Amplitude noise enhancement caused by nonlinear interaction of spontaneous emission field in laser diodes

The amplitude noise spectrum of the total laser output of a nearly single-mode laser diode is enhanced at low frequencies due to the nonlinear interaction between the spontaneous photons and the coherent laser field. This enhancement strongly depends on the spontaneous emission rate, resulting in a dependence of the amplitude noise spectral shape on the spontaneous emission rate. A linearized analytical model which predicts that the amplitude noise spectral shape is independent of the spontaneous emission rate is inadequate. The experimental data are consistent with a numerical simulation of the full nonlinear model.