Influence of spin-orbit interaction on quantum cascade transitions
  We have investigated the effect of spin-orbit (SO) coupling on the emission spectra of a quantum cascade laser. In an externally applied magnetic field parallel to the electron plane, the SO coupling would result in a double-peak structure of the optical spectra. This structure can be observed within some interval of magnetic fields and only for diagonal optical transitions when the SO coupling is different in different quantum wells. 
V. Apalkov, A. Bagga, and T. Chakraborty