Intersubband transitions and ultrafast all-optical modulation using multiple InGaAs-AlAsSb-InP coupled double-quantum-well structures

InP-based InGaAs-AlAs-AlAsSb coupled double-quantum-well structures have been optimized using wave-function engineering techniques to achieve near-infrared intersubband (ISB) transitions. Intersubband transitions at communication wavelengths of 1.3 and 1.55 /spl mu/m can be achieved in both near-symmetric and asymmetric coupled quantum-well structures by tailoring the well width, the central barrier width, and the carrier population in the conduction subband states by controlling either the doping level or the carrier temperature. We demonstrate ultrafast all-optical modulation of interband-resonant light at 1.3 /spl mu/m using intersubband-resonant light pulses at 1.55 /spl mu/m. An ultrafast absorption recovery time of 1.3 ps has been observed at 1.3 /spl mu/m, which can be reduced to 800 fs by probing at a higher energy above the Fermi level in the conduction band.