Optical cables having an inner sheath attached to a metal tube

An optical cable includes a plurality of optical fibers sealed within a metal tube, a polymer inner sheath surrounding the metal tube and operatively connected to the metal tube, and an outer sheath disposed over the polymer inner sheath.

TECHNICAL FIELD

The present invention relates generally to optical cables, and, in particular embodiments, to optical cables capable of maintaining operation in harsh environments.

BACKGROUND

Optical fibers are 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.

Due to the broad range of applications for optical fibers, optical cables may need to be capable of operation in harsh environments. For example, optical cables may be used in harsh environments where high chemical resistance is needed such as in ducts, refineries such as oils and gas plants, mining operations, and the like. Optical cables may also be relied upon to maintain functionality for safety reasons during disaster events. For instance, optical cables may need to be flame retardant, fire resistant, and maintain circuit integrity for as long as possible during a fire. In addition, the performance of optical cables may be adversely affected by pressure events such as bending, buckling, and compressive stresses. For these reasons, optical cables that are resistant to chemicals, fire, and/or mechanical stresses may be desirable.

Optical cables may also be used in applications where electrical signals and/or electrical power are desirable in addition to an optical signal. A hybrid cable may include electrically conductive pathways as well as optical pathways in an integrated cable solution. For example, optical devices and electronic equipment such as machinery, sensors, communication devices, and others may be fed by a hybrid cable. Hybrid cables have been described previously in the art.

A fiber-optic transmission cable for high-stress environments and especially undersea applications is described by Stamnitz in European Patent Publication No. EP0371660A1. The fiber-optic transmission cable comprises one to a large number of optical fibers, electrical conductors, and metallic wire strength members contained within a single cable structure. A specific example is an electro-opto-mechanical cable that includes at least one thin-wall steel alloy tube containing at least one single mode fiber and a void filling gel. A dielectric annulus includes an electrically conductive layer disposed therein. An optional double-layer contrahelical or three or four layer, torque balanced, steel wire strength member provides additional protection as well as capability to be towed, deployed and recovered from the seafloor at abysmal depths.

An undersea telecommunications cable is described by Marlier et al. in U.S. Pat. No. 5,125,061. The undersea telecommunications cable has optical fibers embedded in a material filling a tube which itself lies inside a helical lay of metal wires having high mechanical strength and in which the interstices are filled with a sealing material. The cable includes a first extruded sheath between the tube and the helical lay, and the helical lay is itself covered by a second extruded sheath which is insulating and abrasion resistant, and if the cable is for a remotely-powered link, it includes a conductive strip on the tube or on the first sheath.

SUMMARY

In accordance with an embodiment of the invention, an optical cable includes a plurality of optical fibers sealed within a metal tube, a polymer inner sheath surrounding the metal tube and operatively connected to the metal tube, and an outer sheath surrounding disposed over the polymer inner sheath. In an embodiment, a single layer of armor is disposed between the polymer inner sheath and the outer sheath.

In accordance with another embodiment of the invention, an optical cable includes an optical core comprising a metal tube enclosing a plurality of loose optical fibers. The optical core is configured to resist water penetration. The optical cable further includes a single layer homogeneous inner sheath disposed over and operatively connected to the optical core and an outer sheath. The single layer homogeneous inner sheath is configured to be chemically resistant. The optical cable may also include an armor layer disposed over and physically contacting the single layer homogeneous inner sheath, and the outer sheath disposed over the armor layer. The outer sheath is configured to be flame retardant.

In accordance with still another embodiment of the invention, a hybrid cable includes a plurality of optical fibers sealed within a metal tube and a polyamide inner sheath surrounding the metal tube. The polyamide inner sheath is directly attached to the metal tube. The hybrid cable further includes a conductive layer disposed over and physically contacting the polyamide inner sheath, an intermediate sheath disposed over the conductive layer, and an outer sheath surrounding the intermediate sheath. An armor layer may be disposed between the intermediate sheath and the outer sheath. The hybrid cable is configured to transmit optical signals through the plurality of optical fibers. The hybrid cable is further configured to conduct electrical current through the conductive layer.

In accordance with yet another embodiment of the invention, a method of fabricating an optical cable includes providing a plurality of optical fibers, sealing the plurality of optical fibers within a metal tube, forming a polymer inner sheath surrounding the metal tube and operatively connected to the metal tube, and forming an outer sheath to surround over the polymer inner sheath. In an embodiment, the method further comprises forming a single layer of armor over the polymer inner sheath before forming the outer sheath.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In various embodiments, an optical cable with high chemical resistance, fire resistance, flame retardancy, circuit integrity, and mechanical strength will be described. The optical cable achieves these and other properties by including a chemically resistant layer directly contacting a metal tube that houses optical fibers. The following description describes the exemplary embodiments.

Two conventional optical cables will first be described usingFIGS. 1 and 2. Two embodiment optical cables will then be described usingFIGS. 3 and 4. Two embodiment hybrid cables will then be described usingFIGS. 5 and 6. Several exemplary methods of fabricating embodiment cables will then be described usingFIGS. 7-9. A selection of possible cable diameters and cable diameter ranges will be summarized in Table I.

Referring toFIG. 1, a conventional optical cable100includes a glass fiber reinforced plastic (GFRP) central element150. Thermoplastic polyester tubes152are arranged around the GFRP central element150. Each of the thermoplastic polyester tubes152contains a plurality of optical fibers110and a gel compound122. The conventional optical cable has 72 optical fibers110contained in six thermoplastic polyester tubes152as illustrated inFIG. 1.

The thermoplastic polyester tubes152are surrounded by a heat resistant and swellable core covering124. The heat resistant and swellable core covering124comprises a mica tape for heat resistance and an absorbent powder for water protection. The heat resistant and swellable core covering124is surrounded by a low smoke zero halogen (LS0H) layer154. The GFRP central element150, thermoplastic polyester tubes152, the heat resistant and swellable core covering124, and the LS0H layer154make up a cable core140of the conventional optical cable100.

The cable core140has a conventional core diameter190determined as a function of the number and arrangement of the optical fibers within the thermoplastic polyester tubes152. The total number of optical fibers typically ranges from 6 to 96. The conventional core diameter190has a minimum diameter 6.5 mm for 6 to 36 optical fibers. The diameter increases as the number of optical fibers increases. A conventional optical cable100including 72 optical fibers has a conventional core diameter190of 7.4 mm. Similarly, a conventional optical cable100including 96 optical fibers has a conventional core diameter190of 9 mm.

The cable core140is covered by a multilayer inner sheath142in a radially outer position with respect to LS0H layer154. The multilayer inner sheath142has an aluminum foil132, a high density polyethylene (HDPE) layer156, and a polyamide (PA) layer158. The PA layer158is made of polyamide 12 (also referred to as PA12). The multilayer inner sheath142has a conventional inner sheath diameter192which is limited by the number of layers included in multilayer inner sheath142as well as minimum protection requirements. In order to protect the conventional optical cable100, the conventional inner sheath diameter192cannot be less than 6.9 mm.

An armor layer146is disposed on the multilayer inner sheath142. The armor layer146consists of one layer of galvanized steel wires136. An LS0H outer sheath148covers the armor layer146. Conventional optical cable100has a conventional optical cable diameter199which includes the LS0H outer sheath148. Since the cable core140is also included, the conventional optical cable diameter199is subject to the same limitations as the conventional core diameter190. A conventional optical cable100with a total number of optical fibers in the range of 6 to 36 optical fibers has a conventional optical cable diameter199of 19.8 mm. A conventional optical cable100with 72 optical fibers has a conventional optical cable diameter199of 20.7 mm. Similarly, a conventional optical cable100with 96 optical fibers has a conventional optical cable diameter199of 22.3 mm.

Referring toFIG. 2, a conventional optical cable200has a central strength member250. Fibers210are protected in gel-filled loose tubes252stranded around the central strength member250. A moisture barrier232is made of aluminum copolymer tape that is longitudinally folded around the loose tubes252. A subunit jacket256made of high density polyethylene (HDPE) is arranged over the moisture barrier232. A polyamide jacket258is arranged around the subunit jacket256. An armor246consisting of steel wires, steel wire braids, or corrugated steel tape is formed around the polyamide jacket258. A sheath248consisting of low smoke, zero halogen, flame retardant material or PVC flame retardant and heat and oil resistant material is formed around the armor246.

The conventional optical cable200has a conventional optical cable diameter299subject to the same limitations as the optical core240in a manner similar to conventional optical cable100. The conventional optical cable diameter299cannot be less than 18.0 mm when the conventional optical cable200has a total number of optical fibers in the range of 2 to 72 optical fibers. A conventional optical cable200with 96 optical fibers has a conventional optical cable diameter299of 19.6 mm. A conventional optical cable200with 144 optical fibers has a conventional optical cable diameter299of 23.4 mm.

Several disadvantages may be associated with conventional optical cables. For example, conventional optical cables are relatively thick. Both conventional optical cable100and conventional optical cable200need to have a GFRP central strength member which increases the diameter of the optical core and consequently the diameter of the conventional optical cable. This is because filler tubes containing no optical fibers are included to maintain structural integrity of the cable even when fewer tubes containing optical fibers are needed. Additionally, the multilayer inner sheath of conventional optical cable100and conventional optical cable200increases the total diameter of the cable.

Another disadvantage of conventional optical cables like cable100is the use of mica tape to provide fire resistance. Mica tape complicates manufacturing process flows by requiring that the conventional optical cable be moved to another line to wind the mica tape. The additional processing increases manufacturing costs by increasing manufacturing time and requiring additional machinery. Mica tape is formed by gluing mica flakes onto a glass fiber substrate, and is therefore very fragile. Mica flakes easily peel off during processing which disadvantageously pollutes the working environment. In addition, mica tape is relatively expensive which further increases costs. Cable200, not comprising mica tapes, is not suitable for maintaining circuit integrity under fire according to IEC 60331-25 (1999).

Conventional optical cables also cannot meet all of the protection requirements for certain harsh environments such as those found in the oil and gas industry. For example, optical cables designed for chemically challenging environments such as mines and oil wells have to be simultaneously water resistant, fire resistant, flame retardant, chemically resistant, mechanically stable, and maintaining circuit integrity during a fire. Conventional optical cables disadvantageously lack one or more protection requirements so as to render them unsuitable for use in these harsh environments such as in the oil and gas industry.

Furthermore, it may be desirable to provide electrical connectivity in addition to optical connectivity within a single cable. For example, electrical signals and/or power may be transmitted concurrently within a single optical cable. Electrical power may be advantageous to power remote machinery or sensors, for example. However, conventional optical cables disadvantageously only provide optical connectivity.

The inventors of the present application have found that conventional optical cables fail to meet protection requirements such as fire resistance and circuit integrity in the presence of fire. Furthermore, the inventors of the present application have found that conventional optical cables cannot be made thinner and less expensive while still meeting the protection requirements for harsh environments such as those found in the oil and gas industry. The inventors of the present application also recognize an unmet need in the industry of providing electrical signals and/or power in addition to optical signals using a single cable suitable for use in these harsh environments.

FIG. 3illustrates an exemplary optical cable according to the present disclosure including a single layer inner sheath directly adjacent to a sealed metal tube containing a plurality of optical fibers in accordance with an embodiment of the invention.

Referring toFIG. 3, an optical cable300includes a plurality of optical fibers10sealed within a metal tube30. Any conceivable number of optical fibers may be sealed within the metal tube30. In various embodiments, the number of optical fibers10within the metal tube30is less than 150. However, the number of optical fibers10within the metal tube30may also equal or exceed 150. In one embodiment, the number of optical fibers10within the metal tube30is 48. In another embodiment, the number of optical fibers10within the metal tube30is 12. In still another embodiment, the number of optical fibers10within the metal tube30is 96.

A fill material20may be included to fill empty space and partially or completely immobilize the optical fibers10within the metal tube30. The fill material20may be configured to prevent the propagation of moisture in a longitudinal direction along the optical cable300. For example, the fill material20may include a waterblocking compound. The fill material may also include a hydrogen scavenger. In various embodiments, the fill material20includes an absorbent material for absorbing moisture and water, and includes a super absorbent powder in some embodiments. In other embodiments, the fill material20includes a gel and is a thixotropic gel in some embodiments. In various embodiments, the fill material20is a flooding compound for preventing longitudinal moisture propagation within the metal tube30. Examples of materials suitable as fill material according to the present disclosure are hydrotreated heavy paraffines, hydrotreated neutral C20-50 oils, and polydimethylsiloxane oils. Water-blocking yarns bearing, for example polyacrylate and/or polyacrylamide powder, may also or alternatively be used.

In various embodiments, the metal tube30may be welded or extruded, if possible. The metal tube30may be of steel, for example of stainless steel such as 304 or 304 L stainless steel, or 316 or 316 L stainless steel. The metal tube30may also be implemented using other metals or metal alloys. In one alternative embodiment, the metal tube30is elemental copper (Cu) and is a welded copper tube in one embodiment. In other embodiments, the metal tube30is a copper alloy and is a welded copper alloy tube in one embodiment. In various embodiments, the metal tube30is aluminum and is a welded aluminum tube in one embodiment. Alternatively, metal tube30may be formed from extruded aluminum. When the metal tube30is made of copper, copper alloy or aluminum, it can also carry electric current, as requested by the specific cable application.

The metal tube30, fill material20, and plurality of optical fibers10comprise an optical core40of the optical cable300. Although the plurality of optical fibers10may be partially or completely immobilized by the fill material20, the configuration as illustrated inFIG. 3may be referred to as a loose tube core configuration. A possible advantage of this configuration is that the metal tube30may provide mechanical stability so that a central strength member is unnecessary. Since the metal tube30is sealed by welding or extrusion, it may also function to prevent water ingress into the optical core40. Specifically, the metal tube30may prevent radial water penetration into optical core40.

Still referring toFIG. 3, the optical cable300further includes an inner sheath42surrounding the metal tube30. In various embodiments, the inner sheath42is formed from a single layer of homogeneous polymer material and is a polyamide material in some embodiments. In other embodiments, inner sheath42may include two or more layers. Inner sheath42may also be implemented using other materials such as polyethylene (PE), as an example. Inner sheath42may be configured to protect optical core40from harsh chemicals. A possible advantage of inner sheath42is that sufficient protection from chemicals such as oil, fuel, toluene, water, and others may be obtained using a single layer of material. Consequently, inner sheath42may advantageously be thinner, less expensive, and simpler to fabricate than conventional layers configured to protect an optical core.

When made of polyamide, the inner sheath of the cable of the disclosure was found to be resistant to chemicals such as sodium hydroxide at room temperature, toluene at 50° C., benzene at 50° C., diesel fuel at 50° C., ASTM reference oil 902 at 75° C. and 100° C., ASTM reference oil 903 at 100° C. and 140° C., the inner sheath being tested according to IEC 60811-2-1 (2001).

In one embodiment, inner sheath42is implemented using a single homogeneous layer of nylon 6 (also referred to as PA6). Specifically, nylon 6 has the chemical formula [NH—(CH2)5—CO]nas a repeated unit. For example, as described below, the inventors have found that nylon 6 may be used to form inner sheath42in order to advantageously provide chemical protection while minimizing the thickness of inner sheath42. In another embodiment, inner sheath42is implemented using a single homogeneous layer of nylon 12 (also referred to as PA12). Specifically, nylon 12 has the chemical formula [NH—(CH2)11—CO]nas a repeated unit. Other types of nylon may also be used for inner sheath42such as nylon 6,6. Similarly, other polyamide materials may also be used for inner sheath42. In some applications, other materials such as other polymer materials may also be included in inner sheath42.

An optional adhesion layer26may be disposed between the metal tube30and the inner sheath42. The adhesion layer26may be configured to facilitate bonding of the inner sheath42directly to the metal tube30. The adhesion layer26may also be configured to act as a primer by preparing the outer surface of the metal tube30to be bonded to the inner sheath42. In various embodiments, the adhesion layer26completely fills the space between metal tube30and inner sheath42. As a result, adhesion layer26may also function to prevent or reduce longitudinal water penetration. Suitable adhesives for the cables of the present disclosure are based, for example, on polyamide or polyethylene, optionally admixed with acrylic acid or acrylate polymers.

Optical cable300also includes an armor layer46surrounding the inner sheath42. The armor layer46includes a metal in various embodiments. In one embodiment, armor layer46is a single layer of armor. Implementing armor layer46as a single layer of armor may advantageously enable a smaller overall diameter of optical cable300. Armor layer46may be implemented using a plurality of round wires34. In some embodiments, armor layer46includes stainless steel and in one embodiment is implemented using round galvanized steel wires (SWA) wound in a closed helix around inner sheath42. Alternatively, armor layer46may comprise other types of metal such as steel phosphate, stainless steel, aluminum clad steel, elemental copper (Cu), elemental aluminum (Al), metal alloys, and the like.

The shape of the elementary components of armor layer46is not limited to round wires. Armor layer46may also be implemented using corrugated tape, trapezoidal wires, or flat wires. Further, armor layer46may also be implemented using dielectric strength members such as round glass strength members or flat glass strength members or round aramid wires. Armor layer46may also include additional layers.

Referring again toFIG. 3, the optical cable300further includes an outer sheath48around the armor layer46. The outer sheath48may be advantageously configured to provide substantial fire resistance and flame retardancy. The outer sheath48may also advantageously be heat, oil, and UV resistant. The outer sheath48may optionally produce low smoke and zero halogens in the presence of fire. In some embodiments, the outer sheath48is implemented using an LS0H material as described, for example, in U.S. Pat. No. 6,552,112 which is incorporated herein by reference in its entirety. Specifically, the LS0H material may comprise, for example, (a) a crystalline propylene homopolymer or copolymer; (b) a copolymer of ethylene with at least one alpha-olefin, and optionally with a diene; and (c) natural magnesium hydroxide in an amount such as to impart flame-retardant properties. In other embodiments, the outer sheath48maybe implemented using a PVC material or an HDPE material.

Several representative dimensions of the optical cable300are shown inFIG. 3. The optical core40, which includes the metal tube30, the plurality of optical fibers10, and optionally the fill material20, has a first optical core diameter90. The first optical core diameter90may depend on the number of optical fibers10contained within. First optical core diameter90may further depend on the thickness of metal tube30as well as the presence of additional structural and organizational components included to arrange the plurality of optical fibers10. For example, the thickness of metal tube30may be between 0.1 mm and 0.5 mm and is 0.4 mm in one embodiment. A possible benefit of the metal tube30including loose packed optical fibers10is that the first optical core diameter90is decreased in comparison to conventional optical cores because of reasons described below in more detail.

In various embodiments, the first optical core diameter90is between 1.5 mm and 5.5 mm. In one embodiment, the first optical core diameter90is about 2 mm. As a specific example, an optical core40including 12 optical fibers may have a first optical core diameter90of 2 mm. In other embodiments, the first optical core diameter90is about 3.5 mm. As a specific example, an optical core40including 13 to 48 optical fibers may have a first optical core diameter90of 3.5 mm. In still other embodiments, the first optical core diameter90is about 4.8 mm. As a specific example, an optical core40including 49 to 96 optical fibers may have a first optical core diameter90of 4.8 mm. Other combinations of optical core diameters and numbers of optical fibers are possible. The first optical core diameter90may generally increase as the number of optical fibers increases, but this is not necessarily true in all cases.

In contrast to conventional optical cables designed to be fire resistant and maintain circuit integrity in the presence of fire, optical cable300may not include any fire resistant layer other than metal tube30around the optical core40. For example, conventional optical cables typically utilize a fire resistant tape such as mica tape to achieve the requirements of fire resistant circuit integrity standards such as International Electrotechnical Commission (IEC) 60331-25 (1999). Conventional cables that do not employ some type of heat resistant tape do not pass the IEC 60331-25 (1999) standard.

The inventors of the present application have found that a metal tube such as the metal tube30provides sufficient protection for the optical fibers to maintain circuit integrity during a fire. Specifically, the inventors have conducted circuit integrity tests on cables comprising stainless steel tubes containing unbuffered optical fibers with good results. The cable of the present disclosure successfully passed the circuit integrity tests at 750° C. for 90 min and at 1000° C. for 180 min according to IE C 60331-25 (1999) and at 830° C. for 120 min under impacts according to CEI EN50200 (2015). This finding may be counterintuitive based on known methods and configurations because the optical fibers may be expected to become overheated because of the high thermal conductivity of most metals. Advantageously, using a metal tube containing loose optical fibers may decrease the optical core diameter of embodiment optical and hybrid cables while still maintaining high levels of fire resistance and circuit integrity in the presence of fire.

The inner sheath42has a first inner sheath thickness92. In various embodiments, the first inner sheath thickness92is between 0.4 mm and 3 mm and may range from about 0.3 mm to about 1.5 mm is some embodiments. In one embodiment, the first inner sheath thickness92is about 0.5 mm. As a specific example, an inner sheath42implemented using a homogeneous PA material such as nylon 6 may have a first inner sheath thickness92of about 0.5 mm. In another embodiment, the first inner sheath thickness92is about 1.3 mm. As a specific example, an inner sheath42implemented using a homogeneous PE material may have a first inner sheath thickness92of about 1.3 mm. It should be noted that while the thickness of the adhesion layer26is nonzero it may be made very thin (having a thickness equal to or lower than 0.2 mm) so as to be much smaller than the first optical core diameter90and the first inner sheath thickness92.

The thickness of the inner sheath42may advantageously be made thin in comparison to conventional inner sheath thicknesses. For example, conventional inner sheaths may include multiple layers which increase the thickness of the inner sheath. Conventional inner sheaths used for chemical resistance may employ composite layers made of a PE layer, an aluminum layer, and a PA layer all together. Other conventional inner sheaths may be made very thick in order to use certain materials which may have reduced effectiveness when made thin, especially when used in harsh environments, such as environments where high chemical resistance is important.

The inventors of the present application have found that a single layer of appropriate thickness may be used for the inner sheath42of optical cable300while still maintaining a high level of chemical resistance. For example, the inventors have exposed PE, nylon 6, and nylon 12 to various compounds such as water, oil (IRM 902), fuel (IRM 903), and toluene at various temperatures, as already mentioned above. The inventors have determined, among other results, that a relatively thin layer of polyamide, for example nylon 6 or nylon 12, may be used to protect a metal tube in harsh chemical environments. For example, the thin layer of nylon 6 may range from a thickness of about 0.3 mm to about 1.0 mm. Based on the test results, an inner sheath implemented using a homogeneous PE layer is less efficient in providing protection in harsh chemical environments, particularly environments where oil and gas are present.

Still referring toFIG. 3, the armor layer46of optical cable300has an armor layer thickness96. The armor layer thickness96may be dependent on the mechanical requirements of a given application. In cases where armor layer46is implemented using a single layer of round wires34, the diameter of the round wires34may determine the value of armor layer thickness96. In various embodiments, the armor layer thickness96is between about 0.5 mm and about 3.6 mm. In one embodiment, the armor layer thickness96is about 1.0 mm. For certain applications where very high mechanical strength is desired, armor layer46may be implemented using multiple layers. Armor layer thickness96may exceed 3.6 mm for certain applications.

The outer sheath48has an outer sheath thickness97. The outer sheath thickness97may depend on various desired protection levels such as chemical resistance, heat resistance, flame retardancy, circuit integrity, mechanical stability, and others. The outer sheath thickness97is between about 1.0 mm and about 5.0 mm in various embodiments. In one embodiment, the outer sheath thickness97is 2.2 mm. In another embodiment, the outer sheath thickness97is about 3.0 mm.

The optical cable300has a first optical cable diameter399which depends on the combination of first optical core diameter90, first inner sheath thickness92, armor layer thickness96, and outer sheath thickness97. In various embodiments, the first optical cable diameter399is between 5 mm and 25 mm and ranges from about 5.6 mm to about 21 mm in some embodiments. In one embodiment, the first optical cable diameter399is about 12.5 mm for an optical cable300including 48 optical fibers.

Since the first optical cable diameter399is often primarily dependent on the number of optical fibers10, it may be useful to consider the ratio of the number of included optical fibers to the optical cable diameter. For example, in the preceding example of a first optical cable diameter399of 12.5 mm for an optical cable300including 48 optical fibers, the fiber/diameter ratio is about 3.84 fibers/mm. In general, a higher fiber/diameter ratio indicates a smaller cable and may be desirable in applications for the space devoted to cabling is limited. A table listing various exemplary optical cable diameters and corresponding numbers of optical fibers is shown below in Table I.

The first optical cable diameter399may be much thinner for a given number of optical fibers10than conventional optical cables. In the above example, an optical cable including 48 optical fibers has a fiber/diameter ratio of about 3.48 fibers/mm. Conventional optical cables have a fiber/diameter ratio that is much lower. For example, as previously described in reference toFIG. 1, a conventional optical cable including 36 optical fibers typically has a fiber/diameter ratio of 1.81 fibers/mm. In contrast, embodiments of the present can achieve fiber/diameter ratio greater than 3 fibers/mm and between about 3 fibers/mm to about 8 fibers/mm.

A further advantage of the cable of the present disclosure may be the amount of organic materials contained therein, such amount being largely reduced as compared with a conventional cable. Consequently, the smoke performance and the flame performance may be significantly improved. As a specific example, a cable of the present disclosure has been made that has a transmittivity >90% (98% with a 48 optical fiber cable, and 95% with a 96 optical fiber cable, both having a LS0H outer layer) under smoke test according to IEC 61034-2 (2005), and has successfully passed flame propagation tests according to IEC 60332-1-2 (2004), IEC 60332-3-24 (2000) Cat C, and 60332-3-22 (2009) Cat A.

A cable according to the present disclosure, containing up to 96 optical fibers and having an LS0H outer layer has been classified B2ca-s1a,d2,a1 CPR Class according to Commission Delegated Regulation (EU) 2016/364 of 1 Jul. 2015.

FIG. 4illustrates an exemplary optical cable including a single layer inner sheath directly adjacent to a sealed metal tube containing two or more fiber tubes each containing a plurality of optical fibers in accordance with an embodiment of the invention.

Referring toFIG. 4, an optical cable400includes an optical core41, an inner sheath42, an armor layer46, and an outer sheath48. The optical cable400may be similar to optical cable300as previously described in reference toFIG. 3except for the inclusion of optical core41which includes a multiple set of optical fibers contained within fiber tubes18. Similarly labeled elements may be as previously described and will not be described here in the interest of brevity.

The optical core41may include any number of fiber tubes18, each containing a set of optical fibers10. The fiber tubes18may comprise a polymer material. In various embodiments, the fiber tubes18include a polyester material and are implemented using a thermoplastic polyester material in one embodiment. The fiber tubes18may be configured to organize the optical fibers10within the optical core41. The fiber tubes18may also provide additional mechanical stability and confine an optional fiber tube filler material21. The fiber tube filler material21may be a gel material similar to fill material20, for example. In the cable configuration ofFIG. 4, a silicone based fiber tube filler material21can be employed.

Respective sets of optical fibers10may be the same or different from other sets of optical fibers10. A set of optical fibers10may be a single optical fiber10in some embodiments. There is not theoretical limit to the quantity of optical fibers10in a set of optical fibers. However, practical considerations may limit the number of optical fibers10in a single fiber tube18. As illustrated inFIG. 4, optical core41may include three fiber tubes18containing first, second, and third sets of optical fibers11,12,13. In one embodiment, each of the sets of optical fibers11,12,13consists of twelve optical fibers10. In other embodiments, some or all of the sets of optical fibers11,12,13consist of more or less than twelve optical fibers10.

The optical core41has a second optical core diameter91which may be similar or different from the first optical core diameter90of optical cable300. For example, due to the addition of fiber tubes18, the second optical core diameter91may be larger than first optical core diameter90for a given number of optical fibers10, but this is not necessarily true for all cases. As a result, the second optical cable diameter499of optical cable400may be larger than the first optical cable diameter399of optical cable300for a given number of optical fibers10, but again, this is merely a general guideline rather than a strict requirement.

FIG. 5illustrates an exemplary hybrid cable including a single layer inner sheath directly adjacent to a sealed metal tube containing a plurality of optical fibers as well as an electrically conductive layer in accordance with an embodiment of the invention.

Referring toFIG. 5, a hybrid cable500includes an optical core40, a hybrid inner sheath43, an armor layer46, and an outer sheath48. The hybrid cable500may be similar to embodiment optical cables such as optical cable300as previously described in reference toFIG. 3except that hybrid cable500includes a conductive layer44disposed between a hybrid inner sheath43, made of PA or PE, and an intermediate sheath45, made of PE or ceramifying silicone rubber, insulating the conductive layer44from the armor layer46. Similarly labeled elements may be as previously described and will not be described here in the interest of brevity.

The hybrid cable500may be configured to feed electrical signals and/or power using conductive layer44. The electrical signals and/or power may be either direct current (DC) or alternating current (AC). For example, the hybrid cable500may carry direct current (DC) at 48V at most, and alternate current (AC) at 380V at most, thus qualifying as a low voltage cable. In some cases, the armor layer46may be grounded and utilized as a return path for a power feeding system using hybrid cable500. In various embodiments, conductive layer44is implemented using a plurality of electrically conductive wires38.

In some embodiments, the electrically conductive wires38have a round, solid cross-section. In one embodiment, the electrically conductive wires38are implemented using elemental copper (Cu). In another embodiment, the electrically conductive wires38are implemented using elemental aluminum (Al). The material composition of electrically conductive wires38is not limited to elemental metals and may also be formed from metal alloys, and the like.

The hybrid inner sheath43may be similar to inner sheath42as previously described. Alternatively, hybrid inner sheath43may be different to account for electrical considerations of conductive layer44. The thickness and material composition of optical core41may be dependent on electrical isolation requirements of the optical core41. For example, conventional hybrid cables may utilize multilayered inner sheaths or thick homogeneous PE layers to provide electrical isolation between a conventional conductive layer and a conventional optical core.

Therefore, it may not be immediately apparent to one of ordinary skill in the art whether a thin single layer inner sheath implemented using a material other than a PE material will be sufficient to provide the require electrical isolation. The inventors of the present application have performed tests to verify that thin single layer inner sheaths implemented using alternative materials such as polyamide (PA) materials provide sufficient electrical isolation between an optical core and a conductive layer. In one embodiment, the hybrid inner sheath43comprises nylon 6. A possible benefit of hybrid cable500is that hybrid inner sheath43may be made thinner than conventional inner sheaths as provided by CEI EN 50363-0 (2006) while still maintaining electrical isolation of conductive layer44. The thickness of this layer depends on the level of isolation required by the specific current transported. As an example, for a 12 or 24V DC, a 0.5 mm-thick inner sheath43shall be sufficient.

In various embodiments, intermediate sheath45comprises a PE material such as HDPE. In other embodiments, especially when fire resistance is sought, intermediate sheath45may comprises a PE material and fiber glass or mica tape(s), or fiber glass or mica tape(s) alone, or a ceramifying silicone rubber

In addition to similarly labeled dimensions which may be as previously described, hybrid cable500includes a second inner sheath thickness93, a conductive layer thickness94, and an intermediate sheath thickness95. The second inner sheath thickness93may be similar to the first inner sheath thickness92as previously described with the added possible consideration of electrical isolation between the optical core40and conductive layer44. The intermediate sheath thickness95may be similar to the previously described second inner sheath thickness93. However, there is no strict requirement that the intermediate sheath thickness95be the same, greater than, or less than second inner sheath thickness93for a given application.

In various embodiments, the conductive layer thickness94is between 0.5 mm and 6 mm and ranges from about 0.6 mm to 3.6 mm in some embodiments. For example, the full range conductors may be used from 85 mm2(AWG 3/0) to 2.08 mm2(AWG 14). In one embodiment, the conductive layer thickness94is about 0.6 mm. In another embodiment, the conductive layer thickness94is about 1 mm. For example, if conductive layer44is implemented using 20 copper (Cu) wires with a 1 mm diameter, the copper cross-sectional area may be about 15 mm2.

It should be noted the material composition of conductive layer44may impact the required cross-sectional area of conductive layer44. For example, a conductive layer44that is implemented using aluminum may require aluminum wires that have a diameter about 1.65 times larger than an electrically equivalent conductive layer44implemented using copper wires.

The hybrid cable500has a first hybrid cable diameter599which depends on the combination of first optical core diameter90, second inner sheath thickness93, conductive layer thickness94, intermediate sheath thickness95, armor layer thickness96, and outer sheath thickness97. In various embodiments, the first hybrid cable diameter599is between 7 mm and 35 mm and ranges from about 7.4 mm to about 31.2 mm in some embodiments. In one embodiment, the first hybrid cable diameter599is about 15.5 mm for a hybrid cable500including 48 optical fibers.

As with previous embodiment optical cables, the first hybrid cable diameter599of hybrid cable500may be significantly smaller than conventional hybrid cable diameters. Similarly, hybrid cable500may be uniquely suitable for harsh environments and may meet a large number of protection standards.

FIG. 6illustrates an exemplary hybrid cable including a single layer inner sheath directly adjacent to a sealed metal tube containing two or more fiber tubes each containing a plurality of optical fibers as well as an electrically conductive layer in accordance with an embodiment of the invention.

Referring toFIG. 6, a hybrid cable600includes an optical core41, a hybrid inner sheath43, a conductive layer44, an intermediate sheath45, an armor layer46, and an outer sheath48. The hybrid cable600may be similar to hybrid cable500as previously described in reference toFIG. 5except for the inclusion of an optical core41which includes multiple sets of optical fibers contained within fiber tubes18. The optical core41of hybrid cable600may be as previously described, such as in reference toFIG. 4, for example. Similarly labeled elements may be as previously described and will not be described here in the interest of brevity.

As before, the second optical core diameter91may be similar or different from the first optical core diameter90of hybrid cable500, for example. As a result, the second hybrid cable diameter699of hybrid cable600may be larger than the first hybrid cable diameter599of hybrid cable500for a given number of optical fibers10. As previously described, this is merely a general guideline rather than a strict requirement.

It should be noted that in some embodiment cables, the armor layer may advantageously have a decreased thickness or be removed entirely because of the metal tube of the optical core. For example, a metal tube of sufficient thickness may improve the structural properties of the optical core so that a thinner armor layer or no armor layer may be used to achieve the same overall properties. This may beneficially result in a reduction of the overall thickness of embodiment cables while maintaining desirable structural properties and levels of fire, water, and chemical protection when compared to conventional cables.

FIG. 7illustrates an exemplary method of fabricating an optical cable in accordance with an embodiment of the invention. The method700may be used to fabricate any of the optical cables or hybrid cables described herein. For example, method700may be used to fabricate embodiment optical cables as described in reference toFIG. 3such as optical cable300. The following steps of method700may be performed in any order and are not intended to be exhaustive. Additional steps may be added to method700and one or more steps may be removed from method700as may be apparent to one of ordinary skill in the art. The steps of method700are not necessarily performed sequentially and any number of steps of method700may be performed concurrently.

Step701of fabricating the optical cable includes providing a plurality of optical fibers which are then sealed within a metal tube in step702. The spaces in the metal tube between optical fibers are optionally filled for a fill material in step703. The fill material may be applied before, during, or after step702. In one embodiment, steps702and703are performed concurrently.

The method700of fabricating the optical cable further includes an optional step704of applying an adhesion layer over the outer surface of the metal tube. For example, the adhesion layer may be a primer that prepares the outer surface of the metal tube for direct bonding with a subsequent layer. The outer surface of the metal tube is a major outer surface of the metal tube and the adhesion layer may be applied so that the major outer surface is substantially entirely covered by the adhesion layer and a subsequent bonded layer such as an inner sheath.

Step705of fabricating the optical cable includes forming an inner sheath over the adhesion layer and the outer surface of the metal tube. If step704is omitted, then step705includes forming the inner sheath over only the outer surface of the metal tube. The inner sheath may be formed using an extrusion process. If the inner sheath is a multilayer inner sheath, then a co-extrusion process may be used. If the inner sheath comprises a mixture of materials then a compound extrusion process may be used.

Step706of fabricating the optical cable includes forming an armor layer over the inner sheath. The armor layer may be formed by winding a plurality of strength components in to form closed helix around the inner sheath. As previously described, the strength components may be round metal wires, trapezoidal metal wires, polymer wires, dielectric rods, and the like. Alternatively, the armor layer may be formed from corrugated metal tape which may be applied longitudinally. In some embodiments, the armor layer comprises multiple layers is formed in several steps.

The method700of fabricating the optical cable further includes an optional step707of filling the voids in the armor layer with a fill material. Step708includes forming an outer sheath over the armor layer and the armor fill material if optional step707is included. The outer sheath may be formed using an extrusion process. Similar to step705, the outer sheath may also be formed using a coextrusion or compound extrusion process where applicable.

FIG. 8illustrates another exemplary method of fabricating an optical in accordance with an embodiment of the invention. The method800may be used to fabricate any of the optical cables or hybrid cables described herein. For example, method800may be used to fabricate embodiment optical cables as described in reference toFIG. 4such as optical cable400. The following steps of method800may be performed in any order and are not intended to be exhaustive. Additional steps may be added to method800and one or more steps may be removed from method800as may be apparent to one of ordinary skill in the art. The steps of method800are not necessarily performed sequentially and any number of steps of method800may be performed concurrently.

Step801of fabricating the optical cable includes providing a plurality of sets of optical fibers when are then sealed in respective fiber tubes in step802. The spaces between optical fibers in each of the fiber tubes may optionally be filled with a fiber tube fill material in step803. The fiber tubes may be formed using an extrusion process. Steps802and803may be performed concurrently in some embodiments. In one embodiment, steps802and803are performed concurrently using a co-extrusion process.

Step804of fabricating the optical fiber includes sealing the fiber tubes within a metal tube. An optional step805includes filling the spaces between fiber tubes with a fill material. As with steps702and703of method700, steps804and804may be performed in any order and are performed concurrently in one embodiment. The remaining steps of method800mirror steps704-708of method700.

FIG. 9illustrates an exemplary method of fabricating a hybrid cable in accordance with an embodiment of the invention. The method900may be used to fabricate any of the hybrid cables described herein. For example, method900may be used to fabricate embodiment hybrid cables as described in reference toFIGS. 5 and 6such as hybrid cable500and hybrid cable600. The following steps of method900may be performed in any order and are not intended to be exhaustive. Additional steps may be added to method900and one or more steps may be removed from method900as may be apparent to one of ordinary skill in the art. The steps of method900are not necessarily performed sequentially and any number of steps of method900may be performed concurrently.

The first steps of method900mirror steps701-705of method700. Alternatively, steps801-805of method800may be performed followed by steps704and705of method700. Step905is performed after performing step705in either case and includes forming a conductive layer over the inner sheath. The conductive layer may be formed in a manner similar to the armor layer as previously described. An optional step907includes filling the voids in the conductive layer with a fill material.

Step908of forming the hybrid cable includes forming an intermediate sheath over the conductive layer. The intermediate sheath may be formed in a manner similar to the inner sheath as previously described. Step909includes forming an armor layer over the intermediate sheath and is similar in concept to step706of method700except that the armor layer is being formed over a different sheath. The remaining steps of method900mirror steps707-708of method700.

Table I in the following summarizes several cable diameters and fiber/diameter ratios which may be associated with a specific number of included optical fibers. For example, as described in the above embodiments, some variation in the chosen thicknesses of each of the layers is possible due to specific design considerations. Table I summarizes possible ranges of diameters (and consequently fiber/diameter ratios) corresponding to the number of included optical fibers. The values presented in Table I represent several exemplary configurations of embodiment optical cables and embodiment hybrid cables. However, the given values are not intended to be limiting as it is conceivable that the values may be outside of these ranges in practice.

It should also be noted that, although embodiment cables advantageously provide increased fiber/diameter ratios over conventional cables, some of the possible fiber diameter ratios shown in table1101are lower than those of a conventional cable. For some particularly demanding applications, the thicknesses of the various layers of embodiment cables may be increased in order to improve protection and/or structural properties of the cable which may in turn result in a lower fiber/diameter ratio. Therefore, in these demanding applications, embodiment cables may not be thinner than conventional cables, but may provide improved properties over conventional cables.

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