Coherent Control of a Plasmonic Nanoantenna Integrated on a Silicon Chip

Abstract

Illuminating a plasmonic nanoantenna by a set of coherent light beams should tremendously modify its scattering, absorption, and polarization properties, thus, enabling all-optical dynamic manipulation. However, diffraction inherently makes coherent control of isolated subwavelength-sized nanoantennas highly challenging when illuminated from free-space. Here, we overcome this limitation by placing the nanoantenna at a subwavelength distance of the output facet of silicon waveguides that provide monolithically defined paths for multibeam coherent illumination. Inspired by coherent perfect absorption (CPA) concepts, we demonstrate experimentally modulation of the nanoantenna scattering by more than 1 order of magnitude and of the on-chip transmission by >50% over a ∼200 nm bandwidth at telecom wavelengths by changing the phase between two counter-directional coherent guided beams. Moreover, we demonstrate coherent synthesis of polarization of the radiated field by illuminating the nanoantenna from orthogonal waveguides. Our finding paves the way toward coherent manipulation of nanoantennas and all-optical processing without nonlinearities in an integrated platform.