Metallic nanoparticles and nanoantennas have been extensively studied due to their capability to increase electromagnetic field confinement which is essential in numerous applications ranging from optoelectronics to telecommunication and sensing devices. We show that a double bowtie nanoantenna has a higher electric field confinement in its gap compared to a single bowtie nanoantenna, which is expected to give better fluorescence enhancement of a single emitter placed in the gap. We show that the electric field intensity can be further increased by placing the double bowtie inside a ring grating structure where the excitation of surface plasmon-polaritons (SPPs) is achieved. We perform FDTD simulations to characterise the double bowtie nanoantenna and study the effect of its dimensions on the electric field enhancement in the gap. Our proposed integrated structure with gratings is shown to increase the electric field by a factor of 77 due to a double cavity effect. Next steps would be to study the fluorescence enhancement of emitters placed inside our double bowtie / ring grating nanocavity to see if the strong coupling regime can be attained.
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