Influence of carrier nonuniformity on the phase relationship between frequency and intensity modulation in semiconductor lasers

The modulus and phase of the chirp to modulated power ratio (CPR) was measured for a 1.5- mu m buried-heterostructure laser and a 0.85- mu m channeled-substrate planar (CSP) laser. The results for the phase are inconsistent with previously published expressions including spontaneous emission and spectral hole burning. In particular, the CSP laser exhibits an abrupt phase shift in the CPR. An explanation of this behavior is presented in terms of the influence of a nonuniform carrier density on the phase-amplitude coupling, as expressed by an integral expression for the mode parameter alpha representing the linewidth enhancement factor. Using a simple model for lateral behavior which analytically incorporates diffusion and a nonuniform material alpha parameter, qualitative agreement was obtained with the CSO data. The authors demonstrate the importance of the lateral laser structure on the phase-amplitude coupling in index-guided semiconductor lasers, and the usefulness of CPR phase measurements for laser characterization.< >