Abstract: The invention relates to a microstructured hollow-core fiber comprising a microstructured hollow core extending along the hollow-core fiber. Said hollow core: has microstructures having at least one first refractive index n; is surrounded by an inner fiber cladding having a refractive index n_inner; and has an outer protective cladding which has a protective cladding refractive index n_outer and which sheathes the inner fiber cladding. The hollow-core fiber is characterized in that: the hollow-core fiber has at least one further cladding which is arranged between the inner fiber cladding and the outer protective cladding so as to sheathe the inner fiber cladding and which has a further refractive index n_w; and the further refractive index n_w is greater than the further refractive index.