Highly Efficient and Tailorable On-Chip Metal–Insulator–Metal Plasmonic Nanofocusing Cavity

Simulation techniques were used to investigate the properties of a deep subwavelength-scale on-chip optical cavity composed of a highly efficient metal–insulator–metal 3D-tapered plasmonic nanofocusing waveguide and easily tailorable metal–insulator–metal plasmonic crystals. The configuration described here significantly enhanced the highly efficient field localization in the plasmonic nanofocusing waveguide at the center of the cavity due to the impedance tuning capabilities of the plasmonic crystals. The plasmonic crystals served as nanoscale input and output couplers with designable reflectivities and a clear band-stop regime around the telecommunication wavelength, λ₀ = 1.55 μm. Simulation studies indicated that this configuration could efficiently confine electromagnetic waves on the nanometer length scale through a field intensity enhancement of 7 × 10³ and a Purcell enhancement of 8 × 10³ within a volume of 1.4 × 10^–5 λ₀³. To evaluate the performance of the highly efficient metal–insulator–metal 3D-tapered plasmonic nanofocusing waveguide structure itself, the overall focusing efficiency, that is, the transmission rate from the wavelength-scale input side to the deep subwavelength-scale focusing core in the tapered waveguide, was calculated to be around 85%