LCD-based holographic displays in the making

January 17, 2017 // By Julien Happich
A group of researchers from Soochow University, China, assisted by nano optics fabrication equipment provider SVG Optronics is hoping to bring holographic video displays one step closer to consumers.

Their approach to portable holography is to drastically reduce the computational requirements of refreshing 3D video data by separating the phase information of a lightfield from the amplitude information. Instead of relying on parallax barriers or thin film micro lenses to create stereoscopic multi-views, the researchers rely on a fixed array of voxel-forming nanogratings coupled to an LCD plane used as the light amplitude modulator.

Published in the Optics Express journal, their paper "Multiview holographic 3D dynamic display by combining a nanograting patterned phase plate and LCD" prove the concept with a 640×360 resolution four-view display. Here, each addressable pixel of the 5.5 inch TFT-LCD used to modulate the amplitude information of a lightfield is matched with a nanograting from the fixed 4-view phase plate affixed to the LCD.

Schematic of the holography based multi-view 3D display. The 4-pixel nanogratings on the phase plate sit between the LCD used as a spatial light modulator and the incoming light beam.

With the help of SVG Optronics and a specially devised lithography system, the researchers were able to manufacture diffractive gratings with a period tuneable in steps as small as 1nm. The period and orientation of the nanograting in each of the 4-pixel nanogratings were carefully calculated following holographic recording and readout theory, so that the transmitted light beam converged to four viewing points.

Made out of glass, the phase plate was patterned using a homemade lithography system and positive photoresist. It consisted of nanogratings with a period varied from 550nm to 1000nm. The size of each pixel in the phase plate was 50×65μm, slightly smaller than the 95μm pixel size of the LCD so it would provide an alignment tolerance between the phase plate and the LCD. With each of the nanograting sub-pixels matching one pixel of the LCD, the 4-view phase plate had a total of 1280×720 pixels and the resolution of each view was 640×360.

(a) Photograph of the LCD. (b) Photograph of the 5.5 inch 4-view phase plate. (c) The SEM photo of the 5.5 inch phase plate with nano-gratings. (d) The blow-up SEM photo of nano-grating.