21 May 2018 Characterisation and optimisation of Volume Holographic Optical Elements (VHOEs) in AR combiners for ghost reduction
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Abstract
Studies to integrate increased sensory capacities of the wearer on head mounted displays are growing fast for applications in augmented, virtual and mixed reality. This paper focuses on the characterisation of the combiner of the UNO augmented reality glasses by GlassUp: a volume holographic optical element, recorded at 532 nm on Bayfol® HX, providing high diffraction efficiency over a narrow bandwidth at the desired angles. Furthermore, there is a negligible impact on the head mounted display frontal lens’s width and on the view of the real world. Studying the volume hologram, we developed a characterisation tool that gave us insight into the patterns inside the polymer and served as quality check for UNO. In particular, we designed a setup that provides Total Angular Characterisation through Optical Spectroscopy (TACOS), acquiring the visible spectral response of VHOEs as transmittance, reflectance or dispersion maps at arbitrary angles. Furthermore, it analyses the patterns through a custom fit based on the Kogelnik model. The early stages volumetric holograms presented undesirable secondary efficiency peaks causing ghosts, impairing both the vision of the real world and the image projected by the optical module. TACOS’ custom fit allowed us to conduct a quantitative analysis on the ghosts. In this work, we present an equilibrium study on all these parameters to find the better condition of projection. Moreover, we studied the impact of the recording parameters on the appearance of ghosts, e.g. tuning exposure, power ratios.
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Marco Francardi, Marco Francardi, Nicola Truant, Nicola Truant, Enzo Francesca, Enzo Francesca, Francesco Giartosio, Francesco Giartosio, Thomas Miletti, Thomas Miletti, "Characterisation and optimisation of Volume Holographic Optical Elements (VHOEs) in AR combiners for ghost reduction", Proc. SPIE 10676, Digital Optics for Immersive Displays, 106760E (21 May 2018); doi: 10.1117/12.2306268; https://doi.org/10.1117/12.2306268
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