Ultralow-noise microwave oscillator via optical frequency division with a co-self-injection-locked miniature Fabry-Perot reference

TL;DR

This paper presents a compact, low-noise microwave oscillator using optical frequency division with a miniature Fabry-Perot cavity and optical co-self-injection-locking, achieving performance comparable to complex electronic systems.

Contribution

It introduces a novel combination of ultrahigh-Q miniature Fabry-Perot cavity with optical co-SIL for microwave generation, simplifying the system while maintaining low phase noise.

Findings

Achieved phase noise of -147 dBc/Hz at 4 kHz offset for 10 GHz microwave

Demonstrated a compact, cost-effective, and field-deployable microwave oscillator

Matched performance of state-of-the-art electronically stabilized systems

Abstract

Optical frequency division (OFD) provides the purest microwaves by down-converting the stability of optical cavity references. State-of-the-art references typically rely on electronic co-Pound-Drever-Hall locking to ultrahigh-Q microresonators-a complex approach that introduces servo bumps and increases footprint. Alternatively, optical co-self-injection-locking (co-SIL) offers inherent simplicity but is limited by the large thermo-refractive noise and confined mode volumes of integrated cavities. Here, we demonstrate a two-point OFD-based microwave oscillator that combines an ultrahigh-Q miniature Fabry-Perot cavity with optical co-SIL. Leveraging its low relative phase noise optical reference and combing with an integrated soliton microcomb, the system generates a microwave with phase noise of -147 dBc/Hz at 4 kHz offset (scaled to 10 GHz)-performance rivalling most electronically stabilized systems. This work marries the superior noise floor of ultrahigh-Q cavities with the simplicity of optical locking, providing a compact, cost-effective, and field-deployable path to pure microwaves for next-generation communications, radar and metrology.