Hybrid B-OTDR/Φ-OTDR for multi-parameter measurement from a single end of fiber

Abstract

The multi-parameter sensing is in great demand for comprehensive recognition in various application scenarios. We demonstrate a distributed optical fiber sensor (DOFS) for simultaneous vibration and temperature/strain sensing based on the integration of Brillouin optical time-domain reflectometry (BOTDR) and phase-sensitive optical time-domain reflectometry (Φ-OTDR). A double heterodyne detection configuration is set up to receive the Rayleigh scattering and Brillouin scattering simultaneously, which can enhance the signal-to-noise ratio (SNR) and reduce the polarization fading noise for the Brillouin signal at the same time. Most components in the setup are multiplexed for the Brillouin and Rayleigh signals. The overall cost is much lower than the summation of the BOTDR and the Φ-OTDR setup. In experiments, the setup is capable of measuring temperature change near the end of the 49.9 km long fiber with 0.381 MHz measurement uncertainty and restore different vibration patterns correctly by demodulating the phase variation of Rayleigh scattering signal, owning a 20 m spatial resolution. The sampling rate of the vibration measurement is 1.8 kHz, and the achieved dynamic strain resolution is 1.235 nɛ/√Hz with 100 Hz vibration.

Hybrid Distributed Optical Fiber Sensor for the Multi-Parameter Measurements

“…Both Φ-OTDR and COTDR take advantage of the Rayleigh scattering, and BOTDR and BOTDA use SpBS or SBS light for temperature and strain measurements. Apart from the multi-parameter measurement (temperature, strain, vibration, and loss) based on the integration of discrete sensing characteristics [ 145 , 192 , 193 , 194 , 195 , 196 ], there is also a focus on the handling of the temperature/strain cross-sensitivity among the Brillouin scattering-based sensors with the assistance of Rayleigh scattering [ 172 , 197 , 198 ]. In addition, the combination of BOTDA/BOTDR and frequency-sweeping Rayleigh scattering-based DOFS can provide comprehensive and accurate strain or temperature measurements [ 199 , 200 , 201 ].…”

“…To further simplify the structure of the hybrid system while maintaining the sensing performance, a hybrid Φ-OTDR/BOTDR setup was demonstrated in 2022 [ 145 ]. Since the quantitative demodulation of the Rayleigh scattering phase is crucial for comprehensive vibration measurement, and heterodyne detection is the most effective method to collect the SpBS signal, a double heterodyne detection configuration was proposed.…”

“…Simultaneous temperature/strain and vibration measurements were also carried out using the experimental setup in Figure 10 [ 145 ]. Figure 26 a illustrates the arrangement of the FUT with a total length of 59.9 km, involving a fiber section with a 10 m length wrapped on a piezoelectric transducer (PZT) tube and another fiber loop with a 20 m length immersed in a water bath kettle.…”

“… Experimental setup of the hybrid Φ-OTDR/BOTDR system (reprinted from [ 145 ], under the Open Access Publishing Agreement from © 2022 Optica Publishing Group). …”

“…The joint real-time monitoring of distributed temperature and cracks in a tunnel is also required to reduce the operating risks of transportation facilities [ 142 , 143 , 144 ]. As for power transmission lines, the temperature, strain, and vibration are all indispensable parameters for monitoring specific conditions, such as icing and swing [ 145 ].…”