A low-loss thin-film waveguide for surface plasmon polaritons (SPPs) could aid the development of nanoscale photonic integrated circuits on silicon. Recent research has focused on using SPPs as signal carriers in nanoscale integrated circuits to increase the degree of accumulation and reduce power consumption. But, so far, SPP waveguides have not been suitable for nanoscale integrated circuits. Schematic diagrams and electric field intensity distributions for (a) a multi-slit structure, (b) a disk array, and (c) no diffraction structure at the waveguide end. Courtesy of Toyohashi University of Technology. The new waveguide was developed by Dr. Mitsuo Fukuda and his group at Toyohashi University of Technology. The team deposited a thin gold film on a silicon substrate with a diffraction structure at the end. The diffraction structure guides the SPPs transmitted on the surface (air-gold interface) to the opposite side of the gold-silicon interface, where a Schottky barrier forms. The guided SPPs excite the free electrons in the metal, which then cross over the barrier and are observed as photocurrent. The new waveguide enabled the efficient propagation of polaritons in 1550-nm-wavelength bands, the researchers said. The work was published in Applied Physics Letters (doi: 10.1063/1.4866792). For more information, visit www.tut.ac.jp/english.