The traditional Semiconductor Optical Amplifier (SOA) suffers from slow response, which causes it to be unable to operate at higher speeds. Therefore, our goal is to find a suitable alternative that works at higher speeds with acceptable performance.

Professor LI Wei and Associate Professor Amer Kotb from the Changchun Institute of Optics, Fine Mechanics, and Physics (CIOMP) of the Chinese Academy of Sciences (CAS) in cooperation with Professor Kyriakos Zoiros at the Democritus University of Thrace in Greece were able to adapt the Carrier Reservoir Semiconductor Optical Amplifier (CR-SOA) for the first time to design all-optical logic gates at a data rate of 100 Gb/s.

CR-SOAs exhibit faster gain and phase recovery, which qualifies them to execute all-optically Boolean logic functions at higher rates compared to conventional SOAs. The CR-SOA operation relies on a similar principle as that for a Quantum Dot SOA (QD-SOA). In QD-SOA, the faster response is due to the presence of the wetting layer, which acts as the carrier storage region. In fact, uniform QD-SOAs are less technologically mature and more difficult to fabricate. This essentially means that forming the required carrier reservoir with the available semiconductor processing techniques may be more feasible for CR-SOAs.

In this paper, the authors have made a performance comparison between the CR-SOA- and the conventional bulk SOA-based-all-optical OR logic gate by studying the variation of the quality factor (Q-factor) against various key operating parameters, including the transition time from the carrier reservoir to the active region, the population inversion factor, the injection current, the equivalent pseudorandom binary sequence length, the alpha-factor, the optical confinement factor, the operating data rate, the input pulse energy, and the continuous wave power in the presence of the amplified spontaneous emission noise. The obtained results indicated that the CR-SOA is more suitable for realizing the OR logic gate at 100 Gb/s as it manages to achieve a more than acceptable Q-factor compared to the unacceptable value achieved when using the conventional SOA.

After publishing the results of this research in Optics and Laser Technology, the CR-SOA is expected to play an important future role in the design of advanced optical logic circuits.