Subwavelength Dielectric Film Grating Wide-spectrum Achromatic Phase Retarder

With the development of micro processing technology and the broadening of the micro-optics applications field,micro-optics devices' feature size is shrinking,so the subwavelength grating(SWG)arises at the historic moment.The polarization characteristics are similar to birefringent effects of uniaxial crystal,this suggests that the SWG will be able to achieve the double refraction materials' optical function and it can be used for a variety of functions,such as wave plate,the polarization beam splitter and phase retarder,etc.This thesis mainly focus on the research of wide spectrum achromatic phase retarders with subwavelength grating to analysize the phase difference and the diffraction efficiency of grating(including the diffraction efficiency of reflection and transmission diffraction efficiency)based on the rigorous coupled wave theory.With 90° phase difference as the fitness evaluation function,genetic algorithm toolbox is used for automatic optimization of grating structure parameters.Thus the optimal grating structure parameters are obtained to realize the high precision and high diffraction efficiency of phase retarder.In this paper,the main works are as follows: firstly,the diffraction characteristics of subwavelength grating and multilayer dielectric grating are analyzed,and the process of theoretical analysis are detailed described.Secondly,in allusion the two waves wavelength for 1053 nm and 1550 nm which are used in the phase retarder devices commonly,based on the optimization design method,we design three kinds of grating structure to realize the 1/4 wave plate achromatic phase retarder with wide spectrum and obtain the following results:(1)When the central wavelength is 1550 nm,a single-layer grating structure is designed.In the range from 1350 nm to 1750 nm,the phase retardation of TE wave and TM wave is controlled at 90°±2°.Diffraction efficiencies are above 80% and bandwidth can be up to 400 nm;(2)When the central wavelength is 1053 nm,a sandwich subwavelength metal multilayer dielectric grating structure is designed,the bandwidth is 300 nm,phase retardation is about 90° and the maximum deviation is less than 2.3%.The diffraction efficiencies of TE wave and TM wave are higher than 90%;(3)When the central wavelength is 1053 nm,a achromatic phase delay structure based on a multilayer metal multilayer dielectric grating(MMDG)is designed,and the optimized phase retardation within the range 900~1200 nm,the maximum deviation is less than 4.5%,and the diffraction efficiencies of TE wave and TM wave are higher than 95%.The three kinds of grating structure have a high process tolerance,the performances can meet the requirements of the optical field of phase retarder.