Due to their unique capabilities for implementing all-optical logic gates, quantum-dot semiconductor optical amplifiers (QD-SOAs) are promising candidates to meet the growing demand for greater speeds to cope with the vast information capacity in modern telecommunication networks.

For the first time, Professor Wei Li and Associate Professor Amer Kotb of CIOMP, along with Professor Kyriakos Zoiros of Democritus University of Thrace in Greece, used the turbo-switched Mach-Zehnder interferometers (TS-MZIs) architecture, which incorporates QD-SOAs and is followed by a serially connected delayed interferometer (DI) in a combined scheme (QDSOAs-TS-MZIs-DI), to realize all-optical NOT-AND (NAND) and exclusive-NOR (XNOR) logic operations that run at 1 Tb/s.

In the QDSOAs-TS-MZI architecture, a pair of identical QD-SOAs are cascaded and separated by optical bandpass filters in each interferometric branch. The serially inserted DI, on the other hand, adds a phase difference to the direct and delayed copies of the incoming switched signal. This in turn enhances further the switching performance and speed of the formed logic gates.

The quality factor (Q-factor) and cross-correlation coefficient (XC) for the QDSOAs-TS-MZIs-DI, the TS-MZIs with QDSOAs but no DI (QDSOAs-TS-MZIs), and the conventional MZIs with QDSOAs (QDSOAs-MZIs) are calculated and compared to evaluate the performance of the two considered logic gates at 1 Tb/s.

The comparison reveals that the QDSOAs-TS-MZIs-DI outperforms the other two alternatives (QDSOAs-TS-MZIs and QDSOAs-MZIs), implying that it should be used as a switching module for ultrahigh-speed Boolean logic functions. The numerically-obtained Q-factor and XC values are, respectively, 16.4 and 96% for NAND gate and are 14.7 and 93% for the NXOR using QDSOAs-TS-MZIs-DI at 1 Tb/s.

This scheme published in Pramana-J. of Physics is expected to play an important role in the design of future integrated logic circuits at high speeds with better performance.