Pitchfork bifurcation polarization bistability in laser diodes with external cavities

A new pitchfork bifurcation polarization bistability in laser diodes with a two-armed polarization-selective external cavity is examined theoretically and experimentally. The rate-equation analysis taking into account gain saturation has been carried out using the model for a laser diode whose laser thresholds of the TE and the TM modes can be changed independently through the changing of their photon lifetimes. It is shown from the analysis that pitchfork bifurcation polarization bistability appears when the laser thresholds for both modes are very close to each other and the switching between two stable states is obtained by means of a photon lifetime changing or a coherent or incoherent light injection. In the experiment, a 1.3-μm InGaAsP laser diodes with a T-shaped polarization-selective external cavity mas used. A new type of polarization bistability was observed when one arm was blocked and then recoupled. The two stable states mere also switched by means of an optical injection. All-optical flip-flop operation has been successfully demonstrated by using both TE and TM trigger inputs