JP3320225B2 - Optical fiber amplifier - Google Patents

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 for amplifying an optical signal such as a video signal.

[0002]

2. Description of the Related Art In recent years, with the practical use of rare-earth-doped optical fiber amplifiers capable of amplifying optical signals as light, analog optical transmission systems for realizing long-distance transmission or multiple distribution have been actively developed. . For example, when four stages of optical fiber amplifiers are connected and branched by a 1 × 8 optical branching device,
About 4000 distributions are possible.

In order to perform analog optical transmission, the optical transmission line is required to have low distortion transmission characteristics. However, in the direct intensity modulation method generally used conventionally, the light intensity modulation signal is simultaneously subjected to frequency modulation (wavelength chirping). In addition, since an optical fiber amplifier generally has a wavelength dependence of gain, when the direct intensity modulation signal as described above passes through the optical fiber amplifier, secondary intermodulation distortion occurs, and the optical signal waveform is greatly distorted. I do.

[0004] References (IEEE Photon.Technol.Lett.,
vol.5, no.4, pp414-416, 1993) show that there is a condition for canceling the waveform distortion generated by an optical fiber amplifier and the waveform distortion generated by a laser when the phase relationship is reversed. Have been. However, when a plurality of optical fiber amplifiers are connected in cascade, the secondary distortion generated in the optical fiber amplifier is accumulated and becomes more dominant than the distortion generated in the laser itself, thereby limiting the system performance. Therefore, when a plurality of optical fiber amplifiers are connected in cascade, it is preferable that each of the optical fiber amplifiers has no distortion so that the distortion is not accumulated even when the cascade connection is performed.

As described above, the secondary distortion generated in the optical fiber amplifier is caused by the interaction between the wavelength chirping and the gain tilt (the slope of the gain with respect to the optical wavelength, see FIG. 6). Therefore, if the wavelength of the input light is made to coincide with the wavelength at which the gain tilt becomes zero, the optical fiber amplifier becomes distortionless.
The gain tilt characteristics change depending on the optical power input to the optical fiber amplifier (see FIG. 6). Therefore, there is an input optical power that causes the optical fiber amplifier to be in a distortion-free state at a predetermined wavelength. This will be described below.

FIG. 4 shows a change in second-order distortion (CSO _{LD + AMP} ) after passing through an optical fiber with respect to input optical power in a single-stage optical fiber amplifier. However,
The broken line in the figure indicates the distortion level (CSO _LD ) of the input optical signal. At point A shown in the figure, the distortion (CSO _AMP ) generated in the optical fiber amplifier and the CSO _LD are in opposite phases, and
In addition, the absolute amount of the CSO _AMP is larger. Therefore, the amount of distortion corresponding to the difference between the absolute amounts is CSO _{LD + AMP}
It appears as. Similarly, at point B, CSO _LD and CSO
Although _AMP is reversed phase, since the absolute amount of CSO _AMP is exactly twice the absolute amount of CSO _LD, CSO _{LD + AMP} and CSO
_{The LDs} are apparently equal in size (hereinafter referred to as pseudo-distortion-free operating points). At point C, since the phases of CSO _AMP and CSO _LD are opposite and the absolute amounts are equal, the canceling effect is the largest and CSO _{LD + AMP} takes the minimum value. Point D is CSO
_This is the point where _AMP becomes zero, and the absolute amount of CSO _LD and CSO
_The absolute value of _{LD + AMP} becomes equal (hereinafter referred to as a distortion-free operating point). That is, if the input optical power of the optical fiber amplifier is set at this point D, the optical fiber amplifier can be operated without distortion. At point E, CSO _AMP and CSO _LD are in phase, and the sum of the absolute amounts of CSO _LD and CSO _AMP is CSO _{AMP.
LD + AMP} .

However, light sources can be classified into two types according to the phase state of the generated distortion. That is, there are a type (type X) exhibiting the above-described properties and a type (type Y) that generates a distortion having an opposite phase to the distortion generated in the type X. In type Y, since the phase of the generated distortion is opposite to that of type X, point B in FIG.
Becomes a pseudo distortion-free operating point.

A conventional optical fiber amplifier using such an optical fiber amplifier will be described with reference to FIG.
In this conventional example, three stages of optical fiber amplifiers are connected in cascade, and each optical branching device makes eight branches. At each stage, the optical signal passes through the optical attenuators 501 to 503, and the optical fiber amplifiers 207 to 207-2.
09 is amplified. The optical signals amplified by the optical fiber amplifiers 207 to 209 are respectively split into eight by the 1 × 8 optical splitters 213 to 215 and input to the next-stage optical attenuator. However, the optical signal at the first stage is supplied from the light source 101, and the optical signal split by the 1 × 8 optical splitter at the last stage is output as the output optical signal of the optical fiber amplifier. The optical power input to each optical fiber amplifier is adjusted to a distortion-free operating point by an optical attenuator. At this time, in the conventional optical fiber amplifier,
The input optical power corresponding to the distortion-free operating point is specified in advance,
It was necessary to adjust the optical attenuator manually.

[0009]

However, in order to actually specify the distortion-free operating point, high-precision measurement is required. Also, the strain CSO _LD generated by the light source is actually several dB.
For reasons such as having the above fluctuation range and the possibility of deviation from the set value due to aging,
It is difficult to always operate an optical fiber amplifier at a distortion-free operating point.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the above-mentioned problems of the conventional optical fiber amplifier, to appropriately set the power input to the optical fiber amplifier, and to avoid the accumulation of distortion.

[0011]

In order to achieve the above object, an optical fiber amplifier according to the present invention comprises an optical fiber amplifier and a second amplifier for detecting a waveform distortion level in an optical signal input to the optical fiber amplifier. 1 distortion level detecting section, a second distortion level detecting section for detecting a waveform distortion level in the output optical signal from the optical fiber amplifier, and each distortion detected by the first and second distortion level detecting sections. It has a configuration including an optical level adjustment unit that adjusts the input optical power to the optical fiber amplifier so that the levels always match.

According to a second aspect of the present invention, there is provided an optical fiber amplifying apparatus for detecting a distortion level in an optical signal output from a light source instead of the first distortion level detecting section in the first aspect.
Wherein the optical level adjustment unit adjusts the input optical power to the optical fiber amplifier such that each of the distortion levels detected by the third and second distortion level detection units always coincides with each other. The configuration is such that

An optical fiber amplifier according to a third aspect of the present invention is constituted by cascading a plurality of the optical fiber amplifiers according to the first aspect, and the optical fiber amplifier is connected to the optical fiber amplifier for each of the optical fiber amplifiers. The first distortion level detecting section detects the distortion level in the input optical signal of the above, and the second distortion level detecting section detects the distortion level in the output optical signal from the optical fiber amplifier. The optical level adjustment unit adjusts the input optical power to the optical fiber amplifier so that the respective distortion levels detected by the two distortion level detection units always coincide with each other.

An optical fiber amplifier according to a fourth aspect of the present invention is constructed by cascading a plurality of the optical fiber amplifiers according to the second aspect, and adjusts a distortion level in an output optical signal of the light source to the third distortion. A level detector detects a distortion level in an output optical signal from the optical fiber amplifier for each of the optical fiber amplifiers, and detects a distortion level in the second distortion level detector. The optical level adjustment unit adjusts the input optical power to the optical fiber amplifier so that each of the detected distortion levels always matches the distortion level detected by the third distortion level detection unit. ing.

According to a fifth aspect of the present invention, there is provided an optical fiber amplifier configured by cascading a plurality of the optical fiber amplifiers according to the first aspect, wherein a distortion level detected by the first and second distortion level detectors is provided. Is detected at each stage only for the input / output optical signal of a specific optical fiber amplifier, and the distortion level detected by the first distortion level detection unit and the distortion level detected by the second distortion level detection unit are detected. A configuration is provided in which the input optical powers of the optical fiber amplifiers at the same stage are simultaneously adjusted by the optical level adjusting unit so that the levels match.

An optical fiber amplifier according to a sixth aspect is constructed by cascading a plurality of the optical fiber amplifiers according to the second aspect, and detects the distortion level by the second distortion level detector. In each stage, only the output optical signal of the specific optical fiber amplifier is performed, and the distortion level detected by the second distortion level detector and the distortion level detected by the third distortion level detector match. As described above, the input power of the optical fiber amplifiers in the same stage is simultaneously adjusted by the optical level adjusting unit.

Further, in the optical fiber amplifier according to the present invention, the first or third distortion level detecting section may include a first optical splitting section for splitting an optical signal into two, and the first optical splitting section. A first optical power adjustment unit that receives one of the two optical signals branched by the splitting unit and always outputs an optical signal of a predetermined power regardless of the magnitude of the input power; A first photoelectric conversion unit for converting an optical signal output from the unit to an electric signal, and a first photoelectric conversion unit for transmitting only a distortion component of a predetermined frequency from the electric signal output from the first photoelectric conversion unit. And the second distortion level detecting unit is divided into two by the second optical branching unit, which divides the optical signal output from the optical fiber amplifier into two. One of the optical signals is input to the first optical power adjusting unit. A second optical power adjustment unit that outputs an optical signal having a predetermined power equal to the power of the optical signal to be output, and a second optical power adjustment unit that converts the optical signal output from the second optical power adjustment unit into an electric signal. A photoelectric conversion unit, and the second
And a second filter that transmits only a distortion component of a predetermined frequency from the electric signal output from the photoelectric conversion unit. The optical level adjustment unit is divided into two by the first optical branching unit. The other of the received optical signals is input, the amount of attenuation with respect to the optical signal is adjustable, and an optical attenuator that inputs an output optical signal to the optical fiber amplifier, and a distortion component output from the first filter. A control unit that controls the optical attenuator so that the magnitudes of the distortion components output from the two filters match each other, and the other of the optical signals that are bifurcated by the second optical branch unit. Are used as output optical signals.

The optical fiber amplifier according to the present invention has a configuration in which the control unit controls the bias current of the light source instead of the first optical attenuating unit.

In the optical fiber amplifying device according to the ninth aspect, the optical level adjustment unit may be configured to increase the optical power input to the optical fiber amplifier (ΔP _in ) and the second distortion level corresponding thereto. increase in magnitude of the distortion component input from the detection unit (ΔCSO) and detects, it has a function of determining the sign of ΔCSO / ΔP _in, when the sign of the ΔCSO / ΔP _in is negative input light The function of performing the control according to any one of claims 1 to 8 when the power is increased and becomes positive, or when the sign of ΔCSO / ΔP _in is positive, the input light power is reduced and when the sign becomes Δ, the power becomes negative. It has a configuration having one of the functions for performing the control according to any one of claims 1 to 8.

According to a tenth aspect of the present invention, in the optical fiber amplifying apparatus, the optical level adjusting section sweeps the input optical power to the optical fiber amplifier at the start of the operation, and detects the power by the second distortion level detecting section. And a function of detecting the input optical power at which the distortion level detected by the first or third distortion level detection unit matches and setting the input optical power to a value of a predetermined condition. A configuration for performing the control according to any one of claims 1 to 8 is provided.

The optical fiber amplifier according to the eleventh aspect is configured using the optical fiber amplifier in which the input light power dependency of the waveform distortion is known with respect to the wavelength of the light source, and the input to the optical fiber amplifier. The optical power is set to a predetermined value by manually adjusting the optical level adjusting unit, and the optical power is operated.

[0022]

According to the present invention, the distortion levels at the input and output of each optical fiber amplifier are compared and detected, and the input optical power to the optical fiber amplifier is controlled so that the two levels always match. Alternatively, the distortion level at the output of each optical fiber amplifier is compared with the distortion level at the output of the light source, and the input optical power to the optical fiber amplifier is controlled so that the two always match.

In this way, by controlling the input light power of the optical fiber amplifier to an appropriate value, an optical fiber amplifier in which distortion is not accumulated inside can be obtained.

[0024]

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

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described in which an optical fiber amplifier is connected in one stage. FIG. 1 is a diagram showing a first embodiment of the present invention,
101 is a light source, 102 is a first light branching unit, 103 is a first light branching unit.
The optical power adjustment unit 104 has a first photoelectric conversion unit 104,
5 is a first filter, 106 is an optical attenuator, 107 is an optical fiber amplifier, 108 is a second optical splitter, and 109 is a second optical splitter.
The optical power adjustment unit 110 has a second photoelectric conversion unit 11
1 is a second filter, 112 is a control unit, 113 is a reference signal, and 114 is a comparison signal. Reference numeral 201 denotes a first distortion level detection unit, 204 denotes a light level adjustment unit, and 210 denotes a second distortion level detection unit.
Is a distortion level detection unit.

Here, the first distortion level detecting section 201
A first optical splitter 102, a first optical power adjuster 103,
The second distortion level detecting section 210 includes a first optical-electrical conversion section 104 and a first filter 105, and includes a second optical branching section 108, a second optical power adjusting section 109, and a second optical-electrical section. A conversion unit 110, a second filter 111,
The light level adjusting unit 204 includes the light attenuating unit 106, the control unit 11
2 is comprised.

In such a configuration, an optical signal from the light source 101 is split by the first optical splitter 102 into two. 2
One of the branched optical signals is supplied to the first optical power adjusting unit 10.
After being adjusted to a predetermined optical power in step 3, the first optical-electrical converter 104 converts the optical power into an electric signal. Further, only the distortion component of a predetermined frequency is extracted by the first filter 105,
The reference signal 113 is input to the control unit 112.

The other of the two optical signals split by the first optical splitter passes through the optical attenuator 106 and is input to the optical fiber amplifier 107. The optical signal amplified by the optical fiber amplifier 107 is further divided by the second optical splitter 108 into two.
Branched.

One of the optical signals branched into two by the second optical branching unit 108 is adjusted to a predetermined power by the second optical power adjusting unit 109, and then the electric power is adjusted by the second photoelectric converting unit 110. Converted to a signal. Further, the second filter 111
, Only the distortion component of a predetermined frequency is extracted, and the comparison signal 11
4 is input to the control unit 112.

Here, the predetermined optical power adjusted by the first optical power adjustment unit 103 and input to the first photoelectric conversion unit 104 and the second optical power adjusted by the second optical power adjustment unit 109 are used. By matching the predetermined optical power input to the electrical conversion unit 110, the carrier levels are matched, and comparison can be made only with the distortion level.

The other of the two optical signals split by the second optical splitter 108 is output from the optical fiber amplifier as an output optical signal.

The control section 112 has a function of detecting a change in the comparison signal 114 with respect to a change in the output control signal. That is, the control unit 112 controls the optical fiber amplifier 107
Changing the input light power P _in to increase the amount of P _in ([Delta] P
_in , where the increasing level is positive and the decreasing level is negative), the amount of increase in the distortion level of the optical signal output from the optical fiber amplifier 107 (ΔCSO, where increasing is positive, decreasing is negative). Is detected, and the sign of ΔCSO / ΔP _in is determined. When the sign of ΔCSO / ΔP _in is negative, a control signal for increasing the input optical power, that is, for reducing the attenuation of the optical attenuator is given to the optical attenuator 106. Next, when the sign of ΔCSO / ΔP _in is positive, the comparison signal 114 is compared with the reference signal 113, and the comparison signal 114 ≧
In the case of the reference signal 113, the attenuation is increased and the comparison signal 1
When 14 <reference signal 113, a control signal for reducing the amount of attenuation is provided to optical attenuator 106.

By performing such control, the input optical power to the optical fiber amplifier is reduced to the range α in FIG.
When (ΔCSO / ΔP _in <0), it increases and the area β
(ΔCSO / ΔP _in ≧ 0), and when it is in the region β, it is set to a point where the distortion levels at the input and output of the optical fiber amplifier coincide, that is, a point D in FIG. Therefore,
When a type X light source is used as the light source, the second-order distortion generated in the optical fiber amplifier can be reduced to zero.

It is also possible to use a type Y light source as the light source and control the point at which the secondary distortion generated in the optical fiber amplifier is reduced to zero, that is, the point B in FIG. However, at this time, the control unit 112
Detects the sign of ΔCSO / ΔP _in by changing the P _in, when its value is positive, the direction of reducing the input optical power, i.e. the control signal so as to increase the attenuation of the light attenuator 106 Is given to the light attenuation unit 106. Also,
When the sign of ΔCSO / ΔP _in is negative, the comparison signal 114 is compared with the reference signal 113, and the comparison signal 114 ≧ the reference signal 1
At 13, a control signal is provided to the optical attenuator 106 to reduce the amount of attenuation and to increase the amount of attenuation when the comparison signal 114 <the reference signal 113.

In this embodiment, the first light attenuator 106 is controlled by the controller 112. However, the controller 112 may be configured to control the bias current of the light source.

(Embodiment 2) Hereinafter, as a second embodiment of the present invention, three stages of optical fiber amplifiers are connected,
The case of branching will be described with reference to the drawings.
FIG. 2 is a diagram showing a second embodiment of the present invention.
Is a light source, 113 is a reference signal, 114 is a comparison signal, 201
Reference numerals 203 to 203 denote a first distortion level detection unit, 204 to 206 denote optical level adjustment units, 207 to 209 denote optical fiber amplifiers,
Reference numerals 10 to 212 denote second distortion level detection units and 213 to 215.
Is a 1 × 8 optical splitter.

In such a configuration, the optical signal output from the light source 101 is input to the first distortion level detecting section 201.
The first distortion level detectors 201 to 203 detect a distortion level from a part of the input optical signal and input the reference optical signal 113 to each of the optical level adjusters 204 to 206, and simultaneously output the output optical signal to the optical level adjuster 204. To 206. The optical signals transmitted through the optical level adjustment units 204 to 206 are amplified by the optical fiber amplifiers 207 to 209 and then input to the second distortion level detection units 210 to 212. The second distortion level detectors 210 to 212 detect a distortion level from a part of the input optical signal, and generate a comparison signal 114 for each of the optical level adjusters 20.
4 to 206, and at the same time, an output optical signal is output. The output light of the second distortion level detectors 210 to 212 is 1
The light is split into eight by the × 8 optical splitters 213 to 215, respectively. 1
The optical signals branched into eight by the × 8 optical splitters 213 to 214 are respectively input to the first distortion level detectors 202 to 203 at the next stage, and the optical signals split into eight by the 1 × 8 optical splitter 215 are: It is output from the optical fiber amplifier as an output optical signal of the device. Each of the optical level adjustment units 204 to 206 controls the input optical power of the optical fiber amplifiers 207 to 209 so that the reference signal 113 and the comparison signal 114 always match.

In this embodiment, the embodiment in which three stages of optical fiber amplifiers are used and eight branches are performed by each 1 × 8 optical branching device has been described. The same method can be used for branching.

Further, in this embodiment, the input optical power of each optical fiber amplifier is individually controlled by comparing the distortion components of the respective input and output optical signals. However, as shown in FIG. The distortion components of the input and output optical signals of the fiber amplifier 208h are detected by the first distortion level detection unit 202 and the second distortion level detection unit 211, respectively.
The configuration may be such that the input optical powers of all the optical fiber amplifiers 208 in the same stage are adjusted at the same time so that the two distortion levels match when compared at 05h.

(Embodiment 3) Hereinafter, as a third embodiment of the present invention, three stages of optical fiber amplifiers are connected,
The case of branching will be described with reference to the drawings.
FIG. 3 shows a third embodiment of the present invention.
Is a light source, 113 is a reference signal, 114 is a comparison signal, 204
To 206 are optical level adjustment units, 207 to 209 are optical fiber amplifiers, 210 to 212 are second distortion level detection units,
Reference numerals 13 to 215 denote 1 × 8 optical splitters. These operate similarly to the second embodiment. Further, reference numeral 301 denotes a third distortion level detector.

In such a configuration, the third distortion level detecting section 301 detects a distortion level from a part of the output optical signal of the light source, and uses each optical level adjusting section 204 as the reference signal 113.
At the same time, the output optical signal is input to the optical level adjustment unit 204. 1 × 8 optical splitters 213 to 214
The optical signals branched into 8 by the optical fiber amplifiers are input to the optical level adjusting units 205 to 206 at the next stage, and the optical signals branched into 8 by the 1 × 8 optical splitter 215 are output as the optical signals of the optical fiber amplifier. Output. Also, the optical level adjustment units 204 to 206 control the input optical power of the optical fiber amplifiers 207 to 209 so that the reference signal 113 and the comparison signal 114 always match.

In this embodiment, the embodiment in which three stages of optical fiber amplifiers are used and eight branches are performed by each 1 × 8 optical branching device has been described. Exactly the same method can be used when preparing a container.

Further, in this embodiment, the input optical power of each optical fiber amplifier is individually controlled by comparing the distortion components of the respective input and output optical signals. However, as shown in FIG. The distortion component of the output optical signal of the fiber amplifier 208h is detected by the second distortion level detection unit 211, and the distortion level in the output optical signal of the light source detected by the third distortion level detection unit 301 is detected by the optical level adjustment unit 205h. By comparison, the input optical power of all the optical fiber amplifiers 208 in the same stage may be simultaneously adjusted so that they match.

[0044]

As is apparent from the above description,
The optical fiber amplifier of the present invention can prevent the accumulation of distortion in the optical fiber amplifier by automatically setting the optical power input to each optical fiber amplifier to an appropriate value. is there.

[Brief description of the drawings]

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

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

FIG. 3 is a block diagram of an optical fiber amplifier according to a third embodiment of the present invention.

FIG. 4 is a conceptual diagram illustrating a distortion-free operating point of the optical fiber amplifier.

FIG. 5 is a block diagram of a conventional optical fiber amplifier.

FIG. 6 is a diagram illustrating gain tilt characteristics of an optical fiber amplifier.

FIG. 7 is a diagram illustrating a method for simultaneously adjusting the input optical power of the second-stage optical fiber amplifier in the second embodiment of the present invention.

FIG. 8 is a diagram for explaining a method for simultaneously adjusting the input optical power of the second-stage optical fiber amplifier in the third embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 101 light source 102 first optical branching unit 103 first optical power adjusting unit 104 first optical-electrical conversion unit 105 first filter 106 optical attenuating unit 107 optical fiber amplifier 108 second optical branching unit 109 second light Power adjustment unit 110 Second optical-electric conversion unit 111 Second filter 112 Control unit 113 Reference signal 114 Comparison signal 201-203 First distortion level detection unit 204-206 Optical level adjustment unit 207-209 Optical fiber amplifier 210- 212 Second distortion level detector 213 to 215 1 × 8 optical splitter 301 Third distortion level detector 502 to 503 Optical attenuator

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-216452 (JP, A) JP-A-5-19311 (JP, A) JP-A-4-328906 (JP, A) JP-A-5-216906 343788 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 3/00-3/30 G02F 1/35 H04B 10/00 JICST file (JOIS)

Claims (12)

(57) [Claims] 1. An optical amplification system for inputting an intensity-modulated optical signal to an optical fiber amplifier, and amplifying and outputting the same, detects an optical fiber amplifier and a waveform distortion level in an optical signal input to the optical fiber amplifier. A first distortion level detector, a second distortion level detector for detecting a waveform distortion level in an output optical signal from the optical fiber amplifier, and a first distortion level detector. An optical fiber amplifier, comprising: an optical level adjuster that adjusts input optical power to the optical fiber amplifier so that each distortion level always matches. 2. The apparatus according to claim 1, further comprising: a third distortion level detecting section for detecting a distortion level in an output optical signal of the light source, instead of the first distortion level detecting section.
2. The optical fiber amplifier according to claim 1, wherein the input optical power to the optical fiber amplifier is adjusted so that the respective distortion levels detected by the second distortion level detector and the respective distortion levels always coincide with each other. . 3. The optical fiber amplifier according to claim 1, wherein a plurality of said optical fiber amplifiers are connected in cascade, and for each of said optical fiber amplifiers, a distortion level in an optical signal input to said optical fiber amplifier is set to said first level. The distortion level is detected by the distortion level detector, the distortion level in the output optical signal from the optical fiber amplifier is detected by the second distortion level detector, and each of the distortions detected by the first and second distortion level detectors is detected. An optical fiber amplifier, wherein the input optical power to the optical fiber amplifier is adjusted by the optical level adjustment unit so that the levels always coincide with each other. 4. A distortion level in an output optical signal of a light source is detected by the third distortion level detection unit, wherein the plurality of optical fiber amplification devices according to claim 2 are connected in cascade.
For each of the optical fiber amplifiers, a distortion level in an output optical signal from the optical fiber amplifier is detected by the second distortion level detector, and each of the distortion levels detected by the second distortion level detector is An optical fiber amplifier that adjusts the input light power to the optical fiber amplifier by the optical level adjustment unit so as to always match the distortion level detected by the third distortion level detection unit. 5. The first and second optical fiber amplifiers according to claim 1, wherein the optical fiber amplifiers are connected in cascade.
The distortion level detection unit detects the distortion level only for the input / output optical signal of the specific optical fiber amplifier in each stage, and detects the distortion level detected by the first distortion level detection unit and the second distortion level. 4. The optical fiber according to claim 3, wherein the input optical powers of the optical fiber amplifiers in the same stage are simultaneously adjusted by the optical level adjusting unit so that the distortion levels detected by the level detecting unit match. Amplifying device. 6. The optical fiber amplifier according to claim 2, wherein the plurality of optical fiber amplifiers are connected in cascade, and the detection of the distortion level by the second distortion level detector is performed at each stage by the output light of a specific optical fiber amplifier. The distortion level detected by the second distortion level detector and the third level.
The optical power amplifier according to claim 4, wherein the input powers of the optical fiber amplifiers at the same stage are simultaneously adjusted by the optical level adjusting unit so that the distortion levels detected by the distortion level detecting units match. Fiber amplifier. 7. The first or third distortion level detection unit, comprising: a first optical branching unit that branches an optical signal into two; and an optical signal that is branched into two by the first optical branching unit. A first optical power adjustment unit that receives one of the inputs and always outputs an optical signal of a predetermined power regardless of the magnitude of the input power; and converts the optical signal output from the first optical power adjustment unit into an electric signal. A first photoelectric conversion unit, and an electric signal output from the first photoelectric conversion unit,
A first filter that transmits only a distortion component of a predetermined frequency, wherein the second distortion level detection unit includes a second optical branch unit that branches the optical signal output from the optical fiber amplifier into two. Inputting one of the optical signals branched into two by the second optical branching unit and outputting an optical signal having a predetermined power equal to the power of the optical signal output from the first optical power adjusting unit; A second optical power adjustment unit that converts the optical signal output from the second optical power adjustment unit into an electric signal; and a second optical power conversion unit that is output from the second photoelectric conversion unit. Electrical signal
A second filter that transmits only a distortion component of a predetermined frequency, wherein the optical level adjustment unit receives the other of the optical signals branched into two by the first optical branch unit, and outputs the optical signal. And an optical attenuation unit for inputting an output optical signal to the optical fiber amplifier; a distortion component output from the first filter; and a magnitude of a distortion component output from the second filter. And a control unit that controls the optical attenuator so that the two optical signals are equal to each other, and the other of the optical signals that have been split into two by the second optical splitter is used as the output optical signal of the device. The optical fiber amplifier according to claim 1. 8. The optical fiber amplifier according to claim 7, wherein the control section controls a bias current of a light source instead of the first optical attenuating section. 9. The optical level adjusting unit according to claim 7, wherein the optical power input to the optical fiber amplifier is increased in amount (ΔP _in , where increasing is defined as positive and decreasing is defined as negative). A function of detecting the amount of increase in the magnitude of the distortion component (ΔCSO, where the increase is positive and the decrease is negative) input from the distortion level detection unit, and determines the sign of ΔCSO / ΔP _in The function of performing the control according to any one of claims 1 to 8, wherein the input light power is increased when the sign of the ΔCSO / ΔP _in is negative, and the control is performed when the sign becomes positive, or the ΔCSO / ΔP _in When the sign is positive, the input light power is reduced, and when the sign is negative, the function of performing the control according to any one of claims 1 to 8 is provided. An optical fiber amplifier according to any one of claims 1 to 8. 10. The optical level adjusting section sweeps the input optical power to the optical fiber amplifier at the start of operation, and outputs the first or third distortion level detected by the second distortion level detecting section. 9. The control according to claim 1, further comprising a function of detecting an input light power at which the distortion level detected by the distortion level detection unit is the same and setting it to a value of a predetermined condition among them. The optical fiber amplifier according to claim 1, wherein: 11. An optical fiber amplifier whose input light power dependence of waveform distortion is known for a wavelength of a light source is configured, and input light power to the optical fiber amplifier is manually adjusted by the optical level adjustment unit. 2. The method according to claim 1, wherein the operation is performed after setting to a predetermined value by adjusting.
An optical fiber amplifier according to any one of claims 1 to 8. 12. The optical fiber amplifier according to claim 1, wherein said optical fiber amplifier is used in a region where an increase in output light power with respect to an increase in input light power is saturated.