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The influence of nonuniform current injection along the active region, on the linear operation of a quantum-dot semiconductor optical amplifier (QD-SOA) is investigated. For this purpose, we have utilized some functions to generate various nonuniform current injection profiles. These profiles have been considered in our numerical calculations, where the rate equation model is employed to construct different characteristics of the QD-SOA. We have found that the gain, as well as the crosstalk, of a QD-SOA is closely associated to the variance of the carrier density along the cavity. Simulation results show that nonuniform current injection can be used as a technique for gain enhancement as well as crosstalk suppression.

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Abstract-In free space optical (FSO) communication links, atmospheric turbulence has a significant impact on the quality of a laser beam propagating through the atmosphere. Turbulence results in intensity scintillation, which can severely impair the operation of target designation and FSO communications systems. Two important parameters for describing quality of FSO communications systems are the signal-to-noise ratio (SNR) and the bit error rate (BER). In this paper, using a modified model we analyze the effect of atmospheric turbulence on the SNR and BER for an FSO system in both weak and strong turbulence conditions. I.INTRODUCTION FSO systems or optical wireless communication have many advantages when compared with the free space radio frequency based systems such as: high bandwidth, fast deployment, license-free, light weight and reduced size. Unfortunately, free space channel where light propagates is not ideal, thus leading to and suffers from a number of affects including absorption, scattering or displacement depending on the atmospheric condition. However, in clear atmosphere, with a typical attenuation coefficient of 0.43 dB/km, a major challenge facing FSO systems is the effect of turbulence induced irradiance fluctuation on the system performance especially for a link range exceeding 1 km. Atmospheric turbulence is caused by both spatial and temporal random fluctuations of refractive index due to temperature, pressure, and wind variations along the optical propagation path through the channel [1][2][3][4][5][6][7][8]. In this paper we investigate the turbulence effect on performance of an FSO link. We show that BER performance deteriorates with the index of refraction structure parameter (C

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.