Optical fiber ribbon having a hollow core fiber

Abstract

An optical fiber ribbon includes a plurality of optical fibers that includes at least one hollow core fiber. The ribbon further includes a first matrix layer that encapsulates the plurality of optical fibers and maintains the fibers in a planar arrangement. The ribbon further comprises a second matrix layer. The first matrix layer has a first elastic modulus and the second matrix layer has a second elastic modulus. In exemplary embodiments, the second elastic modulus is at least five times greater than the first elastic modulus.

Description

Title: OPTICAL FIBER RIBBON HAVING A HOLLOW CORE FIBERCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Provisional Application No. 63 / 673,336, filed on July 19, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.BACKGROUND

[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 an optical fiber ribbon that includes at least one hollow-core fiber are described herein. In a first example, an optical fiber ribbon includes a plurality of optical fibers that includes at least one hollow-core fiber. The ribbon further includes a first matrix layer that encapsulates the plurality of optical fibers and maintains the fibers in a planar arrangement. The ribbon further comprises a second matrix layer. The firstmatrix layer has a first elastic modulus and the second matrix layer has a second elastic modulus. In exemplary embodiments, the second elastic modulus is at least five times greater than the first elastic modulus.

[0007] In a second example, the optical fiber ribbon of the first example further includes a third matrix layer that at least partially surrounds the second matrix layer, and a fourth matrix layer that at least partially surrounds the third matrix layer. The third matrix layer may have a lowest modulus of the four matrix layers. The fourth matrix layer may have a highest modulus of the four matrix layers, or a modulus approximately equal to the modulus of the second matrix layer.

[0008] In a third example, the optical fiber ribbon of the first example further includes strength members disposed at opposite ends of the ribbon. In various embodiments, the strength members are at least partially encapsulated in either or both of the first and second matrix layers of the optical fiber ribbon.

[0009] In a fourth aspect, the optical fiber ribbon of the second example includers strength members disposed at opposite ends of the ribbon. In various embodiments, the strength members are at least partially encapsulated in one or more of the first, second, third, or fourth matrix layers.

[0010] 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 intended to 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

[0011] 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.

[0012] FIG. 1 depicts an exemplary hollow-core fiber;

[0013] FIG. 2 depicts an exemplary optical fiber ribbon that incorporates a hollowcore fiber;

[0014] FIG. 3 depicts another exemplary optical fiber ribbon that incorporates a hollow-core fiber;

[0015] FIG. 4 depicts yet another exemplary optical fiber ribbon that incorporates a hollow-core fiber;

[0016] FIG. 5 depicts still another exemplary optical fiber ribbon that incorporates a hollow-core fiber;

[0017] FIG. 6 depicts an exemplary optical fiber cable that includes a ribbon having a hollow-core fiber;

[0018] FIG. 7 depicts another exemplary optical fiber cable that includes a ribbon having a hollow-core fiber.DETAILED DESCRIPTION

[0019] Various technologies pertaining to an optical fiber ribbon having at least one hollow-core fiber 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.

[0020] Moreover, the term “or” is intended to mean an inclusive “or” rather than an exclusive “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 andB” or “ranging from A to B”) are inclusive of their endpoints.

[0021] 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.

[0022] 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.

[0023] In exemplary embodiments, the hollow-core fiber 100 can include one or more coating 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.

[0024] 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 optical fiber ribbons and cables described herein that include ahollow-core fiber are not so-limited. For instance, an optical fiber ribbon or 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, an optical fiber ribbon 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 hollow-core optical fibers are described in at least United States Patent Application Publication No. 2024 / 0036252, the disclosure of which is incorporated herein by reference.

[0025] Whereas conventional solid-core fibers may be sufficiently protected by primary and secondary coatings on the fibers themselves, fiber coatings may be insufficient to prevent signal attenuation in hollow-core fibers in common deployment environments of an optical fiber cable. Accordingly, technologies described herein are configured provide additional protection to a hollow-core fiber.

[0026] Referring now to Fig. 2, an exemplary optical fiber ribbon 200 that includes at least one hollow-core fiber is illustrated. The ribbon 200 includes a plurality of optical fibers 202, at least one of which is a hollow-core fiber (e.g., configured similarly to the hollow-core fiber 100). In some embodiments, all of the optical fibers 202 are hollow-core fibers. In other embodiments, one or more of the optical fibers 202 may be a conventional solid-core optical fiber. In such embodiments, the plurality of optical fibers 202 still includes at least one hollowcore fiber. The fibers 202 are arranged in a planar fashion. Stated differently, the fibers 202 of the ribbon are arranged along a common line 203 that extends approximately through the center of each of the fibers 202.

[0027] Each of the optical fibers 202 can include one or more coatings such as, but not limited to, a primary coating, a secondary coating, and / or a color layer. In embodiments wherein the ribbon 200 includes both hollow-core and solid-core fibers, the hollow-core fibers and the solid-core fibers may have different coatings. It is to be appreciated that, as depicted in Fig. 2, an outer extent of each of the fibers 202 is defined by an exterior surface of an outermost coating of such fiber 202.

[0028] The ribbon 200 further includes a first matrix layer 204 and a second matrix layer 206 that are configured to surround the fibers 202 and protect them from stresses that might otherwise cause attenuation of optical signals propagating in the fibers 202. The first matrix layer 204 can be disposed around and abutting the plurality of optical fibers 202. Whilethe fibers 202 are shown in Fig. 2 as touching one another, it is to be appreciated that the fibers 202 can instead be positioned with space therebetween. In such embodiments, each of the fibers 102 is encapsulated in the first matrix layer 204. The second matrix layer 206 coats an exterior of the first matrix layer 204 such that the first matrix layer 204 is entirely surrounded by the second matrix layer 206.

[0029] The first matrix layer 204 and the second matrix layer 206 can each be formed of a different respective material. Exemplary materials that may be used to form the matrix layers 204, 206 include, but are not limited to, UV-curable acrylate materials, thermoplastics, or thermoset materials. Various exemplary materials from which the matrix layers 204, 206 can be formed are disclosed in United States Patent No. 10,175,436, the entirety of which is incorporated herein by reference. However, it is to be understood that the present disclosure is not so-limited.

[0030] The first matrix layer 204 can be a softer layer that has a lower elastic modulus than the second matrix layer 206. Such a two-layer construction with a soft “primary” matrix layer 204 and a hard “secondary” matrix layer 206 can provide micro-bend resistance to the optical fiber ribbon 200 sufficient to mitigate attenuation in hollow-core fibers that are especially micro-bend-sensitive. In exemplary embodiments, the first matrix layer 204 has a elastic modulus of 100 MPa to 200 MPa, 100 MPa to 175 MPa, or 125 MPa to 175 MPa. In these and various other embodiments, the second matrix layer 206 has a elastic modulus of 1000 MPa to 2000 MPa, 1100 MPa to 1800 MPa, or 1200 MPa to 1700 MPa. Various optical fibers display different levels of micro-bend sensitivity. For example, 50-micron multimode fibers are more micro-bend sensitive than single-mode fibers, and 200-micron coated fibers are 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. 3, another exemplary optical fiber ribbon 300 is illustrated. The optical fiber ribbon 300 is configured in similar fashion to the optical fiber ribbon 200, in that the ribbon 300 includes the plurality of optical fibers 202 that includes at least one hollow-core fiber, the first matrix layer 204, and the second matrix layer 206. The ribbon 300 further includes strength members 302 positioned at opposite ends of the planar arrangement of the optical fibers 202. It is expected that many hollow-core fiber designs will exhibit relatively large minimum bending radii prior to structural failure. In other words, it is expected that hollow-core fibers will break or be rendered irreversibly unable to transmit anoptical signal without undue attenuation after being subjected to bends that are commonly tolerated by solid-core fibers today. It is expected that some hollow-core fiber designs will endure sharp bends without sustaining structural damage but display higher than desired attenuation. In both cases, a bend limiting feature in the ribbon design may be used.

[0032] The strength members 302 of the ribbon 300 are configured to provide bending stiffness to the ribbon 302 in order to prevent the ribbon from being bent past a point at which such irreversible failure or increased attenuation of a hollow-core fiber would occur. Thus, the ribbon 300 can prevent a hollow-core fiber in the optical fibers 202 from being rendered unsuitable for optical transmission due to incorrect handling in a factory or installation in the field. In an exemplary embodiment, the strength members 302 are configured such that a minimum bend radius of the ribbon 300 is greater than or equal to 30 mm, greater than or equal to 100 mm, or greater than or equal to 200 mm.

[0033] The strength members 302 can, by way of non-limiting example, be formed of metal, glass, or composite materials such as fiber-reinforced plastic (e.g., aramid-reinforced plastic, or ARP, or glass-reinforced plastic, or GRP, or carbon fiber composites). In these and other embodiments, the strength members 302 are formed as elongate elements that extend along substantially an entirety of the length of the ribbon 300. In one aspect, the strength members 302 may have a circular cross-section, as shown in Fig. 3. However, in other embodiments the strength members 302 may have cross-sections that are non-circular. Regardless of a shape of the cross-section of the strength members 302, a maximum outer dimension of the strength members 302 (shown in Fig. 3 as diameter d) can be selected to be approximately equal to a height h of the ribbon 300, as defined by an outer surface 304 of the outer ribbon matrix layer 206.

[0034] It is to be appreciated that in some embodiments it may be undesirable to size the strength members 302 sufficiently large to enforce a desired minimum bend radius of the ribbon 300. Accordingly, in some embodiments a size of the strength members 302 is selected according to the size of a desired outer profile of the ribbon 300 (e.g., such that the diameter d of the strength members 302 is approximately equal to a height h of the ribbon 300). In such embodiments, the ribbon 300 may be capable of bending past a desired minimum bend radius of the hollow-core fiber included therein. Nevertheless, the strength members 302 can provide resistance to such bending and discourage an installer from handling the ribbon 300 in such a manner that the ribbon 300 will be bent past a minimum bend radius of the hollow-core fiber.

[0035] It is to be appreciated that while the strength members 302 are shown in Fig. 3 as being in contact with at least a portion of each of the matrix layers 204, 206, the strength members 302 may instead be entirely encapsulated within one or the other of the matrix layers 204, 206.

[0036] Fig. 4 depicts another exemplary optical fiber ribbon 400 that includes at least four matrix layers. The optical fiber ribbon 400 includes a plurality of optical fibers 402, at least one of which is a hollow-core fiber. As in the optical ribbon 200, the optical fibers 402 are arranged in a substantially planar manner, with their respective centers substantially aligned along an axis 203.

[0037] The ribbon 400 further comprises a plurality of matrix layers that surround the optical fibers 402. In particular, the ribbon 400 includes at least four matrix layers 404-410 that are collectively configured to protect the fibers 402 from external stresses placed on the ribbon 400 when the ribbon 400 is handled during manufacturing or when the ribbon 400 is disposed within in a cable that is installed in the field. Like the matrix layers 204, 206, the matrix layers 404-410 can each be formed of a respective curable acrylate material, a thermoplastic, or a thermoset polymer material.

[0038] In the embodiment depicted in Fig. 4, the first matrix layer 404 encapsulates the optical fibers 410 such that the fibers 410 are entirely disposed within the first matrix layer 404. In exemplary embodiments, the first matrix layer 404 comprises a curable material that, when cured, becomes substantially rigid such that the optical fibers 402 are held in their planar configuration by the first matrix layer 404. The first matrix layer 404 can be a relatively soft layer with an elastic modulus of 100 MPa to 200 MPa.

[0039] The second matrix layer 406 surrounds the first matrix layer 406 and provides additional protection to the fibers 402. The second matrix layer 406 is a harder layer than the first matrix layer 404. In exemplary embodiments, the second matrix layer has an elastic modulus of 1200 MPa to 1700 MPa.

[0040] Whereas the first matrix layer 404 and the second matrix layer 406 provide a substantial degree of protection to the fibers 402 of the ribbon 400, in some embodiments it may be desirable for the ribbon 400 to have greater resistance to micro-bending attenuation than the first matrix layer 404 and the second matrix layer 406 provide. Thus, the ribbon 400 includes an additional third matrix layer 408 and fourth matrix layer 410.

[0041] The third matrix layer 408 may be another soft layer having an elastic modulusthat is less than the elastic modulus of the second matrix layer 406. The inventors have determined that in a four-layer construction such as that shown in Fig. 4, the elastic modulus of the third matrix layer 408 has a greater effect on micro-bending resistance of the ribbon 400 than the elastic modulus of the first layer 404. Thus, the third matrix layer 408 may be made from a material having an elastic modulus of 40 MPa to 60 MPa, more particularly 45 MPa to 55 MPa, and still more particularly 47.5 to 52.5 MPa. Such low-modulus materials may be expensive relative to a material used to form the first matrix layer 404, which has a higher modulus than the third matrix layer 408. However, the four-layer construction allows a portion of the ribbon 400 to be formed from a lower cost, intermediate-modulus material (in the first matrix layer 404), while retaining some of the benefits of using the low-modulus material of the third matrix layer 408.

[0042] The fourth matrix layer 410 surrounds the third matrix layer 408 and has an elastic modulus that is much greater than the third matrix layer 408. In exemplary embodiments, the fourth matrix layer 410 can have an elastic modulus of 1000 MPa to 2000 MPa, 1100 MPa to 1800 MPa, or 1200 MPa to 1700 MPa. The fourth matrix layer 410 in particular provides resistance to damage to the ribbon 400 from ordinary handling.

[0043] In the embodiment of the ribbon 400 depicted in Fig. 4, each successive layer in the matrix layers 404-410 is shown as completely surrounding and encapsulating the immediately preceding layer. However, it is to be appreciated that in some embodiments, one or more successive layers in the matrix layers 404-410 could instead only partially surround a preceding layer or layers while remaining consistent with the scope of the present disclosure.

[0044] Referring now to Fig. 5, another exemplary optical fiber ribbon 500 that includes at least one hollow-core fiber is illustrated. The optical fiber ribbon 500 is substantially similar in construction to the ribbon 400, in that the ribbon 500 includes the optical fibers 402 and is formed of four successive matrix layers 404-410. The ribbon 500 further includes strength members 502. The exemplary optical fiber ribbon 500 shown in Fig. 5 has one strength member each at opposite ends of the ribbon 500 such that the fibers 402 are disposed in a row extending between the two strength members 502. In similar fashion to the strength members 302 of the ribbon 300, the strength members 502 can prevent the ribbon 500 from being bent past a minimum bend radius of a hollow-core fiber included in the optical fibers 402. Similarly, the strength members 502 may have diameters that are approximately equal to a height of the ribbon 500 so as to give the ribbon 500 a substantially flat top and bottom surface profile.

[0045] Referring now to Fig. 6, an exemplary optical fiber cable 600 that incorporates an optical fiber ribbon having at least one hollow-core fiber is illustrated. The cable 600 comprises a cable jacket 602 that has an exterior surface 604 an interior surface 606. The exterior surface 604 of the jacket 602 can be an outermost layer of the cable 600 such that the exterior surface 604 defines an exterior surface profile of the cable 600. The interior surface 606 defines a central bore 608 that extends along a length of the cable 600. The central bore 608 may have a substantially circular cross section when looking down a length of the cable 600 (e.g., as shown in Fig. 6).

[0046] The cable 600 further includes one or more optical fiber ribbons 610. In the exemplary embodiment depicted in Fig. 6, the cable 600 includes a ribbon stack 612 that is made up of a plurality of the optical fiber ribbons 610. At least one of the optical fiber ribbons 610 is a ribbon having at least one hollow-core fiber. For instance, one or more of the ribbons 610 can be configured according to any of the exemplary ribbons 200, 300, 400, 500 described above. In some embodiments, each of the optical fiber ribbons 610 is a ribbon having at least one hollow-core fiber. In various exemplary embodiments, one or more of the optical fiber ribbons 610 can be a ribbon formed entirely of conventional solid-core optical fibers.

[0047] Generally, the ribbon stack 612 is formed by arrangement of the ribbons 610 one on top of another and substantially aligned with one another. If the ribbons 610 are of the same width, the ribbon stack 612 may have a rectangular cross-section. It is to be appreciated that if a first portion of the ribbons 610 have a first number of optical fibers and a second portion of the ribbons 610 have a second number of optical fibers, the cross-section of the ribbon stack 612 maybe cruciform. In various embodiments, the ribbon stack 612 may be twisted, or stranded, down its length.

[0048] In various embodiments, the ribbon stack 612 can be formed with one or more binding elements (not shown) holding the ribbon stack 612 in place. By way of example, and not limitation, a polymer element can be extruded about the ribbon stack 612. In such embodiments, the polymer element can hold the ribbon stack 612 sufficiently tightly that the ribbons 610 of the stack 612 bend as a single unit, but loosely enough that the ribbons 610 of the stack 612 are nevertheless able to translate longitudinally with respect to one another during bending.

[0049] The ribbon stack 612 can be configured such that at least a topmost ribbon 614 and a bottommost ribbon 616 each include strength elements 617 disposed at opposite ends ofthe respective ribbon 614, 616. By way of example, the top-most ribbon 614 can be one of the ribbons 300, 500 discussed in greater detail above. As used herein, the topmost ribbon 614 and the bottommost ribbon 616 are to be understood as referring to outermost ribbons on opposite sides of the ribbon stack 612, and are not otherwise intended to be limiting as to the position of such ribbons 614, 616 within the cable 600. In some embodiments, each of the optical fiber ribbons 610 can be an optical fiber ribbon that includes strength elements disposed at its ends (e.g., the ribbons 300, 500).

[0050] The ribbon stack 612 may be subject to high compressive stress at its corners as these corners contact the inner surface 606 of the cable jacket 602 during bending and other handling operations. The strength elements 617 of the topmost ribbon 614 and the bottommost ribbon 616 can take up these compressive stresses, thereby preventing such stresses being transferred to optical fibers at the ends of the ribbons 614, 616. As indicated above with respect to the exemplary ribbons 300, 500, the strength elements 617 can further prevent the ribbons 610 of the ribbon stack 612 from being bent past a minimum bend radius of a hollow-core fiber included in the ribbon stack 612.

[0051] The cable 600 can, in exemplary embodiments, further include a cushioning layer 618 that is disposed between the ribbon stack 612 and the interior surface 606 of the cable jacket 602. The cushioning layer 618 is configured to cushion the ribbons 610 such that compressive stresses on the exterior 604 of the cable 600 are not as readily transmitted to the corner fibers of the ribbon stack 612. In a non-limiting example, the cushioning layer 618 can comprise a foam tape, which may be a water-blocking tape, wherein the foam tape is wrapped around the ribbon stack 612. In another example, the cushioning layer 618 can comprise a foam layer that is extruded around the ribbon stack 612 prior to or at the time of extrusion of the cable jacket 602 about the ribbon stack 612.

[0052] It is to be appreciated that in some embodiments, the cable 600 can include one or more additional strength elements (not shown) that may be disposed within the jacket 602 (i.e., embedded in the material of the jacket 602) or disposed within the central bore 608 of the cable. Such elements can be or include ARP or GRP rods, aramid or glass yams, or the like.

[0053] Referring now to Fig. 7, another exemplary cable 700 that includes an optical fiber ribbon having at least one hollow-core fiber is illustrated. The optical fiber cable 700 is configured to mitigate the potential for optical signal attenuation due to stresses on a hollowcore fiber. In particular, the optical fiber cable 700 is configured to avoid corner-fiber stressesthat may result from compression of a ribbon against an interior surface of a cable jacket. Further, the optical fiber cable 700 is designed to ensure that a hollow-core fiber disposed therein maintains a minimum radius of curvature that is greater than its minimum bend radius.

[0054] The optical fiber cable 700 comprises a cable jacket 702 having an interior cavity 704 disposed therein. The cable jacket 702 is formed in a shape that has a major axis 706 and a minor axis 708, such that in exterior profile the cable jacket 702 is wider than it is tall. In exemplary embodiments, the cable jacket 702 is formed as a rectangle with rounded corners 709 disposed on opposite sides of the interior cavity 704 along the major axis 706. The cavity 704 can be rectangular in shape, with a major axis of the cavity 704 aligned along the major axis 706 of the cable 700.

[0055] The optical fiber cable 700 further comprises an optical fiber ribbon 711 that includes a plurality of optical fibers 712. The plurality of optical fibers 712 includes at least one hollow-core fiber. In exemplary embodiments, the ribbon 711 can be or include any of the ribbons 200, 300, 400, 500 described above. The cable 700 may be especially suited to use of the optical fiber ribbons 200, 400, as the cable 700 does not subject the ribbon 711 to the same compressive stresses at its corners as the round cable 600, due at least in part to the rectangular shape of the cavity 704. It is to be appreciated that the cable 700 can include a plurality of additional optical fiber ribbons 711 to form a ribbon stack.

[0056] It is to be understood that the ribbon 711 can have any of various fiber counts such as, but not limited to, 8, 12, 16, 24, 32, 36, or 48 fibers. The ribbon 711 has a height of one fiber. In general, a wider ribbon yields a shorter ribbon stack for a same number of the optical fibers 212. Thus, it may be desirable to employ wide ribbons in the optical fiber cable 200 to maintain a small distance between the optical fibers 212 and a neutral bending axis of the cable 200, which typically yields less attenuation than when the optical fibers 212 are positioned further away from the neutral axis.

[0057] The optical fiber cable 700 further comprises strength elements 710 that are disposed on opposite sides of the cavity 704 along the major axis 706. The strength elements 710 extend along a length of the cable 700 (i.e., looking into the page in Fig. 7). In various exemplary embodiments, the strength elements 710 can be GRP elements, ARP elements, steel wires, etc. Furthermore, while the optical fiber cable 700 is illustrated with two strength elements 710, it is to be appreciated that each of the depicted strength elements 710 can instead comprise a plurality of strength elements. The strength elements 710 provide tensile strengthto the cable 700, but also inhibit the bending of the cable 700 past a minimum bend radius of a hollow-core fiber included in the optical fiber ribbon 700.

[0058] In the embodiment depicted in Fig. 7, a height, A, of the cavity 704 along the minor axis 708 is greater than a diameter, d, of the strength elements 710. Setting h to be greater than d can facilitate access to the fibers 710 by an installer of the cable 700 in the field. For instance, the installer can align a tool for accessing the cavity 704 by cutting of the jacket 702 with one or more of the strength elements 710. However, it is to be appreciated that in other embodiments, the height h of the cavity 704 can be selected to be less than the diameter d of the strength elements 710. In these embodiments, the strength elements 710 can prevent stresses that are applied to the cable 700 during installation from being transmitted to the cavity 704 and a hollow-core fiber in the optical fibers 712. The optical fiber cable 700 is depicted as including foam layers 714, 716 within the cavity 704. In exemplary embodiments, the foam layers 714, 716 are disposed on opposite sides of the cavity 704 along the minor axis 708 such that the optical fibers 712 are disposed between the foam layers 714, 716. The foam layers 714, 716 can provide additional cushioning for the optical fibers 712 during bending of the cable 700. In various embodiments, the foam layers 714, 716 can have a water-blocking material disposed thereon / therein (e.g., SAP powder).

[0059] 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. 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. An optical fiber ribbon, comprising: a plurality of optical fibers that includes at least one hollow-core fiber; a first matrix layer that encapsulates the plurality of optical fibers, wherein the first matrix layer has a first elastic modulus; and a second matrix layer that at least partially surrounds the first matrix layer, the second matrix layer having a second elastic modulus that is at least five times greater than the first elastic modulus.

2. The optical fiber ribbon of claim 1, wherein the first elastic modulus is 100 to 200 MPa, inclusive.

3. The optical fiber ribbon of claim 1, wherein the second elastic modulus is 1000 to 2000 MPa, inclusive.

4. The optical fiber ribbon of claim 1, further comprising: a first strength member; and a second strength member, wherein the first strength member and the second strength member are disposed at opposite ends of the optical fiber ribbon.

5. The optical fiber ribbon of claim 4, wherein the first strength member and the second strength member are configured such that the optical fiber ribbon has a minimum bend radius of greater than or equal to 30 mm.

6. The optical fiber ribbon of claim 4, wherein the first strength member and the second strength member are at least partially encapsulated in one or more of the first matrix layer or the second matrix layer.

7. The optical fiber ribbon of claim 1, further comprising: a third matrix layer that at least partially surrounds the second matrix layer, the third matrix layer having a third elastic modulus; and a fourth matrix layer that at least partially surrounds the third matrix layer, wherein the fourth matrix layer has a fourth elastic modulus that is at least twenty times the third elastic modulus.

8. The optical fiber ribbon of claim 7, wherein the first elastic modulus ranges from 100 MPa to 200 MPa, inclusive, wherein the second elastic modulus ranges from 1000 MPa to 2000 MPa, inclusive, wherein the third elastic modulus ranges from 40 to 60 MPa, and wherein the fourth elastic modulus ranges from 1000 MPa to 2000 MPa.

9. The optical fiber ribbon of claim 7, further comprising: a first strength member at least partially encapsulated in at least one of the matrix layers; and a second strength member at least partially encapsulated in at least one of the matrix layers, wherein the first strength member and the second strength member are disposed at opposite ends of the optical fiber ribbon.

10. An optical fiber cable, comprising: an optical fiber ribbon, comprising: a plurality of optical fibers that includes at least one hollow-core fiber; a first matrix layer that encapsulates the plurality of optical fibers, wherein the first matrix layer has a first elastic modulus; and a second matrix layer that at least partially surrounds the first matrix layer, the second matrix layer having a second elastic modulus that is at least five times greater than the first elastic modulus; and a cable jacket having an interior surface that defines a central bore of the optical fiber cable, the optical fiber ribbon disposed within the central bore.

11. The optical fiber cable of claim 10, wherein the optical fiber ribbon is a first optical fiber ribbon, the optical fiber cable comprising a plurality of optical fiber ribbons arranged in a ribbon stack, the plurality of optical fiber ribbons including the first optical fiber ribbon, wherein the ribbon stack is disposed within the central bore.

12. The optical fiber cable of claim 11, wherein a top-most of the plurality of optical fiber ribbons in the ribbon stack comprises a first strength element and a second strength element arranged on opposite sides of the top-most optical fiber ribbon, such that the first strength element and the second strength element form comers of the ribbon stack.

13. The optical fiber cable of claim 11, wherein each of the plurality of optical fiber ribbons comprises: a respective plurality of optical fibers that includes at least one hollow-core fiber; a respective first matrix layer that encapsulates the respective plurality of optical fibers; and a respective second matrix layer that at least partially surrounds the respective first matrix layer, wherein an elastic modulus of the respective second matrix layer is at least five times greater than an elastic modulus of the respective first matrix layer.

14. The optical fiber cable of claim 11, wherein the ribbon stack is stranded down a length of the optical fiber cable.

15. The optical fiber cable of claim 11, further comprising a foam layer disposed between the interior surface of the cable jacket and the ribbon stack such that the foam layer cushions the ribbon stack from external stresses applied to the optical fiber cable.

16. The optical fiber cable of claim 11, wherein the central bore has a rectangular crosssection.

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