Characterization of the spatio-temporal response of optical fiber sensors: scattering of spherical waves from a layered cylinder

source: © 2014 Acoustical Society of America

In this study a theoretical framework for calculating the acoustic response of optical fiber-based ultrasound sensors is presented. The acoustic response is evaluated for optical fibers with several layers of coating assuming a harmonic point source with arbitrary position and frequency. First, the fiber is acoustically modeled by a layered cylinder on which spherical waves are impinged. The scattering of the acoustic waves is calculated analytically and used to find the normal components of the strains on the fiber axis. Then, a strain-optic model is used to calculate the phase shift experienced by the guided mode in the fiber owing to the induced strains. The framework is showcased for a silica fiber with two layers of coating for frequencies in the megahertz regime, commonly used in medical imaging applications. The theoretical results are compared to experimental data obtained with a sensing element based on a pi-phase-shifted fiber Bragg grating and with photoacoustically generated ultrasonic signals.
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Spherical waves generated from a point source scatter from the optical fiber which is located at a distance of d from the source. The radii of the glass fiber and the coatings are 62.5, 110, and 130 μm, respectively.

A. Veres, Amir Rosenthal, P. Burgholzer, V. Ntziachristos, and T. Berer, „Characterization of the spatio-temporal response of optical fiber sensors: scattering of spherical waves from a layered cylinder,” J. Acoust. Soc. Am. Vol. 135, pp. 1853-1862 (2014).