Buried channel waveguides for nulling interferometry in 6–20 μm spectral range: Fabrication and preliminary testing

One of the technological challenges of direct observation of extra-solar planets remains to develop a modal filter operating from 6 to 20 μm. In the present paper we present one of the two candidate technologies for the fabrication of such modal filters, together with Fiber Optics: Integrated Optics. The solution based on alltelluride buried channel waveguides was considered. In the so-called waveguides, the vertical confinement of the light is achieved in a higher-index core layer consisting in a 15 μm-thick Ge₁₇Te₈₃ film which is deposited onto a lower-index Te₇₅Ge₁₅Ga₁₀ substrate, and further covered by a lower-index superstrate consisting in a 15 μm-thick Ge₂₄Te₇₆ film. Concerning the horizontal confinement of the light, it is obtained by etching the core layer. As this stage, the all-telluride buried channel waveguides are proved to transmit light from 2 to 5 μm and to behave as channel waveguides with a satisfactory confinement of the light. It confirms the validity of the technology and the good quality of the input and output facets. Tests between 6 and 20 μm are being performed and will allow giving a confirmation of the potential of Te-based integrated optics components for nulling interferometry.