Theoretical Analysis of the Optical Feedback Noise Based on Multimode Model of Semiconductor Lasers

An improved theoretical model to analyze the dynamics and operation of semiconductor lasers under optical feedback has been presented in this paper. A set of rate equations are formulated, in which the self and mutual gain saturation effects among lasing modes, reinjection of delayed feedback light reflected at the surface of the connecting optical device, and Langevin noise sources for the intensity and phase fluctuations are taken into account. The proposed model is applied to 850-nm GaAs lasers operating under optical feedback. The rate equations are calculated by tracing time variation, and frequency spectra of intensity noise are determined with the help of the fast Fourier transform. In this paper, numerical simulations based on our theoretical model confirmed that the feedback noise is classified into two types based on profiles of the frequency spectrum, where one is the low-frequency type and another is the flat type. These properties are in good agreement with those previously obtained in the experimental measurements. This evidence of agreement between experimental results and numerical simulations supports the accuracy of our model.