Indoor / outdoor optical fiber cable for b2ca burn class

Abstract

An optical fiber cable suitable for indoor or outdoor use and meeting the requirements for a B2ca burn class includes a gel-filled buffer tube having one or more optical fibers disposed therein. The cable further includes a flame-retardant bedding compound that surrounds the buffer tube. Still further, the cable includes a flame-retardant outer jacket that surrounds the bedding compound. The cable is capable of satisfying the requirements of the B2ca burn class while preventing longitudinal migration of the one or more optical fibers in vertical cable installations.

Description

Title: INDOOR / OUTDOOR OPTICAL FIBER CABLE FOR B2CA BURN CLASSRELATED APPLICATIONS

[0001] This application claims priority to United States Provisional Patent Application No. 63 / 555,182, filed on February 19, 2024, and entitled “INDOOR / OUTDOOR OPTICAL FIBER CABLE FOR B2CA BURN CLASS,” the entirety of which is incorporated herein by reference.BACKGROUND

[0002] Optical fiber cables are now commonly used to route signals in data networks, including in-building data networks. Within buildings, optical fibers cables may be routed substantially horizontally (e.g., as in a cable routing tray) or substantially vertically (e.g., as “riser” cables). Furthermore, optical fiber cables employed in buildings are commonly required to meet one or more standards set by government regulations that set forth burn performance requirements (e.g., the Construction Products Regulation (CPR) of the European Union).SUMMARY OF THE DISCLOSURE

[0003] 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.

[0004] Various technologies pertaining to an optical fiber cable that is suitable for use as an indoor riser cable are described herein. In an exemplary embodiment, an optical fiber cable comprises a buffer tube having an optical fiber disposed therein. The optical fiber cable further includes a gel that is disposed within the buffer tube and surrounding at least a portion of the optical fiber. The optical fiber cable further comprises a flame-retardant bedding compound that surrounds the buffer tube. Still further, the optical fiber cable comprises a cable jacket that surrounds the bedding compound, which cable jacket may form an outermost layer of the optical fiber cable. In exemplary embodiments, the cable jacket is formed from a flameretardant composition.

[0005] 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

[0006] 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.

[0007] FIG. 1 depicts an exemplary optical fiber cable;

[0008] FIG. 2 is a flow diagram that illustrates an exemplary methodology for making an optical fiber cable.DETAILED DESCRIPTION

[0009] Various technologies pertaining to an indoor / outdoor optical fiber cable capable of meeting the requirements of the B2ca burn class of standard EN 50399 of the CPR of the European Union 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.

[0010] 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.

[0011] Fig. 1 is a cross-sectional view of an exemplary optical fiber cable 100, taken along a direction perpendicular to a length direction of the cable 100. In other words, the cross- sectional view of the cable 100 illustrated in Fig. 1 looks down a length of the cable 100.

[0012] The optical fiber cable 100 addresses several problems that the inventors have observed in other optical fiber cable designs intended for installation in buildings. In particular, the optical fiber cable 100 simultaneously prevents longitudinal migration of optical fibers when the cable 100 is installed in a vertical configuration (such as extending between floors of a multi-floor building) while meeting the stringent flame-retardant requirements of the B2ca bum class of the EN 50399 standard of the Construction Products Regulation (CPR) of the European Union (EU Regulation No. 305 / 2011) in force as of February 13, 2024. The inventors have observed that cables that include water-blocking yarns inside a buffer tube may be susceptible to buffer tube cracking due to stresses placed on the buffer tube by the waterblocking yarns when such a cable is bent. The inventors have further observed that gel-free cable designs that do not employ water-blocking yarns are susceptible to longitudinal migration of optical fibers when these cables are installed in vertical configurations. Unexpectedly, the inventors observed that the optical fiber cable 100 of the present application was capable of meeting the requirements of the B2ca burn class despite including a waterblocking gel, which is flammable. Thus, the optical fiber cable 100 is configured to include the gel in order to inhibit longitudinal migration of the optical fibers 104 while simultaneously satisfying the requirements of the B2ca bum class.

[0013] The cable 100 comprises a buffer tube 102 having a plurality of optical fibers 104 disposed therein. The exemplary cable 100 is depicted in Fig. 1 as having a plurality of twelve optical fibers 104, however it is to be appreciated that the cable 100 can have substantially any number of optical fibers 104. In non-limiting embodiments, the cable 100 can include 2, 4, 6, 8, 12, or 24 of the optical fibers 104.

[0014] The cable 100 includes a gel 106 disposed within the buffer tube 102. The gel 106 fills the buffer tube 102 along at least a portion of the length of the buffer tube 102. In other words, along at least a portion of the length of the buffer tube 102, the gel 106 completely surrounds the optical fibers 104. In various embodiments, the gel 106 completely fills the buffer tube 102 along the entire length of the cable 100. The gel 106 can inhibit the migration of water along the length of the optical fiber cable 100. In some embodiments, the gel 106 is a thixotropic gel.

[0015] The gel 106, in addition to inhibiting migration of water along the length of the optical fiber cable 100 provides mechanical coupling between the optical fibers 104 and an interior surface of the buffer tube 102. Thus, the gel 106 inhibits longitudinal migration of the fibers 104 when the cable 100 is installed vertically. As noted above, the gel 106 may be highly flammable. Accordingly, other components of the cable 100 are constructed to provide sufficient fire-retardant performance as to offset the tendency of the gel 106 to burn when exposed to heat / flame.

[0016] In various embodiments, the buffer tube 102 can have a two-layer construction. In other words, the buffer tube 102 can include a first layer 108 and a second layer 110, wherein the first layer 108 and the second layer 110 have different material compositions. In such embodiments, the first layer 108 and the second layer 110 of the buffer tube 102 can be coextruded, thereby facilitating adhesion between the layers 108, 110. In a non-limiting exemplary embodiment, the first layer 108 of the buffer tube can be formed from polybutylene terephthalate (PBT) and the second layer 110 can be formed of a polycarbonate (PC). It is to be appreciated, however, that the first layer 108 and the second layer 110 of the buffer tube 102 can be formed of materials other than PBT or PC. It is further to be appreciated that the buffer tube 102 can instead have a single-layer construction such that the buffer tube 102 has a single, substantially uniform material composition.

[0017] The optical fiber cable 100 further comprises a plurality of tensile yarns 112 that are disposed around the buffer tube 102. The tensile yarns 112 can be, for example, soft fiberglass yarns. The yarns 112 can be wrapped around the buffer tube 102 (e.g., helically, or in an S-Z stranding pattern) or can simply extend longitudinally in a substantially straight manner. The yarns 112 provide tensile strength to the optical fiber cable 100, allowing the cable 100 to take tensile loads of at least 500 N without failure. In exemplary embodiments, the yarns 112 comprise a plurality of 7 1200 tex fiberglass yarns. In various embodiments, the yarns 112 can have a water-blocking material, such as a superabsorbent polymer (SAP), applied thereto. In such embodiments, the yarns 112 can prevent migration of water along the length of the cable 100 outside of the buffer tube 102. The cable 100 can omit water-blocking tapes, which are generally formed of highly-flammable materials.

[0018] The optical fiber cable 100 further comprises a bedding compound layer 114. The bedding compound layer 114 is formed from a low-smoke, zero-halogen (LSZH) composition that is highly-filled with one or more flame-retardant additives such as alumina trihydrate (ATH) or magnesium hydroxide (MDH). In exemplary embodiments, the beddingcompound used to form the layer 114 comprises 80% or greater by weight of a flame-retardant filler and 20% or less by weight of a polymer component (e.g., a thermoplastic olefin elastomer or TPO). The bedding compound can further be characterized by a limiting oxygen index (LOI), which is the minimum oxygen concentration of an oxygen / nitrogen atmosphere needed to sustain a flame burning on a sample of a material. In exemplary embodiments, the bedding compound layer 114 is formed from a bedding compound that has a LOI of 40% or greater. With more particularity, the bedding compound layer 114 has a LOI of 40%-80%, or more particularly 50%-70%, or still more particularly 60-65%. One such bedding compound is FM 0474 / 5 sold by Melos GmbH of Melle, Germany.

[0019] In various exemplary embodiments, the bedding compound layer 114 can be characterized by the following properties when subjected to a cone calorimetry measurement with heat flux of 50 kW / m2:

[0020] TABLE 1

[0021] The bedding compound layer 114 generally has poor mechanical properties due to its high levels of flame-retardant fillers. Accordingly, the cable 100 further includes an outer jacket layer 116 that is more mechanically robust than the bedding compound layer 114. The outer jacket layer 116 can be a LSZH material that has a different composition than the bedding compound layer 114. For instance, the outer jacket layer 116 can be formed of a material that comprises a thermoplastic and a flame-retardant filler, but that has a lower level of a flame-retardant filler than the bedding compound layer 114. One such material is Conguard® S 6650 S LDD UV, sold by Condor Compounds GmbH of Braunschweig, Germany.

[0022] The materials used for the bedding compound layer 114 and the outer jacket layer 116 can further be selected to facilitate co-extrusion of the two layers 114, 116, which results in good adhesion between the layers 114, 116 and a mechanically robust cable 100. For instance, the bedding compound used to form the bedding compound layer 114 can be selected to have a sufficiently low viscosity to allow efficient co-extrusion processing of the bedding compound layer 114 and the outer jacket layer 116. In exemplary embodiments, the beddingcompound used for the bedding compound layer 114 can have a Mooney viscosity at 100°C of between 20 and 50 MU, more particularly between 25 and 45 MU, and still more particularly between 30 and 40 MU, as measured with a Mooney viscometer according to DIN 53523.

[0023] In order to allow an installer to easily access the fibers 104 in the field, the cable 100 can include one or more ripcords 118. The ripcords 118 can be configured to include a water-blocking component (e.g., an SAP powder disposed thereon). In other embodiments, the ripcords 118 can be configured not to incorporate a water-blocking component. In general, the ripcords 118 are configured to provide sufficient tensile breaking strength and / or elongation at break to allow the bedding compound layer 114 and the outer jacket layer 116 to be torn by the ripcords 118 when the ripcords 118 are pulled.

[0024] It will be appreciated that the sizes of the various components of the optical fiber cable 100 may have an effect on the bum performance of the cable 100 and its ability to meet the requirements of the B2ca bum class. Accordingly, various dimensions of exemplary embodiments of the cable 100 are set forth below that are sufficient to achieve the B2ca burn class. However, it is to be appreciated that dimensions of the various components of the cable 100 may be varied while remaining consistent with the present disclosure and being capable of achieving the B2ca burn class.

[0025] In one exemplary embodiment, the cable 100 includes greater than or equal to 12 and less than 24 of 250-micron optical fibers 104. In this embodiment, the buffer tube 102 has an outer diameter of less than 2.0 mm, the inner layer 108 of the buffer tube 102 has an inner diameter of about 1.4 mm (e.g., 1.4 mm ±0.05 mm), and the outer layer 110 of the buffer tube 102 has an inner diameter of about 1.69 mm (e.g., 1.69 mm ±0.05 mm). In this same embodiment, the bedding compound layer 114 has a minimum wall thickness of at least 0.7 mm, and the outer jacket layer 116 can have a minimum wall thickness of at least 0.5 mm. The cable 100 can have an outside diameter at an outer surface of the outer jacket layer 116 of about 5.6 mm.

[0026] In another exemplary embodiment, the cable 100 includes between 2 and 8 of 250-micron optical fibers 104, inclusive of endpoints (i.e., such that the cable 100 includes at least 2 and as many as 8 optical fibers 104). In this embodiment, the buffer tube 102 has an outer diameter of less than 2.0 mm, the inner layer 108 of the buffer tube 102 has an inner diameter of about 1.4 mm (e.g., 1.4 mm ±0.05 mm), and the outer layer 110 of the buffer tube 102 has an inner diameter of about 1.69 mm (e.g., 1.69 mm ±0.05 mm). It is to be appreciatedthat the cable 100 as constructed according to the embodiment described in this paragraph will have a greater quantity of the gel 106 than the exemplary embodiment described in the preceding paragraph that includes 12-24 250-micron optical fibers. This is due to the lower number of the optical fibers 104 of the embodiment of the cable 100 described in this paragraph. Thus, when the cable 100 includes between 2 and 8 of the 250-micron optical fibers 104, the bedding compound layer 114 can be configured to have a minimum wall thickness of 1.2 mm. The cable 100 of this embodiment that includes 2-8 of the 250-micron optical fibers 104 can retain a minimum wall thickness of the outer jacket layer of at least 0.5 mm, and can retain the outside diameter of about 5.6 mm.

[0027] In yet another exemplary embodiment, the cable 100 includes greater than or equal to 24 of 250-micron optical fibers 104. In this embodiment, the buffer tube 102 has an outer diameter of less than or equal to about 2.15 mm. The inner layer 108 of the buffer tube 102 has an inner diameter of about 1.6 mm (e.g., 1.6 mm ±0.05 mm), the outer layer 110 of the buffer tube 102 has an inner diameter of about 1.9 mm (e.g., 1.9 mm ±0.05 mm). In this embodiment, the bedding compound layer 114 can have a minimum wall thickness of at least 0.7 mm, and the outer jacket layer 116 can have a minimum wall thickness of at least 0.5 mm. In this embodiment, the cable 100 can have an outside diameter at an outer surface of the outer jacket layer 116 of about 5.7 mm.

[0028] In still another exemplary embodiment, the cable 100 includes between 4 and 24 of 200-micron optical fibers 104, inclusive of endpoints. In this embodiment, the buffer tube 102 has an outside diameter of less than or equal to 1.75 mm. The inner layer 108 of the buffer tube 102 can have an inner diameter of about 1.32 mm (e.g., 1.32 mm ±0.05 mm), and the outer layer 110 of the buffer tube 102 can have an inner diameter of about 1.5 mm (e.g., 1.5 mm ±0.05 mm). The bedding compound layer 114 has a minimum wall thickness of at least 0.7 mm. The outer jacket layer 116 has a minimum wall thickness of at least 0.5 mm. In this embodiment, the cable 100 can have an outside diameter at an outer surface of the outer jacket layer 116 of about 5.4 mm.

[0029] In still yet another exemplary embodiment, the cable 100 includes 2 of 200- micron optical fibers 104, inclusive of endpoints. In this embodiment, the buffer tube 102 has an outside diameter of less than or equal to 1.75 mm. The inner layer 108 of the buffer tube 102 can have an inner diameter of about 1.32 mm (e.g., 1.32 mm ±0.05 mm), and the outer layer 110 of the buffer tube 102 can have an inner diameter of about 1.5 mm (e.g., 1.5 mm ±0.05 mm). However, owing to the smaller number of the optical fibers 104 than theembodiment described in the preceding paragraph (i.e., 2 fibers instead of 4-24 fibers), a minimum wall thickness of the bedding compound layer 114 is increased from 0.7 mm to 1.2 mm to offset the increased proportion of the flammable gel 106. The outer jacket layer 116 can retain the minimum wall thickness of at least 0.5 mm, and an outside diameter of the cable 100 can still be about 5.4 mm.

[0030] Burn testing exhibits high variability due to the unpredictable nature of Thus, in a further exemplary embodiment, the cable 100 includes between 2 and 24 of 200-micron optical fibers 104, inclusive of endpoints, and the cable 100 can have the increased wall thickness of the bedding compound layer 114 of about 1.2 mm. In this embodiment, the buffer tube 102 has an outside diameter of less than or equal to 1.75 mm. The inner layer 108 of the buffer tube 102 can have an inner diameter of about 1.32 mm (e.g., 1.32 mm ±0.05 mm), and the outer layer 110 of the buffer tube 102 can have an inner diameter of about 1.5 mm (e.g., 1.5 mm ±0.05 mm). The outer jacket layer 116 has a minimum wall thickness of at least 0.5 mm. In this embodiment, the cable 100 can have an outside diameter at an outer surface of the outer jacket layer 116 of about 6.4 mm.

[0031] Various optical fiber cables were constructed in accordance with the specific embodiments described above and tested for their mechanical and burn performance. Each of these experimental cables employed K880 thixotropic gel available from Info-Gel LLC of Charlotte, North Carolina as the gel 106, Conguard® S 6650 S LDD UV available from Condor Compounds GmbH as its outer jacket layer 116, and FM 0474 / 5 available from Melos GmbH as its bedding compound layer 114 and was found to meet the requirements of the B2ca burn class. However, it is to be appreciated that these cables and results are merely exemplary, and are not intended to provide an exhaustive characterization of the invention of the present disclosure.

[0032] Fig. 2 illustrates an exemplary methodology 200 relating to manufacture of an indoor / outdoor optical fiber cable capable of meeting the B2ca burn class. While the methodology is shown and described as being a series of acts that are performed in a sequence, it is to be understood and appreciated that the methodology is not limited by the order of the sequence. For example, some acts can occur in a different order than what is described herein. In addition, an act can occur concurrently with another act. Further, in some instances, not all acts may be required to implement a methodology described herein.

[0033] The methodology 200 begins at 202 and at 204 a plurality of optical fibers areprovided. The optical fibers can be any of various types of optical fiber such as, for instance, 200-micron optical fibers or 250-micron optical fibers. It is to be appreciated that the optical fibers can be single-mode fibers, multi-mode fibers, single-core fibers, multi-core fibers, or substantially any other type of fiber that is desirably employed in an indoor / outdoor optical fiber cable.

[0034] At 206, a gel-filled buffer tube is formed around the optical fibers. By way of example, and not limitation, a two-layer buffer tube can be formed around the optical fibers by way of co-extrusion of an inner layer and an outer layer of the buffer tube. In such embodiments, the two layers of the buffer tube can be formed from different materials. In various embodiments, the buffer tube that contains the fibers can subsequently be filled with a gel to obtain the gel-filled buffer tube. In other embodiments, the buffer tube can be formed around the gel and the optical fibers in such a manner that the extrudate that forms the buffer tube surrounds and cools around the gel and the optical fibers, thereby resulting in the gel- filled buffer tube in a single pass.

[0035] At 208, a layer of bedding compound and an outer jacket layer of the optical fiber cable are co-extruded around the buffer tube. By co-extruding the bedding compound and the outer jacket layer, good adhesion between the bedding compound layer and the outer jacket layer is achieved. It is to be appreciated that tensile yarns and / or ripcords can be positioned about the buffer tube prior to co-extrusion of the bedding compound and outer jacket layer at 208. Thus, the yarns and / or ripcords can be disposed beneath or embedded in the co-extruded bedding compound and outer jacket layers. The methodology 200 completes at 210.

[0036] 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 cable, comprising: an optical fiber; a buffer tube, the optical fiber being disposed within the buffer tube; a gel that fills at least a portion of a length of the buffer tube such that the gel surrounds at least a portion of a length of the optical fiber, wherein the gel prevents migration of water in a direction of the length of the buffer tube; a layer of a flame-retardant bedding compound that surrounds the buffer tube; and a cable jacket that surrounds the layer of the flame-retardant bedding compound, wherein the optical fiber cable meets requirements for a B2ca bum class as defined by standard EN 50399 of the Construction Products Regulation (CPR) of the European Union in force as of February 13, 2024.

2. The optical fiber cable of claim 1, wherein the flame-retardant bedding compound comprises a low-smoke zero-halogen (LSZH) material.

3. The optical fiber cable of claim 1, wherein the flame-retardant bedding compound comprises at least 80% by weight of a flame-retardant filler.

4. The optical fiber cable of claim 3, wherein the flame-retardant bedding compound further comprises a thermoplastic olefin elastomer (TPO).

5. The optical fiber cable of claim 1, wherein the flame-retardant bedding compound has a limiting oxygen index (LOI) of 40% or greater.

6. The optical fiber cable of claim 1, wherein the layer of the flame-retardant bedding compound is formed by co-extrusion with the cable jacket such that the layer of the flameretardant bedding compound and the cable jacket exhibit adhesion to one another.

7. The optical fiber cable of claim 1, wherein a wall thickness of the cable jacket is at least 0.5 mm.

8. The optical fiber cable of claim 1, wherein a wall thickness of the layer of the flameretardant bedding compound is at least 0.7 mm.

9. The optical fiber cable of claim 1, wherein a wall thickness of the layer of the flameretardant bedding compound is at least 1.2 mm.

10. The optical fiber cable of claim 1, further comprising a plurality of optical fibers that includes the optical fiber and that are disposed within the buffer tube, the plurality of optical fibers characterized by a fiber diameter of approximately 250 microns, wherein a total number of optical fibers in the optical fiber cable is less than or equal to 12, and wherein an inner diameter of the buffer tube is 1.4 mm ± 0.05 mm.

11. The optical fiber cable of claim 10, wherein an outer diameter of the buffer tube is 1.95 mm ± 0.05 mm.

12. The optical fiber cable of claim 11, wherein an outer diameter of the cable jacket is 5.55 mm ± 0.3 mm.

13. The optical fiber cable of claim 1, further comprising a plurality of more than 12 optical fibers that includes the optical fiber and that are disposed within the buffer tube, the plurality of optical fibers characterized by a fiber diameter of approximately 250 microns, wherein an inner diameter of the buffer tube is 1.6 mm ± 0.05 mm.

14. The optical fiber cable of claim 13, wherein an outer diameter of the buffer tube is 2. 1 mm ± 0.05 mm.

15. The optical fiber cable of claim 14, wherein an outer diameter of the cable jacket is 5.7 mm ± 0.3 mm.

16. The optical fiber cable of claim 1, further comprising a plurality of optical fibers that includes the optical fiber and that are disposed within the buffer tube, the plurality of optical fibers characterized by a fiber diameter of approximately 200 microns, wherein an inner diameter of the buffer tube is 1.32 mm ± 0.05 mm.

17. The optical fiber cable of claim 16, wherein an outer diameter of the buffer tube is 1.7 mm ± 0.05 mm.

18. The optical fiber cable of claim 17, wherein an outer diameter of the cable jacket is 5.40 mm ± 0.3 mm.

19. The optical fiber cable of claim 1, further comprising a plurality of tensile strengthening glass yams that are positioned between an outer surface of the buffer tube and the layer of the flame-retardant bedding compound.

20. The optical fiber cable of claim 1, wherein the buffer tube comprises a first layer and a second layer formed of different materials, the second layer surrounding the first layer.

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