Optical fibre loss profile measurement by using intensity-based phase-sensitive OTDR

Abstract

We propose and experimentally demonstrate a method to measure the fibre loss profile using a standard intensity-based phase-sensitive optical time-domain reflectometer (Φ-OTDR) without any hardware modifications. While Φ-OTDR is widely used for distributed acoustic sensing (DAS) applications, fibre loss measurement typically requires a separate OTDR system. Our study shows that by averaging the raw Φ-OTDR traces over time, the coherent backscattered light transitions into an incoherent superposition, producing a trace similar to that of a traditional OTDR. This work incorporates expanded experimental investigation and simulation of temperature fluctuations on the phase and birefringence in the loss measurement by Φ-OTDR. Three groups of simulations were conducted for two types of temperature variations during the averaging period, including linear temperature change, and sinusoidal change. Simulation results show that the simulated temperature variation profiles have minimal impact on the long-term averaged outcomes. Experimental results for a 15 km fibre link with intentionally introduced loss events demonstrate that Φ-OTDR can effectively and accurately measure both fibre loss and event locations. The obtained measurements closely align with those recorded using a conventional OTDR system, confirming the reliability and precision of the proposed method. Notably, the system successfully detected an event with a minimal loss of about 0.13 dB. Additionally, the measurement differences of event losses and linear section attenuations were ≤0.1 dB and ≤0.02 dB/km, respectively. This technique offers a cost-effective solution for integrating OTDR functionality into existing Φ-OTDR systems.