21 May 2018 Ultra-compact pancake optics based on ThinEyes® super-resolution technology for virtual reality headsets
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Abstract
We present an advanced optical design for a high-resolution ultra-compact Virtual Reality headset based on the traditional pancake configuration following optical foveation in the following sense: Firstly, the magnification is variable along the FoV i.e. the VR pixel density is maximum at the center and gradually diminishes towards the edge. Secondly, the optics image quality is also adapted, so the MTF of any gazable field is best when it is directly gazed. The combination of both is designed to fit with the human visual acuity with normal eye movements, so the user does not perceive the lower peripheral resolution at the edges of the FoV. VR pixel resolution (i.e. pixels per degree) of traditional pancake configuration optics is limited to the geometrical distance of the different elements. However, we have broken that compromise by applying Limbak’s ThinEyes® superresolution technology to the design of four aspherical surfaces in a pancake-type configuration, so the VR pixel resolution is dramatically increased at the center of the virtual reality space while maintaining high FoV and excellent imaging quality across the FoV. We make use of a curved reflective polarizer, which could be done in practice by vacuum molding a polymeric one made out of birefringent multilayer technology (as DBEF of 3M). As an example, we present an optical system that uses a standard 2.85“square display, with a pixel pitch of 35.5 microns (1440x1440 pixels). The total track length (eye pupil to display distance) of the system is 36mm with 15 mm eye relief, so the lens thickness is only 21 mm. For a conventional optical design to achieve a higher VR pixel resolution of 24 pixels per degree, the compromise comes in the form of reduced FoV of around 85 deg. These drawbacks do not bound our take on the pancake configuration. Thanks to the optical foveation, this design achieves a focal length of 49 mm at the center of the FoV, resulting in an outstanding VR pixel resolution of 24 pixels per degree at the center with a circular FoV of 100 deg for a 10mm eyebox.
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Bharathwaj Appan Narasimhan, Bharathwaj Appan Narasimhan, } "Ultra-compact pancake optics based on ThinEyes® super-resolution technology for virtual reality headsets", Proc. SPIE 10676, Digital Optics for Immersive Displays, 106761G (21 May 2018); doi: 10.1117/12.2315688; https://doi.org/10.1117/12.2315688
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