@article{kudenov_miskiewicz_sanders_escuti_2016, title={Achromatic Wollaston prism beam splitter using polarization gratings}, volume={41}, ISSN={["1539-4794"]}, DOI={10.1364/ol.41.004461}, abstractNote={We describe a method to achromatize a Wollaston prism beam splitter by combining it with a polarization grating. The advantage of this technique, compared to refractive methods of correction, is that only one type of birefringent crystal is needed. Additionally, the assembly can be made thinner while remaining achromatized. In this Letter, a model for the achromatized grating prism is formulated. Experimental validation is conducted by achromatizing a calcite Wollaston prism (apex angle of 5.35°) using a polarization grating with a spatial period of 253 μm. We found that the primary dispersion was reduced by approximately 6.5 times for wavelengths spanning the conventional F, d, and C Fraunhofer lines (486 to 656 nm).}, number={19}, journal={OPTICS LETTERS}, author={Kudenov, Michael W. and Miskiewicz, Matthew and Sanders, Nathan and Escuti, Michael J.}, year={2016}, month={Oct}, pages={4461–4463} }
 @article{maione_luo_miskiewicz_escuti_kudenov_2016, title={Spatially heterodyned snapshot imaging spectrometer}, volume={55}, ISSN={["2155-3165"]}, DOI={10.1364/ao.55.008667}, abstractNote={Snapshot hyperspectral imaging Fourier transform (SHIFT) spectrometers are a promising technology in optical detection and target identification. For any imaging spectrometer, spatial, spectral, and temporal resolution, along with form factor, power consumption, and computational complexity are often the design considerations for a desired application. Motivated by the need for high spectral resolution systems, capable of real-time implementation, we demonstrate improvements to the spectral resolution and computation trade-space. In this paper, we discuss the implementation of spatial heterodyning, using polarization gratings, to improve the spectral resolution trade space of a SHIFT spectrometer. Additionally, we employ neural networks to reduce the computational complexity required for data reduction, as appropriate for real-time imaging applications. Ultimately, with this method we demonstrate an 87% decrease in processing steps when compared to Fourier techniques. Additionally, we show an 80% reduction in spectral reconstruction error and a 30% increase in spatial fidelity when compared to linear operator techniques.}, number={31}, journal={APPLIED OPTICS}, author={Maione, Bryan D. and Luo, David and Miskiewicz, Matthew and Escuti, Michael and Kudenov, Michael W.}, year={2016}, month={Nov}, pages={8667–8675} }
 @article{xiang_miskiewicz_escuti_2015, title={Distortion-free broadband holograms: A novel class of elements utilizing the wavelength-independent geometric phase}, volume={9386}, ISSN={["1996-756X"]}, DOI={10.1117/12.2084722}, abstractNote={We demonstrate a novel class of elements called Far-Field Geometric Phase Holograms (FGPH) capable of producing far-field output images free of chromatic distortion for a broad range of input wavelengths. The FGPH utilizes the geometric phase which applies the same phase profile to any incident wave regardless of wavelength. Thus, the fidelity of an image produced by an FGPH is the same for all wavelengths. However, being a diffractive element, the FGPH is still dispersive in that the size of a generated image depends on the replay wavelength according to the diffraction equation. In this paper, we give theory for the ideal FGPH element, describing its replay characteristics and unique polarization properties. We experimentally realize an FGPH element using photo-aligned liquid crystals patterned with a direct-write system. We characterize the fabricated element and show the theory to be valid. Generally, this new class of polarization sensitive elements can produce broadband undistorted images with high diffraction efficiency.}, journal={PRACTICAL HOLOGRAPHY XXIX: MATERIALS AND APPLICATIONS}, author={Xiang, Xiao and Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2015} }
 @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{miskiewicz_escuti_2015, title={Optimization of direct-write polarization gratings}, volume={54}, ISSN={["1560-2303"]}, DOI={10.1117/1.oe.54.2.025101}, abstractNote={Abstract. We recently reported on a mathematical formalism for analyzing the result of a direct-write scanning system applied to photoaligned liquid crystal films. We use that formalism to study the direct-write recording of polarization gratings (PGs). First, we evaluate three scan paths in simulation and experiment, describe their tradeoffs and practical constraints, and identify the most favorable. Second, we explore the parameter space of direct-write PGs in simulation, which includes four dimensions in general: grating period, line spacing, beam size, and spatially averaged fluence. Using this analysis, we predict that a certain portion of the parameter space should be optimal, leading to high diffraction efficiency and well-aligned PGs. Finally, we experimentally fabricate and characterize nine PGs with scan parameters within and around this optimal parameter space and conclude that the prediction is validated. This work is the first in-depth study of direct-write PGs; it identifies many challenges and solutions, and shows, for the first time, direct-write recorded PGs with quality equivalent to those recorded via holography. In particular, we demonstrate a PG (20  μm period) with first-order diffraction efficiency 99.5%, 0.2% haze, and polarization contrast of 2000.}, number={2}, journal={OPTICAL ENGINEERING}, author={Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2015}, month={Feb} }
 @article{miskiewicz_schmidt_escuti_2014, title={A 2D FDTD Algorithm for Whole-Hemisphere Incidence on Periodic Media}, volume={62}, ISSN={["1558-2221"]}, DOI={10.1109/tap.2013.2296302}, abstractNote={We present a modified version of the 2D split-field finite difference time domain (FDTD) method which enables efficient simulation of periodic structures. Our algorithm allows for broadband, whole-hemisphere oblique incidence sources with structures that are inhomogeneous in permittivity, conductivity, and permeability. The structures considered are of finite extent in one dimension, periodic in a second orthogonal dimension, and uniform (or homogeneous) in a third dimension. With prior FDTD methods, this required a full 3D simulation space. In this work, we reduce the modeling space from a 3D grid to a 2D grid, while still allowing incident waves to be oblique with respect to that dimension. We derive this new algorithm beginning with a complete source definition that allows for arbitrary polarization and incidence direction. The key update equations are found, and we also give a method for finding the full vectorial far-field orders from the simulation output. We validate the method by simulating an etalon, a Bragg grating, and a photonic band gap structure.}, number={3}, journal={IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION}, author={Miskiewicz, Matthew N. and Schmidt, Stefan and Escuti, Michael J.}, year={2014}, month={Mar}, pages={1348–1353} }
 @article{maione_luo_kudenov_escuti_miskiewicz_2014, title={Birefringent snapshot imaging spatial heterodyne spectrometer}, volume={9099}, ISSN={["1996-756X"]}, DOI={10.1117/12.2049726}, abstractNote={High speed spectral imaging is useful for a variety of tasks spanning industrial monitoring, target detection, and chemical identification. To better meet these needs, compact hyperspectral imaging instrumentation, capable of high spectral resolution and real-time data acquisition and processing, are required. In this paper, we describe the first snapshot imaging spatial heterodyne Fourier transform spectrometer based on birefringent crystals and polarization gratings. This includes details about its architecture, as well as our preliminary proof of concept. Finally, we discuss details related to the calibration of the sensor, including our preliminary investigations into high speed data reconstruction and calibration using neural networks. With such an approach, it may be feasible to reconstruct and calibrate an entire interferogram cube in one step with minimal Fast Fourier Transform (FFT) processing.}, journal={POLARIZATION: MEASUREMENT, ANALYSIS, AND REMOTE SENSING XI}, author={Maione, Bryan D. and Luo, David A. and Kudenov, Michael W. and Escuti, Michael J. and Miskiewicz, Matthew N.}, year={2014} }
 @article{miskiewicz_escuti_2014, title={Direct-writing of complex liquid crystal patterns}, volume={22}, ISSN={["1094-4087"]}, DOI={10.1364/oe.22.012691}, abstractNote={We report on a direct-write system for patterning of arbitrary, high-quality, continuous liquid crystal (LC) alignment patterns. The system uses a focused UV laser and XY scanning stages to expose a photoalignment layer, which then aligns a subsequent LC layer. We intentionally arrange for multiple overlapping exposures of the photoalignment material by a scanned Gaussian beam, often with a plurality of polarizations and intensities, in order to promote continuous and precise LC alignment. This type of exposure protocol has not been well investigated, and sometimes results in unexpected LC responses. Ultimately, this enables us to create continuous alignment patterns with feature sizes smaller than the recording beam. We describe the system design along with a thorough mathematical system description, starting from the direct-write system inputs and ending with the estimated alignment of the LC. We fabricate a number of test patterns to validate our system model, then design and fabricate a number of interesting well-known elements, including a q-plate and polarization grating.}, number={10}, journal={OPTICS EXPRESS}, author={Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2014}, month={May}, pages={12691–12706} }
 @article{otten_snik_kenworthy_miskiewicz_escuti_2014, title={Performance characterization of a broadband vector Apodizing Phase Plate coronagraph}, volume={22}, ISSN={["1094-4087"]}, DOI={10.1364/oe.22.030287}, abstractNote={One of the main challenges for the direct imaging of planets around nearby stars is the suppression of the diffracted halo from the primary star. Coronagraphs are angular filters that suppress this diffracted halo. The Apodizing Phase Plate coronagraph modifies the pupil-plane phase with an anti-symmetric pattern to suppress diffraction over a 180 degree region from 2 to 7 λ/D and achieves a mean raw contrast of 10(-4) in this area, independent of the tip-tilt stability of the system. Current APP coronagraphs implemented using classical phase techniques are limited in bandwidth and suppression region geometry (i.e. only on one side of the star). In this paper, we introduce the vector-APP (vAPP) whose phase pattern is implemented through the vector phase imposed by the orientation of patterned liquid crystals. Beam-splitting according to circular polarization states produces two, complementary PSFs with dark holes on either side. We have developed a prototype vAPP that consists of a stack of three twisting liquid crystal layers to yield a bandwidth of 500 to 900 nm. We characterize the properties of this device using reconstructions of the pupil-plane pattern, and of the ensuing PSF structures. By imaging the pupil between crossed and parallel polarizers we reconstruct the fast axis pattern, transmission, and retardance of the vAPP, and use this as input for a PSF model. This model includes aberrations of the laboratory set-up, and matches the measured PSF, which shows a raw contrast of 10(-3.8) between 2 and 7 λ/D in a 135 degree wedge. The vAPP coronagraph is relatively easy to manufacture and can be implemented together with a broadband quarter-wave plate and Wollaston prism in a pupil wheel in high-contrast imaging instruments. The liquid crystal patterning technique permits the application of extreme phase patterns with deeper contrasts inside the dark holes, and the multilayer liquid crystal achromatization technique enables unprecedented spectral bandwidths for phase-manipulation coronagraphy.}, number={24}, journal={OPTICS EXPRESS}, author={Otten, Gilles P. P. L. and Snik, Frans and Kenworthy, Matthew A. and Miskiewicz, Matthew N. and Escuti, Michael J.}, year={2014}, month={Dec}, pages={30287–30314} }
 @article{kudenov_miskiewicz_escuti_coward_2014, title={Polarization spatial heterodyne interferometer: model and calibration}, volume={53}, ISSN={["1560-2303"]}, DOI={10.1117/1.oe.53.4.044104}, abstractNote={Abstract. Spatial heterodyne interferometry (SHI) is a technique based on Fourier transform spectroscopy. As such, many of the benefits, such as high spectral resolving power, can be realized. Furthermore, unlike a Fourier transform spectrometer, an SHI is able to minimize the number of required samples for a given resolving power and spectral range. The calibration and detailed modeling of a polarization spatial heterodyne interferometer (PSHI) are detailed. Unlike our original first-order ray tracing model, the new model is based on the Jones matrix formalism. Using this improved model, we explore the nonideal aspects of the PSHI, including interference effects caused by retardance errors in the polarization grating and quarter wave plate. To minimize the influence of these errors, a calibration procedure is described based on a linear operator theory. Finally, the Jones matrix model and calibration procedure are validated through a series of simulations and experiments.}, number={4}, journal={OPTICAL ENGINEERING}, author={Kudenov, Michael W. and Miskiewicz, Matthew N. and Escuti, Michael J. and Coward, James F.}, year={2014}, month={Apr} }
 @article{otten_snik_kenworthy_miskiewicz_escuti_codona_2014, title={Vector Apodizing Phase Plate coronagraph: prototyping, characterization and outlook}, volume={9151}, ISSN={["0277-786X"]}, DOI={10.1117/12.2056096}, abstractNote={The Apodizing Phase Plate (APP) is a phase-only pupil-plane coronagraph that suppresses starlight in a D-shaped region from 2 to 7 λ D around a target star. Its performance is insensitive to residual tip-tilt variations from the AO system and telescope structure. Using liquid crystal technology we develop a novel and improved version of the APP: the broadband vector Apodizing Phase Plate (vAPP). The vAPP prototype consists of an achromatic half-wave retarder pattern with a varying fast axis encoding phase structure down to 25 microns. The fast axis encodes the required phase pattern through the vector phase, while multiple twisting liquid crystal layers produce a nearly constant half-wave retardance over a broad bandwidth. Since pupil phase patterns are commonly designed to be antisymmetric, two complementary PSFs are produced with dark holes on opposite sides. We summarize results of the characterization of our latest vAPP prototype in terms of pupil phase reconstruction and PSF contrast performance. The liquid crystal patterning technique allows us to manufacture more extreme phase patterns than was possible before. We consider phase-only patterns that yield higher contrasts and better inner working angles than previous APPs, and patterns that produce dark regions 360 degrees around the PSF core. The possibility of including a phase ramp into the coronagraph is demonstrated, which simplifies the vAPP into a single optic. This additional phase ramp removes the need for a quarter-wave plate and a Wollaston prism, and enables the simplified implementation of a vAPP in a filter wheel at a pupil-plane location. Since the phase ramp is analogous to a polarization grating, it generates a (polarized) spectrum of a planet inside the dark hole, and thus allows for instantaneous characterization of the planet.}, journal={ADVANCES IN OPTICAL AND MECHANICAL TECHNOLOGIES FOR TELESCOPES AND INSTRUMENTATION}, author={Otten, Gilles P. P. L. and Snik, Frans and Kenworthy, Matthew A. and Miskiewicz, Matthew N. and Escuti, Michael J. and Codona, Johanan L.}, year={2014} }
 @article{kudenov_miskiewicz_escuti_coward_2013, title={Compact spatial heterodyne interferometer using polarization gratings}, volume={8873}, ISSN={["1996-756X"]}, DOI={10.1117/12.2024104}, abstractNote={Spatial heterodyne interferometry (SHI) is a spectral measurement technique based on Fourier Transform Spectroscopy (FTS). One main benefit of an FTS lies in its higher spectral resolving power over direct measurement (dispersive) systems; however, accessing this higher resolving power can result in longer measurement times without heterodyning techniques. In this paper, the calibration and modeling of a polarization SHI is detailed, based on the Jones matrix formalism. With this, we explore non-ideal aspects of the polarization grating, such as zero-order light leakage. This light leakage causes crosstalk that can introduce errors in the spectral calibration. To minimize error, a calibration procedure is introduced based on a linear operator theory. Finally, the Jones matrix model and calibration procedure are validated through a series of experiments.}, journal={POLARIZATION SCIENCE AND REMOTE SENSING VI}, author={Kudenov, Michael W. and Miskiewicz, Matthew N. and Escuti, Michael J. and Coward, Jim}, year={2013} }
 @article{miskiewicz_bowen_escuti_2012, title={Efficient 3D FDTD analysis of arbitrary birefringent and dichroic media with obliquely incident sources}, volume={8255}, ISSN={["1996-756X"]}, DOI={10.1117/12.913628}, abstractNote={We have developed a 3D Finite Difference Time Domain (FDTD) algorithm to model obliquely incident waves through arbitrary birefringent and dichroic media with transverse periodic boundaries. Beginning with arbitrary conductivity and permittivity tensors, we employed the split-field method (SFM) to enable broadband sources with oblique incidence. We terminate our boundaries with a uniaxial perfectly matched layer (UPML) in one dimension and periodic boundaries in the other two dimensions. The algorithm is validated via several case studies: a polarizer pair, a twisted nematic liquid crystal, and an array of conducting particles. Using this approach, we simulate for the first time polarization gratings with light obliquely incident in directions orthogonal to the grating vector (i.e., at oblique angles outside the normal diffraction plane).}, journal={PHYSICS AND SIMULATION OF OPTOELECTRONIC DEVICES XX}, author={Miskiewicz, Matthew N. and Bowen, Patrick T. 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{kudenov_miskiewicz_escuti_dereniak_2012, title={Spatial heterodyne interferometry with polarization gratings}, volume={37}, ISSN={["1539-4794"]}, DOI={10.1364/ol.37.004413}, abstractNote={The implementation of a polarization-based spatial heterodyne interferometer (SHI) is described. While a conventional SHI uses a Michelson interferometer and diffraction gratings, our SHI exploits mechanically robust Wollaston prisms and polarization gratings. A theoretical model for the polarization SHI is provided and validated with data from our proof of concept experiments. This device is expected to provide a compact monolithic sensor for subangstrom resolution spectroscopy in remote sensing, biomedical imaging, and machine vision applications.}, number={21}, journal={OPTICS LETTERS}, author={Kudenov, Michael W. and Miskiewicz, Matthew N. and Escuti, Michael J. and Dereniak, Eustace L.}, year={2012}, month={Nov}, pages={4413–4415} }
 @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_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} }