Yao Lishuang

Improvement of Response Performance of Liquid Crystal Optical Devices by using a Low Viscosity Component

Difluorooxymethylene-bridged (CF2O) liquid crystal (LC) with low viscosity is prepared and used as a fast response LC material. When the material is mixed with isothiocyanato LCs with high birefringence, the viscoelastic coefficient of the mixture decreases evidently and, accordingly, the response performance increases. While the concentration of CF2O LCs is about 7%, the LC mixture approximately maintains high birefringence and exhibits a fastest response performance that is 14% higher than that of pure isothiocyanato LCs. Therefore, the LC material and mixing method could find useful applications in optical devices.

Fabrication of a Mono-Domain Alignment Ferroelectric Liquid Crystal Device Using a Polar Self-Assembled Monolayer

A mono-domain ferroelectric liquid crystal device (FLCD) is fabricated using a novel method. The cell used in this method is an asymmetric cell, typically the combination of a polar self-assembled monolayer (SAM) for one substrate and a rubbed polyimide for the other substrate. A defect-free alignment of ferroelectric liquid crystal is fabricated without applying a dc voltage to remove degeneracy in the layer structure. The contact angles of self-assembled monolayer and PI-2942 are measured and the polarity of SAM is higher than the PI alignment. It is found that the polarity of self-assembled monolayer is a key factor in the formation of mono-domain alignment of FLC.

The review of liquid crystal wavefront corrector with fast response property

Liquid crystal wavefront corrector (LCWFC) is an optical device that can modulate wavefront of incident light, and shows advantages of high density pixels, high reliability, and high precision accuracy, and can be used in the field of optical beam shaping, optical information processing and beam transforming. All these application model show broad application prospect of LCWFC. When LCWFC is used in the optics systems, a fast response speed is always required, such as 1 ms. In optical application, specific modulation depth is always required. If the modulation depth is 1 λ , the response time of the commercial LCWFC is slow, such as, 10 ms, which block the application of LCWFC. The response speed of LCWFC always depends on two elements, the properties of LC material and the parameters of LC device. Firstly, fast response liquid crystal material with high birefringence and low viscosity was studied and reviewed in our research group. Secondly, the optimization of LC device parameters and driving method was reviewed. By the research in LC material and device, the response time of LCWFC can be fast to sub-millisecond, which will highly enhance the application region and depth of LCWFC.

Wide-Range Position-Tuning Lasers in Cholesteric Liquid Crystal

A wedge liquid crystal (LC) cell is designed and manufactured, and a dye-doping cholesteric LC laser formed by mutual diffusion of the cholesteric LC with different pitches. A laser that is tunable in the 558-624 nm range is obtained under moderate optical pumping, with a tuning range of 66 nm and a laser spectral tuning resolution of 1 nm, so as to achieve the spatial position of a wide range of tunable lasers. The laser threshold varies at different positions in the device, and the lasing thresholds of the dye-doping cholesteric LC cell at 40 and 9 mu m are 18 and 25 mu J/pulse, respectively. The density of the photonic states is simulated in the experimental sample, and the result is in good agreement with the photonic band gap in our experiment, which not only explains the low-threshold laser at the band gap edge, but also predicts the experiment.

Effect of molecular weight on liquid crystal photoalignment by photosensitive polyester containing thrifluoromethyl moieties

We investigate the liquid-crystal (LC) alignment direction on photoalignment films formed from photosensitive polyester containing thrifluoromethyl moieties (PPDA) with various molecular weights by crossed polarized optical microscopy. It is found that LC alignment behaviour changes with molecular weight of PPDA. The LC alignment on PPDA irradiated films with the highest molecular weight is homogeneous, while those with low and intermediate molecular weights are homeotropic. However, surface morphologies show weak dependence on molecular weight. The surfaces are smooth and there is no clear morphological anisotropy on these aligned films observed by an atomic force microscope. The surface energies of the irradiated films are also measured by using an indirect contact-angle method where both surface energy and its polar component increase with increasing molecular weight. Different polar surface energies can be considered as a main reason for different alignment characteristics.

Alignment behavior of liquid crystals on the crosslinked film of monomers with fluorinated groups

A series of photosensitive monomers, including hexafluorobiphenol A dicinnamate ester (6F-BADE) and fluorinated dicinnamate esters (FDE-n, n=2, 3, 4), were synthesized. These monomers could be crosslinked under irradiation of linearly polarized ultraviolet light. FTIR spectra and GPC spectra were used to measure the results in real time. The results indicated that the crosslinking reaction was [2+2] cycloaddition. The photoalignment films formed by monomers under the ultraviolet light could induce different types of liquid crystal (LC) alignments: 6F-BADE and FDE-n films resulted in vertical and parallel alignments, respectively. AFM images of the surfaces of the alignment showed no obvious anisotropy on the surfaces of these films. Finally, it was found that, using semiempirical method AM1 of quantum mechanics, the difference of the polarities among different monomer molecules was large, which was considered to be the main cause resulting in different LC alignments.