In-Jae Yeo

Speckle suppression in scanning laser displays: aberration and defocusing of the projection system.

Aberration and defocusing effects in the mechanism of speckle suppression in laser projection displays were studied using the Fresnel approximation and the thin lens model. The analysis was performed with the assumption that aberrations change only the phase (and not the amplitude) in the rear principal plane of the display projection system. The analysis showed that aberrations should not have any influence on speckle contrast. It also showed that a screen shift relative to the image plane (defocusing) results only in a rescaling of the scanning beam autocorrelation function, which is equivalent to refocusing the objective lens to a new position of the screen. The optimal beam shape for optimal speckle suppression was also studied. A homogeneous field intensity distribution in the spatial frequency domain was found to provide close to the best speckle suppression.

10-bit Driver IC Using 3-bit DAC Embedded Operational Amplifier for Spatial Optical Modulators (SOMs)

A 10-bit driver IC for laser projection full high-definition TV (HDTV) applications using a spatial optical modulator (SOM) has been developed. For high-speed data transfer between the timing controller and driver IC, the driver IC adopts a mini-LVDS interface that operates up to 400 Mbps. To reduce the chip area, a digital-to-analog converter (DAC) structure including a 7-bit resistor-string DAC and a unity-gain buffer, which has a 3-bit linear DAC, is proposed. The area of the proposed DAC is 40% smaller than that of the typical 8-bit resistor-string DAC. The driver IC, which has 546 channels, is fabricated using a 0.35-mum CMOS process, and its area is 21 700 mum times 3 000 mum. The measured INL and DNL of the output voltages are less than 0.13 LSB, and the settling time is 1.93 mus with 40 pF capacitive loads. The output voltage deviation of the driver IC is achieved as 1.3 mV by compensating the nonuniformity among output channels.

A 10b Driver IC for a Spatial Optical Modulator for Full HDTV Applications

A 10b driver IC for laser projection full HDTV applications uses a 7b resistor-string DAC and a unity-gain buffer with a 3b DAC. The driver has 546 output channels, output voltage deviation of less than 1mV, a 200MHz mini-LVDS interface, and a maximum settling time of 2.4 mus for a 1080pixel spatial optical modulator with 40pF capacitive loads. The IC is fabricated in a 0.35 mum CMOS process and the chip area is 21.7 times3.0 mm2

Spatial optical modulator (SOM): high-density diffractive laser projection display

A new type of diffractive spatial optical modulators, named SOM, has been developed by Samsung Electro-Mechanics for laser projection display. It exhibit inherent advantages of fast response time and high-performance light modulation, suitable for high quality embedded laser projection displays. The calculated efficiency and contrast ratio are 75 % and 800:1 respectively in case of 0th order, 67 % and 1000:1 respectively in case of ±1st order. The response time is as fast as 0.7 &mgr;s. Also we get the displacement of 400 nm enough to display full color with single panel in VGA format, as being 10 V driven. Optical module with VGA was successfully demonstrated for its potential applications in mobile laser projection display such as cellular phone, digital still camera and note PC product. Electrical power consumption is less than 2 W, volume is less than 13 cc. Brightness is enough to watch TV and movie in the open air, being variable up to 6 lm. Even if its optimal diagonal image size is 10 inch, image quality does not deteriorate in the range of 5 to 50 inch because of the merit of focus-free. Due to 100 % fill factor, the image is seamless so as to be unpleasant to see the every pixels partition. High speed of response time can make full color display with 24-bit gray scale and cause no scan line artifact, better than any other devices.

A study of image contrast restriction in displays using diffractive spatial light modulators

The peculiarities of 1D projection displays using spatial light modulators (SLM1) are considered. The conditions for high contrast images in SLM are investigated. It is shown that an amplitude imbalance between the light reflected from the passive and active parts of SLM gratings imposes a limitation on the achievable contrast ratio. This imbalance may come from errors in SLM structure sizes and from diffraction effects inside SLM layers. The key point is the relationship between ridge and hole sizes in SLM diffraction structures. It is shown that odd diffraction orders (especially 1st order) have a significantly decreased sensitivity to ridge/hole tolerances. This phenomenon affects the SLM’s contrast ratio. The optimal ridge/hole ratio for different SLM diffraction orders has been found. To test the theory, experimental samples were manufactured and contrast ratio measurements were carried out. The experimental data are in good agreement with the theoretical results.