Very steep optical thresholding Characteristic using a DFB laser diode and an SOA in an optical feedback scheme

A new optical decision or thresholding circuit, composed of a semiconductor optical amplifier (SOA) and a distributed feedback (DFB) laser diode in an optical feedback scheme is proposed. This new circuit has been studied both by simulations and experiments. Simulations show a very steep optical decision characteristic that rises more then 5 dB over an input power range of less then 0.5 dB. It is also demonstrated that the decision point can easily be shifted by tuning the drive currents of both the laser diode or the SOA or the feedback ratio between them. The principle has been experimentally verified as well, using a discrete SOA and DFB laser diode. We showed a good agreement with the simulation results. Again a very steep optical decision characteristic, combined with the possibility to adjust the decision point was obtained.