¡§Blue phase¡¨ LCD panels features the advantages of superior response times¡Bwide viewing angle and no requirement for alignment by rubbing greater than conventional LCD modes. Thus, recently several groups have been developed both scientific and technological interests in the blue phases. However, the blue phases only exist in the narrow temperature range, typically a few Kelvin below the phase transition temperature of materials, which has been a problem for practical applications such as fast light modulators or display. In this paper, we proposed polymer-stabilized liquid crystalline blue phase by photopolymerizing the monomers in the isotropic phase and discussed the theoretical model to describe the stability of the blue phases. The polymer networks play an important role in stabilizing a liquid crystal blue phase. The morphology of polymer network was determined by the process of polymerization condition, like exposure intensity and temperature. Moreover, scanning electron microscopy (SEM) images were used to understand directly the network structures and to find the regularity of temperature intervals. In the meantime, we successfully extended the temperature range of blue phase over 140oC under suitable conditions. Based on this research results, the different temperature interval properties of cholesteric blue phases will apply on various photoelectric elements in the future.

With exploding growth of information exchanges between people, display has become indispensable in our daily lives. After decades of intensive research and development in materials and devices, and massive investment in manufacturing technologies, liquid crystal display (LCD) has overcome various obstacles and achieved the performance we need, such as wide viewing angle, high contrast ratio, and high resolution, etc. These excellent performances make LCD prevailed in every perspective. Recently, with the demands of energy conservation, a greener LCD with lower power consumption is desired. In order to achieve this goal, new energy-effective driving methods, such as field sequential color display, have been proposed. However, in order to suppress color breakup the LC response time should be faster than 1 ms. To overcome this challenge, various fast-response liquid crystal modes, such as thin cell gap, low viscosity materials, overdrive and undershoot voltages, polymer stabilization, and ferroelectric liquid crystal, are under active investigations. Among these approaches, blue phase liquid crystal (BPLC) shows a greater potential with less fabrication limitations. In this dissertation, the feasibility of polymer-stabilized blue phase liquid crystal for display applications is explored starting from the building blocks of the material system, polymer-stabilization processes, test cell preparations, electro-optical (EO) properties, to suggested approaches for further improvements. iv Because of the nature of blue phase liquid crystals, delicate balance among system components is critically important. Besides the properties of each composition, the preparation process also dictates the EO performance of the self-assembled nano-structured BPLC composite. After the preparation of test cells, EO properties for display applications are investigated and results described. Approaches for further improvements of the EO properties are also suggested in the final part of this dissertation.

Fabry-Pérot (FP) filters are widely used in telecommunications, lasers and spectroscopy to measure the wavelengths of light. The properties of a FP filter depend on the wavelength and incident angle of the light source, the thickness of the etalon and the refractive index of the material between the reflecting surfaces. In previous studies, the nematic liquid crystal (NLC) is employed as the medium of FP filters because of its simple structure and ease of modulation. The directors of the NLC could be rotated by applying an electric field. Due to the birefringence of the NLC, the optical characteristics of the device are polarization dependent. Blue phase liquid crystal (BPLC) is the phase between cholesteric phase and isotropic phase. It¡¦s an optically isotropic material can function as an active index-tuning material adopted in a FP filter, and the characteristics of the BPLC-based FP filter are polarization independent. By applying an electric field, the Kerr effect can be induced due to the local reorientation of liquid crystals in BP structure, leading to the effective index change of BPLC and the transmission peak shifts. Furthermore, the effective index of BPLC approaches the ordinary index of host LCs under increasing electric fields. In addition, the BPLC using polymer network construction can be stabilized in room temperature and improves the convenience of the device. According to the experimental results, the tunability of the BPLC-based FP filter is about 1nm/V. The measured response time of the BPLC-based FP filter is 1ms.

Liquid crystals are a vast and diverse class of materials which ranges from fluids made up of simple rods, polymers and solutions, to elastomers and biological organisms. Liquid crystal phases are neither crystalline, nor a ‘normal’ isotropic liquid, but lie somewhere in between these two common states of matter. Liquid crystals have found enormous use in display devices due to their electro-optic properties. In this thesis, the optical and electro-optical properties of some chiral liquid crystalline phases are studied. The optical and electro-optical behaviour of liquid crystalline blue phases has been investigated via a detailed analysis of the reflection spectrum from thin, vertical field (VF) cells. Spectral analysis in this thesis was performed using a numerical fitting technique based on the Berreman 4x4 matrix method. The validity of the technique was proved through comparisons of independent measurements with the calculated physical parameters. A novel Kerr effect measurement method was proposed in this thesis and a known material was used to verify this new method. The Kerr constant together with its dispersion relation was measured using a white light source. An unusually large Kerr constant, K, is determined in the blue phases of a non-polymer stabilized material, ~ 3x10-9 mV-2 (BPI). The large value of K is attributed to significant pre-transitional values of the dielectric anisotropy and birefringence. K follows an inverse dependence on temperature which is more marked in BPII than BPI, and we consequently suggest that the BPI demonstrates properties best suited to electro-optic devices. The field effects in blue phase include electrostriction and the influence of the Kerr effect was separated from electrostriction phenomena for the first time in this work. Finally in the Kerr effect measurements, the Kerr constant in the optically isotropic dark conglomerate phase of a bent-core material was studied for the first time, with rather low values, ~1x10-11 mV-2. The low Kerr constant can be understood in the context of the physical properties of the material. Supercooling phenomena in the blue phase were studied through an analysis of the optical properties in thin cells. Features including the Bragg reflection peak jump and hysteresis are measured through the reflection spectra. A blue phase sample with a single orientation over an area of millimeters was prepared to help the spectra study of the blue phases. Although some previous reports indicated that there may be a new blue phase in the supercooled region, we find that there is no evidence shows that the supercooled blue phase has a different structure from the BPI.Chiral molecules have been included as dopants in achiral bent-core materials to produce a range of new chiral mixtures. Different host materials and chiral dopants have been used to produce several chiral nematic materials in which the chiral nematic phase, the underlying smectic phase and the blue phases are examined. The order parameter is determined as a function of temperature in the chiral nematic phase, and compared to that determined for several calamitic materials; no discernible difference is found. A study of the pitch divergence in the chiral nematic phase of the bent-core mixtures shows interesting properties at both low temperature (as the smectic phase is approached) and at high temperatures (at the transition to the blue phase). An unusual phase separation of the chiral dopant in the mixtures is reported, and details are deduced through a comparison between different mixtures. It is found that a dopant with similar clearing point to the bent-core material has less likelihood of phase separation. Although the blue phase temperature range is extended in these mixtures in comparison with typical values for calamitic materials, it does not extend beyond 2K in any of the materials. Both blue phase I and the fog phases are observed in these chiral bent core systems, but no BPII is observed in any of the materials studied. The small k33 (~ 2.8 pN at 10 K below clearing point) in the bent-core host material is suggested as one of the reasons that the blue phase range is not enhanced as much as may have been expected from reports by other authors.

Autostereoscopic 2D/3D (two-dimension/three-dimension) switchable display has been attracting great interest in research and practical applications for several years. Among different autostereoscopic solutions, direction-multiplexed 3D displays based on microlens array or parallax barrier are viewed as the most promising candidates, due to their compatibility with conventional 2D display technologies. These 2D/3D switchable display system designs rely on fast switching display panels and photonics devices, including adaptive focus microlens array and switchable slit array. Polymer-stabilized blue phase liquid crystal (PS-BPLC) material provides a possible solution to meet the aforementioned fast response time requirement. However, present display and photonic devices based on blue phase liquid crystals suffer from several drawbacks, such as low contrast ratio, relatively large hysteresis and short lifetime. In this dissertation, we investigate the material properties of PS-BPLC so as to improve the performance of PS-BPLC devices. Then we propose several PS-BPLC devices for the autostereoscopic 2D/3D switchable display system designs. In the first part we evaluate the optical rotatory power (ORP) of blue phase liquid crystal, which is proven to be the primary reason for causing the low contrast ratio of PS-BPLC display systems. Those material parameters affecting the ORP of PS-BPLC are investigated and an empirical equation is proposed to calculate the polarization rotation angle in a PS-BPLC cell. Then several optical compensation methods are proposed to compensate the impact of ORP and to improve the contrast ratio of a display system. The pros and cons of each solution are discussed accordingly. In the second part, we propose two adaptive focus microlens array structures and a high efficiency switchable slit array based on the PS-BPLC materials. By optimizing the design parameters, these devices can be applied to the 2D/3D switchable display systems. In the last section, we focus on another factor that affects the performance and lifetime of PS-BPLC devices and systems: the UV exposure condition. The impact of UV exposure wavelength, dosage, uniformity, and photo-initiator are investigated. We demonstrate that by optimizing the UV exposure condition, we can reduce the hysteresis of PS-BPLC and improve its long term stability.

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 (

Thin-film-transistor (TFT) liquid crystal display (LCD) has been widely used in smartphones, pads, laptops, computer monitors, and large screen televisions, just to name a few. A great deal of effort has been delved into wide viewing angle, high resolution, low power consumption, and vivid color. However, relatively slow response time and low transmittance remain as technical challenges. To improve response time, several approaches have been developed, such as low viscosity liquid crystals, overdrive and undershoot voltage schemes, thin cell gap with a high birefringence liquid crystal, and elevated temperature operation. The state-of-the-art gray-to-gray response time of a nematic LC device is about 5 ms, which is still not fast enough to suppress the motion picture image blur. On the other hand, the LCD panel's transmittance is determined by the backlight, polarizers, TFT aperture ratio, LC transmittance, and color filters. Recently, a fringe-field-switching mode using a negative dielectric anisotropy (Δε) LC (n-FFS) has been demonstrated, showing high transmittance (98%), single gamma curve, and cell gap insensitivity. It has potential to replace the commonly used p-FFS (FFS using positive Δε LC) for mobile displays. With the urgent need of submillisecond response time for enabling color sequential displays, polymer-stabilized blue phase liquid crystal (PS-BPLC) has become an increasingly important technology trend for information display and photonic applications. BPLCs exhibit several attractive features, such as reasonably wide temperature range, 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, hysteresis, residual birefringence, and slow charging issue due to the large capacitance, remain to be overcome before their widespread applications can be realized. The material system of PS-BPLC, including nematic LC host, chiral dopant, and polymer network, are discussed in detail. Each component plays an essential role affecting the electro-optic properties and the stability of PS-BPLC. In a PS-BPLC system, in order to lower the operation voltage the host LC usually has a very large dielectric anisotropy (Δε > 100), which is one order of magnitude larger than that of a nematic LC. Such a large Δε not only leads to high viscosity but also results in a large capacitance. High viscosity slows down the device fabrication process and increases device response time. On the other hand, large capacitance causes slow charging time to each pixel and limits the frame rate. To reduce viscosity, we discovered that by adding a small amount (~6%) of diluters, the response time of the PS-BPLC is reduced by 2X-3X while keeping the Kerr constant more or less unchanged. Besides, several advanced PS-BPLC materials and devices have been demonstrated. By using a large Δε BPLC, we have successfully reduced the voltage to <10V while maintaining submillisecond response time. Finally we demonstrated an electric fieldindeced monodomain PS-BPLC, which enables video-rate reflective display with vivid colors. The highly selective reflection in polarization makes it promising for photonics application. Besides displays in the visible spectral region, LC materials are also very useful electro-optic media for near infrared and mid-wavelength infrared (MWIR) devices. However, large absorption has impeded the widespread application in the MWIR region. With delicate molecular design strategy, we balanced the absorption and liquid crystal phase stability, and proposed a fluoro-terphenyl compound with low absorption in both MWIR and near IR regions. This compound serves as an important first example for future development of low-loss MWIR liquid crystals, which would further expand the application of LCs for amplitude and/or phase modulation in MWIR region.