A microstructured fiber or photonic crystal fiber is described having a doped solid core region and a cladding region, holes being provided in the cladding region, the fiber having a low hybrid splice loss to conventional fiber as well as being able to be tightly bent due to the microstructured cladding. The cladding region can contain a plurality of holes surrounding and distanced from the core. These holes are preferably located symmetrically around the core and extend longitudinally along the length of fiber. The holes may be two or more D-shaped holes or truncated D-shaped holes arranged symmetrically around the care. In other embodiments, the holes comprise hole structures arranged symmetrically around the core in a ring. The holes may be arranged having the inner side facing the core formed from arcs of a circle, e.g. equal arcs of a circle. Between the arcs circular holes may be provided called capillaries, i.e. smaller holes. According to the present invention, any number of holes may surround the core, preferably three or more. The fiber has low loss at small bending radii.
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