Adiabatic Coupling in Tapered Air-Silica Microstructured Optical Fiber

The authors investigate adiabatic mode coupling in tapered air-silica microstructured optical fibers and demonstrate a method that allows for efficient coupling into a high-delta microstructured fiber. We taper a fiber that incorporates a germanium-doped core and an inner- cladding comprising a ring of air-holes region down to an outer diameter of 10 microns, resulting int he contraction of fundamental mode from 10 microns to less than 3 microns, with less than 0.15 dB loss. In the waist region this fiber exhibits widely flattened dispersion characteristics and enhanced peak intensity, allowing for dramatic nonlinear interactions. As an example, we exploit these properties to generate tunable self-frequency shifting Raman solitons over the communications window from 1.3 microns to 1.65 microns. These types of fiber devices are interesting for two reasons: they can be fusion spliced to standard single-mode fibers, with relatively low loss, and are mechanically strong due to the supporting cladding.