Thursday, February 2, 2012
Researchers from the NIST Center
for Nanoscale Science and Technology have made a grating coupler that transmits
over 45% of the incident optical energy from a plane wave into a single surface
plasmon polariton (SPP) mode propagating on a flat gold surface, an
order-of-magnitude increase over any SPP grating coupler reported to date.
Surface plasmons are propagating waves of light tightly
confined to a metal surface via coupling with oscillating electrons in the
metal. SPPs have been used to route signals for optical interconnects and to
concentrate light for molecular sensors.
The researchers’ simple integrated coupler may improve
performance and lower packaging costs for such devices and may also enable
high-frequency optical connections between devices over longer distances. The
researchers developed an analytical model of the coupling process to optimize
the depth, width, and period of the identical rectangular grating groves that
they nanofabricated on a gold surface.
Optical measurements on different sets of gratings confirmed
the model's prediction that the highest efficiency would occur with "critical
coupling," when the scattering by the grating groves is matched to the
intrinsic losses of the SPP propagating on the grating. Because these couplers
can be used to excite surface plasmonic devices more efficiently, the
researchers expect that they will enable the development of a variety of future
on-chip devices.
SOURCE
