Abstract
A strong coupling regime is demonstrated at near infrared between metallic nanoparticle chains (MNP), supporting localized surface plasmons (LSP), and dielectric waveguides (DWGs) having different core materials. MNP chains are deposited on the top of these waveguides in such a way that the two guiding structures are in direct contact with each other. The strong coupling regime implies (i) a strong interpenetration of the bare modes forming two distinct supermodes and (ii) a large power overlap up to the impossibility to distinguish the power quota inside each bare structure. Additionally, since the system involves LSPs, (i) such a strong coupling occurs on a broad band and (ii) the peculiar vortex-like propagation mechanism of the optical power, supported by the MNP chain, leads to a regime where the light is slowed down over a wide wavelength range. Finally, the strong coupling allows the formation of guided supermodes in regions where the bare modes cannot be both guided at the same time. In other words, very high k modes can then be propagated in a dielectric photonic circuit thanks to hybridisation, leading to extremely concentrated propagating wave. Experimental work gives indirect proof of strong coupling regime whatever the waveguide core indexes.
Highlights
Plasmonic surface polariton (SPP) waveguides have attracted an increasing attention in the past few years owing to their ability to confine light below the diffraction limit[1], thereby potentially enabling device miniaturization at the nanoscale with dimensions not accessible with conventional dielectric waveguides
A traditional SOI waveguide, having a Si rectangular core, with height H and width W equal to 220 nm and 500 nm are placed on top of a SiO2 substrate[14], constitutes the dielectric waveguide (DWG) of the coupled system
The regime of strong coupling has been demonstrated for optical systems comprised of a dielectric waveguide and a gold elliptic nanocylinder chain supporting localized surface plasmons guided modes
Summary
Plasmonic surface polariton (SPP) waveguides have attracted an increasing attention in the past few years owing to their ability to confine light below the diffraction limit[1], thereby potentially enabling device miniaturization at the nanoscale with dimensions not accessible with conventional dielectric waveguides. Metallic nanoparticle (MNP) chains, supporting localized surface plasmon (LSP) modes, can confine light at still smaller scales than the SPP systems[7,8,9,10]. Strong coupling has been demonstrated between a surface plasmon propagating on a planar silver thin film and the lowest excited state of CdSe nanocrystals[26] This regime has been claimed for a coupled-waveguide system formed by SOI waveguides and a plasmonic nanogap supporting a propagative surface plasmon polariton[27, 28]. We present a detailed investigation of the coupling regime in optical systems comprised of a dielectric waveguide having small intrinsic losses and a lossy metallic nanoparticle chain deposited on top of the waveguide. Following the improved coupled waveguide mode theory[25], the power maximum in one waveguide is predicted not to spatially coincide with the power minimum in the other one
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