Photonic microwave signals with zeptosecond level absolute timing noise

TL;DR

This paper demonstrates the generation of microwave signals with unprecedented timing noise and stability by transferring optical frequency stability via a low-noise fiber-based comb, surpassing existing sources and enabling advances in various high-precision fields.

Contribution

It introduces a high-fidelity optical-to-microwave frequency transfer technique achieving record low timing noise and stability, with novel measurement methods for ultra-pure microwave signals.

Findings

Fractional frequency stability below 6.5 x 10^-16 at 1 s

Timing noise floor below 41 zs/Hz^1/2

Phase noise below -173 dBc/Hz at 12 GHz

Abstract

Photonic synthesis of radiofrequency revived the quest for unrivalled microwave purity by its seducing ability to convey the benefits of the optics to the microwave world. In this work, we perform a high-fidelity transfer of frequency stability between an optical reference and a microwave signal via a low-noise fiber-based frequency comb and cutting-edge photo-detection techniques. We demonstrate the generation of the purest microwave signal with a fractional frequency stability below 6.5 x 10^-16 at 1 s and a timing noise floor below 41 zs.Hz^-1/2 (phase noise below -173 dBc.Hz^-1 for a 12 GHz carrier). This outclasses existing sources and promises a new era for state-of-the-art microwave generation. The characterization is achieved by building two auxiliary low noise optoelectronic microwave reference and using a heterodyne cross-correlation scheme with lowermost detection noise. This unprecedented level of purity can impact domains such as radar systems, telecommunications and time-frequency metrology. Furthermore, the measurement methods developed here can benefit the characterization of a broad range of signals, beyond comb-based systems.