Coherence and spectral properties of composite-cavity semiconductor lasers

This thesis addresses many current issues in the theoretical and experimental aspects of coherence and spectral properties of semiconductor lasers. It begins with a brief overview of the theory of fluctuations in semiconductor lasers. This includes a study of relative intensity noise, frequency/phase noise, and frequency chirp. A method of spectral linewidth reduction and stabilization is then proposed and analyzed. This method utilizes an atomic resonance in cesium to which a semiconductor laser can be frequency locked. A Van der Pol analysis as well as a rate equation analysis are carried out and predict reductions in the spectral linewidth, frequency chirp, and enhanced frequency stability. Experimental results confirm several aspects of the theory and also introduce the effects of 1/f noise in semiconductor lasers. Spectral linewidth reductions by a factor of 2000 below the solitary laser linewidth are presented. Investigations are then made into the spectral characteristics of multielectrode distributed feedback (DFB) lasers. A novel measurement technique is introduced which utilizes the phase angle between the FM and AM responses for the determination of adiabatic chirp and linewidth enhancement factors. The mode switching properties of these devices are then studied within the context of bistable operation. Bistability in output power and output wavelength is shown and is applied to experiments in stochastic resonance. Using bistable DFB and Fabry-Perot semiconductor lasers, stochastic resonance is demonstrated experimentally in different laser systems as well as in electronic circuits. The effect is analyzed from a rate equation approach as well as a Kramer's escape approach. Results predict a noise suppression at higher even harmonic frequencies which are then experimentally verified