We propose and experimentally demonstrate a fully hybrid distributed sensing scheme that uses a single narrow-band laser to perform fast measurement of the BFS using BOTDA and simultaneous temperature measurement based on spontaneous Raman scattering over 10 km of single mode fiber. The use of cyclic pulse coding effectively reduces the pump peak power levels required for accurate Raman-based distributed temperature measurement, enhancing at the same time the speed of the BFS measurement in the BOTDA technique.
Differential pulse-width-pair BOTDA technique is combined with bi-directional Raman amplification and Simplex
coding to achieve sub-meter spatial resolution over very long sensing distances. Numerical simulations are used to
optimize the power levels of the Raman pumps, avoiding nonlinear effects and pump depletion. Distortions in the
Brillouin gain spectrum due to acoustic-wave pre-excitation are also avoided by numerical optimization of the pulse
width and duty cycle of return-to-zero Simplex coding, providing significant SNR enhancement. We demonstrate 50 cm
spatial resolution over 93 km of standard SMF with a strain/temperature accuracy of 34με/1.7 °C, respectively.
We propose and experimentally demonstrate a hybrid fiber optic sensing technique that effectively combines Brillouin
optical time-domain analysis and a time-domain multiplexing interrogation technique for Fiber Bragg Gratings (FBGs).
The highly-integrated proposed scheme employs broadband apodized low-reflectivity FBGs with a single optical source
and a shared receiver block, allowing for simultaneous measurements of distributed static and discrete dynamic
temperature and strain, over the same sensing fiber.
In this paper we propose the use of optimized bi-directional distributed Raman amplification to enhance the operating
range of Brillouin optical time-domain analysis (BOTDA) sensors. In particular by combining high-power fiber-Raman
lasers and polarization-multiplexed Fabry-Pérot lasers operating at 1450 nm with low relative-intensity-noise (RIN), we
demonstrate distributed sensing (using first-order Raman amplification) over 120 km of standard single-mode fiber with
2 meter spatial resolution and with a strain/temperature accuracy of 45με/2.1°C respectively.
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