Design of ultrafast all-optical pulsed-mode 2 \(\times \) 2 crossbar switch using quantum-dot semiconductor optical amplifier-based Mach–Zehnder interferometer

An all-optical 2 \(\times \) 2 crossbar switch capable of pulsed-mode operation and of handling ultrafast information is proposed and analytically designed. For this purpose, the quantum-dot semiconductor optical amplifier (QD-SOA)-based Mach–Zehnder interferometer (MZI) is employed as two-input two-output switching unit, in which the direction where the input data are forwarded is controlled by a single, purely lightwave excitation of alternating binary content. The performance of the crossbar switch under bitwise pulsed-mode of operation is thoroughly investigated and assessed by means of numerical simulation to find the range of permissible values of critical operating parameters. These parameters are distinguished depending on whether they affect the saturation level of the QD-SOA that is influenced by the optical control signal or translate the associated gain changes into differential phase shift between the MZI arms. This approach highlights the prominent role of the QD-SOA linewidth enhancement factor, which must be chosen to be sufficiently high so that the required switching procedure takes place properly. With this necessary condition, which holds in real QD-SOA devices, it can be determined how the rest parameters must be selected and combined so that the defined performance metrics become acceptable. Finally, an efficient technique for balancing the local extinction ratios in the switched and in the non-switched states of the crossbar configuration is applied in order to optimize its performance and favor its practical use. The guidelines derived for the design of the scheme are technologically satisfiable and can be useful for its implementation and exploitation in diverse switching applications.