Mid-IR intersubband quantum cascade lasers

Quantum cascade lasers are new light sources in the mid-infrared (3.5 - 12 mu m), based on resonant tunneling and optical transitions between quantised conduction band states. Quantum engineering of electronic energy levels and tailoring of the wavefunctions are used to obtain population inversion and optimize the overall laser performance. Advanced structures fi-om a point of view of the quantum design, such as two wavelength emitters, are presented. New waveguide confinement based on surface plasmon are also discussed. In this configuration it is shown that optical confinement can be achieved without the growth of cladding layers. The paper concludes with a general comparative discussion between GaAs/AlGaAs and GaInAs/AlInAs material systems for the new generations of quantum cascade lasers.