Optical fiber cooling tube

DETAILED DESCRIPTION The invention provides an optical fiber cooling tube including an internal cavity adapted to have an optical fiber passed through it and a set of injection passages that are distributed along the tube, open into the cavity, and are oriented in a contraflow direction relative to the direction in which the optical fiber moves.
To optimize the quantity of helium injected, in terms of heat exchange with the optical fiber, i.
e.
to replace firstly the air and then the heated helium as soon as possible and as often as possible with cold helium, the structure of the cooling tube includes either or advantageously both of the following features: firstly, proximity of the walls of the cavity to the boundary layer at the location of the injection passages, in order to inject the cold helium more efficiently, and, secondly, an alternating arrangement of injection channels and aspiration channels, all of which are oriented in a contraflow direction relative to the direction of movement of the optical fiber, in order to aspirate the air or heated helium more efficiently, this alternating arrangement being associated with a small number of openings to the outside so that little air enters the cooling tube.
The proposed cooling tube can be either the same length as and more efficient than those of the prior art or shorter and as efficient, or represent a compromise between those two possibilities.
A short cooling tube is advantageous because it reduces the height of the fiber drawing tower.
According to the invention, it is preferable if the cavity has a cross section that is sufficiently narrow at the injection passages for an exterior surface of a boundary layer of gas entrained by the optical fiber when the tube is in use to be closer to the cavity walls than to an exterior surface of the optical fiber and if the tube further includes a set of aspiration passages that are distributed along the tube, open into the cavity and are oriented in a contraflow direction relative to the direction in which the optical fiber moves, the injection groups, of which there are at least three each comprising one or more injection passages, alternating along the tube with the aspiration groups, of which there are at least three each comprising one or more aspiration passages, the only openings to the outside of the tube being the injection passages, the aspiration passages and the ends of the tube