This thesis is a theoretical and experimental investigation of monolithic linewidth reduction in multiple section distributed-feedback (DFB) lasers and of phase-to-intensity conversion noise due to Rayleigh scattering in optical fiber links. In the first part, the physics of semiconductor laser dynamics and noise is reviewed. A Van der Pol noise analysis of laser amplitude and phase fluctuations is conducted. Linewidth reduction in lasers with intra-cavity dispersive medium is analyzed. The semiconductor laser subjected to an external optical feedback is studied by treating the feedback as a part of facet complex reflectivity.
In the second part, a theoretical study of three section semiconductor DFB lasers is presented. The result shows that under proper pumping and biasing conditions one section lases while the other provide the necessary dispersive optical feedback for noise suppression and, hence, linewidth reduction. The benefits of having such optical feedback on modulation responses is also demonstrated.
An experimental study of three section semiconductor DFB lasers is presented in the third part. Processing and standard testing procedures of the multiple section DFB laser is described. Subsequently the scanning Fabry-Perot, optical spectrum analyzer, and the delayed-self-heterodyne method are used for the measurements.The experimental results demonstrate a moderate reduction in laser linewidth.
In the fourth part, a complete statistical theory, including the effect of random fiber index inhomogeneities, of conversion of fundamental phase fluctuation at semiconductor laser output to intensity noise in long haul optical fiber links due to Rayleigh scattering is developed. Three generic cases are considered.
In part five, a detailed experimental study of Rayleigh induced intensity fluctuations is presented. Comparison between the theoretically predicted and experimentally measured values shows very good agreement.
The impact of Rayleigh scattering on fiber links with periodic optical amplification is considered. The result shows linear accumulation of intensity noise due to Rayleigh scattering. To prevent a quadratic accumulation of the Rayleigh scattering induced intensity noise, optical isolators in very long haul fiber links are required. A reduction scheme of phase-to-intensity conversion noise by phase modulation is subsequentlystudied.
