PHASE AND GROUP INDEXES FOR DOUBLE HETEROSTRUCTURE LASERS

Various models for calculation of refractive indices in semiconductor laser materials are discussed and the results for GaInAsP compounds are compared. It is shown that the modified single-oscillator model appears to be the most reliable. The group index is also considered since it can be found easily from measurements of laser spectra. The value of the group index is more model sensitive than the refractive index, but it is also a function of the active-layer thickness in double heterostructures as a consequence of waveguide dispersion. A simple formula connecting group and phase indices for a symmetrical dielectric slab waveguide is derived and used to calculate the effective group index for double-heterostructure lasers.