Miniaturized frequency comb sources across hard–to–access spectral regions, i.e. mid– and far–infrared, have long been sought. Four–wave–mixing based Quantum Cascade Laser combs (QCL–combs) are ideal candidates, in this respect, due to the unique possibility to tailor their spectral emission by proper nanoscale design of the quantum wells. We have demonstrated full–phase–stabilization of a QCL–comb against the primary frequency standard, proving independent and simultaneous control of the two comb degrees of freedom (modes spacing and frequency offset) at a metrological level. Each emitted mode exhibits a sub–Hz relative frequency stability, while a correlation analysis on the modal phases confirms the high degree of coherence in the device emission, over different power-cycles and over different days. The achievement of fully controlled, phase-stabilized QCL–comb emitters proves that this technology is mature for metrological-grade uses, as well as for an increasing number of scientific and technological applications.
Contact person: Luigi Consolino, INO Sesto Fiorentino