Speckle Noise Evaluation and Reduction of an Edge-Lit Backlight System Utilizing Laser Diodes and an Optical Fiber

Laser diodes allow one to build a very thin, wide-gamut edge-lit backlight system for a direct-view liquid crystal display. An optical fiber is used to transfer its optical power into a light-guide. An ultrasound transmitter attached to the optical fiber is effective for reducing speckle noise because the mechanical vibration introduced averages out the random interference patterns. In experiment, we built a backlight system with a green laser and evaluated speckle noise by taking photographs under the conditions that mimicked human observation. The speckle contrast intrinsic to the laser was reduced from 17% to 2% by turning on the ultrasound transmitter.