LC Technology

Session 7B: LC Technology
Wednesday, Feb. 15, 2017  10:40-12:05
Chair: Ko-Ting Cheng, National Central University, Taiwan
Room: Lecture Hall II
11:05 - 11:20 Paper No.  2017-WED-S0307-O001
Seong Ho Ryu
1D Nanoconfined liquid crystal as an active medium for photonic crystal

The porous anodic aluminum oxide (AAO) was used as a nano-confined geometry where the molecules orientation was successfully controlled by treating inner surface of the AAO with self-assembled monolayers. We systemically investigated the molecular orientation in the AAOs with varied pore diameter and surface anchoring condition by using grazing incidence X-ray diffraction technique. The porous structure of the AAO can be engineered by pulse anodization with alternating constant current, which produces a modulated AAO that selectively reflects a particular wavelength called a photonic crystal (PC). A spectral range of the reflection, photonic bandgap (PBG), is determined by effective refractive index consisted of air and Al2O3 (corresponding to pore wall) and can be shifted by filling other functional materials. We demonstrated the switchable 1D AAO PC using nematic LC doped with an azo LC material. In the N phase, the LC molecules are aligned parallel to the inner surface of the AAO owing to nanoconfinement, which make the LC medium induces ordinary refractive index. Phase transition from N to isotropic phases can be induced by irradiating UV light that triggers photoisomerization of the azo compound. The refractive index is changed from no to isotropic refractive index, which shifts the PBG.

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11:20 - 11:35 Paper No.  2017-WED-S0307-O002
Jae-Won Huh
Dye-doped Cholesteric Liquid Crystal Cell for a Bistable Light Shutter

Recently, see-through displays using organic light emitting diodes (OLEDs) have been considered as one of the next generation displays [1]. However, a see-through display shows poor image quality because each pixel includes transparent window area. Objects behind a display panel are always overlapped with displayed images. Moreover, a see-through OLED display cannot provide black color. This inevitable problem can be solved by placing a light shutter at the backside of a see-through display. In this work, we demonstrate a bistable light shutter using dye-doped ChLCs. For dye-doped ChLCs, we used positive liquid crystal (p-LC) and dual-frequency liquid crystal (DFLC). To realize a bistable light shutter using p-LC, we employed patterned electrodes on both the top and bottom substrates. To improve the electro-optic characteristics in the focal-conic (opaque) state, we used a crossed electrode structure where the top and bottom interdigitated electrodes are crossed to each other. However, a bistable light shutter using p-LC requires complicated electrode structure for switching. To avoid the complicated electrode structure, we can use DFLC. These light shutters can provide black color and hide the objects behind a display panel completely in focal-conic state.

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11:35 - 11:50 Paper No.  2017-WED-S0307-O003
Mao-Chou Tai
Multi-directional Bendable Chiral Nematic Liquid Crystal Polymer Based on Photo Responsive Azobenzene Mesogenic

Stimuli Polymetric liquid crystals hasn’t shown great potential in leagues of neither biomedical, mechanics, nor photonic applications during the past decades. This work is in the lead to demonstrate a multi-directional bending circularly polarizing reflector based on photo-mechanical and meanwhile reacts as a filter by the nature properties of cholesteric liquid crystal polymers. With the help of azobenzene mesogenics of CLCPs, the reflector would be able to select bending angles from 15° to 58° after trans-cis isomerization. Since CLC has the characteristics of reflecting single handedness circularly polarizing light which the photonic band gap is angle-dependent. Therefore, the reflected wavelength could be shifted between 570nm to 670nm with a ~60nm bandwidth. The transitions between trans and cis states could be achieved in ~6s and ~30s. The times are proportional to the intensity of pump lasers. The tunable angle for beam steering is ~54° as the transmittance is below 8% under He-Ne laser. Furthermore, the tunable range is believed to be enhanced by the bandwidth and different wavelength of probe beam after theoretical analyzing. Additionally, the tunable range is independent with the initial angle, proving it flexibility for practical use.

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11:50 - 12:05 Paper No.  2017-WED-S0307-O004
Jia-Heng Dai
Circular-polarization selective gratings based on refilled cholesteric liquid crystal template

In this work, we fabricated optical gratings based on planar CLCs, instead of fingerprint CLCs conventionally. The gratings presented in this work are fabricated on the basis of the CLC template (washing out/refilling) technique. By refilling left- or right-handed CLCs into a right handed CLCs template grating, the refilled CLC template grating can diffract light with specific wavelength in reflection mode. In addition, the refilled CLC template grating shows different diffraction efficiencies for left- and right-handed circularly polarizations (L- and RCP), as shown in Fig. 1. This beam steering element has the features of circularly polarization selectivity and dual operation modes. Therefore, this CLC-based device can be potentially used for applied diffraction elements in optics.

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