A report on the status of astrophotonics for interferometry and beyond

TL;DR

This paper surveys the current status of astrophotonics as applied to interferometry and beyond, tracing a development flow from fabrication platforms to infrastructure interfaces and beam combiners. It highlights concrete demonstrators and on-sky tests—GRAVITY (ABCD IO), ULI-based DBC and nulling (GLINT), and FIRST remapping with on-chip phase control—while identifying challenges in mid-IR performance, long-baseline transport, and space-environment durability. The author emphasizes a rapidly growing, globally distributed community and the strategic importance of coordinated efforts, especially for the ELT era, including potential institutional frameworks to accelerate technology maturation. Overall, astrophotonics is positioned as a key enabler for compact, stable, and highly capable interferometric instruments, with significant implications for future ground- and space-based astronomy.

Abstract

Long-baseline interferometry and high-resolution spectroscopy are two examples of areas that have benefited from astrophotonics devices, but the application range is expanding to other subareas and other wavelength ranges. The VLTI has been one of the pioneering astronomical infrastructure to exploit the potential of astrophotonics instrumentation for high-angular resolution interferometric observations, whereas new opportunities will arise in the context of the future ELTs. In this contribution, I review the current state of the art regarding the interplay between photonic-based solutions and astronomical instrumentation and highlight the growth of the field, as well as its recognition in recent strategy surveys such as the Decadal. I will explain the benefits of different technological platforms making use of photolithography or laser-writing techniques. I will review the most recent results in the field covering simulations, laboratory characterization and on-sky prototyping. Astrophotonics may have a unique role to play in the forthcoming era of new ground-based astronomical facilities, and possibly in the field of space science.

Figures (13)

• Figure 1: An historical perspective to the synergy between instrumentation and observational astronomy, or how new technologies and fundamental discoveries go hand in hand. From Minardi, Harris & Labadie, 2021 Minardi2021 .
• Figure 2: Tentative visualization of the geographical repartition of research groups active in astrophotonics. The graph does not claim full exhaustivity. The color code attempts to coarsely identify the observing technique of main interest of the group, with black assigned to interferometry, green to high-resolution spectroscopy, and red to high-contrast imaging. I emphasize the limits of this approach since many institutions listed here may target several techniques. As an example, the University of Sydney has groups with recognized contributions in astrophotonics applications for both high-resolution spectroscopy and interferometry.
• Figure 3: Yield of the astrophotonics venue in 2022. The technique of high-contrast imaging involving the definition and development of phase masks is not shown here.
• Figure 4: A possible development flow for a photonic-based astronomical instrument.
• Figure 5: Plot giving in y the polarization contrast of an output field versus the angular direction of a linearly polarized input field, in degrees. The entrance polarizer placed before the fiber forces the angle of the input linear polarizer, while the exit analyzer measures the polarization state. A contrast of one indicates a linear polarization, a contrast of zero indicates a circular polarization. The measurement is done at 3.8 $\mu$m.