Addressing nanoantennas with slow Bloch mode cavity: application to optical trapping (Conference Presentation)

Photonic crystal and plasmonic structures are the two main approaches used in nanophotonic for efficiently confining and enhancing the electromagnetic field at subwavelength scale. For these reasons, these two approaches have been both used for the optical trapping of nanometric particle. We present, here, experimental results showing that structures combining both photonic crystal and nanoantennas could lead to improved trapping performances. In previous theoretical papers [1, 2] we have shown that when the critical coupling between a photonic crystal and a nanoantenna is reached, a large Gaussian beam could be efficiently coupled to a single nanoantenna. In this way, it is possible to generate a nanometric hotspot in the nanoantenna leading to a very efficient optical trap. The experimental demonstration of this effect has been obtained on an SOI sample consisting in a gold nanoantenna located at the centre of a photonic crystal cavity. Stable trapping of 100 nm diameter nanoparticle has been observed using a 5mW laser at 1.31µm with a 5µm waist. The nanoparticle are trapped above the nanoantenna gap and a normalized trap stiffness of 0.3 fN.nm-1.mW-1 is measured. This result demonstrates the interest of this approach. We will discuss and compare it to the state of the art of nanotweezers. [1] A. El Eter et al. Opt. Express 22, 14464 (2014). [2] A. Belarouci et al. Opt. Express 18, A381 (2010).