Low-temperature-grown surface-reflection all-optical switch (LOTOS)

The low-temperature-grown surface-reflection all-optical switch, or LOTOS, is an ultrafast saturable absorber made with Be-doped strained InGaAs/InAlAs MQWs. It's operation principle is the carrier-induced change in the excitonic absorption of the MQWs. Its ultrafast operation (250 fs) is a result of the MQW region being grown at a low temperature (200 degreesC) and doped with Be. Large optical nonlinearity is obtained by compressively straining the quantum wells and using a reflection geometry combined with a low-reflectivity DBR: a so-called asymmetric Fabry-Perot etalon with an extremely low finesse. All of these things enable ultrafast all-optical switching operation with a high on/off ratio, a wide range of operating wavelengths, and polarization insensitivity. A spin-polarization scheme results in on/off ratios more than 20 dB better than those obtained with the conventional scheme, and handling the two orthogonal components of the signal pulse at two different points makes the switch operation polarization insensitive. Tests confirm that the LOTOS offers an ultrafast demultiplexer capable of simultaneous multi-output operation future high-speed optical communications systems.