Hiroshi MURATA^1*, Katsuya SHIBASAKI¹, Kazuhisa YAMAMOTO², and Yasuyuki OKAMURA¹

¹Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan
²Photon Pioneers Center, Osaka University, Suita, Osaka 565-0871, Japan

(Received July 1, 2013; Accepted October 2, 2013)

Speckle contrast of images generated by a red semiconductor laser was measured precisely utilizing a state-of-the-art speckle measurement system with a cooled CCD camera with auto-light-power-level adjustments. By using high-frequency signal (∼500 MHz) superposition to the single-mode semiconductor laser, the 3 dB spectrum of the laser beam was broadened from 0.1 to 2.3 nm. As a result, the speckle contrast value was drastically reduced from 0.9 to 0.2.

Key words: speckle noise, laser display, semiconductor laser, relaxation oscillation, optical modulation

^*E-mail address: murata@ee.es.osaka-u.ac.jp