Characterization of radiation pressure and thermal effects in a nanoscale optomechanical cavity

Abstract

Optical forces in guided-wave nanostructures have recently been proposed as an effective means of mechanically actuating and tuning optical components. In this work, we study the properties of a photonic crystal optomechanical cavity consisting of a pair of patterned Si_3N_4 nanobeams. Internal stresses in the stoichiometric Si_3N_4 thin-film are used to produce inter-beam slot-gaps ranging from 560-40 nm. A general pump-probe measurement scheme is described which determines, self-consistently, the contributions of thermo-mechanical, thermo-optic, and radiation pressure effects. For devices with 40 nm slot-gap, the optical gradient force is measured to be 134 fN per cavity photon for the strongly coupled symmetric cavity supermode, producing a static cavity tuning greater than five times that of either the parasitic thermo-mechanical or thermo-optic effects.

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