Method for processing glass filament
A method of processing glass filament comprises: providing a length of glass filament from which a portion is to be separated from the remainder of the filament; directing energy onto the filament in order to cause a decrease in a width of the filament at a desired location for separation of the portion; and causing relative longitudinal movement between the portion and the remainder of the filament to separate the portion from the remainder of the filament at the desired location.
1 . A method of processing glass filament, comprising:
providing a length of glass filament from which a portion is to be separated from the remainder of the filament, the filament having an internal structure comprising one or more longitudinal lumina;
directing energy, in the form of one or more laser beams, plasma beams, or flames, onto the filament in order to cause a decrease in a width of the filament at a desired location for separation of the portion that is sufficient to cause ablation of the glass of the filament at the desired location, wherein the energy is directed at a non-orthogonal angle to the longitudinal axis of the filament and towards the portion so as to reduce condensation of vapour generated by the ablation inside the lumina in the remainder of the filament; and
moving the portion away from the remainder of the filament to obtain the portion separated from the remainder of the filament, the separated portion forming a cane able to be drawn into an optical fibre.
2 . A method according to claim 1 , further comprising drawing the cane into the optical fibre.
3 . A method according to claim 1 , in which the energy is in the form of one or more laser beams or plasma beams applied to the filament.
4 . A method according to claim 3 , in which the energy is directed to at least one focal spot substantially at the surface of the filament at the desired location.
5 . A method according to claim 1 , in which directing energy onto the filament comprises directing energy onto two or more regions circumferentially disposed around the filament at the desired location.
6 . A method according to claim 1 , further comprising causing relative rotational movement between the filament and the energy while directing the energy onto the filament, in order to direct energy onto a region or regions circumferentially disposed around the filament at the desired location.
7 . A method according to claim 1 , in which directing energy onto the filament causes the width of the filament to decrease to zero at the desired location, thereby separating the portion from the remainder of the filament.
8 . A method according to claim 1 , in which directing energy onto the filament reduces the width of the filament at the desired location to greater than zero, and moving the portion away from the remainder of the filament comprises causing relative longitudinal movement between the portion and the remainder of the filament to separate the portion from the remainder of the filament at the desired location.
9 . A method according to claim 8 , further comprising, during the directing energy, holding the remainder of the filament with a first clamp arrangement at a first position, and holding the portion with a second clamp arrangement at a second position longitudinally spaced from the first position, and causing the relative longitudinal movement by increasing the spacing between the first clamp arrangement and the second clamp arrangement.
10 . A method according to claim 8 , further comprising, during the directing energy, holding one of the remainder of the filament or the portion with a clamp arrangement, and causing the relative longitudinal movement by allowing the portion to move under gravity.
11 . A method according to claim 1 , comprising directing energy onto the filament that is sufficient to cause softening and deformation of the glass of the filament into a necked region at the desired location.
12 . A method according to claim 11 , further comprising applying crimping jaws to the softened glass to aid deformation into the necked region.
13 . A method according to claim 11 , in which deformation of the glass into the necked region comprises collapse of the one or more lumina.
14 . A method according to claim 13 , in which the deformation and optionally also the moving of the portion away from the remainder of the filament cause a width of the necked region to decrease to zero, thereby closing the lumina at the separated end of the portion.
15 . A method according to claim 1 , in which the glass is ablated to form a circumferential slot around the filament at the desired location.
16 . A method according to claim 1 , further comprising removing vapour and/or debris generated by the ablation by providing a flow of air to carry vapour and/or debris away from the filament.
17 . A method according to claim 1 , in which the length of glass filament has been drawn from a glass preform and the method is carried out in a draw tower while the filament is being drawn from the glass preform.
18 . A method according to claim 17 , in which the filament is drawn from the glass preform using a cane puller comprising a pair of opposing rotating belts arranged to grip opposite sides of the filament and pull the filament in a longitudinal direction away from the preform.
19 . A method according to claim 18 , in which the pair of opposing rotating belts are arranged such that the axis of rotation of each belt is orthogonal to the longitudinal direction.
20 . A method according to claim 18 , in which the pair of opposing rotating belts are arranged such that the axes of rotation of the belts are at opposite and substantially equal non-orthogonal angles to the longitudinal direction, in order to cause rotation of the drawn filament about its longitudinal axis.