Magdy M. Ibrahim

The effect of electronic feedback on semiconductor lasers

Negative electronic feedback (EFB) has a strong effect on the performance of a bistable laser diode amplifier and on injection-locked lasers. Negative EFB drastically reduces the switching-up input power level and the hysteresis in the input-output power characteristic and in the tuning curves of the bistable laser amplifier. Furthermore, negative EFB leads to a reduction in the time delay associated with optical switching in diode laser amplifiers. This provides a means of enhancing the versatility of the proposed system in some potential applications. For an injected-locked laser, negative EFB achieves a broadening in the locking bandwidth and its dynamically stable region. >

On injection locking of homogeneously broadened lasers

The dynamic rate equations are obtained from a semiclassical analysis for a homogeneously broadened laser operating in two modes with an externally injected signal. The time-dependent behavior of two competing modes can be described by three-coupled first-order nonlinear equations which relate the inversion density and the photon density of the two modes. Considerations regarding injection locking are presented.

Photonic switch using surface-emitting laser diode and APD

A very sensitive photonic switch is proposed by integrating vertically an avalanche photodiode (APD) and a surface-emitting laser diode (VCSEL). The switch requires a very low input optical power of /spl sim/1 nW, and emits a large output of several milliwatts. Both optical and electrical feedback from the VCSEL to the APD are taken into account. A closed-form expression for the switching characteristics is obtained. The dynamics of optical switching is analyzed using a small-signal stability analysis.

A comparison between rate-equation and Fabry-Perot amplifier models of injection locked laser diodes

The rate-equation and the Fabry-Perot amplifier models for injection locked laser diodes are compared. Both models give identical results at the limiting case of no injected signal. The Fabry-Perot model predicts a wider locking bandwidth and is more useful for large signal applications. The rate-equation model is suitable for investigating the dynamic properties. Numerical results from both models are presented.

IP–Multimedia Subsystem (IMS) performance evaluation and benchmarking

Evaluating the IP Multimedia Subsystem (IMS) Performance is very important due to the critical role it plays in the Next Generation Network (NGN) of the Fixed and Mobile Networks. This paper proposes three robust and scalable methods that can be used to evaluate the performance, the Compliance of the IMS controllers and benchmark their different vendors. These methods are, Performance Test, FUZZING Test and the test using Spectra 2|SE tool. These issues are studied experimentally, using Open SIP Express Router (OpenSER), a high performance open source SIP server and SIPp, the de-facto standard for SIP performance benchmarking. It also provides the test results for Open SIP Express Router (OpenSER).

Improving TCP congestion control for wireless sensor networks

The development of wireless technologies makes it necessary to find a way of improving Transmission Control Protocol (TCP) efficiency with regards to optimal utilization of wireless channel capacity. This paper describes a modification to the TCP congestion control for use in wireless sensor networks. It shows that by slightly modifying the algorithm of the TCP, it can be made to respond better to wireless links, while maintaining its advantages on the wired networks at the same time. This is certainly a very desirable feature as the conventional TCP in most cases contradicts the demands of the wireless links of the network. Our simulation results indicate that the modified TCP gives better performance in terms of higher throughput, delay, retransmission, and energy consumption than conventional TCP protocol.

The gain-bandwidth of hybrid optical transistors

A small-signal analysis for the optical gain of hybrid optical transistors is presented. The adjustment of the operating conditions of the nonlinear optical transmission element is compared for both the Fabry-Perot resonator and the mirrorless electrooptic modulator. The optical gain-bandwidth product is obtained for both first-order and second-order feedback electronic circuits. This product is proportional to the circuit bandwidth. The effect of quadratic electronic nonlinearity on the operation is given. >

Injection-locked passively Q-switched lasers

The time-dependent behavior of an injection locked single-mode passively Q -switched laser may be described by three coupled first-order rate equations relating the laser gain, the absorber loss, and the optical power density. Injection locking results in a substantial increase in the mean output power and the output pulse energy and higher pulsation rate than when freely running. Stability analysis allows the determination of the maximum injected power that allows pulsations.

Energy efficient congestion control operation in WSNs

The development of wireless technologies makes it necessary to find a way of improving Transmission Control Protocol (TCP) efficiency with regards to optimal utilization of wireless channel capacity. This paper describes a modification to the TCP congestion control for use in wireless sensor networks. It shows that by slightly modifying the algorithm of the TCP, it can be made to respond better to wireless links, while maintaining its advantages on the wired networks at the same time. This is certainly a very desirable feature as the conventional TCP in most cases contradicts the demands of the wireless links of the network. Our simulation results indicate that the modified TCP gives better performance in terms of higher throughput, delay, retransmission, and energy consumption than conventional TCP protocol.

Modeling of CFOA based non-inverting amplifier using standard hardware description language

This paper presents a model of current feedback operational amplifier (CFOA) based non-inverting amplifier using standard hardware description language (VHDL). Research work explains how to model analog building blocks based on a language used for describing digital hardware. The advantage of modeling using VHDL is investigated. Simulation results using VHDL is given. PSPICE simulation results confirm the VHDL simulation results are also given.