Approaching the Quantum-Limited Precision in Frequency-Comb-Based Spectral Interferometric Ranging

Abstract

Over the last two decades, frequency combs have brought breakthroughs in length metrology with traceability to length standards. In particular, frequency-comb-based spectral interferometry is regarded as a promising technology for next-generation length standards. However, to achieve this, the nanometer-level precision inherent in a laser interferometer is required. Here, distance measurements are reported by frequency-comb-based spectral interferometry with sub-nm precision close to a standard quantum limit. The measurement precision is confirmed as 0.67 nm at an average time of 25 µs. The measurement sensitivity is found to be 4.5·10⁻¹²m/Hz^1/2, close to the quantum-limit. As a practical example of observing precise physical phenomena, remote sound sensing is demonstrated through measuring vibrations induced by acoustic waves. The study will be an important step toward the practical realization of upcoming length standards.