Development of an integrated near-IR astrophotonic spectrograph

Abstract

Here, we present an astrophotonic spectrograph in the near-IR H-band (1.45 -1.65 μm) and a spectral resolution (λ/δλ) of 1500. The main dispersing element of the spectrograph is a photonic chip based on Arrayed-Waveguide- Grating technology. The 1D spectrum produced on the focal plane of the AWG contains overlapping spectral orders, each spanning a 10 nm band in wavelength. These spectral orders are cross-dispersed in the perpendicular direction using a cross-dispersion setup which consists of collimating lenses and a prism and the 2D spectrum is thus imaged onto a near-IR detector. Here, as a proof of concept, we use a few-mode photonic lantern to capture the light and feed the emanating single-mode outputs to the AWG chip for dispersion. The total size of the setup is 50 cm x 30 cm x 20 cm³, nearly the size of a shoebox. This spectrograph will pave the way for future miniaturized integrated photonic spectrographs on large telescopes, particularly for building future photonic multi-object spectrographs.