Design, simulation and characterization of integrated photonic spectrographs for Astronomy I: Generation-I AWG devices based on canonical layouts

TL;DR

This paper reports on the design, simulation, and experimental characterization of first-generation AWG devices on silica for near-infrared astronomical spectroscopy, demonstrating spectral resolving powers up to 18,900 and exploring integration for spectrograph applications.

Contribution

It introduces the initial development and testing of custom AWG devices for astronomy, highlighting design, fabrication, and characterization processes with potential for high-resolution spectrograph integration.

Findings

Achieved spectral resolving powers up to 18,900.

Identified key factors like phase error and birefringence affecting performance.

Demonstrated potential for integration into astronomical spectrographs.

Abstract

We present an experimental study on our first generation of custom-developed arrayed waveguide gratings (AWG) on silica platform for spectroscopic applications in near-infrared astronomy. We provide a comprehensive description of the design, numerical simulation and characterization of several AWG devices aimed at spectral resolving powers of 15,000 - 60,000 in the astronomical H-band. We evaluate the spectral characteristics of the fabricated devices in terms of insertion loss and estimated spectral resolving power and compare the results with numerical simulations. We estimate resolving powers of up to 18,900 from the output channel 3-dB transmission bandwidth. Based on the first characterization results, we select two candidate AWGs for further processing by removal of the output waveguide array and polishing the output facet to optical quality with the goal of integration as the primary diffractive element in a cross-dispersed spectrograph. We further study the imaging properties of the processed AWGs with regards to spectral resolution in direct imaging mode, geometry-related defocus aberration, and polarization sensitivity of the spectral image. We identify phase error control, birefringence control, and aberration suppression as the three key areas of future research and development in the field of high-resolution AWG-based spectroscopy in astronomy.