Developing arrayed waveguide grating spectrographs for multi-object astronomical spectroscopy

TL;DR

This paper demonstrates modifications to arrayed waveguide grating spectrographs that significantly improve spectral resolution and multiplexing capability for astronomical multi-object spectroscopy.

Contribution

It introduces specific chip modifications, such as removing the taper, to enhance resolution and enable simultaneous multi-fiber injection in astronomical spectrographs.

Findings

Spectral resolution increased threefold to 7000 ± 700.

Throughput maintained at approximately 77%.

Simultaneous injection of ~12 fibers achieved within the device's spectral range.

Abstract

With the aim of utilizing arrayed waveguide gratings for multi-object spectroscopy in the field of astronomy, we outline several ways in which standard telecommunications grade chips should be modified. In particular, by removing the parabolic-horn taper or multimode interference coupler, and injecting with an optical fiber directly, the resolving power was increased threefold from 2400 \pm 200 (spectral resolution of 0.63 \pm 0.2 nm) to 7000 \pm 700 (0.22 \pm 0.02 nm) while attaining a throughput of 77 \pm 5%. More importantly, the removal of the taper enabled simultaneous off-axis injection from multiple fibers, significantly increasing the number of spectra that can be obtained at once (i.e. the observing efficiency). Here we report that ~ 12 fibers can be injected simultaneously within the free spectral range of our device, with a 20% reduction in resolving power for fibers placed at 0.8 mm off centre.