Patent Description:
Optical fibers are very small diameter glass strands capable of transmitting an optical signal over great distances, at very high speeds, and with relatively low signal loss relative to standard copper wire networks. Optical cables are therefore widely used in long distance communication and have replaced other technologies such as satellite communication, standard wire communication etc. Besides long distance communication, optical fibers are also used in many applications such as medicine, aviation, computer data servers, etc..

There is a growing need in many applications for optical cables that are able to transfer high data rates while taking minimum space. Such need can arise, for example, in data servers where space for the optical fiber is a critical limiting factor. In particular, data servers are processing increasingly higher amounts of data that require increased connectivity to the data servers. However, the maximum size of the optical cable is limited by the size of the ducts through which the cables have to be passed through. Squeezing the conventional optical cables through the ducts is not a viable option. This is because while conventional optical fibers can transmit more data than copper wires, they are also more prone to damage during installation. The performance of optical fibers within the cables is very sensitive to bending, buckling, or compressive stresses. Excessive compressive stress during manufacture, cable installation, or service can adversely affect the mechanical and optical performance of conventional optical fibers.

Alternately, changing the size of the ducts can be prohibitively expensive especially in already existing installations. <CIT> relates to an optical fibre cable comprising: at least one compliant core unit comprising at least one optical fibre enclosed in and supported by a unitizing structure having an elastic response substantially the same as that of an expanded polymeric foam, and an outer sheath enclosing and supporting said at least one core unit so as to permit relative movement between the core unit and the outer sheath. <CIT> relates to optical fibre cable comprising an optical unit having a plurality of stranded optical fibre ribbons, a tube having the optical unit accommodated therein, and a cable sheath, wherein each of the optical fibre ribbons is intermittently provided with coupling portions, wherein the assembly is in a state where a part of the plurality of tubes is in surface contact with the cable sheath with the tubes being elastically deformed with respect to another tube inside the cable sheath. <CIT> relates to a fibre optic cable comprising: at least one subunit, the subunit including a fibre optic ribbon and a sheath, wherein the sheath is tight-buffered about the fibre optic ribbon, a tube, the tube housing at least a portion of the at least one subunit, thereby forming a tube assembly, a plurality of strength members, the plurality of strength members being disposed radially outward of the tube, and a cable jacket. <CIT> relates to an optical fibre cable comprising: an optical fibre ribbon in a pipe, wherein said ribbon includes at least two optical fibres arranged side by side, and wherein at least two of said optical fibres are bonded intermittently along a length of said fibres <CIT> relates to an optical fiber cable comprising one or more units disposed within a sheath wherein at least one of the units comprises a longitudinal dielectric strength member having a buffer layer that is substantially smooth thereon, with one or more optical fibers helically disposed around the member, and further comprising a tube of polymeric material disposed around the optical fiber, with the interstices within the tube being filled with a waterproofing material. <CIT> relates to an optical fiber cable comprising a central member, at least one substantially fluid impervious tube wound around the central member, a plurality of optical fibers loosely received in the tube, a sheath of plastic material encircling the tube which is around the central member, the plastic material having a predetermined flame propagating value, a thermal barrier layer encircling the tube and the central member and intermediate the tube and the sheath, a water blocking material in any otherwise empty spaces in the tube and between the thermal barrier layer and the tube. <CIT> relates to fiber optic cable comprising a plurality of optical fibers, a sheathing layer of elastomeric polymeric material around each optical fiber in intimate contact with the outer surface of the optical fiber, the elastomeric polymeric material being resiliently compressible, an axial core including a rigid, substantially non-compressible axial member, the axial core being located along the center axis of the cable and extending longitudinally along the center axis of the cable, the sheathed optical fibers being cabled around the axial core, the sheathing layers being compressed against the axial core to be deformed thereby over an extended surface contact with the axial core, and a jacket surrounding the sheathed fibers formed of polymeric material substantially more rigid than the elastomeric polymeric material, the sheathed fibers being held in compression against the axial core by the jacket, whereby the axial core stabilizes the polymeric material layers against differential thermal expansion and contraction relative to the optical fibers.

In accordance with an embodiment of the present invention, an optical cable includes a plurality of deformable buffer tubes, wherein the optical cable includes a rigid strength member and a deformable upjacket surrounds the rigid strength member. Each of the plurality of deformable buffer tubes includes a plurality of flexible ribbons, and each of the flexible ribbons includes a plurality of optical fibers. Each of the plurality of deformable buffer tubes has a non-circular cross-section. An outer jacket surrounds the plurality of deformable buffer tubes.

In accordance with an alternative embodiment of the present invention, an optical cable includes a central strength member, wherein a deformable upjacket surrounds the rigid strength member, and a plurality of buffer tubes disposed around the central strength member, where each of the plurality of buffer tubes includes a buffer tube jacket surrounding a plurality of flexible ribbons. The buffer tube jacket includes a first deformable material that is deformed plastically. Each of the flexible ribbons includes a plurality of optical fibers. An outer jacket surrounds the plurality of buffer tubes.

In accordance with an alternative embodiment of the present invention, an optical cable includes a rigid strength member and a deformable upjacket surrounds the rigid strength member. A plurality of buffer tubes is disposed around the rigid strength member. Each of the plurality of buffer tubes includes a plurality of ribbons, and each of the ribbons includes a plurality of optical fibers, where each of the plurality of buffer tubes includes a first compressive modulus, and the rigid strength member with the deformable upjacket includes a second compressive modulus. A ratio of the first modulus to the second modulus is about <NUM>:<NUM> to <NUM>:<NUM>. An outer jacket surrounds the plurality of buffer tubes.

In accordance with another embodiment, an optical cable includes a plurality of deformable buffer tubes and an outer jacket surrounding the plurality of deformable buffer tubes, wherein the optical cable includes a rigid strength member and a deformable upjacket surrounds the rigid strength member. Each deformable buffer tube of the plurality of deformable buffer tubes includes a single flexible ribbon including a plurality of optical fibers. Each deformable buffer tube further includes an axial cross-section of the deformable buffer tube that includes the single flexible ribbon. The axial cross-section comprises an irregular shape.

In accordance with another embodiment, an optical cable includes a central strength member, a plurality of buffer tubes disposed around the central strength member, wherein a deformable upjacket surrounds the rigid strength member, and an outer jacket surrounding the plurality of buffer tubes. Each of the plurality of buffer tubes includes a buffer tube jacket surrounding a single flexible ribbon. The buffer tube jacket includes a first deformable material that is deformed plastically. Each single flexible ribbon includes a plurality of optical fibers and a first longitudinal length. For each single flexible ribbon, each optical fiber of the plurality of optical fibers is attached to an adjacent optical fiber of the plurality of optical fibers along a bond region including a second longitudinal length that is less than the first longitudinal length.

In accordance with still another embodiment, an optical cable includes a rigid strength member, a deformable upjacket surrounding the rigid strength member, a plurality of buffer tubes disposed around the rigid strength member, and an outer jacket surrounding the plurality of buffer tubes. Each of the plurality of buffer tubes includes a single ribbon including a plurality of optical fibers. Each of the plurality of buffer tubes, including each corresponding ribbon, includes a first compressive modulus. The rigid strength member with the deformable upjacket includes a second compressive modulus. A ratio of the first compressive modulus to the second compressive modulus is about <NUM>:<NUM> to <NUM>:<NUM>.

The making and using of the presently preferred embodiments are discussed in detail below. It should be appreciated, however, that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative of specific ways to make and use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to exemplary embodiments in a specific context, namely design of optical cables having a high density of optical fibers per unit cross-sectional area.

A conventional optical cable will first be described. This is followed by a structural illustration of the design of the optical cable in one embodiment using <FIG>. Next, experimental results that form the basis for selecting materials used in the various embodiments of the present invention will be described using <FIG>. Additional structural embodiments will then be described using <FIG>, and <FIG>. A table summarizing examples of some of the structural embodiments will described using <FIG>.

<FIG> illustrates a conventional optical cable.

The conventional optical cable includes a rigid central strength member <NUM> as illustrated in <FIG>. A conventional upjacket <NUM> surrounds the central strength member <NUM>. The outer cover <NUM> of the optical cable may include several layers such as a water blocking layer <NUM>, and an optional outer strength member <NUM> that may include a steel armor, and an outer jacket <NUM>.

The optical cable further includes conventional buffer tubes <NUM> that contain multiple ribbons <NUM> of optical fibers. Conventional encapsulated ribbons <NUM> are then stacked and arranged into a round shaped conventional buffer tube <NUM>.

The inventors of the present application have found that there is a significant amount of voids or interstices within each of the conventional buffer tubes <NUM>. This is because the round shape of the conventional buffer tubes <NUM> is different from the square shape of the ribbons <NUM>. Further, the conventional buffer tubes <NUM> are rigid and always maintain a round shape. On the other hand, the ribbons <NUM> are rigid and rectilinear in shape. In addition, the standard ribbon <NUM> has a preferential longitudinal bending axis which prevents the ribbon from folding in any other axis which prohibits a high filling ratio for conventional buffer tubes. Consequently, a significant fraction of the buffer tube area is filled with voids that could otherwise be used to hold optical fibers.

In addition, the inventors of the present application have also found that a significant fraction of the area within the optical cable outside of the buffer tubes <NUM> is unutilized because of the round shape of the conventional buffer tubes <NUM>, which cannot be altered due to the associated stiffness and rigidity of these buffer tubes <NUM>. As a consequence, the number of buffer tubes that can be placed within a cable is limited as round shapes intersect with other round shapes along a single line rather than a plane (two cylindrical objects intersect at a line). In other words, a large fraction of the space within the outer jacket <NUM> is empty because the conventional buffer tubes <NUM> are circular in shape leaving interstices <NUM> between adjacent buffer tubes or interstices <NUM> between the conventional buffer tubes <NUM> and the conventional upjacket <NUM>.

For example in <FIG>, when the outer diameter of the conventional upjacket <NUM> is substantially similar to the diameter of the conventional buffer tubes <NUM>, the packing density is mathematically limited. In this example, when there are six conventional buffer tubes <NUM> surrounding a conventional upjacket <NUM>, the minimum amount of void interstices per unit area of the optical cable is <NUM>%. In other words, at least <NUM>% of the optical cable will always be empty space that is left unutilized. As a consequence, the number of optical fibers that can be packed per unit cross-sectional area is limited.

On the other hand, if individual fibers were directly placed within the optical cable without the use of buffer tubes, they would have a higher packing density. However, such a design would make it much more difficult to identify the fibers individually when the total number of fibers within each cable is large, e.g., in the hundreds or thousands.

Therefore, there is a need for a fiber optic cable that provides high packing density of optical fibers while maintaining sufficient structural, thermal, and optical properties. For example, while packing more number of optical fibers, the optical cable also has to have adequate tensile strength, resistance to crushing, resistance to buckling, resistance to thermal contraction while maintaining optical connection.

Embodiments of the present invention avoid the above issues by providing deformable buffer tubes which allows the buffer tubes to be compressed or squeezed together in a tighter configuration. Embodiments of the present invention achieve this by a combination of using flexible ribbons and designing the buffer tube jacket to be deformable. Optionally, embodiments of the present invention further include a deformable upjacket material around the strength members. As the interstices between adjacent buffer tubes are filled by the deforming buffer tubes, more optical fibers are packed within the same dimension cable than possible in a conventional optical cable.

<FIG> illustrates a cross-sectional view of an optical cable not forming part of the claimed invention, wherein <FIG> illustrates projection view of an array of optical fibers that enables such an adaptable design in accordance with embodiments of the present invention, wherein <FIG> illustrates a corresponding cross-sectional area of the array of optical fibers illustrated in <FIG> that enables such an adaptable design in accordance with embodiments of the present invention, wherein <FIG> illustrates a flexible ribbon formed using the array of optical fibers that enables such an adaptable design in accordance with embodiments of the present invention, and wherein <FIG> illustrates a deformable buffer tube formed using a plurality of flexible ribbons that enables such an adaptable design in accordance with embodiments of the present invention.

Referring first to <FIG>, in one or more embodiments, the optical cable comprises a plurality of deformable buffer tubes <NUM> that are formed around a central region. Although six deformable buffer tubes <NUM> are shown in <FIG> (as well as other figures in this application), this number is not necessarily indicative of the total number of deformable buffer tubes <NUM> that will be included. <FIG> (as well as other figures in this application) is not necessarily indicative of the shape of the plurality of deformable buffer tubes <NUM>. In particular, although for practical reasons many of these have been illustrated as circular objects, the plurality of deformable buffer tubes <NUM> are non-circular or shaped irregularly due to deformation. For example, as illustrated in <FIG>, one of the plurality of deformable buffer tubes <NUM> has a first dimension along the radial direction of the optical cable and a second dimension along a direction perpendicular to this radial direction. Unlike conventional buffer tubes, where the first dimension would be equal to the second dimension, the second dimension is different (e.g., smaller or larger) than the first dimension. In particular, depending on where the dimension of the deformable buffer tubes <NUM> is measured, a different dimension may be observed unlike a conventional buffer tube that is circular. In other words, in the cross-sectional view illustrated in <FIG>, the deformable buffer tubes <NUM> have been deformed such that it has a non-circular cross-section.

In one or more embodiments, the central region comprises a central strength member <NUM> surrounded by a conventional upjacket <NUM>. The central strength member <NUM> provides mechanical integrity of the cable when experiencing heavy stress. For example, during installation, the cables may be subjected to significant strain. The central strength member <NUM> is a rigid material and is the primary anti-buckling element in the cable. The central strength member <NUM> resists cable contraction at low temperatures and prevents optical fiber buckling, which would otherwise occur due to coefficient of expansion differential between optical fibers and other plastic cable components. The central strength member <NUM> prevents the cable from being compressed and provides a primary clamping point for hardware used to connect the cable to splice and routing enclosures.

The central strength member <NUM> may be made of metallic elements, glass reinforced composite rods such as glass reinforced epoxy, aramid reinforced composite rods, or composite rods made of some other high modulus, low coefficient of expansion material such as carbon fiber.

The conventional upjacket <NUM> may typically comprise a polymer such as polypropylene. The conventional upjacket <NUM> may also comprise other polymeric materials such as cellular foam polymer, e.g., cellular impact modified, nucleated polypropylene (i.e., nucleated ethylene-propylene copolymer). The upjacket helps to obtain the proper outer diameter of the strength member <NUM> required for the number and size of the buffer tubes to be included in the optical cable. The upjacket around the strength member <NUM> helps to maintain cable rigidity within a reasonable range and also lowers the cost of the cable. However, the thickness of the upjacket <NUM> has to be limited to avoid introducing thermal stress (e.g., as polyethylene has a much higher coefficient of thermal expansion than the central strength member <NUM>).

As illustrated in <FIG>, the plurality of deformable buffer tubes <NUM> are deformed to a non-circular shape that fits within the outer cover <NUM>. The outer cover <NUM> may include a number of layers such as the outer jacket <NUM>, a water blocking layer <NUM>, and an optional outer strength member <NUM>. The outer jacket <NUM> may comprise polyurethane, polyethylene, nylon, or other suitable material. In one embodiment, the outer cover <NUM> includes medium-density polyethylene (MDPE), with a nominal jacket thickness of approximately <NUM>, so as to comply with the standards for fiber optic cables such as Telcordia GR-<NUM>, ICEA-<NUM>. Flame-retardant additives may also be included into the outer cover <NUM>. The water blocking layer <NUM> may include water blocking threads, water blocking tapes, or other super absorbent powder type materials.

Adjacent buffer tubes of the plurality of deformable buffer tubes <NUM> physically contact with each other along a larger distance than the adjacent buffer tubes shown in <FIG>, for example. As a consequence, the amount of voids or interstices <NUM> within the optical cable is significantly reduced. In the illustration of <FIG>, the amount of voids or interstices <NUM> relative to the total cross-sectional area is very small since the plurality of deformable buffer tubes <NUM> have adapted to the shape of the optical cable.

In practice, adjacent deformable buffer tubes <NUM> may adapt slightly differently based on the local stress induced by the outer jacket <NUM> as well as other factors such as the materials being used. However, in various embodiments, the plurality of deformable buffer tubes <NUM> has undergone plastic (or permanent) and elastic deformation during the formation of the optical cable. By undergoing plastic deformation, the plurality of deformable buffer tubes <NUM> have a low stress state (as the energy of deformation has been absorbed). Alternatively, in some embodiments, the plurality of deformable buffer tubes <NUM> are still in the elastic regime and may have undergone substantial elastic deformation.

As will described below in greater detail, in the case of a plurality of flexible ribbons <NUM>, due to the random distribution of each of the plurality of flexible ribbons <NUM> in the deformable buffer tube <NUM>, a highly compact buffer tube structure can be realized. Moreover, due to the aforementioned flexibility of the plurality of flexible ribbons <NUM>, reshaping of the deformable buffer tube <NUM> into non-circular or irregular shapes is possible.

<FIG> illustrate the design of the flexible ribbon and deformable buffer tubes <NUM> that enables such an adaptable design in accordance with embodiments of the present invention.

Referring to <FIG>, as will further described in the following figures, each buffer tube of the plurality of deformable buffer tubes <NUM> comprises a plurality of flexible ribbons <NUM>. Each of the plurality of flexible ribbons <NUM> comprise a plurality of optical fibers <NUM> such as the first, the second, the third, the fourth, the fifth, and the sixth optical fiber <NUM>-<NUM>. <FIG> is not indicative of the total number of optical fibers although only six fibers are shown.

The plurality of optical fibers <NUM> are arranged parallel to each other and are connected at bond regions <NUM>. However, as illustrated in <FIG>, the bond regions <NUM> are arranged across the flexible ribbons <NUM> so as to selectively leave a large surface of the optical cables free of the bonding material that forms the bond region <NUM>. Consequently, the plurality of optical fibers <NUM> maintain a large degree of freedom and can be effectively folded or otherwise randomly positioned when the ribbon is subjected to external stress, for example, as shown in <FIG>.

In various embodiments, the plurality of optical fibers <NUM> can be folded into a densely packed configuration as shown in <FIG>. In one or more embodiments, the folded optical fibers <NUM> may have a non-circular or irregular shape.

<FIG> illustrates a deformable buffer tube comprising a plurality of flexible ribbons that has been deformed during the formation of the optical cable in accordance with an embodiment of the present invention.

The flexible ribbons <NUM> are enclosed by a buffer tube jacket <NUM>. In one or more embodiments, the buffer tube jacket <NUM> comprises polypropylene. In other embodiments, the buffer tube jacket <NUM> comprises cellular polypropylene, polyethylene, nylon, polyamide, polybutylene terephthalate, a polyolefin copolymer comprised of polyethylene and polypropylene, or other materials.

In addition, the flexible ribbons <NUM> may be dispersed within a gel <NUM> that allows the flexible ribbons <NUM> to move around relative to each other. Further, the thickness of the buffer tube jacket <NUM> is maintained to enable the flexibility of the ribbons. The lower thickness of the deformable buffer tubes <NUM> ensures deformation of the buffer tubes when subjected to stress. In particular, the thickness of the buffer tube jacket <NUM> relative to the diameter of the deformable buffer tube <NUM> is maintained within a range of <NUM> to <NUM>. A typical deformable buffer tube prior to deformation has a diameter between <NUM> to <NUM>, for example, <NUM>.

During the formation of the optical cable, the buffer tube may be subjected to compressive stress. Buffer tubes may show increased deformation under an equivalent stress due to the temperature dependent modulus reduction during jacketing. As a consequence, the flexible ribbons <NUM> within the deformable buffer tube <NUM> may rearrange the shape/configuration to compensate or minimize this compressive stress.

As described above, in various embodiments, the optical cables include deformable buffer tubes <NUM>. However, some of the deformation of the deformable buffer tubes <NUM> is caused by a rearrangement of the flexible ribbons within the optical cable and as such does not result in twisting or bending of the optical fibers. Therefore, embodiments of the present invention achieve improved packing density without compromising on mechanical or optical characteristics of the optical cable.

In the conventional design described in <FIG> above, flat optical fiber ribbons are arranged into a rectangular stack that is twisted together to maintain its rectangular shape and to average any compressive or tensile stress on the optical fiber ribbon stack across the different optical fibers down the length of the cable. However, in the various embodiments described in the present application, it is not necessary to twist the ribbons within each deformable buffer tube <NUM> because there is no need to maintain the shape if the ribbons are randomly distributed in the tube.

The foldable flexible ribbons <NUM> are run lengthwise along each deformable buffer tube <NUM>, and each flexible ribbon <NUM> is allowed to take a random configuration. Subsequent twisting, if any, of the plurality of deformable buffer tubes <NUM> while forming the cable is sufficient to average strain across the optical fibers and meet mechanical and optical standards for the fiber optic cable.

Although, in <FIG>, only four flexible ribbons <NUM> are shown to be within the plurality of buffer tubes, in various embodiments, the plurality of deformable buffer tubes <NUM> may include a much larger or even a smaller number of flexible ribbons <NUM>. For example, in one embodiment the plurality of deformable buffer tubes <NUM> may comprise twelve or twenty four flexible ribbons <NUM>. In addition, each of the flexible ribbons <NUM> may include any suitable number of optical fibers <NUM>. The optical fibers <NUM> may have a diameter in the range of <NUM> to <NUM> in various embodiments. For example, each of the flexible ribbons <NUM> may include twelve optical fibers in one illustration. Therefore, in this example, each of the plurality of deformable buffer tubes <NUM> includes <NUM> or <NUM> optical fibers.

Using embodiments of the present invention, the optical cable may have a fiber density of <NUM> fibers per square millimeter (fibers/mm<NUM>) or greater. In one or more embodiments, the fiber density of the optical cable may be between <NUM> fibers/mm<NUM> to <NUM> fibers/mm<NUM>, preferably between <NUM> fibers/mm<NUM> to <NUM> fibers/mm<NUM>.

<FIG> illustrates a further embodiment of the present invention in which no upjacket surrounds the central strength member.

In one or more embodiments, the strength member <NUM> may not include an upjacket material because the deformable buffer tubes <NUM> provide sufficient packing density and relaxation of the built-in stress. Otherwise, this embodiment may be similar to the previous embodiment described in <FIG>.

The diameter of the strength member <NUM> may be similar to the dimension "L" of the deformable buffer tubes <NUM> as shown in <FIG> in one embodiment. In other embodiments, the diameter of the strength member <NUM> may be smaller than the dimension "L" of the deformable buffer tubes <NUM>.

<FIG> illustrate further embodiments of the present invention having an additional deformable upjacket surrounding the central strength member.

In further embodiments, the upjacket material surrounding the strength member <NUM> may also include a deformable material. In various embodiments, the upjacket material is more compressible than the strength member <NUM> that is designed to be rigid.

As a consequence, the optical cable comprises a deformable upjacket <NUM> that has been deformed during the cable formation process. Depending on the deformable upjacket <NUM> material, the deformation of the deformable upjacket <NUM> may be purely elastic or may also include plastic deformation. The deformable nature of the upjacket provides additional way to compress and pack the cables by further improving contact between various components. In particular, the amount of voids or interstices within the optical cable may be further reduced relative to the embodiment of <FIG>. Additionally matching the modulus of interior components within a cable also results in a more equal stress distribution and a relatively lower deformation on the more compliant buffer tubes.

<FIG> illustrates an embodiment in which the buffer tubes as well as the deformable upjacket <NUM> (jacket material surrounding the strength member <NUM>) undergo deformation during the formation of the optical cable.

While <FIG> illustrates a more ideal design, in practice, the deformed buffer tubes may be similar to the structure shown in <FIG>. For example, as illustrated in <FIG>, the deformable buffer tube <NUM> may have a first width W1 along the periphery of the optical cable and a second width W2 towards the central region of the optical cable.

Similarly, instead of abutting the adjacent buffer tube along the entire side, each deformable buffer tube <NUM> physically contacts the adjacent deformable buffer tube <NUM> over a distance d. The distance d may be of the same order as the first width W1 or the second width W2 in one embodiment. In other words, the distance d may be comparable to the first width W1 or the second width W2 in one embodiment. In one embodiment, the distance d may be substantially equal to the first width W1 or the second width W2. In various embodiments, a ratio of the distance d to the first width W1 is about <NUM> to about <NUM>. In one or more embodiments, a ratio of the distance d to the second width W2 is about <NUM> to about <NUM>. In comparison, in the conventional design illustrated in <FIG>, adjacent conventional buffer tubes <NUM> contact with each other at a single point or over very short distances that approximate to a point.

<FIG> illustrates the relationship between tensile modulus and temperature of various upjacket materials.

Referring to <FIG>, the x-axis represents temperature while the y-axis represents tensile modulus in MPa. Tensile modulus of a material is the ratio of the tensile stress applied to a material compared to the resulting extension (strain). For low deformations, compressive modulus is equal to the tensile modulus of the material.

In <FIG>, the first curve C1 represents a variation in tensile modulus of a conventional upjacket material (Conv. Examples of such conventional material can be polypropylene. As illustrated in <FIG>, the tensile modulus increases strongly when the temperature is lowered. In contrast, the second curve C2 represents a variation in tensile modulus of an upjacket material comprising a deformable upjacket material (D. One example of the deformable upjacket material is a thermoplastic elastomer such as santoprene <NUM>-<NUM>.

The deformable buffer tubes <NUM> have a low yield stress and modulus, so a lower modulus upjacket material for the deformable upjacket <NUM> is desired to equalize compressive stresses in the cable during cable compression. If the compressive modulus of the material of the upjacket is much higher than the deformable buffer tubes <NUM>, the tubes will see a much higher deformation (strain) thereby resulting in greater stresses on the optical fibers contained within. In contrast, if the compressive modulus of the material of the upjacket is similar to the deformable buffer tubes <NUM>, the deformable buffer tubes <NUM> have a reduced strain and the fibers contained within are under less stress.

Therefore, the deformable upjacket material is selected to have low shrinkage, low coefficient of thermal expansion, as well as low modulus over a wide temperature range. As illustrated, in various embodiments, the deformable upjacket material is selected to have a room temperature modulus below about 700MPa and a -<NUM> modulus below about <NUM> GPa and a coefficient of thermal expansion below about <NUM> x <NUM>-<NUM>/°C in the temperature range from room temperature to -<NUM>. In one embodiment, the deformable upjacket may be selected to have a modulus between <NUM> MPa and <NUM> MPa within a temperature range between -<NUM> to <NUM>.

In one illustration as represented by the second curve C2, the deformable upjacket material is selected to have a room temperature modulus below about 150MPa and a -<NUM> modulus below about 600MPa and a coefficient of thermal expansion below about <NUM> x <NUM>-<NUM>/°C in the temperature range from room temperature to -<NUM>. In one illustration, santoprene <NUM>-<NUM> has a low modulus and low coefficient of thermal expansion (about <NUM> x <NUM>-<NUM>/°C). As used herein modulus or tensile modulus is determined in accordance with ASTM D638 - <NUM> "Standard Test Method for Tensile Properties of Plastics" published by ASTM International, West Conshohocken, PA, <NUM>.

Referring to the experimental data, a deformable upjacket material comprising santoprene <NUM>-<NUM> exhibits a lower sensitivity to temperature relative to conventional upjacket material. Even at lower end of the test, e.g., at -40C, the deformable upjacket material has a compressive modulus of about <NUM> MPa, which is almost six times smaller than the conventional upjacket material.

<FIG> illustrates the shrinkage stress for various upjacket materials as a function of temperature. The shrinkage stress illustrated in <FIG> was calculated from coefficient of thermal expansion data and modulus data as determined through DMA analysis of the different materials on a TA Instruments DMA <NUM> Dynamic Mechanical Analyzer equipped with liquid nitrogen cooling for sub-ambient temperature operation.

In <FIG>, the third curve C3 represents a conventional upjacket material while the fourth curve C4 represents a deformable upjacket material. As is evident, the conventional upjacket material results in substantially increased shrinkage stress compared to the deformable upjacket material.

<FIG> collectively suggest that replacing the conventional upjacket material with a deformable upjacket material is likely to produce cables with better optical and mechanical performance.

Several tests were performed to determine the viability of applicant's embodiments. One set of the experiments illustrated in <FIG> and <FIG> were performed on samples comprising different upjacket materials.

The experiments illustrated in the tables of <FIG> and <FIG> were performed on optical cables comprising <NUM> optical fibers with six buffer tubes in which one of the buffer tube is a dummy tube filled with gel. The buffer tubes surround a glass reinforced polymer core forming the strength member <NUM>. The compression tests were performed on individual upjacketed central strength member as well as on individual deformable buffer tubes. The compression tests were performed in an Instron <NUM> (S. C5456) testing machine with samples fixed between two four inch parallel plates. A strain rate of <NUM>. 05in/min and ambient temperature of <NUM> was used for the testing. Compressive modulus is determined from the slope of the load - deformation curve before the yield point as illustrated in <FIG>, where the triangles represent the yield point for three different specimens or samples. The obtained modulus (slope of load versus deformation) could be further normalized by the length of sample under compression so as to result in the compressive modulus having the units of MPa or lbf/in<NUM>. The results in <FIG> and <FIG> illustrate the raw numbers prior to such length normalization. The test procedure described herein is for illustrative purposes and is not to be considered as the only way to test for the compressive modulus. It is further noted that a different experimental setup such as, for example, using two inch parallel plates instead of four inch parallel plates, will result in different numbers for the modulus, although the results are expected to be similar qualitatively as well as relatively.

<FIG> illustrates a table summarizing compression test results from testing the central strength member.

First, as illustrated in <FIG>, the compression tests were conducted individually for the upjacketed central strength member, while the upjacket material was varied. In particular, these tests were performed by de-processing a finished optical cable to form individual elements such as an individual buffer tube or an individual strength member encapsulated with the upjacket material.

In the illustrated table, the upjacket diameter is the outer diameter of the upjacket material while the S. diameter is the diameter of the central strength member <NUM>, which in this case comprises a glass reinforced polymer.

The second and third columns show the test results of using a solid polypropylene upjacket material. The compressive modulus of these samples is very high about <NUM>,<NUM> lbf/in, which is the modulus normalized per sample length (noting that modulus is normally expressed in lbf/in<NUM> or MPa) For the fourth to sixth columns, the upjacket material comprises a foamed polypropylene material. The foam content is varied between <NUM>%, <NUM>%, and <NUM>% while keeping the other parameters unchanged. The use of the foamed polypropylene upjacket causes a 2x (half) reduction in the compressive modulus.

The seventh column illustrates the test results from using a deformable material upjacket such as a thermoplastic elastomer such as Santoprene <NUM>-<NUM> CCT. The deformable upjacket material reduces the compressive modulus further to about <NUM>,<NUM> Ibf/in. Compared to the solid polypropylene upjacket, the thermoplastic elastomer results in greater than <NUM>% reduction in compressive modulus. Similarly, compared to the foamed polypropylene upjacket, the thermoplastic elastomer results in greater than <NUM>% reduction in compressive modulus.

<FIG> illustrates a table comparing the compression test results from testing the central strength member to the buffer tube.

The fourth column of <FIG> summarizes the results from <FIG> where the deformable upjacket material has a compressive modulus of about <NUM>,<NUM> Ibf/in. In contrast, the second column and the third column illustrate the compression test results of individual deformable buffer tubes. The second column illustrates the results prior to the deformation of the deformable buffer tubes, i.e., before being placed within an optical cable and compressed. In contrast, the third column illustrates the results after forming compressing the buffer tube within the optical cable and is therefore representative of the real product. The deformed buffer tube exhibits a slightly higher compressive modulus but not significantly different than the undeformed buffer tube. However, more importantly, the deformable buffer tubes have a much smaller compressive modulus than the deformable upjacket material.

In various embodiments, the deformable upjacket material is selected so as to have a compressive modulus similar to the compressive modulus of the buffer tube. In one or more embodiments, the deformable upjacket material is selected such that the ratio of compressive modulus of the buffer tube to the compressive modulus of the deformable upjacket material is less than <NUM>:<NUM>, or in one embodiment to be between <NUM>:<NUM> and <NUM>:<NUM>.

In this example embodiment, the ratio of compressive modulus of the buffer tube to the compressive modulus of the deformable upjacket material is about <NUM>:<NUM>. In contrast, this ratio increases to <NUM>:<NUM> for the foamed polypropylene upjacket and to <NUM>:<NUM> for the solid polypropylene upjacket.

<FIG> describe specific implementations of different designs for the optical cable in accordance with various embodiments of the present invention.

<FIG> illustrate an example embodiment of an optical cable, wherein <FIG> illustrates a cross-sectional design view of the optical cable prior to compression and <FIG> illustrates a corresponding projection view, and wherein <FIG> illustrates a cross-sectional view of the optical cable after compression. <FIG> illustrate the design arrangement and are not representative of the final shape, which will be as discussed above. The circular cross-sections illustrated here are provided for ease of illustration.

Referring to <FIG>, the optical cable comprises an outer cover <NUM> within which six deformable buffer tubes <NUM> labeled herein as 110R, 110B, 110W, 110BK, 110O, and <NUM> are arranged concentrically around a strength member <NUM> that is rigid. The strength member <NUM> is jacketed with a deformable upjacket <NUM>. The outer layer of the deformable buffer tubes 110R, 110B, 110W, 110BK, 110O, and <NUM> may be colored for identification such as red, blue, white, black, orange, green, etc..

<FIG> illustrates the optical cable of <FIG> after compression. Although the cross-section of <FIG> includes some interstices <NUM>, the deformable buffer tubes <NUM> have deformed significantly in trying to lower the amount of area occupied by the interstices <NUM> relative to <FIG>. In various embodiments, in reality, the amount of deformation would depend on both external as well as internal factors. Examples of external factors include the amount of compression applied on the buffer tubes (e.g., arrows in <FIG>), the time for which compression is applied, the temperature at which compression is applied etc., while examples of internal factors include the material and thickness of the buffer tube jacket, the flexibility of the flexible ribbons within the buffer tubes, and the stacking arrangement of the flexible ribbons.

In one example of the optical cable illustrated in <FIG>, the cable diameter is <NUM> and includes six buffer tubes, where each buffer tube contains <NUM> optical fibers in which each fiber has a diameter of <NUM>. Thus, the cable of <FIG> includes <NUM> fibers with a percent fill of about <NUM>%, which is the ratio of the duct size diameter to the cable outer diameter. Thus, the cable of <FIG> can easily pass through a <NUM> inch duct.

<FIG> illustrates a specific design for an optical cable in accordance with an alternative embodiment of the invention, wherein <FIG> illustrates a cross-sectional view of the optical cable prior to compression and <FIG> illustrates a corresponding projection view. As with <FIG>, <FIG> illustrate the design arrangement and are not representative of the final shape.

<FIG> illustrate an alternative design in which the deformable buffer tubes <NUM> are arranged in multiple concentric paths around a central strength member <NUM>. In addition, after the first row of the deformable buffer tubes <NUM> are arranged, a support layer <NUM> may be introduced for reinforcing the first row of the deformable buffer tubes <NUM>. The support layer <NUM> may comprise a material having sufficient property to reinforce the buffer tubes that are enclosed by it but at the same is also 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.

Another set of the deformable buffer tubes <NUM> are arranged around the support layer <NUM>. An outer cover <NUM> is disposed around the multiple rows of the deformable buffer tubes <NUM> and includes an outer jacket of the cable.

Unlike <FIG>, the subsequent cross-section view of the optical cable after undergoing deformation is not illustrated in <FIG>. However, the individual buffer tubes are similarly deformed as described in detail in the prior embodiments.

In an example of the embodiment of <FIG>, the optical cable has a cable diameter of <NUM> with five buffer tubes in the first row and eleven buffer tubes in the second row. Each buffer tube contains <NUM> optical fibers in which each fiber has a diameter of <NUM>. Thus, the cable of <FIG> includes <NUM> fibers with a percent fill of about <NUM>%, which is the ratio of the duct size diameter to the cable outer diameter. Thus, the cable of <FIG> can easily pass through a two inch duct, and perhaps even through a <NUM> inch duct.

<FIG> illustrates a specific design for an optical cable in accordance with an alternative embodiment of the invention, wherein <FIG> illustrates a cross-sectional view of the optical cable prior to compression and <FIG> illustrates a corresponding projection view. Once again, <FIG> illustrate the design arrangement and are not representative of the final shape.

In the embodiment of <FIG>, 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 strength member <NUM>. For example, the thickness of the deformable upjacket <NUM> is larger than the diameter of the strength member <NUM> in the illustrated embodiment. However, in other embodiments, the thickness of the deformable upjacket <NUM> may be the same as the diameter of the strength member <NUM>. In one embodiment, the thickness of the deformable upjacket <NUM> may be similar to the diameter of the strength member <NUM>. Eight buffer tubes are arranged around the outer periphery of the deformable upjacket <NUM>. In an example of the embodiment of <FIG>, the optical cable has a cable diameter of <NUM> with eight buffer tubes. Each buffer tube contains <NUM> optical fibers in which each fiber has a diameter of <NUM>. Thus, the cable of <FIG> includes <NUM> fibers with a percent fill of about <NUM>%, which is the ratio of the duct size diameter to the cable outer diameter. Thus, the cable of <FIG> can easily pass through a two inch duct, and perhaps even through a <NUM> inch duct.

The subsequent cross-section view of the optical cable after undergoing deformation is not illustrated in <FIG>. However, the individual buffer tubes are deformed as described in detail similar to the prior embodiments.

<FIG> illustrates a specific design for an optical cable in accordance with an alternative embodiment of the invention, wherein <FIG> illustrates a cross-sectional view of the optical cable prior to compression and <FIG> illustrates a corresponding projection view. As previously discussed, <FIG> illustrate the design arrangement and are not representative of the final shape.

The optical cable in this embodiment are designed similar to the embodiment of <FIG> in that they do not include an upjacket around the central strength member and further include two rows of buffer tubes around the central region. However, in this embodiment, a smaller number of buffer tubes are arranged in the first row. Instead of five 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 strength member <NUM>. The additional strength members <NUM> are separated from the strength member <NUM> by the deformable 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 deformable buffer tubes <NUM> in the first row. The additional strength members <NUM> provide additional rigidity to the optical cable for supporting a larger number of buffer tubes. In particular, the additional strength members <NUM> along with the strength members <NUM> make better use of space since they are smaller in diameter relative to the deformable buffer tubes <NUM> by at least a factor of two.

Consequently, in the embodiment of <FIG>, three deformable buffer tubes <NUM> are arranged in a first row and enclosed by a support layer <NUM>. Another nine deformable buffer tubes <NUM> are arranged around the support layer <NUM>. In an example of the embodiment of <FIG>, the optical cable has a cable diameter of <NUM>. Each buffer tube contains <NUM> optical fibers in which each fiber has a diameter of <NUM>. Thus, the cable of <FIG> includes <NUM> fibers with a percent fill of about <NUM>%, which is the ratio of the duct size diameter to the cable outer diameter. Thus, the cable of <FIG> can easily pass through a two inch duct.

This embodiment combines features from the prior embodiments described in <FIG>. For example, this embodiment includes a deformable upjacket <NUM> around the strength member <NUM> as described, for example, in <FIG>. Similar to embodiment of <FIG>, a first row of deformable buffer tubes <NUM> is arranged around the deformable upjacket <NUM>. The first row of deformable buffer tubes <NUM> include nine buffer tubes that are enclosed within a support layer <NUM>. A second of deformable buffer tubes <NUM> including fifteen buffer tubes are arranged around the support layer <NUM>.

Consequently, in an example of the embodiment of <FIG>, the optical cable has a cable diameter of <NUM>. Each buffer tube contains <NUM> optical fibers in which each fiber has a diameter of <NUM>. Thus, the cable of <FIG> includes <NUM> fibers with a percent fill of about <NUM>%, which is the ratio of the duct size diameter to the cable outer diameter. Thus, the cable of <FIG> can easily pass through a two inch duct.

This embodiment is similar to <FIG> because it includes additional strength members <NUM> arranged between the deformable buffer tubes <NUM>. Adjacent additional strength members <NUM> are separated from each other as well as from the strength member <NUM> by one of the deformable buffer tubes <NUM>. In one embodiment, the number of the additional strength members <NUM> is the same as the number of the deformable buffer tubes <NUM> in the first row.

Again as in the embodiments of <FIG>, no additional upjacket is used around the strength member <NUM> or the additional strength member <NUM>. However, in some embodiments, either or both of these strength members may be jacketed with a deformable upjacket material.

Consequently, in an example of the embodiment of <FIG>, the optical cable has a cable diameter of <NUM>. Each buffer tube contains <NUM> optical fibers in which each fiber has a diameter of <NUM>. Thus, the cable of <FIG> includes <NUM> fibers with a percent fill of about <NUM>%, which is the ratio of the duct size diameter to the cable outer diameter. Thus, the cable of <FIG> can easily pass through a <NUM> inch duct.

<FIG> illustrates a generic embodiment showing a combination of features described in various embodiments of the present invention. The subsequent cross-section view of the optical cable after undergoing deformation is not illustrated in <FIG>. However, the individual buffer tubes are deformed as described in detail similar to the prior embodiments.

As illustrated in <FIG>, an optical cable may comprise multiple rows of deformable buffer tubes <NUM> arranged around a central strength member <NUM>. As also illustrated in <FIG>, the central strength member may include a deformable upjacket <NUM> surrounding the same. For clarity, not all the elements such as the buffer tubes <NUM> are illustrated. A first row of deformable buffer tubes surround the central strength member <NUM>. In addition, the optical cable may comprise multiple rows of buffer tubes arranged after the first row. In the illustration, two rows of deformable buffer tubes <NUM> are arranged around the first row. Any of the rows may include additional strength member <NUM>. For example, in the illustration, the second and third rows include additional strength members <NUM>. In additional embodiments, the first row may also include additional strength members <NUM>. In addition, the additional strength members <NUM> may be sized differently from the other additional strength members <NUM> in other rows including the central strength member <NUM>. Further, some or all of the additional strength members <NUM> may include a deformable upjacket <NUM> around it.

<FIG> is a table summarizing example embodiments of the different cable design in accordance with various embodiments of the present invention.

As illustrated in the table of <FIG>, a number of specific designs are tabulated. The cable diameter references the outer diameter of the cable while the duct size references the size of the duct through which the cable can pass through. The subsequent columns follow the design arrangement of the buffer tubes within the cable. For example, the total number of buffer tubes is all of the buffer tubes within the cable while the number of rows of buffer tubes represents the number of concentric arrangements of the buffer tubes. For example, <FIG> has two rows (two concentric arrangement of the buffer tubes). The first row of the buffer tube is the row immediately surrounding or adjoining the central strength member. The use of upjacket surrounding the central strength member is summarized as a positive (yes) or a negative (no). In various designs that include additional strength members, the additional strength members may be larger or about the same size as the central strength member. As noted earlier, the fill % is the ratio of the duct size diameter to the cable outer diameter.

As noted in <FIG> and <FIG>, using embodiments of the present invention, a fill % of about <NUM>% to about <NUM>% is obtained. Similarly, the number of fibers per unit area for each cable can be as high as <NUM> fibers/mm<NUM>, or alternately, the number of fibers per unit area for each cable can vary between <NUM> fibers/mm<NUM> to <NUM> fibers/mm<NUM>.

<FIG> illustrates a deformable buffer tube formed using a single flexible ribbon and usable with embodiment optical cables of the present invention. For example, the deformable buffer tube of <FIG> may replace the deformable buffer tubes of any other embodiment optical cables such as the optical cables of <FIG>, <FIG>, <FIG>, <FIG>, and others.

Referring to <FIG>, a deformable buffer tube <NUM> includes a single flexible ribbon <NUM> which may be as previously described. That is, the flexible ribbon <NUM> may include any suitable number of optical fibers. For example the flexible ribbon <NUM> may include first, second, third, fourth, fifth, and sixth optical fibers <NUM>-<NUM> as shown. A possible advantage of including a single flexible ribbon in each deformable buffer tube of an optical cable is to facilitate easier identification of individual optical fibers within the optical cable.

The flexible ribbon <NUM> is enclosed by a buffer tube jacket <NUM> which may be a specific embodiment of other buffer tube jackets described herein, such as the buffer tube jacket <NUM> of <FIG>, for example. Additionally, the buffer tube jacket <NUM> may be smaller than buffer tube jackets that are used to enclose multiple flexible ribbons. Alternatively, the number of optical fibers in the flexible ribbon may be increased compared to embodiments with multiple flexible ribbons per buffer tube jacket and the buffer tube jacket <NUM> may be of equal size or even larger than buffer tube jackets enclosing multiple flexible ribbons.

As discussed above, any of the embodiment optical cables described herein may be implemented using deformable buffer tubes enclosing only a single flexible ribbon. <FIG> specifically illustrate several optical cables comprising a plurality of deformable buffer tubes each enclosing a single flexible ribbon. Similarly labeled elements may be a previously described.

<FIG> illustrates a further embodiment of the present invention having an additional deformable upjacket surrounding the central strength member and including a plurality of deformable buffer tubes each formed using a single flexible ribbon. The optical cable of <FIG> may be a specific implementation of other embodiment optical cables, such as the optical cable of <FIG>, for example. Referring to <FIG>, an optical cable includes a plurality of deformable buffer tubes <NUM> each enclosing a single flexible ribbon. Although illustrated as having six deformable buffer tubes, any suitable number is possible.

<FIG> illustrates a still further embodiment of the present invention having an additional deformable upjacket surrounding the central strength member and including a plurality of deformable buffer tubes each formed using a single flexible ribbon. The optical cable of <FIG> may be a specific implementation of other embodiment optical cables, such as the optical cable of <FIG>, for example.

Referring to <FIG>, an optical cable includes a plurality of deformable buffer tubes <NUM> each enclosing a single flexible ribbon. Including a single flexible ribbon in each deformable buffer tube may advantageously allow one or more dimensions of the deformable buffer tubes <NUM> to be reduced relative to other components of the optical cable, such as the central strength member <NUM>, for example. Accordingly, the diameter of the optical cable may be further reduced.

Each deformable buffer tube <NUM> may have a peripheral width W3, an interior width W4, and a physical contact distance d2 similar to the first width W1, second width W2, and distance d respectively as previously described. In contrast, the peripheral width W3 and the interior width W4 may be made relatively smaller while the number of deformable buffer tubes in the optical cable is increased. For example, as illustrated in <FIG>, nine deformable buffer tubes are included in the optical cable, but larger or smaller numbers deformable buffer tubes that each enclose a single flexible ribbon are also possible.

The ratios of the physical contact distance d2 to the peripheral width W3 and the interior width W4 respectively may advantageously be increased relative to other embodiments due to the decreased size of each deformable buffer tube <NUM> relative to the central strength member <NUM>. In contrast to the peripheral width W3 and the interior width W4 which may decrease relative to the first width W1, second width W2, the physical contact distance d2 may be equal or greater than the distance d of other embodiments.

<FIG> illustrates a further generic embodiment including a plurality of deformable buffer tubes each formed using a single flexible ribbon and showing a combination of features described in various embodiments of the present invention. The optical cable of <FIG> may be a specific implementation of other embodiment optical cables, such as the optical cable of <FIG>, for example. Specifically, the optical cable of <FIG> includes a multiple rows of deformable buffer tubes, each deformable buffer tube <NUM> enclosing a single flexible ribbon. The subsequent cross-section view of the optical cable after undergoing deformation is not illustrated in <FIG>. However, the individual buffer tubes are deformed as described in detail similar to the prior embodiments.

Example embodiments of the present invention are summarized here. Other embodiments can also be understood from the entirety of the specification and the claims filed herein.

Example <NUM>. An optical cable includes a plurality of deformable buffer tubes. Each of the plurality of deformable buffer tubes includes a plurality of flexible ribbons, and each of the flexible ribbons includes a plurality of optical fibers. Each of the plurality of deformable buffer tubes has a non-circular cross-section. An outer jacket surrounds the plurality of deformable buffer tubes.

Example <NUM>. The cable of example <NUM>, where each of the plurality of deformable buffer tubes is configured to be deformed in any direction.

Example <NUM>. The cable of one of examples <NUM> or <NUM>, where the plurality of flexible ribbons is enclosed by a first deformable material that forms part of the outer surface of each of the plurality of buffer tubes.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the first deformable material surrounding the plurality of flexible ribbons includes polypropylene, polyethylene, nylon, polyamide, polybutylene terephthalate, or a polyolefin copolymer included of polyethylene and polypropylene.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the plurality of flexible ribbons is disposed within a gel material.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where each of the plurality of deformable buffer tubes includes a shape or dimension different from all the others of the plurality of deformable buffer tubes.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, further includes a first rigid strength member disposed within the outer jacket.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the rigid strength member is disposed in a central region surrounded by the plurality of deformable buffer tubes.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, further includes a plurality of rigid additional strength members disposed between the plurality of deformable buffer tubes, where the plurality of additional rigid strength members is disposed around the first rigid strength member.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the first rigid strength member is enclosed by a second deformable material.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the second deformable material includes a material having a modulus less than <NUM> GPa at -<NUM>.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the second deformable material includes a material having a modulus between <NUM> MPa and <NUM> MPa within a temperature range between -<NUM> to <NUM>.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where a compressive modulus of the second deformable material is less than a compressive modulus of a first deformable material surrounding the plurality of flexible ribbons.

Example <NUM>. The cable of one of examples <NUM> to <NUM> and <NUM> to <NUM>, where the first deformable material includes polypropylene and the second deformable material includes santoprene <NUM>-<NUM>.

Example <NUM>. An optical cable includes a central strength member and a plurality of buffer tubes disposed around the central strength member, where each of the plurality of buffer tubes includes a buffer tube jacket surrounding a plurality of flexible ribbons. The buffer tube jacket includes a first deformable material that is deformed plastically. Each of the flexible ribbons includes a plurality of optical fibers. An outer jacket surrounds the plurality of buffer tubes.

Example <NUM>. The cable of example <NUM>, where the plurality of buffer tubes are arranged in a plurality of concentric rows around the central strength member.

Example <NUM>. The cable of one of examples <NUM> or <NUM>, further includes additional strength member arranged in one of the plurality of concentric rows.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, further includes a second deformable material surrounding the strength member.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, further includes a second deformable material surrounding the additional strength member.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the first deformable material includes polypropylene.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where a ratio of a thickness of the first deformable material to a cross-sectional width of one of the plurality of buffer tubes is about <NUM> to <NUM>.

Example <NUM>. An optical cable includes a rigid strength member and a deformable upjacket surrounds the rigid strength member. A plurality of buffer tubes is disposed around the rigid strength member. Each of the plurality of buffer tubes includes a plurality of ribbons, and each of the ribbons includes a plurality of optical fibers, where each of the plurality of buffer tubes includes a first compressive modulus, and the rigid strength member with the deformable upjacket includes a second compressive modulus. A ratio of the first modulus to the second modulus is about <NUM>:<NUM> to <NUM>:<NUM>. An outer jacket surrounds the plurality of buffer tubes.

Example <NUM>. The cable of example <NUM>, where the deformable upjacket includes polypropylene based thermoplastic elastomer.

Example <NUM>. The cable of one of examples <NUM> or <NUM>, where the deformable upjacket includes a material having a modulus less than <NUM> MPa at -<NUM>.

Example <NUM>. The cable of one of examples <NUM> to <NUM>, where the deformable upjacket includes a material having a modulus between <NUM> MPa and <NUM> MPa within a temperature range between -<NUM> to <NUM>.

Claim 1:
An optical cable comprising:
a plurality of deformable buffer tubes (<NUM>), wherein each deformable buffer tube of the plurality of deformable buffer tubes (<NUM>) comprises
one or more flexible ribbons (<NUM>) each comprising a plurality of optical fibers (<NUM>), and
an axial cross-section of the deformable buffer tube (<NUM>) that includes the one or more flexible ribbons (<NUM>), and wherein
the axial cross-section comprises an irregular shape due to deformation; and
an outer jacket (<NUM>,<NUM>) surrounding the plurality of deformable buffer tubes (<NUM>),
the plurality of optical fibers (<NUM>) are arranged parallel to each other and are connected at bond regions (<NUM>), wherein the bond regions (<NUM>) are arranged across the flexible ribbons (<NUM>) so as to selectively leave a large surface of the optical fibers (<NUM>) free of bonding material that forms the bond region (<NUM>), wherein
a first rigid strength member (<NUM>) is disposed within the outer jacket, wherein the first rigid strength member (<NUM>) is disposed in a central region surrounded by the plurality of deformable buffer tubes (<NUM>), characterized in that
the first rigid strength member (<NUM>) is enclosed by a second deformable material (<NUM>) comprising a material having a modulus less than <NUM> GPa at -<NUM>, determined in accordance with ASTM D638 - <NUM>.