STUDY OF LASER SPECKLE REDUCTION FOR LASER DISPLAY APPLICATIONS

Abstract

Laser-based projection displays have been under active development over last few years. Lasers are considered as the next generation light sources for projection due to advantages including wide color gamut, high brightness, long lifetime and high electric-optic efficiency. However, speckle phenomenon caused by the coherence of lasers can greatly influence the quality of projected images. A cost effective, easy setup and robust speckle reduction system for laser projection is still very challenging. The aim of this thesis is to investigate practical speckle reduction solutions for laser projection system. The system is divided into different modules and for each module, speckle reduction methods are studied. The study includes a low speckle laser source, an optical engine with integrated speckle reduction methods and a low speckle engineered screen. A standard speckle measurement system corresponding to human perception is also presented. For low speckle laser source, a theoretical model that describes wavelength diversity in speckle reduction is established. The speckle contrast ratio (SCR) of the system can be simulated. The result is experimentally verified. Guidelines for optimized wavelength/power selection for lasers to generate reduced speckle are proposed. After this, a low cost, high compact and high-efficiency speckle reduction optical system using an electric elastomer actuator is studied. Both theoretical analysis and experimental work are presented and a SCR as low as 3.7% was achieved. Besides these two parts, an engineered screen that utilizes micro lens array (MLA) which can greatly reduce speckle is studied. A comprehensive theoretical model was established for the simulation and optimization of MLA in speckle reduction. The simulated results agree well with reported values. Guidelines in MLA selection for laser projection are presented. In the last part, a standard measurement setup of speckle in a laser projection system that matches the human perception is studied. Conditions including camera F/#, focal length, integration time and measuring geometry are discussed and suitable setups are proposed.