when the input signal light power to the erbium-doped fiber 7 changes for some reason during the operation of the optical fiber amplifier, the signal generated by the optical fiber amplifier is generated. There is a problem that the control that minimizes the distortion of light cannot be performed.

The present invention solves such a conventional problem, and an object of the present invention is to provide an excellent optical fiber amplifier which outputs a signal light with a minimum distortion during operation.

[0009]

In order to achieve the above object, the present invention provides an input connector for inputting signal light,
A variable optical attenuator that changes the input signal light power,
An optical coupler that splits the input signal light, a first and a second optical isolator that passes the input signal light and prevents the signal light from returning to the input side, and an optical signal of two different wavelengths are combined. The first and second WDMs that oscillate, the erbium-doped fiber that has the function of amplifying the signal light, and that the input power that minimizes the distortion with respect to a certain pumping light source power is known in advance. An output connector for outputting a signal light, a monitor / control unit for monitoring the power of the signal light demultiplexed by the optical coupler and generating an electric signal for adjusting the variable optical attenuator, and the erbium-doped fiber First and second excitation light sources that excite erbium ions, and first and second excitation light sources that control the intensity of the excitation light output from the excitation light sources to be constant, respectively. Comprising a circuit, the input connector, a variable optical attenuator, an optical coupler, a first optical isolator, a first WDM, erbium-doped fiber, the second WD
M, the second optical isolator, and the output connector are subordinately connected by an optical fiber, and the outputs of the first and second pumping light sources are connected to the pumping light input ports of the first and second WDMs by optical fibers, respectively. The signal light demultiplexed by the optical coupler is connected to the monitor / control section by an optical fiber, and the output of the monitor / control section is electrically connected to the variable optical attenuator.

[0010]

According to the present invention, in the above structure, the input signal light is demultiplexed by the optical coupler, and the control signal is output to the variable optical attenuator in accordance with the input signal light power in the monitor / control section.
By inputting the input signal light power that minimizes the distortion by adjusting the variable optical attenuator to the erbium-doped fiber, it is possible to amplify the optical signal with a small distortion component.

[0011]

【Example】

(Embodiment 1) A first embodiment of the present invention will be described below with reference to FIG.
Will be described with reference to. The same numbers are used for the same components as those described in the conventional example.

FIG. 1 is a block diagram of an optical fiber amplifier according to a first embodiment of the present invention. In FIG. 1, reference numeral 1 is an input connector. Reference numeral 2 denotes a variable optical attenuator, which changes the light input from the point A by an electric signal input from the point I and outputs the light in the direction of the point B. 3 is an optical coupler,
The light input from the B point is demultiplexed in the C point direction and the J point direction. Reference numeral 4 denotes a monitor / control unit, which varies the optical attenuator 2 according to the signal light power input from the point J on the optical coupler 3 side.
The electric signal for adjusting the signal is output in the direction of the point I on the variable optical attenuator 2 side. A first optical isolator 5 has a small loss in the direction from the point C on the input light side to the point D on the opposite side, and a large loss in the direction from the point D to the point C. Therefore, from the point C, Light is passed in the direction toward the point D, and light in the direction from the point D toward the point C is blocked.
A first WDM 6 has a small loss of signal light and a large loss of pumping light between the point D on the first optical isolator 5 side and the point E on the opposite side. Therefore, only the signal light is passed, Further, between the EK points intersecting the DE points, the loss with respect to the signal light is large and the loss with respect to the pumping light is small, so that only the pumping light is passed. Reference numeral 7 is an erbium-doped fiber in which erbium ions are mixed in the optical fiber.
The input light power that amplifies the signal light in the μm band and further minimizes the distortion at a certain pump light source power has been clarified in advance. Reference numeral 8 denotes a second WDM, which passes only the signal light between the point F on the erbium-doped fiber 7 side and the point G on the opposite side, and passes only the pumping light between the points F and L. Reference numeral 9 denotes a second optical isolator, which is a second WDM 8
Only light in the direction from the point G on the side to the point H on the opposite side is passed. Reference numeral 10 is an output connector. Reference numeral 11 denotes a first excitation light source, which outputs light having a wavelength of 1.48 μm,
Input to WDM6. Reference numeral 13 is a first APC / ATC circuit, which supplies a drive current to the first pumping light source 11 so as to keep the optical output of the first pumping light source 11 constant. 12 is the second
Is an excitation light source of, and outputs light with a wavelength of 1.48 μm,
Input to the second WDM 8. 14 is the second APC / AT
This is a C circuit, and a drive current is passed through the second pumping light source 12 so that the optical output of the second pumping light source 12 is constant.

After the input connector 1, the variable optical attenuator 2, the optical coupler 3, the first optical isolator 5, the first WDM 6, the erbium-doped fiber 7, the second WDM 8, the second optical isolator 9, The output connectors 10 are subordinately connected by an optical fiber in this order. The input port of the monitor / control unit 4 is connected to the other output end of the optical coupler 3 by an optical fiber, and the output port is electrically connected to the variable optical attenuator 2. The first APC / ATC circuit 13 is electrically connected to the first pumping light source 11, and the second APC / ATC circuit 13
The TC circuit 14 is electrically connected to the second pumping light source 12.

Next, the operation of the first embodiment will be described. In the first embodiment, the first pump light source 11
The intensity of the excitation light output from the first APC / ATC
It is driven to be constant by the circuit 13, and this pumping light passes through the first WDM 6 and enters the erbium-doped fiber 7 from the first WDM 6 to excite the erbium ion. The intensity of the pumping light output from the second pumping light source 12 is driven by the second APC / ATC circuit 14 to be constant, and this pumping light is supplied to the second WDM 8
Through the second WDM 8 to enter the erbium-doped fiber 7 to excite erbium ions. On the other hand, the signal light input from the input connector 1 is demultiplexed by the optical coupler 3, one of the outputs is input to the monitoring / control unit 4, and the other one of the outputs of the first optical isolator 5 and the first WDM 6. It is sequentially amplified in the erbium-doped fiber 7. The signal light input to the monitoring / control unit 4 inputs an electric signal for adjusting the variable optical attenuator 2 according to the signal light power to the variable optical attenuator 2, and the variable optical attenuator 2 minimizes distortion by the electric signal. The input signal light power is adjusted and input to the first optical isolator 5. On the other hand, the signal light amplified by the erbium-doped fiber 7 passes through the second WDM 8 and the second optical isolator 9 in this order, and is output from the output connector 10.

As described above, according to the first embodiment,
By adjusting the variable optical attenuator 2 by the monitor / control unit 4, the input signal light power that minimizes the distortion can be input to the erbium-doped fiber 7 via the first optical isolator 5 and the first WDM 6. .

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The same components as those described in the first embodiment are designated by the same reference numerals.

FIG. 2 is a block diagram of an optical fiber amplifier according to the second embodiment of the present invention. In FIG. 2, reference numeral 1 is an input connector. An optical coupler 3 demultiplexes the light input from the point A in the directions of the point B and the point I. Reference numeral 5 is a first optical isolator, which is a point C on the opposite side from a point B on the input light side.
The loss is small in the direction toward the point, and the loss is large in the direction from the point C to the point B. Therefore, light is transmitted in the direction from the point B to the point C, and the loss in the direction from the point C to the point B is increased. Block the light. A first WDM 6 has a small loss of signal light and a large loss of pumping light between a point C on the first optical isolator 5 side and a point D on the opposite side. Therefore, only the signal light is passed, Further, between the DJ points intersecting the CD points, the loss with respect to the signal light is large and the loss with respect to the pumping light is small, so that only the pumping light passes through.
Reference numeral 7 is an erbium-doped fiber in which erbium ions are mixed in the optical fiber, which amplifies the signal light in the 1.55 μm band by injecting pumping light of 1.48 μm and further minimizes distortion at a certain input optical power. The light source power is known in advance. 8 is the second WDM
Therefore, only the signal light is passed between the point E on the erbium-doped fiber 7 side and the point F on the opposite side, and only the pumping light is passed between the points EK. Reference numeral 9 denotes a second optical isolator, which passes only the light in the direction from the point F on the second WDM 8 side to the point G on the opposite side. Reference numeral 10 is an output connector. 1
Reference numeral 1 denotes a first excitation light source, which outputs light having a wavelength of 1.48 μm and inputs the light to the first WDM 6. 13 is the first AP
This is a C / ATC circuit, and a drive current is passed through the first pumping light source 11 so that the optical output of the first pumping light source 11 is constant. Reference numeral 12 denotes a second pumping light source, which outputs light having a wavelength of 1.48 μm and inputs the light to the second WDM 8. 14 is the second
In the APC / ATC circuit, the driving current is supplied to the second pumping light source 12 so that the optical output of the second pumping light source 12 is constant. Reference numeral 15 denotes a variable optical attenuator, which changes the light input from the G point on the second optical isolator 9 side by an electric signal input from the L point and outputs it in the H point direction.
Reference numeral 16 is a monitoring / control unit, which is a variable optical attenuator 15 according to the signal light power input from point I on the optical coupler 3 side.
Of the electric signal for adjusting the output optical power of the first pumping light source 11 and the second pumping light source 12 while outputting the electric signal for adjusting the optical power in the direction of the L point on the variable optical attenuator 15 side. APC / ATC circuit 13 and second A
It outputs in the direction of the O and P points on the PC / ATC circuit 14 side. Then, following the input connector 1, an optical coupler 3, a first optical isolator 5, a first WDM 6, an erbium-doped fiber 7, a second WDM 8, a second optical isolator 9, a variable optical attenuator 15, and an output connector. They are connected in a subordinate manner by optical fibers in the order of 10. Monitoring /
The input port of the control unit 16 is connected by an optical fiber to one of the output ends of the optical coupler 3 which is not connected to the first optical isolator 5, and the three output ports are connected to the variable optical attenuator 15 and the first optical isolator 5. The APC / ATC circuit 13 and the second APC / ATC circuit 14 are electrically connected to each other. Also, the first APC / ATC circuit 13 is electrically connected to the first pumping light source 11, and
The PC / ATC circuit 14 is electrically connected to the second excitation light source 12.

Next, the operation of the second embodiment will be described. In the second embodiment, the first pumping light source 11
The intensity of the excitation light output from the first APC / ATC
It is driven to be constant by the circuit 13, and this pumping light passes through the first WDM 6 and enters the erbium-doped fiber 7 from the first WDM 6 to excite the erbium ion. The intensity of the pumping light output from the second pumping light source 12 is driven by the second APC / ATC circuit 14 to be constant, and this pumping light is supplied to the second WDM 8
Through the second WDM 8 to the erbium-doped fiber 7 to excite the erbium-in. On the other hand, the signal light input from the input connector 1 is demultiplexed by the optical coupler 3, one of the outputs is input to the monitoring / control unit 16, and the other is output from the first optical isolator 5 and the first WDM 6. The light is amplified in the erbium-doped fiber 7 in order, and is input to the monitoring / control unit 16 in the order of the second WDM 8 and the second optical isolator 9. Monitoring / control unit 16
Inputs to the variable optical attenuator 15 an electric signal for adjusting the signal light power output from the output connector according to the input signal light power, and at the same time, the first pump light source 11 and the second pump light source 12 An electric signal for adjusting the output power of the above is input to the first APC / ATC circuit 13 and the second APC / ATC circuit 14. The variable optical attenuator 15 adjusts the signal light input from the second optical isolator 9 to a predetermined output light power by the electric signal and outputs the signal light from the output connector 10.

As described above, according to the second embodiment,
By adjusting the variable optical attenuator 15 by the monitor / control unit 16, the pump light source power that minimizes the distortion is set to the first W.
It can be input to the erbium-doped fiber 7 via the DM 6 and the second WDM 8.

[0020]

As is apparent from the above embodiment, the present invention adjusts the input signal light or pumping light source power according to the input signal light power and inputs the erbium-doped fiber, and the distortion is minimized. Since the input signal light or the pumping light source power is input to the erbium-doped fiber, there is an effect that the optical signal can be always amplified while the distortion is minimized during the operation of the optical fiber amplifier.

[Brief description of drawings]

FIG. 1 is a block diagram of an optical fiber amplifier according to a first embodiment of the present invention.

FIG. 2 is a block diagram of an optical fiber amplifier according to a second embodiment of the present invention.

FIG. 3 is a block diagram of a conventional optical fiber amplifier.

[Explanation of symbols]

 1 Input Connector 2,15 Variable Optical Attenuator 3 Optical Coupler 4,16 Monitoring / Control Unit 5 First Optical Isolator 6 First Wavelength Synthesizer (WDM) 7 Erbium Doped Fiber 8 Second Wavelength Synthesizer (WDM) 9 Second Optical Isolator 10 Output Connector 11 First Excitation Light Source 12 Second Excitation Light Source 13 First Control Circuit (APC / ATC Circuit) 14 Second Control Circuit (APC / ATC Circuit)

Claims (2)

[Claims] 1. An input connector for inputting signal light,
A variable optical attenuator that changes the input signal light power,
An optical coupler that splits the input signal light, a first and a second optical isolator that passes the input signal light and prevents the signal light from returning to the input side, and an optical signal of two different wavelengths are combined. An erbium-doped fiber that has a first and a second wavelength synthesizer that oscillate, a function that amplifies the signal light, and that the input power that minimizes the distortion with respect to a certain pump light source power is known in advance; An output connector for outputting the generated signal light, a monitor / control unit for monitoring the power of the signal light demultiplexed by the optical coupler and generating an electric signal for adjusting the variable optical attenuator, and the erbium-doped First and second excitation light sources for exciting erbium ions in the fiber, and first and second control for controlling the intensity of the excitation light output from the excitation light source to be constant, respectively. A control circuit, an input connector,
The variable optical attenuator, the optical coupler, the first optical isolator, the first wavelength synthesizer, the erbium-doped fiber, the second wavelength synthesizer, the second optical isolator, and the output connector are subordinately connected by an optical fiber, and The outputs of the first and second pumping light sources are connected to the pumping light input ports of the first and second wavelength synthesizers respectively by optical fibers, and the signal light demultiplexed by the optical coupler is sent to the monitoring / control unit. An optical fiber amplifier connected by an optical fiber and electrically controlled by connecting the output of the monitoring / control section to the variable optical attenuator so as to minimize distortion of the input light level of the erbium-doped fiber. 2. The monitor / control unit further has a function of outputting a signal to a control circuit to adjust the output power of the pumping light source, and the erbium-doped fiber further has a minimum distortion for a certain input optical power. The pump light source power has been clarified, and the input connector, optical coupler, first optical isolator, first wavelength synthesizer, erbium-doped fiber, second wavelength synthesizer, second optical isolator, variable optical attenuator , The output connector is subordinately connected by an optical fiber, and the output of the monitoring / control unit is first and second.
2. The optical fiber amplifier according to claim 1, wherein the pumping light output is controlled so as to minimize distortion according to the input light of the erbium-doped fiber by electrically connecting to the control circuit and the variable optical attenuator.