Young Mo Hwang

200-in. full-color laser projection display

A 200 inches large-area laser projection display is presented. the laser light processor is mainly composed of a white laser for light source, acousto-optic modulators and the laser beam scanner composed of a galvanometer and a polygon scan mirror. The white light source is a Krypton- Argon laser with main wavelengths 647nm, 515nm, 488nm, respectively. Collimated and focused laser beams are modulated at acousto-optic modulators according to the video signals. Dichroic mirrors are used for separating the white laser beam to red, green, blue light beams and recombining the modulated red, green, blue light beams to one light beam. Recombined laser beam is vertically scanned by a galvanometer running at 60Hz rate and horizontally scanned by the 24 facet polygon scan mirror rotating at the speed of 39,375rpm. Between the polygon scan mirror and the galvanometer, relay lenses are inserted for which horizontally scanned beam is focused onto the galvanometer mirror facet. The size of 4m X 3m image with high resolution is obtained at the throw distance of 7m using 4W white light.

Full color laser projection display using Kr-Ar laser (white laser) beam-scanning technology

Full color laser projection display is realized on the large screen using a krypton-argon laser (white laser) as a light source, and acousto-optic devices as light modulators. The main wavelengths of red, green and blue color are 647, 515, and 488 nm separated by dichroic mirrors which are designed to obtain the best performance for the s-polarized beam with the 45 degree incident angle. The separated beams are modulated by three acousto-optic modulators driven by rf drivers which has energy level of 1 watt at 144 MHz and recombined by dichroic mirrors again. Acousto-optic modulators (AOM) are fabricated to satisfy high diffraction efficiency over 80% and fast rising time less than 50 ns at the video bandwidth of 5 MHz. The recombined three beams (RGB) are scanned by polygonal mirrors for horizontal lines and a galvanometer for vertical lines. The photodiode detection for monitoring of rotary polygonal mirrors is adopted in this system for the compensation of the tolerance in the mechanical scanning to prevent the image joggling in the horizontal direction. The laser projection display system described in this paper is expected to apply HDTV from the exploitation of the acousto- optic modulator with the video bandwidth of 30 MHz.

Compact hybrid video color mixer for large-area laser projection display

The present paper relates to an optical module of a compact hybrid video color mixer for large-area laser projection display. The compact optical arrangement gives a very small- sized and high-performance video image color mixing apparatus which uses a hybrid R/G/B color separator, modulate the light beam using a 3-channels acousto-optic modulator according to the video image signal and combines the modulated R/G/B beams to one beam using a hybrid R/G/B color combiner. A high performance video image projection apparatus can be realized using a light source, a hybrid video color mixer and a X-Y scanner set. The present hybrid video color mixer is suitable for a future domestic laser TV application.

Design and fabrication of dichroic mirrors for color separation and recombination of the Kr-Ar laser (white laser)

Cut-off filters reject all the radiation below and transmit all the above a certain wavelength and vice versa. In this paper, we will study the design and fabrication of a short wave pass or a long wave pass dichroic mirrors for color separation and recombination from the R.G.B. color beam source. In the laser display system, color separation and recombination is very important. We designed the coating layers so that the best performance may be obtained from a 45 degree incident s-polarized light. The following fabrication specification is satisfied in our color separation/recombination of the Kr-Ar laser source. The first dichroic mirror for the blue color separation, maximized on reflectance and transmittance as R > 99% in the blue regions (400 approximately 490 nm) and T > 90% in the green and red region (510 approximately 700 nm). The second dichroic mirror for the color recombination maximized the reflectance and transmittance as R > 99% in the range of 510 approximately 700 nm and T > 90% in the blue color region. In the third dichroic mirror for which it used the color separation and recombination of the green and red simultaneously, maximized the reflectance and transmittance as R > 99% in the green region (510 approximately 560 nm) and T > 90% in the red region. These fabricated mirrors were applied in our laser display projection system. We obtained an excellent result.

Design and fabrication of hybrid dichroic mirrors for light separation/recombination by using a flat plate

We report the design and fabrication of Hybrid Dichroic Mirrors (HDM) for the separation and the recombination of white laser beam by using small sized flat plate for a small Laser Projection Display (LPD) system. This small sized laser projection display system is consist of a white laser, hybrid dichroic mirrors, 3-channel AOM and a beam scanning part. Red, green and blue light beams are separated by one flat plate dichroic mirror and also modulated by the 3-channel AOM, are recombined to one beam by another flat plate dichroic mirror. These hybrid dichroic mirrors are designed to measure the separation and recombination of s-polarized light beams of 647, 515, 488 nm wavelength from the white laser. Key element of the mirror design includes the quarter wavelength multilayers optimized to provide the best performance for the separation and recombination of light beams. The calculated values of the transmittance, which are pass through the hybrid dichroic mirror, are 95% for each separated/recombined color beams. The measured values of transmittance are over 90%.

Three-channel acousto-optic modulator for laser projection display system

A small laser projection display system is designed with a hybrid dichroic mirror for color separation, a hybrid dichroic mirror for color recombination, a 3-channel acousto-optic modulator (AOM) and a scanning part. The 3-channel AOM modulates red, green and blue laser beams. The wavelengths of red, green and blue beams are 647, 515 and 488 nm respectively. The carrier frequencies of each channel of AOM were adjusted to minimize the diffraction angle differences among red, green and blue laser beams. The carrier frequencies are 130, 168, 178 MHz for red, green and blue laser beams respectively. The measured diffraction angle after the carrier frequency control equals to the calculated diffraction angle. The transducer structure of AOM was optimized to get a high diffraction efficiency and to maximize isolation between adjacent channels by a slicing saw, which enhanced the electrical and acoustic isolation. The impedance matching- circuit of each electrode is housed in a separate compartment to suppress electrical crosstalk. The diffraction efficiency and risetime of the 3-channel AOM are over 85% and 50 nsec per each cell. The crosstalk between the channels is less than -30 dB.

High-reflective multilayer coating by using the reflective control wavelength monitoring of layer thicknesses for second harmonic generation (SHG) laser

The aim of present work is the development of a method of high reflective (H/R) optical multilayer coating on KTP and BK-7 Glass with the specification: R (reflectance): greater than or equal to 99.9% at 1064 nm. T (transmittance): greater than or equal to 95% at 532 nm and T (transmittance): greater than or equal to 95% at 809 nm for a second harmonic generation (SHG) laser. The parameters that can be used to reach these goals are the number of layers in the multilayer, the layer thicknesses and refractive indices and extinction coefficients of the individual layers and of surrounding media. Clearly, the more demanding the performance specifications, the more complex is the resulting system. In our case, we have the most demanding performance specification, that is why the technology of obtaining coatings with this specification is very precise and complicated. In order to fulfill the demand of high reflectance at lambda equals 1064 nm it is necessary to deposit 30 or more alternative quarter wavelength thickness layers of ZrO2 and SiO2 and to fulfill the demand of high transmittance at lambda1 equals 532 nm and lambda2 equals 809 nm the SiO2 layer of lambda/8 (last layer) optical thickness is used to suppress the secondary maxima. The perfect suppression of secondary maxima takes place, when we deposit multilayer coating with equal optical thicknesses of high and low refractive indexes layers. The performance of many optical multilayers depends critically on the thicknesses of individual layers. The control of the layer thicknesses during their deposition is therefore very important. The most common techniques used is optical monitoring performing indirectly on a witness glass (or the chip). R (reflectance) optical monitoring is however used to measure the quantities of each layer optical thicknesses in our system. We used different control wavelength to monitor and control each layer optical thickness with different coating materials for compensating the deposited optical thickness.