Quantum-dot Semiconductor Optical Amplifier Research Articles

Design and analysis of all optical frequency encoded X-OR and X-NOR gate using quantum dot semiconductor optical amplifier-Mach Zehnder Interferometer

All optical frequency encoded logic gates XOR and XNOR are designed and simulated using quantum dot semiconductor optical amplifiers (QDSOA) at 1 Tb/s for the first time as far as our knowledge goes. The logic gates use Mach Zehnder Interferometer (MZI) configuration. Simulation of gain and phase dynamics of QDSOA is presented. The present paper investigates output bit patterns using MATLAB. Amplitude Modulation (AM) is calculated and found to be as low as 0.007 dB for unsaturated gain of 10 dB of the QDSOA. A maximum Quality factor 27 dB is calculated for 5mW control power. The paper also investigates the effect of QDSOA length on quality factor. In this paper, I have modified the definitions of AM and Quality Factor (Qfe) to apply in case of frequency encoded logic.

A terabit-per-second all-optical four-bit digital-to-analog converter using quantum dot semiconductor optical amplifiers

An all-optical digital-to-analog converter (DAC) using quantum dot semiconductor optical amplifiers (QDSOAs) is proposed and analyzed. The device operates at low optical power (~ 0.5 mW) at a speed of 1 Tbps. The resolution of the DAC is four bits, and the corresponding step size is 1.068 mW (compared with the ideal value of 1 mW). The dynamic range is found to be 11.47 dB (versus the ideal value of 11.76 dB). The average absolute error for all the states of the proposed optical DAC is 0.53%, with a maximum error of 1.85%, being the first time that such performance has been achieved to the best of the authors’ knowledge. It is shown that the amplified spontaneous emission (ASE) noise has no significant effect on the performance of the DAC.

Optimization of four-wave mixing wavelength conversion in a quantum-dot semiconductor optical amplifier based on the genetic algorithm

A novel approach based on the artificial neural network (ANN) and the genetic algorithm (GA) is presented for optimization of four-wave mixing (FWM) wavelength conversion in a quantum dot semiconductor optical amplifier (QD-SOA). First of all, we propose a simple, accurate, and fast model based on the feedforward ANN for the characteristics of FWM in a QD-SOA. To train the ANN, we collect the required data from a numerical model. In this model, the efficiency of FWM is obtained numerically taken into account the effect of pump/probe and the occupation probability of energy levels by using the slice technique. Then, the optimal design of QD-SOA as the FWM wavelength converter is performed using the GA.

Reconfigurable All-Optical Logic Gates (AND, NOR, NOT, OR) With Quantum-Dot Semiconductor Optical Amplifier and Optical Filter

All-optical logic gates are indispensable modules for executing exclusively by means of light fundamental Boolean operations. Despite intense research in this field, most efforts have not treated these gates in a joint design and operating manner. This causes waste of hardware resources and lack of versatility. In this paper, we theoretically investigate, assess and demonstrate the feasibility of implementing all-optically multiple logic gates (AND, NOR, OR, NOT) at 160 Gb/s by means of a single quantum-dot semiconductor optical amplifier (QD-SOA) and a concatenated optical filter. We follow a methodical approach and conduct a thorough numerical study to derive rules for the selection of the critical operating parameters so that appropriate performance criteria defined for each gate are made acceptable. The intersection of the permissible bounds allows us to specify a combination of parameters’ values which is the same for all gates and guarantees the execution of the corresponding Boolean functions with logically correct and high quality outcome. The proposed scheme can be reconfigured to realize the different gates at 160 Gb/s without changes in its basic setup or driving conditions. This is achieved simply by detuning the optical filter according to the design guidelines of each gate.

Comparison between GaN and InN quantum‐dot semiconductor optical amplifiers

AbstractGaN/Al0.5Ga0.5N and InN/Al0.5Ga0.5N as a III‐nitride quantum dot semiconductor optical amplifiers (QD‐SOAs) are studied in detail in this paper. The optical gain, spontaneous emission rate, and lineshape function are calculated using non‐Markovian relaxation compared with Markovian one. Gain is then connected with the rate equations model to obtain a dB gain, output power, and shot noise in these SOAs. GaN peaked at 351 nm which is preferred in optical coherence tomography applications. InN is peaked at 1028 nm which can be used in gas detection and environmental pollution monitoring. Both structures studied have high gain and low noise and nearly equivalent TE and TM gain which makes them adequate for the use in both these two modes. These calculations show the importance of InN and GaN QD nanostructure in the applications.

Theoretical Demonstration of 250 Gb/s Ultrafast All-Optical Memory Using Mach-Zehnder Interferometers With Quantum-Dot Semiconductor Optical Amplifiers

Ultrafast all-optical memory at 250 Gb/s using Mach-Zehnder interferometers (MZIs) with symmetrical quantum-dot semiconductor optical amplifiers (QDSOAs), acting as all-optical AND gate and regenerator in a loop configuration, is theoretically demonstrated for 500 loop circulations using a return-to-zero modulated format. The memory operation is examined and evaluated by the quality factor ( QF ), which is a more sensitive method of measuring memory quality. The obtained numerical results show that the proposed memory can be operated up to 250 Gb/s for 500 circulations with high QF .

Optimized design of QD-LD toward QD-SOA to achieve 35-dB maximum chip gain with 400-mA injected current

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.

Quantum dot semiconductor optical amplifier: investigation of ultra-fast cross gain modulation in the presence of a second excited state

In this paper, a theoretical model is proposed to investigate and analyze an ultra-fast cross gain modulation (XGM) in quantum dot semiconductor optical amplifiers (QDSOAs). The proposed model is based on a set of carrier’s rate equations, propagation equations for pump and probe signals and phase equations. To investigate the XGM mechanism, nonreturn-to-zero (NRZ) pulse trains with various bitrates are supposed to propagate as the input pump signals through the QDSOA’s active layer. The probe signal is assumed to be a continuous wave (CW) signal. Furthermore, optical gain of quantum dots (QDs) is calculated using a density matrix approach. For the first time, to the best of our knowledge, a second excited state is considered in the band diagram of QDs, to obtain the ultra-fast XGM in QDSOAs. Therefore, in the presented model, the rate equations are written for the carriers in the ground state, first and second excited states (ES2), continuum state and the wetting layer. In the presence of ES2, gain recovery time and gain saturation is reduced and, therefore, ultra-high bitrate pulse trains can be modulated with negligible pattern effects and wave distortion. The effect of the injection current density increment and carrier’s relaxation lifetime decrement are illustrated to show the improvement in the XGM mechanism in the QDSOA. It is shown theoretically that ultra-high bitrate XGM up to 450 Gbps is possible due to the reduced gain recovery time in the presence of ES2. It is demonstrated that at the same pump power for higher injection current densities and lower carrier relaxation lifetimes, the pattern effect and wave distortion has almost vanished. Although, in this case, the extinction ratio (ER) is decreased. It is shown that to recover the ER, the input pump power should be increased. Furthermore, based on the results in the presence of ES2, the ER is decreased by 0.5 dB.

Multi-electrode quantum-dot semiconductor optical amplifier as an intensity modulator of signals in optical communication systems

In this paper, we are going to exhibit the system performance using the single, double and three-electrode quantum-dot semiconductor optical amplifier as an intensity modulator (3E-QD-SOA-IM) of the adaptively modulated optical orthogonal frequency division multiplexing (AMOOFDM) signals in the intensity-modulation direct-detection passive optical network (IMDD-PON) systems. Moreover, to compare the bit-rate versus transmission distance of the proposed fiber link model when using both configurations multi-electrode semiconductor optical amplifier intensity-modulator (ME-SOA-IM) and multi-electrode quantum-dot semiconductor optical amplifier intensity-modulator (ME-QD-SOA-IM), to study the improvement of the transmission capacity, distance reach and power efficiency when applying the proposed configurations for optical access networks for distances ranging from 20 km up to 120 km. The three-electrode configuration solved the nonlinearity of the two-electrode configuration and offered a considerably wider range of optimum operating conditions to achieve up to 35 Gbps. Furthermore, the 3E-QD-SOA-IM showed a better performance over the 3E-SOA-IM over all the 120 km, and a 5 Gbps enhancement in the bitrate with a 20 dB less optical input power at 20 km.

All-optical OR and NOR gates using quantum-dot semiconductor optical amplifiers-assisted turbo-switched Mach-Zehnder interferometer and serially delayed interferometer at 1 Tb/s

The turbo-switch (TS) has proven to enhance the speed of the conventional semiconductor optical amplifier (SOA) up to four times better than the single SOA architecture. A novel performance of all-optical (AO) OR and NOT-OR (NOR) logic gates using TS Mach-Zehnder interferometer (TSMZI) combined with the ultrafast quantum-dot (QD) SOAs and followed by a serially delayed interferometer (DI) is numerically analyzed and investigated at 1 Tb/s. For comparison, the results have been obtained for AO OR and NOR Boolean functions using a DI after QDSOAs-based TSMZI, QDSOAs-based TSMZI, and QDSOAs-based conventional MZI. The achieved results indicate that placing a DI in series with the QDSOAs-TSMZI renders acceptable of OA OR and NOR operations at 1 Tb/s than QDSOAs-TSMZI and QDSOAs-MZI, where this achievement is not possible.

Dynamics of pulse amplification in tapered-waveguide quantum-dot semiconductor optical amplifiers

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.

Effect of time relaxations on the carrier heating of InAs/GaAs quantum dot semiconductor optical amplifier

AbstractCarrier temperature in InAs quantum dot (QD) optical amplifiers has been formalized theoretically by using the double‐excited states system. High current injection gives high carrier temperature and a punch in the curve appears at low current due to the ground state carrier contribution. Increasing carrier‐heating time increased carrier temperature. It is shown the slow relaxation for both the wetting layer to QD and the interdot relaxations are given high carrier temperature. Pulses with wide full width at half‐maximum give high carrier temperature since its recovery time is increased. Free carrier absorption gives a main contribution to the heat in the QD structure.

Optimization of a quantum-dot semiconductor optical amplifier (QD-SOA) design using the genetic algorithm

In this paper, we proposed an intelligence model for the optimal design of the quantum-dot semiconductor optical amplifier (QD-SOA). The intelligence model is designed using the artificial neural network (ANN) and genetic algorithm (GA). We first present a simple, accurate, and fast model based on the feedforward ANN. The required data for training the ANN are collected from the numerical solution. The rate equations based on the occupation probability of energy levels and wave propagation equations in the active region of the QD-SOA are solved numerically to calculate optical gain using the slice technique. Then, by using the obtained ANN model and the GA, a new method to design the optimal structure parameters of the QD-SOA is proposed.

All-optical NOR and XNOR logic gates at 2 Tb/s based on two-photon absorption in quantum-dot semiconductor optical amplifiers

Two-photon absorption (TPA) is a nonlinear absorption process in semiconductors, creating a fast phase change in a low-intensity probe beam. Placing quantum-dots (QDs), on the other hand, in the active region of semiconductor optical amplifiers (SOAs) results in SOAs shorter carrier recovery time and lower gain saturation. Thus, in this article, the physical advantages of both TPA and QDs have been combined to numerically investigate the performance of all-optical NOT-OR (NOR) and exclusive-NOR (XNOR) logic gates, incorporating in Mach–Zehnder interferometers at a data rate of 2 Tb/s. The output quality factor (QF) of the considered Boolean functions against the key operational parameters is assessed and examined, including the impact of amplified spontaneous emission in order to obtain more realistic results. The overall QF in the presence of TPA is always higher than that without TPA.

Research of all-optical NAND gates based on quantum dot semiconductor optical amplifiers cascaded connection XGM and XPM

A novel structure to implement an all-optical NAND gate which utilizes cascaded connection XGM and XPM based on quantum dot semiconductor optical amplifier (QD-SOA) is presented. The QD-SOA carrier and optical field equation are analyzed by establishing static and dynamic models. The performance of all-optical NAND gate has been optimized. The proposed structure can operate error-free at 640 Gb/s as an all-optical NAND gate. At the same time, high extinction ratio(ER) and conversion efficiency can be obtained. The research results have guiding significance for the application of QD-SOA in the design of all-optical NAND gate.

Wideband Steady-State and Pulse Propagation Modeling of a Reflective Quantum-Dot Semiconductor Optical Amplifier

A new time-domain wideband numerical model for simulation of quantum dot-reflective semiconductor optical amplifier (QD-RSOA) steady-state and dynamic behavior, is described. The model is used to investigate 1 ps full-width at half-maximum input Gaussian pulse amplification and also modulation cancellation. A large modulation-cancellation dynamic range of about 35 dB, is predicted for high input powers, which is not attainable in bulk and QW RSOAs. The model can be applied to traveling-wave and reflective QD-SOAs. The combination of the unique features of quantum dots and a reflective structure can be used to realize a colorless modulator for wavelength-division multiplexed passive optical networks (WDM PONs).

Ultra-broadband Optical Gain Engineering in Solution-processed QD-SOA Based on Superimposed Quantum Structure

In this work, the optical gain engineering of an ultra-broadband InGaAs/AlAs solution-processed quantum dot (QD) semiconductor optical amplifier using superimposed quantum structure is investigated. The basic unit in the proposed structure (QDs) is designed and fabricated using solution-processed methods with considerable cost-effectiveness, fabrication ease, and QDs size tunability up to various limits (0.1 nm up to the desired values), considering suitable synthesis methods. Increasing the number of QDs, the device can span more than 1.02 μm (O, C, S, and L bands) using only one type of material for all QDs, and is not restricted to this limit in case of using more QD groups. Also, it can manipulate the optical gain peak value, spectral coverage, and resonant energy for customized optical windows, among which 1.31 μm and 1.55 μm are simulated as widely-applicable cases for model validation. This makes the device a prominent candidate for ultra-wide-bandwidth and also customized-gain applications in general. Variation impact of homogeneous and inhomogeneous broadenings, injection current and number of QD groups on optical gain are explained in detail. Besides proposing a design procedure for implementation of an ultra-broadband optical gain using superimposed QDs in solution-processed technology, the proposed gain engineering idea using this technology provides practically infinite bandwidth and an easy way to realize. By introducing this idea, one more step is actually taken to approach the effectiveness of solution process technology.

Simultaneous all-optical multi logic operation using 3 × 3 interconnecting switch

• 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.

1 Tb/s all-optical XOR and AND gates using quantum-dot semiconductor optical amplifier-based turbo-switched Mach–Zehnder interferometer

The turbo-switch (TS) architecture conceived for speeding up the response of conventional semiconductor optical amplifiers (SOAs) is combined for the first time with the exceptional ultrafast capability of quantum-dot (QD) SOAs. The possibility of exploiting this combination in the Mach–Zehnder interferometer (MZI) for implementing fundamental all-optical (AO) XOR and AND logic gates run at 1 Tb/s is numerically investigated, assessed, and verified. The simulation results demonstrate the superiority of the QDSOA-based TS-MZI scheme over its QDSOA-based MZI counterpart, as quantified by the improved quality factor, which can be achieved under more favorable operating conditions. The outcomes of the conducted theoretical treatment can help execute AO signal processing tasks with enhanced performance while keeping pace with the perpetual increase of single-channel data rates in an efficient and affordable manner.

Two-photon absorption in quantum dot semiconductor optical amplifiers-based all-optical XOR gate at 2 Tb/s

The nonlinear effect of two-photon absorption (TPA) on the performance of all-optical XOR gate using quantum dot semiconductor optical amplifiers (QDSOAs)-assisted Mach–Zehnder interferometer is numerically analyzed and investigated at a data rate of 2 Tb/s. The dependence of the quality factor (QF) on the critical parameters of the input signal and QDSOA is examined and assessed. The obtained QFs for the all-optical XOR gate using QDSOAs-MZI at 2 Tb/s with TPA and without TPA are 14 and 8, respectively.