Noise measurements in two-beam interferometers excited by semiconductor lasers with non-Lorentzian line shapes

An experimental study of phase-induced intensity noise is presented for the case of a Mach-Zehnder interferometer driven by a non-Lorentzian line shape semiconductor laser. The important scales of the noise spectrum in the coherent regime are shown to be related not only to the interferometer differential delay but also to the relaxation-oscillation frequency. It is shown that the periodic nulls in the noise spectrum from a two-beam interferometer locked in quadrature can be washed out at frequencies near the relaxation oscillations of the semiconductor laser. However, when the relaxation-oscillation frequency far exceeds 1/(interferometer differential delay), the classical deep notch at 1/(interferometer differential delay) is recovered and can be used to improve the system signal-to-noise ratio