The Study Of Pico LCoS Projection System With High Uniformity And Light Efficiency

In recent years, the projection display technology has been developed rapidly. As the most important performance indexes of projection optical engine, brightness and uniformity have been attached with much more attention and pursuit. So this paper focuses on the research of pico LCoS projection system with high brightness and uniformity. To achieve the research goal, we will mainly introduce the design of the optical engine from the perspective of polarization recycling method.At the beginning of this paper, three main kinds of projection display systems have been introduced with the working principle and optical structure. Compared to the DLP technology, the light efficiency for pico LCoS optical engine is low though its cost is also low. Because, only the polarized light can be modulated by the LCoS display chip, so polarization recycling is obviously one of the most effective ways to improve the energy efficiency for LCoS optical engine.The main problems for traditional polarization recycling methods lie in fabrication difficulties or light efficiency. In this paper, a new polarization recycling method has been proposed based on the light reshaping with the combination of non-imaging optics and traditional imaging optics. By combining light pipe of non-imaging optics and splitting lens of imaging optics, the output light from LED is reshaped into separated thin beams array, so all the polarized light parts can be polarization recycled and then be collected by the relay lens. Compared to the traditional polarization recycling methods, the new method we proposed here has the following advantages. First, it doesn’t need fly-eyes element or the birefringent crystal block, that avoiding the fabrication difficulties and high cost. Second, it makes use of lighting area superposition principle instead of lighting area splicing to obtain higher illumination uniformity. In addition, the new method doesn’t improve the light efficiency by multiple reflections, so that the light efficiency is relatively high. In conclusion, this new polarization recycling method is quite suitable to be applied in pico LCoS projection system.With this method, two LCoS based pico projection optical engines are designed. The first one is designed with color-filter LCoS, whose diagonal width is0.29" and resolution is852x480. With one watt power consumption of white LED, this optical engine can output light flux of10.5lumens. Another pico optical engine is designed with color-sequential LCoS, whose diagonal width is also0.38", and resolution is640×360. With one watt power consumption of three color LEDs, it can output light flux of17.6lumens. Compared to pico LCoS optical engine without polarization recycling, the light efficiency is highly improved without increasing its aperture, while the thickness of the system is still11mm.