Antenna-Driven Optical Fiber-Based Acousto-Optic Modulation Devices: Electro-Mechanical Model and Experimental Validation.

Acousto-optic modulation (AOM)-based sensors offer distinct advantages compared to their electrical counterparts. The electromagnetic immunity of optical fibers makes AOMs ideal for applications like radio frequency (RF) field measurement inside the bore of a magnetic resonance imaging (MRI) scanner without interfering with the RF environment. These RF field sensors utilize antennae coupled with a radially poled, coaxial piezoelectric transducer over an optical Fiber-Bragg Grating (FBG). The design and optimization of these sensors require a complete electromechanical model of the fiber-transducer composite structure. This study presents an electromechanical equivalent circuit model for antenna-coupled, fiber-based AOMs, toward the determination of the electromechanical frequency response of this type of AOM-based sensor. The transducer model is validated against experimental data on a Zinc Oxide (ZnO)-based acousto-optic phase modulator in 1-800 MHz range, as well as a piezocomposite-based FBG-AOM sensor in the 1-100 MHz range. The antenna-coupled model is validated experimentally utilizing an N-turn loop antenna-coupled sensor for H-field measurements up to 100 MHz. The results also show the utility of sensitive, broadband optical FBG measurements for characterizing piezoelectric materials with high losses, which prevents accurate electrical characterization. The developed and validated model can be beneficial for design optimization of AF-AOM based sensors for different applications.