The optimal design of TIR lens for improving LED illumination uniformity and efficiency

Abstract

With the development of LED technology, LED will potentially replace the traditional light source for its cost and size advantages, especially in the micro-projection system. And since the illumination uniformity and efficiency on spatial light modulators (SLM) are two important factors in evaluating the performance of micro-projection system, tapered light pipe (TLP) and square compound parabolic concentrator (SCPC) are often used as beam shaper in LED-based micro projection system to provide SLM with uniform and efficient illumination. In this paper, in order to overcome the disadvantage of insufficient compactness induced by the working length of TLP or SCPC for the illumination system, a total internal reflection (TIR) lens with rotated and faceted structure is designed with an optimization method to couple and transfer most of the light emitted from LED into a rectangular target plane (RTP) representing SLM. The TIR lens has six surfaces controlled by 17 dimensional parameters and is designed by optimization of dimensional parameters with generic algorithms. In order to provide RTP in fixed position with satisfied illumination uniformity and efficiency, the illumination uniformity and efficiency on RTP are taken into account in the merit function for the optimization process. In Tracepro program, the simulation result of the LED illumination system with the optimized TIR lens shows that the illumination efficiency and uniformity has respectively achieved to 61.9%, 76% with considering the limitation angle of light (15°).