Anatoliy Lapchuk

Speckle suppression in laser display using several partially coherent beams.

An optical scheme for speckle suppression using two or three partially coherent beams in a projection system is proposed. Diffractive optical elements (DOE) placed in the intermediate image plane create several beams carrying the image to a screen. Transparent plates of different thicknesses are placed in the Fourier plane of the projective lens and used for beam decorrelation. The coherence matrix algorithm for speckle suppression is used to calculate the speckle contrast ratio. It is shown that for a small decorrelation length and using the same maximum thickness of the transparent plates, two partially coherent beams would provide better suppression than three beams with different diffraction orders. However, for a large decorrelation length, the three beam setup provides better speckle suppression for all three colors examined with a suppression coefficient close to theoretical limits. Verification of speckle suppression using three-beam decorrelation is reported.

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 novel diffractive micro-optical modulator for mobile display applications

A diffractive optical modulator has been fabricated based on a micromachining process. Novel properties of its fast response time and dynamics were fully understood and demonstrated for the strong potentials in embedded mobile laser display. Bridged thin film piezo-actuators with so called open mirror diffraction structure has been designed. Optical level package also was achieved to successfully prove its display application qualities. Display circuits and driving logic were developed to finally confirm the single-panel laser display at a 240Hz VGA (640×480). With its efficiency of more than 75% and 13cc volume optical engine with the MEMS-based VGA resolution SOM showed 7 lm brightness at a 1.5W electrical power consumption. Detailed design principle, fabrication, packaging and performances of the invented SOM are described.

Fine-pitch high-efficiency spatial optical modulator for mobile display applications

Diffractive spatial optical modulators (SOM) with fine pitch pixel array were introduced for the mobile applications of laser projection display which requires the small volume, low power consumption and high optical efficiency. Micromechanical designs of piezoelectric (PZT) actuator and mirror ribbon structure were optimized for small volume, but keeping the same level of the other performance. Even though the same design rule and fabrication equipment were used for 10 um pitch SOM and 16 um pitch SOM, the optical efficiency of the fine pitch SOM was 78 % for the 0th order diffraction and is better than that of 16 um pitch SOM (73%). The full on/off contrast ratio has no difference between 10 um pitch and 16 um pitch SOM. All the optical characteristics coincide well with the theoretical estimations. High displacement of 500nm, which is enough to modulate the three Red, Green and Blue colors were achieved by the control of the thicknesses and stresses of constituent structural layers. It was found that the stress of Pt/PZT/Pt actuating layer was the main parameter affecting the initial gap height of the ribbon and also its displacement. For improving the optical properties of the SOM devices, the required ribbon-flatness could be achieved by applying a stress gradient on the SiN layer to compensate for the stress unbalance between Al mirror and SiN supprting layer. The temperature sensitive characteristics of the SOM device, which degrades the image quality, could be minimized by a mechanical compensation method using a thermal expansion effect of Si substrates. This concept could be applied in most of the bridge type MEMS structure. The most critical parameter which limit the SOM device lifetime was found to be the ribbon displacement degradation. By using a temperature accelerating lifetime measurement method based on the displacement degradation the estimated lifetime was more than 4,000 hrs and is of acceptable level in the mobile application. In short, the developed fine pitch SOM device, for making small volume of optical module, has sufficient response time and ribbon displacement for modulating the red, blue and green colors with one SOM chip and is suitable for high quality embedded laser projection displays. Optical module with VGA is successfully demonstrated for its potential applications in mobile laser projection display such as a embed projection cellular phone.

Long-term data preservation on sapphire optical discs

The improved scheme of data recording process on an optical disc based on a substrate made of high-stable materials has been proposed. Information layer with depth of 115nm and width of 600nm has been obtained on sapphire substrate by ion-beam etching using improved scheme. These experimental results allow to create the sapphire optical discs for long-term data storage.

Line-defect calibration for line-scanning projection display

A method of line-defect calibration for line-scanning projection display is developed to accomplish acceptable display uniformity. The line scanning display uses a line modulating imaging and scanning device to construct a two-dimensional image. The inherent line-defects in an imaging device and optical lenses are the most fatal performance-degrading factor that should be overcome to reach the basic display uniformity level. Since the human eye recognizes line defects very easily, a method that perfectly removes line defects is required. Most line imaging devices are diffractive optical devices that require a coherent light source. This particular requirement makes the calibration method of sequential single pixel measurement and correction insufficient to take out the line defects distributed on screen due to optical crosstalk. In this report, we present a calibration method using a recursively converging algorithm that successfully transforms the unacceptable line-defected images into a uniform display image.