2023 Astrophotonics Roadmap: Pathways to Realizing Multi-Functional Integrated Astrophotonic Instruments

Photonic technologies offer numerous functionalities that can be used to realize astrophotonic
instruments. The most spectacular example to date is the ESO Gravity instrument at the Very Large
Telescope in Chile that combines the light-gathering power of four 8 m telescopes through a
complex photonic interferometer. Fully integrated astrophotonic devices stand to offer critical
advantages for instrument development, including extreme miniaturization when operating at the
diffraction-limit, as well as integration, superior thermal and mechanical stabilization owing to the
small footprint, and high replicability offering significant cost savings. Numerous astrophotonic
technologies have been developed to address shortcomings of conventional instruments to date,
including for example the development of photonic lanterns to convert from multimode inputs to
single mode outputs, complex aperiodic fiber Bragg gratings to filter OH emission from the
atmosphere, complex beam combiners to enable long baseline interferometry with for example,
ESO Gravity, and laser frequency combs for high precision spectral calibration of spectrometers.
Despite these successes, the facility implementation of photonic solutions in astronomical
instrumentation is currently limited because of (1) low throughputs from coupling to fibers,
coupling fibers to chips, propagation and bend losses, device losses, etc, (2) difficulties with scaling
to large channel count devices needed for large bandwidths and high resolutions, and (3) efficient
integration of photonics with detectors, to name a few. In this roadmap, we identify 24 key areas
that need further development. We outline the challenges and advances needed across those areas
covering design tools, simulation capabilities, fabrication processes, the need for entirely new
components, integration and hybridization and the characterization of devices. To realize these
advances the astrophotonics community will have to work cooperatively with industrial partners
who have more advanced manufacturing capabilities. With the advances described herein,
multi-functional integrated instruments will be realized leading to novel observing capabilities for
both ground and space based platforms, enabling new scientific studies and discoveries.