Characterization of Astrophotonic Components with the CHara ARray Integrated Optics Testbench (CHARIOT)

Photonic components play an important role in the development of astronomical instruments, both to increase the capabilities of instruments at existing telescope facilities and for the next generation of extremely large (30-m class) telescopes. These chip- and fiber-based astrophotonic components [1] can reduce the footprint of instruments as well as their sensitivity to undesired environmental changes. Stellar interferometry has particularly benefited from photonic developments. Here, information about the astronomical source can be extracted from interferometric signals obtained by overlapping light from different telescopes. Photonic beam combiners can overlap multiple beams within a cm-scale device, drastically reducing the required space compared to using bulk optics. In addition, the single-mode waveguides provide spatial filtering, which increases measurement precision. Photolithography-based photonic beam combiners have been successfully used in instruments (e.g. GRAVITY at VLTI), but developments in ultrafast laser inscription (ULI)-based beam combiners are still ongoing. These are currently at technology readiness level (TRL) 3. Due to low photon flux, these photonic components are required to have high throughput, uniform wavelength response, polarisation insensitivity, with operation over a broad wavelength range (several 100 nm). Performance has to be tested in the laboratory, followed by validation on the telescope (TRL 5).