Low threshold current density distributed feedback quantum cascade lasers with deep top gratings.

The authors report on pulsed and continuous-wave operation of single mode tunable distributed feedback quantum cascade lasers at λ∼7.7 μm. A deep top grating and a thin heavily doped InP layer beneath the grating are formed in the upper cladding to obtain simultaneously a strong feedback effect and a low waveguide loss. A “three-well vertical transition” active region is used with a low doped injector. In pulsed operation, a very low threshold current density of 970 A/cm² and a peak power of 75 mW are achieved at 300 K. Reliable single mode emission with a side mode suppression ratio of ∼30 dB is achieved in a large temperature range (155–320 K) with a tuning range of 90 nm. The lasers operate in continuous-wave mode up to 130 K. [ABSTRACT FROM AUTHOR]