Method and apparatus for fabrication of metal-coated optical fiber, and the resulting optical fiber

Abstract

Method and apparatus for producing metal-coated optical fiber involves providing a length of optical fiber having a glass fiber with or without a carbon layer surrounded by a liquid-soluble polymeric coating. The optical fiber is passed through a series of solution baths such that the fiber will contact the solution in each bath for a predetermined dwell time, the series of solution baths effecting removal of the polymer coating and subsequent electroless plating of metal on the glass fiber. The optical fiber is collected after metal plating so that a selected quantity of the metal-coated optical fiber is gathered, Preferably, the glass fiber passes through the series of solution baths without contacting anything except for the respective solution in each.

Claims

1. A method for producing metal-coated optical fiber, said method comprising: (a) providing a length of optical fiber having a glass fiber surrounded by a liquid soluble polymeric coating; (b) passing said optical fiber through a series of solution baths such that the glass fiber will contact the solution in each bath for a predetermined dwell time, the series of solution baths effecting removal of said polymer coating and subsequent plating of metal on the glass fiber, wherein the glass fiber passes through the series of solution baths without contacting anything except for the respective solution in each of said solutions baths and wherein each of said solutions baths comprises a vessel having inlet and outlet holes through which said optical fiber passes horizontally without contacting said vessel; and (c) collecting the optical fiber after metal plating so that a selected quantity of said metal-coated optical fiber is gathered.

2. A method as set forth in claim 1, wherein said glass fiber has a carbon layer.

3. A method as set forth in claim 1, wherein said liquid soluble polymeric coating comprises a polymeric material that is removed by a chemical solvent.

4. A method as set forth in claim 3, wherein said polymeric material that is removed by a chemical solvent comprises acrylate.

5. A method as set forth in claim 1, wherein said liquid soluble polymeric coating, comprises a water soluble polymer.

6. A method as set forth in claim 5, wherein said water soluble polymer is selected from the group consisting of sodium polyacrylater, plyacrylamide, polyvinyl alcohol, polyethyleneimine, polyethylene glycol, and polyvinylpyrrolidone.

7. A method as set forth in claim 5, wherein said water soluble polymer of said polymeric coating is removed by water at substantially room temperature.

8. A method as set forth in claim 7, wherein said water soluble polymer of said polymeric coating is removed by said water in no more than approximately one minute dwell time.

9. A method as set forth in claim 1, wherein liquid in said vessel flows out of said inlet and outlet holes for recirculation.

10. A method as set forth in claim 1, wherein liquid is inhibited from flowing out of said inlet outlet holes due to ambient pressure.

11. A method as set forth in claim 1, wherein said liquid soluble polymeric coating is applied to said glass fiber by passing said glass fiber through at least one die containing a polymer solution.

12. A method as set forth in claim 11, wherein said glass fiber is passed vertically through said at least one die.

13. A method as set forth in claim 11, wherein said polymer has a viscosity of 1-5000 mPa-s.

14. A method as set forth in claim 1, wherein the metal is plated on said glass fiber via an electroless plating process.

15. A method as set forth in claim 14, wherein the metal is selected from a group consisting of nickel, copper, gold, silver, and suitable alloys.

16. A method as set forth in claim 1, wherein said length of optical fiber is between one and ten kilometers in length.

17. A method for producing metal-coated optical fiber, said method comprising: (a) providing a length of optical fiber having a glass fiber surrounded by a water soluble polymeric coating; (b) passing said optical fiber through a water bath to remove said polymeric coating; (c) passing said glass fiber through at least one solution bath after removal of said polymeric coating such that the glass fiber will contact solution therein for a predetermined dwell time in order to achieve electroless plating of metal on the glass fiber, wherein the glass fiber passes through the at least one solution bath without contacting anything except for the in the at least one solution bath and wherein the at least one solution bath comprises a vessel having inlet and outlet holes through which said optical fiber passes horizontally without contacting said vessel; and (d) collecting the optical fiber after metal plating so that a selected quantity of said metal-coated optical fiber is gathered.

18. A method as set forth in claim 17, wherein said glass fiber has a carbon layer.

19. A. method as set forth in claim 17, wherein said water soluble polymer is selected from the group consisting of sodium polyacrylater, plyacrylamide, polyvinyl alcohol, polyethyleneimine, polyethylene glycol, and polyvinylpyrrolidone.

20. A method as set forth in claim 17, wherein said water soluble polymer of said polymeric coating is removed by water at substantially room temperature.

21. A method as set forth in claim 20, wherein said water soluble polymer of said polymeric coating is removed by said water in no more than approximately one minute dwell time.

22. A method as set forth in claim 17, wherein said water soluble polymeric coating is applied to said glass fiber by passing said glass fiber through at least one die containing a polymer solution.

23. A method as set forth in claim 22, wherein said polymer has a viscosity of 1-5000 mPa-s.

24. A method as set forth in claim 17, wherein the metal is selected from a group consisting of nickel, copper, gold, silver, and suitable alloys.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which:

(2) FIG. 1 is a diagrammatic representation showing a batch plating process of the prior art used to create short lengths of metal-coated optical fiber.

(3) FIG. 2 is a diagrammatic representation showing a continuous coating process of the prior art to coat conventional metal wire.

(4) FIG. 3 is a perspective diagrammatic view of a metal-coated optical fiber with layers cut away.

(5) FIG. 4 illustrates an exemplary process for drawing optical fiber and applying a temporary coating thereto.

(6) FIG. 5 illustrates an exemplary process for coating optical fiber with metal in accordance with an embodiment of the present invention.

(7) FIG. 6 is a diagrammatic representation of a bath arrangement that may be used in the process of FIG. 5 in accordance with an embodiment of the present invention.

(8) FIG. 7 is a diagrammatic representation of a bath arrangement that may be used in the process of FIG. 5 in accordance with another embodiment of the present invention.

(9) Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(10) It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions.

(11) The present invention provides various improvements in metal-coated optical fiber and methods of making the same. In particular, metal plating may be applied along continuous lengths of optical fiber (such as lengths up to ten kilometers) with sufficient mechanical strength along the whole length. According to an important aspect of the present invention, metal-coated optical fibers may be coated by a continuous plating process in which a bare fiber enters into several liquid baths without physical contact with any solid materials.

(12) Referring now to FIG. 3, an exemplary metal-coated fiber 10 is illustrated. Fiber 10 includes a glass fiber having a core 12 and a cladding 14. A metal coating 16 surrounds and contains the cladding/core combination. Metal coating 16 may be formed of any suitable metal which may be applied by electroless plating, such as nickel, copper, gold, silver, or suitable alloys. In accordance with a preferred embodiment, the diameter of the cladding/core combination may often be less than about 200 micron with the metal coating 16 often having a diameter less than about ten micron.

(13) Certain aspects of the present invention involve novel methodology and materials for the temporary protective coating applied during the drawing process. In this regard, FIG. 4 illustrates an exemplary fiber drawing process during which a temporary protective coating is applied. Toward this end, various types of possible temporary coatings are contemplated. One skilled in the art will appreciate that the temporary coating should provide enough protection against handling while being easily removable. Normal accrylate coating may be removed by solvent such as dichlormethane, MEK and acetone. While dichloromethane is good for removing acclylate coating, its use presents certain concerns. MEK and acetone are generally effective but each takes long time to remove coating by dissolving and it is also difficult to remove the coating with only MEK or acetone without mechanical touch. Moreover, MEK and acetone are flammable which also presents concerns.

(14) Another candidate for the temporary coating material is wax. For example, wax having a melting temperature of less than 100 deg. C. might be used because it can be removed with hot water. However, the resulting fiber, even after most of the wax is removed, may not have enough elasticity for handling.

(15) To eliminate these issues, some preferred embodiments of the present invention utilize a water soluble polymer for the temporary coating. The water soluble polymer used for the temporary coating has enough elasticity and gives enough protective coating for handling and mechanical strength. In accordance with exemplary methodology, optical fiber coated with water soluble polymer is paid off and enters into a removing bath. Bare fiber without any polymer thus comes out just before proceeding to the plating baths. The resulting bare fiber preferably goes through several liquid baths without physical contact with any solid materials (only liquid) and its fiber surface is processed in liquids such as cleaning, rinsing, dry, sinsetizing and plating. In particular, the fiber preferably travels through the bath solutions without any physical contact with any hard material until the fiber becomes enough robust with metalic deposition growth.

(16) Water soluble polymer becomes solid when it is dried and it becomes liquid when immersed in water. As for water soluble polymer, sodium polyacrylater, plyacrylamide, polyvinyl alcohol, polyethyleneimine, polyethylene glycol, polyvinylpyrrolidone etc. are applicable. Viscosity of the water solution is preferably controlled to be 1-5000 mPa-s is good for application of fiber coating.

(17) One example of a water soluble polymer believed to be suitable for this purpose is vinyl alcohol copolymer (product name nichigo G-polymer OKS-8049, sold by nippon gohsei). In this regard, FIG. 4 illustrates a vertical fiber drawing process where the fiber 18 is continuously coated with water soluble polymer as a temporary protective coating. First, a water soluble polymer solution is prepared with appropriate viscosity by mixing water with G-polymer. Then, water soluble polymer is applied to normal drawing process (as shown in FIG. 4). In one case, for example, optical fiber glass diameter is 125 micron, drawing speed is around 25 m/min, oven temperature is 200 deg. C. The water soluble polymer may be applied in a double layer coating as shown, yielding a coating thickness of about 9 micron. (The optical fiber may or may not have a carbon layer.) Cured fiber is them taken up into reel 20 in desired lengths of several kilometers or more. Typically, there will be no mechanical damage will occur to the fiber during drawing.

(18) FIG. 5 is a diagrammatic representation of an exemplary process in accordance with the present invention for producing metal-coated optical fiber on a continuous basis. According to this embodiment, the fiber 18 is paid off of reel 20 and first passed through a coating removing bath 22 in a manner that does not contact any hard materials. The coating bath contains a suitable liquid to remove the polymer. For example, if the polymer requires removal by chemical solvent (e.g., accrylate removal by MEK or acetone), bath 22 will contain the appropriate solvent. In the case of water soluble polymer coating, bath 22 contains water to remove the polymer. Fiber 18 remains in contact with the removal liquid for a sufficient dwell time for the particular temperature. For example, with the exemplary water soluble polymer referenced above, the water may be at room temperature (i.e., unheated) with a dwell time of no more than about one minute in order to completely remove the polymer. In the case of chemical solvents for removal of other temporary polymer coatings, the process time for removing may be up to approximately 5 min.

(19) After the temporary protective coating is removed, the fiber passes through a series of baths to achieve electroless metal plating. In this example, the successive baths are cleaning bath 24, activator bath 26, accelerator bath 28, and plating bath 30. As will be explained below, each bath preferably has a configuration similar to the coating removing bath which prevents contact of bare fiber with any hard materials. The solution of each bath depends on metal and plating objectives. According to one example, nickel may be plated as thick as 3 micron using nickel phosphorus solution. One skilled in the art will appreciate that the fiber's duration of transit through the process is set so that the fiber will have sufficient dwell time in each bath. Of course, the geometry of the respective baths also contributes to the dwell time in each. In one example, the following parameters may be used: line speed of 0.1 m/min, cleaning 5 min, activator time of 4 min, accelerator 3 min, and plating time of 13 min at 80 deg. C. After plating in bath 30, the continuous process ends at take-up reel (pulley) 32.

(20) As noted, the fiber 18 passes through each of the baths 22, 24, 26, 28, and 30 without contacting anything other than water or the process liquid. At feed reel (pulley) 20, the fiber will have the temporary polymer coating which prevents contact between the optical fiber glass and the pulley. At take-up pulley 32, the fiber has been sufficiently strengthened by the metal coating in order to contacted again.

(21) FIG. 6 illustrates one configuration of an arrangement that can be used in the process of FIG. 5 to ensure that the optical fiber does not contact anything except the water or process solution (depending on which bath). In this case, fiber 18 passes through exits (i.e., fiber inlet and outlet) of a bath where liquid flows out and below the level of liquid. The bath arrangement includes dual cells, an inner cell (vessel) 40 and an outer cell (vessel) 42. Inner cell 40 contains sufficient liquid such that it flows over from exits at each end (as shown). Outer cell 42 receives the liquid which flows out from inner cell 40 for recirculation. The liquid received by outer cell 42 flows to solution reservoir 44. A slight pulling tension applying to fiber will give straight passing through holes or slits of walls without touching.

(22) As shown, solution in reservoir 44 is pumped up into inner cell 40 to keep the fiber immersed in a liquid of the cell. It will be appreciated that the fiber will have a tendency to sag between pulleys 20 and 32 due to gravity. Because the inlet into inner cell 40 from the pump is located at bottom of the cell, this tends to push the fiber up by the flow of the liquid. The upward force counteracts the sagging due to gravity and prevents the fiber from contacting hard components, such as the bottom or walls of inner cell 40. The fiber's vertical position will preferably be controlled to keep constant against sag by monitoring position and adjusting the flow rate of the incoming solution, if necessary.

(23) In an alternative embodiment, fibers may be passed through wet baths without mechanical contact utilizing pressure difference. For example, the inner cell may be enclosed and the ullage space in the cell evacuated. In such an arrangement, a pressure difference is caused between ambient pressure of the outer cell and the ullage space of the inner cell. As a result, the liquid does not flow out from the exit or inlet holes which are located under the level of liquid. A configuration of this concept is shown in FIG. 7.

(24) One skilled in the art will appreciate that various advantages are achieved by a system configured in accordance with the present invention. Notably:

(25) (1) Bare fiber is coated with metal without any mechanical contact with hard materials such as die or pulleys. The mechanical reliability of produced fiber is not consequently degraded. A long fiber without mechanical defects can thus be produced.

(26) (2) The inlet or outlet size of the bath vessels is large enough for a fiber to pass through compared with the size of a die. The coating thickness is not determined by the size of the hole and is instead determined by the process time. Therefore, a thin metal coating can be achieved without mechanical damage.

(27) (3) A thin metal coating achievable according to the process described herein will not cause significant fiber shrinkage due to thermal contraction because of thin layer and low thermal gap. (Because the process temperature is less than 100 deg. C. in preferred embodiments, low loss fiber is achieved.)

(28) Additional advantages are realized by the use of a water soluble polymer for the temporary coating:

(29) (1) Water soluble polymer is coated well in drawing process as well as thermal cure polymer because liquid polymer becomes solid by drying. Good compatibility with conventional thermal cure polymer coating.

(30) (2) The removing solution is just water. It is safe and easy handling.

(31) (3) Dissolution speed is very high. Typical dissolution speed of 10 micron polymer is within 1 min in room temperature water. Hotter water may be used to achieve faster dissolution times.

(32) While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art without departing from the spirit and scope of the present invention. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention as further described in the appended claims.