Yoon-sun Choi

Uniform and stable field emission from printed carbon nanotubes through oxygen trimming

When carbon nanotube field emitters are operated, a few highly protruded ones generate most of the emission currents that cause spatial nonuniformity and fast decay in lifetime behavior. We present a cost-effective means to solve this problem using selective oxidation on those nanotubes emitting higher currents, which is assisted by Joule heating generated during field emission. Our simple technique is potentially useful for the field emission devices such as display, backlight, x-ray tube, and others using multiple carbon nanotube emitters.

Holographic photopolymers of organic/inorganic hybrid interpenetrating networks for reduced volume shrinkage

We demonstrated that holographic photopolymers of organic/inorganic hybrid interpenetrating networks (IPNs) showed both enhanced monomer diffusion and reduced volume shrinkage, simultaneously. Hybrid IPNs were developed from simple in-situ sol-gel reaction: the alkoxysilane of (3-aminopropyl)triethoxysilane (APTES) leads to the formation of inorganic networks, while simultaneously partial introduction of the two amines of APTES into epoxy resins reduced the overall crosslink density of organic networks. In particular, the morphology of hybrid IPNs can be easily controlled by simply adjusting the ratio of APTES to epoxy resins. When the ratio of APTES to oxirane was 7.0 wt %, interpenetrated hard inorganic networks were homogeneously distributed within soft organic networks without aggregation. The present hybrid IPNs were very effective for high performance holographic properties including diffraction efficiency and volume shrinkage. Soft organic networks with low overall crosslink density enabled fast monomer diffusion for photopolymerization, and consequently diffraction efficiency was enhanced. In addition to fast monomer diffusion, locally dispersed inorganic networks dramatically suppressed the volume shrinkage, due to their filler strengthening effect accompanied by an interpenetrating effect. This synergetic effect of hybrid IPNs allows the enhancement of diffraction efficiency without sacrificing volume shrinkage.

Integral imaging with reduced color moire pattern by using a slanted lens array

In this paper, we propose a color moire pattern reduction method in integral three-dimensional imaging by slanting the lens array. The color moire patterns are examined as varying the slanted angles between the lens array and the display panel for choosing the angles for which the pattern is reduced. However, it is difficult to expect the tendency of the pattern. We simulate the color moire pattern on the assumption of ray optics and find out the angle where the moiré is reduced. With the proposed technique clear three dimensional images can be displayed. The explanation of the proposed method will be provided, and the simulation results will be shown. Finally, experimental results will verify the proposed method.

Improvement in the breakdown properties of electrowetting using polyelectrolyte ionic solution.

We report the improvement in the breakdown properties of electrowetting using a mixture of poly(acrylic acid) (PAA) polyelectrolyte and a surfactant (Tween 80, TW80). Onset of breakdown was initially determined via visual observation and further verified by investigating impedance phase shift. Breakdown characteristics of the large-molecule ionic solution were compared with those of conventional electrolytes (Na(2)SO(4)) that produce small molecules. Experiments with various conductivities and hydrophobic coatings on a thin silicon nitride dielectric layer (∼500 Å) showed that the breakdown voltage of the PAA-TW80 system was at least two times higher than that of the Na(2)SO(4)-TW80 system. Our results demonstrate that defects in the dielectric and hydrophobic layers are less vulnerable to larger ionic molecules.

Measurement of the optical characteristics of electrowetting prism array for three-dimensional display

Recently liquid-based optical devices are emerging as attractive components in three-dimensional (3D) display for its compact structure and fast response time. Among them an electrowetting prism array is one of the promising 3D devices. It steers a beam, which enables to provide corresponding perspectives to observer. For high quality autostereoscopic 3D displays the important factors are the beam steering angle and the beam profile, the optical characteristics. In this paper, we propose a method to measure the optical characteristics of the liquid prism and show experimental results on our prototype electrowetting prism array, which consists of prisms with 200um by 200um size. A modified 4-f system is adopted for the proposed method. It provides two kinds of information of the optical characteristics of the liquid prism at the image plane and at the Fourier plane. First, the proposed measurement setup magnifies the image of the liquid micro prism array so that we can observe the status of the each prism array directly with bare eye and align a mask easily for selecting a prism to be examined at the image plane. Secondly, the steering angle can be calculated by measuring the displacement of the beam at the Fourier plane, where the angular profiles that have important information on the oilwater interface is observed precisely. The principle of the proposed method will be explained, and the measured optical characteristics from experimental results on the liquid prism we fabricated will be provided, which proves the validity of the measurement method.

Arrayed beam steering device for advanced 3D displays

An arrayed beam steering device enables much simplified system architectures for high quality multiview 3D displays by adapting time multiplexing and eye tracking scheme. An array device consisting of microscale liquid prisms is presented, where the prism surface between two immiscible liquids is electrically controlled to steer light beams by the principle of electrowetting. An array prototype with 280×280μm pixels was fabricated and demonstrated of its full optical performances. The maximum tilting angle of each prism was measured to be 22.5° in average, with a tracking resolution of less than 0.04°. In this paper, we report a design and fabrication of eletrowetting based prism array, opto-fluidic simulations, optical characterizations, as well as applications to achieve low fatigue 3D displays.

Development of micro variable optics array

This research is on the development of a micro variable optics array which employs electrowetting as the working principle. The single pixel of the array has four separated electrodes and each of them is controlled independently giving the device multi-degree of freedom. The separated electrodes are fabricated using a thick photoresist and electroplating. Several formulas showing the relation among the radius of curvature, the prism angle, and electrowetting parameters are provided. The prism angles are measured to be ±30° and compared to the calculated values. The measurement of the radius of curvature is also presented showing that the various radiuses of curvature are achievable from concave to convex.

Eye Tracking based Glasses-free 3D Display by Dynamic Light Field Rendering

Glasses-free 3D display is developed using dynamic light field rendering algorithm in which light field information is mapped in real time based on 3D eye position. We implemented 31.5″ and 10.1″ prototypes.

Highly efficient diffractive reflector using microgratings for reflective display

A highly efficient diffractive reflector with a rhombus shape angular distribution of reflected light for mobile liquid crystal display is developed. The fabricated diffractive reflector shows enhanced reflectance two times higher than the conventional bumpy reflector. The diffractive reflector composed of 25 surface relief microgratings is fabricated by photoresist patterning and metal deposition. The angular distribution of light that is reflected off the diffractive reflector is measured under specula illumination and diffusive illumination. The sufficient controllability of the angular distribution of the reflected light by the specific design of the period, orientation, and depth of each micrograting is shown.

2D/3D mode switchable backlight design

In this paper we review the 2D/3D mode switching technologies and suggest a new design for the 2D/3D switchable backlight unit (BLU) with the prism-shaped light extracting pattern structured on the light guide plate (LGP).