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

The emerging field of nanophotonics 1 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 polaritons 2 , 3 are among the most promising candidates for subwavelength optical confinement 3 , 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 demands 3 , 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 µm) with strong mode confinement (ranging from λ 2 /400 to λ 2 /40). This approach is fully compatible with semiconductor fabrication techniques and could lead to truly nanoscale semiconductor-based plasmonics and photonics. Xiang Zhang and colleagues from the University of California, Berkeley, propose a new approach for confining light on scales much smaller than the wavelength of light. Using hybrid waveguides that incorporate dielectric and plasmonic waveguiding techniques, they are able to confine surface plasmon polaritons very strongly over large distances. The advance could lead to truly nanoscale plasmonics and photonics.