Perturbation of whispering gallery modes of magnetorheological polydimethylsiloxane spheres by external magnetic field

The effect of external magnetic field on the whispering gallery optical modes (WGM) of Magnetorheological Polydimethylsiloxane (MR-PDMS) spheres is studied. Magnetically polarizable particles are mixed in with the PDMS when it is in liquid form and cured to solidify into spheres with diameters of several hundreds of microns. The spheres are then coated with a layer of pure PDMS with thickness of several microns. Light from a tunable laser is tangentially coupled into this outer layer using a tapered single mode optical fiber in order to excite the optical modes of the sphere. These composite micro-sphere resonators exhibit high Q-factors (~ 106). An analysis is carried out to estimate the WGM shifts induced by the applied magnetic field. An experiment is also carried out to demonstrate the magnetic-field induced WGM shifts in a 400 μm diameter MR-PDMS resonator. The results indicate that MR-PDMS micro-spheres may be used as magnetic field sensors.