Transmission behaviors of single mode hollow metallic waveguides dedicated to mid-infrared nulling interferometry

TL;DR

This study characterizes hollow metallic waveguides for mid-infrared nulling interferometry, highlighting their propagation losses and spatial filtering capabilities despite high attenuation.

Contribution

It provides the first detailed measurements of propagation and coupling losses in hollow metallic waveguides in the mid-infrared range.

Findings

Propagation losses of about 16dB/mm due to skin effect and roughness.

Improved coupling efficiency with added tapers.

HMW exhibit excellent spatial filtering despite high losses.

Abstract

This paper reports the characterization of hollow metallic waveguides (HMW) to be used as single-mode wavefront filters for nulling interferometry in the 6-20 microns range. The measurements presented here were performed using both single-mode and multimode conductive waveguides at 10.6 microns. 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 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.