Photonic-crystal distributed-feedback (PCDFB) lasers have the potential to provide near-diffraction-limited, spectrally pure sources of midwave-infrared radiation. For a first proof-of-principle demonstration, optical lithography and dry etching were used to pattern a second-order two-dimensional rectangular lattice whose grating was tilted by 20degrees relative to the facet normal. The antimonide type-II "W" active region emitted lambda = 4.6-4.7 mum. For pulsed optical pumping, the emission line was much narrower (7-10 nm) than those of Fabry-Perot and angled-grating DFB (alpha-DFB) lasers fabricated from the same wafer, and the beam quality was enhanced by as much as a factor of 5 compared with the alpha-DFB. The observation of two distinct lines in the PCDFB spectrum is attributed to a near-degeneracy of grating resonances at two different symmetry points of the Brillouin zone for the rectangular lattice. Quantum-cascade PCDFB lasers with line width enhancement factors close to zero are projected to emit a single-mode output even when the gain stripe is as wide as 1 mm. (C) 2002 Elsevier Science Ltd. All rights reserved.