WO2006062282A1

WO2006062282A1 - Method of manufacturing air blown optical fiber unit for preventing of deterioration of characteristics in coating layer and gas chamber used therein

Info

Publication number: WO2006062282A1
Application number: PCT/KR2005/002077
Authority: WO
Inventors: Chan-Yong Park
Original assignee: Ls Cable Ltd.
Priority date: 2004-12-08
Filing date: 2005-06-30
Publication date: 2006-06-15
Also published as: KR20060064371A; GB2434924B; GB0709346D0; CN101073026A; KR100654012B1; GB2434924A; JP2008523440A

Abstract

Disclosed is a method of manufacturing an air blown optical fiber unit for prevention of characteristic deterioration of a coating layer, and a gas chamber used therein. This method includes coating a first coating resin on a surface of an optical fiber bundle; introducing the optical fiber bundle coated with the first coating resin into a first curing chamber under inert gas environment and curing the first coating resin to form a first coating layer; coating a second coating resin on a surface of the first coating layer; attaching beads to a surface of the second coating layer; and introducing the optical fiber bundle having the beads attached thereto into a second curing chamber under inert gas environment and curing the second coating resin to form a second coating layer. This method may improve stiffness of the coating layer by intercepting introduction of impurities during the coating layer forming process.

Description

METHOD OF MANUFACTURING AIR BLOWN OPTICAL

FIBER UNIT FOR PREVENTING OF DETERIORATION OF

CHARACTERISTICS IN COATING LAYER AND GAS

CHAMBER USED THEREIN Technical Field

[1] The present invention relates to a method of manufacturing an air blown optical fiber unit and a gas chamber used therein, and more particularly to a method of manufacturing an air blown optical fiber unit for prevention of characteristic deterioration of a coating layer, and a gas chamber used therein. Background Art

[2] For installation of optical fibers, a method of binding or twisting several optical fibers into a cable, and then installing this cable has been mainly used. In this cable installation method, optical fibers much more than required at the point of installation are generally installed in advance with expectation of future demands.

[3] However, since more various kinds of optical fibers are required according to the trend of new communication environments and there have been developed high performance communication systems suitably coping with communication capacity even in restricted optical fiber installation environments, it cannot be considered desirable that a large amount of optical fibers are installed in advance just with expectation of future demands. In particular, in aspect of a user terminal, namely an access network or a premise wiring, a mode of an optical fiber or cable in future cannot be decided at the present point of time. Thus, if a large amount of optical fibers are installed in advance with incurring much expense, there may be a waste of money if a mode of an optical fiber or cable is changed in future.

[4] In order to solve the above problems, a method for installing an optical fiber unit having several optical fiber strands collected therein by air pressure is widely used. This air blown installation method was firstly proposed by British Telecom Co. (see US 4,691,896) in 1980. In this air blown installation method, a polymer installation tube, called a micro tube or duct, having specific constitution and sectional shape is installed at an optical fiber installation spot in advance, and then an air blown optical fiber unit (hereinafter, referred to just as 'an optical fiber unit') is inserted into the micro tube or duct as much as required by air pressure. If optical fibers are installed using the above optical fiber installation method, many advantages are ensured, namely easy installation and removal of optical fibers, reduced costs for initial in- stallation, and easy improvement of performance in future.

[5] FIG. 1 is a schematic view showing an optical fiber unit installation device used in the above air blown installation method. Referring to FIG. 1, the installation device successively inserts an optical fiber unit 1 from an optical fiber unit supplier 2 into an installation tube 4 connected to an outlet C of a blowing head 5 by using a driving roller 3 and a pressing means 6, and at the same time blows compressed air toward the outlet C of the blowing head 5 by using the pressing means 6. Then, the compressed air flows at a fast rate toward the outlet C, and accordingly the optical fiber unit 1 introduced into the blowing head 5 is installed in the installation tube 4 by means of a fluid drag force of the compressed air.

[6] In order to ensure desirable installation of the optical fiber unit 1 in the air blown installation method, the fluid drag force of the compressed air should be great.

[7] The fluid drag force F may

[8]

[9] Equation 1

[10]

[11] (P: compressed air pressure, R : inner diameter of the installation tube, R : outer diameter of the optical fiber unit, L: length of the installation tube)

[12]

[13] In the Equation 1, the inner diameter R of the installation tube and the outer diameter R of the optical fiber unit are already defined in standards. Thus, in order to maximize the fluid drag force F, it is preferred to form irregularity on the surface of the optical fiber unit for increasing a contact area between the compressed air and the optical fiber unit.

[14] US 5,042,907, US 5,555,335, US 5,441,813 and US 6,341,188 disclose various methods for forming irregularities on the surface of an optical fiber.

[15] US 5,042,907 and US 5,555,335 respectively disclose a bead stirring method for coating glass beads previously stirred in a coating resin onto an outer surface of an optical fiber, and a bead attachment method for blowing and attaching glass beads on a coating layer using static elasticity before the coating layer of the optical fiber unit is cured.

[16] In addition, US 5,441,813 and US 6,341,188 disclose a method for forming concave dimples in a surface of an optical fiber unit by using foaming polymer material, and a method for forming irregularities on a surface of an optical fiber unit by winding a fiber made of special material around the coating layer of the optical fiber unit. [17] In the above conventional techniques except for the method using a foaming polymer resin, a radiation curable polymer resin added by an photo initiator is used as a coating resin, so the coating resin is cured using ultraviolet ray, infrared ray or electromagnetic wave to form a coating layer. The coating layer formed as mentioned above needs special surface treatment so as to protect an optical fiber from an external impact and also maximize a fluid drag force of an compressed air during air blown installation, so the curing process of the coating resin is very important together with selection of suitable material.

[18] However, impurities such as moisture (OH) or oxygen (O ) in the air may be introduced into a curing chamber during the coating resin curing process, and these introduced impurities come in contact with the surface of the coating resin and deteriorate properties of the coating layer including its mechanical features. The coating resin is a polymer material causing radical chain polymerization, so the introduced impurities such as moisture (OH) or oxygen (O ) may cause chemical reaction between radicals and impurities, resulting in exhaustion of radicals and decrease of molecular weight of the coating layer, which is a factor of the deterioration of properties of the coating layer.

[19] The optical fiber unit manufactured under the condition containing impurities as mentioned above gives deteriorated properties of the coating layer. Thus, if this optical fiber unit is contacted with standing water for a long time due to the environmental change in an installation tube after the air blown installation, moisture may be absorbed in the coating layer due to the low molecular weight to increase optical losses, and also the coating layer may be easily broken even by a weak impact. Disclosure of Invention

Technical Problem

[20] The present invention is designed to solve the above problems, and therefore it is an object of the invention to provide a method of manufacturing an optical fiber unit, which prevents characteristic deterioration of a coating layer by intercepting reaction between a coating resin and impurities during a coating layer forming process of the optical fiber unit, and a gas chamber used therein. Technical Solution

[21] In order to accomplish the above object, the present invention provides a method of manufacturing an air blown optical fiber unit, which includes (a) coating a first coating resin on a surface of an optical fiber bundle; (b) introducing the optical fiber bundle coated with the first coating resin into a first curing chamber under an inert gas environment and curing the first coating resin to form a first coating layer; (c) coating a second coating resin on a surface of the first coating layer; (d) attaching beads to a surface of the second coating layer; and (e) introducing the optical fiber bundle, to which the beads are attached, into a second curing chamber under an inert gas environment and curing the second coating resin to form a second coating layer.

[22] Here, the method preferably includes, before the step (a), passing the optical fiber bundle through a gas chamber under an inert gas environment.

[23] In addition, the method preferably further includes, before the step (c), passing the optical fiber bundle, on which the first coating layer is formed, through a gas chamber under an inert gas environment.

[24] In addition, in the step (d), the beads are preferably attached on the surface of the second coating resin with passing the optical fiber bundle through a gas chamber under an inert gas environment.

[25] Meanwhile, the inert gas preferably flows in a direction opposite to an introduction direction of the optical fiber that is introduced into the chamber.

[26] In another aspect of the invention, there is also provided a gas chamber used for a process of manufacturing an optical fiber unit, which includes a chamber having an optical fiber input hole and an optical fiber output hole so that an optical fiber (including an optical fiber bundle) or an optical fiber having a coating layer is capable of passing therethrough; a nozzle installed to the optical fiber input hole to inject gas in a direction opposite to an introduction direction of the optical fiber; and a gas injection passage installed to one side of the chamber to communicate with the nozzle for supplying inert gas into the chamber.

Brief Description of the Drawings

[27] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings:

[28] FIG. 1 shows an optical fiber unit installation apparatus used for air blown installation of an optical fiber unit;

[29] FIG. 2 is a perspective view showing a general air blown optical fiber unit;

[30] FIG. 3 shows an optical fiber unit passing through a chamber filled with inert gas according to the present invention; and

[31] FIG. 4 is a flowchart illustrating a method of manufacturing an optical fiber unit according to the present invention. Best Mode for Carrying Out the Invention

[32] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Prior to the description, it should be understood that the terms used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present invention on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the description proposed herein is just a preferable example for the purpose of illustrations only, not intended to limit the scope of the invention, so it should be understood that other equivalents and modifications could be made thereto without departing from the spirit and scope of the invention.

[33] FIG. 2 is a perspective view showing an air blown optical fiber unit. Referring to

FIG. 2, the optical fiber unit 10 includes at least one optical fiber 11, a first coating layer 12 surrounding the optical fiber 11, and a second coating layer 13 surrounding the first coating layer 12 and to which beads 14 are attached.

[34] The optical fiber 11 is a single-mode or multi-mode optical fiber, which has a core layer and a clad layer made of quartz. The optical fiber unit 10 may have a single core or multiple cores as shown in FIG. 2.

[35] The first coating layer 12 directly surrounds the optical fiber 11. The first coating layer 12 is made of radiation curable polymer resin that is cured by radiation, and preferably made of radiation curable acrylate.

[36] The second coating layer 13 surrounds the first coating layer 12. The second coating layer 13 is made of radiation curable polymer resin similarly to the first coating layer 12, but preferably made of radiation curable acrylate having higher Young's modulus than the first coating layer 12 so as to protect the optical fiber 11 against external impacts and keep stiffness of the optical fiber unit during air blown installation. In addition, beads 14 are attached on the surface of the second coating layer 13 so as to improve a fluid drag force of the compressed air during air blown installation.

[37] FIG. 4 is a flowchart illustrating a method of manufacturing the optical fiber unit configured as above according to the present invention, and FIG. 3 shows an optical fiber unit passing through a chamber filled with inert gas according to the present invention. Referring to FIGs. 3 and 4, a single-core or multi-core optical fiber bundle (hereinafter, referred to as an optical fiber) passes through a first chamber filled with inert gas (SlO). The first gas chamber filled with inert gas includes a chamber 21 having an optical fiber input hole and an optical fiber output hole so that the optical fiber 11 may pass through it, a nozzle 23 installed to the optical fiber input hole to inject gas in a direction opposite to an introduction direction of the optical fiber, and a gas injection passage 22 installed to one side of the chamber 21 to communicate with the nozzle 23 for supplying inert gas into the chamber 21, as shown in FIG. 3.

[38] The nozzle 23 has a ring shape in which a plurality of injection holes are formed.

The nozzle 23 passes the optical fiber through a hollow at its center with injecting inert gas in a direction opposite to an introduction direction of the optical fiber through the plurality of injection holes. The gas injected by the nozzle 23 is supplied into the chamber 21 through the gas injection passage 22 installed to one side of the chamber 21. The inert gas may preferably employ nitrogen (N ) or argon (Ar), but not limitedly.

[39] If the optical fiber is introduced into the first gas chamber configured as mentioned above, impurities such as moisture (OH) and oxygen (O ) penetrated into the surface of the optical fiber from the air before the optical fiber is introduced into the first gas chamber are removed by means of the inert gas flowing in a direction opposite to the introduction direction of the optical fiber. After the optical fiber passes through the first gas chamber, the optical fiber passes through a dies of a coating device filled with a first coating resin so that the first coating resin is coated on the surface of the optical fiber (Sl 1). After the first coating resin is coated, the optical fiber is introduced into a first curing chamber and ultraviolet rays are irradiated on the surface of the optical fiber. Then, the first coating resin is cured (S 12), and the first coating layer 12 is formed on the surface of the optical fiber (S 13).

[40] Meanwhile, the first curing chamber is a chamber in which inert gas flows in a direction opposite to the introduction direction of the optical fiber, similarly to the first gas chamber mentioned above, and the first curing chamber is configured identically to the first gas chamber except for being provided with an ultraviolet lamp and a reflection mirror, not shown, in the chamber 21 for curing.

[41] If the optical fiber coated with the first coating resin is introduced into the first curing chamber, introduction of impurities from the external air into the first curing chamber is intercepted by means of the inert gas flowing in a direction opposite to the introduction direction of the optical fiber. Thus, the first coating layer 12 formed under the impurity-free environment does not show extinction of radicals, so optical and mechanical characteristics of the first coating layer 12 are not deteriorated.

[42] After the first coating layer 12 is formed, the optical fiber is introduced into a second gas chamber filled with inert gas so as to remove impurities such as moisture (OH) and oxygen (O ), which are penetrated into the surface of the optical fiber from the air before the optical fiber is introduced into the second gas chamber (S 14). Similarly to the above first gas chamber, the second gas chamber is a chamber in which inert gas flows in a direction opposite to the introduction direction of the optical fiber, and it removes impurities on the surface of the first coating layer 12. After that, the optical fiber passes through a dies of a coating device filled with a second coating resin so that the second coating resin is coated on the surface of the first coating layer 12 (S15).

[43] After the second coating resin is coated, the optical fiber is introduced into a bead attachment chamber so as to attach the beads 14 to the surface of the second coating resin. The beads 14 are preferably spherical glass beads with smooth surfaces so as to decrease friction with an installation tube during the air blown installation.

[44] The beads 14 are attached to the surface of the second coating layer 13 by means of bead blowing. That is to say, turbulence is generated in the bead attachment chamber filled with the beads 14 to attach the beads 14 to the surface of the second coating resin (S 16). However, the turbulence may make impurities be easily attached to the surface of the second coating resin together with the beads 14.

[45] Thus, the bead attachment chamber is also preferably configured so that inert gas flows therein in a direction opposite to the introduction direction of the optical fiber, similarly to the above chambers, which prevents impurities from being introduced into the bead attachment chamber and attached to the surface of the second coating resin.

[46] After the beads 14 are attached, the optical fiber is introduced into a second curing chamber to cure the second coating resin (S 17). The second curing chamber allows inert gas to flow in a direction opposite to the introduction direction of the optical fiber, similarly to the first curing chamber, so that the coating resin may be cured without introduction of impurities.

[47] Hereinafter, characteristics of the optical fiber unit manufactured according to the preferred embodiment of the present invention will be compared with those of an optical fiber unit manufactured according to the prior art. Mode for the Invention

[48] Embodiment

[49] Aggregated 4-core single-mode optical fibers passed through the first gas chamber in which nitrogen gas flows in a direction opposite to an advancing direction of the optical fibers, thereby removing impurities on the surface of the optical fibers. And then, the optical fibers passed through a dies of a coating device filled with the first coating resin so that the first coating resin is coated on the surface of the optical fibers. The first coating resin was radiation curable acrylate. After that, the optical fibers were introduced into the first curing chamber in which nitrogen gas flows in a direction opposite to an introduction direction of the optical fibers, and ultraviolet rays are irradiated thereto to form a first coating layer. After that, the optical fibers passed through the second gas chamber in which nitrogen gas flows in a direction opposite to an advancing direction of the optical fibers to remove impurities on the surface of the optical fibers, and then the optical fibers passed through a dies of a coating device filled with the second coating resin to coat the second coating resin on the surface of the optical fibers. The second coating resin was radiation curable acrylate having higher Young's modulus than the first coating resin. After that, the optical fibers were introduced into the beat attachment chamber so that beads were attached thereto by bead blowing, and then the optical fibers were introduced into the second curing chamber to cure the second coating resin. The bead attachment chamber and the second curing chamber were also configured to attach the beads and cure the second coating resin under the condition that nitrogen gas flowed in a direction opposite to the introduction direction of the optical fibers. As a result of experiments using the optical fiber unit manufactured according to the present invention, it was found that no permanent deformation was generated in the optical fiber unit due to an external force, and the coating resin was excellently cured so that the surface is not sticky just after the manufacturing procedure. In addition, as a result of measuring an optical loss in a state that the optical fiber unit of the present invention having a length of 1 km was soaked in water at 2O⁰C for 2000 hours, the optical loss did not exceed ±0.07 dB/km that is an optical loss standard.

[50]

[51] Comparative Example

[52] Aggregated 4-core single-mode optical fibers passed through a dies of a coating device filled with a first coating resin so that the first coating resin is coated on the surface of the optical fibers. The first coating resin was radiation curable acrylate. After that, the optical fibers were introduced into the first curing chamber, and ultraviolet rays were irradiated thereto to form a first coating layer. After that, the optical fibers passed through a dies of a coating device filled with a second coating resin to coat the second coating resin on the surface of the optical fibers. The second coating resin was radiation curable acrylate having higher Young's modulus than the first coating resin. Then, the optical fibers were introduced into the beat attachment chamber so that beads were attached thereto by bead blowing, and then the optical fibers were introduced into the second curing chamber to cure the second coating resin. As a result of experiments using the optical fiber unit manufactured according to the prior art, it was found that the curing property of the coating resin was deteriorated and thus the surface was sticky. In addition, as a result of measuring an optical loss in a state that the optical fiber unit of the prior art having a length of 1 km was soaked in water at 2O⁰C for 2000 hours, the optical loss exceeded ±0.07 dB/km that is an optical loss standard.

[53]

[54] The present invention has been described in detail. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description. Industrial Applicability [55] According to the present invention, it is possible to manufacture an optical fiber unit having improved stiffness of a coating layer by intercepting introduction of impurities during the coating layer forming process. Thus, the optical fiber unit manufactured according to the present invention has excellent crashworthiness and is capable of advancing straightly, so installation properties are improved and an optical loss is not increased due to absorption of moisture after installation.

Claims

[1] A method of manufacturing an air blown optical fiber unit, comprising:

(a) coating a first coating resin on a surface of an optical fiber bundle;

(b) introducing the optical fiber bundle coated with the first coating resin into a first curing chamber under an inert gas environment and curing the first coating resin to form a first coating layer;

(c) coating a second coating resin on a surface of the first coating layer;

(d) attaching beads to a surface of the second coating layer; and

(e) introducing the optical fiber bundle, to which the beads are attached, into a second curing chamber under an inert gas environment and curing the second coating resin to form a second coating layer.

[2] The method of manufacturing an air blown optical fiber unit according to claim

1, further comprising: before the step (a), passing the optical fiber bundle through a gas chamber under an inert gas environment. [3] The method of manufacturing an air blown optical fiber unit according to claim

1, further comprising: before the step (c), passing the optical fiber bundle, on which the first coating layer is formed, through a gas chamber under an inert gas environment. [4] The method of manufacturing an air blown optical fiber unit according to claim

1, wherein, in the step (d), the beads are attached on the surface of the second coating resin with passing the optical fiber bundle through a gas chamber under an inert gas environment. [5] The method of manufacturing an air blown optical fiber unit according to any of claims 1 to 4, wherein the inert gas flows in a direction opposite to an introduction direction of the optical fiber that is introduced into the chamber. [6] A gas chamber used for a process of manufacturing an optical fiber unit, comprising: a chamber having an optical fiber input hole and an optical fiber output hole so that an optical fiber or an optical fiber having a coating layer is capable of passing therethrough; a nozzle installed to the optical fiber input hole to inject gas in a direction opposite to an introduction direction of the optical fiber; and a gas injection passage installed to one side of the chamber to communicate with the nozzle for supplying inert gas into the chamber.