A high contrast (5:1), 1.3 &mgr;m wavelength opticalandgate is demonstrated using a bistable Fabry–Perot InGaAsP/InP laser amplifier with large gain. Using simple arguments, it is shown that, subject to realistic constraints, the maximum attainable contrast ratio in a bistable Fabry–Perot logic gate is about 10. Unlike bistable amplifiers, there is a significant trade‐off between contrast and gain in passive devices.