CA1313320C - Optical cable - Google Patents
Optical cableInfo
- Publication number
- CA1313320C CA1313320C CA000613481A CA613481A CA1313320C CA 1313320 C CA1313320 C CA 1313320C CA 000613481 A CA000613481 A CA 000613481A CA 613481 A CA613481 A CA 613481A CA 1313320 C CA1313320 C CA 1313320C
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- CA
- Canada
- Prior art keywords
- strength member
- tensile strength
- tubular
- cable
- tensile
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
- G02B6/4479—Manufacturing methods of optical cables
- G02B6/4486—Protective covering
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
- G02B6/44—Mechanical structures for providing tensile strength and external protection for fibres, e.g. optical transmission cables
- G02B6/4401—Optical cables
- G02B6/4429—Means specially adapted for strengthening or protecting the cables
- G02B6/443—Protective covering
- G02B6/4432—Protective covering with fibre reinforcements
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Engineering & Computer Science (AREA)
- Manufacturing & Machinery (AREA)
- Light Guides In General And Applications Therefor (AREA)
Abstract
OPTICAL CABLE
Abstract of the Disclosure An optical cable having a plurality of optical fibers, a cable jacket and a tubular tensile strength member surrounding the plurality of optical fibers as a group. The optical fibers are loosely contained within the tubular tensile strength member which comprises a plurality of tensile filaments with gaps between filaments filled by a rigid material such as an epoxy resin. A water blocking medium may fill the tubular tensile strength member.
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Abstract of the Disclosure An optical cable having a plurality of optical fibers, a cable jacket and a tubular tensile strength member surrounding the plurality of optical fibers as a group. The optical fibers are loosely contained within the tubular tensile strength member which comprises a plurality of tensile filaments with gaps between filaments filled by a rigid material such as an epoxy resin. A water blocking medium may fill the tubular tensile strength member.
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Description
13l332o OPTICAL CABLE
This invention relates to optical cable.
Optical cables have certain common elements.
These include at least one optical fiber for transmission purposes, means for protecting the fiber from damage, and a jacket which provides the outer layer of the cable.
In some cable structures, optical fibers are housed in grooves formed in the outer surface of a central support member, the grooves extendinq around the member either helically in one direction or alternately, in each direction around the member.
In other cable structures, an optical fiber or fibers is housed within a plastic tube located coaxially of the cable. These tubes are normally provided for the sole purpose of forming a passage for the fibers and any protection to prevent crushing of the cable and thus of the fibers is provided by a compression resistant shield which surrounds the fiber carrying tube.
Conventionally, protective tubes are formed from plastics which provide an inadequate tensile strength to protect the optical fibers against tensile loadings. Hence, in conventional cables some other method of providing the necessary tensile strength is required such as steel fila-ments extending longitudinally of the cable and lying exteriorly of the protective tubes. It is normal to provide the steel filaments in a jacket surrounding a protective tube or tubes. A steel sheath around a core of protective tubes may also provide the required tensile strength.
In a proposed structure related to a cable, an optical fiber has a reinforced plastic coating surrounding it. This is described in a paper entitled "New Applications of Pultrusion Technology RP Covered Optical Fiber" by K.
Fuse and Y. Shirasaka and read before the 4Oth Annual Conference in January 1985 of Reinforced Plastics/Composites Institute, The Society of the Plastics Industry Inc. As described in that paper, an optical fiber is surrounded by a buffer material and then enclosed within a tube of re-inforced plastics by a manufacturing process referred to as pultrusion. In this process, reinforcing fibers are coated with a resin and the coated fibers and the pre-buffered optical fiber are passed through a die with the optical fiber located centrally so that the resin on the reinforcing fibers merges to form the plastic coating.
According to the present invention an optical cable is provided having a plurality of optical fibers, a cable jacket and a tubular tensile strength member surround-ing the plurality of optical fibers as a group, the tubular tensile strength member comprising a plurality of tensile filaments with gaps between adjacent tensile filaments filled by a rigid material holding the tensile filaments in their relative positions in which the tensile filaments extend side-by-side longitudinally of the cable, the tensile filaments occupying more volume of the tubular tensile strength member than is occupied by the rigid material, and the cable jacket extruded onto and contacting the tubular tensile strength member and with the tubular tensile strength member having an inner diameter greater than the combined diameters of the optical fibers of the group whereby each optical fiber is radially movable within the tubular tensile strength member.
With the structure according to the invention, the optical fibers are loosely contained within the tubular tensile strength member so as to enable relative longi-tudinal movement of the optical fibers and tube duringflexing or bending of the cable while axial tension is not placed upon the fibers by the surface of the tubular tensile strength member.
In addition, the tubular tensile strength member in the construction of the invention acts as a protective tube for the optical fibers and has mechanical properties which are superior to those offered by a conventional protective tube.
In a cable of the present invention, each longi-tudinally extending tensile filament in the tubular tensilestrength member surrounding the optical fibers is a tensile strength element. Hence, because the tensile filaments are densely packed side-by-side, a tubular tensile strength member of relatively small diameter in the cable of the invention may have a tensile strength comparable to and possibly exceeding the tensile strength of an optical cable of much larger diameter having a protective tube for optical fibers and steel strength elements lying outside the tube, e.g. within the jacket. While an elastomeric jacket is provided around a tubular tensile strength member in the cable of the present invention, it follows that no tensile strength elements are required either within the jacket or in any other location outside the tubular tensile strength member. In a practical example of inventive cable which may dispense with the use of a jacket and steel sheath, the cable may consist of a plurality of optical fibers loosely contained within a tubular tensile strength member having an outside diameter as small as 4.10 mm and an inside diameter of 1.70 mm.
In the tubular tensile strength member of the inventive optical cable, the filaments occupy a greater volume of the tubular strength member than the rigid material, there is preferably at least 70% of the tube volume in the form of tensile filaments with the rigid material in the interstices between the filaments providing the remainder of the volume of the ~ubular tensile strength member. In one particularly practical example, the tensile filaments occupy approximately 80% by volume of the tubular tensile strength member and the rigid material occupies approximately 20% by volume.
The rigid material in the tubular tensile strength member is preferably a thermosetting material such as a polyester or epoxy resin and the tensile filaments are preferably glass filaments, but alternatively may be, for instance, high strength aramid fibers such as "Kevlar"
(trade mark).
In a preferred arrangement, the inside of the tubular tensile strength member unoccupied by the optical fibers is filled with a water bloc-king medium. This water blocking medium may be a viscous water blocking medium or is preferably a thixotropic water blocking medium.
one embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-Figure 1 is an isometric view of part of a cable according to the invention;
Figure 2 is a cross-sectional view taken along the axis of the cable and on a larger scale than Figure 1;
Figure 3 is a cross-sectional view of the cable taken along line III-III in Figure 2;
Figure 4 is a diagrammatic side elevational view of apparatus according to the invention for making the cable of Figures 1 and 2; and Figure 5 is a view similar to Figure 3 of a part of the apparatus on a larger scale.
As shown in Figure 1, an optical cable 10 has a plurality of optical fibers 14 housed within a tubular tensile strength member 16. The strength member 16 is surrounded by a dielectric jacket 18 which may be, for instance, a polyethylene based material.
As can be seen from Figures 1 and 2, the optical fibers 14 have diameters substantially less than the inside diameter of the tubular tensile strength member. As a group, the combined diameters of the fibers are less than the inside diameter of the strength member 16 whereby the fibers are loosely contained and radially movable within the tubular tensile strength member even though there may be ten or more fibers in the cable.
The cable construction of this embodiment does not require a cable sheath or shield to protect the optical fibers as the tubular tensile strength member 16 is capable of withstanding substantial tensile loads with insignificant strain. For the same reason, no tensile strength element outside the tubular tensile strength member 16, such as steel filaments in the jacket are required. In the par-ticular construction shown in Figure 1, the cable is capableof being subjected to a tensile load of 600 lbs. While the strength member 16 satisfactorily protects the fibers from such loading. The outside diameter of the cable of the 1;~3~ZO
embodiment is 6.5 mm and the tubular tensile strength member has an outside diameter of 4.1 mm and an inside diameter of 1.7 mm.
The tubular tensile strength member 16 comprises a plurality of side-by-side and closely packed tensile glass filaments 20 which extend longitudinally of the strength member and are embedded within a continuous phase solidified rigid carrier material 22 which occupy gaps between the filaments 20. The glass filaments 20 occupy at least 70~
and preferably 80% by volume of the strength member 16 with the remainder of the volume of the strength member occupied by the rigid carrier material 22. This rigid carrier material is a polystyrene or polyester based resin. As can be seen from Figure 3, the tensile glass filaments 20 lie in close side-by-side positions while extending longitudinally of the tubular tensile strength member 16. The strength member is capable of withstanding up to 600 lbs tensile load, as has been indicated, and with a minimum strain which prevents tensile loads acting directly upon the fibers themselves. Because the strength member provides the tensile strength of the cable, it is unnecessary to provide the cable with a metal sheath for tensile purposes or to provide tensile strength elements such as steel filaments outside the strength member. Hence, the strength member 16 is simply surrounded by the jacket 18 which is provided solely to protect the tubular tensile strength member from outside environmental conditions.
The tensile glass filaments 20 extend substan-tially longitudinally of the tubular tensile strength member 16 so as to resist any extension of the cable caused by tensile loading such as may occur during bending or twisting of the cable as it is being installed or after installation.
For instance, twenty-four tensile glass filaments are provided with the filaments closely positioned together.
~ach filament comprises a plurality of strands or rovings of glass fibers.
The passage in the center of the tubular tensile strength member 16 is filled by the optical fibers and a 6 13~33ZO
thixotropic water blocking medium which fills any spaces not occupied by the fibers.
The cable is made by the in-line apparatus shown in Figures 4 and 5. Such an apparatus and a method for manufacturing cable of the present invention is the subject of co-pending Application Serial No. 511,890. As may be seen, the apparatus comprises a reservoir 24 holding a bath 26 of the polystyrene or polyester based resin. Downstream along a passline for the groups of tensile glass filaments 20 is disposed a strength member forming means 2~. This forming means comprises a tubular guide means in the form of a stainless steel tube 30 which extends along the passline of the glass fibers and has a polished outer surface.
Surrounding a downstream end portion of the tube 30 is a heating means 32 which comprises a housing 34 shrouding heating elements 36 which may be electrical. As can be seen from Figure 4 the housing 34 has an inner cylindrical surface 38 which is polished and surrounds the downstream end portion of tube 30 while being spaced from it to define a tubular space 40 between the heating element and the tube 30.
Guide means is provided for holding the tensile glass filaments 20 in laterally spaced relationship as they pass through the reservoir 24, for disposing these filaments in spaced apart positions around an arc concentric with the tube 30 and also for causing convergence of the coated tensile filaments towards an upstream inlet end 42 of the tubular space 40 to bring the tensile filaments into close relationship as they enter the space. This guide means comprises a plurality of side-by-side guide pulleys 44, one pulley for each of the tensile filaments. In Figure 4 only one of the guide pulleys 44 is shown as the guide pulleys 44 for all filaments are in alignment in that Figure. From guide pulleys 44 to pulleys 50 lying downstream, the paths of all tensile filaments are in alignment, i.e. around pulleys 46 and 48 so that one only of each of these pulleys and of pulley 50 are shown in Figure 4. The guide means also comprises a circular guide plate 52 through which the tube 30 passes at an upstream end portion of the tube. The guide plate 52 has a plurality of guide holes 54, i.e. one for each of the tensile filaments and these holes are spaced apart around a pitch circle coinciding with the axis of the tube 30 in equally spaced positions around that axis. The guide means also comprises a leadin~ chamfered edge 59 of the housing 34 (see Figure 5) for smoothly contacting the coated tensile filaments as they move into the tubular space 40.
The apparatus also comprises a means for intro-ducing the water blocking thixotropic medium into the tubular tensile strength member 16. This means comprises an applicator 56 which comprises a housing 57 mounted at the upstream end of the tube 30. The housing 57 defines passageways 58 from an inlet 60 to an outlet 62 of the housing to enable the thixotropic medium to be pumped through the inlet 60 from a source not shown, through the passages and out of the housing into the inlet of the tube 30. A pump 64 (see Figure 5) is provided for pressurizing the thixotropic medium so that it is forced along the tube 30. The pump 64 is adjustable in speed to alter the pressure for a reason to be discussed below. At an upstream side of the housing 57 there is provided a concentric inlet tube 66 for admittance of the optical fibers 14 to enable the fibers to be fed into the tubular tensile strength member 16 during its formation, as will now be described.
In use of the apparatus shown in Figures 4 and 5, and as described in co-pending Application Serial No.
511,890, the groups of tensile filaments 20 are mounted respectively upon individual reels 68 upstream of the reservoir 24. Also at the upstream end of the apparatus are disposed a plurality of spools 70, each spool wound with one of the optical fibers 14. The tensile glass filaments 20 are fed around their respective pulleys 44, 46, 48 and 50.
As the tensile filaments are passed through the bath 26, each individual tensile filament becomes coated with the resin which is at room temperature. The coated tensile filaments then proceed from the bath around the pulley 50, 8 131~320 and around any additional guiding pulleys which are required ~not shown) to bring the filaments through individual holes 54 in the guide plate 52 and form them into a circular array surrounding the tube 30. The filaments then are caused to converge towards each other and towards the tube 30 so as to guide them into the tubular space 40. As the filaments enter the tubular space 40, they lie in close relationship and the tubular space 40 becomes filled with the filaments and the resin coating material which surrounds them.
The glass filaments and resin are drawn along their passlines and through the tubular space 40 by a cable reeler 71 and are caused to be molded within the tubular space 40 into the solidified tubular tensile strength member 16 by the heating means 32 operating at the required temperature, in this case approximately 300F, to solidify the resin before it leaves the space. The completely solidified tubular tensile strength member thus moves downstream from within the heater 32.
During the movement of the filaments in the above described manner along their passlines, the fibers 14 are passed from the spool 70 through the tube 66 and device 56 and into the entrance of the tube 30 as shown in Figure 5.
The thixotropic water blocking medium is passed into the passage 58 of the applicator device 56 by the pump 64 so that it surrounds the fibars 14 and is forced in a down-stream direction along the tube 30 and, upon leaving this tube, enters into the solidified tube 16. The flow of the thixotropic medium draws the optical fibers 14 from their spools 70 so as to move them into the tubular tensile strength member 16 as it is being manufactured. Thus the tubular tensile strength member is completely filled by the optical fibers and the water blocking medium.
It is desirable that each of the optical fibers has a greater axial length than the tubular tensile strength member 16 into which it is being fed so that any bending of the tubular tensile strength member 16, in use of the finished cable will merely tend to cause relative axial movement of the tubular tensile strength member and optical fibers in the vicinity of the bend without placing the optical fibers in tension. To enable the length of each optical fiber to be greater than that of the tubular tensile strength member the pressure placed upon the filling medium is changeable by altering the speed of the pump 64 so that an increased flow of the medium will draw the optical fibers from their spools at a greater rate. This drawing action forces the optical fibers along the tube 30 at a greater speed than that of the tensile filaments through the space 40, whereby upon the optical fibers and water blocking medium emerging into the tubular tensile strength member 16 at the downstream end of the guide means 30, the speed of the optical fibers and of the filling medium is reduced.
This leads to a meandering of the optical fibers within the oversize passage of the tube 16 as illustrated by Figure 2.
The degree of this meandering may be controlled by the changing of the speed of the pump 64.
Upon the finished tubular tensile strength member 16 surrounding the optical fibers emerging from the ap-paratus 28, it then proceeds in in-line fashion through a cross-head 72 of an extruder (not shown) in which the strength member is provided with the surrounding jacket 18 to complete the cable 10.
As can be seen from the above embodiment, the cable structure is relatively simple in construction and avoids the necessity of using steel reinforcing elements or a shield surrounding the tubular tensile strength member 16 for protection of the optical fibers during normal tensile loading conditions. It has been shown that the tubular tensile strength member 16, because of its structure, is capable of withstanding significant tensile loads while protecting the optical fibers. The tubular tensile strength member 16 has an inside diameter which is far in excess of that of the combined diameters of the optical fibers so that each of the fibers is radially movable within the tube. The optical fibers have axial lengths which are greater than the axial length of the tubular tensile strength member 16 whereby tensile loads placed upon the tubular tensile strength member and finished cable which tend to stretch the cable will merely tend to straighten the optical fibers, as described, without placing them into tensile loaded con-ditions.
This invention relates to optical cable.
Optical cables have certain common elements.
These include at least one optical fiber for transmission purposes, means for protecting the fiber from damage, and a jacket which provides the outer layer of the cable.
In some cable structures, optical fibers are housed in grooves formed in the outer surface of a central support member, the grooves extendinq around the member either helically in one direction or alternately, in each direction around the member.
In other cable structures, an optical fiber or fibers is housed within a plastic tube located coaxially of the cable. These tubes are normally provided for the sole purpose of forming a passage for the fibers and any protection to prevent crushing of the cable and thus of the fibers is provided by a compression resistant shield which surrounds the fiber carrying tube.
Conventionally, protective tubes are formed from plastics which provide an inadequate tensile strength to protect the optical fibers against tensile loadings. Hence, in conventional cables some other method of providing the necessary tensile strength is required such as steel fila-ments extending longitudinally of the cable and lying exteriorly of the protective tubes. It is normal to provide the steel filaments in a jacket surrounding a protective tube or tubes. A steel sheath around a core of protective tubes may also provide the required tensile strength.
In a proposed structure related to a cable, an optical fiber has a reinforced plastic coating surrounding it. This is described in a paper entitled "New Applications of Pultrusion Technology RP Covered Optical Fiber" by K.
Fuse and Y. Shirasaka and read before the 4Oth Annual Conference in January 1985 of Reinforced Plastics/Composites Institute, The Society of the Plastics Industry Inc. As described in that paper, an optical fiber is surrounded by a buffer material and then enclosed within a tube of re-inforced plastics by a manufacturing process referred to as pultrusion. In this process, reinforcing fibers are coated with a resin and the coated fibers and the pre-buffered optical fiber are passed through a die with the optical fiber located centrally so that the resin on the reinforcing fibers merges to form the plastic coating.
According to the present invention an optical cable is provided having a plurality of optical fibers, a cable jacket and a tubular tensile strength member surround-ing the plurality of optical fibers as a group, the tubular tensile strength member comprising a plurality of tensile filaments with gaps between adjacent tensile filaments filled by a rigid material holding the tensile filaments in their relative positions in which the tensile filaments extend side-by-side longitudinally of the cable, the tensile filaments occupying more volume of the tubular tensile strength member than is occupied by the rigid material, and the cable jacket extruded onto and contacting the tubular tensile strength member and with the tubular tensile strength member having an inner diameter greater than the combined diameters of the optical fibers of the group whereby each optical fiber is radially movable within the tubular tensile strength member.
With the structure according to the invention, the optical fibers are loosely contained within the tubular tensile strength member so as to enable relative longi-tudinal movement of the optical fibers and tube duringflexing or bending of the cable while axial tension is not placed upon the fibers by the surface of the tubular tensile strength member.
In addition, the tubular tensile strength member in the construction of the invention acts as a protective tube for the optical fibers and has mechanical properties which are superior to those offered by a conventional protective tube.
In a cable of the present invention, each longi-tudinally extending tensile filament in the tubular tensilestrength member surrounding the optical fibers is a tensile strength element. Hence, because the tensile filaments are densely packed side-by-side, a tubular tensile strength member of relatively small diameter in the cable of the invention may have a tensile strength comparable to and possibly exceeding the tensile strength of an optical cable of much larger diameter having a protective tube for optical fibers and steel strength elements lying outside the tube, e.g. within the jacket. While an elastomeric jacket is provided around a tubular tensile strength member in the cable of the present invention, it follows that no tensile strength elements are required either within the jacket or in any other location outside the tubular tensile strength member. In a practical example of inventive cable which may dispense with the use of a jacket and steel sheath, the cable may consist of a plurality of optical fibers loosely contained within a tubular tensile strength member having an outside diameter as small as 4.10 mm and an inside diameter of 1.70 mm.
In the tubular tensile strength member of the inventive optical cable, the filaments occupy a greater volume of the tubular strength member than the rigid material, there is preferably at least 70% of the tube volume in the form of tensile filaments with the rigid material in the interstices between the filaments providing the remainder of the volume of the ~ubular tensile strength member. In one particularly practical example, the tensile filaments occupy approximately 80% by volume of the tubular tensile strength member and the rigid material occupies approximately 20% by volume.
The rigid material in the tubular tensile strength member is preferably a thermosetting material such as a polyester or epoxy resin and the tensile filaments are preferably glass filaments, but alternatively may be, for instance, high strength aramid fibers such as "Kevlar"
(trade mark).
In a preferred arrangement, the inside of the tubular tensile strength member unoccupied by the optical fibers is filled with a water bloc-king medium. This water blocking medium may be a viscous water blocking medium or is preferably a thixotropic water blocking medium.
one embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-Figure 1 is an isometric view of part of a cable according to the invention;
Figure 2 is a cross-sectional view taken along the axis of the cable and on a larger scale than Figure 1;
Figure 3 is a cross-sectional view of the cable taken along line III-III in Figure 2;
Figure 4 is a diagrammatic side elevational view of apparatus according to the invention for making the cable of Figures 1 and 2; and Figure 5 is a view similar to Figure 3 of a part of the apparatus on a larger scale.
As shown in Figure 1, an optical cable 10 has a plurality of optical fibers 14 housed within a tubular tensile strength member 16. The strength member 16 is surrounded by a dielectric jacket 18 which may be, for instance, a polyethylene based material.
As can be seen from Figures 1 and 2, the optical fibers 14 have diameters substantially less than the inside diameter of the tubular tensile strength member. As a group, the combined diameters of the fibers are less than the inside diameter of the strength member 16 whereby the fibers are loosely contained and radially movable within the tubular tensile strength member even though there may be ten or more fibers in the cable.
The cable construction of this embodiment does not require a cable sheath or shield to protect the optical fibers as the tubular tensile strength member 16 is capable of withstanding substantial tensile loads with insignificant strain. For the same reason, no tensile strength element outside the tubular tensile strength member 16, such as steel filaments in the jacket are required. In the par-ticular construction shown in Figure 1, the cable is capableof being subjected to a tensile load of 600 lbs. While the strength member 16 satisfactorily protects the fibers from such loading. The outside diameter of the cable of the 1;~3~ZO
embodiment is 6.5 mm and the tubular tensile strength member has an outside diameter of 4.1 mm and an inside diameter of 1.7 mm.
The tubular tensile strength member 16 comprises a plurality of side-by-side and closely packed tensile glass filaments 20 which extend longitudinally of the strength member and are embedded within a continuous phase solidified rigid carrier material 22 which occupy gaps between the filaments 20. The glass filaments 20 occupy at least 70~
and preferably 80% by volume of the strength member 16 with the remainder of the volume of the strength member occupied by the rigid carrier material 22. This rigid carrier material is a polystyrene or polyester based resin. As can be seen from Figure 3, the tensile glass filaments 20 lie in close side-by-side positions while extending longitudinally of the tubular tensile strength member 16. The strength member is capable of withstanding up to 600 lbs tensile load, as has been indicated, and with a minimum strain which prevents tensile loads acting directly upon the fibers themselves. Because the strength member provides the tensile strength of the cable, it is unnecessary to provide the cable with a metal sheath for tensile purposes or to provide tensile strength elements such as steel filaments outside the strength member. Hence, the strength member 16 is simply surrounded by the jacket 18 which is provided solely to protect the tubular tensile strength member from outside environmental conditions.
The tensile glass filaments 20 extend substan-tially longitudinally of the tubular tensile strength member 16 so as to resist any extension of the cable caused by tensile loading such as may occur during bending or twisting of the cable as it is being installed or after installation.
For instance, twenty-four tensile glass filaments are provided with the filaments closely positioned together.
~ach filament comprises a plurality of strands or rovings of glass fibers.
The passage in the center of the tubular tensile strength member 16 is filled by the optical fibers and a 6 13~33ZO
thixotropic water blocking medium which fills any spaces not occupied by the fibers.
The cable is made by the in-line apparatus shown in Figures 4 and 5. Such an apparatus and a method for manufacturing cable of the present invention is the subject of co-pending Application Serial No. 511,890. As may be seen, the apparatus comprises a reservoir 24 holding a bath 26 of the polystyrene or polyester based resin. Downstream along a passline for the groups of tensile glass filaments 20 is disposed a strength member forming means 2~. This forming means comprises a tubular guide means in the form of a stainless steel tube 30 which extends along the passline of the glass fibers and has a polished outer surface.
Surrounding a downstream end portion of the tube 30 is a heating means 32 which comprises a housing 34 shrouding heating elements 36 which may be electrical. As can be seen from Figure 4 the housing 34 has an inner cylindrical surface 38 which is polished and surrounds the downstream end portion of tube 30 while being spaced from it to define a tubular space 40 between the heating element and the tube 30.
Guide means is provided for holding the tensile glass filaments 20 in laterally spaced relationship as they pass through the reservoir 24, for disposing these filaments in spaced apart positions around an arc concentric with the tube 30 and also for causing convergence of the coated tensile filaments towards an upstream inlet end 42 of the tubular space 40 to bring the tensile filaments into close relationship as they enter the space. This guide means comprises a plurality of side-by-side guide pulleys 44, one pulley for each of the tensile filaments. In Figure 4 only one of the guide pulleys 44 is shown as the guide pulleys 44 for all filaments are in alignment in that Figure. From guide pulleys 44 to pulleys 50 lying downstream, the paths of all tensile filaments are in alignment, i.e. around pulleys 46 and 48 so that one only of each of these pulleys and of pulley 50 are shown in Figure 4. The guide means also comprises a circular guide plate 52 through which the tube 30 passes at an upstream end portion of the tube. The guide plate 52 has a plurality of guide holes 54, i.e. one for each of the tensile filaments and these holes are spaced apart around a pitch circle coinciding with the axis of the tube 30 in equally spaced positions around that axis. The guide means also comprises a leadin~ chamfered edge 59 of the housing 34 (see Figure 5) for smoothly contacting the coated tensile filaments as they move into the tubular space 40.
The apparatus also comprises a means for intro-ducing the water blocking thixotropic medium into the tubular tensile strength member 16. This means comprises an applicator 56 which comprises a housing 57 mounted at the upstream end of the tube 30. The housing 57 defines passageways 58 from an inlet 60 to an outlet 62 of the housing to enable the thixotropic medium to be pumped through the inlet 60 from a source not shown, through the passages and out of the housing into the inlet of the tube 30. A pump 64 (see Figure 5) is provided for pressurizing the thixotropic medium so that it is forced along the tube 30. The pump 64 is adjustable in speed to alter the pressure for a reason to be discussed below. At an upstream side of the housing 57 there is provided a concentric inlet tube 66 for admittance of the optical fibers 14 to enable the fibers to be fed into the tubular tensile strength member 16 during its formation, as will now be described.
In use of the apparatus shown in Figures 4 and 5, and as described in co-pending Application Serial No.
511,890, the groups of tensile filaments 20 are mounted respectively upon individual reels 68 upstream of the reservoir 24. Also at the upstream end of the apparatus are disposed a plurality of spools 70, each spool wound with one of the optical fibers 14. The tensile glass filaments 20 are fed around their respective pulleys 44, 46, 48 and 50.
As the tensile filaments are passed through the bath 26, each individual tensile filament becomes coated with the resin which is at room temperature. The coated tensile filaments then proceed from the bath around the pulley 50, 8 131~320 and around any additional guiding pulleys which are required ~not shown) to bring the filaments through individual holes 54 in the guide plate 52 and form them into a circular array surrounding the tube 30. The filaments then are caused to converge towards each other and towards the tube 30 so as to guide them into the tubular space 40. As the filaments enter the tubular space 40, they lie in close relationship and the tubular space 40 becomes filled with the filaments and the resin coating material which surrounds them.
The glass filaments and resin are drawn along their passlines and through the tubular space 40 by a cable reeler 71 and are caused to be molded within the tubular space 40 into the solidified tubular tensile strength member 16 by the heating means 32 operating at the required temperature, in this case approximately 300F, to solidify the resin before it leaves the space. The completely solidified tubular tensile strength member thus moves downstream from within the heater 32.
During the movement of the filaments in the above described manner along their passlines, the fibers 14 are passed from the spool 70 through the tube 66 and device 56 and into the entrance of the tube 30 as shown in Figure 5.
The thixotropic water blocking medium is passed into the passage 58 of the applicator device 56 by the pump 64 so that it surrounds the fibars 14 and is forced in a down-stream direction along the tube 30 and, upon leaving this tube, enters into the solidified tube 16. The flow of the thixotropic medium draws the optical fibers 14 from their spools 70 so as to move them into the tubular tensile strength member 16 as it is being manufactured. Thus the tubular tensile strength member is completely filled by the optical fibers and the water blocking medium.
It is desirable that each of the optical fibers has a greater axial length than the tubular tensile strength member 16 into which it is being fed so that any bending of the tubular tensile strength member 16, in use of the finished cable will merely tend to cause relative axial movement of the tubular tensile strength member and optical fibers in the vicinity of the bend without placing the optical fibers in tension. To enable the length of each optical fiber to be greater than that of the tubular tensile strength member the pressure placed upon the filling medium is changeable by altering the speed of the pump 64 so that an increased flow of the medium will draw the optical fibers from their spools at a greater rate. This drawing action forces the optical fibers along the tube 30 at a greater speed than that of the tensile filaments through the space 40, whereby upon the optical fibers and water blocking medium emerging into the tubular tensile strength member 16 at the downstream end of the guide means 30, the speed of the optical fibers and of the filling medium is reduced.
This leads to a meandering of the optical fibers within the oversize passage of the tube 16 as illustrated by Figure 2.
The degree of this meandering may be controlled by the changing of the speed of the pump 64.
Upon the finished tubular tensile strength member 16 surrounding the optical fibers emerging from the ap-paratus 28, it then proceeds in in-line fashion through a cross-head 72 of an extruder (not shown) in which the strength member is provided with the surrounding jacket 18 to complete the cable 10.
As can be seen from the above embodiment, the cable structure is relatively simple in construction and avoids the necessity of using steel reinforcing elements or a shield surrounding the tubular tensile strength member 16 for protection of the optical fibers during normal tensile loading conditions. It has been shown that the tubular tensile strength member 16, because of its structure, is capable of withstanding significant tensile loads while protecting the optical fibers. The tubular tensile strength member 16 has an inside diameter which is far in excess of that of the combined diameters of the optical fibers so that each of the fibers is radially movable within the tube. The optical fibers have axial lengths which are greater than the axial length of the tubular tensile strength member 16 whereby tensile loads placed upon the tubular tensile strength member and finished cable which tend to stretch the cable will merely tend to straighten the optical fibers, as described, without placing them into tensile loaded con-ditions.
Claims (7)
1, An optical cable having a plurality of optical fibers, a cable jacket and a tubular tensile strength member surrounding the plurality of optical fibers as a group, the tubular tensile strength member comprising a plurality of tensile filaments with gaps between adjacent tensile fila-ments filled by a rigid material holding the tensile fila-ments in their relative positions in which the tensile filaments extend side-by-side longitudinally of the cable, the tensile filaments occupying more volume of the tubular tensile strength member than is occupied by the rigid material, and the cable jacket extruded onto and contacting the tubular tensile strength member and with the tubular tensile strength member having an inner diameter greater than the combined diameters of the optical fibers of the group whereby each optical fiber is radially movable within the tubular tensile strength member.
2. A cable according to claim 1 wherein the rigid material is a thermosetting material such as an epoxy resin.
3. A cable according to claim 1 wherein the inside of the tubular tensile strength member unoccupied by fiber is filled with a water blocking medium.
4. A cable according to claim 1 wherein the inside of the tubular tensile strength member unoccupied by fiber is filled with a viscous water blocking medium.
5. A cable according to claim 1 wherein the inside of the tubular tensile strength member unoccupied by fiber is filled with a thixotropic water blocking medium.
6. A cable according to claim 1 wherein the tensile filaments occupy at least 70% by volume of the tubular tensile strength member, the remainder of the volume of the tubular tensile strength member being occupied by the rigid material.
7. A cable according to claim 1 wherein the axial length of each of the optical fibers is greater than the axial length of the tubular tensile strength member.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000613481A CA1313320C (en) | 1989-09-27 | 1989-09-27 | Optical cable |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000613481A CA1313320C (en) | 1989-09-27 | 1989-09-27 | Optical cable |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1313320C true CA1313320C (en) | 1993-02-02 |
Family
ID=4140709
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000613481A Expired - Fee Related CA1313320C (en) | 1989-09-27 | 1989-09-27 | Optical cable |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1313320C (en) |
-
1989
- 1989-09-27 CA CA000613481A patent/CA1313320C/en not_active Expired - Fee Related
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| MKLA | Lapsed |