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The emerging field of plasmonics is based on exploiting the
coupling between light and collective electronic excitations
within conducting materials known as surface plasmons. Because
the so-called surface plasmon polariton (SPP) modes that arise
from this coupling are not constrained by the optical diffraction
limit, it is hoped that they could enable the construction of
ultracompact optical components. But in order that such
potential can be realized, it is vital that the relatively poor
light- SPP coupling be improved. This is made worse by the
fact that the incident light that is conventionally used to
launch SPPs in a metal film is a significant source of noise,
unless directed away from a region of interest, which then
decreases the signal and increases the system's size. Back-side
illumination of subwavelength apertures in optically thick metal
films eliminates this problem but does not ensure a unique
propagation direction for the SPP.We propose a novel back-side
slit-illumination method that incorporates a periodic array of
grooves carved into the front side of a thick metal film. Bragg
reflection enhances the propagation of SPPs away fromthe array,
enabling them to be unidirectionally launched from, and focused
to, a localized point.
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