Femtosecond All-Optical Switching in AlGaAs Waveguides Using a Time Division Interferometer.

摘要

All-optical switching and signal processing in guided wave devices via third-order nonlinearities is a potentially valuable technique for applications where extremely high speeds are desired. Systematic investigations of ultrafast nonlinearities are relevant to determine the suitability of a material for a particular switching application. All optical switching in single-mode fibers has been achieved using the Kerr effect. Fibers have weak nonlinearity n2 but a high figure of merit n2a, due to the low loss a. Thus hundreds of meters of fiber can be used to switch pulses with powers on the order of those obtained with mode-locked laser diodes. The large physical size and propagation delay times of the switch in these schemes would be prohibitive for some applications. Direct band gap semiconductors such as GaAs have resonant optical nonlinearities near the band edge which are orders of magnitude larger than those in fibers. Thus, problems associated with size and propagation delays can potentially be eliminated. All optical switching of femtosecond pulses in Aluminum Gallium Arsenide waveguides is investigated using a novel time division interferometric technique which eliminates thermal imbalances. In addition to an instantaneous refractive index nonlinearity, free-carrier generation via two-photon absorption produces a response of several hundred picoseconds duration. Reprints. (AW)