Long Wavelength Distributed Feedback Tapered Quantum Cascade Lasers

We present a study on distributed feedback tapered quantum cascade lasers emitting at 14 mu m. The fabricated lasers with taper angles between 0 degrees and 3 degrees exhibited output powers scaling in accordance with the active zone volume increase. Reduced divergence angles as small as 4.2 degrees have been obtained with diffraction limited-beam quality (M2 approximate to 1). With a first order Bragg-grating for single longitudinal mode selection, continuous wave operation was demonstrated up to almost room temperature with side-mode suppression ratios greater than 20 dB.