Sealing hollow core optical fibers

Abstract

A device sealing a plurality of hollow core optical fibers of an optical fiber cable, a method for sealing hollow core optical fibers of an optical fiber cable, and a kit for sealing a plurality of hollow core optical fibers of an end of an optical fiber cable. In use, the device comprises an endcap, a potting compound contained within the endcap, and an end of an optical fiber cable at least partially contained within the endcap; the plurality of hollow core optical fibers extend into the potting compound.

Description

SEALING HOLLOW CORE OPTICAL FIBERSBACKGROUND

[0001] An optical fiber, also known as an optical fibre, is a glass or plastic waveguide that can transmit light along a length of the optical fiber. An optical fiber may be used in a fiber-optic communication system where data is transmitted over long distances and at a high bandwidth. An optical fiber may take a large number of different forms and generally comprises a core surrounded by a cladding with a coating or buffer applied around an outer surface to mechanically protect the optical fiber and / or aid in light transmission along the optical fiber. An optical fiber may comprise a solid core such as the solid core optical fiber or a hollow core such as the hollow core optical fiber illustrated in FIGs. 1 A and IB. Hollow core optical fiber guides light within a hollow region of the fiber.

[0002] FIG. 1 A illustrates a cross-section of a length of hollow core optical fiber 10 illustrated in FIG. IB. The section of FIG. 1A is taken at the dashed line in FIG. IB. Hollow core optical fiber 10 has an outer surface 11 that is an outer surface of a solid outer wall or cladding 12. Within the solid outer wall or cladding 12 is a hollow core 100. Additional structures within the first hollow core optical fiber extend along the length of the hollow core optical fiber. In FIGs. 1A and IB, there are six inner tubular structures 13 and six intermediate tubular structures 14 extending along the length of the fiber. The inner and intermediate tubular structures 13, 14 are substantially equally placed around the hollow' core 100. Within each respective intermediate tubular structure 14 is an inner tubular structure 13 extending along the length of the hollow core optical fiber. The outer wall 11, inner tubular structure 13, and intermediate structure 14 run substantially parallel to each other along the length of the hollow core optical fiber 10.

[0003] The hollow core 100 is a void filled with a fluid. The fluid may be an inert gas such as argon, nitrogen or atmospheric air. Advantages of hollow core optical fiber over solid core optical fiber are that transmitted light travels faster along hollow core optical fiber (lower latency), higher powers can be transmitted over hollow core optical fiber and that light scatter is reduced in hollow core optical fiber therefore attenuation of light travelling along a fiber length is reduced. FIG. IB illustrates a length of hollow core optical fiber 10 with an unsealed end (at the right side of the figure). An unsealed end may be the result of intentional division of a hollow core optical fiber, or may be due to an unintentional breakage of a hollow core optical fiber due to an external factor. Although an open end may provide a small section of a long length of hollow core optical fiber, itallows contamination of the hollow core from external factors. The external factors may be solid, liquid or gas. For example, if a hollow core optical fiber suffers physical damage either intentionally or unintentionally, water may ingress into the hollow core thereby contaminating the hollow core optical fiber and adversely affecting the performance of the hollow core optical fiber for transmitting light therethrough. A liquid, such as water, may move by capillary action along a structure in a hollow core optical fiber from a site of damage. Solids or gasses within a hollow core will increase the number of scattering points thereby increasing loss in the hollow core optical fiber. Contamination may also increase absorption within the hollow core optical fiber or may cause a change in waveguiding or an anti -resonant condition of the hollow core optical fiber that is detrimental to transmittal of light along the hollow core optical fiber.SUMMARY

[0004] The following presents a simplified summary of the disclosure in order to provide a basic understanding to the reader. This summary is not intended to identify key features or essential features of the claimed subject matter nor is it intended to be used to limit the scope of the claimed subject matter. Its sole purpose is to present a selection of concepts disclosed herein in a simplified form as a prelude to the more detailed description that is presented later.

[0005] The invention relates to a device sealing a plurality of hollow core optical fibers of an optical fiber cable, a method for sealing hollow core optical fibers of an optical fiber cable, and a kit for sealing a plurality of hollow core optical fibers of an end of an optical fiber cable. In use, the device comprises an endcap, a potting compound contained within the endcap, and an end of an optical fiber cable at least partially contained within the endcap; the plurality of hollow core optical fibers extend into the potting compound.

[0006] In a first aspect there is a device sealing a plurality of hollow core optical fibers of an optical fiber cable. The device comprises an endcap, a potting compound contained within the endcap, and an end of an optical fiber cable at least partially contained within the endcap. The plurality of hollow core optical fibers extend into the potting compound.

[0007] In a second aspect there is a method for sealing hollow core optical fibers of an optical fiber cable. The method comprises: adding potting compound to an endcap; inserting into the endcap a plurality of hollow core optical fibers of an optical fiber cable; and curing the potting compound.

[0008] In a third aspect there is a kit for sealing a plurality of hollow core optical fibers of an end of an optical fiber cable. The kit comprises a potting compound and an endcap with an opening sized to receive the optical fiber cable.

[0009] Many of the attendant features will be more readily appreciated as the same becomes better understood by reference to the following detailed description considered in connection with the accompanying drawings.DESCRIPTION OF THE DRAWINGS

[0010] The present description will be better understood from the following detailed description read in light of the accompanying drawings, wherein:FIG. 1 A is a cross-section of a hollow core optical fiber of the prior art.FIG. IB is a length of the hollow core optical fiber of the prior art.FIG. 2A illustrates an optical fiber cable end seal of the prior art.FIG. 2B illustrates a finished optical fiber cable end seal of the prior art.FIGs. 3A to 3E illustrate steps for end sealing an optical fiber cable.FIGs. 4A to 4D illustrate alternative endcap cross sections.FIG. 5 is a flow diagram of a method for end sealing an optical fiber cable.Like reference numerals are used to designate like parts in the accompanying drawings.DETAILED DESCRIPTION

[0011] The detailed description provided below in connection with the appended drawings is intended as a description of the present examples and is not intended to represent the only forms in which the present examples are constructed or utilized. The description sets forth the functions of the examples and the sequence of operations for constructing and operating the examples. However, the same or equivalent functions and sequences may be accomplished by different examples.

[0012] An optical fiber cable may contain multiple hollow core optical fibers therein. Each of the optical fibers should have their respective ends sealed to protect the respective end from damage, stop the sharp end from causing a stabbing injury, and / or to prevent contamination of a hollow core optical fiber.

[0013] FIG. 2A illustrates a hollow core optical fiber cable end seal of the prior art. The optical fiber cable 20 is illustrated as having four optical fibers 21 within the cable 20. Each optical fiber 21 is surrounded by a protective buffer 22. The optical fiber cable 20 includes a strength member 23, which is a component designed to provide mechanical support and enhance tensile strength of the cable 20. The strength member 23, if present, may be made from a glass reinforced plastic or another tensile material andmay extend axially along the cable 20. The cable 20 may also comprise reinforcing fibers 24, such aramid yam or fiberglass, extending along the length of the cable. When prepanng the end seal of the cable 20, the reinforcing fibers 24 are trimmed and tape 25 is used to keep reinforcing fibers away from the ends of optical fibers 21.

[0014] The end of each optical fiber 21 has been cut to length, stripped of its protective buffer 22 and a fusion splicer used to seal the end of the optical fiber 21. With hollow core fibers, the fusion splicer heats the fiber to collapse the external and / or internal structures to prevent contamination of one or more voids within the one or more hollow core fibers. The cuts of the lengths of the respective optical fibers are staggered along a central axis of the cable 20. In turn, each cut optical fiber end is protected using a splice protector, which may be a small stainless-steel rod containing a hot-melt adhesive with a heat shrinkable outer tube. FIG. 2A illustrates how the four optical fibers 21 are cut to different lengths to ensure that the sealed cable end diameter is not substantially increased. Should all optical fibers 21 be cut to a same length, outer circumferences of the four splice protectors will abut each other. As the number of optical fibers 21 in a cable 20 is increased, a diameter of a sealed cable end will increase until it reaches a diameter that is impractical or impossible for feeding the cable 21 through an intended path, which may include feeding it, expelling or impelling it through walls or long channels. During a cable feeding process, a sealed cable end may sustain damage as it can be fed for multiple kilometers though pipes, buildings, etc. An issue with the prior art sealing method is that should staggering of optical fiber lengths be used, a length of a sealed section DI will increase. As DI increases, the difficulty of feeding the sealed cable end increases, and also the likelihood of damage during feeding increases. The prior art method is slow and a cable of four optical fibers can take 45-60 minutes to seal. The problems of the prior art sealing method increase as the number of optical fibers in a cable increases, whereby as cables with up to and greater than 64 hollow core optical fibers come into service, the prior art sealing method will become difficult and ever more impractical. Such a sealed 64 hollow core optical fiber cable would have a hugely bulbous end and would take around 230 to 260 minutes to seal and protect, per cable.

[0015] FIG. 2B illustrates a finished optical fiber cable end seal of the prior art method. The finishing consists of a rubber end cap 27 being placed over the strength member 23 of FIG. 2A, and a heat shrink 28 applied to extend from the rubber end cap 27 to the cable 24 covering all the sealed optical fibers.

[0016] FIGs. 3A to 3E illustrate steps for improved techniques for end sealing an optical fiber cable, which overcome the drawbacks of the prior art optical fiber cable end seal techniques described in connection with FIGs 2A and 2B.

[0017] FIG. 3A illustrates an optical fiber cable with four hollow core optical fibers 32 extending from one end. Each optical fiber is within a protective buffer and has been cut to length D2 extending from the cable 30. In one example, D2 is approximately 50 mm. A number of reinforcing fibers 31 that previously formed part of the cable 30 extend from cable 30. Optionally, the reinforcing fibers 31 are trimmed to ensure that they do not interfere with the longer optical fibers 32. Strength member 33 extends from the end of the cable 30 and is cut to length longer than the optical fibers 32 by length D3. In one example, D3 is approximately 5mm.

[0018] FIG. 3B illustrates the optical fiber cable with a heat shrink 37 applied to surround the trimmed ends of the reinforcing fibers 31. In another example, tape may be applied rather than heat shrink.

[0019] FIG. 3C illustrates a preparation of a hollow cable endcap 34 for receiving the end of the cable 30 of FIG. 3B. A liquid potting compound 35 has been prepared and is poured into the hollow endcap 34. In one example, the endcap 34 is half filled with potting compound 35, however the amount of potting compound required is at least sufficient to cover the ends of the optical fibers 32 after the cable 30 is inserted into the endcap 34. Potting compound 35 may be any liquid material with suitable characteristics. The suitable characteristics include that the potting compound will bond with the material of the optical fibers, the material of the protective buffer of the optical fibers, and the material that forms the endcap 34, which may for example be glass, plastic and steel, respectively. The suitable characteristics include that the potting compound will outgas minimally, and prevent water or gas ingress into the optical fibers 32 once the potting compound has cured. The potting compound 35 may, for example, include materials such as epoxy, silicone, or resin groups. The potting compound may cure hard due to a chemical reaction without further intervention, or heat may be required to be applied to the endcap 34 to heat the potting compound 35. The illustrated steps for end sealing an optical fiber cable do not require specialist or expensive equipment to be used, which means that the steps may be performed in the field by an engineer whenever and wherever required.

[0020] FIG. 3D illustrates the optical fibers 32 and strength member 33 being inserted into the endcap 34, which contains the potting compound.

[0021] FIG. 3E illustrates the result of FIG. 3D and the wrapping of heat shrink 36 around the cable 30 and endcap 34. In one example, the endcap 34 may be heated prior to the application of heat shrink 36 in order to cure the potting compound. Alternatively, no such heating is applied to the endcap 34 directly and only to the heat shrink 36. Heating of the heat shrink 36 may also heat the potting compound thereby curing the potting compound. In other examples, a heat shrink may not be used and another type of protective layer be applied around the endcap 34 and cable 30 to form an environmental protection, such as tape.

[0022] The wrapped cable end illustrated in FIG. 3E has a number of advantages. The potting compound 35 seals the ends of the optical fibers 32 avoiding the need of manual sealing by a fusion splicer or another optical fiber cutting / sealing means. The potting compound 35 may ingress into a hollow core of a hollow core optical fiber placed in the potting compound 35 thereby providing a good seal of the end of the hollow core optical fiber preventing later contamination. An endcap may be made of a variety of materials, however if the endcap is made from a hard material, such as a metal, e.g. steel or aluminum, hard plastic, or composite, e.g. carbon fiber, then the endcap will provide environmental protection from shocks and abrasions if the cable is fed through a building or pipe network. A head of the endcap being of greater diameter than the hollow body of the endcap means that environmental protection wrapped around the hollow body is protected during installation of the cable. The rigid strength member 33 extending longer than the optical fibers 32 ensures that the optical fibers 32 are spaced from the end of the endcap 34 so the optical fibers 32 are held away from the end of the endcap 34 and surrounded by the potting compound 35 so that the optical fibers 32 are properly sealed by the potting compound 35.

[0023] FIGs. 4A to 4D illustrate a number of alternative endcap cross sections. FIG. 4A illustrates the endcap 34 illustrated in FIGs. 3C to 3E, which is made from a single piece of material. The length of D4 should be sufficient to receive all optical fibers 32 and a strength member 33, if present, and to enclose them within the endcap 34. In one example D4 is approximately 60 mm. Endcap opening width D6 should be sufficiently large to receive an end of a cable. In one example D6 is approximately 14.6 mm. Endcap length D5 is the length of D4 plus an additional length for a head of the endcap, which may comprise additional material as this will receive the greatest amount of shocks and damage during a cable feeding process. In one example D5 is approximately 70 mm. Endcap head width D7 is greater than endcap opening width D6 so that the wider endcaphead protects any heat shrink or other protective wrapping partially surrounding the endcap. The endcap has a dome shaped head portion for better shock protection and to facilitate feeding feeding the endcap though tight spaces during cable installation.

[0024] FIG. 4B illustrates an endcap that is formed of two parts: an endcap head 340 and a tubular body portion 341 that abuts the head portion 340. The tubular body 341 may be later fixed to the endcap head by a friction fit, soldering, welding, or gluing.

[0025] FIGs. 4C and 4D illustrate alternative endcap cross sections - both are a blind hole with a tubular length, however the endcap 342 example illustrated in FIG. 4C has rounded comers at a head end, and the endcap 343 example illustrated in FIG. 4D that has square comers.

[0026] FIG. 5 is a flow diagram 50 of a method for end sealing an optical fiber cable. The diagram illustrates seven blocks. Optional features are indicated using blocks formed of dashed lines.

[0027] Block 51 involves cutting the hollow core optical fibers to a predetermined length. The length of the fibers is to fit within an endcap and be less than the depth of the endcap. This ensures that the delicate optical fiber cables are fully protected by the endcap.

[0028] Block 52 involves mixing two parts to form a potting compound. A two- part compound may provide a quicker curing compound reducing the time taken to perform the method 50.

[0029] Block 53 involves adding the potting compound to an endcap. The potting compound is uncured and ready to receive optical fibers.

[0030] Block 54 involves inserting into the endcap a plurality of hollow core optical fibers of an optical fiber cable. The potting compound previously added will seal the hollow core optical fibers and hold them in place. Some potting compound may ingress in the hollow cores of the optical fibers providing a good seal and ensuring there is no further external contamination of the hollow cores from the sealed end.

[0031] Block 55 involves inserting into the endcap a strength member longer than the plurality of hollow core optical fibers. The longer strength member will contact and end of the endcap thereby preventing the shorter optical fibers from doing so. This improves the immersion of the ends of the optical fibers in the potting compound as the optical fibers cannot touch the end of the endcap. In turn, this improves the seal of the optical fibers.

[0032] Block 56 involves curing the potting compound. This may involve a heating step, time and / or a further chemical reaction.

[0033] Block 57 involves adding an environmental protection surrounding ajoin between the endcap and the optical fiber cable. This may be heat shrink, tape or the like. The environmental protection protects the end of the cable from damage, especially if the cable end is being fed through structures.

[0034] A kit for sealing a plurality of hollow core optical fibers of an end of an optical fiber cable may be provided to engineers. The kit may include comprising a potting compound, an endcap with an opening sized to receive an optical fiber cable, and a measurement guide indicating a length that the hollow core optical fibers should be cut for optimal sealing in the endcap. The measurement guide may also indicating a length that a strength member of the optical fiber cable should be cut to. The measurement guide may also include instructions for use that correspond to the methods disclosed herein. The kit may also include a length of environmental protection for applying to ajoin between the endcap and the cable.

[0035] Alternatively or in addition to the other examples described herein, examples include any combination of the following:

[0036] Clause A. A device sealing a plurality of hollow core optical fibers of an optical fiber cable, the device comprising: an endcap; a potting compound contained within the endcap; and an end of an optical fiber cable at least partially contained within the endcap; wherein the plurality of hollow core optical fibers extend into the potting compound.

[0037] Clause B. The device of clause A, wherein a strength member runs along the optical fiber cable; and the strength member extends from the end of the optical fiber cable for a first length greater than a second length the plurality of hollow core optical fibers extend from the end of the optical fiber cable.

[0038] Clause C. The device of clause A or B, wherein an environmental protection surrounds ajoin between the endcap and the optical fiber cable.

[0039] Clause D. The device of any of clauses A to C, wherein the endcap is formed from a metallic material.

[0040] Clause E. The device of any of clauses A to D, wherein the endcap has an opening proximal to the end of the optical fiber cable and a head portion distal from the optical fiber cable; and a first outer circumference of the opening is narrower than a second outer circumference of the head portion.

[0041] Clause F. The device of any of clauses A to E, wherein the endcap is cylindrical with one closed end.

[0042] Clause G. The device of clause F, wherein a depth of the closed end of the endcap is greater than a thickness of a cylindrical wall of the endcap.

[0043] Clause H. The device of clause F, wherein the closed end of the endcap has a convex outer surface.

[0044] Clause I. The device of any of clauses A to H, wherein the potting compound comprises silicone.

[0045] Clause J. A method for sealing hollow core optical fibers of an optical fiber cable, the method comprising: adding potting compound to an endcap; inserting into the endcap a plurality of hollow core optical fibers of an optical fiber cable; and curing the potting compound.

[0046] Clause K. The method of clause J further comprising: cutting the hollow core optical fibers to a predetermined length prior to inserting into the endcap.

[0047] Clause L. The method of clause J or K further comprising: inserting into the endcap a strength member longer than the plurality of hollow core optical fibers.

[0048] Clause M. The method of clause K, wherein the strength member is inserted into the endcap until it contacts an inner end surface of the endcap.

[0049] Clause N. The method of any of clauses J to M further comprising: mixing two parts to form the potting compound.

[0050] Clause O. The method of any of clauses J to N further comprising: heating the potting compound in the endcap.

[0051] Clause P. The method of any of clauses J to O further comprising: adding an environmental protection surrounding a join between the endcap and the optical fiber cable.

[0052] Clause Q. The method of any of clauses J to P, wherein the inserting into the endcap the plurality of hollow core optical fibers of the optical fiber cable includes inserting an end of the optical fiber cable at least partially into the endcap.

[0053] Clause R. The method of any of clauses J to Q, wherein the endcap is cylindrical with one closed end.

[0054] Clause S. A kit for sealing a plurality of hollow core optical fibers of an end of an optical fiber cable, the kit comprising: a potting compound; and an endcap with an opening sized to receive the optical fiber cable.

[0055] Clause T. The kit of clause S further comprising: a measurement guide indicating a length that a plurality of hollow core optical fibers of an optical fiber cable should be cut to.

[0056] Clause V. An optical fiber cable endcap, wherein: the endcap has one open end and one closed end; the endcap open and is sized to receive an end of an optical fiber cable; a first outer circumference of the open end is narrower than a second outer circumference of the closed end; and a depth of the closed end is greater than a thickness of a cylindrical wall at the open end.

[0057] Any range or device value given herein may be extended or altered without losing the effect sought, as will be apparent to the skilled person.

[0058] Although the subject matter has been described in language specific to structural features and / or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

[0059] It will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benefits and advantages. It will further be understood that reference to 'an' item refers to one or more of those items.

[0060] The operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate. Additionally, individual blocks may be deleted from any of the methods without departing from the scope of the subject matter described herein. Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought.

[0061] The term 'comprising' is used herein to mean including the method blocks or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements.

[0062] Additionally, as used in this disclosure, phrases of the form “at least one of an A, a B, or a C,” “at least one of A, B, and C,” and the like, should be interpreted to select at least one from the group that comprises “A, B, and C.” Unless explicitly stated otherwise in connection with a particular instance in this disclosure, this manner of phrasing does not mean “at least one of A, at least one of B, and at least one of C.” Asused in this disclosure, the example “at least one of an A, a B, or a C,” would cover any of the following selections: {A}, {B}, {C}, {A, B}, {A, C}, {B, C}, and {A, B, C}.

[0063] It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art. The above specification, examples and data provide a complete description of the structure and use of examples. Although various examples have been described above with a certain degree of particularity, or with reference to one or more individual examples, those skilled in the art could make numerous alterations to the disclosed examples without departing from the scope of this specification.

Claims

CLAIMS1. A device sealing a plurality of hollow core optical fibers of an optical fiber cable, the device comprising: an endcap; a potting compound contained within the endcap; and an end of an optical fiber cable at least partially contained within the endcap; wherein the plurality of hollow core optical fibers extend into the potting compound.

2. The device of claim 1, wherein a strength member runs along the optical fiber cable; and the strength member extends from the end of the optical fiber cable for a first length greater than a second length the plurality' of hollow core optical fibers extend from the end of the optical fiber cable.

3. The device of claim 1, wherein an environmental protection surrounds a join between the endcap and the optical fiber cable.

4. The device of claim 1, wherein the endcap has an opening at one end proximal to the end of the optical fiber cable and a head portion at another end distal from the optical fiber cable; and a first outer circumference of the opening is narrower than a second outer circumference of the head portion.

5. The device of claim 1, wherein the endcap is cylindrical with one closed end.

6. The device of claim 5, wherein a depth of the closed end of the endcap is greater than a thickness of a cylindrical wall of the endcap.

7. The device of claim 5, wherein the closed end of the endcap has a convex outer surface.

8. A method for sealing hollow core optical fibers of an optical fiber cable, the method comprising: adding a potting compound to an endcap; inserting into the endcap a plurality of hollow core optical fibers of an optical fiber cable; and curing the potting compound.

9. The method of claim 8 further comprising: cutting the hollow core optical fibers to a predetermined length prior to inserting into the endcap.

10. The method of claim 8 further comprising: inserting into the endcap a strength member longer than the plurality of hollow core optical fibers.

11. The method of claim 10, wherein the strength member is inserted into the endcap until it contacts an inner end surface of the endcap.

12. The method of claim 8, wherein the inserting into the endcap the plurality of hollow core optical fibers of the optical fiber cable includes inserting an end of the optical fiber cable at least partially into the endcap.

13. The method of claim 8, wherein the endcap is cylindrical with one closed end.

14. A kit for sealing a plurality of hollow core optical fibers of an end of an optical fiber cable, the kit comprising: a potting compound; and an endcap with an opening sized to receive the optical fiber cable.

15. The kit of claim 14 further comprising: a measurement guide indicating a length that a plurality of hollow core optical fibers of an optical fiber cable should be cut to.

Images