@article{kim_li_miskiewicz_oh_kudenov_escuti_2015, title={Fabrication of ideal geometric-phase holograms with arbitrary wavefronts}, volume={2}, ISSN={["2334-2536"]}, DOI={10.1364/optica.2.000958}, abstractNote={Throughout optics and photonics, phase is normally controlled via an optical path difference. Although much less common, an alternative means for phase control exists: a geometric phase (GP) shift occurring when a light wave is transformed through one parameter space, e.g., polarization, in such a way as to create a change in a second parameter, e.g., phase. In thin films and surfaces where only the GP varies spatially—which may be called GP holograms (GPHs)—the phase profile of nearly any (physical or virtual) object can in principle be embodied as an inhomogeneous anisotropy manifesting exceptional diffraction and polarization behavior. Pure GP elements have had poor efficiency and utility up to now, except in isolated cases, due to the lack of fabrication techniques producing elements with an arbitrary spatially varying GP shift at visible and near-infrared wavelengths. Here, we describe two methods to create high-fidelity GPHs, one interferometric and another direct-write, capable of recording the wavefront of nearly any physical or virtual object. We employ photoaligned liquid crystals to record the patterns as an inhomogeneous optical axis profile in thin films with a few μm thickness. We report on eight representative examples, including a GP lens with F/2.3 (at 633 nm) and 99% diffraction efficiency across visible wavelengths, and several GP vortex phase plates with excellent modal purity and remarkably small central defect size (e.g., 0.7 and 7 μm for topological charges of 1 and 8, respectively). We also report on a GP Fourier hologram, a fan-out grid with dozens of far-field spots, and an elaborate phase profile, which showed excellent fidelity and very low leakage wave transmittance and haze. Together, these techniques are the first practical bases for arbitrary GPHs with essentially no loss, high phase gradients (∼rad/μm), novel polarization functionality, and broadband behavior.}, number={11}, journal={OPTICA}, author={Kim, Jihwan and Li, Yanming and Miskiewicz, Matthew N. and Oh, Chulwoo and Kudenov, Michael W. and Escuti, Michael J.}, year={2015}, month={Nov}, pages={958–964} }
 @article{kim_oh_serati_escuti_2011, title={Wide-angle, nonmechanical beam steering with high throughput utilizing polarization gratings}, volume={50}, ISSN={["2155-3165"]}, DOI={10.1364/ao.50.002636}, abstractNote={We introduce and demonstrate a ternary nonmechanical beam steering device based on polarization gratings (PGs). Our beam steering device employs multiple stages consisting of combinations of PGs and wave plates, which allows for a unique three-way (ternary) steering design. Ultrahigh efficiency (∼100%) and polarization sensitive diffraction of individual PGs allow wide steering angles (among three diffracted orders) with extremely high throughput. We report our successful demonstration of the three-stage beam steerer having a 44° field of regard with 1.7° resolution at 1550  nm wavelength. A substantially high throughput of 78%-83% is observed that is mainly limited by electrode absorption and Fresnel losses.}, number={17}, journal={APPLIED OPTICS}, author={Kim, Jihwan and Oh, Chulwoo and Serati, Steve and Escuti, Michael J.}, year={2011}, month={Jun}, pages={2636–2639} }
 @article{oh_kim_muth_serati_escuti_2010, title={High-Throughput Continuous Beam Steering Using Rotating Polarization Gratings}, volume={22}, ISSN={["1041-1135"]}, DOI={10.1109/LPT.2009.2037155}, abstractNote={A new beam steering concept comprising independently rotating, inline polarization gratings (PGs) is experimentally demonstrated. The approach, which we term Risley gratings, achieves high steering throughput within a large field-of-regard (FOR) in a fashion similar to Risley prisms, composed of wedged prisms. However, because PGs are patterned in thin liquid crystal layers, they enable a system with far less thickness, weight, and beam walk-off. Furthermore, large apertures are feasible and wavelengths from visible to infrared can be chosen. Any direction within a solid angle defined by twice the diffraction angle of each PG can be addressed mechanically. Here we demonstrate a Risley grating system with a 62° FOR and 89%-92% transmittance at 1550-nm wavelength, using two PGs with 6-¿m grating period.}, number={4}, journal={IEEE PHOTONICS TECHNOLOGY LETTERS}, author={Oh, Chulwoo and Kim, Jihwan and Muth, John and Serati, Steve and Escuti, Michael J.}, year={2010}, month={Feb}, pages={200–202} }
 @article{oh_escuti_2009, title={Achromatic diffraction from polarization gratings with high efficiency (vol 33, pg 2287, 2008)}, volume={34}, ISSN={["1539-4794"]}, DOI={10.1364/ol.34.003637}, abstractNote={In a previous letter [Opt. Lett.33, 2287 (2008)] the incorrect chiral-molecule concentrations of CB15 and ZLI-811 here provided. That error is corrected here.}, number={23}, journal={OPTICS LETTERS}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2009}, month={Dec}, pages={3637–3637} }
 @article{oh_escuti_2008, title={Achromatic diffraction from polarization gratings with high efficiency}, volume={33}, ISSN={["0146-9592"]}, DOI={10.1364/OL.33.002287}, abstractNote={We demonstrate a broadband, thin-film, polarizing beam splitter based on an anisotropic diffraction grating composed of reactive mesogens (polymerizable liquid crystals). This achromatic polarization grating (PG) manifests high diffraction efficiency (approximately 100%) and high extinction ratio (> or = 1000:1) in both theory and experiment. We show an operational bandwidth Deltalambda/lambda0 approximately 56% (roughly spanning visible wavelength range) that represents more than a fourfold increase of bandwidth over conventional PGs (and significantly larger than any other grating). The diffraction angle and operational region (visible, near-infrared, midwave infrared, and ultraviolet wavelengths) may be easily tailored during fabrication. The essence of the achromatic design is a stack of two chiral PGs with an opposite twist sense and employs the principle of retardation compensation. We fully characterize its optical properties and derive the theoretical diffraction behavior.}, number={20}, journal={OPTICS LETTERS}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2008}, month={Oct}, pages={2287–2289} }
 @article{oh_escuti_2007, title={Numerical analysis of polarization gratings using the finite-difference time-domain method}, volume={76}, ISSN={["1094-1622"]}, DOI={10.1103/physreva.76.043815}, abstractNote={We report the first full numerical analysis of polarization gratings (PGs), and study their most general properties and limits by using the finite-difference time-domain (FDTD) method. In this way, we avoid limiting assumptions on material properties or grating dimensions (e.g., no paraxial approximations) and provide a more complete understanding of PG diffraction behavior. We identify the fundamental delineation between diffraction regimes (thin versus thick) for anisotropic gratings and determine the conditions for $\ensuremath{\approx}100%$ diffraction efficiency in the framework of the coupled-wave $\ensuremath{\rho}$ and $Q$ parameters. Diffraction characteristics including the efficiency, spectral response, and polarization sensitivity are investigated for the two primary types of PGs with linear and circular birefringence. The angular response and finite-grating behavior (i.e., pixelation) are also examined. Comparisons with previous analytic approximations, where applicable, show good agreement.}, number={4}, journal={PHYSICAL REVIEW A}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2007}, month={Oct} }
 @article{oh_escuti_2006, title={Time-domain analysis of periodic anisotropic media at oblique incidence: an efficient FDTD implementation}, volume={14}, ISSN={["1094-4087"]}, DOI={10.1364/OE.14.011870}, abstractNote={We describe an efficient implementation of the finite-difference time-domain (FDTD) method as applied to lightwave propagation through periodic media with arbitrary anisotropy (birefringence). A permittivity tensor with non-diagonal elements is successfully integrated here with periodic boundary conditions, bounded computation space, and the split-field update technique. This enables modeling of periodic structures using only one period even with obliquely incident light in combination with both monochromatic (sinusoidal) and wideband (time-domain pulse) sources. Comparisons with results from other techniques in four validation cases are presented and excellent agreement is obtained. Our implementation is freely available on the Web.}, number={24}, journal={OPTICS EXPRESS}, author={Oh, Chulwoo and Escuti, Michael J.}, year={2006}, month={Nov}, pages={11870–11884} }
 @article{komanduri_jones_oh_escuti, title={Polarization-independent modulation for projection displays using small-period LC polarization gratings}, volume={15}, number={8}, journal={Journal of the Society for Information Display}, author={Komanduri, R. K. and Jones, W. M. and Oh, C. and Escuti, M. J.}, pages={589–594} }