Bragg-resonance-induced Rabi oscillations in photonic lattices

We show that propagation of optical beams in periodic lattices induces power oscillations between the Fourier spectrum peaks, with the indices related by the Bragg resonance condition. In the spatial coordinates, this is reflected in the beam position oscillations. A simple resonant theory explains the phenomenon. The effect can be used for controlled generation of the Floquet-Bloch modes in photonic lattices.     

Bragg-induced oscillations in non-PT complex photonic lattices

We investigate Bragg-induced oscillations in complex non-PT periodic structures, that is, a periodic medium with gain and loss and not necessarily symmetric under the combined action of parity and time reversal operations. We compare our analytic results based on the expansion of the optical field in Bragg-resonant plane waves with a direct numerical integration of the paraxial wave equation beyond the shallow potential approximation and using a wide Gaussian beam as initial condition. In particular, we study under which conditions a mode trapping phenomenon may still be observed and to inspect how the energy exchange between the spectral modes takes place during propagation in this more general class of asymmetric complex potentials.     

Bloch oscillations and Zener tunneling in two-dimensional photonic lattices

We report on the first experimental observation of photonic Bloch oscillations and Zener tunneling in two-dimensional periodic systems. We study the propagation of an optical beam in a square lattice superimposed on a refractive index ramp. We observe oscillations of the beam inside the first Brilloin zone and tunneling of light from the first to the higher-order bands of the lattice band gap spectrum.     

Light propagation and oscillations in two-dimensional graded square photonic lattices

We have studied the optical oscillations and transitions in two-dimensional graded square photonic lattices (GSPL) formed by evanescently coupled optical waveguide arrays with parabolic confinements in all transverse directions. When we retain only the orthogonal couplings, decoupled one-dimensional models can be used to obtain the various normal modes, which correspond to a variety of optical oscillations. Six different combinations of Bloch oscillation (BO), dipole oscillation (DO), and reflections from the boundaries of finite lattice are classified on the phase diagram. If we include the diagonal couplings, transitions among various oscillations are obtained with the Hamiltonian optics approach and confirmed by the field-evolution analysis. We studied in detail a typical example in which a switching occurs from the constituent BO and DO to both DOs in the two orthogonal directions. The method to analyze the complex field evolution in GSPL can be extended to similar systems with different types of lattices and/or confinements.     

Decoherence of rabi oscillations in a single quantum dot

We develop a realistic model of Rabi oscillations in a quantum-dot photodiode. Based in a multiexciton density matrix formulation we show that for short pulses the two-level model fails and higher levels should be taken into account. This affects some of the experimental conclusions, such as the inferred efficiency of the state rotation (population inversion) and the deduced value of the dipole interaction. We also show that the damping observed cannot be explained using constant rates with fixed pulse duration. We demonstrate that the damping observed is in fact induced by an off-resonant excitation to or from the continuum of wetting layer states. Our model describes the nonlinear decoherence behavior observed in recent experiments.     

Saturation and rabi oscillations in resonant multiphoton ionization

We present an analysis of saturation in resonant two-photon ionization which includes bound and continuum energy shifts, induced widths and bound-bound nutational Rabi frequencies at extreme saturation.     

Defect-enhanced resonances in photonic lattices

Abstract

A study of defect-mode propagation in lossless layered photonic media has been performed. We put forward a new proper characteristic of the defect cavity, called the coupling length of the defect, namely, a maximum spatial radius around the defect site, within which the defect mode couples into the tunnelled incident wave. This coupling length allows us to optimize the values of the Q-factor and the transmission coefficient with respect to both the position of the defect and the dielectric permittivity of the defective layer.     

Defect-enhanced resonances in photonic lattices

A study of defect-mode propagation in lossless layered photonic media has been performed. We put forward a new proper characteristic of the defect cavity, called the coupling length of the defect, namely, a maximum spatial radius around the defect site, within which the defect mode couples into the tunnelled incident wave. This coupling length allows us to optimize the values of the Q-factor and the transmission coefficient with respect to both the position of the defect and the dielectric permittivity of the defective layer.     

Self-imaging in photonic crystals in a subwavelength range

Self-imaging was observed in simulations and in microwave experiments that were performed on a face-centered cubic photonic crystal structure. The structure was composed of dielectric spheres that generally were smaller than the incident wavelength. Such self-imaging phenomena occurred along the direction of propagation and at distances smaller than the propagating wavelength.     

Metal-nanoshelled three-dimensional photonic lattices

Micronanostructures prepared by two-photon photopolymerization are utilized as templates for electroless plating of metals, giving rise to an approach for fabricating complex-shaped metal micronanostructures that are so far not achievable by other means. We show that when the coated-layer thickness of a metal coating is larger than a critical value (around 20 nm for silver at 2-3 mum wavelength) associated with the metal's skin depth, the photonic crystals exhibit optical properties more comparable to a solid metal structure than to their polymer counterparts.     

Symmetry breaking in honeycomb photonic lattices

We study the phenomena associated with symmetry breaking in honeycomb photonic lattices. As the honeycomb structure is gradually deformed, conical diffraction around its diabolic points becomes elliptic and eventually no longer occurs. As the deformation is further increased, a gap opens between the first two bands, and the lattice can support a gap soliton. The existence of the gap soliton serves as a means to detect the symmetry breaking and provide an estimate of the size of the gap.     

Beam control in tri-core photonic lattices

We report on theoretical investigations of beam control in one-dimensional tri-core photonic lattices （PLs）. Linear splitting is illustrated in tri-core PLs; the effect of defect strength on the splitting is discussed in depth for single-wavelength light. We reveal that splitting disappears when the defect strength trends to zero, while reoccurring under nonlinearity. Multi-color splitting and active control are also proposed in such photonic structures.     

Defect modes in one-dimensional photonic lattices

Linear defect modes in one-dimensional photonic lattices are studied theoretically. For negative (repulsive) defects, various localized defect modes are found. The strongest confinement of the defect modes appears when the lattice intensity at the defect site is nonzero rather than zero. When launched at small angles into such a defect site of the lattice, a Gaussian beam can be trapped and undergo snake oscillations under appropriate conditions.     

Inhibited emission in photonic woodpile lattices

The emission and transmission properties of realistic photonic-band-structure woodpile lattices are investigated by use of a scattering-matrix treatment. Lattices with three to nine layers are studied, and the results are interpreted with band-structure calculations for an infinite lattice. Calculations of the total radiative loss rate for a source within the lattice show that these structures can provide significant inhibition of emission, with values as low as 3% of the free-space value in the nine-layer structure.     

Gaussian-induced rotation in periodic photonic lattices

We numerically investigate time-dependent rotation of counterpropagating mutually incoherent self-trapped Gaussian beams in periodic optically induced fixed photonic lattices. We demonstrate the relation between such rotation and less confined discrete solitonic solutions.     

Surface solitons in chirped photonic lattices

We study surface modes at the edge of a semi-infinite chirped photonic lattice in the framework of an effective discrete nonlinear model. We demonstrate that the lattice chirp can change dramatically the conditions for the mode localization near the surface, and we find numerically the families of discrete surface solitons in this case. Such solitons do not require any minimum power to exist provided the chirp parameter exceeds some critical value. We also analyze how the chirp modifies the interaction of a soliton with the lattice edge.     

Multivortex solitons in triangular photonic lattices

We introduce a novel class of stable lattice solitons with a complex phase structure composed of many single-charge discrete vortices in a triangular photonic lattice. We demonstrate that such nonlinear self-trapped states are linked to the resonant Bloch modes, which bear a honeycomb pattern of phase dislocations.     

Reduced-symmetry two-dimensional solitons in photonic lattices

We demonstrate theoretically and experimentally a novel type of localized beam supported by the combined effects of total internal and Bragg reflection in nonlinear two-dimensional square periodic structures. Such localized states exhibit strong anisotropy in their mobility properties, being highly mobile in one direction and trapped in the other, making them promising candidates for optical routing in nonlinear lattices.     

Boundary-induced Anderson localization in photonic lattices

We analyze numerically localization of light in linear square waveguide arrays restricted in one dimension (“ribbons”), whose boundaries are disordered in propagation constant and/or coupling. We find that the disordered boundary induces a localization tendency in the bulk even for relatively wide ribbons.     

Squeezing and rabi oscillations in the Dicke model within and without rotating-wave approximation

The Dicke model is investigated within and without rotating-wave approximation in the case of a lossless resonant cavity. Numerical results for the time evolution of the atomic population inversion, dipole moment and atomic and field squeezing parameters for an initial field are presented for different numbers of atoms. The significant influence of the counter-rotating terms on the squeezing and collapse (revival) phenomena is pointed out.