Bragg compensated non-normal incidence HOE fabrication for occlusion capable near eye display

volume Holographic Optical Elements (VHOE) are being developed for use in image combiners and waveguide couplers within the near eye display(NED). VHOEs have the potential to replace conventional geometric optics and can perform multiple functions in a lightweight thin layer, depending on the recorded hologram design. However, due to high dispersion and the angular and spectral selectivity of VHOEs, bespoke solutions are needed for every new system design and it is important to be able to fabricate at a given recording wavelength (with available lasers) regardless of the intended operating wavelength of the VHOE. To alleviate the problem, we have proposed a Bragg angle compensation model, enabling recording at wavelengths distinct from the reconstructing/operating wavelength. Here the model is used to fabricate stacked VHOEs for an occlusion-capable NED design that utilizes both Uv and visible light sources. The experimental results show that the VHOE has a precision of ±1°from the desired diffraction angle when recorded in 532nm and reconstructed in 405nm and the experimental Bragg curve is measured up to 90% Diffraction Efficiency. The modulation transfer function of the VHOE is measured at 16 cycles per degree.