Fabrication of far infrared rib waveguides based on Te-Ge-Ga films deposited by co-thermal evaporation

In the present paper we focus on the fabrication of rib waveguides being able to work in the large infrared window [6-20 mu m], compatible with the Darwin mission requirements. The rib waveguides to be realized are based on etched thick films of telluride materials deposited on telluride glass. The choice of the Te75Ge15Ga10 material as the substrate is justified by its excellent transmission in the infrared region and its thermal stability. Films of the ternary system made of Te, Ge and Ga were investigated as the core layer and the superstrate. Details are provided on the film deposition and etching technologies: (i) Te-Ge-Ga films are prepared by co-thermal evaporation from the pure elements Te, Ge and Ga; (ii) the geometry of the as-obtained films is modified by reactive ion etching under an atmosphere of CHF3 + O-2 or CH4 + H-2. First results concerning Te-Ge binary films are particularly interesting.