SAT.STFR.FRQ (UWA) Detail Design Report (LOW)

TL;DR

This paper discusses the design considerations for a phase-stable optical frequency transfer system crucial for maintaining coherence in the SKA radio telescope array, focusing on long-distance fibre-optic link stability.

Contribution

It presents a detailed design report for a phase-stabilized optical frequency transfer system tailored for the SKA's long fibre links, addressing environmental perturbation challenges.

Findings

Analysis of fibre-optic link noise sources

Design specifications for active stabilization system

Expected phase stability performance

Abstract

The Square Kilometre Array (SKA) project is an international effort to build the world's most sensitive radio telescope operating in the 50 MHz to 14 GHz frequency range. Construction of the SKA is divided into phases, with the first phase (SKA1) accounting for the first 10% of the telescope's receiving capacity. During SKA1, a Low-Frequency Aperture Array (LFAA) comprising over a hundred thousand individual dipole antenna elements will be constructed in Western Australia (SKA1-LOW), while an array of 197 parabolic-receptor antennas, incorporating the 64 receptors of MeerKAT, will be constructed in South Africa (SKA1-MID). Radio telescope arrays, such as the SKA, require phase-coherent reference signals to be transmitted to each antenna site in the array. In the case of the SKA, these reference signals are generated at a central site and transmitted to the antenna sites via fibre-optic cables up to 175 km in length. Environmental perturbations affect the optical path length of the fibre and act to degrade the phase stability of the reference signals received at the antennas, which has the ultimate effect of reducing the fidelity and dynamic range of the data . Given the combination of long fibre distances and relatively high frequencies of the transmitted reference signals, the SKA needs to employ actively-stabilised frequency transfer technologies to suppress the fibre-optic link noise in order to maintain phase-coherence across the array.