Delivery fiber assembly and a broad band source

A delivery fiber assembly configured for delivering broad band light and comprising a microstructured delivery fiber and a connector member, said delivery fiber having a longitudinal axis, an input end for launching light and a delivery end for delivering light, said delivery fiber comprises a core region and a cladding region surrounding the core region wherein the cladding region comprises a cladding background material having a refractive index Nbg and a plurality of inclusions of solid material having a refractive index up to Ninc and extending in the direction of longitudinal axis of the delivery fiber, wherein Ninc<Nbg and the plurality of inclusions in the cladding region is arranged in a cross-sectional pattern comprising at least two rings of inclusions surrounding the core region, said core region having a diameter up to about 15 μm, said connector member being mounted to said delivery fiber at a delivery end section of the delivery fiber, said delivery fiber defining a bandwidth of about 200 nm or more in which a transmission loss is less than 0.5 dB/m at all wavelengths within the bandwidth.