Hussein Taleb

Phase Recovery Acceleration in Quantum-Dot Semiconductor Optical Amplifiers

In this paper, the acceleration of phase recovery in quantum-dot semiconductor optical amplifiers (QD-SOAs) is investigated by employing optical pumping (OP) scheme. For this purpose, the state space theory has been used to derive a dynamic model for the QD-SOA. The derived nonlinear state space model is employed to simulate the gain and phase responses of the device. For the first time, we show that OP can realize a shorter phase recovery time in comparison with electrical pumping (EP) scheme under equal pumping powers. We found that under OP, the contribution of slow phase recovery component induced by the slow carrier dynamics of the carrier reservoir is drastically reduced, and consequently, a fast phase response becomes feasible. Also, we found that under EP, the gain is recovered within a shorter time compared to OP scheme.

Design of a low-power all-optical NOR gate using photonic crystal quantum-dot semiconductor optical amplifiers

Design and simulation of a novel all-optical logic gate (AOLG) based on photonic crystal quantum-dot semiconductor optical amplifiers (PC-QDSOAs) is reported for the first time. For this purpose, a flat-band slow-light QD-based active photonic crystal waveguide (APCW) is designed and employed for implementation of an all-optical NOR gate in a symmetric Mach-Zehnder interferometer configuration. Then, the performance of the NOR gate is investigated using a comprehensive nonlinear state space model (NSSM). Simulation results demonstrate that PC-QDSOAs present an interesting platform for realizing ultracompact AOLGs with low power consumption.

Ultrafast All-Optical Signal Processing Using Optically Pumped QDSOA-Based Mach–Zehnder Interferometers

In this paper, we investigate the performance of all-optical logic circuits using quantum-dot semiconductor optical amplifier Mach-Zehnder interferometer (QDSOA-MZI) structures. For the first time, temporal changes in the linewidth enhancement factor (LEF) is analyzed under both optical and electrical pumping schemes using the nonlinear state space model (NSSM) for QDSOAs. We found that significant reduction in the LEF recovery time along with significant increasing in the LEF value of QDSOAs are two important factors that enhance the performance of optically pumped QDSOA-MZI-based all-optical logic gates. Simulation results show that optically pumped QDSOA-MZI structures can be used for implementation of all-optical logic circuits that can operate at bit rates higher than 160 Gb/s, which can never be reached using conventional electrical pumping schemes due to the long-phase recovery time in an electrically pumped QDSOAs. Furthermore, we study the effect of homogeneous broadening on the performance of all-optical logic gates. Moreover, dynamic response of a four-input all-optical XOR gate as a simple all-optical logic circuit is investigated and effect of cascading of optical gates on the performance of all-optical logic circuits is studied.

Modeling and Design of Photonic Crystal Quantum-Dot Semiconductor Optical Amplifiers

A novel design of electrically pumped photonic crystal quantum-dot semiconductor optical amplifiers (PC-QDSOAs) is presented in this paper. Therefore, we design a single-mode flat-band slow light photonic crystal waveguide (SL-PCW) for an InAs/GaAs QDSOA in which the pumping is done by passing a current through a laterally doped p+-p-n+ structure. In addition, for the first time to our knowledge, we propose a nonlinear state space model (NSSM) for PC-QDSOAs, in which the effects of the SL-PCW dispersion relation as well as the effects of the homogeneous and inhomogeneous broadenings of QDs are considered. To do so, the SL effects on the gain enhancement factor and increase of the optical losses are evaluated by considering the wavelength dependence of the modal confinement factor, the group index dispersion, and the SL-enhanced absorption and scattering losses in the SL-PCWs with QD active region. The gain saturation characteristics and modal gain spectra of the PC-QDSOA are investigated under different conditions including pump current and the amplifier length. Simulation results show that the SL-PCWs can be used to reduce the transparency current of the amplifier by a factor of 20 and even more compared with the conventional QDSOAs based on ridge waveguide structures, and enhance the net modal gain of the QD active region by a factor of two to six over a broad wavelength range of about 62 nm. We found that the power consumption of PC-QDSOAs can be decreased by a factor of about 100, and also the amplifier length can be reduced by a factor of five and beyond, compared with the conventional QDSOAs. The results of this paper are useful for many applications where low power consumption and small size of the optical amplifiers are important.

Optical Gain, Phase, and Refractive Index Dynamics in Photonic Crystal Quantum-Dot Semiconductor Optical Amplifiers

In this paper, the gain, phase, and refractive index dynamics of photonic crystal quantum-dot semiconductor optical amplifiers (PC-QDSOAs) are investigated for the first time. For this purpose, we establish a comprehensive nonlinear state space model with 1088 state variables to simulate the carrier dynamics of the inhomogeneously broadened InAs/GaAs QD active region embedded in a flat-band slow-light photonic crystal waveguide. The gain and phase recovery responses are monitored during the amplification of an ultrashort pump pulse. Simulation results show that changes in refractive index in the PC-QDSOA active region are much stronger than the index changes in the conventional QDSOAs. In addition, the gain and phase recovery time in PC-QDSOAs are similar to those in the conventional QDSOAs based on ridge waveguide structures. Also, we found that the injected current and the consumed power in PC-QDSOAs can be two orders of magnitude less than those values in the conventional QDSOAs.

Quantum-Dot Semiconductor Optical Amplifiers: State Space Model versus Rate Equation Model

A simple and accurate dynamic model for QD-SOAs is proposed. The proposed model is based on the state space theory, where by eliminating the distance dependence of the rate equation model of the QD-SOA; we derive a state space model for the device. A comparison is made between the rate equation model and the state space model under both steady state and transient regimes. Simulation results demonstrate that the derived state space model not only is much simpler and faster than the rate equation model, but also it is as accurate as the rate equation model.