# 45 km ROTDR with 0.5 m/0.11 °C via complex-domain square-wave width-chirp pulse compression

## TL;DR

This paper introduces a new pulse compression technique that improves the performance of fiber optic temperature sensing by decoupling sensing range, resolution, and accuracy.

## Contribution

A novel complex-domain square-wave width-chirp pulse compression method is proposed to overcome the trade-off between sensing metrics.

## Key findings

- The method achieves 45 km sensing distance with 0.5 m spatial resolution and 0.11°C temperature accuracy.
- Complex-domain matched filtering provides a 15.09 dB gain in signal-to-noise ratio.
- The technique is extensible to Brillouin and Rayleigh scattering systems.

## Abstract

Raman optical time-domain reflectometry (ROTDR) inherently balances sensing range, spatial resolution, and temperature accuracy through the pulse duration dictated by the OTDR position principle. However, optimizing one metric conventionally degrades the others, forming a theoretical trade-off. This work introduces complex-domain square-wave width-chirp pulse compression to break that physical limitation. The steep edges and rich high-order harmonics of complex-domain square-wave width-chirp pulse undergo matched filtering, producing a compressed δ-pulse whose full width at half maximum, rather than the original pulse duration, now governs sensing spatial resolution. Complex-domain matched filtering, implemented via a conjugate time-reversal filter, achieves a 15.09 dB gain in signal-to-noise ratio, while the complex-domain envelope extraction method isolates and removes Raman phase noise. The proposed scheme simultaneously achieves 45 km sensing distance, 0.5 m spatial resolution, and 0.11 °C temperature accuracy, demonstrating complete decoupling of these metrics from the pulse duration. The proposed framework offers a new paradigm for long-range, high-precision distributed temperature sensing and is extensible to Brillouin and Rayleigh scattering systems.

This work proposes a complex-domain square-wave width-chirp pulse compression scheme, achieving simultaneous improvement of spatial resolution, sensing distance, and temperature accuracy in the field of Raman distributed fiber optic sensing.