Long wavelength distributed feedback tapered quantum cascade lasers

We present a study on distributed feedback tapered quantum cascade lasers emitting at 14 µm. The fabricated lasers with taper angles between 0° and 3° exhibited output powers scaling in accordance with the active zone volume increase. Reduced divergence angles as small as 4.2° have been obtained with diffraction limited-beam quality (M² ≈ 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.