Near-field optical transducer for nanomechanical resonators

We show that a single-mode tapered-fiber waveguide can be used as a sensitive transducer to couple to the motion of a nanomechanical resonator. When the waveguide and the resonator are sufficiently close to each other, small mechanical oscillations of the resonator can be actuated efficiently by the optical dipole force. Scattering of evanescent waves confined around the waveguide and the ensuing modulation in the optical transmission through the waveguide allow for sensitive detection of the resonator oscillations. Using this technique, we have measured high-frequency nanomechanical resonances with a $∼150fmHz−1/2$ noise floor at a detection power of $∼100μW$⁠. The tapered-fiber waveguide provides a single seamless transduction interface between the device chip and the measurement equipment, thus offering potential for use outside of the research laboratory.