Analysis of PbSe claddings on BaF2 waveguides

Mode coupling between a dielectric waveguide and a semiconductor cladding has been investigated for a number of possible applications.1,2 In this paper, we present an analysis of the modes that propagate in a waveguide structure consisting of a IV-VI semiconductor cladding on a II-A fluoride insulator. The IV-VI semiconductors, commonly known as lead salts, are of interest for infrared detector use and because they can be grown as lattice-matched layers on II-A fluoride insulators. The structure analyzed consisted of an air cover layer, a lead selenide (PbSe) cladding, a barium fluoride (BaF2) guiding layer, and a calcium fluoride (CaF2) substrate. For a free-space wavelength of 3.4 μm and a BaF2 thickness of 5 μm, the mode index and attenuation constant were determined as functions of the PbSe thickness. From these data, we determined the mode set for the waveguide structure and examined the mode coupling that occurs between the BaF2 and the PbSe. Our results indicate that a significant amount of energy can be coupled into the PbSe cladding, suggesting that efficient integrated waveguide photodetectors and polarizers are feasible. Such devices would be suitable for use with optical fiber systems and optical integrated circuits operating in the 3-5-μm range. References