Method for producing an optical fiber having low polarization mode dispersion
View Patent ↗A method for producing an optical fiber having low polarization mode dispersion, by the steps of a) providing an optical fiber perform of glass material; b) heating the glass material of an end portion of the optical fiber perform; c) drawing the heated glass material at a drawing speed V to form an optical fiber, the drawn glass material having a viscous zone; and d) applying to the optical fiber a substantially sinusoidal spin, which is transmitted to the viscous zone, the spin function frequency ν, the viscous zone length L and the drawing speed V being such that both a torsion and at least a 50% detorsion are applied to the viscous zone.
1. A method for producing an optical fiber having low polarization mode dispersion, comprising the steps of
a) providing an optical fiber preform of glass material;
b) heating the glass material of an end portion of the optical fiber preform in a furnace;
c) drawing the heated glass material at a drawing speed V to form an optical fiber, each portion of the drawn glass material having a viscous zone when passing through the furnace, the viscous zone having a viscous zone length L; and
d) applying to the optical fiber a substantially sinusoidal spin, which is transmitted to the viscous zone;
characterized in that the spin function frequency ν, the viscous zone length L and the drawing speed V being such that both a torsion and at least a 50% detorsion are applied to the viscous zone of each portion of the drawn glass material, and a recovery of at least 50% occurs in the optical fiber.
2. The method according to claim 1 , wherein the spin function frequency ν, the viscous zone length L and the drawing speed V are such that 1.2*L≦V/ν≦6.7*L.
3. The method according to claim 1 , wherein the spin function frequency ν, the viscous zone length L and the drawing speed V are such that both a torsion and at least a 60% detorsion are applied to the viscous zone of each portion of the drawn glass material.
4. The method according to claim 3 , wherein the spin function frequency ν, the viscous zone length L and the drawing speed V are such that 1.7*L≦V/ν≦3.3*L.
5. The method according to claim 1 , wherein the spin function frequency ν, spin function amplitude θ 0 and the drawing speed V are such that the maximum applied torsion is at least of 4 turns/meter.
6. The method according to claim 1 , wherein the spin function frequency ν, the spin function amplitude θ 0 and the drawing speed V are such that the maximum frozen-in torsion is no more than 4 turns/meter.
7. The method according to claim 6 , wherein the spin function amplitude θ 0 (in turns) is such that (2V)/(νπ)≦θ 0 ≦(2V)/[νπ(1−R)], wherein V is the drawing speed (in meters/second), ν is the spin function frequency (in Hz), R is the ratio (T appl −T fr )/T appl , T appl is the maximum actually applied torsion and T fr is the maximum frozen-in torsion.