The process of multiwavelengh detection by a single system is possible when considering multilevel structures. Indeed, in a quantum structure with specific profile, levels can be confined in a single band leading to Infrared intersubband transitions which may be responsible of strong enough absorption. In this work we present the theoretical determination of the absorption spectra in a specific GaAs/AlGaAs superlattice containing four confined minibands. For this, we have calculated the electronic states, the dipole matrix elements and the Fermi level's position versus temperature and doping. We analyze the importance of the different transitions absorption peaks and their behavior when varying either the temperature or the free electrons density, both in the parabolic and the non parabolic cases.