Diffraction and fringe field effects in small pixel devices

Liquid crystal displays (LCDs) are currently dominating the flat panel and mobile display market segment because of their excellent performance in power consumption, contrast ratio, viewing angle and refresh rate. The LCD technology has proven itself as relatively low-cost and ultimately scalable with screen diagonals that may exceed 100 inch. Liquid Crystal on Silicon (LCOS) microdisplays are miniature liquid crystal devices on a silicon substrate that operate in a reflective mode in contrast to the conventional transmissive LCDs. LCOS devices with SVGA resolution (800x600) have become available with a pixel size down to 5.4µm. Together with the proprietary Digital Light Processing (DLP) technology of Texas Instruments, LCOS devices are dominating the projector market segment. Furthermore, the technology is well-suited for application in picoprojector technologies and LCOS devices are excellent vehicles for phase modulation in holographic projector systems.

Reducing the pixel dimensions is conceptually a straightforward approach to further increase the resolution of LCOS devices for a given active area to improve the device performance. In addition to many technological challenges, decreasing the pixel size to below 5µm also leads to more fundamental questions on the device behavior. Diffraction effects will start to play an important role Once the structure features approach the light wavelength, so rigorous optical modeling will be required. Furthermore, also boundary effects due to elastic distortion of the liquid crystal between neighboring pixels will become more important. Both effects are investigated in detail from simulations and experiments. More information on the optical simulations can be found here.

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