Ultrahigh-speed distributed Brillouin reflectometry

Abstract

Optical fibre sensors based on Brillouin scattering have been vigorously studied in the context of structural health monitoring on account of their capacity for distributed strain and temperature measurements. However, real-time distributed strain measurement has been achieved only for two-end-access systems; such systems reduce the degree of freedom in embedding the sensors into structures, and furthermore render the measurement no longer feasible when extremely high loss or breakage occurs at a point along the sensing fibre. Here, we demonstrate real-time distributed measurement with an intrinsically one-end-access reflectometry configuration by using a correlation-domain technique. In this method, the Brillouin gain spectrum is obtained at high speed using a voltage-controlled oscillator, and the Brillouin frequency shift is converted into a phase delay of a synchronous sinusoidal waveform; the phase delay is subsequently converted into a voltage, which can be directly measured. When a single-point measurement is performed at an arbitrary position, a strain sampling rate of up to 100 kHz is experimentally verified by detecting locally applied dynamic strain at 1 kHz. When distributed measurements are performed at 100 points with 10 times averaging, a repetition rate of 100 Hz is verified by tracking a mechanical wave propagating along the fibre. Some drawbacks of this ultrahigh-speed configuration, including the reduced measurement accuracy, lowered spatial resolution and limited strain dynamic range, are also discussed.

Recent Advances in Brillouin Optical Correlation-Domain Reflectometry

“…An apodization scheme based on synchronous intensity modulation [53] and a lock-in detection scheme [54] were also performed to suppress the noise floor and to enhance the strain dynamic range, etc. Finally, to achieve high-speed operation (the sampling rate was limited to <20 Hz in the standard configuration [55]), phase-detected BOCDR [56][57][58] and slope-assisted BOCDR were developed. In both schemes, the idea for high-speed operation is the same; namely, the omission of the frequency-scanning process for acquiring the BGS.…”

“…Even if the BFS change is so large that ν B0 gets out of the linear region, so long as P B0 is in one-to-one correspondence with the BFS, this system operates properly (with a reduced sensitivity) by simple nonlinear compensation. One may point out that the noise floor of correlation-domain techniques is influenced by the sidelobes of the correlation peak and that the slope-assisted configuration does not work properly in principle, but this issue can be mitigated if we accept the deterioration of the spatial resolution to some extent just in the same manner as in the phase-detected BOCDR [56]. Figure 5.…”

Observation of multimodal interference in millimeter-long polymer optical fibers

“…Sensing technology of strain and temperature using optical fibers has been an active area of research for many decades, and a wide variety of configurations have been developed thus far. They operate based on fiber Bragg gratings [1,2,3], long-period gratings [4,5], Brillouin scattering [6,7,8,9], Raman scattering [10,11], optical interference [12,13,14,15,16,17,18,19,20,21,22,23,24], and many others. Among numerous types of interference-based sensors, those based on intermodal interference in multimode fibers (MMFs) have recently attracted a considerable attention owing to their system simplicity and cost efficiency.…”

150 km fast BOTDA based on the optical chirp chain probe wave and Brillouin loss scheme

“…Brillouin optical fiber sensors have the capacity to resolve more than one million points [1], obtain a high-speed strain sampling rate [2], and achieve a long sensing distance [3]. In applications, long-range distributed Brillouin optical fiber sensors are promising tools to monitor large-scale structures such as power cables, railways, and oil and gas pipelines.…”