Design And Coupling Efficiency Of Liquid Crystal Grating

As a kind of wearable display device,the head mounted display needs to meet the characteristics of miniaturization,lightweight and color saturation.The optical waveguide with small volume and light weight is one of the most potential technical solutions to realize AR display.The volume of the whole system is determined by the coupling elements of light in and light out,as well as the miniaturized display devices.It is of great significance to study and prepare the coupling elements with high coupling efficiency.In order to fabricate small size head mounted display with excellent performance,an optimization method for the current waveguide structure was presented from the point of view of waveguide coupling elements and the design of the whole display system.A new structure of liquid crystal grating,polarization volume grating(PVG),was studied.The grating is made of liquid crystal and retains the properties of volume holographic grating,such as Bragg diffraction,and has a larger response bandwidth.At the same time,the polarization sensitivity of liquid crystal polarization grating(LCPG)is also retained.PVG is placed in the waveguide application environment for joint modeling and simulation,and the coupling efficiency and response bandwidth of PVG under different conditions are analyzed and compared by using the finite element method.The fabrication process and related parameters of liquid crystal grating are studied.By improving the exposure optical path of polarization holography and the key technology of fabricating liquid crystal grating,the PVG waveguide structure with high diffraction efficiency is obtained.A compact waveguide display system was also proposed.The light source and the spatial light modulator(SLM)are separately placed at different positions on the outside of the waveguide.The transmission PVG with large angle and high Bragg diffraction efficiency is used as the input coupling optical element.One side of the PVG is closely attached to the waveguide surface,and the other side is closely attached to the reflective SLM.The light source is located on the opposite side of the waveguide surface where the input coupling optical element is located,so as to realize the ultra-thin waveguide display system.The simulation results show that the transmission PVG can be used as the input coupling optical element to realize the waveguide optical imaging.The system can reduce the size of the waveguide from multiple dimensions by rearranging the components,greatly reducing the volume and weight of the waveguide system,which is conducive to the development of miniaturization of the head mounted display.