Evaluation of the Pressure Sensing Capabilities for Pure Radial Acoustic Mode Exited by Optomechanic Interaction in SMF-28 Optical Fiber

Given the critical need for precise pressure measurements in various fields like fossil fuel exploration, underwater environments, aerospace engineering, and industrial processes, fiber optic-based sensing techniques have emerged as a promising solution. These techniques offer inherent advantages such as small size, lightweight, and immunity to electromagnetic interference. A promising mechanism for fiber optic pressure sensing is forward-stimulated Brillouin scattering (FSBS). FSBS is an optomechanical interaction that involves two copropagating optical waves and nearly transverse acoustic mode resonances (AMR's) supported by the optical fiber. Pure radial, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$R_{0,m}$</tex>, acoustic mode resonances can be stimulated in single-mode optical fibers [1]. The frequency at which <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$R_{0.m}$</tex> modes are excited can be approximated by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{0,m}\displaystyle \approx\frac{V_{L}}{2\pi a}(c_{m}-\frac{16\alpha^{2}-1}{8c_{m}})$</tex>, where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$a$</tex> is the radius of the fiber, V<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> is the longitudinal acoustic velocity. The coefficient <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$c_{m}=(m\pi-\pi/4)$</tex> being <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$m(m=1,2,3\ldots)$</tex> an integer denoting the mode order order [2]. By analyzing the frequency shift of the FSBS spectrum, precise determination of environmental parameters becomes feasible. Presure applied to the fiber have an impact of the longitudinal acoustic velocity [3].