Efficient suppression of diode-laser phase noise by optical filtering

Abstract

We show that the excess phase noise of an amplified diode laser can be efficiently suppressed by double passage through a high-finesse cavity. The cavity transmits 18% of the injected optical power in double pass and reduces the power spectral density of excess phase noise at 1 MHz by 85 dB. If the filtered light is homodyned with a coherent state of light on a 50–50 beam splitter, the intensity noise of the emerging field in one port cannot exceed the shot-noise level by more than 0.022 dB at 1 MHz for 1 mW of optical power. This level of noise suppression may allow diode lasers to be used in phase-noise-sensitive experiments.