semiconductor waveguide facet reflectivity problem

The problem of the facet reflectivity of a semiconductor slab waveguide is reexamined as an extension of Ikegami's original approach but which includes radiation-like modes. The latter are included, using a guide-within-a-guide geometry, as modes bound to a thick air-cladding guide which contains the core profile of interest. In this model with a relatively simple analysis, the coupleing from the foundamental mode to radiation modes can be analyzed. The cross-coupling to the radiation modes is considered in detail for the simple double heterostructure waveguide and is shown to be important only for large core-caldding index differences and for strong modal confinement where it results in the true facet loss. The conditions for this are the same as for low threshhold lasers so that the loss sets a maximum limit on the equivalnet internal quantum efficiency. A separate one-dimensional finite element, numerical mode matching program, which treats evanescent and propagating radiation modes, is used as a comparison. The two methods of accounting for radiation modes are shown to be in good agreement: both predict reduced extremes in reflectivity when compared with the original Ikegami modal. Modern graded core cases are treated as general examples along with the specific quantum well laser structures taken from the literature. These include II-VI and III-V structures spanning wavelengths from 0.5(mu-meters) to 10.0(mu-meters).