Photonic crystal is the periodic structure with different refractive index media. Its photonic-bandgap characteristics could be used to make the photonic crystal lasers. Because of the difficulty of fabrication, the development of three-dimensional photonic crystal is far behind the two-dimensional and one-dimensional photonic crystals. Blue phase liquid crystals are formed by periodic lattice structure with double-twisted cylinder, therefore it is a three-dimensional self-assembled photonic crystal. The objective in this study is to fabricate the three-dimensional photonic crystal blue phase liquid crystal laser by investigating the materials and the fabricating conditions. In this thesis, we doped the laser dye in the blue phase liquid crystal to make the laser device. Firstly, we studied blue phase temperature range and Bragg reflection wavelength under different material ratio. The blue phase lattice structures under different cool rate and surface treatment could be investigated by observing Kossel diagram . According to the experiment results, three-dimensional blue phase photonic crystal laser under room temperature could be achieved through appropriate material ratio, and its Bragg reflection wavelength is corresponds to the emission spectrum of the doped laser dye. By decreasing the cooling rate and the adapting homogeneous alignment of the substrates, the laser output will become more stable. As the result, we successfully fabricated the three-dimensional liquid crystal blue phase laser device at room temperature, and measured three-dimensional laser output. In addition, We study the relations between the laser emission direction and the alignment direction, and the temperature tuning characteristics of the laser wavelength. These results are very useful for the development of the three dimension tunable laser.

¡§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.

This study presents an optically switchable band gap of a 3D photonic crystal that is based on an azobenzene-doped liquid crystal blue phase. The trans-cis photoisomerization of azobenzene was induced by irradiation using 473nm light, and caused the deformation of the cubic unit cell of the blue phase and a shift in the photonic band gap. The fast back-isomerization of azobenzene was induced by irradiation with 532nm light. The crystalline structure was verified using a Kossel diffraction diagram. An optically addressable blue phase display, based on Bragg reflection from the photonic band gap, is also demonstrated. It can be written, erased, and rewritten repeatedly and exhibits a bright saturated color.

Blue-Phase liquid crystal display possesses potential to become next generation display technology because of its submillisecond response time, alignment-layer-free process and wide view angle. Intrinsically, BP only operates across a narrow temperature range due to the influence of intrinsic structural defects. Recently, the temperature range of BP has been successfully extended beyond 60K through the polymer-stabilized effect. Unfortunately, the structure of the polymer networks poses a number of problems, for instance, hysteresis effect, which degrades the accuracy of grayscale control, and residual birefringence, which decreases the contrast ratio of LCDs. This paper investigates the voltage-induced hysteresis and residual birefringence in the polymer-stabilized blue phase I and II, under various phase separation conditions and material ratio. Based on experiment result, the polymer network morphology, distribution and pure BP temperature can result in a variety of PSBP electro-optical properties. Hysteresis and residual transmittance free PSBP display could be achieved by choosing appropriated phase separation condition and material ratio. Key word¡Gblue phase¡Bmonomer¡Bhysteresis¡Bresidual transmittance

In previous studies, I learned the curing of the electro-optical effects in polymer stabilize blue phase liquid crystal under different temperature, such as the hysteresis effect, residual transmittance, drive voltage. So find out before curing blue phase temperature range is very important. Since previous studies have used methods is polarizing microscope and measuring reflectance spectra. In order to the blue phase be used in the display. If we use of Bragg reflectors in the visible blue phase liquid crystal. Resulting in the dark state is not good, the contrast reduction, so we must use the blue phase liquid crystal reflectance spectra in the non-visible light. But this liquid crystal cannot use the previously described methods to define the blue phase liquid crystal temperature range. In our experiment, we use different ways to recognized liquid crystal. We have used polarizing microscope, DSC, Kossel diagram and measuring reflectance spectra. We cannot see blue phase by polarizing microscope and Kossel diagram because the blue phase liquid crystal reflectance spectra in the non-visible light. The liquid crystal material absorbs the UV light. Our DSC resolution is not enough to found the blue phase temperature range. When we recognized liquid crystal, we found the light run through the liquid crystal box. In different phase have different lateral scattering intensity. When we cooling temperature can found the lateral scattering intensity is weak in isotropic. When we phase enter the blue phase II, the lateral scattering intensity rise slowly. When the blue phase II into the blue phase I, we can see first decreased and then increased curve. Last when into the cholesterol phase, the lateral scattering intensity rises quickly. We observe this property can discriminate the blue phase temperature range. When we found the blue phase temperature range, we analyze the hysteresis and drive voltage in different curing temperature. We found this material property. When we curing in high temperature. The drive voltage has decrease, but the hysteresis has increase. When curing in low temperature. The drive voltage has increase, but the hysteresis has decrease. Last we use SEM analyze the polymer structure. But we lost the slight polymer structure when we wash the liquid crystal. So we cannot analyze the slight polymer structure.

In this study, a liquid crystal Fresnel lens based on the cholesteric blue phase liquid crystals is proposed. Blue phases are liquid-crystalline phases that appear in a very small temperature range between a cholesteric phase and an isotropic phase. There are three types of blue phases; BP¢¹,BP¢º and BP¢». The BP¢¹ and BP¢º are characterized by a spatially periodic director field with lattice constants comparable to the wavelength of visible light. Because of the structural symmetry, blue phases are optically isotropic. In this study, the electro-optical properties of the BP¢º under different applied voltages are investigated. The results reveal that the Bragg reflection of the BPII has a red shift by increasing the applied voltage and a phase transition from BPII to cholesteric phase occurs at the high voltage regime (>100V). Based on the results, an electrically controlled blue phase Fresnel lens with polarization independence and high diffraction efficiency is demonstrated.

This study researches the nonlinear optical properties of the blue phase liquid crystals using the Z-scan technique. The purpose is to investigate the non-linear effect of the blue phase liquid crystals induced by the thermal and the liquid crystal reorientation effect. The Z-scan technique is common method to measure the non-linear index n2 and the non-linear absorption coefficient of materials. The measurement of the optical Kerr constant using Z-scan is based on the principle of spatial beam distortion due to the self-focusing or self-defocusing. For typical nematic liquid crystals, the nonlinear effect in the nematic phase is large than that in the isotropic phase. However, due to the anisotropic properties of the liquid crystal, the light-induced nonlinear effect in the nematic phase is polarization dependency. Unlike nematic phase, the blue phase is optical isotropic duo to its symmetric structure, and therefore blue phase are polarization independent and provide a larger non-linear effect. The experiments to measure the nonlinear refractive index n2 are as follows: firstly, a linearly polarized Ar+ laser light (£f=532nm) is focused in the z direction onto the sample via lens, and the detector was set behind the sample. Sequentially, the light intensity is recorded while the sample is scanned near the beam waist of the green laser. Finally, the non-linear index n2 of the material is derived from mathematical calculation. The study investigated two kinds of material, pure blue phase liquid crystal and dye-doped blue phase liquid crystal, and measured their non-linear index n2 in the blue phase and isotropic phase, respectively. The experimental results show that the non-linear index n2 of dye-doped blue phase liquid crystal is 100~1000 times as large as this of the pure blue phase liquid crystal at the blue phase. Besides, compared with isotropic phase in the blue phase liquid crystal, the blue phase actually possesses larger non-linear index n2. This experiment confirms that the nonlinear effect can be induced using linearly polarized Ar+ laser, and the nonlinear refractive index n2 can be measured using Z-scan technique.

In this study, we researched three kinds of surface treatment (no surface treatment, homogeneous alignment (HA) and vertical alignment (VA)) effect for the optoelectronic properties of cholesteric blue phase liquid crystals (BPLCs). We demonstrate the surface treatments have influence on the temperature range of BPLCs. The VA-BPLC possesses the widest temperature range, about 6.0 ¢J. The temperature range of both no surface treatment BPLC and HA-BPLC are about 5.5 ¢J. In the process of cooling, the surface treatments will restrain the change of the pitch of BPLC. Besides, surface treatment will let the crystalline of BPLC shipshape, so that it can reduce the scattering of the reflection light of BPLC. In the vertical electric field, the reflection wavelength of BPLC will be red-shift when the applied voltage increased. The reflection wavelength of the HA-BPLC can be tuned about 90 nm. The reflection wavelength of the VA-BPLC can be tuned about 120 nm. We have demonstrated the treatment of vertical alignment will reduce the operating voltage of BPLC.

In this study, we study three kinds of surface treatments in the blue phase lasers. Three kinds of surface treatments include no surface treatment, homogeneous alignment ,HA, and vertical alignment ,VA. Blue Phase liquid crystal is a three-dimensional photonic crystal, and it can be used to be a laser cavity. When the blue phase doped with a laser dye, a laser emission can be observed under appropriate pumping energy. In the first part, we fabricate the blue phase lasers with three kinds of surface, there are different surface treatments to study the surface effect of the optoelectronic properties. It is found that the threshold pumping power is significantly decreased under a surface treatment on glass substrate. In the second part, we change cooling rate in the formation of the blue phase liquid crystals, and study the optoelectronic properties of blue phase lasers. The experiment results reveal that the slower cooling rate leads to a order blue phase substrate, resulting in a lower threshold pumping energy of the blue phase laser.

In this study, we study polymer-dispersed blue-phase liquid-crystal (PDBPLC)films. The PDBPLC film is fabricated by using BPLC instead of nematic LC in a PDLC film. The experimental results show that the PDBPLC films and can be switchable as the conventional PDLC. The polymer morphology of the PDBPLC is affected by the concentration of monomer in the BPLC/monomer mixture. The PDBPLC exhibits a good contrast ratio with monomer concentration of 39.17 wt%. The rise time of PDBPLC films decreases as the polymer concentration increases. Moreover, the results also show that a complete phase separation occurs with the exposure time of 20 minutes. For the future work, we will improve the high driving voltage and low ratio of the PDBPLC film.