The major efficiency loss in current liquid crystal displays(LCD) are the absorption in polarizers and
color filter, and both can be resolved with decent backlight design which takes light polarization and color
separation into consideration. Those improvement schemes on the backlight normally will not trade off
the image quality readily achieved in the commercial LCD. Both polarization and color separation
schemes for the backlight are reviewed with categorization on the basic concept, followed by the proposal
of possible combinations for both direct lit and edge lit configuration with the consideration on the
availability of associated components. Two total solutions, including polarization conversion module for
LED and pixelized backlight with RGB LED for direct lit and edge lit respectively, are given with
demonstration of preliminary result achieved so far as the efficiency improvement schemes for LCD
backlight.
Laser is an ideal illumination light source for liquid crystal projection displays in terms of source Etendue and
polarization. In order to make a conversion from a circular Gaussian laser beam profile to a rectangular uniform
distribution on the microdisplay, a double side microlens array has been proposed as a homogenizer, and a cylindrical
lens is exploited for shaping the aspect ratio of illumination pattern. The design and simulation based on scalar
diffraction theory have shown that two identical lenslet arrays on each side of a thin plastic substrate with a lateral shift
of half diagonal pitch can convert laser beam into a uniform square illumination at a specified near field. The pitch and
curvature of the lenslet are major parameters for modifying the illumination distance, area and uniformity. The proposed
lenslet array will provide an economical solution for the illumination optics of laser based light valve projector due to its
regular and circular lenslet profile.
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