The modeling and design of fiber lasers is an essential element of their development process. One of the areas of particular interest during the last years is the development of lanthanide ion-doped fiber lasers which operate at wavelengths exceeding 2000 nm. There are two main host glass materials developed for this purpose: fluoride and chalcogenide. One of the main specific aims of this contribution is therefore to comparatively study the properties of various numerical algorithms applicable to the design and modeling of fiber lasers operating at wavelengths exceeding 2000 nm. Hence, the convergence properties of selected algorithms implemented within various software environments are studied with a particular focus on the CPU time and calculation residual.
As the number of active OWC installations is growing fast, the standards for compatibility of co-existing neighbouring systems are being developed. The paper addresses the Laser Safety (IEC standards), ITU-T Study Group 15 standards (G.640 Co-location longitudinally compatible interfaces for free space optical systems), ITU-Radiocommunication Sector standards (P.1817-1 Propagation data required for the design of terrestrial free-space optical links), and the IEEE Work in Progress - standardization activity on Visible Light Communications. International standards of FSO communications have been reviewed and discussed. ITU, IEC, and IEEE International standards for Free-Space Optical links have been reviewed. The system reliability and availability as well as security issues will be addressed as well in the talk.
A photonic crystal (PhC) is a periodic structure with periodicity comparable with the wavelength of light, having a photonic band gap in the visible range. In this contribution we discuss the possible use of PhCs as strain sensors, based on the observation that a distortion in the crystal structure produces a change in the reflected bandwidth. First, we demonstrate the feasible fabrication of a PhC having sub-micrometric polystyrene colloidal spheres in a PDMS matrix on a rubber substrate, and we demonstrate that the photonic properties change with substrate elongation according to theoretical prediction. The crystal sensitivity to strain depends directly on interplanar spacing and on Poisson’s ratio. To enhance the crystal strain resolution, we propose to fabricate inverse photonic crystals with FCC structure, which are known from the literature to exhibit a high negative Poisson's ratio. We carried out a theoretical investigation to predict the opto-mechanical response of inverse PhCs, and carried out preliminary tests to demonstrate their fabrication feasibility.
Transparent glass-ceramics are nanocomposite materials which offer specific characteristics of capital importance in photonics. This kind of two-phase materials is constituted by nanocrystals embedded in a glass matrix and the respective composition and volume fractions of crystalline and amorphous phase determine the properties of the glass-ceramic. Among these properties transparency is crucial, in particular when confined structures, such as dielectric optical waveguides and optical fibers, are considered, and the number of papers devoted to this topic is continuously increasing. Another important point is the role of the nanocrystals when activated by luminescent species, as rare earth ions, and their effect on the spectroscopic properties of the glass-ceramic. The presence of the crystalline environment around the rare earth ion allows high absorption and emission cross sections, reduction of the non-radiative relaxation thanks to the lower phonon cut-off energy, and tailoring of the ion-ion interaction by the control of the rare earth ion partition. This last point is crucial and still object of intense experimental and theoretical studies. The composition of the glass matrix also impacts the properties of the rare earth ions located in nanoparticles. Moreover, some kinds of nanocrystals can play as effective rare earth sensitizers. Fabrication, assessment and application of glass-ceramic photonic systems, especially waveguides, deserve an appropriate discussion which is the aim of this paper, focused on luminescent glass-ceramics. In this work, a brief historical review, consolidated results and recent advances in this important scientific and technological area will be presented, and some perspectives will be outlined.
We consider the design methods and operation principles of a fast-response optical sensor for precise measurement of small temperature variations, which is based on ring resonators of micron size made from waveguides with one or two slots filled by a liquid crystal. The sensor sensitivity and measurement region can be changed by modifying the parameters of the waveguide or resonator, such as width of the waveguide strips or slots, slot separation, resonator bend radius, coefficient of coupling between the ring and input/output waveguides, etc. We analyzed the dependence of the transverse field distribution and effective indices of the orthogonally polarized modes in the slot and double-slot waveguides on the waveguide and resonator parameters, and we have considered the optimization of the temperature sensor structure based on such waveguides.
We propose the method of calculation of the dispersion characteristics and field distribution of the modes in straight and bent multi-core microstructured fibers. The method is implemented for the analysis of the birefringence in dual-core microstructured fibers in dependence on the fiber parameters (air hole diameter, hole separation, distance between guiding cores) and bend radius. The term "birefringence" we understand here in the wide sense including both the difference of the parameters of orthogonally polarized modes (polarization birefringence) and the difference of the parameters of two supermodes with identical field distribution propagating in dual-core microstructured fibers (supermode birefringence). The optimization of the parameters of such fibers using as vector bend sensors is considered.
This report shortly describes calculation method related to guiding properties of the microstructure fibres. For the
modelling of wave propagation in such fibres in linear and nonlinear regimes the finite-difference vectorial-beam-propagation
method (FD-VBMP) has been chosen. This method offers high accuracy and allows investigating
longitudinally varying structures or propagation of optical waves with amplitudes varying under the effect of nonlinearity
and loss. In order to take into account the effects related to the finite fibre dimensions the transparent boundary
conditions (TBC) was used. The Split-Step Local Error method is implemented for correct estimation of the influence of
nonlinearity on the wave propagation in microstructure fibres. On the basis of this method the complete algorithm for the
numerical simulation of the wave propagation in microstructure fibres under the effect of nonlinearity has been
developed. The method allows optimising the structure of photonic crystal fibres (PCF) for maximising or minimising
nonlinear effects. Investigation of the properties of a wavelength converter based on a microstructure fibre was carried
out using simulation results in the nonlinear case. Modification of the method for optimisation of connection between
microstructure fibres and conventional fibres is also considered.
Optical properties of photonic crystal heterostructures with embedded n-i-p-i superlattices are studied. Nonlinear behavior of the transmission and reflection spectra near the defect mode is investigated. Self-consistent calculations of the output performance characteristics are performed using the transfer-matrix method and taking into account the gain saturation. Features and characteristic parameters of the nonlinear gain in active n-i-p-i layers are determined. Detail analysis of the gain saturation and accompanying nonlinear refraction effects is carried out for one-dimensional photonic crystal heterostructure amplifiers in the GaAs-GaInP system having at the central part an active "defect" from the doubled GaAs n-i-p-i crystal. The gain saturation in the active layers in the vicinity of the defect changes the index contrast of the photonic structure and makes worse the emission at the defect mode. Spectral bistability effect which can be exhibited in photonic crystal heterostructure amplifiers is predicted and the hysteresis loop and other attending phenomena are described. The bistability behavior and modulation response efficiency demonstrate the potential possibilities of the photonic crystal heterostructures with n-i-p-i layers as high-speed optical amplifiers and switches.
While Internet traffic increases dramatically and now it exceeds the almost stable voice traffic, new efficient solutions for network architecture are sought. One of the main problems to be resolved is the basic concept of the future network performance. While actual networks are based on 'circuit switching' connection networks with IP packets forwarded given the network offers some free resources, a number of researchers foresee the future network as a 'packet switched' connectionless network which would support also the traditional real time services with phone calls as the most representative example. This is driven by the growing use of voice over IP services. Unfortunately, the Quality of Service is actually not sufficient for wide acceptance of that technique. In fact, Internet is based on the 'best-effort' principle in what it fudamentally differs from circuit-switched network which has been developed uniquely to provide excellent voice quality during last century. Moreover, the reliability of the network is a crucial factor in emergency communications, what has recently became a subject of intense activity at national and international scale. As a consequence, the idea of dropping the converged network with voice-over-IP concept is hard to accept for a great majority and those expressing it are usually looked as strange or even dangerous individuals. Nevertheless, those fundamental difficulties become obvious for a growing number of people who approach the future network evolution more fundamentally, and try to trace reasonable and economic ways of the future network development. The author of this paper has extensively developed a concept of a "hybrid network" which consists of real-time subnetwork and packet network separated in the optical frequency domain that will be discussed in detail in this paper. This optimized network concept is intended to guarantee both reliability of the network and Quality of Service as well.
There are reported the fundamentals and results of numerical investigation of the influence of the nonlinear optical phenomena on transmission quality and nonlinear products accumulation in multispan dense wavelength-division multiplexed (DWDM) optical fiber telecommunication systems. Four-Wave Mixing (FWM), Self-Phase Modulation (SPM), Cross- Phase Modulation (XPM), and Stimulated Raman Scattering (SRS) phenomena are taken into account. Various types of optical fibers as well as different channel number and channel spacing are taken into account in the analysis.
A new Two-Beam-Propagation Method algorithm for simulation of Second Harmonic Generation (SHG) process in planar optical waveguides is presented. The model accounts for an evolution of two beams propagating simultaneously: the fundamental and the second-harmonic one. Physically, the model consists of a separation of the propagation step and the nonlinear phase and amplitude compensation step. Mathematical formulation of the model is reported and some of its special features are discussed. The method can be easily generalized to investigated SHG processes in optical guides made from media with gain and/or loss. Also other nonlinear wave interactions such as self-phase modulation and cross-phase modulation can be dealt with using the method.
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