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Flat focusing mirrors without any optical axis have been investigated by two-dimensional chirped photonic crystals. The principle of flat focusing mirror is similar to Veselago flat lens, which allows the beam focusing in the near field. The key idea of 2D chirped PhCs is to provide anomalous diffraction that can restrain a beam spreading and even focus a divergent beam upon reflection. Different...
The microchip lasers, being sources of coherent light, suffer from one serious drawback: low spatial quality of the beam, strongly reducing the brightness of emitted radiation. Attempts to improve the beam quality, such as pump-beam guiding, external feedback, either strongly reduce the emission power, or drastically increase the size and complexity of the lasers. Here we propose that specially designed...
Microchip lasers (and generally most micro-size lasers, like diode lasers or VCELS) being extremely compact and efficient sources of the coherent radiation, suffer from one drawback: the low spatial quality of the emitted beam. Only at low power emission regimes (close from the generation threshold) the microchip lasers can emit the beams and pulses of a reasonable spatial quality. Every attempt to...
Photonic crystal waveguides supporting band gap guided modes hold great potential to tailor the group velocity of propagating light. We propose and explore different wavelength demultiplexer design approaches that utilize slow light concept. By altering the dielectric filling factors of each waveguide segment, one can show that different frequencies can be separated and extracted at different locations...
The spatial modulation of pump in broad emission area semiconductor amplifiers has two important advantages in this kind of devices. A 2-dimensional periodic modulation of the pump profile introduces by one side, a filtering effect and an improvement of the beam quality. Moreover, the spatial modulation changes the effective diffraction inside the material and reduces the modulation instability generated...
We investigate spatial propagation effect behind the Photonic Crystal under particular dispersion conditions, which lead to a near field focusing. We analyze and experimentally demonstrate full two-dimensional near field focusing of light beams at visible frequencies behind the flat three-dimensional woodpile photonic crystal. Experimental results correspond well with numerical FDTD calculations as...
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...
Photonic crystals (PhCs) are materials with spatially modulated refraction index on a wavelength scale. They are well-known due to their temporal dispersion and photonic band-gaps, but also for the spatial dispersion properties, allowing the management of spatial propagation properties of light. For particular geometries PhCs may provide non-diffractive propagation of light or even negative spatial...
Spatial filtering is broadly used to improve the spatial quality of light beams. The conventional technique of spatial filtering uses a confocal system of lenses. Recently, alternative methods for spatial filtering have been proposed, based on periodically micro-modulated refractive index materials on a wavelength scale - the Photonic Crystals (PhCs).
We investigate different linear effects that appear in the light beam propagation behind a three-dimensional woodpile photonic crystal. On one hand we report and analyse experimental observation of narrow and well collimated laser beam formation behind the photonic crystal. We show that this collimation depends on the input laser beam focusing conditions. On the other hand we also report the first...
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...
In this paper, plane-mirror Fabry-Perot resonators filled by photonic crystals, i.e., with periodic intracavity refraction index modulation is investigated experimentally and theoretically. In order to achieve the effect of 2D intracavity index modulation the phase diffraction gratings were fabricated on the surfaces of the mirrors. The diffraction properties of such resonators can be manipulated,...
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...
This article proposes an alternative method for spatial filtering based on the propagation of the beam through a thin slice of photonic crystal. With this method, undesired spatial spectra components are strongly deflected, whereas the "clean" part of the beam propagates through the crystal without any deflection and losses.
We predict, that extremely narrow beams (of the width of few wavelengths) can be used for an efficient second harmonic generation in quadratic-nonlinear photonic crystals, tuned to the subdiffractive (self-collimating) regime simultaneously for the both, fundamental and the second harmonics, waves. We prove the idea analytically, by harmonic expansion technique, and numerically, by finite difference...
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