All-telluride waveguides for nulling interferometry in the 6–20 µm spectral range: Fabrication and testing

The feasibility of two types of all-telluride integrated optics devices being able to single-mode guiding of light in the spectral ranges [6 - 11 μm] and [10 - 20 μm], respectively, is demonstrated. The so-called rib waveguides show a several micron thick Te₈₂Ge₁₈ film deposited onto a Te₇₅Ge₁₅Ga₁₀ bulk glass substrate by thermal co-evaporation and further etched by reactive ion etching in CHF₃/O₂/Ar atmosphere. First, the slab waveguides obtained before etching were highlighted to transmit light in the whole spectral range, from 6 to 20 μm. The etched structures were then proved to behave as channel waveguides with a satisfactory confinement of light. To end, optical losses of about 4 dB·cm^-1 and modal filtering with a light rejection efficiency of 6.10^-5 were obtained on a very first sample of the [6 - 11 μm] type. These results allowed validating our technological solution for the fabrication of micro-components for spatial interferometry.