  Photonics 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. Integrated
astrophotonic devices stand to offer critical advantages for instrument
development, including extreme miniaturization, as well as integration,
superior thermal and mechanical stabilization owing to the small footprint, and
high replicability offering cost savings. Numerous astrophotonic technologies
have been developed to address shortcomings of conventional instruments to
date, including for example the development of photonic lanterns, complex
aperiodic fiber Bragg gratings, complex beam combiners to enable long baseline
interferometry, 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 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 instruments will be realized leading to novel observing
capabilities for both ground and space platforms.
