The "vanishing-core" tapered coupler is an all-fiber device that efficiently couples light between a standard low-numerical- aperture (NA) waveguide, such as a standard silica fiber, and a high-NA waveguide or device with a dissimilar mode field profile, such as a planar waveguide or laser diode. The coupler is comprised of a central core surrounded by a concentric secondary core for low-NA coupling on one side of the device. The central core effectively disappears on the tapered end of the device. Light escaping the "vanishing-core" at the tapered end of the fiber is confined in the secondary core by the surrounding cladding for high-NA coupling. This lens-less, low-insertion-loss solution obviates the need for a significant air gap between coupled components required in lensed fibers and thereby enables the use of index matching compounds. The all-fiber design also facilitates polarization selective and polarizing coupling and provides a path towards a high density of passively aligned interconnects.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.