Research On Signal Processing Method Of Sinusoidal Phase Modulated Laser Interferometer For Nanometer Displacement Measurement

With the development of chip manufacturing,achieving nanometer-precision in a large range of displacement measurement is an urgent problem to be solved to improve the current chip manufacturing level.In the field of nanometer measurement,laser interferometry technology stands out due to its advantages of high measurement accuracy,fast speed,and wide range.In the laser interferometry technology field,the measurement technology represented by a single-frequency laser interferometer,it has the advantages of simple structure and non-contact measurement,and is widely used.In this paper,a sinusoidal phase modulation interferometer based on a single-frequency laser interferometer is taken as the research object.Starting from reducing the nonlinearity in the displacement measurement results,a nonlinear error-compensated laser-modulated interferometric nanometer displacement measurement system is designed and its performance is studied by carry out related experiments.In this paper,a signal processing method of sinusoidal phase-modulated laser interferometer for nanometer displacement measurement is proposed to achieve largescale and high-precision displacement measurement.The thesis discusses the principle of the signal processing method of sinusoidal phase-modulated laser interferometer for nanometer displacement measurement from two aspects: sinusoidal phase modulation technology and phase modulation demodulation principle.First of all,the sinusoidal phase modulation and demodulation technology is deeply researched,the principle of transverse electro-optical phase modulation technology to realize sinusoidal phase modulation is discussed,the principle of carrier phase modulation and demodulation method is analyzed,and the focus is on the source of the error in PGC-Arctan phase demodulation method.A PGC phase demodulation nonlinear error compensation method based on Kalman filtering is proposed,a phase demodulation system based on FPGA is designed,and the nonlinear error compensation is performed using the Kalman filtering method.Also design the computer software of Lab VIEW which can realize real-time control of each module in the measurement system during the measurement process,and display and save the measurement results in real time.In order to verify the feasibility of the proposed signal processing method of sinusoidal phase-modulated laser interferometer for nanometer displacement measurement,the nonlinear error compensation laser modulation interferometer was built and debugged,and the nonlinear error compensation method of PGC phase demodulation based on Kalman filter and the performance of sinusoidal phase modulation laser interferometer are tested and measured.In the experiment of the PGC phase demodulation nonlinear error compensation method based on Kalman filtering,the phase demodulation resolution experiment shows that the phase demodulation accuracy reaches 0.01°,and the error deviation is less than 0.05° within the 360° phase change range.It shows the high precision of the phase demodulation method.At the same time,the modified contrast experiment verifies the effectiveness and accuracy of the designed PGC phase demodulation method based on Kalman filtering.In the displacement measurement experiment of sinusoidal phase modulated laser interferometer,with the position of the precision displacement positioning platform as a reference,the mean and standard deviation of the displacement error in the nano-scale displacement measurement experiment do not exceed 1 nm;the mean value of displacement error in micron displacement experiment is in the range of 1 nm,and the standard deviation of displacement error is in the range of 1.05 nm to 2.43 nm;the mean value of displacement error in millimeter-scale displacement measurement experiments is in the range of 0.089μm to 0.105μm,and the standard deviation of displacement error is in the range of 0.326μm to 0.417μm.These displacement measurement results show that the sinusoidal phase-modulated laser interferometer nanometer displacement measurement system has nano-level measurement accuracy in the nano-,micro-,and millimeter-level measurement ranges.The THD of the sinusoidal motion measurement results decreased from 0.732% and 0.751% to 0.049% and 0.068%,and the SINAD increased from 42.715 d B and 44.487 d B to 66.056 d B and 62.259 d B;the residual nonlinear error of the step displacement measurement results did not exceed 0.15 nm.The experimental results of nonlinear error correction show the effectiveness of sinusoidal phase-modulated laser interferometer nanometer displacement measurement system in reducing the nonlinear errors in the displacement measurement results.The above experiments comprehensively verify the feasibility and effectiveness of the proposed signal processing method of sinusoidal phase-modulated laser interferometer for nanometer displacement measurement.