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We show how a periodic modulation of loss on the wavelength scale provides negative diffraction propagation. In particular, we consider a 2D square arrangement of lossy cylinders embedded in air, with no index contrast. The phase-shifts accumulated in propagation trough such a structure, with flat-flat interfaces, are then compensated by normal diffraction in air leading to a substantial focalization...
We predict and show the existence of unlocked evanescent waves in two dimensional periodic structures. In a one dimensional periodic structure an evanescent mode are located either at the center or at the boundary of the Brillouin Zone, and the real part of wave-vectors is locked either to zero or to the modulation vector of the periodicity. However, we report an unexpected observation that this is...
The propagation of light through materials with periodically modulated gain can present different effects that are analyzed in the paper. The characterization of these gain/loss metamaterials (GLM) with a two-dimensional modulation predicts the mode locked states and effects like non diffractive propagation of beams, superluminar light propagation regimes and superdiffusion due to angular gain dependence...
We report first experimental evidences of spatial filtering of light beam in three-dimensional photonic crystals. The photonic crystals were fabricated in a glass bulk, where the refraction index was modified by applying femtosecond laser pulses. We observe the modification of the angular spectra (the far field) in the central maximum of the transmitted radiation in accordance with the theory of spatial...
The aim of the present work is to convert radiation from a very narrow beam at the fundamental frequency in a very narrow beam at the second harmonic (SH) frequency. Therefore, it is needed the subdiffractive propagation condition for both fundamental and second harmonic waves. However, for an efficient second harmonic generation (SHG) there are two other conditions to be fulfilled: the phase matching...
We are making a study of the out-of-plane losses for the second harmonic generation process in planar two-dimensional photonic crystals made from Al0.3Ga0.7As. We found that for the rhombic symmetry of the lattice it can be obtained a structure in which the out-of-plane losses vanish for both fundamental and second harmonic waves in conditions of very small diffraction for the second harmonic wave...
We predict self-collimation and superdiffusion of light propagating in materials with periodically modulated gain/loss profile. The modulation is parallel and transverse to the light propagation direction and its periodicity is on the wavelength scale. The self-collimation (or diffraction-free propagation) of the beams is found, which is similar to that observed in photonic crystals. The superdiffusion...
It is well known, that the materials with the refractive index modulated in space on the wavelength scale, i.e. the photonic crystals (PCs), bring about a significant modification of the propagation properties of waves, both in time and space domains. In time domain the usual (temporal) dispersion is modified, and photonic band gaps appear in the frequency spectra. In the space domain, the spatial...
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