Resonant Optical Nonlinearities from Intersubband Transitions in GaN/AlN Quantum Wells

We measured the resonant nonlinear optical response of the intersubband transitions in GaN/AlGaN multiple quantum well structures. The measured value for the nonlinear susceptibility is found to be much smaller than previous theoretical predictions. This is attributed to a large electron dephasing due to material imperfections. We show that at higher incident intensities, absorption saturation is possible, and measure the saturation intensity for various wavelength around the transition resonance. We also discuss the prospects of using such structures as building blocks for all-optical nonlinear switches, in light of our experimental findings.