Research On The Diffraction Characteristics Of Sub-wavelength Sandwich Metal Gratings

The research and preparation of sub-wavelength metal grating optical devices have received much attention in recent years.Due to its unique diffraction characteristics,it is widely used in the production of quarter wave plates,polarizers,polarization beam splitters,phase retarders and other devices.They have high diffraction efficiency,high extinction,and stable optical properties.It is of great significance to systematically study the diffraction characteristics of subwavelength metal gratings for the preparation and development of subwavelength metal grating optical devices.In this paper,a genetic algorithm is used to optimize the structural parameters of sub-wavelength metal gratings.The rigorous coupled wave theory is used to analyze the grating diffraction efficiency,extinction ratio,process tolerance and other characteristics,and has made important research results.Provides theoretical guidance for subsequent process preparation.(1)A single-layer subwavelength metal grating was designed.The influence of period,groove depth,and duty cycle on its diffraction efficiency was studied.The grating parameters were optimized using a genetic algorithm,and the polarization beam splitting at a central wavelength of 800 nm was obtained.(2)Design a sandwich metal grating model,calculate and analyze the rigorous coupled wave calculation process of the sandwich metal grating,and study the influence of different grating parameters on its diffraction characteristics.The grating reflection diffraction efficiency is successfully increased by changing the thickness of the cover layer.The highest diffraction efficiency is 97% at the center wavelength and the highest extinction ratio is 35 d B.(3)An embedded sandwich metal grating polarization beam splitter was designed using an embedded sandwich metal grating to achieve high diffraction efficiency,high extinction ratio,and large process tolerance requirements.The incident wavelength is between 1000 nm and 1150 nm,and more than 95% of diffraction efficiency and 25 d B extinction ratio are obtained.The tolerances for the duty cycle,period,and groove depth are 0.04,80 nm,and 50 nm,respectively.