WO2004066008A1

WO2004066008A1 - Optical fiber unit for air blown installation, method and apparatus for manufacturing the same

Info

Publication number: WO2004066008A1
Application number: PCT/KR2004/000118
Authority: WO
Inventors: Bong-Hoon Lee; Chan-Yong Park
Original assignee: Lg Cable Ltd.
Priority date: 2003-01-24
Filing date: 2004-01-20
Publication date: 2004-08-05
Also published as: KR100633905B1; KR20040068502A

Abstract

An optical fiber unit for air blown installation includes an optical fiber, and a protective layer surrounding the optical fiber. At least one concave strip is formed on the outer surface of the protective layer along a longitudinal direction of the protective layer, thereby increasing surface resistance against the blown air and improving work efficiency for the air blown installation. The concave strip has a spiral, waved or zigzag shape on the outer circumference of the protective layer, and has a sectional shape of triangle, semicircle, arc or rectangle. The optical fiber is in a type of single core, two cores or ribbon, and the protective layer is configured with a buffer layer, or buffer layer/sheath, or buffer layer/intermediate layer/sheath.

Description

OPTICAL FIBER UNIT FOR AIR BLOWN INSTALLATION, METHOD AND

APPARATUS FOR MANUFACTURING THE SAME

TECHNICAL FIELD

The present invention relates to an optical fiber unit, and more particularly to an

optical fiber unit for air blown installation and its manufacturing method and apparatus.

BACKGROUND ART

An optical fiber is broadly used for long-distance rapid transmission owing to its low transmission loss and great bandwidth. However, since the optical fiber itself is very weak to external impact or bending, the optical fiber is drawn in a fiber shape and

coated with polymer materials to prevent from being damaged during installation.

In order to install the optical fiber, several optical fibers are conventionally

bound or twisted into a cable. An optical cable has 6xn or 12xn optical fibers, and the

amount of optical fibers is generally much more than required at the installation point on

consideration of further consumption. However, as the communication system

becomes more diversified for suitably coping with new communication circumstance

and capacity and various kinds of optical fibers also come out accordingly, the

conventional method of laying a large amount of specific optical fibers without

consideration of future environments is not considered as a proper one. In addition, in aspects of the access network or the premise wiring, it is very difficult to predict which

optical fiber or optical cable is applied in the future. Thus, laying a large amount of

specific optical cables at a great cost is economically not desirable. Meanwhile, a method of installing an optical fiber unit having several optical fibers by air pressure is recently widely adopted for the purpose of installing the optical fibers in a narrow space. This attempt for installing an optical fiber unit by air pressure is firstly proposed in US Pat. No. 4,961,896 filed in 1980 and owned by British Telecom. This technique called Air Blown Fiber (hereinafter, referred to as ABF) is conducted in a way of laying a polymer tube having a diameter of 5 to 8 mm, called a micro tube or duct, with a special configuration for lubrication in advance so that an optical fiber may be additionally installed when required, and then installing a optical fiber unit having 1 to 12 cores into the tube as much as a desired length by blowing it by air pressure. This ABF is advantageously easy to install and remove together with small size and good flexibility, so an initial installation cost is reduced and an additional installation also gives a less burden. In addition, the ABF may be easily upgraded, thereby attracting much attention. The ABF is particularly suitable for indoor use such as FTTH (Fiber To The Home) and home network. Since the tube used for installing the ABF is laid in advance, the ABF hardly suffers from area restrictions though there is no sufficient installation space to spare in the tube. Now, a general procedure related to installation of the ABF is described.

At first, a tube dedicated to air blown installation is laid in a necessary region in advance. A required ABF is then installed by blown air into the tube with the use of an air blown installation equipment such as a blowing head. This ABF is installed using fluid drag force, differently from other existing methods. _ Thus, the.optical fiber unit has configuration and material on its outer surface, which is capable of maximizing the fluid drag force. In addition, since installation features such as installation length or minimum installation radius are changed depending on the configuration and material of the ABS outer surface, the shape and material design of the outer surface is very

important.

So far, various kinds of ABF structures are proposed to increased the fluid drag

force, representatively in US Pat. Nos. 5,042,907, 5,533,164, 5,555,335, 4,440,053, 6,341,188 and so on. These documents mainly disclose improvements of the ABF outer surface.

First, US5,042,907 proposes an optical fiber unit using glass beads 5 on its outer

surface so as to receive more air pressure, as shown in FIG. 1. In order to form the glass beads 5 on the outer surface of the optical fiber, the glass beads 5 are stirred

beforehand in a coating resin of the optical fiber 1, and then coated uniformly on the

outer surface. However, this method has some requirements that the glass bead 5

existing in the resin 4 of the outer surface should be relatively larger than the thickness

of the coating layer and have a high Young's modulus to give a propulsive force. As a

result, the optical fiber unit has a relatively bad bend characteristic, and cracks are apt to

be generated between the glass beads 5 and the resin 4 and propagated to inside of the optical fiber.

To solve this problem, a technique for inserting an intermediate layer 3 between the inner buffer layer 2 and the resin 4 of the outer surface has been proposed.

However, this technique requires repeating the coating processes at least three times, thereby complicating its procedure and increasing the relevant costs.

FIG. 2 shows a technique proposed in US5,555,335 as another prior art. Referring to FIG. 2, without stirring the glass beads 5 in advance, the glass beads are blown to a resin after the resin is coated on the optical fiber 1 but before being cured so that the glass beads are attached to the outer surface 6 of the optical fiber by static electricity. However, in this method, the adhering strength is not uniformly distributed between the glass beads and the outer surface of the optical fiber, so it is hardly applied to the actual procedure. In particular, if some glass beads fall down, these glass beads may damage an optical fiber unit or cause critical problem to the human body since a worker may inhale the glass beads.

As still another prior art, US5,441,813 proposed a technique of forming a dimple on the surface of an optical fiber with the use of foaming polymer materials so that the optical fiber unit may receive more air pressure. However, the foaming polymer materials may increase frictional coefficient of the ABF outer surface, so a short length can be installed at once. In addition, the polymer materials deteriorate low temperature characteristics and strength of the optical fiber unit.

There are also proposed a technique of winding a fiber made of special materials around a ribbon-type optical fiber. However, since the ribbon-type optical fiber has a direction against the bending, it is apt to be bent to only one direction when being installed.

DISCLOSURE OF INVENTION The present invention is designed to solve the problems of the prior art, and therefore an object of the invention is to provide an optical fiber unit for air blown installation which is capable of receiving more fluid drag force without generating a direction during the air blown installation, and be manufactured more safely because of not using the conventional fine particles such as glass or ceramic.

Another object of the invention is to provide a method for manufacturing an optical fiber unit for air blown installation, which may manufacture the above-mentioned optical fiber unit in a simple way. Still another object of the invention is to provide an apparatus for manufacturing the above-mentioned optical fiber unit for air blown installation.

In order to accomplish the above object, the present invention provides an optical fiber unit for air blown installation, which is installed into a tube, the optical fiber unit including: at least one optical fiber, each having a core and a clad; and a protective layer for surrounding the optical fiber, wherein at least one concave strip is formed on an outer surface of the protective layer along a longitudinal direction of the protective layer.

At this time, the concave strip may be formed on the outer surface of the protective layer in a spiral, waved or zigzag pattern. Furthermore, the concave strip may also be formed discontinuously.

In addition, the concave strip may have a sectional shape of triangle, semicircle, arc or rectangle.

At this time, it is possible that the optical fiber unit comprises a plurality of optical fibers, and the plurality of optical fibers are provided in the protective layer in a ribbon type, and a tension reinforcing member may be further provided in a ribbon type together with the ribbon-type optical fiber to reinforce tensile force.

In addition, in the above configuration, the protective layer may be composed of only a buffer layer, or a buffer and a sheath, or a buffer layer, an intermediate layer and a sheath. At this time, an least an outermost layer of the protective layer on which the concave strip is formed preferably has a secant modulus of 100 to 1000 MPa at 2.5%

strain.

In another aspect of the invention, there is also provided a method for manufacturing an optical fiber unit for air blown installation, which is installed into a

tube, the method including: supplying an optical fiber unit having at least one optical

fiber and a protective layer surrounding the optical fiber; and forming at least one concave strip on an outer surface of the supplied optical fiber unit along a longitudinal direction of the protective layer.

Preferably, the concave strip forming step is conducted by a mechanical

processing machine, and the mechanical processing machine forms the concave strip on the outer surface of the protective layer by means of groove cutting.

The mechanical processing machine may conduct the groove cutting with rotating in one direction while the optical fiber unit is moving in order to form a spiral

concave strip on the outer surface of the protective layer, or conduct the groove cutting

with alternatively rotating clockwise and counterclockwise while the optical fiber unit is

moving in order to form a waved or zigzag concave strip on the outer surface of the protective layer. Furthermore, the mechanical processing machine may conduct the

groove cutting discontinuously while the optical fiber unit is moving in order to form a

discontinuous spiral concave strip on the outer surface of the protective layer.

In addition, the optical fiber unit having a concave strip on its outer surface as

mentioned above may also be manufactured according to a method for manufacturing an

optical fiber unit for air blown installation, which includes the steps of: passing at least one optical fiber, each having a core and a clad, through a coating die in which at least one protrusion having a predetermined shape is formed in an inner hollow

circumference thereof; and supplying a polymer resin on an outer surface of the optical fiber so as to form a protective layer on an outer surface of which at least one concave layer is formed.

According to still another aspect of the present invention, there is also provided

an apparatus for manufacturing an optical fiber unit for air blown installation, which is installed into a tube, which includes a supply unit for supplying an optical fiber unit having at least one optical fiber and at least one protective layer surrounding the optical

fiber; a cutting unit for forming at least one concave strip on an outer surface of the

protective layer of the supplied optical fiber unit along a longitudinal direction of the protective layer by means of groove cutting; and a take-up device for winding the optical fiber unit processed by the cutting unit.

On the while, the optical fiber unit having a concave strip on its outer surface as

mentioned above may also be manufactured with the use of an apparatus for

manufacturing an optical fiber unit for air blown installation, which includes: a supply unit for supplying at least one optical fiber, each having a core and a clad; a coating die

through which the supplied optical fiber is passed, the coating die supplying a polymer

resin on an outer surface of the optical fiber so as to form a protective layer; and a

take-up device for winding an optical fiber unit in which the protective layer is formed by the coating die, wherein the coating die has at least one protrusion of a predetermined

shape on an inner circumference thereof so as to form at least one concave strip on the outer surface of the protective layer. BRIEF DESCRIPTION OF THE DRAWINGS

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:

FIG. 1 is a sectional view showing an optical fiber unit according to the prior art;

FIG.2 is a sectional view showing another optical fiber unit for air blown

installation according to the prior art;

FIG. 3 is a perspective view showing an optical fiber unit for air blown installation according to an embodiment of the present invention;

FIG. 4 is a perspective view showing an optical fiber unit for air blown

installation according to another embodiment of the present invention;

FIG. 5 is a perspective view showing an optical fiber unit for air blown installation according to still another embodiment of the present invention;

FIGs. 6a to 6f are sectional views showing various optical fiber units on the

surface of which various shapes of concave strips are formed;

FIGs. 7a to 7c are sectional views showing optical fiber units, each having an

optical fiber ribbon, on the surface of which various shapes of concave strips are formed;

FIG. 8 is a schematic view showing equipment for manufacturing an optical fiber unit according to an embodiment of the present invention; and

FIG. 9 is a schematic view showing equipment for manufacturing an optical fiber unit according to another embodiment of the present invention. BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in

detail referring to the accompanying drawings. Prior to the description, it should be

understood that the terms used in the specification and 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.

FIG. 3 is a perspective view showing an optical fiber unit for air blown

installation according to an embodiment of the present invention. Referring to FIG. 3,

the optical fiber unit of the present invention has at least one optical fiber 10 and a

protective layer 20.

The optical fiber 10 is a quartz or plastic optical fiber, which has a core and a clad. In addition, at least one optical fiber 10 is provided in a single core type or a

ribbon type. Around the above-mentioned optical fiber 10, first and second coating

layers may be formed for protection of the optical fiber. These coating layers play a role of protecting the inner layer from dusts or moisture, and are made of silicon or similar buffer materials. In addition, as the second coating layer, a coloring coating

layer for identifying the kind of optical fiber may be used. If sufficient strippability is required according to the kind of polymer resin applied to the coloring coating layer, jelly or silicon oil for an optical cable may be coated on the outer surface of the coloring coating layer.

The protective layer 20 is formed around the aforementioned optical fiber 10, or

around the coating layers if the first and second coating layers are formed. The protective layer 20 may be composed of one layer, or it is also possible to laminate

various kinds of protective layers. In the drawings, it is described that the protective layer 20 has a dual configuration having a buffer layer 22 and a sheath 24, as an

example. Here, the buffer layer 22 is a protective layer which directly surrounds the optical fiber 10, while the sheath 24 is a protective layer on which a concave strip 30 described later is formed. The protective layer 20 of the present invention however

may include various modifications, not limited to the above case. For example, the protective layer 20 may include only the buffer layer 22, or additionally include an

intermediate layer between the buffer layer 22 and the sheath 24. Various kinds of

such protective layers 20 will be described later in more detail. In addition, the

protective layer 20 plays various rolls such as protecting the optical fiber, ensuring

rigidity of the optical fiber or the like depending on the kind of an actually used protective layer.

On the optical fiber unit configured as above, a concave strip 30 is formed for

helping air blown installation of the optical fiber unit. The concave strip 30 is formed

on the outer surface of the protective layer 20 by means of mechanical processing. In particular, in case the protective layer 20 has multiple layers, the concave strip 30 is

formed on the outer surface of the outermost protective layer. The concave strip 30 is formed on the outer surface of the protective layer 20 along a longitudinal direction of the protective layer 20. In addition, though it is depicted on the drawings that only one concave strip 30 is formed on the outer surface

of the protective layer 20, it is also possible to form a plurality of concave strips 30 at

the same time. In addition, though the concave strip 30 may be formed straightly on the outer surface of the protective layer 20, it is more preferable that the concave strip 30 has a curved pattern so as to receive more air pressure during the air blown

installation. FIG. 3 shows as an example that the concave strip 30 is spirally formed

on the outer surface of the protective layer 20. The concave strip 30 is formed by processing successive grooves on the outer surface of the protective layer 20 by means of mechanical processing. At this time, the

sectional shape of the concave strip 30 is determined by the shape of a cutting tool used

for the mechanical processing. Various shapes such as triangle having a blunt end, semicircle, arc, rectangle and trapezoid may be applied to the section of the concave strip 30.

The concave strip 30 formed on the outer surface of the protective layer 20 as

described above plays a role of reducing a contact area with the tube inside and

increasing a contact area with the air when the optical fiber unit is installed at a narrow

space such as in a tube. That is to say, the concave strip 30 decreases a contact area

between the outer surface of the protective layer 20 and the inner surface of the tube, thereby reducing a frictional force between them, while the concave strip 30 increases a contact area exposed to the air flow so that the optical fiber unit may be more easily installed by a compressed air. The concave strip 30 formed as described above helps the optical fiber unit be

installed more easily by increasing a resistance force against the air flow around the protective layer 20 during the air blown installation of the optical fiber unit. In

particular, in case the concave strip 30 has a spiral pattern as in this embodiment, the resistance against the air pressure is more increased than the concave strip has a straight pattern.

Thus, the present invention does not need to attach particles such as polymer

beads or glass beads on the outer surface of the protective layer 20 separately, and does

not require for stirring or adhering the beads in a resin. FIG. 4 shows an optical fiber unit according to another embodiment of the

present invention. The optical fiber unit of this embodiment is similar to that of FIG. 3,

except that a concave strip 40 formed on the surface of the protective layer 20 has a different pattern.

In this embodiment, the concave strip 40 has a waved pattern on the outer

surface of the protective layer 20. , It is also possible to form a plurality of such

concave strips 40 on the outer surface of the protective layer 20. If the waved concave

strip 40 is formed as mentioned above, the air flow around the concave strip 40 is

resisted in both directions alternatively according to the pattern of the concave strip 40.

Thus, while the concave strip 30 of the former embodiment receives air resistance in

one direction so that the optical fiber unit may be twisted in the direction during the air blown installation, the concave strip 40 of this embodiment receives air resistance in both opposite directions alternatively so that the optical fiber unit may be installed without twisting. Meanwhile, though it is illustrated and described in this embodiment that the

concave strip 40 has a waved pattern, the present invention is not limited to that case. For example, the concave strip may have various patterns such as a zigzag pattern or a trapezoidal pattern.

FIG. 5 shows an optical fiber unit according to still another embodiment of the present invention. The optical fiber unit of this embodiment is similar to ones shown

in FIGs. 3 and 4, except that a concave strip 50 formed on the surface of the protective layer 20 has a different pattern.

In this embodiment, the concave strip 50 has a discontinuous waved pattern on

the outer surface of the protective layer 20. It is possible that a plurality of such

concave strips 50 are formed on the outer surface of the protective layer 20. If such a discontinuous waved concave strip 50 is formed as mentioned above, an air flow around

the concave strip 50 receives resistances in both opposite directions alternatively, as in

the case of the concave strip 40 shown in FIG. 4. Thus, the concave strip 50 of this

embodiment also has an advantage that it may be installed without twisting due to the alternative resistances.

Meanwhile, though it is depicted and explained that the discontinuous concave

strip 50 has a waved pattern, the present invention is not limited to that case. For

example, it is also possible that the spiral concave strip 30 shown in FIG. 3 is discontinuously formed.

The concave strips 30, 40 and 50 having various patterns as shown in FIGs. 3 to

5 may obtain such patterns by means of operation methods of a processing device used for forming the concave strips. That is to say, if the processing device is rotated in only one direction while a concave strip is formed, the spiral concave strip 30 shown in FIG. 3 is formed, while if the processing device is rotated alternatively in both opposite

directions, the waved concave strip 40 shown in FIG. 4 is formed. In addition, if the processing device is operated discontinuously, the discontinuous concave strip 50 shown in FIG. 5 is formed. Moreover, the concave strip may have various patterns besides the aforementioned patterns, and the operation method of the processing device

is determined according to the pattern, of course. Such a processing device and its

operation method will be described later in more detail.

FIGs. 6a to 6f show optical fiber units configured so that a single-core or two-core optical fiber is surrounded by various kinds of protective layers.

First, the optical fiber unit shown in FIG. 6a includes the optical fiber 10 therein,

and only the buffer layer 22 is provided around the optical fiber 10 as a protective layer.

In addition, the aforementioned concave strip 30 is formed on the outer surface of the buffer layer 22. Of course, the concave strip 30 formed on the outer surface of the

buffer layer 22 may have various patterns such as spiral or waved patterns, and its

section may also adopt various shapes.

The optical fiber unit of FIG. 6a has the simplest configuration of an optical

fiber unit, in which the buffer layer 22 directly surrounds the optical fiber and acts as a

protective layer by itself. Thus, the buffer layer 22 is preferably made of harder

materials than a general one for ensuring rigidity of the optical fiber unit and easy processing of the concave strip 30. The buffer layer 22 used in this embodiment

preferably has an elastic coefficient in which a secant modulus is more than 20 MPa at 2.5% strain, more preferably more than 100 MPa. The optical fiber unit shown in FIG. 6b is similar to that of FIG. 6a, except that a

sheath 24 is additionally formed around the buffer layer 22. Thus, the concave strip 30

is formed on the outer surface of the sheath 24, which is the outermost layer of the optical fiber unit. In this embodiment, since the sheath 24 is formed around the buffer layer 22, the

buffer layer 22 may be made of materials generally used in the art. Meanwhile, a

material of the sheath 24 positioned around the buffer layer 22 should be determined on

the consideration of rigidity of the optical fiber unit and easy processing of the concave strip 30. If a modulus of the sheath 24 is too low, the optical fiber unit may not be

installed straight. On the while, if the modulus of the sheath 24 is too high, cracks are apt to be generated in the sheath 24 due to the bending. Thus, the modulus of the

sheath 24 is preferably in the range of 400 to 1000 MPa at 2.5% strain, more preferably 500 to 800 MPa at 2.5% strain.

The optical fiber unit shown in FIG. 6c is configured so that an intermediate

layer 26 is added to the optical fiber unit of FIG. 6b. The intermediate layer 26 is

positioned between the buffer layer 22 and the sheath 24, and not directly influenced by

the concave strip 30. When a crack is generated in the sheath 24, the intermediate

layer 26 plays a role of protecting the optical fiber by preventing the crack from being

propagated inside the optical fiber unit. In this embodiment, a modulus of the sheath

24 is preferably in the range of 400 to 1000 MPa at 2.5% strain, more preferably 500 to 800 MPa at 2.5% strain. In addition, in this embodiment, the concave strip 30 is

formed on the outer surface of the sheath 24, which is positioned outermost in the optical fiber unit. The optical fiber unit shown in FIG. 6d is similar to that of FIG. 6b, except that a first coating layer 12 and a second coating layer 14 are additionally formed between the optical fiber 10 and the buffer layer 22. The first coating layer 12 acts for protecting the optical fiber 10, while the second coating layer 14 is a coloring coating layer for identifying the optical fiber 10. In this embodiment, a modulus of the sheath 24 is

preferably in the range of 400 to 1000 MPa at 2.5% strain, more preferably 500 to 800

MPa at 2.5% strain. In addition, in this embodiment, the concave strip 30 is formed on the outer surface of the sheath 24, which is positioned outermost in the optical fiber unit.

The optical fiber unit shown in FIG. 6e is similar to that of FIG. 6d, except that

an intermediate layer 26 for protecting the optical fiber so that a crack possibly

generated in the sheath 24 is not propagated inside the optical fiber unit is additionally formed between the coloring coating layer 14 and the buffer layer 22. In this

embodiment, a modulus of the sheath 24 is preferably in the range of 400 to 1000 MPa

at 2.5% strain, more preferably 500 to 800 MPa at 2.5% strain. In addition, in this

embodiment, the concave strip 30 is formed on the outer surface of the sheath 24, which

is positioned outermost in the optical fiber unit.

FIGs. 6a to 6e show as an example that only one optical fiber 10 is used in the

optical fiber unit, i.e. a single-core optical fiber unit. However, the present invention is

not limited to the single-core optical fiber unit. For example, the present invention

may be applied to a two-core optical fiber unit as shown in FIG. 6f. In FIG. 6f, it is depicted as an example that a protective layer of the optical fiber unit has a similar configuration to that of FIG. 6e, and two optical fibers 10 are located in the protective

layer. In addition, each optical fiber 10 is surrounded by the first coating layer 12 and the coloring coating layer 14. Even in this embodiment, a modulus of the sheath 24 is preferably in the range of 400 to 1000 MPa at 2.5% strain, more preferably 500 to 800 MPa at 2.5% strain. In addition, in this embodiment, the concave strip 30 is formed on

the outer surface of the sheath 24, which is positioned outermost in the optical fiber unit. Referring to FIGs. 6a to 6f again, it is illustrated that two to four concave strips

30 are formed on the outer surface of the protective layer of the optical fiber unit.

However, it should be understood that the number of concave strips 30 may be changed

as required. In addition, the concave strip 30 formed on the protective layer in these

embodiments may be formed in various patterns such as spiral and waved patterns or formed discontinuously. Moreover, the concave strip may have various sectional shapes such as triangle, semi-circle, arc and rectangle according to the shape of the

processing device.

Though not shown in the figures, the buffer layer 22 used in the protective layer

may have a plurality of granular hollows therein. These hollows are just for reducing

the weight of the buffer layer 22, and have no relation to the fluid drag force of the

optical fiber unit.

FIGs. 7a to 7c show optical fiber units adopting a ribbon-type optical fiber in which optical fibers 10 are surrounded by a ribbon 16.

First, the optical fiber unit shown in FIG. 7a is configured so that the buffer layer

22 surrounds a ribbon-type optical fiber. In the ribbon-type optical fiber, a plurality of

general optical fibers or firstly-coated optical fibers 10 are bound by the ribbon 16. The ribbon 16 is made of polyethylene (PE), polyurethane, polyvinyl chloride (PVC) or

the like, and plays a role of binding and protecting the plurality of optical fibers 10 from external environments. I

In addition, the aforementioned concave strip 30 is formed on the outer surface of the buffer layer 22. The concave strip 30 may have various types of patterns such as

spiral or waved pattern, and its section may be variously configured. In the optical fiber unit of FIG. 7a, the buffer layer 22 directly surrounds the ribbon-type optical fibers 10 and acts as a protective layer. Thus, in this embodiment,

the buffer layer is preferably made of harder materials than a general one for the purpose

of rigidity of the optical fiber unit and easy processing of the concave strip 30. The buffer layer 22 used in this embodiment preferably has an elastic coefficient in which a

secant modulus is more than 20 MPa at 2.5% strain, more preferably more than 100 MPa.

The optical fiber unit shown in FIG. 7b is similar to that of FIG. 7a, except that a

coloring coating layer 14 is additionally formed around each optical fiber in the ribbon

16, and a sheath 24 is additionally formed around the buffer layer 22. Thus, the

concave strip 30 is formed on the outer surface of the sheath 24, which is an outermost

layer of the optical fiber unit.

In this embodiment, since the sheath 24 is formed around the buffer layer 22, the

buffer layer 22 may be made of materials generally used in the art. Meanwhile, the

sheath 24 positioned around the buffer layer 22 preferably has a modulus in the range of

400 to 1000 MPa at 2.5% strain on the consideration of rigidity of the optical fiber unit and easy processing of the concave strip 30, more preferably 500 to 800 MPa at 2.5% strain.

The optical fiber unit shown in FIG. 7c is configured so that an intermediate layer 26 is added to the optical fiber unit of FIG. 7b. The intermediate layer 26 is positioned between the buffer layer 22 and the sheath 24, and not directly influenced by the concave strip 30. In addition, in this embodiment, the concave strip 30 is formed

on the outer surface of the sheath 24, which is positioned outermost in the optical fiber

unit, like the embodiment of FIG. 7b.

In the examples of FIGs. 7a to 7c, the number of concave strips 30 formed on the

outer surface of the protective layer of the optical fiber unit may be changed as required,

and may be formed in various patterns such as spiral and waved patterns or formed

discontinuously. Such concave strips having various patterns may have various sectional shapes such as triangle, semi-circle, arc and rectangle according to the shape of the processing device, of course.

Though not shown in the figures, in case a plurality of optical fibers 10 are

bound by the ribbon 16 as shown in FIGs. 7a to 7c, a tension reinforcing member may be installed together with the optical fibers in the optical fiber unit. The tension

reinforcing member may be installed either additionally together with the plurality of

optical fibers 10 or by replacing a pair of the optical fibers with the tension reinforcing

member. At this time, the tension reinforcing member plays a role of reinforcing

tensile strength of the optical fiber unit. The number of tension reinforcing members

may be changed according to its environments. In addition, the tension reinforcing

member may be made of a fiber or a wire, and preferably Kevlar or Aramid is used for the tension reinforcing member.

FIG. 8 shows an apparatus for manufacturing an optical fiber unit for air blown

installation according to an embodiment of the present invention. The apparatus for manufacturing an optical fiber unit and its manufacturing procedure will be described here with reference to FIG. 8.

In order to manufacture an optical fiber unit according to the present invention, it is sufficient to add a device for forming a concave strip on the outer surface of the protective layer of the optical fiber unit together with the conventional equipment.

Thus, the following description will be focused on the process of forming a concave strip while the existing equipment will be explained in brief.

First, to manufacture an optical fiber unit according to the present invention, a payoff 60 for supplying an optical fiber and a take-up device 100 for winding the optical fiber are used. That is to say, the optical fiber is supplied through the payoff 60 and then made into an optical fiber unit through a series of processes, and then the made optical fiber unit is wound around the take-up device 100.

The optical fiber supplied from the payoff 60 is firstly guided to a coating die 70. At this time, a guide roller 62 may be installed adjacent to the coating die 70 so that the optical fiber may have a suitable advancing direction to the coating die 70. The coating die 70 coats a protective layer such as a buffer layer or a sheath on the surface of the optical fiber to make the optical fiber unit, and then supplies the coated optical fiber unit to an ultraviolet (UV) curing device 80.

At this time, the protective layer coated on the surface of the optical fiber is being significantly heated, which is not suitable for works such as a surface processing.

Thus, the UV curing device 80 radiates ultraviolet rays to the optical fiber unit so as to cure the coated protective layer. The optical fiber unit having the cured protective layer as mentioned above is then supplied to a mechanical processing machine (e.g., a cutting unit) 90.

The mechanical processing machine 90 forms the aforementioned concave strip on the outer surface of the cured protective layer while the optical fiber unit is

progressed. At this time, the mechanical processing machine 90 preferably employs • the groove cutting, and a cutting tool (not shown) of a predetermined shape is prepared

for this purpose. In addition, as shown in FIGs. 3 and 4, the mechanical processing machine 90 should be rotated in a predetermined way so as to process the concave strip in a spiral or waved pattern, and a motor 92 is connected to the mechanical processing

machine 90 in this reason. The motor 92 rotates the mechanical processing machine

90 based on the center of the optical fiber unit. In addition, the motor 92 may be connected to a controller 94 and then operated according to commands of the controller 94.

At this time, in order to process the spiral concave strip 30 shown in FIG. 3 on

the outer surface of the optical fiber unit, the mechanical processing machine 90 is

rotated in only one direction. That is to say, since the optical fiber unit keeps moving

while the concave strip is formed, if the groove cutting is performed with rotating the

mechanical processing machine 90 at an appropriate speed, the spiral concave strip 30

as shown in FIG. 3 is formed.

Meanwhile, in order to process the waved concave strip 40 as shown in FIG. 4

on the outer surface of the optical fiber unit, the mechanical processing machine 90 is rotated alternatively clockwise and counterclockwise. Thus, the motor 92 should be

able to give both clockwise and counterclockwise rotations, and a rotational direction of the motor 92 may be changed according to a predetermined condition of the controller 94.

In order to process the discontinuous concave strip 50 as shown in FIG. 5 on the outer surface of the optical fiber unit, the groove processing is performed discontinuously with periodically advancing and retreating the cutting tool for cutting a groove to form the concave strip 50 on the outer surface of the protective layer 20 while the mechanical processing machine 90 is rotated either in one direction or in clockwise/counterclockwise directions alternatively. At this time, the controller 94 controls advance and retreat of the cutting tool together with rotational direction and speed of the mechanical processing machine 90. If the concave strip processing procedure is finished, the optical fiber unit according to the present invention is completed, and the completed optical fiber unit is supplied to and wound around the take-up device 100.

FIG. 9 is a sectional view (a) showing a coating die 70' for forming the concave strip 30 according to another embodiment of the present invention, and a front view (b) showing an exit of the coating die 70'. Now, method and apparatus for manufacturing an optical fiber unit according to this embodiment are described in detail with reference to FIG. 9.

In this embodiment, the protective layer is formed together with the concave strip 30 therein during the coating process in which the protective layer 20 is formed around the optical fiber 10, different from the former embodiment referring to FIG. 8.

That is to way, in this embodiment, the modified coating die 70' shown in FIG. 9 is used instead of the general coating die 70 of FIG. 8, and the mechanical processing machine

70 of FIG. 8 is not used. The coating die 70' shown in FIG. 9 coats the protective layer 20 on the optical fiber 10 by passing the optical fiber 10 into a nipple 71 in a direction of the arrow A and supplying a polymer resin in a direction of the arrow B on the outer surface of the optical fiber 10. The exit of the coating die 70' basically has a circular shape, but at least one protrusion 72 in a shape of triangle, rectangle, semi-circle, arc, trapezoid, convex and so on is formed on the inner circumference of the exit, as shown in FIG. 9 (b).

Thus, if the optical fiber 10 is passed through the coating die 70' and a polymer resin is supplied on the outer surface of the optical fiber 10, the protective layer 20 is coated on the outer surface of the optical fiber 10 and the concave strip is formed on the protective layer 20 according to the shape of the protrusion 72 at the same time.

Meanwhile, the motor 92 and the controller 94 shown in FIG. 8 may also be connected to the coating die 70' of this embodiment so that the coating die 70' may rotate to form the concave strip in a spiral or waved pattern. Thus, if the coating die 70' is rotated clockwise and/or counterclockwise in the coating process on a plane perpendicular to the advancing direction of the optical fiber, or if the optical fiber 10 is rotated in a similar way, it is possible to manufacture an optical fiber unit coated with a protective layer on the outer surface of which a concave strip of various patterns such as a spiral or waved pattern is formed. The optical fiber coated by the protective layer having the concave strip as mentioned above is then wound around the take-up device 100 via the UV curing device 80 and the guide roller 64 of FIG. 8.

The optical fiber 10 passing through the coating die 70' in this embodiment may be a single-core optical fiber, a multi-core optical fiber as shown in FIG. 6f, or a

ribbon-type optical fiber as shown in FIGs. 7a to 7c. Furthermore, it is also possible to form the sheath 24 having a concave strip by passing an optical fiber, which is already coated with the buffer layer 22, through the coating die of FIG. 9.

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

The optical fiber unit for air blown installation according to the present

invention has an advantage of improving efficiency of the air blown installation by

increasing a surface resistance against air pressure through a simple process of forming

a concave strip on the outer surface of the protective layer surrounding the optical fiber.

In addition, the optical fiber unit of the present invention shows great

productivity since it does not require conventional complicated processes for mixing

and coating fine particles and polymer resin or attaching fine particles on a polymer

resin surface not cured. Moreover, conventional problems such as crack generation

which is commonly generated between the resin and the fine particles or crack propagation inside the optical fiber unit is significantly decreased.

Furthermore, the optical fiber unit of the present invention prevents thermal

cracks generated by the difference of thermal deformation coefficients between the resin and the fine particles such as glass beads, and solves the problems that the glass bead is broken down in the optical fiber unit.

Since the optical fiber unit manufacturing method of the present invention does not require the process of coating or attaching fine particles from outside, it is possible to reduce the material cost and manufacturing cost, and prevent thermal deterioration of the work environments due to the fine particles.

In addition, since the morphology suitable for air blown installation is made in a mechanical manner just after the external protective layer of polymer material is cured or when the protective is coated, the manufacturing method of the present invention is very simple. Moreover, such an optical fiber unit does not cause fine particle breakdown or separation while it is kept in the custody or installed into a tube, so it is safer and more convenient than the conventional one.

Claims

What is claimed is:

1. An optical fiber unit for air blown installation, which is installed into a

tube, comprising: at least one optical fiber, each having a core and a clad; and a protective layer for surrounding the optical fiber, wherein at least one concave strip is formed on an outer surface of the protective

layer along a longitudinal direction of the protective layer.

2. An optical fiber unit for air blown installation according to claim 1,

wherein the concave strip is formed on the outer surface of the protective layer

in a spiral, waved or zigzag pattern.

3. An optical fiber unit for air blown installation according to claim 1,

wherein the concave strip is formed discontinuously.

4. An optical fiber unit for air blown installation according to claim 1, wherein the concave strip has a sectional shape of triangle, semicircle, arc or rectangle.

5. An optical fiber unit for air blown installation according to claim 1, wherein the optical fiber unit comprises a plurality of optical fibers, and the

plurality of optical fibers are provided in the protective layer in a ribbon type.

6. An optical fiber unit for air blown installation according to claim 5, further comprising a tension reinforcing member in the protective layer for reinforcing

tensile force.

7. An optical fiber unit for air blown installation according to claim 5,

wherein the tension reinforcing member is made of any of Kevlar, Aramid and wire.

8. An optical fiber unit for air blown installation according to claim 1,

wherein the protective layer has a plurality of granular hollows therein for reducing weight.

9. An optical fiber unit for air blown installation according to claim 1,

wherein the protective layer includes:

a buffer layer surrounding the optical fiber; and a sheath surrounding the buffer layer and having the concave strip on a surface thereof.

10. An optical fiber unit for air blown installation according to claim 1,

wherein an least an outermost layer of the protective layer on which the concave strip is formed has a secant modulus of 100 to 1000 MPa at 2.5% strain.

11. An optical fiber unit for air blown installation according to claim 10, wherein the outermost layer of the protective layer has a secant modulus of 500 to 800 MPa at 2.5% strain.

12. An optical fiber unit for air blown installation according to claim 9, wherein the protective layer further includes an intermediate layer between the buffer layer and the sheath in order to prevent cracks, generated in the sheath, from

being propagated through the protective layer.

13. A method for manufacturing an optical fiber unit for air blown

installation, which is installed into a tube, comprising:

supplying an optical fiber unit having at least one optical fiber and a protective

layer surrounding the optical fiber; and forming at least one concave strip on an outer surface of the supplied optical

fiber unit along a longitudinal direction of the protective layer.

14. A method for manufacturing an optical fiber unit for air blown

installation according to claim 13,

wherein the concave strip forming step is conducted by a mechanical processing

machine, and the mechanical processing machine forms the concave strip on the outer surface of the protective layer by means of groove cutting.

15. A method for manufacturing an optical fiber unit for air blown installation according to claim 14, wherein the mechanical processing machine conducts the groove cutting with

rotating in one direction while the optical fiber unit is moving in order to form a spiral

concave strip on the outer surface of the protective layer.

16. A method for manufacturing an optical fiber unit for air blown

installation according to claim 14,

wherein the mechanical processing machine conducts the groove cutting with alternatively rotating clockwise and counterclockwise while the optical fiber unit is moving in order to form a waved or zigzag concave strip on the outer surface of the protective layer.

17. A method for manufacturing an optical fiber unit for air blown installation according to claim 14,

wherein the mechanical processing machine conducts the groove cutting

discontinuously while the optical fiber unit is moving in order to form a discontinuous

spiral concave strip on the outer surface of the protective layer.

18. A method for manufacturing an optical fiber unit for air blown installation, which is installed into a tube, comprising:

passing at least one optical fiber, each having- a core and a- clad, through a

coating die in which at least one protrusion having a predetermined shape is formed in an inner hollow circumference thereof; and supplying a polymer resin on an outer surface of the optical fiber so as to form a

protective layer on an outer surface of which at least one concave layer is formed.

19. A method for manufacturing an optical fiber unit for air blown

installation according to claim 18, wherein the coating die is rotated in one direction while the optical fiber is passing so that a spiral concave strip is formed on the outer surface of the protective

layer.

20. A method for manufacturing an optical fiber unit for air blown

installation according to claim 18, wherein the coating die is alternatively rotated clockwise and counterclockwise

while the optical fiber is passing so that a waved or zigzag concave strip is formed on

the outer surface of the protective layer.

21. An apparatus for manufacturing an optical fiber unit for air blown

installation, which is installed into a tube, comprising:

means for supplying an optical fiber unit having at least one optical fiber and at

least one protective layer surrounding the optical fiber; a cutting means for forming at least one concave strip on an outer surface of the protective layer of the supplied optical fiber unit along a longitudinal direction of the

protective layer by means of groove cutting; and

a take-up means for winding the optical fiber unit processed by the cutting means.

22. An apparatus for manufacturing an optical fiber unit for air blown

installation according to claim 21, wherein a motor for giving a one-directional rotational force is connected to the

cutting means, and the cutting means is rotated in one direction by the motor while the optical fiber unit is moving in order to form a spiral concave strip on the outer surface of

the protective layer.

23. An apparatus for manufacturing an optical fiber unit for air blown

installation according to claim 21, wherein a motor for giving a bi-directional rotational force is connected to the

cutting means, and the cutting means is alternatively rotated clockwise and

counterclockwise while the optical fiber unit is moving in order to form a waved or

zigzag concave strip on the outer surface of the protective layer.

24. An apparatus for manufacturing an optical fiber unit for air blown

installation according to claim 21,

wherein the cutting means conducts the groove cutting discontinuously while the

optical fiber unit is supplied so as to form a discontinuous spiral concave strip on the outer surface of the protective layer.

25. An apparatus for manufacturing an optical fiber unit for air blown installation, which is installed into a tube, comprising: means for supplying at least one optical fiber, each having a core and a clad; a coating die through which the supplied optical fiber is passed, the coating die supplying a polymer resin on an outer surface of the optical fiber so as to form a protective layer; and a take-up means for winding an optical fiber unit in which the protective layer is formed by the coating die, wherein the coating die has at least one protrusion of a predetermined shape on an inner circumference thereof so as to form at least one concave strip on the outer surface of the protective layer.

26. An apparatus for manufacturing an optical fiber unit for air blown installation according to claim 25, wherein a motor for giving a one-directional rotational force is connected to the cutting means, and the cutting means is rotated in one direction by the motor while the optical fiber unit is moving in order to form a spiral concave strip on the outer surface of the protective layer.

27. An apparatus for manufacturing an optical fiber unit for air blown installation according to claim 25, wherein, a motor for giving a bi-directional rotational force is connected to the cutting means, and the cutting means is alternatively rotated clockwise and counterclockwise while the optical fiber unit is moving in order to form a waved or zigzag concave strip on the outer surface of the protective layer.