Abstract

Optical modulators typically transmit some amount of optical carrier power along with the imposed sidebands. Phase modulators do so inherently, yet intensity modulators in practice also transmit carrier at a typical level of -30 dB below the input power. Acoustooptic modulators are nominally single sideband, yet typically -50 dB of the carrier power leaks into the output. Optical carrier energy is often unwanted, especially in certain optical communications and signal processing applications. Our own work involves the optical processing of communications signals from an active antenna array in which the presence of an optical carrier introduces undesired spurious signal correlations. Suppression of an optical carrier from a RF modulated laser beam of wavelength 532 nm is performed using two-beam coupling in photorefractive barium titanate. A theoretical analysis reveals that perfect suppression can be achieved at specific modulation strength, which depends on the gain and intensity ratio between the two beams. The experiments achieve a maximum of -72.9±2.4 dB carrier suppression at the theoretically ideal modulation strength, and -61.0±2.4 dB for small modulation strengths. The results are better than and comparable to, respectively, the highest reported measurements of which we are aware.

© 2001 Optical Society of America