Realization of all-optical flip-flop using directionally coupled bistable laser diode

A novel all-optical flip-flop device has been realized using a directionally-coupled bistable laser diode (DC-BLD). We have fabricated the DC-BLD by a conventional fabrication technique of LDs. To separate the adjacent electrodes of the directional coupler, an oblique electron-beam evaporation technique was developed. By this self-align process, the two adjacent waveguides of the directional coupler were electrically isolated without employing any additional lithography step. Using the fabricated DC-BLD, all-optical flip-flop has been demonstrated due to the nonlinear effects of the saturable absorber and the directional coupler. The flip-flop operation has been achieved with sufficiently small input optical power level around 0 dBm.