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
  • G02B6/4401—Optical cables
  • G02B6/4407—Optical cables with internal fluted support member
  • G02B6/4408—Groove structures in support members to decrease or harmonise transmission losses in ribbon cables
• • 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
  • G02B6/4403—Optical cables with ribbon 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
  • G02B6/4479—Manufacturing methods of optical cables
  • G02B6/448—Ribbon cables

Definitions

• This invention relates to an optical fibre cable comprising one or more fibre ribbons consisting of a plurality of optical fibres positioned side by side, the fibre ribbons being arranged into a stack; and a protective element comprising a cavity substantially rectangular in cross-section and surrounding the stack of fibre ribbons, the stack of fibre ribbons being arranged to run in the cavity in a wavelike manner in the longitudinal direction of the fibre ribbons.
• fibre ribbons allows a high fibre packing density with respect to the external dimen ⁇ sions of the cable.
• the use of fibre ribbons has also problems which are mainly associated with the fact that fibre ribbons can be bent in the direction of a single axis and twisted into a large spiral only.
• such fibre ribbons must have an extra length with respect to their protective element. This requirement can be met either by forcing the fibre ribbons to run in a wavelike manner within the protective element or arranging the grooves in which the fibre ribbons are positioned to extend in a reverse-stranded manner in the longitudinal direction of the protective element.
• An advantage of the latter alternative is that the cable can be bent in every direction, whereas the groove frame is difficult to produce from desired materials and the stranding of fibre ribbons into the grooves is slow and liable to disturbances, in addition to which a complicated machinery is required.
• An optical fibre cable of the type described in the introductory chapter, in turn, is known from e.g. WO Patent Application 91/00536.
• this cable struc- ture a stack of fibre ribbons is passed through an extrusion head where a protective element is formed around it.
• a cavity substantially rectangular in cross-section is provided centrally in the protective element for the stack of fibre ribbons.
• the protective element then has to be heat-treated in order to shrink it to such an extent that the stack of fibre ribbons within it will be positioned in a wavelike manner.
• fibres in the stack are provided with extra length as compared with the length of the protective element. This is necessary in order that the cable would be able to adapt to different temperature con ⁇ ditions. Temperature variations cause considerable variation in the length of the plastic protective element whereas the length of optical fibres made of a glass material is substantially constant.
• the filler material used for filling the cavity provided within the protective element for the stack of fibre ribbons to prevent the penetration of moisture into cavity has to have a low viscosity as the stack of fibre ribbons and the filler material have to be introduced into the protective element through a common conduit.
• the object of the present invention is to provide a protective element for an optical fibre cable of the type described in the introductory chapter while avoiding the above problems.
• the protective element comprises at least one prefabricated profile part defining a trough space for the stack of fibre ribbons; and a surface forming the bottom of the trough space of the profile part is corrugated in the longitudinal direction of the trough. Accordingly, a trough-shaped profile of high dimensional accuracy is manufactured first.
• a stack of fibre ribbons is then fitted in the trough of the prefabricated profile and forced to follow the shape of the bottom of the trough.
• the profile is closed by a sheathing, and members increasing the tensile strength in the longitudinal direction of the cable may be embedded in the sheathing.
• a second embodiment of the optical fibre cable according to the invention is characterized in that the protective element comprises two prefabricated parts defining therebetween the cavity substantially rectangular in cross-section for the stack of fibre ribbons when brought together; and a surface of at least one part of the protective element defining the cavity is corrugated in the longitudinal direction of the cavity.
• the prefabricated parts as such define a closed space having a desired substantially rect ⁇ angular cross-section when they are positioned against each other.
• the parts may be symmetrical trough-shaped profiles; they may also be different from each other so that one part forms at least most of the cavity while the other closes the space, acting as a cover.
• the required extra length of the stack of fibre ribbons with respect to the protective element is achieved similarly as in the first embodiment, i.e.
• the protective element defines a trough space, being substantially U-shaped in cross- section, and the other part forms a cover for the trough space
• the part forming the cover comprises a projection extending between the walls forming the sides of the trough space and extending substantially between the walls. In this way the trough space can be maintained in desired dimen ⁇ sions and no external compression pressures are able to reduce the width of the cavity.
• the protective element comprises two pre ⁇ fabricated parts, it is further preferable that the parts of the protective element comprise locking means for interlocking them.
• the operation of the locking means may be based e.g. on the elasticity of one part so that its locking means can be forced into engage ⁇ ment with the locking means of the other part.
• Various dovetail structures or the like may thus be used advantageously as locking means.
• the space between the inner walls of the cavity within the cable and the stack of fibre ribbons is preferably filled with a filler material. This can be effected in a very simple manner as the prefabricated profile parts are forced into engagement at a pre ⁇ determined point of the cable production line, and so it is easy to provide a suitable nozzle head at this point for injecting the filler material into the protective element after the interconnection of the parts.
• Figure 1 is a cross-sectional v ⁇ ew of a first illustrating embodiment of the cable according to the invention
• Figure 2 is a cross-sectional view of a protect ⁇ ive element contained in a second illustrating embodi ⁇ ment of the cable according to the invention
• Figure 3 is a longitudinal sectional view of the protective element shown in Figure 2.
• Figure 4 shows a portion of the production line of the cable according to the invention when using the protective element shown in Figures 2 and 3 for the stack of fibre ribbons.
• Figure 1 shows a cross-section of the first illustrating embodiment of the optical fibre cable according to the invention.
• a stack 1 of optical fibre ribbons 2 is positioned within a protective element 3 comprising a prefabricated profile.
• the cross-section of the protective element 3 is H-shaped, comprising two trough spaces 4 U-shaped in cross-section for the stacks 1 of fibre ribbons.
• the bottoms of these trough spaces are corrugated longitudinally of the troughs (not shown in Figure 1) so as to provide the stacks of fibre ribbons with a required extra length when they are brought to follow the corrugation.
• the trough spaces 4 are closed by a cable sheathing 12.
• the cable shown in Figure 1 further comprises supporting threads 13 of which two threads are positioned within the sheathing 12 and one thread within the prefabricated profile 5.
• the purpose of the supporting threads made of e.g. metal is to provide the cable with adequate tensile strength. Of course, adequate tensile strength could also be achieved by suitably selecting the material of the profile 5. It may be made e.g. of a composite material or some other suitable material.
• Figures 2 and 3 are a cross-sectional view and a longitudinal sectional view, respectively, of the protective element contained in the cable according to the second embodiment of the invention.
• the protective element 3 shown in Figures 2 and 3 comprises two prefabricated parts 5 and 6.
• the part 5 comprises a U- shaped trough 4 which is closed by means of the part 6.
• a surface 7 forming the bottom of the trough 4 of the part 5 is corrugated in the longitudinal direction of the part
• the part 6 forming a cover for the part 5 comprises a projection 9 which is arranged to protrude between walls 8 forming the sides of the U-shaped part 5. In this way none of the fibre ribbons 2 in the stack 1 is able to penetrate into the gap between the parts 5 and
• the projection 9 also prevents the sides of the part 5 from collapsing towards each other e.g. when an external force is exerted on the cable in the direc- tion of the sides.
• the reference numeral 10 indicates structural elements partly contained in the part 5 and partly in the part 6 of the protective element and interlocking the parts.
• the structural locking means 10 are substantially dove ⁇ tail-shaped.
• the parts 5 and 6 thus stay in engagement with each other without any special measures after they have been brought together.
• the parts may be simply pressed together when the part 6 is made of a suitably elastic material. It is, of course, also possible to interconnect the parts by e.g. ultrasonic welding or hot seaming or by fitting straps around the parts. Such techniques could be used e.g. to join together two identical profiles U-shaped in cross- section.
• Figure 4 illustrates a process for introducing the stack 1 of fibre ribbons and the filler material 11 into the protective element of the type shown in Figures 2 and 3.
• the parts 5 and 6 of the protective element are moved at an equal speed forwards in the direction of the arrow A.
• the stack 1 of fibre ribbons 2 is first introduced into the part 5 of the protective element comprising the trough space.
• the parts 5 and 6 are brought against each other and forced into engage ⁇ ment with each other e.g. by means of press and support rolls 14.
• a feed nozzle 15 for the filler material 11 is passed between the parts 5 and 6 within the area of the rolls 14 at a point where the parts 5 and 6 are already in engagement with each other.
• the filler material or grease is fed under pressure from a suitable source (not shown) into a tube 16 connected to the nozzle 15.
• the pressure of the filler material 11 is monitored by means of a pressure gauge 17 fitted in the tube 16.
• the pressure of the filler material 11 presses the stack 1 of fibre ribbons against the corrugated bottom 7 of the bottom part 5 of the protective element. In this way the stack 1 of fibre ribbons is forced to follow the shape of the bottom of the profile 5 very simply and efficiently, and so the fibre ribbons 2 will be provided with a sufficient extra length with respect to the total length of the protective element and thus the finished cable.
• optical fibre cable according to the inven ⁇ tion and especially the protective element provided within it for the stack(s) of fibre ribbons have been described above only by two illustrating embodiments. It is thus to be understood that the shape of the protective element can be varied substantially with ⁇ out, however, deviating from the scope of protection defined in the attached claims. Accordingly, the protective element may comprise several trough spaces or cavities positioned side by side for the stacks of fibre ribbons. Furthermore, it is possible to position several protective elements according to Figures 2 and 3 r for instance, within the same cable.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Insulated Conductors (AREA)
• Light Guides In General And Applications Therefor (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=8535276

Family Applications (1)

Country Status (2)

Cited By (2)

Citations (1)

• 1992
  • 1992-05-12 FI FI922146A patent/FI90146C/fi not_active IP Right Cessation
• 1993
  • 1993-05-03 WO PCT/FI1993/000189 patent/WO1993023778A1/en active Application Filing

Patent Citations (1)

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