LINEWIDTH REDUCTION OF DSM LASERS DUE TO EFFECTS OF COMPOSITE CAVITY AND DISTRIBUTED REFLECTORS

Spectral properties of dynamic single-mode (DSM) lasers are theoretica lly analyzed in terms of the effects of composite cavity and distribut ed reflectors. We find unique reduction mechanisms of adiabatic chirp and linewidth in distributed reflector (DR) lasers and complex-coupled (CC) (i.e., gain + index-coupled) DSM lasers. Introducing convenient functions of effective length and detuning coefficient, these reductio n mechanisms are explained from the viewpoints of modal phase and moda l gain behaviors. For CC-DSM lasers, it is shown that the arrangement of index and gain corrugation, namely, anti-phase or in-phase combinat ion, will suppress or enhance an effective linewidth enhancement facto r alpha(eff), respectively. Numerical results show that DR structures are much superior in the spectral and single-mode properties to DFB an d DBR structures, both in index-coupled (IC) and CC lasers. By introdu cing gain coupling into the IC-DFB laser, alpha(eff) can be reduced to half the material alpha, and it will be further reduced by adopting t he CC-DR laser structure proposed here.