All-optical flip-flop contrast enhancement based on bistable polarisation rotation within Fabry–Perót SOA

Switching-contrast enhancement of over 28 dB for all-optical flip-flop (AOFF) operation of a Fabry-Perót semiconductor optical amplifier (SOA) is experimentally demonstrated. Although the two stable flip-flop states of such a device are typically distinguished by their optical power, it is demonstrated that each stable state can also exhibit a unique state of polarisation (SOP). This bistable polarisation rotation (BPR) is leveraged to achieve extreme contrast enhancement by aligning the AOFF reset-state SOP to the blocking axis of a linear polariser, producing a contrast of 36.6 dB. This contrast-enhancement technique is applicable to other AOFFs based on resonant-type SOAs (RT-SOAs) and Kerr-nonlinear media, substantially improving their applicability to advanced photonic-switching applications.