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Picosecond and subpicosecond all-optical switching using near-infrared intersubband transitions was demonstrated in an InGaAs/AlAs/AlAsSb quantum well structure. For a multiple quantum well structure, strong absorption at wavelengths shorter than 1.7 μm was obtained. An inter-subband-pump and inter-band-probe measurement was performed on this material system using a femtosecond optical parametric amplifier system and white-light generation. Inter- and intra-subband relaxation was observed by measuring the time-wavelength resolved interband absorption induced by intersubband excitation. The present results demonstrate its applicability for ultrafast, highly efficient, all-optical modulators and switches.