Single-Mode Quantum Cascade Laser at $5.1~\mu \text{m}$ With Slotted Refractive Index Modulation

We presented a technique to realize single-mode quantum cascade lasers by simply etching several large-period slots in the ridge, which leads to refractive index perturbations and mirror-loss spectrum variation at different wavelengths stemming from high-order slot feedback. Stable single-mode operation is realized as a result of the reduced mirror-loss at the designed wavelength. A side-mode-suppression-ratio of about 20 dB for all measured temperatures and peak output power of about 500 mW in pulsed operation at room temperature have been achieved.