The linear and nonlinear behaviour of intersubband transitions of cubic GaN/AlN multi quantum well (QW) structures in the IR spectral region is investigated. In this study photoluminescence, IR absorption as well as pump-probe measurements are done. Two cubic GaN/AlN multi quantum wells with Si content of N-Si similar to 10(19) cm(-3) in the cubic GaN quantum wells were grown on 3C-SiC (001) substrate by radio-frequency plasma-assisted molecular beam epitaxy. A broad IR absorption with a FWHM of 370 meV was found with a maximum at 0.7 eV, corresponding to the intersubband transition of the multi quantum wells. The nonlinear optical measurement reveals a clear change of transmission for a pump pulse with an angle of incidence of 65 degrees. Furthermore, transmission electron microscopy measurements are used to determine the real layer thicknesses. These thickness values are exploited in the calculation with the Schrdinger-Poisson solver nextnano 3. The simulated transition energies agree very well with the experimental data for the photoluminescence and the absorption measurement. (C) 2017 Elsevier B.V. All rights reserved.