Patent Description:
An optical fiber is a flexible and transparent fiber, used as a medium for transmitting light. An optical fiber has a small diameter and is typically comprised of a glass optical core, glass cladding, and a polymeric protective layer with overall diameter of about <NUM> microns or smaller. Optical fibers are typically bundled and encapsulated in a polymeric sheath, forming a buffer tube. Several buffer tubes are stranded around a central strength member and then jacketed in a common cable design. An optical cable is typically used to provide high speed, low loss, and high data rate information transmission over long distances. Optical cables are immune to electromagnetic interference and have found usage in a variety of industries, for example in medicine, flight, and telecommunications.

The buffer tubes can be filled with petroleum-based filling compounds to minimize friction and stress between the optical fibers and the surrounding polymeric sheath. The petroleum-based filling compound also effectively blocks water from migrating along the buffer tube, which prevents long-term damage to optical fibers. However, greasy filling compounds are messy and present handling inconveniences during manufacturing, installation, and access.

Dry-cable buffer tube designs exclude the filling compound and are more convenient for cable access, cable repair, and splicing, but suffer from static electric buildup. In addition, the optical fibers have a tendency to stick to the polymeric buffer tubes during and after the buffering extrusion process resulting in excess fiber length (EFL) control issues. Excess fiber length can also occur as a result of buffer tube shrinkage during processing and thereafter as post-extrusion shrinkage (PES). Too much excess fiber length can lead to undesirable attenuation in the optical cable.

Gel-free buffer tube designs typically include a non-greasy lubricant to reduce static and stiction. However, flow and leakage of the lubricant from the buffer tubes may occur during cable storage and installation.

<CIT> relates to an optical-fiber buffer tube, comprising an optical fiber comprising a glass fiber and one or more optical-fiber coating layers surrounding the glass fiber, a chemically modified polydimethylsiloxane prewetting agent applied to the optical fiber's outermost optical-fiber coating layer, and a polymeric sheath enclosing the optical fiber and the prewetting agent applied to said optical fiber's outermost optical-fiber coating layer.

<CIT> relates to a tubeless fiber optic cable comprising: at least one optical fiber; at least two strength members; a cable jacket, the cable jacket having a cavity wherein the at least one optical fiber is disposed within the cavity and the at least two strength members are disposed on opposite sides of the cavity and attached to the cable jacket; and a coupling agent, the coupling agent disposed within the cavity for coupling the at least one optical fiber to the fiber optic cable, but the coupling agent does not substantially fill a cross-sectional area of the cavity. The coupling agent is a suitable material such as a gel, a paste, a wax, a grease, emulsion having the liquid driven off.

<CIT> relates to a cable comprising: an outer sheath that has an inner wall defining a longitudinal cavity; a plurality of elements extending within the cavity, at least one of said elements comprising a sheath made of a thermoplastic polymer material; and a lubricant film at least partially covering the outside surface of at least one of said elements, wherein the lubricant film comprises silicone oil or polydimethylsiloxane.

Various aspects of the invention, which relates to a buffer tube, a method of manufacturing a buffer tube and an optical cable are described in the appended claims <NUM>-<NUM>.

In the present disclosure, various elements or components, described with reference to one figure, are denoted by the same reference in any subsequent figure. The description of such previously described elements will not be repeated as to not overburden the reader. Additionally, the figures are schematic representations and are not necessarily drawn to scale.

This disclosure relates to the application of an emulsion lubricant during the manufacturing of a gel-free buffer tube. The emulsion lubricant is mostly composed of water and smaller amounts of silicone and traces of emulsifying agent. The emulsion lubricant contains between about <NUM> percent to about <NUM> percent water, less than about <NUM> percent silicone, and less than <NUM> percent of emulsifying agent. In an example embodiment, the percentage of water is about <NUM> percent to about <NUM> percent, and the percentage of silicone is less than about <NUM> percent. A freezing point depressant may be added to the emulsion to prevent the emulsion from freezing at low temperatures. Examples of freezing point depressants are ethylene glycol, propylene glycol, some other alcohol, or some other water-soluble compound or mixture that depresses the freezing point of the emulsion when put into solution with the water component. If the freezing point depressant is added, a reduction of the water in the formulation is adjusted accordingly. Non-electrolytic freezing point depressants are preferred to prevent antagonistic action with the superabsorbent materials within the buffer tube.

In an embodiment, a controlled amount of emulsion lubricant is applied to the surface of one or more optical fibers prior to applying the swellable-thread and prior to extruding the polymeric sheath around the pre-wet optical fibers and water swellable-thread. The emulsion lubricant can be selectively applied using, for example, a wiping die or a misting spray process in a pre-wet or misting chamber. In some embodiments, the entrance to the chamber may be tapered. In some embodiments, the exit point of the chamber may have a designed land length that advantageously controls the amount of emulsion lubricant applied to the optical fibers.

The application rate of the emulsion lubricant applied to a single optical fiber may range from about <NUM> grams per fiber kilometer (g/fkm) to about <NUM>/fkm.

In one embodiment, a molten polymeric sheath surrounding a water-swellable material (e.g., swellable-thread) is then extruded around the pre-wet optical fibers to form a loose buffer tube. After the swellable-thread surrounds the pre-wet optical fibers, the ions in the swellable-thread absorb the water of the emulsion lubricant, leaving a thin layer of silicone between the bundle of optical fibers and the swellable-thread / polymeric sheath - the absorption of the water is a fairly quick interaction. The remaining silicone layer provides mechanical coupling and reduces stiction and buildup of static charges without the drippage observed in conventional gel-free buffer-tubes. As will be understood, the remaining silicone layer comprises some water in small amounts.

In another embodiment, the optical fibers are coated with an ultraviolet (UV) cured swellable coating that absorbs the water from the emulsion lubricant on the pre-wet optical fiber.

Aspects of disclosure provide a buffer tube design where an optical fiber is coated with a thin layer of silicone that advantageously reduces stiction and prevents the buildup of static electric charges during cable access, cable repair, and splicing. In one embodiment, the entirety of the water is absorbed by the swellable-thread and no lubricant flow is observed. Furthermore, the amount of silicone used in embodiments of this disclosure is substantially less than that used in prior art gel-free loose tube designs containing more typical silicone lubricants. Thus, providing a low-cost and environmental friendly solution for the manufacturing of optical cable buffer tubes. The emulsion is also typically far easier to remove from the fibers than traditional silicones due to the inclusion of the emulsifying agent. These and other aspects are discussed in greater detail below.

<FIG> illustrates a cross-sectional view of a conventional buffer tube <NUM>. The buffer tube <NUM> includes a polymeric sheath <NUM> surrounding optical fibers <NUM> and filled with a filling compound <NUM>. For purposes of clarity and consistency, the term "buffer tube," as used herein, generally refers to the combination of the optical fibers <NUM> and the surrounding polymeric sheath <NUM>.

The filling compound <NUM> is a petroleum-based filling compound (e.g., grease or grease-like gels). The filling compound <NUM>, being a thixotropic material, mechanically couples the optical fibers <NUM> to the polymeric sheath <NUM>. This prevents the optical fibers <NUM> from retracting inside the buffer tube <NUM> as the buffer tube <NUM> is processed during, for example, manufacturing (e.g., as the cable is installed or otherwise handled in the field) or subjected to thermally induced dimensional changes from environmental exposure. The filling compound <NUM> also prevents the ingress of water into the buffer tube <NUM>.

A substantial disadvantage of the filling compound <NUM> is the added inconvenience present during cable access, cable repair, and optical fiber splicing, in addition to its higher cost. Thixotropic filling greases are relatively heavy and messy, and thus hinder connection and splicing operations. The presence of the filling compound <NUM> requires cleaning the petroleum-based material from the optical fibers <NUM> prior to splicing - and occasionally from equipment and handling personal. This is a messy and time-consuming operation. Consequently, using conventional filling grease is undesirable.

<FIG> illustrates a cross-sectional view of a conventional dry-cable or loose-tube design buffer tube <NUM>. The buffer tube <NUM> includes a water-blocking element <NUM> positioned within the polymeric sheath <NUM>. The water-blocking element <NUM>, in the form of a water-swellable powder, can bound to a carrier tape or yarn, and can be readily removed during field operations (e.g., splicing).

Dry-cable designs eliminate the need for the filling compound (e.g., grease) while providing mechanical coupling and water-blocking functionalities. Generally, a dry-cable buffer tube is substantially free from thixotropic compositions (e.g., grease or grease-like gels), however, a totally dry design may eliminate the filling compound <NUM> from within the buffer tube altogether.

A substantial disadvantage of the dry-cable design is that the optical fibers <NUM> build up a charge of static electricity during processing, which cause the optical fibers <NUM> to repel one another. In this scenario, for example during extrusion, the optical fibers <NUM> will be forced into and likely stick to the molten inner wall of the polymeric sheath <NUM>. The sticking results in elevated optical fiber attenuation and may persist until the buffer tube <NUM> is opened for purposes of accessing the optical fibers <NUM>. The buildup of the static charge increases the difficulty of capturing optical fibers for splicing, connecting, or ribbonizing.

Another significant disadvantage of the dry-cable design is that after formation of the extruded buffer tube <NUM> around the optical fibers <NUM>, the optical fibers <NUM> tend to stick to the inner surface of the solidified buffer tube <NUM>. The stiction (i.e., force required to cause the optical fibers <NUM> to move when in contact with the polymeric sheath <NUM>) results in increased and / or highly variable excess fiber length (EFL) during manufacturing. Moreover, the stiction could have a negative impact to the operation of the clincher, which is an EFL controlling device that may be used in a loose tube buffering process. The stiction phenomenon can be the result of a static electricity, as well as simple contact and surface forces between the optical fiber <NUM> and the surrounding polymeric sheath <NUM>. Consequently, dry-cable designs offer added challenges for buffer tube manufacturing.

<FIG> illustrates a cross-sectional view of a conventional gel-free buffer tube <NUM>. In a gel-free buffer tube design, an alternative to the filing compound and dry-cable design, the buffer tube <NUM> includes a gel-free lubricant / fluid <NUM>. The fluid <NUM> provides lubrication and static elimination during processing. Unlike in gel-filled tubes, the lubricant layer accounts for a small fraction of the gap between the fiber bundle and the buffer tube. Increased interfacial interaction and adhesion between the fluid <NUM> and the optical fiber's outermost coating (e.g., a secondary coating or, if present, an ink layer) may help to retain the fluid <NUM> on the optical fiber <NUM> during manufacturing, storage, and installation of the buffer tube <NUM>. Selective application of the fluid <NUM> reduces stiction between the optical fiber <NUM> and the surrounding polymeric sheath <NUM> (e.g., during manufacturing, storage, and/or installation). The interfacial interaction, however, may sometimes have limitations on flow reduction on the fluid.

The fluid <NUM> also reduces and overcomes the static electrical charge and provides mechanical coupling by holding the optical fibers <NUM> in an easily manageable stack or bundle. The fluid <NUM> also prevents the optical fibers <NUM> from sticking to the wall of the buffer tube <NUM> during extrusion, allowing the excess fiber length to be reduced and controlled to acceptable and precise levels. Additionally, the lubricant or fluid allows for proper ratio of optical fiber <NUM> to buffer tube <NUM> length.

A disadvantage in existing gel-free buffer-tubes is that normal lubricating oils, within the desired viscosity range, tend to flow out of the buffer tube <NUM> when the buffer tube <NUM> (e.g., as incorporated into a cable) is positioned, for example, in a vertical orientation. Likewise, conventional lubricants pool in the buffer tube <NUM> when stored on a reel (e.g., a wound cable that includes a multitude of loose buffer tubes). An increase in the fluid viscosity (i.e., viscosity pertains to the relationship between force and the rate of flow) may reduce the rate of lubricant flow but does not prevent the flow of the fluid and the increase in viscosity may cause undesirable effects such as yield stress to the optical cable as high viscosity tends to retard wetting and spreading. Embodiments of this disclosure provide a solution to fluid flow within a gel-free buffer tube design.

<FIG> illustrate cross-sectional views of various embodiments of a buffer tube fabricated using an emulsion lubricant. <FIG> illustrates a cross-sectional view of an embodiment buffer tube <NUM> having a swellable-thread <NUM> and fabricated using an emulsion lubricant. The emulsion lubricant is applied to the surface of the optical fibers <NUM> prior to the polymeric sheath <NUM> and the swellable-thread <NUM> extruding around the optical fibers <NUM>. After the swellable-thread <NUM> surrounds the optical fibers <NUM>, the ions in the swellable-thread <NUM> absorb the water of the emulsion lubricant, leaving a thin layer of silicone <NUM> between the optical fibers <NUM> and the swellable-thread <NUM> / polymeric sheath <NUM> - the absorption of the water is a fairly quick interaction.

Silicone molecules, for example, forming a monolayer of silicone, coated over the bundle of optical fibers may be sufficient to increase the lubricity of the fibers. However, multiple layers of silicone coated over the optical fibers may also be contemplated. The remaining thin layer of silicone <NUM> provides mechanical lubrication and reduces stiction and buildup of static charges without the drippage observed in conventional gel-free buffer-tubes, for example in the buffer tube <NUM> discussed above.

It should be noted that the embodiment of <FIG> does not affect any functional aspect of the buffer tube <NUM> or of the optical cable during operation. It advantageously improves the cleaning of the optical fibers <NUM> during splicing and provides for an easier fiber optic access.

Advantageously, the thin layer of silicone <NUM> on the surface of the optical fibers <NUM> is much thinner than that of the filling compound or lubricant in the previous embodiments, resulting in less silicone to be used in the manufacturing of the buffer tube <NUM>. Furthermore, as water provides the majority of the emulsion lubricant, the emulsion lubricant provides a low cost and environmentally friendly alternative to the conventional petroleum based filling compounds and lubricants.

The emulsion lubricant contains between about <NUM> percent to about <NUM> percent water, less than about <NUM> percent silicone, and less than <NUM> percent of emulsifying agent. In a preferred embodiment, the percentage of water is about <NUM> percent to about <NUM> percent, and the percentage of silicone is less than about <NUM> percent.

In an example embodiment, the silicone emulsion may be a compound similar to Armor All ™, which is used as a gloss enhancer and protectant for plastics. Antioxidants can be included in this type of formulation to provide protection to the plastic or rubber. In another example embodiment, the silicone-based emulsion may be polywater FFTx, which is commercially available.

In another example embodiment, the silicone may be polydimethylsiloxane with a viscosity of <NUM> cP and corresponding to a chemical abstracts service (<NPL>. A polydimethylsiloxane having a modified polymeric chain backbone may also be used. The polydimethylsiloxane is typically modified with functional groups including alkyl, polyglycol, polyether, amino, halogenated groups, or other such functional groups, to modify affinity, wetting, and interfacial-adhesion properties (e.g., with respect to optical-fiber coatings).

In yet another example embodiment, the silicone may be a functionalized silicone, such as Lurol <NUM>, a textile-yarn spin finish with an improved adhesion tension to optical fiber coating that is made available from Goulston Technologies, Inc. (Monroe, N. Lurol <NUM> is chemically functionalized, which slightly alters the surface tension and adhesive tension values from a standard polydimethylsiloxane fluid.

In another example embodiment, the emulsion lubricant may be SP9650 from Momentive Performance Materials or Rhodorsil Fluid 47V50 from BlueStar Silicones.

Generally, the viscosity of the silicone may range from about <NUM> centipoise (cP) / millipascal seconds (mPa. s) to about <NUM> cP. In one embodiment, the viscosity of the silicone may range from about <NUM> cP to about <NUM> cP.

In an embodiment, the emulsifying agent is a silicone surfactant, such as dimethicone copolyol, hydroxy terminated dimethicone copolyol, methoxy terminated dimethicone copolyol, or Nonylphenol. In other embodiments, the emulsifying agent is an ionic, a non-ionic surfactant, an amphoteric surfactant, or a combination (i.e., mixture) thereof.

In a non-limiting example, the optical fibers <NUM> may be loosely placed in the buffer tube <NUM>. Because the optical fibers <NUM> typically bunch together within the buffer tube <NUM>, the optical fibers <NUM> are depicted in <FIG> as centrally located bundles within the buffer tube <NUM>. However, other arrangements are contemplated.

The swellable-thread <NUM> is positioned within the polymeric sheath <NUM> and is a superabsorbent material capable of absorbing water. In an embodiment, the swellable-thread <NUM> may be a tape or a yarn carrying a water-swellable material (e.g., water-swellable powder). The swellable-thread <NUM> is dry to the touch and may be helically wrapped around the optical fibers <NUM> before the polymeric sheath <NUM> is extruded around the optical fibers <NUM> within the buffer tube's annular space. Alternatively, the swellable-thread <NUM> may be a water-swellable yarn (e.g., a thread-sized water-blocking element) positioned longitudinally (e.g., adjacent to the pre-wet optical fibers) within the buffer tube's annular space.

In an embodiment, the polymeric sheath <NUM> is made from polyolefin (e.g., nucleated or non-nucleated polyethylene, nucleated polypropylene, or a copolymer or blend thereof), polyester (e.g., polybutylene terephthalate), a polyamide (e.g., nylon), or a flame retardant composition, such as a low-smoke, zero-halogen (LSZH) compound, a flame retardant polyvinyl chloride (PVC), or a polyvinylidene difluoride (PVDF) copolymer.

The polymeric sheath <NUM> may be formed of one or more layers. The layers may be homogeneous or include mixtures or blends of various materials within each layer. The polymeric sheath may be extruded (e.g., an extruded polymeric material). As an example, the polymeric sheath may include a material to provide high temperature and chemical resistance (e.g., an aromatic material or polysulfone material).

<FIG> illustrates a cross-sectional view of an embodiment buffer tube <NUM> having a ultraviolet (UV) cured swellable coating <NUM> over the bundle of optical cables and fabricated using an emulsion lubricant. Although buffer tubes typically have a circular cross section (e.g., buffer tube <NUM>), buffer tubes alternatively may have an irregular or non-circular shape (e.g., an oval or a trapezoidal cross-section). Buffer tube <NUM> illustrates a buffer tube having an irregular or non-circular shape.

Unlike the buffer tube <NUM>, which has a swellable-thread <NUM>, the buffer tube <NUM> has a UV cured swellable coating <NUM>. The UV cured swellable coating <NUM> is applied to the optical fibers <NUM> prior to the buffering process. The UV cured swellable coating <NUM>, similar to the swellable-thread <NUM>, absorbs the water in the emulsion lubricant.

To the extent that non-circular buffer tubes are used, the longest inner cross-sectional width of the buffer tube <NUM> can be used to define the diameter of a theoretical circularized buffer tube cross-sectional area.

<FIG> illustrates a cross-sectional view of an embodiment buffer tube <NUM> having a swellable-thread <NUM> and fabricated using an emulsion lubricant. Unlike the buffer tubes <NUM> and <NUM>, the swellable-thread <NUM> is surrounded by the one or more optical fibers <NUM>. The optical fibers <NUM> may be arranged around the swellable-thread <NUM> after the application of the emulsion lubricant. The swellable-thread <NUM> absorbs the water in the emulsion lubricant, leaving a layer of silicone <NUM> between the optical fibers <NUM> and the polymeric buffer tube <NUM>. In some embodiments, the buffer tube <NUM> may have an irregular or non-circular shape.

<FIG> illustrates a cross-sectional view of an embodiment buffer tube <NUM> having a swellable-thread <NUM> and fabricated using an emulsion lubricant. Unlike the buffer tubes <NUM>, <NUM>, and <NUM>, the swellable-thread <NUM> is interwoven between the optical fibers <NUM>. The swellable-thread <NUM> absorbs the water in the emulsion lubricant, leaving a layer of silicone <NUM> between the optical fibers <NUM> and the polymeric buffer tube <NUM>. In some embodiments, the buffer tube <NUM> may have an irregular or non-circular shape. In some embodiments, the swellable-thread <NUM> may consist of more than one thread. As an example, the swellable-thread <NUM> may include several water-absorbent threads interwoven between the several optical fibers <NUM>.

<FIG> is a flowchart of an embodiment method <NUM> for fabricating an optical cable with a buffer tube <NUM>,<NUM>, <NUM>, or <NUM> and using an emulsion lubricant. At step <NUM>, the optical fibers are first rolled, or guided with a guiding die, in the form of the bundle of optical fibers in an irregular or circular shape.

At step <NUM>, a static electricity discharger may be used to remove the repelling force among fibers thus keeping all of the fibers in a bundle. The bundle of optical fibers enter a chamber, for example, at an entry-die or coating head. In some embodiments, the entrance to the chamber may be tapered to advantageously eliminate the negative effects of a sharp edge.

Optical fibers may be deployed in either a single-fiber loose buffer tube or a multi-fiber loose buffer tube. With respect to the latter, multiple optical fibers may be bundled or stranded within a buffer tube or other structure. In this regard, within a multi-fiber loose buffer tube, fiber sub-bundles may be separated with binders (e.g., each fiber sub-bundle is enveloped in a binder). Moreover, fan-out tubing may be installed at the termination of such loose buffer tubes to directly terminate loose-buffered optical fibers with field-installed connectors.

The optical fibers are typically densely packed, bundled in ribbons, and arranged in a stacked form. By separating different bundles of optical fibers <NUM> within different buffer tubes, cable operators and / or installers are assisted with a more organized cable management arrangement.

In general, it is desirable to increase the filling of optical elements (e.g., optical fibers) in buffer tubes or optical cables, subject to other constraints (e.g., cable or mid-span attenuation). The optical elements themselves may be designed for increased packing density. As an example, the optical fiber <NUM> may possess modified properties, such as improved refractive-index profile, core or cladding dimensions, or primary-coating thickness and/or modulus, to improve microbending and macrobending characteristics.

At step <NUM>, the bundle of optical fibers <NUM> are then soaked with the emulsion lubricant inside the chamber. In an embodiment, the emulsion lubricant is applied to the bundle of fiber optics <NUM> using a spray process, for example, in a misting chamber. In such an embodiment, the application rate of the emulsion lubricant is controlled by the misting rate. In some embodiments, the emulsion lubricant is applied to the surface of the bundle of optical fibers <NUM> using, for example, a wiping die process in a pre-wet chamber or a chamber filled with the emulsion lubricant. The prewet chamber is built in this manner so that an adequate emulsion lubricant fluid head pressure may be established. This may be accomplished by properly differentiating the positions of the emulsion entry pot and the overflow pot. The emulsion lubricant is sufficiently applied on the outer surface of the fiber bundle only.

The majority of the emulsion lubricant is applied onto the outer surface of the bundle of the optical fibers <NUM> and a minimal amount within the interior of the bundle of optical fibers <NUM>. In an embodiment, the pre-wet is applied over bundles of twelve optical fibers. Although embodiments with less or more optical fibers <NUM> per buffer tube may be contemplated.

Generally, it is desirable to reduce the amount of silicone applied to the bundle of optical fibers <NUM>. It has been observed that the percentage of emulsifying agent is (i) directly related to the percentage of silicone in the emulsion lubricant and that (ii) the amount of silicone capable of being dissolved in water, using the emulsifying agent, has an upper limit, at which point the emulsion lubricant becomes unstable and the silicone segregates out. Therefore, the proper percentage of the composition is essential.

At step <NUM>, the bundle of optical fibers <NUM>, soaked in the emulsion lubricant, pass through a chamber-wiping die (e.g., exit-die) to remove any excess emulsion lubricant. In some embodiments, the exit point of the chamber may have a designed "land" length. It is observed, due to slight variations in the outer diameter of bundles of optical fibers <NUM>, some excess silicone may be necessary to improve process reliability. However, it is preferable to minimize the excess silicone as excess silicone may result in dripping and difficulties in splicing of the optical fibers <NUM>.

The wiping die helps to control the application rate of the emulsion lubricant, providing a uniform emulsion lubricant coating. In an embodiment, the diameter of the wiping die is sized nominally slightly larger than the outer diameter of the bundle of optical fibers <NUM>. In one embodiment, the wiping die may be a hole in a piece of metal.

The land length that advantageously controls the amount of emulsion lubricant applied onto the bundle of optical fibers <NUM>. The land length may be from about <NUM> to about <NUM>. It is noted that excessively long land length may result in increased optical fiber tension. Additionally, lubricant can push into the bundle of optical fibers as a result of a long land length. The lubricant penetrates the fiber bundle resulting in excessive amounts of silicone lubricant on fibers.

In an example embodiment, an optical fiber <NUM> has an outer diameter of <NUM> micrometers (µm) and a cross-sectional area of about <NUM> millimeter squared (mm<NUM>). A bundle of twelve of such optical fibers <NUM> has a cross-sectional area of about <NUM><NUM>. An exit-die of a chamber with an approximate diameter of <NUM> has a cross-sectional area of about <NUM><NUM>. The chamber includes a tapered entrance and a land length of about <NUM>. This results in a fill ratio of about <NUM> %.

The nominal application rate of the emulsion lubricant may be about <NUM> grams / fiber-kilometer (g/fkm) for a single optical fiber or about <NUM>/fkm for a bundle of twelve optical fibers. The application rate of emulsion lubricant may range from about <NUM>/fkm for a single optical fiber or about <NUM>/fkm for a bundle of twelve optical fibers to about <NUM>/fkm for a single optical fiber or <NUM>/fkm for a bundle of twelve optical fibers.

In one embodiment, the application rate of the emulsion lubricant may range from about <NUM>/fkm for a single optical fiber or about <NUM>/fkm for a bundle of twelve optical fibers to about <NUM>/fkm for a single optical fiber or about <NUM>/fkm for a bundle of twelve optical fibers. Preferentially a reduced application at a level of <NUM>/fkm or below is desired.

At step <NUM>, a swellable-thread is added to the one or more optical fibers. The ions in the swellable-thread <NUM> absorb the water of the emulsion lubricant, leaving a thin layer of silicone around the optical fibers. In one embodiment, the swellable-thread <NUM> surrounds the one or more optical fibers <NUM>. In another embodiment, the swellable-thread <NUM> is surrounded by the one or more optical fibers <NUM>. In yet another embodiment, the swellable-thread <NUM> is interwoven with the one or more optical fibers. In this embodiment, the swellable-thread <NUM> is located in-between the one or more optical fibers. In the embodiments where the water swellable-thread is surrounded by, interwoven with, or located in-between the one or more optical fibers, step <NUM> may take place simultaneously with step <NUM>.

At step <NUM>, the swellable-thread <NUM> resulting bundle is positioned within the polymeric buffer tube <NUM>. In one embodiment, the swellable-thread <NUM> is a UV cured swellable coating. In another embodiment, the swellable-thread <NUM> is a tape or a yarn carrying a water-swellable material (e.g., water-swellable powder). In an embodiment, the emulsion lubricant may be used in combination with a water resistant optical fiber coating and coloring system as some optical fiber coatings have shown an increase in attenuation after soaking water.

Optionally, at step <NUM>, the buffer tubes are provided externally adjacent to a central strength member or a radial strength member (RSM). In some embodiments, the optical cable may not have a rigid strength member.

At step <NUM>, a protective outer jacket <NUM> is provided around the buffer tubes <NUM> and the central strength member <NUM> to form an optical cable.

<FIG> illustrates a cross-sectional view of an embodiment optical cable <NUM>. The optical cable <NUM> includes a central strength member <NUM>, buffer tubes <NUM>, and a protective outer jacket <NUM>. The central strength member <NUM> is positioned at the middle of the optical cable <NUM>. Buffer tubes <NUM> are provided externally adjacent to the central strength member <NUM>. Each buffer tube <NUM> contains one or more optical fibers <NUM>. The protective outer jacket <NUM> is provided around the buffer tubes <NUM> and the central strength member <NUM>.

The central strength member <NUM> is made from a rigid material, such as metallic elements, glass reinforced composite rods (e.g., glass-reinforced epoxy), aramid reinforced composite rods, or composite rods made from material with high modulus and low coefficient of expansion (e.g., carbon fiber). The central strength member <NUM> is the primary anti-buckling element in the optical cable <NUM> and provides mechanical integrity to the optical cable <NUM>, particularly under heavy stress.

As an example, during installation, the optical cable <NUM> may be subjected to significant strain. The central strength member <NUM> provides tensile strength to keep optical fibers <NUM> within the designated strain limit. The central strength member <NUM> also resists cable contraction at low temperatures and prevents optical fiber buckling, which would otherwise occur due to differential coefficient of expansion between optical fibers and other plastic cable components. The central strength member <NUM> additionally prevents the optical cable <NUM> from being compressed and provides a primary clamping point for hardware used to connect the cable to the splice or routing enclosures.

The buffer tube <NUM> may include single-mode optical fibers and/or multimode optical fibers. An optical fiber <NUM> typically includes a component glass fiber (i.e., glass core and surrounding cladding layers) and one or more coating layers (e.g., primary coating and second coating). At least one of the coating layers - typically the secondary coating - may be colored and/or possess other markings to help identify individual fibers. Alternatively, a tertiary ink layer may surround the primary and secondary coatings, in which case the tertiary ink layer is considered to be the outermost optical-fiber coating layer.

The respective coating layers typically possess a urethane-acrylate chemistry. As an example, after curing, an exemplary urethane-acrylate primary coating might possess (i) an in situ modulus of less than about <NUM> millipascal (MPa) (e.g., less than <NUM> MPa, such as between about <NUM> MPa and <NUM> MPa) and (ii) a glass transition temperature of less than about - <NUM>° Celsius (C), and an exemplary urethane-acrylate secondary coating might possess a modulus of between about <NUM> MPa and <NUM>,<NUM> MPa (e.g., about <NUM> MPa) as disclosed in commonly assigned <CIT> for a Microbend-Resistant Optical Fiber (Overton) and/or commonly assigned <CIT> for a Reduced-Diameter Optical Fiber (Overton).

In one embodiment, the optical fibers <NUM> include one or more multimode optical fibers (e.g., conventional multimode optical fibers with a <NUM>-micron core, such as OM2 multimode optical fibers, that comply with the ITU-T G. <NUM> recommendations). An exemplary multimode optical fiber that may be employed is MaxCap™ multimode optical fibers (OM2+, OM3, or OM4), which are commercially available from Draka (Claremont, N. In another embodiment, the present buffer tube includes a plurality of standard single-mode optical fibers (SSMF).

In contrast, in accordance with the ITU-T G. <NUM> recommendations, standard multimode optical fibers have macrobending losses of (i) no more than <NUM> dB at a wavelength of <NUM> nanometers for a winding of two turns around a spool with a bending radius of <NUM> millimeters and (ii) no more than <NUM> dB at a wavelength of <NUM> nanometers for a winding of two turns around a spool with a bending radius of <NUM> millimeters. Moreover, as measured using a winding of two turns around a spool with a bending radius of <NUM> millimeters, such standard multimode optical fibers typically have macrobending losses of (i) greater than <NUM> dB, more typically greater than <NUM> dB (e.g., <NUM> dB or more), at a wavelength of <NUM> nanometers and (ii) greater than <NUM> dB, more typically greater than <NUM> dB (e.g., <NUM> dB or more), at a wavelength of <NUM> nanometers.

Multimode optical fibers are advantageous, because their relatively large core diameter facilitates easy connectorization. Accordingly, it is within the scope of the present disclosure to employ multimode optical fibers having enlarged core diameters (e.g., <NUM> microns or greater), such as between about <NUM> microns and <NUM> microns (e.g., about <NUM> microns).

In yet another embodiment, the buffer tube includes a plurality of bend-insensitive single-mode optical fibers. Bend-insensitive optical fibers perform better (i.e., are less susceptible to attenuation) than standard optical fibers in the mid-span temperature-cycle test at high buffer-tube filling coefficients. Accordingly, bend-insensitive optical fibers facilitate a reduction in buffer-tube inner diameter and/or an increase in EFL tolerance.

The buffer tube may include bend-insensitive multimode optical fibers, such as MaxCap™-BB-OMx multimode optical fibers, which are commercially available from Draka (Claremont, N. In this regard, bend-insensitive multimode optical fibers typically have macrobending losses of (i) no more than <NUM> dB at a wavelength of <NUM> nanometers for a winding of two turns around a spool with a bending radius of <NUM> millimeters and (ii) no more than <NUM> dB at a wavelength of <NUM> nanometers for a winding of two turns around a spool with a bending radius of <NUM> millimeters.

Moreover, the buffer tubes typically have excess fiber length (EFL) of less than about <NUM> percent, typically less than about <NUM> percent (e.g., <NUM> percent or less). Excess fiber length may be determined by sectioning a ten-meter sample of the buffer tube that has equilibrated for at least <NUM> hours after manufacture and thereupon comparing the length of constituent optical fibers against the sectioned ten-meter sample.

Although the foregoing description discusses loose buffer tubes containing discrete optical fibers (i.e., non-ribbonized optical fibers), the present disclosure also embraces buffer tubes containing optical-fiber ribbons. The pre-wetting agent should possess an excellent surface affinity, wetting, and/or interfacial adhesion with the outer ribbon matrix material (e.g., a urethane-acrylate composition).

In this regard, optical fibers <NUM> may be sandwiched, encapsulated, and/or edge bonded to form an optical fiber ribbon. Optical fiber ribbons can be divisible into subunits (e.g., a twelve-fiber ribbon that is splittable into six-fiber subunits). Moreover, a plurality of such optical fiber ribbons may be aggregated to form a ribbon stack, which can have various sizes and shapes.

As an example, it is possible to form a rectangular ribbon stack or a ribbon stack in which the uppermost and lowermost optical fiber ribbons have fewer optical fibers <NUM> than those toward the center of the stack. This construction may be useful to increase the density of optical elements (e.g., optical fibers) within the buffer tube <NUM> and/or optical cable <NUM>.

By way of example, a rectangular ribbon stack may be formed with or without a central twist (i.e., a "primary twist"). A ribbon stack is typically manufactured with rotational twist to allow the buffer tube <NUM> or optical cable <NUM> to bend without placing excessive mechanical stress on the optical fibers <NUM> during winding, installation, and use. In a structural variation, a twisted (or untwisted) rectangular ribbon stack may be further formed into a coil-like configuration (e.g., a helix) or a wave-like configuration (e.g., a sinusoid). In other words, the ribbon stack may possess regular "secondary" deformations.

A plurality of buffer tubes <NUM> may be positioned externally adjacent to and stranded around the central strength member <NUM>. This stranding can be accomplished helically in one direction, known as "S" or "Z" stranding, or via Reverse Oscillated Lay stranding, known as "S-Z" stranding. Stranding about the central strength member <NUM> reduces optical fiber strain when optical cable strain occurs during installation and use. Minimizing fiber strain benefits both tensile cable strain and longitudinal compressive cable strain during installation or operating conditions.

With respect to tensile cable strain, which may occur during installation, the optical cable <NUM> will become longer while the optical fibers <NUM> can migrate closer to the cable's neutral axis to reduce, if not eliminate, the strain being translated to the optical fibers <NUM>. With respect to longitudinal compressive strain, which may occur at low operating temperatures due to shrinkage of the cable components, the optical fibers <NUM> will migrate farther away from the cable's neutral axis to reduce, if not eliminate, the compressive strain being translated to the optical fibers <NUM>.

In a stranding variation, two or more substantially concentric layers of buffer tubes may be positioned around a central strength member <NUM>. In a further variation, multiple stranding elements (e.g., multiple buffer tubes stranded around a strength member) may themselves be stranded around each other or around a central strength member <NUM>.

Alternatively, a plurality of the present buffer tubes may be simply placed externally adjacent to the central strength member <NUM> (i.e., the buffer tubes <NUM> are not intentionally stranded or arranged around the central strength member <NUM> in a particular manner and run substantially parallel to the central strength member <NUM>).

Alternatively still, the optical fibers <NUM> may be positioned within a central buffer tube (i.e., the central buffer tube cable has a central buffer tube rather than a central strength member). Such a central buffer tube cable may position strength members elsewhere. For instance, metallic or non-metallic (e.g., GRP) strength members may be positioned within the cable sheath itself, and/or one or more layers of high-strength yarns (e.g., aramid or non-aramid yarns) may be positioned parallel to or wrapped (e.g., contra-helically) around the central buffer tube (i.e., within the cable's interior space). As will be understood by those having ordinary skill in the art, such strength yarns provide tensile strength to optical cables <NUM>. Likewise, strength members can be included within the buffer tube's casing. Strength yarns may be coated with a lubricant (e.g., fluoropolymers), which may reduce unwanted attenuation in optical cable <NUM> (e.g., rectangular, flat ribbon cables or round, loose tube cables) that are subjected to relatively tight bends (i.e., a low bend radius). Moreover, the presence of a lubricant on strength yarns (e.g., aramid strength yarns) may facilitate removal of the cable jacketing by reducing unwanted bonding between the strength yarns and the surrounding cable jacket.

In another cabling embodiment, multiple buffer tubes may be stranded around themselves without the presence of a central member. These stranded buffer tubes may be surrounded by a protective tube. The protective tube may serve as the outer casing of the optical cables <NUM> or may be further surrounded by an outer sheath. The protective tube may either tightly surround or loosely surround the stranded buffer tubes.

Additional elements may be included within a cable core. As an example, copper cables or other active transmission elements may be stranded or otherwise bundled within the cable sheath. Passive elements may also be placed within the cable core, such as between the interior walls of the buffer tubes and the enclosed optical fibers <NUM>. Alternatively and by way of example, passive elements may be placed outside the buffer tubes between the respective exterior walls of the buffer tubes and the interior wall of the cable jacket, or within the interior space of a buffer-tube-free cable.

As an example, yarns, nonwovens, fabrics (e.g., tapes), foams, or other materials containing water-swellable material and/or coated with water-swellable materials (e.g., including super absorbent polymers (SAPs), such as SAP powder) may be employed to provide water blocking and/or to couple the optical fibers <NUM> to the surrounding buffer tube and/or cable jacketing (e.g., via adhesion, friction, and/or compression).

Moreover, an adhesive (e.g., a hot-melt adhesive or curable adhesive, such as a silicone acrylate cross-linked by exposure to actinic radiation) may be provided on one or more passive elements (e.g., water-swellable material) to bond the elements to the buffer tube. An adhesive material may also be used to bond the water-swellable element to optical fibers <NUM> within the buffer tube.

Cable enclosing buffer tubes may have a sheath formed from various materials in various designs. Cable sheathing may be formed from polymeric materials such as, for example, polyethylene, polypropylene, polyvinyl chloride (PVC), polyamides (e.g., nylon), polyester (e.g., PBT), fluorinated plastics (e.g., perfluorethylene propylene, polyvinyl fluoride, or polyvinylidene difluoride), and ethylene vinyl acetate. The sheath and/or buffer tube materials may also contain other additives, such as nucleating agents, flame-retardants, smoke-retardants, antioxidants, UV absorbers, and/or plasticizers.

The cable sheathing may be a single jacket formed from a dielectric material (e.g., non-conducting polymers), with or without supplemental structural components that may be used to improve the protection (e.g., from rodents) and strength provided by the cable sheath. As an example, one or more layers of metallic (e.g., steel) tape, along with one or more dielectric jackets, may form the cable sheathing. Metallic or fiberglass reinforcing rods (e.g., GRP) may also be incorporated into the sheath. In addition, aramid, fiberglass, or polyester yarns may be employed under the various sheath materials (e.g., between the cable sheath and the cable core), and/or ripcords may be positioned, for example, within the cable sheath. Similar to buffer tubes <NUM>, optical cable sheaths typically have a circular cross section, but optical cable sheaths alternatively may have an irregular or non-circular shape (e.g., an oval, trapezoidal, or flat cross-section).

As noted, the optical fibers <NUM> (e.g., loose or ribbonized fibers) in the buffer tube <NUM> may be stranded (e.g., around a central strength member). In such configurations, an optical cable protective outer sheath may have a textured outer surface that periodically varies lengthwise along the optical cable <NUM> in a manner that replicates the stranded shape of the underlying buffer tubes <NUM>. The textured profile of the protective outer sheath can improve the blowing performance of the optical cable <NUM>. The textured surface reduces the contact surface between the cable and the duct or microduct and increases the friction between the blowing medium (e.g., air) and the optical cable <NUM>. The protective outer sheath may be made of a low coefficient-of-friction material, which can facilitate blown installation. Moreover, the protective outer sheath can be provided with a lubricant to further facilitate blown installation.

In accordance with the foregoing, the buffer tubes <NUM> may be assembled into various optical cables. An exemplary optical cable may include a plurality of buffer tubes <NUM> (e.g., between two and twelve buffer tubes <NUM>, such as ten buffer tubes shown in <FIG>). The individual buffer tubes are in close proximity to the other buffer tubes <NUM> and the central strength member <NUM>. As an example, in an optical cable <NUM> containing ten buffer tubes, an individual buffer tube may contact two adjacent buffer tubes, the central strength member <NUM>, and the protective outer jacket <NUM> (i.e., the ten buffer tubes are positioned around the central strength member <NUM> as depicted in <FIG>).

Typically, all of the buffer tubes within a single optical cable have the same outer diameters and inner diameters. As an example, if the optical cable contains ten buffer tubes, all ten buffer tubes have the same outer diameter and inner diameter. The buffer tubes in accordance with the present disclosure may have an outer diameter ranging from about <NUM> millimeters to about <NUM> millimeters (e.g., about <NUM> to <NUM> millimeters). In an embodiment, the buffer tubes <NUM> may have an outer diameter of about <NUM> millimeters. In another embodiment, the buffer tubes <NUM> may have an outer diameter of less than about <NUM> millimeters (e.g., about <NUM> to <NUM> millimeters). In yet another embodiment, the buffer tubes <NUM> may have an outer diameter of <NUM> millimeters and an inner diameter of <NUM> millimeters. That said, buffer tubes having varying inner diameters and varying outer diameters are within the scope of the present disclosure. The shapes of the buffer tubes within a single optical cable may vary (i.e., all of the buffer tubes are not required to have the same shape).

The optical fibers <NUM>, which are coated with a thin layer of emulsion lubricant in accordance with the present disclosure, may be distributed evenly among the buffer tubes <NUM> (i.e., each buffer tube contains an equal number of optical fibers <NUM>). As an example, an optical cable <NUM> containing <NUM> optical fibers <NUM> and ten buffer tubes <NUM> may have twenty-four optical fibers per buffer tube <NUM>. In one exemplary embodiment, the optical cable <NUM> includes twelve buffer tubes <NUM>, each buffer tube containing twenty-four, pre-wet optical fibers.

The buffer tubes <NUM> containing the optical fibers <NUM> may be stranded around the central strength member <NUM>. As an example, the buffer tubes <NUM> can be positioned externally adjacent to and stranded around the central strength member <NUM>. The stranding can be accomplished in one direction, helically, known as "S" stranding, or Reverse Oscillated Lay stranding, known as "S-Z" stranding. Stranding about the central strength member <NUM> increases the operational and installation flexibility of the optical cable <NUM>. S-Z stranding, for example, allows easy unraveling of the buffer tubes <NUM> for mid-span access.

In other embodiments, the buffer tubes <NUM> containing the optical fibers <NUM> are simply placed externally adjacent to the central strength member <NUM> (i.e., the buffer tubes <NUM> are not intentionally stranded or arranged around the central strength member <NUM> in a particular manner and run substantially parallel to the central strength member <NUM>).

The protective outer jacket <NUM> encapsulates the one or more buffer tubes <NUM>. In some embodiments, the protective outer jacket <NUM> maintains a substantially uniform thickness over the length of the optical cable <NUM>. The thickness of the protective outer jacket <NUM> may be adjusted to reduce or increase the overall diameter of the optical cable <NUM> or to provide greater protection to the optical cable <NUM>. In one embodiment, the protective outer jacket <NUM> is <NUM> millimeter thick.

The protective outer jacket <NUM> may be made of a low coefficient-of-friction material, which can facilitate blown installation. Yet, in other embodiments, the protective outer jacket <NUM> can be provided with a lubricant to further facilitate blown installation. The protective outer jacket <NUM> is typically made of polymeric materials, such as polyurethane, polyethylene, nylon, PVC or other suitable material. The protective outer jacket <NUM> may include other materials known to be suitable for use as a protective outer jacket.

In some embodiments, the protective outer jacket <NUM> fits tightly around and conforms to the outside of the buffer tubes <NUM> in such a way that it substantially fills the gaps between adjacent buffer tubes. In this particular embodiment, the protective outer jacket <NUM> is thin (e.g., <NUM> millimeter thick or so) so that the external surface of the optical cable <NUM> is textured rather than smooth.

In some embodiments, the buffer tubes <NUM> are stranded (e.g., S stranded or S-Z stranded) around the central strength member <NUM>. In such embodiments, the textured outer surface of the optical cable <NUM> periodically varies lengthwise along the optical cable <NUM> in a manner that replicates the stranded shape of the underlying buffer tubes <NUM>. The textured profile of the protective outer jacket <NUM> of this embodiment further improves the blowing performance of the optical cable <NUM>. The textured surface reduces the contact surface between the optical cable <NUM> and the microduct and increases the friction between the blowing medium (e.g., air or liquid) and the optical cable <NUM>.

While it is understood that an optical cable may include multiple buffer tubes, each encapsulating multiple optical fibers, a limited number of symmetric buffer tubes and optical fibers <NUM> are illustrated in <FIG> for simplicity of discussion and illustration. Additionally, each buffer tube <NUM> and/or optical fiber <NUM> may have the same or different inner and outer diameter dimension. The shapes of the buffer tubes within a single optical cable may vary (i.e., all of the buffer tubes <NUM> are not required to have the same shape). These are not intended to limit the embodiment in <FIG>. Exemplary optical cable designs are disclosed in commonly assigned <CIT>. It should be noted that although <FIG> includes the buffer tube <NUM> as an example buffer tube in the optical cable <NUM>, optical cables having buffer tube <NUM> or a combination of buffer tube <NUM> and / or <NUM> may also be contemplated.

As an emulsion system may entrain water into the fiber optic buffer tube, and some optical fibers and optical fiber coating systems can show sensitivity to water, it may be beneficial that the system be environmentally robust to the presence of water in the emulsion. The optical fiber coating, inking, and emulsion system may be capable of withstanding a period of at least <NUM> days of water exposure or humidity conditioning tests at <NUM> degrees Celsius (° C) with an increase in attenuation that is less than <NUM> decibel / kilometer (dB/km), and preferentially less than <NUM> dB/km at a wavelength of <NUM> nanometer (nm). Examples of such testing could be water immersion or conditioning at elevated humidity (<NUM>%) of buffer tubes containing the fiber/emulsion system. An example of test results are included in the Table <NUM> below.

In the Table <NUM> above, the least square approximation (LSA) measurement of the attenuation (Atten) per kilometer (km) in decibels (Atten. LSA (dB/km)) for an initial measurement at room temperature (RT), initial measurement at <NUM>° C, and a final measurement (after <NUM> days) at <NUM> ° C are shown. The various rows (BL, OR, etc.) are illustrative of a variety of parts that are used to determine a change in attenuation. As illustrated in the Table <NUM> above, the change in the least square approximation measurement of the attenuation per kilometer (Δ Atten. LSA (dB/km) is less than <NUM>.

<FIG> illustrates a cross-sectional view of an embodiment buffer tube <NUM> manufactured using an emulsion lubricant. As shown, a first thin layer of silicone <NUM> covers about a <NUM> degree portion (i.e., Θ<NUM> = <NUM> degrees) of the circumference of the outer surface of the optical fibers <NUM>. A second thin layer of silicone <NUM> covers about a <NUM> degree portion (i.e., Θ<NUM> = <NUM> degrees) of the circumference of the outer surface of the optical fibers <NUM>. A third layer of silicone <NUM> covers about a <NUM> degree portion (i.e., Θ<NUM> = <NUM> degrees) of the outer surface of the optical fibers <NUM>. A fourth layer of silicone <NUM> covers about a <NUM> degree (i.e., Θ<NUM> = <NUM> degrees) portion of the outer surface of the optical fibers <NUM>. The thin layer of silicone <NUM>, <NUM>, <NUM>, and <NUM> consists of layers of interconnected silicon and oxygen atoms located at the surface of the bundle of optical fibers <NUM>.

As illustrated, the third layer of silicone <NUM> and fourth layer of silicone <NUM> are comprised of molecules of silicone. The first layer of silicone <NUM> and second layer of silicone <NUM> are discontinuous from the other layers. In other embodiments, the thin layer of silicone may consist of one or more continuous or discontinuous layers of silicone covering some - at least <NUM> percent of the circumference and up to a <NUM>-degree coverage of the circumference of the outer surface of the optical fibers. The thin layer of silicone may be monolayer (e.g., about <NUM> or <NUM> angstroms) or multi layers of molecules having a thickness (i.e., depth) of between about <NUM> nanometers (nm) to <NUM>. The illustration in Figure of <NUM> is for discussion purposes and is a non-limiting example. As an example, the optical fibers may be arranged in a non-circular formation.

The thin layer of silicone is different from a silicone powder. A silicone powder, such as a silicone resin powder (e.g., crosslinked structure), a silicone rubber powder (crosslinked polymer), or a hybrid silicone powder (e.g., rubber powders covered with resin) by itself or within a resin or ink includes a number of discontinuous spherical shaped molecules. The presence of silicone powders can be differentiated from a silicone fluid by a combination of examination under a microscope and Fourier-transform infrared spectroscopy (FTIR) identification of the powder species. The thin layer of silicone remains in the buffer tube after absorption of the water from the emulsion lubricant that was applied to the one or more optical fibers during manufacturing the buffer tube. Not all water from the emulsion lubricant is absorbed by the swellable-thread and some small amount of water remains present in the thin layer of silicone, while most of the water is absorbed in the swellable-thread.

<FIG> is a FTIR illustrating a first infrared spectrum <NUM> of a fiber surface removed from a first buffer tube manufactured using an embodiment emulsion lubricant such as Polywater FFTx. A second infrared spectrum <NUM> water and a third infrared spectrum <NUM> of a third gel-free buffer tube manufactured using functionalized silicone are also illustrated. The fiber surface from a fiber in a first buffer tube manufactured using an emulsion lubricant is as discussed in one embodiment and has a FTIR spectrum that is uniquely identifiable from a standard silicone lubricant, functionalized silicone lubricant, or silicone powder.

As an example, at around a wavenumber of <NUM>-<NUM>, a characteristic absorption (i.e., bond vibration frequency) associated with hydroxyl (OH) functionality of water is present in the thin layer of silicone and in the infrared spectrum <NUM> associated with the thin layer of silicone. The thin layer of silicone also contains other peaks corresponding to specific bond vibrational frequencies. Thus, an infrared spectroscopy can be used to detect and differentiate between the emulsion based lubricant and other fiber lubricant systems used in optical buffer tube manufacturing.

As the percentage of silicone used to manufacture an optical cable buffer tube using the emulsion process - as disclosed in the embodiments above - is less than about <NUM> % (e.g., less than about <NUM> % to about <NUM> %), the total amount of silicone used to manufacture an optical cable can be reduced by a factor of about <NUM> in comparison to a gel-free loose buffer tube manufactured using, for example, functionalized silicone as a lubricant.

<FIG> illustrate a specific design for an optical cable <NUM> in accordance with an alternative embodiment of the disclosure, wherein <FIG> illustrates a cross-sectional view of the optical cable <NUM> prior to compression and <FIG> illustrates a corresponding projection view.

<FIG> illustrate an alternative design of an optical cable <NUM> in which the buffer tubes <NUM> are arranged in multiple concentric paths around a central strength member <NUM>. In addition, after the first row of the buffer tubes <NUM> are arranged, a support layer <NUM> may be introduced for reinforcing the first row of the buffer tubes <NUM>. The support layer <NUM> may comprise a material having sufficient property to reinforce the buffer tubes <NUM> that are enclosed by it and deformable so that it can be squeezed or deformed. Examples of materials used for the support layer <NUM> include polypropylene, polyethylene, nylon, polyurethane, and others.

In an example embodiment, the optical cable <NUM> may have five buffer tubes <NUM> in the first row and eleven buffer tubes <NUM> in the second row. Each buffer tube <NUM> contains <NUM> optical fibers <NUM>.

A deformable upjacket <NUM> surrounds the central strength member <NUM>. In various embodiments, the thickness of the deformable upjacket <NUM> may be different from the diameter of the central strength member <NUM>. As illustrated, the thickness of the deformable upjacket <NUM> may be larger than the diameter of the central strength member <NUM>. However, in other embodiments, the thickness of the deformable upjacket <NUM> may be the same as the diameter of the central strength member <NUM>. In one embodiment, the thickness of the deformable upjacket <NUM> may be similar to the diameter of the central strength member <NUM>. The buffer tubes <NUM> are arranged around the outer periphery of the deformable upjacket <NUM>.

In an exemplary embodiment, the optical cable <NUM> may have eight buffer tubes. Each buffer tube may contain <NUM> optical fibers. Thus, the optical cable <NUM> includes <NUM> fibers.

<FIG> illustrate a specific design for an optical cable <NUM> in accordance with an alternative embodiment of the invention, wherein <FIG> illustrates a cross-sectional view of the optical cable <NUM> prior to compression and <FIG> illustrates a corresponding projection view.

The optical cable <NUM> is designed similar to the embodiment of <FIG> in that they include an support layer <NUM> around the central strength member <NUM> and further include two rows of buffer tubes <NUM> around the central region. However, in this embodiment, a smaller number of buffer tubes <NUM> are arranged in the first row. Instead of six buffer tubes arranged in <FIG>, in this embodiment three buffer tubes are arranged in the first row.

However, unlike the prior embodiments, this embodiment also includes additional strength members <NUM> that are placed around the central strength member <NUM>. The additional strength members <NUM> are separated from the central strength member <NUM> by the buffer tubes <NUM> in the first row. In one embodiment, the number of the additional strength members <NUM> is the same as the number of the buffer tubes <NUM> in the first row. The additional strength members <NUM> provide additional rigidity to the optical cable <NUM> for supporting a larger number of buffer tubes <NUM>. In particular, the additional strength members <NUM> along with the central strength member <NUM> make better use of space since they are smaller in diameter relative to the buffer tubes <NUM> by at least a factor of two.

Consequently, in the embodiment of <FIG>, three deformable buffer tubes are arranged in a first row and enclosed by a support layer <NUM>. Another ten buffer tubes are arranged around the support layer <NUM>.

An optical cable may be deployed for use in a communication system (e.g., networking or telecommunications). A communication system may include optical cables <NUM> architecture such as fiber-to-the-node (FTTN), fiber-to-the-telecommunications enclosure (FTTE), fiber-to-the-curb (FTTC), fiber-to-the-building (FTTB), and fiber-to-the-home (FTTH), as well as long-haul or metro architecture. Moreover, an optical module or a storage box that includes a housing may receive a wound portion of the optical fiber disclosed herein. By way of example, the optical fiber may be wound around a bending radius of less than about <NUM> millimeters (e.g., <NUM> millimeters or less, such as about <NUM> millimeters) in the optical module or the storage box.

Optical cables containing optical fibers as disclosed may be variously deployed, including as drop cables, distribution cables, feeder cables, trunk cables, and stub cables, each of which may have varying operational requirements (e.g., temperature range, crush resistance, UV resistance, and minimum bend radius).

Such optical cables may be installed within ducts, microducts, plenums, or risers. By way of example, an optical cable may be installed in an existing duct or microduct by pulling or blowing (e.g., using compressed air).

In general, to achieve satisfactory long-distance blowing performance (e.g., between about <NUM> to <NUM>,<NUM> meters (<NUM>,<NUM> to <NUM>,<NUM> feet) or more or more), the outer cable diameter of an optical fiber cable should be no more than about <NUM> to <NUM> percent of the duct's or microduct's inner diameter.

Moreover, the optical cables may be directly buried in the ground or, as an aerial cable, suspended from a pole or pylon. An aerial cable may be self-supporting, or secured or lashed to a support (e.g., messenger wire or another cable). Exemplary aerial optical cables include overhead ground wires (OPGW), all-dielectric self-supporting cables (ADSS), all dielectric lash cables (AD-Lash), and figure-eight cables, each of which is well understood by those having ordinary skill in the art. Figure-eight cables and other designs can be directly buried or installed into ducts, and may optionally include a toning element, such as a metallic wire, so that they can be found with a metal detector.

To effectively employ the present optical fibers in a transmission system, connections are required at various points in the network. Optical fiber connections are typically made by fusion splicing, mechanical splicing, or mechanical connectors. During the splicing operation at low temperatures, mitigation of possible freezing of the water of emulsion may be desired. In particular, if normal evaporation and diffusion processes have not led to migration of water out of the buffer tube. In order to depress the freezing point of the water of emulsion, the aqueous portion of the emulsion can be modified to include a freezing point depressant (i.e., antifreeze) to render the freezing point of the emulsion below the desired access temperature. The freezing point depressant may be, for example, such as propylene glycol, methanol (e.g., methyl alcohol, carbinol, wood alcohol, wood naphtha, wood spirits, etc.), ethylene glycol, or glycerol to render the freezing point below the desired access temperature.

The fiber coating system within this cable combined with the fiber lubricant system shall also be a compatible system. As the emulsion lubricant may entrain water into the fiber optic buffer tube, the buffer tube and coated fiber system shall be able to withstand at least a <NUM> day exposure to <NUM> at a relative humidity of <NUM> and preferentially at least a <NUM> day exposure at <NUM> and a relative humidity of <NUM> with an attenuation change in the <NUM>-<NUM> wavelength range of ≤<NUM>.

By way of example, the present optical fiber may be incorporated into single-fiber drop cables, such as those employed for Multiple Dwelling Unit (MDU) applications. In such deployments, the cable jacketing must exhibit crush resistance, abrasion resistance, puncture resistance, thermal stability, and fire resistance as required by building codes. An exemplary material for such cable jackets is thermally stable, flame-retardant polyurethane (PUR), which mechanically protects the optical fibers yet is sufficiently flexible to facilitate easy MDU installations. Alternatively, a flame-retardant polyolefin or polyvinyl chloride sheath may be used.

In general, a strength member is typically in the form of a rod or braided/helically wound wires or fibers, though other configurations are also possible.

The mating ends of connectors can be installed to the optical fiber ends either in the field (e.g., at the network location) or in a factory prior to installation into the network. The ends of the connectors are mated in the field in order to connect the optical fibers together or connect the optical fibers to the passive or active components. As an example, certain optical fiber cable assemblies (e.g., furcation assemblies) can separate and convey individual optical fibers from a multiple optical fiber cable to connectors in a protective manner.

The deployment of such optical cables may include supplemental equipment, which itself may employ the present optical fiber as previously disclosed. For instance, an amplifier may be included to improve optical signals. Dispersion compensating modules may be installed to reduce the effects of chromatic dispersion and polarization mode dispersion. Splice boxes, pedestals, and distribution frames, which may be protected by an enclosure, may likewise be included. Additional elements include, for example, remote terminal switches, optical network units, optical splitters, and central office switches.

Claim 1:
A buffer tube (<NUM>, <NUM>, <NUM>, <NUM>), comprising:
a bundle of optical fibers (<NUM>) comprising an outer surface area, and
a swellable-thread (<NUM>) comprising a hydrophilic base material comprising water, wherein
a layer of silicone is present between the bundle of optical fibers (<NUM>) and the swellable-thread (<NUM>) and contacts at least a part of the outer surface area,
the layer of silicone is applied as an emulsion lubricant to the bundle of optical fibers, the emulsion lubricant comprising silicone, water, and an emulsifying agent, the layer of silicone remaining on the outer surface area after the water is absorbed by the swellable-thread, and the emulsifying agent comprises dimethicone copolyol, hydroxy terminated dimethicone copolyol, methoxy terminated dimethicone copolyol, nonylphenol, or a combination thereof.