Mach-Zehnder interferometer based all optical flip-flop
  For the first time an all optical flip-flop is demonstrated based on two coupled Mach-Zehnder interferometers which contain semiconductor optical amplifiers in their arms. The flip-flop operation is discussed and it is demonstrated using commercially available fiber pigtailed devices. Being based on Mach-Zehnder interferometers, the flip-flop has potential for very high speed operation. 
Martin T.Hill, H. de Waardt, G. D. Khoe, H. J. S. Dorren