Solitons in PT–symmetric optical lattices with spatially periodic modulation of nonlinearity

We study the existence and stability of solitons forming in PT–symmetric optical lattices with spatially periodic modulation of the local strength of the nonlinear media. We found that the spatial modulation of the nonlinearity significantly affects the stability of solitons in PT–symmetric optical lattices. With the decrease of the strength of nonlinear refractive index modulation, the soliton's stability domain increases, whereas with the increase of the period of nonlinear refractive index modulation, the corresponding soliton's stability range narrows. In addition, we also investigate the influence of variation of the amplitude of the linear PT–symmetric lattice potential on soliton dynamics, in the presence of spatially periodic modulation of nonlinearity.     

Spinning solitons in cubic-quintic nonlinear media

We review recent theoretical results concerning the existence, stability and unique features of families of bright vortex solitons (doughnuts, or ‘spinning’ solitons) in both conservative and dissipative cubic-quintic nonlinear media.     

Two-photon cooperative emission in the presence of athermal electromagnetic field

The possibility of cooperative spontaneous two-photon emission of an extended radiators system and the influence of the external thermal electromagnetic field on the spontaneous emission rate, in such a system, are investigated. It is concluded that, in an external electromagnetic field, the two-photon cooperative emission rate increases significantly. The importance of this effect on the emission of gamma rays from inverted long-lived isomers triggered by X-ray thermal fields, is emphasized. This revised version was published online in August 2006 with corrections to the Cover Date.     

Few-cycle solitons in supercontinuum generation dynamics

We review several propagation models that do not rely on the slowly-varying-envelope approximation (SVEA), and can thus be considered as fundamental models addressing the formation and propagation of few-cycle pulsed field structures and solitary waves arising in the course of intense ultrashort optical pulse evolution in nonlinear media and beyond octave-bandwidth optical spectrum broadening. These generic models are: the modified-Korteweg-de Vries (mKdV), the sine-Gordon (sG), and the mixed mKdV-sG equations. To include wave polarization dynamics, the vector extensions of both mKdV and sG equations are introduced. Multi-octave-spanning supercontinuum generation and few-cycle soliton structures are highlighted from numerical simulations.     

Propagation and stability of the stationary stripe nonlinear guided waves in a symmetric structure with a nonlinear film

Abstact The propagation and stability of the stationary stripe nonlinear guided waves in an antiwaveguide symmetric layered structure containing a nonlinear film are simulated numerically. The symmetric, antisymmetric and asymmetric modes are considered, in both Kerr-law and saturable instantaneous self-focusing nonlinearity cases. The numerical calculations support the statement that stationary stripe nonlinear guided waves are always unstable on propagation for Kerr-law nonlinearities and the use of saturable nonlinear films leads to stability on propagation for effective indices corresponding to the ascending branches of the nonlinear dispersion curves.     

Collisions between discrete spatiotemporal Ginzburg-Landau solitons

We report systematic results of collisions between discrete spatiotemporal Ginzburg-Landau solitons in waveguide arrays. Depending on the value of the kick parameter (collision momentum), four generic outcomes are identified in the case of collision of two identical solitons located at equal distances from the edge of the waveguide array: (a) merger of the solitons into a single one, at small values of the kick parameter, (b) creation of an extra soliton at intermediate values of the collision momentum, (c) quasi-elastic interactions at both intermediate values of the kick parameter (for relatively small values of the cubic gain) and at large values of the kick parameter (for relatively high values of cubic gain), and (d) soliton spreading at relatively large values of the collision momentum but only in the case of relatively small values of the cubic gain. In the case of collision of two non-identical solitons located at different distances from the edge of the waveguide array four generic outcomes were identified too: (e) soliton bouncing, accompanied by a sharp modification of soliton velocities during the interaction process, for relatively small values of the collision momentum, (f) soliton creation at intermediate values of the kick parameter and for relatively low values of the cubic gain, (g) soliton spreading (in time) at intermediate values of the collision momentum and for relatively high values of the cubic gain, and (h) quasi-elastic interactions at large values of the the kick parameter.     

A simple green function approach to the Dicke model with external fields

Using the technique of double-time temperature-dependent Green functions, the lack of phase transition in the Dicke model with external fields is proved.     

Stable spinning optical solitons in three dimensions

We introduce spatiotemporal spinning solitons (vortex tori) of the three-dimensional nonlinear Schr?dinger equation with focusing cubic and defocusing quintic nonlinearities. The first ever found completely stable spatiotemporal vortex solitons are demonstrated. A general conclusion is that stable spinning solitons are possible as a result of competition between focusing and defocusing nonlinearities.