Optical shift register based on an optical flip-flop memory with a single active element

We present an optical shift register that consist out of two serially connected optical flip-flop memories driven by common clock pulses. Each optical flip-flop consists out of two ring lasers sharing a single active element, which makes the optical flip-flops easily cascade with each other. The two cascaded optical flip-flops are controlled by the clock pulses in such a way that the input data set the new state of the first optical flipflop, after the state of the first flip-flop has been transferred to the second optical flip-flop. The concept is demonstrated at an operation speed of 20 kHz, which is limited by the 10 m long laser cavities formed by the fiber pig-tailed components.