Optical frequency comb integration in radio telescopes: advancing signal generation and phase calibration

TL;DR

This paper demonstrates the use of optical frequency combs for generating stable RF signals in VLBI telescopes, improving phase calibration and signal quality for high-resolution astronomical observations.

Contribution

It introduces an optical frequency comb-based method for RF signal generation and distribution in VLBI, enabling better phase stability and calibration.

Findings

Successful detection of VLBI fringes using OFC-derived signals

RF-comb characteristics suitable for phase calibration extracted

Enhanced potential for next-generation broadband VLBI measurements

Abstract

Very long baseline interferometry (VLBI) enables high-angular-resolution observations in astronomy and geodesy by synthesizing a virtual telescope with baselines spanning hundreds to thousands of kilometres. Achieving high instrumental phase stability in VLBI relies on the generation of high-quality, atomic-referenced RF local oscillator (LO) and RF-comb signals for the effective downconversion of celestial RF signals and precise phase calibration, respectively. As observing frequencies move into higher ranges with wider bandwidth, conventional electronic methods face significant challenges in maintaining the quality of these signals. Here, we demonstrate that an optical frequency comb (OFC) can be used as a versatile tool to generate and distribute low-noise and atomic-referenced RF-comb and RF-LO signals in the VLBI telescope. Hydrogen maser-stabilized optical pulses are transmitted over a timing-stabilized fibre link from the observatory building to the VLBI receiver system at the telescope, where photodetection converts them into the required RF-comb and RF-LO signals. In VLBI test observation, we successfully detected VLBI fringes and extracted the RF-combs characteristics in a format suitable for VLBI instrumental phase calibration. These results highlight the high potential of OFC-based technology for enhancing next-generation broadband VLBI measurements, advancing astrophysical research and facilitating intercontinental clock comparison.