Publications by authors named "Guanjun Tan"

13 Publications

  • Page 1 of 1

Absorption-based polarization gratings.

Opt Express 2020 Apr;28(9):13907-13912

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 varying the dye material. Since these gratings generate first-order diffracted beams with orthogonal circular polarizations, they can be utilized as key components in polarimetry systems. Meanwhile, due to their absorptive nature, these polarization gratings can function as LED-compatible polarization masks for photopatterning while fabricating various liquid crystal devices.
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http://dx.doi.org/10.1364/OE.392550DOI Listing
April 2020

Multi-primary-color quantum-dot down-converting films for display applications.

Opt Express 2019 Sep;27(20):28480-28493

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 measured results show that the QD film can expand display color gamut to 118.60% of Rec. 2020 and can cover the entire Pointer's gamut. The issues of blue light absorption and film thickness are analyzed in detail. The combination of MPC technology and QDDCF is a potential strategy to realize ultra wide color gamut for emerging display technologies.
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http://dx.doi.org/10.1364/OE.27.028480DOI Listing
September 2019

Angular color shift of micro-LED displays.

Opt Express 2019 Jun;27(12):A746-A757

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 address this issue, we first analyze the angular distributions of RGB micro-LEDs and obtain good agreement between simulation and experiment. Next, we propose a device structure with top black matrix and taper angle in micro-LEDs, which greatly suppresses the color shift while keeping a reasonably high light extraction efficiency.
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http://dx.doi.org/10.1364/OE.27.00A746DOI Listing
June 2019

Improving near-eye display resolution by polarization multiplexing.

Opt Express 2019 May;27(11):15327-15334

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 lightweight nature of PBD, this approach has potential applications in near-eye display systems. Moreover, the same concept can be extended to projection displays with proper modifications.
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http://dx.doi.org/10.1364/OE.27.015327DOI Listing
May 2019

Novel liquid crystal photonic devices enabled by two-photon polymerization [Invited].

Opt Express 2019 Apr;27(8):11472-11491

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 report recent advances of two-photon polymerization-based direct-laser writing enabled LC devices. Firstly, we describe the basic working principle of two-photon polymerization. With this powerful fabrication technique, we can generate anchoring energy by surface morphology to align LC directors on different form factors. To prove this concept, we demonstrate LC alignment on planar, curvilinear surfaces as well as in three-dimensional volumes. Based on the results, we further propose a novel, ultra-broadband, twisted-nematic diffractive waveplate that can potentially be fulfilled by this technique. Next, we briefly discuss the current status of direct-laser writing on LC reactive mesogens and its potential applications. Finally, we present two design challenges: fabrication yield and polymer relaxation/deformation, remaining to be overcome.
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http://dx.doi.org/10.1364/OE.27.011472DOI Listing
April 2019

Foveated imaging for near-eye displays.

Opt Express 2018 Sep;26(19):25076-25085

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 wide FOV but relatively low resolution for the surrounding region, while the second one offers an ultra-high resolution for the central fovea region, by an optical minifying system which enhances the effective resolution by 5 ×. In addition, a switchable Pancharatnam-Berry phase deflector is employed to shift the high-resolution region. The proposed design effectively reduces the pixelation and screen-door effect in near-eye displays.
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http://dx.doi.org/10.1364/OE.26.025076DOI Listing
September 2018

Polarization-multiplexed multiplane display.

Opt Lett 2018 Nov;43(22):5651-5654

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 display system is constructed without space- or time-multiplexing operations, to suppress the vergence-accommodation conflict successfully.
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http://dx.doi.org/10.1364/OL.43.005651DOI Listing
November 2018

High dynamic range liquid crystal displays with a mini-LED backlight.

Opt Express 2018 Jun;26(13):16572-16584

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 (CR) and dimming zone number. Based on our results, to suppress the halo effect to indistinguishable level, a LCD with CR≈5000:1 requires about 200 local dimming zones, while for a LCD with CR≈2000:1 the required dimming zone number is over 3000. Our model provides useful guidelines to optimize the mini-LED backlit LCDs for achieving dynamic contrast ratio comparable to organic LED displays.
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http://dx.doi.org/10.1364/OE.26.016572DOI Listing
June 2018

Depolarization effect in liquid crystal displays.

Opt Express 2017 May;25(10):11315-11328

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 the analysis using our new model, the maximum CR of a multi-domain vertical alignment (MVA) LCD can reach > 20,000:1, while for the fringe-field switching (FFS) mode it can reach > 3000:1. We also discuss other approaches to further enhance the CR. Our model is a powerful tool to analyze the CR degradation mechanism and to guide the future LCD device and material optimizations.
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http://dx.doi.org/10.1364/OE.25.011315DOI Listing
May 2017

Enlarging the color gamut of liquid crystal displays with a functional reflective polarizer.

Opt Express 2017 Jan;25(1):102-111

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% NTSC standard, which is comparable to the cadmium-based quantum dot (QD) backlight. If a narrow-band color filter is employed, the color gamut can be further enhanced to 135% NTSC. Our design offers an alternative approach to QDs, while keeping low cost and long lifetime. Such a simple yet efficient approach would find widespread applications for enlarging the color gamut of LCDs.
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http://dx.doi.org/10.1364/OE.25.000102DOI Listing
January 2017

A Low Voltage Liquid Crystal Phase Grating with Switchable Diffraction Angles.

Sci Rep 2017 01 5;7:39923. Epub 2017 Jan 5.

College of Optics and Photonics, University of Central Florida, Orlando, Florida 32816, USA.

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 grating periods can be formed by controlling the applied voltage, resulting in switchable diffraction angles. In our design, the 1 diffraction order occurs at 4.3°, while the 2 order appears at 8.6°. 2) The required voltage to achieve peak diffraction efficiency (η~32%) for the 1 order is only 4.4 V at λ = 633 nm as compared to 70 V for a conventional FFS-based phase grating in which α ≈ 7°, while the 2 order (η~27%) is 15 V. 3). The measured rise and decay time for the 1 order is 7.62 ms and 6.75 ms, and for the 2 order is 0.75 ms and 3.87 ms, respectively. To understand the physical mechanisms, we also perform device simulations. Good agreement between experiment and simulation is obtained.
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http://dx.doi.org/10.1038/srep39923DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5214749PMC
January 2017

Functional reflective polarizer for augmented reality and color vision deficiency.

Opt Express 2016 Mar;24(5):5431-5441

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 system is relatively high as compared to a polarizing beam splitter or a conventional reflective polarizer. Such a functional reflective polarizer can also be used for vehicular displays. For the second example, the functional reflective polarizer is specially tailored to help those people with color vision deficiency.
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http://dx.doi.org/10.1364/OE.24.005431DOI Listing
March 2016

Large-angle and high-efficiency tunable phase grating using fringe field switching liquid crystal.

Opt Express 2015 May;23(9):12274-85

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 time remains relatively fast even at -40°C. A simulation model is developed to explain the experimental results and good agreement is obtained. We also demonstrate a blazed phase grating to achieve tunable beam steering between 0th, 1st and 2nd orders.
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http://dx.doi.org/10.1364/OE.23.012274DOI Listing
May 2015