Modal Filtering for Nulling Interferometry-First Single-Mode Conductive   Waveguides in the Mid-Infrared
  This paper presents the work achieved for the manufacturing and characterization of first single-mode waveguides to be used as modal filters for nulling interferometry in the mid-infrared range [4-20 um]. As very high dynamic range is mandatory for detection of Earth-like planets, modal filtering is one of the most stringent instrumental aspects. The hollow metallic waveguides (HMW) presented here are manufactured using micro-machining techniques. Single-mode behavior has been investigated in laboratory through a technique of polarization analysis while transmission features have been measured using flux relative comparison. The single-mode behavior have been assessed at lambda=10.6 um for rectangular waveguides with dimensions a=10 um and b<5.3 um with an accuracy of ~2.5 %. The tests have shown that a single-polarization state can be maintained in the waveguide. A comparison with results on multi-mode HMW is proposed. Excess losses of 2.4 dB (~ 58 % transmission) have been measured for a single-mode waveguide. In particular, the importance of coupling conditions into the waveguide is emphasized here. The goal of manufacturing and characterizing the first single-mode HMW for the mid-infrared has been achieved. This opens the road to the use of integrated optics for interferometry in the mentioned spectral range. 
L. Labadie, P. Labeye, P. Kern, I. Schanen, B. Arezki, J.-E. Broquin