An intersubband quantum cascade laser structure includes multiple coupled
laser stages, wherein each stage has a multilayer structure including an
electron injector, an active region with at least one quantum well, and
an electron reflector. Electrons injected from the injector into the
active region at a high energy level relax to a lower energy level with
the emission of a photon at, for example, mid-infrared wavelengths. The
reflector reflects electrons at the higher energy level at which they
were injected and transmits electrons from the lower energy level after
emission of a photon. Multiple layers of semiconductor are formed on each
side of the multistage structure to provide conduction across the device
and to provide optical confinement of the photons emitted.