130 research outputs found
Third-harmonic generation in photonic topological metasurfaces
We study nonlinear effects in two-dimensional photonic metasurfaces
supporting topologically-protected helical edge states at the nanoscale. We
observe strong third-harmonic generation mediated by optical nonlinearities
boosted by multipolar Mie resonances of silicon nanoparticles. Variation of the
pump-beam wavelength enables independent high-contrast imaging of either bulk
modes or spin-momentum-locked edge states. We demonstrate topology-driven
tunable localization of the generated harmonic fields and map the
pseudospin-dependent unidirectional waveguiding of the edge states bypassing
sharp corners. Our observations establish dielectric metasurfaces as a
promising platform for the robust generation and transport of photons in
topological photonic nanostructures.Comment: 5 pages, 5 figure
Topological states in disordered arrays of dielectric nanoparticles
We study the interplay between disorder and topology for the localized edge
states of light in topological zigzag arrays of resonant dielectric
nanoparticles. We characterize topological properties by the winding number
that depends on both zigzag angle and spacing between nanoparticles in the
array. For equal-spacing arrays, the system may have two values of the winding
number or , and it demonstrates localization at the edges even in
the presence of disorder, being consistent with experimental observations for
finite-length nanodisk structures. For staggered-spacing arrays, the system
possesses richer topological phases characterized by the winding numbers
, or , which depend on the averaged zigzag angle and disorder
strength. In a sharp contrast to the equal-spacing zigzag arrays,
staggered-spacing arrays reveal two types of topological phase transitions
induced by the angle disorder, (i) and (ii)
. More importantly, the spectrum of
staggered-spacing arrays may remain gapped even in the case of a strong
disorder.Comment: 10 pages, 10 figure
Nonlinear imaging with all-dielectric metasurfaces
Nonlinear metasurfaces incorporate many of the functionalities of their
linear counterparts such as wavefront shaping but simultaneously they perform
nonlinear optical transformations. This dual functionality leads to a rather
unintuitive physical behavior which is still widely unexplored for many
photonic applications. The nonlinear processes render some basic principles
governing the functionality of linear metasurfaces not directly applicable,
such as the superposition principle and the geometric optics approximation. On
the other hand, nonlinear metasurfaces facilitate new phenomena that are not
possible in the linear regime. Here, we study the imaging of objects through a
dielectric nonlinear metalens. We illuminate objects by infrared light and
record their generated images at the visible third-harmonic wavelengths. We
revisit the classical lens theory and suggest a generalized Gaussian lens
equation for nonlinear imaging, verified both experimentally and analytically.
We also demonstrate experimentally higher-order spatial correlations
facilitated by the nonlinear metalens, resulting in additional image features
Nonlinear Dielectric Metalenses: Imaging and Higher-Order Correlations
We demonstrate the first highly efficient all-dielectric nonlinear metalens that realizes
third-harmonic imaging accompanied by spatial third-order correlations carrying information about
coherence effects. We describe this metalens analytically with a generalized nonlinear lens equation.We acknowledge a support from the Australia-Germany Joint Research Co-operation Scheme and the German Academic Exchange Service (DAAD)
Transparent Dielectric Metasurfaces for Spatial Mode Multiplexing
Expanding the use of physical degrees of freedom to employ spatial multiplexing of data in optical communication is considered to be the most disruptive and effective solution for meeting the capacity demand of the growing information traffic. Development of space division–multiplexing methods stimulated research on spatial encoding, detection, and processing of data, attracting interest from various fields of science. Here a passive all-dielectric metasurface with near-unity transmission is demonstrated that engineers spatial mode profiles, potentially of an arbitrary complexity. The broadband response of the metasurface covers all S, C, and L bands of fiber communications. Unlike conventional phase plates, the metasurface allows for both phase and polarization conversion, providing full flexibility for the mode engineering. The dielectric metasurface is employed for mode multiplexing in a free-space optical communication system with an extinction ratio in excess of 20 dB over the whole C-band with negligible penalty even for 100 Gb s−1 data transmission. These results merge two seemingly different fields, optical communication and metamaterials, and they suggest a novel approach for an ultimate miniaturization of mode multiplexers and advanced LiFi technologies
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