2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments
Authors: Jovanovic Nemanja , Gatkine Pradip , Anugu Narsireddy , Amezcua-Correa Rodrigo , Basu Thakur Ritoban , Beichman Charles , Bender Chad F. , Berger Jean-Philippe , Bigioli Azzurra , Bland-Hawthorn Joss , Bourdarot Guillaume , Bradford Charles M , Broeke Ronald , Bryant Julia , Bundy Kevin , Cheriton Ross , Cvetojevic Nick , Diab Momen , Diddams Scott A , Dinkelaker Aline N , Duis Jeroen , Eikenberry Stephen , Ellis Simon , Endo Akira , Figer Donald F , Fitzgerald Michael P. , Gris-Sanchez Itandehui , Gross Simon , Grossard Ludovic , Guyon Olivier , Haffert Sebastiaan Y , Halverson Samuel , Harris Robert J , He Jinping , Herr Tobias , Hottinger Philipp , Huby Elsa , Ireland Michael , Jenson-Clem Rebecca , Jewell Jeffrey , Jocou Laurent , Kraus Stefan , Labadie Lucas , Lacour Sylvestre , Laugier Romain , Ławniczuk Katarzyna , Lin Jonathan , Leifer Stephanie , Leon-Saval Sergio , Martin Guillermo , Martinache Frantz , Martinod Marc-Antoine , Mazin Benjamin A , Minardi Stefano , Monnier John D , Moreira Reinan , Mourard Denis , Nayak Abani Shankar , Norris Barnaby , Obrzud Ewelina , Perraut Karine , Reynaud François , Sallum Steph , Schiminovich David , Schwab Christian , Serbayn Eugene , Soliman Sherif , Stoll Andreas , Tang Liang , Tuthill Peter , Vahala Kerry , Vasisht Gautam , Veilleux Sylvain , Walter Alexander B , Wollack Edward J , Xin Yinzi , Yang Zongyin , Yerolatsitis Stephanos , Zhang Yang , Zou Chang-Ling 
Published: July 2023

Abstract
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.