CN104236537A - Light source intensity noise suppression digital double closed-loop method based on intensity modulator - Google Patents

Abstract

The invention discloses a light source intensity noise suppression digital double closed-loop method based on an intensity modulator, belonging to the technical field of fiber optic gyroscopes. The method comprises the following steps: suppressing intensity noise and stabilizing operating points of the intensity modulator by adopting the digital double closed loops; preprocessing, digitalizing, filtering and performing phase compensation on a light intensity signal output by a photoelectric detector during intensity noise suppression, simulating and feeding back the signal to the intensity modulator; in the process of stabilizing an offset operating point of the intensity modulator, acquiring bias voltage of the intensity modulator at the maximum optical output power point and the minimum optical output power point by scanning the bias voltage, acquiring the bias voltage of the operating point by using an average power method, acquiring the output voltage of the photoelectric detector in real time, thereby acquiring the bias voltage difference which is fed back to the intensity modulator. According to the method disclosed by the invention, the problems of low closed-loop precision and poor noise suppression effect are solved, and a signal to noise ratio of a light source of the fiber-optic gyroscope is improved, so that the offset operating point of the intensity modulator does not drift any more, and the operation is stable.

Description

Light source intensity noise based on intensity modulator suppresses digital double closed-loop method

Technical field

The invention belongs to fiber-optics gyroscope field, be specifically related to the suppression technology of the intensity noise to optical fibre gyro superfluorescent fiber sources, be specifically related to a kind of light source intensity noise based on intensity modulator and suppress digital double closed-loop method.

Background technology

Optical fibre gyro, as development a kind of novel inertia angular-rate sensor very rapidly, becomes main separation inertia device, becomes the main direction of studying of inertia device of future generation in increasing field.Optical fibre gyro is except having movement-less part, except the advantage of error that causes without acceleration, and an important difference of itself and traditional electro-mechanical gyro there is larger optical noise, and wherein main a kind of noise is the noise that wide spectrum light source brings.

The noise of optical fibre gyro directly affects the performance index such as random walk coefficient, zero inclined instability of optical fibre gyro, and directly decides the minimum detection sensitivity of optical fibre gyro, so it is very important for carrying out suppression to the noise of optical fibre gyro.

The noise of the wide spectrum light source of optical fibre gyro mainly comprises thermonoise, shot noise and intensity noise.Intensity noise is because the beat frequency of wide spectrum light source causes, be due to various Fourier (Fourier) component of wide spectrum light source between the additional noise that causes of beat frequency, its size increases along with the increase of the light intensity of light source.The size of intensity noise is directly proportional to the size of light source output power, when light source power exceeds certain value, intensity noise just exceedes shot noise and thermonoise, at this moment, signal to noise ratio (S/N ratio) will no longer improve along with the increase of luminous power, but leveling off to a saturation value, intensity noise just becomes topmost part in source noise.

Suppress the intensity noise in optical fibre gyro light source, effectively can improve the signal to noise ratio (S/N ratio) of optical fibre gyro, thus improve the accuracy of detection of optical fibre gyro, significant to the practical application realizing optical fibre gyro.At present, optical fibre gyro intensity noise suppression technology method mainly contains: intensity noise cancellation techniques scheme, adopt high speed intensity modulator scheme and subtract each other compensation technique scheme etc.

In these methods, the scheme adopting high speed intensity modulator is a kind of method that Application comparison is many in recent years, as shown in Figure 1, this restraining device mainly comprises the structure of the device that a kind of intensity noise that this method provides suppresses: the servo controller in light light source, intensity modulator, coupling mechanism, photo-detector and high broadband.The principle of work of this restraining device is as follows: intensity modulator is at a high speed placed between optical fiber source and coupling mechanism, and the light signal sent from light light source arrives intensity modulator, and intensity modulator is modulated the light signal received; Intensity modulator is by the light output through ovennodulation to coupling mechanism, and a part of light that coupling mechanism separates is detected by photo-detector, and photo-detector carries out sampling to the light signal received and obtains current signal and be converted to voltage signal.Voltage signal outputs on the servo controller of high bandwidth by photo-detector, after this servo controller processes the voltage signal received, provides a negative feedback control signal to intensity modulator.Then, intensity modulator utilizes above-mentioned negative feedback control signal to suppress the intensity noise of subsequently received light signal.

Digital intensity noise Restrain measurement based on intensity modulator mainly comprises high speed intensity modulator, fiber coupler, photodetector, wave filter and broadband control circuit.The program mainly comprises: carry out sampling to the light signal of intensity modulator output and obtain voltage signal, demodulation is carried out to described voltage signal, produce control signal according to demodulation result, described control signal comprises the power control signal adjusted optical signal power and the modulated square wave signal adjusted the working point of intensity modulator.Described intensity modulator is modulated according to the power of control power signal to the light signal received in the control signal received, according to the modulated square wave signal in the control signal received, the working point of intensity modulator is adjusted, makes the working point of intensity modulator keep stable.There is following shortcoming in the program:

1) for the working point control of intensity modulator, the scheme detecting modulated square wave is employed.In the program, modulated square wave signal must be introduced.The introducing of this signal, can affect the inhibition for intensity noise when intensity modulator normally works, this modulated square wave signal is for the process of restraint speckle simultaneously, is also a kind of introducing of noise.For noise suppressing system, new noise of introducing has very large harm for system, even can cause the inefficacy of whole suppression system.

2) in the program, the closed loop Restrainable algorithms subproblem that intensity noise suppresses is more, the effect that close-loop feedback controls is also not obvious, simultaneously in closed loop Restrainable algorithms, do not consider the link of phase compensation, produce phase drift in causing closed loop to suppress, this phase drift directly causes the effect of restraint speckle in closed loop procedure well not played.

In the analog feedback control program of working strength modulator, the analog servomechanism circuit that high bandwidth servo loop uses, the structure of the program as shown in Figure 2.Can find out, this closed loop feedback scheme and the digital intensity noise Restrain measurement based on intensity modulator similar, but the program uses analog servomechanism controller, does not suppress intensity modulator simultaneously.As shown in Figure 3,301 and 302 what indicate is two operational amplifiers to the sketch of the servo loop in the program.The first order discharge circuit of servo control loop is that high-pass filtering is amplified, and only provides gain to frequency more than bias modulation frequency.In the frequency lower than bias modulation frequency, the gain of first order discharge circuit is very little, is determined by electric capacity C1, resistance R1 and resistance R3.The peak value of gain generally appears near bias modulation frequency, and is determined by resistance R1 and electric capacity C2.In order to make servo loop stablize, when total open-loop gain is more than 1, the gain of this one-level should remain constant.The second level discharge circuit of servo loop is similarly high-pass filtering and amplifies, and only provide gain to frequency more than bias modulation frequency, in the frequency lower than bias modulation frequency, signal gain is very little.There is two problems in the program:

1) Primary Component used in the program is intensity modulator, the major issue existed in its work is exactly the drifting problem of intensity modulator working point, the working point of this device is very easily subject to the impact of the environmental factor changes such as environment temperature, humidity and electromagnetic field, the drift of working point directly causes system to decline for intensity noise inhibition, control signal is unstable, even makes whole suppression thrashing.But do not use any technology to solve this problem in the program.

2) in the program, the control accuracy in analog servomechanism loop is lower, and the effect suppressed intensity noise is poor, and simultaneously owing to using mimic channel to control, change suppresses quite to bother during frequency range, needs to change whole servo control loop.

Summary of the invention

The present invention improves the digital closed loop scheme that the intensity noise based on intensity modulator suppresses, object is bad in order to solve the closed-loop precision occurred in current similar scheme, the problem of noise suppression effect difference, simultaneously, the present invention also reaches good noise suppression effect, improves the signal to noise ratio (S/N ratio) of optical fibre gyro light source.

The invention provides a kind of light source intensity noise based on intensity modulator and suppress digital double closed-loop method, based on the light source intensity noise Restrain measurement of existing intensity modulator, adopt the scheme of digital double closed-loop, use two closed loops, be used for respectively carrying out the suppression of intensity noise and the stable of intensity modulator working point, first closed loop working strength modulator carries out the suppression of intensity noise, second closed loop is used for the bias voltage of strength of stability modulator working point, or be called the offset operation point of strength of stability modulator, the offset operation of intensity modulator point is no longer drifted about, working stability.

The bias voltage of the second closed-loop stabilization intensity modulator working point in the present invention, carries out control two parts when comprising start job search point and work.

Start shooting job search point specifically: the bias voltage of intensity modulator is scanned, from-V _πscan V _π, V _πfor the half-wave voltage of intensity modulator, record the output voltage of photodetector during each scan values, find maximal value and the minimum value of the output voltage of photodetector, correspondence finds bias voltage V during the maximum Output optical power point of intensity modulator _b0maxwith bias voltage V during minimum Output optical power point _b0min, then start arranges the bias voltage V of intensity modulator _b0for:

$V_{b0}=\frac{1}{2}{V}_{b0\min }+\frac{1}{2}{V}_{b0\max }$

V _b0the desired output voltage of photodetector when the output voltage of corresponding photodetector is working point.

Carry out during work controlling specifically: the output voltage of Real-Time Monitoring photodetector, the desired output voltage of photodetector when the actual output voltage of photodetector and working point is compared, obtain corresponding bias voltage difference, the bias voltage difference obtained is fed back to intensity modulator, and the bias voltage of control intensity modulator is at [V _b0-a, V _b0+ b] in, wherein parameter a and b value are all within [0,0.5].

In the present invention, the first closed loop working strength modulator carries out the step of the suppression of intensity noise and is:

1st step, carries out pre-service to the light intensity signal that photodetector exports, and removes low-frequency component in light intensity signal and by light intensity signal digitizing;

2nd step, carries out filtering by the digital luminous intensity signal obtained, the phase stabilization of holding signal;

3rd step, carries out phase compensation to filtered digital luminous intensity signal, specifically: according to the time delay at centre frequency place, carries out time bias at full frequency band to filtered signal;

4th step, is converted to simulation light intensity signal by the digital luminous intensity signal after phase compensation, feeds back to the radio frequency control end of intensity modulator.

Advantage of the present invention and good effect are:

(1) the present invention adopts the intensity noise of the scheme of digital double closed-loop to optical fibre gyro light source to suppress, solve closed-loop precision bad, the problem of noise suppression effect difference, reach good noise suppression effect, improve the signal to noise ratio (S/N ratio) of optical fibre gyro light source, improve the performance of whole system, and use digital stream network loop in the present invention, change suppresses only to need the program changed in digital logic device can change suppression frequency range during frequency range;

(2) present invention uses new noise suppressing method, squelch can be made to reach preferably effect, greatly improve the effect of squelch, the phase delay of noise suppressing method controlled simultaneously and compensate, make whole system phase place to keep stable, make the impact of phase place on closed loop squelch drop to minimum;

(3) in the second closed loop of offset operation point control, present invention uses the method for average power, avoid the scheme that adds modulated square wave and intensity modulator is normally worked the impact that i.e. intensity noise suppresses; In offset operation point control, except not adding except modulation signal, the coefficient in the average power used can change according to the change of the requirement of controlled working point, and controlled intensity modulator can be made to be operated in minimum point, intermediate point and peak.

Accompanying drawing explanation

Fig. 1 is the structural representation adopting high speed intensity modulator to suppress light source intensity noise;

Fig. 2 is the analog feedback control program schematic diagram of working strength modulator;

Fig. 3 is the structural representation of servo control loop in the analog feedback control program of working strength modulator;

Fig. 4 is the principle schematic that light source intensity noise of the present invention suppresses digital double closed-loop method;

Fig. 5 is intensity modulator P-V curve map.

Embodiment

Below in conjunction with drawings and Examples, the present invention is described in further detail.

Light source intensity noise based on intensity modulator of the present invention suppresses digital double closed-loop method, adopt the scheme of digital double closed-loop, use two closed loops, be used for carrying out the suppression of intensity noise and the stable of intensity modulator working point respectively, and two have been carried out to similar scheme before improve greatly.First the present invention proposes a kind of new closed loop noise suppressing method, employ the design philosophy design noise suppressing method of optimization wave filter, noise suppressing system can be made to reach good effect.In the closed loop suppressing method used, add the link of signal phase delay compensation, make whole system phase place to keep stable, make the impact of phase place on closed loop squelch drop to minimum.This closed loop suppressing method can make the effect of closed loop squelch be greatly improved, and most noise can both be inhibited.Next the present invention is directed to intensity modulator offset operation point control loop and is optimized, and devises offset operation point close-loop feedback new departure.For needing the scheme adding modulated square wave to improve before, employing average power method, adding modulated square wave before avoiding in scheme and intensity modulator is normally worked the impact that i.e. intensity noise suppresses.Simultaneously by an initialized process, reduce fluctuating widely of bias voltage in the course of work as far as possible.

System used in the present invention is the digital double closed-loop intensity noise suppression system based on intensity modulator.What working strength modulator suppressed optical fibre gyro light source intensity noise has had certain application, the principal feature of the program is that working strength modulator carries out close-loop feedback control, by the output of adjusting strength modulator, reach the object suppressing light source intensity noise.

Due to rapidity and the convenience of digital closed loop, use the method for digital closed loop to carry out control intensity modulator, and then light source intensity noise is suppressed.Simultaneously, due in the course of work of intensity modulator, there will be the drift of working point, affect the work of intensity modulator, the present invention adopts the method for digital closed loop to carry out the drift of the working point of inhibition strength modulator equally, and therefore the present invention uses the method for digital double closed-loop to suppress the intensity noise of optical fibre gyro light source.

Light source intensity noise based on intensity modulator of the present invention suppresses digital double closed-loop side's ratio juris as shown in Figure 4.As shown in Figure 4, in the scheme of this two close cycles, the first closed loop obtains the strength signal of light source by photodetector, and by digital filtering and phase compensation process, obtain the value of feedback of digital closed loop, feed back to intensity modulator, realize suppressing the close-loop feedback of intensity noise by intensity modulator; Second closed loop obtains the strength signal of light source by photodetector, the power signal by intensity modulator is obtained by light intensity signal, and then by power detection method, obtain the burning voltage of the offset operation point of intensity modulator, and be added in intensity modulator, realize controlling the close-loop feedback of the offset operation point of intensity modulator.

Intensity noise suppressing method proposed by the invention comprises following step, and wherein, the 2nd step and the 3rd step realize in the servo controller in high broadband:

1st step, carries out pre-service to the light intensity signal that photodetector exports, and removes low-frequency component in light intensity signal and by light intensity signal digitizing.Suppression target due to intensity noise suppression is the high frequency noise content in light source, therefore when pre-service, by low frequency noise component filtering, avoids having an impact to follow-up signal process.Meanwhile, the light intensity signal exported due to photodetector is simulating signal, so must sample, obtains digital luminous intensity signal and is used for digital closed loop process.

2nd step, suppresses system by the digital luminous intensity signal obtained through pre-service by the noise servo of design, carries out digital filtering, with the phase stabilization of holding signal.Noise servo suppresses system i.e. filtering system.

This step noise servo suppresses the method for designing of system as follows:

Noise servo in this closed loop suppresses system to carry out fast closed-loop FEEDBACK CONTROL due to needs, and the phase delay therefore for system has very high requirement, needs to keep strict accurate phase-delay characteristic.The present invention uses the method for optimized design to carry out the design that noise servo suppresses system, and such method for designing can ensure phase-delay characteristic, makes phase delay minimum simultaneously, makes fast closed-loop FEEDBACK CONTROL become possibility.The method of optimal design is exactly the Distribution of Zeros position regulating filtering system, makes actual frequency response H (e ^{j ω}) and ideal frequency response H _d(e ^{j ω}) between absolute deviation minimum, ω represents angular frequency, and j represents imaginary part.Use Chebyshev to wait the so a kind of optimal-design method of ripple approximatioss in the embodiment of the present invention, adopt the criterion of " maximum error is minimum " to obtain best filtering system, and optimum solution is unique.Also can use other filtering algorithm, to the compensation of phase delay, as long as good filter effect can be reached, and phase place can be made to keep stable.

Chebyshev's equiripple approximation adopts Weighted approximation error E (e ^{j ω}) minimumly design the method for filtering system for starting point.

E(e ^jω)＝W(e ^jω)[H _d(e ^jω)-H(e ^jω)] (1)

In formula, W (e ^{j ω}) be weighting function, in the frequency range that tolerance is high, larger weighted value can be got, otherwise get less weighted value.For this filtering system, H (e ^{j ω}) can be expressed as

$H\left(e^{\mathrm{j\ω}}\right)=e^{-\frac{\mathrm{jM\ω}}{2}}\underset{k=0}{\overset{\frac{(M+1)}{2}-1}{\mathrm{\Σ}}}2h\left(k\right)\cos \left(\mathrm{\ω}(\frac{M}{2}-k)\right)---\left(2\right)$

This equation is the error equation of this filtering system, and wherein, M represents the sampling number before this filtering sampling, and h (k) represents the frequency response values at k point place.

Owing to can be ensured the phase propetry of filtering system by symmetry, so design can only be considered amplitude versus frequency characte and not consider phase-frequency characteristic.Therefore, can use replace H (e ^{j ω}), namely

$\hat{H}\left(e^{\mathrm{j\ω}}\right)=e^{-\frac{\mathrm{jM\ω}}{2}}\underset{k=0}{\overset{\frac{(M+1)}{2}-1}{\mathrm{\Σ}}}2h\left(k\right)\cos \left(\mathrm{\ω}(\frac{M}{2}-k)\right)---\left(3\right)$

Use this approximate error equation to calculate, use Lei meter Zi algorithm to calculate during calculating, obtain the transfer function H (z) of filtering system, z is complex variable.

3rd step, carries out phase compensation through Phase Compensation Algorithm again by the signal of filtering system.Due to the linear phase characteristic of this filtering system, phase delay is certain, so phase compensation can be converted into time bias at this.In the present invention, time bias part is realized by all-pass filter, namely on full frequency band, carries out certain phase place to signal advanced.By the phase delay of estimation filter system, and estimate the time delay at centre frequency place, carry out phase compensation for centre frequency, sampling all-pass filter carries out time bias, also can have good phase compensation effect in other frequency ranges that need suppress.

4th step, digital luminous intensity signal after phase compensation is intended (DAC) process by digital revolving die, be converted to simulation light intensity signal, feed back to radio frequency (RF) control end of intensity modulator, reach the object suppressing required frequency range intensity noise.

On the basis proposing new intensity noise suppressing method, present invention uses new intensity modulator offset operation point control scheme.Need before this new technology solves to add the shortcoming that modulated square wave just can carry out offset operation point control, avoid and add modulated square wave intensity modulator is normally worked the impact that i.e. intensity noise suppresses.The principle of the program is as follows:

Intensity modulator is made up of two Y waveguide, and principle of work is equivalent to Mach-Zehnder type interferometer, and during work, the working point of intensity modulator is very easily subject to the impact of environmental factor, there is the problem of drift.

The output signal function expression of intensity modulator is as follows:

This function representation intensity modulator output intensity and the relation between input light intensity and bias voltage.P _outit is the luminous power that intensity modulator exports; P _init is the luminous power of input; V _b0the bias voltage of working point, V _bmthe operating voltage of intensity modulator, i.e. modulation voltage when () is t t; V _πcanonical parameter and the half-wave voltage of intensity modulator, represent by the output of intensity modulator from maximum be transferred to minimum time required change magnitude of voltage; because outside environmental elements is as stable, that vibration causes operating point drift random phase shift.Therefore V is worked as _bmwhen () is zero t, when namely intensity modulator does not work, P-V relation curve as shown in Figure 5.In Fig. 5, horizontal ordinate represents bias voltage V _b, ordinate represents Output optical power P _out.

As seen from Figure 5, when intensity modulator is operated in Quad+ or Quad-, P-V curve approximation is in linearly, and now output power is the intermediate value of peak power and minimum power.At this moment operating voltage V is added _bmt (), the effect that operating voltage can be made to produce is similar to linearly, therefore should by the offset operation point control of intensity modulator at this place.The impact being subject to outside environmental elements due to intensity modulator can cause operating point drift, and therefore the present invention devises the stable closed loop of intensity modulator offset operation point.At this, the present invention uses the scheme of power measurement, without the need to adding low-frequency modulation signal, also would not affect the normal work of intensity modulator.Its principle of work is as described below:

Because the output signal function of intensity modulator is such as formula shown in (4), when intensity modulator is not started working, V _bmt the voltage of () is zero, above formula can be rewritten as:

Can know, as output voltage P _outobtain maximal value P _outmaxtime, the right of formula (5) obtains maximal value, now

Namely

Suppose k=0, bias voltage V during the maximum Output optical power point of intensity modulator can be obtained _b0maxvalue be

As output voltage P _outobtain minimum value P _outmintime, the right of formula (5) obtains minimum value, now

Namely

Suppose k=0, bias voltage V during the minimum Output optical power point of intensity modulator can be obtained _b0minfor

When intensity modulator is operated in desired linear work point, output power is the intermediate value of peak power output and minimum output power.Therefore, bias voltage value P corresponding when the present invention calculates linear work point according to following formula _{working point}as follows:

By P _outmaxand P _outminsubstitute into above formula can obtain:

Output signal function during working point is as follows:

By upper (13) and (14) two formulas, can obtain, when working point:

Can be solved by above formula, v when can solve working point further _b0value be

Can by V during working point _b0by V _b0minand V _b0maxrepresent:

$V_{b0}=\frac{1}{2}{V}_{b0\min }+\frac{1}{2}{V}_{b0\max }---\left(17\right)$

Therefore, to utilize the method for average power to carry out the step of intensity modulator offset operation point control as follows in the present invention:

The scheme that average power is measured is carried out intensity modulator offset operation point and is stablized, and carries out controlling two parts for a long time when comprising start job search point and work.

The process that start working point is found is as follows:

By servo controller, intensity modulator is carried out to the scanning of bias voltage, from-V _πscan V _π, arranging sweep spacing is 0.01V.V _πit is the half-wave voltage of intensity modulator.Sweep spacing can set as required, and the 0.01V arranged in the embodiment of the present invention can obtain operating bias voltage more accurately, and does not need the scan values recording much larger number.

In the process of bias voltage scanning, the magnitude of voltage that when recording each scan values, photodetector exports.The magnitude of voltage exported due to photodetector and the proportional relation of Output optical power of intensity modulator, therefore can obtain the Output optical power of intensity modulator indirectly by recording voltage value.By the magnitude of voltage that recording light electric explorer exports, maximal value and the minimum value of wherein photodetector output voltage can be obtained.These two points are the maximum Output optical power point P of intensity modulator _outmaxwith minimum Output optical power point P _outmin.

Then corresponding bias voltage V when can check in maximum Output optical power point and minimum Output optical power point _b0maxand V _b0min.Bias voltage V when can obtaining correct bias working point by the formula released (17) above _b0.

Scanning process of now starting shooting terminates, the V of output _b0be the bias voltage of correct working point, the bias voltage arranging intensity modulator start is V _b0.

During work, the process that servo controller carries out intensity modulator offset operation point stable is as follows:

Obtained the photodetector output voltage of the Output optical power of intensity modulator in working point and its correspondence by start scanning, operationally, by Real-Time Monitoring, obtain real-time photodetector output voltage.V is found by inquiry scan record _b0the output voltage of corresponding photodetector, using this voltage as the desirable output voltage of photodetector during working point.

The output voltage desirable by photodetector when real-time photodetector output voltage and working point compares, obtain the difference of actual output voltage and desired output voltage, corresponding bias voltage difference is obtained according to this difference, bias voltage difference is inputed to direct current (DC) end of intensity modulator as value of feedback, the bias voltage of control intensity modulator and V _b0between error remain in real time within a limit value, and then reach closed loop and adjust in real time.Such as, if the bias voltage of control intensity modulator is at [V _b0-a, V _b0+ b] in, wherein parameter a and b value are all within [0,0.5], can set according to specific needs.The proportional relation of Output optical power of the magnitude of voltage that photodetector exports and intensity modulator, can calculate the proportionate relationship between the output voltage of photodetector and the bias voltage of intensity modulator according to scanning record value before.After the actual output voltage obtaining photodetector, by the scanning record value before inquiry or according to the proportionate relationship calculated, bias voltage corresponding to the actual output voltage of photodetector and operating bias voltage V can be obtained _b0difference, by bias voltage difference the cutting in intensity modulator obtained, with the bias voltage of strength of stability modulator working point.

Claims (3)

1. the light source intensity noise based on intensity modulator suppresses a digital double closed-loop method, and adopt two closed loops, the first closed loop working strength modulator carries out the suppression of intensity noise; It is characterized in that: the second closed loop is used for the bias voltage of strength of stability modulator working point; The bias voltage of strength of stability modulator working point carries out control two parts when comprising start job search point and work;

Described start job search point, specifically: the bias voltage of intensity modulator is scanned, from-V _πscan V _π, V _πfor the half-wave voltage of intensity modulator, record the output voltage of photodetector during each scan values, find maximal value and the minimum value of the output voltage of photodetector, correspondence finds bias voltage V during the maximum Output optical power point of intensity modulator _b0maxwith bias voltage V during minimum Output optical power point _b0min; Then start arranges the bias voltage V of intensity modulator _b0for:

$V_{b0}=\frac{1}{2}{V}_{b0\min }+\frac{1}{2}{V}_{b0\max }$

V _b0the desired output voltage of photodetector when the output voltage of corresponding photodetector is working point;

Control during described work, specifically: the output voltage of Real-Time Monitoring photodetector, compare the desired output voltage of photodetector during actual output voltage and the working point of photodetector, obtain corresponding bias voltage difference, bias voltage difference is fed back to intensity modulator, and the bias voltage of control intensity modulator is at [V _b0-a, V _b0+ b] in, wherein parameter a and b value are all within [0,0.5].

2. a kind of light source intensity noise based on intensity modulator according to claim 1 suppresses digital double closed-loop method, and it is characterized in that, described working strength modulator carries out the suppression of intensity noise, and concrete steps are as follows:

1st step, carries out pre-service to the light intensity signal that photodetector exports, and removes low-frequency component in light intensity signal and by light intensity signal digitizing;

2nd step, carries out filtering by the digital luminous intensity signal obtained, the phase stabilization of holding signal;

3rd step, carries out phase compensation to filtered digital luminous intensity signal, specifically: according to the time delay at centre frequency place, carries out time bias at full frequency band to filtered signal;

4th step, is converted to simulation light intensity signal by the digital luminous intensity signal after phase compensation, feeds back to the radio frequency control end of intensity modulator.

3. a kind of light source intensity noise based on intensity modulator according to claim 1 and 2 suppresses digital double closed-loop method, and it is characterized in that, described scans the bias voltage of intensity modulator, and arranging sweep spacing is 0.01V.