EFFECTS OF HOLE BURNING, CARRIER-INDUCED LOSSES AND THE CARRIER-DEPENDENT DIFFERENTIAL GAIN ON THE STATIC CHARACTERISTICS OF DFB LASERS

A model solving the steady-state laser equations above threshold is presented. It calculates important laser parameters such as the threshold losses, emitted optical power, gain margin between the main and secondary modes and spectral linewidth of any index-grating DFB laser structure. A more exact theoretical linewidth calculation considering nonuniform carrier densities and gain saturation is reported. Good agreement with experiments is found on phase-shifted lasers. The model is used to investigate the factors that determine the importance of spatial hole burning and propose general design rules to reduce this effect. Gain compression combined with carrier-dependent losses is shown to limit the differential external efficiency and cause the emission wavelength to decrease and the spectral linewidth to rebroaden at high output power. Adding carrier-dependent compression factor and differential gain results in a linewidth saturation at moderate powers, comparable to experimental values.