Illumination System Of Optical Engine For Solid-state Volumetric True-3D Display

Solid-state volumetric true-3D display projects the image information on the 3D physical space through a high-speed projection optical engine. Based on the visual persistence of eyes, people can perceive the depth information of an image. The display space consists of 20 layers of liquid crystal shutters. To avoid image flickers, the projection frequency should reach 1200Hz; At the fact that the transmittance of 20-layer liquid crystal shutters is lower, the illumination system should provide high luminance to guarantee high display brightness; The transmittance of one liquid crystal shutter is different for different wavelength spectrum. To guarantee the accuracy of display color, the color temperature should be adjustable. Based on these requirements, the illumination system of solid-state volumetric true-3D display should provide high projection frequency, high brightness and adjustable color temperature.After the analysis of common projection optical engines, the illumination system of 3-DMD projection optical engine is designed. The luminance of the projection light source is computed theoretically. The calculation results are then corrected according to the spectrum curve of liquid crystal shutters. With the considerations of brightness, life and heat dissipation, the projection light source with high-power RGB LEDs and a white LED is put forward. Based on the optical characteristics of chosen LEDs, the collimator designed by refraction-and-reflection mixed method is applied. In order to reduce the light source volume, the X-Cube prisms are used to combine colors. Based on the conservation of Etendue, the light tunnel is designed. To realize spatial color separating and combining, the TIR prisms and Philips prisms are used. After those, the simulation of the illumination system is performed to optimize the designed results.Based on the theoretical design and simulation, the prototype of the solid-state volumetric true-3D display is developed. The experimental test results show that the divergence angle of the LED has been reduced to ±20° by applying the collimator. The luminous flux emitted from the projection lens reaches 1388.611m. The average screen brightness is about 123cd/m2. The color gamut reaches 78.43%of the NTSC standard. The prototype presents the merits of vivid colors, strong stereoscopic impression and no perceived flickers. The proposed illumination system satisfies the requirements of the solid-state volumetric true-3D display.