On the design of ultrafast all-optical NOT gate using quantum-dot semiconductor optical amplifier-based Mach–Zehnder interferometer

The feasibility of implementing an ultrafast NOT gate by means of a two-input Mach–Zehnder interferometer (MZI) that employs quantum-dot semiconductor optical amplifiers (QD-SOAs) is theoretically explored and shown. For this purpose a numerical treatment is conducted by modeling the propagation of strong pulses through a QD-SOA and the resultant change of the QD-SOA gain dynamics. This procedure allows to evaluate the impact of the critical parameters on the MZI complementary output port and find which is the most appropriate way to be selected and combined. The analysis of the simulation results reveals that with the non-data driven QD-SOA constantly held in the linear gain regime, the other QD-SOA, which is perturbed by the data to be logically inverted, must be operated in a nonlinear regime. This is defined by the drop of the specific QD-SOA gain by approximately 5.5 dB from its unsaturated value, which is caused by a data peak power being 4 dB higher than its saturation input power. Moreover, in order for the design to be complete, both QD-SOAs must be of medium length, provide a maximum modal gain such that their net gain exceeds by two orders of magnitude that at transparency, be biased at moderate current density and exhibit an electron relaxation time from the excited state to the ground state as fast as possible. Provided that these conditions are satisfied then a more than adequate extinction ratio can be obtained, which ensures that Boolean NOT logic is executed at 160 Gb/s both with logical correctness and high quality using QD-SOAs in a structurally simple, power efficient and operationally flexible version of the MZI.

► All-optical NOT gate is predicted to be feasible at 160 Gb/s with QD SOA-based MZI.
► Employed MZI is structurally simple, power efficient and operationally flexible.
► Numerical simulation to evaluate impact of critical parameters on extinction ratio.
► Extraction of design rules to enable correct and high quality NOT operation.
► QD SOA in upper MZI arm must be operated in proper nonlinear gain regime.