JP2003243750A - Gain tilt compensator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gain tilt compensator wherein a gain thereof is suppressed from being varied owing to a change in an installation environment such as temperature in the gain of EDFA and is flattened stably. <P>SOLUTION: A gain tilt compensator comprises a thulium doped optical fiber 1, an input signal optical power monitor 5 for receiving a part of signal light inputted into the thulium doped optical fiber 1, an output signal optical power monitor 10 for receiving a part of signal light outputted from the thulium added optical fiber 1, a light source 7 for emitting absorption amount control light for controlling the amount of absorption of light in the thulium doped optical fiber 1, and sending the absorption amount control light to the thulium added optical fiber 1, and a control circuit 11 for changing the power of the absorption amount control light outputted from the light source 7 in response to a power ratio of the input signal light and the output signal light from the input signal light power monitor 5 and the output signal light power monitor 10. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to wavelength division multiplexing (WD).
M) In the gain of an erbium-doped optical fiber amplifier used in an optical transmission system or the like, it is possible to suppress deterioration of gain flatness due to a change in installation environment such as temperature and to achieve more stable gain flattening. Regarding compensator.

[0002]

2. Description of the Related Art In order to cope with a rapid increase in communication demand in recent years, an optical communication system has been constructed in which a high-density wavelength division multiplexing (DWDM) optical transmission system or the like is introduced. In an optical communication system such as a wavelength division multiplexing (WDM) optical transmission system, erbium (E) is used for the purpose of compensating for attenuation of signal light.
r), neodymium (Nd), thulium (Tm), praseodymium (Pr) and other rare earth element ions are used as a gain medium in an optical amplifier having a rare earth-doped optical fiber whose core is doped.

In an erbium-doped optical fiber amplifier (EDFA) using an erbium-doped optical fiber, the amplification wavelength band is a low-loss wavelength band (1.55 μm band) of a silica optical fiber.
It is used in a WDM optical transmission system because it can easily obtain high efficiency, high gain, and low noise amplification characteristics. In particular, in wide-band, long-distance communication, in order to reduce variations in peak power of signal light wavelength and deterioration of signal-to-noise ratio, an optical amplifier used in a WDM optical transmission system has a signal light wavelength band It is necessary to show a gain flatness that can obtain a substantially constant gain over the entire area. For this reason, in the EDFA, a gain equalizer or the like is used to flatten the gain (hereinafter, referred to as “gain equalization”).

[0004]

Generally, a long period fiber grating, an etalon filter, or the like is used as a gain equalizer for gain equalization. However, these gain equalizers are designed to only flatten the gain in certain operating conditions of the EDFA. Therefore, in the conventional EDFA,
The gain varies depending on the transmission loss of the optical fiber, the power of the input signal light to the EDFA, the number of channels of the signal light, the environmental temperature, and the like, and the variation of the gain shows wavelength dependence. Is damaged.

The present invention has been made in view of the above circumstances, and provides a gain tilt compensator capable of suppressing the fluctuation of the gain due to the change of the installation environment such as the temperature of the EDFA and performing the stable flattening of the gain. The challenge is to provide.

[0006]

Means for Solving the Problems The above problem is solved by the thulium-doped optical fiber for inputting / outputting signal light, a part of the input signal light input to the thulium-doped optical fiber, and the output from the thulium-doped optical fiber. Optical power monitor for receiving a part of the output signal light to be converted into an electric signal, and generating an absorption control light for controlling the absorption amount of light in the thulium-doped optical fiber, and generating the absorption control light. To the thulium-doped optical fiber, and a control circuit that changes the power of the absorption control light output from the light source according to the power ratio of the input signal light and the output signal light from the optical power monitor. It can be solved by a gain slope compensator. The problem is to generate a thulium-doped optical fiber for inputting / outputting a signal light and an absorption amount control light for controlling an absorption amount of light in the thulium-doped optical fiber, and add the absorption amount control light to the thulium-doped optical fiber. A light source to send to the optical fiber,
An optical power monitor that receives the absorption control light transmitted through the thulium-doped optical fiber and converts it into an electric signal, and changes the power of the absorption control light from the light source based on the electric signal from the optical power monitor. And a control circuit for controlling the gain slope compensator.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention is described in detail below.
FIG. 1 is a schematic configuration diagram showing a first embodiment of a gain tilt compensator of the present invention. In FIG. 1, reference numeral 1 is a thulium-doped optical fiber, which is a single-mode optical fiber in which a rare earth element thulium is added to the core of a silica optical fiber or the core and a clad portion adjacent to the core by about 1000 ppm.

In the gain tilt compensator of this embodiment, the optical isolator 2 is provided at the input end of the thulium-doped optical fiber 1.
Are connected. A first tap coupler 3 is connected to the input end of the optical isolator 2. This first
The optical transmission line 4 is connected to the input end of the tap coupler 3. The first tap coupler 3 has two output ends, one output end is connected to the optical isolator 2, and the other output end is connected to the input signal optical power monitor 5. Has been done. As a result, the first tap coupler 3 splits the signal light from the optical transmission line 4, inputs a part of this signal light into the input signal light power monitor 5, and adds most of this signal light to thulium. It is adapted to be input to the optical fiber 1. A photodiode (PD), a photomultiplier tube, or the like is used as the input signal light power monitor 5, but a photodiode is preferably used because it is excellent in the efficiency of converting signal light into an electric signal.

At the output end of the thulium-doped optical fiber 1,
A wavelength division multiplexing (hereinafter abbreviated as "WDM") coupler 6 is connected. The WDM coupler 6 has two input ends, the thulium-doped optical fiber 1 is connected to one input end, and the light source 7 is connected to the other input end. The second tap coupler 8 is connected to the output terminal of the WDM coupler 6. This second tap coupler 8 is
The optical transmission line 9 has one output end.
Is connected, and the output signal light power monitor 10 is connected to the other output end. As a result, the second tap coupler 8 splits the signal light from the WDM coupler 6, inputs a part of this signal light to the output signal light power monitor 10, and outputs most of this signal light to the optical transmission line. It is designed to output to 9. A semiconductor laser (LD) is preferably used as the light source 7. Further, as the output signal light power monitor 10, a photodiode, a photomultiplier tube, or the like is used as in the input signal light power monitor 5. However, since it is excellent in the efficiency of converting the signal light into an electric signal, Diodes are preferably used. Further, the input signal light power monitor 5, the light source 7, and the output signal light power monitor 10 are connected to the control circuit 11. When using the gain tilt compensator of this embodiment, an optical amplifier such as an erbium-doped optical fiber amplifier is connected to the front stage of the optical transmission line 4 or the rear stage of the optical transmission line 9.

Next, the operation of the gain slope compensator of this embodiment will be described. In the gain tilt compensator of this embodiment, the wavelength-multiplexed signal light is transmitted from the optical transmission line 4 to the first
Is input to the tap coupler 3, the signal light is branched by the first tap coupler 3, a part of the signal light is input (received) to the input signal light power monitor 5, and most of the signal light is input. It is input to the thulium-doped optical fiber 1. The signal light received by the input signal light power monitor 5 is converted by the input signal light power monitor 5 into an electric signal corresponding to the light reception level, that is, the power of the signal light. Further, the signal light output from the thulium-doped optical fiber 1 is transmitted through the WDM coupler 6 and input to the second tap coupler 8, and the signal light is branched by the second tap coupler 8 to generate the signal light. Is input (received) to the output signal light power monitor 10, and most of this signal light is output from the optical transmission line 9. The signal light received by the output signal light power monitor 10 is converted by the output signal light power monitor 10 into an electric signal corresponding to the light reception level, that is, the power of the signal light.

The electric signal converted by the input signal light power monitor 5 and the output signal light power monitor 10 is input to the control circuit 11, which controls the power and output of the input signal light of the gain tilt compensator. The ratio of signal to power is detected. Then, the power of the absorption amount control light output from the light source 7 is controlled by the control circuit 11 so that this ratio becomes a target value, and this absorption amount control light is output from the light source 7. The absorption amount control light output from the light source 7 is input to the thulium-doped optical fiber 1 via the WDM coupler 6. A part of the absorption amount control light input to the thulium-doped optical fiber 1 is absorbed by the thulium addition optical fiber 1, and the absorption amount control light that is not absorbed is output from the thulium-doped optical fiber 1. The absorption amount control light output from the thulium-doped optical fiber 1 is input to the optical isolator 2 and is not output to the first tap coupler 3.

Here, FIG. 2 is a graph showing the relationship between the absorption loss of the gain tilt compensator of this embodiment and the wavelength of the signal light when the power of the absorption control light is changed. Here, the wavelength of the absorption control light is 1610 nm. From FIG. 2, the gain slope compensator of this embodiment shows different absorption losses according to the power of the absorption amount control light, and the graphs showing the relationship between the absorption loss and the wavelength of the signal light have different slopes. I understand. That is, it is understood that the gain slope compensator of this embodiment can control the absorption loss of the gain slope compensator by changing the power of the absorption amount control light.

FIG. 3 shows the ratio of the power of the input signal light received by the input signal light power monitor 5 to the power of the output signal received by the output signal light power monitor 10 in the gain slope compensator of this embodiment. 3 is a graph showing the relationship between the absorption power and the power of absorption control light. It can be seen from FIG. 3 that the ratio between the power of the input signal light and the power of the output signal light can be arbitrarily adjusted by changing the power of the absorption control light. Further, from the relationship obtained from this graph, it is possible to obtain the ratio of the power of the input signal light and the power of the output signal light for obtaining the target absorption loss.

As described above, according to the gain slope compensator of this embodiment, the power of the absorption control light is adjusted while the control circuit 11 monitors the ratio of the power of the input signal light and the power of the output signal light. By doing so, the desired absorption loss can be obtained. Therefore, according to the gain tilt compensator of this embodiment, stable gain equalization can be performed even if the installation environment changes.

FIG. 4 is a schematic configuration diagram showing a second embodiment of the gain tilt compensator of the present invention. In the following description, the same components as those of the first embodiment are designated by the same reference numerals, and the description thereof will be omitted or simplified.
In the gain tilt compensator of this embodiment, the first WDM coupler 12 is connected to the input end of the thulium-doped optical fiber 1. The optical transmission line 4 is connected to the input end of the first WDM coupler 12. The thulium-doped optical fiber 1 is connected to the output end of the first WDM coupler 12. Further, the first WDM coupler 12 has two output ends, one output end is connected to the thulium-doped optical fiber 1, and the other output end is connected to the thulium-doped optical fiber 1. Transmitted absorption amount control light power monitor 1 for receiving a part or all of the absorption amount control light transmitted through
3 is connected. Transmission and absorption control optical power monitor 1
The same as the input signal light power monitor 5 described above is used as 3.

A second WDM coupler 14 is connected to the output end of the thulium-doped optical fiber 1. Second
The WDM coupler 14 has two input ends, the thulium-doped optical fiber 1 is connected to one input end, and the light source 7 is connected to the other input end. The optical transmission line 9 is connected to the output terminal of the second WDM coupler 14. Further, the transmission / absorption amount control light power monitor 13 and the light source 7 are connected to the control circuit 11.

Next, the operation of the gain slope compensator of this embodiment will be described. In the gain tilt compensator of this embodiment, the wavelength-multiplexed signal light is transmitted from the optical transmission line 4 to the first
The light is transmitted through the WDM coupler 12 and is input to the thulium-doped optical fiber 1. Part of this signal light is absorbed by the thulium-doped optical fiber 1, and the signal light not absorbed is the second light.
The light is transmitted through the WDM coupler 14 and output from the optical transmission line 9. Further, the absorption amount control light output from the light source 7 passes through the second WDM coupler 14 and is input to the thulium-doped optical fiber 1. Part of this absorption amount control light is absorbed by the thulium-doped optical fiber 1, and the absorption amount control light that is not absorbed is transmitted through the second WDM coupler 14 and input to the transmitted absorption amount control light power monitor 13 (received light). ) Will be done. The absorption amount control light received by the transmission / absorption amount control light power monitor 13 is transmitted by the transmission / absorption amount control light power monitor 13.
It is converted into an electric signal corresponding to the received light level, that is, the power of the absorption control light. The electric signal converted by the transmission / absorption control light power monitor 13 is input to the control circuit 11, and the power of the absorption control light emitted from the light source 7 is arbitrarily set by the control circuit 11 according to the level of the electric signal. Adjusted.

FIG. 5 shows the power of the absorption amount control light transmitted through the thulium-doped optical fiber 1 and received by the transmitted absorption amount control light power monitor 13 and the light source 7 in the gain tilt compensator of this embodiment. It is a graph which shows the relationship with the power of the absorbed absorption control light. It can be seen from FIG. 5 that the power of the absorption control light received by the transmitted absorption control light power monitor 13 can be arbitrarily adjusted by changing the power of the absorption control light emitted from the light source 7.
From the relationship obtained from this graph and the relationship obtained from the graph shown in FIG. 2, in the gain tilt compensator of this embodiment, the transmission absorption amount control optical power monitor 13 for obtaining the target absorption loss is used. The power of the absorption control light received can be obtained. Therefore, according to the gain tilt compensator of this embodiment, while the power of the absorption control light received by the transmission absorption control light power monitor 13 is monitored by the control circuit 11, the absorption control light emitted from the light source 7 is emitted. By adjusting the power of, the target absorption loss can be obtained. Therefore, according to the gain tilt compensator of this embodiment, stable gain equalization can be performed even if the installation environment changes.

[0019]

As described above, according to the gain tilt compensator of the present invention, even in the WDM optical transmission system, even if the installation environment of the optical amplifier connected to the gain tilt compensator changes, it is stable. The gain equalization can be performed.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a first embodiment of a gain tilt compensator of the present invention.

[FIG. 2] When the power of the absorption control light is changed,
6 is a graph showing the relationship between the absorption loss of the gain tilt compensator of the first embodiment and the wavelength of signal light.

FIG. 3 shows the power of the input signal light received by the input signal light power monitor 5 and the power of the output signal received by the output signal light power monitor 10 in the first embodiment of the gain tilt compensator of the present invention. 5 is a graph showing the relationship between the ratio of the above and the power of the absorption control light.

FIG. 4 is a schematic configuration diagram showing a second embodiment of a gain tilt compensator of the present invention.

FIG. 5 is a diagram showing a gain tilt compensator according to a second embodiment of the present invention, in which the power of the absorption control light transmitted through the thulium-doped optical fiber 1 and received by the transmission absorption control light power monitor 13 and the light source 7 7 is a graph showing the relationship with the power of the absorption amount control light emitted from.

[Explanation of symbols]

1 ... Thulium-doped optical fiber, 2 ... Optical isolator,
3 ... First tap coupler, 4, 9 ... Optical transmission line, 5 ... Input signal optical power monitor, 6 ... WDM coupler, 7 ... Light source, 8 ... Second Tap coupler, 10 ... Output signal light power monitor, 11 ... Control circuit, 12 ... First WDM coupler, 13 ... Transmission absorption amount control light power monitor, 14 ... Second WDM Coupler

Claims (2)

[Claims] 1. A thulium-doped optical fiber for inputting and outputting signal light, a part of the input signal light input to the thulium-doped optical fiber, and a part of the output signal light output from the thulium-doped optical fiber. An optical power monitor that receives the light and converts it into an electric signal, and generates an absorption amount control light for controlling the amount of light absorption in the thulium-doped optical fiber, and sends the absorption amount control light to the thulium-doped optical fiber. A gain slope, comprising: a light source; and a control circuit that changes the power of the absorption amount control light output from the light source according to the power ratio between the input signal light and the output signal light from the optical power monitor. Compensator. 2. A thulium-doped optical fiber for inputting / outputting a signal light, and an absorption amount control light for controlling an absorption amount of light in the thulium-doped optical fiber is generated, and the absorption amount control light is supplied to the thulium. A light source to be sent to the doped optical fiber, an optical power monitor that receives the absorption control light transmitted through the thulium-doped optical fiber and converts it into an electrical signal, and from the light source based on the electrical signal from the optical power monitor. A gain slope compensator comprising: a control circuit that changes the power of the absorption control light.