GB2115574A - An improved optical fibre element - Google Patents

An improved optical fibre element Download PDF

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Publication number
GB2115574A
GB2115574A GB08304092A GB8304092A GB2115574A GB 2115574 A GB2115574 A GB 2115574A GB 08304092 A GB08304092 A GB 08304092A GB 8304092 A GB8304092 A GB 8304092A GB 2115574 A GB2115574 A GB 2115574A
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United Kingdom
Prior art keywords
optical
optical fibre
bore
fibres
fibre element
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GB08304092A
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GB2115574B (en
GB8304092D0 (en
Inventor
David James Greene
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Balfour Beatty PLC
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BICC PLC
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Priority to GB08304092A priority Critical patent/GB2115574B/en
Publication of GB8304092D0 publication Critical patent/GB8304092D0/en
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    • 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
    • G02B6/441—Optical cables built up from sub-bundles
    • G02B6/4413—Helical structure
    • 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

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Communication Cables (AREA)

Abstract

An optical fibre element for use as a component of an optical or electrical cable or which may itself constitute an optical cable comprises a flexible elongate body 1 having a bore 2; separate optical fibres loosely housed in, circumferentially spaced around, and following a helical path or oscillating lay along the length of, the bore; and means 5 retaining the circumferentially spaced fibres adjacent the boundary wall of the bore. The boundary wall of the bore preferably has circumferentially spaced grooves extending helically or with an oscillating lay along the bore in which the optical fibres 4 are housed. The retaining means 5 may be a grease, an inorganic fibrous wool or a tape transversely folded into more than one convolute turn. All such retaining means 5 permit transverse movement of the optical fibres 4 towards the axis of the bore 2 when the optical fibre element is subjected to a tensile stress. <IMAGE>

Description

SPECIFICATION An improved optical fibre element This invention relates to optical cables for the transmission of the ultra-violet, visible and infrared regions of the electromagnetic spectrum, which regions, for convenience, will hereinafter all be included in the generic term "light" and especially, but not exclusively, to optical cables for use in the communications field adapted for transmission of light having a wavelength within the range 0.8 to 2.1 micrometers.
It is an object of the present invention to provide an improved optical fibre element which may be used as a component element of an optical cable or of an electric cable or which may itself constitute an optical cable.
According to the invention, the improved optical fibre element comprises a flexible elongate body having throughout its length at least one bore; a plurality of separate optical fibres and/or optical bundles as hereinafter defined loosely housed in, circumferentially spaced around, and following a helical or oscillating lay along the length of, the bore; and means retaining the circumferentially spaced optical fibres and/or optical bundles adjacent the boundary wall of the bore, which retaining means is of such a form that, when the optical fibre element is subjected to a tensile stress sufficient to cause an optical fibre and/or optical bundle to straighten, the retaining means will permit transverse movement of the optical fibre and/or optical bundle with respect to the elongate body in a direction towards the axis of the bore.
By the expression "optical bundle" is meant a group of optical fibres or a group of fibres including one or more optical fibres and one or more non-optical reinforcing fibres or other reinforcing elongate elements.
Since, when the optical fibre element is subjected to a tensile stress, the retaining means permits the optical fibres and/or optical bundles loosely housed in the bore to move transversely with respect to the elongate body in a direction towards the axis of the bore, risk of breakage of an optical fibre and/or optical bundle is substantially reduced.
Preferably, to prevent circumferential movement of an optical fibre and/or optical bundle with respect to another optical fibre and/or optical bundle, the inner surface of the boundary wall of the bore in the flexible elongate body has a plurality of circumferentially spaced grooves which extend helically or with an oscillating lay along the length of the body and the optical fibres and/or optical bundles are retained in at least some of the grooves by the retaining means.
Preferred retaining means includes a waterimpermeable medium of a grease-like nature which substantially fills those parts of the bore not occupied by the optical fibres and/or optical bundles throughout its length; a wool of inorganic fibrous material which substantially fills those parts of the bore not occupied by the optical fibres and/or optical bundles throughout its length; chopped inorganic fibres which substantially fill those parts of the bore not occupied by the optical fibres and/or optical bundles throughout its length; and a longitudinally extending tape which is transversely folded into more than one convolute turn and which is of such a material that, when the optical fibre element is subjected to a tensile stress and optical fibres and/or optical bundles are caused to straighten, adjacent turns on the tape will slide circumferentially over one another to reduce the transverse dimension of the retaining means and so permit transverse movement of the optical fibres and/or optical bundles in a direction towards the axis of the bore. A preferred greaselike water-impermeable medium consists of, or includes as a major constituent, petroleum jelly. A preferred wool of inorganic fibrous material is a wool of silica fibres. Preferred chopped inorganic fibres are chopped silica fibres. A preferred longitudinally extending, convolutely wound tape is made of polyethylene terephthalate or aromatic polyimide.
The flexible elongate body may be made of metal or metal alloy or it may be made of rubber or plastics material.
Where the flexible elongate body is made of metal or metal alloy, it may comprise an extrudate of substantially C-shaped cross-section, e.g. of aluminium or an aluminium-based alloy, which is transversely folded to form a substantially circumferentially rigid tube. Such a tube may constitute the substantially circumferentially rigid core of an overhead electric conductor as described and claimed in our British Patent No.
1598438.
Where the flexible elongate body is of rubber or plastics material, the optical fibre element may constitute an optical guide loosely housed in the bore of the substantially circumferentially rigid core of an overhead electric conductor as described and claimed in the specification of our British Patent No. 1 598438.
When the flexible elongate body is of rubber or plastics material, it may have a plurality of elongate reinforcing elements embedded in it at circumferentially spaced positions. Where the inner surface of the boundary wall of the bore in the flexible elongate body has a plurality of circumferentially spaced grooves, an elongate reinforcing element may be embedded in the body between each pair of adjacent grooves.
The preferred method of making the improved optical fibre element as hereinbefore described having a flexible elongate body of rubber or plastics material comprises extruding a circumferential wall of rubber or plastics material having in its internal surface a plurality of circumferentially spaced, longitudinally extending grooves; feeding into at least some of the grooves in the circumferential wall as the wall is being formed separate optical fibres and/or optical bundles as hereinbefore defined, the overall diameter of the or each optical fibre and/or optical bundle having regard to the cross-sectional area of its associated groove being such that the optical fibre and/or optical bundle is loosely housed in the groove; feeding into the bore of the circumferential wall as the wall is being formed means retaining the optical fibres and/or optical bundles in said grooves, which retaining means is of such a form that, when the optical fibre element is subjected to a tensile stress sufficient to cause an optical fibre and/or optical bundle to straighten, the retaining means will permit transverse movement of the optical fibre and/or optical bundle with respect to the elongate body in a direction towards the axis of the bore; and twisting the circumferential wall, or causing the circumferential wall to oscillate, about its axis as it is being formed so that each longitudinally extending groove follows a helical or oscillating path about the longitudinal axis of the elongate body.
Preferably, the orifice of the extrusion machine employed is defined by an outer die and, surrounded by and co-axial with the outer die, an inner die or point having a throughbore for passage of the retaining means and a plurality of circumferentially spaced, longitudinally extending, outwardly projecting ribs which form the longitudinally extending grooves in the circumferential wall and in each of at least some of which is a bore for passage of a separate optical fibre and/or optical bundle. The inner die is preferably caused to oscillate about its axis so that each longitudinally extending groove follows a helical path about the longitudinal axis of the elongate body, the direction of lay of each groove reversing at spaced positions along the length of the element.Alternatively, the inner die may be caused to rotate about the longitudinal axis of the elongate body but, in this case, preferably the reels from which optical fibres are fed are mounted at circumferentially spaced positions around an input unit which is rotatably driven about the axis of the advancing element in the same rotational direction and at the same speed as the inner die (along the lines of a planetary detorsioning stranding machine head) to compensate for any torque or twist imparted into each optical fibre.
To avoid risk that an optical fibre and/or optical bundle may stick to a boundary surface of a groove, each optical fibre and/or optical bundle may be dusted with a dusting powder such as French chalk or talc upstream of extrusion of the circumferential wall.
The invention is further illustrated by a description, by way of example, of four preferred forms of optical fibre element and of the preferred method of and apparatus for making a preferred optical fibre element, with reference to the accompanying drawings, in which: Figure 1 is a transverse cross-sectional view of one preferred form of optical fibre element; Figure 2 is a transverse cross-sectional view of a second preferred form of optical fibre element; Figure 3 is a transverse cross-sectional view of a third form of optical fibre element; Figure 4 is a transverse cross-sectional view of a fourth form of optical fibre element; Figure 5 is a sectional side view of the extrusion head of an extrusion machine illustrating extrusion of the preferred optical fibre element shown in Figure 1; and Figure 6 is the front end view of the inner die shown in Figure 5, drawn on an enlarged scale.
The preferred form of optical fibre element shown in Figure 1 comprises an extruded body 1 of plastics material having in the inner surface of the boundary wall of its bore 2 a plurality of circumferentially spaced grooves 3 each extending with an oscillating lay along the length of the body. Loosely housed in each of the grooves 3 is an optical fibre 4. The optical fibres 4 are retained in the grooves 3 by petroleum jelly 5 which substantially fills the bore 2 throughout the length of the body 1 and which, when the optical fibre element is subjected to a tensile stress sufficient to cause an optical fibre to straighten, permits transverse movement of the optical fibre with respect to the body out of its groove in a direction towards the axis of the bore.
The second preferred form of optical fibre element shown in Figure 2 comprises an extruded body 11 of plastics material having in the inner surface of the boundary wall of its bore 12 a plurality of circumferentially spaced grooves 13 each following a helical path along the length of the body. Loosely housed in each of the grooves 13 is an optical fibre 14. The optical fibres 14 are retained in the grooves 13 by a wool 1 5 of silica fibres, which wool serves as a retaining means in a simiiar manner to the petroleum jelly 5 in the optical fibre element shown in Figure 1.
The third preferred form of optical fibre element shown in Figure 3 comprises an extruded body 21 of plastics material having in the inner surface of the boundary wall of its bore 22 a plurality of circumferentially spaced grooves 23 each extending with an oscillating lay along the length of the body. Loosely housed in each of the grooves 23 is an optical fibre 24.The optical fibres 24 are retained in the grooves 23 by a longitudinally extending tape 25 of polyethylene terephthalate which is transversely folded into approximately two convolute turns such that, when the optical fibre element is subjected to a tensile stress and optical fibres are caused to straighten, adjacent turns of the tape will slide circumferentially over one another to reduce the transverse dimension of the convolute turns and so permit transverse movement of the optical fibres in a direction towards the axis of the bore.
The fourth preferred form of optical fibre element shown in Figure 4 comprises an extrudate 31 of aluminium alloy of substantially C-shaped cross-section which is transversely folded to form a substantially circumferentially rigid tube having a bore 32. Loosely housed in the bore 32 are circumferentially spaced optical fibres 34. The optical fibres 34 are retained adjacent the inner surface of the boundary wall of the bore 32 by chopped silica fibres 35 which substantially fill those parts of the bore not occupied by the optical fibres throughout its length and which, when the optical fibre element is subjected to a tensile stress sufficient to cause an optical fibre to straighten, permit transverse movement of the optical fibre with respect to the body in a direction towards the axis of the bore.
The first preferred form of optical fibre element shown in Figure 1 is manufactured using an extrusion machine having an extrusion head as illustrated in Figures 5 and 6. The orifice of the extrusion machine is defied by an outer die 41 and, surrounded by and coaxial with the outer die, an inner die or point 42 having a throughbore 43 and a plurality of circumferentially spaced, longitudinally extending outwardly projecting ribs 44 in each of which is a bore 46. The inner die 42 is rotatably driven about its axis through gearing 47 and, by periodic reversing of the drive motor (not shown), can be caused to oscillate about its axis.
The elongate body 1 of plastics material is extruded by the extrusion machine and, because the inner die 42 is caused to oscillate about its axis, each longitudinally extending groove 3 formed in the body by the ribs 44, follows a helical path about the longitudinal axis of the body, the direction of lay of each groove reversing at spaced positions along the length of the body.
As the elongate body 1 is being extruded, separate optical fibres 4 are fed into the bores 46 in the ribs 44 so that they will pass into the grooves 3 in the boundary wall of the extruded body as it is being formed, the overall diameter of each optical fibre having regard to the cross-sectional area of its associated groove being such that the optical fibre is loosely housed in the groove. At the same time, petroleum jelly 5 is injected through the bore 43 of the inner die 42 into the bore 2 of the extruded body 1, the rate of injection of petroleum jelly being such that the bore of the body is substantially filled with petroleum jelly throughout its length.

Claims (23)

Claims
1. An optical fibre element comprising a flexible elongate body having throughout its length at least one bore; a plurality of separate optical fibres and/or optical bundles as hereinbefore defined loosely housed in, circumferentially spaced around, and following a helical or oscillating lay along the length of, the bore; and means retaining the circumferentially spaced optical fibres and/or optical bundles adjacent the boundary wall of the bore, which retaining means is of such a form that, when the optical fibre element is subjected to a tensile stress sufficient to cause an optical fibre and/or optical bundle to straighten, the retaining means will permit transverse movement of the optical fibre and/or optical bundle with respect to the elongate body in a direction towards the axis of the bore.
2. An optical fibre element comprising a flexible elongate body having throughout its length at least one bore, the inner surface of the boundary wall of the bore having a plurality of circumferentially spaced grooves which extend helically or with an oscillating lay along the length of the body; a plurality of separate optical fibres and/or optical bundles as hereinbefore defined loosely housed in at least some of the grooves; and means retaining the circumferentially spaced optical fibres and/or optical bundles within the grooves, which retaining means is of such a form that, when the optical fibre element is subjected to a tensile stress sufficient to cause an optical fibre and/or optical bundle to straighten, the retaining means will permit transverse movement of the optical fibre and/or optical bundle with respect to the elongate body in a direction towards the axis of the bore.
3. An optical fibre element as claimed in Claim 1 or 2, wherein the flexible elongate body is made of metal or metal alloy.
4. An optical fibre element as claimed in Claim 3, wherein the flexible elongate body comprises an extrudate of substantially C-shaped crosssection which is transversely folded to form a substantially circumferentially rigid tube.
5. An optical fibre element as claimed in Claim 1 or 2, wherein the flexible elongate body is made of rubber or plastics material.
6. An optical fibre element as claimed in Claim 5, wherein the flexible elongate body has a plurality of elongate reinforcing elements embedded in it at circumferentially spaced positions.
7. An optical fibre element as claimed in Claim 6 in which the inner surface of the boundary wall of the bore in the flexible elongate body has a plurality of circumferentially spaced grooves in at least some of which optical fibres and/or optical bundles are loosely housed, wherein an elongate reinforcing member is embedded in the body between each pair of adjacent grooves.
8. An optical fibre element as claimed in any one of the preceding Claims, wherein the retaining means is a water-impermeable medium of a grease-like nature which substantially fills those parts of the bore not occupied by the optical fibres and/or optical bundles throughout its length.
9. An optical fibre element as claimed in Claim 8, wherein the grease-like water-impermeable medium consists of, or includes as a major constituent, petroleum jelly.
10. An optical fibre element as claimed in any one of Claims 1 to 7, wherein the retaining means comprises a wool of inorganic fibrous material which substantially fills those parts of the bore not occupied by the optical fibres and/or optical bundles throughout its length.
11. An optical fibre element as claimed in Claim 10, wherein the wool of inorganic fibrous material is a wool of silica fibres.
12. An optical fibre element as claimed in any one of Claims 1 to 7, wherein the retaining means comprises chopped inorganic fibres which substantially fill those parts of the bore not occupied by the optical fibres and/or optical bundles throughout its length.
13. An optical fibre element as claimed in Claim 12, wherein the chopped inorganic fibres are chopped silica fibres.
14. An optical fibre element as claimed in any one of Claims 1 to 7, wherein the retaining means comprises a longitudinally extending tape which is transversely folded into more than one convolute turn and which is of such a material that, when the optical fibre element is subjected to a tensile stress and optical fibres and/or optical bundles are caused to straighten, adjacent turns of the tape will slide circumferentially over one another to reduce the transverse dimension of one retaining means and so permit transverse movement of the optical fibres and/or optical bundles in a direction towards the axis of the bore.
1 5. An optical fibre element as claimed in Claim 14, wherein the longitudinally extending, convolutely wound tape is made of polyethylene terephthalate or aromatic polyimide.
1 6. A method of making an optical fibre element which comprises extruding a circumferential wall of rubber or plastics material having in its internal surface a plurality of circumferentially spaced, longitudinally extending grooves; feeding into at least some of the grooves in the circumferential wall as the wall is being formed separate optical fibres and/or optical bundles as hereinbefore defined, the overall diameter of the or each optical fibre and/or optical bundle having regard to the cross-sectional area of its associated groove being such that the optical fibre and/or optical bundle is loosely housed in the groove; feeding into the bore of the circumferential wall as the wall is being formed means retaining the optical fibres and/or optical bundles in said grooves, which retaining means is of such a form that, when the optical fibre element is subjected to a tensile stress sufficient to cause an optical fibre and/or optical bundle to straighten, the retaining means will permit transverse movement of the optical fibre and/or optical bundle with respect to the elongate body in a direction towards the axis of the bore; and twisting the circumferential wall, or causing the circumferential wall to oscillate, about its axis as it is being formed so that each longitudinally extending groove follows a helical or oscillating path about the longitudinal axis of the elongate body.
1 7. A method as claimed in Claim 16, wherein the orifice of the extrusion machine employed is defined by an outer die and, surrounded by and co-axial with the outer die, an inner die or point having a throughbore for passage of the retaining means and a plurality of circumferentially spaced, longitudinally extending, outwardly projecting ribs which form the longitudinally extending grooves in the circumferential wall and in each of at least some of which is a bore for passage of a separate optical fibre and/or optical bundle.
18. A method as claimed in Claim 17, wherein the inner die is caused to oscillate about its axis so that each longitudinally extending groove follows a helical path about the longitudinal axis of the elongate body, the direction of lay of each groove reversing at spaced positions along the length of the element.
19. A method as claimed in Claim 17, wherein the inner die is caused to rotate about the longitudinal axis of the elongate body.
20. A method as claimed in Claim 19, wherein the reels from which optical fibres are fed are mounted at circumferentially spaced positions around an input unit which is rotatably driven about the axis of the advancing element in the same rotational direction and at the same speed as the inner die to compensate for any torque or twist imparted into each optical fibre.
21. A method as claimed in any one of Claims 1 6 to 20, wherein each optical fibre and/or optical bundle is dusted with a dusting powder upstream of extrusion of the circumferential wall.
22. An optical fibre element substantially as hereinbefore described with reference to and as shown in any one of Figures 1 to 4 of the accompanying drawings.
23. A method of making an optical fibre element substantially as hereinbefore described with reference to Figures 5 and 6 of the accompanying drawings.
GB08304092A 1982-02-15 1983-02-15 An improved optical fibre element Expired GB2115574B (en)

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GB08304092A GB2115574B (en) 1982-02-15 1983-02-15 An improved optical fibre element

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GB8304092D0 GB8304092D0 (en) 1983-03-16
GB2115574A true GB2115574A (en) 1983-09-07
GB2115574B GB2115574B (en) 1985-09-18

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0136887A2 (en) * 1983-10-05 1985-04-10 International Standard Electric Corporation Dielectric optical fibre cable
GB2169099A (en) * 1982-12-13 1986-07-02 Raychem Ltd Fibre optic cable for use at high voltage
GB2169100A (en) * 1982-12-13 1986-07-02 Raychem Ltd Fibre optic cable for use at high voltage

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2169099A (en) * 1982-12-13 1986-07-02 Raychem Ltd Fibre optic cable for use at high voltage
GB2169100A (en) * 1982-12-13 1986-07-02 Raychem Ltd Fibre optic cable for use at high voltage
EP0136887A2 (en) * 1983-10-05 1985-04-10 International Standard Electric Corporation Dielectric optical fibre cable
EP0136887A3 (en) * 1983-10-05 1985-05-08 International Standard Electric Corporation Dielectric optical fibre cable

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Publication number Publication date
GB2115574B (en) 1985-09-18
GB8304092D0 (en) 1983-03-16

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