Dong-Woo Kim

Polarization-insensitive liquid crystal Fresnel lens of dynamic focusing in an orthogonal binary configuration

We report on a polarization-insensitive liquid crystal (LC) Fresnel lens with the centrosymmetry of dynamic focusing in an orthogonally alternating hybrid configuration. The polarization-insensitive Fresnel lens having such successive orthogonal hybrid alignment in two adjacent zones was fabricated using a single-masking process through two-step exposure of a linearly polarized ultraviolet light. It was found that the dynamic focusing property of the LC Fresnel lens is electrically controllable and entirely centrosymmetrical irrespective of the polarization state of an incident light.

Multimode transflective liquid crystal display with a single cell gap using a self-masking process of photoalignment

We demonstrate a transflective liquid crystal display (LCD), doped with a chiral agent to produce a low helical twisting power, in a multimode configuration consisting of the homogeneous alignment and the hybrid alignment. The multimode transflective LCD was fabricated by a single-step exposure of the UV light through an array of metal reflectors used as an amplitude photomask which gives an alternating homogeneous and homeotropic LC geometry. This single-step UV exposure produces no cell gap variations. In our configuration, the electro-optical disparity between the transmissive region and the reflective region was found to be significantly reduced by the low helical twisting power of the chiral dopant.

Mechanical stability of a flexible ferroelectric liquid crystal display with a periodic array of columnar spacers

We report on a high-speed flexible display based on a deformed helix ferroelectric liquid crystal (DHFLC) in a vertically aligned configuration. The mechanical stability of the flexible DHFLC display was achieved using a periodic array of columnar spacers formed directly on the top side of in-plane electrodes by the photolithography technique. Several unique features of display performances such as flexibility, uniform alignment, fast response, and gray scale capability were obtained. The switching time was found to be a few hundred microseconds.

Polarization-invariant grating based on a photoaligned liquid crystal in an oppositely twisted binary configuration

We demonstrate a polarization-invariant liquid-crystal (LC) grating in an oppositely twisted and mutually orthogonal configuration. The polarization-invariant LC grating with high diffraction efficiency is fabricated using a single-masking process with two-step exposure of a linearly polarized ultraviolet light. It is found that the zeroth- and the first-order diffracted beams are linearly polarized and perpendicular to each other irrespective of the incident polarization for the phase retardation of m pi (m=integer).

Low-Leakage Polymeric Thin-Film Transistors Fabricated by Laser Assisted Lift-Off Technique

Organic thin-film transistors (OTFTs) based on a semiconducting polymer have been fabricated using a patterning method of the selective wettability. Laser assisted lift-off (LALO) technique, ablating selectively the hydrophobic layer by an excimer laser, was used for producing a semiconducting polymer channel in the OTFT with high resolution. The selective wettability of a semiconducting polymer, poly(9-9-dioctylfluorene-co-bithiophene) (F8T2), dissolved in a polar solvent was found to define precisely the pattering resolution of the active channel. It is demonstrated that in the F8T2 TFTs fabricated using the LALO technique, the leakage of the gate current is drastically reduced.

P-100: A Transflective Liquid Crystal Display in a Multimode Configuration

We report on a transflective liquid crystal display (LCD) in a multimode configuration consisting of an electrically controllable birefringence mode and a hybrid aligned nematic mode. In this configuration, the multimode transflective LCD was obtained by a single-step exposure of ultraviolet light, blocked by a metal reflector in the reflective area as an amplitude photomask, producing an alternating homogeneous and homeotropic geometry with no additional fabrication processes and cell gap variations.

New Configuration of a Transflective Liquid Crystal Display Having a Single Cell Gap and a Single Liquid Crystal Mode

We report on a new tranflective liquid crystal display (LCD) mode having a single cell gap and a single LC mode. For this display mode, a low twisted nematic liquid crystal cell, having the twist angle of 60°, is used for both transmissive and reflective applications. The measured electro-optic characteristics of our transflective cell agree well with numerical simulation results. It is found that the transmittance and the reflectance become identical to each other in the high voltage regime. The new transflective configuration is useful for mobile LCD applications.

A Rotatable Waveplate Using a Vertically Aligned Deformed-Helix Ferroelectric Liquid Crystal

We report on a rotatable waveplate using a vertically aligned deformed-helix ferroelectric liquid crystal (DHFLC) in the presence of the in-plane rotating electric field. In such device configuration, the helix of the FLC is continuously deformed and thus the effective birefringence increases as the in-plane electric field increases. The VA-DHFLC rotatable waveplate composed of radially distributed electrodes can transform the polarization state (PS) of an input beam to any PS on the order of 10 μ sec. This rotatable waveplate would be useful for polarization control in optical communication systems.

High-speed infrared phase modulators using short helical pitch ferroelectric liquid crystals.

A fast phase modulator based on ferroelectric liquid crystal (FLC) is demonstrated and its performances characterized. For uniform alignment and pure phase modulation, we propose a new FLC device configuration using short helical pitch material and homeotropic alignment structure. This device is driven by periodic in-plane electrode stripes implemented on the surface of both cell substrates. As a result, we have obtained large phase modulation (> 2pi at lambda=1.55 microm) and fast response (< 200 microsec).

Liquid Crystal Lens Array with High Fill-Factor Fabricated by an Imprinting Technique

We propose a high fill-factor configuration of a liquid crystal (LC) lens array fabricated by an imprinting technique. The bottom substrate of our LC lens array has a periodically concave electrode which forms an array of concave square apertures. The electrode on the imprinted concave structure produces a centro-symmetric inhomogeneous electric field which can be used for controlling the distribution of the refractive index in the LC layer. The focal length was found to vary in the range of a few centimeters. Moreover, unlike other LC lens arrays, the square aperture of each elemental lens allows for a high fill-factor. Our LC lens array is expected to be useful for various optical systems with high optical efficiency.