Modal reflectivity of uptapered, tilted-facet, and antireflection-coated diode-laser amplifiers

A numerical analysis of the modal reflectivity of tilted-facet laser-diode amplifiers is presented. It is shown that, with slightly angled facets, a large reduction of the reflectivity in a monomode diode should be achievable for TE and TM modes simultaneously either by applying a single-layer antireflection coating and optimizing the thickness and the width of the diode waveguide or by adiabatically uptapering the waveguide ends. A further significant reduction can be obtained by combining an antireflection coating with an uptapered waveguide. The characteristics of the dependence of the reflectivity on tilt angle and waveguide width and thickness are explained in terms of spectral overlaps between incident and reflected modes. The characteristic minima of the reflectivity are attributed to the oscillatory behavior of the spectra.