The present invention relates to a novel group of cladding and core designs, especially for use in optical fibres, which provides enhanced dispersion compensating properties through waveguiding of higher-order modes. In a first aspect, the present invention relates to an optical fibre comprising: A central region (41) having a centre radius r SUBcentre, max/SUB and an effective refractive index nSUBcentre.eff/SUB A core region (43), having a core radius rSUBcore-max/SUB,a maximum refractive index nSUBcore,max/SUB, and an effective refractive index ncore,eff A cladding region (45, 46) having a cladding radius rciadding,max, a maximum refractive index nSUBclad,max/SUB, an effective refractive index nciad,effand/or a resultant geometrical index nSUBg,clad/SUB In preferred embodiments, the core region and or the cladding region comprise a photonic crystal structure.
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