155 research outputs found

    High Efficiency and Wide Color Gamut Liquid Crystal Displays

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    Liquid crystal display (LCD) has become ubiquitous and indispensable in our daily life. Recently, it faces strong competition from organic light emitting diode (OLED). In order to maintain a strong leader position, LCD camp has an urgent need to enrich the color performance and reduce the power consumption. This dissertation focuses on solving these two emerging and important challenges. In the first part of the dissertation we investigate the quantum dot (QD) technology to improve the both the color gamut and the light efficiency of LCD. QD emits saturated color and grants LCD the capability to reproduce color vivid images. Moreover, the QD emission spectrum can be custom designed to match to transmission band of color filters. To fully take advantage of QD\u27s unique features, we propose a systematic modelling of the LCD backlight and optimize the QD spectrum to simultaneously maximize the color gamut and light efficiency. Moreover, QD enhanced LCD demonstrates several advantages: excellent ambient contrast, negligible color shift and controllable white point. Besides three primary LCD, We also present a spatiotemporal four-primary QD enhanced LCD. The LCD\u27s color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5Γ— increment in spatial resolution, 2Γ— brightness enhancement, slightly larger color gamut and mitigated LC response requirement (~4ms). It can be employed in the commercial TV to meet the challenging Energy star 6 regulation. Besides conventional LCD, we also extend the QD applications to liquid displays and smart lighting devices. The second part of this dissertation focuses on improving the LCD light efficiency. Conventional LCD system has fairly low light efficiency (4%~7%) since polarizers and color filters absorb 50% and 67% of the incoming light respectively. We propose two approaches to reduce the light loss within polarizers and color filters. The first method is a polarization preserving backlight system. It can be combined with linearly polarized light source to boost the LCD efficiency. Moreover, this polarization preserving backlight offers high polarization efficiency (~77.8%), 2.4Γ— on-axis luminance enhancement, and no need for extra optics films. The second approach is a LCD backlight system with simultaneous color/polarization recycling. We design a novel polarizing color filter with high transmittance ( \u3e 90%), low absorption loss (~3.3%), high extinction ratio (\u3e10,000:1) and large angular tolerance (up to Β±50˚). This polarizing color filter can be used in LCD system to introduce the color/polarization recycling and accordingly boost LCD efficiency by ~3 times. These two approaches open new gateway for ultra-low power LCDs. In the final session of this dissertation, we demonstrate a low power and color vivid reflective liquid crystal on silicon (LCOS) display with low viscosity liquid crystal mixture. Compared with commercial LC material, the new LC mixture offers ~4X faster response at 20oC and ~8X faster response at -20Β°C. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: submillisecond response time at room temperature, vivid color even at -20oC, high brightness, excellent ambient contrast ratio, and suppressed color breakup. With this material improvement, LCOS display can be promising for the emerging wearable display market

    Advanced liquid crystal displays with supreme image qualities

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    Several metrics are commonly used to evaluate the performance of display devices. In this dissertation, we analyze three key parameters: fast response time, wide color gamut, and high contrast ratio, which affect the final perceived image quality. Firstly, we investigate how response time affects the motion blur, and then discover the 2-ms rule. With advanced low-viscosity materials, new operation modes, and backlight modulation technique, liquid crystal displays (LCDs) with an unnoticeable image blur can be realized. Its performance is comparable to an impulse-type display, like cathode ray tube (CRT). Next, we propose two novel backlight configurations to improve an LCD\u27s color gamut. One is to use a functional reflective polarizer (FRP), acting as a notch filter to block the unwanted light, and the other is to combine FRP with a patterned half-wave plate to suppress the crosstalk between blue and green/red lights. In experiment, we achieved 97.3% Rec. 2020 in CIE 1976 color space, which is approaching the color gamut of a laser projector. Finally, to enhance an LCD\u27s contrast ratio, we proposed a novel device configuration by adding an in-cell polarizer between LC layer and color filter array. The CR for a vertically-aligned LCD is improved from 5000:1 to 20,000:1, and the CR for a fringe field switching LCD is improved from 2000:1 to over 3000:1. To further enlarge CR to fulfill the high dynamic range requirement, a dual-panel LCD system is proposed and the measured contrast ratio exceeds 1,000,000:1. Overall speaking, such an innovated LCD exhibits supreme image qualities with motion picture response time comparable to CRT, vivid color to laser projector, and contrast ratio to OLED. Along with other outstanding features, like high peak brightness, high resolution density, long lifetime, and low cost, LCD would continue to maintain its dominance in consumer electronics in the foreseeable future

    μ•‘μ •κΈ°λ°˜ λ°œκ΄‘ν˜• λ””μŠ€ν”Œλ ˆμ΄λ₯Ό μœ„ν•œ μš©μ•‘κ³΅μ • λ‚΄μž¬ν˜• νŽΈκ΄‘νŒμ— κ΄€ν•œ 연ꡬ

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    ν•™μœ„λ…Όλ¬Έ (석사) -- μ„œμšΈλŒ€ν•™κ΅ λŒ€ν•™μ› : κ³΅κ³ΌλŒ€ν•™ 전기·정보곡학뢀, 2020. 8. 이신두.Recently, the advancement of the liquid crystal display (LCD) technology has greatly focused on the clear image quality together with the natural color. According to the demand for the image quality, the in-cell polarizers have been attracted much attention owing to the advantages of improving the contrast ratio and reducing the thickness of LCD. In this work, we proposed the QD-based emissive LCD with the in-cell polarizer composed of dichroic dyes. The in-cell polarizer was fabricated through the solution-processing of a dichroic dye solution. The QD layer was constructed on the inner surface of the top substrate, and the in-cell polarizer was subsequently prepared on the QD layer to prevent the depolarization of the emission light and the degradation of the QDs. The intensity of the incident light for exciting QDs was modulated by the phase retardation through the LC layer, depending on the magnitude of the applied voltage. This leads directly to the modulation of the emission spectra of QDs with the color gamut extended to about 80 % of the BT.2020 standard. The architecture based on the in-cell polarizer will provide a simple and viable method of constructing the QD-based emissive LCD with high color purity in a cost-effective manner.졜근 μ•‘μ • λ””μŠ€ν”Œλ ˆμ΄(LCD) κΈ°μˆ λ“€μ€ μžμ—°μŠ€λŸ¬μš΄ 색상과 λ”λΆˆμ–΄ μ„ λͺ…ν•œ ν™”μ§ˆμ„ μ€‘μ‹¬μœΌλ‘œ 크게 λ°œμ „ν–ˆλ‹€. κ³ ν™”μ§ˆ μ˜μƒμ— λŒ€ν•œ μˆ˜μš”μ™€ ν•¨κ»˜, λ‚΄μž¬ν˜• νŽΈκ΄‘νŒ (in-cell polarizer)λŠ” λŒ€μ‘°μœ¨ ν–₯상과 LCD λ‘κ»˜ κ°μ†ŒλΌλŠ” λ‹€μ–‘ν•œ μž₯μ λ“€λ‘œ 인해 더 λ§Žμ€ 관심을 λŒμ—ˆλ‹€. λ³Έ μ—°κ΅¬μ—μ„œλŠ” 이색성 μ—Όλ£Œλ‘œ κ΅¬μ„±λœ, λ‚΄μž¬ν˜• νŽΈκ΄‘νŒλ₯Ό μ μš©ν•œ μ–‘μžμ  기반 κ΄‘ λ°œκ΄‘ μ•‘μ • λ””μŠ€ν”Œλ ˆμ΄λ₯Ό μ œμ•ˆν•˜μ˜€λ‹€. μ–‘μžμ  측은 상단 기판의 λ‚΄λΆ€ ν‘œλ©΄μ— κ΅¬μ„±λ˜μ—ˆκ³ , 이후 μ–‘μžμ  측에 λ‚΄μž¬ν˜• νŽΈκ΄‘νŒλ₯Ό λ„μž…ν•˜μ—¬ μž…μ‚¬κ΄‘μ˜ νŽΈκ΄‘μƒνƒœλ₯Ό μœ μ§€ν•˜κ³  μ–‘μžμ μ˜ μ„±λŠ₯ μ €ν•˜λ₯Ό λ°©μ§€ν•˜μ˜€λ‹€. λ‚΄μž¬ν˜• νŽΈκ΄‘νŒμ€ μš©μ•‘ 곡정을 톡해 이색성 μ—Όλ£Œλ₯Ό μ •λ ¬ν•˜μ—¬ μ œμž‘λ˜μ—ˆλ‹€. μ–‘μžμ  κ΄‘ λ°œκ΄‘μ„ μœ„ν•œ μž…μ‚¬κ΄‘μ˜ μ„ΈκΈ°λŠ” 적용된 μ „μ••μ˜ 세기에 따라 μ•‘μ • 셀을 ν†΅ν•œ μœ„μƒ 지연에 μ˜ν•΄ λ³€μ‘°λ˜μ—ˆλ‹€. μ΄λŠ” 색 μ˜μ—­μ΄ BT.2020 ν‘œμ€€μ˜ μ•½ 80%κΉŒμ§€ ν™•μž₯된 높은 색 μˆœλ„λ₯Ό 보여쀀닀. λ‚΄μž¬ν˜• νŽΈκ΄‘νŒμ— κΈ°λ°˜ν•œ μ•‘μ • λ””μŠ€ν”Œλ ˆμ΄ κ΅¬μ‘°λŠ” λΉ„μš©-효율적인 λ°©λ²•μœΌλ‘œ 높은 색 μˆœλ„λ₯Ό 가진 μ–‘μžμ  기반 κ΄‘ λ°œκ΄‘ μ•‘μ • λ””μŠ€ν”Œλ ˆμ΄λ₯Ό κ΅¬μ„±ν•˜λŠ” κ°„λ‹¨ν•˜κ³  μ‹€ν–‰κ°€λŠ₯ν•œ 방법을 μ œκ³΅ν•  것이닀.1. Introduction 1 1.1. Overview of liquid crystal-based displays 1 1.1.1. Main LCD Modes 3 1.1.2. Types of backlight unit for LCDs 9 1.2. Outline of thesis 15 2. LCD with QD color filters 16 2.1. Types of polarizers 16 2.2. Architecture of QD-LCD with in-cell polarizer 19 3. Experiments 24 3.1. Fabrication of photoluminescence QD patterns 24 3.2. Dichroic dye-based in-cell polarizer 26 3.3. Solution-processed in-cell polarizer with QD-based LC cell 29 3.4. Measurements of optical and photoluminescence characteristics 30 4. Results and Discussion 31 4.1. Analysis of polarizing characteristics of in-cell polarizer 31 4.2. Photoluminescence characteristics of QD-based LC cell with in-cell polarizer 34 4.3. Microscopic images of QD-based LC cell with in-cell polarizer 35 5. Conclusion 38 Bibliography 39 κ΅­λ¬Έ 초둝 43Maste

    High-dynamic-range Foveated Near-eye Display System

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    Wearable near-eye display has found widespread applications in education, gaming, entertainment, engineering, military training, and healthcare, just to name a few. However, the visual experience provided by current near-eye displays still falls short to what we can perceive in the real world. Three major challenges remain to be overcome: 1) limited dynamic range in display brightness and contrast, 2) inadequate angular resolution, and 3) vergence-accommodation conflict (VAC) issue. This dissertation is devoted to addressing these three critical issues from both display panel development and optical system design viewpoints. A high-dynamic-range (HDR) display requires both high peak brightness and excellent dark state. In the second and third chapters, two mainstream display technologies, namely liquid crystal display (LCD) and organic light emitting diode (OLED), are investigated to extend their dynamic range. On one hand, LCD can easily boost its peak brightness to over 1000 nits, but it is challenging to lower the dark state to \u3c 0.01 nits. To achieve HDR, we propose to use a mini-LED local dimming backlight. Based on our simulations and subjective experiments, we establish practical guidelines to correlate the device contrast ratio, viewing distance, and required local dimming zone number. On the other hand, self-emissive OLED display exhibits a true dark state, but boosting its peak brightness would unavoidably cause compromised lifetime. We propose a systematic approach to enhance OLED\u27s optical efficiency while keeping indistinguishable angular color shift. These findings will shed new light to guide future HDR display designs. In Chapter four, in order to improve angular resolution, we demonstrate a multi-resolution foveated display system with two display panels and an optical combiner. The first display panel provides wide field of view for peripheral vision, while the second panel offers ultra-high resolution for the central fovea. By an optical minifying system, both 4x and 5x enhanced resolutions are demonstrated. In addition, a Pancharatnam-Berry phase deflector is applied to actively shift the high-resolution region, in order to enable eye-tracking function. The proposed design effectively reduces the pixelation and screen-door effect in near-eye displays. The VAC issue in stereoscopic displays is believed to be the main cause of visual discomfort and fatigue when wearing VR headsets. In Chapter five, we propose a novel polarization-multiplexing approach to achieve multiplane display. A polarization-sensitive Pancharatnam-Berry phase lens and a spatial polarization modulator are employed to simultaneously create two independent focal planes. This method enables generation of two image planes without the need of temporal multiplexing. Therefore, it can effectively reduce the frame rate by one-half. In Chapter six, we briefly summarize our major accomplishments

    High dynamic range display systems

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    High contrast ratio (CR) enables a display system to faithfully reproduce the real objects. However, achieving high contrast, especially high ambient contrast (ACR), is a challenging task. In this dissertation, two display systems with high CR are discussed: high ACR augmented reality (AR) display and high dynamic range (HDR) display. For an AR display, we improved its ACR by incorporating a tunable transmittance liquid crystal (LC) film. The film has high tunable transmittance range, fast response time, and is fail-safe. To reduce the weight and size of a display system, we proposed a functional reflective polarizer, which can also help people with color vision deficiency. As for the HDR display, we improved all three aspects of the hardware requirements: contrast ratio, color gamut and bit-depth. By stacking two liquid crystal display (LCD) panels together, we have achieved CR over one million to one, 14-bit depth with 5V operation voltage, and pixel-by-pixel local dimming. To widen color gamut, both photoluminescent and electroluminescent quantum dots (QDs) have been investigated. Our analysis shows that with QD approach, it is possible to achieve over 90% of the Rec. 2020 color gamut for a HDR display. Another goal of an HDR display is to achieve the 12-bit perceptual quantizer (PQ) curve covering from 0 to 10,000 nits. Our experimental results indicate that this is difficult with a single LCD panel because of the sluggish response time. To overcome this challenge, we proposed a method to drive the light emitting diode (LED) backlight and the LCD panel simultaneously. Besides relatively fast response time, this approach can also mitigate the imaging noise. Finally yet importantly, we improved the display pipeline by using a HDR gamut mapping approach to display HDR contents adaptively based on display specifications. A psychophysical experiment was conducted to determine the display requirements

    OLEDs AND E-PAPER. Disruptive Potential for the European Display Industry

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    DG ENTR and JRC/IPTS of the European Commission have launched a series of studies to analyse prospects of success for European ICT industries with respect to emerging technologies. This report concerns display technologies (Organic Light Emitting Diodes and Electronic Paper - or OLEDs and e-paper for short). It assesses whether these technologies could be disruptive, and how well placed EU firms would be to take advantage of this disruption In general, displays are an increasingly important segment of the ICT sector. Since the 1990s and following the introduction of flat panel displays (FPDs), the global display industry has grown dramatically. The market is now (2009) worth about ΒΏ 100 billion. Geo-politically, the industry is dominated by Asian suppliers, with European companies relegated to a few vertical niches and parts of the value chain (e.g. research, supply of material and equipment). However, a number of new technologies are entering the market, e.g. OLEDs and electronic paper. Such emerging technologies may provide an opportunity for European enterprises to (re-)enter or strengthen their competitive position. OLEDs are composed of polymers that emit light when a current is passed through them. E-paper, on the other hand, is a portable, reusable storage and display medium, typically thin and flexible. Both OLEDs and e-paper have the potential to disrupt the existing displays market, but it is still too soon to say with certainty whether this will occur and when. Success for OLEDs depends on two key technical advances: first, the operating lifetime, and second, the production process. E-paper has a highly disruptive potential since it opens the door to new applications, largely text-based, not just in ICTs but also in consumer goods, pictures and advertising that could use its key properties. It could also displace display technologies that offer text-reading functions in ICT terminals such as tablet notebooks. There are three discrete segments in the OLED value chain where any discontinuity could offer EU firms the opportunity to play a more significant part in the displays sector: (1) original R&D and IPR for devices and for the manufacturing process and material supply/verification; (2) bulk materials for manufacture and glass; and (3) process equipment:. For the e-paper value chain, we can see that the entry of EU suppliers is perhaps possible across more value chain segments than for OLEDs. Apart from the ones mentioned for OLEDs, there are opportunities to enter into complete devices and content provision. In terms of vertical segments, the point of entry in OLED FPDs for Europe is most likely to be in the mass production of smaller FPDs for mobile handsets. In conclusion, OLEDs and e-paper have the potential to disrupt current displays market and in so doing they may enable EU companies to enter at selected points in the value chain to compete with the Asian ICT industry.JRC.J.4-Information Societ

    TV Energy Consumption Trends and Energy-Efficiency Improvement Options

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    Vertical Field Switching Blue Phase Liquid Crystals For Field Sequential Color Displays

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    Low power consumption is a critical requirement for all liquid crystal display (LCD) devices. A field sequential color (FSC) LCD was proposed by using red (R), green (G) and blue (B) LEDs and removing the lossy component of color filters which only transmits ~30% of the incoming white light. Without color filters, FSC LCDs exhibit a ~3X higher optical efficiency and 3X higher resolution density as compared to the conventional color filters-based LCDs. However, color breakup (CBU) is a most disturbing defect that degrades the image quality in FSC displays. CBU can be observed in stationary or moving images. It manifests in FSC LCDs when there is a relative speed between the images and observers’ eyes, and the observer will see the color splitting patterns or rainbow effect at the boundary between two different colors. In Chapter 2, we introduce a five-primary display by adding additional yellow(Y) and cyan(C) colors. From the analysis and simulations, five primaries can provide wide color gamut and meanwhile the white brightness is increased, as compared to the three-primary. Based on the five-primary theorem, we propose a method to reduce CBU of FSC LCDs by using RGBYC LEDs instead of RGB LEDs in the second section. Without increasing the sub-frame rate as three-primary LCDs, we can reduce the CBU by utilizing proper color sequence and weighting ratios. In addition, the color gamut achieves 140% NTSC and the white brightness increases by more than 13%, as compared to the three-primary FSC LCDs. Another strategy to suppress CBU is using higher field frequency, such as 540 Hz or even up to 1000 Hz. However, this approach needs liquid crystals with a very fast response time

    Options Under Uncertainty: An Empirical Investigation of Patterns of Commitment in Display Technologies in the Flat Panel TV Set Industry

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    This dissertation considers fundamental questions about real options reasoning and its application in the face of uncertainty: do firms behave as real options reasoning predicts, and are there performance benefits from its application? The concept of uncertainty is further developed by considering two primary types: technological uncertainty and market needs uncertainty. A qualitative industry level historical case study is performed on the flat panel TV industry, chosen because it exhibits high technological uncertainty and low market needs uncertainty. Real options logic predicts, in such an industry, that firms will develop and maintain technology options until uncertainty is resolved. Firm level case studies for major incumbent Japanese TV set manufacturers and other relevant firms are performed. Comparison across the cases, and between several specific firms is conducted to test and further develop theory. The firms studied are found to generally behave as predicted by real options logic. Evidence from the study does not present a clear relation between options-related behavior and performance. Although this study identifies evidence not holding options can have large negative performance results, firms holding options as predicted by theory did not realize lasting performance improvements. With one exception, firms attempting to leverage technological capabilities into improved market positions were unable to realize durable improvements in their positions. The development and release of flat panel TV coincided with changes in performance for many firms in the industry; however, these performance changes were short lived. By the end of the study period, industry players had generally returned to the trajectories they were previously on. Between-case analysis of several outlying firms in the sample provides a rich and nuanced view of requirements for firms to dramatically improve performance in the face of high technological uncertainty in a market with very large size potential and relatively well-understood customer needs. This research contributes to the empirical literature on real options and is novel amongst academic research in its coverage of the flat panel display history using Japanese sources. Finally, this dissertation includes managerial implications regarding the usefulness of real options reasoning as well as practical issues in its implementation
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