Lei Teng

High-sensitivity distributed transverse load sensor with an elliptical-core fiber based on Brillouin dynamic gratings.

A high-sensitivity distributed transverse load sensor based on Brillouin dynamic gratings (BDGs) is proposed and demonstrated experimentally for the first time, to the best of our knowledge. The principle is to measure the transverse-load-induced birefringence change through exciting and probing a BDG in an elliptical-core polarization-maintaining fiber. A distributed measurement of transverse load is demonstrated experimentally using a 10 m sensing fiber, which features high sensitivity to a transverse load with a measurement accuracy as high as 0.8×10(-3)  N/mm at a 20 cm spatial resolution.

Temperature-compensated distributed hydrostatic pressure sensor with a thin-diameter polarization-maintaining photonic crystal fiber based on Brillouin dynamic gratings.

A temperature-compensated distributed hydrostatic pressure sensor based on Brillouin dynamic gratings (BDGs) is proposed and demonstrated experimentally for the first time, to the best of our knowledge. The principle is to measure the hydrostatic pressure induced birefringence changes through exciting and probing the BDGs in a thin-diameter pure silica polarization-maintaining photonic crystal fiber. The temperature cross-talk to the hydrostatic pressure sensing can be compensated through measuring the temperature-induced Brillouin frequency shift (BFS) changes using Brillouin optical time-domain analysis. A distributed measurement of hydrostatic pressure is demonstrated experimentally using a 4-m sensing fiber, which has a high sensitivity, with a maximum measurement error less than 0.03 MPa at a 20-cm spatial resolution.

Phase-shifted Brillouin dynamic gratings using single pump phase-modulation: proof of concept

Two novel phase-shifted Brillouin dynamic gratings (PS-BDGs) are proposed using single pump phase-modulation (SPPM) in a polarization maintaining fiber (PMF) for the first time to our knowledge. Firstly, based on the stimulated Brillouin scattering (SBS), a transient PS-BDG with a 3-dB bandwidth of 354MHz is written by a 2-ns pump1 pulse and a 100-ps pump2 pulse, where the phase of pump1 pulse is shifted with π from its middle point through phase modulation. Then, with a high repetition rate of 250MHz for both pump pulses, an enhanced PS-BDG with a deep notch depth is obtained and its notch frequency can be easily tuned by changing the phase shift. We demonstrate a proof-of-concept experiment of the transient PS-BDG and show the notch frequency changing by tuning the phase shift. The proposed PS-BDGs have important potential applications in microwave photonics, all-optical signal processing and RoF (radio-over-fiber) networks.

Detecting cm-scale hot spot over 24-km-long single-mode fiber by using differential pulse pair BOTDA based on double-peak spectrum

In distributed Brillouin optical fiber sensor when the length of the perturbation to be detected is much smaller than the spatial resolution that is defined by the pulse width, the measured Brillouin gain spectrum (BGS) experiences two or multiple peaks. In this work, we propose and demonstrate a technique using differential pulse pair Brillouin optical time-domain analysis (DPP-BOTDA) based on double-peak BGS to enhance small-scale events detection capability, where two types of single mode fiber (main fiber and secondary fiber) with 116 MHz Brillouin frequency shift (BFS) difference have been used. We have realized detection of a 5-cm hot spot at the far end of 24-km single mode fiber by employing a 50-cm spatial resolution DPP-BOTDA with only 1GS/s sampling rate (corresponding to 10 cm/point). The BFS at the far end of 24-km sensing fiber has been measured with 0.54 MHz standard deviation which corresponds to a 0.5°C temperature accuracy. This technique is simple and cost effective because it is implemented using the similar experimental setup of the standard BOTDA, however, it should be noted that the consecutive small-scale events have to be separated by a minimum length corresponding to the spatial resolution defined by the pulse width difference.

Distributed hydrostatic pressure sensor using a thin-diameter and polarization-maintaining photonics crystal fiber based on Brillouin dynamic gratings

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.

High-sensitivity distributed static pressure sensor based on Brillouin dynamic grating

Brillouin dynamic gratings (BDGs) has been, in recent years, addressed using a polarization-maintaining fiber with many prominent advantages and proved that the BDGs have a profound high sensitivity to fiber birefringence changes. When the two parallel polarized counter-propagating pump waves with a frequency offset of fiber Brillouin frequency shift, and the orthogonally polarized probe pulse wave satisfied with the phase-matching condition, the BDGs would be excited through stimulated Brillouin scattering and read, while the optical frequency difference between the pump and probe waves is determined by the birefringence. The birefringence-induced frequency shift (BireFS) associated with the impact of external environment may be affected by local static pressure. Though the measurement of the BireFS changes along the fiber, one can realize a distributed fiber static pressure sensing. In our presentation, a temperature-insensitive distributed static pressure sensor based on BDGs is proposed and experimentally demonstrated for the first time, to the best of our knowledge. The measurement principle is to interrogate the static-pressure-induced fiber birefringence changes through generating and mapping the BDGs in the fiber under test (FUT). The experimental setup adopted two pump waves to excite a BDG and a short probe pulse to read the Brillouin grating spectrum associated with the birefringence with a spatial resolution of 20 cm. The sensing technique features a distributed measurement, temperature-insensitivity and high sensitivity to the static pressure. The distributed transverse load measurement experiment is conducted in an temperature-insensitive elliptical-core polarization-maintaining fiber with a measurement accuracy as high as 0.8 × 10-3 N/mm; and the distributed hydrostatic pressure measurement experiment is also performed in a thin-diameter pure silica polarization-maintaining photonic crystal fiber with a measurement accuracy as high as 0.025MPa with a character of temperature compensation.

1200°C high-temperature distributed optical fiber sensing by using brillouin optical time domain analysis

An up to 1100°C and 1200°C high-temperature distributed Brillouin sensing based on a GeO 2 -doped single mode fiber (SMF) and a pure-silica photonics crystal fiber (PCF) are demonstrated, respectively. We found that the BFS dependence on temperature of SMF and PCF 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. A Brillouin frequency shift (BFS) hopping is observed in both kinds of fiber between 800°C–900°C in the first annealing process and after that the BFS exhibits the stability and repeatability with a measurement accuracy as high as ±1.42°C for SMF and ±2.6°C for PCF, respectively. The BFS hopping is a highly temperature-dependent behavior, which means that a high-temperature (> 800°C) would accelerate the process of BFS hopping to reach a stable state and after BFS hopping, both SMF and PCF shows good repeatability from 1000°C to 1100°C and 1000°C to 1200°C without annealing. The process of coating burning of silica fiber not only introduces a loss induced by micro-bending but also imposes a compressive stress on the bare fiber, which contributes to an additional BFS variation at the temperature period of coating burning (272°C–564°C).

Characterization of phase-shifted Brillouin dynamic gratings in a polarization maintaining fiber

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.

Temperature-compensated distributed hydrostatic pressure Brillouin sensor using a thin-diameter and high-birefrigent photonics crystal fiber

In this work, 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. The hydrostatic pressure sensing is realized through measuring the pressure-induced birefringence changes through exciting and probing the BDGs; while the temperature can be compensated by measuring the temperature-induced Brillouin frequency shift (BFS) through differential pulsewidth pair Brillouin optical time-domain analysis (DPP-BOTDA). The thin-diameter high-birefringent PM-PCF is used as the fiber under test and its porous-structure cladding is liable to be deformed exhibiting a high sensitivity to pressure. A distributed measurement with a 20-cm spatial resolution and a measurement accuracy as high as 0.025 MPa is reported.

High-sensitive distributed transverse load sensing based on Brillouin dynamic gratings

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.