| Traditional micro-electro-mechanical system(MEMS)gyroscopes have the advantages of small size,low cost and high reliability,and are widely used in many fields such as aerospace.At present,most MEMS gyroscopes rely on capacitance detection.As the size of micro-inertial devices continue to shrink,the parasitic effects of capacitance become obvious,which limits its application in the field of high-precision measurement.Although the traditional optical gyroscope based on the Sagnac effect has high detection precision,it is difficult to be compatible with MEMS technology,which brings great challenges to miniaturization.In order to overcome it,this paper presents a micro-opto-electro-mechanical system(MOEMS)gyroscope based on the whispering gallery mode(WGM)resonator.The MOEMS gyroscopes achieve angular velocity detection through the single-chip integration of microoptical devices and gyroscopes.While inheriting many advantages of traditional gyroscopes,it has successfully achieved photoelectric separation,avoiding the contradiction that dynamic range and accuracy are difficult to balance.This paper has carried out a series of research work on this type of gyroscope,the main contents are as follow:(1)Study on the Principle of Disk Resonator Gyroscopes and Micro-Optical devicesThe working principle of the MEMS disk resonator gyroscope is studied,and the wineglass mode in the second-order mode is analyzed.The working principle of micro-optical devices including WGM resonators,optical waveguides and grating couplers,and the coupling mechanism of WGM resonators and waveguides are analyzed,and the key parameters for measuring device characteristics are analyzed.The combination of micro-optical devices and gyroscopes is used to obtain the corresponding relationship between the deformation and spectral line drift.The feasibility of the MOEMS gyroscope is demonstrated.(2)Simulation and Optimization of the Micro-optical DevicesA commonly used numerical method of computer modeling of electromagnetic fields is introduced,namely the finite-difference time-domain(FDTD)method.Based on the FDTD method,the WGM resonator coupling optical waveguide and grating coupler are simulated and analyzed.Two different materials,silicon and silicon nitride,are compared and discussed.The parameters such as the diameter of the microcavity,the coupling gap,and the waveguide width are used to study the coupling state and quality factor.The influence of the losses caused by fabrication errors are also studied.Meanwhile,the coupling efficiency of the grating couplers is optimized using simulation tools,and the optimal parameters are obtained by continuously adjusting the parameters such as the grating period,depth,duty cycle,and incident light angle.(3)Fabrication of MOEMS GyroscopesThe fabrication process of the MOEMS gyroscopes is designed,and the prototype of the gyroscope is processed independently.Aiming at the many problems encountered in fabrication,through continuous adjustment of process steps and parameters,seeking optimization and solutions.The research focused on the processing of nano-scale micro-optical devices,using electron beam lithography as a pattering scheme,comparing the patterns produced by various of exposure doses and size of doses areas,and trying a variety of process combinations to etch the structure.Finally,gyroscope resonators,micro-optical devices and glass capping are obtained,and the packaging technology are also researched to some extent.(4)Design and Implementation of Measurement and Control SchemeThe overall measurement and control scheme of MOEMS gyroscope is designed,including electric drive scheme and optical detect scheme.Aiming ate the electric drive scheme,a dual closed-loop drive circuit based on phase-locked loop(PLL)for frequency controlling and automatic gain control(AGC)for amplitude controlling are adopted.The digital circuit is implemented in FPGA using Verilog language.Verification of frequency and amplitude tracking characteristics is carried out using MATLAB and Modelsim software.Preliminary tests of the gyroscope are performed. |
