WO1994023323A1

WO1994023323A1 - Optical fibre ribbon

Info

Publication number: WO1994023323A1
Application number: PCT/FI1994/000122
Authority: WO
Inventors: Jussi Ravela
Original assignee: Nokia Kaapeli Oy
Priority date: 1993-04-05
Filing date: 1994-03-30
Publication date: 1994-10-13
Also published as: FI93152C; AU6378294A; FI931529A0; FI93152B

Abstract

The invention relates to an optical fibre ribbon (30; 40; 50; 60), comprising at least two optical fibres (11) extending in the longitudinal direction of the ribbon, the longitudinal axes of which fibres are substantially parallel with each other and which fibres are substantially in the same plane in the direction transverse to the fibre ribbon. In order to provide a fibre ribbon structure, which is as easy-manufactured as possible and capable of implementing easily different division ratios between the fibres when branching the fibre ribbon, the fibre ribbon structure has been weakened at least at one fibre by varying at least one coating layer (32, 33, 34a, 34b) of said fibre with respect to the corresponding layers of the other fibres. In one preferred embodiment, the weakening has been implemented by a structure in which the colour layer (34a; 34b) surrounding a fibre adjacent to a desired division surface (C) is thicker than the colour layer (34) surrounding the other fibres (11).

Description

Optical fibre ribbon

The invention relates to an optical fibre rib¬ bon comprising at least two optical fibres extending in the longitudinal direction of the ribbon, the lon¬ gitudinal axes of which fibres are substantially par¬ allel with each other and which fibres are substanti¬ ally in the same plane in the direction transverse to the fibre ribbon. It is previously known to use in a cable opti¬ cal fibre ribbons, comprising typically 4 to 12 coated and mutually parallel optical fibres and a protective cover made of plastic material to unite these fibres. It is also possible to form a fibre ribbon in such a manner that outer coating layers surrounding each fibre, i.e. their edge areas bearing against each other, are joined to each other by an adhesive, for instance.

Fibre ribbons have several advantages compared to individual fibres, and therefore, they have been of more and more increasing interest lately. Except that fibre ribbons make (telecommunications) cables with high transmission capacity possible (which is very significant because of the rapidly increasing demand for data transmission), they also offer a structure, by means of which it will be simpler to install and maintain a cabling, because the need to handle individual fibres decreases. For instance, individual fibres can be spliced and jointed by splicing and jointing a considerably bigger fibre ribbon, if it is possible to determine and maintain the positions of the fibres in the ribbon. All fibres of the fibre ribbon can thus be spliced to another similar ribbon or to a connector of a terminal by one peeling and one welding operation. Economical and technical points of view favour¬ ing an increasing number of fibres in a ribbon, a situation easily arises, e.g. in connection with branching a cable, that it is not necessary to splice all fibres of the ribbon simultaneously, but only four fibres of twelve, for instance, shall be spliced to the mid-span branching. A situation like this creates a need to divide the fibre ribbon into mod¬ ules or subsections, which can be released from the fibre ribbon without breaking its structure.

It is known to divide a fibre ribbon into modules or subsections as described above by assem¬ bling fibre ribbons manufactured in separate pro¬ cesses into bigger entities. Figure 1 shows such a fibre ribbon, which comprises eight mutually parallel optical fibres 11, each of them having separate coat¬ ing layers. Fibre ribbons A and B have at first been manufactured in separate processes, each ribbon com¬ prising four fibres and a uniting outer layer 12 and 13, respectively. These two fibre ribbons have been assembled into a ribbon by coating them with a common coating layer 14. However, the above procedure pre¬ supposes two relatively expensive processes for pro¬ viding a broad fibre ribbon. The finished product obtained in this way is not homogenic either, but a spacing between fibres at a division surface differs from the mutual distance between the other fibres, which may make a splicing of an undivided fibre rib¬ bon more difficult. This drawback concerns also the solution set forth in the Patent Application GB-A-2187865, in which a splicing of a fibre ribbon is facilitated by making the mutual distance between the fibres at the division surface bigger than the mutual distance be- tween the other fibres. It is also known to run a so-called division groove into the outermost layer of the ribbon, the so-called matrix layer, by means of a shaped tool and possibly to fill it with some suitable material dif- fering from the material of the matrix layer. Such an alternative is shown in Figure 2, in which the un¬ filled division groove is indicated by reference nu¬ meral 21 (for the other parts are used the same ref¬ erence numerals as in Figure 1). This solution again requires a separate combination of tools (a nozzle combination) for each module combination; for a 12- fibre ribbon, for instance, divisions 6+6, 4+4+4, etc. In addition, the ribbon manufacturing process, sensible as such already, becomes more difficult, if the matrix layer shall also have a controlled shape with a groove, especially if the groove shall be filled with a differing material as well. (For in¬ stance, the width of a 12-fibre ribbon is about 3 mm, due to which it is not quite simple to form a divi- sion groove in a controlled way into the matrix lay¬ er, just between the desired fibres. ) For so-called edge-bonded fibres, which are not surrounded by a matrix layer (or have a very thin surrounding matrix layer), this method is not at all suitable. The object of the present invention is to get rid of the above problems and to provide a fibre rib¬ bon structure, which is as easy-manufactured as pos¬ sible and capable of implementing different division ratios. This is achieved by means of a fibre ribbon according to the invention, which ribbon is charac¬ terized in that the fibre ribbon structure has been weakened at least at one fibre by varying at least one coating layer of said fibre with respect to the corresponding layers of the other fibres. The idea of the invention is to weaken a fibre ribbon structure at one fibre (or two fibres) adja¬ cent to a division surface by varying at least one coating layer of said fibres with respect to the cor¬ responding layer/layers of the other fibres. In this connection, the coating layers of the fibres signify one of those layers by which the fibre has been coat¬ ed since it was uncoated.

Thanks to the solution of the invention, a weakening may be provided in connection with the man- ufacture of each fibre, whereby the manufacture and a later handling of the fibre ribbon, e.g. cabling, correspond to the handling of a normal fibre ribbon as well as possible.

According to one preferred embodiment of the invention, a weakening is provided by means of a structure in which a colour layer surrounding the fibres adjacent to the division surface is thicker than a colour layer surrounding the other fibres.

In the following, the invention and preferred embodiments thereof will be described in greater de¬ tail with reference to Figures 3 and 6 by examples according to the attached drawings, in which

Figure 1 shows a cross-section of a broad fibre ribbon according to the prior art, Figure 2 shows a cross-section of another broad fibre ribbon according to the prior art,

Figure 3 shows a cross-section of a first embo¬ diment of a broad fibre ribbon according to the in¬ vention, Figure 4 shows a cross-section of a second em¬ bodiment of the broad fibre ribbon according to the invention,

Figure 5 shows a cross-section of a third embo¬ diment of the broad fibre ribbon according to the in- ven ion, and Figure 6 shows a cross-section of a fourth em¬ bodiment of the broad fibre ribbon according to the invention.

Figure 3 shows a cross-section of a fibre rib- bon 30 according to a first embodiment of the inven¬ tion. In this case, the fibre ribbon comprises eight parallel optical fibres 11, which are positioned sub¬ stantially in the same plane in the direction trans¬ verse to the fibre ribbon and the longitudinal axes of which are substantially parallel with the longi¬ tudinal axis of the fibre ribbon. To begin with, each optical fibre 11 comprises an uncoated fibre 31 manu¬ factured of e.g. quartz glass, the diameter of the fibre being typically of the order of 0,125 mm. This uncoated fibre is coated with a first, so-called primary coating 32. The diameter of the primary coat¬ ed fibre is typically between 0,180 and 0,200 mm. The primary coating again is coated with another, so- called secondary coating 33, which is a harder layer than the primary coating. The diameter of the second¬ ary coated fibre is typically between 0,240 and 0,255 mm. The primary and secondary coatings are typically manufactured of some UV curable acrylate, e.g. sili- cone, epoxy or urethane acrylate. Each secondary coating is surrounded by a thin colour layer 34 typically consisting of some UV cur¬ able acrylate as well, to which has been added colour pigment. By means of the different colours of the colour layers, the different fibres are identified from each other. A colouring of a fibre (i.e. coating with a colour layer) takes place in a separate device in such a manner known per se that a secondary coated fibre is drawn at a constant speed and tension through a colouring nozzle. In the colouring nozzle, the fibre will be surrounded by the UV acrylate layer 34 containing colour pigments. Colouring agent is introduced into the nozzle by means of a hose from a pressurized vessel. After the fibre has been colour¬ ed, it is led into a UV irradiation equipment, in which the colour layer is cured in a shielding gas by means of UV radiation. The irradiation equipment ty¬ pically comprises 1 or 2 UV lamps, the radiation from which is distributed evenly around the fibre by means of curved mirrors. As shielding gas is used e.g. ni- trogen. By means of the shielding gas, a disadvanta¬ geous influence of possible oxygen molecules on the curing reaction is prevented.

According to the invention, the thickness of colour layers 34a and 34b on fibres on both sides of a desired division surface C (a plane between desired fibres perpendicular to the transverse direction of a fibre) has been increased with respect to the thick¬ ness of the colour layers 34 on the other fibres. The division surface is the surface along which the fibre ribbon breaks when bended, which means that the fibre ribbon is divided into several parts, in this case two, each of them comprising four fibres. The thickness of the thinner colour layers 34 is typical¬ ly between 3 and 6 μm, while the thickness of the layers 34a and 34b is preferably between 8 and 12 μm. The thickness of a colour layer is primarily cont¬ rolled by means of the hole diameter of a colouring nozzle. This hole is clearly bigger than an un- coloured fibre and somewhat bigger than the coloured fibre diameter strived for. If the diameter of a sec¬ ondary coated fibre is e.g. 240 μm, the diameter of a coloured fibre is typically e.g. 246 to 252 μm (thinner colour layer) and the diameter of the nozzle 255 to 260 μm. When a thicker colour layer is used, the latter dimensions are 256 to 264 μm (coloured fibre) and 265 to 275 μm (nozzle), respectively. The thickness of a colour layer may also be slightly in¬ fluenced by the feed pressure of the colouring agent and the drawing speed of the fibre. The viscosity of the colouring agent also has a minor influence on the thickness of the colour layer created. In total, the thickness of the colour layer can be controlled to a great extent by means of empirical quantities.

A weakening effect provided by the thicker col- our layers 34a and 34b is described in greater detail in the following.

Firstly, the thickness of the colour layers ad¬ justs the thickness of a common coating layer 14 at a fibre. The thicker the colour layer is, the smaller is the surface of fracture F between the outer sur¬ face of the colour layer and the outer surface of the coating layer 14. According to the invention, it is preferable to dimension the common coating layer 14 very thin, in which case a change of thickness of the colour layer causes a relatively great change in the thickness of the coating layer 14 at said points. A 3 to 9 μm change of thickness of the colour layer may be e.g. of the order of 50 % of the thickness X of the coating layer at upper and lower fringes of those fibres which have a thinner colour layer. The differ¬ ence in thickness between the colour layers 34 and 34a/34b may also correspond to the thickness X of the coating layer, in which case the surface of fracture vanishes entirely at the thicker colour layer (the common coating layer 14 disappears entirely at the upper and lower edges of the thicker colour layers 34a and 34b). Such an embodiment is shown in Figure 4.

Secondly, a weakening may also be provided at the thicker colour layers 34a and 34b between said fibres and the surrounding coating layer 14 by ar¬ ranging a lower adhesion between said colour layers and the common coating layer 14 than between the other colour layers 34 and the coating layer 14. The adhesion between a colour layer and the coating layer can be adjusted by adjusting the degree of curing of the colour layer, for instance. Generally speaking, the degree of curing of an underlying material af¬ fects the adhesion of a material to be laid thereon in such a way that a higher degree of curing de¬ creases the adhesion. The curing of a colour layer can be controlled by means of several different fac¬ tors or a combination thereof. These factors are:

- amount of UV radiation a colour layer is ex- posed to

- radiation wavelength of UV lamps

- flow of shielding gas.

Primarily, the curing is controlled by means of the amount of UV radiation. Due to a bigger colour mass per length unit of a thicker colour layer, said fibres need more radiation for reaching at least the same degree of curing as the fibres with thinner col¬ our layers. The amount of radiation can be affected by the drawing speed of the fibres (the smaller the drawing speed is, the longer is the radiation time and the higher the degree of curing) and by the num¬ ber of UV lamps used as well as by the radiation in¬ tensity. The wavelength of the lamps has an influence on how deep into the material the irradiation ex- tends. It is preferable to use for curing at least two lamps, one of which is a so-called H-lamp operat¬ ing in the wavelength range 300 to 400 n and attend¬ ing to surface curing and the other one of which is a so-called D-lamp operating in the wavelength range 300 to 400 nm and attending to deep curing. Especial- ly by adjusting the radiation intensity and the amount of radiation from the H-lamp, it is possible to influence the adhesion between a colour layer and the coating layer. Additionally, it shall be noted that different colour qualities demand different amounts of radia¬ tion so that a sufficient degree of curing can be achieved and the adhesions of different colour quali¬ ties to a coating material differ from each other already as such (regardless of the degree of curing). So-called ribbon fibre colours have been developed expressly for decreasing the adhesion, and therefore, it is preferable to use just such ribbon fibre col¬ ours for colour layers. It may also be possible to provide a sufficient weakening effect simply by using different colour materials (differing from the colour material of the other fibres) for desired fibres.

Instead of increasing the thickness of the col¬ our layers, it is possible to keep it unchanged and to adjust only the adhesion of the colour layers to the coating layer by the means described above. Fig¬ ure 5 shows a fibre ribbon structure 50 according to a third embodiment of the invention, the starting point being a known structure, in which all colour layers are essentially equally thick. A weakening (lower adhesion to the coating layer 14) has now been provided according to the invention in areas D and E of the colour layers 34a and 34b, which areas are indicated by means of a broken line. This is possible in principle e.g. by exposing the areas D and E dur¬ ing curing to more radiation by focussing and/or re¬ stricting the radiation. Especially in connection with so-called on-line colouring, the fibres being coloured in the same line with assembling into rib- bon, it is, in principle, possible to direct the ra- diation this accurately. On the other hand, fibres coloured in a separate process and wound on a coil after the colouring may not be irradiated this ac¬ curately in practice. A weakening effect (lower adhesion to the coat¬ ing layer 14) may also be provided by treating the colour layer with an agent facilitating release, e.g. with a release agent facilitating a release of fibres from the coating material. This embodiment is indi- cated by reference numeral 60 in Figure 6, in which the separately treated colour layers 34a and 34b are indicated by broken lines and reference mark H. This agent contributing to a release may be driven around the fibres of the division surface by wipers at the assembling stage, before the fibres go to a coating tool. By means of the release agent, it is also pos¬ sible to create a lower adhesion for the areas D and E of Figure 5 by leading the release agent only to the fibre sides bearing against the division surface. All the above examples relate to a treatment of a colour layer for providing a weakening. It is also possible in principle to provide a weakening by vary¬ ing the primary or secondary layer, e.g. by making the primary and/or secondary layer of desired fibres thicker than the corresponding layers of the other fibres, in which case said fibres have a larger area bearing against the surrounding common coating layer of the fibre ribbon. Differences in the common area lead, on the one hand, to differences in the adhesion between said layers and, on the other hand, to dif¬ ferences in the thickness of the coating layer sur¬ rounding the fibres at separate fibres. Due to this difference in thickness, the surface of fracture F of the surrounding layer is of different size at the separate fibres. A variation in the properties of the primary and/or secondary layers, e.g. a change of thickness, may thus be made regardless of whether separate colour layers are used on fibres or not.

However, changing the thickness of the primary and/or secondary layers is not an embodiment as pre¬ ferable as changing the thickness of a colour layer, for changes in the primary and/or secondary layers affect the behaviour of the fibre itself (e.g. tempe¬ rature behaviour) clearly more than changes in a col- our layer. By changing the properties of the colour layers, it is thus clearly simpler to effect changes which are not of significance for the behaviour of the fibre itself. A substantial factor is expressly that using means improving the dividability of the fibre ribbon does not in the least impair the optical properties of the fibres of the ribbon in any circum¬ stances.

Though the invention has above been described with reference to the examples of the attached draw- ings, it is clear that the invention is not restrict¬ ed to that, but it can be varied within the scope of the inventive idea set forth above and in the attach¬ ed claims. Even though examples presented above con¬ cern a fibre ribbon structure corresponding to a so- called encapsulated structure, the solution of the invention may also be used in connection with a so- called edge-bonded fibre ribbon equally well. An en¬ capsulated structure may also comprise several common coating layers, in which case a weakening is directed to a boundary surface between the outermost layer of a fibre and the coating layer bearing against it and to the common thickness of the coating layers at said fibres. It is not necessary either to provide the individual fibres both with a primary and a secondary coating, but they can be surrounded by one layer only (which may have a softer inner part and a harder outer part, however). Further, a weakening may be provided by treating one or several coating layer/s of one single fibre or part thereof, and the above means may be combined to intensify the weakening ef¬ fect. The fibre ribbon may also have more than one division surface. Moreover, the fibre ribbon may be divided unsymmetrically, by dividing a 12-fibre rib¬ bon, for instance, in the ratio 2+4+6.

Claims

Claims:

1. Optical fibre ribbon (30; 40; 50; 60), com¬ prising at least two optical fibres (11) extending in the longitudinal direction of the ribbon, the longi¬ tudinal axes of which fibres are substantially par¬ allel with each other and which fibres are substan¬ tially in the same plane in the direction transverse to the fibre ribbon, c h a r a c t e r i z e d iri that the fibre ribbon structure has been weakened at least at one fibre by varying at least one coating layer (32, 33, 34a, 34b) of said fibre with respect to the corresponding layers of the other fibres.

2. Fibre ribbon according to claim 1, c h a r- a c t e r i z e d in that an adhesion between the outermost layer of a fibre (11) and a surrounding common layer (14) of the fibre ribbon has been weak¬ ened at least at said one fibre compared to the adhe¬ sion between the outermost layer of the other fibres of the fibre ribbon and said common layer (14).

3. Fibre ribbon according to claim 1, in which the outermost layer of at least part of the fibres is a colour layer (34) intended for the identification of fibres, c h a r a c t e r i z e d in that the colour layer (34a; 34b) surrounding a fibre adjacent to a desired division surface (C) is thicker than the colour layer (34) surrounding the other fibres (11).

4. Fibre ribbon according to claim 3, c h a r¬ a c t e r i z e d in that the difference in thick- ness between the colour layer (34a; 34b) of the fibre adjacent to the desired division surface (C) and the colour layer (34) surrounding the other fibres (11) corresponds substantially to the thickness (X) of a coating layer (14) of the fibre ribbon at the fibres having a thinner colour layer.

5. Fibre ribbon according to claim 2, c h a r¬ a c t e r i z e d in that the outermost layer (34a; 34b) of the fibre adjacent to a desired division sur¬ face (C) has been made harder in the areas (D, E) facing the division surface.

6. Fibre ribbon according to claim 2, c h a r¬ a c t e r i z e d in that the outermost layer (34a; 34b) of the fibre adjacent to a desired division sur¬ face (C) has been treated with an agent facilitating release.