Optically pumped parametric amplification for micromechanical oscillators

Micromechanical oscillators in the rf range were fabricated in the form of silicon discs supported by a SiO₂ pillar at the disk center. A low-power laser beam, (P_laser∼100 μW), focused at the periphery of the disk, causes a significant change of the effective spring constant producing a frequency shift, Δf(Δf/f∼10^-4). The high quality factor, Q, of the disk oscillator (Q∼10⁴) allows us to realize parametric amplification of the disk's vibrations through a double frequency modulation of the laser power. An amplitude gain of up to 30 was demonstrated, with further increase limited by nonlinear behavior and self-generation. Phase dependence, inherent in degenerate parametric amplification, was also observed. Using this technique, the sensitivity of detection of a small force is greatly enhanced.