Ultrasmall subwavelength nanorod plasmonic cavity.

We propose an ultrasmall plasmonic cavity consisting of a high-index/low-index dielectric nanorod covered with silver. Full three-dimensional subwavelength confinement of the surface-plasmon polaritons was achieved at the high-index dielectric-silver interface without propagating to the low-index dielectric-silver interface. The numerical simulations showed that the plasmonic mode excited in this cavity has a deep subwavelength mode volume of 0.0038(λ/2n)(3) and a quality factor of 1500 at 40 K, and consequently a large Purcell factor of ∼2×10(5). Therefore, this plasmonic cavity is expected to be useful for the demonstration of high-efficiency single photon sources or low-threshold lasers in an ultracompact nanophotonic circuit.