Adiabatic coupling in tapered air-silica microstructured optical fiber

We study adiabatic mode propagation in tapered air-silica microstructured o ptical fibers and demonstrate efficient coupling into a robust high-delta m icrostructured fiber. In the waist region of the taper, the core mode is ti ghtly confined by the air holes and exhibits properties similar to a high-d elta waveguide such as enhanced peak intensity and widely flattened anomalo us dispersion. We exploit these properties to generate tunable self-frequen cy shifting Raman solitons over the communications window from 1.3 mum to 1 .65 mum, with over 60% conversion efficiency, These fiber devices are pract ical for several reasons: they can he fusion spliced to standard single-mod e fibers with relatively low loss, they are mechanically strong, due to the supporting cladding, and because the mode is isolated from the surrounding air interface, they can potentially be recoated allowing for packaging.