113 research outputs found
Transmission of plasmons through a nanowire
Exact quantitative understanding of plasmon propagation along nanowires is
mandatory for designing and creating functional devices. Here we investigate
plasmon transmission through top-down fabricated monocrystalline gold nanowires
on a glass substrate. We show that the transmission through finite-length
nanowires can be described by Fabry-P\'{e}rot oscillations that beat with
free-space propagating light launched at the incoupling end. Using an extended
Fabry-P\'{e}rot model, experimental and simulated length dependent transmission
signals agree quantitatively with a fully analytical model.Comment: 5 pages, 4 figure
Impedance matching and emission properties of optical antennas in a nanophotonic circuit
An experimentally realizable prototype nanophotonic circuit consisting of a
receiving and an emitting nano antenna connected by a two-wire optical
transmission line is studied using finite-difference time- and frequency-domain
simulations. To optimize the coupling between nanophotonic circuit elements we
apply impedance matching concepts in analogy to radio frequency technology. We
show that the degree of impedance matching, and in particular the impedance of
the transmitting nano antenna, can be inferred from the experimentally
accessible standing wave pattern on the transmission line. We demonstrate the
possibility of matching the nano antenna impedance to the transmission line
characteristic impedance by variations of the antenna length and width
realizable by modern microfabrication techniques. The radiation efficiency of
the transmitting antenna also depends on its geometry but is independent of the
degree of impedance matching. Our systems approach to nanophotonics provides
the basis for realizing general nanophotonic circuits and a large variety of
derived novel devices
Electromechanically Tunable Suspended Optical Nano-antenna
Coupling mechanical degrees of freedom with plasmonic resonances has
potential applications in optomechanics, sensing, and active plasmonics. Here
we demonstrate a suspended two-wire plasmonic nano-antenna acting like a
nano-electrometer. The antenna wires are supported and electrically connected
via thin leads without disturbing the antenna resonance. As a voltage is
applied, equal charges are induced on both antenna wires. The resulting
equilibrium between the repulsive Coulomb force and the restoring elastic
bending force enables us to precisely control the gap size. As a result the
resonance wavelength and the field enhancement of the suspended optical
nano-antenna (SONA) can be reversibly tuned. Our experiments highlight the
potential to realize large bandwidth optical nanoelectromechanical systems
(NEMS)
Evolutionary optimization of optical antennas
The design of nano-antennas is so far mainly inspired by radio-frequency
technology. However, material properties and experimental settings need to be
reconsidered at optical frequencies, which entails the need for alternative
optimal antenna designs. Here a checkerboard-type, initially random array of
gold cubes is subjected to evolutionary optimization. To illustrate the power
of the approach we demonstrate that by optimizing the near-field intensity
enhancement the evolutionary algorithm finds a new antenna geometry,
essentially a split-ring/two-wire antenna hybrid which surpasses by far the
performance of a conventional gap antenna by shifting the n=1 split-ring
resonance into the optical regime.Comment: Also see Supplementary material, as attached to the main pape
Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption
Coherent perfect absorption (CPA) describes the absence of all outgoing modes
from a lossy resonator, driven by lossless incoming modes. Here, we show that
for nanoresonators that also exhibit radiative losses, e.g. plasmonic
nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA
outgoing modes are suppressed only for a subset of (guided plasmonic) modes
while other (radiative) modes are treated as additional loss channels - a
situation typically referred to as perfect impedance matching. Here we make use
of gCPA to show how to achieve perfect impedance matching between a single
nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both
radiant and subradiant characteristics are considered. We further demonstrate
potential applications in back-ground-free sensing
Driving plasmonic nanoantennas at perfect impedance matching using generalized coherent perfect absorption
Coherent perfect absorption (CPA) describes the absence of all outgoing modes from a lossy resonator, driven by lossless incoming modes. Here, we show that for nanoresonators that also exhibit radiative losses, e.g., plasmonic nanoantennas, a generalized version of CPA (gCPA) can be applied. In gCPA outgoing modes are suppressed only for a subset of (guided plasmonic) modes while other (radiative) modes are treated as additional loss channels - a situation typically referred to as perfect impedance matching. Here we make use of gCPA to show how to achieve perfect impedance matching between a single nanowire plasmonic waveguide and a plasmonic nanoantenna. Antennas with both radiant and subradiant characteristics are considered. We further demonstrate potential applications in background-free sensing
Second harmonic generation from plasmonic hotspots by controlled local symmetry breaking
Bonding resonant modes of plasmonic nanoantennas with narrow gaps exhibit
very large local field enhancement. These hotspots are highly attractive for
boosting optical nonlinearities, such as second harmonic generation. However,
for resonant symmetric gap antennas, the strong second harmonic sources created
at the gap interfaces oscillate out-of-phase and therefore interfere
destructively in the far-field. Here, we use an advanced nanofabrication
approach to systematically break the local symmetry of nanoscopic antenna gaps
while retaining the bonding resonant antenna mode at the fundamental frequency
and the concomitant intensity hotspot. We find that antennas with the strongest
local symmetry breaking emit correspondingly intense second harmonic radiation
as compared to symmetric reference structures. By combining these findings with
second harmonic radiation patterns as well as quantitative nonlinear
simulations, we obtain remarkably detailed insights into the mechanism of
second harmonic generation at the nanoscale. Our findings open new perspectives
for the realization of non-reciprocal nanoscale systems, where local symmetry
breaking is crucial to create unique functionalities
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