JPH09185092A - Optical fiber amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably control the output signal level of the optical fiber amplifier. SOLUTION: An input optical signal λs and excitation light λp are inputted to an optical amplification fiber 12 through an wavelength multiplexer(WDM) coupler 11 and the signal is amplified. A filter 13 removes components other than the neighborhood of signal wavelength from an optical signal S12 outputted from the fiber 12. The optical signal 512 made incident upon a photodiode (PD) 14a is converted into an electric signal and the electric signal is amplified by a wide band amplifier 14b. The amplitude of an output signal S14 from the amplifier 14b is detected by a peak detection circuit 15. A difference S16 between the detection value S15 of the circuit 15 and reference voltage S17 is inversely amplified by an operational amplifier 18. An output signal S18 from the amplifier 18 is inputted to a laser diode(LD) 19 and the light emission quantity of the LD 19 is controlled so that the detection value S15 becomes the same level as the reference voltage S17. Consequently the amplitude of the output signal S14 from the amplifier 14b is fixed.

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 for, for example, long distance data transmission.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing an example of a conventional optical fiber amplifier. This optical fiber amplifier is a wavelength division multiplexer (Wavelength Division Multiplexing) that multiplexes an input optical signal λs from a transmitter (not shown) and pumping light λp.
Hereinafter, it will be referred to as a WDM coupler) 1. The output side of the WDM coupler 1 is connected to the input side of the two-branch optical coupler 3 via the optical amplification fiber 2. Optical amplification fiber 2
Is an optical amplifier fiber such as an erbium-doped optical fiber, and the energy of the pump light λp is transferred to the input light signal λs by propagating both the input light signal λs and the pump light λp in the fiber. , The input optical signal λ
It has a function of amplifying s. The first port (output side) 3a of the two-branch optical coupler 3 is connected to a photodiode (hereinafter referred to as PD) 5a in the optical receiver 5 via a filter 4 that passes only the signal light wavelength, and the PD 5a The output side is connected to the wide band amplifier 5b in the optical receiver 5. The output side of the wide band amplifier 5b is connected to, for example, a multiplexer (not shown).

On the other hand, the second port 3 of the two-branch optical coupler 3
b is connected to the input side of the PD 6 which detects the value of the optical power from the output signal S3b of the second port 3b. P
The output side of D6 is connected to the first input terminal of the subtractor 7. A reference voltage source 8 is connected to the second input terminal of the subtractor 7. The subtractor 7 has a function of subtracting the reference voltage S8, which is the output signal of the reference voltage source 8, from the output signal S6 of the PD 6. The output terminal of the subtractor 7 is connected to the input side of the driver circuit 9. Driver circuit 9
Is composed of, for example, an operational amplifier (hereinafter referred to as an operational amplifier) and a current amplification stage. The output side of the driver circuit 9 is connected to the input side of a laser diode (hereinafter referred to as LD) 10. The LD 10 receives the pumping light λp based on the output signal S9 of the driver circuit 9.
Has the function of outputting. In this optical fiber amplifier, by using the optical amplification fiber 2 as a preamplifier of the optical receiver 5, the sensitivity of the optical receiver 5 is improved by 10 dB or more as compared with the case where the optical amplification fiber 2 is not used. It is an effective means for increasing the gain of the transmission system of the backbone system and the distribution system (that is, the subscriber system) in a line such as a long distance telephone. The driver circuit 9 controls the current supplied to the LD 10 so that the optical output power from the optical amplification fiber 2 becomes constant.

[0004]

However, the optical fiber amplifier of FIG. 2 has the following problems. That is, in the optical fiber amplifier of FIG. 2, the signal light component from the optical amplification fiber 2 and the noise light (Amplified Spontaneous Emis
sion (hereinafter referred to as ASE light) component, and the light amount of the pumping light λp is controlled based on the sum power, so that the optical output power from the optical amplification fiber 2 becomes constant. The output optical signal level is not always constant. FIG. 3 is a diagram showing the power distribution of the signal light and the ASE light from the optical amplification fiber 2 in FIG. 2, where the vertical axis represents power and the horizontal axis represents wavelength. In addition, FIG.
It is a schematic diagram which shows the power of the signal light and ASE light from the inside optical amplification fiber 2, and the power is taken on the vertical axis and the time is taken on the horizontal axis. The problems of the optical fiber amplifier of FIG. 2 will be described with reference to these drawings. When the power of the input optical signal λs decreases, the driver circuit 9 increases the light emission amount of the LD 10. Therefore, the gain of the optical amplifying fiber 2 increases, so that the ratio of the component of the ASE light to the signal light component becomes relatively high, and even if the total power is constant, the power of the signal light decreases and the optical receiver 5 There is a problem that stable signal reception becomes difficult.

[0005]

In order to solve the above-mentioned problems, the first invention is to input an input optical signal composed of light of a predetermined wavelength in an optical fiber amplifier and excite the input optical signal. An optical amplification fiber that amplifies by light, and a pumping light source that generates the pumping light for the optical amplification fiber,
A filter that passes a component in the vicinity of the predetermined wavelength from the output optical signal of the optical amplification fiber, an optical receiver that converts the output optical signal of the filter into an electrical signal, and the electrical signal output from the optical receiver And a feedback circuit that controls the amount of light emitted from the excitation light source so that the detection value of the peak detection circuit reaches a desired level. According to the first aspect of the present invention, since the optical fiber amplifier is configured as described above, the input light signal is input to the optical amplification fiber, the pump light is input from the pump light source at the same time, and the input light signal is amplified. It The output optical signal of the optical amplification fiber is input to the filter, and the component near the predetermined wavelength passes through. The optical signal output from the filter is converted into an electrical signal by the optical receiver. Next, the amplitude of the electric signal output from the optical receiver is detected by a peak detection circuit. The detection value of the peak detection circuit is controlled to a desired level by controlling the amount of light emitted from the excitation light source with a feedback circuit. Therefore, stable signal reception is performed by the optical receiver.

According to a second aspect of the invention, the optical amplifying fiber of the first aspect of the invention, a pumping light source, and a branch for branching the power of the optical signal obtained by branching a part of the optical signal output from the optical amplifying fiber into two systems of the same level. Means, a first filter having a predetermined pass band width, and passing a component near the wavelength of the input optical signal from one output optical signal of the branching means, and a predetermined filter different from the first filter. A second filter having a pass band width, which passes a component near the wavelength of the input optical signal from the other output optical signal of the branching unit, and the output optical signal of the first filter is converted into an electric signal. A first photoelectric converter,
A second photoelectric converter that converts the output optical signal of the second filter into an electrical signal; a difference circuit that subtracts the output signal of the second photoelectric converter from the output signal of the first photoelectric converter; A feedback circuit that controls the amount of light emitted from the pumping light source so that the output signal of the difference circuit has a desired level, and a third filter that passes a component near the predetermined wavelength from the output optical signal of the optical amplification fiber. And an optical receiver for converting the output optical signal of the third filter into an electrical signal.

Further, in the difference circuit, when the pass bandwidths of the first filter and the second filter are the same, the difference circuit converts the output signal of the first photoelectric converter from the output signal of the second photoelectric converter. When the signal light power obtained by amplifying the input optical signal is extracted from the output optical signal of the optical amplification fiber by subtracting the output signal, and the pass bandwidths of the first filter and the second filter are different, The output signal of the first photoelectric converter is corrected to a value corresponding to the same pass bandwidth based on the ratio of the respective pass bandwidths, and the corrected output signal of the first photoelectric converter is converted into the first signal from the corrected output signal of the first photoelectric converter. The signal light power is extracted by subtracting the output signal of the second photoelectric converter. According to this second invention,
At the same time that the input optical signal is input to the optical amplification fiber, the excitation light is input from the excitation light source, and the input optical signal is amplified. The power of the optical signal obtained by branching a part of the output optical signal of the optical amplification fiber is branched by the branching means into two systems of the same level. One output optical signal of the branching unit is input to the first filter, and a component near the wavelength of the input optical signal passes. On the other hand, the other output optical signal of the branching unit is input to the second filter, and a component near the wavelength of the input optical signal and different from the first filter passes.

Further, the output optical signal of the first filter is converted into an electric signal by the first photoelectric converter, and the output optical signal of the second filter is converted into an electric signal by the second photoelectric converter. It Then, the difference circuit subtracts the output signal of the second photoelectric converter from the output signal of the first photoelectric converter, and outputs the signal light power obtained by amplifying the input light signal. However, when the pass bandwidths of the second filter and the third filter are the same, in the difference circuit,
By subtracting the output signal of the second photoelectric converter from the output signal of the first photoelectric converter, signal light power is extracted from the output optical signal of the optical amplification fiber. When the passband widths of the second filter and the third filter are different, either the output signal of the first photoelectric converter or the output signal of the second photoelectric converter is used in the difference circuit. Subtracting the output signal of the second photoelectric converter from the output signal of the first photoelectric converter after one is corrected to a value corresponding to the same pass bandwidth based on the ratio of the respective pass bandwidths. Thus, the signal light power is extracted. Further, the output signal of the difference circuit, that is, the signal light power, is controlled to a desired level by controlling the amount of light emitted from the pumping light source by the feedback circuit. Therefore, the output optical signal of the optical amplifying fiber is controlled to a desired level and input to the first filter, and the component near the predetermined wavelength passes through. Then, the output optical signal of the first filter is input to the optical receiver, and the optical receiver stably receives the signal. Therefore, the above problem can be solved.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment FIG. 1 is a configuration diagram of an optical fiber amplifier showing a first embodiment of the present invention. This optical fiber amplifier has a WDM coupler 11 that multiplexes an input optical signal λs from a transmitter (not shown) and pumping light λp. The output side of the WDM coupler 11 is connected to the input side of the optical amplification fiber 12. The optical amplifying fiber 12 is composed of an optical amplifier fiber such as an erbium-doped optical fiber, similar to the conventional optical amplifying fiber 2 in FIG. 2, and both the input optical signal λs and the pumping light λp pass through the fiber. By propagating, the energy of the pumping light λp is transferred to the input optical signal λs, and has a function of amplifying the input optical signal λs. The output side of the optical amplification fiber 12 is connected to the PD 14a in the optical receiver 14 via the filter 13 that transmits only the signal light wavelength, and the output side of the PD 14a is connected to the wide band amplifier 14b in the optical receiver 14. ing. The output side of the wide band amplifier 14b is connected to, for example, a multiplexer (not shown).

On the other hand, the output side of the broadband amplifier 14b is connected to the input side of the peak detection circuit 15. The peak detection circuit 15 has a function of detecting and holding the peak value of the amplitude of the output signal S14 of the broadband amplifier 14b.
The output side of the peak detection circuit 15 is connected to the first input terminal of the subtractor 16. The reference voltage source 17 is connected to the second input terminal of the subtractor 16. The reference voltage source 17 has an output signal S14 of the wide band amplifier 14b.
The reference voltage S17, which is a desired level of, is set. The subtractor 16 outputs the output signal S1 of the peak detection circuit 15.
5 to the reference voltage S17 which is the output signal of the reference voltage source 17.
Has the function of reducing. The output terminal of the subtractor 17 is
It is connected to the input side of the operational amplifier 18, which is a feedback circuit. The output side of the operational amplifier 18 is LD1 which is a pumping light source.
9 is connected to the input side. The operational amplifier 18 has a function of inverting and amplifying the output signal S17 of the subtractor 17 and controlling the light emission amount of the LD 19. The LD 19 has a function of outputting the excitation light λp based on the output signal S18 of the operational amplifier 18.

Next, the operation of FIG. 1 will be described. The input optical signal λs passes through the WDM coupler 11 and the optical amplification fiber 12
To enter. At this time, the excitation light λp from the LD 19 is simultaneously emitted.
Input into the optical amplifying fiber 12 via the WDM coupler 11, and both the input optical signal λs and the pumping light λp propagate through the optical amplifying fiber 12 so that the energy of the pumping light λp becomes the input optical signal λs. Then, the input optical signal λs is amplified. The output optical signal S12 of the optical amplification fiber 12 is
Components other than those in the vicinity of the signal wavelength are removed by the filter 13, are further incident on the PD 14a, are converted from optical signals into electric signals, and are amplified by the broadband amplifier 14b. Next, the amplitude of the output signal S14 of the broadband amplifier 14b is the peak detection circuit 1
5 is detected. A difference S16 between the detected value S15 and the reference voltage S17 is inverted and amplified by the operational amplifier 18. The output signal S18 of the operational amplifier 18 is input to the LD 19, and the light emission amount of the LD 19 is controlled so that the detected value S15 becomes the same level as the reference voltage S17. Therefore, the amplitude of the output signal S14 of the broadband amplifier 14b becomes constant. As described above, in the first embodiment, the amplitude of the output signal S14 of the optical receiver 14 is detected by the peak detection circuit 15,
The light emission amount of the LD 19 is controlled by the operational amplifier 18 so that the detected value S15 becomes the same level as the reference voltage S17. Therefore, stable signal reception is performed by the optical receiver 14.

Second Embodiment FIG. 5 is a configuration diagram of an optical fiber amplifier showing a second embodiment of the present invention. Elements common to those in FIG. 1 are designated by common reference numerals. . This optical fiber amplifier is shown in FIG.
The optical fiber amplifier has a WDM coupler 11. The output side of the WDM coupler 11 is connected to the input side of the optical amplification fiber 12. The output side of the optical amplification fiber 12 is connected to the input side of the two-branch optical coupler 21. First port (output side) 21 of two-branch optical coupler 21
a is connected to the PD 14a in the optical receiver 14 via the third filter 13 that transmits only the signal light wavelength.
The output side of 14a is a broadband amplifier 14b in the optical receiver 14.
It is connected to the. The output side of the wide band amplifier 14b is connected to, for example, a multiplexer (not shown).

On the other hand, the second port 21b of the two-branch optical coupler 21 is connected to the input side of the 3 dB coupler 22 which is a branching means. The 3 dB coupler 22 has a function of branching the power of the optical signal obtained by branching a part of the output optical signal S12 of the optical amplification fiber 12 by the two-branching optical coupler 21 into two systems of the same level. The first port 22a and the second port 22b of the 3 dB coupler 22 have a first filter 23 and a second port 22b, which are narrow band optical filters of the same bandwidth that do not overlap the signal light wavelength and the center wavelength in the vicinity thereof. The two filters 24 are connected to the respective input sides. Each output side of the filters 23 and 24 has a filter 23,
The output lights S23 and S24 of 24 are respectively connected to the respective input sides of PDs 25 and 26 which are photoelectric converters for receiving and converting the output lights S23 and S24 into electric signals. The output sides of the PDs 25 and 26 are connected to the output signals S25 and S26 of the PDs 25 and 26, respectively.
Is connected to the input side of the difference circuit 27 that takes the difference value S27 of. The output side of the difference circuit 27 is connected to the first input terminal of the subtractor 16. A reference voltage source 17A is connected to the second input terminal of the subtractor 16. The reference voltage source 17A has an output signal (that is,
Reference voltage S17A that is the desired level of the difference value S27)
Is set. Hereinafter, the configuration is the same as that of FIG.

FIG. 6 is a diagram showing the characteristics of the filters 23 and 24 and the distribution of the ASE light power ase in FIG. 5, with the vertical axis representing power and the horizontal axis representing wavelength. The operation of FIG. 5 will be described with reference to this figure. Optical filter 23,
When the bandwidths of 24 are the same and the central wavelengths are close to each other, the wavelength distribution of the ASE light of the output optical signal S12 of the optical amplification fiber 12 is wider than that of the signal light. The latter of the optical power and the ASE optical power is almost equal to the ASE optical power of the output light S24 of the filter 24. Therefore, the difference value S27 of the output power of both filters output from the difference circuit 27 becomes the signal light power obtained by amplifying the input light signal λs. Further, the operational amplifier 18 controls the light emission amount of the LD 19 so that the difference value S27 becomes the set value S17A. Therefore, similarly to FIG. 1, the amplitude of the output signal S14 of the wide band amplifier 14b becomes constant. As described above, in the second embodiment, the difference value S27 of the output powers of the filters 23 and 24, that is, the signal light power is output from the difference circuit 27, and the difference value S27 becomes the same level as the reference voltage S17A. Thus, the amount of light emitted from the LD 19 is controlled by the operational amplifier 18. Therefore, stable signal reception is performed by the optical receiver 14.

The present invention is not limited to the above embodiment,
Various modifications are possible. For example, there are the following modifications. (A) In the second embodiment, the optical amplification fiber 12
Although the pumping light λp is injected from the front side of the optical amplifier via the WDM coupler 11, it may be injected from the rear side of the optical amplifying fiber 12 in the direction opposite to the input optical signal λs. In this case, the WDM coupler 11 is installed between the optical amplification fiber 12 and the two-branch optical coupler 21. (B) In the second embodiment, the passband widths of the filters 23 and 24 do not have to be the same as long as the ratio is known. That is, when the passband widths of the filters 23 and 24 are different, one of the output signal S25 of the PD 25 and the output signal S26 of the photoelectric converter 26 is set to the same passband width based on the ratio of the passband widths. The signal light power may be extracted by subtracting the output signal S24 of the photoelectric converter 24 from the output signal S23 of the PD 23 after correction to the corresponding value.

[0016]

As described in detail above, according to the first aspect of the invention, the amplitude of the output signal of the optical receiver is detected by the peak detection circuit, and the feedback circuit is controlled so that the detected value becomes a desired level. Since the light emission amount of the excitation light source is controlled by this, stable signal reception can be performed by the optical receiver. According to the second invention, the difference value between the output powers of the first filter and the second filter, that is, the signal light power obtained by amplifying the input optical signal is output from the difference circuit, and the difference value becomes a desired level. Since the amount of light emitted from the excitation light source is controlled by the feedback circuit as described above, stable signal reception can be performed by the optical receiver.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an optical fiber amplifier showing a first embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of a conventional optical fiber amplifier.

FIG. 3 is a diagram showing power distributions of signal light and ASE light.

FIG. 4 is a schematic diagram showing powers of signal light and ASE light.

FIG. 5 is a configuration diagram of an optical fiber amplifier showing a second embodiment of the present invention.

6 is a characteristic and ASE of filters 23 and 24 in FIG.
It is a figure which shows the distribution of optical power ase.

[Explanation of symbols]

12 optical amplification fiber 13, 23, 24 filter 14 optical receiver 15 peak detection circuit 18 feedback circuit 19 laser diode (excitation light source) 22 3 dB coupler (branching means) 25, 26 photodiode (photoelectric converter) 27 differential circuit λs input light Signal λp Pump light

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location H04B 10/17 H04B 9/00 J 10/16

Claims (2)

[Claims] 1. An optical amplification fiber for inputting an input optical signal composed of light of a predetermined wavelength and amplifying the input optical signal by pumping light, and pumping for generating the pumping light to the optical amplification fiber. A light source, a filter that passes a component in the vicinity of the predetermined wavelength from the output optical signal of the optical amplification fiber, an optical receiver that converts the output optical signal of the filter into an electrical signal, and an output from the optical receiver A peak detection circuit that detects the amplitude of the electric signal, and a feedback circuit that controls the amount of light emitted from the excitation light source so that the detection value of the peak detection circuit is at a desired level. Fiber amplifier. 2. The optical amplification fiber and the pumping light source according to claim 1, branching means for branching the power of the optical signal obtained by branching a part of the output optical signal of the optical amplification fiber into two systems of the same level, A first filter having a pass band width of 1 and passing a component near the wavelength of the input optical signal from one output optical signal of the branching means, and a predetermined pass band width different from the first filter. A second filter having a second filter that passes a component near the wavelength of the input optical signal from the other output optical signal of the branching unit; and a first photoelectric converter that converts the output optical signal of the first filter into an electrical signal. A converter, a second photoelectric converter for converting an output optical signal of the second filter into an electric signal, and an output signal of the second photoelectric converter from an output signal of the first photoelectric converter Difference circuit and output of the difference circuit A feedback circuit that controls the amount of light emitted from the pumping light source so that the signal has a desired level, a third filter that passes a component near the predetermined wavelength from the output optical signal of the optical amplification fiber, and the third filter. An optical receiver for converting an output optical signal of the filter into an electric signal, wherein the difference circuit is configured such that when the pass bandwidths of the first filter and the second filter are the same, By subtracting the output signal of the second photoelectric converter from the output signal of the converter, the optical signal power obtained by amplifying the input optical signal is extracted from the output optical signal of the optical amplification fiber, and the first filter and When the passband widths of the second filter are different, the output signal of the first photoelectric converter is corrected to a value corresponding to the same passband width based on the ratio of the passband widths, and is corrected. That said first Optical fiber amplifier, characterized in that the arrangement for extracting the signal light power by the output signals of the photoelectric converters subtracting the output signal of the second photoelectric converter.