All-Optical Clocked Flip-Flops Exploiting SOA-Based SR Latches and Logic Gates

All-optical flip-flops are key components for photonic digital processing in next generation optical networks and optical computing. In most digital applications signals synchronization with an external reference clock is a basic feature. In this paper an entire set of all-optical clocked flip-flops, including SR, D, T, and JK types is proposed and demonstrated. Each configuration employs a single SR latch and optical logic gates previously introduced in literature. The bi-stable element is based on a gain quenching mechanism between two coupled ring lasers using a semiconductor optical amplifier (SOA) as active element. A ∩B, A ∩B , and A ∩B ∩C logic functions, where A, B and C are the clock and the control signals respectively, are carried out by exploiting four wave mixing (FWM) and cross gain modulation (XGM) nonlinear effects in SOAs. Different flip-flop logical functionalities are obtained by adding to the latch scheme one of the logic gates, or a combination of them. Performance evaluation in terms of extinction ratio demonstrates the effectiveness of the proposed schemes. Speed limitation of flip-flop switching operation is also investigated and photonic integration is identified as a feasible solution to increase the functioning speed beyond GHz.