Abstract
This paper reports the characterization of hollow metallic waveguides (HMW) to be used as single-mode wavefront filters for nulling interferometry in the 6-20microm range. The measurements presented here were performed using both single-mode and multimode conductive waveguides at 10.6microm. We found propagation losses of about 16dB/mm, which are mainly due to the theoretical skin effect absorption in addition to the roughness of the waveguide's metallic walls. The input and output coupling efficiency of our samples has been improved by adding tapers to minimize the impedance mismatch. A proper distinction between propagation losses and coupling losses is presented. Despite their elevate propagation losses, HMW show excellent spatial filtering capabilities in a spectral range where photonics technologies are only emerging.
Highlights
In the context of the search for new extrasolar systems, the direct detection of Earth-like planets around main sequence stars is facing serious constraints both in terms of angular resolution (< 0.1 arcsec) and brightness contrast (>106) between the star and the planetary companion
This paper reports the characterization of hollow metallic waveguides (HMW) to be used as single-mode wavefront filters for nulling interferometry in the 6-20μm range
We presented in this paper the characterization at λ=10.6μm of conductive waveguides with different geometries, including channel waveguides, bent waveguides and beam splitters
Summary
In the context of the search for new extrasolar systems, the direct detection of Earth-like planets around main sequence stars is facing serious constraints both in terms of angular resolution (< 0.1 arcsec) and brightness contrast (>106) between the star and the planetary companion. Nulling interferometry [1] is a coronographic technique at very high angular resolution, adapted to the search and characterization of extrasolar planets in the mid-infrared range (6-20μm), where the relative Earth/Sun contrast is more favorable. As in classical co-axial stellar interferometer, the rejection ratio of a nuller can be sensitively degraded by the effect of low-order and high-order wavefront errors, which can be efficiently filtered out by mean of single-mode optical waveguides [3]. In addition to their filtering properties, single mode waveguides can be integrated in stable, light and compact optical chips to ensure more complex functions like multiple beams combination [4].
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