Extraordinary nonlinear transmission modulation in a doubly-resonant optomechanical structure

International audienceNanoscale-engineered optical systems have been thoroughly investigated for a few decades due to their fascinating abilities to confine and enhance electromagnetic fields in very sub-wavelength and have a large number of applications in domains like biosensing, enhanced-Raman spectroscopy, metamaterials, photothermal therapy, and plasmomechanics. In addition, the recent astonishing ability of phononic crystals to control acoustic or elastic waves has been demonstrated. As an elastic wave modulates in time both the shape and the refractive index of the supporting structure, it is possible to influence the optical response of the same system. We propose a subwavelength optomechanical structure that instead relies on a double resonance to achieve strong modulation at near-infrared wavelengths. Precisely, we investigate the coupling between an optical Fano resonant mode and phononic resonances carried within a 2D metamaterial. The latter was designed to exhibit simultaneous phononic and photonic high Q-factor resonances and it is composed of silver slits deposited on a lithium niobate substrate. The phononic properties are first determined and show that several vibration modes can be electrically induced through the specific design of the structure that behaves as an interdigitated transducer. The structure geometries for each mode is then determined over an acoustic period and used to point out the optical transmission modifications when the structure is illuminated at the normal incidence by a linearly polarized plane wave. Original results are obtained for some modes (the first two odd phononic modes) showing a very efficient and non-linear modification of the transmitted intensity. Different operating procedures are then explored by changing the operation optical wavelength value. This study opens the way to the design of a new generation of extremely miniaturized optoacoustic devices