Spectral shift of quantum-cascade laser emission under the action of control voltage

Spectral redistribution of the intensity of short- and long-wavelength emission components within gain bandwidth of a 7- to 8-$\mu$m quantum-cascade laser under the action of control voltage is demonstrated. As the voltage was increased from 10.5 to 18.2 V, the wavelength of maximum laser emission intensity shifted by approximately 200 nm. The maximum bandwidth of laser gain was about 300 nm (at a temperature of 80 K). The quantum-cascade laser heterostructure was grown by molecular beam epitaxy. The laser active region design was based on double-phonon depopulation of the lower level as implemented on In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As heteropair of solid alloys lattice-matched with an InP substrate.