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

TL;DR

This paper investigates the interplay of radiation pressure and thermal effects in a nanoscale silicon nitride optomechanical cavity, demonstrating significant optical gradient forces and cavity tuning capabilities.

Contribution

It introduces a self-consistent pump-probe measurement scheme to distinguish thermo-mechanical, thermo-optic, and radiation pressure effects in a nanobeam cavity.

Findings

Radiation pressure force measured at 134fN per photon for 40nm gap.

Static cavity tuning exceeds thermo-mechanical and thermo-optic effects.

Inter-beam gap controlled by internal stresses in silicon nitride.

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 silicon nitride nanobeams. Internal stresses in the stoichiometric silicon nitride thin-film are used to produce inter-beam slot-gaps ranging from 560 to 40nm. 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 40nm slot-gap, the optical gradient force is measured to be 134fN 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.