Dynamics of a two-mode semiconductor laser

The authors analyze the properties of a semiconductor laser in a ring cavity when two modes can oscillate. With this model it is shown that phase-sensitive mode-mode interactions can influence the laser dynamics through their dependence on the spatial Fourier components of the carrier density. In particular, these interactions provide a mechanism by which single-mode solutions are destabilized while periodic and quasi-periodic two-mode solutions can occur     

光学特异材料的设计

In this contribution we review our latest achievements of combined experimental and theoretical studies to tailor the properties of optical metamaterials（MMs） at will. We give three examples of metamaterial designs that have been realized by means of electron-beam lithography and whose spectroscopic characteristics have been comprehensively investigated. In every case, our experiments are complemented by rigorous numer ical simulations. Particular emphasis is put on the significance of such tailored effective properties of optical MMs     

Simulation of femtosecond pulse propagation in air

We present numerical simulations of the propagation of intense spatio-temporal fields propagating in air. Characteristic parameters of the propagation like peak intensities, plasma densities and diameters of the plasma channels are obtained. The evolution of the spectral content of the pulses is investigated and, in agreement with recent experiments, white-light supercontinuum generation is observed. We show in which areas of the pulse the supercontinuum is generated and conclude that self-phase modulation is responsible for the spectral broadening. Furthermore we investigate azimuthal instabilities of intense rotationally symmetric pulsed beams propagating in air. Although the spatial-temporal evolution of the field is strongly influenced by the onset of plasma generation, the instabilities are basically caused by the Kerr effect. We conclude that calculations assuming rotational symmetry become unrealistic due to the fast growth of azimuthal instabilities in the focal region.     

Double hump solitary waves in quadratic media with walk-off – domain of existence,stability and decay scenarios

We analytically determine the domain of existence of double hump solitary wave solutions in quadratic media with walk-off. Although a linear stability analysis reveals that these solutions are always unstable the instability gain can be very small for certain parameters. This has important implications for all-optical switching applications. The ultimate decay is prompted by the destruction of an exact phase difference π between the two humps of the fundamental frequency wave and follows different scenarios.     

Longitudinal-differential interferometry: direct imaging of axial superluminal phase propagation

We introduce and demonstrate a new interferometric method called longitudinal-differential (LD) interferometry, which measures the spatially resolved phase difference of the scattered field by an object relative to the illumination. This method is combined with a high-resolution interference microscope that allows recording three-dimensional field distributions in amplitude and phase. The method is applied to study the axial phase behavior of Arago spots, an effect observable in low-Fresnel-number systems behind objects with a size comparable to the wavelength. We directly observe the initial phase delay in the Arago spot and prove that the local phase velocity exceeds the speed of light in air. Such LD phase studies are applicable not only to the Arago spot but also to other kinds of light interactions with wavelength-scale objects, e.g., photonic nanojets.     

Self-guiding of infrared and visible light in photonic crystal slabs

We experimentally demonstrate diffractionless guidance and efficient routing of light in two-dimensional photonic crystal slabs at infrared and visible wavelengths. Our particular design allows for simultaneous guidance of TE and TM polarized light beams at the same wavelength. Routing performance and possibilities of propagation loss reduction are investigated experimentally. Experimental results are in excellent agreement with three-dimensional simulations.     

Effects of anisotropic disorder in an optical metamaterial

We consider the effect of disorder in one transverse dimension, termed anisotropic disorder, on the optical properties of a metamaterial consisting of cut-wire-pair meta-atoms. The work comprises experimental and numerical studies. The appropriate samples were fabricated and their optical properties quantified in the far-field. For comparison large-scale rigorous numerical simulations were performed. We observe excellent agreement between experiment and theory. Based on our results we reveal how the electric dipole interactions between adjacent meta-atoms affect the overall spectral response of the metamaterial. Our main observation is a polarization-sensitive degradation of the symmetric resonance for anisotropic disorder.     

Resonances of split-ring resonator metamaterials in the near infrared

We study the spectral response of optical metamaterials consisting of gold split-ring resonators. We utilize reflection spectroscopy in the near infrared region at normal incidence in the experiments. Our theoretical modeling is based on rigorous diffraction theory. We perform a comprehensive analysis of the dependence of the features of both the electric and the oscillating-circuit resonance on the geometry of the metamaterial. We show that theory and experiment are in good agreement. PACS 73.20.Mf; 78.67.-n; 78.66.Sq; 78.67.Bf     

Quadratic cavity solitons-the up-conversion case

We derive mean-field equations for intra-cavity second-harmonic generation. Based on this model, we show that a variety of quadratic cavity solitons can exist. Highly symmetric and resting cavity solitons originate from primary bifurcations of the underlying stationary plane wave solutions. For certain control parameters, these solutions may undergo a secondary bifurcation leading to symmetry-reduced and/or moving/breathing quadratic cavity solitons. In particular, we predict for the first time the existence of triangular cavity solitons and derive a criterion for an nonequilibrium Ising-Bloch transition.     

Design of an artificial three-dimensional composite metamaterial with magnetic resonances in the visible range of the electromagnetic spectrum

We propose an artificial three-dimensional material that exhibits a strong resonance in the effective permeability in the visible spectral domain. This material may be implemented in a two-step procedure. First, a metamaterial made of densely packed metallic nanoparticles is fabricated that shows a Lorentz-type resonance in the permittivity at the collective plasmon frequency. Second, spheres are formed out of this material and arranged in a cubic lattice. This meta-metamaterial exhibits a strong resonance in the permeability which is caused by a Mie resonance associated with the magnetic mode of a single metamaterial sphere. Realization of this material based on self-organization in liquid crystals and the limitations of the approach are discussed.