Speckle Reduction by Optimized Multimode Fiber Combined With Dielectric Elastomer Actuator and Lightpipe Homogenizer

Speckle, due to the interference of coherent light having random phases, can seriously degrade image quality in a laser based projection system. The speckle is even worse when the diode pumped solid state (DPSS) lasers are used as light sources since the laser linewidth from the DPSS lasers is usually very narrow. In this paper, a de-speckle system consisting of a multimode fiber (MMF), a dielectric elastomer actuator (DEA) and a lightpipe is proposed and demonstrated, which can reduce speckle significantly. The speckle reduction components used in the system are optimized, taking into account speckle reduction ability and optical efficiency. The proposed de-speckle system is low in cost and easy to set up. It features a low optical power penalty and is compatible with large venue laser projection for applications such as digital cinema. In the proposed de-speckle system, test images captured by a camera with a setup following the recently proposed speckle measurement standard can achieve a speckle contrast ratio as low as 4.7%. By adding a voice coil motor (VCM) to vibrate the MMF to generate temporal diversity, the speckle contrast ratio can be further reduced to 3.7%.