2,237 research outputs found
Localization of Two-Component Bose-Einstein Condensates in Optical Lattices
We reveal underlying principles of nonlinear localization of a two-component
Bose-Einstein condensate loaded into a one-dimensional optical lattice. Our
theory shows that spin-dependent optical lattices can be used to manipulate
both the type and magnitude of nonlinear interaction between the ultracold
atomic species and to observe nontrivial two-componentnlocalized states of a
condensate in both bands and gaps of the matter-wave band-gap structure.Comment: 4 pages, 4 figure
Simple and efficient generation of gap solitons in Bose-Einstein condensates
We suggest an efficient method for generating matter-wave gap solitons in a
repulsive Bose-Einstein condensate, when the gap soliton is formed from a
condensate cloud in a harmonic trap after turning on a one-dimensional optical
lattice. We demonstrate numerically that this approach does not require
preparing the initial atomic wave packet in a specific state corresponding to
the edge of the Brillouin zone of the spectrum, and losses that occur during
the soliton generation process can be suppressed by an appropriate adiabatic
switching of the optical lattice.Comment: 7 pages, 10 figure
Dark soliton past a finite-size obstacle
We consider the collision of a dark soliton with an obstacle in a
quasi-one-dimensional Bose condensate. We show that in many respects the
soliton behaves as an effective classical particle of mass twice the mass of a
bare particle, evolving in an effective potential which is a convolution of the
actual potential describing the obstacle. Radiative effects beyond this
approximation are also taken into account. The emitted waves are shown to form
two counterpropagating wave packets, both moving at the speed of sound. We
determine, at leading order, the total amount of radiation emitted during the
collision and compute the acceleration of the soliton due to the collisional
process. It is found that the radiative process is quenched when the velocity
of the soliton reaches the velocity of sound in the system
Second-harmonic generation in subwavelength graphene waveguides
We suggest a novel approach for generating second-harmonic radiation in
subwavelength graphene waveguides. We demonstrate that quadratic phase matching
between the plasmonic guided modes of different symmetries can be achieved in a
planar double-layer geometry when conductivity of one of the layers becomes
spatially modulated. We predict theoretically that, owing to graphene nonlocal
conductivity, the second-order nonlinear processes can be actualized for
interacting plasmonic modes with an effective grating coupler to allow external
pumping of the structure and output of the radiation at the double frequency.Comment: 5 pages, 3 figure
Discrete solitons and nonlinear surface modes in semi-infinite waveguide arrays
We discuss the formation of self-trapped localized states near the edge of a
semi-infinite array of nonlinear waveguides. We study a crossover from
nonlinear surface states to discrete solitons by analyzing the families of odd
and even modes centered at different distances from the surface, and reveal the
physical mechanism of the nonlinearity-induced stabilization of surface modes.Comment: 4 double-column pages, 5 figures, submitted to Optics Letter
Broadband light coupling to dielectric slot waveguides with tapered plasmonic nanoantennas
We propose and theoretically verify an efficient mechanism of broadband
coupling between incident light and on-chip dielectric slot waveguide by
employing a tapered plasmonic nanoantenna. Nanoantenna receives free space
radiation and couples it to a dielectric slot waveguide with the efficiency of
up to 20% in a broad spectral range, having a small footprint as compared with
the currently used narrowband dielectric grating couplers. We argue that the
frequency selective properties of such nanoantennas also allow for using them
as ultrasmall on-chip multiplexer/demultiplexer devices
Necklace-ring vector solitons
We introduce novel classes of optical vector solitons that consist of incoherently coupled self-trapped “necklace” beams carrying zero, integer, and even fractional angular momentum. Because of the stabilizing mutual attraction between the components, such stationary localized structures exhibit quasistable propagation for much larger distances than the corresponding scalar vortex solitons and expanding scalar necklace beams
Optical bistability in a nonlinear photonic crystal waveguide notch filter
Optical bistability occurs when the effects of nonlinear behaviour of materials cause hysteresis in the transmission and reflection of a device. A possible mechanism for this is a strong dependence of the optical intensity on the index of refraction, e.g. in a cavity near resonance. In a 2- dimensional photonic crystal composed of rods of high-index material in air, a waveguide can be created by removing a line of rods. When a cavity is made by taking away several rods perpendicular to the waveguide, a notch filter characteristic in the transmission occurs. Due to the high intensity in the cavity in resonance, nonlinear effects are enhanced. This paper shows numerical simulations of bistability in the transmission and in the field inside the cavity both when a material inside the cavity has third-order (Kerr-type) nonlinear effects, and when the high-index rods themselves are nonlinear
Nonlinear guided waves and spatial solitons in a periodic layered medium
We overview the properties of nonlinear guided waves and (bright and dark)
spatial optical solitons in a periodic medium created by a sequence of linear
and nonlinear layers. First, we consider a single layer with a cubic nonlinear
response (a nonlinear waveguide) embedded into a periodic layered linear
medium, and describe nonlinear localized modes (guided waves and Bragg-like
localized gap modes) and their stability. Then, we study modulational
instability as well as the existence and stability of discrete spatial solitons
in a periodic array of identical nonlinear layers, a one-dimensional nonlinear
photonic crystal. Both similarities and differences with the models described
by the discrete nonlinear Schrodinger equation (derived in the tight-binding
approximation) and coupled-mode theory (valid for the shallow periodic
modulations) are emphasized.Comment: 10 pages, 14 figure
- …