JP2010165988A - Gain equalizing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform gain slope correction, both securely and readily, even when there are gain slope change characteristics different from each other in a signal band. <P>SOLUTION: From an optical signal input from an optical transmission path, a controls signal that control the optical signal is extracted by a BPF 105, the optical signal and excitation light that excites the optical signal are coupled by a WDM coupler 103 and output as an optical output signal; the signal level of an optical light output signal transmitted by an EDF 102, that operates in the same signal band as that of an EDF arranged in the optical transmission path, is attenuated by a variable attenuator 109, based on the control signal; the excitation light that makes constant the signal level of the optical output signal whose signal level is attenuated by the variable attenuator 109 is output from an excitation section 112 to the WDM coupler 103; and the optical output signal is output from a branch coupler 110 to the optical transmission path. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a gain equalizer connected to an optical transmission line for transmitting an optical signal.

  In recent years, when the gain of a gain device that amplifies an optical signal changes depending on the wavelength, a gain equalizer is used to compensate for the wavelength dependence of the gain.

  FIG. 2 is a diagram showing an embodiment of a general gain equalization apparatus (variable type).

  The gain equalization apparatus 1000 illustrated in FIG. 2 includes a branch coupler 1001, a BPF 1005, a PD 1006, a control circuit 1008, and a gain equalization device 1013.

  In the gain equalization apparatus 1000 shown in FIG. 2, an optical signal is input from the branch coupler 1001, passes through a gain equalization device 1013 that performs gain equalization of the optical signal, and after gain equalization, optical transmission is performed. Is output to the road.

  The optical signal is branched by a branch coupler 1001 and a control (SV) signal arranged at a specific wavelength is extracted by a BPF (band pass filter) 1005. A control (SV) signal is converted into an electric signal by a PD (PhotoDetector) 1006 and then input to the control circuit 1008. Based on a control (SV) signal input to the control circuit 1008, the gain equalization device 1013 is controlled.

  However, the gain equalization device 1013 used in the gain equalization apparatus 1000 as shown in FIG. 2 has the following problems.

  In WDM (Wavelength Division Multiplexing) communication, which has been rapidly spreading in recent years, the signal band has been expanded in order to increase the communication capacity.

  FIG. 3 is a diagram showing EDFA gain tilt gain dependency.

  As shown in FIG. 3, the band characteristics of an EDFA (Erbium Doped Fiber Amplifier: an optical amplifier using an optical fiber in which an erbium element is added to the core) inserted into an optical transmission line are short wavelength side and long wavelength side with a certain wavelength as a boundary. Have different characteristics of gain slope change characteristics with respect to gain changes.

  In the signal band before the band is expanded by WDM or the like, there is only one type of change in the slope of the relative gain with respect to the band as shown in FIG. However, in the signal band after the band is expanded by WDM or the like, there are two types of changes in the slope of the relative gain with respect to the band as shown in FIG.

  FIG. 4 is a diagram illustrating band characteristics of the gain equalization device.

  As shown in FIG. 4, gain equalization can be performed by a general gain equalization device in a signal band having the same gain slope change characteristic for all signal bands. However, gain equalization with a general gain equalization device is difficult in the case of having a plurality of gain tilt change characteristics due to signal band expansion.

  In view of this, there has been considered an apparatus capable of performing gain correction according to output power fluctuation characteristics by providing WDM couplers and EDFs in multiple stages (see, for example, Patent Document 1).

JP 2006-295113 A

  However, the optical amplifier (gain equalization apparatus) described in Patent Document 1 requires multiple stages of connection of WDM couplers and EDFs, and the apparatus configuration is complicated. Therefore, there are problems that the manufacturing cost becomes expensive and the failure rate of the entire apparatus becomes high.

  An object of the present invention is to provide a gain equalizer that solves the above-described problems.

The gain equalization apparatus of the present invention is
A gain equalizer connected to an optical transmission line for transmitting an optical signal,
A bandpass filter for extracting a control signal for controlling the optical signal from the optical signal input to the gain equalizer;
A coupling unit that couples the optical signal and pumping light that excites the optical signal and outputs an optical output signal;
An EDF that operates in the same signal band as an EDF (Erbium Doped Fiber) disposed in the optical transmission line and transmits the optical output signal;
A variable attenuator for attenuating the signal level of the optical output signal transmitted by the EDF based on the control signal;
A pumping unit that outputs the pumping light to the coupling unit so that the signal level of the optical output signal in which the variable attenuator attenuates the signal level is constant;
A first branching unit for branching the optical output signal to the optical transmission path and the pumping unit;

  As described above, in the present invention, the control signal for controlling the optical signal is extracted from the optical signal input from the optical transmission line by the bandpass filter, and the optical signal and the excitation light for exciting the optical signal are extracted by the coupling unit. Combined and output as an optical output signal, attenuates the signal level of the optical output signal transmitted by the EDF operating in the same signal band as the EDF arranged in the optical transmission line based on the control signal with a variable attenuator, The pumping light is output from the pumping unit to the coupling unit so that the signal level of the optical output signal whose signal level is attenuated by the variable attenuator is constant, and the optical output signal is output from the first branch unit to the optical transmission line. Because of the configuration, even when the signal bands have different gain tilt change characteristics in the signal band, the gain tilt correction can be performed reliably and easily.

It is a figure which shows one Embodiment of the gain equalization apparatus of this invention. It is a figure which shows one form of a general gain equalization apparatus (variable type). It is a figure which shows EDFA gain inclination gain dependence. It is a figure which shows the band characteristic of a gain equalization device.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a diagram showing an embodiment of a gain equalization apparatus according to the present invention.

  In this embodiment, as shown in FIG. 1, a gain equalization apparatus 100 includes a branch coupler 101, 110, an EDF 102, a WDM coupler 103, an isolator 104, a BPF 105, a PD 106, a control circuit 108, and a variable attenuator. 109 and an excitation unit 112 are provided.

  The branch coupler 101 is a second branch unit that branches an optical signal input from the optical transmission line to the gain equalization apparatus 100 to the WDM coupler 103 and the BPF 105 and outputs the branched signal.

  The WDM coupler 103 is a coupling unit that couples the optical signal output from the branch coupler 101 and the excitation light output from the LD 107 and outputs the combined optical signal to the EDF 102.

  The EDF 102 operates in the same signal band as an EDF (Erbium Doped Fiber) arranged in an optical transmission line, and is an optical fiber that transmits an optical output signal output from the WDM coupler 103.

  The variable attenuator 109 attenuates the signal level of the optical output signal transmitted by the EDF 102 based on the attenuation signal output from the control circuit 108. The variable attenuator 109 outputs an optical output signal with the signal level attenuated to the isolator 104.

  The isolator 104 transmits the optical output signal output from the variable attenuator 109 to the branch coupler 110 and prevents reflected return light to the variable attenuator 109.

  The branch coupler 110 is a first branch unit that outputs the optical output signal transmitted by the isolator 104 to the optical transmission path and the pump unit 112.

  The BPF 105 is a band filter (Band Pass Filter) that extracts a control (SV) signal arranged at a specific wavelength from the optical signal output from the branch coupler 101. Further, the BPF 105 outputs a control signal extracted from the optical signal to the PD 106. This control signal is a signal for controlling the optical signal.

  The PD 106 is a photodetector (PhotoDetector) that converts a control signal output from the BPF 105 from an optical signal to an electrical signal. Further, the PD 106 outputs a control signal converted into an electric signal to the control circuit 108.

  The control circuit 108 is an attenuator control unit that controls the degree of attenuation by which the variable attenuator 109 attenuates the signal level based on the control signal output from the PD 106. Based on the control signal output from the PD 106, the control circuit 108 calculates the attenuation that the variable attenuator 109 attenuates, and outputs an attenuation signal indicating the calculated attenuation to the variable attenuator 109.

  The pumping unit 112 outputs pumping light to the WDM coupler 103 so that the signal level of the optical output signal whose signal level is attenuated by the variable attenuator 109 becomes constant.

  Further, the excitation unit 112 includes an LD 107 and a control circuit 111.

  The control circuit 111 is a pumping control unit that instructs the LD 107 to output pumping light so that the signal level of the light output signal is constant.

  The LD 107 is a laser diode (Laser-Diode) that outputs excitation light to the WDM coupler 103 in accordance with an instruction from the control circuit 111.

  The operation in the embodiment shown in FIG. 1 will be described below.

  The optical signal input from the optical transmission line to the gain equalization apparatus 100 passes through the path from the input of the branch coupler 101 to the output of the branch coupler 110, and is output as an optical output signal to the optical transmission line after gain equalization. Is done. At this time, the optical signal becomes an optical output signal combined with the pumping light output from the LD 107, is transmitted through the built-in EDF 102, the signal level is attenuated by the variable attenuator 109, and the optical transmission line from the branch coupler 110 is attenuated. Is output.

  The optical output signal output to the optical transmission line is branched by the branch coupler 110 and output to the optical transmission line and the pumping unit 112. The optical output signal output to the pumping unit 112 is a circuit for controlling the pumping LD composed of the WDM coupler 103 and the pumping unit 112, and the output level of the optical output signal output from the gain equalization apparatus 100 is constant. It is controlled to become. By this control, the signal level output from the gain equalization apparatus 100 becomes a constant value and does not affect the transmission characteristics at the subsequent stage of the gain equalization apparatus 100.

  An optical signal input from the optical transmission line to the gain equalization apparatus 100 is branched by the branch coupler 101 and output to the WDM coupler 103 and the BPF 105. Using the optical signal output to the BPF 105, the loss (attenuation) in the variable attenuator 109 is controlled by a circuit constituted by the BPF 105, the PD 106, the control circuit 108, and the variable attenuator 109. Specifically, a control signal is extracted from the optical signal by the BPF 105, the control signal is converted into an electric signal by the PD 106, and the attenuation degree in the variable attenuator 109 is calculated from the control circuit 108. Then, an attenuation signal indicating the calculated attenuation is output from the control circuit 108 to the variable attenuator 109, and the signal level of the optical output signal is attenuated by the variable attenuator 109 based on the attenuation signal. As a result, when the loss of the variable attenuator 109 changes in order to make the output of the gain equalizer 100 described above constant, the internal gain of the gain equalizer 100 changes. As a result, the gain equalizer 100 The gain slope will be controlled.

  Regarding the loss (attenuation) control of the variable attenuator 109, the transmission characteristic of the optical transmission line upstream of the gain equalization apparatus 100 is changed to a higher gain side (a gain increasing side) as shown in FIG. If so, the loss of the variable attenuator 109 is controlled to be small in order to reduce the internal gain of the gain equalizer 100. On the other hand, when the transmission characteristic before the gain equalizer 100 is changed to a smaller gain side (a side where the gain is reduced) as shown in FIG. 3, in order to increase the internal gain of the gain equalizer 100, Control is performed so that the loss of the variable attenuator 109 increases. In this way, the transmission characteristic after passing through the gain equalization apparatus 100 is compensated by giving the characteristic opposite to that of the optical transmission line.

  As described above, since the gain equalization apparatus 100 includes the EDFA that operates in the same signal band as the EDFA arranged in the optical transmission line, the gain equalization apparatus 100 has a plurality of gain tilt change characteristics different from each other in the signal band. Even in this case, gain tilt compensation can be reliably performed. In addition, since the EDFA is built in the gain equalizer 100, the relay span including the gain equalizer can be expanded.

  The gain equalization apparatus 100 of the present invention is a gain equalization arranged to compensate for a gain tilt shift caused by manufacturing variations of submarine repeaters and submarine cables arranged in a transmission line in a long-distance submarine WDM transmission system. Used as a device.

100 Gain Equalizer 101, 110 Branch Coupler 102 EDF
103 WDM coupler 104 isolator 105 BPF
106 PD
107 LD
108, 111 Control circuit 109 Variable attenuator 112 Excitation unit

Claims (6)

A gain equalizer connected to an optical transmission line for transmitting an optical signal,
A bandpass filter for extracting a control signal for controlling the optical signal from the optical signal input to the gain equalizer;
A coupling unit that couples the optical signal and pumping light that excites the optical signal and outputs an optical output signal;
An EDF that operates in the same signal band as an EDF (Erbium Doped Fiber) disposed in the optical transmission line and transmits the optical output signal;
A variable attenuator for attenuating the signal level of the optical output signal transmitted by the EDF based on the control signal;
A pumping unit for outputting the pumping light to the coupling unit so that the signal level of the optical output signal whose signal level is attenuated by the variable attenuator is constant;
A gain equalization apparatus comprising: a first branching unit that branches and outputs the optical output signal to the optical transmission line and the pumping unit. The gain equalization apparatus according to claim 1,
Based on the control signal, it has an attenuator control unit that calculates the attenuation that the variable attenuator attenuates, and outputs an attenuation signal indicating the calculated attenuation to the variable attenuator,
The variable attenuator attenuates the signal level of the optical output signal based on the attenuation signal output from the attenuator control unit. The gain equalization apparatus according to claim 2,
The attenuator control unit calculates the degree of attenuation such that the loss of the variable attenuator becomes small when the transmission characteristic of the optical signal input to the gain equalization apparatus changes to the side where the gain increases. A gain equalization characterized in that when the transmission characteristic of an optical signal input to the gain equalization apparatus changes to a side where the gain decreases, an attenuation is calculated so that the loss of the variable attenuator increases. apparatus. The gain equalization apparatus according to claim 1,
The excitation unit is
A laser diode that outputs the excitation light to the coupling unit;
A gain equalization apparatus comprising: a pump control unit that instructs the laser diode to output the pump light so that a signal level of the light output signal is constant. The gain equalization apparatus according to claim 1,
A second branching unit for branching and outputting the optical signal input to the gain equalizer to the coupling unit and the bandpass filter;
The bandpass filter extracts the control signal from the optical signal output by the second branching unit,
The coupling unit combines the optical signal output from the second branch unit and the pumping light and outputs the combined optical signal as an optical output signal. The gain equalization apparatus according to any one of claims 1 to 5,
A gain equalization apparatus used for a WDM (Wavelength Division Multiplexing) transmission system.

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