Research On Signal Intensity Detection And Non-orthogonal Error Correction Of Homodyne Laser Interferometer Based On LCVR

Recent years,homodyne laser interferometer has been more and more extensively applied in length measurement verification,measuring nanometer equipment integration,material property testing and dynamics testing of micro-electromechanical systems.However,the non-orthogonal error in the interferometry is a major obstacle to the development of accuracy.The whole period interference signal detection is a necessary means to adjust the azimuth of interference signal and maximize the interference signal,and it is urgent to measure the intensity of interferometer when the interferometer is stationary such as aero-engine and machine tool spindle.This dissertation "Research on signal intensity detection and non-orthogonal error correction of homodyne laser interferometer based on LCVR" mainly focuses on the whole period signal intensity detection when homodyne laser interferometer remains stationary and the non-orthogonal error existing in homodyne laser interferometer.Firstly,in this dissertation,a new technique for detecting the amplitude of homodyne laser interference signal is put forward,which uses liquid crystal phase variable delay(LCVR)to generate interference signal with whole period while the interferometer is still,and detect the amplitude,displaying the interference signal in real time by LabVIEW.Then a new four-channel optical path to receive interference signal is proposed and studied,using LCVR to correct non-orthogonal errors.Finally,aiming at the problem that the change of temperature will affect the accuracy of LCVR correction,a real-time non-orthogonal error correction technology is designed to suppress the non-orthogonal error introduced by temperature change and ensure the measurement accuracy.The central work of this research is as shown below:For optical path adjustment,it is impossible to move the measured object arbitrarily to obtain the whole-period interference signal.This dissertation puts forward a scheme of using LCVR to generate the interference signal with whole period while the interferometer is still.Firstly,LCVR is used to generate phase delay difference of more than 2? in the horizontal and vertical polarization components of linearly polarized laser,so as to generate the interference signal with whole period.Then,two interference signals are uploaded to FPGA for amplitude calculation and sum of squares calculation.Finally,they are uploaded to the upper computer LabVIEW to display in real time.It realizes the generation of interference signal and detection of interference signal in real-time.Aiming at the existing electrical correction method reduces the accuracy of non-orthogonal errors at the expense of the effective amplitude of signal,this dissertation proposes a homodyne laser interferometric optical path which can correct non-orthogonal errors.LCVR is used to compensate the phase delay differences caused by the NPBS,and then to correct the non-orthogonal error.On this basis,the unequal amplitude error of the orthogonal signal is eliminated by using the FPGA.In order to solve the problem that the phase delay caused by LCVR will be changed by the change of ambient temperature,which will affect the compensation of NPBS phase delay and reduce the accuracy of correction method,a real-time correction algorithm of non-orthogonal error is designed in this dissertation.Firstly,two interferometric signals are preprocessed to eliminate unequal amplitude error,then the sinusoidal and cosine values of the angle of non-orthogonal error including two interferometric signals are obtained by digital adder/subtractor and amplitude calculation;then the angle of non-orthogonal error is calculated by CORDIC algorithm;the relationship between driving voltage and phase delay of LCVR is used to change the magnitude of driving voltage.In this way,the influence of temperature variation on non-orthogonal error is restrained,so that the non-orthogonal error correction method proposed can adapt to temperature variation very well.Based on previous research,an ultra-precision homodyne laser interferometer to elimate non-orthogonal error is se up.And by using the upper computer,the measurement data can be acquired,analysed and shown in real time.By measuring the Jones matrix of NPBS,it is determined that the phase delay differences caused by NPBS for reflected and transmitted light is 22.28°,which shows it is the main cause of non-orthogonal error.The experimental results show that the non-orthogonal error angle of the two interference signals of the homodyne laser interferometer developed in this dissertationis less than 0.0045°,and the corresponding non-orthogonal error is within 2 pm;the residual non-orthogonal error angle after real-time correction of non-orthogonal error is less than 0.4°,and the corresponding non-orthogonal error is within 0.17 nm in the process of temperature change from 25 to 40?.