Nonlinear intersubband optical absorptions in a multiple quantum wells with an applied electric field

In multiple quantum wells system, a large dipole strength and a narrow band width were observed. This suggests that the intersubband optical transitions in a quantum well may have very large optical nonlinearities. The intersubband transition have potential for device applications in far-infrared laser amplifiers, photodetectors and high-speed electrooptical modulators. In device design, the region of input optical density for linear response is a very important parameter. And the optical saturation is related with tunnelling effects and the intersubband relaxations. So the intersubband nonlinear absorption is very valuble for a fundamental and a practical point of views. Recently, there are some works on this region [1], [2].