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∼7.7μm. 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 970A∕cm2 and a peak power of 75mW are achieved at 300K. Reliable single mode emission with a side mode suppression ratio of ∼30dB is achieved in a large temperature range (155–320K) with a tuning range of 90nm. The lasers operate in continuous-wave mode up to 130K.

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