Design concept of an FLC-NLC combined circular polarization switch for 3D laser pico-projectors

Abstract

At present, LED-based pico-projectors are in widespread use. However, with the requirement for compact size, the demand for laser-light-source-based pico-projectors is expected to increase in the near future. Furthermore, picoprojectors with 3D capabilities are desired. 3D projectors employ either an active shutter system or a passive shutter system. We have proposed a novel combined circular polarization switch for 3D laser pico-projectors with passive shutter glasses, which consists of a high speed ferroelectric liquid crystal (FLC) linear polarization switch and a multiorder quarter-wave plate using a nematic liquid crystal (NLC) for RGB color chromatic dispersion compensation. In this study, we present a design concept of the polarization switch and we demonstrate that it affords increased bandwidth compared to the achromatic compensation method using an FLC with low order compensation films. The adjustment for each RGB laser wavelength using an additional polymer film working in the target range of 445 – 640 nm is also indicated. By using this novel design, when the permissible crosstalk level is 0.5%, the available wavelength range broadens from 59% to 91% of the target range. In addition, we fabricate a prototype based on the design concept and evaluate its crosstalk and 3D performance, which are important parameters for a 3D projector, in combination with a MEMS system. The proposed switch can be placed in the path of a combined RGB laser beam, and it is suitable for both imager-based and scanning-MEMS-based systems because of its simple structure and compact design.