Ultrafast All-Optical Signal Processing Using Optically Pumped QDSOA-Based Mach–Zehnder Interferometers

In this paper, we investigate the performance of all-optical logic circuits using quantum-dot semiconductor optical amplifier Mach-Zehnder interferometer (QDSOA-MZI) structures. For the first time, temporal changes in the linewidth enhancement factor (LEF) is analyzed under both optical and electrical pumping schemes using the nonlinear state space model (NSSM) for QDSOAs. We found that significant reduction in the LEF recovery time along with significant increasing in the LEF value of QDSOAs are two important factors that enhance the performance of optically pumped QDSOA-MZI-based all-optical logic gates. Simulation results show that optically pumped QDSOA-MZI structures can be used for implementation of all-optical logic circuits that can operate at bit rates higher than 160 Gb/s, which can never be reached using conventional electrical pumping schemes due to the long-phase recovery time in an electrically pumped QDSOAs. Furthermore, we study the effect of homogeneous broadening on the performance of all-optical logic gates. Moreover, dynamic response of a four-input all-optical XOR gate as a simple all-optical logic circuit is investigated and effect of cascading of optical gates on the performance of all-optical logic circuits is studied.