362 research outputs found
Elastic Modulus of Amorphous SiO\u3csub\u3e2\u3c/sub\u3e Nanowires
Amorphous SiO2 nanowires with diameter ranging from 50 to 100 nm were synthesized using chemical vapor deposition(CVD) under an argon atmosphere at atmospheric pressure. Nanoscale three-point bending tests were performed directly on individual amorphous SiO2 nanowires using an atomic force microscope (AFM).Elastic modulus of the amorphous SiO2 nanowires was measured to be 76.6±7.2GPa, which is close to the reported value of the bulk SiO2 and thermally grown SiO2 thin films, but lower than that of plasma-enhanced CVD SiO2 thin films. The amorphous SiO2 nanowires exhibit brittle fracture failure in bending
Formation Mechanism of Guided Resonances and Bound States in the Continuum in Photonic Crystal Slabs
We develop a formalism, based on the mode expansion method, to describe the
guided resonances and bound states in the continuum (BICs) in photonic crystal
slabs with one-dimensional periodicity. This approach provides analytic
insights to the formation mechanisms of these states: the guided resonances
arise from the transverse Fabry-P\'erot condition, and the divergence of the
resonance lifetimes at the BICs is explained by a destructive interference of
radiation from different propagating components inside the slab. We show BICs
at the center and on the edge of the Brillouin zone protected by symmetry, as
well as BICs at generic wave vectors not protected by symmetry.Comment: 12 pages, 3 figure
Valley-Hall photonic topological insulators with dual-band kink states
Extensive researches have revealed that valley, a binary degree of freedom
(DOF), can be an excellent candidate of information carrier. Recently, valley
DOF has been introduced into photonic systems, and several valley-Hall photonic
topological insulators (PTIs) have been experimentally demonstrated. However,
in the previous valley-Hall PTIs, topological kink states only work at a single
frequency band, which limits potential applications in multiband waveguides,
filters, communications, and so on. To overcome this challenge, here we
experimentally demonstrate a valley-Hall PTI, where the topological kink states
exist at two separated frequency bands, in a microwave substrate-integrated
circuitry. Both the simulated and experimental results demonstrate the
dual-band valley-Hall topological kink states are robust against the sharp
bends of the internal domain wall with negligible inter-valley scattering. Our
work may pave the way for multi-channel substrate-integrated photonic devices
with high efficiency and high capacity for information communications and
processing
Realization of a three-dimensional photonic topological insulator
Confining photons in a finite volume is in high demand in modern photonic
devices. This motivated decades ago the invention of photonic crystals,
featured with a photonic bandgap forbidding light propagation in all
directions. Recently, inspired by the discoveries of topological insulators
(TIs), the confinement of photons with topological protection has been
demonstrated in two-dimensional (2D) photonic structures known as photonic TIs,
with promising applications in topological lasers and robust optical delay
lines. However, a fully three-dimensional (3D) topological photonic bandgap has
never before been achieved. Here, we experimentally demonstrate a 3D photonic
TI with an extremely wide (> 25% bandwidth) 3D topological bandgap. The sample
consists of split-ring resonators (SRRs) with strong magneto-electric coupling
and behaves as a 'weak TI', or a stack of 2D quantum spin Hall insulators.
Using direct field measurements, we map out both the gapped bulk bandstructure
and the Dirac-like dispersion of the photonic surface states, and demonstrate
robust photonic propagation along a non-planar surface. Our work extends the
family of 3D TIs from fermions to bosons and paves the way for applications in
topological photonic cavities, circuits, and lasers in 3D geometries
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