Subpicosecond saturation of intersubband absorption in (CdS/ZnSe)/BeTe quantum-well waveguides at telecommunication wavelength

Ultrafast all-optical switching at an optical communication wavelength has been investigated by utilizing an intersubband transition (ISBT) of II-VI-based multiple quantum wells (MQWs) fabricated in high-mesa waveguide devices. The waveguide structure consists of a CdS/ZnSe/BeTe MQW core layer and two top and bottom ZnMgBeSe quaternary cladding layers grown by molecular beam epitaxy on a (001) GaAs substrate. A marked increase in waveguide transmittance was observed only for transverse-magnetic-polarized subpicosecond pulse with increasing incident pulse energy at lambda=1.57 mu m, indicative of the ISBT absorption saturation. The pulse energy necessary for a 10 dB transmittance increase is as low as 13.3 pJ for a waveguide device with 2.7 mu m mesa, and the saturation pulse energy can be even further reduced by employing a narrower mesa structure. Ultrafast gate switching within a time window of 0.56 ps was also demonstrated with pump pulse at lambda=1.57 mu m and probe pulse at lambda=1.63 mu m in this waveguide device. (C) 2005 American Institute of Physics.