Anisotropic magnetic response of opto-mechanical resonance in a high Q microbubble optical resonator filled with magnetic fluids

We reported the opposite change of the resonant frequency of mechanical modes in magnetic fluid-filled optical microbubble resonators (MF-filled MBRs) under a magnetic field. Such change was found to come from the anisotropic responses of the acoustic wave to the aligned MF. The acoustic wave in the wineglass mechanical mode propagates along azimuthally and that of the breathing mechanical mode propagates axially; therefore, the acoustic wave of the two modes interacts with the aligned magnetic particle chain differently, leading to the opposite change of the resonant frequency. Anisotropy also results in the opposite change of the resonant frequency of the same mechanical mode when the magnetic field is applied in orthogonal directions. Our work provides what we believe to be a novel optomechanical system with rich resonance manipulation capabilities.