High-frequency microoptoelectromechanical systems (MOEMS) are proposed as active devices for radio frequency signal processing. Parametric amplification (PA), generation, frequency modulation and frequency conversion on the micromechanical level were demonstrated at MHz range by microfabricated single-crystal silicon mechanical resonators. A focused laser beam was used to pump energy into the motion of the oscillator, to control the frequency response and to provide a carrier signal for the frequency up-conversion. Laser light interaction with the microelectromechanical system (MEMS) was realized through the stress pattern induced within the microfabricated structure by the focused laser beam. Stress-induced stiffening of the oscillator provides control over the effective spring constant and leads to a parametric mechanism for amplification of mechanical vibrations. Periodic modulation of the laser intensity synchronized with the driving force allowed us to demonstrate a degenerate (phase-sensitive) PA scheme with gain in access of 30dB. Design of the oscillator as a part of the built-in Fabry-Perot cavity provides auto-modulation of the effective spring constant as a result of the position-dependent absorption of the light by the oscillator. The auto-modulation mechanism allows a parametric self-excitation induced by continuous wave (CW) laser beam. Self-sustained generation was observed when laser power exceeded a threshold of few hundred microWatts. Nonlinear effects cause frequency dependence vs. laser power, providing a mechanism for frequency modulation of the self-generated vibrations. The same type of optical scheme can also work as an ideal frequency mixer, which combines the self-generated response with an external high-frequency modulation of the laser intensity.
Micromechanical oscillators in the radio frequency (rf) range were fabricated in the form of silicon discs supported by a SiO2 pillar at the disc center. Effective spring constant of this oscillator can be controlled within the range (Delta) f/f approximately 10-4 by a low power laser beam, (Plaser approximately 100 (mu) W), focused at the periphery of the disc. Parametric amplification of the disc's vibrations was achieved through a double frequency modulation of the laser power. An amplitude gain of up to 30 was demonstrated, with further increase limited by non-linear behavior and self-generation. Phase dependence, inherent in degenerate parametric amplification, was also observed. Self- modulation of the CW laser beam (Plaser approximately 100 (mu) W) provided by placing the disc oscillator into an interference pattern setup can lead to parametric self- excitation.
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