All-optical switching using ultrafast intersubband transitions in InGaAs/AlAsSb coupled triple quantum well structures

The intersubband transition (ISBT) in quantum wells is attractive due to its ultrafast relaxation, large transition dipole moment, and widely tunable transition wavelength. Recently ISBT at communication wavelengths up to 1.45 /spl mu/m was reported for InGaAs/AlAsSb quantum wells. However, for such short wavelength the intersubband relaxation rate can hardly exceed 10/sup 12/ s/sup -1/ which will be required for all-optical switches applicable to a multi-terabit communication network system. To overcome this problem coupled double quantum well (C-DQW) for ISBT has been proposed for tailoring electron-phonon scattering processes and the possibility of acceleration of intersubband relaxation in C-DQW has been previously shown. Such a technique of tailoring both the transition energies and scattering processes in quantum well structures is extremely important for the design of practical devices. Based on this technique, we propose in this paper a novel coupled triple quantum well (C-TQW) structure which enables further speed-up of ISBT responses useful for ultrafast multi-wavelength all-optical switching at the wavelength from 1.3 /spl mu/m to 1.5 /spl mu/m. We show the capability of 300/spl sim/500 fs all-optical switching at 1.5 /spl mu/m utilizing the enhanced electron-phonon scattering in InGaAs/AlAsSb C-TQW on InP substrates.