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This investigation reports all optical parity generators and checkers based on quantum dot semiconductor optical amplifiers at 200 Gb/s. The proposed circuit has been realized by using SOA-MZI configuration with a quantum dot as an active region in SOA. A parity generator consists of three inputs and utilizes 2 XOR logic while a parity checker employs 3 XOR logic with 4 inputs. Cross-phase modulation in SOA has been exploited in the design of XOR logic. MZI configuration converts phase modulation to amplitude modulation to achieve desired boolean equation of XOR. A wide and clear eye diagram has been obtained for the parity generator and checker outputs. The quality factor for the parity generator and checker outputs obtained are 17.2 and 15.1 respectively also the extinction ratio for both outputs are more than 15 dB. [ABSTRACT FROM AUTHOR]

The performance of NOR functions implemented all-optically (AO) using quantum dot semiconductor optical amplifier (QD-SOA) and quantum dot reflective semiconductor optical amplifier (QD-RSOA) based on cross gain modulation effect is simulated and investigated. The dependence of the output extinction ratio and conversion efficiency on key parameters is analyzed and assessed. The obtained results show that the NOR AO Boolean functions can simultaneously be realized with the employed scheme with logical correctness, high output extinction ratio and conversion efficiency. [ABSTRACT FROM AUTHOR]

• A 3 × 3 all-optical interconnecting switch has been designed. • Three quantum dot semiconductor optical amplifier assisted Mach-Zehnder interferometers have been used. • This circuit performs logical operations also. • We use routing mechanism to perform these logical operations. • Numerical simulations have been done to measure the performance of this proposed design. A 3 × 3 all-optical interconnecting switch using three quantum dot semiconductor optical amplifier assisted Mach-Zehnder interferometers (QDSOA-MZI) has been designed. It can transmit input data to any output port without blocking other input data. Adjusting inputs and routing algorithm, the data can be achieved at any output ports. Using this mechanism, simultaneous all-optical multi-logic operation has been carried out. Numerical simulation has been done to calculate the performance of this proposed design. [ABSTRACT FROM AUTHOR]

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 wavelength-division multiplexing/time-division multiplexing (WDM/TDM) network exploiting the broad wavelength range of T-band (1000–1260 nm) is proposed. The network is based on different wavebands of downlink and uplink channels, with each transmitter consisting of a wavelength tunable laser utilized for more than one user through wavelength tuning. The downlink section of the network also introduces interconnecting optical lines and semiconductor optical amplifiers (SOAs), pairing up each of the downlink wavebands to provide structural redundancy by allowing transmitters to be shared between the paired wavebands through TDM. Quantum dot (QD)-based wavelength tunable lasers and SOAs were fabricated for a preliminary demonstration experiment. Error-free transmission with less than 1 dB of power penalty was obtained for a wavelength range of 24.2 nm (5.6 THz). The QD-SOAs exhibited a decent rise and fall time, as well as extinction ratios throughout the wavelength range, which enable it to be used as path switches.

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]

All-optical logic and arithmetic operations are expected to play an important role in high-speed communication systems. In this paper, we have presented a model to perform two basic arithmetic operations (addition/subtraction) on two binary digits based on a quantum dot semiconductor optical amplifier (QD-SOA)-assisted Mach-Zehnder interferometer. Using two QD-SOA-based switches, we have designed a half adder/subtractor circuit. The main advantage of this circuit is that simultaneous addition and subtraction operations are realized at the outputs. This circuit is designed theoretically and verified through numerical simulations. The theoretical study is carried out by taking into account the effect of amplified spontaneous emission. The dependence of the peak data power and that of the QD-SOA current density and length on the ER and Q factor of the switching outcome are explored and assessed by means of numerical simulations. The desirable device parameters has been examined in order to obtain the optimum best performance. [ABSTRACT FROM AUTHOR]

ABSTRACT We theoretically analyze the performance and gain properties of the quantum dot semiconductor optical amplifier's (QD-SOA) performance using a three-state mode and a universal two-level model. Although the first model describes the semiconductor optical amplifier's (SOA's) behavior with the photon numbers and the other in optical powers, these two are found to have a same format and the second one can also well describe the QD-SOA's behavior. Then, the QD-SOA's energy efficiency's dependence on its active region length is deduced with the two-level model; theoretical results indicate that the SOA's maximal energy efficiency climbs with input optical power while the energy-efficient active region length decreases linearly with increase of the power in dBm. Experimental results show that the efficiency optimized input power is proportional with the SOA's work current and saturation power just as predicted. These theory and experimental results may be guidelines for the energy-efficient SOA designing and applications. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:896-901, 2015 [ABSTRACT FROM AUTHOR]

An all-optical delay flip flop is designed and described using two quantum dot semiconductor assisted Mach-Zehnder interferometers in this study. The flip flop has one enable input that allows for both positive and negative edge triggered operation without changing the design of the circuit. It is reconfigurable by design. Numerical simulations have been conducted to assess the performance of the circuit. [ABSTRACT FROM PUBLISHER]

An all-optical multibit correlator using the multistage cascaded quantum dots semiconductor optical amplifiers Mach-Zehnder interferometer (QD-SOA MZI) is presented with the example of an 8-bits correlator. The simulations demonstrate the correlator pulse with ultrahigh quality at the bit rate of 500 Gbps. For the ultrahigh bit-rate applications, the ultrafast dynamics of the QD-SOA are investigated with the pulse/spectra distortion, gain dynamics, phase dynamics, and the frequency chirp of the optical pulse. All-optical logical gates XOR and AND based on the QD-SOA MZI are simulated with the consideration of many nonlinear dynamics, such as the carrier injection, carrier depletion, carrier density fluctuation, carrier heating, and the spectra hole-burning in the rate equations scheme. [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 present a novel scheme for high-speed multiwavelength clock recovery using a low finesse Fabry-Perot filter and a quantum-dot semiconductor optical amplifier. Performance evaluation based on extensive numerical analysis reveals that the proposed configuration can acquire clock from 40- and 160-Gb/s input data packet streams at four wavelengths with very short rise- and fall-times. [ABSTRACT FROM PUBLISHER]

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]