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 propose a bend-insensitive distributed Brillouin optical fiber sensing by using a singlemode-multimode-singlemode optical fiber structure for the first time to the best of our knowledge. The sensing fiber is a graded-index multimode fiber (GI-MMF) sandwiched by two standard single-mode fibers (SMFs) with centrally alignment splicing at the interface between GI-MMF and SMF to excite the fundamental mode only in GI-MMF. The sensing system can resist a minimal bend radius of 1.25mm while maintaining the measurement performance, with which the measured coefficient of strain is 421.6MHz/%. We also demonstrate that the higher-order modes exciting in GI-MMF can be easily influenced by bending, so that the fundamental mode exciting is essential for bend-insensitive distributed sensing.
We demonstrate an up to 1200°C high-temperature distributed Brillouin sensing based on a pure-silica photonics crystal
fiber. A Brillouin frequency shift (BFS) hopping is observed between 800°C-900°C for the first annealing process and
after that the BFS exhibits the stability and repeatability with a measurement accuracy as high as ±2 °C . The BFS
dependence on temperature in the range of room temperature to 1200°C agrees well with an exponential function instead
of a linear function, which is mainly attributed by the change of the acoustic velocity in a silica fiber.