Picosecond all-optical switching using tunneling and spin-relaxation in quantum well structures

We propose and demonstrate two approaches for controlling the recovery time from excitonic absorption bleaching. Each approach has a new feature that the recovery time of optical nonlinearity is controlled by the tunneling or the spin-relaxation effect in quantum well structures. In the tunneling bi-quantum well structure utilizing the tunneling effect, the recovery time is reduced to the picosecond region with the reduction of tunneling barrier thickness. The recovery time is three orders of magnitude shorter than the nanosecond recovery of conventional multiple quantum wells (MQW). The spin relaxation of MQW has been shown to be as fast as several tens of picoseconds. The all-optical gate operations of a Fabry-Perot etalon are demonstrated with a full signal recovery of 17 ps using tunneling and 7-ps recovery using spin relaxation.