D. I. Sementsov

Amplification of frequency-modulated soliton-like pulses in inhomogeneous optical waveguides with normal dispersion

The possibility of effective amplification of self-similar frequency-modulated pulses (FMPs) in longitudinally inhomogeneous active optical waveguides is studied. Peculiarities of the dynamics of parabolic pulses with a constant frequency modulation rate are considered. An optimal profile of variation of the group velocity dispersion was obtained in correspondence with optimal amplification of a similariton-like pulse. The use of FMPs in amplifying and longitudinally inhomogeneous optical waveguides with a correspondingly matched profile of normal dispersion of group velocities is shown to be capable of providing for an amplification of subpicosecond pulses up to energies above 1 nJ.

Dynamics of frequency-modulated soliton-like pulses in a longitudinally inhomogeneous active optical waveguide

Conditions of the formation and amplification of frequency-modulated soliton-like pulses in longitudinally inhomogeneous active optical waveguides with anomalous dispersion of group velocities are studied. Group velocity dispersion profiles that are necessary for existence and amplification for active and passive optical waveguides are determined, and the dependences on the distance passed along the waveguide, duration, and chirp of the pulse are established.

Modulation instability of pulsed radiation in an optical waveguide in the presence of the traveling refractive index wave

The conditions for the onset of modulation instability of wave packets in an optical waveguide in the presence of the traveling refractive index wave are investigated. An expression governing the growth rate of a small harmonic perturbation at the early development stage of the modulation instability is obtained. Based on numerical analysis, the behavior of the wave packet at the developed modulation instability stage is studied for different parameters of the waveguide and the refractive index wave.

Wave packet dynamics in a nonlinear tunnel-coupled structure of right- and left-handed media

The dynamics of a wave packet formed by tunnel-coupled forward and backward waves in a waveguide structure consisting of media with different signs of real parts of their refractive indices is investigated. Expressions for coupled-wave amplitude and reflection and transmission coefficients that are corrected for absorption are derived in the linear approximation. The expressions governing the wave-packet duration and propagation velocity of its envelope maximum are derived, taking into account the second-order dispersion, cubic nonlinearity, and dispersion of the nonlinearity. The possibility of efficient control of the forward wave velocity by applying an external magnetic field is demonstrated.

Modulation instability of wave packets in a Gires–Tournois interferometer

We study the specific features of the perturbation dynamics of a wave packet in a Gires–Tournois interferometer. We obtain a dispersion relationship that relates the perturbation parameters to the parameters of the structure and pump wave, the analytical expressions for the gain increment of a harmonic perturbation and other important characteristics that determine the dynamics of the modulation instability of the reflected wave. Based on numerical simulation, we plot the dependences of the dispersion and nonlinearity parameters and the gain increment on the spacing between the interferometer mirrors, the angle of incidence of the radiation onto the mirrors, and the radiation intensity.

Wave properties of surface polaritons in the dielectric-high-temperature superconductor-dielectric structure

The specific features of the surface polariton propagation in the dielectric-high-temperature superconductor-dielectric symmetric structure have been investigated in the temperature region T < Tc/2, where the structure can be considered as non-absorbing. It has been shown that the dispersion curves contain two polariton branches, i.e., high-frequency and low-frequency ones, which correspond to symmetric and antisymmetric distributions of transverse components of the wave field. For the high-frequency branch, there is a propagation constant range where the group velocity and energy flux directions are opposite to the phase velocity direction. In this range, a significant deceleration of polariton waves is also observed.

A ring optical generator of terahertz and far-infrared radiation

Specific features of difference-frequency generation of terahertz radiation in the regime of parametric microwave generation in a nonlinear crystal are investigated. It is suggested to use a periodic stripe structure formed in the crystal to achieve phase matching. The dynamics of the wave at difference frequency, which falls into terahertz or far-IR spectral region, is determined based on solution of the set of parametric interaction equations taking into consideration quadratic and cubic nonlinearities.

Perfect tunneling of a structure containing a left-handed material layer

Tunneling of monochromatic radiation obliquely incident on a plane-layered structure is investigated. In the structure, a left-handed material layer (with a negative refractive index) is surrounded by layers with positive refractive indexes. Conditions for resonance amplification of evanescent waves that occurs simultaneously with perfect tunneling, i.e., reflection-free transmission of radiation through the plane-layered structure, are revealed.

Dynamics of the lattice of magnetic nanodipoles with cubic anisotropy

The 5 × 5 square lattices of magnetic dipoles with cubic crystallographic anisotropy were investigated by the computer simulation method. The conditions for implementing the random orientation of lattice configurations, each of which are characterized by a certain response to the influence of an external magnetic pulse, as well as by the established regime of the oscillation of the total magnetic moment under the influence of an alternating field, are revealed. Regular vibration modes with a doubled frequency and quasi-periodic and chaotic modes are detected. The dependence of the system response on the parameters of the magnetic field pulse is studied.

Cross-modulation instability in inhomogeneous normal-dispersion fiber amplifiers

The conditions of the onset of a modulation instability of the signal wave in a doped fiber due to nonlinear cross-modulation interaction with the pump wave are investigated. The analysis takes into consideration the pump depletion and the group-velocity mismatch of the interacting waves. A dispersion relation coupling perturbation parameters with those of pump, analytic expressions governing the integral growth rate of a harmonic perturbation, and other important characteristics determining the dynamics of the signal-wave cross-modulation instability are obtained. Based on computer simulation, the behavior of the above characteristics as a function of the initial signal-wave power, fiber length, and group-velocity mismatch of the pump and signal waves is investigated.