Ultra-fast quantum-well saturable absorber devices and their application to all-optical regeneration of telecommunication optical signals

We review recent advances in the investigation of vertical cavity saturable absorber devices and their use for the all-optical regeneration of telecommunication signals in ultra-long-haul transmission systems. Such devices are polarization-insensitive and operate as fully passive nonlinear optical elements. Two approaches for obtaining fast recovery absorber materials are described, relying upon ion irradiation or upon iron doping. The vertical micro-cavity devices are designed so as to optimize the switching contrast and the operating power. Their functional behaviour as extinction ratio amplifiers has been characterized and their optimal operating conditions have been determined. The potential application of these devices to all-optical regeneration has been investigated through numerical simulations and fully demonstrated in several long-distance transmission loop experiments, with results obtained at 10, 20 and 40 Gbit/s, showing significant improvements in system haul or operational margins. A four-channel fibered module has also been fabricated, as a perspective towards the development of wavelength division multiplexing (WDM) saturable absorber modules.     

Comparative study of various methods for extraction of multi- quantum wells Schottky diode parameters

In this work, forward current voltage characteristics for multi-quantum wells Al_0.33Ga_0.67As Schottky diode were measured at temperature ranges from 100 to 300 K. The main parameters of this Schottky diode, such as the ideality factor, barrier height, series resistance and saturation current, have been extracted using both analytical and heuristics methods. Differential evolution (DE), particle swarm optimization (PSO) and artificial bee colony (ABC) have been chosen as candidate heuristics algorithms, while Cheung technic was selected as analytical extraction method. The obtained results show clearly the high performance of DE algorithms in terms of parameters accuracy, convergence speed and robustness.     

Shape retrieval through normalized B-splines curves

Multimedia Tools and Applications - This paper proposes a new technique for 2D shape modeling and retrieval based only on curves defined from shape boundary. Firstly, a shape representation system...     

On how Pachycondyla apicalis ants suggest a new search algorithm

In this paper we present a new optimization algorithm based on a model of the foraging behavior of a population of primitive ants (Pachycondyla apicalis). These ants are characterized by a relatively simple but efficient strategy for prey search in which individuals hunt alone and try to cover a given area around their nest. The ant colony search behavior consists of a set of parallel local searches on hunting sites with a sensitivity to successful sites. Also, their nest is periodically moved. Accordingly, the proposed algorithm performs parallel random searches in the neighborhood of points called hunting sites. Hunting sites are created in the neighborhood of a point called nest. At constant intervals of time the nest is moved, which corresponds to a restart operator which re-initializes the parallel searches. We have applied this algorithm, called API, to numerical optimization problems with encouraging results.     

Oswaldocruzia venezuelensis sp. n. (Nematoda:Trichostrongylina, Molineoidea), a parasite of Bufo marinus from Venezuela

A new species of Oswaldocruzia Travassos, 1917, a parasite of Bufo marinus L. from Venezuela, is described. Like most Neotropical Oswaldocruzia, Oswaldocruzia venezuelensis sp. n. is characterized by spicules with three principal branches: blade, shoe and fork, and by a division of the fork within the distal third of the spicule length. O. vaucheri Ben Slimane et Durette-Desset, 1993 is the most closely related species due to its caudal bursa of type II and its cervical alae of the same shape but it differs in the following characters: the position of the papillae of rays 4 situated nearer the papillae of rays 3 rather than rays 5, a higher percentage of the ridges in the oesophageal region, the cervical alae three times longer and sharp and the spicular fork divided less deeply.     

Spectral coded phase bipolar OCDMA technological implementation thanks to low index modulation filters

Telecommunication Systems - Optical code division multiple access (OCDMA) systems are attracting an increasing interest in optical fiber communication. This is due to the various advantages that...     

Tight bounds on the error probability of coded modulation schemesin Rayleigh fading channels

This paper presents a tight upper bound on the bit error performance of coded modulation schemes in Rayleigh fading channels. Upper and lower bounds on the pairwise error probability are first derived. The upper bound is then expressed in a product form to be used with the transfer function bounding technique. This upper bound has the same simplicity as the union-Chernoff bound while providing closer results to the exact expression. Examples for the case of four-state and eight-state TCM 8PSK schemes are also given to illustrate the tightness and the application of this upper bound