Study On Preparation Method Of Body Holographic Grating For Plate Waveguide

Volume Holographic Grating(VHG)have been widely used in waveguide display and mobile navigation due to the advantages of high diffraction efficiency,simple preparation,low noise,and high resolution.In recent years,with the rapid development of science,technology and military affairs,higher requirements for the helmet display and AR.VHG,as the core optical element of the whole display system,has the advantages of small volume and light weight,It can realize the coupling and coupling function of the incoming ray.Combined with the diffraction characteristics of the holographic graster and the full reflection characteristics of the waveguide,it can get high quality and large output of the image in the flat waveguide display system.In order to solve the problem of low diffraction efficiency in plate waveguide transmission,we study the theoretical calculation,simulation and sample preparation of VHG,which is of great significance for further expanding the application range of holographic optical components.Firstly,expand the principle of flat waveguide display system and analyze and calculate the grille structure with diffraction characteristics.VHG recording and the reproduction process and Kogelnik coupled wave theory are described,and then calculate the diffraction characteristics of the reflection and transmission holographic grating elements and show that the refractive index adjustment system and grating thickness d are important factors that determine the diffraction of the holographic grating efficiency.The analysis shows that the diffraction efficiency within a certain film thickness,there is wave peak and valley value,and the reflection type is similar to the logarithmic curve.When the grille thickness reaches a certain value,the diffraction efficiency reaches 100%and no longer changes,so the reflection holographic grating is easier to prepare and has a wider application range.Secondly,the reflective holographic grating with beam coupling/coupling in the time domain,and the influence of different height,refractive index regulation system and cycle change on the primary diffraction efficiency were analyzed.The results show that the reflective holographic grating with refractive index modulation can improve the diffraction efficiency and improve the transmission efficiency of the plate waveguide display system.The simulation calculation method also provides guidance for the preparation of reflective holographic grating.On the premise of theoretical design and simulation optimization,finally,a reflective volume holographic grating with refractive index modulation is fabricated by using dichromated gelatin(DCG)with good photosensitivity and high resolution as holographic recording medium.According to the experimental conditions,an asymmetric reflective holographic exposure optical path with the recording wavelength of 442nm was built,and the diffraction efficiency of the experimental sample was measured after exposure and post-processing.The results show that the reflective VHG with diffraction performance close to the theoretical design can be obtained by controlling the preparation,recording conditions,exposure time,water washing,dehydration and other post-processing processes of DCG holographic dry plate.The-1 diffraction intensity and incident intensity are measured by spectrophotometer.The diffraction efficiency can reach 61.8%when the reconstruction wavelength is 632.8 nm.The verification results show that the reflective volume holographic grating can be transmitted in the flat waveguide.This process provides practical guidance for the preparation of holographic optical elements in display system.