Method for manufacturing a preform for optical fibers

Patent metadata

Field	Value
Publication number	US-11780762-B2
Application number	US-201616081244-A
Country	US
Kind code	B2
Filing date	Mar 3, 2016
Priority date	Mar 3, 2016
Publication date	Oct 10, 2023
Grant date	Oct 10, 2023

Abstract

The present invention relates to a method for manufacturing a preform for optical fibers, which method comprises the sequential steps of: i) deposition of non-vitrified silica layers on the inner surface of a hollow substrate tube; ii) deposition of vitrified silica layers inside the hollow substrate tube on the inner surface of the non-vitrified silica layers deposited in step i); iii) removal of the hollow substrate tube from the vitrified silica layers deposited in step ii) and the non-vitrified silica layers deposited in step i) to obtain a deposited tube; iv) optional collapsing said deposited tube obtained in step iii) to obtain a deposited rod comprising from the periphery to the center at least one inner optical cladding and an optical core; v) preparation of an intermediate layer by the steps of: * deposition of non-vitrified silica layers on the outside surface of the deposited tube obtained in step iii) or deposited rod obtained in step iv) with a flame hydrolysis process in an outer reaction zone using glass-forming precursors, and subsequently; * drying and consolidating said non-vitrified silica layers into a vitrified fluorine-doped silica intermediate cladding layer; and * in case preceding step iv) was omitted collapsing; to provide a solid rod comprising from the periphery to the center the intermediate layer, at least one inner optical cladding and an optical core; wherein a fluorine-comprising gas is used during the deposition and/or drying and/or consolidating and wherein the intermediate layer has a ratio between the outer diameter of the intermediate cladding layer (C) to the outer diameter of the optical core (A) that is at least 3.5; vi) deposition of natural silica on the outside surface of the intermediate cladding layer of the solid rod obtained in step v) by melting natural silica particles in an outer deposition zone to produce an outer cladding whereby a preform is obtained.

First claim

The invention claimed is:

1. A method for manufacturing a preform for optical fibers, comprising the sequential steps of:
i) depositing inner non-vitrified silica layers on the inner surface of a hollow substrate tube by a first inner plasma reaction zone having first reaction conditions, wherein the first inner plasma reaction zone is created in the interior of the hollow substrate tube by means of electromagnetic radiation;
ii) depositing vitrified silica layers inside the hollow substrate tube on the inner surface of the inner non-vitrified silica layers deposited in step i) by a second inner plasma reaction zone having second reaction conditions, wherein the second inner plasma reaction zone is created in the interior of the hollow substrate tube by means of electromagnetic radiation and wherein the vitrified silica layers comprise at least an inner optical cladding layer and an optical core layer;
iii) removing the hollow substrate tube from the vitrified silica layers deposited in step ii) to obtain a deposited tube;
iv) optionally collapsing the deposited tube obtained in step iii) to obtain a deposited rod comprising from its periphery to its center at least one inner optical cladding layer and an optical core;
v) preparing an intermediate cladding layer by the steps of:
depositing outer non-vitrified silica layers on the outside surface of the deposited tube obtained in step iii) or the deposited rod obtained in step iv) with a flame hydrolysis process in an outer reaction zone using one or more glass-forming precursors, and subsequently;
drying and consolidating the outer non-vitrified silica layers into a vitrified fluorine-doped silica intermediate cladding layer; and
in case preceding step iv) was omitted, collapsing the deposited tube with the vitrified intermediate cladding layer;

to provide a solid rod comprising from its periphery to its center an intermediate cladding layer, at least one inner optical cladding layer, and an optical core; wherein a fluorine-comprising gas is used during depositing and/or drying and/or consolidating and wherein the ratio between the outer diameter of the intermediate cladding layer (C), which is formed via outside deposition, and the outer diameter of the optical core (A), which is formed via inside deposition, is at least 3.5; and
vi) depositing natural silica on an outside surface of the intermediate cladding layer of the solid rod obtained in step v) by melting natural silica particles in an outer deposition zone to produce an outer cladding whereby a preform is obtained, wherein particles of natural silica having iron impurities of more than 0 ppm iron and less than 0.5 ppm iron are deposited by gravity at a rate between 30 g/min and 150 g/min from a feed pipe moving in translation parallel to the solid rod;
wherein step ii) comprises depositing one or more layers of vitrified fluorine-doped silica having a refractive index difference with undoped silica of between −1×10 −3 and −10×10 −3 to form at least one inner optical cladding layer; and
wherein the absolute difference in refractive index between the preform's intermediate cladding layer and the preform's outer cladding is between 0 and 1×10 −3 .

2. The method according to claim 1 , wherein the intermediate cladding layer is doped with at least 1100 ppm of fluorine.

3. The method according to claim 1 , wherein the fluorine-comprising gas is used while consolidating the outer non-vitrified layers in step v) and/or wherein the fluorine-comprising gas is selected from the group consisting of SiF 4 , SF 6 , CF 4 , and C 2 F 6 .

4. The method according to claim 1 , wherein the C/A ratio is at least 4.0.

5. The method according to claim 1 , wherein the one or more glass-forming precursors used in step v) are gaseous silicon precursors.

6. The method according to claim 1 , wherein a plasma flame is used to deposit natural silica in step vi).

7. The method according to claim 1 , wherein the fluorine-comprising gas is used during the drying of the outer non-vitrified silica layers deposited in step v).

8. The method according to claim 7 , wherein preparing an intermediate cladding layer in step v) comprises simultaneously drying and doping with fluorine of the outer non-vitrified glass layers by heating the entire deposited tube or deposited rod to a temperature between 1000° C. and 1350° C. and by exposing the deposited tube or deposited rod to an atmosphere containing the fluorine-comprising gas and a chlorine-comprising gas, the content of the fluorine-comprising gas in the atmosphere being 0.01% to 0.50% by volume.

9. The method according to claim 8 , wherein the simultaneously drying and doping with fluorine the outer non-vitrified glass layers is followed by consolidating the outer non-vitrified glass layers at a consolidation temperature of 1500° C. to 1650° C.

10. The method according to claim 1 , comprising drawing the preform to obtain an optical fiber having an optical core, an inner optical cladding, an intermediate cladding, and an outer cladding.

11. The method according to claim 10 , wherein the outer diameter of the optical fiber's optical core is between 8 and 10 micrometers.

12. The method according to claim 10 , wherein the outer diameter of the optical fiber's inner optical cladding is between 16 and 24 micrometers.

13. The method according to claim 10 , wherein the outer diameter of the optical fiber's intermediate cladding layer is between 28 and 40 micrometers.

14. The method according to claim 10 , wherein the optical fiber's outer cladding has a diameter of between 100 and 150 micrometers.

15. The method according to claim 10 , wherein the optical fiber is a single mode optical fiber.

16. The method according to claim 10 , wherein the outer diameter of the optical core is 8.5 micrometers, the outer diameter of the optical fiber's inner optical cladding is 20 micrometers, the outer diameter of the optical fiber's intermediate cladding layer is 34 micrometers, and the diameter of the optical fiber's outer cladding is 125 micrometers.

17. The method according to claim 1 , wherein the one or more glass-forming precursors used in step v) are a tetra silicon halide or a cyclopolydimethyl siloxane having the formula [(CH 3 ) 2 SiO] y wherein y is 4, 5, or 6.

18. The method according to claim 1 , wherein the one or more glass-forming precursors used in step v) include SiCl 4 or octamethylcyclotetrasiloxane (OMCTS).

19. The method according to claim 1 , wherein:
in step ii), the inner optical cladding layer directly surrounds the optical core layer; and
in step v), intermediate cladding layer directly surrounds the inner optical cladding layer such that, within the solid rod, the intermediate cladding's inner diameter is the same as the inner optical cladding's outer diameter and the inner optical cladding's inner diameter is the same as the optical core's outer diameter.

20. The method according to claim 1 , wherein the C/A ratio of at least 3.5 between the outer diameter of the preform's intermediate cladding layer (C) and the outer diameter of the preform's optical core (A) ensures sufficient distance between the preform's optical core and the preform's outer cladding so that in an optical fiber drawn from the preform attenuation does not noticeably increase at a wavelength of 1550 nanometers.

Assignees

• Prysmian Spa

Inventors

• Gonnet Cedric
• Adigrat Antonio
• Cocchini Franco
• Schiaffo Antonio
• Milicevic Igor
• Van Stralen Mattheus Jacobus Nicolaas
• Krabshuis Gertjan

Classifications

• C03B2203/24

  Single mode [SM or monomode] · CPC title

• C03B2203/23

  Double or multiple optical cladding profiles · CPC title

• C03B37/01853

  Thermal after-treatment of preforms, e.g. dehydrating, consolidating, sintering · CPC title

• C03B37/0183 Primary

  for plasma within a tube substrate · CPC title

• C03B37/01291

  by progressive melting, e.g. melting glass powder during delivery to and adhering the so-formed melt to a target or preform, e.g. the Plasma Oxidation Deposition [POD] process · CPC title