A novel backlight unit for volume-holographic optical elements-based time-multiplexed three-dimensional displays

In volume-holographic optical elements (VHOEs)-based time-sequential three-dimensional (3-D) displays, two reference beams generated from a backlight unit (BLU) illuminate VHOEs, and from which object beams satisfying the Brag condition are then diffracted. These beams form a pair of alternating light fields for stereo 3-D view. Since this system operates based on diffraction optics, its performance highly depends on the degrees of collimation and uniformity of the reference beams. Thus, a new BLU system to generate uniformly-collimated reference beams for the VHOEs-based 3-D display is proposed by combined use of a light-guide-plate (LGP) grooved with an array of angle-variant flat-top prisms, and two LED light sources attached with reflection-type beam collimators. Simulation results with LightTools 7.1 show that the average full-width at half maximum (FWHM), backshift ratio and intensity uniformity of the LGP output beam of the proposed system have been significantly reduced down to 2.8° and 0.4%, and increased up to 90.9%, respectively, from the values of 51.8°, 26.5% and 24.5% of the conventional system. They represent 18.5-, 66.3- and 3.7-fold improvements of those values in the proposed system, respectively. These successful results confirm the feasibility of the proposed system in the practical VHOEs-based 3-D display.