A METHOD OF FIBER PRODUCTION

Abstract

A method of producing a microstructured optical fiber is disclosed. The method includes providing a preform and drawing the preform. The preform has a center axis, a length and a first end and a second end and has at least one longitudinal hole extending lengthwise. The method includes inserting a first end of a pressure tube into the hole of the preform at the first end of the preform and subjecting the hole of the preform to a controlled pressure via the pressure tube during the drawing.

Claims

1. A method of producing a microstructured optical fiber, the method comprising providing a preform and drawing the preform, wherein the preform having a center axis, a length and a first end and a second end and comprises at least one longitudinal hole extending lengthwise, and wherein the method comprises inserting a first end of a pressure tube into said hole of said preform at the first end of the preform and subjecting said hole of said preform to a controlled pressure via said pressure tube during the drawing.

2. The method of claim 1, wherein the method comprises drawing the preform to the microstructured optical fiber in one or more drawing steps, wherein at least one of the drawing steps comprises subjecting said hole of said preform to a controlled pressure via said pressure tube during the drawing.

3. The method of claim 2, wherein the drawing steps comprise a pre-drawing step, preferably the pre-drawing step comprises subjecting said hole of said element to a controlled pressure via said pressure tube during the drawing.

4. The method of claim 2 or claim 3, wherein the drawing steps comprise a final-drawing step, preferably the final-drawing step comprises subjecting said hole of said element to a controlled pressure via said pressure tube during the drawing.

5. The method of any one of the preceding claims, wherein the at least one longitudinal hole is open at the first end of the preform for facilitating insertion of the first end of the pressure tube into said hole.

6. The method of any one of the preceding claims, wherein the at least one longitudinal hole is closed at a distance from the first end of the preform, such as closer to the second end than the first end of the preform, such as at the second end of the preform.

7. The method of any one of the preceding claims, wherein the microstructured optical fiber is drawn from its second end.

8. The method of any one of the preceding claims, wherein at least a pressure tube length section comprising said first end of said pressure tube is inserted into said hole.

9. The method of claim 8, wherein the pressure tube length section is about 50% or less of an entire pressure tube length, wherein the pressure tube length section preferably has a length of from about 1 mm to about 20 cm, such as from about 2 mm to about 5 cm, such as from about 0.5 to about 1 cm.

10. The method of claim 8, wherein the longitudinal hole has a length and the pressure tube length section has a length of at least about 50% of the length of the longitudinal hole, such as at least about 80% of the length of the longitudinal hole, such as at least about 90% of the length of the longitudinal hole, such as substantially the length of the longitudinal hole.

11. The method of claim 8 or claim 10, wherein the method comprises inserting the pressure tube length section into said hole of said preform to provide that the pressure tube length section becomes a part of the preform.

12. The method of any one of claims 8, 10 and 11, wherein the method comprises inserting the pressure tube length section into said hole of said preform and drawing the preform to the microstructured optical fiber comprising at least a part of the pressure tube length section.

13. The method of any one of claims 8 and 10-12, wherein the pressure tube length section is of silica preferably comprising an index-changing dopant and/or active material dopant, preferably the background material for the longitudinal hole is silica, more preferably the pressure tube length section material and the background material for the longitudinal hole differs with respect to presence and or amount of at least one dopant.

14. The method of any one of the preceding claims, wherein said pressure tube or at least said pressure tube length section of said pressure tube has an average outer diameter which is from about 50% up to 100% of an average inner diameter of said hole at said first preform end, such as from about 80% to about 99%, of said average inner diameter of said hole at said preform end, such as at least about 90%, such as at least about 95% of said average inner diameter of said hole at said preform end.

15. The method of any one of the preceding claims, wherein said pressure tube is in gas communication with a pressure source for controlling the pressure of said hole, more preferably said pressure tube is connected to a pressure supply at a supply opening, such as a supply opening at a second end of the pressure tube.

16. The method of any one of the preceding claims, wherein said pressure tube has a supply section which is outside said hole, said supply section is preferably in gas communication with said pressure source for controlling the pressure of said hole, more preferably said pressure tube is connected to said pressure supply at a supply opening, such as a supply opening at the supply section.

17. The method of any one of the preceding claims, wherein said pressure tube is of silica, preferably at least said supply section of said pressure tube has an outer polymer coating, optionally said pressure tube length section is free of polymer coating.

18. The method of any one of the preceding claims, wherein the method comprises regulating the pressure in the pressure tube such that the pressure tube is self-sealing to said longitudinal hole.

19. The method of any one of the preceding claims, wherein the method comprises regulating the pressure in the pressure tube such that the pressure in the pressure tube is higher than a pressure acting on the outer side of the pressure tube.

20. The method of any one of the preceding claims, wherein the preform comprises a plurality of longitudinal holes extending along its length, and wherein the method comprises inserting a first end of respective pressure tubes into each of a plurality of said holes of said preform at the first end of the preform and subjecting said hole of said preform to a controlled pressure via said pressure tubes during the drawing.

21. The method of claim 20, wherein each of said respective pressure tubes is in gas communication with a pressure source for controlling the pressure of said holes.

22. The method of claim 20 or claim 21, wherein each of said respective pressure tubes is in gas communication with a common pressure source for a common controlling of the pressure of said holes.

23. The method of claim 20 or claim 21, wherein each of said respective pressure tubes is in gas communication with respective pressures source for individual or group wise controlling of the pressure of said holes.

24. The method of claim 23, wherein the method comprises adjusting said respective pressures sources to provide the pressure control at respective pressures.

25. The method of any one of the preceding claims, wherein the drawing of said preform comprises drawing of the preform to said microstructured optical fiber in a drawing tower, wherein the preform is subjected to at least one pressure control at its first end section, preferably two or more independently controlled pressure controls at respective pressures.

26. The method of any one of the preceding claims, wherein the preform comprises a plurality of hollow tubes, such as capillary tubes fused together or to another part of the preform, the method comprises inserting a first end of respective pressure tubes into each of said hollow tubes of said preform at the first end of the preform and subjecting said hollow tubes to a controlled pressure via said pressure tubes during the drawing.

27. The method of any one of the preceding claims, wherein the preform comprises an outer cladding hollow tube and a plurality of inner cladding hollow tubes, wherein the inner cladding hollow tubes are arranged inside and fused to the outer cladding hollow tubes, the method comprises inserting a first end of respective pressure tubes into each of said inner cladding hollow tubes of said preform at the first end of the preform and subjecting said hollow tubes to a controlled pressure via said pressure tubes during the drawing.

28. The method of claim 27, wherein said inner cladding hollow tubes are not touching each other, the inner cladding hollow tubes preferably comprise 5, 6, 7 or 8 inner cladding tubes.

29. The method of any one of the preceding claims, wherein the preform is a preform assembly obtained from assembling a preform center element with a length and a first and a second end and at least one preform ring element with a ring shaped wall, and arranging the ring shaped wall to surround said preform center element to form a ring wall preform center interface, wherein the preform assembly has a first end section comprising said first end of said preform center element and said first end of said ring shaped wall, the preform assembly preferably comprises an overcladding tube with a length and a first and a second end and a bore where the ring shaped ring wall is inside said bore of said overcladding tube to form a ring wall overcladding tube interface, wherein the preform assembly has a first end section comprising said first end of said preform center element, said first end of said preform ring element and said first end of said overcladding tube.

30. The method of claim 29, wherein said method comprises subjecting at least one of said of said ring wall preform center interface and said ring wall overcladding tube interface to a reduced pressure during at least a part of the drawing.

31. The method of claim 29 or claim 30, wherein the preform center element comprises said at least one longitudinal hole and the method comprises inserting said first end of said pressure tube into said hole of said preform center element and subjecting said hole of said preform center element to a preform center controlled pressure via said pressure tube during the drawing.

32. The method of claim 31, wherein said at least one longitudinal hole comprises at least a first category hole and at least a second category hole extending in length of the preform center element, said method comprising subjecting said at least one first category hole to a first preform center controlled pressure and subjecting said at least one second category hole to a second preform center controlled pressure during the drawing.

33. The method of any one of claims 29-32, wherein the preform ring element comprises at least one hollow tube with a hole and/or at least one interspace hole extending in length direction of the preform ring element, said method comprising subjecting said at least one hole of said preform ring element to a preform ring element controlled pressure during the drawing, preferably said preform ring element controlled pressure is controlled independently of at least one other controlled pressure during the drawing, such as said preform center controlled pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0079] The above and/or additional objects, features and advantages of the present invention will be further elucidated by the following illustrative and non-limiting description of embodiments of the present invention, with reference to the appended drawings.

[0080] FIG. 1 illustrates a pressure control arrangement of a fiber drawing tower and a part of a preform ready for being drawn to an optical fiber.

[0081] FIG. 2 illustrates another pressure control arrangement of a fiber drawing tower and a part of a preform ready for being drawn to an optical fiber.

[0082] FIG. 3 illustrates a first end of a preform with a plurality of longitudinal holes and where the first ends of the respective pressure tubes are inserted into the respective holes for pressure controlling of the holes during drawing.

[0083] FIG. 4 illustrates a first end of another preform with a plurality of longitudinal holes and where the first ends of the respective pressure tubes are inserted into the respective holes for pressure controlling of the holes during drawing.

[0084] FIG. 5 illustrates an embodiment comprising a first end and second end of a preform about to be drawn.

[0085] The figures are schematic and may be simplified for clarity. Throughout, the same reference numerals are used for identical or corresponding parts.

[0086] Further scope of applicability of the present invention will become apparent from the description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

[0087] FIG. 1 shows a pressure control arrangement comprising a pressure control cap 136 with a pressurization arrangement comprising from top and downwards a first, a second, and a third chamber C1, C2, C3 and with corresponding pressure tube connections P1, P2 and P3. The pressure control cap 136 may have further chambers and corresponding pressure tube connections, if desired e.g. as described in co-pending application PCT/DK2016/050364. The pressure tube connections P1, P2 and P3 may be connected directly or indirectly e.g. with not shown connectors to individual or common pressure supply units for controlling the pressure in the respective chambers, preferably individually from each other.

[0088] A preform 131 a preform e.g. as described above and/or in co-pending application PCT/DK2016/050364 is held in the pressure control cap 136, such that a part comprising the first end 131a of the preform 131 is arranged in the second chamber C2 and a part 132 of the preform 131 at a distance from its first end 131a is arranged in the third chamber C3. The pressure control cap 136 is sealed to a not shown overcladding surrounding the preform 131 to seal off the lowermost chamber, which in the exemplified embodiment is the third chamber. Where the preform 131 is a preform center element, the pressure control arrangement preferably comprises one or more additional chambers for control of holes in the ring element(s) as described above and/or in co-pending application PCT/DK2016/050364.

[0089] The preform 131 comprises a number of secondary holes 131b which terminate at the first end 131a of the preform 131 such that they are in gas communication with the second chamber C2. A number of primary holes of the preform 131 are in gas communication with the first chamber C1 via pressure tubes 134. The secondary holes and the primary holes may be equal or different. The pressure tubes 134here illustrated with two pressure tubes 134 for simplificationare partly inserted into the primary holes such that a pressure tube length section comprising a first end of the respective pressure tubes 134 are inserted into respective holes.

[0090] Seals 137 are provided for sealing off the chambers C1, C2 and C3 from each other.

[0091] During drawing the pressure in the three chambers C1, C2, C3 are controlled via the corresponding pressure tube connections P1, P2 and P3.

[0092] Advantageously the pressure in the third chamber is relatively low, e.g. near vacuum to ensure that the overcladding or an optional ring element surrounding the preform 131 seals tightly onto the preform 131 and preferably fuses to the preform 131. The pressure in the first and the second chambers C1, C2 is advantageously controlled such that the primary holes and the secondary holes 131b of the preform results in holes in the fibers with different cross-section. For example the pressure in the first chamber C1 may be higher than the pressure in the second chamber C2.

[0093] Many other configurations may be applied to provide individual control of respective holes and/or interfaces.

[0094] FIG. 2 is a variation of the embodiment shown in FIG. 1

[0095] FIG. 2 shows a pressure control arrangement comprising a pressure control cap 146 with a pressurization arrangement comprising from top and downwards a common first and second chamber C2 and a third chamber C3. Compared to the embodiment of FIG. 1 the first and second chambers are combined to a common second chamber C2. Two pressure tube connections P1 and P2 are connected to the common chamber C2 and a pressure tube connection P3 is connected to the third chamber C3.

[0096] A preform 141 which may be as the preform 131 as shown in FIG. 1 is held in the pressure control cap 146, such that a part comprising the first end 141a of the preform 131 is arranged in the common chamber C2 and a part 142 of the preform 141 at a distance from its first end 141a is arranged in the third chamber C3.

[0097] The pressure control cap 146 is sealed to a not shown overcladding surrounding the preform 141 to seal off the lowermost chamber, which in the exemplified embodiment is the third chamber e.g. as described for the embodiment of FIG. 1.

[0098] The preform 141 comprises a number of secondary holes 141b which terminate at the first end 141a of the preform 141 such that they are in gas communication with the second chamber C2. A number of primary holes of the preform 141 are in gas communication directly with the pressure tube connection P1 via pressure tubes 144. A seal P1a are arranged to seal off the first pressure tube connection P1 from the common chamber C2, Thereby the pressure in the common chamber C2 is pressure controllable via the second pressure tube connection only.

[0099] The pressure tubes 144here illustrated with two pressure tubes 144 for simplificationare partly inserted into the primary holes such that a pressure tube length section comprising a first end of the respective pressure tubes 144 are inserted into respective holes.

[0100] Seals 147 are provided for sealing off the common chamber C2 from the third chamber C3.

[0101] During drawing the pressure in two chambers C2, C3 are controlled via the corresponding pressure tube connections P2 and P3 and the pressure in the pressure tube in gas communication with the primary holes are controlled via the pressure tube connections P1.

[0102] The preform shown in FIG. 3 comprises a plurality of longitudinal holes 151a,151b. Only the first end (end-facet) 150 of the preform is shown. An innermost ring of holes 151a (primary holes), defines a preform core 152. The remaining holes 151b (secondary holes) are arranged in rings encircling the innermost ring of holes 151a. Pressure tubes 154 are arranged to connect each of the primary holes 151a to a pressure supply for controlling the pressure within the primary holes 151a during drawing. For simplification only three of the pressure tubes 154 are shown. A pressure tube length section 154a inserted in the hole of each pressure tube is advantageously uncoated silica, whereas the remaining part of the pressure tube 154, referred to as the pressure tube supply section is polymer coated silica. The pressure in the secondary holes may advantageously be controlled in a pressure chamber such as shown in FIGS. 1 and 2.

[0103] During drawing the pressure in respectively the primary and the secondary holes 151a, 151b, may advantageously be controlled such that the primary holes 151a in the drawn optical fiber have larger cross-sectional diameter than the secondary holes 151b.

[0104] The preform shown in FIG. 4 is advantageously a preform for a hollow core fiber as described in PCT/DK2016/050460.

[0105] The preform comprises a preform outer cladding region 165 and 7 hollow preform tubes 161a, 161b arranged in a non-touching ring (i.e. the tubes are not touching each other) surrounded by and fused to the preform outer cladding region 165.

[0106] The pressure tubes 164 are arranged to connect each of three of the preform tubes 161a (primary hollow tubes) to a not shown pressure supply for control of the pressure in the primary hollow tubes 161a during drawing. A pressure tube length section 164a inserted into the hole of each primary hollow tubes 161a is advantageously uncoated silica, whereas the remaining part of the pressure tube 164, referred to as the pressure tube supply section is polymer coated silica. The pressure in the secondary hollow tubes 161b may advantageously be controlled in a pressure chamber such as shown in FIGS. 1 and 2.

[0107] The preform 171 shown in FIG. 5 comprises a first end 170 and a second end 173 wherein the second end 173 of the preform is tapered to be ready for being drawn to a fiber. The signs indicate that the preform may have any length.

[0108] The preform 171 comprises a plurality of longitudinal holes 171a. Pressure tubes 174 are inserted into the holesfor the illustration only two pressure tubes 174 are shown, but it should be understood that pressure tubes may be inserted int0 each of the holes 171a. The pressure tube length sections 174a inserted into the holes extends sufficiently long into the holes, e.g. substantially in the entire length of the holes, so that the material of the pressure tube length section will be drawn to become part of the fiber.

[0109] When the drawing is initiated and an increased pressure is applied it the holes 171a via the pressure tubes 174, the pressure tubes will initially expand to the size of the holes 171 and thereby the pressure in the holes 171a may be controlled during the drawing.