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Highlights • Nonlinear effect of TPA on all-optical gates are realized using QDSOA at 2 Tb/s. • Impact of critical performance parameters on QF is numerically analyzed. • All-optical operations are executed with the employed scheme with twice as high QF than without TPA. Abstract The performance of all-optical AND, OR, and NAND gates based on quantum dot semiconductor optical amplifiers (QDSOAs), which are either incorporated in properly configured Mach-Zehnder interferometer or combined with a delayed interferometer, is theoretically investigated at a data rate of 2 Tb/s when the nonlinear effect of two-photon absorption (TPA) is exploited in these active devices. The impact of the input signal and QDSOA key parameters on the quality factor (QF) is assessed. The obtained results indicate that these Boolean functions can be executed at 2 Tb/s with almost as twice as high QF than without TPA. [ABSTRACT FROM AUTHOR]

A detailed numerical investigation of polarization-independent quantum dot InAs/GaAs semiconductor optical amplifier (PIQS) based on a technique called mode propagation tuning (MPT) without the need for the polarization controller (PC) is reported, which can solve the limitation caused by polarization sensitivity in a semiconductor optical amplifier (SOA). Our calculations show that by a suitable tuning of the thickness of the active layer, only the TE 0 and TM 0 modes can propagate. Moreover, the gain saturation behavior of this SOA was measured at 1.55 μ m and found to be polarization-independent (PI). At active layer thickness of 1.7 μ m, the confinement factor was 0.75 and 0.7 for TE 0 and TM 0 modes, respectively, which leads to a gain difference up to 0.1 dB. The rate equations of the QD-SOA were also solved and a fiber to fiber gain of 22 dB was obtained. Additionally, a numerical simulation is presented which shows that the residual gain ripple and polarization sensitivity are sufficiently reduced when residual facet reflectivities of the SOA are in the range below 10 - 4 . In addition, the full-width at half-maximum of the horizontal and vertical far-field patterns (FFPs) are measured as 30° × 30°. The proposed structure can be used for logical applications. [ABSTRACT FROM AUTHOR]

Abstract: The outstanding features of Quantum Dot Semiconductor Optical Amplifiers (QD-SOA’s) such as all-optical signal processing and signal regeneration are caused them are widely used in the optical communication systems. Due to the nano structure of these amplifiers, accurate design and modelling of them is a complex and challenging problem. This paper addresses design a QD-SOA. We present a novel method based on genetic algorithm to design QD-SOA. Since it is essential to having a model for designing, a numerical model is obtained in the first step. Then, an artificial neural network model is made using training data sampled from numerical model. The experiments show the proposed neural model has high accuracy as well as low computation time. In the next step, we convert the design problem to a genetic algorithm problem. Using neural model, the suitable fitness function is defined. The user can optimize the cost of production by setting the weight for the design parameters. The proposed system finds the best solution that satisfies desired gain regarding the production cost. [Copyright &y& Elsevier]

Abstract: This paper presents the parameter design and performance analysis of a 160Gb/s all-optical XOR gate based on cross-gain modulation (XGM) in a nonlinear Mach–Zehnder interferometer (MZI) with quantum dot semiconductor optical amplifiers (QD-SOAs). Detailed numerical simulations of the QD-SOA parameters and optical signal parameters are performed to elevate the gate performance. With the optimized parameters, a Q factor over 8dB is obtained. The possibility of operating at higher speed of the XOR gate is demonstrated as well. The results will be helpful for the design and performance analysis of practical quantum dot devices. [Copyright &y& Elsevier]

We measured the characteristics of Quantum Dot Semiconductor Optical Amplifiers (QD-SOA) with 25 stacked layers of InAs/InGaAlAs QDs grown on InP(311)B substrate. The temperature dependence of threshold current and lasing peak wavelength in C-band of QD-Laser Diode (QD-LD) were analyzed over its operating range of 15–80 °C. The chip gains of 3 device lengths (1.5, 2 and 2.4 mm) were compared under varied injected currents up to 500 mA. To avoid overheat and chip damage during measurements, the pulse current source with 1% and 10% duty cycles was used. Based on our best results of 2-mm long QD-SOA with 25 stacked QD layers, the 1% pulse is preferable because of its lower heating and additional chip gain of 11.9 dB. Hence, the highest chip gain of 35 dB was achieved at 400-mA injected current, as well as the highest 3-dB saturation output power at 20.9 dBm. According to the plot of chip gain versus wavelength, it shows 3-dB gain spectrum over 20 nm and the highest peak at 1570-nm wavelength with 500-mA injected current. In addition, the results of another QD-SOA module showed 15.4-dB Input Power Dynamic Range (IPDR), faster response time due to less pattern effect and error-free transmission of 40 Gb/s data over 20-km Single Mode Fiber (SMF) link. • Strain compensation technique is critical in the fabrication of highly stacked QD. • QD-SOA's structure is optimized for a very high chip gain: 35 dB at 400-mA current. • QD-SOA module is evaluated for IPDR, pattern effect, and 40 Gb/s data over 20-km SMF. [ABSTRACT FROM AUTHOR]

Tapered-waveguide quantum dot semiconductor optical amplifiers (TW-QDSOAs) have been modeled using numerical calculation of the rate and propagation equations in this article and the amplification characteristics and dynamics of pulse propagation in non-tapered QDSOA, linear, and exponential TW-QDSOA structures have been studied and compared in detail. It has been found that TW-QDSOAs apply less distortion to the amplified pulse and have greater optical gain than non-tapered QDSOA. In TW-QDSOAs, the amplified pulse becomes much less broadening and this amount is negligible, therefore the pulse bit rate can be increased. While the amplified pulse in a non-tapered QDSOA is much broadening than the TW-QDSOAs. The carrier density distribution and dependency of the amplifier gain to the output energy for both non-tapered and tapered structures have been studied. The carrier density and gain in non-tapered QDSOA decreases more than TW-QDSOAs, indicating that the tapered amplifiers are saturated at higher input energies. Our obtained results agree well with those previously obtained for conventional tapered amplifiers. [ABSTRACT FROM AUTHOR]