20 ps Transition Time All-Optical SOA-Based Flip-Flop Used for Photonic 10 Gb/s Switching Operation Without Any Bit Loss

A novel scheme for integrable ultrafast all-optical flip-flop is demonstrated. Transition times as low as 20 ps with a contrast ratio higher than 17.5 dB have been experimentally measured. All-optical switching operation in a 2 $\times$2 spatial and wavelength preserving switch is reported with a power penalty of about 1 dB. The proposed solution exploits the fast falling edge provided by a semiconductor optical amplifier (SOA) based optical flip-flop. Numerical investigations already demonstrated high extinction ratios (>40 dB) and low switching energies (15.6 fJ) for integrated optical flip-flop. On the other hand, slow rising times, due to the cavity length, intrinsically limit such configurations. By using SOA-based logic gates, two flip-flop outputs are combined in a new bistable signal. Both the new rising and falling edges are related to the primary flip-flop falling edge. This way it is possible to eliminate the intrinsic slow rising time that limits the flip-flop configuration based on the coupled ring lasers, without excessively increasing the complexity of the structure and maintaining a reasonably high contrast ratio. Furthermore, the noise on the high level has been improved due to the regenerative properties of the logic gates based on cross-gain modulation and cross-phase modulation in a single nonlinear SOA. Finally, flip-flop output has been used to drive a 2$\times$ 2 all-optical spatial and wavelength preserving switch based on SOAs. For cross/bar switch configurations, 10 Gb/s error-free operation has been obtained without bit loss.