Broadband mid-infrared directional and multimode interference couplers in GLS glass fabricated using femtosecond laser direct-writing

Understanding how solar systems form and determining how unique Earth is within the Universe are some of modern astronomy's biggest quests. To date, the majority of exoplanets have been discovered using indirect techniques. Unlike indirect techniques, direct imaging separates the light from the host star and orbiting planet, enabling measurement of an exoplanet's composition for instance. Yet, direct imaging is challenging due to the small angular separation between the objects and the overwhelming glare of the host star compared to the dim planet. A powerful technique that can provide high angular resolution and contrast is nulling interferometry [1]. Astronomical interferometry has tremendously benefited from using photonic technologies developed for telecommunication, such as optical fibres and integrated photonics to provide spatial filtering of the stellar light for improved interferometric contrast as well as robustness to environmental influences [2]. However, telecommunication technology is not compatible with the mid-infrared, a spectral region of particular interest for detecting young exoplanets.