Study On Optical Detection Method Of Mems Gyroscope

Due to the development of micro-electro-mechanical system(MEMS),low cost and small volume MEMS gyroscope has been widely used,but most micromechanical gyroscopes rely on capacitance detection,which made them easily disturbed by parasitic effects.Meanwhile,it limited the micro gyroscope having both high precision and dynamic performance at same time,so the gyrscope could not be applied in some special conditions.At the same time,the traditional optical gyroscope has high precision,anti-electromagnetic interference and other advantages.However,its low integration level and high cost make the miniaturization of optical gyroscope very difficult.In order to overcome the disadvantages of the two kinds of gyroscopes and produce a type of micromachined gyroscopes with both high accuracy and low noise level,the optical detection methods of MEMS gyroscope were studied in the paper.The displacement and strain sensitivity of double-layer subwavelength(SW)grating and whispering gallery mode(WGM)resonator were deeply analyzed.Introducing the two optical elements into two different kinds of micromachined gyroscopes,the single-mass gyroscope based on SW grating and the disk resonantor gyroscope based on WGM resonator were designed.The properties of these microelectro-mechanical(MOEMS)gyroscopes were detailedly analyzed and optimized.The main contents of this thesis are as follows:(1)Study on Optical Properties of Microoptical ElementsFirstly,based on Fraunhofer diffraction grating equation,the static optical properties of SW were analyzed.Then,the diffraction equations of the double grating wass deduced,while the field distribution of double SW gratings was obtained through the equations.After that,the relationship between diffraction intensity variation and grating displacement of the double SW gratings was studied.On the other hand,the modes and transmission spectrum of the WGM resonator were obtained from the study of geometrical optics and electromagnetic field distribution.Baesd on that,the relationship between the transmission spectrum drift and the cavity strain was studied in the thesis.(2)Study of Mechanical Characteristics and Working Principle of MOEMS GyroscopesFirstly,the working principles of single-mass MEMS gyroscope and disk resonator were deeply studied,and the dynamic models of them were obtained during the process.Secondly,the vibration characteristics of single-mass gyroscope and the "wine-galss" mode of disk resonator are analyzed,and the formulas of their mechanical sensitivity were concluded at the same time.Based on the conclusions,the process from angular velocity to displacement to diffraction intensity in the single-mass gyroscope with dual sub-wavelength gratings was analyzed.Similarly,another MOEMS gyroscope was formed combining the disk resonator and the WGM resonator.In this gyroscope,the working princle is based on the converting process from angular velocity to displacement to strain to spectral line drift.Both processes were detailed described in the thesis,which also demonstrated the working principles of two kinds of moems gyroscopes at the same time.(3)Simulation and Optimization of the MOEMS gyroscopesIn this paper,the finite-difference time-domain method(FDTD)was introduced,while two kinds of optical elements were simulated with FDTD Solutions software.For SW gratings,the effects of the period,thickness,duty cycle and gap of the double SW gratings on the first-order diffraction were studied.Similarly,for the WGM resonator,we designed its optical waveguide with the help of FDTD simulation.The relationship between structural parameters(including the cavity radius,the gap between the waveguide and the cavity,the width of the waveguide)and the Q value and the mode of the resonator were studied.Baesd on the results,the structure parameters of the resonator are optimized.Further more,through ANSYS and COMSOL simulations,the influence of the spoke and ring parameters of disk resonator on its Q value and frequency splitting of the resonator was analyzed,and the optimizated parameters were carried out.Finally,the effect of cross-coupling on the WGM resonator MOEMS gyroscope was studied,and a signal processing method was designed to extract and suppress the orthogonal signals to improve the performance of the gyroscope.(4)Design of Manufacture Process and Test Scheme for two MOEMS gyroscopesThe manufacture processes of two kinds of MOEMS gyroscopes based on SW grating and WGM resonator were designed respectively.At the same time,some processes are simplified to reduce the processing cost.Finally,the circuit and optical circuit of two kinds of MOEMS gyroscope were designed to meet the needs for testing.