Ms. Lingshan Li Profile

Lingshan Li

Senior Optical Engineer

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Proceedings Article | 21 August 2020 Presentation + Paper

Solc-style birefringent color filters based on multi-twist retarders

Lingshan Li, Shuojia Shi, Michael Escuti

Proceedings Volume 11483, 114830N (2020) https://doi.org/10.1117/12.2569133

KEYWORDS: Optical filters, Wave plates, Polarization

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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°.

Proceedings Article | 20 August 2020 Poster + Paper

Color-selective geometric phase lens for apochromatic lens system

Lingshan Li, Jihwan Kim, Shuojia Shi, Michael Escuti

Proceedings Volume 11472, 1147219 (2020) https://doi.org/10.1117/12.2569165

KEYWORDS: Diffraction, Polarization, Liquid crystals, Colorimetry, Optical filters, Chromatic aberrations

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Thin lenses have potentially much lower weight and volume than traditional refractive lenses, and therefore enable compelling solutions in augmented-/virtual-/mixed-reality (AR/VR/MR) headsets. The geometric-phase lens (GPL), formed either with liquid crystals (LCs) or metasurfaces, is emerging as a leading technology because of its ability to implement arbitrary aspherical phase profiles and its potential for low loss and minimal ghosting. However, a strong chromatic dispersion is inherent to each singlet. One prior method to overcome this employs a stack of multiple achromatic GPLs acting on all colors simultaneously with color filters and other waveplates to achieve an apochromatic lens system. Another concept in the prior art is to use multiple color-selective GPLs (CS-GPLs) wherein each diffracts only a single color while transmitting the others. In this work, we report on a family of color-selective GPLs with highly chromatic efficiency spectra, made using multi-twist LC coatings. In both theory and experiment, we show the diffraction efficiency of red, green, and blue lenses is high (< 91%) while the complementary colors of each coating are almost fully transmitted undiffracted. The CS-GPLs is a promising optical element to provide a new route to mitigate the chromatic abberation in the AR/VR/MR lens system.

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