In the past few years advance in nanofabrication techniques have made it possible to make well-like compound semiconductor structures of low nanometer size.In these structures

the state of the electron in the direction perpendicular to the length of the well is quantized with sufficiently large separation in energy levels and the motion of the electron parallel to the length is that of a quasi-free electron.One of the most remarkable properties of these one-dimensional electron system is that the optical transitions between the size-quantized subbands are feasible.The result shows there is a large optical nonlinearities in asymmetric quantum wells.The problem of optical saturation of intersubband absorption has recently attracted considerable attention.The problem is very important to the development of superlattice devices such as fast infrared detectors and modulators because one needs to know the range of input optical intensities for which linear operation is possible.The analytical expression of the linear and the third-order nonlinear optical intersubband absorption coefficients are obtained in P schl-Teller wells using the density matrix formalism taking into account the intrasubband relaxation.Since there are two adjustable parameters κ and λ in P schl-Teller wells

the shapes of the wells will change with the change of the parameters κ and λ

accordingly the linear and the third-order nonlinear optical absorption coefficients will change with the parameters κ and λ.It is shown that the optical absorption coefficient depends on the parameter

and the optical intensity strongly.The absorption saturation will occur with I increase.Numerical results are presented for a typical AlGaAs/GaAs P schl-Teller well.