CN1081414C - Method of realizing dynamic gain spectrum equalization of wave-sharing complex system and its equalizing amplifier - Google Patents

Abstract

The present invention relates to a method for equalizing dynamic gains in a wavelength division multiplex optical fiber communication network and an automatically gain equalizing optical fiber amplifier thereof. The present invention is characterized in that a gain locking method and a gain spectrum flatting method are simultaneously adopted inside an optical fiber doped amplifier. The equalizing amplifier provided by the present invention is characterized in that the amplifier comprises a feedback unit and an optical fiber filter, wherein the feedback unit realizing gain locking is connected with the inner part of the amplifier, and the optical fiber filter realizing gain spectrum flatness is inserted in the doped optical fibers. The new method has the characteristics of simplicity, effectivity, absolute equalization and random equalization. Thereby, the equalizing amplifier is suitable for the dynamic gain equalization of an optical network as well as a point-to-point multiloop system.

Description

Realize the method and the equalizer amplifier thereof of wavelength-division multiplex system dynamic gain spectral balancing

The invention belongs to the photoelectron technology field, particularly the method for Dynamic Gain Equalizer and automatic gain balance fiber amplifier thereof in the division multiplex fibre-optic communication wave network.

In recent years, along with the mushroom development that global information infrastructure engineering is built, adopt erbium-doped fiber amplifier (ED) FA) wavelength division multiplexing (WDM) transmission technology become the dominant direction of two-forty, high-capacity optical fiber communication and network technical development.But because the intrinsic unevenness of Er-doped fiber gain spectral, especially cause the competition of interchannel based on the spectral property of HOMOGENEOUS BROADENING, each channel signal of different wave length gain by fiber amplifier the time is different, and this gain inequality also can be accumulated increase with the cascade amplification.In the point-to-point wdm system of long distance, the gain peak that the deflection long wavelength appears in the gain spectral that the EDFA cascade amplifies also makes signal-to-noise ratio degradation, even can cause some channel gain to increase severely and other channel is suppressed; In multi-multipoint fiber optic network, because the transmission path of different channels may be different, the number of channel by EDFA also may change with the reconstruct or the upper and lower of channel of network, and this will cause the saltus step of EDFA operating state on the site; In addition, in comprising the mixing wdm system of different-format signal, lower (higher (＞3dBm) the vision signal conllinear transmission of＜10dBm) baseband digital signal and input power of input power, not only can cause the huge differential of interchannel gain and power, in case and video signal interruption, EDFA promptly jumps to the small-signal state from dark saturation condition, and this will cause the gain drastic change of digital channel and make receiving terminal suffer unacceptable power fluctuation.All these problems make the WDM+EDFA transmission technology further move towards practicability and through engineering approaches runs into serious hindrance.

For addressing this problem, people have proposed to realize the notion of gain balance.The Dynamic Gain Equalizer of WDM+EDFA transmission system comprises the requirement of two aspects: when (1) a plurality of channel li in certain bandwidth range amplified simultaneously, each channel gain G (li) was basic identical; When analog signal was amplified, differential gain dG (l)/d1 was as far as possible little, and this is referred to as the smooth of gain spectral; (2) channel increases, subtracts or the power of a certain channel when changing, and to the not significantly influence of gain of this channel or other channel, promptly keeps gain constant during signal power variations, and this is called strangulation (i.e. locking) or automatic gain control of gain.

In recent years, the method at the dynamic evolution people of channel gain in the actual WDM+EDFA system have proposed multiple gain balance mainly contains:

1. input power preemphasis: amplify the channel gain distribution of accumulate distortion with reference to actual multiloop loop system because of single-stage or cascade, rationally regulate the input power of each channel and make the power of each channel of receiving terminal equal substantially at system's transmitting terminal.

2. lump equalization filtering: amplify the shape of accumulate gain spectral that distorts because of cascade according to actual multiloop loop system, inserting a loss spectra and the balanced optical filter of the lump of distortion gain spectral complementation (as long period fiber grating etc.) after several EDFA scabbles gain spectral, for the decay of compensating filter, adopt EDFA to amplify again simultaneously to signal power.

3. acousto-optic filtering is regulated: the fluctuation FEEDBACK CONTROL of exporting each channel power by amplifier is series at the multichannel band resistance acousto-optic filter on the amplifier output light path, thereby the power output of regulating each channel makes it equal.As shown in Figure 1, output at amplifier EDFA inserts acousto-optic filter, with fiber coupler extension output light, each channel is through separately filter (F1, F2, F3) behind the demultiplexing, separately by photo-detector (PD1, PD2, PD3) conversion becomes the signal of telecommunication (size of signal is corresponding with the power of each channel respectively), with one of them channel serves as with reference to after the gained signal of telecommunication is compared, the filtering loss of FEEDBACK CONTROL acousto-optic filter respective radio-frequency passage respectively, thus the gain of adjusting each channel keeps equating.

Though above-mentioned these methods make the Dynamic Gain Equalizer problem of WDM+EDFA transmission system be eased to a certain extent, and limitation is separately all arranged." input power preemphasis " method and " lump equalization filtering " are though the method simple possible, but the differentiation and the channel configuration of accumulation gain amplifier spectrum, power level, EDFA characteristic and transmission range multiple factors such as (being EDFA progression) is relevant, thereby the design of the adjusting of channel input power or lump filtering characteristic must match with the overall arrangement of system transmissions parameter, balanced effect can only just be arranged with respect to specific point-to-point transmission system, run on the channel, down or other reason cause then complete failure of situation that channel power rises and falls, as seen these class methods are not suitable for the WDM optical-fiber network." acousto-optic filtering adjusting " is though the method ability of equalization has remedied above-mentioned deficiency, the dynamic equalization that also can be used for the WDM optical-fiber network, but also there is many-sided shortcoming: one, require acousto-optic filter to have the radio-frequency channel identical with the transmission channel number, and need transmitting optical channel to each, to carry out filter solution respectively multiplexing, uses through the signal of telecommunication of opto-electronic conversion gained and realize control to the radio-frequency channel, not only technical sophistication, and cost is extremely expensive, and its degree is upgraded with the increase of transmission channel number; Its two, when adopting waveguide type integrated acousto-optic filter to carry out FEEDBACK CONTROL, unavoidably will introduce big clean insertion loss (loss of every acousto-optic filter is up to 9dB), therefore, the practicality of this balancing technique also is subjected to suitable restriction.

Thereby, seek a kind of generally acknowledged perfect practical technical scheme and realize that dynamically utilization gain balance down just becomes current WDM+EDFA Networks of Fiber Communications Study on Technology in the world and develops the ultimate challenge that faces.

Purpose of the present invention is intended to the weak point at existing dynamic equalizing technology, proposes to adopt a kind of new equalizer amplifier to realize the method for WDM+EDFA system dynamics gain balance, and its core is to set up gain strangulation and smooth mechanism simultaneously in amplifier inside.Therefore, this new method is not only effectively simple, and has absolute equilibrium and with meeting balanced characteristics, make this equalizer amplifier both be applicable to point-to-point multiloop loop system, also is suitable for the Dynamic Gain Equalizer of optical-fiber network.

The present invention proposes a kind of method that realizes the wavelength-division multiplex system Dynamic Gain Equalizer, it is characterized in that, takes the method for gain locking and gain spectrum flattening simultaneously in doped optical fibre amplifier inside.

Said gain locking method can be to set up laserresonator in the doped fiber district of said amplifier, by frequency-selecting swash penetrate make Amplifier Gain and gain spectral relatively with excitation wavelength under threshold value lock, it can also be lead division beam split from said amplifier, after converting the signal of telecommunication to, control the pumping current of this amplifier with this signal feedback again and make gain keep constant.

Said gain spectrum flattening method can be the doped fiber cascade compensation of selecting the different gains spectral property for use.Can also be in said doped fiber, to insert the filter of realizing gain spectrum flattening.

The equalizer amplifier of the realization wavelength-division multiplex system Dynamic Gain Equalizer that the present invention proposes, comprise doped gain fiber, fiber coupler, fibre optic isolater and the pump laser diode and the drive circuit thereof that are connected as a single entity, it is characterized in that being connected with the feedback unit of realizing gain locking in the said amplifier, also be included in and insert the optical fiber filter of realizing gain spectrum flattening in the said doped fiber.

Said feedback unit is for being provided with laserresonator in said doped fiber district, described laserresonator can be to be connected with the annular chamber that fiber coupler forms at the two ends of doped fiber section, also can be to be connected with fiber grating to constitute the straight chamber of F-P at the two ends of doped fiber section.Said feedback unit can also be beam splitter to be set and to receive the photelectric receiver of the part light that beam splitter tells at said amplifier I/O end, and the output of this photelectric receiver links to each other with said drive circuit.

The doped fiber of described different gains spectral property comprises the erbium optical fiber of heavily doped aluminium, the erbium optical fiber of fluoride glass matrix or the erbium optical fiber that the opposite aluminium/phosphorus of gain spectral slope trend is mixed altogether etc.Described optical fiber filter is the broadband optical filter that the loss spectra and the gain spectral evolving trend of doped fiber become complementary distribution, comprises the broadband filter or the arrowband comb type multi-channel filter of areflexia types such as long period fiber grating or biconical fiber.

Said amplifier can be single-stage or multistage doped fiber cascade amplifier, and said feedback unit can be in one or more part or all of sections that are located at one-level or a plurality of doped fibers.

Operation principle division of the present invention is as follows:

1. the locking of gain spectral: this is the basis and the prerequisite of novel equalizer amplifier proposed by the invention, and the method that can adopt existing full light feedback or light-electricity to feed back realizes.

Light-electric feedback transmitter is to draw the part output light of EDFA or collect the spontaneous emission light that Er-doped fiber leaks, and becomes the signal of telecommunication through opto-electronic conversion, and the pumping current from circuit FEEDBACK CONTROL EDFA makes gain keep constant then.

Full light feedback transmitter is to adopt optical fiber to close/light feedback formation laser generation that channel-splitting filter or fiber grating will a certain suitable wavelength in EDFA, and the autoregulation that utilizes laser power to change with the population inversion level is kept the constant of gain.According to the operation principle of laser, the condition of laser stabilization vibration is that the gain at excitation wavelength place equals loss, that is:

G(λ ₁)＝Loss(λ ₁) (1)

In the formula, G, Loss (l ₁) represent wavelength l respectively ₁The overall gain and the cavity total loss at place.And the gain of laser wave strong point can be expressed as in the Er-doped fiber: $G\left({\mathrm{\λ}}_1\right)=G_0\left({\mathrm{\λ}}_1\right){(1+\frac{P_1}{P_{\mathrm{sat},l}})}^{-1}-----\left(2\right)$

Wherein, P ₁The expression laser power, P _{Sat, l}The saturation power of expression laser wave strong point.G ₀(l ₁) small signal gain of expression laser wave strong point, it depends on pumping level (being the population inversion level).When the input of the flashlight of other wavelength, flashlight consumption part inverted population and obtain amplifying is simultaneously because reflecting level decline makes small signal gain G ₀(l ₁) reduce.In order to keep laser generation, laser power P ₁To keep laser gain G (l thereupon descending ₁) constant, simultaneously, the gain of signal wave strong point also remains unchanged.When input signal increases G ₀(l ₁) further descend, until G ₀(l ₁) the G (l that causes of decline ₁) descending finally makes laser oscillation condition (1) formula not satisfy, laser extinguishes, and minimum detectable signal power at this moment is called Amplifier Gain strangulation dynamic range.

The multiplication factor of any one section Er-doped fiber can be represented with following formula with the signal wavelength change: $G\left(\mathrm{\λ}\right)=\exp \left\{\underset{0}{\overset{l}{\∫}}(g^{*}\left(\mathrm{\λ}\right)\frac{n_2}{n_1}-\mathrm{\α}\left(\mathrm{\λ}\right)\frac{n_1}{n_1})\mathrm{dz}\right\}-----\left(3\right)$

Wherein, n ₁, n ₂Be respectively corresponding energy level and last energy level population down, n _tFor erbium ion sum and n is arranged _t=n ₁+ n ₂, g ^*, a is respectively the gain and the absorption coefficient of Er-doped fiber, they are the function of wavelength, L is an Er-doped fiber length.Because the gain characteristic of Er-doped fiber is based on even broadening, the amplification of being excited that the input signal of any wavelength causes can change population n ₁, n ₂The final multiplication factor that changes under other wavelength, the gain cross-couplings effect of Here it is interchannel.For a finished product amplifier, its parameter g ^*, a and L be all definite, when pumping fully and signal hour, n ₂＞＞n ₁, multiplication factor is by first decision of (3) formula, and when signal was big, inverted population consumed more, and multiplication factor is by the difference decision of two of (3) formulas.Promptly, that is to say that the change of amplifier saturation depth will cause the change of gain spectral by the decision of population inversion level.But in the amplifier of full light feedback oscillator strangulation, as long as laser exists, signal power size no matter, inverted population is clamped at the threshold level of laser all the time, thereby gain spectral is also by strangulation.In the amplifier of light-electric feedback oscillator strangulation, in case realized gain locking to a certain channel must also having kept the constant of inverted population by the control pumping current, therefore, gain spectral also is blocked.

2. the leveling of locking gain spectral: under normally used signal power level or in the gain locking dynamic range that requires usually, Amplifier Gain spectrum presents a gain peak at 1558-1560nm place, and this is that intrinsic property by erbium/aluminium codoped optical fiber commonly used determines.Adopt opposite optical fiber of gain spectral slope trend such as fluoride glass matrix erbium optical fiber or the common Er-doped fiber of aluminium/phosphorus etc. to use with common erbium/aluminium codoped optical fiber cascade coupling, can obtain calibration result to a certain degree, but this at all this change Er-doped fiber promptly can not guarantee under any degree of saturation, all to keep the smooth of gain spectral based on the gain attribute of even broadening.At with the corresponding saturation depth of locking dynamic range of designing requirement, can in the gain light path, insert loss spectra and become the broadband optical filter of inverting distribution that gain spectral is flattened with gain spectral.

3. isolating cascade amplifies: the gain of EDFA and noise characteristic depend on the particle counter-rotating degree in the pump erbium-doped optical fiber.Use the sharp gain locking amplifier of penetrating of frequency-selecting of single hop Er-doped fiber, owing to always work in the dark saturation condition of low reflecting level, be difficult to obtain simultaneously high-gain, high power and low-noise characteristic, can adopt cascade to amplify light channel structure for further improving the locking amplification performance.The applicant once disclosed a kind of technology in the Chinese patent " distribution pumping cascade fiber amplifier " (patent No. ZL9603208.5) of application on February 9th, 1996, adopt optical isolator that EDFA is divided into two-stage.Because optical isolator has stopped the influence of back level ASE to prime effectively, thereby the first order might be in high reflecting level and be operated in high-gain, low noise state.If adopt this cascade structure and implement the high-power state that the gain locking measure makes it to be operated in low reflecting level, simultaneously, cooperate suitable gain spectrum flattening means, just can guarantee in enough big input dynamic range, to reach high-gain, high-power and low noise and gain spectrum flattening, constant good characteristic.

The present invention propose with equalizer amplifier realize the outstanding advantage of the method for wavelength-division multiplex system Dynamic Gain Equalizer be diversity gain locking, smooth and enlarging function in one, need not other equalizing device in the system.In addition, equalizer amplifier can not rely on the apparent situation of system parameter and independent design, and the dynamic change of system parameter does not influence its balanced operation characteristic yet.The technical characterstic of the equalizer amplifier that the present invention proposes is: the first, and introduce feedback mechanism amplifier gain spectrum is locked, the cross-gain coupling of different wave length interchannel is suppressed, and under the different capacity level, keep constant; The second, introduce filter shape mechanism in the process that locking is amplified with the gain spectral leveling, make the signal gain of each wavelength under the different capacity level identical and be clamped at a fixed numbers; The 3rd, further introduce and isolate the cascade amplification mechanism, thereby the flat gain that is implemented under high-gain, high power, the low noise operating state locks with inhibition amplified spont-aneous emission (ASE).

Brief Description Of Drawings:

Fig. 1 adopts tunable acousto-optic filter to carry out the principle schematic of Dynamic Gain Equalizer;

Fig. 2 is the light channel structure schematic diagram of a kind of photoelectricity mixing feedback equalization amplifier embodiment of the present invention ();

Fig. 3 is the light channel structure schematic diagram of a kind of full light feedback equalization amplifier embodiment of the present invention (two);

Fig. 4 is the test result of the full light feedback equalization Amplifier Gain of the embodiment of the invention (), noise factor and input signal power relation;

Fig. 5 is the test result of the full gain of light feedback equalization amplifier under different wave length of the embodiment of the invention (-).

Two kinds of Dynamic Gain Equalizer fiber amplifier embodiment light channel structures that the present invention develops as shown in Figures 2 and 3.Be described in detail as follows in conjunction with the accompanying drawings:

Embodiment (one) comprises as shown in Figure 2: channel-splitting filter BS12, optical isolator ISO11, doped fiber EDF11, wavelength division multiplexing optical fiber coupler MUX11, optical isolator ISO12, coupler MUX12, doped fiber EDF12, biconical fiber filter BFF1, doped fiber EDF13, coupler MUX13, optical isolator ISO13 and channel-splitting filter BS13 are linked in sequence light channel structure as shown in the figure.121 ends of optical branching filter BS12 and 133 ends of optical branching filter BS13 are used separately as the signal input part and the output of whole amplifier.111 ends of coupler MUX11 and MUX12 link to each other with the B113 end with the B112 of channel-splitting filter BS11 respectively with 121 ends, and the B111 end of BS11 links to each other with pumping laser pipe LD11, and 131 ends of coupler MUX13 also link to each other with pumping laser pipe LD12.The course of work of this amplifier is as follows: pump light is respectively from three fiber coupler BUX11, MUX12 and MUX13 inject three sections doped fibers, flashlight is through channel-splitting filter BS12, isolator ISO11 enters first section doping EDF11 optical fiber and amplifies, then through coupler MUX11, isolator ISO12 and coupler MUX12 enter second section doped fiber EDF12 secondary and amplify, enter the 3rd section doped fiber EDF13 after the flashlight process bipyramid filter BFF11 filtering after secondary amplifies and amplify once more, after coupler MUX13, output isolator ISO13 also exports through channel-splitting filter BS13.Wherein, channel-splitting filter BS12 and channel-splitting filter BS12 are optically coupled to photoelectric detector PD 11 and PD12 with small part input signal light and output signal respectively, convert to behind the corresponding signal of telecommunication by control circuit CC11 handle produce feedback signal control pump diode LD12 drive current to keep the gain constant of whole amplifier.The filtering spectrum of bipyramid filter BFF11 and Amplifier Gain spectrum are complementary, are used to improve the gain spectral characteristic.

Embodiment (two) as shown in Figure 3, comprise: optical isolator ISO21, doped fiber EDF21, wavelength division multiplexing optical fiber coupler MUX21, optical isolator ISO22, fiber grating FBG21, coupler MUX22, doped fiber EDF22, biconical fiber filter BFF21, doped fiber EDF23, coupler MUX23 and fiber grating FBG22 and optical isolator ISO23 are linked in sequence light channel structure as shown in the figure.The output of the input of optical isolator ISO21 and optical isolator ISO23 is used separately as the signal input part and the output of whole amplifier.211 ends of coupler MUX21 and MUX22 link to each other with the B213 end with the B212 of channel-splitting filter BS21 respectively with 221 ends, B211 end and the pumping laser pipe LD21 fiber coupler MUX21 of BS21, optical isolator ISO22, fiber grating FBG21, coupler MUX22, doped fiber EDF22, biconical fiber filter BFF21, doped fiber EDF23, coupler MUX23 and fiber grating FBG22 are linked in sequence light channel structure as shown in the figure with optical isolator ISO23, and the output of the input of optical isolator ISO21 and optical isolator ISO23 is used separately as the signal input part and the output of whole amplifier.211 ends of coupler MUX21 and MUX22 link to each other with the B213 end with the B212 of channel-splitting filter BS21 respectively with 221 ends, B211 end and the pumping laser pipe LD21 fiber coupler MUX21 of BS21, optical isolator ISO22, fiber grating FBG21, coupler MUX22, doped fiber EDF22, biconical fiber filter BFF21, doped fiber EDF23, coupler MUX23 and fiber grating FBG22 are linked in sequence light channel structure as shown in the figure with optical isolator ISO23, and the output of the input of optical isolator ISO21 and optical isolator ISO23 is used separately as the signal input part and the output of whole amplifier.211 ends of coupler MUX21 and MUX22 and 221 ends can not be kept with channel-splitting filter BS21 μ respectively.The filtering spectrum of bipyramid filter BFF21 and amplifier with laser generation the time the gain spectral complementation, be used to improve the gain spectral characteristic.

The model that 2 power of employing are 90mW among the embodiment (two) is that the 980nm laser diode of SDLO-2004-100 is made pumping source, the about 200mA of operating current, about 25 ℃ of working temperature; Erbium/aluminium codoped optical fiber numerical aperture 0.21, cut-off wavelength 0.9 μ m is respectively 3.29dB/m and 4.57dB/m, the first segment length 6m, the second segment length 9m, the 3rd segment length 12m to the absorption of pump light and flashlight; Used three fiber couplers are EPTSMWDM980/1550 wavelength division multiplexing optical fiber coupler, insert loss less than 0.1dB, and isolation is greater than 20dB; Used three #I-15-PIPT-X-1A optical isolators insert loss less than 0.5dB, and isolation is greater than 20dB; Used channel-splitting filter is an EPTSMWDM980 optical fiber channel-splitting filter.Test result is shown in Fig. 4,5, adopt the DFB laser of 1553nm wavelength to make signal source, record-40 ~-input range of 17dBm in gain constant be 33dB, the strangulation dynamic range that promptly gains 23dB, noise factor is about 6dB (comprising the loss of input isolator) in this dynamic range, recording multi-wavelength signals-1dB bandwidth with equivalent saturation conditions wide spectrum light source method of testing is that (1547 ~ 1561nm), experiment proves also in input dynamic range that input signal power changes to 14nm and gain spectral is constant.Adopt components identical also to obtain similar result among the embodiment ().Realize the gain strangulation in the time of the similar performance index and increase the smooth experimental result of spectrum having not yet to see report.

Claims (10)

1. method that realizes the wavelength-division multiplex system Dynamic Gain Equalizer, it is characterized in that, take the method for gain locking and gain spectrum flattening simultaneously in doped optical fibre amplifier inside, said gain locking method is to set up laserresonator in the doped fiber district of said amplifier, by frequency-selecting swash penetrate make Amplifier Gain and gain spectral relatively with excitation wavelength under threshold value lock; Said gain spectrum flattening method is the doped fiber cascade compensation of selecting the different gains spectral property for use, and the doped fiber of described different gains spectral property comprises the erbium optical fiber of heavily doped aluminium, the erbium optical fiber of fluoride glass matrix or the erbium optical fiber that the opposite aluminium/phosphorus of gain spectral slope trend is mixed altogether.

2. method that realizes the wavelength-division multiplex system Dynamic Gain Equalizer, it is characterized in that, take the method for gain locking and gain spectrum flattening simultaneously in doped optical fibre amplifier inside, said gain locking method is to set up laserresonator in the doped fiber district of said amplifier, by frequency-selecting swash penetrate make Amplifier Gain and gain spectral relatively with excitation wavelength under threshold value lock; Said gain spectrum flattening method is to insert the filter of realizing gain spectrum flattening in said doped fiber.

3. method that realizes the wavelength-division multiplex system Dynamic Gain Equalizer, it is characterized in that, take the method for gain locking and gain spectrum flattening simultaneously in doped optical fibre amplifier inside, said gain locking method is lead division beam split from said amplifier, after converting the signal of telecommunication to, control the pumping current of this amplifier with this signal feedback again and make gain keep constant; Said gain spectrum flattening method is the doped fiber cascade compensation of selecting the different gains spectral property for use, and the doped fiber of described different gains spectral property comprises the erbium optical fiber of heavily doped aluminium, the erbium optical fiber of fluoride glass matrix or the erbium optical fiber that the opposite aluminium/phosphorus of gain spectral slope trend is mixed altogether etc.

4. method that realizes the wavelength-division multiplex system Dynamic Gain Equalizer, it is characterized in that, take the method for gain locking and gain spectrum flattening simultaneously in doped optical fibre amplifier inside, said gain locking method is lead division beam split from said amplifier, after converting the signal of telecommunication to, control the pumping current of this amplifier with this signal feedback again and make gain keep constant; Said gain spectrum flattening method is to insert the filter of realizing gain spectrum flattening in said doped fiber.

5. one kind is used for realizing the equalizer amplifier of method according to claim 1, comprise doped gain fiber, fiber coupler, fibre optic isolater and the pump laser diode and the drive circuit thereof that are connected as a single entity, it is characterized in that being connected with the feedback unit of realizing gain locking in the said amplifier, also be included in and insert the optical fiber filter of realizing gain spectrum flattening in the said doped fiber.

6. equalizer amplifier as claimed in claim 5 is characterized in that, said feedback unit is for being provided with laserresonator in said doped fiber district, and described laserresonator forms annular chamber for be connected with fiber coupler at the two ends of doped fiber section.

7. equalizer amplifier as claimed in claim 5 is characterized in that, said feedback unit is for being provided with laserresonator in said doped fiber district, and described laserresonator constitutes the straight chamber of F-P for be connected with fiber grating at the two ends of doped fiber section.

8. equalizer amplifier as claimed in claim 5, it is characterized in that, said feedback unit is for being provided with beam splitter and receiving the photelectric receiver of the part light that beam splitter tells at said amplifier I/O end, the output of this photelectric receiver links to each other with said drive circuit.

9. equalizer amplifier as claimed in claim 5, it is characterized in that, described optical fiber filter is the broadband optical filter that the loss spectra and the gain spectral evolving trend of doped fiber become complementary distribution, comprises the broadband filter or the arrowband comb type multi-channel filter of areflexia types such as long period fiber grating or biconical fiber.

10. equalizer amplifier as claimed in claim 5 is characterized in that, said amplifier is multistage doped fiber cascade amplifier, and said feedback unit is a plurality of, can be located at respectively in part doped fiber section or the whole doped fiber section.

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