High-power continuous-wave quantum cascade lasers

摘要

High-power continuous-wave (CW) laser action is reported for anGaInAs-AlInAs quantum cascade structure operating in the mid-infraredn(Λ≃5 Μm). Gain optimization and reduced heating effectsnhave been achieved by employing a modulation-doped funnel injector withna three-well vertical-transition active region and by adopting InP asnthe waveguide cladding material to improve thermal dissipation andnlateral conductance. A CW optical power as high as 0.7 W per facet hasnbeen obtained at 20 K with a slope efficiency of 582 mW/A, whichncorresponds to a value of the differential quantum efficiencynΗd=4.78 much larger than unity, proving that eachnelectron injected above threshold contributes to the optical field annumber of photons equal to the number of periods in the structure. Thenlasers have been operated CW up to 110 K and more than 200 mW per facetnhave still been measured at liquid nitrogen temperature. The highnoverall performance of the lasers is also attested by the largen“wall plug” efficiency, which, for the best device, has beenncomputed to be more than 8.5% at 20 K. The spectral analysis has shownnfinally that the emission is single-mode for some devices up to morenthan 300 mW at low temperature