Single-Mode Tunable Quantum Cascade Distributed Feedback and Multiple-Wavelength Quantum Cascade Lasers

Abstract—Single mode and tunable Quantum Cascade Distributed Feedback (QCDFB) lasers in the wavelength range from 4.5 to 16.5 mm are reviewed. In the case of QC-lasers with dielectric waveguides, DFB lasers are fabricated either with a topgrating approach, which is simpler to manufacture, or a buried grating with epitaxial regrowth, which generally has a higher single-mode yield as a result of a larger coupling factor. Long-wavelength QC-DFB lasers based on surface plasmon waveguides use bi-metal gratings for Bragg reflection. Single-mode emission with a side-mode suppression ratio of 30 dB and a tunability (depending on wavelength) of 0.3 - 1.0 nm/K heat sink temperature or of 20 - 40 nm/A continuous wave current are customarily achieved. These features together with the potential for high optical