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Optical resonators containing saturable absorbers (saturable resonators) have nonlinear characteristics and can exhibit hysteresis. This is demonstrated experimentally at 10.6 μ wavelength. A saturable resonator is used to switch out the CO2 laser light from its cavity and for repetitive Q-switching. Devices are described to obtain variable length pulses, infinite pulse trains, logical operations on two signals, and memory functions.

In this letter, we demonstrate all-optical nonlinear switching in compact GaAs-AlGaAs microring resonators at the 1.55-m wavelength. Switching is accomplished in the pump-and-probe configuration in which the pump-and-probe signals are tuned to different resonance wavelengths of the microring. Refractive index change in the microring due to free carriers generated by two photon absorption is used to switch the probe beam in and out of resonance. Measured transient responses of the pump and probe through the microring show good agreement with theoretical predictions based on nonlinear pump-probe interaction due to two photon absorption.Index Terms-All-optical switching, microrings, photonic switching, pump and probe, semiconductor microresonators, two photon absorption.

We investigate a strategy for M-ary discrimination of nonorthogonal phase states with error rates below the homodyne limit. This strategy uses feed forward to update a reference field and signal nulling for the state discrimination. We experimentally analyze the receiver performance using postprocessing and a Bayesian strategy to emulate the feed-forward process. This analysis shows that for a moderate system detection efficiency, it is possible to surpass the homodyne error limit for quadrature phase-shift keying signals using feed forward.

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