CN102353341A - Phase-modulating synchronous-integral phase-shifting interference-measuring method and device - Google Patents

Abstract

The invention belongs to an optical testing technology. In order to monitor and control a phase-modulating degree in real time and realize the high-precision dynamic measurement for the surface topography of an optical lens, the wave aberration of the optical lens, an optical transfer function and the like, the invention adopts a phase-modulating synchronous-integral phase-shifting interference-measuring method and device, and has the technical scheme that the phase-modulating synchronous-integral phase-shifting interference-measuring method comprises the following steps of: driving a laser device to generate laser by adopting a laser-device driver, enabling the laser to reach a measuring mirror after sequentially passing through a focusing lens, a semi-transmitting semi-reflecting mirror, a beam-expanding and collimating lens, a small semi-transmitting semi-reflecting mirror and a reference mirror, sending the reflected signal of the small semi-transmitting semi-reflecting mirror into a PD (Photoelectric Detector), and finally sending the reflected signal of the semi-transmitting semi-reflecting mirror to a computer for processing after entering a video camera; and carrying out the measurement and the stabilization of the phase-modulating degree and the synchronous control of phase differences theta according to a formula that phase information is only related to the phase differences theta among a CCD (Charge-Coupled Device)-camera measuring signal, the phase-modulating degree z, a CCD-camera exposure signal and a phase-modulating signal and phase-modulating coefficients m. The method and the device are mainly applied to optical testing.

Description

Phase modulation (PM) synchronous integration phase shift interference measuring method and device

Technical field

The invention belongs to optical testing technology, relate to advanced optical instrument manufacturing, specifically relate to phase modulation (PM) synchronous integration phase shift interference measuring method and device.

Background technology

Optical interference detects and is divided into interference (like equal inclination interference and equal thickness interference) in general sense, difference interference and accurate difference interference.The general interference because precision is not high, poor stability is difficult to optical surface and detects.Difference interference needs the high light source of frequency difference degree of stability, and it is very big to handle the measurement data amount, lacks the measurement of full field ability, is used for the high-precision dot information measurement more.Accurate difference interference is called phase shift interference again, and it has also reduced the requirement to light source through stepping or phase shift continuously when suppressing environmental interference, and along with the development of photoelectron technology and integrated circuit technique, the measurement of high precision whole audience phase shift interference is achieved.The phase shift mode comprises the piezoelectric crystal method, photoelectric crystal method, polarization phase-shifting method, doppler shift method, magneto-optical method, liquid crystal Method and rotation optical flat method etc., but all has hysteresis, shortcomings such as non-linear and mechanical vibration.Laser instrument internal modulation phase-shifting technique has overcome above-mentioned shortcoming, is used widely.It utilizes the characteristic of the output optical frequency variation of laser instrument to carry out the respective phase adjusting, and it is simple to have method, insensitive to vibrating, and reduces advantages such as environmental requirement, but also has frequency drift, shortcomings such as output intensity variation.The stepping phase shift is of long duration, and it is directly perceived to find the solution the phase method for position through least square method, but responsive to phase displacement error, its measuring accuracy is mainly determined by phase-shifter.Continuous phase is adjusted to and overcomes spectrum leakage and light intensity variation, is main with sinusoidal phase modulation, also derives various algorithms simultaneously.

People such as Osami Sasaki proposed sinusoidal phase modulation synchronous integration algorithm (integrating-bucket method) and were applied to interferometry [1] in 1986.Through piezoelectric ceramic sinusoidal phase modulation (PM) and CCD camera synchronization integration, the control system parameter obtains the PHASE DISTRIBUTION figure of body surface, and precision reaches 1.0-1.5nm.Arnaud Dubois proposes 4 step synchronous integration algorithms [2] in calendar year 2001; One-period is divided into four sections, in four sections, respectively light intensity is carried out integration, analyzed the influence of shot noise and quantizing noise simultaneously measuring accuracy; Through optimizing, precision has reached 1nm.Takamasa Suzuki etc. are at the height [3] on use dual laser cooperation synchronous integration algorithm scaffold tower rank in 2002, and relative accuracy is better than 1.5%.Yu-Lung Lo etc. measured [4] to main shaft and phase delay with the synchronous integration algorithm application in 2006 in whole audience heterodyne system polariscope system; It is sinusoidal wave as modulation signal that they adopt sawtooth wave to replace; 3 step synchronous integration algorithms have been proposed thus; Only need integration can obtain the tangent value of phase place for three times; Striped degree of stability and measuring accuracy all near 4 step synchronous integration algorithms, have reduced calculated amount.Yuankai K.Tao etc. adopted N step synchronous integration algorithm [5] and in the limit of integration, have added the time delay of CCD camera in 2008.2010, Dongmei Guo used 4 step synchronous integration algorithms with synchronous integration algorithm application [6] in the self-mixed interference appearance, adds the closed loop phase control, and precision has reached 0.15nm.

The above results shows the continuous phase-shift method strong anti-interference performance of sinusoidal phase modulation, can realize kinetic measurement, and precision reaches Subnano-class, but the measurement of phase modulation (PM) degree and stable rare research, and this key of sinusoidal phase modulation just.

[1]Osami?Sasaki，Hirokazu?Okazaki，Makoto?Sakai，“Sinusoidal?phase?modulating?interferometer?using?the?integrating-bucket?method”，APPLIED?OPTIC，1987，Vol.26，No.6：1089-1093

[2]Arnaud?Dubois，“Phase-map?measurements?by?interferometry?with?sinusoidal?phase?modulation?and?four?mtegrating?buckets”，J.Opt.Soc..Am.A，2001，Vol.18，No.8：1972-1979.

[3]Takamasa?Suzuki，Takayuki?Yazawa，Osami?Sasaki，“Two-wavelength?laser?diode?interferometer?with?time-sharing?sinusoidal?phase?modulation”，APPLIED?OPTICS，2002，Vol.41，No.10：1972-1976.

[4]Yu-Lung?Lo，Hung-Wei?Chih，Cheng-Yen?Yeh，Tsung-Chih?Yu，“Full-field?heterodyne?polariscope?with?an?image?signal?processing?method?for?principal?axis?and?phase?retardation?measurements”，APPLIED?OPTICS，2006，Vol.45，No.31：8006-8012.

[5]Yuankai?K.Tao，Mingtao?Zhao，Joseph?A.Izatt.“High-speed?complex?conjugate?resolved?retinal?spectral?domain?optical?coherence?tomography?using?sinusoidal?phase?modulation”，OPTICS?LETTERS，2009，Vol.32，No.20：2918-2920.

[6]Dongmei?Guo，Ming?Wang，“Self-mixing?interferometry?based?on?sinusoidal?phase?modulation?and?integrating-bucket?method”，Optics?Communications，2010，283：2186-2192.

Summary of the invention

For overcoming the deficiency of prior art, on the basis of traditional phase shift interference technology, develop new phase shift interference measuring technique.Phase modulation (PM) degree survey control technology is introduced in the sinusoidal phase modulation synchronous integration phase shift interference measuring technique; Monitor in real time and the control phase degree of modulation; Realize the sinusoidal phase modulation synchronous integration algorithm of band degree of modulation feedback; Realization is to the optical lens surface topography; The optical lens wave aberration, the Dynamic High-accuracy of optical transfer function etc. is measured.For reaching above-mentioned purpose, the technical scheme that the present invention takes is that phase modulation (PM) synchronous integration phase shift interference measuring method comprises the following steps:

Adopt the laser driver drive laser to produce laser; Arrive through condenser lens, semi-transparent semi-reflecting lens, beam-expanding collimation lens, little semi-transparent semi-reflecting mirror, reference mirror successively and measure mirror; Little semi-transparent semi-reflecting specular signal is sent into photoelectric detector PD, and semi-transparent semi-reflecting specular signal is finally sent Computer Processing after getting into video camera;

According to phase information just and CCD camera measuring-signal, phase modulation (PM) degree z differs θ, the following formula that power modulation factor m is relevant between CCD camera exposure signal and the phase modulated signal:

α=arctg (M ∑ _s-N ∑ _C)/(P ∑ _C-Q ∑ _s), by above-mentioned formula, carry out the measurement of phase modulation (PM) degree and stablize, differ the synchro control of θ;

Carry out the measurement and stable being specially of phase modulation (PM) degree: interference signal is following:

S(t)＝A+Bcos[zcos(ωt+θ)+α]＝A+Bcos(α)[J ₀(z)-2J ₂(z)cos(2ωt+2θ)+...]

-Bsin(α)[2J ₁(z)cos(ωt+θ)-2J ₃(z)cos(3ωt+3θ)...]

After S (t) is the bandpass filter of ω through centre frequency, with amplitude be G ₁Signal G ₁Cos (ω t+ θ)) multiplies each other,, obtain V through low-pass filtering ₁=-BG ₁Sin (α) J ₁(z);

After S (t) is the bandpass filter of 2 ω through centre frequency, with amplitude be G ₂Signal G ₂Cos (2 ω t+2 θ) multiplies each other, and through low-pass filtering, obtains V ₂=-BG ₂Cos (α) J ₂(z);

After S (t) is the bandpass filter of 3 ω through centre frequency, with amplitude be G ₃Signal G ₃Cos (3 ω t+3 θ) multiplies each other, and through low-pass filtering, obtains V ₃=BG ₃Sin (α) J ₃(z);

Because G ₁, G ₂, G ₃Be constant, by V ₁, V ₂And V ₃

And then the iteration optimizing obtains phase modulation (PM) degree z value, simultaneously through observing V ₂Realization is to the monitoring of semaphore size;

The synchro control that differs θ is specially: produce control signal through the CPU control module; The square wave and the sine wave of control Direct Digital Frequency Synthesizers DDS output variable frequency; Be respectively applied for CCD camera exposure signal and phase modulated signal; Make the two precise synchronization; Through the register setting, control the phase differential between CCD camera exposure signal and the phase modulated signal simultaneously.

Carry out the measurement and stable being specially of phase modulation (PM) degree:

Through pull-in frequency is ω ₀And much smaller than the sinusoidal signal of ω modulated laser together, then interference signal is:

S(t)＝A+Bcos[z?cos(ωt+θ)+α+hcos(ω ₀t+θ)]

Because α+hcos (ω in a short time ₀T+ θ) can regard stable direct current signal H as,

S(t)＝A+Bcos(H)[J ₀(z)-2J ₂(z)cos(2ωt+2θ)+...]

-Bsin(H)[2J ₁(z)cos(ωt+θ)-2J ₃(z)cos(3ωt+3θ)...]

After S (t) is the bandpass filter of ω through centre frequency, with amplitude be G ₁Signal G ₁Cos (ω t+ θ)) multiplies each other,, obtain V through low-pass filtering ₁=-BG ₁Sin (H) J ₁(z), after S (t) is the bandpass filter of 2 ω through centre frequency, with amplitude be G ₂Signal G ₂Cos (2 ω t+2 θ) multiplies each other, and through low-pass filtering, obtains V ₂=-BG ₂Cos (H) J ₂(z), by V ₁, V ₂Obtain:

${\left(\frac{V_1}{{\mathrm{BG}}_1{J}_1\left(z\right)}\right)}^2+{\left(\frac{V_2}{{\mathrm{BG}}_2{J}_2\left(z\right)}\right)}^2=1$

This formula is an elliptic equation, through ellipse fitting, finds the solution elliptic parameter, makes BG ₁J ₁(z)=and a, BG ₂J ₂(z)=b,

$\frac{J_1\left(z\right)}{J_2\left(z\right)}=\frac{{\mathrm{aG}}_2}{{\mathrm{bG}}_1}$

And then phase modulation (PM) degree z value is obtained in the iteration optimizing.

Phase modulation (PM) synchronous integration phase shift interference measurement mechanism; Structure is: the laser driver drive laser produces laser, and line focus lens, semi-transparent semi-reflecting lens, beam-expanding collimation lens, little semi-transparent semi-reflecting mirror, reference mirror arrive the measurement mirror successively; Little semi-transparent semi-reflecting specular signal is sent into photoelectric detector PD, and semi-transparent semi-reflecting specular signal is finally sent Computer Processing after getting into video camera;

Photoelectric detector PD outputs to stepping phase-shift phase metering circuit;

Stepping phase-shift phase metering circuit comprises three passages, and three passages are: successively the centre frequency of Xiang Lianing be after the bandpass filter of ω, multiplier, low-pass filtering; Successively the centre frequency of Xiang Lianing be after the bandpass filter of 2 ω, multiplier, low-pass filtering; Successively the centre frequency of Xiang Lianing be after the bandpass filter of 3 ω, multiplier, low-pass filtering;

Also comprise:

The CPU control module is used to produce control signal, the square wave and the sine wave of control Direct Digital Frequency Synthesizers DDS output variable frequency;

Direct Digital Frequency Synthesizers DDS is used to export the square wave and the sine wave of variable frequency, is respectively applied for CCD camera exposure signal and phase modulated signal, makes the two precise synchronization;

Register, through the register setting, the phase differential between control CCD camera exposure signal and the phase modulated signal.

The present invention has following technique effect:

The invention provides sinusoidal phase modulation synchronous integration phase shift interference and measure new improving one's methods; The problem that can not accurately measure and control to phase modulation (PM) degree in the sinusoidal phase modulation integral algorithm and CCD camera acquired signal and phase modulated signal phase differential; Introducing the phase modulation (PM) degree measures and control technology; Realized the dynamic locking of phase modulation (PM) degree; Differ through CCD camera acquired signal and phase modulated signal phase differential synchronous control technique are stable, assurance is provided for realizing high-precision sinusoidal phase modulation algorithm.Because system adopts closed loop configuration, antijamming capability is strong, has avoided the common interferometer shortcoming responsive to environmental interference, can be used for in-site measurement and correction.Simultaneity factor has kinetic measurement and monitoring capacity.Therefore native system can be realized to the optical lens surface topography wave aberration, the dynamic high-accuracy measurement of optical transfer function etc.

Description of drawings

Fig. 1 illustrates of the present invention based on the phase shift interference measuring method method system chart that exchanges little phase modulation (PM) phase control.

Among Fig. 1: 1 is laser driver; 2 is laser instrument; 3 is condenser lens; 4 semi-transparent semi-reflecting lens; 5 is the beam-expanding collimation lens; 6 is little semi-transparent semi-reflecting mirror; 7 is reference mirror; 8 for measuring mirror; 9 is photodetector; 10 are stepping phase-shift phase metering circuit; 11 are stepping phase-shift phase stabilization control circuit; 12 is the CCD camera; 13 is computer measurement software.

Measuring-signal when Fig. 2 is shown in the phase modulation (PM) degree and is 0.15rad.

Fig. 3 gathers the signal of four width of cloth images through the CCD camera synchronization.

Embodiment

Adopt non-equilibrium interferometer structure,, make laser output wavelength be sinusoidal variations, thereby realize sinusoidal phase modulation, utilize the CCD camera simultaneously, obtain multiple image at an inter-sync modulation period integration through the laser instrument internal modulation.Theoretical analysis shows, when the phase modulation (PM) degree controls to certain definite value, can obtain quite high phase shift interference measuring accuracy.To the phase modulation (PM) degree, the phase differential between CCD camera exposure signal and the phase modulated signal is accurately measured control, and the method for directly being found the solution optical element surface phase place by CCD camera image signal is the phase shift of sinusoidal phase modulation synchronous integration.

In the synchronous integration algorithm, by quoted passage ^{[1] [2]}Analyze, phase modulation (PM) degree error, the error of CCD camera acquired signal and phase modulated signal phase differential are the major obstacles that measuring accuracy improves, and when phase modulation (PM) degree sum of errors phase difference error during all less than 0.01rad, phase measurement accuracy is above λ/500.The present invention is directed to the characteristics of synchronous integration algorithm, phase modulation (PM) degree feedback technique introduced in the sinusoidal phase modulation interferometer, through high-precise synchronization with differ control, realize high-acruracy survey to phase place.

Below in conjunction with accompanying drawing and embodiment further explain the present invention.

Measuring principle is described:

Like Fig. 1; Adopt the fizeau interferometer structure; The light of 7 and 8 reflections forms to interfere and is received respectively by CCD camera and PD, and the signal among the PD is used for realizing real-time phase modulation measurement and control, and CCD camera measuring-signal is realized the measurement of optical element surface phase place through the synchronous integration algorithm.

The interference signal of CCD camera collection is:

S (t)=[1-mcos (ω t+ θ)] A+Bcos[zcos (ω t+ θ)+α] } (formula 1)

M power modulation factor wherein, w modulates angular frequency, and CCD camera synchronization acquired signal and modulating signal phase postpone to be θ, and A and B are the background light intensity coefficient and the contrast ratings of interferometer, and z is a phase modulation (PM) degree coefficient, α _d(x, y, the t) phase change that causes for face to be measured,

α=4 π l/ λ+α _d(x, y, t) (formula 2)

Wherein l is the optical path difference of reference mirror and mirror to be measured, and λ is the laser instrument output light wavelength, and (x is a to be measured coordinate figure of going up point y), and t is the time.

To be measured height change

D (x, y, t)=λ ₀α _d(x, y, t)/4 π (formula 3)

Order?

(formula 4)

The signal of gathering four width of cloth images through the CCD camera synchronization like Fig. 3 is:

$E_p={\∫}_{\frac{p-1}{4}T}^{\frac{p}{4}T}s\left(t\right)\mathrm{dt},$ P=1,2,3,4 (formulas 5)

Order:

(Equation 6)

(Equation 7)

Wherein, p=1,2,3,4.

Then have:

$E_p=\frac{T}{4}[A+{\mathrm{BJ}}_0\left(z\right)\cos \mathrm{\α}]+\frac{T}{2\mathrm{\π}}m[A+{\mathrm{BJ}}_0\left(z\right)\cos \mathrm{\α}][\sin (\frac{\mathrm{p\π}}{2}+\mathrm{\θ})$

$+\cos (\frac{\mathrm{p\π}}{2}+\mathrm{\θ})]+B\cos \mathrm{\α}{U}_p-B\sin \mathrm{\α}{V}_P$

(formula 8)

Wherein, p=1,2,3,4.

Order:

N＝-U ₁+U ₂+U ₃-U ₄，M＝-U ₁+U ₂-U ₃+U ₄

P=V ₁-V ₂-V ₃+ V ₄, Q=V ₁-V ₂+ V ₃-V ₄(formula 9)

Then have:

∑ _s=-E ₁+ E ₂+ E ₃-E ₄=NBcos α+PB sin α (formula 10)

∑ _C=-E ₁+ E ₂-E ₃+ E ₄=MBcos α+QBsin α (formula 11)

α=arctg (M ∑ _s-N ∑ _C)/(P ∑ _C-Q ∑ _s) (formula 12)

Thereby phase information just and CCD camera measuring-signal, and phase modulation (PM) degree z differs θ between CCD camera exposure signal and the phase modulated signal, and power modulation factor m is relevant.Therefore the measurement of phase modulation (PM) degree and stable, the synchro control that differs θ between CCD camera exposure signal and the phase modulated signal is the gordian technique of system.

Phase modulation (PM) degree feedback control technology

Measuring method 1: when ignoring the laser power variation, be ω through pull-in frequency ₀And much smaller than the sinusoidal signal of ω modulated laser together, then interference signal is:

S (t)=A+Bcos[z cos (ω t+ θ)+α+hcos (ω ₀T+ θ)] (formula 13)

Because α+hcos (ω in a short time ₀T+ θ) can regard stable direct current signal H as,

S(t)＝A+Bcos(H)[J ₀(z)-2J ₂(z)cos(2ωt+2θ)+...]

-Bsin(H)[2J ₁(z)cos(ωt+θ)-2J ₃(z)cos(3ωt+3θ)...]

(formula 14)

After S (t) is the bandpass filter of ω through centre frequency, with amplitude be G ₁Signal G ₁Cos (ω t+ θ)) multiplies each other,, obtain V through low-pass filtering ₁=-BG ₁Sin (H) J ₁(z).

(formula 15)

After S (t) is the bandpass filter of 2 ω through centre frequency, with amplitude be G ₂Signal G ₂Cos (2 ω t+2 θ) multiplies each other, and through low-pass filtering, obtains V ₂=-BG ₂Cos (H) J ₂(z).

(formula 16)

Obtain by formula 15 and formula 16:

${\left(\frac{V_1}{{\mathrm{BG}}_1{J}_1\left(z\right)}\right)}^2+{\left(\frac{V_2}{{\mathrm{BG}}_2{J}_2\left(z\right)}\right)}^2=1$ (formula 17)

This formula is an elliptic equation, through ellipse fitting, finds the solution elliptic parameter, makes BG ₁J ₁(z)=and a, BG ₂J ₂(z)=b,

$\frac{J_1\left(z\right)}{J_2\left(z\right)}=\frac{{\mathrm{aG}}_2}{{\mathrm{bG}}_1}$ (formula 17)

And then phase modulation (PM) degree z value is obtained in the iteration optimizing.

Measuring method 2: when ignoring laser power and change, and when not introducing low frequency component:

S(t)＝A+Bcos[zcos(ωt+θ)+α]＝A+Bcos(α)[J ₀(z)-2J ₂(z)cos(2ωt+2θ)+...]

-Bsin(α)[2J ₁(z)cos(ωt+θ)-2J ₃(z)cos(3ωt+3θ)...]

(formula 19)

J wherein ₀, J ₁... be Bezier expansion coefficient item, after S (t) is the bandpass filter of ω through centre frequency, with amplitude be G ₁Signal G ₁Cos (ω t+ θ)) multiplies each other,, obtain V through low-pass filtering ₁=-BG ₁Sin (α) J ₁(z).

(formula 20)

After S (t) is the bandpass filter of 2 ω through centre frequency, with amplitude be G ₂Signal G ₂Cos (2 ω t+2 θ) multiplies each other, and through low-pass filtering, obtains V ₂=-BG ₂Cos (α) J ₂(z).(formula 21)

After S (t) is the bandpass filter of 3 ω through centre frequency, with amplitude be G ₃Signal G ₃Cos (3 ω t+3 θ) multiplies each other, and through low-pass filtering, obtains V ₃=BG ₃Sin (α) J ₃(z).(formula 22)

Because G ₁, G ₂, G ₃Be constant, get by formula 20 and formula 24

(formula 23)

And then the iteration optimizing obtains phase modulation (PM) degree z value, simultaneously through observing V ₂Realization is to the monitoring of semaphore size.This measuring method can be fed back and the Measurement Phase degree of modulation in real time, simultaneously feedback stability phase modulation (PM) degree.

Through comparing and measuring method 1 and measuring method 2, method 1 method is directly perceived, needs to introduce low frequency component, and method 2 can realize real-time monitoring.Therefore be adjusted near the optimum angle degree of modulation (as 2.45) through method 1 when phase modulation (PM) is spent, through method 2 fine settings with realize the real-time feedback of phase modulation (PM) degree.Because l＞＞d (x, y, t), d (x, y, t) optical element surface height change, then z=4 π Δ λ wherein _MaxL/ λ 20=4 π β Δ I _MaxL/ λ 20 wherein β is the wavelength-modulated coefficient of laser instrument, Δ λ _Max, I _MaxBe respectively wavelength and electric current AC signal modulation amplitude.Thus can be through changing the AC signal modulation amplitude, stable and control phase degree of modulation.By on can know, can pass through measurement and feedback that photodetector (PD) is realized the phase modulation (PM) degree.

Synchronous and the phase differential control of CCD camera exposure signal and phase modulated signal

The design hardware circuit is realized the synchronous of CCD camera exposure signal and phase modulated signal and phase differential control.Like Fig. 2; Through the CPU control module (like FPGA; DSP etc.) produce control signal; The square wave and the sine wave of control DDS (Direct Digital Frequency Synthesizers) output variable frequency; Be respectively applied for CCD camera exposure signal and phase modulated signal; Make the two precise synchronization, simultaneously through the register setting, the phase differential between control CCD camera exposure signal and the phase modulated signal.

Claims (3)

1. a phase modulation (PM) synchronous integration phase shift interference measuring method is characterized in that, may further comprise the steps:

Adopt the laser driver drive laser to produce laser; Arrive through condenser lens, semi-transparent semi-reflecting lens, beam-expanding collimation lens, little semi-transparent semi-reflecting mirror, reference mirror successively and measure mirror; Little semi-transparent semi-reflecting specular signal is sent into photoelectric detector PD, and semi-transparent semi-reflecting specular signal is finally sent Computer Processing after getting into video camera;

According to phase information just and CCD camera measuring-signal, phase modulation (PM) degree z differs θ, the following formula that power modulation factor m is relevant between CCD camera exposure signal and the phase modulated signal:

α=arctg (M ∑ _s-N ∑ _C)/(P ∑ _C-Q ∑ _s), by above-mentioned formula, carry out the measurement of phase modulation (PM) degree and stablize, differ the synchro control of θ;

Carry out the measurement and stable being specially of phase modulation (PM) degree: interference signal is following:

S(t)＝A+Bcos[zcos(ωt+θ)+α]＝A+Bcos(α)[J ₀(z)-2J ₂(z)cos(2ωt+2θ)+...]

-Bsin(α)[2J ₁(z)cos(ωt+θ)-2J ₃(z)cos(3ωt+3θ)...]

After S (t) is the bandpass filter of ω through centre frequency, with amplitude be G ₁Signal G ₁Cos (ω t+ θ)) multiplies each other,, obtain V through low-pass filtering ₁=-BG ₁Sin (α) J ₁(z);

After S (t) is the bandpass filter of 2 ω through centre frequency, with amplitude be G ₂Signal G ₂Cos (2 ω t+2 θ) multiplies each other, and through low-pass filtering, obtains V ₂=-BG ₂Cos (α) J ₂(z);

After S (t) is the bandpass filter of 3 ω through centre frequency, with amplitude be G ₃Signal G ₃Cos (3 ω t+3 θ) multiplies each other, and through low-pass filtering, obtains V ₃=BG ₃Sin (α) J ₃(z);

Because G ₁, G ₂, G ₃Be constant, by V ₁, V ₂And V ₃

And then the iteration optimizing obtains phase modulation (PM) degree z value, simultaneously through observing V ₂Realization is to the monitoring of semaphore size;

The synchro control that differs θ is specially: produce control signal through the CPU control module; The square wave and the sine wave of control Direct Digital Frequency Synthesizers DDS output variable frequency; Be respectively applied for CCD camera exposure signal and phase modulated signal; Make the two precise synchronization; Through the register setting, control the phase differential between CCD camera exposure signal and the phase modulated signal simultaneously.

2. the method for claim 1 is characterized in that, carries out the measurement and stable being specially of phase modulation (PM) degree:

Through pull-in frequency is ω ₀And much smaller than the sinusoidal signal of ω modulated laser together, then interference signal is:

S(t)＝A+Bcos[z?cos(ωt+θ)+α+hcos(ω ₀t+θ)]

Because α+hcos (ω in a short time ₀T+ θ) can regard stable direct current signal H as,

S(t)＝A+Bcos(H)[J ₀(z)-2J ₂(z)cos(2ωt+2θ)+...]

-Bsin(H)[2J ₁(z)cos(ωt+θ)-2J ₃(z)cos(3ωt+3θ)...]

After S (t) is the bandpass filter of ω through centre frequency, with amplitude be G ₁Signal G ₁Cos (ω t+ θ)) multiplies each other,, obtain V through low-pass filtering ₁=-BG ₁Sin (H) J ₁(z), after S (t) is the bandpass filter of 2 ω through centre frequency, with amplitude be G ₂Signal G ₂Cos (2 ω t+2 θ) multiplies each other, and through low-pass filtering, obtains V ₂=-BG ₂Cos (H) J ₂(z), by V ₁, V ₂Obtain:

${\left(\frac{V_1}{{\mathrm{BG}}_1{J}_1\left(z\right)}\right)}^2+{\left(\frac{V_2}{{\mathrm{BG}}_2{J}_2\left(z\right)}\right)}^2=1$

This formula is an elliptic equation, through ellipse fitting, finds the solution elliptic parameter, makes BG ₁J ₁(z)=and a, BG ₂J ₂(z)=b,

$\frac{J_1\left(z\right)}{J_2\left(z\right)}=\frac{a{G}_2}{{\mathrm{bG}}_1}$

And then phase modulation (PM) degree z value is obtained in the iteration optimizing.

3. phase modulation (PM) synchronous integration phase shift interference measurement mechanism; It is characterized in that; Structure is: the laser driver drive laser produces laser, and line focus lens, semi-transparent semi-reflecting lens, beam-expanding collimation lens, little semi-transparent semi-reflecting mirror, reference mirror arrive the measurement mirror successively; Little semi-transparent semi-reflecting specular signal is sent into photoelectric detector PD, and semi-transparent semi-reflecting specular signal is finally sent Computer Processing after getting into video camera;

Photoelectric detector PD outputs to stepping phase-shift phase metering circuit;

Stepping phase-shift phase metering circuit comprises three passages, and three passages are: successively the centre frequency of Xiang Lianing be after the bandpass filter of ω, multiplier, low-pass filtering; Successively the centre frequency of Xiang Lianing be after the bandpass filter of 2 ω, multiplier, low-pass filtering; Successively the centre frequency of Xiang Lianing be after the bandpass filter of 3 ω, multiplier, low-pass filtering;

Also comprise:

The CPU control module is used to produce control signal, the square wave and the sine wave of control Direct Digital Frequency Synthesizers DDS output variable frequency;

Direct Digital Frequency Synthesizers DDS is used to export the square wave and the sine wave of variable frequency, is respectively applied for CCD camera exposure signal and phase modulated signal, makes the two precise synchronization;

Register, through the register setting, the phase differential between control CCD camera exposure signal and the phase modulated signal.

Images