Tight buffer for hollow core fibers

Abstract

An optical fiber cable comprises at least one hollow-core fiber having a tight buffer formed around the hollow-core fiber. The tight buffer has a multi-layer construction whereby an inner layer is tightly formed around an outer surface of the hollow-core fiber and an outer layer is tightly formed around the inner layer. The inner layer is formed of a soft material having a low elastic modulus, whereas the outer layer is formed of a material having a higher elastic modulus than the inner layer.

Description

Title: TIGHT BUFFER FOR HOLLOW CORE FIBERSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Provisional Application No. 63 / 675,765, filed on July 26, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.BACKGRUND

[0002] Optical fiber cables generally include one or more optical fibers that are disposed within a cable jacket. Such optical fiber cables may include any of various additional elements such as strength members, water-blocking elements, buffer tubes, or the like, depending upon an application of the optical fiber cable.

[0003] Conventionally, an optical fiber includes a core, a cladding, and one or more coatings that are applied to the cladding in order to protect the optical fiber from damage or stresses that may induce attenuation of an optical signal that propagates in the core. In a conventional optical fiber, the core is a solid, glass element within which an optical signal will propagate.

[0004] More recently, hollow-core fibers have been developed. Hollow-core fibers have various constructions, but are generally characterized in that an optical signal propagates through non-solid free space in air or a vacuum (i.e., a “hollow core”). Due to the propagation of an optical signal in air or vacuum rather than a solid glass core of a conventional optical fiber (a “solid-core fiber”), the latency of an optical signal propagating in a hollow-core fiber is typically lower than the latency of an optical signal propagating in a solid-core fiber.SUMMARY OF THE DISCLOSURE

[0005] The following is a brief summary of subject matter that is described in greater detail herein. This summary is not intended to be limiting as to the scope of the claims.

[0006] Various technologies pertaining to tight-buffered hollow-core fibers and cables including tight-buffered hollow-core fibers are described herein.

[0007] The above summary presents a simplified summary in order to provide a basic understanding of some aspects of the systems and / or methods discussed herein. This summary is not an extensive overview of the systems and / or methods discussed herein. It is not intendedto identify key or critical elements or to delineate the scope of such systems and / or methods. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.BRIEF DESCRIPTION OF THE DRAWINGS

[0008] The accompanying drawings are included to provide a further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and operation of the various embodiments.

[0009] FIG. 1 depicts an exemplary hollow-core fiber;

[0010] FIG. 2 depicts an exemplary tight-buffered hollow-core fiber;

[0011] FIG. 3 depicts another exemplary tight-buffered hollow-core fiber;

[0012] FIG. 4 depicts an exemplary optical fiber cable that incorporates a tight- buffered hollow-core fiber;

[0013] FIG. 5 depicts still another exemplary optical fiber cable that incorporates a tight-buffered hollow-core fiber;

[0014] FIG. 6 depicts yet another optical fiber cable that incorporates a tight-buffered hollow-core fiber;DETAILED DESCRIPTION

[0015] Various technologies pertaining to tight-buffered hollow-core fibers and cables incorporating tight-buffered hollow core fibers are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more aspects. It may be evident, however, that such aspect(s) may be practiced without these specific details. In other instances, well-known structures and devices may be shown in block diagram form in order to facilitate describing one or more aspects. Further, it is to be understood that functionality that is described as being carried out by certain system components may be performed by multiple components. Similarly, for instance, a component may be configured to perform functionality that is described as being carried out by multiple components.

[0016] Moreover, the term “or” is intended to mean an inclusive “or” rather than anexclusive “or”. That is, unless specified otherwise, or clear from the context, the phrase “X employs A or B” is intended to mean any of the natural inclusive permutations. That is, the phrase “X employs A or B” is satisfied by any of the following instances: X employs A; X employs B; or X employs both A and B. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from the context to be directed to a singular form. Additionally, as used herein, the term “exemplary” is intended to mean serving as an illustration or example of something, and is not intended to indicate a preference. Furthermore, unless otherwise specified or clear from context, ranges disclosed herein (e.g., “between A and B” or “ranging from A to B”) are inclusive of their endpoints.

[0017] While hollow-core fibers may be suitable for transmitting optical signals with lower latency than conventional solid-core fibers, various hollow-core fiber designs may be more susceptible than solid-core fibers to damage and / or stress-induced attenuation. Accordingly, optical fiber cables incorporating hollow-core fibers are subject to different design considerations and constraints than cables that include only solid-core fibers.

[0018] Referring now to Fig. 1, a cross-sectional view of an exemplary hollow-core fiber 100 is illustrated. The hollow-core fiber 100 comprises an outer cladding 102, a plurality of capillary tubes 104, and a hollow core region 106 defined by the plurality of capillary tubes 104. The outer cladding 102 can comprise or consist of a silica-based glass. Moreover, each of the capillary tubes 104 can comprise or consist of a silica-based glass. The capillary tubes 104 are each depicted in the hollow-core fiber 100 as having a plurality of nested capillaries 108, wherein a nested capillary 108 is a tube that is disposed within an interior cavity 110 of its respective capillary tube 104. The nested capillaries 108 can each comprise or consist of a silica-based glass. The hollow-core fiber 100 depicted in Fig. 1 is shown as having six of the capillary tubes 104, but it is to be appreciated that a hollow-core fiber can have various numbers of capillary tubes (e.g., 2, 4, 6, or 8 capillary tubes). Furthermore, the hollow-core fiber 100 depicted in Fig. 1 is shown as having three nested capillaries 108 in each of the capillary tubes 104, but it is to be appreciated that a hollow-core fiber can have various numbers of nested capillaries disposed within a single capillary tube (e.g., 1, 2, 3, 4, or 5 nested capillaries). It is further to be appreciated that in embodiments wherein the hollow-core fiber 100 has a plurality of the nested capillaries 108 within a single capillary tube 104, the nested capillaries 108 within a same capillary tube 104 may be the same size or different sizes.

[0019] In exemplary embodiments, the hollow-core fiber 100 can include one or morecoating layers (not shown) on the exterior surface of the outer cladding 102. In some embodiments, these coatings may be substantially similar to the primary and secondary coatings of conventional solid-core fibers. In further embodiments, one or more of the coatings can be or include a colorant to facilitate identification of the hollow-core fiber from among a group of optical fibers.

[0020] The hollow-core fiber 100 depicted in Fig. 1 is one example of a category of hollow-core fibers that is referred to as an anti-resonant hollow-core fiber. It is to be appreciated, however, that tight-buffered hollow-core fibers and cables described herein that include a hollow-core fiber are not so-limited. For instance, a tight-buffered hollow-core fiber or a cable described herein can incorporate types of hollow-core fibers other than anti-resonant hollow-core fibers to the extent that such fibers exhibit high micro-bend attenuation or high minimum bend radius, as described in greater detail below. In another example, tight-buffered optical fiber or cable described herein can incorporate an anti-resonant hollow-core fiber that has a design differing from that shown in Fig. 1. Various additional aspects relating to hollowcore optical fibers are described in at least United States Patent Application Publication No. 2024 / 0036252, the disclosure of which is incorporated herein by reference.

[0021] Conventional solid-core fibers are commonly offered in a “tight-buffered” configuration in which a polymeric sheath is formed about the solid-core fiber, such that the polymeric sheath is tightly drawn on an outer surface of the optical fiber (i.e., in direct contact with the outer surface of the optical fiber). Such tight-buffer sheaths may be formed of PVC or a low-smoke, zero-halogen (LSZH) polymer composition. The tight-buffer of a conventional solid-core fiber provides robustness in handling and protection to a fiber during installation of an optical connector on the fiber.

[0022] As noted above, hollow-core fibers are subject to greater stress- induced attenuation than solid-core fibers. Thus, tight-buffer sheaths employed with conventional solid-core fibers may be insufficient to prevent undesirable signal attenuation in hollow-core fibers that may result from common deployment environments of an optical fiber cable. Accordingly, technologies described herein are configured provide additional protection to a hollow-core fiber.

[0023] Referring now to Fig. 2, an exemplary tight-buffered hollow-core fiber 200 is illustrated. The tight-buffered hollow-core fiber 200 comprises a hollow-core fiber 202. The hollow-core fiber 202 can be any of various hollow-core fibers such as, but not limited to, thehollow-core fiber 100. The tight-buffered hollow-core fiber 200 further comprises a dual-layer buffer 204 that is drawn tightly around an outer surface 206 of the hollow-core fiber 200 such that the dual-layer buffer 204 is in direct contact with the outer surface 206 of the hollow-core fiber 200. It is to be appreciated that the outer surface 206 of the hollow-core fiber 202 may be an outer surface of a cladding of the hollow-core fiber 202, or an outer surface of one or more coatings of the hollow-core fiber 202.

[0024] The dual-layer buffer 204 comprises an inner layer 208 and an outer layer 210. The inner layer 208 surrounds and is tightly drawn around the outer surface 206 of the hollowcore fiber 100. The outer layer 210 surrounds and is tightly drawn around the inner layer 208. Together, the dual-layer buffer 204 provides resistance to optical signal attenuation in the hollow-core fiber 202 caused by micro-bending.

[0025] The inner layer 208 is a relatively soft layer, having an elastic modulus of 50 MPa to 100 MPa, inclusive. The outer layer 210 is a relatively hard layer, having an elastic modulus of at least 700 MPa. Such a two-layer construction with a soft inner layer and a hard outer layer can provide micro-bend resistance to the hollow-core optical fiber 202 that is sufficient to mitigate micro-bend attenuation that would otherwise impair the utility of the hollow-core fiber 202 in a typical cable installation. In exemplary embodiments, each of the inner layer 208 and the outer layer 210 may be formed from a respective UV-curable acrylate.

[0026] An outer diameter of the tight-buffered hollow-core fiber 200 is the maximum outer dimension of the outer layer 210, and can be any of various diameters such as, but not limited to, about 900 microns, about 750 microns, or about 500 microns.

[0027] Referring now to Fig. 3, another exemplary tight-buffered hollow-core fiber 300 is illustrated. The tight-buffered hollow-core fiber 300 includes a hollow-core fiber 302 and a multi-layer buffer 304 that comprises at least three layers: an inner layer 306, an intermediate layer 308, and an outer polymeric layer 310. Like the tight-buffered hollow-core fiber 200, the inner layer 306 is tightly drawn around an outer surface of the hollow-core fiber 302. The intermediate layer 308 surrounds and is tightly drawn around the inner layer 306. The outer polymeric layer 310 is tightly drawn around the intermediate layer 308.

[0028] The inner layer 306 and the intermediate layer 308 may be formed of respective UV-curable acrylate materials. In exemplary embodiments, the inner layer 306 is a relatively soft layer having a modulus of 50 MPa to 100 MPa, inclusive. In various embodiments, the intermediate layer 308 is a relatively hard layer having a modulus of at least 700 MPa. Theouter polymeric layer 310 may be any of various polymeric materials including, but not limited to, PVC or an LSZH material.

[0029] UV-curable acrylate materials tend to be expensive relative to polymeric materials, including PVC and other LSZH materials. Accordingly, the outer polymeric layer 310 can comprise a relatively large portion of the multi-layer buffer 304. In an exemplary embodiment, the outer polymeric layer 310 has a greater wall thickness than any of the other layers 306, 308 of the buffer 304. In another exemplary embodiment, the outer polymeric layer 310 contributes at least 50% of the wall thickness of the multi-layer buffer 304. In still further embodiments, the outer polymeric layer 310 contributes a greater portion of a cross- sectional area of the buffer 304 looking down a length of the tight-buffered hollow core fiber 300. In yet further embodiments, the outer polymeric layer 310 contributes at least 50% of such cross-sectional area of the buffer 304.

[0030] It is to be appreciated that multi-layer tight buffer constructions described herein may be suitable for use with fibers other than hollow-core fibers. By way of example, 50-micron multimode optical fibers are typically more micro-bend sensitive than single-mode fibers, and 200-micron coated fibers are typically more micro-bend sensitive than 250-micron coated fibers. The technologies described herein could also be applied to such micro-bend sensitive fibers in addition to hollow-core fibers.

[0031] Referring now to Fig. 4, an exemplary optical fiber cable 400 that incorporates a tight-buffered hollow-core fiber is illustrated. The cable 400 includes a jacket 402 that has an inner surface 404 and an outer surface 406. The inner surface 404 of the jacket 402 defines a central bore 408 of the cable 400 within which other elements of the cable 400 are disposed. The outer surface 406 of the jacket 402 defines an outermost surface 410 of the cable 400. The cable jacket 402 can be formed from any of various materials. In various embodiments, the cable jacket 402 can comprise PVC, an LSZH material, polyethylene (PE), or other polymer.

[0032] The cable 400 further includes at least one tight-buffered hollow-core fiber 412 disposed within the central bore. In exemplary embodiments, the tight-buffered hollow-core fiber 412 can be configured in similar manner to any of the tight-buffered hollow-core fibers 200, 300 described herein. It is to be appreciated that in some embodiments, the cable 400 can include at least one solid-core fiber 414 in addition to the hollow-core fiber 412. In other embodiments, the cable 400 can be limited to carrying hollow-core fibers, omitting solid-core fibers.

[0033] The cable 400 can include a tensile strength layer 416 that is configured to provide strength to the cable 400 against tensile loads. In a non-limiting example, the tensile strength layer 416 can be formed from a plurality of tensile yarns (e.g., aramid yams).

[0034] In the exemplary cable 400, the tight-buffered fibers 412, 414 are shown in a configuration wherein free space exists around the tight-buffered fibers 412, 414. In other words, the tensile layer 416 and the tight-buffered fibers 412, 414 do not take up all of the space inside the central bore 408 of the cable.

[0035] Referring now to Fig. 5, another exemplary cable 500 is shown, wherein the cable 500 includes a tight-buffered hollow-core fiber 502 and a cable jacket 504 that is tightly- drawn around the fiber 502. In other words, the cable jacket 504 is in direct contact with an outer surface of the fiber 502 and there is substantially no free space within which the tight- buffered hollow-core fiber 502 can move. The exemplary cable 500 includes a plurality of strength elements 506 that may be, for example, aramid or glass fiber yarns, fiber-reinforced plastic members, or the like. In exemplary embodiments, the strength elements 506 can be embedded in the jacket 504, thereby allowing the jacket 504 to be tightly drawn around the fiber 502.

[0036] Referring now to Fig. 6, another exemplary cable 600 is shown, wherein the cable 600 includes a plurality of tight-buffered fibers 602 arranged in an inner layer 604 and an outer layer 606. Any or all of the tight-buffered fibers 602 can be a tight-buffered hollow core fiber, such as the tight-buffered hollow core fibers 200, 300 described above. One or more of the tight-buffered fibers 602 can be a conventional solid-core fiber. For instance, the cable 600 includes tight-buffered solid-core fiber 608. In the exemplary cable 600 shown in Fig. 6, the inner layer 604 of fibers consists of three tight-buffered fibers 602, whereas the outer layer 606 of fibers consists of 9 tight-buffered fibers 602. However, it is to be understood that a similarly configured cable can have substantially any number of tight-buffered fibers 602 in each of its layers 604, 606. Furthermore, a number of layers of the tight-buffered fibers 602 is not limited to two.

[0037] The inner layer 604 of fibers 602 can be surrounded by a tensile strength layer 610 that comprises a plurality of tensile yarns. The cable 600 can further include a central strength element 612 around which the inner layer 604 of fibers 602 is arranged. The central strength element 612 can be a tensile strength yam, or in some embodiments can be a fiber- reinforced plastic or other composite rod. In various embodiments, the tensile strength layer610 can be replaced by a thin polymeric film that constraints the inner layer 604 of the tight- buffered fibers 502, holding them in contact with one another and / or with the central strength element 612.

[0038] The outer layer 606 of the fibers 602 is arranged around the strength layer 610. Surrounding the outer layer 606 of the fibers 602 is a second strength layer 614. Surrounding the second strength layer 614 is a cable jacket 616 that defines an outer surface 618 of the cable 600.

[0039] In various embodiments, one or more of the layers 604, 606 of fibers 602 can be stranded. However, in other embodiments, either or both of the layers 604, 606 may be lain longitudinally (i.e., not stranded). In one exemplary embodiment, the inner layer 604 can comprise tight-buffered hollow core fibers (e.g., the fibers 200 or 300) that are lain longitudinally. In such exemplary embodiment, the outer layer 606 can be stranded around the inner layer 604. In one aspect, a layer that includes hollow-core fibers is lain longitudinally while a layer that includes conventional solid-core fibers is stranded.

[0040] It is to be appreciated that in any of the cables 400-600, one or more hollowcore fibers can be replaced by solid-core fibers consistent with the present disclosure. In other words, the cables 400-600 may be hybrid cables that include both hollow-core fibers and conventional solid-core fibers.

[0041] What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable modification or alteration of the above systems, devices, or methodologies for purposes of describing the aforementioned aspects, but one of ordinary skill in the art can recognize that many further modifications and permutations of various aspects are possible. For instance, tight-buffered hollow-core fibers described herein can be incorporated into any of various cable designs while remaining consistent with the present disclosure. Accordingly, the described aspects are intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.

Claims

What is claimed is:

1. A tight-buffered hollow-core fiber, comprising: a hollow-core fiber having an outer surface, the hollow-core fiber comprising: a cavity that defines a propagation region within which an optical signal can propagate, the propagation region occupied by a gas or a vacuum; and a cladding that surrounds the cavity; and a multi-layer tight buffer that surrounds the hollow-core fiber, the multi-layer tight buffer comprising: a first layer that surrounds and is in contact with the outer surface of the hollow-core fiber, the first layer having a first modulus of 50 MPa to 100 MPa; and a second layer that surrounds the first layer, the second layer having a second modulus that is greater than the first modulus.

2. The tight-buffered hollow-core fiber of claim 1, wherein the second modulus is at least 700 MPa.

3. The tight-buffered hollow-core fiber of claim 1, further comprising: a third layer that surrounds the second layer, the third layer comprising a polymeric material.

4. The tight-buffer hollow-core fiber of claim 3, wherein the polymeric material comprises polyvinyl chloride (PVC).

5. The tight-buffer hollow-core fiber of claim 3, wherein the polymeric material is a low-smoke, zero-halogen material.

6. The tight-buffer hollow-core fiber of claim 1, wherein at least one of the first layer or the second layer is a UV-cured acrylate material.

7. An optical fiber cable, comprising: a tight-buffered hollow-core fiber having an outer surface, the tight-buffered hollowcore fiber comprising: a cavity that defines a propagation region within which an optical signal can propagate, the propagation region occupied by a gas or a vacuum; a cladding that surrounds the cavity; and a multi-layer tight buffer that surrounds the hollow-core fiber, the multi-layer tight buffer comprising: a first layer that surrounds and is in contact with the outer surface of the hollow-core fiber, the first layer having a first modulus; and a second layer that surrounds the first layer, the second layer having a second modulus that is greater than the first modulus; and a cable jacket having an inner surface that defines a central bore, the tight-buffered hollow-core fiber being disposed within the central bore.

8. The optical fiber cable of claim 7, wherein the tight-buffered hollow-core fiber is a first tight-buffered hollow-core fiber, and wherein the optical fiber cable comprises a plurality of tight-buffered hollow-core fibers that includes the first tight-buffered hollow-core fiber.

9. The optical fiber cable of claim 8, wherein the plurality of tight-buffered hollow-core fibers are arranged in a first layer and a second layer, the second layer surrounding the first layer.

10. The optical fiber cable of claim 8, wherein the plurality of tight-buffered hollow-core fibers are arranged longitudinally.

11. The optical fiber cable of claim 7, further comprising a tight-buffered solid-core fiber having a single-layer polymeric tight buffer.

12. The optical fiber cable of claim 7, wherein the first modulus is 50 MPa to 100 MPa.

13. The optical fiber cable of claim 12, wherein the second modulus is at least 700 MPa.

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