CN103322925B - The optical heterodyne interference method of nonlinearity erron is eliminated based on phaselocked loop filter method - Google Patents
The optical heterodyne interference method of nonlinearity erron is eliminated based on phaselocked loop filter method Download PDFInfo
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Abstract
The optical heterodyne interference method eliminating nonlinearity erron based on phaselocked loop filter method belongs to laser heterodyne interferometry field, the method is in the light path that there is nonlinearity erron interference component, reach out at least 3 road signals and periodicity nonlinearity erron interference component respective in making wherein at least 3 tunnels, phasing degree on the signal frequency composition that will be eliminated is within the scope of a corresponding angle of circumference or get rid of in a corresponding circle week angular region after integral multiple angle of circumference different, and in analog electrical signal passage, adopt phase locked loop filter to carry out filtering to signal, to adopt follow-up electronics process eliminate or suppress interference component after analogue to digital conversion.The present invention can eliminate the particular harmonic composition of nonlinearity erron or interference, and its adjustment process is very easy to, and improves system performance, reduces cost.
Description
Technical field
The invention belongs to laser heterodyne interferometry (HeterodyneInterferometry) fields of measurement, be specifically related to a kind of laser heterodyne interferometry measuring method eliminating nonlinearity erron fundamental frequency based on phaselocked loop filter method exempting from accurate adjustment.
Background technology
Laser heterodyne interference system can be used for measuring the physical quantity such as displacement, length, is one of best nano measurement method.This system is in the frequency or phase place change tested displacement being converted to heterodyne signal, again by this measure of the change out, because the frequency of heterodyne signal is more much lower than optical frequency, photosignal easily processes, can through electronic fine-grained and reach higher Measurement Resolution, resolution can reach micromicron (pm) or better.
But ubiquity non-linear (nonlinearity) problem in optical heterodyne interference method, these factors can be the main source of error of displacement measurement, make its precision generally only have nanoscale to tens nanometer, its reason is that the light beam that frequency is different can not well be separated.These periodic nonlinearity erron problems are the obstacles of this art always.
Constantly invent some methods improved both at home and abroad for many years, but also there are some restriction or problems more, such as Badami and Pattersom uses ratemeter and frequency spectrograph directly measure nonlinearity erron composition in a mobile system and compensate; TaeBongEom and TaeYoungChoi etc. carry out compensating non-linear error to the method for carrying out ellipse fitting after phase signal integration.These methods can when there is no other auxiliary interferometer compensating non-linear error, but system complex, and need a large amount of fluctuation signal cycles and relative a large amount of computing, the real-time that impact is measured.Be disclose a kind of new method in the Chinese invention patent of CN101660924 at publication number, the method can address this problem effectively, if but wish to obtain very accurate result, also need point-device optics to regulate, this precise optical regulates usually more difficult.
Summary of the invention
In order to the system complex, the operand that solve the existence of existing laser heterodyne interference system are large, the coarse technical matters of poor real, result, the invention provides a kind of based on phaselocked loop filtering and FFT(Fast Fourier Transform (FFT)) algorithm eliminates the optical heterodyne interference method of nonlinearity erron, the particular harmonic composition of nonlinearity erron or interference can be eliminated, and remove from and eliminate precision optics regulating device required for nonlinearity erron and minute adjustment process, this adjustment is made to become very easy, significantly improve system performance simultaneously, reduce costs.
The electric signal that the AC signal that the photodetector output terminal of laser heterodyne interference systematic survey light arm obtains is is frequency with alien frequencies optical frequency difference, its additional phase differential and measured position move into accurate proportionate relationship.But wherein contain so-called nonlinearity erron, be mainly distributed on the first harmonic (generally also can be called fundamental frequency according to Fourier series character, be a kind of spatial frequency) of Fourier spectrum.Method of the present invention can eliminate the fundamental component of nonlinearity erron; In fact method of the present invention is all effective to arbitrary a certain frequency, and without the need to doing special minute adjustment to optical system.
Also exist in the signal light path of nonlinearity erron interference component in laser heterodyne interference system, obtain at least 3 road signals (passage), by by carry be detected signal light arm at least 3 interference light photodetecting part are set method obtain these signals, and to make wherein to have at least in 3 tunnels the phase angle of nonlinearity erron first harmonic (or other frequency content) contained separately different in a corresponding circumference, so just obtain sufficient information, the process such as weighted sum superposition in face after enable pass and fundamental frequency (or any one frequency) composition that eliminates in nonlinearity erron.The method different in a corresponding circumference of the phase angle realizing first harmonic (or other frequency content) is a lot, the phase angle of corresponding first harmonic such as can be changed by adjustment light path, by the error measurement method of disclosed first harmonic in prior art, the amplitude and the starting phase angle that obtain first harmonic can be easy to.Generally, the phase angle of the several signals error of different light paths is usually unequal, if the situation having phase angle equal, can be known by the method measuring phase angle in prior art, and makes them unequal by adjustment light path.Furtherly, generally our optical system of setting up at random, do not have nonlinearity erron phasing degree in any 2 tunnels identical in a corresponding circumference, if but after completing the adjustment of optical system, the phase angle of the 2 road nonlinearity erron first harmonics (or other frequency content that will be eliminated) in 3 tunnels is more or less the same, the amplitude of the useful signal after affecting weighted stacking, thus the signal to noise ratio (S/N ratio) of impact output signal, at this moment we roughly can adjust the difference of phase angle relative to (frequency content that will be eliminated of nonlinearity erron) signal phase angle corresponding in other passages of the frequency content that will be eliminated in 1-2 road wherein, it is made to increase to some extent fully till (namely enough).There are now a lot of detection nonlinearity erron first harmonic (or other frequency content that will be eliminated) phase places and the method for amplitude, as " measuring method of laser heterodyne interference nonlinearity erron " " Beijing University of Technology's journal " the 6th phase in 2010 of Chen Hongfang etc.; " the novel measuring method of a kind of laser heterodyne interference nonlinearity erron " of Zhong Zhi etc., optoelectronic laser, 2005, etc.The method of adjustment phase angle can realize by regulating the optical path difference between two light participating in interference.
Based on the periodicity of hamonic function, certainly as usually, several integral multiple angles of circumference comprised can be got rid of disregard (no longer doing similar prompting below) in above-mentioned phase differential.
Adopt and carry out subsequent treatment in the following method: first hypothesis only has the situation of 3 road signals, 3 road signals is carried out phase compare with reference signal respectively, until solve 3 displacements.The phase place of the nonlinearity erron at this moment in each passage is different.
Known by proof below, have non-vanishing weighting coefficient array can make superposition after the fundamental frequency of nonlinearity erron or the amplitude of other frequency contents be zero, and retain useful signal.
In above-mentioned 3 displacements solved, the displacement measurement on the i-th tunnel can be expressed as:
Wherein, equal sign right-hand member Section 1 χ is real physical displacement, and Section 2 is the primary components of nonlinearity erron, certainly illustrates that content of the present invention also without loss of generality with first harmonic here; A is coefficient, and expressing nonlinearity erron amplitude, is generally an a small amount of, but does not make approximate processing in derivation afterwards.
be the initial phase angle of nonlinearity erron, λ is optical wavelength.Here the wave number in nonlinearity erron item
what represent is first harmonic composition, and by the situation of measuring prism individual reflection.For the situation of second harmonic, this can become
By 3 result weighted stacking, be normalized into:
One group of new ki, just in order to neatly pro forma, can be regarded as new weighting coefficient.Our object finds one group of ki to make: X=x.
By above-mentioned condition, we can obtain system of linear equations below:
The factor arrays of variable ki is 3 rank square formations of full rank, and the system of equations about ki has untrivialo solution.That is, can make
To sum up, demonstrated after such weighted stacking, the first harmonic composition of nonlinearity erron is eliminated.
If
in have any 2 difference 180 °, problem can be made to become simple and favourable, this situation generally needs accurate optics adjustment just can obtain, and the 2 road signals only needing non-linear component to differ 180 ° just enough eliminate the nonlinearity erron composition of characteristic frequency, than being illustrated in more detail in this that patent of invention mentioned in the introduction.
To this, we have solved the nonlinearity erron problem in laser heterodyne interference in 3 dimensional linear spaces of electronics.
For the situation with more than 3 road signals (passage), we at least can retain the different signal of 3 road phase angles in advance, again by any road Signal averaging in 3 tunnels of all the other several signals and reservation, and changed into each 3 non-vanishing tunnels of phase angle difference in certain frequency of nonlinearity erron.So just dissolve the problem solved above becoming, i.e. the situation of 3 passages, and be proven.Certainly also can not adopt the processing procedure being first simplified to 3 tunnels recited above, but together complete in weighted overlap-add procedure.
Obtain correct weighting coefficient array by following method in practice and eliminate error percentage: (1) is by linear for 2 wherein superposition, because in 2 dimension spaces of this certain harmonic components nonlinear, one group of substrate of this two paths of signals Special composition, so any one vector can be generated by adjustment superposition coefficient, we allow the vector generated be just in time that direction is contrary with the 3rd signal (vector) on certain harmonic components nonlinear, then by the signal of generation and the 3rd signal (vector) linear superposition, adjustment weighting coefficient just can make certain harmonic components nonlinear be kept to zero completely mutually, and useful signal can still be retained.(2) electricity consumption tune method can repeat the weighting coefficient on alternate sweep at least 2 tunnel, measure nonlinearity erron value in the output after superposition simultaneously, make it constantly reduce, until be zero.(3) adopt the most basic method, after phase angle described in the every road of measurement and amplitude, directly calculated by analytic method, also can adopt the thinking in (1) here, but be not decompose adjustment, but decoupled method, no longer carefully separate here.That is, finding that first harmonic error can be cancelled each other by weighted stacking, thus after removing the above-mentioned principle of error percentage, the weighted stacking mode be applicable to can be selected according to the related content of the present invention's record, just can realize the elimination of first harmonic error.The method of above-mentioned multiple acquisition weighting coefficient is only used to be convenient to enumerating of understanding, is not the restriction completely to technical scheme.
In order to remove corresponding optics accurate adjustment from, eliminate or suppress nonlinearity erron, and be conducive to retaining useful signal and selecting rational parameter, preferably, the difference between the phase angle on the signal frequency composition that will be eliminated of 3 at least 3 road signals periodicity nonlinearity errons is made to be not less than 60 degree.This is because we always can, easily by regulating or arranging, make the declinate between any two-phase not too little in practice.Theoretical and experiment all illustrates, a rational numerical value using 60 ° of lower limits as this angle, this is beneficial to the signal to noise ratio (S/N ratio) after process, the amplitude of useful signal lower than single channel of output can not be made after weighted stacking, as long as attempt blindly fixingly affecting device in the light path of phase differential between 3 tunnels 3 to 5 times at random simultaneously, roughly just once chance meets this condition, thus " adjustment-free " that realize mechanically, and eliminate corresponding adjuster, make adjustment or the work that arranges become simple and easy.Composition adjusts nothing, and then checks the amplitude of useful signal, if too low, just illustrate and does not have to meet " 60 degree of conditions " or similar standard.It is complete whether inspection adjusts, and having eliminated error can judge by such as adopting more accurate surveying instrument to carry out the methods such as results contrast.
This " minute adjustment " by electronics replaces the release precision optical machinery of " minute adjustment " of optics to regulate or exempts from the method for optics accurate adjustment, and cost is significantly reduced, and the accuracy requirement regulated optics can decline more than 2-3 the order of magnitude.And the precision that whole system shows on nonlinearity erron characteristic frequency is also significantly improved.
Clearly, whether the ultimate principle of the method and the advantage itself existed and meaning, and adopt integrated optics mode, comprises optical fiber solutions, or bulk wave mode etc. is irrelevant.The method is all effective for the periodic error in all laser heterodyne interferometry systems, as long as we can obtain the different signal of its interference component phase place of at least 3 roads.
Laser heterodyne interference signal is typical weak signal, and in the exquisite system of this elimination nonlinearity erron, particularly more require that signal is pure, the wave filter in analog electrical signal is very important link in system.Consider that the useful signal of this system is single some composition frequently, when testee exists speed and acceleration, the rate of change of frequency displacement and frequency will be there is.The wave filter of simple inductance and capacitance type is longer for the corresponding time of input signal phase place, limits the movement velocity of object being measured under the requirement of precision.Phase locked loop filter then can address this problem preferably, it has very low phase noise and extraordinary transient phase error and static phase error index, accurately can measure the immediate movement of object in motion, the even immediate movement of object in acceleration; Complete machine index can be promoted.Interpretation can be carried out to the phase place being no less than 3 road signals respectively by fft algorithm after phase-locked filtering, then be weighted again after displacement calculating section calculates displacement and to eliminate with overlap-add procedure or to suppress these interference components.
Before weighted stacking part, increase phase-locked filtering part also make each road information obtained full amplitude before weighted stacking, that obtain abundant filtering, comprise the phase relation etc. of phase relation between the signal of each road and interference component, this category information is useful in some cases, is such as conducive to determining weighting coefficient array etc.
Based on foregoing, the invention provides a kind of first harmonic or other frequency content that can eliminate or reduce periodically nonlinearity erron, improve measuring accuracy, the optical heterodyne interference method of the corresponding precision optics that omits adjustment, namely the optical heterodyne interference method of nonlinearity erron is eliminated based on phaselocked loop filter method, the method is: in the light path that there is nonlinearity erron interference component, at least 3 road measuring-signals and 1 tunnel reference signal is obtained by light splitting, and make the phasing degree of the respective periodicity nonlinearity erron of wherein at least 3 road measuring-signals in the frequency content that will be eliminated different within the scope of a corresponding angle of circumference, at least 3 road measuring-signals and 1 tunnel reference signal are separately converted to corresponding at least 3 drive test amount analog electrical signals and 1 tunnel reference analog electrical signal, the first filtering and analog to digital conversion are carried out respectively in each road of described at least 3 drive test amount analog electrical signals, and correspondence obtains at least 3 drive test amount digital electric signals, the second filtering and analog to digital conversion are carried out with reference to analog electrical signal in 1 tunnel, and correspondence obtains 1 road reference number electric signal, described at least 3 drive test amount digital electric signals are inputted corresponding FFT phase place reading module respectively with 1 road reference number electric signal, calculates at least 3 drive test amount signal phase angles and 1 reference signal phasing degree, tunnel, the cycle count of phase compare and phase differential is carried out at described at least 3 drive test amount signal phase angles and 1 reference signal phasing degree, tunnel respectively, and is converted into displacement, obtains at least 3 tunnel displacement measurement, now contains nonlinearity erron in the displacement measurement of each road, the at least 3 tunnel displacement measurement obtained are carried out real number ranking operation, then carries out additive operation and can obtain final measurement, described first filtering comprises employing phase locked loop filter.
The phase differential of at least 3 periodicity nonlinearity errons in above-mentioned at least 3 road measuring-signals is not less than 60 °.
Above-mentioned first filtering and the second filtering adopt different types of wave filter.
Above-mentioned first filtering and the second filtering adopt the wave filter of identical type.
The step obtaining at least 3 road measuring-signals and 1 tunnel reference signal above by light splitting comprises: the A road light signal of output obtains A1, A2 respectively by least 4 light-dividing devices successively ... An road light signal, wherein n >=4; The B road light signal with the A road light signal exported with frequency difference obtains B1 road light signal by light-dividing device, obtains B2 successively after all the other light signals of B road are reflected by reflection unit by light-dividing device ... Bn road light signal, wherein n >=4; A1 road light signal and B1 road light signal interfere formation reference signal, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 road measuring-signal to Bn road light signal respectively.
Generally in phaselocked loop, the principle of work of phase detector all will be subject to the impact of noise or even other frequency contents, and in input signal, the interference of other frequency contents can cause phase detector output noise.So added low-pass filter or bandpass filter before phase detector, it is useful for carrying out filtering to simulating signal.The effect of this wave filter is important, it can not make up by any wave filter after phaselocked loop.
Adopt the fft algorithm in digital processing accurately can obtain phase differential as stated above, the movement velocity of system under test (SUT) directly can also be obtained by the variable of frequency, the Broad Spectrum Analysis of Infinitesimal of FFT is also applicable to large velocity range, can be used for making assessment and diagnosis to each signalling channel, also can share with other system.
Another technical scheme of the present invention is: a kind of laser heterodyne interferometry device adopting above-mentioned optical heterodyne interference method, comprising: the first light-dividing device, and the light signal light splitting of A road is obtained A1, A2 ... An road light signal, wherein n >=4; Second light-dividing device, obtains B1 road light signal and remaining light signal thereof by the B road light signal light splitting that the A road light signal with output has frequency difference, and all the other light signals described are obtained B2 by the second light-dividing device light splitting after reflection unit reflection ... Bn road light signal, wherein n >=4; Interfere forming apparatus, make A1 road light signal and B1 road light signal interfere the reference signal formed, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 road measuring-signal to Bn road light signal respectively; Signal detecting device, is converted to 1 tunnel with reference to analog electrical signal, n-1 drive test amount analog electrical signal respectively by above-mentioned 1 tunnel reference signal, n-1 road measuring-signal; First filtering and modular converter, carry out the first filtering and analog to digital conversion respectively to n-1 drive test amount analog electrical signal, and correspondence obtains n-1 drive test amount digital electric signal; Second filtering and modular converter, carry out the second filtering and analog to digital conversion to 1 tunnel with reference to analog electrical signal, correspondence obtains 1 road reference number electric signal; FFT phase place reading module, calculates n-1 drive test amount digital electric signal phasing degree and 1 reference number electrical signal phase angle, road; Displacement computing module, according to n-1 drive test amount digital electric signal phasing degree and 1 reference number electrical signal phase angle, road, calculates n-1 road displacement measurement; Weighted stacking module, carries out real number ranking operation and additive operation by the n-1 road displacement measurement obtained.
Present invention omits explanation and the statement of some prior aries, row as omit to the details such as the wiring board distribution filtering electric capacity of FFT system employing theorem in one's power, power-supply system, the amplifier set by system-gain, the discussion of general foundation and block diagram etc.
The invention has the beneficial effects as follows: the present invention is in common laser heterodyne interference system-based, creatively optical path is divided into multichannel, carry out the process such as adjustment, signal transacting, weighted stacking of electronics respectively, with the length of electronics minute adjustment, light filling minute adjustment short, omitted complicated optics accurate adjustment or other non-electronic adjustment, the substitute is the adjustment and signal processing method elimination nonlinearity erron that adopt electronics, reduce the complexity of pH effect, reduce cost, improve efficiency.Simultaneously, effectively eliminate or reduce significantly the periodic interference components such as nonlinearity erron and then improve measuring accuracy or reduce interference, coordinate fast fourier transform algorithm accurately to try to achieve signal phase simultaneously, and make that the measuring accuracy of whole system improves by the phase locked loop filter that particular design is selected, antijamming capability is strong, stable, be conducive to large-scale production, production cost is low.
Accompanying drawing explanation
Fig. 1 the present invention is based on the opticator schematic diagram that phaselocked loop filter method eliminates the optical heterodyne interference method of nonlinearity erron.
Fig. 2 is the phase locked loop filter circuit diagram in the present invention.
Fig. 3 the present invention is based on the principle schematic that phaselocked loop filter method eliminates the optical heterodyne interference method of nonlinearity erron.
Embodiment
Below in conjunction with accompanying drawing, the present invention is described in further details.
The system realizing the optical heterodyne interference method that the present invention is based on phaselocked loop filter method elimination nonlinearity erron can be divided into opticator and electrical signal processing section afterwards.Wherein the principle of opticator as shown in Figure 1, and the present invention, on the basis of an original opticator, adds the part in dotted line frame in figure.
First, set forth the opticator principle of work of original heterodyne interferometry system: send laser by laser instrument 101, acousto-optical device 103 is incided through Part I catoptron 102, Part II catoptron 114 is shone after shift frequency, transmitted light is reflected by measuring prism 115, incide Part III catoptron 111, reflecting part and another Ray Of Light are interfered through the first polaroid 131.The light that reflected by Part I catoptron 102 (it provide reference ray for each road interference portion below) is through the first catoptron 125, again after Part IV catoptron 124, Part V catoptron 123, Part VI catoptron 122, second catoptron 121, together incide the first polaroid 131 with the reflected light of Part III catoptron 111, the interference light of its outgoing converts the difference frequency part of two light to electric signal by the first photodetector 141.This electric signal, as measuring-signal, has wherein included the displacement information obtained above measuring prism 115, also containing nonlinearity erron composition.
The light that the light reflected by Part II catoptron 114 and Part IV catoptron 124 reflect converges, incide the second polaroid 134, the interference light of its outgoing converts the difference frequency part of two light to electric signal by the second photodetector 144, and this electric signal is exactly reference signal.
Above-mentioned laser instrument 101, Part I catoptron 102 and acousto-optical device 103 constitute the double-frequency laser generator that frequency has elementary errors, also can be replaced by other scheme.
Invention increases the part in dotted line frame in Fig. 1, it mainly comprises two new measurement light arm/light paths and corresponding circuit part.
Together with original the first smooth arm be made up of Part III catoptron 111, first polaroid 131, first photodetector 141 etc. in figure, have three light arms, or be called three optical paths, and obtain that measuring-signal exports 1 thus, measuring-signal export 2 and measuring-signal export 3, structurally smooth arm is identical to these two new measurement light arms with first.Add reference signal, four road signals export altogether, and this four roads signal just constitutes the output of opticator, is transferred to electrical signal processing section below, as described in Figure 3.
In electrical signal processing section, its signal is respectively through the phase locked loop filter (be respectively in Fig. 3 211,221,231,241 for first passage to the filtering part of four-way) shown in Fig. 2; Analog to digital conversion part (be respectively in figure 212,222,232,242 for first passage to four-way); The part calculating phase angle in system described in Fig. 3 is called FFT part (be in figure 213,223,233,243 for first to fourth passage); Then three tunnel measurement data carry out the cycle count of phase compare and phase differential respectively in displacement calculating section (be 214 in figure, 224,234 respectively for the first to third channel) and reference signal, and be converted into displacement, complete corresponding displacement measurement, obtain the measurement result on each road; The same nonlinearity erron containing respective destruction system accuracy in certain result.The measurement result on Zai Jiang tri-tunnel is delivered to weighted stacking arithmetic section 301 respectively and is carried out real number ranking operation, and then do additive operation and just can draw last measurement result, the fundamental frequency of its nonlinearity erron has been eliminated or has significantly suppressed.
Claims (7)
1. eliminate the optical heterodyne interference method of nonlinearity erron based on phaselocked loop filter method, it is characterized in that: the method comprises:
In the light path that there is nonlinearity erron interference component, obtain at least 3 road measuring-signals and 1 tunnel reference signal by light splitting, and make the phasing degree of the respective periodicity nonlinearity erron of wherein at least 3 road measuring-signals in the frequency content that will be eliminated different within the scope of a corresponding angle of circumference;
At least 3 road measuring-signals and 1 tunnel reference signal are separately converted to corresponding at least 3 drive test amount analog electrical signals and 1 tunnel reference analog electrical signal;
The first filtering and analog to digital conversion are carried out respectively in each road of described at least 3 drive test amount analog electrical signals, and correspondence obtains at least 3 drive test amount digital electric signals; The second filtering and analog to digital conversion are carried out with reference to analog electrical signal in 1 tunnel, and correspondence obtains 1 road reference number electric signal;
Described at least 3 drive test amount digital electric signals are inputted corresponding FFT phase place reading module respectively with 1 road reference number electric signal, calculates at least 3 drive test amount signal phase angles and 1 reference signal phasing degree, tunnel;
The cycle count of phase compare and phase differential is carried out at described at least 3 drive test amount signal phase angles and 1 reference signal phasing degree, tunnel respectively, and is converted into displacement, obtains at least 3 tunnel displacement measurement, now contains nonlinearity erron in the displacement measurement of each road;
At least 3 tunnel displacement measurement obtained are carried out real number ranking operation, then carries out additive operation and can obtain final measurement;
Described first filtering comprises employing phase locked loop filter.
2. eliminate the optical heterodyne interference method of nonlinearity erron as claimed in claim 1 based on phaselocked loop filter method, it is characterized in that: described first filtering adds low-pass filter before being also included in described phase locked loop filter or bandpass filter carries out filtering.
3. eliminate the optical heterodyne interference method of nonlinearity erron as claimed in claim 1 based on phaselocked loop filter method, it is characterized in that: the phase differential of at least 3 periodicity nonlinearity errons in described at least 3 road measuring-signals is not less than 60 °.
4. eliminate the optical heterodyne interference method of nonlinearity erron as claimed in claim 1 based on phaselocked loop filter method, it is characterized in that: described first filtering and the second filtering adopt different types of wave filter.
5. eliminate the optical heterodyne interference method of nonlinearity erron as claimed in claim 1 based on phaselocked loop filter method, it is characterized in that: described first filtering and the second filtering adopt the wave filter of identical type.
6. the optical heterodyne interference method of nonlinearity erron is eliminated as claimed in claim 1 based on phaselocked loop filter method, it is characterized in that: the step being obtained at least 3 road measuring-signals and 1 tunnel reference signal by light splitting is comprised: the A road light signal of output obtains A1, A2 respectively by least 4 light-dividing devices successively ... An road light signal, wherein n >=4; The B road light signal with the A road light signal exported with frequency difference obtains B1 road light signal by light-dividing device, obtains B2 successively after all the other light signals of B road are reflected by reflection unit by light-dividing device ... Bn road light signal, wherein n >=4; A1 road light signal and B1 road light signal interfere formation reference signal, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 road measuring-signal to Bn road light signal respectively.
7. adopt the laser heterodyne interferometry device eliminating the optical heterodyne interference method of nonlinearity erron based on phaselocked loop filter method as described in any one of claim 1-6, it is characterized in that: comprising:
First light-dividing device, obtains A1, A2 by the light signal light splitting of A road ... An road light signal, wherein n >=4;
Second light-dividing device, obtains B1 road light signal and remaining light signal thereof by the B road light signal light splitting that the A road light signal with output has frequency difference, and all the other light signals described are obtained B2 by the second light-dividing device light splitting after reflection unit reflection ... Bn road light signal, wherein n >=4;
Interfere forming apparatus, make A1 road light signal and B1 road light signal interfere the reference signal formed, A2 ... An road light signal and B2 ... the corresponding interference forms n-1 road measuring-signal to Bn road light signal respectively;
Signal detecting device, is converted to 1 tunnel with reference to analog electrical signal, n-1 drive test amount analog electrical signal respectively by above-mentioned 1 tunnel reference signal, n-1 road measuring-signal;
First filtering and modular converter, carry out the first filtering and analog to digital conversion respectively to n-1 drive test amount analog electrical signal, and correspondence obtains n-1 drive test amount digital electric signal;
Second filtering and modular converter, carry out the second filtering and analog to digital conversion to 1 tunnel with reference to analog electrical signal, correspondence obtains 1 road reference number electric signal;
FFT phase place reading module, calculates n-1 drive test amount digital electric signal phasing degree and 1 reference number electrical signal phase angle, road;
Displacement computing module, according to n-1 drive test amount digital electric signal phasing degree and 1 reference number electrical signal phase angle, road, calculates n-1 road displacement measurement;
Weighted stacking module, carries out real number ranking operation and additive operation by the n-1 road displacement measurement obtained.
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