Abstract

It is well known that semiconductor materials display large and fast electronic nonlinearities at optical frequencies in the vicinity of their fundamental band gap. This suggests that semiconductors should be suitable materials for fabricating fast and short nonlinear directional couplers (NLDC). For a NLDC operating in cw mode, a low-power input signal introduced into one channel will emerge from a second adjacent waveguide, whereas a high-power signal would remain in the input channel. However, for pulses, the distribution of powers in the input leads to pulse breakup and part of the input energy is always transferred to the second channel. This crosstalk places a limitation on the applications of NLDCs for all-optical switching. In this talk we will discuss methods for obtaining pulse switching in active semiconductor NLDCs. Active couplers have a distinct advantage over their passive counterparts in that they should be cascadable. We have found that single pulse switching is difficult to achieve because of pulse breakup effects for pulse lengths >1 ps. However, for short pulses (<1 ps), the effects of group velocity dispersion become relevant and can lead to improved switching. In addition, we will show that it is possible to obtain 100% switching of a probe pulse by pumping the device either externally or optically.

© 1990 Optical Society of America