The distributed measurement of salinity is experimentally demonstrated by Brillouin dynamic grating (BDG) The position-resolved salinity change can be measured by mapping the birefringence change through the BDG, where the salinity altering can induce the swelling or shrinking actions of the PI coating through absorbing or releasing water. Four sensors with the coating thickness of 5 μm, 8 μm, 15 μm, and 20 μm were fabricated as demos to characterize the salinity sensitivity of the sensors, with 30.1 MHz/(mol/L) for 5 μm, 75.4 MHz/(mol/L) for 8 μm, 119.2 MHz/(mol/L) for 15 μm, and 139.6 MHz/(mol/L) for 20 μm, respectively. The proposed sensor shows a linear and reproducible response to the salinity change, and its measurement uncertainty is less than 10 MHz, corresponding to the obtained maximum salinity accuracy of 0.072 mol/L.
A distributed hydrostatic pressure sensor based on Brillouin dynamic gratings (BDGs) was proposed and demonstrated for the first time to the best of our knowledge. Through measuring the pressure-induced birefringence changes through exciting and probing the BDGs, the hydrostatic pressure sensing is realized. The thin-diameter PM-PCF is used as the fiber under test. The temperature can be compensated by measuring the temperature-induced Brillouin frequency shift (BFS) through differential pulse-width pair Brillouin optical time-domain analysis (DPP-BOTDA). A distributed measurement is reported with a 20-cm spatial resolution and measurement accuracy as high as 0.025 MPa.
We numerically calculate and experimentally investigate the characterization of phase-shifted Brillouin dynamic gratings
(PS-BDGs) in a polarization maintaining fiber (PMF). A phase-shifted point is induced into the middle of a conventional
BDG through phase-modulating one of the two pump pulse, generating a PS-BDG thanks to the stimulated Brillouin
scattering (SBS). When the frequency difference between a high frequency pump1 pulse with 1ns and π-1ns and a low
frequency pump2 pulse with 100ps is equal to the Brillouin frequency shift of the PMF, a transient PS-BDG with a 3dBbandwidth
of 354MHz of the notch spectrum is simulated based on the coupled-wave equations of BDG. By increasing
the repetition rate up to 250MHz, an enhanced PS-BDG with a deep notch depth is obtained since the residual acoustic
wave of the former SBS process is enhanced by the optical waves of the latter SBS process. Then a proof-of-concept
experiment is built to verify the transient PS-BDG and the results show that the notch feature is consistent with the
simulation results and the notch frequency of the PS-BDG can be changed by tuning the phase shift Δϕ . The proposed
PS-BDGs have important potential applications in optical fiber sensing, microwave photonics, all-optical signal
processing and RoF (radio-over-fiber) networks.
We report on a high-sensitive distributed transverse load sensing based on Brillouin dynamic gratings (BDGs) for the first time to the best of our knowledge. The sensing mechanism is to measure the transverse-load induced birefringence through exciting and probing a BDG in an elliptical-core polarization-maintaining fiber. A distributed measurement of transverse load is experimentally demonstrated with a 20-cm spatial resolution, and the measurement accuracy is as high as 4.8x10-4N/mm, which improves by three orders of magnitude compared with the prior techniques.
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