Hyung-Wook Jeon

Electrical and thermoelectrical properties of undoped Bi2Te3-Sb2Te3 and Bi2Te3-Sb2Te3-Sb2Se3 single crystals

Abstract The thermoelectric properties and Hall effects of a number of undoped Bi 2 Te 3 -Sb 2 Te 3 pseudo-binary and Bi 2 Te 3 -Sb 2 Te 3 -5%Sb 2 Se 3 pseudo-ternary single crystal alloys grown by the Bridgman method were measured over the temperature range from 77 to 580 K. All of the alloys showed p -type extrinsic conduction and the analysis of the Seebeck coefficient and electrical conductivity in the extrinsic range indicated partial degeneracy at the lower temperatures. The Seebeck coefficient and energy gap of the pseudo-ternary alloy increased and the electrical conductivity decreased with the addition of Sb 2 Se 3 . It was proved by the Hall measurement that the carrier concentration increased with increasing amount of Sb 2 Te 3 , and decreased with the addition of Sb 2 Se 3 , while the Hall mobility was constant except for the Sb 2 Te 3 -rich region at room temperature. The scattering of carriers in these alloys can be expressed as acoustic-mode lattice scattering and two-phonon processes. The figure of merit shows a maximum at a carrier concentration of about 4.0 × 10 19 cm −3 at room temperature.

Multiview 3D imaging system with full-color capabilities

A multiview 3D imaging system utilizing a holographic screen is described. This system is consisted of a horizontal array of 8 cameras, a signal converter, a full color beam projector and a full color holographic screen. The camera array is composed of 8 CCD cameras having VGA image quality. The cameras are aligned in an arc having the radius of curvature 3 m. The separation between each camera is 3.5 cm. The signal converter is to convert 8 parallel image data from the camera array into a time multiplexed image signal train for each of 3 TV primary colors, and to control the system. The image sampling from each camera of the camera array is done by the field image rate as in the usual TV. The total image fields are 480 per second. The beam projector is consisted of 3 CRTs for the 3 primary colors, a large aperture objective and an 8 strips LCD shutter for each CRT. The projector is to extract 8 view images from the time multiplexed image signal train and projects the images on the holographic screen through the 8 strips LCD shutter located in front of each projectors objective lens. The switching of each strip in the shutter is synchronized with the camera sampling sequence by the signal converter. The holographic screen has the property of a spherical mirror and can create 6 viewing zones. This system can also display PC animated images. The images displayed on the screen are impressive.

Direct image transmission through a multimode optical fiber

One-way transmission of a multipixel image through the multimode optical fiber based on the phase-conjugation principle is realized. Adistortion-compensating hologram for each pixel of an image to be transmitted is superposed on a photoplate. Each hologram is recorded with a reference beam of different beam incidence angle to provide proper wave-front correction for each pixel without any interference from other pixels. The reference beams are holographically generated from a photoplate in which small holographic lenslets are aligned in a matrix pattern. Images of up to 25 pixels are transmitted through the fiber experimentally.

Image-tiling system using optically addressed spatial light modulator for high-resolution and multiview 3D display

A miniature electrically addressed spatial light modulator (EASLM) using standard CMOS processing comprises a crystalline silicon transistor array underlying a layer of ferroelectric liquid crystals and is intended for use in optical information processing as a high-frame rate input device. But the resolution is insufficient for modern video display. We have investigated a display system that tile the image from the EASLM on a pixilated optically addressed spatial light modulator (OASLM) using a binary phase hologram. This system consists of a ferroelectric liquid crystal EASLM with 320 X 240 pixels, a high frame rate video signal controller, a 532 nm laser as a light source of video projector, a binary phase hologram for 4 X 4 image multiplying and a 4 X 4 pixilated OASLM, with the optics for projecting video images. The threshold sensitivity of the OASLM is about 10 (mu) W/cm2 and its spatial resolution is about 50 lp/mm. The binary phase hologram is designed to fan out the asymmetric project image into 3 X 4 in the ratio of horizontal and vertical size for being memorized on the one part of the pixilated OASLM. The experimental value of the diffractive efficiency of the hologram is quite similar to the theoretical value, but the zeroth of diffractive beam is not removed completely. The displayed video image has a very high-resolution of 1280 X 960 pixels or a 3D display of 4 X 4 multiviews, depending on the images of the video projector.

Achromatized transmission-type holographic screen for a multiview stereoscopic image system

The main drawback of the use of transmission-type holographic screens is poor color reproduction caused by their high spectral dispersion. For overcoming this drawback, a long, narrow diffusing slit is used as an object when recording the screen. The necessary size and position of the slit relative to the photoplate and to the recording and reconstruction beams are determined by the phase relations of the beams. By use of the slit, holographic screens of 30 cm x 40 cm are recorded with a diverging reference beam and are used to display a multiview full-color stereoscopic image. The images displayed on the screen show no sign of color separation except near the edges of the screen. The image brightness on the screen is high enough that it can be watched in a normally illuminated room.

HOLOGRAPHIC VIDEO SYSTEM WITH A PULSE LASER

A holographic video system operated by a pulse laser is described. The use of a pulse laser as the light source allows the polygon mirror (or scanners) in the system to be eliminated. At the same time, a single long aperture acousto-optic modulator (AOM) is replaced by 6 small aperture AOMs linearly aligned and a still polygon mirror set is used. The effective aperture length of the 6-AOM-combination is 6 times that of an individual AOM. Since in this system the computer-generated-hologram (CGH) data is divided into 6 equal parts and loaded into the corresponding AOMs independently and synchronously, the loading time of CGH data to an AOM is reduced. This system can display 36,864 (in the horizontal direction)×128 (in the vertical direction) holographic fringe data points in binary format and operate at a rate of 60 frames per second using a personal computer.

Sliding-aperture multiview 3D camera-projector system and its application for 3D image transmission and IR to visible conversion

A new architecture of the 3-D multiview camera and projector is presented. Camera optical system consist of a single wide aperture objective, a secondary (small) objective, a field lens and a scanner. Projector supplementary includes rear projection pupil forming screen. The system is intended for sequential 2-D prospective images acquisition and projection while the small working aperture is sliding across the opening of the big size objective lens or the spherical mirror. Both horizontal and full parallax imaging are possible. The system can transmit 3-D images in real time through fiber bundles, free space, and video image transmission lines. This system can also be used for real time conversion of infrared 3-D images. With this system, clear multiview stereoscopic images of real scene can be displayed with 30 degrees view zone angle.

Two-dimensional spectral multiplexing method for direct image transmission through an optical fiber

A method of parallel image transmission through a single optical fiber based on 2-D spectral multiplexing is presented. The method is realized with the multistripe holographic diffraction gratings. Each stripe in the gratings has its own ruling period and height. An experimental setup for the parallel image transmission is described and the transmitted images are represented.

Full-color reflection-type holographic screen

A full color reflection type holographic screen having the spectral range of reflection, 470 to 620 nm is made of DuPont photopolymer film type OmniDex 706 with color tuning film CTF-75-24.6 by controlling the tuning process to have the chirp type fringes. A small size diffuser is used to modify the reference beam in a single beam recording scheme to increase the viewing zone size of the screen. Intermodulation fringes due to the diffuser do not deteriorate the performances of the screen because of insensitivity of photopolymer to large period fringes. The screen shows very low level of scattering when looking through it. The screen has both properties of a diffuser and a spherical mirror.

Solid state lasers for color holography

The problems in recording, copying and reconstruction of color transmission and reflection holograms are discussed with respect to the following source laser parameters: (a) a set of RGB (red, green, blue) wavelengths, (b) spectral bandwidth (temporal coherence), (c) spatial coherence, and (d) output power. The analysis of different optical schemes for color holography with referring to the parameters mentioned above suggests the necessity of having various lasers with different spatial, temporal and power characteristics. Based on the analysis, solid-state lasers with intracavity as well as extracavity frequency conversion examined as an efficient source of RGB (red, green, blue)--wavelengths under various operating regimes: CW, quasi-CW (with high repetition rate--up to 1,000 kHz), pulse, Q-switch, mode-locking etc. The possible optical schemes of such lasers are proposed and their parameters are discussed.