An improved quantum cascade laser, the improvement comprising a longitudinally non-uniform dielectric waveguide. The waveguide includes a longitudinally straight section and a longitudinally tapered section. The length of the tapered section is between 5% and 50% of the total cavity length. The tapered section tapers at a taper angle from the facet width to the ridge width. The taper angle is smaller than the delineation angle of the waveguide.