A stabilized 18 GHz chip-scale optical frequency comb at 2.8x10-16 relative inaccuracy

TL;DR

This paper demonstrates a fully stabilized CMOS-compatible optical frequency comb at 18 GHz with ultra-high precision, achieving a relative inaccuracy of 2.8×10⁻¹⁶, suitable for advanced scientific and technological applications.

Contribution

It introduces a novel method for full stabilization of chip-scale microcombs, significantly improving their stability and accuracy for practical use.

Findings

Achieved residual instability of 3.6 mHz/√s with active stabilization.

Demonstrated tooth-to-tooth frequency inaccuracy of 53 mHz.

Reaches 2.8×10⁻¹⁶ relative inaccuracy, unprecedented at chip scale.

Abstract

Optical frequency combs, coherent light sources that connect optical frequencies with microwave oscillations, have become the enabling tool for precision spectroscopy, optical clockwork and attosecond physics over the past decades. Current benchmark systems are self-referenced femtosecond mode-locked lasers, but four-wave-mixing in high-Q resonators have emerged as alternative platforms. Here we report the generation and full stabilization of CMOS-compatible optical frequency combs. The spiral microcomb's two degrees-of-freedom, one of the comb line and the native 18 GHz comb spacing, are first simultaneously phase-locked to known optical and microwave references. Second, with pump power control, active comb spacing stabilization improves the long-term stability by six orders-of-magnitude, reaching an instrument-limited 3.6 mHz/sqrt(t) residual instability. Third, referencing thirty-three of the nitride frequency comb lines against a fiber comb, we demonstrate the comb tooth-to-tooth frequency relative inaccuracy down to 53 mHz and 2.8x10-16, heralding unprecedented chip-scale applications in precision spectroscopy, coherent communications, and astronomical spectrography.