Liquid crystal polarization optics based on photoalignment technique has found pervasive applications in next-generation display platforms like virtual reality and augmented reality. Its large-scale ...fabrication, however, remains a big challenge due to the high demands in small feature size, fast processing speed, and defects-free alignment quality during the photoalignment process, especially for large-angle reflective devices. Here we propose a new concept of holo-imprinting based on non-contact replication of polarization pattern with a reflective liquid crystal hologram as a template. Our theoretical analysis and experimental results validate the possibility of generating a high-quality polarization pattern exploiting the self-interfering beams of reflective holograms. The method can be extended to numerous devices, from transmissive to reflective, from small angle to large angle, and from grating, lens, to freeform optics. Its widespread impact on the fabrication of liquid crystal polarization optics for advanced display and imaging systems is foreseeable.
Liquid crystal displays (LCDs) and photonic devices play a pivotal role to augmented reality (AR) and virtual reality (VR). The recently emerging high-dynamic-range (HDR) mini-LED backlit LCDs ...significantly boost the image quality and brightness and reduce the power consumption for VR displays. Such a light engine is particularly attractive for compensating the optical loss of pancake structure to achieve compact and lightweight VR headsets. On the other hand, high-resolution-density, and high-brightness liquid-crystal-on-silicon (LCoS) is a promising image source for the see-through AR displays, especially under high ambient lighting conditions. Meanwhile, the high-speed LCoS spatial light modulators open a new door for holographic displays and focal surface displays. Finally, the ultrathin planar diffractive LC optical elements, such as geometric phase LC grating and lens, have found useful applications in AR and VR for enhancing resolution, widening field-of-view, suppressing chromatic aberrations, creating multiplanes to overcome the vergence-accommodation conflict, and dynamic pupil steering to achieve gaze-matched Maxwellian displays, just to name a few. The operation principles, potential applications, and future challenges of these advanced LC devices will be discussed.
Abstract
Diffractive liquid-crystal optics is a promising optical element for virtual reality (VR) and mixed reality as it provides an ultrathin formfactor and lightweight for human factors and ...ergonomics. However, its severe chromatic aberrations impose a big challenge for full-color display applications. In this study, we demonstrate an achromatic diffractive liquid-crystal device to overcome this longstanding chromatic aberration issue. The proposed device consists of three stacked diffractive liquid crystal optical elements with specifically designed spectral response and polarization selectivity. The concept is validated by both simulations and experiments. Our experimental results show a significant improvement in imaging performance with two types of light engines: a laser projector and an organic light-emitting diode display panel. In addition, our simulation results indicate that the lateral color shift is reduced by ~100 times in comparison with conventional broadband diffractive liquid-crystal lens. Potential applications for VR-enabled metaverse, spatial computing, and digital twins that have found widespread applications in smart tourism, smart education, smart healthcare, smart manufacturing, and smart construction are foreseeable.
A novel beam steering angle expander is demonstrated by cascading two polymeric liquid crystal polarization lenses with different diopters. The lens module performs as a planar telescope, which has ...features such as a light weight, low cost, and high precision. The magnifier offers wide-angle, continuous steering when integrated with an active fine-angle beam steering device. The potential application for LiDAR is emphasized.
We report a new mixture, which is modified from Merck TL-216, for liquid-crystal-on-silicon spatial light modulators (SLMs). To achieve 2π phase change at λ = 633 nm with 5 V operation voltage, the ...measured response time is about 3 ms at 50 °C. Meanwhile, our mixture exhibits no sign of photodegradation and even the total dosage has exceeded 400 MJ/cm2 at a blue laser wavelength λ = 465 nm. In comparison, E7 died at about 30 MJ/cm2. Widespread applications of this material for high brightness SLMs, near-eye displays, and head-up displays are foreseeable.
A submillisecond-response and light scattering-free polymer-network liquid crystal (PNLC) for infrared spatial light modulators is demonstrated. Our new liquid crystal host exhibits a higher ...birefringence, comparable dielectric anisotropy, and slightly lower visco-elastic constant than a commonly employed commercial material, HTG-135200. Moreover, the electro-optical performance of our PNLCs with different monomer concentrations, cell gaps, and liquid crystal (LC) hosts is compared and discussed from four aspects: operating voltage, hysteresis, relaxation time, and light scattering loss. The temperature effect on hysteresis is also analyzed. Potential applications of PNLCs for laser beam steering and spatial light modulators especially in the infrared region are foreseeable.
Color-converted micro-light-emitting diode (micro-LED) displays with wide color gamut, high ambient contrast ratio, and fast response time are emerging as a potentially disruptive technology. ...However, due to limited optical density and thickness of the color-conversion film, the blue light leakage and low color-conversion efficiency still hinder their widespread applications. In this paper, we demonstrate a patterned cholesteric liquid crystal (CLC) polymer film with two special optical functionalities. On the green and red sub-pixels, the corresponding planar CLC texture acts as a distributed Bragg reflector for the blue light, which in turn improves the color conversion efficiency and expands the color gamut. On the blue sub-pixels, the corresponding focal-conic CLC texture acts as light scattering medium, which helps to reduce the angular color shift. Further analysis reveals that the patterned CLC film can alleviate the crosstalk between green and blue color filters. Therefore, compared to the display system without such a CLC film, our proposed device structure increases the color conversion efficiency by 143% (at ~90% Rec. 2020) and reduces average angular color shift Δu'v' from 0.03 to 0.018 at the viewing angle with the most severe color shift. Such a patterned CLC film is applicable to all kinds of color-conversion display systems, including organic and inorganic phosphors.
We use a simple photoalignment method to fabricate four reflective cholesteric liquid crystal (CLC) polymeric lenses with diameter D=2.45 cm and low f-numbers (f/2, f/0.9, f/0.45, f/0.33) at 550 nm. ...Such a flat CLC lens can be converging or diverging, depending on the handedness and direction of the incident light. Our CLC lenses can achieve ∼85% diffraction efficiency for a designated polarization state and manifest decent imaging ability.
Three-dimensional (3D) displays have been vastly investigated in the past few decades. Recent development of augmented reality (AR) and virtual reality (VR) has further demanded to compress the 3D ...display system into a compact platform, such as wearable near-eye displays. Holographic optical elements (HOEs) have received widespread attention owing to their lightweight, thin formfactor, and low cost, and thus have been widely deployed in various 3D display systems. In this review article, we first describe the working principle of some 3D techniques used in AR and VR headsets, and then present 3D display systems employing HOEs, and finally analyze how HOEs influence the system design and performance.
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