Broadly wavelength-tunable external cavity, mid-infrared quantum cascade lasers

Wavelength tuning over 120 nm for a grating-coupled 5.1-/spl mu/m quantum-cascade type-I laser was studied for temperature from 80 to 243 K (-30/spl deg/C). Both the Littman-Metcalf and first-order grating direct feedback cavity configurations were used with similar tuning results. The goal is to achieve broad tunability, and the result is a combined grating and temperature tuning of 245 nm, from 5.040 to 5.285 /spl mu/m. The laser was designed for predominantly single-mode or at most, two-longitudinal mode operation. The instrument-limited laser linewidth was less than the cavity longitudinal mode spacing. Stepping-motor control of the grating allowed 0.4-GHz wavelength increments (35 pm) to be realized with high reproducibility. A current-induced wavelength shift of /spl sim/2-3 GHz was observed, corresponding to an effective refractive index change of /spl sim/10/sup -3/. Analysis indicates that single-mode, continuously tunable operation is feasible with a more optimal device and cavity.