Abstract: A head (10) for laying optical fibers (2) in alternating lay grooves (1A) in a cylindrical core (1), the head comprising a die-holder (11) interconnecting three dies: an inlet die (12); an indexing die (13) including indexing combs; and an insertion die (14); each optical fiber being guided through an orifice (12A) in the inlet die, then through an orifice (13A) in the indexing die, and finally being laid in a groove of the core by the insertion die, said head further including, upstream from the inlet die, a fixed mandrel (20) through which the core passes, said mandrel being constituted by a tube (21) having a front guide (22) disposed at its upstream end with the optical fibers passing through said front guide, said mandrel further including a series of rotating disks (23) located between said front guide and said inlet die.