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

Abstract

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 λ=1.57μm, indicative of the ISBT absorption saturation. The pulse energy necessary for a 10dB transmittance increase is as low as 13.3pJ for a waveguide device with 2.7μm 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 0.56ps was also demonstrated with pump pulse at λ=1.57μm and probe pulse at λ=1.63μm in this waveguide device.