Grating Interferometer Simulation Based On ZEMAX

In this paper,a two-degree-of-freedom grating interferometer measurement system is discussed based on the background of ultra-precision measurement requirements of the lithography machine.The optical path structure and measurement principle of the grating interferometer were introduced and deduced,and the measurement principle of the grating interferometer was verified based on the heterodyne phase solution method.A signal contrast and displacement measurement simulation based on optical software ZEMAX was proposed.Based on this method,the effect of grating angle rotation on the signal contrast and displacement measurement of grating interferometer was analyzed.Finally,a tolerance evaluation method based on Monte Carlo simulation and a tolerance optimization distribution method based on the minimum processing difficulty were proposed.The optimum angle tolerance band for each optical element in the read-head is measured.The ZEMAX-based simulation method presented in this thesis has the characteristics of universality,simple modeling,dynamic signal simulation,and high accuracy.The specific work of this paper is as follows:For a 2-DOF grating interferometer discussed in this paper,a simulation method based on optical simulation software ZEMAX is proposed.This method is used in conjunction with ZEMAX and MATLAB to perform dynamic signal simulation of a grating interferometer,which allows for simulation analysis of interferometer signal contrast and measurement displacement.The correctness of the simulation method was verified by experiments,and a two-degree-of-freedom grating interferometer experiment platform was successfully constructed.The measurement principle verification was completed using the heterodyne solution method.During the angle measurement of the grating interferometer,the angular rotation of the measuring grating will directly affect the signal contrast and thus affect the signal-to-noise ratio.According to the signal contrast simulation method,the influence of angular rotation of the measuring grating on the contrast of the signal in the grating interferometer is analyzed,and the allowable value of the angle rotation of the grating is obtained according to the system design requirements.According to the displacement measurement simulation method,the displacement measurement error caused by measuring the angle rotation of the grating is analyzed.In order to constrain the size of the grating interferometer,an integrated grating interferometer must be processed,and the size of its processing tolerance will affect the final signal contrast.At present,there is no relevant research on the processing tolerances of grating interferometers.Therefore,according to the signal contrast simulation method,a tolerance evaluation method based on Monte Carlo simulation is proposed.The BP neural network is used to fit the relationship between the signal contrast and the optical component angle deviation.Based on the above research contents,a method for optimizing tolerance distribution of grating interferometers based on the minimum processing difficulty is proposed,and the optimum angle tolerance band of each optical element in the reading head of the grating interferometer is obtained.