Observation of anticorrelated modal noise in a quasi-single-mode laser diode with a Michelson interferometer

Abstract

The light emitted by a quasi-single-mode free-running laser diode is sent through a Michelson interferometer, and the intensity noise of the outgoing light is studied with respect to the path difference between the two arms of the interferometer. The level of this noise is determined by very strong anticorrelations between the main mode and the many very weak, but noisy, longitudinal side modes. The different interference patterns of these various modes can modify the noise compensation effect, leading to a large excess noise. Phase-noise effects also come into the picture, since a Michelson interferometer tuned around a nonzero path difference is a dispersive element capable of converting phase noise into intensity noise. The observed data is in good agreement with a phenomenological model that attributes phase noise and correlated intensity noises to all the modes. The parameters of this model can be inferred from the experimental data.