CN104236537B - Light source intensity noise based on intensity modulator suppresses digital double closed-loop method - Google Patents

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

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CN104236537B
CN104236537B CN201410462716.3A CN201410462716A CN104236537B CN 104236537 B CN104236537 B CN 104236537B CN 201410462716 A CN201410462716 A CN 201410462716A CN 104236537 B CN104236537 B CN 104236537B
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intensity
intensity modulator
modulator
noise
bias voltage
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CN104236537A (en
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李立京
郑月
魏超
杨德伟
张春熹
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Beihang University
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    • GPHYSICS
    • G01MEASURING; TESTING
    • G01CMEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C19/00Gyroscopes; Turn-sensitive devices using vibrating masses; Turn-sensitive devices without moving masses; Measuring angular rate using gyroscopic effects
    • G01C19/58Turn-sensitive devices without moving masses
    • G01C19/64Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams
    • G01C19/72Gyrometers using the Sagnac effect, i.e. rotation-induced shifts between counter-rotating electromagnetic beams with counter-rotating light beams in a passive ring, e.g. fibre laser gyrometers
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01CMEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C25/00Manufacturing, calibrating, cleaning, or repairing instruments or devices referred to in the other groups of this subclass

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  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The present invention is that a kind of light source intensity noise based on intensity modulator suppresses digital double closed-loop method, belongs to fiber-optics gyroscope field.This method carries out the suppression of intensity noise and the stabilization of intensity modulator operating point using digital double closed-loop loop;When intensity noise suppresses, the light intensity signal that photodetector is exported is pre-processed, digitized, is filtered and phase compensation after, then simulated feed back to intensity modulator;During the offset operation point of strength of stability modulator, bias voltage when obtaining intensity modulator maximum output luminous power point and minimum Output optical power point by scanning bias voltage, the bias voltage of operating point is obtained using mean power method, and intensity modulator is fed back to by the output voltage acquisition bias voltage difference for gathering photodetector in real time.It is bad that the present invention solves closed-loop precision, the problem of noise suppression effect is poor, improves the signal to noise ratio of optical fibre gyro light source, the offset operation point of intensity modulator is no longer drifted about, working stability.

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, and in particular to optical fibre gyro is made an uproar with the intensity of superfluorescent fiber sources The suppression technology of sound, and in particular to a kind of light source intensity noise based on intensity modulator suppresses digital double closed-loop method.
Background technology
Optical fibre gyro is as a kind of extremely rapid new inertia angular-rate sensor of development, in increasing field Inertia device is selected as main, the main direction of studying as inertia device of future generation.Optical fibre gyro except with movement-less part, Outside advantage without error caused by acceleration, an important difference of itself and traditional electro-mechanical gyro is to there is larger optics to make an uproar Sound, and wherein a kind of main noise is the noise that wide spectrum light source is brought.
The noise of optical fibre gyro directly affects the performance indications such as the random walk coefficient of optical fibre gyro, zero inclined unstability, And the minimum detection sensitivity of optical fibre gyro is directly decide, so the noise progress suppression to optical fibre gyro is extremely important 's.
The noise of the wide spectrum light source of optical fibre gyro mainly includes thermal noise, shot noise and intensity noise.Intensity noise is Due to caused by the beat frequency of wide spectrum light source, be due to wide spectrum light source various Fourier (Fourier) component between beat frequency draw The additional noise risen, its size increases with the increase of the light intensity of light source.The size and light source output power of intensity noise Size be directly proportional, when light source power exceed certain value when, intensity noise just exceed shot noise and thermal noise, at this moment, noise Than that no longer will be improved with the increase of luminous power, but level off to a saturation value, intensity noise just turns into source noise Topmost part.
Suppress the intensity noise in optical fibre gyro light source, the signal to noise ratio of optical fibre gyro can be effectively improved, so as to improve The accuracy of detection of optical fibre gyro, to realizing that the practical application of optical fibre gyro is significant.At present, optical fibre gyro intensity noise Suppression technology method mainly has:Intensity noise cancellation techniques scheme, using high speed intensity modulator scheme and subtract each other compensation technique Scheme etc..
In these methods, it is to apply a kind of more methods in recent years using the scheme of high speed intensity modulator, this The structure for the device that a kind of intensity noise that the method for kind is provided suppresses is as shown in figure 1, the restraining device mainly includes:Light light Source, intensity modulator, coupler, the servo controller in photo-detector and high broadband.The operation principle of the restraining device is as follows:It is high The intensity modulator of speed is placed between optical fiber source and coupler, and the optical signal sent from light light source reaches intensity modulator, Intensity modulator is modulated to the optical signal received;Intensity modulator is by the light output through ovennodulation to coupler, coupling A part of light that device is separated is detected by photo-detector, and photo-detector sample obtaining current signal to the optical signal received And be converted to voltage signal.Voltage signal is output on the servo controller of high bandwidth by photo-detector, the servo controller pair The voltage signal received handled after there is provided a negative feedback control signal to intensity modulator.Then, intensity modulator Suppress the intensity noise of subsequently received optical signal using above-mentioned negative feedback control signal.
Digital intensity noise Restrain measurement based on intensity modulator mainly includes high speed intensity modulator, fiber coupling Device, photodetector, wave filter and broadband control circuit.The program mainly includes:The optical signal that intensity modulator is exported is entered Row sampling obtains voltage signal, and the voltage signal is demodulated, and control signal, the control letter are produced according to demodulation result Number include the tune that the power control signal that is adjusted to optical signal power and the operating point to intensity modulator are adjusted Square-wave signal processed.Control power signal of the intensity modulator in the control signal received is to the optical signal that receives Power be modulated, the modulated square wave signal in the control signal received is carried out to the operating point of intensity modulator Adjustment, makes the operating point of intensity modulator keep stable.The program has the disadvantage that:
1) for the working point control of intensity modulator, the scheme of detection modulated square wave has been used.In the program, it is necessary to Introduce modulated square wave signal.The introducing of the signal, can influence suppression during intensity modulator normal work for intensity noise to imitate Really, it is also a kind of introducing of noise while the modulated square wave signal is for suppressing the process of noise.For noise suppressed system For system, the new noise that introduces has very big harm for system, results even in the failure of whole suppression system.
2) in the program, the closed loop restrainable algorithms subproblem that intensity noise suppresses is more, the effect of closed loop feedback control Not substantially, while in closed loop restrainable algorithms, not considering the link of phase compensation, closed loop is caused to produce phase drift in suppressing Move, the effect that the phase drift directly results in suppression noise in closed loop procedure is not played well.
In the analog feedback control program of use intensity modulator, the analog servomechanism circuit that high bandwidth servo loop is used, The structure of the program is as shown in Figure 2.As can be seen that the closed loop feedback scheme and the digital intensity noise suppression based on intensity modulator Scheme processed is similar, but the program uses analog servomechanism controller, while not suppressing to intensity modulator.The party The sketch of servo loop in case is as shown in figure 3,301 and 302 indicated is two operational amplifiers.Servo control loop First order discharge circuit amplifies for high-pass filtering, only provides gain to frequency more than bias modulation frequency.Adjusted less than biasing In the frequency of frequency processed, the gain very little of first order discharge circuit is determined by electric capacity C1, resistance R1 and resistance R3.The peak of gain Value is generally present near bias modulation frequency, and is determined by resistance R1 and electric capacity C2.In order that servo loop is stable, when total When 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 Filter and amplification, only provides gain to frequency more than bias modulation frequency, in the frequency less than bias modulation frequency, and signal increases Beneficial very little.The program has two:
1) Primary Component used in the program is intensity modulator, and major issue present in its work is exactly that intensity is adjusted The drifting problem of device operating point processed, the operating point of the device is highly prone to the change of the environmental factors such as environment temperature, humidity and electromagnetic field The influence of change, the drift of operating point directly results in system and declined for intensity noise inhibition, and control signal is unstable, even Whole suppression system is set to fail.But any technology is not used in the program to solve this problem.
2) control accuracy in analog servomechanism loop is relatively low in the program, and the effect suppressed to intensity noise is poor, while by In using analog circuit to be controlled, change suppresses fairly cumbersome during frequency range, it is necessary to be carried out to whole servo control loop Change.
The content of the invention
The present invention is improved to the digital closed loop scheme that the intensity noise based on intensity modulator suppresses, in order to The closed-loop precision for solving to occur in similar scheme at present is bad, the problem of noise suppression effect is poor, meanwhile, the present invention also reach compared with Good noise suppression effect, improves the signal to noise ratio of optical fibre gyro light source.
Suppress digital double closed-loop method the invention provides a kind of light source intensity noise based on intensity modulator, based on existing There is the light source intensity noise Restrain measurement of intensity modulator, using the scheme of digital double closed-loop, use two closed loops, difference For carrying out the suppression of intensity noise and the stabilization of intensity modulator operating point, the first closed loop use intensity modulator is carried out The suppression of intensity noise, the second closed loop is used for the bias voltage of strength of stability modulator operating point, or is strength of stability The offset operation point of modulator, makes the offset operation point of intensity modulator no longer drift about, working stability.
The bias voltage of second closed-loop stabilization intensity modulator operating point in the present invention, including start job search point and work As when be controlled two parts.
Start job search point be specifically:The bias voltage of intensity modulator is scanned, from-VπScan Vπ, VπFor The half-wave voltage of intensity modulator, the output voltage of photodetector when recording each scan values, finds the defeated of photodetector Go out the maximum and minimum value of voltage, correspondence finds bias voltage V during intensity modulator maximum output luminous power pointb0maxMost Bias voltage V during small Output optical power pointb0min, then start shooting and the bias voltage V of intensity modulator be setb0For:
Vb0The desired output voltage of photodetector when the output voltage of corresponding photodetector is operating point.
It is controlled specifically during work:The output voltage of photodetector is monitored in real time, by the reality of photodetector The desired output voltage of photodetector is compared when output voltage is with operating point, obtains corresponding bias voltage difference, will Obtained bias voltage difference feeds back to intensity modulator, controls the bias voltage of intensity modulator in [Vb0-a,Vb0+ b] in, Wherein parameter a and b values are within [0,0.5].
It is the step of the suppression of the first closed loop use intensity modulator progress intensity noise in the present invention:
1st step, is pre-processed to the light intensity signal that photodetector is exported, and the low-frequency component in removal light intensity signal is simultaneously Light intensity signal is digitized;
2nd step, obtained digital luminous intensity signal is filtered, and keeps the phase stabilization of signal;
3rd step, phase compensation is carried out to filtered digital luminous intensity signal, is specifically:According to the time at centre frequency Delay, time bias is carried out in 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 intensity modulated The radio frequency control end of device.
Advantages of the present invention is with good effect:
(1) present invention is suppressed using the scheme of digital double closed-loop to optical fibre gyro with the intensity noise of light source, is solved Closed-loop precision is bad, the problem of noise suppression effect is poor, reaches preferable noise suppression effect, improves optical fibre gyro light source Signal to noise ratio, improves the performance of whole system, and digital stream network loop is used in the present invention, and change suppresses only to need during frequency range The program changed in digital logic device can be changed to suppressing frequency range;
(2) present invention uses new noise suppressing method, noise suppressed can be made to reach preferably effect, greatly carried The high effect of noise suppressed, while the phase delay to noise suppressing method is controlled and compensated so that whole system Kept in phase stable so that influence of the phase to closed loop noise suppressed is minimized;
(3) in the second closed loop that offset operation point is controlled, present invention uses the method for mean power, it is to avoid The scheme for adding modulated square wave is the influence of intensity noise suppression for intensity modulator normal work;In the control of offset operation point In, in addition to being added without modulated signal, the coefficient in used mean power can be according to the requirement of controlled operating point Change and change, controlled intensity modulator can be made to be operated in minimum point, intermediate point and peak.
Brief description of the drawings
Fig. 1 is the structural representation for suppressing light source intensity noise using high speed intensity modulator;
Fig. 2 is the analog feedback control program schematic diagram of use intensity modulator;
Fig. 3 be use intensity modulator analog feedback control program in servo control loop structural representation;
Fig. 4 is that the light source intensity noise of the present invention suppresses the principle schematic of digital double closed-loop method;
Fig. 5 is intensity modulator P-V curve maps.
Embodiment
Below in conjunction with drawings and examples, the present invention is described in further detail.
The light source intensity noise based on intensity modulator of the present invention suppresses digital double closed-loop method, using digital double closed-loop Scheme, using two closed loops, be respectively intended to carry out suppression and the stabilization of intensity modulator operating point of intensity noise, and Two big improvement have been carried out to similar scheme before.The present invention proposes a kind of new closed loop noise suppressing method first, uses The design philosophy design noise suppressing method of wave filter is optimized, the noise suppressing system is reached preferable effect.Institute In the closed loop suppressing method used, the link of signal phase delay compensation is added so that keep stable in whole system phase, So that influence of the phase to closed loop noise suppressed is minimized.The closed loop suppressing method can obtain the effect of closed loop noise suppressed To very big raising, most noises can be inhibited.Secondly the present invention is directed to the point control of intensity modulator offset operation Loop processed is optimized, and devises offset operation point closed loop feedback new departure.Side for needing addition modulated square wave before Case is improved, used mean power method, it is to avoid before add modulated square wave in scheme for intensity modulator just Normal work is the influence that intensity noise suppresses.Simultaneously by the process of an initialization, reduce in the course of work and bias as far as possible Voltage fluctuates widely.
System used in the present invention is the digital double closed-loop intensity noise suppression system based on intensity modulator.Using strong What degree modulator suppressed optical fibre gyro light source intensity noise had certain application, and the program is mainly characterized by using strong Spend modulator and carry out closed loop feedback control, by the output of adjusting strength modulator, reach the purpose for suppressing light source intensity noise.
Due to the rapidity and convenience of digital closed loop, intensity modulator is controlled using the method for digital closed loop, and then Light source intensity noise is suppressed.Simultaneously as in the course of work of intensity modulator, it may appear that the drift of operating point, shadow The work of intensity modulator is rung, it is equally utilized in the present invention that the method for digital closed loop carrys out the drift of the operating point of inhibition strength modulator Move, therefore the present invention suppresses the intensity noise of optical fibre gyro light source using the method for digital double closed-loop.
The light source intensity noise based on intensity modulator of the present invention suppresses principle such as Fig. 4 institutes of digital double closed-loop method Show.As shown in figure 4, in the scheme of the two close cycles, the first closed loop obtains the strength signal of light source by photodetector, and passes through Digital filtering and phase compensation processing, obtain the value of feedback of digital closed loop, feed back to intensity modulator, real by intensity modulator Now the closed loop feedback to intensity noise suppresses;Second closed loop obtains the strength signal of light source by photodetector, passes through light intensity Signal obtains the power signal by intensity modulator, and then by power detection method, obtains the biasing work of intensity modulator Make the burning voltage of point, and be added in intensity modulator, realize the closed loop feedback control to the offset operation point of intensity modulator.
Intensity noise suppressing method proposed by the invention includes following steps, wherein, the 2nd step and the 3rd step be Realized in the servo controller in high broadband:
1st step, is pre-processed to the light intensity signal that photodetector is exported, and the low-frequency component in removal light intensity signal is simultaneously Light intensity signal is digitized.It is the high frequency noise content in light source due to the suppression target that intensity noise suppresses, therefore is locating in advance During reason, low frequency noise component is filtered out, it is to avoid influence is produced on follow-up signal processing.Simultaneously as photodetector output Light intensity signal is analog signal, so must be sampled, obtains digital luminous intensity signal for digital closed loop processing.
2nd step, by the digital luminous intensity signal obtained by pretreatment by the noise servo suppression system of design, enters line number Word is filtered, to keep the phase stabilization of signal.I.e. noise servo suppression system filtering system.
The design method of this step noise servo suppression system is as follows:
Noise servo suppression system in the closed loop carries out fast closed-loop feedback control due to needing, therefore for system Phase delay has very high requirement, it is necessary to keep strict accurate phase-delay characteristic.The present invention uses optimized design Method carries out the design of noise servo suppression system, and such design method can ensure phase-delay characteristic, while making phase Position delay is minimum so that fast closed-loop feedback control is possibly realized.The method of optimal design is exactly the zero point for adjusting filtering system Distributing position so that actual frequency response H (e) and ideal frequency response Hd(e) between absolute deviation it is minimum, ω is represented Angular frequency, j represents imaginary part.Such a optimal design side of the ripple approximatioss such as Chebyshev is used in the embodiment of the present invention Method, optimal filtering system is obtained using the criterion of " worst error is minimum ", and optimum solution is unique.Other filters can also be used Ripple algorithm, the compensation to phase delay as long as preferable filter effect can be reached, and can make phase keep stable.
Chebyshev's equiripple approximation is to use Weighted approximation error E (e) minimum starting point design filtering system Method.
E(e)=W (e)[Hd(e)-H(e)] (1)
In formula, W (e) it is weighting function, in the high frequency range of tolerance, larger weighted value can be taken, is otherwise taken Less weighted value.For this filtering system, H (e) can be expressed as
The equation is the error equation of the filtering system, wherein, M represents the sampled point before this filtering sampling Number, h (k) represents the frequency response values at k points.
Due to the phase characteristic of filtering system can be ensured by symmetry, so design can only consider amplitude versus frequency characte Without considering phase-frequency characteristic.Therefore, it is possible to useTo replace H (e), i.e.,
Calculated using the approximate error equation, calculated, filtered using Lei meter Zi algorithms during calculating System transter H (z), z are complex variable.
3rd step, phase compensation is carried out by the signal of filtering system by Phase Compensation Algorithm again.Due to the filtering system Linear phase characteristic, phase delay is certain, so phase compensation can be converted into time bias herein.In the present invention In, time bias part is realized by all-pass filter, i.e., it is advanced to carry out certain phase to signal on full frequency band.By estimating The phase delay of filter system is calculated, and estimates the time delay at centre frequency, phase compensation is carried out for centre frequency, adopts Sample all-pass filter carries out time bias, can also have preferable phase compensation effect in other frequency ranges that need to suppress.
4th step, intends (DAC) processing by digital revolving die by the digital luminous intensity signal after phase compensation, is converted to mould Intend light intensity signal, feed back to radio frequency (RF) control end of intensity modulator, reach the purpose of frequency range intensity noise required for suppressing.
On the basis of new intensity noise suppressing method is proposed, present invention uses new intensity modulator offset operation Point control program.The new technology needs addition modulated square wave to be just biased the shortcoming of working point control before solving, keep away Exempt to add the influence that modulated square wave suppresses intensity modulator normal work i.e. intensity noise.The principle of the program is as follows:
Intensity modulator is made up of double Y waveguides, and operation principle is equivalent to Mach-Zehnder type interferometers, during work, by force The operating point of degree modulator is highly prone to the influence of environmental factor, the problem of there is drift.
The output signal function expression of intensity modulator is as follows:
Relation between this function representation intensity modulator output intensity and input light intensity and bias voltage.PoutIt is The luminous power of intensity modulator output;PinIt is the luminous power of input;Vb0It is the bias voltage of operating point, Vbm(t) when being t The operating voltage of intensity modulator, i.e. modulation voltage;VπIt is the canonical parameter i.e. half-wave voltage of intensity modulator, represents intensity The output of modulator from maximum be transferred to minimum when required change magnitude of voltage;It is due to that outside environmental elements are such as stable, shakes It is dynamic to cause the random phase shift of operating point drift.Therefore V is worked asbm(t) when being zero, i.e., when intensity modulator does not work, P-V relation curves As shown in Figure 5.In Fig. 5, abscissa represents bias voltage Vb, ordinate represents Output optical power Pout
As seen from Figure 5, when intensity modulator is operated in Quad+ or Quad-, P-V curve approximations in linear, this When power output be peak power and minimum power median.At this moment operating voltage V is addedbm(t) operating voltage can, be caused Produced effect is similar to linearly, therefore should be by the offset operation point control of intensity modulator in this place.Because intensity is adjusted Device processed is influenceed that operating point drift can be caused by outside environmental elements, therefore the present invention devises intensity modulator offset operation The stable closed loop of point.Here, the present invention, without adding low-frequency modulation signal, also would not using the scheme of power measurement Influence the normal work of intensity modulator.Its operation principle is as described below:
Due to shown in the output signal function such as formula (4) of intensity modulator, when intensity modulator is not started working, Vbm (t) voltage is zero, and above formula can be rewritten as:
It is recognised that as output voltage PoutObtain maximum PoutmaxWhen, the right of formula (5) obtains maximum, now
I.e.
Assuming that k=0, can obtain bias voltage V during intensity modulator maximum output luminous power pointb0maxValue be
As output voltage PoutObtain minimum value PoutminWhen, the right of formula (5) obtains minimum value, now
I.e.
Assuming that k=0, can obtain bias voltage V during intensity modulator minimum Output optical power pointb0minFor
When intensity modulator is operated in desired linear work point, power output is peak power output and minimum output The median of power.Therefore, the present invention calculates corresponding bias voltage value P during linear work point according to following formulaOperating pointIt is as follows:
By PoutmaxAnd PoutminSubstituting into above formula can obtain:
Output signal function during operating point is as follows:
By upper (13) and (14) two formulas, it can obtain, at operating point:
It can be solved by above formula,V when can further solve operating pointb0Value be
Can be by V during operating pointb0By Vb0minAnd Vb0maxTo represent:
Therefore, the step of present invention is controlled using the method progress intensity modulator offset operation point of mean power is as follows:
The scheme of mean power measurement carries out intensity modulator offset operation point stabilization, including start job search point and work Two parts of control for a long time are carried out when making.
The process that start operating point is found is as follows:
The scanning of voltage is biased to intensity modulator by servo controller, from-VπScan Vπ, sweep spacing is set For 0.01V.VπIt is the half-wave voltage of intensity modulator.Sweep spacing can be set as needed, be set in the embodiment of the present invention 0.01V can obtain accurate operating bias voltage, and need not record the scan values of much larger number.
During bias voltage is scanned, the magnitude of voltage that photodetector is exported when recording each scan values.Due to light The magnitude of voltage relation proportional to the Output optical power of intensity modulator of electric explorer output, therefore recording voltage value can be passed through The Output optical power of intensity modulator is obtained indirectly.By recording the magnitude of voltage that photodetector is exported, wherein light can be obtained The maximum and minimum value of electric explorer output voltage.The two points are the maximum output luminous power point of intensity modulator PoutmaxWith minimum Output optical power point Poutmin
Then correspond to bias voltage V when can check in maximum output luminous power point and minimum Output optical power pointb0maxWith Vb0min.Bias voltage V when can obtain correct bias operating point by the formula (17) released aboveb0
Now start scanning process terminates, the V of outputb0The bias voltage of as correct operating point, sets intensity modulated The bias voltage of device start is Vb0
During work, it is as follows that servo controller carries out the stable process of intensity modulator offset operation point:
Output optical power of the intensity modulator in operating point photodetector corresponding with its is obtained by scanning of starting shooting defeated Go out voltage, operationally, by monitoring in real time, obtain real-time photodetector output voltage.Looked for by inquiry scan record To Vb0The output voltage of corresponding photodetector, regard the voltage as the preferable output voltage of photodetector during operating point.
The preferable output voltage of photodetector is compared during by real-time photodetector output voltage with operating point Compared with, the difference of actual output voltage and desired output voltage is obtained, corresponding bias voltage difference is obtained according to the difference, will be inclined Direct current (DC) end that voltage difference inputs to intensity modulator as value of feedback is put, the bias voltage and V of intensity modulator is controlledb0 Between error be maintained in real time within a limit value, and then reach that closed loop is adjusted in real time.For example, setting control intensity modulated The bias voltage of device is in [Vb0-a,Vb0+ b] in, wherein parameter a and b values can be come according to specific needs within [0,0.5] Setting.The magnitude of voltage relation proportional to the Output optical power of intensity modulator of photodetector output, according to scanning before Record value can calculate the proportionate relationship between the output voltage of photodetector and the bias voltage of intensity modulator.Obtaining After the actual output voltage of photodetector, the ratio obtained by the scanning record value before inquiry or according to calculating is closed System, can obtain the corresponding bias voltage of actual output voltage and operating bias voltage V of photodetectorb0Difference, will To bias voltage difference cutting in intensity modulator, with the bias voltage of strength of stability modulator operating point.

Claims (2)

1. a kind of light source intensity noise based on intensity modulator suppresses digital double closed-loop method, using two closed loops, the One closed loop use intensity modulator carries out the suppression of intensity noise;It is characterized in that:Second closed loop is used for stable strong Spend the bias voltage of modulator operating point;The bias voltage of strength of stability modulator operating point includes start job search point and work As when be controlled two parts;
Described start job search point, be specifically:The bias voltage of intensity modulator is scanned, from-VπScan Vπ, VπFor the half-wave voltage of intensity modulator, the output voltage of photodetector, finds photodetector when recording each scan values Output voltage maximum and minimum value, bias voltage V when correspondence finds intensity modulator maximum output luminous power pointb0max Bias voltage V during with minimum Output optical power pointb0min;Then start sets the bias voltage V of intensity modulatorb0For:
Vb0The desired output voltage of photodetector when the output voltage of corresponding photodetector is operating point;
It is controlled during described work, is specifically:The output voltage of monitoring photodetector, compares photodetector in real time The desired output voltage of photodetector when actual output voltage is with operating point, obtains corresponding bias voltage difference, will bias Voltage difference feeds back to intensity modulator, controls the bias voltage of intensity modulator in [Vb0-a,Vb0+ b] in, wherein parameter a and B values are within [0,0.5];
Described use intensity modulator carries out the suppression of intensity noise, comprises the following steps that:
1st step, is pre-processed to the light intensity signal that photodetector is exported, the low-frequency component in removal light intensity signal and by light Strong signal digitlization;
2nd step, obtained digital luminous intensity signal is filtered, and keeps the phase stabilization of signal;
3rd step, phase compensation is carried out to filtered digital luminous intensity signal, is specifically:According to the time delay at centre frequency, Time bias is carried out to filtered signal in full frequency band;
4th step, is converted to simulation light intensity signal by the digital luminous intensity signal after phase compensation, feeds back to intensity modulator Radio frequency control end.
2. a kind of light source intensity noise based on intensity modulator according to claim 1 suppresses digital double closed-loop method, Characterized in that, the bias voltage to intensity modulator is scanned, setting sweep spacing is 0.01V.
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