Whispering-Gallery Modes to Investigate Opto-Mechanical Interactions in Optical Fibers

Whispering galley modes (WGM) are optical resonances that can exist in circularly symmetric dielectric resonators where the electromagnetic field is confined near to the surface of the resonator. Optical fibers are cylindrical microresonators with WGM resonances with quality factors up to 10 ⁷ . WGMs resonance frequencies are sensitive to perturbations in both the dimensions of the resonant cavity and to changes in the material, which has been exploited in numerous sensing and characterization applications [1]–[2]. Acoustic oscillations inside the dielectric microresonator can modify the refractive index of the material due to the elasto-optic effect and also the transverse dimensions of the resonator. Therefore, they can eventually be detected using WGMs. In this work, we take advantage of this mechanisms, and we demonstrate a novel optical technique to detect transverse acoustic mode resonances (TAMRs) in optical fibers using WGMs. TAMRs are excited by the optical beam propagating in the fiber core and are responsible for the forward Brillouin scattering effect. They feature strain components only in the transverse plane of the waveguide axis.