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Title: FAST RESPONSE LIQUID CRYSTAL DEVICES.
Creator: Wu, Yung-Hsun, Wu, Shin-Tson, University of Central Florida
Abstract / Description: Liquid crystal (LC) has been widely used for displays, spatial light modulators, variable optical attenuators (VOAs) and other tunable photonic devices. The response time of these devices is mainly determined by the employed liquid crystal material. How to obtain fast response for the LC devices is a fundamentally important and technically challenging task. In this dissertation, we investigate several methods to improve liquid crystal response time, for examples, using dual-frequency liquid...
Show moreLiquid crystal (LC) has been widely used for displays, spatial light modulators, variable optical attenuators (VOAs) and other tunable photonic devices. The response time of these devices is mainly determined by the employed liquid crystal material. How to obtain fast response for the LC devices is a fundamentally important and technically challenging task. In this dissertation, we investigate several methods to improve liquid crystal response time, for examples, using dual-frequency liquid crystals, polymer stabilized liquid crystals, and sheared polymer network liquid crystals. We discover a new class of material, denoted as sheared polymer network liquid crystal (SPNLC) which exhibits a submillisecond response time. First, dual-frequency liquid crystals and polymer network methods are demonstrated as examples for the variable optical attenuators. Variable optical attenuator (VOA) is a key component in optical communications. Especially, the sheared PNLC VOA shows the best result; its dynamic range reaches 43 dB while the response time is in the submillisecond range at 1550 nm wavelength, which is 50 times faster than the commercial LC-based VOA. Second, we report a new device called axially-symmetric sheared polymer network liquid crystals (AS-SPNLC) and use it as LC devices. An axially-symmetric sheared polymer network liquid crystal has several attractive features: 1) it is polarization independent, 2) it has gradient phase change, and 3) its response time is fast. It can be used for polarization converter and divergent LC lens. In addition, a new method for simultaneously measuring the phase retardation and optic axis of a compensation film is demonstrated using an axially-symmetric sheared polymer network liquid crystal. This simple technique can be used for simultaneously measuring the optic axis and phase retardations of both A- and C-plates. These compensation films have been used extensively in wide-view LCD industry. Therefore, this method will make an important impact to the LCD industry.
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Date Issued: 2006
Identifier: CFE0000980, ucf:46708
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000980

Title: FAST RESPONSE DUAL FREQUENCYLIQUID CRYSTAL MATERIALS.
Creator: song, qiong, Wu, Shin-Tson, University of Central Florida
Abstract / Description: Dual frequency liquid crystal (DFLC) exhibits a positive dielectric anisotropy at low frequencies and negative dielectric anisotropy at high frequencies. The frequency where dielectric anisotropy is zero is called crossover frequency. DFLC can achieve fast rise time and fast decay time with the assistance of applied voltage. However, one drawback of DFLC is that it has dielectric heating effect when driven at a high frequency. Thus, the first part of this dissertation is to develop low...
Show moreDual frequency liquid crystal (DFLC) exhibits a positive dielectric anisotropy at low frequencies and negative dielectric anisotropy at high frequencies. The frequency where dielectric anisotropy is zero is called crossover frequency. DFLC can achieve fast rise time and fast decay time with the assistance of applied voltage. However, one drawback of DFLC is that it has dielectric heating effect when driven at a high frequency. Thus, the first part of this dissertation is to develop low crossover frequency DFLC materials. The dielectric relaxation and physical properties of some single- and double-ester compounds were investigated. Experimental results indicate that the double-ester compound exhibits a ~ 3 X lower dielectric relaxation frequencies and larger dielectric anisotropy than the single ester, but its viscosity is also higher. More generally, ten groups of dual frequency liquid crystals were compared in terms of dielectric relaxation frequency and dielectric anisotropy. The dielectric relaxation theory was discussed at last. To realize fast response time, high birefringence and low viscosity LC are required. From these two aspects, firstly four new high birefringence laterally difluoro phenyl tolane liquid crystals with a negative dielectric anisotropy were studied. These materials are used to enhance the birefringence of DFLC. They have a fairly small heat fusion enthalpy (~3000 cal/mol) which improves their solubility in a host. We dope 10 wt% of each compound into a commercial negative mixture N1 and measured their birefringence, viscoelastic constant and figure of merit. Birefringence varies very little among homologues while viscoelastic constant increases as alkyl chain length increases. Secondly, we studied the effects of six diluters for lowering the viscosity while stabilizing the vertical alignment (VA) of the laterally difluoro terphenyl host mixture at elevated temperatures. The pros and cons of each diluter are analyzed. These lateral difluoro terphenyls exhibit a high birefringence, fairly low viscosity, and modest dielectric anisotropy, but their molecular alignment in a VA cell is gradually deteriorated at elevated temperatures as their concentration increases. As a result, the device contrast ratio is decreased noticeably due to the light leakage through the crossed polarizers. Finally, liquid crystal doped with metallic nanoparticles, such as Pd, Ag, or Ag-Pd, which are protected with ligand molecules, such as nematic liquid crystal were studied. The metal nanoparticles doped LC exhibit a frequency modulation (FM) electro-optical (EO) response in the millisecond to submillisecond range together with the ordinary root-mean-square voltage response.
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Date Issued: 2010
Identifier: CFE0003152, ucf:48593
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003152

Title: Submillisecond-response blue phase liquid crystals for display applications.
Creator: Chen, Kuan-Ming, Wu, Shintson, Likamwa, Patrick, Hagan, David, Fang, Jiyu, University of Central Florida
Abstract / Description: 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....
Show moreWith 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. 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.
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Date Issued: 2012
Identifier: CFE0004243, ucf:49499
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004243

Title: Advanced liquid crystal displays with supreme image qualities.
Creator: Chen, Haiwei, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, Dong, Yajie, University of Central Florida
Abstract / Description: 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...
Show moreSeveral 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's 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's 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.
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Date Issued: 2017
Identifier: CFE0006864, ucf:51758
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006864

Title: CHOLESTERIC LIQUID CRYSTAL PHOTONIC CRYSTAL LASERS AND PHOTONIC DEVICES.
Creator: Zhou, Ying, Wu, Shin-Tson, University of Central Florida
Abstract / Description: This dissertation discusses cholesteric liquid crystals (CLCs) and polymers based photonic devices including one-dimensional (1D) photonic crystal lasers and broadband circular polarizers. CLCs showing unique self-organized chiral structures have been widely used in bistable displays, flexible displays, and reflectors. However, the photonic band gap they exhibit opens a new way for generating laser light at the photonic band edge (PBE) or inside the band gap. When doped with an emissive laser...
Show moreThis dissertation discusses cholesteric liquid crystals (CLCs) and polymers based photonic devices including one-dimensional (1D) photonic crystal lasers and broadband circular polarizers. CLCs showing unique self-organized chiral structures have been widely used in bistable displays, flexible displays, and reflectors. However, the photonic band gap they exhibit opens a new way for generating laser light at the photonic band edge (PBE) or inside the band gap. When doped with an emissive laser dye, cholesteric liquid crystals provide distributed feedback so that mirrorless lasing is hence possible. Due to the limited surface anchoring, the thickness of gain medium and feedback length is tens of micrometers. Therefore lasing efficiency is quite limited and laser beam is highly divergent. To meet the challenges, we demonstrated several new methods to enhance the laser emission while reducing the beam divergence from a cholesteric liquid crystal laser. Enhanced laser emission is demonstrated by incorporating a single external CLC reflector as a polarization conserved reflector. Because the distributed feedback from the active layer is polarization selective, a CLC reflector preserves the original polarization of the reflected light and a further stimulated amplification ensues. As a result of virtually doubled feedback length, the output is dramatically enhanced in the same circular polarization state. Meanwhile, the laser beam divergence is dramatically reduced due to the increased cavity length from micrometer to millimeter scale. Enhanced laser emission is also demonstrated by the in-cell metallic reflector because the active layer is pumped twice. Unlike a CLC reflector, the output from a mirror-reflected CLC laser is linearly polarized as a result of coherent superposition of two orthogonal circular polarization states. The output linear polarization direction can be well controlled and fine tuned by varying the operating temperature and cell gap. Enhanced laser emission is further demonstrated in a hybrid photonic band edge - Fabry-Perot (FP) type structure by sandwiching the CLC active layer within a circular polarized resonator consisting of two CLC reflectors. The resonator generates multiple FP modes while preserving the PBE mode from the active layer. More importantly this band edge mode can be greatly enhanced by the external resonator under some conditions. Theoretical analysis is conducted based on 4×4 transfer matrix and scattering matrix and the results are consistent with our experimental observations. To make the CLC laser more compact and miniaturized, we have developed a flexible polymer laser using dye-doped cholesteric polymeric films. By stacking the mirror reflecting layer, the active layer and the CLC reflecting layer, enhanced laser emission was observed in opposite-handed circular polarization state, because of the light recycling effect. On the other hand, we use the stacked cholesteric liquid crystal films, or the cholesteric liquid crystals and polymer composite films to demonstrate the single film broadband circular polarizers, which are helpful for converting a randomly polarized light into linear polarization. New fabrication methods are proposed and the circular polarizers cover ~280 nm in the visible spectral range. Both theoretical simulation and experimental results are presented with a good match.
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Date Issued: 2008
Identifier: CFE0002198, ucf:47891
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0002198

Title: fast-response liquid crystals for photonic and display applications.
Creator: Sun, Jie, Wu, Shintson, Likamwa, Patrick, Schoenfeld, Winston, Wu, Xinzhang, University of Central Florida
Abstract / Description: Liquid crystals (LCs) are attractive for many applications such as information displays, spatial light modulators, and adaptive optics because the optical properties of these devices are electrically tunable. For most display and photonic applications, response time is a critical parameter especially for spatial light modulators that requires at least 2? phase change. This problem gets more severe as the wavelength increases because a thicker LC layer is needed, which results in a slower...
Show moreLiquid crystals (LCs) are attractive for many applications such as information displays, spatial light modulators, and adaptive optics because the optical properties of these devices are electrically tunable. For most display and photonic applications, response time is a critical parameter especially for spatial light modulators that requires at least 2? phase change. This problem gets more severe as the wavelength increases because a thicker LC layer is needed, which results in a slower response time. A typical E7 nematic liquid crystal cell with 2? phase change shows a response time longer than 100 ms at room temperature, which is too slow. Therefore, solutions for achieving fast response time are in high demand.In this dissertation, several approaches for achieving submillisecond response time are investigated. In Chapter 2, we begin by introducing dual frequency liquid crystals (DFLCs) which provide possibility to achieve submillisecond rise time and decay time. We developed a DFLC mixture with a record-high birefringence (?n=0.39 at ?=633nm) based on phenyl-tolane compounds, which exhibit a positive dielectric anisotropy (??) and modest dielectric relaxation frequency. In Chapter 3, a phase modulator with 4? phase change and 400 (&)#181;s average gray-to-gray response time is demonstrated using a sheared polymer network liquid crystal (SPNLC). This device exhibits a low scattering at ?=532 nm due to the employed material set and shearing technique. We also discuss the application of SPNLCs for 3D displays.In Chapter 4, we studied the temperature effect on the splay elastic constant of polymer network liquid crystal (PNLC). Due to the existence of polymer network, the temperature dependent splay elastic constant of the LC cell deviates from the model for nematic LCs. In Chapter 5, we focus on PNLC light modulators. This technology is attractive because it can achieve submillisecond response time while maintaining a large phase change. However, the light scattering loss caused by grain boundaries of liquid crystal multi-domains at voltage-on state hinders the widespread application of PNLCs. By optimizing liquid crystal host, polymer, and proper curing process, we successfully eliminate light scattering from short wave infrared region (1.55 ?m) to visible range. In Chapter 6, we introduce a reconfigurable fabrication technique of tunable liquid crystal devices. Based on this technique and our scattering-free PNLCs, we developed a series of fast switching LC devices such as LC prism, grating and lens. The application of this technology in 3D lenticular lens development is also discussed. This technique provides a great flexibility for designing and fabricating LC photonic devices with desired refractive index profile.
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Date Issued: 2013
Identifier: CFE0005063, ucf:49968
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005063

Title: LIQUID CRYSTAL MATERIALS AND TUNABLE DEVICES FOR OPTICAL COMMUNICATIONS.
Creator: Du, Fang, Wu, Shin-Tson, University of Central Florida
Abstract / Description: In this dissertation, liquid crystal materials and devices are investigated in meeting the challenges for photonics and communications applications. The first part deals with polymer-stabilized liquid crystal (PSLC) materials and devices. Three polymer-stabilized liquid crystal systems are developed for optical communications. The second part reports the experimental investigation of a novel liquid-crystal-infiltrated photonic crystal fiber (PCF) and explores its applications in fiber-optic...
Show moreIn this dissertation, liquid crystal materials and devices are investigated in meeting the challenges for photonics and communications applications. The first part deals with polymer-stabilized liquid crystal (PSLC) materials and devices. Three polymer-stabilized liquid crystal systems are developed for optical communications. The second part reports the experimental investigation of a novel liquid-crystal-infiltrated photonic crystal fiber (PCF) and explores its applications in fiber-optic communications. The curing temperature is found to have significant effects on the PSLC performance. The electro-optic properties of nematic polymer network liquid crystal (PNLC) at different curing temperatures are investigated experimentally. At high curing temperature, a high contrast, low drive voltage, and small hysteresis PNLC is obtained as a result of the formed large LC micro-domains. With the help of curing temperature effect, it is able to develop PNLC based optical devices with highly desirable performances for optical communications. Such high performance is generally considered difficult to realize for a PNLC. In fact, the poor performance of PNLC, especially at long wavelengths, has hindered it from practical applications for optical communications for a long time. Therefore, the optimal curing temperature effect discovered in this thesis would enable PSLCs for practical industrial applications. Further more, high birefringence LCs play an important role for near infrared photonic devices. The isothiocyanato tolane liquid crystals exhibit a high birefringence and low viscosity. The high birefringence LC dramatically improves the PSLC contrast ratio while keeping a low drive voltage and fast response time. A free-space optical device by PNLC is experimentally demonstrated and its properties characterized. Most LC devices are polarization sensitive. To overcome this drawback, we have investigated the polymer-stabilized cholesteric LC (PSCLC). Combining the curing temperature effect and high birefringence LC, a polarization independent fiber-optical device is realized with over 30 dB attenuation, ~12 Vrms drive voltage and 11/28 milliseconds (rise/decay) response times. A polymer-stabilized twisted nematic LC (PS TNLC) is also proposed as a variable optical attenuator for optical communications. By using the polarization control system, the device is polarization independent. The polymer network in a PS TNLC not only results in a fast response time (0.9/9 milliseconds for rise/decay respectively), but also removes the backflow effect of TNLC which occurs in the high voltage regime.
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Date Issued: 2005
Identifier: CFE0000485, ucf:46361
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000485

Title: HIGH BIREFRINGENCE LIQUID CRYSTALS FOR OPTICAL COMMUNICATIONS.
Creator: Parish, Amanda, Wu, Shin-Tson, University of Central Florida
Abstract / Description: High birefringence (n>0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving fast response time and improved diffraction efficiency. In this thesis, the mesomorphic and electro-optic properties of several new fluorinated isothiocyanate (NCS) terphenyl and phenyl tolane single compounds and mixtures are reported. The single compounds demonstrated n~0.35-0.52 in the visible spectral region at room...
Show moreHigh birefringence (n>0.4) nematic liquid crystals are particularly attractive for infrared applications because they enable a thinner cell gap to be used for achieving fast response time and improved diffraction efficiency. In this thesis, the mesomorphic and electro-optic properties of several new fluorinated isothiocyanate (NCS) terphenyl and phenyl tolane single compounds and mixtures are reported. The single compounds demonstrated n~0.35-0.52 in the visible spectral region at room temperature and exhibit relatively low viscosity. It was found that lateral fluorine substitutions and short alkyl chains eliminate smectic phase and lower the melting temperature of the single compounds. However, the consequence of using highly conjugated compounds to improve electro-optic properties is that the nematic phase is exhibited at high temperatures, over 100C, and therefore single compounds cannot be used for device applications. Therefore, several mixtures based on the terphenyl and phenyl-tolane compounds were formulated and evaluated. The purpose of mixtures is to find the optimum balance between electro-optic performance and the mesomorphic properties that determine the operating temperature range. It was found that mixture formulations greatly improved mesomorphic properties to produce nematic phase at or near room temperature and suppressed smectic phase to below 0C or eliminating completely. The analysis presented evaluates the benefits of lowering the operating temperature versus the consequence of degrading the electro-optic properties.
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Date Issued: 2007
Identifier: CFE0001882, ucf:47397
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001882

Title: FAST-RESPONSE LIQUID CRYSTAL DISPLAYS.
Creator: jiao, meizi, Wu, Shin-Tson, University of Central Florida
Abstract / Description: After about five decades of extensive material research and device development, followed by massive investment in manufacturing technology, thin-film-transistor liquid-crystal-display (TFT-LCD) has finally become the dominant flat panel display technology. Nowadays, LCD performances, such as viewing angle, contrast ratio, and resolution, have reached acceptable levels. The remaining major technical challenges are response time, light efficiency, and sunlight readability. Fast response time is...
Show moreAfter about five decades of extensive material research and device development, followed by massive investment in manufacturing technology, thin-film-transistor liquid-crystal-display (TFT-LCD) has finally become the dominant flat panel display technology. Nowadays, LCD performances, such as viewing angle, contrast ratio, and resolution, have reached acceptable levels. The remaining major technical challenges are response time, light efficiency, and sunlight readability. Fast response time is desired to reduce motion blur and to enable field sequential color displays using red (R), green (G), and blue (B) LEDs (light emitting diodes) without noticeable color breakup. Sequential RGB colors would eliminate the commonly used spatial color filters which in turn enhances light efficiency and resolution density by ~ 3X. In this dissertation, several new approaches for achieving fast-response LCDs are explored. From material viewpoint, the most straightforward approach for achieving fast response time is to employ a thin cell gap with high birefringence and low viscosity liquid crystal (LC). We investigated the thin cell approach theoretically and experimentally. Voltage shielding effect and anchoring energy effect of alignment layers are found to play important roles on operating voltage and response time. Simulations are carried out to understand the underlying physics and confirm the experimental results quantitatively. Another approach to realize fast response time is to explore novel device configuration. Here, we proposed a dual fringing-field switching (DFFS) mode in which small LC domains are formed following the distribution of fringing fields. Therefore, it exhibits submillisecond response time without using thin cell or overdrive/undershoot voltage method. The response time of the DFFS mode is ~20X faster than a conventional vertical aligned LCD. In addition, high optical efficiency is achieved from the complementary top and bottom active LC domains. Two transmissive and one transflective LCDs using DFFS mode are conceived and their electro-optical properties investigated. A shortcoming of DFFS LCDs is their fabrication complexity. To keep the advantages of this fast-response mode while avoiding the requirement of double-TFTs and pixel registration, we modified the device structure to transflective LCD which uses a single TFT in each pixel and vertical aligned positive dielectric anisotropy LC. Two types of electrodes are considered: fringing-field switching (FFS) and in-plane switching (IPS). Besides fast response time and high transmittance, such a transflective LCD shows good sunlight readability. As nematic LC is gradually approaching to its limit in term of response time, polymer-stabilized blue phase (PSBP) LCD is emerging. It has potential to become next-generation display because of following revolutionary features: submillisecond response time, no need for alignment layer, good dark state and symmetric viewing angle, and cell gap insensitivity if IPS electrode is employed. In this dissertation, we studied the material-property correlation of Kerr effect-induced birefringence in nano-structured PSBP LC composites. Furthermore, a new device configuration of BP LCD with corrugated electrodes is proposed to solve two critical technical issues: high driving voltage and relatively low transmittance. The on-state voltage can be reduced from ~35 Vrms to ~10 Vrms which will enable TFT addressing, and the transmittance is improved from ~65% to ~85%. This new device configuration will accelerate the emergence of PSBP LCD. Wide view is another important requirement for a high-end display. Several new LCD configurations with negative A-plate and biaxial plate as phase compensation films are proposed to achieve wide view and broadband operation. The underlying working principles are studied and detailed display performances are included in this dissertation.
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Date Issued: 2010
Identifier: CFE0003435, ucf:48399
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003435

Title: Advanced Blue Phase Liquid Crystal Displays.
Creator: Xu, Daming, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, Fang, Jiyu, University of Central Florida
Abstract / Description: 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...
Show moreThin-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 (>) 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.
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Date Issued: 2016
Identifier: CFE0006200, ucf:51101
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006200

Title: Low Voltage Blue Phase Liquid Crystal Displays.
Creator: Rao, Linghui, Wu, Shintson, Vanstryland, Eric, Zeldovich, Boris, Wu, Xinzhang, University of Central Florida
Abstract / Description: From cell phones, laptops, desktops, TVs, to projectors, high reliability LCDs have become indispensable in our daily life. Tremendous progress in liquid crystal displays (LCDs) has been made after decades of extensive research and development in materials, device configurations and manufacturing technology. Nowadays, the most critical issue on viewing angle has been solved using multidomain structures and optical film compensation. Slow response time has been improved to 2-5 ms with low...
Show moreFrom cell phones, laptops, desktops, TVs, to projectors, high reliability LCDs have become indispensable in our daily life. Tremendous progress in liquid crystal displays (LCDs) has been made after decades of extensive research and development in materials, device configurations and manufacturing technology. Nowadays, the most critical issue on viewing angle has been solved using multidomain structures and optical film compensation. Slow response time has been improved to 2-5 ms with low viscosity LC material, overdrive and undershoot voltage, and thin cell gap approach. Moving image blur has been significantly reduced by impulse driving and frame insertion. Contrast ratio in excess of one million-to-1 has been achieved through local dimming of the segmented LED backlight. The color gamut would exceed 100% of the NTSC (National Television System Committee), if RGB LEDs are used. Besides these technological advances, the cost has been reduced dramatically by investing in advanced manufacturing technologies. Polymer-stabilized blue phase liquid crystal displays (BPLCDs) based on Kerr effect is emerging as a potential next-generation display technology. In comparison to conventional nematic devices, the polymer-stabilized BPLCDs exhibit following attractive features: (1) submillisecond response time, (2) no need for molecular alignment layers, (3) optically isotropic dark state when sandwiched between crossed polarizers, and (4) transmittance is insensitive to cell gap when the in-plane electrodes are employed. However, aside from these great potentials, there are still some tough technical issues remain to be addressed. The major challenges are: 1) the operating voltage is still too high (~50 Volts vs. 5 Volts for conventional nematic LCDs), and the transmittance is relatively low (~65% vs. 85% for nematic LCDs), 2) the hysteresis effect and residual birefringence effect are still noticeable, 3) the mesogenic temperature range is still not wide enough for practical applications (?40 oC to 80 oC), and 4) the ionic impurities in these polymer-stabilized nano-structured LC composites could degrade the voltage holding ratio, which causes image sticking.In this dissertation, the BPLC materials are studied and the new BPLC device structures are designed to optimize display performances. From material aspect, the electro-optical properties of blue phase liquid crystals are studied based on Kerr effect. Temperature effects on polymer-stabilized blue phase or optically isotropic liquid crystal displays are investigated through the measurement of voltage dependent transmittance under different temperatures. The physical models for the temperature dependency of Kerr constant, induced birefringence and response time in BPLCs are first proposed and experimentally validated. In addition, we have demonstrated a polymer-stabilized BPLC mixture with a large Kerr constant K~13.7 nm/V2 at 20 oC at 633 nm. These models would set useful guidelines for optimizing material performances. From devices side, the basic operation principle of blue phase LCD is introduced. A numerical model is developed to simulate the electro-optic properties of blue phase LCDs based on in-plane-switching (IPS) structure. Detailed electrode dimension effect, distribution of induced birefringence, cell gap effect, correlation between operation voltage and Kerr constant, and wavelength dispersion are investigated. Viewing angle is another important parameter. We have optimized the device configurations according to the device physics studied. With proper new device designs, the operating voltage is decreased dramatically from around 50 Volts to below 10 Volts with a reasonably high transmittance (~70%) which enables the BPLCDs to be addressed by amorphous silicon thin-film transistors (TFTs). Moreover, weak wavelength dispersion, samll color shift, and low hysteresis BPLCDs are achieved after their root causes being unveiled. Optimization of device configurations plays a critical role to the widespread applications of BPLCDs.In addition to displays, blue phase liquid crystals can also be used for photonic applications, such as light modulator, phase grating, adaptive lens and photonic crystals. We will introduce the application of blue phase liquid crystal as a modulator to realize a viewing angle controllable display. The viewing angle can be tuned continuously and precisely with a fast response time. The detailed design and performance are also presented in this dissertation.
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Date Issued: 2012
Identifier: CFE0004625, ucf:49930
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004625

Title: STUDIES OF LIQUID CRYSTAL RESPONSE TIME.
Creator: Wang, Haiying, Wu, Shin-Tson, University of Central Florida
Abstract / Description: In this dissertation, the response time issue of the liquid crystal (LC) devices is investigated in meeting the challenges for display and photonic applications. The correlation between the LC director response time and the optical response time is derived theoretically and confirmed experimentally. A major contribution of this thesis is that, based on the small angle approximation, we derive rigorous analytical solutions for correlating the LC director response time to its consequent optical...
Show moreIn this dissertation, the response time issue of the liquid crystal (LC) devices is investigated in meeting the challenges for display and photonic applications. The correlation between the LC director response time and the optical response time is derived theoretically and confirmed experimentally. A major contribution of this thesis is that, based on the small angle approximation, we derive rigorous analytical solutions for correlating the LC director response time to its consequent optical response times (both rise and decay) of a vertical-aligned nematic LC cell. This work successfully fills the gap in the literature of LCD switching dynamics. An important effect related to response time, backflow is analyzed using a homogeneous LC cell in an infrared wavelength. The Leslie viscosity coefficients can hardly be found in the literature. A new effective approach to estimate the Leslie coefficients of LC mixtures based on MBBA data is proposed in this dissertation. Using this method, the Leslie coefficients of the LC material under study can be extracted based on its order parameters. The simulation results agree with the experimental data very well. This method provides a useful tool for analyzing the dynamic response including backflow. Cell gap is an important factor affecting the LC response time. Usually a thinner cell gap is chosen to achieve faster response time, since normally both rise and decay times are known to be proportional to d2. However, they are valid only in the region. In the large voltage region where , the optical decay time is independent of d. In this thesis, we find that between these two extremes the response time is basically linearly proportional to d. Our analytical derivation is validated by experimental results. Therefore, in the whole voltage region, the physical picture of the optical response time as a function of the cell gap is completed. This analysis is useful for understanding the grayscale switching behaviors of the LC phase modulators. In conclusion, this dissertation has solved some important issues related to LC optical response time and supplied valuable tools for scientists and engineers to numerically analyze the LC dynamics.
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Date Issued: 2005
Identifier: CFE0000796, ucf:46558
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0000796

Title: PROPAGATION EFFECT IN INHOMOGENEOUS MEDIA, INCLUDING MEDIA WITH LIGHT-INDUCED AND FIXED GRATINGS.
Creator: TSAI, CHANG-CHING, Zeldovich, Boris, University of Central Florida
Abstract / Description: Optical waves propagation in various types of volume gratings, materials with constant impendence and optical fibers are studied. Instability of cross–phase modulation and of Energy transfer via GRON-type (Grating-type Orientational Nonlinearity in Liquid Crystal) Stimulated Scattering is numerically observed. Two diffractive optical elements made of volume gratings are suggested and analyzed. A transmission hologram based on the analogy with Stimulated Raman Adiabatic Passage (STIRAP)...
Show moreOptical waves propagation in various types of volume gratings, materials with constant impendence and optical fibers are studied. Instability of cross–phase modulation and of Energy transfer via GRON-type (Grating-type Orientational Nonlinearity in Liquid Crystal) Stimulated Scattering is numerically observed. Two diffractive optical elements made of volume gratings are suggested and analyzed. A transmission hologram based on the analogy with Stimulated Raman Adiabatic Passage (STIRAP) in nonlinear optics is proposed. This transmission hologram demonstrates high diffraction efficiency and low sensitivity to polarization and hologram strength. The other is a reflection hologram with two crossed-gratings. It features good angular selectivity in comparison with the poor angular selectivity of conventional Bragg grating mirror. This defense also contains the approximation of Maxwell equations for the description of depolarized light sources and polarization-insensitive detectors. A scalar wave equation, Z-Helmholtz equation, is proposed and discussed in the approximation of constant impedance media. As examples, this equation successfully describes a) Fresnel transmission coefficient, and b) Goose-Hanschen shift in total internal reflection, for depolarized incident light and, at the same time, polarization-insensitive detectors. Evolution of polarization during light propagation in an inhomogeneous locally isotropic medium, and also in a single-mode fiber is described by Rytov's non-rotation equation. With arbitrary chosen real unit vector, the complete description of polarization change can be described in a single rotation angle obtained from the integral of rotation rate. Based on introduction of this reference frame, a device is suggested as rigid body's rotation sensor due to polarization change in a twisted fiber.
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Date Issued: 2006
Identifier: CFE0001198, ucf:46861
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0001198

Title: SELF-ASSEMBLY OF SQUARAINE DYES.
Creator: Qaddoura, Maher, Belfield, Kevin, University of Central Florida
Abstract / Description: Squaraine dyes have been a subject of extensive investigations lately due to their wide applications in important technological fields such as bioimaging probes, bioconjucation, second generation photosensitizers for photodynamic therapy, second harmonic generating organic dyes, two-photon absorbing materials with large cross section values, and, finally, photoconducting materials in photovoltaic cells. While a large number of patents and papers has been produced regarding their applications...
Show moreSquaraine dyes have been a subject of extensive investigations lately due to their wide applications in important technological fields such as bioimaging probes, bioconjucation, second generation photosensitizers for photodynamic therapy, second harmonic generating organic dyes, two-photon absorbing materials with large cross section values, and, finally, photoconducting materials in photovoltaic cells. While a large number of patents and papers has been produced regarding their applications limited work has been done concerning their thermotropic behavior, including their liquid crystalline properties, or correlation of the crystalline structure to both the solid state aggregation and their photophysical properties. In the first chapter of this dissertation, a series of squaraine dyes, based on 2, 4-bis squaraine including ethyl, propyl, butyl, pentyl, hexyl, and heptyl derivatives, were synthesized by condensation of the corresponding 4-(N,N-di-n-alkylamino)-2-hydroxyphenol with squaric acid. The thermal behavior of the series was recorded using both thermogravemetic analysis (TGA) and differential scanning calorimetry (DSC) while their crystalline structures were elucidated via single crystal X-ray diffraction. The length of the alkyl chain proved to have a significant effect on both the thermotropic behavior and the crystalline structure of the squaraine series. Two derivatives, butyl and heptyl, revealed the presence of liquid crystalline mesophases, smectic and nematic, respectively, that were confirmed and characterized via polarized light microscopy (PLM) and X-ray diffraction. In the second chapter, J- and H- aggregates were investigated in thin films by UV-vis spectroscopy; several of the derivatives formed H- and/or J-aggregates upon thin film formation via spin coating before and after thermal annealing, as indicated by UV-vis spectroscopy. The molecular structure, crystal structure, aggregation, and thermal behavior provide insight into the supramolecular assembly of this important class of materials. Photophysical measurements revealed large molar absorptivity, reasonably high fluorescence quantum yields, and significant fluorescence anisotropy, making these derivatives suitable candidates for a number of electro-optic and photonics applications. The third chapter was devoted to investigate liquid crystal-directed supramolecular assembly of a squaraine dye. Thus, The squaraine (SQ) dye, 2, 4-bis squaraine was used to prepare a series of SQ dye/cholesteryl pelargonate mixtures with varying dye concentrations (1%, 3%, 7.5%, 10.8%, 15%, and 20% w/w). Their phase transitions were investigated using differential scanning calorimetry, polarized light microscopy and X-ray diffraction. The squaraine dye itself exhibits no liquid crystalline behavior. The concentration of the dye in the cholesteric compound proved to have a significant effect on the dye aggregation behavior and phase transitions in cholesteryl pelargonate manifested by the appearance of new mesophases and formation of J- and H- aggregates. The texture morphology, X-ray diffraction analyses, and UV-vis absorbance spectra provide compelling evidence of the viability of the self-assembly of squaraines in the liquid crystalline mesophase. In the last chapter we will discuss possible modifications that can improve the aggregation systems.
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Date Issued: 2011
Identifier: CFE0003717, ucf:48773
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0003717

Title: High Performance Liquid Crystals for Displays and Spatial Light Modulators.
Creator: Peng, Fenglin, Wu, Shintson, Moharam, Jim, Zeldovich, Boris, Fang, Jiyu, University of Central Florida
Abstract / Description: Liquid crystals (LCs) are an amazing class of soft materials which have been widely used in the visible, infrared (IR), millimeter wave, and terahertz spectral regions. Both amplitude modulation (e.g. displays) and phase modulation (e.g. spatial light modulators (SLMs) for adaptive optics and adaptive lens) have been investigated extensively. Thin-film-transistor liquid crystal displays (TFT-LCDs) have become ubiquitous in our daily lives. Its widespread applications span from TVs, monitors,...
Show moreLiquid crystals (LCs) are an amazing class of soft materials which have been widely used in the visible, infrared (IR), millimeter wave, and terahertz spectral regions. Both amplitude modulation (e.g. displays) and phase modulation (e.g. spatial light modulators (SLMs) for adaptive optics and adaptive lens) have been investigated extensively. Thin-film-transistor liquid crystal displays (TFT-LCDs) have become ubiquitous in our daily lives. Its widespread applications span from TVs, monitors, tablets, smartphones, augmented reality, virtual reality, to vehicle displays. LCD shows advantages in 1) high resolution, 2) long lifetime, 3) vivid colors using quantum dots backlight, and 4) high dynamic contrast ratio employing local dimming technology. However, LCD exhibits a serious problem, which is slow response time. Therefore, it is commonly perceived that LCD exhibits a more severe image blur than organic light emitting diode (OLED) displays. Indeed, the response time of LCD is ~100x slower than that of OLED. To evaluate image blurs, Motion Picture Response Time (MPRT) has been proposed to quantify the visual performance of a moving object. MPRT is jointly governed by three factors: the sample and hold effect of an active matrix display, motion pursuing, and human vision system. It is a complicated problem and is difficult to obtain analytical solution. In this thesis, we analyze the sample-and-hold effects and derive a simple equation to correlate MPRT with LC response time, TFT frame rate, and duty ratio. From our analytical equation, we find that as long as an LCD's response time is less than 2 ms, its MPRT would be comparable to that of OLED at the same frame rate, even if the OLED's response time is assumed to be zero. To further reduce MPRT, we could boost the frame rate to 144 Hz or reduce the duty ratio through backlight modulation. This discovery sheds new physical insights for LCDs to achieve CRT-like displays with negligible image blurs. In addition to displays, LCs are widely employed in SLMs for modulating the phase and polarization of an incident light. This is because LCs possess high birefringence and relatively low absorption from the visible, IR, to terahertz regions. The useful applications include adaptive lens, adaptive optics, fiber-optic communication, antenna, and phase shifter. Fast response time is a common requirement for the abovementioned photonic devices. To achieve fast response time while maintaining 2-pi phase change, polymer-stabilized blue phase liquid crystal (BPLC) and polymer-network liquid crystal (PNLC) are promising candidates for the visible and IR SLMs, respectively. However, the operation voltage of present BPLC and PNLC devices is too high. To reduce operation voltage while keeping fast response time, we developed a new device configuration for BPLC SLM to work in the visible region. The new device structure allows the incident laser beam to traverse the BPLC layer four times before exiting the reflective SLM. As a result, the 2-pi phase change voltage is reduced to below 24V, which is the maximum attainable voltage for a high resolution liquid-crystal-on-silicon device. On the other hand, PNLC is a better candidate for the IR SLM because several high birefringence LC materials can be used. To reduce the operation voltage of a PNLC, we have investigated following three approaches: 1) developing large dielectric anisotropy and high birefringence (?n) LC materials, 2) optimizing polymer concentration, and 3) optimizing UV curing conditions. In the visible and near IR regions, most LCs are highly transparent. However, to extend the electro-optic application of LCs into MWIR and LWIR, absorption loss becomes a critical issue. In the MWIR region, several fundamental molecular vibration bands and overtones exist, which contribute to high absorption loss. The absorbed light turns to heat and then alters the birefringence locally, which in turns causes spatially non-uniform phase modulation. To suppress the optical loss, we have taken following approaches: (1) Designing high birefringence to minimize the LC layer thickness; (2) Shifting the absorption bands outside the spectral region of interest by deuteration, fluorination, or chlorination; (3) Reducing the overtone absorption by using a short alkyl chain. As a result, we have developed several low loss and high birefringence chlorinated LCs for the first time. To achieve fast response time, we demonstrated a PNLC with 2-pi phase change at MWIR and response time less than 5 ms. Molecular tailoring strategies for extending liquid crystal SLM into long-wavelength infrared (LWIR) are also explored.
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Date Issued: 2017
Identifier: CFE0006636, ucf:51230
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006636

Title: High Efficiency and Wide Color Gamut Liquid Crystal Displays.
Creator: Luo, Zhenyue, Wu, Shintson, Kik, Pieter, Schoenfeld, Winston, Fang, Jiyu, University of Central Florida
Abstract / Description: 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...
Show moreLiquid 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's 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's color is generated partially from time domain and partially from spatial domain. As a result, this LCD mode offers 1.5(&)#215; increment in spatial resolution, 2(&)#215; 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%), 2.4(&)#215; 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 ((>)90%), low absorption loss (~3.3%), high extinction ratio ((>)10,000:1) and large angular tolerance (up to (&)#177;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 ?20oC. This fast response LC material enables the field-sequential-color (FSC) driving for power saving. It also leads to several attractive advantages: sub-millisecond 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.
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Date Issued: 2015
Identifier: CFE0006225, ucf:51078
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0006225

Title: Optical Fluid-based Photonic and Display Devices.
Creator: Xu, Su, Wu, Shintson, Li, Guifang, Moharam, M., Wu, Xinzhang, University of Central Florida
Abstract / Description: Conventional solid-state photonic devices exhibit an ultra-high optical performance and durability, but minimal adaptability. Recently, optical fluid-based photonic and display devices are emerging. By dynamically manipulating the optical interface formed by liquids, the optical output can be reconfigured or adaptively tuned in real time. Such devices exhibit some unique characteristics that are not achievable in conventional solid-state photonic devices. Therefore, they open a gateway for...
Show moreConventional solid-state photonic devices exhibit an ultra-high optical performance and durability, but minimal adaptability. Recently, optical fluid-based photonic and display devices are emerging. By dynamically manipulating the optical interface formed by liquids, the optical output can be reconfigured or adaptively tuned in real time. Such devices exhibit some unique characteristics that are not achievable in conventional solid-state photonic devices. Therefore, they open a gateway for new applications, such as image and signal processing, optical communication, sensing, and lab-on-a-chip, etc. Different operation principles of optical fluid-based photonic devices have been proposed, for instance fluidic pressure, electrochemistry, thermal effect, environmentally adaptive hydrogel, electro-wetting and dielectrophoresis. In this dissertation, several novel optical fluid-based photonic and display devices are demonstrated. Their working principles are described and electro-optic properties investigated.The first part involves photonic devices based on fluidic pressure. Here, we present a membrane-encapsulated liquid lens actuated by a photo-activated polymer. This approach paves a way to achieve non-mechanical driving and easy integration with other photonic devices. Next, we develop a mechanical-wetting lens for visible and short-wavelength infrared applications. Such a device concept can be extended to longer wavelength if proper liquids are employed.In the second part, we reveal some new photonic and display devices based on dielectrophoretic effects. We conceive a dielectric liquid microlens with well-shaped electrode for fixing the droplet position and lowering the operating voltage. To widen the dynamic range, we demonstrate an approach to enable focus tuning from negative to positive or vice versa in a single dielectric lens without any moving part. The possibility of fabricating microlens arrays with different aperture and density using a simple method is also proposed. Furthermore, the fundamental electro-optic characteristics of dielectric liquid droplets are studied from the aspects of operating voltage, frequency and droplet size. In addition to dielectric liquid lenses, we also demonstrate some new optical switches based on dielectrophoretic effect, e.g., optical switch based on voltage-stretchable liquid crystal droplet, variable aperture or position-shifting droplet. These devices work well in the visible and near infrared spectral ranges. We also extend this approach to display and show a polarizer-free and color filter-free display. Simple fabrication, low power consumption, polarization independence, relatively low operating voltage as well as reasonably fast switching time are their key features.
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Date Issued: 2012
Identifier: CFE0004620, ucf:49943
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0004620

Title: Low Absorption Liquid Crystal Materials for Midwave Infrared.
Creator: Creekmore, Amy, Wu, Shintson, Moharam, Jim, Likamwa, Patrick, University of Central Florida
Abstract / Description: Liquid crystal is an amazing class of soft matters with applications spanning from visible, infrared, millimeter wave, to terahertz. In addition to direct-view displays and projection displays, liquid crystal is also widely used in adaptive optics, tunable-focus lens, and laser beam steering. Although the visible region has well developed materials and mixtures for the vast variety of applications, the midwave infrared (MWIR) region of the electromagnetic spectrum invites much development as...
Show moreLiquid crystal is an amazing class of soft matters with applications spanning from visible, infrared, millimeter wave, to terahertz. In addition to direct-view displays and projection displays, liquid crystal is also widely used in adaptive optics, tunable-focus lens, and laser beam steering. Although the visible region has well developed materials and mixtures for the vast variety of applications, the midwave infrared (MWIR) region of the electromagnetic spectrum invites much development as only a few materials have been developed with these applications in mind. Unlike visible region, the major challenge for mid-wave infrared liquid crystal is inherently large absorption loss. To reduce absorption, some molecular engineering approaches have been considered, such as deuteration, fluorination, and chlorination. The fluorine and chlorine not only act as the polar group to provide dipole moment but also helps shift some vibration absorption bands outside the MWIR window. Long phenyl ring compounds, fluorinated tolane materials, and chlorinated terphenyl mixtures are explored; as well as a look as the potential bromine might introduce for future development. In this thesis, we first review the current materials and their performance in the mid-wave infrared region, explain the need for higher performing liquid crystals, and then discuss the methodology of compound development and mixture formulation. Some new chlorinated liquid crystal compounds are synthesized, mixture formulated, and their properties evaluated. Finally, we will explain the future work which needs to be performed in this field.
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Date Issued: 2014
Identifier: CFE0005594, ucf:50243
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005594

Title: Liquid Crystal-Based Biosensors for the Detection of Bile Acids.
Creator: He, Sihui, Wu, Shintson, Kuebler, Stephen, Kik, Pieter, Fang, Jiyu, University of Central Florida
Abstract / Description: Bile acids are physiologically important metabolites, which are synthesized in liver as the end products of cholesterol metabolism and then secreted into intestine. They are amphiphilic molecules which play a critical role in the digestion and absorption of fats and fat-soluble vitamins through emulsification. The concentration of bile acids is an indicator for liver function. Individual suffering from liver diseases has a sharp increase in bile acid concentrations. Hence, the concentration...
Show moreBile acids are physiologically important metabolites, which are synthesized in liver as the end products of cholesterol metabolism and then secreted into intestine. They are amphiphilic molecules which play a critical role in the digestion and absorption of fats and fat-soluble vitamins through emulsification. The concentration of bile acids is an indicator for liver function. Individual suffering from liver diseases has a sharp increase in bile acid concentrations. Hence, the concentration level of bile acids has long been used as a biomarker for the early diagnosis of intestinal and liver diseases.Conventional methods of bile acid detection such as chromatography-mass spectrometry and enzymatic reactions are complex and expensive. It is highly desired to have a simple, fast, and low-cost detection of bile acids that is available for self-testing or point-of-care testing. To achieve this goal, we develop a liquid crystal-based biosensor for the detection of bile acids. The sensor platform is based on the anchoring transition of liquid crystals (LCs) at the sodium dodecyl sulfate (SDS)-laden LC/aqueous interface for the detection of bile acids in aqueous solution. The first part of this dissertation focuses on the detection mechanism of bile acids. Our studies show that the displacement of SDS from the LC/aqueous interface by the competitive adsorption of bile acids induces a homeotropic-to-planar anchoring transition of the LC at the interface, providing an optical signature for the simple and rapid detection of bile acids. The adsorption of bile acids on the interface was found to follow Langmuir-Freundlich isotherm. The adsorption kinetics of different bile acids is compared. We find that both the number and position of hydroxyl groups of bile acids affect their adsorption kinetics. The different optical patterns of LC films formed by the adsorption of bile acids are also discussed. The second part of this dissertation studies the effect of solution conditions, surfactants, and liquid crystals on the detection limit of the LC-based biosensor for bile acids. Low pH and high ionic strength in the aqueous solution can reduce the electrostatic interaction between SDS and bile acids, which leads to a decreased detection limit. Surfactants with smaller headgroup and lower packing density also help to reduce the detection limit. To further reduce the detection limit, we investigate the effect of LC structures and find that LCs with a shorter chain length give lower detection limits. Also, by substituting a phenyl ring with a cyclohexane ring, we find that the detection limit is further reduced due to the decrease of the interaction between the phenyl rings of LCs. By mixing different LCs together, the detection limit can be linearly tuned from 160 (&)#181;M to 1.5 (&)#181;M, which is comparable to the traditional methods. But the LC-based biosensors have much simpler design and manufacture process.The third part of this dissertation is to apply this LC-based biosensor to the detection of urinary bile acids. We test the influence of several potential interfering species such as urea, creatinine, uric acid and ascorbic acid by conducting experiments in synthetic urine. By adjusting the concentration of SDS, we are able to eliminate the impact of those interfering species, and demonstrate that the LC-based biosensors can selectively detect urinary bile acids in human urine, suggesting its potential for screening liver dysfunctions. The final part of this dissertation is to investigate the application of LC-based biosensors in detecting the lipolysis process by porcine pancreatic lipase (PPL). It has been a long-standing argument over the role of bile salts on the activity of PPL. Thus, we study the time course of the hydrolysis of phospholipid L-dipalmitoylphosphatidylcholine (L-DPPC) by PPL at LC/aqueous interface. The hydrolysis of L-DPPC leads to a homeotropic-to-tilted anchoring transition of the LC at the interface, which allows the hydrolysis process to be monitored by a polarizing optical microscope. The microscopy image analysis reveals a lag-burst kinetics where a lag phase is followed by a burst phase. The effect of bile acids on these two phases is studied. We find that the activity of PPL both in the presence and absence of colipase can be improved by increasing the concentration of bile acids. The improvement becomes more distinct in the presence of colipase.
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Date Issued: 2015
Identifier: CFE0005804, ucf:50028
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005804

Title: Optically isotropic liquid crystals for display and photonic applications.
Creator: Yan, Jin, Wu, Shintson, Zeldovich, Boris, Schoenfeld, Winston, Fang, Jiyu, University of Central Florida
Abstract / Description: For the past few decades, tremendous progress has been made on liquid crystal display (LCD) technologies in terms of stability, resolution, contrast ratio, and viewing angle. The remaining challenge is response time. The state-of-the-art response time of a nematic liquid crystal is a few milliseconds. Faster response time is desirable in order to reduce motion blur and to realize color sequential display using RGB LEDs, which triples the optical efficiency and resolution density. Polymer...
Show moreFor the past few decades, tremendous progress has been made on liquid crystal display (LCD) technologies in terms of stability, resolution, contrast ratio, and viewing angle. The remaining challenge is response time. The state-of-the-art response time of a nematic liquid crystal is a few milliseconds. Faster response time is desirable in order to reduce motion blur and to realize color sequential display using RGB LEDs, which triples the optical efficiency and resolution density. Polymer-stabilized blue phase liquid crystal (PS-BPLC) is a strong candidate for achieving fast response time because its self-assembled cubic structure greatly reduces the coherence length. The response time is typically in the submillisecond range and can even reach microsecond under optimized conditions. Moreover, it exhibit several attractive features, such as no need for surface alignment layer, intrinsic wide viewing angle, and cell gap insensitivity if an in-plane-switching (IPS) cell is employed. In this dissertation, recent progresses in polymer-stabilized blue phases, or more generally optically-isotropic liquid crystals, are presented. Potential applications in display and photonic devices are also demonstrated.In Chapter 1, a brief introduction of optically isotropic liquid crystals is given. In Chapter 2, we investigate each component of polymer-stabilized blue phase materials and provide guidelines for material preparation and optimization. In Chapter 3, the electro-optical properties of PS-BPLCs, including electric-field-induced birefringence and dynamic behaviors are characterized. Theoretical models are proposed to explain the physical phenomena. Good agreements between experimental data and models are obtained. The proposed models also provide useful guidelines for both material and device optimizations. Four display and photonic devices using PS-BPLCs are demonstrated in Chapter 4. First, by red-shifting the Bragg reflection and using circular polarizers, we reduce the LCD driving voltage by 35% as compared to a short-pitch BPLC while maintaining high contrast ratio and submillisecond response time. Second, a turning film which is critically needed for widening the viewing angle of a vertical field switching (VFS) BPLC mode is designed. With this film, the viewing angle of VFS is widened to (&)#177; 80(&)deg; in horizontal direction and (&)#177; 50(&)deg; in vertical direction. Without this turning film, the viewing angle is only (&)#177;30(&)deg;, which is too narrow for most applications. Third, a reflective BPLC display with vivid colors, submillisecond response time, and natural grayscales is demonstrated for the first time. The proposed BPLC reflective display opens a new gateway for 3D reflective displays; it could make significant impact to display industry. Finally, we demonstrate a tunable phase grating with a high diffraction efficiency of 40% and submillisecond response time. This tunable grating exhibits great potential for photonic and display applications, such as optical interconnects, beam steering, and projection displays.
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Date Issued: 2013
Identifier: CFE0005279, ucf:50551
Format: Document (PDF)
PURL: http://purl.flvc.org/ucf/fd/CFE0005279

Liquid crystal (7)	+ -
liquid crystal (7)	+ -
liquid crystal display (5)	+ -
liquid crystals (5)	+ -
Liquid Crystal (3)	+ -

Liquid crystals (3)	+ -
blue phase (3)	+ -
display (3)	+ -
fast response (3)	+ -
optics (3)	+ -
self-assembly (3)	+ -
blue phase liquid crystal (2)	+ -
contrast ratio (2)	+ -
liquid crystal displays (2)	+ -
low voltage (2)	+ -
response time (2)	+ -
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Adaptive Optics (1)	+ -
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Augmented reality (1)	+ -
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University of Central Florida (41)	+ -
Wu, Shintson (20)	+ -
Wu, Shin-Tson (14)	+ -
Fang, Jiyu (12)	+ -
Likamwa, Patrick (9)	+ -

Moharam, Jim (7)	+ -
Zeldovich, Boris (7)	+ -
Schoenfeld, Winston (5)	+ -
Wu, Xinzhang (5)	+ -
Dong, Yajie (3)	+ -
Kik, Pieter (3)	+ -
Amezcua Correa, Rodrigo (1)	+ -
An, Linan (1)	+ -
Belfield, Kevin (1)	+ -
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Chen, Kuan-Ming (1)	+ -
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Cheng, Hui-Chuan (1)	+ -
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Cho, Hyoung Jin (1)	+ -
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Deng, Jinan (1)	+ -
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Du, Fang (1)	+ -
Fan, Yun-Hsing (1)	+ -
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