All-Optical Logic Gate Using Cross-Gain Modulation Of Quantum-Dot Semiconductor Optical Amplifier

Quantum-dot semiconductor optical amplifiers (QD-SOA) are regarded as a promising candidate for all-optical wavelength converters and logic gates due to their unique advantages over other optical amplifiers such as low threshold current, ultrafast gain recovery, low noise figure (NF), high differential gain, and high modulation bandwidth. All-optical wavelength converters and logic gates based on QD-SOA have the capability of high-speed information processing, and become key components in the next-generation flexible all-optical networks.In this work, the propagation of the photons in the active region is calculated by dividing the SOA into several sections. For each section, the numerical integration of the 3-level rate equations for the QD-SOA is performed, and the carrier densities are considered constant for each time step. At first, the fundamental characteristics in the active region of QD-SOA such as the carrier distribution and fast gain recovery have been researched. Second, we analyze the chirp characteristics of the wavelength converted signal based on the cross-gain modulation (XGM) in QD-SOA. By introducing the amplified spontaneous emission (ASE) noise equivalent model, we analyze the influence of noise on the wavelength conversion system based on QD-SOA-MZI configuration, and optimize the system parameters to minimize the effects of noise. Besides, in the capability of 160 Gb/s operation of all-optical logic OR gate and XOR gate based on QD-SOA-MZI configuration have been studied, and the performance of logic gates have been analyzed in detail.Numerical results show that, the gain recovery time for the QD-SOA is shorter than that for the Bulk-SOA, and moreover, the recovery process can be accelerated by increasing the injection current density and the electron relaxation time from the WL to the ES. In addition, the chirp of the converted signal can be increased by increasing the injection current, pump signal power, and input signal rate, and can also be increased by decreasing the probe signal power. QD-SOA is suitable for wavelength conversion due to the low linewidth enhancement factor as well as it robust to the optical wavelength. Therefore, we can optimize these parameters to obtain the low chirp. Besides, the ASE noise can deteriorate the performance of the converter. However, the noise transfer in the wavelength conversion can be suppressed for high injection current density and low probe power. Meanwhile, high contrast ratio and low pattern effect of the converted signal can be achieved by optimizing the pump power.The result of all-optical OR logic gate shows that, high performance can be achieved by increasing the injection current and pump signal power, as well as decreasing the electron relaxation time from the WL to the ES, the linewidth enhancement factor and confinement factor. The input signal pulse width can also affect the performance, and there is an optimum value which leads to the highest quality of OR logic gate. To improve the performance of XOR operation, we can increase the injection current or decrease the electron relaxation time from the WL to the ES. input signal power and pulse width. In addition, the performance of XOR logic gate can be improved by additional control pulse. However, the increase of control pulse power would deteriorate the output signal, and then the control pulse power should be chosen properly.