Guangyu Zhang

Dependence of Brillouin frequency shift on radial and axial strain in silica optical fibers

Brillouin frequency shift (BFS) in a single-mode optical fiber has been measured as a function of both radial and axial strain via the Brillouin optical time domain analysis technique. The effects of the two kinds of strain on the BFS are decoupled by making fiber pretensioned and relaxed while applying pressure. Linear relations have been found between the BFS and both kinds of strain. The radial strain coefficient C(vε(r)) is found to be 0.029 MHz/με, and the axial strain coefficient C(vε(a)) is 0.053 MHz/με. The result may give impetus to some potential applications of the optical fibers, such as a distributed pressure sensor based on Brillouin scattering.

Pressure Sensitization of Brillouin Frequency Shift in Optical Fibers With Double-Layer Polymer Coatings

This paper performs a theoretical and experimental analysis of the pressure sensitivity of Brillouin frequency shift (PSoBFS) in silica optical fibers with double-layer polymer coatings. It is predicted numerically that the coated fibers have enhanced (ideally over 20 times) PSoBFS as compared with a bare fiber. In addition, the enhancement becomes obvious while the outer coating has a lower Youngs modulus and Poissons ratio, as well as larger thickness. Three fibers with different outer coatings are experimented via the Brillouin optical time domain analysis technique. The experimental results agree with the theoretical prediction. This quantitative evaluation can be guidable for designing BFS-based pressure sensors with coated fibers.