Adaptive Liquid Crystal Windows

Energy consumption by private and commercial sectors in the U.S. has steadily grown over the last decade. The uncertainty in future availability of imported oil, on which the energy consumption relies strongly, resulted in a dramatic increase in the cost of energy. About 20% of this consumption are used to heat and cool houses and commercial buildings. To reduce dependence on the foreign oil and cut down emission of greenhouse gases, it is necessary to eliminate losses and reduce total energy consumption by buildings. To achieve this goal it is necessary to redefine the role of the conventional windows. At a minimum, windows should stop being a source for energy loss. Ideally, windows should become a source of energy, providing net gain to reduce energy used to heat and cool homes. It is possible to have a net energy gain from a window if its light transmission can be dynamically altered, ideally electronically without the need of operator assistance, providing optimal control of the solar gain that varies with season and climate in the U.S. In addition, the window must not require power from the building for operation. Resolution of this problem is a societal challenge and of national interest and will have a broad global impact. For this purpose, the year-round, allclimate window solution to provide an electronically variable solar heat gain coefficient (SHGC) with a wide dynamic range is needed. AlphaMicron, Inc. (AMI) developed and manufactured 1ft × 1ft prototype panels for the world’s first auto-adjusting Adaptive Liquid Crystal Windows (ALCWs) that can operate from sunlight without the need for external power source and demonstrate an electronically adjustable SHGC. This novel windows are based on AlphaMicron’s patented e-Tint® technology, a guesthost liquid crystal system implemented on flexible, optically clear plastic films. This technology is suitable both for OEM and aftermarket (retro-fitting) lamination to new and existing windows. Low level of power consumption by ALCWs allows for on-board power electronics for automatic matching of transmission through windows to varying climate conditions without drawing the power from the power grid. ALCWs are capable of transmitting more sunlight in winters to assist in heating and less sunlight in summers to minimize overheating. As such, they can change the window from being a source of energy loss to a source of energy gain. In addition, the scalable AMI’s roll-to-roll process, proved by making 1ft × 1ftALCW prototype panels, allows for cost-effective production of large-scale window panels along with capability to change easily their color and shape. In addition to architectural glazing in houses and commercial buildings, ALCWs can be used in other applications where control of sunlight is needed, such as green houses, used by commercial produce growers and botanical gardens, cars, aircrafts, etc

Quantum dot polymer composite materials for light management in optoelectronic devices

This dissertation will highlight a path to achieve high conversion efficiency of optoelectronic devices, including photovoltaic concentrators and LED display modules. Semiconductor nanocrystals, also known as quantum dots (QDs), serve as the pivotal luminescent materials in these devices. A quantum dots encapsulation method was developed here to homogeneously disperse QDs in a transparent polymer matrix, enabling high optical quality devices and thorough investigation of light material interactions. A luminescent solar concentrator (LSC) typically consists of a luminophore embedded in a polymer sheet with a high-performance solar cell attached at the side. In such a device, sunlight is absorbed in a luminophore, emitted into the waveguide modes of the polymer sheet, and directed to a photovoltaic cell where it is absorbed and converted to electricity. Since the area of the polymer sheet is greater than the area of the photovoltaic cell, concentration of the solar photon flux is achieved. Approaching high concentration ratio will require a luminophore with large Stokes Shift, high quantum yield, minimal overlap between absorption and emission, and a narrow emission spectrum. We have examined the performance of LSCs utilizing CdSe/CdS core-shell QDs, with significantly reduced absorption-emission overlap and long propagation distances in the waveguide. Furthermore, a distributed Bragg reflector dramatically mitigates the negative impact of scattering in the waveguide, allowing efficient photon collection and concentration ratio. White-light LED is achieved by using a phosphor material to convert monochromatic light from a blue or UV LED to broad-spectrum white light. However, tradition yellow phosphors suffer from low color rendering index due to the broad emission spectrum of the phosphors. QDs have been proposed as better candidate than traditional yellow phosphors due to their narrow and tunable emission spectrum, and wide absorption spectrum in the UV-blue spectrum range. We have fabricated QD-polymer thin films as color conversion layers on blue LED via different methods, including spin-coating, drop casting and electrohydrodynamic jet printing. The polymer surface has been incorporated with nano-sized features to create photonic crystal structure. Up to 8 times QD excitation and emission enhancement have been demonstrated. We have also designed and fabricated QD-polymer based concentrating cavity on blue LED that acts both as color conversion layer and light concentrator. Distributed Bragg reflector and sputtered silver have been used as reflectors surrounding QD-polymer thin film. The exterior of the concentrator cavity was coated with black absorber to suppress light reflection, and a small aperture in the center allows concentrated photons to exit. High power conversion efficiency and high ambient contrast have been achieved in module devices

High-dynamic-range Foveated Near-eye Display System

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

Eurodisplay 2019

The collection includes abstracts of reports selected by the program by the conference committee

Advanced Blue Phase Liquid Crystal Displays

Thin-film transistor (TFT) liquid crystal displays (LCDs) have become indispensable in our daily lives. Their widespread applications range from smartphones, laptops, TVs to navigational devices, data projectors and wearable displays. Over past decades, massive efforts have been invested in device development, material characterization and manufacturing technology. As a result, the performance of LCDs, such as viewing angle, contrast ratio, color gamut and resolution, have been improved significantly. Nonetheless, there are still urgent needs for fast response time and low power consumption. Fast response time helps reduce motion image blurs and enable color sequential displays. The latter is particularly attractive since it eliminates spatial color filters, which in turn triples optical efficiency and resolution density. The power consumption can be reduced greatly by using color sequential displays, but liquid crystals with submillisecond response time are required to minimize color breakup. The state-of-the-art gray-to-gray response time of nematic LCDs is about 5ms, which is too slow to meet this requirement. With the urgent needs for submillisecond response time, polymer-stabilized blue phase liquid crystal is emerging as a strong candidate for achieving this goal. Compared to conventional nematic LCDs, blue phase LCDs exhibit several revolutionary features: submillisecond gray-to-gray response time, no need for alignment layer, optically isotropic voltage-off state, and large cell gap tolerance. However, some bottlenecks such as high operation voltage, low optical transmittance, noticeable hysteresis and slow TFT charging remain to be overcome before their widespread applications can be realized. This dissertation is dedicated to addressing these challenges from material development and device design viewpoints. First, we started to investigate the device physics of blue phase LCDs. We have built a numerical model based on the refraction effect for simulating the electro-optics of blue phase devices. The model well agrees with experimental data. Based on this model, we explored approaches from device and material viewpoints to achieve low operation voltage. On the device side, with protrusion and etched electrodes, we can reduce the operating voltage to below 10V and enhance the transmittance to over 80%. On the material side, high Kerr constant is indeed helpful for lowering the operation voltage, but we also need to pay attention to the individual ?n and ?? values of liquid crystal host according to the device structures employed. High-?? LC hosts help enhance Kerr constant, leading to a reduced operation voltage; but they may be subject to serious capacitance charging issues due to the huge dielectric anisotropy. Our model provides important guidelines for future device design and material development. To further enhance transmittance and reduce voltage, we have proposed a Z-shaped electrode structure. By optimizing the device structure, we have successfully reduced the operating voltage to ~8V and enhanced optical transmittance to \u3e 95% based on a lower-?? LC host not subjecting to charging issues, showing comparable or even better performance than the mainstream LCDs. This is the first approach to achieve such a high transmittance in blue phase devices without using a directional backlight. By using zigzag structure, the color shift and gray inversion are in unnoticeable range. In addition, hysteresis affects the accuracy of grayscale control and should be suppressed. We have proposed a double exponential model to analyze the electric field effects of blue phase, and found that electrostriction effect is the root cause for hysteresis under strong electric field. To suppress the electrostriction effect in blue phase, a method to stabilize the blue phase lattice via linear photo-polymerization is demonstrated for the first time. By illuminating the mono-functional and the di-functional monomers with a linearly polarized UV beam, we can form anisotropic polymer networks, which in turn lead to anisotropic electrostrictions. In experiments, we found that when the polarization of UV light is perpendicular to the stripe electrodes, the electrostriction effect can be strongly suppressed. The resulting hysteresis is reduced from 6.95% to 0.36% and response time is improved by a factor of two. We foresee this approach will guide future manufacturing process. The approaches and studies presented in this dissertation are expected to advance the blue phase LCDs to a new level and accelerate their emergence as next-generation display technology. It is foreseeable that the widespread application of blue phase LCDs is around the corner

The smart contact lens: from an artificial iris to a contact lens display

Contactlenzen zijn ruim gekend als passieve hulpmiddelen voor visuele correctie, maar in het laatste decennium is er een nieuw onderzoeksdomein ontstaan naar zogenaamde 'slimme' contactlenzen. Door het toevoegen van elektronische componenten en andere actieve elementen kunnen nieuwe functionaliteiten aan contactlenzen worden gegeven zoals het meten van biomedische parameters, actieve visuscorrectie en Augmented Reality. Met het oog op potentiele toepassingen in actieve visuscorrectie en Augmented Reality, werd er in dit onderzoek werd gekeken hoe klassieke LCD technologie geïntegreerd kan worden in contactlenzen. Gebaseerd op bestaande fabricagemethoden van flexibele beeldschermen werd een nieuw productieproces opgesteld dat toeliet om een sferisch vervormde vloeibaarkristal-cel te produceren die dun genoeg was om in een contactlens geïntegreerd to worden. Hierna werden de eerste mogelijke applicaties zoals een artificiële iris en een actieve multifocaallens verkend en werd er gekeken wat de verdere uitdagingen waren om tot een heus contactlensbeeldscherm te komen

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

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 ¿ 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