Bragg polarization gratings used as switchable elements in AR/VR holographic displays

The high coherence of laser light sources is a key to the application of diffractive optics usable in holographic AR/VR displays. This can be combined with switchable diffractive elements, which are advantageous for several optical functions used in immersive holographic displays such as shutters, polarization filters, for rapid beam deflection and selection. We demonstrate a compact, effective and robust diffraction wide-angle switchable beam-deflecting device based on circular polarization gratings possessing Bragg-performances (Bragg-PG) and a polarization switch. Such grating/polarization switch pair may, for instance, be a discrete switchable deflection element or as a switching element for pre-deflection with field lenses for application in holographic AR/VR displays. Micrometer-thick circular polarization gratings characterized by high diffraction efficiency (DE > 95%), large diffraction angles (< 30°) and wide angular and wavelength acceptance were developed. In the presented embodiment, the output signal is controlled between the zero- and first-diffraction orders by the handedness of circular polarization of the incident light. Forming a stack of two such oppositely aligned gratings can double the deflection angle. These gratings are the result of a two-step photochemichal/thermal processing procedure of a photocrosslinkable liquid crystalline polymer (LCP). The holographic patterning provides a high spatial resolution (period < 700 nm) and the arbitrary orientation of the LC director as well as high optical quality and thermal and chemical stability of the final gratings. Highly efficient (diffraction efficiency, DE > 95% in the vis spectral range) and stable symmetric and slanted circular Bragg polarization gratings were fabricated using the developed material and processing technique. The high usable diffraction angles combined with high DE make the Bragg-PG attractive for HMD AR/VR applications because of the system inherent short focus lengths and large numerical apertures needed to meet the low space budget in HMD and other optical systems.

[1]  Michael J. Escuti,et al.  Polarization-independent tunable optical filters based on bilayer polarization gratings , 2008, Organic Photonics + Electronics.

[2]  H. Kogelnik.  Coupled wave theory for thick hologram gratings , 1969 .

[3]  Joachim Stumpe,et al.  Photo-Induced Alignment of LC Polymers by Photoorientation and Thermotropic Self-Organization , 2001 .

[4]  Szabolcs Deladi,et al.  Control of an electrowetting-based beam deflector , 2010 .

[5]  R. Häussler,et al.  Large holographic 3D display for real-time computer-generated holography , 2017, Other Conferences.

[6]  B. D. Cook,et al.  Unified Approach to Ultrasonic Light Diffraction , 1967, IEEE Transactions on Sonics and Ultrasonics.

[7]  Nelson V. Tabiryan,et al.  OPTICAL AXIS GRATINGS IN LIQUID CRYSTALS AND THEIR USE FOR POLARIZATION INSENSITIVE OPTICAL SWITCHING , 2009 .

[8]  Michael J. Escuti,et al.  Compact spectrophotometer using polarization-independent liquid crystal tunable optical filters , 2007, SPIE Organic Photonics + Electronics.

[9]  Hang,et al.  Polarization volume grating with high efficiency and large diffraction angle , 2016 .

[10]  Hong Hua,et al.  A compact eyetracked optical see-through head-mounted display , 2012, Electronic Imaging.

[11]  Michael J. Escuti,et al.  Numerical analysis of polarization gratings using the finite-difference time-domain method , 2007 .

[12]  Chulwoo Oh,et al.  Achromatic diffraction from polarization gratings with high efficiency. , 2008, Optics letters.

[13]  Dirk J. Broer,et al.  Generation of Anisotropic Emission by Light-Induced Orientation of Liquid Crystalline Polymers , 2011 .

[14]  Ludmila Nikolova,et al.  Diffraction Efficiency and Selectivity of Polarization Holographic Recording , 1984 .

[15]  Thad Starner,et al.  A review of head-mounted displays (HMD) technologies and applications for consumer electronics , 2013, Defense, Security, and Sensing.

[16]  Hiroshi Ono,et al.  Polarization Holographic Device Using Photoreactive Polymer Liquid Crystals , 2005 .

[17]  Akira Emoto,et al.  Highly stable polarization gratings in photocrosslinkable polymer liquid crystals , 2003 .

[18]  Michael J. Escuti,et al.  Simplified spectropolarimetry using reactive mesogen polarization gratings , 2006, SPIE Optics + Photonics.

[19]  Gregory P. Crawford,et al.  Liquid-crystal diffraction gratings using polarization holography alignment techniques , 2005 .

[20]  Alexander A. Cameron.  Optical waveguide technology and its application in head-mounted displays , 2012, Defense + Commercial Sensing.

[21]  R Häussler,et al.  Large real-time holographic 3D displays: enabling components and results. , 2017, Applied optics.

[22]  Hong Hua,et al.  Head-Mounted Display Systems , 2005 .

[23]  M. Moharam,et al.  Criterion for Bragg and Raman-Nath diffraction regimes. , 1978, Applied optics.

[24]  Christof Pruss,et al.  Active and Passive LC Based Polarization Elements , 2014 .

[25]  Hong Hua,et al.  Design of a polarized head-mounted projection display using FLCOS microdisplays , 2007, SPIE OPTO.

[26]  Y. Gritsai,et al.  Fabrication and performance of efficient thin circular polarization gratings with Bragg properties using bulk photo-alignment of a liquid crystalline polymer , 2018 .

[27]  J Turunen,et al.  Paraxial-domain diffractive elements with 100% efficiency based on polarization gratings. , 2000, Optics letters.

[28]  Ludmila Nikolova,et al.  High-sensitivity material with reversible photo-induced anisotropy , 1983 .

[29]  Michael J. Escuti,et al.  34.4L: Late‐News Paper: Polarization Independent Projection Systems Using Thin Film Polymer Polarization Gratings and Standard Liquid Crystal Microdisplays , 2009 .