Abd El-Naser A. Mohamed

Optical Image Encryption Based on Chaotic Baker Map and Double Random Phase Encoding

This paper presents a new technique for optical image encryption based on chaotic Baker map and Double Random Phase Encoding (DRPE). This technique is implemented in two layers to enhance the security level of the classical DRPE. The first layer is a pre-processing layer, which is performed with the chaotic Baker map on the original image. In the second layer, the classical DRPE is utilized. Matlab simulation experiments show that the proposed technique enhances the security level of the DRPE, and at the same time has a better immunity to noise.

Speed Response and Performance Degradation of High Temperature Gamma Irradiated Silicon PIN Photodiodes

In the present paper, we have been investigated deeply and parametrically the speed response of Si PIN photodiodes employed in high temperature-irradiated environment. The radiation-induced photodiodes defects can modify the initial doping concentrations, creating generation-recombination centres and introducing trapping of carriers. Additionally, rate of the lattice defects is thermally activated and reduces for increasing irradiation temperature as a result of annealing of the damage. Nonlinear relations are correlated to investigate the current-voltage and capacitance-voltage dependences of the Si PIN photodiodes, where thermal and gamma irradiation effects are considered over the practical ranges of interest. Both the ambient temperature and the irradiation dose possess sever effects on the electro-optical characteristics and consequently the photo-response time and SNR of Si PIN photodiodes. In this paper, we derive the transient response of a Si PIN photodiode for photogeneration currents, when it is exposed to gamma radiation at high temperature. An exact model is obtained, which may be used to optimize the responsivity and speed of these irradiated devices over wide range of the affecting parameters.

Recent Advances of Distributed Optical Fiber Raman Amplifiers in Ultra Wide Wavelength Division Multiplexing Telecommunication Networks

ABSTRACT Recently, many research works have been focused on the fiber optic devices for optical communication systems. One of the main interests is on the optical amplifiers to boost a weak signal in the communication systems. In order to overcome the limitations imposed by electrical regeneration, a means of optical amplification was sought. The competing technology emerged: the first was Raman amplification. One reason was that the optical pump powers required for Raman amplification were significantly higher than that for Erbium doped fiber amplifier (EDFA), and the pump laser technology could not reliably deliver the required powers. However, with the improvement of pump laser technology Raman amplification is now an important means of expanding span transmission reach and capacity. We have deeply studied an analytical model for optical distributed Raman amplifiers (DRAs) in the transmission signal power and pump power within Raman amplification technique in co-pumped, counter-pumped, and bi-directional pumping direction configurations through different types of fiber cable media. The validity of this model was confirmed by using experimental data and numerical simulations. Keywords: Distributed Raman amplifier, Fiber link media, Signal power, Pump power, and Raman gain efficiency.

Multiple access interference cancelation technique in optical CDMA systems

This paper presents a simple and efficient multiple access interference (MAI) cancelation technique in optical code division multiple access (OCDMA) system. The proposed technique is based on hybrid frequency shift keying (FSK) with an enhanced modified prime code as a signature sequence for coding techniques. Coherent FSK modulation along with incoherent demodulation using Arrayed-Waveguide Grating has been examined in the transceiver structure. In the proposed technique, a reference signal is constructed by using one of the addressed spreading sequences, and MAI cancelation is performed by subtracting the reference signal from the received signal of the desired user. The performance of the proposed FSK-OCDMA system is compared with the performance of the existing pulse position modulation (PPM)–OCDMA system. The simulation results reveal that the bit-error rate performance of the proposed technique is superior to the performance of the pulse position modulation (PPM) technique. Also, the results indicate that the proposed technique is very power efficient, and when the bit rate is constant, the network capacity can be expanded to accommodate a large number of simultaneous active users with low error rate. Moreover, the proposed technique simplifies the hardware of the receiver design.

Performance enhancement of IM/DD optical wireless systems

Due to the fast development of telecommunications and the great demand of bandwidth, optical wireless communication (OWC) has become a promising trend. OWC offers flexible networks for both indoor and outdoor communications providing high security, high speed and a license free spectrum. Data transmission over indoor OWC systems with diffused channel model at high speed will extend the channel impulse response over several symbol periods with many reflections causing inter-symbol interference. This interference distorts the data symbols being transmitted and affects the signal recovery at the receiver side. This paper studies error control coding for OWC systems over additive white Gaussian noise and ceiling bounce channel models. It considers Hamming coding and channel equalization for unipolar optical orthogonal frequency division multiplexing (OFDM) system. The objective is to mitigate the channel distortion, and hence achieve reliable transmission and correct detection at the receiver side.

Optical Cross Connect Performance Enhancement in Optical Ring Metro Network for Extended Number of Users and Different Bit Rates Employment

Optical cross connect (OXC) is important device that play a vital role in switching high speed optical signals and in our case as high speed switch to open the first ring to the second ring to become one ring in case of path failure or during maintenance in any node in this path and also if the failure path get in service it switch the two ring again to become isolated from each other. This paper has presented different enhancement techniques to increase number of users at different bit rates and also increased the transmission distance between nodes. Its main advantages have made it to disaster path in case of any failure cause in any node or path between two optical cross connect OXC. That is no doubt that crosstalk, dispersion and noise are produced when OXC separates incoming optical signals onto different output paths.

Performance Evaluation of SAC-OCDMA System in Free Space Optics and Optical Fiber System Based on Different Types of Codes

In this paper, the Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA) system performance is investigated both in Free Space Optics (FSO) and Optical Fiber Systems (OFS) scenarios focusing on different types of codes. The codes having low cross correlation such as Random Diagonal (RD) and Khazani-Syed (KS), and zero cross correlation such as Zero Cross Correlation (ZCC) and Multi-Diagonal (MD) are used. In the FSO scenario, moderate turbulence and hazy weather conditions are considered. In the OFS scenario, nonlinear effects, attenuation, and dispersion are taken into consideration. Also, the performance of various codes is evaluated under different rain attenuation conditions. The simulation results show that the SAC-OCDMA codes performance is media-dependent. The ZCC codes give better performance than low cross correlation codes in both FSO and OFS scenarios. The MD code gives the best code performance in both scenarios with the ZCC code following. The RD code provides better performance than the KS code in the OFS scenario. However, in the FSO scenario, the KS code performs better than the RD code under the turbulence effect. Furthermore, the MD code performance under different bit rates is investigated to support tri-play services. Its security performance is also investigated.

Light wave transmission through free space using atmospheric laser links with adaptive equalization

Abstract. The utilization of adaptive equalization in the design of atmospheric laser link transceiver architectures that can be used for television and broadcast signal interconnect between the external place of event and the master control room is suggested. At the transmitter side of the proposed transceiver; an array of atmospheric laser sources, digital signal processing, and optical radiators are used to send light waves in free space. At the receiver side, an adaptive finite impulse response least mean square (LMS) equalizer with activity detection guidance (ADG) and tap decoupling (TD) is used to mitigate the effect of channel impairments. The performance of the suggested adaptive equalizer is compared with that of the conventional adaptive equalizer based only on the standard LMS algorithm. The simulation results revealed that the adaptive LMS equalizer with ADG and TD is a promising solution for the inter-symbol interference problem in optical wireless communication systems.

SUPPORTING DISTRESS SIGNALS OVER LOW EARTH ORBIT MOBILE SATELLITE SYSTEMS FOR EMERGENCY INFORMATION ACQUISITION

Low earth orbit (LEO) satellite systems allow a broad range of services to be provided using small, lightweight, cellular-like portable telephones. Exploiting LEO satellites to support distress signals for aircrafts, ships and international travelers is explored in the current paper. A multi-service priority-oriented algorithm is proposed for handling voice, data and emergency signals over LEO satellites. The emergency signal is privileged with service priority so that rescue operation can be carried out as soon as possible. The priority mechanism includes channel reservation as well as joining a queue if no free channel is available as long as the request is roaming in the handover area. In addition, a simplified but efficient approach is suggested for locating the object of an imminent danger situation. As LEO satellites are non-geostationary, the visible period of each spot-beam is small. Consequently, a teletraffic model, that accommodates the mobility of spot-beams as well as the resulting handover rate, is developed in order to gauge the performance of the proposed algorithm. Numerical results for access denying and service-dropping rates are presented for nominal system parameters.

Combating performance degradation in optical channels using successful noise reduction adaptive equalizer

Optical communications either wire or wireless are a promising candidate to support multimedia such as: “local area network (LAN), wide area network (WAN), metropolitan area network (MAN), wireless optical microwave link for TV and broadcast as well as the inter satellite link communications”. Where, they have substantial advantages such as ultra high bit rate, extremely high speed, secure and immune communications. However, its high-speed data transfer, transmission distance and bandwidth often limited by pulse dispersion which causes pulse brooding and hence signal distortion or inter symbol interference (I.S.I). The current paper, proposes an adaptive equalizer by integrating the fractional spaced equalizer (FSE) with decision feedback equalizer (DFE) for optical channel to remedy the problem of pulse dispersion effect in optical link, in addition, for further improvement in the performance of the equalizer we propose adopting the activity detection guidance (ADG) with tap decoupling (TD) in the fractional spaced decision feedback equalizer (FSDFE) to get fruitful outcomes in the performance of the system without shortcomings. Where, we could improve the stability, the steady-state error performance and the convergence rate. A typical optical channel will be analyzed; channel equalization will be performed using the addressed structures of adaptive equalizer. Numerical results have been carried out using a careful choice for the parameters which affect the equalizer performance such as: noise variance has been set at 0.1 and the adaptation step size has been set at 0.005 and the adaptation of FSDFE has been run for 30000 sample input. The simulation results revealed that: the FSDFE with ADG and TD offers a superior performance than its counterpart without ADG and TD. Where, it offers improvement in the effectiveness of amplitude distortion. Moreover, as the impulse response of a typical optical link would have regions that are essentially zero, the employment of the ADG scheme would further enhances the steady-state error performance and convergence rate.