# Frequency-comb enabled spectrum-correlation reflectometry for distributed fiber-optic sensing

## TL;DR

A new fiber-optic sensing method uses frequency combs to improve measurement speed and accuracy for large-scale monitoring.

## Contribution

A novel spectral analysis framework using optical frequency combs for parallel interrogation in distributed fiber-optic sensing.

## Key findings

- The method achieves more than tenfold improvement in measurement speed compared to existing spectral analysis methods.
- It enables vibration amplitude monitoring with a dynamic strain measurement range expanded by over an order of magnitude.
- The approach circumvents phase unwrapping issues and interference fading in phase-sensitive systems.

## Abstract

Distributed fiber-optic sensing has become an indispensable tool for large-scale structural and environmental monitoring, where spectral interrogation of backscattering light enables high-precision quantitative measurement of external perturbations. Conventional spectral analysis methods, typically based on frequency-domain serial interrogation or time-to-frequency mapping, face inherent trade-offs between measurement speed, dynamic strain measurement range, and system complexity. Here, we present a distributed frequency comb enabled spectrum-correlation reflectometry as a universal spectral analysis framework that leverages optical frequency comb for parallel multi-frequency interrogation, which is experimentally demonstrated in a phase-sensitive optical time-domain reflectometry (φ-OTDR) system. This method eliminates the need for large frequency scans, achieving more than tenfold improvement in measurement speed over the state-of-the-art spectral analysis methods. Compared to existing phase-demodulated φ-OTDR systems, this method enables vibration amplitude monitoring with a dynamic strain measurement range expanded by more than an order of magnitude, while intrinsically circumventing phase unwrapping issues and interference fading. This work establishes a new paradigm for distributed spectral analysis, providing a flexible and robust platform for a wide range of sensing technologies, including Rayleigh and Brillouin-based schemes, which may have significant impact for geophysics, seismology, civil engineering, and other fields.

Frequency-comb enabled spectrum-correlation reflectometry employs a dual-sideband interleaved configuration to perform parallel multi-frequency interrogation, providing high frequency response over a broad optical spectral range.