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

Abstract

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.

Introductory Chapter: The Fame of Quantum Dots in Space-age Improvements for Multifunctional Application

“…• Trap engineering in PbSe quantum dots for photodetectors [19] • Wave function engineering-Type-I/II Excitons [20] • Large-scale production of quantum dots for energy storage applications [21] • Efficient calibration of crosstalk in a quadruple quantum dot array [22] Photonic devices • Quantum dot-Si photonic integrated circuits [23] • High-quality quantum dot laser/waveguide [24] • QDs and nano-photonic waveguides [25] Optoelectronics • Semiconductor quantum dot for photovoltaic applications [26] • Quantum dot optoelectronics [27] • Quantum dot semiconductor optical amplifiers (QD-SOA) [28] • Flexible quantum dot light-emitting diodes [29] Electronics • Single-electron transistors with quantum dots [30] • High-Performance quantum dot thin-Film transistors [31] • Integrated circuits (VLSI, hybrid integrated) [32] • Single quantum emitter detection with amateur CCD [33] Electricity (without semiconductors)…”