1,721,130 research outputs found
Wavelength shifting in photonic bandgap microcavities with isotropic media
No full textBy coupled mode theory in the time domain and a finite-difference time-domain code, we investigate wavelength shifting and frequency conversion via four-wave mixing inside a photonic crystal wire in an isotropic Kerr material. The three-dimensional time-resolved analysis yields ultrafast and all-optically tunable frequency conversion of a signal/channel about the pump frequency
Doubly resonant Bragg simultons via second-harmonic generation
No full textWe predict that the combined effect of quadratic nonlinearity and dispersion induced by a periodic variation of the linear susceptibility can give rise to simultaneous localization of counterpropagating waves at different carrier frequencies, in the form of two envelope solitary waves (i.e., gap or Bragg resonance simultons). Our predictions stemming from an analytical approach are confirmed numerically with finite boundary conditions in a variety of qualitatively different situations
Frequency generation within the forbidden band gap: All optical Rabi-like splitting in photonic crystals and microcavities
No full textBased on three-dimensional time domain numerical simulations of the nonlinear dispersive Maxwell equations, we find evidence of all optical splitting of defect states in a photonic band gap structure. The result is analogous to the well known Rabi splitting and optical nutation in atomic two-level systems, and can be used for controlled in-gap generation of optical frequencies. Photon-echo-like behavior and third harmonic generation are also investigated
Spatial optical solitons in bulk nematic liquid crystals
No full textWe present an overview of our recent experimental results on two-dimensional optical spatial solitons in voltage biased planar cells with nematic liquid crystals. Excitation, induced waveguiding, and interactions are illustrated and interpreted in terms of the inherent re-orientational, non-resonant and nonlocal nonlinear response
Parametric gap solitons in quadratic media
No full textLocalized energy states such as two-color gap solitons are
theoretically and numerically predicted in a periodic structure in the
presence of a frequency doubling nonlinearity. These parametric solitons
exhibit appealing features as compared to the Kerr case. Novel
e®ects such as merging and all-optical bu®ering are envisaged
Near-Infrared Switching of Light-Guided Random Laser
No full textWe report on all-optical modulation and switching of light-guided random laser emission in optically pumped dye-doped nematic liquid crystals, whereby a continuous-wave near-infrared beam at 1.064 micrometer, non-resonant with the medium and collinear with the pump source, forms a reorientational spatial soliton. Such soliton-assisted cavity-less laser exhibits a beam character with directional emission and smooth transverse profile and can be either switched-on or made more efficient by injecting a mW input beam. We achieve energy amplifications of laser emission in excess of 18 dB by injecting a 6 mW near-infrared beam
Cavityless oscillator via backward quasi-phase-matched second-harmonic generation
No full textIn an amplifier, nonlinear feedback from mismatched backward second-harmonic generation leads to strong enhancement of parametric conversion. With reference to LiNbO3 quasi-phase-matched waveguides, we propose a parametric bistable device that operates simultaneously in two colors and in the cw or the self-pulsed regime
Self-confined light waves in nematic liquid crystals
Full text linkThe study of light beams propagating in the nonlinear, dispersive, birefringent and nonlocal medium of nematic liquid crystals has attracted widespread interest in the last twenty years or so. We review hereby the underlying physics, theoretical modelling and numerical approximations for nonlinear beam propagation in planar cells filled with nematic liquid crystals, including bright and dark solitary waves, as well as optical vortices. The pertinent governing equations consist of a nonlinear Schrödinger-type equation for the light beam and an elliptic equation for the medium response. Since the nonlinear and coupled nature of this system presents difficulties in terms of finding exact solutions, we outline the various approaches used to resolve them, pinpointing the good agreement obtained with numerical solutions and experimental results. Measurement and material details complement the theoretical narration to underline the power of the modelling
Electro-optic beam steering with nematicons
No full textWe analyze a novel geometry expressly designed to maximize the bias-controlled deflection of self-confined light beams in nematic liquid crystals (NLC). We use a self-confined beam and a dielectric interface defined by external voltages, ranging from total internal reflection (TIR) to refraction depending on the applied bias. The optimization of the deflection angle is achieved by using comb electrodes in a planar cell employing planarly oriented NLC molecules. We predict a maximum deflection of 70 with the standard mixture E7. © 2012 Copyright Taylor and Francis Group, LLC
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