Abstract
We propose and study an integrated refractive index sensor which is based on a plasmonic slot waveguide cavity. In this device, a guided mode supported by a silicon photonic wire waveguide is vertically coupled to a metal-dielectric-metal cavity separated by a silicon oxide spacer. We perform an in-depth study that links the geometrical parameters of the sensor to the coupling mechanism and sensitivity of the plasmonic slot waveguide cavity. Simulation results promise that local changes of refractive index can be measured with a high sensitivity of around 600 nm/RIU in a femto-liter volume. These results are obtained with three-dimensional time and frequency domain simulations. Thanks to the high field enhancement in the slot of the plasmonic cavity, a high local sensitivity to changes of refractive index is obtained. Moreover, the high level of achieved decoupling between the bulk and the local sensitivity complies well with the requirements of biomolecular sensing.
Highlights
The ability of metal-dielectric interfaces to sustain localized electromagnetic modes known as surface plasmon polaritons (SPP) allows confinement and guiding light in volumes smaller than the diffraction limit over a couple of micrometers in the visible spectrum
Similar results were obtained by localized surface plasmon resonance (LSPR) supported by metallic nanoparticles [6, 7] which reveals that for small molecule detection, LSPR can excel Surface plasmon resonance (SPR) because it is more sensitive to changes in refractive index close to its surface [8]
As the plasmonic slot waveguide cavity (PSWC) is excited by a dielectric waveguide, we need to perform a modal analysis of the dielectric waveguide itself and of the coupled system i.e. the dielectric waveguide coupled to the plasmonic slot waveguide to optimize it
Summary
The ability of metal-dielectric interfaces to sustain localized electromagnetic modes known as surface plasmon polaritons (SPP) allows confinement and guiding light in volumes smaller than the diffraction limit over a couple of micrometers in the visible spectrum. Similar results were obtained by localized surface plasmon resonance (LSPR) supported by metallic nanoparticles [6, 7] which reveals that for small molecule detection, LSPR can excel SPR because it is more sensitive to changes in refractive index close to its surface [8].
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