Abstract
Pico projector is expected to be an ideal solution for mobile device because it can provide large display size with small device volume down to below 5c.c. However, the efficiency is so far the major hurdle for commercialization, especially for mobile devices where power budget is limited. There are three major types of architecture for pico projector, LCoS, DLP and MEMS scanning mirror, among them the efficiency of MEMS type is the highest due to its energy being consumed only when needed. The work in this thesis focuses on the laser beam quality, including the shape and energy distribution profile of the beam spot, and the tolerance issue which is relevant to the spatial convergence of three color image components. The quality of all these parameters will be reflected on the scanned image performance. The approach to improve the beam quality from diode laser is to use refractive/diffractive hybrid optical component, where the refractive surface performs collimation and the diffractive one for beam shaping. The target is to make a square beam spot with top hat energy distribution at a distance of 70cm from the projector. The refractive collimating lens has been designed and simulated with LightTools, whereas the binary phase type diffractive beam shaper has been optimized with iterative Fourier transform algorithm (IFTA) written in MATLAB program. The measured energy distribution and beam shape from a red diode laser was used in both designs. The collimation lens element has been made and tested, and the result shows good match between simulated and measured beam spot. The binary beam shaper with four phase level has been checked with simulation based on scalar diffraction theory, and the result shows a clearly visible square shape, leaving the uniformity to be improved. Because the tolerance of single element for beam collimation and shaping is as tight as 0.99 um, a two lens module with an air gap in between has been proposed for making the solution more practical. The tolerance analysis shows that the tolerance for lens assembly increases to 1.27 um for the positive plus negative lens combination and 1.79 um for the two positive lens combination.