Electromagnetic radiation can exert forces on material objects. These forces are extremely feeble but manifest themselves in special circumstances (e.g., in the tails of comets). Recently, thanks to the progress in micro- and nanofabrication, there has been a surge of interest in the manipulation the center-of-mass motion of small mechanical oscillators by radiation forces. Among various sub-micron optomechanical systems presently investigated, suspended membranes containing a photonic crystal cavity are promising candidates.Confining and co-localizing phonons and photons
Photonic crystal defect cavities have been widely studied in nanophotonics and quantum optics. In close collaboration with the group of Tobias Kippenberg at EPFL , We demonstrated optomechanical coupling in such a defect cavity . The experimental setup can be seen in Fig. 1 (Left). The brownian motion of a suspended photonic crystal membrane embedding a defect cavity is investigated by evanescently coupling a laser into the optical cavity and locking it to a slightly higher frequency close to the resonance to avoid thermal effects and to transduce the motion of the membrane on the frequency noise spectrum of the transmitted laser.
These measurements reveal two families of modes. At low frequency (below 200 MHz), drum modes of the whole membrane are observed, while at high frequency (around 1 GHz), the resonator exhibits modes localized within the defect cavity. These latter modes correspond to a deformation of the core of the defect cavity surrounded by holes. Due to the strong confinement and colocalization of photons and phonons in these high-frequency localized modes, the coupling between light and these mechanical modes is one order of magnitude higher than that observed in more conventional mechanical resonators (such as beams or microtores).
This enhanced photon-phonon coupling may be used in a variety of future experiments, both on a fundamental level (quantum back-action effects...) and on a more technological level (radiation-pressure clocks or actuators...). Such experiments will strongly benefit from a fully integrated system, by use of integrated waveguides carrying light close to the nanomechanical devices (see Fig. 1 right).
Optomechanical Coupling in a Two-Dimensional
Photonic Crystal Defect Cavity,