118 research outputs found
Geometric potential and transport in photonic topological crystals
We report on the experimental realization of an optical analogue of a quantum
geometric potential for light wave packets constrained on thin dielectric
guiding layers fabricated in silica by the femtosecond laser writing
technology. We further demonstrate the optical version of a topological
crystal, with the observation of Bloch oscillations and Zener tunneling of
purely geometric nature
Two-dimensional solitons at interfaces between binary superlattices and homogeneous lattices
We report on the experimental observation of two-dimensional surface solitons
residing at the interface between a homogeneous square lattice and a
superlattice that consists of alternating "deep" and "shallow" waveguides. By
exciting single waveguides in the first row of the superlattice, we show that
solitons centered on deep sites require much lower powers than their respective
counterparts centered on shallow sites. Despite the fact that the average
refractive index of the superlattice waveguides is equal to the refractive
index of the homogeneous lattice, the interface results in clearly asymmetric
output patterns.Comment: 16 pages, 5 figures, to appear in Physical Review
Surface Gap Soliton Ground States for the Nonlinear Schr\"{o}dinger Equation
We consider the nonlinear Schr\"{o}dinger equation , with and and with periodic in each coordinate direction. This problem
describes the interface of two periodic media, e.g. photonic crystals. We study
the existence of ground state solutions (surface gap soliton ground
states) for . Using a concentration compactness
argument, we provide an abstract criterion for the existence based on ground
state energies of each periodic problem (with and ) as well as a more practical
criterion based on ground states themselves. Examples of interfaces satisfying
these criteria are provided. In 1D it is shown that, surprisingly, the criteria
can be reduced to conditions on the linear Bloch waves of the operators
and .Comment: definition of ground and bound states added, assumption (H2) weakened
(sign changing nonlinearity is now allowed); 33 pages, 4 figure
Topological dipole Floquet solitons
We theoretically introduce a type of topological dipole soliton propagating in a Floquet topological insulator based on a kagome array of helical waveguides. Such solitons bifurcate from two edge states belonging to different topological gaps and have bright envelopes of different symmetries: fundamental for one component, and dipole for the other. The formation of dipole solitons is enabled by unique spectral features of the kagome array which allow the simultaneous coexistence of two topological edge states from different gaps at the same boundary. Notably, these states have equal and nearly vanishing group velocities as well as the same sign of the effective dispersion coefficients. We derive envelope equations describing the components of dipole solitons and demonstrate in full continuous simulations that such states indeed can survive over hundreds of helix periods without any noticeable radiation into the bulk.Y.V.K. and S.K.I. acknowledge funding of this study by RFBR and DFG according to Research Project No. 18- 502-12080. A.S. acknowledges funding from the Deutsche Forschungsgemeinschaft (Grants No. BL 574/13-1, No. SZ 276/19-1, and No. SZ 276/20-1). Y.V.K. and L.T. acknowledge support from the Government of Spain (Severo Ochoa CEX2019-000910-S), Fundació Cellex, Fundació Mir-Puig, Generalitat de Catalunya (CERCA). V.V.K. acknowledges financial support from the Portuguese Foundation for Science and Technology (FCT) under Contract No. UIDB/00618/2020.Peer ReviewedPostprint (author's final draft
Biphoton generation in quadratic waveguide arrays: A classical optical simulation
Quantum entanglement, the non-separability of a multipartite wave function,
became essential in understanding the non-locality of quantum mechanics. In
optics, this non-locality can be demonstrated on impressively large length
scales, as photons travel with the speed of light and interact only weakly with
their environment. With the discovery of spontaneous parametric down-conversion
(SPDC) in nonlinear crystals, an efficient source for entangled photon pairs,
so-called biphotons, became available. It has recently been shown that SPDC can
also be implemented in nonlinear arrays of evanescently coupled waveguides
which allows the generation and the investigation of correlated quantum walks
of such biphotons in an integrated device. Here, we analytically and
experimentally demonstrate that the biphoton degrees of freedom are entailed in
an additional spatial dimension, therefore the SPDC and the subsequent quantum
random walk in one-dimensional (1D) arrays can be simulated through classical
optical beam propagation in a two-dimensional (2D) photonic lattice. Thereby,
the output intensity images directly represent the biphoton correlations and
exhibit a clear violation of a Bell-type inequality
Nonlinearity-induced photonic topological insulator
The hallmark feature of topological insulators renders edge transport
virtually impervious to scattering at defects and lattice disorder. In our
work, we experimentally demonstrate a topological system, using a photonic
platform, in which the very existence of the topological phase is brought about
by nonlinearity. Whereas in the linear regime, the lattice structure remains
topologically trivial, light beams launched above a certain power threshold
drive the system into its transient topological regime, and thereby define a
nonlinear unidirectional channel along its edge. Our work studies topological
properties of matter in the nonlinear regime, and may pave the way towards
compact devices that harness topological features in an on-demand fashion
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