Patent Description:
The disclosure relates generally to optical communication cables and more particularly to high fiber count optical communication cables with outside diameters configured to fit into ducts of specified dimensions. High fiber count optical communication cables may be used, for example, in hyper data center applications where the demand for fiber counts in a single cable may exceed <NUM>,<NUM> fibers. Yet often the need exists to use existing ducts having small inside diameters for routing of these high fiber density cables. In addition, fiber density inside cables is an important factor in total cost for network installers. Doubling the fiber count in the existing cable diameter, for example, can save more money in installation costs (i.e., not requiring a new duct, not requiring a second cable pull) than the actual cost of the higher density cable.

Today's conventional ribbon cables are based on technologies that have changed very little for nearly twenty years. For example, conventional <NUM> fiber ribbon stacks typically comprise eighteen <NUM> fiber ribbons. As cable prices have decreased over the years, cable installation costs have continued to increase. Accordingly, there is a desire to put more fibers in the same space in order to reduce total installed costs. The trend is toward smaller diameter cables and/or the most fibers possible that can fit inside a given diameter duct space.

Cable suppliers have been working on higher fiber density cable solutions, resulting in, for example, <NUM> fiber cable solutions with cable diameters similar to the <NUM> fiber cable solutions of yesteryear. Some such cable solutions rely on rollable ribbon concepts, which incorporate, for example, intermittent webs lightly tacking the fibers together to create flexible ribbons that can be more easily rolled to conform to high density packing in a cable jacket or duct.

Cable density can be reviewed in terms of jacket outer diameter, in terms of inside the jacket inner diameter, and in terms of inside the subunit diameter. Conventional loose tube cables with <NUM> fiber may have fiber densities of <NUM>% in the jacket outer diameter (i.e., the area ratio of the sum of the areas using the colored fiber diameters divided by the total area of the jacket outer diameter), <NUM>% inside the jacket inner diameter, and <NUM>% inside the subunit (e.g., inside a 'buffer tube' or sheath).

Colored fiber area to 'cable unit' area ratios may be converted to 'fibers per mm2'. Table <NUM> below illustrates this relationship:.

As shown, an area ratio of <NUM>% colored fiber area to cable unit area with <NUM> colored fiber has <NUM> fibers per mm<NUM>, and a similar area ratio with <NUM> colored fiber has <NUM> fibers per mm<NUM>.

Loose fibers (i.e., totally un-connected fibers) have the ability to be packed tightly inside cable units. Some of today's micro cables have extremely high loose fiber densities, such as the Corning 288F MiniXtend® HD cable with <NUM> fiber at a density or area ratio of <NUM>%, the Corning 72F MiniXtend® cable with <NUM> fiber at a density or area ration of <NUM>%, and the Prysmian Group 864F FlexTube® cable with <NUM> fiber at a density or area ratio of <NUM>% inside the subunits. These cables have high densities in the outer jacket density, of <NUM>%, <NUM>% and <NUM>% respectively, versus <NUM>% for conventional loose tube cables. However, single fiber splicing may be very time and labor consuming with loose fiber cables resulting in higher implementation costs compared to cables that allow mass fusion splicing. There is a desire to be able to mass fusion splice twelve fiber (12F) groups that are already aligned in color order within a cable. Loose fiber cables may be ribbonized in the field after cable stripping, however resulting in additional time and cost.

Newer cable designs employ rollable or pliable ribbons, which are typically ribbons having fibers that are intermittently connected with conventional ribbon matrix along the longitudinal length rather than having completely solid ribbon matrix surrounding the individual fibers along the entire longitudinal length. Intermittent connections allow the 12F ribbons to roll up almost like loose fibers versus remaining in a rigid 1Fx12F array. Intermittent connections also maintain the <NUM> fiber color orientation for the mass fusion splice after the rollable ribbon is removed from the cable and flattened.

Attenuation of the fibers inside the cable due to the stresses induced during cable manufacturing and coiling, and due to cable tension and bending during field installation, is a primary concern for these high fiber density rollable ribbon cables. Bending attenuation is characterized as mainly macrobending attenuation, but microbending attenuation can also be significant. Conventional cables having lower densities typically use standard G. D fibers with Mode Field Diameters (MFDs) of <NUM>. In high density cables, as the fiber count increases, the physics of the bending problem - the minimum bend diameter of any one fiber within the cable - may require more bend insensitive fiber with MFDs of <NUM> or lower.

For example, a cable designer may start with G. D fiber in a lower fiber count cable having a lower density ratio, and as fiber count increases, rely on more bend insensitive fiber,.

A2/B2 or even G. B3, to achieve acceptable cabled attenuation values from cable manufacturing and through the rigors of cable installation. If fibers used in a cable have a MFD of < <NUM> microns (e.g., <NUM> or <NUM> microns), this may create a mode-field mismatch. Splicing <NUM> MFD fibers to pre-existing or pre-installed <NUM> MFD fibers may result in the appearance of bad splices to a field technician.

Moreover, identification of 12F ribbons and groups of ribbons in the high fiber count cables may become difficult. Many conventional high density rollable ribbon cables on the market today have no routable subunits to keep groups of ribbons separated and identified once separated from the jacket. Identification is needed at initial install, but also at restoration events and other future network maintenance events, for example during new end-user-customer adds and changes. Upon jacket removal, conventional cables rely on colored binder threads or slotted core structures to identify and/or group sets of rollable ribbons. For example, in certain conventional high fiber count cables, once the jacket is removed, groups of rollable ribbons (e.g., twelve groups of twelve 12F rollable ribbons) may be separately identified by colored binder threads. However, when handling these groups, the binder threads can easily separate and/or unwind from the core, and the identification of that group is immediately lost.

In slotted core cables, upon jacket removal, groups of pliable or rollable ribbons (e.g., 432F or thirty six 12F pliable or rollable ribbons) may be separated or removed from each of the slots. Upon removal from the slot, however, there is no other method within the cable construction to keep the fibers (e.g., 432F) from one slot separately identified from the fibers in the other slots.

For these types of conventional cables, a separately obtained set of parts outside the cable itself must be used and applied to manage the bundles of rollable ribbons until splicing and containment is complete. These additional parts and systems as well as the associated methods of handling and splicing require additional installer time, cost and patience. In addition, during future time of restoration, the separately obtained set of parts must be re-obtained to help keep ribbons and fibers organized once again.

During initial installation and/or future openings of closures or cabinets, the separated and unorganized intermittently connected fibers and ribbons lack protection. Loose fibers between connection points are notorious for catching on anything and everything. Accordingly, field technicians may be instructed to install sleeves or furcation tubes to protect and organize the exposed fibers, adding yet additional material cost as well as time and effort to an installation. Finally, although intermittently connected fiber ribbons may foster 12F mass fusion splicing as compared to loose 12F fiber splicing, the intermittently connected fiber ribbon is not as easy and fast to identify and splice as conventional solid matrix ribbons. Intermittently connected or rollable ribbons must rely on complicated marking schemes, such as ring or tally mark identification, for identification of individual fibers. Rather, solid ribbons allow direct printing onto the solid matrix with legible characters. Additional information like fiber type (e.g., G. D) or fiber diameter (e.g., <NUM> or <NUM>) can be printed in characters on the solid matrix ribbons which is not possible when relying on a tally marking system that is typical of some conventional rollable ribbon high fiber count cables.

Also, while the fiber colors may remain in order, the intermittently connected ribbon must still be manipulated and handled carefully to prepare for splicing, compared to conventional solid matrix ribbons which are more robust.

To enable easier handling for splicing in the field, a high density ribbon stack cable is needed with ribbons that retain at least some of the solid structure of conventional ribbons when compared, for example, to the rollable ribbon solutions of conventional cables.

<CIT> relates to an optical fiber cable including one or more optical fibers surrounded by a buffer tube having a buffer-tube filling coefficient of greater than <NUM>. <CIT> relates to a high-fiber-density optical-fiber cable including stranded flextubes having a micromodule filling coefficient greater than <NUM>. <CIT> shows an optical fiber ribbon with resin potions at plural places that connect adjacent optical fibers.

There is provided an optical fiber cable according to claim <NUM>.

The flexible sheath may be an extruded PVC material that conforms to the shape of the ribbon stack and keeps all of the ribbons acting as a unitary body during bending, but which is just loose enough around the ribbon group that when a length of subunit is (individually or as a group inside the cable) bent and coiled, the individual ribbons are free to adjust themselves longitudinally with respect to each other, thereby preventing any one ribbon from buckling during cable bending.

The flexible PVC material of the sheath enables very high density ribbon cable designs with a fiber density range of <NUM> to <NUM>% of the jacket outer diameter, <NUM>-<NUM>% inside the jacket inner diameter and <NUM>-<NUM>% inside the core subunits while preserving attenuation performance using G. D fiber, for example.

Referring to <FIG>, an optical communication cable, shown as cable <NUM>, is shown according to an exemplary embodiment. Cable <NUM> includes a cable body, shown as cable jacket <NUM>, having an inner surface <NUM> defining an internal area or region within which various cable components or core elements as discussed below are located and an outer surface <NUM> generally defining an outside diameter (OD) of the cable <NUM>. Generally, a plurality of optical fibers <NUM> is included among the cable components, and the cable <NUM> provides structure and protection to the plurality of optical fibers <NUM> during and after installation (e.g., protection during handling, protection from elements, protection from vermin, etc.).

In accordance with aspects of the present disclosure, a first type of core element may be an optical transmission core subunit <NUM> comprising an optical fiber group <NUM> of individual optical fibers located within a thin sheath <NUM>. A plurality of these optical transmission core subunits <NUM> may be provided wound in a pattern or arrangement (e.g., a spiral pattern, a helical pattern, SZ pattern, etc.). Together, the stranded and/or grouped optical transmission core subunits <NUM> may form a core <NUM> of cable <NUM>. The plurality of optical transmission core subunits <NUM> may be wound around a central support member, or as shown in <FIG>, the core <NUM> may be free of conventional strength members. The cable <NUM> may derive strength characteristics from the configuration of the optical transmission core subunits <NUM> themselves and/or the jacket <NUM> which may include embedded strength members.

At least one enclosing element <NUM>, such as a film binder, binder tapes, armor or armor tape, or a water-swellable tape, for example, may be provided to surround the core <NUM> between the core and the jacket <NUM>. In the case of the enclosing element <NUM> being a film or membrane, located around the stranded subunits <NUM>,, the film may be an extruded thin film that cools to provide an inwardly directed force on to the core subunits <NUM> and other core elements, which may include filler rods or tubes and a central strength member, for example. The inwardly directed force provided by the film assists to hold stranded subunits <NUM> in relative position with respect to one another. Thus, in some embodiments, an interference fit is provided between the outer surfaces of the core elements and the film such that the film acts to provide an inwardly directed force onto the core elements of cable <NUM> to prevent/resist unraveling of the wound core elements, for example.

In various embodiments, the film forming the enclosing element <NUM> is formed from a first material, and jacket <NUM> may be formed from a second material. In various embodiments, the first material is different from the second material. In some such embodiments, the material type of the first material is different from the material type of the second material. In various embodiments, the film may be formed from a variety of extruded polymer materials. In various embodiments, the film may be formed from low-density polyethylene (LDPE), polyester, or polypropylene. In one embodiment, the film is formed from a linear LDPE. In one embodiment, the film is formed from an LDPE material having a modulus of elasticity between <NUM> MPa and <NUM> MPa, and more specifically about <NUM> MPa (e.g., <NUM> MPa plus or minus <NUM> percent). In one embodiment, the film is formed from a polyester material having a modulus of elasticity between <NUM> MPa and <NUM> MPa, and more specifically about <NUM> MPa (e.g., <NUM> MPa plus or minus <NUM> percent). In various embodiments, the material of the film may include a coloring material. In addition, the film may include UV stabilizing compounds and may include weakened areas (e.g., lower thickness areas) that facilitate tearing.

As noted above, the first material of the film may be different from the second material of jacket <NUM>. In some such embodiments, the film may be formed from a first material that is extruded at an earlier time or earlier stage in cable production than jacket <NUM>. In such embodiments, the film is formed prior to formation of jacket <NUM>. In some such embodiments, a first extrusion process forms the film at an earlier time in cable production, and a second extrusion process forms jacket <NUM> at a later time in cable production. In some such embodiments, the first material of the film and the second material of jacket <NUM> are the same type of material (e.g., both are MDPE, PP, etc.) that are associated with cable <NUM> at different time points during production of cable <NUM>. In other embodiments, the first material of the film and the second material of jacket <NUM> are the different types of material (e.g., the film is a LDPE and jacket <NUM> is MDPE) and may also be associated with cable <NUM> at different time points during production of cable <NUM>.

The film may also be a thick film, for example having a thickness of <NUM> millimeters or more, wherein the film that is the enclosing element <NUM> is the sole or primary protection for the core <NUM>. A thin jacket <NUM> may be extruded over the thick film.

The jacket <NUM> may be formed from an extruded polymer material having a wall thickness <NUM> of between <NUM> and <NUM>. In accordance with aspects of the present disclosure, the wall thickness <NUM> of the jacket <NUM> may be in the range of <NUM>-<NUM>% of the outside diameter (OD) of the jacket <NUM> for balancing kink resistance with overall cable flexibility of the cable <NUM>.

In accordance with yet other aspects of the present disclosure, the jacket <NUM> may be a co-extruded polymer jacket with a bonded nylon layer, for example, having the same total wall thickness, or a dual-layer jacket of similar thickness with stranded strength elements between the layers. The stranded strength elements may be aramid yarns or impregnated fiberglass strands, for example, that cover <NUM>-<NUM>% of the inner jacket layer and allow portions of the outer jacket layer to bond to the inner jacket layer during the extrusion process.

The jacket <NUM> may be comprised of a base material such as polyethylene, polypropylene, ethylene-propylene, copolymers, polystyrene and styrene copolymers, polyvinyl chloride, polyamide (i.e., nylon), polyesters such as polyethylene terephthalate, polyetheretherketone, polyphenylene sulfide, polyetherimide, polybutylene terephthalate, as well as other plastic materials. In accordance with aspects of the present disclosure, the jacket <NUM> may be made of low density, medium density or high density polyethylene materials. Such polyethylene materials can include low density, medium density or high density ultra-high molecular weight polyethylene materials. The jacket <NUM> may include low-smoke zero halogen materials such as low-smoke zero halogen polyolefins and polycarbons.

As shown in <FIG>, pairs of strength members <NUM> are arranged on opposite sides of the cable <NUM> cross section. The jacket <NUM>, the core subunits <NUM>, the enclosing element <NUM>, and the strength members <NUM> can all extend longitudinally along the entire or substantially all of the length of the cable <NUM>. The strength members <NUM> are wholly or substantially embedded in the cable jacket <NUM>. In the illustrated embodiment, the strength members <NUM> are circular in cross-section with each strength member <NUM> having a diameter in the range of <NUM> to <NUM>, for example <NUM> in the case of a cable <NUM> having an OD of <NUM>, wherein the wall thickness of the jacket <NUM> is approximately <NUM>. The "strength member height" <NUM> is defined as the spacing between the outermost edges (shown as the uppermost and lowest edges in <FIG>) of the outermost strength members on one side of the cable. As also shown in <FIG>, the strength members <NUM> may abut one another so the strength member height <NUM> is the sum of the diameters of the strength members <NUM> on each side of the cable <NUM>. For example, where the strength members <NUM> have a strength member diameter of <NUM>, the strength member height <NUM> would be equal to <NUM> if the strength members <NUM> are abutting.

By having a plurality of strength members <NUM> on opposite sides of the cable <NUM>, as shown in <FIG>, the outside diameter of the strength members <NUM> may be reduced, which in turn allows a reduction in the wall thickness of the jacket <NUM> necessary to provide the strength, flexibility, and protective qualities desired.

Although shown with strength members <NUM> on substantially diametrically opposed sides of the cable <NUM>, other suitable configurations not part of the claimed invention may include, for example, the strength members <NUM> arranged at locations offset from the diametrical configuration described above or, for example, a plurality of individual strength members <NUM> arranged radially at substantially evenly spacial points around the circumference of the cable. The latter arrangement of the strength members <NUM> may be used, for example, to eliminate preferential bend planes from forming in the cable <NUM>.

The strength members <NUM> may be dielectric rigid/semi-rigid strength members, such as glass-reinforced polymer (GRP) rods with circular cross-sections, although other suitable materials (e.g. steel) and/or cross-sections may be used. In accordance with yet other aspects of the present invention, the strength members <NUM> may be aramid yarns or impregnated fiber glass yarns, for example. The strength members <NUM> may be encapsulated in a suitable bonding material, such as an ethyl acrylic acid (EAA) copolymer material, to enhance the bonding characteristics of the strength members <NUM> to the jacket <NUM>. The strength members <NUM> may thus provide tensile strength to the cable <NUM> while providing resistance to jacket shrinkage during the jacket extrusion process and cold weather cycling down to -<NUM>.

In accordance with yet other aspects of the present disclosure, not part of the claimed invention, as shown in <FIG>, a cable <NUM> may incorporate many of the same features discussed above with reference to <FIG>. However, the cable <NUM> may have only one strength member <NUM> on each side of the cable in a substantially diametrically opposed relationship rather than the pairs of strength members <NUM> shown in <FIG>,. Moreover, the strength members <NUM> may have non-circular geometric properties, such as being ovular or generally rectangular in cross-sectional shape. By flattening a typically round strength member <NUM> to be an ovular or a generally more flat rectangular strength member <NUM>, the wall thickness of the jacket <NUM> in the area of the strength members <NUM> may be further reduced while continuing to provide the necessary strength, flexibility, and protective qualities to the cable <NUM>. For example, as shown in <FIG>, compared to a cable with four strength elements <NUM> of <NUM> GRP's have an EA (modulus of elasticity x cross-sectional area) of 660kN and a total wall thickness of approximately <NUM> with <NUM> of jacket over the GRPs. Cable <NUM> may have only two strength members <NUM> that are only <NUM> wide and have a strength member height <NUM> of <NUM> with <NUM> of wall inside of each strength member <NUM> and approximately <NUM> of wall thickness outside of the strength member <NUM> for a total wall thickness of approximately <NUM>. The resultant EA of 660kN for the cable <NUM> is the same as that of the cable <NUM> having four strength members <NUM>. In general, the EA of the jacket <NUM> with dielectric strength members <NUM> may be greater than 400kN with a total wall thickness including the strength members <NUM> being less than <NUM>. The EA of the jacket <NUM> with strength members <NUM> comprising steel wire, for example, may be greater than 400kN with a total wall thickness including the strength members <NUM> being less than <NUM>.

As shown in <FIG>, ripcords <NUM> may be provided to, upon application of a sufficient outwardly directed pulling force, rip through at least a portion of one of the cable components, for example, the enclosing element <NUM> and/or the jacket <NUM> to provide access to the core <NUM>. In addition to or in place of the ripcords <NUM>, the jacket <NUM> may comprise access features <NUM> that facilitate access to the core <NUM>. For example, a pair of diametrically opposed discontinuities may be co-extruded to extend along the length of the jacket <NUM> to enable easy separation of the jacket along a centerline of the cable <NUM>.

The cable jacket <NUM> may include one or more embedded elongate members, shown as access features <NUM>. In general, access features <NUM> are elongate members or structures embedded within the material of cable jacket <NUM>. In various embodiments, access features <NUM> are contiguous members that extend the length of cable jacket <NUM> between the first and second ends of the cable.

In general, cable jacket <NUM> is made from a first material, and access features <NUM> are made from a second material that is different from the first material. The difference in materials provides a discontinuity or weakness within cable jacket <NUM> at the location of access features <NUM>. These discontinuities provide an access point that allows a user of cable <NUM> to split cable jacket <NUM> when access to subunits <NUM> may be desired. In various embodiments, access features <NUM> may be formed from a material (e.g., a polypropylene/polyethylene blend) with low bonding relative to the material of cable jacket <NUM> (e.g., a medium density polyethylene) that allows for jacket splitting by the user. In various embodiments, access features <NUM> may be formed (e.g., coextruded) as described below. In other embodiments, access features <NUM> are non-extruded elements, such as rip cords, that are embedded in the material of cable jacket <NUM>.

In the exemplary embodiment, the access features <NUM> are bonded to the main portion of the jacket when the jacket <NUM> is extruded. The main portion and the access features <NUM> can be formed from extrudable polymers, so that as the extrudate used to form the main portion of the jacket <NUM> and the access features <NUM> cools and solidifies, the extrudates become bonded at an interface of the access features <NUM>. When the access features <NUM> are formed while extruding in the same step as the main portion of the jacket <NUM>, the bond between access features <NUM> and the remainder of the jacket <NUM> can be generally described as enabled by polymer chain entanglement as the jacket <NUM> solidifies. The jacket <NUM> accordingly comprises a cohesive composite structure. The interfaces may be a transition region between the materials of the main portion of the jacket <NUM> and the access features <NUM>.

The access features <NUM> can be relatively narrow strips in the jacket <NUM>, and may occupy relatively small portions of the jacket cross-sectional area. In <FIG>, two access features <NUM> are formed in the jacket <NUM> to facilitate opening of the jacket. However, the number, spacing, shape, composition and other aspects of the access features <NUM> can be varied.

In accordance with aspects of the disclosure, the main portion of the jacket <NUM> may be extruded from medium density polyethylene (MDPE), and the access features <NUM> may be extruded from polypropylene (PP). The jacket <NUM> may be formed in a coextrusion process so that the main portion of the jacket <NUM> and the access features <NUM> bond during cooling to form relatively strong bonds at the interfaces. In accordance with yet other aspects of the disclosure, tactile or visual features may be provided on an exterior of the cable <NUM> to serve as location features for locating the access features <NUM>.

<FIG> is an enlarged view of a core subunit <NUM> showing the optical fiber group <NUM> surrounded by the sheath <NUM>. Each optical fiber group <NUM> may comprise any multiple of optical fiber layer <NUM>. Each optical fiber layer <NUM> may comprise a plurality of fibers grouped into sets and connected, intermittently or continuously, to form base ribbons <NUM> arranged in substantially horizontal fashion. In accordance with aspects of the present disclosure, the base ribbons <NUM> may be comprised of four, eight, twelve, sixteen, twenty four or thirty six optical fibers <NUM> encased in a conventional cured ribbon matrix. As shown in <FIG>, the base ribbons <NUM> may be comprised of twelve or twenty four optical fibers <NUM> encased in a conventional cured ribbon matrix to form twelve-fiber (12F) and twenty-four fiber (24F) base ribbons <NUM>.

In the case of a 24F base ribbon <NUM>, for example, the 24F ribbon may have a feature, such as a weakened portion or preferential tear feature, for easily separating the 24F ribbon or folding the 24F ribbon into a plurality of ribbons of smaller fiber counts, such as two 12F ribbons for ease in splicing or stacking. Optical fiber ribbons with manufactured weakened portions for allowing groups of fibers in the ribbon to be separated or folded into subunits, such as the types of ribbons disclosed in <CIT> may be used for the base ribbons <NUM> disclosed herein.

Although rollable ribbons may comprise the base ribbons <NUM> used to form the ribbon layers <NUM> disclosed herein, aspects of the present disclosure may be directed toward ribbons having a more solid, continuous ribbon matrix to overcome difficulties in handling and splicing experienced with intermittently connected or rollable ribbons. In particular, mass fusion splicing of multiple 12F <NUM> or <NUM> ribbons, for example, is easier and faster than similar mass fusing splicing of flexible rollable ribbons and much easier and faster than field ribbonizing loose fibers or single fiber mass fusion. Although referred to herein as <NUM> fiber or <NUM> fiber, the actual diameters of fibers may differ in accordance with various attributes. For example, although referred to as <NUM> fiber, the actual diameter of the fiber may be closer to <NUM> when accounting for a coloring layer that may be separately applied to the individual fibers for efficient identification.

In accordance with aspects of the present disclosure, the base ribbons <NUM> disclosed herein may comprise a single layer matrix or a dual layer matrix having an inner matrix and an outer matrix. The single layer matrix or the inner matrix and/or outer matrix of the dual layer matrix may comprise a resin matrix material that is mixed with a pigmented material to produce a tinted color appearance. In accordance with yet other aspects, the resin matrix material may be colored by use of an organic or inorganic dye in the resin matrix material. The coloring of the matrix material may be adjusted to provide varying degrees of tint or opacity. The coloring of the ribbon matrix may produce various shades or tints of white, blue, orange, green, brown, and slate, for example, although other colors such as red, black, yellow, violet, rose and aqua may be provided for as well. In accordance with yet other aspects of the present disclosure, the inner matrix of a dual layer matrix may be tinted and the outer matrix may be formed from a second resin matrix material that is substantially transparent to permit easy viewing of the tinted matrix color of the inner matrix, for example. In accordance with yet other aspects of the present disclosure, prior to application of the transparent second resin matrix, printed characters may be applied to the inner matrix to further identify characteristics of the base ribbon <NUM>, in addition to color coding, and may include such information as fiber type, fiber size, ribbon number, etc. Ink jet printing, laser ablation printing, printing wheels, or any other suitable printing techniques may be used to provide further ribbon identification in addition to the matrix tinting. Placement of the print characters between the inner matrix and the outer matrix may prevent smearing or abrasion of the characters during use in the field. In addition, by intentionally using print with intended contrast to particular colors, the ability to read in low light conditions, for example, can be greatly enhanced. Although described above with an inner matrix having a tinted coloring and the outer matrix being substantially transparent, one or both of the inner matrix and the outer matrix may have a tinted coloring and/or be substantially transparent.

Each optical fiber group <NUM> may comprise any number of stacked optical fiber layers <NUM>, wherein the optical fiber layer <NUM> is of varying width to create a stepped perimeter of the optical fiber group <NUM>. According to the claimed invention, as shown in <FIG>, optical fiber group <NUM> includes a medial subgroup <NUM> of stacked optical fiber ribbons with at least one set of lateral subgroups 44a, 44b on opposing sides thereof. As shown, medial subgroup <NUM> may have eight optical fiber layers <NUM> of 24F ribbons, each layer comprising one 24F ribbon (preferably separable into two 12F ribbons) or two 12F ribbons aligned side-by-side; and lateral subgroups 44a, 44b may each comprise four optical fiber layers <NUM> of 12F ribbons such that each core subunit <NUM> as shown has a total of <NUM> individual optical fibers <NUM>.

In accordance with yet other aspects of the present disclosure, optical fiber layers <NUM> may include 16F ribbons with <NUM> fibers colored to <NUM>, which makes each 16F ribbon approximately <NUM> wide. This may still fit in conventional <NUM> spaced 12F ribbon mass fusion splicers. By going to 16F per mass fusion splice, total splice time for a given fiber count may be reduced by <NUM>% (e.g., a 192F cable has sixteen 12F ribbons; another 192F cable has twelve 16F ribbons). If as expected the time to splice per ribbon is equivalent, then splicing 192F in a subunit with 16F ribbons can be completed in <NUM>% less time than 192F in a comparable 12F base cable. Various configurations of 16F optical fiber groups <NUM> may be stacked using 8F, 16F, 24F, 32F ribbons. Also, configurations of 256F core subunits <NUM> with 16F ribbons may be stranded together. For example, <NUM> core subunits <NUM> around <NUM> core subunits <NUM> with a foam central core, for example, may provide for a <NUM> fiber cable.

As shown in <FIG>, cable <NUM> may have a core <NUM> with, for example, a total of twelve core subunits <NUM>. As shown, the core <NUM> may be configured such that nine of the core subunits <NUM> are stranded externally around three centrally located core subunits <NUM>. A water swellable tape or helically stranded yarns, for example, may be provided to secure and/or bind the three centrally located core elements during manufacture. Alternatively, the core <NUM> may be stranded on a planetary helical strander such that no binders or central member is required to manufacture the cable <NUM>. The resulting cable <NUM> has a total fiber count of <NUM> fibers when adding the <NUM> fibers per core subunit <NUM> in each of the twelve core subunits <NUM>. When configured with minimal free space in accordance with aspects of the present disclosure, the cable <NUM> may have an outside diameter of <NUM> (<NUM> inches) and an area fill ratio of <NUM>%, enabling the cable <NUM> to fit easily inside a conventional <NUM> inch (~<NUM>) duct.

The number of optical fiber layers <NUM> and the number of fiber ribbons comprising a layer in each subgroup may vary depending on the size of the cable desired and the fiber density necessary to accommodate fiber demand for that particular cable size. Each optical fiber layer <NUM> may contain at least one respective layer having at least one optical fiber ribbon, and although described previously as comprising 24F or 12F ribbons, other size optical fibers ribbons may be used such as <NUM> fiber (16F), eight fiber (8F) ribbons, six fiber (6F) ribbons, or four fiber (4F) ribbons. Each subgroup is progressively smaller, starting at the medial subgroup and moving to the lateral subgroups. Optical fiber ribbon group <NUM> can therefore define a step-like profile that can be generally symmetrical about medial subgroup <NUM>. The step-like profile can define a high fiber packing density by substantially filling up the volume of the core <NUM> with, for example, sets of optical fiber ribbons. The width w and/or height h can be constant from step to step, or they may become progressively smaller or larger from step to step in the profile. Moreover, by changing the fiber size from <NUM> to <NUM>, or increasing the number of fibers in the core subunits <NUM>, may result in even higher fiber densities when comparing similar fiber counts and cable dimensions. In addition, the optical fiber ribbon group <NUM> may be comprised of a plurality of optical fiber layers <NUM> of equal width and fiber size, thus presenting a cross-sectional footprint more resembling a rectangle or square and absent the step-like profiles described above.

For example, although specific sizes and configurations are shown and described with respect to <FIG>, such as a two layer cable having a nine (<NUM>) around three (<NUM>) core subunit stranding, other configurations are contemplated included a cable having just one core subunit <NUM> in the center, one layer of six stranded subunits <NUM>, other two layer configurations such as twelve (<NUM>) around six (<NUM>) core subunits <NUM>, or three layer configurations, such as fifteen (<NUM>) core subunits <NUM> stranded around a middle layer of nine (<NUM>) core subunits <NUM> that may in turn be stranded around an inner layer of three (<NUM>) core subunits <NUM>. When combined with <NUM> fiber, for example, high fiber count high density cables with fiber counts of more than <NUM> fibers which may still fit in a two inch (~<NUM>) duct are contemplated.

In normal cable processing where there are multiple subunits being stranded, the subunits are usually helically stranded together with a specific laylength to foster cable bending without undue stress on the subunits. Without stranding, during cable bending, the subunits on the inside of the bend compress and buckle while the subunits on the outside of the bend are put under tension and want to move toward the neutral axis of the cable bend. The stranding process 'averages' the subunit position in the cable. On average, with a stranded subunit, the subunit's center of bending becomes the center of the cable. However, within any one laylength of a stranded subunit, approximately half of the subunit length is under tension while the other half is under compression. If the cable jacket is loose enough, the part of the subunit in tension on the outside of the bend will pull the appropriate amount of length from the part of the subunit experiencing compression on the inside of the bend, which allows the subunit stress to essentially zero out. This mechanism is termed "longitudinal translation" herein. If the jacket <NUM> is extruded too tightly around the core <NUM> of stranded core subunits <NUM>, the jacket <NUM> creates radial normal forces which the subunits have to overcome before they can longitudinally translate during cable bending.

The sheath <NUM> may be made of a peelable plasticized PVC material tightly extruded to surround each ribbon group <NUM> in each core subunit <NUM>. The sheath <NUM> may be a single extruded layer of plasticized PVC that is both thin (e.g., a thickness of between. <NUM>, preferably about. <NUM>) and comprised of a soft material that easily separates by manually pinching the sheath material. The extruded sheath <NUM> is tight in that it conforms to the shape of the ribbon group <NUM> and keeps all of the individual ribbons <NUM> acting as a whole during longitudinal translation between the subunits inside the cable during cable bending. By maintaining all of the ribbons acting as a whole, the core subunits in accordance with aspects of this disclosure keep any one ribbon from buckling during cable bending. The ability of the sheath <NUM> to perform this function would also keep any one fiber in a rollable ribbon format from buckling during subunit longitudinal translation. Although embodiments disclosed herein may have an entirely continuous sheath <NUM>, i.e., whole simultaneously in a radial and a longitudinal direction along the entire length of the cable, embodiments may also include a sheath <NUM> having non-continuous features, such as holes, windows, slits, or gaps, for example, such that a surface area of the sheath <NUM> with the non-continuous features is at least <NUM>% of the surface area if the sheath <NUM> was entirely continuous.

Table <NUM> below illustrates the elastic modulus of sheath <NUM> (comprising a plasticized PVC material) with respect to temperature. As indicated in Table <NUM>, the elastic modulus of sheath <NUM> at room temperature is less than <NUM> MPa and rises to only approximately <NUM> MPa at cold temperatures (e.g., -<NUM>). Comparatively, a typical fiber optic cable jacket, such as one comprising a medium density polyethylene (MDPE) material, has a higher modulus than <NUM> MPa at room temperature. <IMG>
<IMG>.

Combined with the thin walls of the sheath <NUM>, an EA (modulus x cross-sectional area) of the sheath <NUM> is very low, approximately <NUM> Newtons, for a subunit <NUM> having an effective diameter of approximately <NUM>. The sheath area (A) for a thin sheath <NUM> having <NUM> thickness may be calculated as the (squared value of the effective outer diameter of the sheath (e.g., (<NUM>) <NUM>) minus the squared value of the effective inner diameter of the sheath (e.g., (<NUM>) <NUM>)) * PI/<NUM>. Comparatively, a typical fiber optic cable jacket of MDPE which is thicker and has a higher modulus of greater than <NUM> MPa has an EA of <NUM>,<NUM> Newtons at room temperature. The material properties of the extruded sheath <NUM> ensure the sheath <NUM> does not create undue normal force against the ribbon group <NUM>.

In accordance with yet other aspects of the present disclosure, as shown in <FIG>, a vacuum may be applied to the extrusion line to cause the sheath <NUM> to be pulled down more tightly against the ribbons <NUM> of the ribbon group <NUM>. In this regard, the sheath <NUM> may form concave bridging portions <NUM> at the step locations of the ribbon group <NUM>. Vacuum extruding the sheath <NUM> substantially reduces the free space in the subunit <NUM> as compared to a conventionally extruded buffer tube. Moreover, during cold temperature cycles, and in combination with the stepped shape of the ribbon group <NUM>, the vacuum fitted sheath <NUM> provides the ability to stretch in the direction of the arrow <NUM> to prevent normal forces being applied against the ribbon group <NUM> by the sheath <NUM>. The conformal sheath <NUM> has a fiber fill ratio greater than the maximum fill ratio of a round tube. As a result, the conformal sheath <NUM> may rotate with the ribbon array due to mechanical interference associated with the non-circular shape of the array. The sheath <NUM> also secures the relative position of each ribbon within the array and presents a consistent boundary between the edges of the ribbon array and surrounding cable elements.

As shown in <FIG>, the sheath <NUM> may be extruded around a stack of conventional ribbons where the ribbons are two different widths (12F ribbons and 24F ribbons). However, the extruded sheath <NUM> may be applied to any of a number of fiber bundle arrangements, for example a ribbon stack of one ribbon width (e.g., <NUM> x 12F ribbons), or intermittently connected rollable ribbons. The extruded sheath <NUM> may also contain sub-bundles of fibers, for example multiple fiber groups of rollable or conventional ribbons inside binder threads all inside the extruded sheath <NUM>. The extruded sheath <NUM> may be generally round, square, rectangular or other shapes, and each individual sheath <NUM> in a cable having a bundle of core subunits <NUM> may be colored a different color to enhance configuration management and routing of the fibers in the separate subunits <NUM>. Additional print markings may be provided on the outside of the sheath <NUM> to provide additional configuration or product information, such as numbering to identify individual core subunits <NUM> and/or, for example, information about the types of fibers contained in each core subunit <NUM>.

Although the sheath <NUM> is described above as tight, at the same time the extruded sheath <NUM> is loose or just loose enough such that when a length of a core subunit <NUM> is (individually or as a group inside the cable) bent and coiled, the individual ribbons <NUM> are free to adjust themselves longitudinally with respect to each other, longitudinally translating inside or within the extruded sheath <NUM>, relieving bending stresses and keeping the individual ribbons <NUM> from buckling. This applies to fibers in a rollable ribbon configuration as well. The special material of the sheath <NUM> does not squeeze radially or continue to squeeze radially and create normal forces between the ribbons or fibers that would hinder individual core subunit <NUM> longitudinal translation.

Each individual ribbon group <NUM> is stranded to twist longitudinally within the core subunit <NUM>. The stranded laylength of the ribbon groups <NUM> should be in the range of <NUM>-<NUM> based on residual fiber strain due to stranding (twisting). The ribbon group laylength and core subunit <NUM> stranding pitch should not have the same value, due to a differential length buildup between the top and bottom ribbons. For cables made with unidirectional tube stranding (not SZ), the ribbon strand may be in one direction, and the core subunit strand is in the other direction (regular lay). In accordance with other embodiments, the cables with unidirectional tube stranding may be made with the ribbon group strand and the core subunit strands being stranded in the same direction (lang lay). In the case of cables with a lang lay configuration, differential length builds up since one ribbon is always towards the center of the cable and one ribbon is always on the outside of the cable during this condition. Differential buildup leads to high excess ribbon length (ERL) and macrobending.

To reduce differential length buildup and maintain minimum strain on the ribbon group <NUM>, various configurations may be used, such as a <NUM> ribbon group laylength and a <NUM> stranded core subunit laylength, a <NUM> ribbon group laylength and <NUM> stranded core subunit laylength, a <NUM> ribbon group laylength and <NUM> stranded core subunit laylength, and/or other suitable configurations in which the ribbon group <NUM> and the core subunit <NUM> laylengths vary. The stranding of the core subunits <NUM> may be loose enough that the core elements <NUM> may adjust longitudinally or "longitudinally translate" during bending and tensile.

The sheath <NUM> may be a continuously (radially and longitudinally continuous) applied thermoplastic material. Optical fibers and ribbons made from optical fibers have a high tensile rigidity due to the strength of the glass fibers but a low buckling threshold due the small diameter of each fiber. Bending performance is enhanced by stranding but the optical fibers must be able to slide by compressive force applied at distance of about <NUM>/<NUM> of the stranding pitch without buckling to prevent signal loss. The conformal sheath <NUM> functions as a boundary to limit separation between the ribbons <NUM> within the array due to buckling forces during normal handling of the cable or subunit. The continuous sheath <NUM> prevents localized ribbon or fiber buckling issues that can occur in cables with unbound ribbons or fibers or in cables with ribbon or fibers bound with binder yarns, for example, wherein there is sufficient free space or gaps for the fibers or ribbons to buckle through the binders. These macrobend events can be described as statistical outliers, where the majority of fiber length does not have a bend problem, but only a very small fraction of the length has a bend or buckling problem. Much of optical cable design and attenuation performance in standard loose tube fiber optic cables, or in cables with less than <NUM>% area ratio comes down to managing outlier attenuation bends. For a fiber optic cable to have good attenuation in bending and tension during installation, handling, and lifetime operation, the fibers individually and in aggregate must be able to find a path to relieve bending stresses, whether tensile or contractive.

By having a subunit fiber density of <NUM>% or greater, but more preferably <NUM>%, or most preferably <NUM>% or greater inside the continuous extruded sheath <NUM>, individual fibers of a rollable ribbon cannot find their own path separate from the subunit group that would cause macrobending attenuation outliers. On the other hand, a ribbon group <NUM> with high fiber density inside the extruded sheath <NUM> ensures that individual ribbons are not capable of buckling. In accordance with embodiments of the present disclosure, a core subunit <NUM> having a 288F ribbon group <NUM> configuration as shown in <FIG>, i.e., a medial subgroup <NUM> of eight stacked 24F ribbons and lateral subgroups 44a, 44b of four 12F ribbons each, has an inside the subunit fiber area ratio of <NUM>% to <NUM>%, meaning that <NUM>% - <NUM>% of the entire area inside of sheath <NUM> is occupied by actual optical fibers and the remaining <NUM>% - <NUM>% of inside area is primarily ribbon matrix material and/or limited free space. In one particular embodiment, having a vacuum fitted sheath <NUM>, the inside the subunit fiber area ration is <NUM>%. The same ratios generally apply whether the fibers are <NUM> micron fibers or <NUM> micron fibers, although the inside area of the core subunit <NUM> is reduced when using <NUM> micron fibers. Cable density can also be reviewed in terms of the jacket outer diameter and in terms of inside the jacket inner diameter. Cables in accordance with aspects of the present disclosure may have a fiber density range of <NUM> to <NUM>% on the jacket outer diameter and <NUM>-<NUM>% inside the jacket inner diameter.

Buckling forces within the core subunit <NUM> are limited by several design factors in addition to limiting the residual radial compression due to the material properties the sheath <NUM>, including the relationship of the friction coefficient between ribbons, between the ribbons <NUM> and the sheath <NUM>, and between the sheaths <NUM> of individual subunits <NUM> and surrounding cable elements (e.g., other subunits <NUM> and/or the enclosing element <NUM>); stranding; and limiting residual radial compression within the surrounding cable structure. For example, to enable efficient longitudinal translation between the core subunits <NUM> within the cable <NUM> during bending, while ensuring that each individual ribbon group <NUM> and corresponding subunit <NUM> act as one unit, the friction between two or more subunits <NUM> and/or between the subunits <NUM> and the enclosing element <NUM> should be lower than the friction between the sheath <NUM> of a subunit <NUM> and the ribbon group <NUM> contained therein.

Friction testing was performed in accordance with guidelines provided by ASTM D <NUM>-<NUM> with noted variations. The test involved using an MTS 5kN load frame and an MTS 5N load cell with a ribbon or PVC base having a width of <NUM> or <NUM> and a <NUM> aluminum sled with beveled edge and a <NUM> PVC insert having a width of <NUM>. In some cases, deviations to the ASTM recommendations were made to sled weight and width, and foam backing. Several variations were utilized to process the PVC into sheet form including milling of the compound prior to processing the compression molded plaques, processing of the compression molded plaques without milling, processing of the compression molded plaques with a mylar film to produce a surface finish.

The mean kinetic Coefficient of Friction (CoF) between core subunits <NUM> (i.e., between sheath <NUM> of a first core subunit <NUM> and sheath <NUM> of a second core subunit <NUM>) was measured at approximately <NUM>, which is the average of data from samples prepared with mylar film peeled from surface. A range for mean CoF between subunits may be between <NUM> to <NUM>. Similarly, the mean kinetic CoF between a core subunit <NUM> and an enclosing element <NUM>, in this case a non-woven water-swellable tape, was approximately <NUM>. A range for mean CoF between subunits and the enclosing element <NUM> may be between <NUM> to <NUM>.

In accordance with other aspects of the present disclosure, a suitable friction reduction agent, such as talc or silicone powder, for example, may be added to the outer surface of the sheath <NUM> and or the inner surface of the enclosing element <NUM>. With talc dusted on the PVC sheath surfaces for testing, the mean kinetic CoF between core subunits <NUM> (i.e., between sheath <NUM> of a first core subunit <NUM> and sheath <NUM> of a second core subunit <NUM>) was reduced to approximately <NUM>, while the mean kinetic CoF between a core subunit <NUM> and an enclosing element <NUM>, both dusted with talc, remained approximately <NUM>. The mean kinetic CoF between a ribbon group <NUM> and the sheath <NUM> of a corresponding core subunit <NUM> was measured at <NUM>. A range for mean CoF between a ribbon group and the sheath of a corresponding core subunit may be <NUM> to <NUM>.

As noted, by maintaining of CoF ratio of the CoF between ribbon and sheath that is at least three times greater and up to ten times greater than the CoF between core subunits and other cable elements (e.g., other core subunits and/or the enclosing element), the core subunits <NUM> can slide (longitudinally translate) within the cable <NUM> during bending, while high friction between the ribbons and the inner surface of the sheath <NUM> maintains the ribbon group <NUM> and the sheath <NUM> acting as one unit. When a cable bends, the cable attempts to take an oval form. Normal forces coming from cable ovality press the core subunits together and the core subunits in turn squeeze the ribbons. The higher CoF between the PVC material of the subunit sheath and the ribbons as compared to the CoF between the subunits and/or subunits and the waterswellable tape enclosing element, enables and even fosters subunit translation (the sheath and ribbons moving together as a unitary body) and maintenance of attenuation well within acceptable limits.

As shown in <FIG>, a minimum tube inside diameter (TID) of the sheath <NUM> may be less than a maximum diagonal dimension (DD) of the ribbon group <NUM>. The thin walls of the sheath <NUM> reduce strain on the ribbon group <NUM> and individual ribbons or fiber caused by shrink-back when the tubes cool after extrusion. Shrink-back is further reduced by the tight coupling of the sheath <NUM> to the ribbon group <NUM>. However, the soft nature of the material used for the sheath <NUM> permits sufficient ribbon and fiber movement during bending and twisting to reduce strain on the fiber group <NUM> and attenuation on individual fibers, particularly corner fibers in contact with the inside of the sheath <NUM> walls. In addition, the low-compression modulus of the sheath <NUM> provides a softer surface than typical subunit walls, such as conventional buffer tubes, which prevents microbending in the corner fibers while allowing a limited amount of ribbon movement and stack adjustment during cable bending and twisting. The softer material of sheath <NUM> allows corners fibers to move to reduce stress on the individual corner fibers and attenuation degradation.

In accordance with aspects of the present disclosure, waterblocking material, such as super-absorbent polymer (SAP) powder may be added to the interior of the sheath <NUM>. Waterblocking SAP - when water is not present - is a hard particle that may cause microbending (like pressing a fiber into sandpaper) when the ribbon stack is forced against a tube wall during cable bending or coiling, tensile testing and/or temperature cycling. Specifically, the ribbon stack corner fibers exhibit the most microbend attenuation since these fibers are in direct contact with the waterblocking powder and the tube wall.

Compared to conventional buffer tubes, however, the softer material of sheath <NUM> alleviates microbend attenuation issues due to the addition of waterblocking SAP powders to an interior of sheath <NUM>. Conventional buffer tubes, for example, are unable to absorb the localized pressure created when the powder is compressed between the hard matrix of ribbon group <NUM> and the buffer tubes, resulting in microbend attenuation. The softer material of the sheath <NUM> is able to compress and absorb these localized stresses thus preventing the microbend attenuation issues typical of conventional buffer tube designs and allowing the addition of water blocking powder to the interior of the sheath <NUM>. SAP powders having an average particle size of between <NUM> micron and <NUM> microns may be used. For example, in embodiments, the average particle size of the superabsorbent polymer powder may be less than or equal to <NUM> microns. In other embodiments, the average particle size of the superabsorbent polymer powders may be less than or equal to <NUM> microns. In still other embodiments, the average particle size of the superabsorbent polymer powders may be less than or equal to <NUM> microns, and in yet other embodiments, the average particle size of the superabsorbent polymer powders may be less than or equal to <NUM> microns. Further, the SAP powders may have particles that are by design spherical in shape.

Although small SAP powder sizes may be used, in certain other embodiments, SAP powders with average particle sizes of greater than <NUM> microns may be used. In particular, because of the softer material of the sheath <NUM>, as discussed above, the microbend attenuation problems one would expect to see in a cable with such high fiber density and limited free space is reduced or eliminated. The sheath <NUM> absorbs much of the stress that would be transferred to ribbons and/or fibers associated with SAP powder and conventional hard buffer tube designs.

The tight ribbon stack of the ribbon group <NUM> prevents migration of SAP powder between the individual ribbons <NUM>. By preventing migration of the SAP powder between ribbons, attenuation issues caused by microbend attenuation as a result of the SAP powder being pressed between two hard ribbons may be prevented. The use of larger SAP powders with average particle sizes of greater than <NUM> microns may further prevent against SAP powder migrating between individual ribbons.

Although disclosed as SAP powders, other water blocking materials, such as swellable hot melts incorporating SAP particles, may be applied to the interior of the sheath <NUM> and/or onto surfaces of the ribbon group <NUM>, preferably at locations where free space may exist, such as at the corners of step increases between fiber counts in fiber subgroups. In this manner, water migration in the limited free spaces in the high density cables of the present disclosure may be reduced or prevented. In addition, the SAP powders as applied may serve as a friction reducing agent between, for example, the ribbon group <NUM> and the sheath <NUM>.

As shown in <FIG>, the enclosing element <NUM> may be a water blocking element such as a tape with embedded or applied SAP powder. Additionally, as shown in <FIG>, a core water-blocking element <NUM>, which may be a non-woven water blocking tape, for example, may be incorporated into the center of the cable during manufacture. For example, the core water-blocking element <NUM> may be introduced during the stranding process of the subunits <NUM> in a manner that the core water-blocking element <NUM> randomly bunches and squeezes into the interstitial spaces between the inner-most set of core subunits <NUM>. As shown in <FIG>, the core water-blocking element <NUM> may be a water-blocking tape having a lateral dimension much greater than the effective diameter of any of the core subunits <NUM>. As shown in <FIG>, the water-blocking element <NUM> may be manufactured to form a shape having three legs extending from the cable center. Each leg may be comprised of one or more layers of the water-blocking element material and be offset from each of the other legs by approximately <NUM>° radially when viewed in cross-section.

When referring to the effective diameter of a core subunit <NUM>, because the sheath <NUM> and the ribbon group <NUM> may not necessarily present a round or circular cross-sectional shape, one must first determine the major and minor diagonal dimension of the core subunit <NUM>, shown as arrows <NUM> and <NUM>, respectively, in <FIG>. The effective diameter of the core subunit <NUM> is the average of the major diagonal dimension <NUM> and the minor diagonal dimension <NUM>. For example, for the a 288F subunit made with <NUM> fiber ribbons as shown in <FIG>, the major diagonal dimension <NUM> is <NUM> and the minor diagonal dimension <NUM> is <NUM>, respectively. Averaging these, this core subunit <NUM> effective diameter is <NUM>.

The lateral dimension of the core water-blocking element <NUM> is must be substantially larger than the effective diameter of the innermost core subunits <NUM> to serve the purpose of waterblocking through random bunching and placement into the interstitial spaces between the innermost set of core subunits <NUM>. For example, the core water-blocking element <NUM> may also be a non-woven swellable tape similar to or the same as the swellable tape used as the enclosing element <NUM>, with similar CoF. The tape is extremely thin and may have a lateral dimension of between <NUM> and up to <NUM>, preferably between <NUM> and <NUM>.

In accordance with other aspects of the present disclosure, in addition to or in lieu of the enclosing element <NUM>, small particles (i.e., ~<NUM>) may be introduced into the interior of the jacket <NUM> and or interior of the enclosing element <NUM>, to reduce friction between the core subunits <NUM> and the jacket. These particles could be selected from, but are not limited to, the following examples: graphite, UHMW beads, silicone, talc, and superabsorbent polymers (e.g. sodium polyacrylate). A reduction in friction allows the core subunits <NUM> enables the core subunits <NUM> to more easily longitudinally translate to find the path of least strain during bending.

In various embodiments, sheath <NUM> may be colored and/or printed upon to identify the core subunits <NUM> and/or other properties of core components such as the type of optical fibers <NUM> (e.g., <NUM> or <NUM>) comprising the fiber group <NUM>.

<FIG> illustrate various cables manufactured in accordance with the features and principles disclosed herein. <FIG> illustrates a cable <NUM> having six subunits <NUM> with each subunit having <NUM> fibers. The fibers are <NUM> fibers. This results in a cable with <NUM>,<NUM> fibers in a jacket having an outer radius of approximately <NUM> inches or <NUM> millimeters. <FIG> has been described and comprises a cable <NUM> having twelve subunits <NUM> with each subunit having <NUM> fibers. The fibers are <NUM> fibers. This results in a cable with <NUM>,<NUM> fibers in a jacket having an outer radius of approximately <NUM> inches or <NUM> millimeters. <FIG> illustrates a cable <NUM> having six subunits <NUM> with each subunit having <NUM> fibers. The fibers are <NUM> fibers. This results in a cable with <NUM>,<NUM> fibers in a jacket having an outer radius of approximately <NUM> inches or <NUM> millimeters. <FIG> illustrates a cable <NUM> having twelve subunits <NUM> with each subunit having <NUM> fibers. The fibers are <NUM> fibers. This results in a cable with <NUM>,<NUM> fibers in a jacket having an outer radius of approximately <NUM> inches or <NUM> millimeters. <FIG> illustrates a cable <NUM> having twelve subunits <NUM> with each subunit having <NUM> fibers. The fibers are <NUM> fibers. This results in a cable with <NUM>,<NUM> fibers in a jacket having an outer radius of approximately <NUM> inches or <NUM> millimeters.

According to one aspect of the present embodiment, as shown in <FIG>, for example, the jacket <NUM> may may include jacket features to promote easy access to the cable core and/or cable components such as sensing fibers. The cable jacket <NUM> may include one or more embedded elongate members, shown as access features <NUM>. In general, access features <NUM> are elongate members or structures embedded within the material of cable jacket <NUM>. In various embodiments, access features <NUM> are contiguous members that extend the length of cable jacket <NUM> between the first and second ends of the cable.

In accordance with aspects of the disclosure, the main portion of the jacket <NUM> may be extruded from medium density polyethylene (MDPE), and the access features <NUM> may be extruded from polypropylene (PP). The jacket <NUM> may be formed in a coextrusion process so that the main portion of the jacket <NUM> and the access features <NUM> bond during cooling to form relatively strong bonds at the interfaces.

In accordance with yet other aspects of the present disclosure, <FIG> illustrates use of a foam filler rod <NUM> in cables such as cable <NUM>, for example, in which there may be an empty space at center of the core of the cable. The foam filler rod <NUM> assists to distribute external forces on the cable across multiple fibers and over some length to increase the overall load and deflection the cable is able to withstand before reaching attenuation limits during testing. For example, an <NUM>% density reduction foamed core doubled the average crush load during load characterization testing and reduced failure rate from <NUM>% to <NUM>% for GR-<NUM> standard crush tests. Moreover, the foam filler rod <NUM> prevents subunits from moving into the center of the stranded subunits, which ensures all subunits are the same length and tensile loads are distributed across all subunits and contributes to a round finished cable for easier jetting installation with current equipment.

In accordance with aspects of the present disclosure, attributes of a preferred foamed filler rod include low tensile strength to prevent crush force during tensile testing on subunits on the compression side of the central member and an <NUM>% density reduction of LDPE material to adequately provide distribution of external forces. The outside diameter of the foam filler rod <NUM> may be geometrically optimized for the number of subunits in accordance with the chart below. The sizing targets a <NUM>-<NUM>% gap between the foam filler rod and the subunits.

The optical fibers discussed herein include optical fibers that may be flexible, transparent optical fibers made of glass or plastic. The fibers may function as a waveguide to transmit light between the two ends of the optical fiber. The optical fibers include a transparent core surrounded by a transparent cladding material with a lower index of refraction. Light may be kept in the core by total internal reflection. Glass optical fibers may comprise silica, but some other materials such as fluorozirconate, fluoroaluminate, and chalcogenide glasses, as well as crystalline materials, such as sapphire, may be used. The light may be guided down the core of the optical fibers by an optical cladding with a lower refractive index that traps light in the core through total internal reflection. The cladding may be coated by a buffer and/or another coating(s) that protects it from moisture and/or physical damage and/or provides distinguishing markings. These coatings may be UV-cured urethane acrylate composite materials applied to the outside of the optical fiber during the drawing process. The coatings may protect the strands of glass fiber.

Fiber types in may include G. These fiber types can have a <NUM> MFD from <NUM> to <NUM> microns. However, fiber having an MFD ≥ <NUM> microns may be preferred because of compatibility with legacy cable and ease of splicing. The novel extruded sheath <NUM> and resultant cable performance enhancements enable use of fibers having MFD of ≥ <NUM> microns at <NUM>. In accordance with aspects of the present disclosure, these high fiber count cable designs enable fibers having MFD of ≥ <NUM> microns at <NUM> (e.g., <NUM>, <NUM>, <NUM>, <NUM> microns at <NUM>) while meeting attenuation requirements, which is preferred due to no mode field mismatch when splicing to the other fibers in existing networks. The higher cost, special bend fibers with MFDs at <NUM> or other lower MFDs may be used in cases where there is a particularly identified requirement, for example if the stripped fiber is stored outside the cable in a very tight splice tray. In addition, the special bend fibers may enable even smaller diameter cables with higher densities if the fibers are less than <NUM> microns in diameter, such as <NUM> microns or less.

Claim 1:
An optical fiber cable comprising:
a plurality of stranded core subunits (<NUM>), each core subunit (<NUM>) comprising a flexible sheath (<NUM>) and a plurality of ribbons (<NUM>) arranged in a ribbon group (<NUM>), wherein the ribbon group (<NUM>) includes a medial subgroup (<NUM>) of stacked optical fiber ribbons (<NUM>) with at least one set of lateral subgroups (44a, 44b) on opposite sides thereof, wherein each subgroup is progressively smaller starting at the medial subgroup (<NUM>) and moving to the lateral subgroups (44a, 44b), wherein each ribbon (<NUM>) of the plurality of ribbons (<NUM>) comprises a plurality of optical fibers (<NUM>) such that <NUM>-<NUM>% of the cross-sectional area inside the sheath (<NUM>) is occupied by the optical fibers (<NUM>); and
a jacket (<NUM>) surrounding the plurality of stranded core subunits (<NUM>),
characterized in that the sheath (<NUM>) is tight in that it conforms to a shape of the ribbon group (<NUM>) and keeps all of the individual ribbons (<NUM>) acting as a whole during longitudinal translation between the subunits (<NUM>) inside the cable during cable bending, wherein the sheath (<NUM>) comprises an extruded polymer material having a modulus of elasticity less than <NUM> MPa at room temperature, and the jacket (<NUM>) comprises at least two strength elements (<NUM>,<NUM>), each strength element (<NUM>,<NUM>) on diametrically opposite sides of the cable (<NUM>), wherein the at least two strength elements (<NUM>,<NUM>) comprise two pairs of strength elements, each pair of strength elements embedded within the jacket (<NUM>) on diametrically opposite sides of the cable.