Astrophotonic micro-spectrographs in the era of ELTs

TL;DR

This paper reviews the development of astrophotonic micro-spectrographs for Extremely Large Telescopes, highlighting current technologies, performance comparisons, and future needs for multimode devices to enhance throughput and reduce complexity.

Contribution

It provides an inventory of current integrated micro-spectrograph technologies and compares their performance, emphasizing the potential of photonic lanterns and the need for multimode solutions.

Findings

Photonic lanterns enable single-mode spectrograph performance.

Multimode devices are essential for improved throughput and sensitivity.

Integrated micro-spectrographs can reduce instrument size and complexity.

Abstract

The next generation of Extremely Large Telescopes (ELT), with diameters up to 39 meters, will start opera- tion in the next decade and promises new challenges in the development of instruments. The growing field of astrophotonics (the use of photonic technologies in astronomy) can partly solve this problem by allowing mass production of fully integrated and robust instruments combining various optical functions, with the potential to reduce the size, complexity and cost of instruments. In this paper, we focus on developments in integrated micro-spectrographs and their potential for ELTs. We take an inventory of the identified technologies currently in development, and compare the performance of the different concepts. We show that in the current context of single-mode instruments, integrated spectrographs making use of, e.g., a photonic lantern can be a solution to reach the desired performance. However, in the longer term, there is a clear need to develop multimode devices to improve overall the throughput and sensitivity, while decreasing the instrument complexity.