Design of ultrafast all-optical 4-bit parity generator and checker using quantum-dot semiconductor optical amplifier-based Mach-Zehnder interferometer

The feasibility of implementing all-optically an ultrafast 4-bit parity generator and checker using the quantum-dot semiconductor optical amplifier (QD-SOA)-based Mach-Zehnder Interferometer (MZI) as XOR gate is theoretically investigated and demonstrated. The proposed circuit exploits an architecture where four XOR gates are concatenated in a modular manner. The first XOR gate drives the control input of the second one whose other control port receives the current bit of the word that undergoes parity processing. This interconnection is repeated up to the fourth XOR gate, on which an extra bit is applied. Depending on the binary value of this bit, the same circuit can operate both as parity generator and checker and support both even and odd parity. The performance of the scheme critically depends on the total amplitude modulation (AM) at its output. By conducting numerical simulation the impact of the key data signal and QD-SOAs parameters on this metric is evaluated. The outcome of this treatment allows to specify the permissible range of these parameters as well as an appropriate combination of them that renders the AM acceptable and ensures logically correct operation. The obtained results also demonstrate the ability of the QD-SOA-based MZI XOR gate to be cascaded and form more complex circuits of enhanced functionality.