Reflective bistability in 1.55 μm laser diode amplifiers

Bistable laser amplifiers are attractive for potential application in optical switching because of very low input optical requirement, high extinction ratio and the presence of optical gain. Optical bistability (OB) arises from gain saturation and the associated nonlinear refraction combined with the effect of feedback in the laser cavity. We present the experimental results of bistable characteristics for the case of a 1.55 μm symmetric Fabry-Perot (F-P) laser amplifier with uncoated facets. This paper reports a particularly rich variety of behaviour for reflected signals. Three main forms of hysteresis loops are observed on reflection. The hysteresis loop changes from anticlockwise to clockwise hysteresis in the optical input-output characteristic when the drive current or initial phase detuning is changed. The “butterfly” hysteresis loop is observed experimentally at optical input power as low as 260 μW for a drive current equal to 90% of the lasing threshold. The dependence of the optical bistability on drive current, initial phase detuning and injected optical power has been investigated. In the bistable light output-initial phase detuning characteristic, the optimum frequency is shifted downward with an increase in the injected power or the drive current. All measurements are in good agreement with an analytical model