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ABSTRACT: We describe theoretically and observe experimentally the formation of a
surface state in a semi-infnite waveguide array with side-coupled waveguide,
designed to simultaneously achieve Fano and Fabry-Perot resonances. We
demonstrate that the surface mode is compact, with all energy concentrated in
few waveguides at the edge and no field penetration beyond the side-coupled
waveguide position. Furthermore, we show that by broadening the spectral band
in the rest of the waveguide array it is possible to suppress exponentially
localized modes, whereas the Fano state having the eigenvalue embedded in the
continuum is preserved.
04/2013;
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ABSTRACT: We predict that nonlinear waveguides which support frozen light associated with a degenerate photonic band edge, where the dispersion relation is locally quartic, exhibit a tunable, all-optical switching response. The thresholds for switching are orders-of-magnitude lower than at regular band edges. By adjusting the input condition, bistability can be eliminated, preventing switching hysteresis.
Optics Express 11/2012; 20(24):27363-8. · 3.59 Impact Factor
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ABSTRACT: We study photon-pair generation in arrays of cubic nonlinear waveguides through spontaneous four-wave mixing. We analyze numerically the quantum statistics of photon pairs at the array output as a function of waveguide dispersion and pump beam power. We show flexible spatial quantum state control such as pump-power-controlled transition between bunching and anti-bunching correlations due to nonlinear self-focusing.
Optics Express 11/2012; 20(24):27441-6. · 3.59 Impact Factor
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ABSTRACT: 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.
05/2012;
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ABSTRACT: We study the propagation and localization of light beams in azimuthally modulated Bessel photonic lattices induced optically
in photorefractive crystals; such lattices resemble highly nonlinear micro-structured fibres. We report on the experimental
observation of discrete diffraction, nonlinear localization, and subsequent formation of spatial solitons. Our experimental
results are confirmed by direct numerical simulations.
Journal of Materials Science Materials in Electronics 04/2012; 18:277-283. · 1.08 Impact Factor
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ABSTRACT: We overview our recent theoretical results on spatio-spectral control, diffraction management, and broadband all-optical switching
of polychromatic light in periodically curved one and two dimensional arrays of coupled optical waveguides. In particular,
we show that polychromatic light beams and patterns produced by white-light and supercontinuum sources can experience wavelength-independent normal, anomalous, or zero diffraction in specially designed structures. We also demonstrate that in the nonlinear regime,
it is possible to achieve broadband all-optical switching of polychromatic light in a directional waveguide coupler with special bending of the waveguide axes. Our results suggest
novel opportunities for creation of all-optical logical gates and switches which can operate in a very broad frequency region,
e.g., covering the entire visible spectrum.
Central European Journal of Physics 04/2012; 6(3):593-602. · 0.91 Impact Factor
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ABSTRACT: We suggest an application of pump-degenerate four-wave mixing process in tapered waveguides for generation of ultrashort pulses with central frequency tunable over the material transparency range. Our method can produce strongly compressed frequency-converted pulses in presence of group-velocity mismatch and group-velocity dispersion. Additionally, the proposed technique does not require pulse phase synchronization and effectively operates for strongly chirped pump pulses, thus enabling the use of longer nonlinear media for high conversion efficiency.
Optics Letters 02/2012; 37(4):446-8. · 3.40 Impact Factor
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ABSTRACT: We develop novel designs enabling slow-light propagation with vanishing group-velocity dispersion ("frozen light") and slow-light with large delay-bandwidth product, in periodic nanowires. Our design is based on symmetry-breaking of periodic nanowire waveguides and we demonstrate its vailidy through two- and three-dimensional simulations. The slow-light is associated with a stationary inflection point which appears through coupling between forward and backward waveguide modes. The mode coupling also leads to evanescent modes, which enable efficient light coupling to the slow mode.
Optics Express 02/2012; 20(4):3519-28. · 3.59 Impact Factor
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ABSTRACT: We analyze the process of photon-pair generation with simultaneous quantum walks in a quadratic nonlinear waveguide array. We demonstrate that the spontaneous parametric down-conversion in the array allows for creating quantum states with strongly pronounced spatial correlations, which are qualitatively different from those possible in bulk crystals or through quantum walks in linear waveguide arrays. Most importantly, the photon correlations can be controlled entirely classically by varying the spatial profile of the pump beam or the phase-matching conditions.
Physical Review Letters 01/2012; 108(2):023601. · 7.37 Impact Factor
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ABSTRACT: We describe families of discrete solitons in quadratic waveguide arrays supported by competing cascaded nonlinear interactions between one fundamental and two second-harmonic modes. We characterize the existence, stability, and excitation dynamics of these solitons and show that their features may resemble those of solitons in saturable media. Our results also demonstrate that a power threshold may appear for soliton formation, leading to a suppression of beam self-focusing which explains recent experimental observations.
Phys. Rev. A. 11/2011; 84(5).
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ABSTRACT: We study experimentally and numerically the dynamics of a recently found topological phase transition for discrete quadratic solitons with linearly coupled SH waves. We find that, although no stationary states are excited in the experimental situation, the generic feature of the phase transition of the SH is preserved. By utilizing simulations of the coupled mode equations we identify the complex processes leading to the phase transition involving spatial focusing and the generation of new frequency components. These distinct signatures of the dynamic phase transition are also demonstrated experimentally.
Optics Express 11/2011; 19(23):23188-201. · 3.59 Impact Factor
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Photonics and Nanostructures - Fundamentals and Applications 10/2011; 9(4):295. · 1.68 Impact Factor
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ABSTRACT: Degenerate band edges (DBEs) of a photonic bandgap have the form (ω-ω(D)) ∝k(2m) for integers m>1, with ω(D) the frequency at the band edge. We show theoretically that DBEs lead to efficient coupling into slow-light modes without a transition region, and that the field strength in the slow mode can far exceed that in the incoming medium. A method is proposed to create a DBE of arbitrary order m by coupling m optical modes with multiple superimposed gratings. The enhanced coupling near a DBE occurs because of the presence of one or more evanescent modes, which are absent at conventional quadratic band edges. We furthermore show that the coupling can be increased or suppressed by varying the number of excited evanescent waves.
Optics Letters 08/2011; 36(16):3257-9. · 3.40 Impact Factor
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ABSTRACT: We review both theoretical and experimental advances in the recently emerged
physics of modulated photonic lattices. Artificial periodic dielectric media,
such as photonic crystals and photonic lattices, provide a powerful tool for
the control of the fundamental properties of light propagation in photonic
structures. Photonic lattices are arrays of coupled optical waveguides, where
the light propagation becomes effectively discretized. Such photonic structures
allow one to study many useful optical analogies with other fields, such as the
physics of solid state and electron theory. In particular, the light
propagation in periodic photonic structures resembles the motion of electrons
in a crystalline lattice of semiconductor materials. The discretized nature of
light propagation gives rise to many new phenomena which are not possible in
homogeneous bulk media, such as discrete diffraction and diffraction
management, discrete and gap solitons, and discrete surface waves. Recently, it
was discovered that applying periodic modulation to a photonic lattice by
varying its geometry or refractive index is very much similar to applying a
bias to control the motion of electrons in a crystalline lattice. An interplay
between periodicity and modulation in photonic lattices opens up unique
opportunities for tailoring diffraction and dispersion properties of light as
well as controlling nonlinear interactions.
07/2011;
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ABSTRACT: We realize experimentally a true reflectionless potential, which facilitates nonresonant unity transmission for all incident waves and at the same time supports localized modes. We utilize arrays of evanescently coupled optical waveguides, where a particular modulation of the transverse waveguide separations provides a physical realization of reflectionless Ablowitz-Ladik soliton potentials.
Physical Review Letters 05/2011; 106(19):193903. · 7.37 Impact Factor
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ABSTRACT: We demonstrate the fabrication by direct laser writing and the operation of a directional coupler containing Bragg gratings in each waveguide. We achieve high-precision control over the longitudinal shift between the gratings, which feature first-order Bragg resonance at telecommunication wavelengths. We observe fundamental differences between light transmission characteristics in couplers with unshifted and shifted gratings in agreement with theoretical predictions.
Optics Letters 04/2011; 36(8):1380-2. · 3.40 Impact Factor
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ABSTRACT: We experimentally study the fields close to an interface between two photonic crystal waveguides that have different dispersion properties. After the transition from a waveguide in which the group velocity of light is v(g) ~ c/10 to a waveguide in which it is v(g) ~ c/100, we observe a gradual increase in the field intensity and the lateral spreading of the mode. We attribute this evolution to the existence of a weakly evanescent mode that exponentially decays away from the interface. We compare this to the situation where the transition between the waveguides only leads to a minor change in group velocity and show that, in that case, the evolution is absent. Furthermore, we apply novel numerical mode extraction techniques to confirm experimental results.
Optics Letters 04/2011; 36(7):1170-2. · 3.40 Impact Factor
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ABSTRACT: We report the experimental observation of tunneling of slow and fast electromagnetic modes in coupled periodic waveguides shifted longitudinally by half of modulation period. According to the symmetry analysis, such a coupler supports two electromagnetic modes with exactly matched slow or fast group velocities but different phase velocities for frequencies close to the edge of the photonic band. We confirm the predicted properties of the modes by directly extracting their dispersion and group velocities from the near-field measurements using specialized Bloch-wave spectral analysis method.
Applied Physics Letters 02/2011; 98(6):061909-061909-3. · 3.84 Impact Factor
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ABSTRACT: We study two-color parametric nonlinear modes in waveguide arrays with a quadratic nonlinear response. We predict theoretically and observe experimentally a new type of phase transition manifested in an abrupt power-controlled change of the mode structure from unstaggered to staggered, due to the interplay of localization and synchronization in parametrically driven discrete systems.
Physical Review Letters 12/2010; 105(23):233905. · 7.37 Impact Factor
