Ozan Cakmakci

Ozan Cakmakci

Ozan is a lead optical engineer working on Project Glass at Google[x]. His research interests include optical system design, freeform optics, kernel methods, gradient index optics, and diffractive optics.

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Google Publications
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    Holographic pancake optics for thin and lightweight optical see-through augmented reality
    Peter Bosel
    Yi Qin
    Gordon Wetzstein
    Opt. Express, 29(2021), pp. 35206-35215
    Preview abstract Holographic pancake optics have been designed and fabricated in eyewear display optics literature dating back to 1985, however, a see-through pancake optic solution has not been demonstrated to date. The key contribution here is the first full-color volume holographic pancake optic in an optical see-through configuration for applications in mobile augmented reality. Specifically, the full-color volume holographic pancake is combined with a flat lightguide in order to achieve the optical see-through property. The fabricated hardware optics has a measured field of view of 29 degrees (horizontal) by 12 degrees (vertical) and a measured large eyebox that allows a ±10 mm horizontal motion and ∼±3 mm vertical motion for a 4 mm diameter pupil. The measured modulation transfer function (average orientation) is 10% contrast at 10 lp/deg. Three holograms were characterized with respect to their diffraction efficiency, angular bandwidth, focal length, haze, and thickness parameters. The phase function in the reflection mode hologram implements a spherical mirror that has a relatively simple recording geometry. View details
    Preview abstract Vergence-accommodation conflict (VAC) is a major challenge in optical-see through augmented reality (AR) system. To resolve this conflict, many approaches are proposed, for instance, by means of adjustment of the projected virtual image to coincide with the surroundings, called image registration, which is more often referred to as varifocal function. In this paper, a varifocal AR system is demonstrated by adopting electrically tunable liquid crystal (LC) plane-parallel plates to solve VAC problem. The LC plates provide electrically tunable optical paths when the directors of LC molecules are re-orientated with applied voltages, which leads to a corresponding change of light speed for an extraordinary wave. To provide a sufficient tunable optical path, three pieces of multiple-layered LC structures are used with the total thickness of the active LC layers (∼510 μm). In experiments, the projected virtual image can be adjusted from 1.4 m to 2.1 m away from the AR system, while the thickness of LC plane-parallel plates are only less than 3 mm without any mechanical moving part. When light propagates in the uniaxial LC layers, the wave vector and the Poynting vector are different. The longitudinal displacement of the image plane is determined by Poynting vectors rather than wave vectors. As a result, the analysis of the AR system should be based on Poynting vectors during geometrical optical analysis. Surprisingly, the tunable range of the longitudinal displacement of Poynting vectors is 2-fold larger than the tunable range of the wave vectors. Moreover, the virtual image shifts in opposite directions with respect to the Poynting vectors and wave vectors. The proposed AR system is not only simple but also thin, and it exhibits a large clear aperture. The investigation here paves the way to a simple solution of the VAC problem for augmented reality systems. View details
    Analysis of 3D Eyebox in Augmented and Virtual Reality Optics
    David Morris Hoffman
    Nikhil Balram
    Society of information display, Society of information display(2019)
    Preview abstract The eyebox volume is a key design parameter in the optical design of augmented and virtual reality optics. The extent of the eyebox volume determines the experience of a user in seeing the entire virtual magnified image. Furthermore, a 3D description of eyebox facilitates the design of augmented and virtual reality products for a population of users. We define 3D eyebox and discuss visualization approaches to communicate it within interdisciplinary product design groups focused on research and development of augmented and virtual reality optics. View details
    Preview abstract We present an underexplored variation of the classical optical freeform prism design that incorporates 3 optical surfaces. This optical architecture can make use of one, two, or three freeform surfaces. Our initial prototype uses a single freeform surface along with a sphere and a flat surface to simplify manufacturing complexity. There are two key contributions in this paper that to our knowledge have not been achieved previously: 1) the design of a thin, 4 mm to 1 mm gradient thickness, curved freeform lightguide (nearly 4x thinner than the original freeform prism), and 2) lightguide fabrication utilizing ophthalmic machines. This particular optical design makes combined use of total internal reflections and partial reflections. The advantages of this optical architecture include the curved optical surfaces that eliminate the optical collimator requirement in flat lightguides, a relatively large eyebox, and a manufacturing approach that reuses the standard ophthalmic process for fabricating the eyeside and worldside optical surfaces. The limitations of the optical design are low efficiency (∼ 5%), multiple image artifacts, and lack of optical see-through. View details
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