Abstract
Using Bloch modes to study the extraordinary transmission of light through a periodic array of slits in a metallic host, we discuss the differing roles of surface plasmon polaritons and Wood's anomalies in the observed behavior of such structures. Under certain circumstances, the first few excited modes appear to play a decisive role in determining the transmission efficiency of the array. Surface plasmon excitations tend to reduce the transmissivity of a semi-infinitely thick slit array, yet, paradoxically, the same reduction can account for enhanced transmission in an array of finite thickness tau, provided that tau is tuned to a Fabry-Perot-like resonance between the entrance and exit facets of the slit array. At the Wood anomaly, power redistribution produces sharp peaks in the diffraction efficiencies of various reflected and transmitted orders of the semi-infinite structure. With skew incidence, the degenerate states split, resulting in two peaks and two valleys, as observed by Wood in his 1902 experiments.
Highlights
The extraordinary transmission of electromagnetic waves through single apertures or periodic arrays of such apertures has been the subject of theoretical and experimental investigations for several years [1,2,3,4,5,6,7,8,9,10,11]
For the role of surface plasmon polaritons (SPP) in the transmission process, Cao and Lalanne [7] followed a strict definition and, using a rigorous coupled-wave analysis (RCWA), concluded that SPP plays a negative role in the transmission enhancement
In a semi-infinite slit array located in the half-space z > 0 and illuminated by a plane-wave arriving from the free space region z < 0, the strength of the various excited modes can be determined by matching the boundary conditions at the entrance facet of the slit array, namely, in the xy-plane located at z = 0
Summary
The extraordinary transmission of electromagnetic waves through single apertures or periodic arrays of such apertures has been the subject of theoretical and experimental investigations for several years [1,2,3,4,5,6,7,8,9,10,11]. For a single subwavelength slit aperture [10, 11], transmission of the TM mode turns out to be so high that SPP excitation alone may not suffice to explain the results These contradictions in belief and discrepancies in analysis highlight the need for a satisfactory explanation of SPP-related phenomena. When a periodic array of slits (either empty or filled with a dielectric) is introduced in a semi-infinite metallic host, under certain circumstances, the electromagnetic waves excited at the entrance facet will have the SPP character. In a semi-infinite slit array located in the half-space z > 0 and illuminated by a plane-wave arriving from the free space region z < 0, the strength of the various excited modes can be determined by matching the boundary conditions at the entrance facet of the slit array, namely, in the xy-plane located at z = 0 This is done, where we minimize (simultaneously) the difference between the tangential E-fields, as well as that between the tangential H-fields, across the interface.
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