Astrophotonic Solutions for Spectral Cross-Correlation Techniques

TL;DR

This paper introduces innovative astrophotonic devices that perform spectral cross-correlation optically, simplifying spectroscopic instruments and enabling low-cost, on-site detection of molecular species and stellar radial velocities.

Contribution

It presents two novel photonic platform designs—silicon and fibre-based—for on-device spectral cross-correlation, advancing compact and cost-effective astrophysical spectroscopy.

Findings

Successfully detected molecular gas in laboratory tests

Developed silicon photonic ring resonators for cross-correlation

Created fibre Bragg gratings with strain-modulated spectra

Abstract

Using photonic devices, we developed a new approach to traditional spectroscopy where the spectral cross-correlation with a template spectrum can be done entirely on-device. By creating photonic devices with a carefully designed, modulated transmission spectrum, the cross-correlation can be carried out optically without requiring any dispersion, vastly simplifying the instrument and reducing its cost. The measured correlation lag can be used for detecting atomic/molecular species within and determining the radial velocity of a particular astrophysical object. We present an overview of two design approaches that are currently being developed that use different photonic platforms: silicon and fibre-based photonics. The silicon photonic approach utilizes ring resonators that can be thermo-optically modulated to carry out the cross-correlation. The fibre approach uses customized fibre Bragg gratings (FBGs) with transmission spectra that can be strain-modulated. Both approaches have been able to detect molecular gas in a lab setting, and we are now in the process of on-sky testing. Lastly, we discuss the future for these types of devices as their simplicity opens up the possibility of developing low-cost, purpose-built multi-object or integral field spectroscopic instruments that could make significant contributions to scientific programs requiring stellar RV measurements and exoplanet detections.