Eunje Jang

Electrooptic temperature sensor based on a Fabry-Pe/spl acute/rot resonator with a liquid crystal film

An electrooptic (EO) temperature sensor based on a Fabry-Pe/spl acute/rot (FP) resonator with a nematic liquid crystal (NLC) film is proposed. A novel compensation scheme of the EO effect allows for precise determination of temperature by monitoring the resonant wavelength of the NLC FP sensor. The proposed EO temperature sensor provides good stability, high resolution, self-calibration capability, and low driving voltage.

Multistage optical memory of a liquid crystal diffraction grating in a single beam rewriting scheme

The authors report on the multistage optical memory of a liquid crystal (LC) diffraction grating fabricated using a dye-dispersed LC/polymer composite medium. Under a single pump beam, the reorientation of dye molecules, confined within spatially periodic interpolymer networks produced by a patterned exposure of ultraviolet light, allows for a pure optic-axis modulation which gives high diffraction efficiency in a planar LC configuration. The resultant multistage optical memory of the LC grating is controlled solely by the polarization state of a single rewriting beam without the use of an erasing step prior to every rewriting process.

Solvent effect of the fibrillar morphology on the power conversion efficiency of a polymer photovoltaic cell in a diffusive heterojunction

We describe the solvent-dependent morphology of a conjugated polymer, poly(3-hexylthiophene) (P3HT) interfaced with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and the evolution of the resulting inter-connected fibrillar structure (ICFS) in a diffusive bilayer heterojunction (DBHJ). It is found that the fibrillar structure of the P3HT is preferentially developed in a poor solvent and less soluble than an amorphous structure and the ICFS improves the power conversion efficiency (ηp) significantly. Among four different solvents chlorobenzene, dichlorobenzene, chloroform and p-xylene studied, p-xylene results in ηp ≈ 3% whereas chlorobenzene yields only 0.5%. This indicates clearly that the formation of the ICFS plays a critical role to induce high exciton generation/dissociation to produce spatially uninterrupted pathways for the charge transport, and to enhance ηp of a polymer photovoltaic device in the DBHJ configuration. (Some figures may appear in colour only in the online journal)

Design and Fabrication of High-Performance Liquid Crystal Gratings

We present basic principles of designing and fabricating high-performance liquid crystal (LC) gratings with binary alignment structures which produce a variety of the diffraction properties. The periodic binary structure in the LC layer was fabricated through a selective irradiation of the UV light using the single-masking process. An alternating homeotropic and hybrid alignment configuration produces the input polarization-dependent diffraction suitable for the polarization-separating devices while an oppositely twisted binary alignment configuration gives the input polarization-insensitive diffraction. It is found that a dye-doped bidirectional alignment configuration can be used for obtaining optically controllable polarization properties.

Design of a Polarization-Insensitive Diffraction Grating Device Based on a Dye-Doped Liquid Crystal in Polymer Networks

ABSTRACT We demonstrate a polarization-insensitive grating device based on a liquid crystal (LC) doped with azo-dyes in polymer networks. The polarization-insensitive diffraction is obtained by periodically modulating the optic axis of a homogeneously aligned nematic LC layer. The polymer networks formed in the doped LC medium play a critical role in achieving the optic axis modulation of the LC by a single pump irradiation. The optically induced effect in the dye-doped LC system is permanent, polarization-insensitive, and electrically controllable.

Stability of Optical Reorientation of Nematic Liquid Crystals Doped with Azo-Dyes in Polymer Networks

We report on the stability of the optical reorientation of doped nematic liquid crystals(LCs)with azo-dyes in polymer networks. The photo-reactive polymer networks formed within the doped LC medium play a critical role in achieving the stable optical reorientation of the LC originating from the trans-cis transformation of the dye molecules. Moreover, the photo-reactive polymer layer on the substrate surface is required to produce the surface memory effect of the dye-doped LC. The optically induced memory is well retained in the dye-doped LC only in the presence of the polymer network medium.

Pretilt Control of a Nematic Liquid Crystal on Polymer Layers by Atmospheric Plasma Irradiation

We present the pretilt control of a nematic liquid crystal (LC) on polymer layers exposed to a plasma beam under atmospheric pressure. Depending on the exposure parameters of the atmospheric pressure plasma (APP) in a sheetlike shape, the vertical or the planar alignment with a variable pretilt can be produced on a homeotropic polyimide (PI) layer. The polar anchoring energy of the APP-exposed PI layer is of the order of 10-4 J/m2, comparable to the rubbed PI layer. Our approach to the plasma-assisted LC alignment under ambient pressure would be applicable for the in-line process of producing wideviewing LC displays with multidomains.

Electrically and Optically Controllable Liquid Crystal Grating with a Patterned Surface-Command Layer

We propose a liquid crystal (LC) binary grating that can be controlled both electrically and optically in a simple scheme. The optical control scheme is obtained through the surface-induced reorientation of the LC molecules on a patterned surface-command layer by a single pump irradiation. The electrical control of the diffraction efficiency is achieved through the change in the phase retardation by the application of a bias voltage for given optically induced LC director distribution. In a coupled scheme of the optical and electrical control, the diffraction efficiency can be easily optimized.

Photo-Triggering of the Membrane Gates in Photo-Responsive Polymer for Drug Release

The use of light stimulus for triggering drug is a promising method for accurate drug delivery. A new approach using azopolymer membrane and laser holography was investigated for developing light-triggering drug delivery system. Polymeric drug delivery system was prepared by covering azopolymer membrane on a drug agent. Holographic laser interference generated surface relief grating pattern on the azopolymer surface. The widths and depths of gates on the polymer membrane were easily modified by adjusting incident angle and irradiation time. Ar laser made the polymeric membrane permeable to the drug agent and release it in a solution. This result indicated that the azopolymer and laser holography would provide a strong foundation for the light-triggering drug delivery system

Defect-free deformed-helix ferroelectric liquid-crystal mode in a vertically aligned configuration (Invited Paper)

— A novel deformed-helix ferroelectric liquid-crystal (DHFLC) mode in a vertically aligned (VA) configuration is described. In this configuration, several unique features of display performance such as uniform alignment, fast response, and analog gray-scale capability are obtained. Particularly, this VA-DHFLC mode allows for the defect-free uniform alignment of both the FLC molecules and the smectic layers over a large area without employing additional processes such as rubbing or electric-field treatment that are generally required for planar FLC modes. Based on the VA-DHFLC mode, a transflective display having a single-gap geometry with in-plane electrodes on two substrates in the transmissive regions and on one substrate in the reflective regions is described.