Guanjun Tan

Apple Inc.

The “Patterned-Liquid-Crystal for Novel Displays” is a Special Issue focused on new insights and explorations in the field of liquid crystals arranged in a periodic patterned way [...]

The ultimate augmented reality (AR) should be a glass-type see-through display with uncompromised optical performances. The major technical challenge of present AR display systems is to fulfill wide field-of-view (FOV) and large eye box simultaneously for a comfortable visual experience. Here, we propose a novel scanning waveguide display to break...

Fast‐switching liquid crystal Pancharatnam‐Berry (PB) optical elements for near‐eye and head‐up displays are reviewed. A submillisecond‐response PB deflector helps double the apparent resolution and enable foveated display with eye‐tracking. A PB lens enables time‐ and polarization‐multiplexed multi‐focal‐plane displays to overcome the vergence‐acc...

A novel scanning waveguide display is proposed and experimentally realized. The core component, an off‐axis reflective lens array with f‐number of 0.75, is fabricated by photo‐alignment technique combined with cholesteric liquid crystal. The system has a diagonal field of view of 100°, exceeding theoretical limit of traditional waveguide displays.

Ambient light excitation in quantum dots‐converted micro‐LED displays is analyzed and the calculated results agree well with simulations. By depositing a layer of color filter and reducing the area ratio of quantum dots, the display's ambient contrast ratio can be improved to adequately readable under full daylight.

Nowadays, displays are ubiquitous in our daily lives. Long-time exposure to a display’s unnatural light could influence the user’s circadian rhythm, especially at night. Here, we propose a four-color micro-light-emitting diode (LED) display to achieve low circadian action for nighttime uses. Specifically, we evaluate the RGBW-type (red, green, blue...

A novel augmented reality display is proposed to achieve a field of view of 100°, while maintaining a good form factor with a glass‐thin waveguide combiner. The out‐coupler consists of an array of off‐axis diffractive lenslets with extremely low f‐number. A breadboard system is built and its performance characterized, combined with analysis and dis...

We demonstrate an absorption-based polarization grating made of dichroic dye-doped polymerizable liquid crystal. These gratings manifest a polarization-sensitive diffraction efficiency over the absorption band of the employed dye material, based on our theoretical analysis and experimental evidence. The spectral range can be easily tailored by vary...

We propose and fabricate a multi-primary-color (MPC) quantum-dot down-converting film (QDDCF). A four-primary-color QDDCF composed of red (R), yellowish green (YG), bluish green (BG), and blue (B) subpixels was fabricated via totally five rounds of photolithographic processes. A verification platform was built up using a laser projector, and the me...

Sidewall emission of a micro-scale light emitting diode (micro-LED) improves the light extraction efficiency, but it causes mismatched angular distributions between AlGaInP-based red micro-LED and InGaN-based blue/green counterparts due to material difference. As a result, color shift of RGB micro-LED displays may become visually noticeable. To add...

We demonstrate a multi‐resolution foveated display, to achieve retina‐level angular resolution while keeping wide field‐of‐view (FOV), with two display panels and an optical combiner. The first panel provides a wide FOV and the second one offers an ultra‐high resolution for the central fovea region, by an optical minifying system which enhances the...

With funnel‐tube array, the optical efficiency of the color‐converted micro‐LED display is improved by ~3X, while the crosstalk is eliminated. After optimization of the taper angle, the ambient contrast ratio is also improved due to higher light intensity.

The Pancharatnam‐Berry phase optical elements (PBOEs) are utilized to enhance the performance of head‐up displays (HUDs). The PB lenses provide varifocal functionality, while the PB deflectors can function as optical combiners and waveguide couplers. Rigorous coupled wave analysis based on scattering matrix is also developed and applied for structu...

We propose a high dynamic range (HDR) mini‐LED enhanced liquid crystal display (LCD) system. Through both numerical simulations and human visual perception experiments, we find that the halo effect (light leakage between adjacent black and bright pixels) can be suppressed to unnoticeable level by optimizing the LCD contrast ratio, number of local d...

Herein, we report a one‐step, general synthesis method that can convert commercial light‐diffusing polymer microspheres into highly luminescent perovskite‐based downconverters at an extremely low cost. The as‐synthesized perovskite‐on‐polymer microspheres (PPMs) offer widely tunable, highly saturated colors with light‐diffusing capability. Moreover...

We build a four‐plane near‐eye display (NED) system with a passive Pancharatnam‐Berry lens and two polarization‐modulated LCDs combined by a non‐polarizing beam splitter. The system well addresses the vergence‐accommodation conflict. At the same time, it provides adequate planes to render high quality 3D scenes without sacrificing the frame rate du...

We present here an optical approach to boost the apparent pixel density by utilizing the superimposition of two shifted-pixel grids generated by a Pancharatnam-Berry deflector (PBD). The content of the two shifted pixel grids are presented to the observer's eye simultaneously using a polarization-multiplexing method. Considering the compact and lig...

Liquid-crystal-based Pancharatnam–Berry phase optical elements (PBOEs), also known as diffractive wave plates (DWPs), geometric phase optics (GPO), or geometric phase holograms (GPHs), are functional planar structures with patterned orientation of anisotropy axis. Several scientifically interesting yet practically useful electro-optical effects, su...

In addition to displays, liquid crystals (LCs) have also found widespread applications in photonic devices, such as adaptive lens, adaptive optics, and sensors, because of their responses to electric field, temperature, and light. As the fabrication technique advances, more sophisticated devices can be designed and created. In this review, we repor...

Remote downconverters such as phosphors or quantum dots that are physically separated from the blue light-emitting diode (LED) chips can strongly enhance the luminescence efficiency of solid-state lighting (SSL) and liquid-crystal displays (LCDs) because of their reduced light reabsorption. However, the high cost of traditional remote downconverter...

A full‐color micro‐LED display can be achieved by red, green, and blue (RGB) chips or by a blue/ultraviolet (UV) micro‐LED array to pump downconverters. The latter helps relieve the burden of epitaxial growth of tri‐color micro‐LED chips. However, such a color‐converted micro‐LED system usually suffers from color crosstalk and low efficiency due to...

The Pancharatnam‐Berry optical elements (PBOEs) are utilized to enhance the performance of head‐up displays (HUDs). The Pancharatnam‐Berry lenses (PBLs) provide varifocal functionality and compensate chromatic aberrations, while the Pancharatnam‐Berry deflectors (PBDs) can function as optical combiners and waveguide couplers. Moreover, the Rigorous...

Color-converted micro-LED displays consist of a mono-color micro-LED array and color conversion materials to achieve full color, while relieving the burden of epitaxial growth of three-color micro-LEDs. However, it usually suffers from low efficiency and color crosstalk due to the limited optical density of color conversion materials. With funnel-t...

We demonstrate a polarization-multiplexed multiplane display system for near-eye applications. A polarization-sensitive Pancharatnam–Berry phase lens is implemented to generate two focal depths simultaneously. A spatial polarization modulator is utilized to direct the two images to designated focal planes. Based on this design, a dual-focal-plane d...

The angular resolution of current near-eye display devices is still far below human-eye acuity. How to achieve retina-level resolution while keeping wide field-of-view (FOV) remains a great challenge. In this work, we demonstrate a multi-resolution foveated display with two display panels and an optical combiner. The first display panel provides a...

We analyze the performance of high dynamic range liquid crystal displays (LCDs) using a two-dimensional local dimming mini-LED backlight. The halo effect of such a HDR display system is investigated by both numerical simulation and human visual perception experiment. The halo effect is mainly governed by two factors: intrinsic LCD contrast ratio (C...

We develop a rigorous model to simulate an LCD's contrast ratio (CR) and viewing angle by considering the depolarization effect. To improve CR, an in‐cell polarizer is added between LC layer and color filter array. The obtained maximum CR of a multi‐domain vertical alignment LCD is boosted to > 20,000:1.

We developed a simple, low‐cost process to convert commercial light diffusing powders into perovskite‐based tunable downconverters with high stability and superior color purity. Uniform illumination with desired color can be achieved with polymer films integrating such down‐converting light diffusers.

We analyse the ambient contrast ratio (ACR) of LCDs and OLED displays at different viewing angles for smartphones, TVs, and public displays. Four primary factors affecting the ACR are surface reflection, light leakage of polarizer, device contrast ratio, and display brightness. Methods for enhancing the ACR of LCDs and OLEDs are discussed.

Microcavity in organic light emitting diode (OLED) contributes to enhance the optical efficiency and color saturation. While a major tradeoff of strong cavity effect is its apparent angular color shift, especially for the RGB‐based OLED displays due to their subpixels' mismatched emission angular distributions. We propose a systematic optimization...

Based on the recent development of Pancharatnam—Berry deflectors and lenses (PBDs and PBLs), we propose a compact and lightweight near‐eye display system with depth adaption. The compact design results from the polarization selectivity of PBD waveguide coupler, and the fast‐switching PBLs can be exploited for generating correct light fields.

We develop an experimentally validated numerical simulation model to characterize the electro‐optic properties of uniform standing helix (USH) cholesteric liquid crystal displays. Based on the proposed numerical model, the viewing angle properties are analyzed by taking the optical polarization rotation effect into consideration. Furthermore, we pr...

Based on the recent development of Pancharatnam–Berry deflectors and lenses, we propose a compact and lightweight near‐eye display system with depth adaption. The compact design results from the polarization selectivity of Pancharatnam–Berry deflector waveguide coupler, and the fast‐switching Pancharatnam–Berry lenses can be exploited for generatin...

Microcavites contribute to enhancing the optical efficiency and color saturation of an organic light emitting diode (OLED) display. A major tradeoff of the strong cavity effect is its apparent color shift, especially for RGB-based OLED displays, due to their mismatched angular intensity distributions. To mitigate the color shift, in this work we fi...

We systematically analyze the ambient contrast ratio (ACR) of liquid crystal displays (LCDs) and organic light-emitting diode (OLED) displays for smartphones, TVs, and public displays. The influencing factors such as display brightness, ambient light illuminance, and surface reflection are investigated in detail. At low ambient light conditions, hi...

Polarizer, as an indispensable optical element, has been widely used in various optical systems, which splits a beam into two beams of orthogonal linear polarizations. Due to the appearance of the vector optical field (VOF) and its unique properties, the vector polarizer also meets the requirement in a wide variety of applications. Here we present...

Submillisecond response times and low operation voltage are critical to next generation liquid crystal display and photonic devices. In this paper, we review the recent progress of three fast response short-pitch cholesteric liquid crystal modes: blue phase (BP), uniform standing helix (USH), and uniform lying helix (ULH). This review starts with a...

Sunlight readability is a critical requirement for display devices, especially for mobile displays. Anti-reflection (AR) films can greatly improve sunlight readability by reducing the surface reflection. In this work, we demonstrate a broadband moth-eye-like AR surface on a flexible substrate, intended for flexible display applications. The motheye...

We develop a rigorous model to simulate an LCD's contrast ratio (CR) and viewing angle by considering the depolarization effect in thin-film transistor substrate, LC layer, color filter (CF) array, etc. To mitigate the depolarization effect, we propose a new device structure by adding a thin in-cell polarizer between LC layer and CF array. Based on...

A macroscopic model is developed for analyzing the electro-optics of short-pitch uniform lying helix (ULH) cholesteric liquid crystals (CLCs). Both flexoelectric effect and dielectric effect make important contributions to the maximum transmittance and operation voltage of the ULH devices. Based on the proposed macroscopic approximation, we derive...

A reasonably good alignment of a uniform lying helix (ULH) liquid crystal is achieved and its gray-to-gray (GTG) response time investigated. The averaged GTG rise time is 0.35 ms and fall time is 0.53 ms. Such a fast response time helps suppress image blurs and color breakup for field-sequential color displays.

A functional reflective polarizer is added to an LCD's backlight unit to suppress the crosstalk between RGB primary colors. When integrated with a commercial two-phosphor-converted white light-emitting diode (2pc-WLED), the color gamut of the LCD can be boosted to 133.9% NTSC in CIE 1976, which is comparable to the quantum dot-enhanced backlight.

A broadband anti-reflection surface with moth-eye structure for sunlight readable flexible displays is demonstrated. The proposed nanostructure exhibits excellent anti-reflection performance (luminous reflectance 0.23%), low haze (0.95%), great flexibility (curve radius <8 mm), high hardness (>3H) and self-cleaning characteristics. A numerical mode...

An optimized blue-phase liquid crystal (BPLC) with a moderate dielectric constant, manageable capacitor charging time, high voltage holding ratio, and submillisecond gray-to-gray response time at room temperature is developed. Using protruded triangular IPS electrodes, the operation voltage can be reduced to 15V while keeping ~74% transmittance. Su...

The figure of merit (FoM) is defined to evaluate the performance of ULH devices. The trade-offs between operation voltage, transmittance, and response time in uniform lying helix (ULH) cholesteric liquid crystals (CLC) are investigated. Excellent agreement between theory and experiment is achieved. The viewing angle of ULH displays is also studied....

A switchable lens based on a cycloidal diffractive waveplate and a polarization rotator is demonstrated. This switchable lens has advantages in fast response time, low chromatic aberration, and low operation voltage. Its potential applications include wearable virtual reality, augmented reality, and other head-mounted display devices.

We report an optimized blue phase liquid crystal (BPLC) mixture JC-BP08 for field-sequential-color (FSC) display applications. JC-BP08 exhibits several attractive features: 1) its fast average gray-to-gray response time enables FSC display, which in turn triples the resolution density and optical efficiency. 2) Its voltage holding ratio is >99.4% a...

In this review paper,we report recent progress on Pancharatnam-Berry (PB) phase optical elements, such as lens, grating, and deflector. PB lenses exhibit a fast switching time between two or more focal lengths with large diopter change and aperture size, which is particularly attractive for addressing the accommodation mismatch in head-mounted disp...

We propose to add a functional reflective polarizer (FRP) in the backlight unit to suppress the crosstalk between red, green and blue color filters of a liquid crystal display (LCD) panel. When incorporated with a commercial two-phosphor-converted white light-emitting diode (2pc-WLED), the color gamut of the LCD can be improved from 92% to 115% NTS...

We demonstrate a simple yet high performance phase grating with switchable diffraction angles using a fringe field switching (FFS) liquid crystal (LC) cell. The LC rubbing angle is parallel to the FFS electrodes (i.e. α = 0°), leading to symmetric LC director distribution in a voltage-on state. Such a grating exhibits three unique features: 1) Two...

A high ambient contrast ratio display device using a transparent organic light emitting diode (OLED) or transparent quantum-dot light-emitting diode (QLED) with embedded multilayered structure and absorber is proposed and its performance is simulated. With the help of multilayered structure, the device structure allows almost all ambient light to g...

We propose a switchable multi-angle grating for steering the light between nine different angles from 0° to 16° with an interval of 2°. It shows great promises for eye-tracking applications in head-mounted displays.

We report a compact, yet high ambient contrast ratio augmented reality system by incorporating a tunable transmittance liquid crystal cell and a thin reflective polarizer. Moreover, if we replace the reflective polarizer with a functional reflective polarizer, the system would benefit those users with color vision deficiency.

A high ambient contrast ratio display device using a transparent OLED or transparent Quantum-dot LED (QLED) with embedded multilayered structure and absorber is proposed. With the help of the multilayered structure, the device structure allows almost all ambient light to get through the display and be absorbed by the absorber. Because the reflected...

A semi-empirical equation is developed to characterize the optical decay time of in-plane switching (IPS) and fringe field switching (FFS) liquid crystal displays. Good agreement between simulation and experiment is obtained. Moreover, this equation provides a simple yet accurate method to measure the twist elastic constant K22 of liquid crystals.

We report a functional reflective polarizer that can be incorporated into a compact augmented reality system. The design principle of the functional reflective polarizer is explained and two design examples are illustrated. In the first example, with the specially designed functional reflective polarizer, the transmittance of the augment reality sy...

We have proposed a compact, yet high ambient contrast ratio augmented reality (AR) system by incorporating a tunable transmittance liquid crystal (LC) cell and a thin functional reflective polarizer. The broadband polarization-independent guest–host LC cell can change the transmittance from ~73% to ~26% with merely 8 V. Its response time (~50 ms) i...

We report a low-voltage and submillisecond-response polymerstabilized hyper-twisted-nematic (HTN) liquid crystal cell with a large dielectric anisotropy host mixture. To correct the measured voltagedependent transmittance, we have to take the voltage shielding effect of the alignment layers into consideration. Both Kerr effect and flexoelectro-opti...

A semi-empirical equation is developed to characterize the optical decay time of in-plane switching (IPS) and fringe field switching (FFS) liquid crystal displays. This equation takes the effects of elastic constants, cell gap, liquid crystal material, rubbing angle, and anchoring strength into account simultaneously. Good agreement between simulat...

We propose a switchable phase grating using fringe field switching (FFS) cells. The FFS phase grating possesses several attractive features: large diffraction angle, high diffraction efficiency, fast response time, and high contrast ratio. It can diffract >32% light to ± 2nd orders with a large diffraction angle of 12.1°. Meanwhile, its response ti...