Research On The Optical Properties Of Planar Optical Waveguide System

With the development of the information age,near-eye display(NED)technology has achieved wide applications in military,commercialized,and civilianized areas.The structure of NED has also changed from the traditional folding lens type to the optical waveguide.the optical structure of traditional NED is relatively complicated,consisting of several lens-based optical paths,which results in a huge and cumbersome system.Planar optical waveguide structure can reduce the complexity of the optical system,making the entire system more compact and lightweight.However,optical waveguide based NED is not mature and there stillexits problems such as low light energy utilization,small field of view,and difficulty in preparing high-quality diffraction gratings.Therefore,this thesis analyzes and solves the common problems existing in the optical waveguide system.In order to solve the problem of high cost,long circle of electron beam processing,the thesis firstly designs the structure of the grating.With fixed grating period,the diffraction efficiency of the grating is set to be design goal.The scalar theory is applied and it is found that the grating with a right triangle structure can achieve higher diffractive efficiency.The vector theory is then utilized to optimize the parameters of the grating profile.The designed grating profile is introduced into the optical waveguide system.Because the designed grating period is in the order of micrometers,the incident angle of input light has to be very large to guarantee total reflection in the waveguide.With large incident angle,the grating diffraction efficiency will be reduced,which leads to a decrease in the utilization of light energy in the entire system.In order to guarantee total reflection of vertically incident light,a wedge-shaped optical waveguide structure is proposed.The proposed structure not only improves the system's light energy utilization rate but also increases the field of view and angle uniformity.In order to achieve a larger exit pupil display area,the proposed wedge-shaped optical waveguide system is expanded for the exit pupil.To ensure the continuity and uniformity of the expanded exit pupil image,the wedge-shaped waveguide structure with the expansion of the exit pupil is optimized.Finally,the maskless lithography direct writing technology is used to prepare the right-angle triangular grating.In order to solve the problem that the diffraction efficiency of the actual prepared grating is lower than the theoretical value,the effect ofhigh-frequency information on the surface profile of the grating is analyzed from the perspective of Fourier series,which can theoretically analyze the relationship between grating profile and diffraction efficiency.