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

Ryan M Camacho,Oskar Painter,Jasper Chan,Matt Eichenfield

doi:10.1364/oe.17.015726

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 Si3N4 nanobeams. Internal stresses in the stoichiometric Si3N4 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.

Highlights

In an adiabatic limit [10,29], the radiation pressure force can be related to the gradient of the internal optical cavity energy, FOM = −∂(Nhωc)/∂α = −NhgOM, where N is the stored photon number and α is a displacement factor related to the movement of the nanobeams
In the case of the odd parity anti-bonded cavity modes, the resonance frequency decreases with increasing slot-gap, resulting in a negative gOM and an optical force that pushes the beams apart
For the limited model in which we consider optomechanical, thermo-mechanical, and thermo-optic sources of mode tuning, the induced frequency shift in a given mode can be separated into two components, one which is mechanical in nature and depends upon the reaction of a given mode to the deflection of the nanobeams, the other which is independent of the type of mode and is only dependent upon the intensity of the internal cavity field: Δωi j = δαig j + ctoNi, (1)

Summary

Introduction

In an adiabatic limit [10,29], the radiation pressure force can be related to the gradient of the internal optical cavity energy, FOM = −∂(Nhωc)/∂α = −NhgOM, where N is the stored photon number and α is a displacement factor related to the movement of the nanobeams

Results

Conclusion