Quantum-dot Semiconductor Optical Amplifier Research Articles

40 Gb/s wavelength conversion via four-wave mixing in a quantum-dot semiconductor optical amplifier

The static and dynamic characteristics of degenerate four-wave mixing in a quantum dot semiconductor optical amplifier are investigated. A high chip conversion efficiency of 1.5 dB at 0.3 nm detuning, a low (< 5 dB) asymmetry of up and down conversion and a spectral conversion range of 15 nm with an optical signal-to-noise ratio above 20 dB is observed. The comparison of pumping near the gain peak and at the edge of the gain spectrum reveals the optical signal-to-noise ratio as the crucial parameter for error-free wavelength conversion. Small-signal bandwidths well beyond 40 GHz and 40 Gb/s error-free 5 nm wavelength down conversion with penalties below 1 dB are presented. Due to the optical signal-to-noise ratio limitation, wavelength up conversion is error-free at a pump wavelength of 1311 nm with a penalty of 2.5 dB, whereas an error floor is observed for pumping at 1291 nm. A dual pump configuration is demonstrated, to extend the wavelength conversion range enabling 15.4 nm error-free wavelength up conversion with 3.5 dB penalty caused by the additional saturation of the second pump. This is the first time that 40 Gb/s error-free wavelength conversion via four-wave mixing in quantum-dot semiconductor optical amplifiers is presented.

Quantum dot semiconductor optical amplifiers: optical pumping versus electricalpumping

A comprehensive comparison between the characteristics of conventional electrical pumpingand the new optical pumping (OP) schemes in quantum dot semiconductor opticalamplifiers (QD-SOAs) has been done and has proved that the optical pumping scheme cansignificantly improve the dynamical properties of QD-SOAs. Analytical solutions have beenpresented to justify the optical properties in both pumping methods in CW operationmode. Also, pulse-mode operation has been investigated through numerically solved rateequations. Besides obviating the deficiencies of electrical pumping, optically pumped SOAs(OP-SOAs) can be attractive alternatives for high-speed all-optical signal processing.

Optical buffering up to 160 Gb/s employing a quantum dot semiconductor optical amplifier-based architecture

The authors demonstrate an optical buffer architecture which is implemented using quantum dot semiconductor optical amplifiers (QD-SOAs) in order to achieve wavelength conversion with regenerative capabilities, for all optical packet switched networks. The architecture consists of cascaded programmable delay stages that minimise the number of wavelength converters required to implement the buffer. Physical layer simulations have been performed in order to reveal the potential of this scheme as well as the operating and device parameters of QD-SOA-based wavelength converters. The results obtained have indicated that, up to three time-slot interchanger (TSI) cascaded stages show good performance at 160 Gb/s in the 1550 nm communication window.

Time-Domain Travelling-Wave Model for Quantum Dot Passively Mode-Locked Lasers

We present a time-domain travelling-wave model for the simulation of passive mode-locking in quantum dot (QD) lasers; accurate expressions for the time varying QD optical susceptibility and the QD spontaneous emission noise source are introduced in the 1-D wave equations and numerically described using a set of infinite-impulse response filters. The inhomogeneous broadening of the density of states of the whole QD ensemble as well as the homogeneous linewidth of each QD interband transition are properly taken into account in the model. Population dynamics in the QD, quantum well, and barrier states under both forward and reverse bias conditions are modeled via proper sets of multi-population rate equations coupled with the field propagation equations. The model is first applied to the study of gain and absorption recovery in a QD semiconductor optical amplifier under both forward and reverse bias conditions. Simulations of passive mode-locking in a two-section QD laser are then performed as a function of the bias parameters. Gain and absorption dynamics leading to the generation of mode-locking pulses is described. The onset of a trailing-edge instability at low currents is observed and fully explained in the framework of the described model.

Operation of quantum-dot semiconductor optical amplifiers under nonuniform current injection

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.

An integrated circuit subsystem of quantum dot semiconductor optical amplifier coupled with electro-absorption modulator and its application in wavelength conversion

A multi-section circuit model of quantum dot semiconductor optical amplifier is proposed by employing the standard rate equations. Using this model, gain spectra, saturation property, and occupation probability of quantum dot semiconductor optical amplifier are analyzed by PSPICE simulation. An integrated circuit subsystem of quantum dot semiconductor optical amplifier cascaded with electro-absorption modulator is also derived to investigate the patterning effect reduction in wavelength conversion.

Gain dynamics of an InAs/InGaAsP quantum dot semiconductor optical amplifier operating at 1.5 μm

The gain and phase dynamics of a high quality quantum dot semiconductor optical amplifier were measured at various wavelengths. In the ground state (GS), the amplitude of the slow component was negligible and the fast dominant gain recovery time was 0.7 ps. In the excited state (ES), the slow component was not negligible although small. The time required to recover from 90% to 10% was 2.0 ps in the GS but gradually increased to 31 ps in the ES. This finding predicts no pattern effects in the GS, but finite pattern effects in the ES.

Design of quantum dot semiconductor optical amplifier by intelligence methods

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.

ZnSe / ZnS Quantum-Dot Semiconductor Optical Amplifiers

ZnSe quantum dot (QD) semiconductor optical amplifier (SOA) is studied theoretically using net gain for linear Absorption coefficient and linear emission and these results are used to calculate noise figure and small-signal gain.

Cascading enables ultrafast gain recovery dynamics of quantum dot semiconductor optical amplifiers

In this work the ultrafast gain recovery dynamics of a quantum dot semiconductor optical amplifier is investigated on the basis of semiconductor Bloch equations including microscopically calculated carrier-carrier scattering rates between the two-dimensional carrier reservoir and the confined quantum dot ground and first excited state. By analyzing the different scattering contributions we show that the cascading process makes a major contribution to the ultrafast recovery dynamics.

Cross-Gain Modulation in Quantum-Dot SOA at 1550 nm

We experimentally study the cross-gain modulation (XGM) in an InAs/InGaAsP/InP columnar quantum-dot semiconductor optical amplifier working in the 1550-nm spectral region. We report 12-nm wavelength conversion of 10, 20, 40, 80, and 160 Gb/s return-to-zero (RZ) signals. We find that pure XGM is effective for wavelength conversion without significant pattern effects up to around 40 Gb/s. At higher bit rates, distortion-free conversion can be obtained by exploiting jointly XGM and some cross-phase modulation that arises at the same time in the amplifier. This can be easily achieved by using a slightly blue-shifted output band-pass filter. By testing the signal integrity by means of the factor analysis, we also find that the XGM transfer function attenuates the input intensity noise. Finally, we show how the output inverse-RZ signals obtained in the XGM conversion can be format-converted back to RZ by side-band filtering.

Quantum dot semiconductor optical amplifiers at 1.3 µm for applications in all-optical communication networks

Single- and multi-channel amplifications using a quantum dot (QD) semiconductor optical amplifier (SOA) for data signals up to 80 Gb s−1 are investigated. A reach extension of 30 km for 40 Gb s−1 NRZ OOK data signals resulting in a total transmission distance of 75 km is presented. 80 Gb s−1 RZ OOK single-channel amplification demonstrates pattern-effect-free operation up to 6 dBm input power and 6 dB gain compression. Additional 40 Gb s−1 NRZ OOK interfering channels induce low crosstalk up to −6 dBm channel input powers (OSNR penalty below −3 dB at a BER of 10−9) proving the suitability for multi-channel booster amplification. Wavelength conversion via four-wave mixing is found to be feasible with less than 1 dB received power penalty at a BER of 10−9 for downconversion and is limited only by the achievable OSNR for upconversion. Using cross-gain modulation open eye diagrams are demonstrated for 80 Gb s−1 RZ OOK wavelength conversion. Therefore, QD SOAs demonstrate their suitability for a variety of applications in future all-optical ultra-high-speed networks toward 100 Gb s−1.

Influence of the pump wavelength on the gain and phase recovery of quantum-dot semiconductor optical amplifiers

We numerically investigate the influence of the pump-probe wavelength on the gain and phase recovery dynamics of quantum-dot (QD) semiconductor optical amplifiers (SOAs). The temporal variations of the gain and phase recovery response are calculated at various pump-probe wavelengths, covering the emission wavelength of both the QD ground and excited states. The gain recovery becomes faster at the longer pump-probe wavelength due to the enlarged carrier escape time. The initial phase change turns from a negative to a positive value as the pump-probe wavelength becomes smaller, which is determined by the spectral position of the pump-probe wavelength in reference to the Gaussian-shaped inhomogeneous broadening. The calculated results agree with the previous experimental results measured by other experimental groups.

Effect of Inhomogeneous Broadening on Gain and Phase Recovery of Quantum-Dot Semiconductor Optical Amplifiers

We numerically investigate the effect of inhomogeneous broadening caused by quantum-dot (QD) size fluctuations on the gain and phase recovery of QD semiconductor optical amplifiers (SOAs). We establish 1088 coupled rate equations to simulate the carrier dynamics of the inhomogeneously broadened QD ensembles as inhomogeneous broadening increases. When all the QD ensembles are identical and inhomogeneous broadening becomes zero, eight coupled rate equations are solved for the homogeneous QDs. The gain and phase recovery responses are calculated when an ultrashort pump pulse is injected into a QD SOA. As the inhomogeneous broadening increases, the slow component of the phase recovery at the QD ground state increases due to the enlarged contribution from the slow phase recovery of carrier reservoirs such as the QD excited states. By separately calculating the gain and phase recovery responses of the homogeneous QDs with different sizes, we identify how increasing inhomogeneous broadening affects the enlarged slow phase recovery components from carrier reservoirs. We also demonstrate that the effect of inhomogeneous broadening on the temporal variation of the α-factor is more significant compared to the injection pump power.

Linear and Nonlinear Gain of Sb-Based Quantum-Dot Semiconductor Optical Amplifiers

Linear and Nonlinear Gain of Sb-Based Quantum-Dot Semiconductor Optical Amplifiers

Enhancement of gain recovery rate and cross-gain modulation bandwidth using a two-electrode quantum-dot semiconductor optical amplifier

A two-electrode quantum-dot semiconductor optical amplifier (QD-SOA) is proposed to enhance gain recovery rate and cross-gain modulation (XGM) bandwidth. In the theoretical model, electron and hole dynamics as well as the carrier diffusion are accounted for in the quantum-dot rate equations, which are solved with forward and backward propagation equations of signal and amplified spontaneous emission. The simulation results show that two-electrode QD-SOA can distribute injection current density nonuniformly to maintain carriers in carrier reservoirs of quantum dot sufficient along the entire cavity length of the semiconductor optical amplifier, thus making gain saturation dynamics dominated by spectral hole burning at lower bias current than common QD-SOA. Besides, distributing more current density in the second section of the two-electrode QD-SOA at higher bias can greatly accelerate gain recovery as well as expand the XGM bandwidth.

Vertical stacking of InAs quantum dots for polarization-insensitive semiconductor optical amplifiers

In this paper, we report a control of the polarization property in quantum dot semiconductor optical amplifiers (QD-SOAs) using vertically-stacked, electronically-coupled InAs/GaAs QDs grown by molecular beam epitaxy. By optimizing the number of stacked layers and intermediate GaAs thickness, the 9-stacked QDs demonstrated the polarization-insensitive operation within 1.2 dB in the 1.3-mm optical communication band. Our results demonstrate that the electronically-coupled QDs are useful to realize the polarization-insensitive QD-SOAs.

Circuit modeling of quantum dot semiconductor optical amplifier

A circuit model of a quantum dot semiconductor optical amplifier is proposed by employing standard rate equations. Using this model, the saturation property and dynamic performance of the quantum dot semiconductor optical amplifier are analyzed by PSPICE simulation. We also investigate wavelength conversion based on cross-gain modulation for the quantum dot semiconductor optical amplifier. The corresponding results are in agreement with the previous published works.

Linearity and nonlinearity of quantum-dot semiconductor optical amplifiers

Linearity and nonlinearity of quantum-dot semiconductor optical amplifiers (QD-SOAs) are analyzed in this paper using numerical and analytical solutions. The basic formulas are derived from rate equations of multiple-states QD-SOAs. The solutions reveal that linearity and nonlinearity of QD-SOAs, which is quantificationally characterized by the maximal linear output power and the nonlinear factor, are strongly dependent on injected current, modal gain and spontaneous radiative lifetime. Additionally, the solutions also provide some useful suggestions in designing and using of QD-SOAs, either be used in linear or nonlinear operational region.

Gain Dynamics in Quantum-Dot Semiconductor Optical Amplifiers at 1550 nm

We report an experimental study of the gain recovery of an InAs-InGaAsP-InP columnar-quantum-dot semiconductor optical amplifier around 1550 nm. We find a three-step recovery process that gives around 85% gain recovery in only 10 ps and 100% in around 30 ps in case of a quite complete gain saturation. We also give a possible physical explanation for the peculiar gain dynamics.