We have investigated intersubband absorptions between the conduction ground state and the first excited state of two AlxGa1−xAs/GaAs/AlxGa1−xAs multiple quantum well structures with x=0.3 and 85 Å well width, and with x=0.57 and 96 Å well width. Small-signal measurements show absorption peaks at 10.45 and 10.15 μm, respectively. Under an intense resonant excitation from a pulsed CO2 laser, saturation of the intersubband absorption occurred. The saturation intensity is estimated to be 340±120 kW/cm2 for the first sample and 375±120 kW/cm2 for the second. From these values, we have deduced subband decay times of the order of 10.6±3.5 ps for the first sample and 15.5±5 ps for the second.

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Reçu le 1er juillet 1988, accepté le 20 septembre 1988) Résumé. 2014 Les transitions optiques entre niveaux de la bande de conduction des puits quantiques font l'objet d'études approfondies pour le développement de photodétecteurs infrarouges rapides et de nouveaux dispositifs opto-électroniques. La non-linéarité liée à la saturation de la transition d'absorption intrabande est démontrée. L'étude nous permet d'identifier les mécanismes de relaxation intrabande.Abstract. 2014 Optical transitions between confined energy levels of the conduction band of quantum well structures are of great interest for the development of fast infrared detectors and new optoelectronic devices. The non-linearity due to the intersubband absorption saturation is investigated. The intersubband relaxation processes are identified.

We give experimental results for amplitude and phase modulation by free-carrier injection in planar and rib waveguides at a wavelength of 10.6 microm. These waveguides have been formed by metal-organic chemical-vapor deposition of InP and GalnAs layers on InP substrates. Absorptions of 95% associated with phase shifts greater than 3pi have been measured for injection-current densities below 1 A/cm(2) with a planar guiding structure and drive currents of approximately 10 mA for typical channel waveguides.