Abstract

For a single-mode laser it is generally believed that far above threshold the detected noise level is determined by the pump noise if the quantum efficiency of conversion from pump excitation quantum to detected photons is close to unity [1]. This allows the generation of sub-shotnoise light by operating a semiconductor laser far above threshold with a quiet pump. We have found, however, that weak nonorthogonality of the cavity eigenmodes can add significant Petermann excess noise. This seriously impedes intensity noise squeezing even for an effectively single mode laser, i.e. a laser in which the intensity noise of the lasing mode is equal to the intensity noise of the total light output. The crucial point is that nonorthogonality leads to effects in the intensity noise in first order of the non-lasing mode amplitudes, in contrast to the usually considered second-order multi-mode effects (see [1] for a review).

© 2000 IEEE