Long range Coherent-Optical Frequency Domain Reflectometry for large scale fibre sensing

In recent years, significant technological progress has demonstrated the feasibility of using the long distance fiber optic links as large-scale distributed networks for environmental sensing [1]. The French national research infrastructure REFIMEVE [2] currently distributes an ultra-stable optical frequency reference (ultranarrow linewidth laser referenced to a metrological source at 1542 nm) across more than 9000 km of fibre links connecting laboratories throughout France and Europe. The optical reference is transferred through RENATER fibre network using bi-directional optical amplifiers and regeneration laser stations [3]. The light propagates back and forth in the same fiber enabling to maximize the cancellation of the noise induced by the optical link. The infrastructure has demonstrated strong potential for geophysical studies [4] as the cancelled noises are linked to the seismic noise integrated along the fibers. In this context, the European project SENSEI (Smart European Networks for Sensing the Environment and Internet Quality) [5] aims to harness this potential by developing the next generation photonic technologies for detecting both natural phenomena, such as earthquakes, volcano activity, and anthropogenic events including construction activity or vehicular traffic.

Within this framework, one of our objectives is to develop a coherent optical frequency domain reflectometry (C-OFDR) [6] sensing device based on a low noise laser in order to extend the sensing range of existing setups and add location capability to our previous result. In our setup, the output of a low noise laser is frequency modulated and a fibre under test is measured in a Michelson interferometer configuration. By analysing the Rayleigh backscattered signal along the fibre, the system enables detailed diagnostics of the fibre. As a first demonstration, we tested a prototype over a long-range fibre link extending up to 410 km. The system successfully identified the location of the optical amplifier and a PC connector placed at the end of the fibre with km scale spatial resolution. In future work, we plan to implement a transportable acquisition setup and deploy the C-OFDR system on an operational fiber network to evaluate its performance under real field conditions.

References:

[1] G. Marra et al., Science 361 (2018), https://doi.org/10.1126/science.aat4458

[2] REFIMEVE, https://www.refimeve.fr/en/homepage/

[3] O. Lopez et al., Opt. Express 20, 23518-23526 (2012) https://doi.org/10.1364/OE.20.023518

[4] M. B. K. Tønnes, Thesis (2022), https://hal.science/tel-03984045v1

[5] SENSEI, https://senseiproject.eu/

[6] C. Liang et al., IEEE Access. 9 (2021), DOI : 10.1109/ACCESS.2021.3061250