Method for producing a preform mould for optical fibres

A method for the production of a preform blank for optical fibres, which has a core and an outer jacket of fused silica or doped fused silica, which incorporates the following process stages: preparing a tube (1) as an outer fused silica jacket; inserting at least one porous or loose material element (2) into the fused silica tube; connecting the extremities (4, 6) of the fused silica jacket tube to a gas feed and discharge system; heat-treating the fused silica/porous or loose material element at approximately 1000 DEG C in the gaseous atmosphere which is passed through the porous or loose material element; sealing off one extremity (4) of the fused silica jacket tube; vitrifying the porous or loose material element whilst maintaining a reduced pressure in the fused silica jacket tube and simultaneously drawing into the preform blank whilst shrinking-on the fused silica outer jacket during traversal of a heating section.