Mechanical Tuning of WGM Silica Microspheres and WGM-Based Strain Gauge-Geometrical Considerations

In this paper we present an experimental demonstration and a theoretical study on mechanical tuning of whispering gallery modes (WGMs) of double-tailed silica microspheres. The mechanical tuning is performed by applying tensile stress on double-tailed microspheres with a variety of diameters. The dependence of the tuning sensitivity on some geometrical considerations of the double-tailed microsphere is studied and demonstrated experimentally for the first time to the best of our knowledge. The tuning sensitivity is calculated for various microspheres using a simplified analytical model, and the calculation are compared with the measured values. The comparison shows good agreement between the calculated and measured values. As shown in the paper, the sensitivity increases with increasing the radius ratio of the fiber tails and that of the microspheres; the
${R_f}/{R_s}$
ratio. A strain-gauge based on a double-tailed microsphere with a sensitivity of 0.33 pm/µϵ is demonstrated, with a detection limit of ∼ 0.02
μ
ϵ.