JP2000183431A - Optical amplifier stabilized at input level - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an input level stabilized optical amplifier, capable of controlling the gain at a fixed value with a simple control circuit, with respect to the optical amplifier to be subjected to wavelength multiplex transmission. SOLUTION: A signal source 3 generates signal light, having a wavelength different from that of an inputted signal light. A coupler 1a combines the inputted signal light and the signal light outputted from the signal source 3 and outputs the combined signal light to a coupler 1b. The coupler 1b distributes the power of the signal light inputted from the coupler 1a and outputs a part of the distributed power to a light receiver 4a and the remaining to an optical amplifying part 2. The amplifying part 2 optically amplifies the power of the signal light inputted from the coupler 1b and outputs an optically amplified power. The light receiver 4a optoelectrically converts the signal light inputted from the coupler 1b and generates a current which corresponds to the power of the signal light. A level fixed control circuit 5a controls the signal source 3, so that the current generated from the light receiver 4a is fixed. Consequently, a signal level inputted to the amplifying part 2 is held at a fixed value, and the stabilized operation of the optical amplifier is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical amplifier used for wavelength division multiplexing transmission, and to an input level stabilized optical amplifier.

[0002]

2. Description of the Related Art As a conventional control method of an optical amplifier, there are generally known an output constant control for controlling an output level to be constant with respect to a fluctuation of an input level and a gain constant control for controlling a gain to be constant. ing. FIG. 15 is a block diagram showing a configuration of an optical amplifier to which conventional gain constant control is applied. In this conventional system, the input level is monitored by the photodetector 4a and the output level is monitored by the photodetector 4b.
And 19b respectively convert to a decibel value, and the division circuit 20 obtains the difference, and the level constant control circuit 5c controls the optical amplification unit 2 so that the difference becomes constant.

However, the logarithmic circuit 19a applied here
And 19b have a problem that the circuit configuration is complicated and it is difficult to secure sufficient accuracy. For this reason, a control circuit for an optical amplifier that does not particularly require constant gain control includes:
In many cases, simple and accurate output constant control was applied.

[0004] Wavelength division multiplexing is a method of expanding transmission capacity by using signal light of a plurality of wavelengths in optical communication. In the optical amplifier applied to the wavelength division multiplexing transmission, since the wavelength division multiplexed signal light is collectively amplified, it is important that the wavelength characteristic of the gain is flat. However, since constant gain control is indispensable to keep the gain wavelength characteristic flat, the need for constant gain control is increasing.However, it is possible to perform constant gain control with simple control using an optical amplifier. Did not.

[0005]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and in an optical amplifier applied to wavelength-division multiplexing transmission, input level stabilization capable of realizing constant gain control with a simple control circuit. It is an object to provide an optical amplifier.

[0006]

In order to achieve the above object, an input level stabilized optical amplifier according to the present invention combines and distributes signal light, and performs optical / electrical conversion of the signal light. A light-receiving conversion unit, an optical amplification unit that amplifies the signal light, and a signal light that is multiplexed with the signal light input from the outside to stabilize the input level. Signal light generating means for generating signal light, and level-constant control means for controlling the signal level from the signal light generating means to control the light-receiving current of the light-receiving conversion means to be constant. And

Further, an input level stabilized optical amplifier according to the present invention comprises a signal light combining / distributing means for combining and distributing signal light, a light receiving / converting means for optically / electrically converting the signal light, and an optical amplifier for amplifying the signal light. Means, to stabilize the input level, the signal light to be multiplexed with the signal light input from the outside, the signal light generating means to generate a signal light of a wavelength different from the signal light input from the outside, Level-constant control means for adjusting the signal level from the signal light generating means to control the light receiving current of the light receiving and converting means to be constant; and signal light inputted from the light amplifying means through the signal light combining / distributing means. Second light-receiving conversion means for converting light into electricity
And a second constant level control means for controlling the light amplifying means so that the current generated by the second light receiving and converting means is constant.

Further, the input level stabilized optical amplifier according to the present invention is characterized in that it has a generated signal removing means for removing the signal light generated by the signal light generating means from the output of the optical amplifying means.

Further, the input level stabilized optical amplifier according to the present invention is characterized in that, in order to stabilize the input level, the white light output from the optical amplifying means is added to the signal light multiplexed with the signal light input from the outside. It is characterized by having a demultiplexing means for using noise light and an attenuation means for controlling the insertion loss of the white noise light.

The input level stabilized optical amplifier according to the present invention is characterized in that the demultiplexing means is a comb filter.

[0011]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing the first principle of the present invention. As shown in FIG. 1, the first principle of the optical amplifier according to the present invention is based on a coupler 1a and a coupler 1a.
b, an optical amplifier 2, a signal source 3, a light receiver 4a, and a constant level control circuit 5a.

In FIG. 1, a signal source 3 generates signal light having a wavelength different from that of input signal light. The coupler 1a combines the input signal light and the signal light from the signal source 3 and outputs the combined signal light to the coupler 1b. The coupler 1b distributes the power of the signal light input from the coupler 1a, and partially distributes the power to the light receiver 4a.
The remainder is output to the optical amplifier 2. The optical amplifying unit 2 includes a coupler 1
b, and amplifies and outputs the power of the signal light input from b. The light receiver 4a performs optical / electrical conversion of the signal light input from the coupler 1b, and generates a current corresponding to the power of the signal light. The constant level control circuit 5a controls the signal source 3 so that the current generated by the light receiver 4a is constant.

As described above, even if the input signal level fluctuates, the level-constant control circuit 5a controls the signal level from the signal source 3 so that the light-receiving current of the light-receiving device 4a becomes constant. Therefore, the signal level input to the optical amplifier 2 is kept constant. Thereby, a stable operation of the optical amplifier can be realized.

FIG. 2 is a block diagram showing the second principle of the present invention. As shown in FIG. 2, in FIG. 2, a coupler 1c, a light receiver 4b, and a constant level control circuit 5b are added to the first principle of FIG. This added circuit is a circuit for controlling the optical amplification unit 2. The coupler 1c distributes the power of the signal light input from the optical amplifying unit 2 and partially
b and the remainder from the output. The light receiver 4b optically / electrically converts the signal light input from the coupler 1c, and generates a current corresponding to the power of the signal light. The constant level control circuit 5b controls the optical amplifier 2 so that the current generated by the light receiver 4b is constant.

As described above, the level-constant control circuit 5b adjusts the optical amplifying unit 2 to control the light-receiving current of the light-receiving unit 4b so as to be constant. In addition to the level, the signal level output from the optical amplifier 2 is also kept constant. Thereby, constant gain control of the optical amplifier can be realized.

FIG. 3 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a first embodiment of the present invention using the first principle of the present invention shown in FIG. As shown in FIG. 3, the optical amplifier according to the present invention includes a WDM coupler 6, which is a wavelength division multiplexing coupler as a coupler for inputting signal light and a signal source, a branching coupler 7a, and an LD module 9 as a signal source. And a PD module 10 as a light receiver
and an erbium-doped fiber amplifier E as an optical amplifier
It comprises a DFA 8 and a constant level control circuit 5a.

In FIG. 3, this optical amplifier has a wavelength of 155.
Since the signal light of 2 nm is amplified, the wavelength of the LD module 9 which is a signal source is set to 1542 nm which is different from the input signal light. LD module 9
Can be adjusted in the range of 0 to 1 mW by the drive current. The WDM coupler 6 couples the input signal light and the signal light from the LD module 9 by 1d by wavelength synthesis.
This is a micro-optics coupler that combines with low insertion loss of B or less.

The branch coupler 7a transfers, for example, 90% of the power of the signal light input from the WDM coupler 6 to the EDFA 8,
10% is output to the PD module 10a.
The PD module 10a generates a current of about 1 mA for 1 mW of signal light input from the branch coupler 7a.
The level-constant control circuit 5a is an analog circuit, and an LD for controlling the current generated by the PD module 10a to be constant.
The drive current of the module 9 is controlled.

FIG. 4 is a block diagram showing the configuration of the erbium-doped fiber amplifier EDFA 8 shown in FIG. In FIG. 4, the EDFA 8 is an erbium-doped fiber E
This is an optical fiber amplifier that optically amplifies a signal light in the 1550 nm band using the DF 13 as an amplification medium. The optical output can be adjusted by the drive current of the pump LD 14.

FIG. 5 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a second embodiment of the present invention using the second principle of the present invention shown in FIG. As shown in FIG. 5, FIG. 5 is a circuit diagram showing the first embodiment of FIG.
, A PD module 10b as a light receiver, and a constant level control circuit 5b. This added circuit is a circuit for controlling the EDFA 8 which is an optical amplifier.

The branch coupler 7b outputs, for example, 95% of the power of the signal light input from the EDFA 8 from the output.
5% is output to the PD module 10b. The PD module 10b is connected to the signal light 1m input from the branch coupler 7b.
A current of about 1 mA is generated for W. The constant level control circuit 5b is an analog circuit, and the PD module 10
The drive current of the excitation LD 14 in the EDFA 8 is controlled so that the current generated by b becomes constant.

The individual components used in the configuration of the first embodiment of the present invention shown in FIG. 3 and the second embodiment of the present invention shown in FIG. 5 are examples of use, and the present invention is limited to these components. It was not done.

Next, the operation of the first embodiment shown in FIG. 3 will be described with reference to FIG. The signal level input to the WDM coupler 6 varies in a range from -20 dBm to -5 dBm. When the input signal level is -5 dBm, the signal level from the LD module 9 is -20 dBm
By setting the constant level control circuit 5a so that
The input to the EDFA 8 is a WDM coupler 6 and a branch coupler 7
a is reduced by the insertion loss of -6 dB at 1552 nm.
It becomes -21 dBm at m and 1542 nm, and it becomes 0.26 mW in total.

Here, the input signal level is -20.
When the current reaches dBm, the drive current of the LD module 9 is controlled so that the current generated by the PD module 10a becomes constant. As a result, the signal level from the LD module 9 becomes -5 dBm, and the input to the EDFA 8 becomes Similarly, it is -21 dBm at 1552 nm and -6 dBm at 1542 nm, which is 0.26 mW in total. Thus, the input signal level is between -20 dBm and -5 dB.
In the range of Bm, the input to EDFA 8 is always 0.2
6 mW.

Next, the operation of the second embodiment shown in FIG. 5 will be described with reference to FIG. The output from the optical amplifier is always +10 dBm by the constant level control circuit 5b.
Becomes The signal level input to the WDM coupler 6 is −
It varies in the range of 20 dBm to -5 dBm. When the input signal level is -5 dBm, the input to the EDFA 8 is 1552, as described in the operation of the first embodiment of FIG.
-6 dBm at nm and -21 dBm at 1542 nm. If the light is amplified by the EDFA 8 with the same gain, the output from the optical amplifier is +9.9 d at 1552 nm.
It becomes -5.1 dBm at Bm and 1542 nm, and it becomes +10 dBm in total. The gain at this time is 15.9 dB
Becomes

The input signal level is -20 dB.
m, the input to the EDFA 8 is -21 dB at 1552 nm, as described in the operation of the first embodiment of FIG.
m and -6 dBm at 1542 nm. EDFA8
, The output from the optical amplifier will be −5.1 dBm at 1552 nm and 1542
It becomes +9.9 dBm in nm, and it becomes +10 dBm in total. The gain at this time is 15.9 dB. Thus, the input signal level is -20 dBm to -5 dBm.
, The gain of the EDFA 8 is always 15.9d
B.

FIG. 6 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a third embodiment using the first principle of the present invention shown in FIG. FIG. 6 is an improvement of the configuration of FIG. 1 by adding a filter 15 to the configuration of FIG. In FIG. 1, the signal from the signal source 3 mounted inside the optical amplifier is also output, but in FIG. 6, the signal can be removed by the filter 15.

When a laser diode LD is used as the signal source 3 in FIGS. 1 and 6, the influence of the nonlinear phenomenon in the optical amplifier 2 can be suppressed by increasing the line width by direct modulation. In addition, by using an LED as the signal source 3 in FIGS. 1 and 6, it is possible to suppress the effects of the nonlinear phenomenon in the optical amplifier 2 and hole burning. Further, by using a multi-wavelength light source as the signal source 3 in FIGS. 1 and 6, it is possible to suppress the effects of non-linear phenomena in the optical amplifier 2 and hole burning.

FIG. 7 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a fourth embodiment using the second principle of the present invention shown in FIG. FIG. 7 is an improvement of the configuration of FIG. 2 by adding a filter 15 to the configuration of FIG. In FIG. 2, a signal from the signal source 3 mounted inside the optical amplifier is also output, but in FIG. 7, the signal can be removed by the filter 15.

When a laser diode LD is used as the signal source 3 in FIGS. 2 and 7, by expanding the line width by direct modulation, the influence of the nonlinear phenomenon in the optical amplifier 2 can be suppressed. In addition, by using an LED as the signal source 3 in FIGS. 2 and 7, it is possible to suppress the effects of non-linear phenomena in the optical amplifier 2 and hole burning. Further, by using a multi-wavelength light source as the signal source 3 in FIGS. 2 and 7, it is possible to suppress the effects of non-linear phenomena in the optical amplifier 2 and hole burning.

FIG. 8 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a fifth embodiment in which the first principle of the present invention shown in FIG. 1 is improved. In FIG. 1, it is necessary to mount the signal source 3 inside the optical amplifier, but in FIG. 8, white noise light output from the optical amplifier 2 is used instead of the signal source 3. FIG. 10 is a spectrum diagram showing an output spectrum from the optical amplifier 2. The demultiplexing circuit 16 in FIG.
In the spectrum shown in FIG. 10, a part or all of the signal light and the white noise light is separated, and is configured by a WDM coupler or a combination of a branch coupler and a filter. The attenuator 17 is an optical component that can control the insertion loss, and is used to control the level of the white noise light input to the coupler 1a.

FIG. 9 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a sixth embodiment in which the second principle of the present invention shown in FIG. 2 is improved. In FIG. 2, the signal source 3 needs to be mounted inside the optical amplifier. In FIG. 9, white noise light output from the optical amplifier 2 is used instead of the signal source 3. FIG. 10 is a spectrum diagram showing an output spectrum from the optical amplifier 2. The demultiplexing circuit 16 in FIG.
In the spectrum shown in FIG. 10, a part or all of the signal light and the white noise light is separated, and is configured by a WDM coupler or a combination of a branch coupler and a filter. The attenuator 17 is an optical component that can control the insertion loss, and is used to control the level of the white noise light input to the coupler 1a.

FIG. 11 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a seventh embodiment in which the sixth embodiment of FIG. 9 is applied to an optical amplifier for multi-wavelength collective amplification.
FIG. 12 shows an output spectrum from the optical amplifying unit 2, FIG. 13 shows a spectrum of signal light separated by the comb filter 18 of FIG. 11 and output to the output, and FIG. 14 similarly shows a white light output to the attenuator. This is the spectrum of noise light. As described above, the comb filter 18 separates white noise light between wavelength-multiplexed signals by extracting the white noise light. In the multi-wavelength batch amplification optical amplifier, the input level fluctuates due to a change in the number of simultaneously input signal wavelengths. However, the input level to the optical amplification unit 2 is kept constant using the white noise light of the spectrum shown in FIG. , The fluctuation of the input wavelength can be suppressed, and a stable operation including multi-wavelength collective amplification characteristics can be realized.

[0034]

As described above, according to the present invention, by adjusting the signal level from the signal source mounted inside the optical amplifier, the optical level can be controlled with respect to the fluctuation of the signal level input from outside the optical amplifier. The signal level input to the amplifier is kept constant, and the stable operation of the optical amplifier can be realized.

Further, according to the present invention, since the signal level input to the optical amplifier is kept constant, the constant gain control of the optical amplifier can be realized with a simple control circuit.

Further, according to the present invention, a signal from a signal source mounted inside an optical amplifier can be removed from an output.

Further, according to the present invention, in order to stabilize the input level, white noise light output from the optical amplifier can be used instead of the signal source mounted inside the optical amplifier.

Further, according to the present invention, the comb filter is used for the demultiplexing means via the coupler from the optical amplifying unit, so that the comb filter separates out the white noise light between the wavelength multiplexed signals. Therefore, by keeping the input level to the optical amplifier unit constant, a stable operation including multi-wavelength collective amplification characteristics can be realized.

[Brief description of the drawings]

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

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

FIG. 3 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a first embodiment of the present invention using the first principle of the present invention shown in FIG. 1;

FIG. 4 shows an erbium-doped fiber amplifier ED shown in FIG.
FIG. 3 is a block diagram illustrating a configuration of an FA.

FIG. 5 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a second embodiment of the present invention using the second principle of the present invention shown in FIG. 2;

FIG. 6 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a third embodiment using the first principle of the present invention shown in FIG. 1;

FIG. 7 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a fourth embodiment using the second principle of the present invention shown in FIG. 2;

FIG. 8 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a fifth embodiment in which the first principle of the present invention shown in FIG. 1 is improved.

FIG. 9 is a block diagram showing a configuration of an input level stabilized optical amplifier according to a sixth embodiment in which the second principle of the present invention shown in FIG. 2 is improved.

FIG. 10 is a spectrum diagram showing an output spectrum from the optical amplifier shown in FIGS. 8 and 9;

FIG. 11 is a block diagram showing the configuration of an input level stabilized optical amplifier according to a seventh embodiment in which the sixth embodiment of FIG. 9 is applied to an optical amplifier for multi-wavelength collective amplification.

FIG. 12 is a spectrum diagram showing an output spectrum from the optical amplifier in FIG. 11;

FIG. 13 is a spectrum diagram of signal light separated by the comb filter of FIG. 11 and output to an output.

FIG. 14 is a spectrum diagram of white noise light output to the attenuator of FIG. 11;

FIG. 15 is a block diagram showing a configuration of an optical amplifier to which conventional gain constant control is applied.

[Explanation of symbols]

 1a, 1b, 1c Coupler 2 Optical amplifier 3 Signal source 4a, 4b Light receiver 5a, 5b Level constant control circuit

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Claims (7)

[Claims] A signal light combining / distributing means for combining and distributing the signal light; a light receiving / converting means for optically / electrically converting the signal light; an optical amplifying means for amplifying the signal light; A signal light generating unit that generates a signal light having a wavelength different from that of the signal light input from the outside to a signal light to be multiplexed with the signal light input from the outside, and adjusting a signal level from the signal light generating unit. An input level stabilized optical amplifier, further comprising a level constant control means for controlling the light receiving current of the light receiving conversion means to be constant. 2. Signal light combining / distributing means for combining and distributing signal light, light receiving / converting means for optically / electrically converting signal light, optical amplifying means for amplifying signal light, and stabilizing an input level. A signal light generating unit that generates a signal light having a wavelength different from that of the signal light input from the outside to a signal light to be multiplexed with the signal light input from the outside, and adjusting a signal level from the signal light generating unit. Level control means for controlling the light receiving current of the light receiving and converting means to be constant; and second light receiving and converting means for optically / electrically converting the signal light input from the optical amplifying means through the signal light combining and distributing means. And a second constant level control means for controlling the optical amplification means so that the current generated by the second light reception conversion means is constant. 3. An input level stabilized optical amplifier according to claim 1, further comprising a generated signal removing means for removing a signal light generated by said signal light generating means from an output of said optical amplifying means. 4. The input level stabilized optical amplifier according to claim 2, further comprising a generated signal removing means for removing the signal light generated by said signal light generating means from the output of said optical amplifying means. 5. A demultiplexing means for using a white noise light output from the optical amplifying means for a signal light to be multiplexed with a signal light input from the outside to stabilize an input level; 2. An input level stabilized optical amplifier according to claim 1, further comprising an attenuating means for controlling an insertion loss of white noise light. 6. A demultiplexing means for using white noise light output from the optical amplifying means as signal light to be multiplexed with signal light input from the outside to stabilize an input level; 3. The input level stabilized optical amplifier according to claim 2, further comprising: an attenuator for controlling an insertion loss of the white noise light. 7. An input level stabilized optical amplifier according to claim 5, wherein said demultiplexing means is a comb filter.