Saturation of the non-linear absorption in n-i-p-i multiple quantum well structures

A theoretical model to simulate the non-linear optical processes in n-i-p-i multiple quantum well (MQW) structures is presented. Using this model, the non-linear optical absorption modulation of the n-i-p-i MQW structure was studied. It was found that the large change in absorption across the intrinsic layer at low light intensity is due to the large asymmetry of the ratio of the excited carrier transit time to its lifetime of 5 × 10−2. The ratio of τ0/τexp of excess carrier lifetime at zero illumination intensity and at 10 mW cm−2 is found to be about 1.56 × 104. Saturation in the absorption at a light intensity of 10 mW cm−2 is due to the fact that the energy at the bottom of the quantum well is below the conduction band edge of the doped layers.