Mid-infrared nulling interferometry beam combiners using asymmetric directional couplers

We demonstrate reproducible asymmetric directional couplers in gallium-lanthanum-sulfide (GLS) chalcogenide glass, using ultrafast laser inscription (ULI). This enables on-chip high-contrast nulling interferometry in the mid-infrared, specifically aimed at detecting giant exoplanets in the astronomical L ′ band (3.5−4.0 μm). By leveraging a classical two-telescope integrated optics beam combination scheme and conducting characterization in a laboratory environment, we demonstrate an extinction ratio of ∼10 −2 across 3.65−3.85 μm.