Highly directional emission from photonic crystal waveguides of subwavelength width.

Recently it has been shown that it is possible to achieve directional emission out of a subwavelength aperture in a periodically corrugated metallic thin film. We report on theoretical and experimental studies of a related phenomenon concerning light emitted from photonic crystal waveguides that are less than a wavelength wide. We find that the termination of the photonic crystal end facets and an appropriate choice of the wavelength are instrumental in achieving very low numerical apertures. Our results hold promise for the combination of photonic crystal waveguides with conventional optical systems such as fibers, waveguides, and freely propagating light beams.