The present invention relates to a novel group of cladding and core designs, especially for use in optical fibres, which provides enhanced dispersion properties through waveguiding of higher-order modes. In a first aspect, the present invention relates to an optical fibre with a waveguide structure for supporting the transmission of light at a predetermined or operating wavelength λ0, said optical fibre having a longitudinal direction and a cross-section perpendicular to said longitudinal direction, said optical fibre comprising: a central region (41) having a centre axis in said longitudinal direction, said central region extending along and including said centre axis, said central region having an outer periphery with a maximum distance to the centre axis rcentre,max, a minimum refractive index ncentre,min, an effective refractive index ncentre,eff and/or a resultant geometrical index ng,centre, a core region (43) extending along said longitudinal direction and surrounding said central region (41), said core region having an inner periphery that coincides with the outer periphery of the central region, an outer periphery with a maximum distance to the centre axis rcore,max, a maximum refractive index ncore,max, an effective refractive index ncore,eff and/or a resultant geometrical index ng,core, a cladding region (45, 46) extending along said longitudinal direction, said cladding region surrounding and neighbouring said core region (43), said cladding region having an inner periphery that coincides with the outer periphery of the core region, an outer periphery with a maximum distance to a centre axis rcladding,max, a maximum refractive index nclad,max, an effective refractive index nclad,eff and/or a resultant geometrical index ng,clad. Here, it is preferred that ncentre,eff is equal to or lower than nclad,eff and nclad,eff is lower than ncore,eff at the wavelength λ0, and/or it is preferred that ng,centre is equal to or lower than ng,clad and ng,clad is lower than ng,core at the wavelength λ0. In preferred embodiments, the core region and/or the cladding region comprise (micro-)structural features. The invention further relates to a dispersion compensating module comprising and a preform for producing said optical fibres. The invention may e.g. find applications in high capacity, high transmission rate optical communications systems, e.g. WDM-systems.
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