1,468 research outputs found
Correlation of circular differential optical absorption with geometric chirality in plasmonic meta-atoms
We report a strong correlation between the calculated broadband circular differential optical absorption (CDOA) and the geometric chirality of plasmonic meta-atoms with two-dimensional chirality. We investigate this correlation using three common gold meta-atom geometries: L-shapes, triangles, and nanorod dimers, over a broad range of geometric parameters. We show that this correlation holds for both contiguous plasmonic meta-atoms and non-contiguous structures which support plasmonic coupling effects. A potential application for this correlation is the rapid optimization of plasmonic nanostructure for maximum broadband CDOA
Impact of nonlinear loss on Stimulated Brillouin Scattering
We study the impact of two-photon absorption (2PA) and fifth-order nonlinear
loss such as 2PA-induced free-carrier absorption in semiconductors on the
performance of Stimulated Brillouin Scattering devices. We formulate the
equations of motion including effective loss coefficients, whose explicit
expressions are provided for numerical evaluation in any waveguide geometry. We
find that 2PA results in a monotonic, algebraic relationship between
amplification, waveguide length and pump power, whereas fifth-order losses lead
to a non-monotonic relationship. We define a figure of merit for materials and
waveguide designs in the presence of fifth-order losses. From this, we
determine the optimal waveguide length for the case of 2PA alone and upper
bounds for the total Stokes amplification for the case of 2PA as well as
fifth-order losses. The analysis is performed analytically using a small-signal
approximation and is compared to numerical solutions of the full nonlinear
modal equations
Power limits and a figure of merit for stimulated Brillouin scattering in the presence of third and fifth order loss
We derive a set of design guidelines and a figure of merit to aid the
engineering process of on-chip waveguides for strong Stimulated Brillouin
Scattering (SBS). To this end, we examine the impact of several types of loss
on the total amplification of the Stokes wave that can be achieved via SBS. We
account for linear loss and nonlinear loss of third order (two-photon
absorption, 2PA) and fifth order, most notably 2PA-induced free carrier
absorption (FCA). From this, we derive an upper bound for the output power of
continuous-wave Brillouin-lasers and show that the optimal operating conditions
and maximal realisable Stokes amplification of any given waveguide structure
are determined by a dimensionless parameter involving the
SBS-gain and all loss parameters. We provide simple expressions for optimal
pump power, waveguide length and realisable amplification and demonstrate their
utility in two example systems. Notably, we find that 2PA-induced FCA is a
serious limitation to SBS in silicon and germanium for wavelengths shorter than
2200nm and 3600nm, respectively. In contrast, three-photon absorption is of no
practical significance
Benchmarking five numerical simulation techniques for computing resonance wavelengths and quality factors in photonic crystal membrane line defect cavities
We present numerical studies of two photonic crystal membrane microcavities,
a short line-defect cavity with relatively low quality () factor and a
longer cavity with high . We use five state-of-the-art numerical simulation
techniques to compute the cavity factor and the resonance wavelength
for the fundamental cavity mode in both structures. For each method,
the relevant computational parameters are systematically varied to estimate the
computational uncertainty. We show that some methods are more suitable than
others for treating these challenging geometries.Comment: Revised and final version for publication. 28 pages, 10 figures, 7
table
Insights into directional scattering : from coupled dipoles to asymmetric dimer nanoantennas
Strong and directionally specific forward scattering from optical nanoantennas is of utmost importance for various applications in the broader context of photovoltaics and integrated light sources. Here, we outline a simple yet powerful design principle to perceive a nanoantenna that provides directional scattering into a higher index substrate based on the interference of multiple electric dipoles. A structural implementation of the electric dipole distribution is possible using plasmonic nanoparticles with a fairly simple geometry, i.e. two coupled rectangular nanoparticles, forming a dimer, on top of a substrate. The key to achieve directionality is to choose a sufficiently large size for the nanoparticles. This promotes the excitation of vertical electric dipole moments due to the bi-anisotropy of the nanoantenna. In turn, asymmetric scattering is obtained by ensuring the appropriate phase relation between the vertical electric dipole moments. The scattering strength and angular spread for an optimized nanoantenna can be shown to be broadband and robust against changes in the incidence angle. The scattering directionality is maintained even for an array configuration of the dimer. It only requires the preferred scattering direction of the isolated nanoantenna not to be prohibited by interferenc
- …