Buffered optical fiber and telecommunications cable

[0001] The invention relates to the field of telecommunication cables made of optical fibers, and more particularly so-called buffered fiber cables in which each optical fiber is buffered.

[0002] Buffered fiber cables are known as "buffered optical fiber cables" and have been described in particular in US-A3,980,390 and US-A-4,629,286.

[0003] In a manner known per se, the optical fiber comprises a central core, with the function of transmitting and optionally amplifying the optical signal, the optical cladding, with the function of limiting the optical signal in the core. The fiber also contains a protective coating consisting of a polymer material capable of cross-linking, which provides mechanical protection and sealing for the optical fiber. The optical fiber, with its coating, has standardized dimensions to allow optical coupling with other fibers and / or optical module connectors. Usually, single-mode fiber has a normalized diameter of 125 pm for optical conductor and 250 pm with coating. In addition to the coating, the buffered optical fiber contains a protective buffer surrounding the coated fiber. This protective buffer is located outside the fiber coating and is not comparable to the optical coating of the fiber that surrounds the middle core. The external protective buffer may consist of thermoplastic material and allow the fiber outer diameter to be increased to a normalized value of 900 pm.

[0004] Buffered fiber cables can be used in indoor telecommunications networks. Individual access to each fiber should be possible quickly and easily when spreading in a given building. To this end, operators make a diversion on the telecommunications cable; a hole is made in the cable and one or more fibers are collected to provide the optical system with a signal. Due to the increased diameter of 900 pm of buffered fiber, handling of this redirected fiber can be facilitated and can be directly connected to certain optical modules.

[0005] There are cables with closely buffered fibers known as "closely."

"Buffered fibers" in which the protective buffer adheres strongly to the fiber coating. This structure is strong and remains stable over the entire temperature range of using the cable, i.e. usually from -40 ° C to + 70 ° C. However, with this structure, you cannot access 250 pm fiber on more than a few centimeters. In fact, when the buffer is removed, due to its strong adhesion to the coating, the fiber coating also breaks, leaving the optical conductor exposed. This can be a disadvantage when freezing the unbuffered fibers in, for example, a housing.

[0006] There are also cables with semi-tight buffered fibers, known as "semi-tight buffered fibers", in which the protective buffer is separated from the fiber coating, for example, by air or fill gel. With this structure, the protective buffer can be removed without damaging the fiber coating, but the structure is not stable in the temperature range of using the cable. In fact, the thermoplastic of the protective buffer may be deformed due to temperature changes, which introduces the axial stress of the buffered fiber and increases damping. The shrinkage of the protective buffer under the influence of a temperature drop can thus introduce a "piston effect" at the end of the redirected fiber, which will make any operation of connecting to the optical module delicate.

[0007] Detaching the protection buffer and the fiber coating is also a problem during the diversion operation. To redirect the buffered fiber, the operator pulls the fiber through the redirection window; this tensioning force is applied to the protective buffer, which can be flexibly extended and cause a shift between the length of the redirected optical fiber in relation to the length of the protective buffer being drawn. This shift also causes attenuation of the optical signal transmitted by the fiber.

[0008] Therefore, efforts have been made to make buffered optical fibers with a protective buffer that will be sufficiently coupled to the fiber coating to avoid displacement, but which can be easily removed without damaging the coating so as to gain access to 250 μιτι of the fiber on at least one subway.

[0009] Document US-A-5,181,268 describes a buffered optical fiber comprising an intermediate layer between a coating of 250 μιη fiber and 900 μιη protective buffer.

EP 2 232 318 Β1

Thanks to the intermediate layer, friction can be reduced between the protective buffer and the coating to facilitate removal of the protective buffer without damaging the coating. This document proposes an intermediate layer consisting of a solid lubricant and a binder. The lubricant may be TEFLON and the binder may be an acrylic polymer.

[0010] EP 0 838 703 discloses a buffered optical fiber comprising an interface between the optical fiber coating and the protective buffer.

[0011] EP 0 410 622 discloses a buffered optical fiber containing a separation material between the optical fiber coating and the protective buffer.

[0012] EP 0 287 016 discloses a buffered optical fiber comprising an intermediate layer between the optical fiber coating and the protective buffer.

[0013] US 2003/185529 discloses a buffered optical fiber comprising an intermediate layer between the optical fiber coating and the protective buffer.

[0014] The intermediate layer proposed in US-A-5,181,268 cannot be extruded in parallel with the protective buffer, but requires a special application. In particular, it is necessary for the fiber to be coated with an intermediate layer that has passed through the drying oven before adding the outer protective layer. The intermediate layer of US-A-5,181,268 complicates the method of making a cable and increases its price. In addition, TEFLON contains fluorine (polytetraflouoroethylene) and is therefore not halogen-free. Currently, some legislation, in particular European legislation, imposes the use of halogen-free plastics only in indoor buildings. Therefore, the cable from US-A-5,181,268 would not be suitable for building wiring according to these regulations.

[0015] Document EP-A-0 690 033 also describes a buffered optical fiber comprising an intermediate layer between a coating of 250 pm fiber and 900 pm protective buffer. This document indicates that the intermediate layer of US-A-5,181,268 does not adhere sufficiently to the fiber coating, does not allow for linear production at high speed and is not sufficiently uniform. To solve these identified problems, EP-A-0 690 033 proposes a crosslinked intermediate layer containing ultra-high density polyethylene (UNMWPE) or TEFLON

2322 232 318 Β1 mixed with a binder capable of photocrosslinking, such as a urethane polymer.

[0016] Document US-A-6,775,443 also describes a buffered optical fiber comprising an intermediate layer between a coating of 250 pm fiber and 900 pm protective buffer. This document proposes a crosslinked intermediate layer containing a urethaneacrylate matrix containing oligomers, monomers, photoinitiator and antioxidant in combination with a liquid reaction release substance such as liquid silicone.

[0017] Intermediate layers proposed in documents EP-A-0 690 033 and US-A6,775,443 should be crosslinked; therefore, their passage under W lamps should be foreseen, and the use of an intermediate layer cannot be easily combined with the extrusion of an external protective buffer. In addition, materials capable of photocrosslinking are relatively expensive.

[0018] Therefore, there is a need for a buffered optical fiber comprising an intermediate layer that can be applied without slowing the fiber production method and having a limited cost. The intermediate layer should guarantee adequate coupling between the fiber coating and the external protective buffer to avoid displacement of the buffer relative to the fiber, without applying mechanical stress to the fiber, and should allow quick and easy removal of the protective buffer without damaging the fiber coating.

[0019] To this end, the invention proposes the use of a hot melt sealing material with the possibility of peeling to make an intermediate layer. This material does not require any drying or cross-linking and can also be applied as an external buffer.

[0020] More specifically, the invention proposes buffered optical fiber comprising:

middle core surrounded by an optical mantle; a coating surrounding the optical cladding; protective buffer surrounding the coating;

an intermediate layer between the coating and the protective buffer, wherein

EP 2 232 318 Β1 said intermediate layer is made of a detachable thermofusible sealing material, characterized in that the thermofusible material is a thermoplastic material that becomes fluid under the influence of heat, and the detachable sealing material is a temporary protective material that can be remove, leaving no traces, so that when the protective buffer and intermediate layer are removed, the optical fiber coating remains substantially intact.

[0021] According to embodiments, the fiber of the invention may further have one or more of the following features:

the intermediate layer material has a softening point above + 70 ° C; the intermediate layer material has a glass transition temperature below -40 ° C; the intermediate layer is translucent;

the intermediate layer has a thickness between 15 μπι and 35 pm;

the intermediate layer material is a thermoplastic with a flexible gel consistency in the temperature range between -40 ° C and + 70 ° C;

the intermediate layer material contains synthetic hydrocarbon polymers;

the protective buffer material is selected from polyethylene terephthalate (PBT), nucleated polyethylene terephthalate, low-shrink polyethylene terephthalate, polyamide 12 (PA12), amorphous polyamide 12, polyamide 11, polyvinyl chloride (PVC), nylon, polyethylene (PE), non-halogenated (HFFR), urethane polymer, polyester or mixtures thereof.

[0022] The invention relates to telecommunications cables comprising a plurality of buffered optical fibers according to the present invention. The invention further relates to a method of producing buffered optical fiber comprising the following steps:

providing coated optical fiber;

coextrusion on the coated fiber intermediate layer and external protective buffer;

2322 232 318 Β1, said interlayer being made of a detachable thermofusible sealing material, characterized by the fact that the thermofusible material is a thermoplastic material that becomes fluid under the influence of heat, and the detachable sealing material is a temporary protective material that can be removed without leaving any traces, so that when the protective buffer (15) and intermediate layer (14) are removed, the coating (15) of the optical fiber (10) remains substantially intact.

[0023] In one embodiment, the step of providing the coated optical fiber is preferably performed by drawing the optical fiber preform so as to form a central core and optical cladding, and by applying a coating surrounding the optical cladding.

[0024] According to one embodiment, the intermediate layer extrusion step was performed in parallel with the protection buffer extrusion. The extrusion step can be carried out at a temperature comprised between 130 ° C and 160 ° C.

[0025] Other features and advantages of the invention will become apparent upon reading the following description of embodiments of the invention given by way of example and with reference to the accompanying drawings in which;

Fig. 1 is a cross-sectional view of a buffered optical fiber according to the invention;

Fig. 2 is a buffered optical fiber cable.

[0026] Fig. 1 shows a buffered optical fiber according to the invention. The buffered optical fiber 10 comprises a central core 11 surrounded by an optical cladding 12 and a coating 13. The central core 10 of single-mode optical fiber has a normalized diameter of 8 to 9 pm, and the optical fiber with its coating 13 has a normalized outer diameter of 250 pm. Fig. 1 is a diagram and is scaled. The fiber according to the invention is buffered, i.e. it additionally contains a protective buffer 15 surrounding the coating 13. In one embodiment, the outer diameter of the fiber is increased to a normalized value of 900 pm.

[0027] The fiber coating 13 typically contains one or more layers of acrylic resins

EP 2 232 318 Β1 capable of photocrosslinking. The coating 13 may be colored to facilitate the location of the fibers in the cable.

[0028] The protective buffer 15, known as the "buffer", is usually made of thermoplastic or urethaneacrylate. In particular, it is known how to make a protective buffer 15 made of plastic selected from polyethylene terephthalate (PBT), nucleated polyethylene terephthalate, low-shrinkable polyethylene terephthalate, polyamide 12 (PA12), amorphous polyamide 12, polyamide 11, polyvinyl chloride (PVC), nylon, polyethylene PE), halogen-free flame retardants (HFRR), urethane polymer, polyester or a mixture thereof.

[0029] The fiber according to the invention further comprises an intermediate layer 14 between the optical fiber coating 13 and the outer protective buffer 15. According to the invention, this intermediate layer 14 is made of a thermofusible sealing material with the possibility of peeling. By thermofusible material is meant a thermoplastic material that becomes liquid under the influence of heat; this material is generally referred to as "hot melting". A seal material that can be peeled off is a temporary protective material that can be removed without leaving any residue; this material is generally referred to as "peelable". When the peelable sealing material is removed, the optical fiber coating remains substantially intact, i.e., intact.

[0030] Intermediate layer 14 may be formed of a thermoplastic gel, such as, for example, a thermoplastic gel formed from synthetic hydrocarbon polymers. Such material is in particular sold by Henkel® under the name Macroplast CF 405. Such material has the consistency of a flexible gel over the entire operating temperature range of the cable, i.e. usually from -40 ° C to + 70 ° C. The elasticity of the intermediate layer material reduces mechanical stress, while guaranteeing adequate coupling between the fiber coating and the external protective buffer.

[0031] The use of a thermoplastic material as defined above allows the intermediate layer and outer protective buffer to be extruded at the same manufacturing stage, for example at the same time. Therefore, the introduction of intermediate layer 14 into buffered fiber requires only

EP 2 232 318 Β1 melter and injector, and does not require any additional manufacturing step. The cost of the thermofusible sealing material with the option of peeling is also lower than the cost of the cross-linkable material. Therefore, the cost of producing the buffered fiber according to the invention is reduced compared to the solutions described in the prior art.

[0032] The material of the intermediate layer 14 has a softening point above + 70 ° C, i.e. the maximum temperature range for using buffered fiber. The material from intermediate layer 14 also has a glass transition temperature below 40 ° C, i.e. below the minimum temperature range for using buffered fiber. Therefore, the material of the intermediate layer 14 remains stable throughout the entire temperature range for using the optical fibers of the invention. By way of example, the softening point of macroplast CF 405 is around + 97 ° C and the glass transition temperature of macroplast CF 405 is -80 ° C.

[0033] The intermediate fiber layer 14 according to the invention is an interface between the fiber coating 13 and the external protective buffer 15. The thickness of the intermediate layer 14 may be between 15 pm and 35 pm. The thickness of the intermediate layer should not be too large, so as not to reduce too much the thickness of the outer protective buffer 15, which has a normalized outer diameter. Too much reduction in the outer protective buffer thickness could have detrimental effects with loss of mechanical strength of the buffered fiber. However, the thickness of the intermediate layer 14 should be sufficient to provide the expected coupling between the external protective buffer and the optical fiber.

[0034] The material selected for the intermediate layer 14 has a flexible consistency, so that it provides adequate coupling between the protective buffer 15 and the optical fiber without causing any stress in the fiber. For example, the hardness of the Macruplast CF 405 gel was assessed by so-called cone penetration measurement. The equipment used in the measurement is that described in the French standard NFT60119. For an application time of 5 seconds, the measured transmittances were 70 tenths at 20 ° C, 35 tenths at -40 ° C, and 140 tenths at 70 ° C. Thus, in the operating temperature range of the cable with optical fibers (40 / + 70 ° C), the gel from the intermediate layer retains its elastic consistency, so that

ΕΡ2 232 318 Β1 causes no stress in the fiber, especially at low temperatures.

[0035] The material selected for this intermediate layer 14 can also ensure that the protective buffer 15 is properly detached without damaging the fiber coating 13. Applicant has conducted tests of an intermediate layer 14 with a thickness of 25 pm made of Macroplast CF 405 from Henkel® and an external protective buffer of PA12. Fragments of the protective buffer 100 mm long were discovered, revealing the coating of the actual fiber without any damage. Thus, in less than one minute, more than one meter of fiber was buffered without damaging the 250 pm optical fiber.

[0036] The material from the intermediate layer 14 is further compatible with any material that can be used to form the external protective buffer 15. Polyamide 12 (PA12) can advantageously be used to form protective buffer 15 in combination with Macroplast CF 405 for intermediate layer 14, because both of these materials are translucent and the color of the fiber coating 13 is then visible through protective buffer 15; it is not necessary to stain the protection buffer 15 to support the identification of the fibers in the cable.

[0037] Fig. 2 is a cross-sectional view of the telecommunications cable 20 containing buffered optical fibers 10. In a manner known per se, the telecommunications cable has a central core 21 receiving optical fibers. Optical fibers can be free or grouped into modules or micromodules, and can be buffered or not. In fig. 2 the optical fibers 10 are buffered and free with an intermediate layer between the fiber coating and the external protective buffer, this intermediate layer being made of a thermofusible sealing material with the possibility of peeling.

[0038] The cable of Fig. 2 also includes a buffer 22 surrounding the central core 21. The buffer 22 of the cable 20 may be of a polymer material, generally a halogen-free flame retardant (HFFR) material. Cable buffer 22 contains reinforcing components 23 for limiting cable deformation due to traction forces, for example when laying cable in conduit, limiting cable axial deformation during shrinkage and expansion, when the latter is subject to large temperature changes, compensating for compressive and expansion forces caused by the buffer 22.

EP 2 232 318 Β1 [0039] The telecommunications cable according to the invention is particularly well suited, for example, for distributing an optical telecommunications network in a building. The redirection of the fibers to the optical system from the cable of Fig. 2 is carried out as follows: in the cable buffer 22 two notches are made to form the first hole through which the fiber 10 is cut, and the second hole through which the cut fiber 10 is drawn in for redirection. The fiber diversion is preferably carried out over 20 meters. Therefore, the filling level of the cable should not be too high.

[0040] With the intermediate layer 14 of buffered fiber 10 according to the invention, a displacement of the fiber relative to the outer protective buffer 15, through which mainly traction force is exerted, can be avoided. When the fiber is redirected, the intention is to gain access to 250 pm of fiber. To this end, the fiber 10 is buffered, i.e. the external protective buffer 15 is broken. With the help of the intermediate layer 14, this operation of breaking the protective buffer 15 can be performed over a length of over 1 meter without any damage to the fiber. 250 pm fiber can then be stored in an optical enclosure with less space required than for 900 pm buffered fiber.

[0041] Furthermore, the fiber of the invention can be made using available equipment and without including an additional step. In the perse known method, an optical fiber is made by pulling the fiber from an optical fiber preform that defines the middle core and optical fiber jacket. The coating, generally colored resin capable of photocrosslinking, is applied in accordance with the stretched fiber. The protective buffer 15 can be extruded around the fiber immediately after the optical fiber is drawn, i.e. linearly. In another embodiment, buffer 15 can be extruded onto a fiber that is unwound from a drum, i.e. non-linearly. According to the invention, the intermediate layer 14 of detachable thermofusible sealing material is extruded in parallel with the protective buffer 15. The intermediate layer extrusion operation can be carried out at a temperature comprised between 130 ° C and 160 ° C, preferably around 140 ° C. No additional crosslinking or drying step is necessary. Thus, the cost of producing the fiber according to the invention is limited.

[0042] Of course, the present invention is not limited to the embodiments

EP 2 232 318 opisanych1 described by way of example; in particular, the invention is not limited to the values ​​of the diameters indicated. New standards not yet adopted may impose other fiber diameter values ​​or protective buffer diameter values ​​without excluding the use of the invention, but the invention may be used for other optical fiber that does not meet the criteria of the standards. Furthermore, the materials listed for the coating and external protective buffer may differ from those mentioned by way of example in the description above.

EP 2 232 318 Β1