Abstract
A detailed theoretical study of composite plasmonic waveguide structures is reported. Expressions for modal expansion coefficients, optical transmittance and surface intensity are presented and used to describe the behavior of dielectric channel waveguides containing a short gold-coated section. The superstrate refractive index is shown to control modal beating and modal attenuation in the gold-coated region leading to distinctive features in the surface intensity and device transmittance. The model presented allows detailed prediction of device performance, enabling improved design of highly sensitive miniature devices for evanescent refractometry and vibrational spectroscopy, and can be extended to the design and optimization of composite waveguides structures with nano-patterned overlayers.
Highlights
Hybrid plasmonic devices incorporating dielectric and metallic waveguiding structures [1, 2] offer great potential for ultra-compact high performance devices from polarizers [3] and sensors [4], through surface-enhanced Raman spectrometers [5,6], to telecommunications filters [7] and all-optical switches
A detailed theoretical study of a composite-plasmonic waveguide structure based on channel waveguides is given in this paper, yielding detailed information on the excitation of modes in the composite structure from an input dielectric waveguide, their propagation over the gold-coated region, the transmittance of the device into an output dielectric waveguide, and the optical intensity at the surface of the gold film
It was observed that modal beating in the gold-coated region, which strongly affects surface intensity and transmittance, can be controlled through the superstrate index, and that the transmission and surface intensity behavior is dominated by the behavior of the hybrid dielectric-plasmonic mode (HDM) in terms of its excitation and attenuation
Summary
Hybrid plasmonic devices incorporating dielectric and metallic waveguiding structures [1, 2] offer great potential for ultra-compact high performance devices from polarizers [3] and sensors [4], through surface-enhanced Raman spectrometers [5,6], to telecommunications filters [7] and all-optical switches. The HDM mode propagation loss, on the other hand, the lowest, shows a resonant increase around a superstrate index of 1.365 The effective indices and propagation losses of SPP-s and SPP-a, on the other hand, vary linearly with superstrate index (note the scale change) This behavior is similar to that shown by similar modes supported by thin metallic films [28]. It should be noted that for low superstrate indices no bound SPP-s mode exists and the supported mode is leaky
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