Research On Characteristic Of Super Diffraction Grating In Waveguide Collimated Projection System

Waveguide collimated projection system is the most advanced head-projection system,which uses micro collimated lens to convert images into parallel lights to couple into the planar waveguide plate and to spread in total reflection in the wave guide plate,so spatial light paths is compressed.The advantages of this system are small occupancy,light weight and large exit pupil etc.Waveguide collimated projection system is the transmission system,the outside scenery can be observed by human eyes through the waveguide plate,meanwhile the image information and environmental information can be received.This system has a good application prospect and research value.The super diffraction grating is the core unit of the waveguide collimated projection system,which determines the performance of the system and the related parameters.In order to break the foreign monopoly on related technologies,this paper designed the super diffraction grating of a new type of waveguide collimated projection system,the main work and innovation of this paper are as follows:1.This thesis has analyzed and summarized the operating principle and process of the waveguide collimated projection system's related patents of the BAE system company.The thesis also discussed the relay lens,light source,the way of light beam coupling,the thickness of waveguide plate,and the characteristic of super diffraction grating built-in in the waveguide plate.The conclusion supported the system simulation is that the super diffraction grating has the characteristics of restraining the high-order diffraction,the gradation diffraction efficiency,and the immutability of diffraction efficiency when the angle of incidence is changed,2.The derivation of RCWA is based on periodic binary grating,and the RCWA is applied to solve the diffraction efficiency of arbitrary gratings.According to RCWA,wrote and verified the Matlab program,which can be used to solve the diffraction efficiency of coated blazed grating,binary grating and so on.3.Analyze the characteristic of the super diffraction grating,and determine the parameters of the super diffraction grating based on the simulation experiment of the most advanced waveguide collimated projection system.Respectively simulate the coupling grating,steering grating and imaging grating,and obtain the suitable f grating parameters or the system.The field of view of the waveguide collimated projection system based on the super diffraction grating can reach 24.8° * 30°.4.The measurement experiment of grating diffraction efficiency is based on the Thorlab Company's GR13-1850 blazed grating.The TiO₂ thin film thickness of GR13-1850 blazed gratings are respectively 10 nm,20nm,30 nm,40nm,60 nm.According to the measuring result of the diffraction efficiency,come to the conclusions: 1)after plating the TiO₂ thin film,with the change of the incident angle of GR13-1850 blazed grating,the diffraction efficiency keep constant within a certain range.2)the diffraction efficiency of the grating can be changed by thickness of the TiO₂ film.3)TiO₂ can be used as the coating material of the super diffraction grating in the waveguide collimated projection system.