21 May 2018 Understanding waveguide-based architecture and ways to robust monolithic optical combiner for smart glasses
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With the emergence of Augmented Reality (AR) and Virtual Reality (VR) headset during the past decade, firms and academic laboratory have worked on the design of optical combiners to increase the performances and form factor of the optical combiners. Most of the smart glasses on the market have the asset of being small, which eases the integration of the combiner in a head worn device. Most of them (Google glass, Vusix) use prism-like architecture, where the collimation and deflection of the light is performed by one single optical piece. This approach reduces the size and tolerance issues of the device. Other companies (Optinvent, Microsoft, Lumus) came with waveguide architecture, in which the light is collimated by a lens or group of lens, injected in a slab waveguide and extracted in front of the eye of the user. This way, the image is brought right in front of the eye, where prism like architecture displays an image in the peripheral sight of the user. These optical combiners however suffer from low tolerances and fabrication complexity as several pieces are combined. The injection and extraction of image rays in the waveguide can be performed either by holograms or slanted mirrors. Each technology has its downturns but for now the performances of holographic combiners were deceiving, resulting in chromatic dispersion and thus degradation of MTF. This paper relates the work on a waveguide-type optical architecture designed for smart glasses. The system described in this paper was conceived as a solution for smart glasses uses, for which the main concerns are the size of the eye box, adaptability, and a small form factor. Good optical performances were obtained, with a resolution of around 1.2px/arcmin, together with a large eye box.
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Vincent Brac de la Perrière, "Understanding waveguide-based architecture and ways to robust monolithic optical combiner for smart glasses ", Proc. SPIE 10676, Digital Optics for Immersive Displays, 106761D (21 May 2018); doi: 10.1117/12.2315681; https://doi.org/10.1117/12.2315681

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