2023 Astrophotonics Roadmap: pathways to realizing multi-functional integrated astrophotonic instruments

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 offer critical advantages for instrument development, including extreme miniaturization when operating at the diffraction-limit, plus 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 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, beam combiners enabling 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. In this roadmap, we identify 23 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.

Laboratory demonstration of a Photonic Lantern Nuller in monochromatic and broadband light

“…Therefore, more work should be invested in creating MSPLs with lower levels of cross-talk, as this would result in deeper, naturally broadband nulls that would relieve additional demand on the wavefront control system. 18 Lastly, although the lantern we use in this work is optimized for 1550 nm, silica-based mode-selective lanterns can be designed to operate at different wavelengths, ranging from the visible spectrum up to about 2 um. However, other fiber technologies 19 would be needed to access wavelengths outside of this range.…”

Real-time Experimental Demonstrations of a Photonic Lantern Wave-front Sensor

“…Importantly, when used to couple the aberrated telescope beam in the focal plane, PLs already have utility in several high-contrast imaging applications, including spectro-imaging and starlight nulling. PLs are also uniquely suited to couple aberrated telescope light into highly stable diffraction-limited spectrometers (Lin et al 2021), enabling direct exoplanet spectroscopy, and can serve as a gateway into a wider ecosystem of astrophotonic devices such as arrayed waveguide gratings and photonic integrated circuits (Jovanovic et al 2023). Simultaneously, low-spatial-frequency aberrations such as NCPAs and LWE modes can be sensed in the true science focal plane by monitoring the fluxes of the lantern's outputs.…”