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.
Studies on Head Mounted Displays (HMDs) to integrate increased sensory capacities to the wearer are growing fast over the years for applications in Augmented (AR), Virtual (VR) and Mixed Reality (MR). In this work, we focus our attention on the characterisation of the projected image from the Optical Module (OM) equipped on board of “F4” model (AR mask for industrial users) produced by GlassUp. We have used our own system to test the quality assessment process, but it can be applied also to other kinds of OM. The major difference between real eye and the emulated one is that in the first one the projected image is elaborated as a continuum by our brain while in the second one the acquiring detector is discretised in pixels. After a proper resize, the images acquired by the detector (1900x1200 px) can be analysed with respect to the original images used as input for the display in the OM (640x480 px). Based on the Structural Similarity (SSIM) theory, we propose the definition of a new index (F-SSIM) to extract more reliable information on the quality of projected images. This approach can be used both for hardware validation trial and evaluation of digital corrections for the pincushion and vignetting optical distortions. The quality assessments proposed in this work define an innovative resize approach of the reference and acquired images for an optimal structural similarity comparison. The results for F-SSIM and SSIM analysis are compared and discussed.
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