Optically induced intersubband absorption in biased double quantum wells

We present a new all-optical infrared modulator, which is based on biased double quantum wells. The electric field separates the photogenerated electrons and holes and hence increases their lifetime τ: the photoinduced infrared absorption is therefore enhanced. An increase of the modulation efficiency by two or three orders of magnitude is predicted and an enhancement of at least 20 has been observed at 4 K. At high pump power (150 mW), the linear dependence of the absorption as a function of applied bias is observed and discussed. We have also observed photoinduced intersubband transitions in the valence band in both infrared polarizations.