Design and Fabrication of Diffractive Color Separation Grating for Optimized Power and Color Performance
Date Issued
2009
Date
2009
Author(s)
Liu, Dong-Lu
Abstract
It is fundamental to use the color filter (CF) in LCD systems to achieve a full-color display. For this purpose, however, the total power efficiency will drop to 24.89% as the light passes through the CF. In order to solve this problem, we have developed a novel approach by inserting a diffractive color separation grating between the backlight and the CF to spatially separate the backlight into three bands (R,G,B) in advance. Then the three bands arrive at their corresponding sub-pixels to reduce the loss of backlight. The efficiency computation of color separation grating presented by Dammann in 1978 is based on Fraunhofer diffraction theory. We take white light LED as our computation example and tune the variables, such as the number of the steps and height of the grating and the central wavelength to get optimum improvement. The computation results demonstrate that we can get the best power efficiency up to 47.3% and the gamut area can be improved up to 89.12%. In order to evaluate the influence of efficiency in practical cases, including oblique incidence and finite element factor, we try to obtain closed-form formula for the efficiency of Dammann grating such that we can use the formula to compute space distribution of different color and furthermore to evaluate the total power efficiency. We also analyze the effect of the three main possible errors, including lateral misalignment, etching error, and line-width error, on the efficiency of 4-level phase color separation grating during the multiple binary mask fabrication. Finally, we use VLSI-like fabrication process to make the test device and verify whether efficiency of the practical device is coincident with the theoretical result.
Subjects
color separation grating
Type
thesis
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