Mustapha Razzak

Optical post-equalization based on self-imaging

Optical fibre transmission systems operate in the presence of inter-symbol interference (ISI) caused by chromatic dispersion (CD), polarization-mode dispersion (PMD), and other impairments. As the transmission rate increases, ISI mitigation becomes mandatory. Many schemes for dispersion compensation have been proposed. We present and discuss a new optical method for post-compensating the chromatic dispersion in a particular dispersive medium, namely the single mode fibre. This method is based on the self-imaging phenomenon known as the temporal Talbot effect. The main advantage of our method results in using standard optical fibres instead of special fibres. We also have all freedom in subdividing and processing sequences of the dispersed optical signal.

Liquid crystal-based optical space switches fordwdm networks

This paper addresses the issue of using conventional liquid crystal materials as reconfigurable holographic or diffractive phase elements within optical space switches and the resulting constraints in their choice and use in a telecommunication environment. We discuss the advantage of this technology for implementing holographic-based approaches with respect to other techniques. As an illustration we give two examples which illustrate two generic architectures and complementary use of liquid crystal to implement them. Finally, we give some trends on implementations of high channel capacity space switches based on this technology.RésuméCet article traite de l’utilisation de cristaux liquides pour la génération de structures diffractives de phase au sein de commutateurs optiques spatiaux. Nous discutons des problèmes posés par leur application aux télécommunications et soulignons les avantages de cette approche par rapport à d’autres techniques. Nous présentons ensuite deux exemples de réalisation mettant en oeuvre des architectures optiques et des types de cristaux liquides différents. Finalement, nous décrivons les évolutions techniques nécessaires au développement de systèmes de grande capacité à partir de cette technologie.

Guest Editorial: Special Issue on: WiMAX security and applications

Worldwide Interoperability for Microwave Access (WiMAX) aims to provide high-speed, high-bandwidth, and high-capacity Broadband Wireless Access (BWA) for residential as well as enterprise applications. WiMAX is designed to provide high data rate multimedia services, e.g., voice, data, Internet, email, instant messenger, and games. The security of WiMAX has been under researchers’ scrutiny for the last few years. Both architectures and protocols on WiMAX security have been extensively studied in academics and industries. Several articles, survey reports, and research papers have been published and a number of flaws have been highlighted in the literature. The IEEE Committee has published several revisions of the IEEE 802.16 standard since its initial release in 2001, but many of the vulnerabilities have still been left unattended in the standard. Ensuring the security of these complex and yet resource constraint systems has emerged as one of the most pressing challenges. The aim of this Special Issue is to bring together researchers and practitioners in related areas and to encourage interchange and cooperation under the context of WiMAX security between the research community and the industrial/ consumer community. With regard to such cyber security aspects, there is an increasing demand for measures to guarantee and fully attain the authentication, confidentiality, data integrity, privacy, access control, non-repudiation, and availability of system services. The first paper in this Special Issue by Barghava et al.: discusses security problems, with a focus on collaborative attacks, in the WiMAX scenario. The WiMAX protocol suite, which includes but is not limited to DOCSIS, DES, and AES, consists of a large number of protocols. The authors presented briefly the WiMAX standard and its vulnerabilities. They pinpoint the problems with individual protocols in the WiMAX protocol suite, and discuss collaborative attacks on WiMAX systems. Then several typical WiMAX attack scenarios were presented, including: bringing a large number of attackers to increase their computation power and break WiMAX protocols; assembling a sufficient number of attackers to influence the decision-making of core machines, which includes routing attacks and Sybil attacks, and exploiting implementations that do not conform to the WiMAX specification completely, causing interoperability problems among various protocols, including the ones in typical WiMAX/WiFi/LAN deployment scenarios. Then the authors presented theoretical models and practical solutions to profile, model, and analyze collaborative attacks in WiMAX. Employed attack graphs to vulnerability were analyzed. Experimental results are carried out to verify the models and validate the analysis. Du et al.: study the rekeying issue in IEEE 802.16e WiMAX networks. The existing rekeying scheme— the Multicast and Broadcast Rekeying Algorithm (MBRA) unicasts new keys to each subscriber station (SS). This scheme does not scale well since it incurs large communication overheads when the number of SSs increases. In this work, first a general tree-based rekeying scheme was proposed, which is more efficient than the MBRA. Also formulate an optimization problem to determine the optimal tree structure for given number of SSs. Furthermore, a novel and efficient rekeying scheme for WiMAX networks was presented. The new rekeying scheme utilizes efficient

A web-based user friendly simulator of optical fiber communication systems

A simulation tool in optical networks design and evaluation is suggested. This user friendly software, baptized “SystemBuild”, is a powerful tool to simulate optical fiber communication systems and can be easily used for both educational and research purposes. People modeling optical networks can use it to investigate the usefulness and the accuracy of their model as well as the performances of the system they intend to implement. This Web-based software needs neither a license nor an installation. Merely, a conventional Internet browser supporting Java plug-in is necessary. Moreover, the software can run in all platforms that include the Java Virtual Machine (jvm). Signals and values can be directly checked by moving the mouse pointer over the component’s connectors allowing an easy debugging and assistance to the users to build a complex system. The quality of collaboration is offered thanks to the free code access to the platform.RésuméNous proposons un outil de simulation destiné à la conception et l’évaluation des réseaux optiques. Ce logiciel, baptisé «SystemBuild», constitue un outil performant pour simuler les systèmes de communications à fibre optique. Il est destiné à la fois pour la recherche et l’enseignement. Il permet entre autre aux personnes désirant modéliser des réseaux d’apprécier l’utilité et la précision de leur modèle ainsi que d’évaluer les performances du système à implémenter. SystemBuild est une application libre (gpl: General Public Licence) utilisable avec un fureteur internet disposant du plug-in Java offrant une compatibilité avec toute plateforme disposant de la machine virtuelle Java (jvm). Aucune licence ni installation n’est nécessaire. A chaque étape de la simulation, l’utilisateur peut afficher les valeurs ainsi que les signaux seulement par passage du pointeur de la souris sur le connecteur considéré. Cela assiste les utilisateurs pour construire un système plus complexe. La mise en disposition du code source donne au logiciel une dimension de collaboration.

Effect of chromatic dispersion on fiber over wireless systems

Ad hoc wireless networks can be described as dynamic multi-hop wireless networks with mobile nodes. However, the mobility condition can be relaxed, and we can consider an ad hoc wireless network as a reconfigurable network where all the nodes are connected to the local environment through wireless links, and where there is not a central or dominant nodes opposed to, for example, the case of cellular wireless networks where a base station is located in each cell. When ad-hoc networks are backboned by fibers, distortion of the optical link presents one of the major issues. In this paper, we will be addressing one of the fundamental problems, namely chromatic dispersion compensation in the fiber optic prior reaching the access points. This will ensure an adequate better quality of signal in the applied network.

A new optical post-equalization based on self-imaging

Driven by the worlds growing need for communication bandwidth, progress is constantly being reported in building newer fibers that are capable of handling the rapid increase in traffic. However, building an optical fiber link is a major investment, one that is very expensive to replace. A major impairment that restricts the achievement of higher bit rates with standard single mode fiber is chromatic dispersion. This is particularly problematic for systems operating in the 1550 nm band, where the chromatic dispersion limit decreases rapidly in inverse proportion to the square of the bit rate. For the first time, to the best of our knowledge, this document illustrates a new optical technique to post compensate optically the chromatic dispersion in fiber using temporal Talbot effect in ranges exceeding the 40G bit/s. We propose a new optical post equalization solutions based on the self imaging of Talbot effect.

Step wise algorithm for simulating wave propagation in bright solitons

Light propagation trough dispersive media was the object of intensive research. Split-step methods such as optical fibers based on Fourier transform were among the most interesting methods. This method shows well the interplay between the dispersion and nonlinear effects in the optical fiber. We provide here some results of the split-step Fourier method applied to the simulation of wave propagation in a dispersive medium.