Study On Holographic Optical Elements Applied To Near Eye Display

With the increasing demand for portable display,near-eye display technology has been widely used in military,commercial and civil fields.The traditional turn-back near-eye system has been replaced by the waveguide system.Waveguide-based near-eye display can fold the optical path,reduce the complexity of the optical system,and make the whole system more compact and lightweight.Because of its small size,light weight and many functions,holographic optical elements present great potentials in near-eye display.At present,the waveguide display techniques based on holographic optical elements are not mature enough,and there are many problems,such as low light efficiency,small field of view,poor image quality,and difficulty in preparing volume holographic grating.Aiming at the disadvantages of small angular bandwidth,low diffraction efficiency,and huge volume with collimation system,two kinds of volume holographic gratings are designed,which can effectively improve the performance and efficiency of volume holographic grating.In order to solve the problems of small angular bandwidth and low average diffraction efficiency,a volume holographic grating is designed and fabricated based on the asymmetric oblique recording and Kogelnik coupled wave theory.The relationship between the recording parameters and the diffraction efficiency of a volume holographic grating under TE and TM polariztion is discussed first,and the range of recording parameters under high average diffraction efficiency is found.Then the relationship between the recording parameters in this range and the angular bandwidth of the volume holographic grating is further analyzed,which could obtain the best recording parameters of the volume holographic grating with large angular bandwidth and high diffraction efficiency.The experimental results show that when the incident angle of the reference light is 25° and the incident angle of the signal light is 30°,the angular bandwidth of the prepared volume holographic grating reaches ±15°,and the diffraction efficiency is 90%.Another kind of volume holographic grating with large angular bandwidth and collimation function is designed.When the scattering angle of the scattered light is 46° and the incident angle of the reference light is 35°,the scattering volume holographic grating is prepared.The practical test shows that the field of view reaches 46° and the diffraction efficiency is 75%.Finally,holographic interference method is used to fabricate volume holographic gratings with large angle bandwidth and high diffraction efficiency as well as scattering volume holographic gratings.With the consideration that the diffraction efficiency of the actual grating was lower than the theoretical value,the experimental exposure parameters and post-processing parameters are analyzed,and the ideal processing parameters are obtained.