@article{li_shi_kim_escuti_2022, title={Color-selective geometric-phase lenses for focusing and imaging based on liquid crystal polymer films}, volume={30}, ISSN={["1094-4087"]}, url={https://doi.org/10.1364/OE.444578}, DOI={10.1364/OE.444578}, abstractNote={The geometric-phase lens (GPLs) with small form factor compared to traditional refractive lenses has been identified as a compelling solution in augmented-/virtual-/mixed-reality (AR/VR/MR) headsets. Formed either with liquid crystals (LCs) or metasurfaces, the GPL is a type of emerging leading technology that implements the arbitrary aspheric phase to realize low loss and minimal ghosting. However, the inherent chromatic abberation (CA) of GPLs can significantly degrade the image quality. A possible solution is the independent spectral phase implementation for RGB. In this work, we propose the design of three types of multi-twist LC based color-selective GPLs (CS-GPLs), exhibiting highly chromatic efficiency spectra with diameter 30 mm, focal length around 41.2~mm, and F −number 1.37. Through theoretical and experimental validation, each type of CS-GPL manifests high diffraction efficiency (>91%) on respective primary color of orthogonal polarization and high transmission on the complementary color of input polarization. The triplet composed by RGB CS-GPLs demonstrates relative contrast ratio and minimal ghosting. The strong color and polarization dependency of CS-GPLs not only provide a novel technique to mitigate CA but also offer more design freedom in the AR/VR/MR polarization and imaging system.}, number={2}, journal={OPTICS EXPRESS}, publisher={The Optical Society}, author={Li, Lingshan and Shi, Shuojia and Kim, Jihwan and Escuti, Michael J.}, year={2022}, month={Jan}, pages={2487–2502} }
 @article{kim_escuti_2019, title={Polarization grating exposure method with easily tunable period via dual rotating polarization grating masks}, volume={36}, ISSN={["1520-8540"]}, DOI={10.1364/JOSAB.36.000D42}, abstractNote={We introduce a new approach, to the best of our knowledge, to record polarization gratings (PGs) based on dual rotating polarization grating masks. In prior approaches, the linear variation of the orientation angle of the PG pattern was accomplished using discrete holographic optics, which require careful precision alignment, and wherein the relative distances between those optics limit the upper range of PG periods that can be made. Conversely, the setup described and demonstrated here as a single stage is very compact and more robust to vibration compared to other approaches. Moreover, this approach can easily tune the PG period while maintaining the compact size of the setup. This technique enables easy fabrication of arbitrarily large-period PGs. In this work, we discuss general design principles and critically evaluate this fabrication method, as compared to the best of prior approaches.}, number={5}, journal={JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS}, author={Kim, Jihwan and Escuti, Michael J.}, year={2019}, month={May}, pages={D42–D46} }
 @article{snik_rodenhuis_escuti_brickson_hornburg_kim_kievid_groenhuijsen_roosegaarde_2019, title={Producing true-color rainbows with patterned multi-layer liquid-crystal polarization gratings}, volume={9}, ISSN={["2159-3930"]}, DOI={10.1364/OME.9.001583}, abstractNote={We present the technical design of the art installation Rainbow Station, that projects a 40-m diameter true-color rainbow. The core technology is comprised of a patterned polarization grating that produces the rainbow with the correct shape and correct color order. We achieve an effective grating period as small as 1.55 µm, and obtain high diffraction efficiency over the entire visible spectral range thanks to a multi-layer liquid-crystal implementation. The -1 spectral order is suppressed by circular polarization filtering.}, number={4}, journal={OPTICAL MATERIALS EXPRESS}, author={Snik, Frans and Rodenhuis, Michiel and Escuti, Michael J. and Brickson, Leandra and Hornburg, Kathryn and Kim, Jihwan and Kievid, Chris and Groenhuijsen, Sebastiaan and Roosegaarde, Daan}, year={2019}, month={Apr}, pages={1583–1589} }
 @article{xiang_kim_escuti_2018, title={Bragg polarization gratings for wide angular bandwidth and high efficiency at steep deflection angles}, volume={8}, ISSN={["2045-2322"]}, url={https://doi.org/10.1038/s41598-018-25535-0}, DOI={10.1038/s41598-018-25535-0}, abstractNote={Abstract}, number={1}, journal={SCIENTIFIC REPORTS}, publisher={Springer Nature}, author={Xiang, Xiao and Kim, Jihwan and Escuti, Michael J.}, year={2018}, month={May} }
 @article{hornburg_xiang_kim_kudenov_escuti_2018, title={Design and fabrication of an aspheric geometric-phase lens doublet}, volume={10735}, ISSN={["1996-756X"]}, DOI={10.1117/12.2322327}, abstractNote={A prior simulation-only study of aspherical phase profiles [Hornburg et al, Proc SPIE 10743, 10743-4 (2018)] in geometric-phase lenses (GPLs) indicated that aspherical doublet lens systems should provide substantially improved off-axis performance than those using spherical phase profiles. In this work, we fabricate a liquid crystal GPL doublet (24.5 mm diameter, 40 mm back focal length at 633 nm) and compare it to with a reference spherical GPL singlet. We characterized the liquid crystal alignment quality, efficiencies, and spot performance. With these compact GP lens systems, we realize improved performance for wider fields of view, while maintaining low loss.}, journal={LIQUID CRYSTALS XXII}, author={Hornburg, Kathryn J. and Xiang, Xiao and Kim, Jihwan and Kudenov, Michael W. and Escuti, Michael J.}, year={2018} }
 @article{xiang_kim_escuti_2018, title={Wide Field-of-View Nanoscale Bragg Liquid Crystal Polarization Gratings}, volume={10555}, ISSN={["1996-756X"]}, DOI={10.1117/12.2303994}, abstractNote={Here, we demonstrate a liquid crystal (LC) polymer Bragg polarization grating (PG) with large angular band- width and high efficiency in transmission-mode for 532 nm wavelength and 400 nm period. The field-of-view (FOV ) is increased significantly while preserving high diffraction efficiency by realizing a monolithic grating comprising two different slants. Using rigorous coupled-wave analysis simulation, we identified a structure with 48° FOV and 70% average first-order efficiency. We then experimentally fabricated and characterized the grating with a photo-aligned LC polymer network, also known as reactive mesogens. We measured 40° FOV and nearly 80% average diffraction efficiency. With this broadened and fairly uniform angular response, this wide FOV Bragg PG is a compelling option for large deflection-angle applications, including near-eye display in augmented reality systems, waveguide based illumination, and beam steering.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES XIII}, author={Xiang, Xiao and Kim, Jihwan and Escuti, Michael J.}, year={2018} }
 @article{homburg_kim_escuti_2017, title={Experimental characterization of a F/1.5 geometric-phase lens with high achromatic efficiency and low aberration}, volume={10125}, ISBN={["978-1-5106-0692-0"]}, ISSN={["0277-786X"]}, DOI={10.1117/12.2258545}, abstractNote={We report on the properties of a fast F/1.5 geometric-phase lens with a focal length of 37 mm at 633 nm and a 24.5 mm diameter. This lens employs photo-aligned liquid crystal layers to implement the spatially varying Pancharatnam-Berry phase, leading to the expected polarization- and wavelength-dependent focusing. An achromatic spectrum is achieved using (chiral nematic) multi-twist retarder coatings, with high first-order (≥98%) and low zero-order (≤1%) transmittance across 450-700 nm. We measure traditional optical metrics of the GP lens including focused spot profile and modulation transfer function through knife edge testing and NBS 1963a resolution charts. This work includes a comparison to similar F/# conventional thick and thin lenses.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES XII}, author={Homburg, Kathryn J. and Kim, Jihwan and Escuti, Michael J.}, year={2017} }
 @article{xiang_kim_escuti_2017, title={Far-field and Fresnel Liquid Crystal Geometric Phase Holograms via Direct-Write Photo-Alignment}, volume={7}, ISSN={["2073-4352"]}, DOI={10.3390/cryst7120383}, abstractNote={We study computer-generated geometric-phase holograms (GPHs) realized by photo-aligned liquid crystals, in both simulation and experiment. We demonstrate both far-field and Fresnel holograms capable of producing far-field and near-field images with preserved fidelity for all wavelengths. The GPHs are fabricated by patterning a photo-alignment layer (PAL) using a direct-write laser scanner and coating the surface with a polymerizable liquid crystal (i.e., a reactive mesogen). We study various recording pixel sizes, down to 3 μm, that are easily recorded in the PAL. We characterize the fabricated elements and find good agreement with theory and numerical simulation. Because of the wavelength independent geometric phase, the (phase) fidelity of the replay images is preserved for all wavelengths, unlike conventional dynamic phase holograms. However, governed by the diffraction equation, the size and location of a reconstructed image depends on the replay wavelength for far-field and near-field GPHs, respectively. These offer interesting opportunities for white-light holography.}, number={12}, journal={CRYSTALS}, author={Xiang, Xiao and Kim, Jihwan and Escuti, Michael J.}, year={2017}, month={Dec} }
 @article{xiang_kim_komanduri_escuti_2017, title={Nanoscale liquid crystal polymer Bragg polarization gratings}, volume={25}, ISSN={["1094-4087"]}, DOI={10.1364/oe.25.019298}, abstractNote={We experimentally demonstrate nearly ideal liquid crystal (LC) polymer Bragg polarization gratings (PGs) operating at a visible wavelength of 450 nm and with a sub-wavelength period of 335 nm. Bragg PGs employ the geometric (Pancharatnam-Berry) phase, and have many properties fundamentally different than their isotropic analog. However, until now Bragg PGs with nanoscale periods (e.g., < 800 nm) have not been realized. Using photo-alignment polymers and high-birefringence LC materials, we employ multiple thin sublayers to overcome the critical thickness threshold, and use chiral dopants to induce a helical twist that effectively generates a slanted grating. These LC polymer Bragg PGs manifest 85-99% first-order efficiency, 19-29° field-of-view, Q ≈ 17, 200 nm spectral bandwidth, 84° deflection angle in air (in one case), and efficient waveguide-coupling (in another case). Compared to surface-relief and volume-holographic gratings, they show high efficiency with larger angular/spectral bandwidths and potentially simpler fabrication. These nanoscale Bragg PGs manifest a 6π rad/μm phase gradient, the largest reported for a geometric-phase hologram while maintaining a first-order efficiency near 100%.}, number={16}, journal={OPTICS EXPRESS}, author={Xiang, Xiao and Kim, Jihwan and Komanduri, Ravi and Escuti, Michael J.}, year={2017}, month={Aug}, pages={19298–19308} }
 @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_miskiewicz_serati_escuti_2015, title={Nonmechanical Laser Beam Steering Based on Polymer Polarization Gratings: Design Optimization and Demonstration}, volume={33}, ISSN={["1558-2213"]}, DOI={10.1109/jlt.2015.2392694}, abstractNote={We present a wide-angle, nonmechanical laser beam steerer based on polymer polarization gratings with an optimal design approach for maximizing field-of-regard (FOR). The steering design offers exponential scaling of the number of steering angles, called suprabinary steering. The design approach can be easily adapted for any 1-D or 2-D (e.g, symmetric or asymmetric FOR) beam steering. We simulate a system using a finite difference and ray tracing tools and fabricate coarse beam steerer with 65° FOR with ~8° resolution at 1550 nm. We demonstrate high optical throughput (84%-87%) that can be substantially improved by optimizing substrates and electrode materials. This beam steerer can achieve very low sidelobes and supports comparatively large beam diameters paired with a very thin assembly and low beam walk-off. We also demonstrate using a certain type of LC variable retarder that the total switching time from any steering angle to another can be 1.7 ms or better.}, number={10}, journal={JOURNAL OF LIGHTWAVE TECHNOLOGY}, author={Kim, Jihwan and Miskiewicz, Matthew N. and Serati, Steve and Escuti, Michael J.}, year={2015}, month={May}, pages={2068–2077} }
 @article{kim_komanduri_escuti_2012, title={A compact holographic recording setup for tuning pitch using polarizing prisms}, volume={8281}, ISSN={["0277-786X"]}, DOI={10.1117/12.913952}, abstractNote={We introduce and demonstrate a new holographic recording technique based on birefringent prisms for creating polarization gratings (PGs). Conventional holographic arrangements for creating PGs consist of several polarization and collimating optics that are carefully aligned with each other, and often require substantial physical space. Both the size and the relative distance between these optics increase for large exposure areas, that limit the range of grating period achievable. Moreover, the cost and complexity associated with the mounting of the several elements also increases, and therefore such approaches are not viable for large area PGs and large volume manufacturing. To overcome the above limitations, we propose new approach using multiple polarizing prisms to record PGs that is compact, scalable for large areas, and enables easy tuning of the grating period by simple rotation of at most two elements.}, journal={PRACTICAL HOLOGRAPHY XXVI: MATERIALS AND APPLICATIONS}, author={Kim, Jihwan and Komanduri, Ravi K. and Escuti, Michael J.}, year={2012} }
 @article{kim_komanduri_lawler_kekas_escuti_2012, title={Efficient and monolithic polarization conversion system based on a polarization grating}, volume={51}, ISSN={["2155-3165"]}, DOI={10.1364/ao.51.004852}, abstractNote={We introduce a new polarization conversion system (PCS) based on a liquid-crystal polarization grating (PG) and louvered wave plate. A simple arrangement of these elements laminated between two microlens arrays results in a compact and monolithic element, with the ability to nearly completely convert unpolarized input into linearly polarized output across most of the visible bandwidth. In our first prototypes, this PG-PCS approach manifests nearly 90% conversion efficiency of unpolarized to polarized for ±11° input light divergence, leading to an energy efficient picoprojector that presents high efficacy (12 lm/W) with good color uniformity.}, number={20}, journal={APPLIED OPTICS}, author={Kim, Jihwan and Komanduri, Ravi K. and Lawler, Kristopher F. and Kekas, D. Jason and Escuti, Michael J.}, year={2012}, month={Jul}, pages={4852–4857} }
 @article{komanduri_kim_lawler_escuti_2012, title={Multi-twist retarders for broadband polarization transformation}, volume={8279}, ISSN={["0277-786X"]}, DOI={10.1117/12.913795}, abstractNote={We introduce a family of broadband retarders, comprised of a low number of twisted nematic liquid crystal layers, that accomplishes well-controlled polarization transformation for nearly any bandwidth desired. For example, we show that broadband linear to circular polarization conversion can be achieved with only two twist layers where the performance matches the popular three-waveplate approach by Pancharatnam. Using liquid crystal polymers on a single substrate, we show how these multi-twist retarders are embodied as a monolithic birefringent plate with excellent performance and potentially very low cost.}, journal={EMERGING LIQUID CRYSTAL TECHNOLOGIES VII}, author={Komanduri, Ravi K. and Kim, Jihwan and Lawler, Kristopher F. and Escuti, Michael J.}, year={2012} }
 @article{miskiewicz_kim_li_komanduri_escuti_2012, title={Progress on large-area polarization grating fabrication}, volume={8395}, ISSN={["0277-786X"]}, DOI={10.1117/12.921572}, abstractNote={Over the last several years, we have pioneered liquid crystal polarization gratings (PGs), in both switchable and polymer versions. We have also introduced their use in many applications, including mechanical/non-mechanical laser beam steering and polarization imaging/sensing. Until now, conventional holographic congurations were used to create PGs where the diameter of the active area was limited to 1-2 inches. In this paper, we discuss a new holography setup to fabricate large area PGs using spherical waves as the diverging coherent beams. Various design parameters of this setup are examined for impact on the quality of the recorded PG profile. Using this setup, we demonstrate a large area polymer PG with approximately 66 inch square area, and present detailed characterization.}, journal={ACQUISITION, TRACKING, POINTING, AND LASER SYSTEMS TECHNOLOGIES XXVI}, author={Miskiewicz, Matthew N. and Kim, Jihwan and Li, Yanming and Komanduri, Ravi K. and Escuti, Michael J.}, year={2012} }
 @article{kim_miskiewicz_serati_escuti_2011, title={Demonstration of large-angle nonmechanical laser beam steering based on LC polymer polarization gratings}, volume={8052}, ISSN={["1996-756X"]}, DOI={10.1117/12.886508}, abstractNote={Polarization gratings (PGs) as polarization sensitive diffractive optical elements work in broadband (UV to Mid- IR) with nearly 100% diffraction efficiency. We have introduced and utilized the PGs in different types of beam steering modules presented in our previous papers. Here, we describe and demonstrate a nonmechanical beam steering device based on passive gratings, liquid crystal (LC) polymer PGs. The device covers a large-angle Field-Of-Regard (FOR) with high efficiency, and is based on a stack of alternating LC half-wave plates and LC polymer PGs. The half-wave plates are switchable and are used to select the handedness of the circularly polarized input beam. The polymer PGs diffract the input beam to either of the first diffraction orders based on the circular handedness of the beam previously selected. When compared with conventional beam steering methods based on active gratings (ternary and quasi-ternary designs), this technique is experimentally able to steer an equivalent number of angles with similar efficiency, but fewer LC cells, and hence, fewer transparent electrodes and lower absorption. We successfully demonstrate the ability to steer 80° FOR with roughly 2.6° resolution at 1064 nm wavelength.}, journal={ACQUISITION, TRACKING, POINTING, AND LASER SYSTEMS TECHNOLOGIES XXV}, author={Kim, Jihwan and Miskiewicz, Matthew N. and Serati, Steve and Escuti, Michael J.}, year={2011} }
 @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{kim_miskiewicz_serati_escuti_2010, title={High efficiency quasi-ternary design for nonmechanical beam-steering utilizing polarization gratings}, volume={7816}, ISSN={["1996-756X"]}, DOI={10.1117/12.860885}, abstractNote={We introduce and demonstrate a quasi-ternary nonmechanical beam steering design based on Polarization Gratings (PGs). That uses a single wave plate and N PGs to generate 2(N+1)-1 steering angles. When compared to conventional binary (2N) or ternary (3N) liquid crystal PG steering designs, this technique uses fewer elements arranged in a simpler configuration to obtain the same number of steering angles. This advantageous property can be achieved by selecting proper diffraction angles and alignment of the PGs. Due to fewer elements per stage, losses due to electrode absorption and Fresnel reflections are reduced, thereby increasing the overall steering efficiency. Using this approach, we demonstrate a four-stage (N = 4) quasi-ternary beam steering device that achieves 52° Field Of Regard (FOR) with 1.7° resolution (31 steering angles) at 1550 nm wavelength.}, journal={ADVANCED WAVEFRONT CONTROL: METHODS, DEVICES, AND APPLICATIONS VIII}, author={Kim, Jihwan and Miskiewicz, Matthew N. and Serati, Steve and Escuti, Michael J.}, year={2010} }