Ultra-low-phase-noise cryocooled microwave dielectric-sapphire-resonator oscillators with 1 x 10^-16 frequency instability

TL;DR

This paper reports the development of cryogenic sapphire resonator oscillators with extremely low phase noise and fractional frequency stability reaching 1 x 10^-16, surpassing previous microwave sources.

Contribution

The authors demonstrate ultra-low-phase-noise cryogenic sapphire oscillators with record stability, using a low-vibration cryocooler to achieve unprecedented performance.

Findings

Phase noise of -105 dBc/Hz at 1 Hz offset

Fractional frequency stability of 5.3 x 10^-16 tau^-1/2 + 9 x 10^-17

Stability limited by flicker frequency noise floor below 1 x 10^-16

Abstract

Two nominally identical ultra-stable cryogenic microwave oscillators are compared. Each incorporates a dielectric-sapphire resonator cooled to near 6 K in an ultra-low vibration cryostat using a low-vibration pulse-tube cryocooler. The phase noise for a single oscillator is measured at -105 dBc/Hz at 1 Hz offset on the 11.2 GHz carrier. The oscillator fractional frequency stability is characterized in terms of Allan deviation by 5.3 x 10^-16 tau^-1/2 + 9 x 10^-17 for integration times 0.1 s < tau < 1000 s and is limited by a flicker frequency noise floor below 1 x 10^-16. This result is better than any other microwave source even those generated from an optical comb phase-locked to a room temperature ultra-stable optical cavity.