207 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
Modelling of standard and specialty fibre-based systems using finite element methods
We report on the investigation of an approach for modelling light
transmission through systems consisting of several jointed optical fibres, in
which the analytical modelling of the waveguides was replaced by Finite Element
Modelling (FEM) simulations. To validate this approach we first performed FEM
analysis of standard fibres and used this to evaluate the coupling efficiency
between two singlemode fibres under different conditions. The results of these
simulations were successfully compared with those obtained using classical
analytical approaches, by demonstrating a maximum loss deviation of about 0.4
%. Further, we performed other more complex simulations that we compared again
to the analytical models. FEM simulations allow addressing any type of guiding
structure, without limitations on the complexity of the geometrical waveguide
cross section and involved materials. We propose as example of application the
modelling of the light transmitted through a system made of a hollow core
photonic crystal fibre spliced between two singlemode standard optical fibres,
and qualitatively compare the results of the simulation with experimental
results.Comment: Proceedings article, SPIE conference "Fiber Lasers and Glass
Photonics: Materials through Applications
Online measurement of optical fibre geometry during manufacturing
Online measurement of diameters and concentricities of optical fibre layers,
and the coating layer in particular, is one of the challenges in fibre
manufacturing. Currently available instruments can measure concentricity and
diameter of layers offline, and are not suitable for precise monitoring or
control of the manufacturing process in real time. In this work, we use two
laser beams, positioned orthogonally to illuminate the fibre from two sides,
and calculate deviations from the expected geometry by analysing the scattering
pattern. To measure the diffraction pattern we use two 8K linear array
detectors, with the scattered light incident directly on the sensors. Each
detector is capturing approximately 90 degree angular range directly behind the
fibre. The two measurement channels are positioned at different heights. The
scattered pattern is modelled mathematically with finite-element and
Fourier-modal methods, with various diameter and concentricity deviations. The
sensitivities of the changes in the scattering pattern are identified in
respect to these deviations. Since calculations are computationally intensive,
the sensitivities are pre-calculated in advance, and the real-time measurement
is based on pattern recognition. The symmetry of the pattern is used to
differentiate between diameter and concentricity variations. We performed
online measurements with the prototype instrument in production conditions, and
show that this method is sensitive enough to measure deviations of under 1
{\mu}m in diameter and concentricity of the coating layer.Comment: Proceedings article, SPIE conference "Fiber Lasers and Glass
Photonics: Materials through Applications
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