In this paper we present the numerical results of the optical response of doped Ga group V (N, As, Sb) compounds in the medium IR and THz wave spectrum. Specific features of the optical response depends on the strength of the LO phonon-plasmon coupling, which can be controlled by the free carrier concentration and the compound composition. The impact of this coupling will be evaluated at different free carrier concentrations. Potential applications will be discussed for CO2 laser wavelengths and for a new generation of THz lasers.