HK1165561A - Optical fiber assemblies having a powder or powder blend at least partially mechanically attached - Google Patents

Description

Optical fiber assembly with at least partially mechanically attached powder or powder mixture

Technical Field

The present invention generally relates to optical fiber assemblies for transmitting optical signals. More particularly, the present invention relates to fiber optic assemblies including a powder or powder blend for blocking water.

Background

Communication networks are used to carry a variety of signals such as voice, video, data, and the like. As communications applications require greater bandwidth, communications networks are being converted to fiber optic cables having optical fibers because the cables are capable of carrying a very large amount of bandwidth compared to copper conductors. Furthermore, fiber optic cables are much smaller and lighter than copper cables having the same bandwidth capacity.

In some applications, the fiber optic cable is exposed to moisture, which may enter the fiber optic cable over time. To address this moisture problem, fiber optic cables used in these applications include one or more components that block the migration of water along the cable. By way of example, conventional fiber optic cables block water migration through the use of filling and/or liquid-resistant materials such as gels or greases within the cable. The filler material refers to the gel or grease within the tube or cavity with the optical fiber, while the liquid-resistant material refers to the gel or grease within the cable but outside the cavity containing the optical fiber. The gel or grease acts by filling the space (i.e., void) so that water does not have a path along it within the cable. In addition, in addition to water blocking, gel or grease filling materials have other advantages, such as cushioning and coupling of optical fibers, which help to maintain optical performance during mechanical or environmental events affecting the cable. In short, the gel or grease filling material is a multifunctional material.

However, gel or grease filling materials also have disadvantages. For example, gels or greases are dirty and may drip from the cable end. Another disadvantage is that the filler material must be removed from the optical fiber when the optical connection is to be made, which adds time and complexity to the craft. In addition, removing the gel or grease requires the craftsman to bring the removal material for removing the gel or grease to the site. Thus, there has long been a need for a fiber optic cable that eliminates the gel or grease material, yet provides all of the benefits associated with gel or grease materials.

Early cable designs blocked the migration of water along the cable by using dry water blocking components such as tape or yarn on the outside of the buffer tube without the need for a liquid blocking material. Unlike gels or greases, dry water-blocking components are not dirty and leave no residue to be removed. These dry water-blocking components typically include Super Absorbent Polymers (SAPs) that absorb water and swell to block the water pathway, thereby blocking the migration of water along the cable. Generally, the water-swellable component uses a yarn or tape as a carrier for the SAP. Since the water-swellable yarns and tapes are first used outside the cavity housing the optical fibers, there is no need to address additional functions such as coupling and optical attenuation other than water blocking.

Finally, fiber optic cables use water-swellable yarns, tapes, or Super Absorbent Polymers (SAPs) in place of gel or grease filling materials within the tubes that surround the optical fibers. In general, the water-swellable yarn or tape has sufficient water-blocking capability, but does not provide all of the functions of a gel or grease filling material such as padding and bonding. For example, water-swellable tapes and yarns are bulky due to their relatively large size compared to typical optical fibers and/or may have relatively rough surfaces. For this reason, water-swellable yarns or tapes may cause problems if the optical fibers are pressed against the optical fibers. Also, SAP can cause problems if pressed against the fiber. In other words, optical fibers pressed against conventional water-swellable yarns, tapes, and/or SAPs may experience microbending, which may result in undesirable levels of light attenuation and/or cause other problems. Furthermore, if the cable is not of a stranded design, the desired level of fiber to tube coupling may be a problem since stranding accomplishes the coupling.

By way of example, U.S. Pat. No. 4,909,592 discloses a conventional water-swellable component for use within a buffer tube having optical fibers. However, the inclusion of conventional water-swellable components within the buffer tube may still result in problems with the performance of the fiber optic cable that limit use and/or other design changes. For example, fiber optic cables that use conventional water-swellable yarns within a buffer tube require larger buffer tubes to minimize interaction between the conventional water-swellable yarns and the optical fibers and/or to limit the environment in which the fiber optic cable is used.

Other early cable designs used tube assemblies that were highly filled with loose SAP powder to block water migration within the cable. However, the use of loose SAP powder within the fiber optic cable creates problems because SAP powder may accumulate/migrate at some locations within the fiber optic cable (i.e., SAP powder accumulates at low points due to gravity and/or vibration when wound on a reel) by not being attached to a carrier such as a yarn or tape, thereby causing inconsistent water blocking within the fiber optic cable. Also, loose SAP powder is free to fall from the tube ends. Fig. 1 and 2 show a cross-sectional view and a longitudinal cross-sectional view, respectively, of a conventional dry fiber optic assembly 10, the dry fiber optic assembly 10 having a plurality of optical fibers 1 and a loose water-swellable powder 3 disposed within a tube 5, as schematically illustrated. As shown, conventional dry fiber optic assemblies 10 use a relatively large amount of SAP powder 3 within the tube 5 to block water migration therein. Other conventional cable components used embed SAP powder in the outer surface of the tube as described in us patent 5,388,175. However, embedding the SAP in the outer surface greatly reduces its effectiveness because water cannot reach the embedded particles.

The present invention addresses the long-felt need for a dry fiber optic assembly that provides suitable optical and mechanical properties while being acceptable to the craft.

Disclosure of Invention

The present invention is directed to a dry fiber optic assembly that uses a powder or powder mixture that is at least partially mechanically attached to the wall of the assembly. The fiber optic assembly may include one or more optical fibers and a powder or powder mixture within a tube, cavity, cable, or the like. Further, one or more fiber optic components may be used in the fiber optic cable or may form the fiber optic cable itself. For example, the powder or powder blend may include a water-swellable powder for blocking the migration of water along the assembly, thereby effectively blocking the migration of water. In other embodiments, the powder or powder mixture may have additional and/or other properties, such as flame retardancy or other suitable properties, in addition to water blocking.

It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the detailed description, serve to explain the principles and operations of the invention.

Drawings

FIG. 1 is a cross-sectional view of a conventional fiber optic assembly that blocks water migration therein using a relatively large amount of water-swellable powder loosely disposed therein.

Fig. 2 is a longitudinal cross-sectional view of the conventional fiber optic assembly of fig. 1.

FIGS. 3 and 3A are cross-sectional views of fiber optic assemblies having water-swellable powder for blocking water migration, according to various embodiments.

FIG. 4 is a greatly enlarged longitudinal cross-sectional view of the fiber optic assembly of FIG. 3.

Fig. 5 is a photograph showing an enlarged view of the inner wall of the tube to which the powder is mechanically attached, the region of interest being indicated by a boxed area.

Fig. 5a is a photograph of fig. 5 identifying the powder using a software package to determine the percentage of surface area of the region of interest to which the powder is mechanically attached.

Fig. 6 is a cross-sectional view of a cable using the fiber optic assembly of fig. 3 in a stranded loose tube cable.

FIG. 7 is a cross-sectional view of another fiber optic cable according to another embodiment.

Fig. 8 is a cross-sectional view of another fiber optic cable according to the present invention.

Fig. 9 is a cross-sectional view of another fiber optic cable according to the present invention.

Fig. 10 is a cross-sectional view of another fiber optic cable according to the present invention.

Fig. 11 is a cross-sectional view of another fiber optic cable according to the present invention.

Detailed Description

The present invention has several advantages over conventional dry fiber optic assemblies that use water-swellable powder. One advantage is that the fiber optic assembly of the present invention provides for the mechanical attachment of at least a portion of the water-swellable powder or powder blend to less than all of the surface area of the fiber optic assembly surface (i.e., the tube or cavity wall) while still effectively blocking water migration. Furthermore, the presence of the water-swellable powder within the fiber optic assembly or cable is nearly transparent to the craft because it is mechanically attached and a relatively low amount can be used. In addition, no gel or grease removal fiber cleaning is necessary prior to connectorization, nor is it necessary to remove or cut components such as water-swellable tapes or yarns. Another advantage of having at least a portion of the powder or powder mixture mechanically attached to the inner surface of the tube, cavity, etc. is that it does not migrate as loose powder as conventional dry fiber optic assemblies. In addition, the tube or cavity of the fiber optic assembly of the present invention has a smaller size than conventional dry fiber optic cable assemblies that use tape or yarn as the carrier. As used herein, fiber optic assemblies include tube assemblies without strength members, tube assemblies with strength members, fiber optic cables, and the like.

Reference will now be made in detail to the present preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. Fig. 3 and 4 show a cross-sectional view and an enlarged longitudinal cross-sectional view, respectively, of a fiber optic assembly 100 (i.e., a tube assembly) according to a first embodiment. Fiber optic assembly 100 includes a plurality of optical fibers 102, a water-swellable powder or powder blend 104, and a tube 106. The optical fiber 102 may be any suitable type of optical waveguide now known or later developed. Further, the optical fibers may be a portion of an optical fiber ribbon, a fiber bundle, or the like. Optionally, the optical fibers 102 are colored by an outer ink layer (not visible) for identification and are loosely disposed within the tube 106. In other words, optical fiber 102 is an unbuffered optical fiber, but the concepts of the present invention can also be used with optical fibers having other configurations, such as buffered, ribbonized, stranded optical fibers. In further embodiments, the concepts disclosed herein may be used with hollow fillets that do not include optical fibers therein. As shown, in general, water-swellable powder 104 is shown disposed adjacent an inner surface of tube 106, a portion of which is mechanically attached, as described herein. Furthermore, water-swellable powder 104 is mechanically attached to a relatively small percentage of the surface area of the inner wall of the tube such that its use in fiber optic assembly 100 is nearly transparent to the craft, but surprisingly effective in providing adequate water-blocking performance. Additionally, the fiber optic assembly 100 need not include additional components within the tube 106 for blocking water migration, but it may include other cable components.

Unlike conventional fiber optic tube assemblies, the fiber optic tube assemblies of the present invention have a relatively high level of mechanically attached water-swellable powder 104, yet are capable of blocking tap water from a one meter head for 24 hours over a one meter length. As used herein, tap water is defined as water having a salt level of 1% by weight or less. Similarly, the fiber optic tube assembly of the present invention is also capable of blocking up to 3% by weight of saline solution for up to 24 hours within 3 meters, and depending on the design, the blocking properties allow the 3% saline solution to linger for even 24 hours within about 1 meter. The mechanical attachment of the powder causes a portion of the water-swellable particles to protrude out of the surface so that if water enters the cavity it can come into contact with the particles. Theoretically, after water contacts the water-swellable particles and begins to swell, portions of the particles break through to the outside of the surface so that they can fully swell and/or move to form water-blocking plugs with other particles. In other words, if the powder particles remain attached to the surface or embedded therein as in conventional designs, they cannot fully expand and will be less effective because they cannot coalesce with other particles. Thus, when mechanically attached, the particles should have a portion thereof protruding outside the surface and not fully embedded therein. It should also be understood that not all of the water-swellable powder or powder blend is mechanically attached to the surface, but rather there is some loose powder.

By way of example, water-swellable powder 104 is located within a tube having an inner wall with a given surface area per meter length. In one embodiment, about 30% or less of the surface area of the inner tube wall has mechanically attached water-swellable powder and/or powder blend, but other percentages are possible, such as 25% or less. Furthermore, the mechanical attachment may be generally uniformly located on the surface, as previously described, 30% or less of the entire surface. Instead, the mechanical attachment may be concentrated in the longitudinal strips, such as 100% or less of the mechanical attachment in one or more strips covering 30% or less of the surface area, and 0% of the mechanical attachment elsewhere, as schematically shown in fig. 3A. By way of example, if the tube has an inner diameter of about 2 millimeters (0.002 meters), the surface area per meter length is calculated to be about 0.00628 square meters (pi x 0.002 meters x 1 meter), and the surface area of the water-swellable powder or powder blend is mechanically attached to the inner wall is about 0.002 square meters or less (i.e., about one-third of the surface area per meter).

The measurement of the surface area with the water-swellable powder or powder blend mechanically attached to the wall was performed as follows: several regions of interest (i.e., sample regions) such as five 1 mm square regions of interest spaced along the tube are averaged, the regions are magnified using a microscope and the average of the five sample regions is determined. Specifically, each square millimeter sample area was magnified 50 times and examined using an Image analysis software package, such as I-Solutions software available from Image and Microscope Technology of Vancouver, British Columbia, Canada. FIG. 5 is a magnified view (about 50 times) of the inner wall of a tube with powder mechanically attached thereto, viewed using I-Solutions software after any loose water-swellable powder or powder blend has been removed. Specifically, a sample length of about 100 mm long is cut, and the optical fiber is removed from the first end of the tube. Thereafter, the second end of the sample is cut about 10-15 millimeters, thereby splitting a portion of the sample in half. Any loose powder is then removed from the sample by tapping the second end (i.e. the split end) of the tube at least three times while maintaining the tube in a near upright position so that any loose powder falls from the sample. Finally, a portion of the divided end is removed from the sample to view under magnification. Fig. 5 shows a region of interest 150 illustrated by a boxed area (i.e., the area within the dashed box is the region of interest).

Fig. 5a is the same graph as shown in fig. 5, with the powder within the region of interest 150 identified using software to determine the percentage of surface area within the region of interest 150 to which the powder is mechanically attached. In other words, the software enables the measurement of the percentage of surface area with powder mechanically attached, since the grey scale difference can show up relative to the tube wall the surface area with powder mechanically attached to it. When using software to determine the percentage of surface area with mechanical attachment, the limit illumination should be adjusted appropriately to see the contrast between the regions. In particular, the angle of incidence of the illumination should provide a suitable distinction and oversaturation of light should be avoided so that the contrast between the regions is easily visible. The region of interest 150 shown in fig. 5a has about 30% or less of the powder mechanically attached to the region of interest 150, as shown. In other embodiments, the powder may be mechanically attached to 25% or less of the surface area. Further, the size and shape of the powder can be observed from the image.

The total percentage of water-swellable powder or powder blend mechanically attached to the fiber optic assembly may be quantified, except that the surface area of the tube or cavity has a particular percentage of mechanical attachment. Illustratively, a relatively high level of portion (by weight) (i.e., 45% or more) of the water-swellable powder or powder blend 104 is mechanically attached to the inner tube wall, and the remaining 55% of the powder or powder blend is loosely disposed within the tube. By way of example, if the fiber optic assembly has 0.10 grams of powder per meter length, about 0.045 grams or more of powder is mechanically attached to the fiber optic assembly per meter length, and 0.055 grams or less of powder per meter is loose powder. Of course, the total weight percent of mechanically attached powder may have other values, such as 50% or more, 55% or more, 60% or more, 75% or more, 80% or more, 90% or more, or 95% or more, leaving 40% or more, 20% or more, 10% or more, or 5% or more, respectively, of the powder loosely disposed within the tube or cavity. Table 1 below shows in tabular form an example of the above total percentage of mechanically attached powder for a concentration level of 0.10 grams of powder per meter length, but other concentration level values are possible.

Table 1: examples of the total percentage of mechanically attached powder

The total weight percent of mechanically attached powder can be determined by averaging the measured or calculated weight of mechanically attached powder per meter length divided by the total weight of powder per meter length located within the tube or cavity. Conversely, the total weight percent of loosely disposed powder may be determined by averaging the measured or calculated weight of powder disposed per meter of long loose divided by the total weight of powder per meter of long located within the tube or cavity. However, it is easier and more accurate to measure the percentage of mechanically attached powder or powder mixture. Additionally, if one of the percentages is known, the other percentage may be calculated by subtraction.

In further embodiments, the fiber optic assembly may also have a relatively small average concentration of powder per meter, thereby making the powder in the fiber optic assembly nearly transparent to the craft. For example, for a tube having an inner diameter of 2.0 millimeters, the optical fiber assembly 100 can have about 0.02 grams of powder per meter length while still being suitable for blocking a one meter head of tap water for 24 hours over a one meter length, although other suitable higher or lower concentration levels (i.e., weight per meter) are possible. In addition, the average concentration level may be scaled based on the cavity size.

By way of example, a 2.0 millimeter inner diameter tube has a cavity cross-sectional area of about 3.14 square millimeters, thereby producing a normalized concentration value of about 0.01 grams (rounded up) of water-swellable powder per meter of the tube assembly. In other words, the normalized concentration per square millimeter of cavity cross-sectional area is given by: the average concentration of the water-swellable powder, e.g., 0.02 grams per meter length, is divided by the cavity cross-sectional area of about 3 square millimeters to produce a normalized concentration value. In this example, the normalized concentration value is about 0.01 grams (rounded up) of water-swellable powder per meter of long tube per square millimeter of cavity cross-sectional area. Thus, for a cavity of a tube or fiber optic cable having a particular cross-sectional area, the average concentration of water-swellable powder in grams per meter can be scaled (i.e., calculated) accordingly by using a normalized concentration value, such as 0.01 grams of water-swellable powder per meter length per square millimeter of cavity cross-sectional area. Illustratively, if the cavity cross-sectional area is 5 square millimeters and a normalized concentration value of 0.01 grams per meter is desired, the fiber optic assembly has 0.05 grams of powder per meter length of cavity. In other embodiments, higher or lower normalized concentration values are possible, such as between 0.005 grams per meter and 0.02 grams per meter. In general, as the cross-sectional area of the cavity of the tube or the like increases, the amount of water-swellable powder required to effectively block water migration along the tube may generally increase proportionately to effectively block water.

The weight of the water-swellable powder per meter length of the fiber optic assembly (i.e., concentration per meter length) is calculated using the following procedure. A representative number of samples, such as 5 one meter samples, are cut from the fiber optic tube assembly to be tested. It is preferred to take these samples along different longitudinal sections of the fiber optic assembly rather than sequentially cutting the samples from the fiber optic assembly. Each one meter sample with the optical fibers and water-swellable powder in the tube is weighed using a suitably accurate and precise scale to determine the total weight of the sample. Thereafter, the optical fiber (along with any other removable cable components within the tube, cavity, etc.) is pulled from the tube. The optical fibers (and any other cable components) are wiped with fine paper to remove any water-swellable powder thereon, then rinsed with water and wiped again with a wet towel, allowed to dry, and then wiped with alcohol and allowed to dry thoroughly. Thereafter, the optical fibers (and other cable components) are weighed to determine their weight without the water-swellable powder. Next, optionally, the tube (without the optical fiber and other cable components) is weighed to determine the weight with the powder therein to verify the results. The tube is then opened and beaten at least three times along its longitudinal length using a suitable tool so that loose powder falls out of the tube and is then weighed to determine the weight of the tube with the mechanically attached particles. Thereafter, the remaining water-swellable powder therein can be wiped from the tube, rinsed with water and wiped again with a wet towel, allowed to dry, then wiped with alcohol and allowed to dry thoroughly, care being taken to ensure that almost all of the powder or powder mixture is completely removed, and then the "clean" tube is weighed to determine its weight without the water-swellable powder. Further, a portion of the fiber or tube may be viewed under magnification to determine if the powder has been properly removed prior to weighing. Thereafter, the sum of the weight of the optical fibers (and other cable components) along with the weight of the tube is subtracted from the total weight of the sample to determine the weight of the water-swellable powder in the corresponding sample. This process is repeated for each of a representative number of samples. The average concentration of the water-swellable powder can be calculated by summing all calculated weights of the sample water-swellable powder and then dividing by the number of samples to obtain the average concentration of water-swellable powder per meter of the fiber optic assembly.

Although the optical fibers may contact the powder or powder mixture, the fiber optic tube assembly and/or the fiber optic cable, such as fiber optic assembly 100, maintains the optical properties of the optical fibers 102 therein. For example, the optical fiber of the fiber optic tube assembly has a maximum optical attenuation of about 0.15db/km or less at a reference wavelength of 1550 nanometers during standard temperature cycling under GR-20 (temperature cycling down to-40 ℃). For example, a typical average optical attenuation at a reference wavelength of 1550 nm during a standard temperature cycle at-40 ℃ is about 0.05 db/km. Further, advantageously, the fiber optic tube assembly has been temperature cycled down to-60 ℃ at a reference wavelength of 1550 nanometers using a process similar to GR-20, but still has an attenuation of about 0.25db/km or less without having to modify the design.

One factor that may affect optical performance is the maximum particle size, average particle, and/or particle size distribution of water-swellable powder 104, which may affect microbending if optical fibers contact (i.e., press against) the water-swellable particles. In addition, the use of a water-swellable powder with relatively small particles improves the transparency of the water-swellable powder to the craftsman when the tube is opened. The average particle size of the water-swellable powder is preferably about 150 microns or less, but other suitable average particle sizes are possible, such as 60 microns or less. The skilled person understands that since the powder is sieved using a mesh of appropriate size, it has a distribution of particle sizes. For example, individual particles may have an aspect ratio (i.e., longer than width) that still fits through the screen in one direction and larger than the average particle size. The use of an SAP having a slightly larger average maximum particle size may still provide acceptable performance, but the use of a larger maximum particle size increases the likelihood of experiencing increased light attenuation. In addition, the shape of the particles may also affect the likelihood of experiencing increased light attenuation. In other words, particles with rounded surfaces are less likely than particles with rough surfaces to suffer from elevated levels of light attenuation. One illustrative water-swellable powder is a cross-linked sodium polyacrylate available under the trade name Cabloc GR-211 from Evonik, Inc. of Greensboro, N.C. The particle distribution of the illustrative water-swellable powder is given in table 2.

Table 2: particle distribution of illustrative water-swellable powders

Particle size	Approximate percentage
		Greater than 63 microns	0.2％
45-63 microns	25.7％
		25-44 microns	28.2％
Less than 25 microns	45.9％

Of course, other powders, powder mixtures and/or other particle distributions are possible. Another suitable crosslinked sodium polyacrylate is available from Absorbent Technologies, inc. under the tradename Aquakeep J550P, but other types of water-swellable materials are possible. By way of example, another suitable water-swellable powder is a copolymer of acrylate and polyacrylamide, which is effective with respect to saline solutions. Additionally, powder blends of two or more materials and/or water-swellable powders are also possible, such as blends of slow-and fast-expanding water-swellable powders. Likewise, the blend of water-swellable powders may include a first water-swellable powder that is highly effective for saline solutions and a second water-swellable powder that is effective for tap water. The powder blend may also include components that are not inherently water swellable. By way of example, small amounts of silica, such as up to 3% fumed silica, may be added to the water-swellable powder to improve flow properties and/or inhibit anti-caking due to moisture absorption. Additionally, the concepts of the present invention enable the use of other types of particles, with or without water-swellable particles, such as flame retardant particles (e.g., aluminum trihydrate, magnesium hydroxide, etc.), dry lubricants such as talc, graphite, boron, and the like.

Another factor to consider in selecting a water-swellable material is its absorbent capacity. The absorption capacity is the amount of water that the water-swellable material can absorb per gram of water and is typically measured in grams of water absorbed per gram of water-swellable material. In one embodiment, the water-swellable material preferably has an absorption capacity of at least about 100 grams of water per gram of water-swellable material, although other values lower or higher are possible. For example, the water-swellable material may have an absorbent capacity of about 200 grams or more per gram of material, about 300 grams or more per gram of material, or about 400 grams or more per gram of material. Several factors can affect the material absorption capacity, such as material type, degree of crosslinking, surface area, and the like.

Another factor that affects optical performance is Excess Fiber Length (EFL) or Excess Ribbon Length (ERL). As used herein, excess fiber length may refer to EFL or ERL, but in general ERL refers only to excess ribbon length. The fiber optic assembly of the present invention as shown in fig. 3 preferably has an excess fiber length in the range of about-0.1% to about 0.3% to produce an acceptable shrink and stretch window depending on the tube inner diameter, but other suitable excess fiber length or excess ribbon length values particularly suited for fiber optic assemblies of other configurations/designs are possible.

In addition, the powder or powder mixture inhibits adhesion between the optical fiber and the tube without the use of a separating layer or other material. In particular, fiber optic assemblies have problems with the optical fibers contacting and adhering to the tube when the tube is in a molten state when extruded around the optical fibers. If the fiber sticks to the inside of the tube, this can cause the fiber path to distort (i.e., the fiber is prevented from moving at that point), which can produce undesirable levels of optical attenuation. As shown in fig. 3 and 4, tube 106 is positioned around optical fibers 102 of optical fiber assembly 100 without the use of additional materials or components as a spacer layer (e.g., without gel, grease, yarn, tape, etc.) to inhibit contact between the optical fibers and the molten tube. Since the water-swellable powder is a cross-linked material, it does not promote adhesion thereto at typical extrusion molding temperatures, thereby inhibiting adhesion. Thus, water-swellable powder 104 tends to act as a separation layer because it inhibits optical fibers 102 from adhering to the molten tube during manufacture. However, other cable components may be included within the tube or cavity.

In addition, water-swellable powder 104 serves to reduce friction between the optical fibers and the tube or cavity wall by acting as a slip layer. In short, the particles of water-swellable powder 104 act like ball bearings between optical fibers 102 and the inner wall of the tube to reduce friction therebetween and enable the optical fibers to move to a "relaxed state". In other variations, embodiments of the present invention optionally use a lubricant in or on the outer layer of the optical fiber to reduce the risk of adhesion of the optical fiber to the extruded tube and/or reduce friction therebetween. For example, the optical fibers 102 may include an outer layer, such as ink, with a suitable lubricant to inhibit the optical fibers 102 from adhering to the molten tube 106 during extrusion of the tube. Suitable lubricants include silicone oils, talc, silica, and the like, used in amounts which will inhibit "caking" and which are located in or on the outer layer. Other methods may also be used to inhibit adhesion of the optical fiber to the tube. For example, the tube 106 may include one or more suitable polymer fillers to inhibit adhesion of the optical fibers to the tube. In addition, the use of tubes of other polymeric materials, such as highly filled PVC, can also inhibit adhesion of the optical fibers to the tubes. Further, the tube 106 may have a double layer structure with an inner layer of the tube having one or more suitable polymer fillers to inhibit adhesion. Another method of inhibiting adhesion of the optical fibers is to apply a lubricant to the inner wall of the tube or cavity immediately after tube formation.

The tube 106 may use any suitable polymeric material for enclosing and protecting the optical fibers 102 therein. For example, the tube 106 may be polypropylene (PP), Polyethylene (PE), or a blend of materials such as a blend of PE and Ethylene Vinyl Acetate (EVA). In other embodiments, tube 106 is formed from a flame retardant material such as flame retardant polyethylene, flame retardant polypropylene, polyvinyl chloride (PVC), or polyvinylidene fluoride PVDF, thereby forming a portion of a flame retardant fiber optic cable. However, to make a flame retardant fiber optic cable, tube 106 need not be formed from a flame retardant material. In other embodiments, the tube 106 may comprise a thin sheath that can be easily torn by a craftsman without the use of tools. For example, the tube 106 is formed of a highly filled material so that it can be easily torn by a craftsman using only fingers. By way of example, the easily tearable tube may comprise a filler material such as polybutylene terephthalate (PBT), polycarbonate and/or polyethylene (material) and/or Ethylene Vinyl Acetate (EVA) or other mixtures thereof with fillers such as chalk, talc, etc.; however, other suitable materials are possible, such as UV curable acrylates. Generally speaking, all other things being equal, tube 106 may have a smaller inner diameter ID than a dry tube assembly that includes a water-swellable yarn, tape or filament (i.e., a carrier for SAP) and optical fibers. This is because the tube 106 does not have to provide space for both the optical fibers and the carrier (i.e., yarn or tape) of the SAP, and thus the inner diameter ID can be smaller. For example, it may also be advantageous for the tube 106 to have a smaller inner diameter ID, as this allows for a smaller outer diameter, a softer assembly with a smaller bend radius (which may reduce kinking) may weigh less per unit length, and a longer length may be mounted on the spool.

Illustratively, 12 standard sized 250 micron optical fibers having an overall diameter of about 1.2 millimeters can be housed in a tube or cavity having an inner diameter ID, e.g., about 1.7 millimeters or less, such as 1.6 millimeters, or even 1.5 millimeters or 1.4 millimeters, and still have suitable properties as low as-40 ℃. Other suitable tube inner diameters ID are possible, and ID may depend on the number of fibers within the tube or cavity. By way of comparison, a conventional fiber optic assembly having 12 optical fibers and a plurality of water-swellable yarns requires an inner diameter of about 2.0 millimeters to accommodate both the water-swellable yarns and the optical fibers.

Mechanical attachment of the water-swellable particles or powder mixture 104 may be accomplished by any suitable manufacturing process. One way of performing mechanical attachment is to provide the powder particles with the appropriate momentum so that they impact a cone of molten polymer that forms a tube 106 upon exiting the extrusion machine. While the inner surface of the tube 106 is still in a molten state, at least a portion of the powder particles mechanically adhere and/or transfer to the inner surface when the appropriate momentum is provided. In general, suitable momentum can be obtained by applying a force to impart a velocity to the particles, such as by air jets and/or by electrostatic charges. By way of example, a powder having an average particle size of 60 microns or less may be directed into the melt tube at an exit velocity of about 20 meters per second to achieve mechanical attachment of the powder.

FIG. 6 is a cross-sectional view of a fiber optic cable 60 using several fiber optic assemblies 100 according to the present invention. As shown, fiber optic assembly 100 is stranded about central member 61 along with a plurality of filler rods 62 and a plurality of tensile strength yarns 63, and a water-swellable tape 65 is disposed about the fiber optic assembly to form a fiber optic cable core (not numbered). Cable 60 further includes a cable jacket disposed about the cable core for protecting the cable core. Any suitable reinforcement may be used to stretch the reinforcing yarns 63, such as aramid, fiberglass, and the like. Cable 60 may also include other components such as one or more water-swellable yarns or water-swellable tapes disposed about central member 61. Additionally, the cable may eliminate unnecessary components such as a center piece or other cable components. The cable jacket 68 of the cables 60a and 60b may use any suitable material, such as a polymer, for environmental protection.

In one embodiment, the cable jacket 68 is formed from a flame retardant material, thereby making the cable flame retardant. Likewise, the tube 106 of the fiber optic assembly 100 may also be formed from a flame retardant material, although the use of a flame retardant for the tube may not be necessary to make a flame retardant fiber optic cable. By way of example, the flame retardant fiber optic cable may include a cable jacket 68 formed from polyvinylidene fluoride (PVDF) and a tube 106 formed from polyvinyl chloride (PVC). Of course, it is also possible to use other flame retardant materials, such as flame retardant polyethylene or flame retardant polypropylene.

FIG. 7 is a cross-sectional view of fiber optic cable 70 similar to fiber optic cable 60, further including armor 77. Similar to cable 60, cable 70 includes a plurality of fiber optic assemblies 100 stranded about a central member 71 along with a plurality of filler rods 72 and a water-swellable tape 75, thereby forming a cable core (not numbered). Armor 77 is positioned about water-swellable tape 75 and, as shown, is formed of a metallic material, although other suitable materials may be used for the armor such as polymers. Cable 70 also includes a cable jacket 78 positioned about armor 77.

FIG. 8 is a cross-sectional view of another fiber optic cable 80 configured as a monotube fiber optic cable design. More specifically, fiber optic cable 80 includes a unitary fiber optic assembly (not numbered) similar to fiber optic assembly 100 having optical fibers 102 and water-swellable powder 104 within a tube 106, but it also includes a plurality of optional coupling elements 81 for providing coupling forces with optical fibers 102. Since this is a single tube design, coupling is not provided by stranding fiber optic assemblies like cables 60 and 70. The coupling element 81 may be any suitable structure and/or material such as a wire, filament, yarn, tape, elastomeric element, etc. that may be wrapped around the optical fiber or longitudinally disposed in the tube or cavity. Other variations for creating the coupling include surface roughness on the inner surface of the tube or cavity or extruding materials such as elastomers, volatile glues, etc. on the fiber. Other embodiments may include any other suitable coupling elements, as desired. Cable 80 also includes a plurality of strength members 88 such as tensile yarns disposed radially outwardly of tube 106, although other types of strength members are possible such as GRPs. A cable jacket 88 is positioned around strength members 88 for environmental protection.

Although the previous embodiments describe the fiber optic assembly or cable as being round, it may have other shapes and/or include other components. For example, FIG. 9 is a cross-sectional view of a fiber optic cable 90 according to the present invention. Cable 90 includes optical fibers 102 and water-swellable powder 104 within cavity 96 of cable jacket 98, which is essentially a tube for a fiber optic assembly. In this embodiment, cable jacket 98 is non-circular and forms cavity 96 for housing optical fibers 102 and water-swellable powder 104. In short, cable 90 is tubeless in construction because optical fibers 102 are accessible once cable jacket 98 is open. In other words, the fiber optic cable does not include a buffer tube, but rather the fiber optic cable jacket 98 is a tube. In addition, tube 98 (i.e., the cable jacket) includes strength members 97 therein (i.e., encased within the cable jacket) and on either side of cavity 96, thereby forming a reinforced tube or cable sheath. Of course, cavity 96 can have other shapes, such as generally rectangular, to generally conform to the shape of one or more fiber optic ribbons.

Fig. 9 and similar tubeless fiber optic cables may themselves be manufactured by elastically straining the strength members while the cable jacket is extruded thereover to create and/or control excess fiber length/excess ribbon length (EFL/ERL). Cable 90 has a generally flat shape, but the concept of elastically stretching the strength members can be adapted to any suitable cable cross-sectional shape, such as circular. Specifically, strength members 97 are paid-off respective spools under relatively high tension (e.g., between about 100 to about 400 pounds) using respective strength member capstans, thereby elastically stretching strength members 97 such that an excess fiber length EFL (or ERL) is created in cable 90. In other words, after the tension is released on strength members 97, they return to their original unstressed length (i.e., shorten), thereby creating an EFL because the optical fibers are introduced into the cable at the same length as the tensioned strength members but the optical fibers are not stretched. In other words, the amount of EFL produced is approximately equal to the strength member strain (i.e., the elastic extension of the strength member) plus any elastic shrinkage of the cable jacket that may occur. Strength member strain can produce significant amounts of EFL or ERL in a single pass, such as 10% or more, 25% or more, 50% or more, and even up to 80% or more of the total EFL or ERL within the cable. In addition, elastic stretching of the strength members is advantageous because it enables precise control of the amount of EFL or ERL introduced into the cable and greatly reduces strength member shuttling because the finished cable jacket is in compression rather than tension. For manufacturing cable 90, about 95% of the EFL is introduced into the cable by elastically stretching the strength members. Briefly, a cable jacket (i.e., tube) is being applied about the optical fibers, water-swellable powder and strength members by a cross-head extruder while strength members 97 are elastically stretched. After extrusion, cable 90 is quenched in a water bath while the strength members are still elastically stretched, thereby allowing the cable jacket to "freeze" on the stretched strength members. Cable 90 is then pulled through the manufacturing line using one or more tracks and then wound onto a take-up reel under low tension (i.e., the tensile force that elastically stretches the strength members is released, and the strength members return to a relaxed length, thereby creating ERL or EFL in the cable). Of course, this is merely an illustrative production line and other modifications are possible.

FIG. 10 shows a cross-sectional view of fiber optic cable 110 having main cable body 101 and toneable protrusion 103. Fiber optic cable 110 includes a fiber optic assembly 100 having optical fibers 102 and water-swellable powder 104 within a tube 106. Fiber optic cable 110 may also include one or more water-swellable yarns (not visible) or water-swellable tapes disposed about tube 106 for blocking the migration of water along the fiber optic cable outside of fiber optic assembly 100. Cable 110 also includes a plurality of strength members 107, such as GRPs, positioned on either side of tube 106. Although the stiffeners 107 are shown as being slightly spaced from the tube 106, they may also contact the tube 106. In addition, other materials may be used for the reinforcement 107, such as steel wire or other suitable members. Cable 110 also includes a cable jacket 108 formed of a suitable polymer that forms a portion of main cable body 101 and toneable protrusion 103, as shown. Toneable protrusion 103 includes a tone detection wire 103a that is a suitable conductive element, such as a copper wire or copper-clad steel wire, that is adapted to transmit a signal for locating optical cable 110 when embedded. By way of example, audio detection wire 103a is a 24AWG gauge copper wire. In addition, toneable protrusion 103 has a frangible web portion (not numbered) for separating the toneable protrusion from main cable body 101 when desired, such as prior to connectorization. Of course, other variations are possible.

Fig. 11 shows a cross-sectional view of a fiber optic cable 120 that is tubeless (i.e., the cable jacket acts as a tube) having a plurality of optical fiber ribbons 122 therein (as shown by the horizontal lines). Although cable 120 is shown as a generally flat cable design, it may have other suitable shapes such as variations of flat cables or round cables. As described above, fiber optic cable 120 is manufactured similarly to the fiber optic cable of FIG. 9. Optical fiber ribbons include a plurality of optical fibers (not visible) that are attached together using a suitable matrix material, such as a UV curable matrix. Specifically, cable 120 includes 4 ribbons 122, each having 24 optical fibers for a total of 96 optical fibers, forming a ribbon stack (not numbered). Similar cables may have other fiber counts within the ribbon and/or cable. As described above, fiber optic cable 120 includes water-swellable powder 104 mechanically attached at least in part to an inner surface of cavity 126 of cable jacket 128 and/or on a fiber optic ribbon. For example, the powder or powder mixture 104 has a normalized concentration of about 0.01 grams or less per meter for each square millimeter of the cavity 126 of the fiber optic assembly, although other suitable concentrations may be used. By way of example, cavity 126 is sized to receive a fiber optic ribbon (i.e., a fiber optic component) and has a cavity width in millimeters and a cavity height in millimeters, which are multiplied together to calculate a cavity cross-sectional area in millimeters squared. The ribbon stack also has a total cross-sectional area in square millimeters. The average concentration of the water-swellable powder can be calculated using the cavity cross-sectional area or the effective cavity cross-sectional area. The effective cavity cross-sectional area is defined as the cavity cross-sectional area minus the cross-sectional area of the desired component therein, such as a fiber optic ribbon within the cavity. Illustratively, the effective cross-sectional area is calculated by subtracting the cross-sectional area of the fiber optic ribbon from the cavity cross-sectional area, which results in an effective cavity cross-sectional area in square millimeters. Thus, in this design, the average concentration of the amount of water-swellable powder is calculated by taking the desired normalized concentration (grams per meter length of the assembly per square millimeter of the cavity) times the effective cavity cross-sectional area (square millimeters), which results in an average concentration of water-swellable powder in grams per meter length of the assembly.

Additionally, fiber optic cable 120 optionally includes one or more coupling elements 121, as shown in phantom. When one or more coupling elements 121 are included, less of the water-swellable powder 104 can transfer to the inner surface of cavity 126 because coupling elements 121 can inhibit transfer (i.e., they are between a portion of the fiber optic ribbon and the cavity wall). More specifically, cable 120 has two coupling elements formed from longitudinal foam strips (indicated by the hatched rectangles) or other suitable coupling elements located on both sides of the ribbon stack such that coupling elements 121 sandwich optical fiber ribbons 122 therebetween. Following is a determination of water-encountering using the effective cavity cross-sectional area of the larger cavity having fiber optic ribbons and coupling elements thereinRepresentative examples of average concentrations of expanded powders. In this example, cavity 126 is sized to receive 4 ribbons (i.e., fiber members) of 24 fibers and has a cavity width of about 8.2 millimeters and a cavity height of 5.2 millimeters, which are multiplied together to calculate a cavity cross-sectional area of about 43 square millimeters. The ribbon stack also has a total cross-sectional area of about 7.4 square millimeters, and the sum of the coupling elements has a cross-sectional area of about 27.2 square millimeters. Thus, for this example, the effective cross-sectional area (i.e., 43 mm) is calculated by subtracting the cross-sectional areas of the ribbons and coupling elements from the cavity cross-sectional area²-7.4mm²-27.2mm²) This results in an effective cavity cross-sectional area of about 8 square millimeters. Thus, the average concentration of the amount of water-swellable powder for this design is calculated by taking the desired normalized concentration times the effective cavity cross-sectional area (i.e., 0.01 grams per meter length per square millimeter times 8 square millimeters), which results in an average concentration of about 0.08 grams per meter length for the cavity of this example that surrounds 96 optical fibers in the ribbon stack. Although the average concentration of water-swellable powder is relatively large, it is still a trace amount for water blocking a relatively large effective cavity cross-sectional area, which is barely noticeable by the craft, yet effectively blocks water migration along the cable cavity. Of course, other examples of these concepts are possible in accordance with the present invention.

Additionally, for this design, for a 30 meter length of fiber optic cable having one or more coupling elements 121, coupling elements 121 provide a coupling force to the optical fibers of at least about 0.1625 newtons per fiber. Illustratively, for a 30 meter length cable, a cable having a single 12-fiber ribbon should have a coupling force of about 1.95 newtons or greater. Likewise, for a 30 meter length cable, a similar cable having a single 4-fiber ribbon should have a coupling force of about 0.650 newtons or greater. The measurement of the coupling force is done by taking a 30 meter sample of the cable, pulling the first end of the fiber (or ribbon), and measuring the force required to move the second end of the fiber (or ribbon). In other words, the Excess Fiber Length (EFL) or Excess Ribbon Length (ERL) must be straightened so that the coupling force is the force required to move the entire fiber length within a 30 meter cable sample. In addition to providing coupling, coupling elements 121 can line the ribbon stack while still allowing movement of the ribbons.

Ribbons 122 of this design generally have a greater ERL than the tube design because the stack of ribbons is not stranded. By way of example, ribbons 122 have an ERL in the range of about 0.1% to about 1.2% or more, and the amount of ERL can vary with the number of ribbons in the stack, and the strength members should be elastically stretchable in a range similar to the desired ERL. Additionally, fiber optic cable 120 may elastically stretch one or more strength members 127 using a similar manufacturing process as described in connection with fiber optic cable 90, thereby creating ERL. Specifically, first strength component 127 and second strength component 127 on opposite sides of cavity 126 are elastically stretched a predetermined amount during extrusion of cable jacket 128. Additionally, fiber optic cable 120 may be part of a distribution fiber optic assembly having one or more optical fibers for distribution. The fiber drop for distribution may be spliced to a tether, connected to a ferrule/connector, or merely left as a splice ready for splicing by a craftsman.

Many modifications and other embodiments of the invention within the scope of the appended claims will be apparent to those skilled in the art. For example, the concepts of the present invention may be used with any suitable cable design and/or manufacturing method. For example, the illustrated embodiments may include other suitable cable components such as armor layers, coupling elements, different cross-sectional shapes, and the like. Thus, the present invention is intended to cover such modifications and embodiments, as well as those embodiments, which would be apparent to those skilled in the art.

Claims (46)

1. A fiber optic assembly, comprising:

at least one optical fiber;

a tube having an inner wall with a surface area per meter, and the at least one optical fiber is positioned within the tube; and

a water-swellable powder positioned within the tube for blocking water migration, a portion of the water-swellable powder being mechanically attached to an inner wall of the tube, wherein about 30% or less of the surface area of the inner tube wall is mechanically attached with the water-swellable powder.

2. The fiber optic assembly of claim 1, wherein at least about 10% or more of the water-swellable powder by weight per meter is mechanically attached to the inner wall of the tube.

3. The fiber optic assembly of claims 1 or 2, wherein at least about 5% by weight of the water-swellable powder is not mechanically attached to the inner wall of the tube.

4. The fiber optic assembly of claims 1-3, the water-swellable powder having an average particle size of about 150 microns or less.

5. The fiber optic assembly of claims 1-3, wherein the fiber optic assembly further includes a non-water-swellable powder within the tube.

6. The fiber optic assembly of claims 1-5, wherein the water-swellable powder has an average concentration of about 0.02 grams or less per meter of tube, wherein the tube is capable of blocking one meter of head of tap water for 24 hours over a length of one meter.

7. The fiber optic assembly of claims 1-6, the tube having an inner diameter of about 2.0 millimeters or less.

8. The fiber optic assembly of claims 1-7, further comprising a coupling element for providing a coupling force between the at least one optical fiber and the tube.

9. The fiber optic assembly of claims 1-8, which is a fiber optic cable further comprising a member selected from the group consisting of: armor layers, ripcords, strength members, water-swellable components, cable jackets, cores, coupling elements, and audio detection elements.

10. The fiber optic assembly of claims 1-8, wherein the fiber optic assembly forms a portion of a fiber optic cable or forms a portion of a flame retardant fiber optic cable.

11. The fiber optic assembly of claims 1-10, the at least one optical fiber being a portion of a fiber optic ribbon.

12. The fiber optic assembly of claims 1-7, the at least one optical fiber being a portion of a fiber optic ribbon, and further comprising a first coupling element and a second coupling element, wherein the first coupling element and the second coupling element are disposed on opposite sides of the fiber optic ribbon.

13. The fiber optic assembly of claims 1-12, wherein the water-swellable powder includes a blend of two or more different types of materials.

14. A fiber optic assembly, comprising:

at least one optical fiber;

a tube having an inner wall and the at least one optical fiber positioned within the tube; and

a water-swellable powder positioned within the tube to block water migration, a portion of the water-swellable powder mechanically attached to an inner wall of the tube, wherein about 45% or more of the weight of the water-swellable powder per meter is mechanically attached to the inner wall of the tube, and about 5% or more of the weight of the water-swellable powder per meter is loosely disposed within the tube.

15. The fiber optic assembly of claim 14, wherein the inner wall of the tube has a surface area per meter and at least about 10% or more of the surface area is mechanically attached with the water-swellable powder.

16. The fiber optic assembly of claims 14 or 15, wherein at least about 5% by weight of the water-swellable powder is not mechanically attached to the inner wall of the tube.

17. The fiber optic assembly of claims 14-16, the water-swellable powder having an average particle size of about 150 microns or less.

18. The fiber optic assembly of claims 14-17, wherein the fiber optic assembly further includes a non-water-swellable powder within the tube.

19. The fiber optic assembly of claims 14-18, wherein the water-swellable powder has an average concentration of about 0.02 grams or less per meter of tube, wherein the tube is capable of blocking one meter of head of tap water for 24 hours over a length of one meter.

20. The fiber optic assembly of claims 14-19, the tube having an inner diameter of about 2.0 millimeters or less.

21. The fiber optic assembly of claims 14-20, further comprising a coupling element for providing a coupling force between the at least one optical fiber and the tube.

22. The fiber optic assembly of claims 14-21, which is a fiber optic cable further comprising a member selected from the group consisting of: armor layers, ripcords, strength members, water-swellable components, cable jackets, cores, coupling elements, and audio detection elements.

23. The fiber optic assembly of claims 14-21, wherein the fiber optic assembly forms a portion of a fiber optic cable or forms a portion of a flame retardant fiber optic cable.

24. The fiber optic assembly of claims 14-23, the at least one optical fiber being a portion of a fiber optic ribbon.

25. The fiber optic assembly of claims 14-23, the at least one optical fiber being a portion of a fiber optic ribbon, and further comprising a first coupling element and a second coupling element, wherein the first coupling element and the second coupling element are disposed on opposite sides of the fiber optic ribbon.

26. The fiber optic assembly of claims 14-25, wherein the water-swellable powder includes a blend of two or more different types of materials.

27. A fiber optic assembly, comprising:

at least one optical fiber;

a tube having an inner wall with a surface area per meter, and the at least one optical fiber is positioned within the tube; and

a powder mixture located within the tube, a portion of the powder mixture being mechanically attached to an inner wall of the tube, wherein about 30% or less of a surface area of the powder mixture is mechanically attached per meter of the inner wall of the tube.

28. The fiber optic assembly of claim 27, wherein at least about 10% or more by weight of the powder mixture per meter is mechanically attached to the inner wall of the tube.

29. The fiber optic assembly of claims 27 or 28, wherein at least about 5% by weight of the powder mixture is not mechanically attached to the inner wall of the tube.

30. The fiber optic assembly of claims 27-29, wherein the powder blend includes a water-swellable powder.

31. The fiber optic assembly of claim 30, wherein the average concentration of the powder mixture is about 0.02 grams or less per meter of tube, wherein the tube is capable of blocking a one meter head of tap water for 24 hours over a length of one meter.

32. The fiber optic assembly of claims 27-31, the powder mixture having an average particle size of about 150 microns or less.

33. The fiber optic assembly of claims 27-32, the tube having an inner diameter of about 2.0 millimeters or less.

34. The fiber optic assembly of claims 27-33, further comprising a coupling element for providing a coupling force between the at least one optical fiber and the tube.

35. The fiber optic assembly of claims 27-34, which is a fiber optic cable further comprising a member selected from the group consisting of: armor layers, ripcords, strength members, water-swellable components, cable jackets, cores, coupling elements, and audio detection elements.

36. The fiber optic assembly of claims 27-34, wherein the fiber optic assembly forms a portion of a fiber optic cable or forms a portion of a flame retardant fiber optic cable.

37. The fiber optic assembly of claims 27-36, the at least one optical fiber being a portion of a fiber optic ribbon.

38. The fiber optic assembly of claims 27-36, the at least one optical fiber being a portion of a fiber optic ribbon, and further comprising a first coupling element and a second coupling element, wherein the first coupling element and the second coupling element are disposed on opposite sides of the fiber optic ribbon.

39. The fiber optic assembly of claims 27-38, wherein the powder mixture includes a material from the group consisting of: fumed silica, flame retardant substances, talc, dry lubricants, graphite, boron, microspheres, and/or water-swellable powders.

40. A fiber optic assembly, comprising:

at least one optical fiber;

a tube having an inner wall and the at least one optical fiber positioned within the tube; and

a powder mixture located within the tube, a portion of the powder mixture being mechanically attached to an inner wall of the tube, wherein about 45% or more by weight of the powder mixture per meter is mechanically attached to the inner wall of the tube, and about 5% or more by weight of the powder mixture is loosely disposed within the tube.

41. The fiber optic assembly of claim 40, wherein the powder mixture comprises a material from the group consisting of: fumed silica, flame retardant substances, talc, dry lubricants, graphite, boron, microspheres, and/or water-swellable powders.

42. The fiber optic assembly of claim 40, wherein the powder blend includes at least 50% by weight of the water-swellable powder.

43. A fiber optic assembly, comprising:

at least one optical fiber;

a tube having an inner wall with a surface area per meter and a cavity cross-sectional area measured in square millimeters, wherein the at least one optical fiber is located within the tube; and

a water-swellable powder positioned within the tube to block water migration, a portion of the water-swellable powder being mechanically attached to an inner wall of the tube, wherein about 30% or less of the surface area of the inner wall of the tube has the water-swellable powder mechanically attached thereto, and the water-swellable powder has a normalized concentration of about 0.01 grams or less per meter of tube per square millimeter of cavity cross-sectional area to calculate an average concentration of the water-swellable powder in grams per meter.

44. The fiber optic assembly of claim 43, wherein the cavity cross-sectional area used to calculate the average concentration is an effective cavity cross-sectional area defined as the sum of the cavity cross-sectional area minus the cross-sectional area of at least one optical fiber plus the cross-sectional area of any other fiber optic component within the cavity cross-sectional area.

45. A fiber optic assembly, comprising:

at least one optical fiber;

a tube having an inner wall with a surface area per meter and a cavity cross-sectional area measured in square millimeters, wherein the at least one optical fiber is located within the tube; and

a water-swellable powder positioned within the tube to block water migration, a portion of the water-swellable powder being mechanically attached to an inner wall of the tube, wherein about 45% or more by weight of the powder mixture per meter is mechanically attached to the tube inner wall, and about 5% or more by weight of the powder mixture is loosely disposed within the tube, and the water-swellable powder having a normalized concentration of about 0.01 grams or less per meter of tube per square millimeter of cavity cross-sectional area to calculate an average concentration of the water-swellable powder in grams per meter.

46. The fiber optic assembly of claim 45, wherein the cavity cross-sectional area used to calculate the average concentration is an effective cavity cross-sectional area defined as the sum of the cavity cross-sectional area minus the cross-sectional area of at least one optical fiber plus the cross-sectional area of any other fiber optic component within the cavity cross-sectional area.