Collimated backlight for displays and microprojectors

A backlight illuminator with low divergence angle will significantly improve the efficiency, contrast and color gamut of liquid-crystal displays (LCDs) and micro-projectors. However, converting light from a light-emitting diode (LED) with large angle of divergence into a low-angle of divergence beam using a device that is only a few mm thick is extremely challenging task. Here, we propose a novel solution to this problem by using an optimized light-guide collimator and a quasi-diffractive-optical element. The idea is to illuminate the screen with LED through a parabolic waveguide/funnel that converts a point source into a collimated beam with relatively small diameter. The collimated beam at the output of the parabolic collimator is aligned at an angle to a prismatic quassi diffractive optical element (DOE) fabricated on top of a piece of glass. The illumination at an angle increases the size of the illuminating spot and the goal of the DOE is to correct the propagation direction of the illuminating beam. The proposed concept is demonstrated via preliminary numerical and experimental results.