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Summary form only given. Air-silica microstructured fibers (ASMF) incorporate air holes within the cladding region that run along the length of the fiber (Kaiser and Astle, 1974). Recently there has been renewed interest in such fibers because the microstructured region provides extra degrees of freedom in manipulating mode propagation, which can be exploited in a range of different applications (Birks et al, 1997; Ranka et al, 2000; Eggleton et al, 2000; Chandalia et al, 2001). To date, research has primarily focused on understanding the guidance properties of fundamental modes localized in the core region, for example, bend loss, cutoff wavelength, mode field diameter, and dispersion. A broader class of applications for ASMF, which we consider in this paper, is in the design of optical components, such as grating-based filters (Eggleton et al, 2000), and novel tapered fiber devices (Chandalia et al, 2001). In these applications, core mode guidance can be associated with total internal reflection in a high-index doped region (e.g. germanium doped core). The microstructure cladding region is then exploited to manipulate the propagation of higher order cladding modes, and, in the context of tapered fiber devices, ensures a mechanically robust device that can be spliced to standard fiber with low insertion loss, enabling a dramatically efficient nonlinear process including widely tunable Raman soliton generation.