No. 1-2 (2000)
Published:
2000-06-30
ARTICLES FROM THIS ISSUE
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The present and future of nonlinear optics applications in photonic telecommunication networks
Abstract
A state-of-the art of photonic telecommunication technology is reviewed and possible directions of future developments are outlined. In particular, the impact of nonlinear optical phenomena inherent to silica glass on the transmission performance of wavelength-division multiplexed optical signal through fibres is discussed. Also potential applications of nonlinear photonic devices for the purposes of optical signal processing that is foreseen in future all-optical networks are pointed out.
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New pico- and femtosecond laser based sources: from the Infra-Red to the XUV
Abstract
In this paper, we review a number of recent developments concerning laser or laser-based sources generating pico- or subpicosecond pulses of light at wavelengths now ranging from the mid Infra-Red (50 um) to the XUV (11.9 nm). Those include the new generation of ,,Chirp Pulse Amplification`` laser systems, Free Electron Lasers operating in the IR or visible range, and a number of laser driven sources covering the XUV range, generally based on the high intensity irradiation of solid or gaseous targets. The main perspectives, applications and essential issues concerning such sources are discussed.
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Control of the effects of crystal dispersion at different orders in the mixing of three phase-matched waves on a 5- to 100-fs time scale
Abstract
A number of manners to obtain first-order achromatic phase matching of both type I and type II are presented and the most advantageous ones are identified to generate high-spectral quality 100-fs pulses by either parametric generation or frequency up-conversion. In the case of frequency-doubling high-energy 5-fs Ti:sapphire pulses, a non-collinear phase-matching I geometry in a b-barium borate crystal cut at 44 deg is devised that should allow high conversion efficiency, virtually without pulse lengthening and intra-pulse frequency chirp due to group-velocity dispersion.
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Nonlinear optics of the thin-film quasiwaveguide amplifier: applications to directional switching in the optical communication systems
Abstract
We examine nonlinear optical effects in the active medium of the thin-film quasiwaveguide amplifier-oscillator with injection of the external signal. The injection locking has been obtained in the case when both the frequency and the direction of propagation of the injected signal differ from those for a free-running thin-film laser which offers a possibility for the frequency and directional switching of the output of the thin-film laser. The effects of four wave mixing and phase conjugation have been discussed in the active medium of the thin-film laser when additional mirrors forming an external resonator have been used.
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Optical Josephson effects using phase-conjugating mirrors: an analogy with superconductors
Abstract
Motivated by the analogy between a phase-conjugating mirror (PCM) and a superconductor, we search for optical counterparts of the well-known DC and AC Josephson effects. We show that in a system consisting of two PCM`s separated by vacuum an ,,optical supercurrent`` arises as a function of an applied phase difference between the PCM`s, which is the optical analogue of the DC supercurrent flowing in a superconducting weak link. The corresponding AC effect occurs when the two PCM`s are pumped by light of a different frequency, causing the phase difference to oscillate in time with the frequency difference.
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Linear and nonlinear optical spectroscopy of CdS nanoparticles in Nafion membranes
Abstract
CdS nanoparticles embedded in Nafion membranes were studied by a variety of optical spectroscopic methods. Quantum confinement was achieved (particle mean diameter of 40 A) and the growth was found to follow a linear temporal kinetic law. Discrete energy levels were observable, even at room temperature. They could be attributed to light hole and heavy hole 1S and 2S transitions. The experimental results are in good agreement with theoretical calculations of light hole and heavy hole masses in the cases of cubic CdS. An enhancement of the nonlinear susceptibility X(3) at the quantized exciton energy levels was observed. The clusters were found to be photo-unstable, with a diffusion-limited growth rate due to Ostwald ripening.
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Growth and study of nonlinear optical crystals at the Hungarian Academy of Sciences
Abstract
The former Research Laboratory for Crystal Physics continues the growth and defect structure investigation of nonlinear optical single crystals in a new organization, as a part of the Research Institute for Solid State Physics and Optics, Hungarian Academy of Sciences. The aim of the activity is to prepare specific crystals for basic and applied research as well as for applications. We improve the quality or modify the properties of well known nonlinear oxide and borate crystals and develop new materials. The principle nonlinear optical crystals in our profile are the followings: Paratellurite (TeO2), congruent, Mg-doped and stoichiometric lithium niobate (LiNbO3), a variety of sillenite structured crystals (Bi12}MeO20, Me=Si, Ge, Ti, etc.), bismuth tellurite (Bi2TeO5 and nonlinear borates (BBO-b-BaB2O4, LBO-LiB3O5, LTB-Li2B4O7, CLBO-CsLiB6O10 and YAB-YAl3(BO3)4). Details of the crystal preparation and the major achievements are discussed in the paper.
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The possible mechanism for a frequency shift by a time-varying of medium features
Abstract
The optical frequency shift of an electromagnetic wave reflecting from a boundary of a medium is studies for two cases: for temporal variations of medium permittivity, and for a moving plasma boundary. It has been shown that a simultaneous occurrence of both cases leads to an enhanced frequency shift.
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Power penalty caused by Stimulated Raman Scattering in WDM Systems
Abstract
In this paper we present results of an investigation into the power penalty introduced by Stimulated Raman Scattering (SRS) in WDM systems with concentration on application of dispersion-shifted single-mode optical fibres (G.653) and unequal channel allocation schemes. System parameters based on ITU-T Recommendation G.692 and analytic formulas were used in calculations. It is shown that SRS does present a practical limitation to the multichannel systems. We also indicate limitations of the G.692 Recommendation and we point at directions of study in the area of nonlinear phenomena and multichannel systems.
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Ultra-short optical pulses having initial chirp
Abstract
Arbitrary shape optical pulses in nonlinear guides are discussed. The Nonlinear Schrodinger Equation for complex initial conditions is solved numerically using Split-Step Fourier Method and some selected results for solitons are presented. The computations confirm physical expectations of an influence of the chirp magnitude on pulse propagation in nonlinear guide.
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Impact of nonlinear optical phenomena on dense wavelength division multiplexed transmission in fibre telecommunication systems
Abstract
In the paper results of analysis of nonlinear phenomena in optical fibres: Self-Phase Modulation, Cross-Phase Modulation, Four-Wave Mixing and Stimulated Raman Scattering and their influence on Dense-Wavelength Division Multiplexed system performance are reported. Different non-uniform optical channel allocation schemes based on ITU Recommendation G.692 100 GHz frequency grid are compared with uniform channel distribution. The level of nonlinear cross-talk is determined for different levels of the total optical power. As an example a 10 Gbit/s D-WDM dispersion-shifted single mode fibre link with dispersion-compensating fibres is envisaged. The directions for optimization of the system design in view of actual international standardization trends are pointed out.
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Optical pulse splitting under temporal variations of reflecting medium
Abstract
A possibility of light pulse transformation by transient reflecting medium is investigated theoretically. After solving 1D problem of such a reflection one estimates such a transformation in a plane optical waveguide with time-dependent conductivity of one of the reflected media. Three types of the conductivity time-dependences are considered: harmonic, Bessel-like and splash-like ones. Obtained results show a possibility of pulse splitting under an influence of time-harmonic conductivity and pulse collapse vy the other considered nonstationarities.
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Recent advances in PBG structures
Abstract
We propose a review of word science achievements in the extremely extended for the recent few years field of photonic band gap structures. The review concerns both theoretical and experimental investigations on PBG structures toward fabrication of the most optimal ones for different applications. The attention is given to the obtained results as well as to the used and developed methods.
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Dielectric photonic quasi-crystals with doubled quasi-periodicity
Abstract
Optical range electromagnetic field interaction with inhomogeneous finite dielectric media is investigated. New method for analysis of this interaction in 1D case based on integral equations for fields in transient media is proposed. Some special cases of quasi-periodical structures with doubled quasi-periodicity are investigated numerically. A possibility to obtain good filtering properties in such structures for small number of quasi-periods is shown.
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Reflection from layered dielectric structures with combined regular and random inhomogeneities
Abstract
Optical wave reflection from a layered half-space with regular and random inhomogeneities where the regular perturbations correspond to a linear waveguide near the half-space boundary. Random inhomogeneities are simulated in the frame of the white noise model. The problem is solved analytically in a framework of the embedding method which reduces a boundary problem to the problem with initial values considering the field as a function of the half-space boundary coordinate and obtaining then its solution as a steady-state probability density of the reflection coefficient phase. Numerical calculations revealed some features of the field behaviour under the combined influence of regular and random inhomogeneities such as the reflection coefficient phase increasing inhomogeneity from uniform distribution for small regular inhomogeneities toward a strong peak at the phase equal to pi/2 for increasing ones, and some fine effects which are still greater then the calculation accuracy. -
New method of numerical modelling of optical field transformation by inhomogeneous semiconductor layer with time-varying parameters
Abstract
A time-domain model of a semiconductor layer with time-dependent inhomogeneous permittivity or conductivity is investigated by solving direct and inverse problems using a novel method, revealing a possibility of wavelength shifting and other desirable optical field transformation, as well as a remote diagnostics of fast time-varying inhomogeneous structures.
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Side lobes reducing by variation of array apperture edge shape
Abstract
A possibility of side lobes level reducing in plane antenna array by creation of aperture comb edge in arrays with rectangular and circular aperture shape together with usage of different types of reducing to the array edges amplitude distributions is investigated by computer analysis. It is shown that usage of the comb structure in combination with the reducing amplitude distribution enables one to reach the side lobes level reducing in the array to -27 - -29 dB. diagnostics of fast time-varying inhomogeneous structures.
