Ultrafast high-contrast all-optical switching using spin polarization in low-temperature-grown multiple quantum wells

We have demonstrated an ultrafast high-contrast surface-reflection all-optical switch using a spin-polarization scheme. The device is made with low-temperature-grown Be-doped strained InGaAs/InAlAs multiple quantum wells. It has a photoresponse of 300 fs due to ultrafast electron trapping. The on/off ratios have been drastically improved by more than 20 dB, and reached over 30 and 40 dB at pump pulse energies of 4 and 14 pJ, respectively. Furthermore, we have obtained polarization insensitive operation by handling the two orthogonal components of the signal pulse at two different points.