Abstract

The use of passive integrated optics for astronomy has a long history, in particular at near-infrared wavelengths with the highly successful VLTI/GRAVITY instrument [1] built around a four-telescope silica-based beam combiner core unit. The clear instrumental advantages of photonic-based interferometric beam combiners have motivated the extension of the technology towards mid-infrared wavelengths in the last decade, which has been pursued with increasing success by different groups [2,3,4]. These laboratory-based results are now materializing in the development of the new instrument NOTT/ASGARD, the first long-baseline self-calibrating nulling instrument at the VLTI (Paranal, Chile) operating in a mid-infrared astronomical band. It will be the first nuller to directly resolve the snow line, which is where most giant exoplanets may form. Their surface temperature makes them more efficiently observable in the astronomical L' band [5]. A key component of the instrument is a compact integrated optics beam combiner based on the “Double Bracewell” architecture, which implements nulling interferometry [6].

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