3,355 research outputs found
Beam-Size Invariant Spectropolarimeters Using Gap-Plasmon Metasurfaces
Metasurfaces enable exceptional control over the light with surface-confined
planar components, offering the fascinating possibility of very dense
integration and miniaturization in photonics. Here, we design, fabricate and
experimentally demonstrate chip-size plasmonic spectropolarimeters for
simultaneous polarization state and wavelength determination.
Spectropolarimeters, consisting of three gap-plasmon phase-gradient
metasurfaces that occupy 120{\deg} circular sectors each, diffract normally
incident light to six predesigned directions, whose azimuthal angles are
proportional to the light wavelength, while contrasts in the corresponding
diffraction intensities provide a direct measure of the incident polarization
state through retrieval of the associated Stokes parameters. The
proof-of-concept 96-{\mu}m-diameter spectropolarimeter operating in the
wavelength range of 750-950nm exhibits the expected polarization selectivity
and high angular dispersion. Moreover, we show that, due to the circular-sector
design, polarization analysis can be conducted for optical beams of different
diameters without prior calibration, demonstrating thereby the beam-size
invariant functionality. The proposed spectropolarimeters are compact,
cost-effective, robust, and promise high-performance real-time polarization and
spectral measurements
Anapole-Assisted Strong Field Enhancement in Individual All-Dielectric Nanostructures
High-index dielectric nanostructures have recently become prominent forefront
alternatives for manipulating light at the nanoscale. Their electric and
magnetic resonances with intriguing characteristics endow them with a unique
ability to strongly enhance near-field effects with minimal absorption. Similar
to their metallic counterparts, dielectric oligomers consisting of two or more
coupled particles are generally employed to create localized optical fields.
Here we show that individual all-dielectric nanostructures, with rational
designs, can produce strong electric fields with intensity enhancements
exceeding 3 orders of magnitude. Such a striking effect is demonstrated within
a Si nanodisk by fully exploiting anapole generation and simultaneously
introducing a slot area with high-contrast interfaces. By performing
finite-difference time-domain simulations and multipole decomposition analysis,
we systematically investigate both far-field and near-field properties of the
slotted disk and reveal a subtle interplay among different resonant modes of
the system. Furthermore, while electric fields at anapole modes are typically
internal, i.e., found inside nanostructures, our slotted configuration
generates external hotspots with electric fields additionally enhanced by
virtue of boundary conditions. These electric hotspots are thereby directly
accessible to nearby molecules or quantum emitters, opening up new
possibilities for single-particle enhanced spectroscopies or single-photon
emission enhancement due to large Purcell effects. Our presented design
methodology is also readily extendable to other materials and other geometries,
which may unlock enormous potential for sensing and quantum nanophotonic
applications
Direct amplitude-phase near-field observation of higher-order anapole states
Anapole states associated with the resonant suppression of electric-dipole
scattering exhibit minimized extinction and maximized storage of
electromagnetic energy inside a particle. Using numerical simulations, optical
extinction spectroscopy and amplitude-phase near-field mapping of silicon
dielectric disks, we demonstrate high-order anapole states in the near-infrared
wavelength range (900-1700 nm). We develop the procedure for unambiguously
identifying anapole states by monitoring the normal component of the electric
near-field and experimentally detect the first two anapole states as verified
by far-field extinction spectroscopy and confirmed with the numerical
simulations. We demonstrate that higher order anapole states possess stronger
energy concentration and narrower resonances, a remarkable feature that is
advantageous for their applications in metasurfaces and nanophotonics
components, such as non-linear higher-harmonic generators and nanoscale lasers
High-efficiency silicon metasurface mirror on a sapphire substrate
For a possible implementation of high-efficiency Si-nanosphere metasurface mirrors functioning at telecom wavelengths in future gravitational wave detectors, exact dimensional and configuration parameters of the total system, including substrate and protective coating, have to be determined a priori. The reflectivity of such multi-layer metasurfaces with embedded Si nanoparticles and their potential limitations need to be investigated. Here we present the results on how the substrate and protective layer influence optical properties and demonstrate how dimensional and material characteristics of the structure alter light reflectivity. Additionally, we consider the impact of manufacturing imperfections, such as fluctuations of Si nanoparticle sizes and their exact placement, on the metasurface reflectivity. Finally, we demonstrate how high reflectivity of the system can be preserved under variations of the protective layer thickness, incident angle of light, and its polarization
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