MXPA96002631A - Best optic fiber cable - Google Patents

Abstract

Currently, two types of protection to optical fibers are known. One type adhered, characterized by the extrusion of a plastic material applied on and in direct contact with the fiber optic. Another uses as protection loose tubes on one or more fibers that are contained inside the tubes together with a filling material as protection of the fibers against the entry of moisture. The improvements to the optical cable are based on a loose tube type construction, which are wired in a helical or bidirectional (sz) form around a lightweight central element with low mechanical memory. This central element constitutes a traction element when the cable is subjected to tension forces caused by the installation, and a balancing element of expansion and contraction forces caused by the operation of the cable in the limits of its thermal range. A layer of aramid fiber or glass fibers is applied to the core formed by the central element and the loose tubes, which together with the central element contributes to a greater tension during the installation. On this set is applied one or more plastic covers that serve as support to one or two metallic placed in longitudinal form. A final plastic cover is applied as final protection

Description

IMPROVED OPTICAL FIBER CABLE BACKGROUND OF THE INVENTION Different techniques are currently known to produce a wide variety of fiber optic cables for tele communications, by means of these optical elements it is possible to establish a physical link for telecommunication between telephony centers of computers, telecontrol and sipri lares. Said telecommunication is made with electronic signals and based on light beams.

I The above mentioned fiber optic filaments are small in dimensions, with diameters generally less than one millimeter. It is convenient to give them adequate protection to use them in great lengths. One type of protection already in use is the so-called adhered type, which is made by extruding a plastic or similar material, over and in with direct tactol with said filaments.

Optical cables typically use optical fibers with attached protection, such as wiring elements. In Mexican Patent No. 159491 the improvements to said cables are presented, which are characterized by the use of loose tubes as wiring elements. These rubber tubes in turn are characterized by being a protection for one or more filaments of optical fiber, which are contained inside the same tubes. Said tubes are also characterized by containing the filaments alone or together with a filling material for the protection of the filaments against the possible ingress of moisture into the tubes.

Dry tubes will be understood as those that do not have a filling material and filled tubes, which should be understood as those tubes that have said filling material. In turn, this filling material is characterized by having a consistency such that it protects the filaments, being repellent to moisture and at the same time allows the mobility of those filaments inside the tube that contains them, Improvements to the optical cable are also characterized by having the loose tubes (dry or filled) wired by unidirectional or bidirectional helical application around a central traction element. This central element of traction is characterized for being used for - the pulling of the optical cable during its installation. This tensile element is also characterized by having a breaking load capable of supporting the weight, and the tension of a continuous length (without joints) and finite of the opti- cal cable in its installation. The loose tubes are maintained on the central element by applying an assembly element thereon. On this set, one or two plastic covers are extruded, under which metallic ribbons are placed-longitudinally positioned for the mechanical protection of the optical cable of the present invention.

The applicant has developed an optical fiber cable - which improves the above qualities through a new manufacturing technique. I The improvements to the optical cable are based on a loose tube type construction, which are wired in a unidirectional or bidirectional (sz) licoidal form of a lightweight central element with low mechanical memory. This central element constitutes a traction element when the cable subjected them to tension forces caused by the installation and a balancing element of forces of expansion and contra? caused by the operation of the cable in the limits -of its thermal range.

A layer of aramid fiber or glass fibers is applied on the core formed by the central element and the loose tubes, which together with the central element contributes to a greater tension during the installation. On top of this, one or more plastic covers are applied, which serve as support for one or two metal strips placed in longitudinal form. A final plastic cover is applied as final protection.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1. Corresponds to a cut of a perspective view i < I an improved fiber optic cable for teleco ! •, munication, showing the tube-loosening construction (12) for optical fibers (11) with a pultruded central reinforcement (15).

FIG. 2. Corresponds to a sectional cut of an improved fiber optic cable of Figure 1.

The invention is described below according to the drawings of figures 1 and 2 in order to better clarify the same but of course without restricting its scope.

DETAILED DESCRIPTION OF THE INVENTION The present invention describes and claims improvements to an optical cable for telecommunications containing one or more optical fiber filaments. Said filaments are used as physical link means for electronic communication, based on light beams, between information telecommunication, signaling, television or similar centers.

The optical fiber cable 10 comprises a plurality of loose tubes 12 arranged longitudinally and surrounding a pultruded central reinforcement 15, inside the tubes, loosely inserted the optical fiber filaments 11. l The optical fiber filaments are manufactured regularly with - a primary protection of acrylate taking them to a final diameter of 0.25 millimeters. A secondary type of protection proposed for such filaments is the extrusion application of a plastic cover in direct contact with the filaments. This type of secondary protection can be identified as a type of protection. In general, fiber optic cables have been constructed using fibers with attached protection, wired helically around a central element.

I The alternate method of secondary protection presented here is containing one or more fiber optic filaments inside a plastic tube. With the proper selection of the inner diameter of the tube, the optical fibers do not directly receive the forces from the outside. Since the said filaments can have some freedom of movement within the tubes, this type of secondary protection can be identified as loose type protection.

To the set of loose tubes and central reinforcement is applied a layer of aramid fiber or glass fibers 16 followed by a second cover of polyethylene 7. The assembly thus coated includes a protection of one or more metal strips 18 and is finally covered with a cover of polyethylene 19. The metallic tape corresponds to a steel reinforcement of at least 0.15 mm. of thickness and with both sides covered with a plastic material of the second cover. Steel corrugations are applied to this steel tape, to the length of it and it is applied longitudinally on the first cover covering it and in an overlap of the tape on itself at least 3 mm. minimum.

This width must be calculated with respect to the outer diameter of the first cover and taking into account the virtual increase of the same due to the corrugations of the steel tape, the corrugations of the mentioned one! Steel tape are made in order to obtain the appropriate flexibility of the optical cable that is described.

The improvements to the optical cable described herein, are characterized by containing one or more optical fibers 11, within one or more loose tubes 12. The inner diameter of the tube 12 is calculated based on the parameter called total range of motion that establishes a relationship between the space of free movement that has one or several fibers and the angle at which the tubes are deposited around the central reinforcement and is equal to the margin to tension + margin to compression. The outside diameter is determined based on the mechanical stress that the tube has to withstand and according to the type of material used in its manufacture. The materials may be elastomeric thermoplastic polymers or polyamides, and any of the ellcj > s may or may not contain fluorine or chlorine to prevent them from spreading the flame or to make them resistant to certain solvents.

The manufacture of the loose tubes 12 is carried out with an extruder machine by the process known as tubula do. Each fiber filament 11 is controlled by means of a motorized uncoiler with electronic feedback so as to maintain a uniform tension during the tubing process. The fiber or set of fibers reaches the extrusion head where they are guided to the interior by means of a capillary tube of two sections of different diameter that are divided by a filler injector, the difference between the diameters of the capillary tube causes a pressure in the direction of the line direction that prevents the filling material gel 13, 14 from having turbulences that affect the process. The capillary tube reaches the outlet of the extrusion guide where it penetrates the interior of the tube, depositing the optical fibers and the filling material inside the tube. Finally the tube passes through water channels for its cooling before being rolled.

The filling material is a hydrophobic flooding glue suitable to prevent the entry of moisture into the tubes. Said gel is thixotropic and maintains an adequate viscosity to avoid draining or inadequate hardening in the range of operating temperatures for which the cable was designed, values ranging from -40 to 85 ° C. This material must be compatible with the materials with which it has contact during the operation of the cable. The filling material is pumped from its original container to a degassing chamber where it is released from the air that for some reason has been trapped in the material. From this point the material is pumped to the extrusion head by means of a gear pump at a constant pressure. The final part of the path is constituted by a heating coil in order to guarantee a homogeneous temperature of the material upon entering the extrusion head. ' Due to the thermomechanical characteristics of the (plastics it is important to control the shrinkage that the tube may have during its manufacturing process, in this way it will keep under control the length of optical fiber deposited in the tube, at this length it will it knows it as an excess of fiber, a parameter that is of vital importance to guarantee the good operation of the cable within the conditions for which it was designed The present invention contemplates three different means to achieve said control. Stretch index of the tube, and is based on a proportional ratio between the final dimensions of the tube and the dimensions of the tools used for its manufacture.The second means is the control of the tension of unwinding of the optical fiber, of the tens tube windings and cooling channel temperatures, and lastly, the most important is a pulley located at the n the first part of the cooling channel that compensates for the variations that the process may have - due to the sliding of the point where the fibers are inserted into the tube and which are of the order of tenths of a millimeter. This

Claims (7)

The pulley is made as a conglomeration pulley and can be static or dynamic according to the physical characteristics of the cooling channel. The tubes are wired around a central reinforcement 15 of low weight, high resistance to tension and little mechanical memory, characteristics that make the cable have a better performance in its operation. The central reinforcement can be coated on its periphery with some type of plastic in order to increase its diameter if the design requires it. The use of metallic reinforcements is not contemplated due to the high mechanical memory they offer. Having described the invention is considered a novelty and therefore the content is claimed in the following: R E I V I N D I C A C I O N E S '

1. An improved fiber optic cable for telecommunications which comprises as cabling elements a plurality of loose tubes, arranged longitudinally and surrounding; to a pultruded central reinforcement, to form a tubular assembly characterized in that said assembly is applied to it; a layer of aramid fiber or glass fibers to obtain a greater tension during the installation of the cable; immediately includes one or more plastic covers arranged longitudinally to support one or more metallic ribbons • corrugated that are incorporated peripherally to the set; and a plastic final cover, the loose tubes containing one or more optical fibers with freedom of movement and a gel filling both in the inner and outer sections of the holded tubes. '

2. An improved fiber optic cable, according to clause 1, characterized in that the pulsed central reinforcement is a light element with low mechanical memory.

3. An optical fiber cable improved in accordance with clause 1, characterized in that the loose tubes are wired with respect to the central reinforcement in unidirectional or bidirectional helical form (sz).

4. An improved fiber optic cable, in accordance with clauses 1 and 2, characterized in that the central reinforcement constitutes a tensile element when the cable is subjected to tension forces caused by the installation and a balancing element of expansion forces and contraction caused by the operation of the cable in the limits of its thermal range.

5. An improved fiber optic cable, characterized in that the loose tubes are extruded by tubular and the fiber optic filaments are controlled by a motorized unwinder with electronic feedback to maintain a uniform tension during the tubing process, the fiber being -set of fibers guided from the extrusion head to the interior by means of a capillary tube of two sections of diameter which are divided by an injector of filling material; the difference between the diameters of the capillary tube causes a pressure in the direction of the line direction which prevents the filling material from having turbulences that affect the process.

6. An optical fiber cable improved in accordance with clause 5, characterized in that the capillary tube reaches the exit of the extrusion guide where it penetrates to the interior of the tube depositing the optical fibers and the filling material inside the tube, and later to cooling in water channels.

7. An improved fiber optic cable according to clause 5, characterized in that the shrinkage of the loose tube is compensated with an excess length of optical fiber and controlled according to the index of stretching of the tube; uncoiling strains of the fiber, rolling tensions of the tube and cooling temperatures; and a static or dynamic congruence pulley arranged in the cooling channel to compensate for the variations of the process due to the sliding of the point where the fibers are inserted into the tube and which are of the order of tenths of a millimeter.