Research On Stress Measurement Method For Optical Glass Based On Heterodyne And MEMS Scanning Technology

The residual stress for optical elements is a major problem affecting the performance of optical precision measurement and stability of imaging systems.Residual stress may occur in the process of forming,annealing,polishing,coating,optical assembly and laser maching of optical glass.In view of the challenges of complex process and limited aperture of common stress measurement methods for optical elements,a new stress measurement method based on laser heterodyne technology and MEMS scanning technology is proposed and studied in this paper.According to the stress birefringence effect,the stress measurement is transformed into the optical path difference measurement caused by birefringence,and the signal light is demodulated by laser heterodyne detection.This paper establishes the basic structure of the measurement system,deduces its theoretical model in detail,simulates the digital phase difference extraction algorithm,and designs a MEMS/f-θ lens optical scanning system with large aperture.This method has the advantages of high precision,fast speed and simple process.It has broad application prospects for the measurement of optical materials with large aperture.The main work and research contents of this paper include the following aspects:1.A set of stress measurement system is designed,combining laser heterodyne technology with MEMS scanning technology.And the selection scheme of each module is proposed based on the actual device parameters.The simulation test of the stress measurement system based on laser heterodyne technology is carried out,which proves the feasibility of the system scheme.2.The theoretical model of laser heterodyne detection is established.Aiming at the problems of polarization state matching,spatial phase matching and amplitude matching,the key factors affecting the effect of laser heterodyne detection system are studied.Focusing on the heterodyne detection system with photoconductive detector,the variation law of signalto-noise ratio with optical power of local oscillator under constant current and constant voltage bias mode is analyzed.3.The phase detection accuracies of cross-correlation function method,least square method and maximum likelihood method in the case of high sampling and low sampling are analyzed and compared.And the optimal matching parameters of these methods are obtained.4.Based on the scanning principle of MEMS mirror and the imaging characteristics of f-θ lens,the scanning optical system is designed,where the measuring beam scans on the target to be measured with uniform and vertical scanning.The scanning frequencies of fast axis and slow axis of MEMS scanning mirror are 1200 Hz and 170 Hz,respectively,and the transverse and longitudinal spatial scanning angles of MEMS mirror are 30 °and 20 °,respectively.The f-θ lens is a lens group composed of three different materials,with a system focal length of 432 mm.The distortion aberration of MEMS/f-θ lens optical scanning system is less than 0.1%.The results show that all parameters meet the expected design indexes.