Ultrafast all-optical digital comparator using quantum-dot semiconductor optical amplifiers

In this investigation, three types of 160 Gb/s all-optical digital comparators using quantum-dot semiconductor optical amplifiers (QD-SOAs) are constructed. These configurations have different combination patterns of logic gates and QD-SOAs. Based on numerical simulations, we investigate and evaluate the performance of the devices in terms of the number of logic gates and QD-SOAs, and the value of the extinction ratio (ER). In addition, we demonstrate the effect of amplified spontaneous emission (ASE) noise on the ER and Q-factor. The results show that two of the three configurations are superior to the other configuration in terms of circuit complexity, value of ER, and sensitivity to injection current. Moreover, these two configurations achieve ER values over 10 dB and Q-factor over 9, even when intense ASE noise is considered. The proposed configurations have several advantages such as high quality, easy configuration, insensitivity to injection current, and strong noise robustness, which are favorable for practical applications. This investigation also facilitates the specification of the pros and cons of each configuration, and the determination of the appropriate comparator according to the desired requirements.