Fast and Slow Light in a Phase-Sensitive Optical Amplifier

Phase-sensitive optical amplifiers (PSAs) have the ability to noiselessly amplify and deamplify signals and thus have great potential in both classical and quantum communication. Here we construct a PSA using a double-lambda four-wave mixing scheme on the D1 line of rubidium in a warm vapor cell. An intensity-modulated beam is used as an input to the optical amplifier and the gain and delay of the output is measured. It is found that when the sidebands of the signal are unbalanced the signal develops an apparent advance or delay, similar to fast- and slow-light phenomena. The difference, however, is that the advance or delay depends on the relative phase of all three beams contributing to the four-wave mixing process rather than the optical frequency. It was found that the sidebands of the signal can be systematically imbalanced via misalignment to an optical fiber after the acousto-optic modulator used to modulate the beam. The advance and delay for several different sideband imbalances was measured and found to be consistent with a model of an ideal PSA.