（文献）Novel Diffractive Optical Components for Near to Eye Displays

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Diffractive Optical Elements (DOE’s) on planar waveguides can be used to miniaturize the optics of a Virtual Reality Display(VRD). A biocular VRD that uses the diffractive planar waveguide as an Exit Pupil Expander (EPE) is ergonomically excellent but suffers from low efficiency and from uneven light distribution in the perceived virtual image. Using novel diffractive structures the efficiency of the system can be dramatically improved and an excellent performance over a wide Field of View (FOV) can be achieved. In this paper it is shown that with deep slanted grating profiles more than 90% diffraction efficiency can be reached and that etendue of the system is improved. It is also shown that the binary sub-wavelength gratings with a proper groove shape are not polarization sensitive. The performance of the EPE plate can be optimized using the filling ratio, the grating depth and the slanting angle as tuning parameters. The volume production methods of the deep slanted grating structures are discussed and some experimental results are shown.