A simple model for the intensity noise of single mode class-A lasers

Single frequency class-A semiconductor (SC) lasers based on a long or a high-Q cavity configuration can be shot noise limited over a large spectral bandwidth. It results from adiabatic elimination of carriers leading to relaxation oscillation free operation. Nevertheless, some excess noise can be observed at the low frequencies and at multiples of the cavity free spectral range (FSR). Although the level of the excess noise in this type of lasers is low, its presence can be inconvenient for some stringent applications such as distribution of high purity radar signals. The optimization of the laser requires a quantitative prediction of its noise characteristics according to the cavity parameters. We propose, here, a simple model devoted to this purpose. The model predictions are compared with measurements performed on a class-A SC laser.