The current idea of smart cities based on the Internet of Things requires the real-time monitoring of facilities, particularly large facilities (such as rail transit systems, large bridges, and buildings), which can supply information regarding their surrounding environment and allow assessments of their health.
Working principle of the hybrid DFOS system. Image Credit: Linjing Huang, Xinyu Fan, Haijun He, Lianshan Yan, Zuyuan He
Distributed fiber-optic sensing (DFOS) systems, which demand long-distance simultaneous measurements through a sensing fiber, are in great demand for many industrial applications as an accurate real-time monitoring tool.
The use of most DFOS systems, however, is constrained by the fact that they can often only measure a single type of parameter. Additionally, it is difficult and expensive to simply combine various DFOS systems.
A group of researchers from Shanghai Jiao Tong University in China developed a condensed hybrid DFOS system for simultaneously measuring many parameters along the sensing fiber in a new study that was published in Light: Advanced Manufacturing.
The team was led by Professor Xinyu Fan. They employed a standard single-mode fiber as a sensor to gather data on the temperature, strain, and vibration of the optical fiber, which had a length of several kilometers.
They combined three different backscattered lightwave techniques and streamlined the hybrid systems. The complexity of the application is substantially reduced by the suggested hybrid system, which only needs one light source, two receiving ends, and a single access to the fiber for launching a light wave.
As a result, the streamlined hybrid system can be utilized for perimeter security, automated control, and real-time monitoring of large structures. The method has the potential to be a potent instrument for encouraging the development of smart cities.
Among the several DFOS systems, phase-sensitive optical time-domain reflectometry (φ-OTDR), which makes use of Rayleigh backscattering, is used to assess dynamic parameters like vibration. With a high signal-to-noise ratio, stimulated Brillouin scattering-based Brillouin optical time domain analysis (BOTDA) is used to monitor temperature and static strains.
Since Raman scattering is solely temperature sensitive, it can be employed in Raman optical time-domain reflectometry (ROTDR) to determine the distributed temperature without being affected by strain.
The three various scattering techniques are combined by the hybrid DFOS system. In addition to being utilized for vibration sensing, Rayleigh scattering also serves as the probe for the Brillouin scattering process, which is used to monitor temperature and strain. The temperature-strain cross-sensitivity is eliminated via Raman scattering.
To separate the Raman scattering of two pulses with very close optical frequencies, pulse code modulation is used. A single-end simplified hybrid DFOS system can monitor multiple variables simultaneously in this way.
The hybrid system demonstrates its capability to accurately measure temperature, strain, and vibration along a single-mode fiber that is 9 kilometers long.
Journal Reference
Huang, L., et al. (2023) Single-end hybrid Rayleigh Brillouin and Raman distributed fibre-optic sensing system. Light: Advanced Manufacturing. doi:10.37188/lam.2023.016.