Clock Noise Cancellation in Heterodyne Links between Optical Cavities for Space-Borne Gravitational-Wave Telescopes

TL;DR

This paper introduces a novel clock noise cancellation method for heterodyne interferometry in space-based gravitational-wave detectors, enhancing sensitivity by eliminating clock jitter effects.

Contribution

It proposes a scheme using dual heterodyne signals with positive and negative beat notes to cancel clock noise without additional modulation.

Findings

The method effectively cancels clock jitter under realistic conditions.

Simulations show the approach recovers original sensitivity and improves SNR by √2 for shot noise.

The scheme is validated with parameters from the B-DECIGO concept.

Abstract

Space-borne gravitational-wave telescopes are key to extend the observation band below $10\,\mathrm{Hz}$. The use of inter-satellite optical cavities linked by heterodyne interferometry is a promising approach to reach the sensitivity level of $10^{-22}/\sqrt{\mathrm{Hz}}$ in the decihertz band. While heterodyne interferometry is advantageous for relaxing arm-length control requirements, it introduces susceptibility to clock jitter, which can be a significant noise source. In the back-linked Fabry--Perot (BLFP) interferometer aiming at the decihertz band, the required clock stability exceeds that of current space-qualified oscillators by more than an order of magnitude. We propose a clock noise cancellation scheme that uses two heterodyne signals with positive and negative beat-note frequencies, naturally obtained using both incoming and outgoing laser beams of arm cavities without additional clock modulation schemes. By forming a weighted combination of these signals with time-dependent coefficients, clock jitter contributions are eliminated while preserving gravitational-wave information. We present the theoretical framework, analyze performance under realistic arm-length drifts, and validate the approach through time-domain simulations using parameters from the B-DECIGO concept. Results show that the synthesized signal recovers the original sensitivity and even improves the signal-to-noise ratio by a factor of $\sqrt{2}$ for shot noise.