Adiabatic and nonadiabatic nanofocusing of plasmons by tapered gap plasmon waveguides

Adiabatic and nonadiabatic nanofocusing of plasmons in tapered gap plasmon waveguides is analyzed using the finite-difference time-domain algorithm. Optimal adaptors between two different subwavelength waveguides and conditions for maximal local field enhancement are determined, investigated, and explained on the basis of dissipative and reflective losses in the taper. Nanofocusing of plasmons into a gap of similar to 1 nm width with more than 20 times increase in the plasmon energy density is demonstrated in a silver-vacuum taper of similar to 1 mu m long. Comparison with the approximate theory based on the geometrical optics approximation is conducted

A hybrid plasmonic waveguide for subwavelength confinement and long-range propagation

The emerging field of nanophotonics1 addresses the critical challenge of manipulating light on scales much smaller than the wavelength. However, very few feasible practical approaches exist at present. Surface plasmon polaritons2, 3 are among the most promising candidates for subwavelength optical confinement3, 4, 5, 6, 7, 8, 9, 10. However, studies of long-range surface plasmon polaritons have only demonstrated optical confinement comparable to that of conventional dielectric waveguides, because of practical issues including optical losses and stringent fabrication demands3, 11, 12, 13. Here, we propose a new approach that integrates dielectric waveguiding with plasmonics. The hybrid optical waveguide consists of a dielectric nanowire separated from a metal surface by a nanoscale dielectric gap. The coupling between the plasmonic and waveguide modes across the gap enables 'capacitor-like' energy storage that allows effective subwavelength transmission in non-metallic regions. In this way, surface plasmon polaritons can travel over large distances (40–150 microm) with strong mode confinement (ranging from lambda2/400 to lambda2/40). This approach is fully compatible with semiconductor fabrication techniques and could lead to truly nanoscale semiconductor-based plasmonics and photonics