ImagineOptix / NCSU Presents at 2017 SPIE Photonics West Conference

Symposium: SPIE OPTO 
Symposium Dates: 28 January – 2 February 2017 
Symposium Location: San Francisco, California United States 
Conference 10125: Emerging Liquid Crystal Technologies XII 

Presentation Title: Numerical analysis of Bragg regime polarization gratings by rigorous coupled-wave analysis
Session 3: Applications, Materials, and Processes II
When: Monday 30 January 2017
Time: 4:30 PM – 4:50 PM
Location: Room 309 (South Esplanade)
Paper: 10127-12
Author(s): Xiao Xiang, Michael J. Escuti, North Carolina State Univ. (United States)
We report on the numerical analysis of liquid crystal based Bragg polarization gratings (PGs), and study their general diffraction properties by Rigorous Coupled-Wave Analysis (RCWA). Different from traditional Bragg (isotropic) gratings, Bragg PGs are verified to have high diffraction efficiency for large field of view, which is ideal for exit-pupil-expanders in waveguide-based head-mounted-displays, spectroscopy, and fiber-optic telecommunication systems. The RCWA approach provides a rigorous and accurate solution for transmittance and reflectance without paraxial approximations at much lower computational cost, as compared to other pure numerical and analytical methods. Diffraction characteristics including angular response, spectral response and polarization sensitivity are investigated.

Presentation Title: Experimental realization of Bragg liquid crystal polarization gratings (Invited Paper)
Session 9: Emerging Technologies and Displays
When: Wednesday 1 February 2017
Time: 2:35 PM – 3:00 PM
Location: Room 125 (North Exhibit Level)
Paper: 10125-56
Author(s): Michael J. Escuti, Xiao Xiang, Jihwan Kim, North Carolina State Univ. (United States); Ravi K. Komanduri, ImagineOptix Corp. (United States)
We have successfully realized liquid crystal polarization gratings (PGs) with > 90% diffraction efficiency, at periods down to 335 nm, when illuminated with visible light. We have also realized experimentally the technique of slanting the grating vector using chiral dopants, effectively providing a complete and compelling analog to conventional Bragg volume holograms. Bragg PGs employ geometric phase, also called the Pancharatnam-Berry phase, rather than the conventional dynamic phase, and this leads to unique and often unexpected optical behavior. In one configuration, these gratings will diffract first-order light into high-index waveguide angles from on-axis directions, or alternatively, can produce wide chromatic dispersion into air. We employ photo-aligned reactive mesogens, also called liquid crystal polymer networks, and both spin-coating and holographic lithography. While liquid crystal PGs with relatively large periods (≥ 2 µm) were realized with high efficiency over the past decade, small period liquid crystal PGs (< 1 µm) were considered by some to have several fundamental challenges making them experimentally impossible. However, we have overcome these challenges. In this talk, we will discuss how we have done so, report on the experimental behavior of these Bragg PGs including their spectral, field-of-view (FOV), and polarization, and discuss the vast array of applications now possible, including head-mounted-displays, blazed gratings for spectroscopy and telecom, beam combining, and optical remote sensing. Presentation Title: Experimental realization and characterization of a F/1.5 geometric-phase lens with high-achromatic efficiency and low aberration Session 8: Lenses and Diffractive Optics When: Wednesday 1 February 2017 Time: 2:20 PM - 2:35 PM Location: Room 125 (North Exhibit Level) Paper: 10125-42 Author(s): Kathryn J. Hornburg, Jihwan Kim, Michael J. Escuti, North Carolina State Univ. (United States) Abstract: We report on the fabrication and properties of a 24.5 mm diameter and 0.45 mm thick lens that manifests F/1.5 at 633 nm and has high efficiency across 450-700 nm. This lens is a type of Geometric-Phase Lens (i.e., Pancharatnam-Berry lens) formed as a thin-film of photo-aligned liquid crystal. It has strong polarization dependence and wavelength-dependent focal length. Prior work on Geometric-Phase Lenses in liquid crystals and metasurfaces has been limited to larger F/#s (≥F/2.1 or ≥F/7, respectively) or small areas (≤16mm or <5mm, respectively), or both. This talk reports on the largest and fastest Geometric-Phase Lens reported to date.

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