Optical fiber having a multimode core (10) comprising:--a first zone (11),
which is homogeneous, made of a first material, which has a first
refractive index;--a second zone (12) made of at least one second
material, which has a second refractive index, which is less than the
first index, that second zone (12) being peripherally arranged with
respect to the first zone (11), said first and second zones being
configured so that the interface between those zones defines, in a
transverse plane, a contour which has a star shape such that the
multimode transmission characteristics of the fiber are equivalent to
those of a graded-index fiber. Application in dual-core amplifying fibers
or lasers or in transmission fibers for local networks.