Experimental measurement of plasmonic nanostructures embedded in silicon   waveguide gaps
  In this work, we report numerical simulations and experiments of the optical response of a gold nanostrip embedded in a silicon strip waveguide gap at telecom wavelengths. We show that the spectral features observed in transmission and reflection when the metallic nanostructure is inserted in the gap are extremely different to those observed in free-space excitation. First, we find that interference between the guided field and the electric dipolar resonance of the metallic nanostructure results in high-contrast (> 10) spectral features showing an asymmetric Fano spectral profile. Secondly, we reveal a crossing in the transmission and reflection responses close to the nanostructure resonance wavelength as a key feature of our system. This approach, which can be realized using standard semiconductor nanofabrication tools, could lead to fully exploit the extreme properties of subwavelength metallic nanostructures in an on-chip configuration, with special relevance in fields such as biosensing or optical switching. 
Alba Espinosa-Soria, Amadeu Griol and Alejandro Mart\'inez
physics.optics