Che Ju Hsu

Using photopolymerization to achieve tunable liquid crystal lenses with coaxial bifocals

Liquid crystal (LC) lenses with circular hole-patterned electrodes possess the excellent capabilities of tunable focal lengths. In this paper, we demonstrate the performance of a specific LC lens with tunable coaxial bifocals (CB) synthesized via photopolymerization of LC cells. The characteristics of tunable CB are clearly exhibited when the voltage applied is continuously increased, eventually disappearing until only one focus is left when significantly higher voltages are applied. We simultaneously demonstrate two types of tunable CB LC lenses fabricated via different photocurable processes and determine their optical functions.

Preventing occurrence of disclination lines in liquid crystal lenses with a large aperture by means of polymer stabilization

Liquid crystal (LC) lenses with a circularly hole-patterned electrode possess excellent characteristics in optical performance, especially for the capability of tunable focal lengths. But, non-uniformly symmetrical electric fields in LC lenses usually induce disclination lines when operating. In general, the occurrence of disclination lines not only degrades their optical capability such as imaging performance, but also spends more time for tuning focal lengths. In this paper, we use a way of polymer stabilization to successfully prevent the disclination lines in LC lenses. Even arbitrarily adjusting the applied voltages in LC lenses, it seems no occurrence of disclination lines again. In addition, we compare the basic optical performance for LC lenses with or without polymer stabilization. From experimental results, it shows that they almost have the same optical performance.

Holographic polymer networks formed in liquid crystal phase modulators via a He-Ne laser to achieve ultra-fast optical response

The holographic polymer network formed in liquid crystal (LC) phase modulators via a He-Ne laser in this study demonstrates ultra-fast optically response and low light scattering. These advantages are mainly caused by the small LC domains and uniform polymer network when processing LC cells via holographic exposure to a He-Ne laser. The use of this method to fabricate LC cells as phase modulators results in a decay time of 49 μs under 2π phase modulation at room temperature. The predicted fast optical response can be achieved when operating devices at high temperatures.

Fast response time in liquid crystal cells doped with low concentrations of reactive mesogen via photopolymerization at low temperature

Liquid crystal (LC) cells with photopolymers usually exhibit a fast response time but inevitably present decreased optical transmittance and lower contrast ratio due to incomplete dark states. In this study, we show that this issue can be improved when photopolymerization at low temperature is considered. Comparing performance with the 4 wt% RM257-doped fringe-field switching (FFS) LC cell photopolymerized at room temperature, the 1.4 wt% RM257-doped FFS LC cell photopolymerized at low temperature (273 K) shows better contrast ratio and lower operating voltage. In addition, the electrostriction effect can be also reduced in LC cells with lower RM257-doped concentration. As a result, the 1.4 wt% RM257-doped FFS cell shows a response time as fast as that in the 4 wt% RM257-doped FFS cell. Meanwhile, the average response time for gray-to-gray switching of the optimal FFS cell is 4.9 ms.

Experimental Analysis to Avoid Migrating Zigzag Lines Occurring in Homogeneously Aligned Liquid Crystal Lenses with a Hole-Patterned Electrode

For our beginning study in large apertures of liquid crystal (LC) lenses, both disclination line and zigzag line are usually occurred in cells. Disclination lines possibly appear and then disappear if we slowly increase applied voltages and/or fabricate LC lens with thicker upper glass substrates. But, zigzag lines always appear near the edges of LC lens. Unfortunately, zigzag lines and disclination lines will possibly link each other, and permanently stay in cells to degrade performance of LC lens. In this paper, we experimentally study and conclude that the suitable rubbing conditions in cells will effectively prevent this problem of linked lines.

Dual-View Blue Phase Liquid Crystal Display

In this paper, we propose a dual-view (DV) liquid crystal display (LCD) using blue phase (BP) liquid crystal (LC) in conjunction with the patterned electrode cell. Given the optically isotropic state of the BP LC material, the DV BP LCD is equipped with a low dark state and, therefore, a high contrast ratio that exceeds 1000 in the intended viewing direction. The patterned electrode structure provides inclined electric field parallel to the unintended viewing direction and creates approximately zero phase retardation, thus suppressing light leakage in the unintended viewing direction.

The effects of silica nanoparticles on blue-phase liquid crystals

ABSTRACT We investigate the effects of hydrophobic silica nanoparticles (SNs) on blue-phase liquid crystals (BPLCs). The optical microscope and reflection spectra observation reveal that a tiny hydrophobic SN dopant stabilises the BPLC phase, and widens the temperature range of the BP I phase. Furthermore, the doped dilute SNs can fine-tune their positions to relax the formation stress of the BPLC lattices, and slightly increase the platelet sizes of the BPLCs. The doped SNs also decrease the driving voltage and response time of the BPLC cell, because the added SNs decrease the elastic constant of the LC host and the relaxation time constant of the BPLC mixture. Graphical Abstract

Self-assembled polymer gravel array in prepolymer-doped nematic liquid crystals

We demonstrate a new method to fabricate a large-area polymer gravel array. The formation of the polymer gravel array on the substrates of the liquid crystal (LC) cell during polymerization is attributed to the surface tension interaction among the LC, prepolymer, and substrate surface. The gravel can be oriented along the rubbing direction of the substrate. Moreover, the diameter and pitch of the oriented gravel array can be controlled by means of UV curing intensity and supplied voltage under curing because of the competition between the dipole and quadrupole interactions of the colloidal prepolymer droplets. The estimated anchoring energy given by the oriented polymer gravel array can align LCs. The possible application of the formed periodical gravel array on optical devices is explained in this paper.

Adjustable Bistability and Hysteresis Loop in a Nd:GdVO4 Laser with an Intracavity Liquid Crystal Cell

Adjustable optical bistability and spatial hysteresis appearing in a Nd:GdVO4 laser with an intracavity liquid crystal (LC) cell were achieved. On the basis of optically induced LC reorientations and the varying magnitude of the order parameter, two types of LC were used to easily control the characteristics of hysteresis with a single control variable. Using an electrically driven twisted-nematic LC, an adjustable hysteresis area as well as a switching-on pump power was demonstrated and periodic spatiotemporal patterns were observed. By contrast, amplified hysteresis loops were obtained by increasing the rotation angle of homogeneous LC cells with a nearly invariable switching-on pump power.