NL1019447C2 - Tube structure with spirally arranged bundle of empty mini tubes for glass fibre cable network, has specific coil length to winding radius ratio - Google Patents

Abstract

The coil length of the bundle is less than 50 times the winding radius. Independent claims are also included for (a) a glass fibre cable comprising the above tube structure, in which one or more of the mini-tubes (3) contain a loose tube (2) housing one or more glass fibres (1a, 1b) and (b) a method for making the tube structure.

Description

0 .A. 1019447, Beh. to our letter of 4 March 2003 "f

Title: Pipe structure for a fiber optic network as well as a fiber optic cable comprising such a pipe structure and a method for laying such a pipe structure or fiber optic cable

The invention relates to a tubular structure for a fiber optic network, the tubular structure consisting of a bundle of mini-tubes coiled, as well as a fiber optic cable comprising such a tubular structure and a method for laying such a tubular structure or fiber optic cable.

Advanced telecommunication networks make use of glass fibers. To protect the vulnerable glass fibers, they are "cabled". Such a cable must offer protection against mechanical influences and environmental influences, in particular water. The latter protection is obtained by applying the correct glass fibers and cable materials and possibly a moisture screen. This aspect is not taken into consideration here. Mechanical violence can occur in the transverse direction, impact, and in the longitudinal direction, as pushing or pulling forces. Protection against impact is achieved, for example, by applying (underground) protection tubes or ducts. Protection against forces in the longitudinal direction is very important for glass fibers. Glass is a strong but also a brittle material. With a long time under tensile stress, cracks can grow in the surface and breakage can occur. A fiber optic under push or tensile stress can also result in additional signal damping. This is especially the case with pushing stress, in which the so-called buckling occurs and the fiber is pressed against the side. "Microbending" occurs, the cause of the signal attenuation. In addition to external forces on the cable, temperature variations can also lead to stress on the glass fiber, due to the differences in thermal expansion of glass and the cable materials. The plastics used for cables have thermal expansion coefficients that are many times larger than those of glass.

For the reasons mentioned above, an attempt is often made to make the cables in such a way that the glass fibers remain without voltage during installation and use.

A known construction for this is the so-called loose tube cable, as described in: G. Mahlke, P. Gössing, "Fiber optic cables: fundamentals, cable engineering, systems", Siemens, Berlin and Munich (D) 1993. The glass fibers are spacious here in a tube, also called tube, which is usually made from PBTP or polycarbonate and which is wrapped in a spiral shape around a central element. The fiberglass will usually be positioned as much as possible in the middle of the tube. The cable can therefore become shorter and longer, the so-called elongation margin, without the glass fibers being pressed against the wall of the tubes. After all, the position of the glass fiber goes outwards or inwards, as a result of which the length of the spiral fiber 15 can remain constant. The created elongation margin allows the cable to shrink and expand over a certain temperature range, the so-called temperature window, without the fiber optic being pressed against the loose tube. Furthermore, one or more tensile reinforcing elements, for example a central element, can be incorporated in the cable, which also exhibit as little thermal expansion as possible. A drawback of such cables is that it is difficult to make taps, because welds must be made in the glass fiber.

From the above-mentioned book, cable constructions are also known with a central, spacious tube, the so-called strained loose cables, in which the glass fibers have the space to have sufficient "excess length" because they form a "free" spiral in the tube. Even now, variations in the length of the cable can be caught within certain limits. A special variant is the so-called Spiral Space cable, as described in SF-A-86481, where the hollow space in the central tube already has a spiral shape. Here too, 30 branches are difficult.

1019447 1 3 •

The fiber optic cables described above are mainly used in long-distance connections for the telecommunications network. Currently, however, more and more applications are taking place in the connection network, the so-called FTTH (Fiber To The Home). Known constructions here are "JETnet", as described in: "JETnet". W. Griffioen, A. van Wingerden, C. van ‘t Hul,“ Versatile outside plant solution for optical access networks ”,

Proc. 48th IWCS (1999), 152-156 and "blown fiber", as described in: "Blown fiber". EP-A-0.108.590. With these techniques, cables or "fiber members" are blown into pre-installed bundles of mini tubes, usually from HDPE. With these tubes a branch can be made in advance, after which the glass fibers are only blown. Therefore, no welds need to be made in the glass fibers. For "blown fiber" so-called "tight" bundles with mini tubes are used, which are difficult to install in tubes or ducts due to their rigidity. Single bundles are used with "JETnet". In both cases, the mini-tubes are substantially stretched. The dimensions of the mini-tubes are moreover such that only stretched constructions are possible for the cables or glass fibers in the tubes.

For sufficient compactness, "JETnet" uses a central steel tube for the cable, so this is a special version of a strained loose tube cable. This has the advantage that the structure has a small expansion coefficient, because the expansion coefficient of metal is many times smaller than that of plastic. The disadvantage of this construction is that it is relatively expensive, especially with low-fiber units. Moreover, the cable is fairly stiff, so that tight bends are difficult to overcome.

For sufficient compactness, a special stretched "tight" construction with plastic and Aramide fibers (Kevlar, Twaron) or glass rovins is used with the "blown fiber" technique for the "fiber member", these are glass filaments, with or without plastic coating. The Aramid fibers can even compensate for the thermal expansion of the plastic. To also function in the compressive part 1019447 1 4 • a good matrix of both materials must be formed. The disadvantage of this construction is also that it is relatively expensive, especially with low-fiber units. Furthermore, the very flexible "fiber member" is sometimes difficult to blow in, partly due to static electricity.

As is apparent from the foregoing, although various solutions exist for manufacturing cable structures provided with or provided with glass fibers, there is still no solution whereby the requirements of reliability, in particular for so-called FTTH applications, are met. particularly adequate protection against forces in the longitudinal direction, and low cost. This last aspect is especially essential for an economically attractive expansion of FTTH.

It is an object of the invention to provide a cable structure that does satisfy all of these requirements.

To this end, the invention provides a structure consisting of a bundle of empty tubes spiraled, characterized in that the stroke length of the spirally bundled bundle is smaller than 50 times the winding radius.

In the following, such a bundle of empty mini-tubes that is spirally twisted into a "cable", further called spiral bundle. The spiral bundle according to the invention is first installed, for example in a protective tube or duet. A spiral bundle is easier to install than a stretched "tight" bundle, because it is less rigid. The mini-tubes can then be coupled to other spiral bundles, which have a similar construction, so as to form a branched network. Loose tubes with glass fibers are now blown into the 25 empty tubes of this network. These do not need any further reinforcement against tension because there is hardly any more force on the spiral bundle when it is installed and because the loose tubes are also in a spiral shape here, just like with a loose tube cable. After installation, there are usually also fewer temperature variations, especially underground, and here too the spiral shape 1 0194 47 5 provides for the collection of thermal expansion. The final fiber optic cable is therefore only formed in the field.

The mini-tubes can be arranged according to a spiral rotating in one direction, but the spiral bundles can also alternately rotate to the left and to the right. This is known in the cable industry as the SZ stroke.

According to a first embodiment, the mini-tubes are spirally wound around a central element, such as a metal wire, a cable or also a tube.

According to a second embodiment, the mini-tubes without central element are blown into a tube in a spiral shape.

It is noted that the article "Jetnet / sup R /, versatile access network solutions" by G. Brown et al., CSELT Technical Reports, April 1998, CSELT, Italy, page 236, describes the use of a bundle of tubes, wherein the bundle assumes a "helical shape" when installed. The stroke length (10 m), however, is 870 times as large as the winding radius (11.5 mm).

The loose tube is a cheap to produce semi-finished product with which many years of experience have been gained. It is therefore no problem at all to position glass fibers in the middle of the loose tubes. Furthermore, it is also not critical how exactly the loose tubes are blown into the mini tubes. The spiral with elongation margin is nevertheless realized. This is not the case if fibers or "fiber members" were blown directly into the mini-tubes of the structure according to the invention. The fibers can then lie tightly against the inside, or the outside, of the coil.

25 Because the loose tubes lie in the mini-tubes with play, on the one hand there is still some extra elongation margin, but on the other hand there is no connection between the tension-strengthening element of the cable and the loose tubes. As a result, the temperature window will be slightly smaller than for normal loose tube cables with the same geometry for the loose tubes. As discussed above, however, the cable properties need not apply until after the installation of the coil, when the tensile forces and temperature variations are lower. Furthermore, with traditional cabling, when the loose tubes collapse, some uncontrolled elongation occurs, so that a slightly larger elongation margin must be chosen to compensate for this. This is not necessary when the loose tubes are subsequently blown in, which happens at normal temperature and low tensile stress, with virtually no elongation occurring.

At first glance, it seems very difficult to install loose tubes in a tube that has been twisted into a spiral. Pushing and pulling 10 does not work, because the loose tube then quickly pulls itself into the continuous "bend", the so-called capstans effect. See also: W. Griffioen, “Installation of optical cables in ducts”, Plumettaz, Bex (CH) 1993. Blowing in also seems very difficult, even though the capstan effect does not occur because the blowing forces are uniformly distributed over the length. The friction due to the stiffness of the loose tube in bends seems to be insurmountable when blowing, because the effective forces here are so low. The friction due to the stiffness of the loose tube, however, theoretically only occurs at the ends thereof, ie at the front end of the loose tube and where it is introduced into the spiral bundle. There is sufficient compensation on the input side because the blower unit is pushing there. At the front end of the loose tube, however, there is no compensation for the aforementioned friction. However, a solution can be offered by locally compensating the force at the front end of the loose tube by a semi-open shuttle, of the type described in EP-A-0.445.858.

Another possibility is to use a stretched rod-shaped attachment, for example from FRP (fiber reinforced plastic), with approximately the same rigidity as that of the loose tube. Such an extension piece, which is coupled to the front end of the loose tube, can prevent the front end of the loose tube from following the curvature of the spiral under the occurrence of torsion.

In the above embodiments, the spiral bundles are first installed empty, and only then are the loose tubes with the glass fibers 5 arranged therein. However, it is also possible to install the loose tubes in advance. This can be done by blowing in the spiral bundle at the factory. But also extrusion of the mini tube around the loose tube, and only then collapse into a spiral bundle is possible. In the latter case, the position of the loose tube in the mini tube can also be optimized and additional elongation margin is obtained.

When the bundle of mini tubes, without a central element, is blown into a tube in a spiral shape, this is again the easiest in a prefabricated version. The bundle of mini-tubes is then blown in according to the technique described in US-A-5,884,384, but now the tube 15 is rotated about its longitudinal axis during the blow-in. Optionally, the reels with mini-tubes are also rotated about an axis perpendicular to the unwinding axis to compensate for twisting of the tubes.

The invention also relates to a fiber optic cable comprising a central longitudinal element around which a bundle of tubes 20 is spiraled, wherein a loose tube containing one or more glass fibers is present in one or more tubes.

The invention further relates to a method for manufacturing a tubular structure for a fiber optic network, characterized in that a tubular structure consisting of a bundle of empty mini-tubes is formed in a spiral, the bundle is subsequently installed and is installed in one or more of a loose tube containing one or more glass fibers is installed in the mini-tubes of the installed bundle.

The invention also relates to a method for manufacturing a fiber optic cable, characterized in that a tube structure consisting of a spiral-wound bundle of empty 8 mini-tubes is formed and that in one or more of these mini-tubes a loose tube with one or more more glass fiber is installed.

The invention also relates to a method for manufacturing a fiber optic cable, characterized in that a mini-tube is formed by means of extrusion over a loose tube containing one or more glass fibers and that a number of mini-tubes thus formed are formed into a spiral-shaped bundle Being hit.

The invention finally relates to a method in which a structure, comprising a bundle of empty tubes wound in a spiral, is installed along a predetermined path and after installation in one or more of the empty tubes a loose tube containing a glass fiber element is inserted through it is injected by blowing.

The invention will be explained below with reference to exemplary embodiments and calculations, with reference to the drawing. Figure 1 shows a cross-section of a fiber optic cable according to the invention; figure 2a a protective tube with a number of fiber optic cables according to figure 1 therein; Figure 2b shows a variant of figure 2a with a second variant of a fiber optic cable; Figure 3 shows an example of a structure for FTTH with the fiber optic cable according to Figure 2; Figure 4 shows a protective tube with a fiber optic cable according to the invention wound around a tube as a central element; Figure 5 shows an example of a structure for FTTH with a fiber optic cable according to Figure 4; figure 6 shows a sketch to explain the calculations; figure 7 a sketch for explaining the calculation of the elongation margin; and Figure 8 shows an example of a semi-open shuttle.

In the following, the inside and outside diameter of a tube are indicated with Diameter internal / Diameter external.

The invention is illustrated with reference to FIG. 1-5 explained for a 5 cabling for "Fiber To The Home" (FTTH) with two fibers la, b per home. These fibers fit into a 1.0 / 1.5 mm loose tube, such as in use with fiber optic cables for over 20 years. This loose tube, in turn, fits into a 3 / 2.4 mm mini tube 3. Standard couplings already exist for this outer size of the mini tube. An example of a spiral bundle 5 with seven mini-tubes, which has a total diameter of 10 mm, is shown in Figure 1. The mini-tubes 3 are spirally wound around the central element 4. The central element may, for example, consist of a rod of the FRP (fiber reinforced plastic), which is often used for cable production, which may or may not be provided with a plastic cover made of, for example, PE (polyethylene). A number of the spiral bundles 5 of Figure 1 can in turn be blown in bundles into tubes 6.

Figure 2a gives an example of seven spiral bundles in a 50/40 mm protective tube 6a. Figure 2b shows an example of seven 7 mm spiral bundles with three mini tubes 3 / 2.4 mm in a 32/26 mm protective tube 6b. It is also possible to use a tube and a copper twisted pair, making hybrid networks possible. The latter bundles can, for example, be used to enter the houses in their entirety.

With the spiral bundles of Figure 2 a structure can be made that fits nicely with structures that are currently used in copper connection networks, as schematically shown in Figure 3. For distribution, a 50/40 mm protective tube 6a with seven spiral bundles of seven tubes is laid . This distribution part can be coupled to the "drop" part, consisting of a 32/26 mm protective tube 6b with seven spiral bundles of 10134; 7 10 three tubes, which can be laid largely parallel to the tube 6a. Branches to the housings 7 can be made by coupling the 7 mm spiral bundles as a whole to spiral bundles of the same type that enter the housings, which can be installed in a 25/19 5 mm protective tube. The spiral bundles do not have to be peeled open tube by tube. Coupling of individual tubes from the spiral bundles takes place at the transition points from the distribution to the "drop" part.

It is also possible to wrap the tubes around a central element 10 which is formed by a cable or a central tube. Figure 4 shows an example of twelve tubes 13 with a diameter of 3 / 2.4 mm, which are wrapped around a 10/8 mm tube 14. This assembly can be installed in a 25/20 mm protective tube 16. Assemble and installation can in principle be done in a single operation. It is also possible to extrude the protective tube 16 around the spiral bundle, both loosely and tightly. The resulting (empty) bundle / cable can be filled as follows: a 48-fiber steel tube cable 11 (JETnet) for the supply to a welding point 17 and 2-fiber loose tubes 12 for the branch to the housings, from the weld. This can be done in two ways in this hybrid construction: back, along the tube 14 filled with the supply cable 11, and forward, along the part of the tube 14 without the supply cable. In total, 24 houses can be reached in this way and the fiber number of the loose tubes corresponds to that of the supply cable.

Figure 5 shows schematically an example of the network structure proposed above. A 10 mm tube 14 in the center of the spiral bundle can be coupled to a 10 mm tube 15 in a JETnet structure with, for example, five 10 mm tubes in a 40/32 mm protection tube 18, via a Y-coupling 19 between the protection tubes. The 48-fiber cable 11 can then be blown through the Y-coupling without welding.

11

If the loose tubes with glass fibers have already been factory blown into the mini tubes, branches in the network can also be made in a simple manner if the branch length is not too large. For this purpose, a mini tube is opened in two places. First the mini tube is cut open at the location of the branch, without damaging the loose tube. Further on, over a distance that is at least equal to the branch length, both the mini tube and the loose tube are cut with fibers. The length for the branch can then be withdrawn and reinstalled in the branch.

10 Withdrawing the loose tube through a spiral-shaped mini tube is only possible over a very short length. It will usually be necessary to blow here too. Even more practical is suctioning, as described in US-A-6,089,546, because this can take place at the location of the branch itself. A somewhat shorter length is achieved because a maximum pressure difference of only 15 1 bar is achieved with suction. If the taps are not too far from the end of the spiral bundle, there is no need for a second intersection of the mini tube and the loose tube.

In the following, the principle of the invention will be explained on the basis of calculations, with reference to Figure 6. For the calculations, use is partly made of the formulas described in: W. Griffioen, "Installation of optical cables in ducts" , Plumettaz, Bex (CH) 1993.

For a fiberglass with diameter Df that is in the middle of a loose tube with inner diameter Di that is spiraled with a winding radius Rw and stroke length P, the elongation margin <? Can be calculated approximately from: / 12

For several fibers, an effective diameter should be chosen for Df, for 2 fibers 0.416 mm. The effective bending radius Re of the twisted mini-tube results from: 5 p2

Re = ^ ή 4 n2Rw

This fact is important for the blowability in the event that a semi-open shuttle is not used. The following data are also of importance: the already present force F in the loose tube (due to the fact that the loose tube is difficult to push through the bend due to its stiffness), the weight W of the loose tube per unit of length, the outer diameter Dc of the loose tube, the inner diameter Dd of the mini tube, the pressures at the beginning and the end of the mini tube pi and 15 pa, the length l of the mini tube, the coefficient of friction ƒ between cable and mini tube. The build-up of force cLF over a piece of dx for a loose tube that is blown into a mini-tube that has been driven into a helix can be calculated. For the worst case situation at the start of the mini tube, where the blowing force is the smallest, the following applies: 20 dF = f \ w2 + - + (β / γ2) 2 -π ° 0 ° ά (Ρί ~ Pa) dx) V / ^ Pi

Here B is a bucket term that follows from the stiffness B of the loose tube with: 25 b - Dd- ° c

π 2B

13

The loose tube experiences an opposing force at the front end as a result of the helix. The following applies: 3 Bf | B yj6 (Dd -Dc) R1 2 Re 5

This opposing force is normally compensated for by blowing and pushing forces from the length of the loose tube behind the front end. In a helix, however, the forces only extend over a short stretch due to the continuous bending radius. As a result, it will usually not be possible to participate sufficiently behind the loose tube to compensate for the force at the front end. The loose tube can only be blown in if the following applies from the front end (LP <0. This results in a maximum length for turbulent flow: 15 / <_ * DcDd [pf ~ Pa) 8 / Pi <Jw2 + {F / Re ) 2 + (BF 2) 2

The maximum length that can be blown in can be considerably increased by using a semi-open shuttle, which has approximately 1 bar of pressure and allows the rest of the air flow through. The force of the semi-open shuttle, equal to nDd214 x 1 bar, must then be large enough to compensate for the opposing force at the front end of the loose tube. In that case F = 0 in the above formula applies. A simple semi-open shuttle can be made from a suction-closing shuttle with a hole with radius rh in which the following are met: Φκ = 0.5 & zt-, 2c—

Pa * f) 14

Herein c is the sound velocity of air under atmospheric conditions (340 m / s at 15 ° C) and Φν is the volume flow of the compressed air in the mini tube of the desired length, for turbulent flow following from: 5 (D2-D2) - (Dd -Dcf) 5/1 (p} -pl f7 Φ ^ 2-26-for-Νί

And for laminar flow following from: 10 * _ * {D2d-D2cf) <Dd-Dcf) 2 Pj-Pa V 128 // /

Herein μ is the dynamic viscosity of air (l, 8xl0-5 Pas), pa the density of air under atmospheric pressure (1.3 kg / m3) and Dcf is a number indicating the filling of the mini tube with a loose tube, equal to Dc as the 15 mini-tube is filled and equal to zero if no filling is present. The gap in the semi-open shuttle is calculated for an unfilled mini tube.

The flow is laminar and turbulent for a Reynolds number Re, respectively, smaller and greater than 2000. This number follows from: 20 pv (Dd-Dcf)

Re = -— μ

Herein υ is the velocity of the airflow, equal to 4Φν / -K {Dd2-Dcf). With laminar flow the distribution of the "grip" of the air flow over the loose tube and the wall of the mini tube will change slightly, to the detriment of that on the loose tube. The bladder forces on the loose tube are therefore somewhat lower with laminar flow. With relatively high filling of the mini tube through the t 15 loose tube, however, this will only be a small effect. The calculated maximum installation length l will only decrease with a few percent.

Calculation example 1 The first embodiment is as described in detail above. Df equals 0.416 mm, Di equals 1 mm and Rw equals 3.5 mm. A stretching margin ε of 0.17% then follows with a stroke length P of 150 mm. The thermal expansion coefficients of fiberglass and loose tube (polycarbonate), off and ate, are 0.45x10'6 K1 and 70x106 K1 respectively (for comparison 13χ106 K1 and 80χ10'6 K'1 for steel and PBTP respectively). An elongation margin of 0.17% corresponds to a temperature window of ± 24 K. Sufficient for underground, but above ground use requires a somewhat shorter stroke length, for example 105 mm to achieve a window of ± 50 K.

For the effective bending radius Re of the twisted mini-tube follows 166 mm, no problem for the glass fibers which can easily be bent to a bending radius of 30 mm. The following data applies to the loose tube: Dc = 1.5 mm, W = 0.0185 N / m and B = 0.0004 Nm2. Dd = 2.4 mm and ƒ = 0.1 for the mini-tube. The compressed air pressure at the start pi = 10 bar. This results in a counteracting force F of 0.0073 N to push the loose tube through the helix. The power of the semi-open shuttle, of which Figure 8 shows an example, of 0.44 N is more than sufficient for compensation. The bladder length that follows without and with semi-open shuttle is 294 and 757 m respectively. After some optimization and / or increasing the blowing pressure, 800 m is achievable, just enough for the distributive and "drop" part of the connection network.

In the case that the semi-open shuttle sufficiently compensates for the force at the head of the loose tube, a bladder length l of 800 m is achievable. The flow hierbijν here is 0.05 1 / s for an unfilled mini tube and laminar flow. A hole with rh = 0.1 mm (diameter approximately 0.2 mm) in the semi-open shuttle follows. The velocity of the air is 11 m / s, which gives a Reynolds number from 1950. The flow is therefore just laminar, certainly with a filled mini-tube.

5

Calculation example 2

The second embodiment is based on 7 / 5.5 mm mini tubes. A 2.3 / 3.1 mm loose tube with 24 fibers fits easily into this. The effective diameter for the glass fiber bundle Df is equal to 1.326 mm, Di 10 to 2.3 mm and Rw to 7 mm. A stretching margin of 0.32% follows with a stroke length P of 200 mm. The elongation margin gives a temperature window of ± 47 K. with free shrinking and expansion of the loose tube.

152 mm follows for the effective bending radius Re of the twisted mini-tube. The following data applies to the loose tube: 15 Dc = 3.1 mm, W ~ 0.086 N / m and B = 0.0057 Nm2. Dd - 5.5 mm and / = 0.1 apply to the mini-tube. The compressed air pressure at the start pi = 10 bar. From this follows a counteracting force F of 0.36 N to push the loose tube through the helix. The power of the 2.3 N semi-open shuttle is more than sufficient for compensation. The bladder length that follows without and with semi-open shuttle 20 is 28 and 771 m respectively. After some optimization and / or increasing the blowing pressure, 800 m can be achieved.

In the case that the semi-open shuttle sufficiently compensates for the force at the head of the loose tube, a bladder length l of 800 m is achievable. The flow hierbijν here is 1.041 / s for an unfilled mini tube and turbulent flow. A hole with rh = 0.41 mm in the semi-open shuttle follows. For the velocity of the air follows 43 m / s which gives a Reynolds number of 17400. Indeed, more than turbulent indeed, also the case for a filled mini-tube (v = 24 m / s and Re = 4190).

17

Figure 7 gives an example of the geometry of a (beaten) loose tube construction. With most fiber optic cables, the shape is about the same, but there are differences in size. With the same shape, the dimensions are the same and for example the ratio ξ 5 between the effective space of the glass fibers and the winding radius is constant:

Di ~ Df ξ = - = const.

In the calculation examples 1 and 2, this ratio is 0.17 and 0.14, respectively. The value is usually around 0.15. The formula for the elongation margin can be rewritten as follows: It follows for a stroke length P of 50 times the winding radius Rw a elongation margin s of only 0.11%. This elongation margin is actually too small to obtain a sufficient temperature window and sufficient elongation resistance. With even larger P / Rw, the elongation margin becomes even smaller. Fiber-optic cables with a loose tube construction therefore always have a relatively shorter stroke length.

Claims (17)

Tubular structure for a fiber optic network, the tubular structure consisting of a spiral-wound bundle of empty mini-tubes, characterized in that the stroke length of the spiral-wound bundle is less than 50 times the winding radius. 5 2. Tube structure according to claim 1, characterized in that the mini-tubes are arranged around a central element. 3. Tube structure according to claim 2, characterized in that the central element is a tube. Pipe structure according to claim 2, characterized in that the central element is a cable. 5. Tube structure according to claim 1, characterized in that the mini-tubes are arranged as a loose spiral bundle in an envelope tube. A tube structure according to any one of claims 1-5, characterized in that at least one of the mini-tubes is provided with a loose tube containing one or more glass fibers, wherein both the loose tube and the glass fiber (s) with some play are located in their respective enclosures. 7. Fiber-optic cable, characterized by a tube structure consisting of a bundle of empty mini-tubes spiraled, one or more of which are provided with a loose tube containing one or more glass fibers. 1019447 1 J 19 8. Fiber-optic cable as claimed in claim 7, characterized in that the stroke length of the spiral-wound bundle is less than 50 times the winding radius. 9. A method for manufacturing a tubular structure for a fiber optic network, wherein a tubular structure consisting of a spiral-wound bundle of empty mini-tubes is formed, which bundle is subsequently installed, characterized in that in one or more of the mini-tubes of the installed bundle loose tube containing one or more glass fibers 10 is installed. A method according to claim 9, characterized in that the stroke length of the spiral-wound bundle is less than 50 times the winding radius. 11. A method for manufacturing a fiber optic cable, characterized in that a tube structure consisting of a bundle of empty mini-tubes is formed and that a loose tube with one or more glass fibers is installed in one or more of these mini-tubes. 20 12. A method for manufacturing a fiber optic cable, characterized in that a mini-tube is formed by means of extrusion over a loose tube containing one or more glass fibers and that a number of mini-tubes thus formed are formed into a spiral-shaped bundle. 25 A method according to any one of claims 9-12, characterized in that the mini-tubes are wrapped around a central element. 14. Method as claimed in claim 13, characterized in that the central element is a tube or a cable. 1019447 1 * 20 Method according to one of claims 9 to 12, characterized in that the mini-tubes are formed as a spiral-shaped bundle in an envelope tube. Method according to claim 9, 10 or 11, characterized in that the loose tubes are installed in the mini-tubes by means of blowing in. 17. Method as claimed in claim 16, characterized in that the loose tubes are provided on their front sides with a semi-open shuttle or with an on-set piece. 1019447 "