All-Optical $N$ -Bits Shift Register Exploiting a Ring Buffer Based on Semiconductor Optical Amplifier

The design and experimental characterization of an all-optical circular shift register are presented. The proposed scheme consists of a fiber loop optical buffer and a bit selecting circuit. A semiconductor optical amplifier (SOA) is used as an active element in the buffer structure, while the bit selecting circuit exploits Kerr effect in a highly nonlinear medium. The scheme is designed to store an N-bit sequence and to return the bits one by one at a lower clock rate, achieving proper circulating shift register functionality. Photonic integration is possible thanks to the presence of SOA in the buffer loop and to the absence of erbium-doped fiber amplifier-based feedbacks. Moreover, the increase in the number of bits to be stored does not increase the scheme complexity. Experimental validation is demonstrated for , and a signal-to-noise ratio per bit penalty equal to 5.6 dB is achieved at a bit error rate equal to with respect to the input sequence.