Continuous-wave operation of distributed feedback AlAs/GaAs quantum cascade lasers

Summary form only given. Quantum cascade lasers QCLs are powerful light emitters in the mid infrared. For chemical sensing, single mode emission is advantageous. We fabricated first order distributed feedback lasers to achieve single mode emission. The emission wavelength is continuously tunable according to the temperature dependence of the effective refractive index, which shifts the Bragg wavelength. A rigorously on-resonant Floquet-Bloch analysis of the waveguide grating problem was used to design the grating geometry and the cladding layer thickness. The active material consists of 40 periods of an AlAs/GaAs chirped superlattice, grown by solid source molecular beam epitaxy. A double plasmon enhanced waveguide is used for vertical optical confinement while lateral electrical and optical confinement is achieved by deep etched ridges. The Bragg grating is defined by contact lithography and etched into the surface of the top cladding layer, thus avoiding the need of regrowth. The whole grating region is covered with gold, resulting in a large contact area. The lasers, with as cleaved facets, are soldered with In on Cu-plates (epilayer up) and mounted in a flow cryostat.