Optical properties of epitaxial LaF3/SrF2/GaAs(111) heterostructure waveguides fabricated by molecular beam epitaxy

Thin film slab waveguides of lanthanum fluoride clad with strontium fluoride grown epitaxially on GaAs (111) are characterized by optical and structural techniques. Crystallinity, surface roughness, refractive indexes and propagation loss measurements suggest that these structures show promise for monolithically integrated infrared (IR) pumped IR down-conversion and visible upconversion laser devices. Propagation losses as low as 3.7 dB/cm at 633 nm were measured in samples which show waveguide propagation over distances of several centimeters. Simulation of the scattering losses due to surface roughness provides an approximate delineation of surface and nonsurface contributions to the optical loss. Typical root-mean-square surface roughness of the lanthanum fluoride layer was on the order of 3 nm. The morphology appears to be dominated by grain boundaries