Abstract

Cavity-optomechanical systems in which the optical cavity frequency is dependent upon the square of the mechanical displacement, so-called quadratic coupling [1], have been proposed as a means of performing quantum non-demolition measurement of mechanical motion, squeezing of the mechanical field, and measurement of phonon shot noise [2]. Quadratic coupling arises naturally in multi-moded optical systems such as the membrane-in-the-middle (MIM) Fabry-Perot cavity system [3]; however, achieving significant quadratic coupling strengths is still a challenge. Here we present the design, fabrication, and characterization of a tunable, multi-moded photonic crystal optomechanical resonator capable of large quadratic coupling. The device is a double-slotted photonic crystal in which we tune the optical mode frequencies using electrostatic actuation of the slot widths (see Fig. 1a). Application of a voltage across the tuning capacitors connected to the two outer photonic crystal slabs can be used to drive the system from the linear regime into quadratic coupling regime. Measurements of the mechanical power spectral density, as shown in Fig. 1b, provide a direct signatures of the linear and quadratic coupling to mechanical modes of the structure.

© 2015 IEEE