@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{altaqui_schrickx_sen_li_rech_lee_balar_you_kim_escuti_et al._2021, title={Bio-inspired spectropolarimetric sensor based on tandem organic photodetectors and multi-twist liquid crystals}, volume={29}, ISSN={["1094-4087"]}, url={https://doi.org/10.1364/OE.431858}, DOI={10.1364/OE.431858}, abstractNote={Simultaneous spectral and polarimetric imaging enables versatile detection and multimodal characterization of targets of interest. Current architectures incorporate a 2×2 pixel arrangement to acquire the full linear polarimetric information causing spatial sampling artifacts. Additionally, they suffer from limited spectral selectivity and high color crosstalk. Here, we demonstrate a bio-inspired spectral and polarization sensor structure based on integrating semitransparent polarization-sensitive organic photovoltaics (P-OPVs) and liquid crystal polymer (LCP) retarders in a tandem configuration. Color tuning is realized by leveraging the dynamic chromatic retardation control of LCP films, while polarization sensitivity is realized by exploiting the flexible anisotropic properties of P-OPVs. The structure is marked by its ultra-thin design and its ability to detect spectral and polarimetric contents along the same optical axis, thereby overcoming the inherent limitations associated with conventional division-of-focal plane sensors.}, number={26}, journal={OPTICS EXPRESS}, publisher={The Optical Society}, author={Altaqui, Ali and Schrickx, Harry and Sen, Pratik and Li, Lingshan and Rech, Jeromy and Lee, Jin-Woo and Balar, Nrup and You, Wei and Kim, Bumjoon J. and Escuti, Michael and et al.}, year={2021}, month={Dec}, pages={43953–43969} }
 @article{li_shi_escuti_2021, title={Improved saturation and wide-viewing angle color filters based on multi-twist retarders}, volume={29}, ISSN={["1094-4087"]}, DOI={10.1364/OE.416961}, abstractNote={Birefringent color filters serve a critical role in next-generation display systems, including augmented-/virtual-/mixed-reality headsets, and many types of optical remote sensing. Most prior polarization interference filters (PIFs) employ many individually aligned plates that enable only relatively thick color filters (≥100s of µm), are usually limited to small clear apertures (few cm), and offer poor off-axis performance. Here, we report on a family of monolithic, thin-film, birefringent PIFs formed using liquid crystal polymer (LCP) network materials, also known as reactive mesogens. These multi-twist retarders (MTRs) are only a few µm thick and have a single alignment surface. They offer high color saturation with a notch-type pass/stopband, analogous to Solc PIFs and stable off-axis performance. Here, we apply simplifying assumptions inspired by Solc PIFs, and develop a design method resulting in MTRs with an alternating achiral/chiral architecture. We theoretically and experimentally presented three types of MTR color filters (blue-yellow, green-magenta, and cyan-red), which manifest strong color filtering behavior and improved angular performance (up to ±20°) with larger color space coverage and high total light efficiency compared to their Solc filters counterparts. Such high-saturated and wide-viewing MTR color filters can be promising elements to maintain the system field of view (FOV) in the next-generation displays or spectral imaging applications.}, number={3}, journal={OPTICS EXPRESS}, author={Li, Lingshan and Shi, Shuojia and Escuti, Michael J.}, year={2021}, month={Feb}, pages={4124–4138} }
 @article{li_escuti_2021, title={Super achromatic wide-angle quarter-wave plates using multi-twist retarders}, volume={29}, ISSN={["1094-4087"]}, DOI={10.1364/OE.418197}, abstractNote={The achromaticity and wide-angle property of quarter-wave plates (QWPs) are crucial for the color uniformity and image resolution of the future displays such as virtual reality (VR) pancake lens and augmented reality (AR) waveguide/focusing systems. However, most reported achromatic wide-angle QWPs designs composed by stacks of different birefringent plates are too complicated with limited achromaticity and wide-angle performance. The multi-twist retarders (MTR) QWPs presented in previous work already showed its potential to achieve high achromaticity in RGB using one monolithic film in normal incidence, but the incompetent polarization control in blue-violet limits its application in LED-based polarization-sensitive AR/VR headsets. In this work, we theoretically investigate a new type of MTR QWPs achieving super achromaticity from violet to red with average ellipticity 43° and simultaneously maintaining wide-viewing angle up to ±45°, which enables a precise polarization control within the field-of-view (FOV) of current AV/VR headset. The new proposed MTR QWP is also reported to obtain average reflection luminance leakage 0.15~% and maximum leakage 0.23~%, making it a promising element to reduce polarization leakage and enhance image resolution in the next-generation displays.}, number={5}, journal={OPTICS EXPRESS}, author={Li, Lingshan and Escuti, Michael J.}, year={2021}, month={Mar}, pages={7464–7478} }
 @article{li_shi_escuti_2020, title={Solc-style color filters based on multi-twist retarders}, volume={11483}, ISSN={["1996-756X"]}, DOI={10.1117/12.2569133}, abstractNote={Birefringent color filters serve a critical role in next generation display systems, including augmented-/virtual- /mixed-reality headsets, and many types of optical remote sensing. Most prior polarization interference filters (PIFs) employ many individually aligned plates that enable only relatively thick color filters (≥ 100s of μm), are usually limited to small clear apertures (few cm), and offer poor off-axis performance. Here, we report on a family of monolithic, thin-film, birefringent PIFs formed using liquid crystal polymer (LCP) network materials, also known as reactive mesogens. These multi-twist retarders (MTRs) are only a few µm thick and have a single alignment surface. They offer high color saturation with a notch-type pass/stopband, analogous to Solc filters, and improved off-axis performance and large-area scalability. Here, we apply simplifying assumptions inspired by Solc-type PIFs, and develop a design method resulting in MTRs with an alternating achiral/chiral architecture. We design three representative color filters (blue-yellow, green-magenta, and cyan-red), and fabricate them. The resulting experimental films manifest strong color filtering behavior, with high saturation and uniformity. We study the color differences for oblique incidence, showing modest change within AOI ≤ 20°.}, journal={NOVEL OPTICAL SYSTEMS, METHODS, AND APPLICATIONS XXIII}, author={Li, Lingshan and Shi, Shuojia and Escuti, Michael J.}, year={2020} }
 @article{wang_liu_zhao_li_li_lian_gao_huang_2019, title={Fabry-Perot type resonant modes of exciton luminescence in Cu2O nanowires}, volume={3}, ISSN={["2399-6528"]}, DOI={10.1088/2399-6528/ab31ca}, abstractNote={Single Cu2O nanowires (NWs) were fabricated by the two-step method we reported previously (Wang et al 2014 RSC Advances 4 37542). Band-edge exciton photoluminescence (PL) was observed from individual NWs at room temperature using excitation at 325 nm. The PL signals were assigned to Fabry–Perot (F-P) type standing waves in a right cylindrical dielectric cavity (resonator) for a representative range of different wire lengths and diameters. We found that the mode spacing of F-P resonances varied inversely as the NW length as expected. For the region of NW diameters from 140 to 200 nm, and NW length between 2–5 mm, E-field simulations by COMSOL Multiphysics finite element analysis indicate that the main F-P mode propagating inside the NW is the HE11 mode. When the diameter exceeds 200 nm, there are at least two F-P type modes supported in the NWs. Our results further the understanding of exciton photoluminescence in Cu2O NWs and demonstrates the existence of enhanced mode frequencies based on the geometry of the optical micro-cavity. We further identify potential applications in exciton-driven optoelectronic devices and light emission enhanced by optical micro-cavities.}, number={8}, journal={JOURNAL OF PHYSICS COMMUNICATIONS}, author={Wang, Peng and Liu, Guipeng and Zhao, Xinhong and Li, Hairong and Li, Lingshan and Lian, Junbo and Gao, Xiaohu and Huang, Zeyu}, year={2019}, month={Aug} }