Optimization Design Of Diffractive Grating Couplers For Large Exit Pupil And Wide Field Of View Optical Waveguide

Augmented reality(AR)can realize immersive three-dimensional information display,and enhance people ’s interactive experience with the surrounding real world by superimposing information such as sound,video,and graphics in real time.AR display has a wide range of application scenarios in military,civil and other fields,and has important research value.With the continuous development of augmented reality display technology,the optical waveguide scheme has advantages in device volume,exit pupil area and field of view,and has gradually become the mainstream scheme of AR display.The optical waveguide scheme uses the total reflection condition of the waveguide medium to transmit the light field at an extremely low loss.The diffractive optical waveguide realizes the coupling control of the optical field through the grating device,which has higher design freedom and is easy to integrate.This thesis focuses on improving the uniformity of the exit pupil expansion of the surface relief grating(SRG)optical waveguide scheme and extending the angular bandwidth of the VHG in the volume holographic grating(VHG)waveguide scheme.Based on the theories of grating diffraction,holographic interference and rigorous coupled wave analysis,the modulation effect of the grating structure to the optical field in the waveguide is explored,and the performance of the grating coupling device is improved.The specific research works are as follows:Firstly,the analysis method of diffraction characteristics of grating coupler in optical waveguide scheme is studied.The electromagnetic field model of SRG and VHG is established by rigorous coupled wave theory.The influence of different grating groove structures on the diffraction characteristics of SRG is explored.The structural parameters of SRG coupler in optical waveguide are optimized to match the design requirements of exit pupil expansion in waveguide system.According to the unique recording and reconstruction method of VHG,the diffraction characteristics of VHG under Bragg conditions are explored,which lays a theoretical foundation for expand the angular bandwidth of VHG by multiplexing interference fringes with equal period and variational inclination angles.Secondly,the continuity and uniformity of large exit pupil plane of SRG optical waveguide is studied.A one-dimensional exit pupil expansion model of the optical waveguide is established to meet the design requirements of the continuity and uniformity of the exit pupil expansion.By adding a rectangular groove turning grating and changing the propagation direction of the total reflection of the coupling light in the waveguide,the two-dimensional exit pupil expansion of the optical waveguide is realized,and the eye movement range is expanded.In this thesis,the design results of one-dimensional pupil expansion of optical waveguide under TM polarization at 530 nm wavelength are simulated.The exit pupil surface of 1×4 array is obtained,and the uniformity error of exit pupil surface is 3.37%.In the two-dimensional dilated pupil design results,the exit pupil surface of the 3×4 array is obtained,and the uniformity error of the exit pupil surface is 8.83%.Third,the study of VHG multiplexing extended angle bandwidth.Based on the VHG Bragg condition and multiplexing theory,this thesis proposes a VHG structure that multiplexing interference fringes with equal period and variational inclination angles,establishes a theoretical model for calculating the refractive index of multiplexed VHG,and explores the influence of different recording conditions on the angular bandwidth of the VHG multiplexing interference fringes with equal period and variable inclination angles.In the TE and TM polarization states with a wavelength of530 nm,the angular bandwidth of the VHG is expanded to 3.6° and 3.3° after multiplexing three interference fringes with equal period variable inclination angles,respectively.Compared with the VHG recording a single interference fringe,the angular bandwidth is doubled.In this thesis,the simulation model of exit pupil expansion design is established for SRG optical waveguide,and the continuity and uniformity of exit pupil intensity are optimized.The method of VHG multiplexing interference fringes with equal period and variable inclination angles is proposed,which expands the angular response bandwidth of the VHG coupler and provides theoretical guidance for the realization of large exit pupil wide field of view optical waveguide near-eye display.