# Long-range, phase-and-polarization diversity coherent reflectometer

## TL;DR

This paper presents a novel coherent reflectometer that achieves high spatial resolution over long fiber links using phase and polarization diversity, spectral compression, and a fiber laser, without high-speed electronics.

## Contribution

It introduces a fiber reflectometer combining optical time and frequency domain techniques with phase and polarization diversity for enhanced long-distance resolution.

## Key findings

- Achieved 2.5 mm resolution at 10 km fiber length.
- First report of such high resolution for reflective fiber reflectometry at this distance.
- Demonstrated improved sensitivity and discrimination against Rayleigh backscattering.

## Abstract

A coherent, short-length reference arm reflectometer, which utilizes a 76-MHz repetition rate mode-locked fiber laser, was investigated experimentally for long fiber links (> 10 km). The reflectometer combines the advantages of optical time-domain and frequency-domain reflectometry without the need for high-speed photodetectors and electronics to achieve high spatial resolution of 2.5 mm at 10 km. To our knowledge, this is the highest resolution reported for fiber reflectometry at this distance for reflective type event using non-photon-counting detection. Phase and polarization diversity detection, combined with spectral compression using frequency-chirp, are proposed to improve sensitivity and discrimination against the fiber Rayleigh backscattering background.

---
Source: https://tomesphere.com/paper/1908.00626