Abstract: Single-mode quantum cascade lasers having shaped cavities of various geometries are provided. The shaped cavities function as monolithic coupled resonators, and permit single-mode operation of the lasers. A folded or hairpin-shaped cavity could be provided, having a plurality of straight segments interconnected with a curved segment. Additionally, a shaped cavity could be provided having a single straight segment interconnected at one end to a curved segment. The curved segment could also be tapered in shape, such that the width of the curved segment decreases toward one end of the curved segment. A laser which includes a shaped cavity having two interconnected, folded shaped cavities is also provided.