<title>Ultrafast all-optical modulation using intersubband transition in GaAs/AlGaAs quantum wells</title>

Abstract

A picosecond modulation of interband (IB) resonant light (approximately 800 nm) by intersubband (ISB) resonant light (approximately 7 micrometers ) in n-doped GaAs/AlGaAs quantum wells is demonstrated. Two-color pump-probe measurements are carried out by using ultrashort (approximately 120 fs) ISB (pump) and IB (probe) light pulses at room temperature. Ultrafast modulation (FWHM approximately 1.3 ps) of the IB light is clearly observed with a low pump pulse energy of about 4 fJ/micrometers 2. The observed modulation depth is approximately 8.5% which corresponds to the absorption coefficient change of as large as approximately 1000 cm-1. The modulation depth decreases when the pump pulse wavelength is detuned from the ISB absorption peak. The modulation dependence on the ISB light pulse energy is also measured. The carrier relaxation mechanism in high and low excitation conditions is discussed by employing a numerical simulation of the relaxation process of electron-- longitudinal optical phonon systems. The results indicate that the utilization of the intersubband transition is promising for the ultrashort all-optical modulation and switching.© (2000) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.