Extraordinary optical transmission through metallic gratings is mediated by Fabry-Perot cavity modes inside the apertures and surface waves propagating along the grating. Anomalous features arise in the grating transmission spectrum when the optical period for the surface wave is equal to the grating pitch. The surface waves can be plasmonic in nature or due to diffracted orders propagating parallel to the surface. At optical frequencies, plasmonic effects are well separated from Wood-Rayleigh anomalies. The plasmonic band gap properties were determined with COMSOL by propagating a plasmon on a smooth Ag surface followed with a section containing a series of air gaps. The reflection spectrum for the plasmons shows a well defined frequency gap for plasmon propagation. The COMSOL simulations for light transmitted through the grating reveal anomalies in the vicinity of the plasmonic band gap. At the center frequency of the gap where surface waves are forbidden, the transmission through the grating is very low and the reflection is 98%. Standing waves are formed at the band edges and the fields become localized. At the high energy band edge the electric field localizes in the low index medium and the magnetic field in the high index medium. The field localization reverses at the low energy band edge. As a result of the localization at the band edges, the surface plasmons couple strongly to the Fabry-Perot cavity modes at the high energy band edge leading to enhanced transmission through the grating with the opposite properties for the low energy band edge. © 2011 SPIE.
Enhanced and suppressed transmission through metal gratings at the plasmonic band edges
De Ceglia D.;Vincenti M. A.;
2011-01-01
Abstract
Extraordinary optical transmission through metallic gratings is mediated by Fabry-Perot cavity modes inside the apertures and surface waves propagating along the grating. Anomalous features arise in the grating transmission spectrum when the optical period for the surface wave is equal to the grating pitch. The surface waves can be plasmonic in nature or due to diffracted orders propagating parallel to the surface. At optical frequencies, plasmonic effects are well separated from Wood-Rayleigh anomalies. The plasmonic band gap properties were determined with COMSOL by propagating a plasmon on a smooth Ag surface followed with a section containing a series of air gaps. The reflection spectrum for the plasmons shows a well defined frequency gap for plasmon propagation. The COMSOL simulations for light transmitted through the grating reveal anomalies in the vicinity of the plasmonic band gap. At the center frequency of the gap where surface waves are forbidden, the transmission through the grating is very low and the reflection is 98%. Standing waves are formed at the band edges and the fields become localized. At the high energy band edge the electric field localizes in the low index medium and the magnetic field in the high index medium. The field localization reverses at the low energy band edge. As a result of the localization at the band edges, the surface plasmons couple strongly to the Fabry-Perot cavity modes at the high energy band edge leading to enhanced transmission through the grating with the opposite properties for the low energy band edge. © 2011 SPIE.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
