JPH11337781A - Coated plastic optical fiber and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a coated plastic optical fiber in which the bending loss is made small. SOLUTION: The coated plastic optical fiber has first and second coating layers in sequence from the optical fiber side on the outside wall of the plastic optical fiber 1, and consists of a resin having a lower tensile elastic modulus than that of a resin, in which the first coating layer 2 constitutes an optical fiber clad part, and a resin having a higher tensile elastic modulus then that of a resin, in which the second coating layer 3 constitutes an optical fiber clad part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated plastic optical fiber having a practically high optical fiber strength and excellent bending resistance and a method for producing the same.

[0002]

2. Description of the Related Art Optical communication has been remarkably developed in recent years centering on silica-based optical fibers, and at present, almost all long-distance trunk lines and submarine cables employ optical communication. The quartz optical fiber used for these is a type called a single mode (SM), and has a high bandwidth, particularly suitable for long-distance communication.
It is characterized by low transmission loss. Separately, a multimode (MM) type quartz fiber is often used for a backbone of a local area network (LAN). The SM type has a core diameter of 7 to 8 μm (all “diameters” in the present specification represent diameters).
The M type has a core diameter of 50 μm and a core diameter of 62.5 μm, and both have the same cladding diameter of 125 μm.

[0003] These quartz fibers are made of a strand of wire whose outer periphery is coated with a layer called a buffer layer, a core wire of which the outer periphery is coated with a nylon-based resin, and a Kevlar fiber reinforced vinyl chloride resin as a reinforcing material on the outer periphery thereof. A typical configuration is a so-called cord or the like covered with. These cord-shaped optical fibers have sufficient strength,
Regarding joining, since various connectors such as ST, SC and FC types have been developed, LA
It can function sufficiently as a communication fiber for networks such as N.

[0004] However, these quartz fibers are disadvantageous in that the core diameter is small and the connectors used for joining the quartz fibers are required to have high precision, so that the joining is required by skilled personnel and the construction cost is high. In particular, in a case where there are many joints in short-range communication, there is a problem that the installation cost becomes extremely high. In addition, since it is reinforced, the "tensile elastic modulus" (hereinafter, also simply referred to as "elastic modulus") is high, but there is a disadvantage that it is weak to impact and easily broken.

[0005] To solve these problems, plastic optical fibers have been proposed. Typical plastic optical fibers include graded index (SI) polymethyl methacrylate (PMMA) optical fibers.

The PMMA optical fiber has a core diameter of about 980.
μm, the clad diameter is 1000 μm, and the outer periphery is coated with polyethylene to have a diameter of 2200 μm.
Since the core diameter is large, an inexpensive resin connector can be used, the connection is easy and the construction cost is low, and the strength is sufficient because the optical fiber diameter is large.
There are drawbacks such as that the wavelength of a light source that can be used is limited due to light absorption, transmission loss is large, transmission distance is short, and the band is low due to the SI type. A refractive index distribution type (GI) PMMA optical fiber has been proposed as a method for improving these performances (WO93-08488), and it has become possible to increase the bandwidth, but it is difficult to improve the transmission distance and the wavelength limitation of the light source. It is.

As a method of improving these basic performances,
A GI plastic optical fiber made of a fluororesin has been proposed (WO95-28660). This fluororesin optical fiber can be used in a wide wavelength range of 650 to 1300 nm, and exhibits excellent basic performance such that transmission loss is small and the band is high. However, considering the practical performance of an optical fiber, the light receiving area of a high-bandwidth light receiving element is small, so to increase the coupling efficiency with the light receiving element, the diameter of the optical fiber must be reduced according to the light receiving element. There is a problem that the strength of the optical fiber is reduced.

[0008] In order to increase the strength of the optical fiber, a method of coating a reinforcing layer on the outer periphery thereof is generally used. For example, as described above, there is a method using a reinforcing fiber such as Kevlar as in the case of the quartz fiber.However, in this case, there is a disadvantage that the reinforcing fiber treatment is troublesome in joining with the connector or bonding the fibers, and the process becomes complicated. is there.

[0009] A method of coating with a high-strength high-modulus resin for reinforcement is also conceivable, but in this case, there is a drawback that transmission loss when the optical fiber is bent, so-called bending loss, increases. As means for solving this, it has been proposed to provide a gap between the optical fiber and the reinforcing coating, or to provide a foamed resin layer and reflect and confine the leaked light when bent by the air layer (Japanese Patent Application Laid-Open No. HEI 9-103572). 9-21832
7, JP-A-9-236735) has a problem that it is difficult to control the shape and thickness of the voids, and it is difficult to control the foaming, resulting in a large variation in wire diameter and a large non-circularity.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide an optical fiber having a low transmission loss and a high bandwidth, having a sufficiently large practical strength and a small bending loss. Another object of the present invention is to provide an inexpensive coated plastic optical fiber that can be easily connected and a method of manufacturing the same.

[0011]

Means for Solving the Problems The present invention is the following invention. (1) A coated plastic optical fiber having a first coating layer and a second coating layer on the outer periphery of a plastic optical fiber in order from the optical fiber side, wherein the first coating layer has a lower tensile elasticity than a resin constituting an optical fiber clad portion. A coated plastic optical fiber comprising: a resin having a modulus of elasticity; and wherein the second coating layer is made of a resin having a higher tensile modulus than the resin constituting the optical fiber cladding portion. (2) A coated plastic optical fiber is obtained by melt-spinning a plastic optical fiber precursor having a resin layer for forming a first coating layer and a resin layer for forming a second coating layer. A method for producing the coated plastic optical fiber.

(3) The cladding material and the core material of the plastic optical fiber, the resin for forming the first coating layer, and the resin for forming the second coating layer are simultaneously extruded from an extruder and coated integrally. A method for producing the above coated plastic optical fiber, comprising obtaining a plastic optical fiber. (4) The coated plastic optical fiber is obtained by simultaneously or separately coating the resin for forming the first coating layer and the second coating layer on the outer periphery of the plastic optical fiber in order from the optical fiber side. Manufacturing method of coated plastic optical fiber. (5) The method for producing a coated plastic optical fiber described above, wherein a coated plastic optical fiber is obtained by coating a resin for forming a second coating layer on the outer periphery of the plastic optical fiber having the first coating layer.

The plastic optical fiber in the present invention means "an optical fiber element in which at least a light transmitting portion is made of plastic" (hereinafter, simply abbreviated as an optical fiber). Here, the light transmitting portion refers to the core portion in the case of the SI type optical fiber including the core and the cladding, and in the case of the GI type optical fiber, 5% or more of the maximum intensity in the intensity distribution of the light in the fiber radial direction emitted from the fiber. The part that occupies. In the following description, the GI optical fiber portion occupied by less than 5% of the maximum intensity in the intensity distribution of light emitted from the GI optical fiber in the radial direction of the fiber is called a clad.

In general, in order to increase the coupling efficiency between the light source and the optical fiber and further increase the coupling efficiency between the optical fibers to facilitate the bonding, it is preferable that the core diameter of the optical fiber is large, and the inexpensive resin connector is used. From the viewpoint of using a core, a core diameter of 100 μm or more is preferable.

On the other hand, considering the coupling with the light receiving element, the core diameter is preferably as small as possible. In particular, when the purpose is to transmit in a high band of 1 Gbps or more, the diameter of the light receiving element capable of receiving a high band optical signal is 40 mm. １００100 μm, and the core diameter of the optical fiber is preferably 250 μm or less even when a light collecting means using a ball lens is considered. 100-2
The clad thickness is 10 to 2 for a core diameter of 50 μm.
If the thickness is about 0 μm, the function as an optical fiber can be sufficiently exhibited, but in this case, the tensile strength of the optical fiber is insufficient.

In order to increase the strength, the clad must be thick,
In other words, the diameter of the optical fiber may be increased, but in this case, the bending loss of the fiber increases. The optical fiber material is highly refined because it needs to be optically superior, even if it is a clad, and is expensive compared to general-purpose resins, so there is a problem from the viewpoint of providing an inexpensive optical fiber. . As another method of increasing the strength by using an inexpensive general-purpose resin, a method of coating and reinforcing the optical fiber with a general-purpose resin having a high elastic modulus can be considered, but in this case, an increase in bending loss cannot be avoided.

When analyzing the causes of bending loss, one is that the higher-order mode escapes outside the optical fiber when the optical fiber is bent, and the other is that a stress is applied to the optical fiber due to the bending to cause a loss. That is. In particular, since the plastic optical fiber has a smaller elastic modulus than the quartz fiber, the increase in transmission loss when receiving pressure is large.

When the cladding is thickened or covered with a high modulus resin, the reinforcing layer made of the clad or the high modulus resin coating is deformed, and the application of pressure to the optical fiber becomes a major factor. The loss increases extremely. As a result of theoretically estimating the amount of this deformation, it was found to be very small, less than a few μm, depending on the elastic modulus and coating thickness of a practical resin, depending on the elastic modulus and thickness of the reinforcing coating layer. Was.

Therefore, as a result of diligent studies on a method of alleviating the deformation amount as small as several μm, a structure in which a buffer layer made of a resin having a low elastic modulus is provided between an optical fiber and a reinforcing layer made of a resin coating having a high elastic modulus has been proposed. I found it.

That is, a first coating layer made of a resin having a lower elastic modulus than the optical fiber is provided on the outer circumference of the optical fiber, and a second coating layer made of a resin having a higher elastic modulus than the optical fiber is provided on the outer circumference thereof. As a result, a coated optical fiber having low bending loss while realizing high strength was obtained.

FIG. 1 shows an embodiment of a coated optical fiber according to the present invention. In FIG. 1A, 1 is an optical fiber, 2 is a first coating layer made of a resin having a lower elastic modulus than the optical fiber, and 3 is a second coating layer made of a resin having a higher elastic modulus than the optical fiber. As shown in FIG. 1B, a so-called protective layer 4 for protecting the optical fiber from an external environment can be further provided.

As the resin constituting the optical fiber cladding in the present invention, various resins are used as long as the resin has a higher elastic modulus than the resin for forming the first coating layer and has a lower elastic modulus than the resin for forming the second coating layer. Resin can be used.

For example, tetrafluoroethylene / perfluoro (alkyl vinyl ether) copolymer, polyperfluoro (butenyl vinyl ether), polyperfluoro (2,2-dimethyl-1,3-dioxole), tetrafluoroethylene / perfluoro (2 2-dimethyl-1,3-dioxole) copolymer and the like.
Fluorinated resin without H bond, partially fluorinated resin such as "polymethyl methacrylate, polycarbonate, polystyrene" in which some hydrogen atoms in the molecule are replaced with fluorine atoms, and polyvinylidene fluoride, etc. Partially deuterated resins such as "polymethyl methacrylate, polycarbonate and polystyrene" replaced with hydrogen atoms, polymethyl methacrylate, polycyclohexyl methacrylate, polystyrene, polyphenyl methacrylate, ethylene / vinyl acetate copolymer, polyacetal, polycarbonate, poly One or more resins selected from vinyl acetate and the like can be used.

The resin constituting the optical fiber cladding preferably has an elastic modulus of 50 to 140 kg / mm ² .

The optical fiber is made of the above-mentioned fluororesin or partially fluorine-based resin because the core diameter is relatively large, so that connection is easy and an inexpensive plastic connector can be used, the transmission loss is small, and the usable wavelength range is wide. Fluorine-based plastic optical fibers using a modified resin for the optical fiber cladding part and the core part are preferred. More preferably, it is a fluorine-based plastic optical fiber in which a fluorine-based resin having substantially no C—H bond is used for the optical fiber cladding part and the core part.

As the SI-type fluorine-based plastic optical fiber, those known in Japanese Patent Application Laid-Open No. 4-189882 and the like can be mentioned. Examples of the GI type fluorine-based plastic optical fiber include those known in JP-A-8-5848 and the like.

The GI optical fiber is preferably composed of a polymer having a refractive index difference and a diffusing substance, and the diffusing substance is distributed in the polymer with a concentration gradient along a specific direction. A GI-type fluoroplastic optical fiber in which the polymer is a fluoropolymer and the diffusing material is a low molecular weight fluorine-based compound is more preferable because it has a low transmission loss and a high transmission band in a wide transmission range. 8
-5848 etc.).

In this case, the number average molecular weight of the fluoropolymer is preferably 10,000 to 5 million, more preferably 50,000 to 1 million. The number average molecular weight of the low molecular weight fluorine compound is 30.
0 or more and less than 10,000 are preferred, and 300 to 5,
000 is more preferred.

The resin for forming the first coating layer may be any resin as long as it has a lower elastic modulus than the resin constituting the optical fiber cladding portion, and particularly has an elastic modulus of 50 kg / mm ^2.
Resins of less than 25 kg / mm ² are particularly preferred in terms of high buffering effect. The thickness of the first coating layer is preferably 5 to 50 μm, and 10 to 30 μm.
More preferably, it is μm.

As such a resin, an ultraviolet-curable silicone resin, an ultraviolet-curable acrylic silicone resin,
Photocurable resins such as UV-curable acrylic urethane resin, polyurethane, polyethylene, polypropylene, olefin-based thermoplastic elastomer, styrene-based thermoplastic elastomer, vinyl chloride-based thermoplastic elastomer, ethylene / vinyl acetate copolymer, polyvinylidene chloride Specific examples thereof include thermoplastic resins such as polyvinylidene fluoride and polyvinyl acetate, but are not limited thereto.

The resin for forming the second coating layer may be any resin as long as it has higher elasticity than the resin constituting the optical fiber clad portion, and particularly has an elastic modulus of 140 kg / mm ^2.
A super resin is preferable, and a resin of 160 kg / mm ² or more is particularly preferable in that the reinforcing effect is high. Also, the second
The thickness of the coating layer is preferably from 50 to 500 μm, more preferably from 100 to 300 μm.

Specific examples of such a resin include polymethyl methacrylate, polyethyl methacrylate, polycyclohexyl methacrylate, polystyrene, styrene / acrylonitrile copolymer, polyacetal, polycarbonate, aliphatic polyamide, aromatic polyamide, and polyvinyl chloride. However, the present invention is not limited to these.

Further, in the present invention, a resin layer functioning as a protective layer outside the second coating layer, for example, polyethylene, polyvinyl chloride, polyurethane, ethylene / tetrafluoroethylene copolymer, hexafluoropropylene / tetrafluoroethylene A copolymer or the like may be further coated. The thickness of the protective layer is preferably from 100 to 2000 μm, more preferably from 300 to 1000 μm.

As a method for producing the coated optical fiber of the present invention, a preform method and an extrusion method described below are preferable.

In the preform method, a plastic optical fiber precursor (hereinafter, referred to as a coated optical fiber precursor) having a resin layer for forming a first coating layer and a second coating layer is melt-spun to obtain a first coating. The optical fiber in which the second coating layer is integrated can be rationally manufactured.

In the present invention, the optical fiber precursor means a hollow or solid resin molded product that becomes an optical fiber when melt-spun. In addition, the resin layer for forming the first coating layer means a resin layer that becomes the first coating layer of the optical fiber when melt-spun, and the resin layer for forming the second coating layer is It means a resin layer that becomes a second coating layer of the optical fiber when spun.

The resin layer for forming the first coating layer may be a resin layer provided on the optical fiber precursor, and may be a resin hollow molded article that can be inserted with the optical fiber precursor. Or a resin layer provided on the inner peripheral surface of the “hollow molded body of resin to be the second coating layer”.

The resin layer for forming the second coating layer may be a resin layer provided on the resin layer serving as the first coating layer.
It may be a resin layer provided on the outer peripheral surface of the “first hollow resin molded body”, or a “second hollow resin molded article” into which the hollow molded article can be inserted. ,
The resin layer for forming the first coating layer may be a “hollow molded article of resin to be the second coating layer” into which the optical fiber precursor provided on the optical fiber precursor can be inserted. The "hollow resin molded article to be the second coating layer" into which the inserted "hollow resin molded article to be the first coating layer" may be inserted.

An optical fiber precursor, for example, a GI type optical fiber comprising a polymer having a refractive index difference and a diffusing substance, wherein the diffusing substance is distributed with a concentration gradient along a specific direction in the polymer. The precursor is obtained by forming a hollow tube made of a polymer by a rotational molding method, and diffusing a diffusion material into the polymer from the inner wall surface of the hollow tube while rotating the hollow tube.

The method for obtaining the coated optical fiber precursor includes the following methods (1-1) and (1-2). (1-1) An optical fiber precursor formed of a hollow tube is formed by a rotational molding method. Separately, a resin layer for forming a second coating layer made of a hollow tube is formed by a rotation molding method using a resin for forming a second coating layer, and the inner surface of the hollow tube is formed by a rotation molding method. Forming a “resin layer for forming the first coating layer” on the inner peripheral surface by forming a resin layer for forming the first coating layer, thereby forming a “hollow resin tube to be the second coating layer” I do. An optical fiber precursor consisting of a hollow tube is inserted into the hollow portion of a “resin hollow tube to be a second coating layer” having a resin layer for forming the first coating layer on the inner peripheral surface, and the coated optical fiber precursor is Get the body. (1-2) A resin hollow tube to be the second coating layer is formed by a rotational molding method. A resin layer for forming a first coating layer and an optical fiber precursor are formed in this order on the inner surface of the hollow tube by a rotational molding method to obtain a coated optical fiber precursor.

In the extrusion method, the following (2-1) to
A method such as (2-3) can be adopted. (2-1) A resin and an optical fiber for forming the first coating layer and the second coating layer are simultaneously extruded from an extruder and integrally molded to obtain a coated optical fiber. (2-2) The resin for forming the first coating layer and the optical fiber are simultaneously melt-extruded from an extruder and integrally molded to obtain an optical fiber having the first coating layer. In the step, a resin for forming the second coating layer is extruded and coated to obtain a coated optical fiber. (2-3) The cladding material of the optical fiber, the core material of the optical fiber, the resin for forming the first coating layer, and the resin for forming the second coating layer are simultaneously extruded from an extruder and integrally molded. Obtain a coated optical fiber.

In the present invention, the cladding material of an optical fiber means a material for forming a cladding in an SI type optical fiber, and a core having a cladding or a light intensity distribution close to the cladding in a GI type optical fiber. Means the material to be formed. The core material of the optical fiber means a material for forming the core in both the SI type optical fiber and the GI type optical fiber.

[0043]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for producing a coated optical fiber according to the present invention will be described below with reference to embodiments.

Example 1 (Example) Polyperfluoro (butenyl vinyl ether) [PBVE] having a modulus of elasticity of 140 kg / mm ² as a cladding material
Was used to form a hollow tube having an inner diameter of 6 mm and an outer diameter of 15 mm by a rotational molding method. Next, 14 wt% of chlorotrifluoroethylene [CTFE] oligomer is injected into the hollow portion, and the CTFE oligomer is diffused in the outer peripheral direction by rotating at a temperature of 250 ° C., and gradually decreases from the hollow inner wall portion to the clad portion. An optical fiber precursor (inner diameter 6 mm, outer diameter 15 mm) having a refractive index distribution was obtained.

On the other hand, a hollow tube having an inner diameter of 18 mm and an outer diameter of 45 mm was prepared by rotational molding using a polycarbonate resin having an elastic modulus of 170 kg / mm ² as a resin for forming the second coating layer. A polyethylene resin having a modulus of elasticity of 15 kg / mm ² , which is a resin for forming the first coating layer, is put into the hollow portion of the hollow tube and rotation molding is continued, and the inner diameter of the polyethylene resin is 15.5 mm and the outer diameter of the polyethylene resin is reduced. Diameter 18
A hollow tube of covering material having an outer diameter of 45 mm and a polycarbonate resin diameter of 45 mm was prepared.

The precursor of the optical fiber is inserted into the hollow portion of the coating material hollow tube, and further, these are placed in a heat-shrinkable tube of a tetrafluoroethylene / hexafluoropropylene copolymer and heated at 150 ° C. After the integration, the heat-shrinkable tube was peeled off to obtain a coated optical fiber precursor.

The precursor 5 was placed in an electric furnace 6 as shown in FIG.
And spinning at 240 ° C. using a
The film was wound using the winder 9 at a speed of 0 m / min. The outer diameter of the core of the coated GI optical fiber 7 thus obtained was 120 μm, the outer diameter of the clad was 240 μm, the outer diameter of the first coating layer was 290 μm, and the outer diameter of the second coating layer was 800 μm. When the performance of the optical fiber was measured, the transmission loss showed an excellent value of 60 dB / km at a wavelength of 1300 nm. The tensile strength of the optical fiber is 4.2 kg and the radius is 10
The increase in loss when a 180-degree bending test was performed at 0.
It was 6 dB.

Example 2 (Comparative Example) A coating having a core outer diameter of 120 μm, a cladding outer diameter of 240 μm, and a second coating layer outer diameter of 800 μm was performed in the same manner as in Example 1 except that the first coating layer made of polyethylene resin was not provided. A GI optical fiber was obtained. When the performance of the optical fiber was measured, the transmission loss was 60 dB / wavelength at 1300 nm.
km, optical fiber tensile strength 4.3kg, radius 10m
The increase in loss when a 180 degree bending test was performed at 2.0 m was 2.0.
dB.

Example 3 (Example) Example 1 except that the concentration of the CTFE oligomer was 12% by weight.
A hollow optical fiber precursor having an inner diameter of 6 mm and an outer diameter of 15 mm was prepared in the same manner as described above. As shown in FIG. 3, the precursor 10 is heated and spun at 240 ° C. in an electric furnace 6 to obtain an optical fiber 11, and an ultraviolet-curable silicone resin as a first coating layer is coated on the outer periphery with an ultraviolet-curable silicone resin. After being supplied from the silicone resin tank 12 to the die 13 for coating, the resin is irradiated with ultraviolet light from the lamp 14 and cured to obtain the first-layer coated optical fiber 15.
/ Mm ² polymethyl methacrylate resin extruder 1
From 6, it was extruded using a second coating layer die 17 to form a second coating layer, cooled in a water tank 18, and wound up using a winder 9 at a speed of 15 m / min. The elastic modulus of the cured silicone resin was 5 kg / mm ² .

The outer diameter of the core of the obtained coated GI optical fiber was 110 μm, the outer diameter of the cladding was 280 μm, the outer diameter of the first coating layer was 330 μm, and the outer diameter of the second coating layer was 650 μm. When the performance of the optical fiber was measured, the transmission loss showed an excellent value of 80 dB / km at a wavelength of 1300 nm. The optical fiber has a tensile strength of 5.2 kg and a radius of 10
The increase in loss when a 180-degree bending test was performed at 0.
It was 8 dB.

Example 4 (Comparative Example) A core outer diameter of 11 was obtained in the same manner as in Example 3 except that the first coating layer made of an ultraviolet-curable silicone resin was not provided.
0 μm, cladding outer diameter 280 μm, second coating layer outer diameter 65
A 0 μm coated GI optical fiber was obtained. When the performance of the optical fiber was measured, the transmission loss was 80 dB / km at a wavelength of 1300 nm, the tensile strength of the optical fiber was 5.4 kg,
The loss increase when performing a 180 degree bending test at a radius of 10 mm was 2.1 dB.

Example 5 (Example) A hollow optical fiber precursor having an inner diameter of 6 mm and an outer diameter of 15 mm was prepared in the same manner as in Example 1. The precursor 19 was heated and spun at 240 ° C. in an electric furnace 6 as shown in FIG. 4 to obtain an optical fiber 11, and a first coating layer and a second coating layer were continuously formed on the outer periphery thereof. Coated by extrusion method.

That is, a polyethylene resin having an elastic modulus of 5 kg / mm ² was used as a resin for forming the first coating layer.
170 k elastic modulus as resin for forming the second coating layer
g / mm ² of polycarbonate resin is supplied to a die 21 from an extruder 20 and an extruder 16, respectively.

The optical fiber 11 is introduced into the die 21 and is coated with the resin extruded from the discharge ports for the first and second coating layers, which are arranged concentrically and doubly on the outer periphery at the outlet thereof. Then, after being rapidly cooled in the cooling water tank 17, it was wound up by the winder 9 at a speed of 12 m / min.

The outer diameter of the core of the obtained coated GI optical fiber was 130 μm, the outer diameter of the clad was 250 μm, the outer diameter of the first coating layer was 300 μm, and the outer diameter of the second coating layer was 900 μm. When the performance of the optical fiber was measured, the transmission loss showed an excellent value of 50 dB / km at a wavelength of 1300 nm. The tensile strength of the optical fiber is 6.6 kg and the radius is 10
The increase in loss when a 180-degree bending test was performed at 0.
It was 4 dB.

Example 6 (Example) PB having an elastic modulus of 140 kg / mm ² as a cladding material
VE was used, and a core material obtained by adding 15% by weight of CTFE oligomer to PBVE was used. As shown in FIG. 5, the core material is extruded from the center of the die 24 using the extruder 22, and the clad material is then extruded using the extruder 23 to the outer periphery of the core material in the die 24 so as to surround the core. As the core / cladding is in contact in a molten state, the CTFE oligomer in the core diffuses into the outer cladding, and the refractive index gradually decreases from the core center to the cladding. The resulting refractive index distribution was formed.

On the other hand, a polyethylene resin having an elastic modulus of 15 kg / mm ² was used as a resin for forming the first coating layer, and a 170 kg elastic modulus was used as a resin for forming the second coating layer.
/ Mm ² , which are supplied to a die 24 from an extruder 20 and an extruder 16, respectively.

The resin integrated with the core / clad is supplied to the exit of the die 24 from the discharge ports for the first and second coating layers, which are arranged concentrically and doubly, with the resin for the first and second coating layers. It was simultaneously extruded and then quickly cooled in the cooling water tank 17, and then wound up by the winder 9 at a speed of 20 m / min.

The outer diameter of the core of the obtained coated GI optical fiber was 150 μm, the outer diameter of the clad was 300 μm, the outer diameter of the first coating layer was 380 μm, and the outer diameter of the second coating layer was 750 μm. When the performance of the optical fiber was measured, the transmission loss showed an excellent value of 50 dB / km at a wavelength of 1300 nm. The optical fiber strength is 3.6 kg and the bending loss is 0.3 kg.
It was 6 dB.

Example 7 (Comparative Example) Coating having a core outer diameter of 150 μm, a cladding outer diameter of 300 μm, and a second coating layer outer diameter of 750 μm was performed in the same manner as in Example 6, except that the first coating layer made of polyethylene resin was not provided. A GI optical fiber was obtained. When the performance of the optical fiber was measured, the transmission loss was 50 dB / at a wavelength of 1300 nm.
km, optical fiber tensile strength 3.8kg, radius 10m
The increase in loss when performing a 180 degree bending test at m is 2.4.
dB.

Example 8 (Example) Using the same core material and clad material as in Example 6, the core material was extruded from the center of a die 25 using an extruder 22 as shown in FIG. The extruder 23 was used to extrude the outer periphery of the core material in the die 25 so as to surround the core, and the core / cladding was integrated.

Further, since the core / cladding is in contact in a molten state, the CTFE oligomer in the core diffuses into the outer cladding, whereby the refractive index gradually decreases from the core center to the cladding. After the rate distribution is formed and then extruded from the die 25 outlet,
The optical fiber 27 was obtained by cooling in the water tank 26. Thereafter, the outer periphery of the optical fiber 27 was continuously coated with a first coating layer and a second coating layer by an extrusion method.

That is, a polyethylene resin having an elastic modulus of 15 kg / mm ² was used as a resin for forming the first coating layer, and a polyethylene resin having an elastic modulus of 17 kg was used as a resin for forming the second coating layer.
A polycarbonate resin of 0 kg / mm ² was used.
Supplied to The optical fiber 27 is introduced into the die 21 and is coated at the outlet thereof with the resin extruded from the discharge ports for the first and second coating layers, which are arranged on the outer periphery of the die 21 in a concentric circle. After being rapidly cooled in the cooling water tank 17, it was wound by the winder 9 at a speed of 15 m / min.

The outer diameter of the core of the obtained coated GI optical fiber was 140 μm, the outer diameter of the clad was 250 μm, the outer diameter of the first coating layer was 280 μm, and the outer diameter of the second coating layer was 900 μm. When the performance of the optical fiber was measured, the transmission loss showed an excellent value of 50 dB / km at a wavelength of 1300 nm. The optical fiber strength is 5.5 kg, and the bending loss is 0.4 kg.
It was 6 dB.

Example 9 (Comparative Example) Coating having a core outer diameter of 140 μm, a cladding outer diameter of 250 μm, and a second coating layer outer diameter of 900 μm was performed in the same manner as in Example 8, except that the first coating layer made of polyethylene resin was not provided. A GI optical fiber was obtained. When the performance of the optical fiber was measured, the transmission loss was 50 dB / at a wavelength of 1300 nm.
km, optical fiber tensile strength is 5.7kg, radius 10m
The increase in loss when a 180 degree bending test was performed at 2.5 m was 2.5.
dB.

Example 10 (Example) A polymethyl methacrylate resin having an elastic modulus of 200 kg / mm ² was used for the core material, and an elastic modulus of 110 kg / mm ² was used for the clad material.
Copolymer of 35 mol% of tetrafluoroethylene / 65 mol% of perfluoro (2,2-dimethyl-1,3-dioxole), a polyethylene resin having an elastic modulus of 15 kg / mm ² as a resin for forming the first coating layer Is used as a resin for forming the second coating layer and has an elastic modulus of 330 kg / m.
except using polymethyl methacrylate resin m ² was obtained a coated plastic optical fiber in the same manner as Example 8. However, when the core material and the clad material are used, mutual diffusion in a molten state does not occur, so that the optical fiber is an SI type.

The outer diameter of the core of the obtained coated SI optical fiber was 300 μm, the outer diameter of the clad was 350 μm, the outer diameter of the first coating layer was 400 μm, and the outer diameter of the second coating layer was 700 μm. When the performance of the optical fiber was measured, the transmission loss was as good as 150 dB / km at a wavelength of 650 nm. The optical fiber strength is 5.5 kg and the bending loss is 0.9 dB.
Met.

[0068]

According to the present invention, a low elastic modulus coating layer and a high elastic modulus coating layer are sequentially provided on the outer peripheral portion of an optical fiber, and the practical strength can be sufficiently increased by the high elastic modulus coating layer. In addition, since the deformation of the high elasticity coating layer when the optical fiber is bent by the low elasticity coating layer can be absorbed, the bending loss can be reduced. According to the present invention, it is possible to use an inexpensive general-purpose resin for the high elastic modulus layer, to reduce the cost of optical fiber, and to be particularly suitable for communication over a short distance, such as data transmission and video transmission in a LAN or home network. A coated optical fiber is obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a coated optical fiber of the present invention.

FIG. 2 is a schematic diagram for explaining an example of a method for producing a coated optical fiber by a preform method according to the present invention.

FIG. 3 is a schematic diagram for explaining an example of a method for producing a coated optical fiber by a preform method according to the present invention.

FIG. 4 is a schematic diagram for explaining an example of a method for producing a coated optical fiber by a preform method according to the present invention.

FIG. 5 is a schematic diagram for explaining an example of a method for producing a coated optical fiber by the extrusion method of the present invention.

FIG. 6 is a schematic view for explaining an example of a method for producing a coated optical fiber by the extrusion method of the present invention.

[Explanation of symbols]

1: optical fiber 2: first coating layer 3: second coating layer 4: protective coating layer 5: coated optical fiber precursor 6: heating furnace 7: coated optical fiber 8: take-up machine 9: take-up machine 10: optical fiber Precursor 11: Optical fiber 12: Ultraviolet-curable silicone resin tank 13: Ultraviolet-curable silicone resin-coated die 14: Ultraviolet irradiation lamp 15: First-layer coated optical fiber 16: Second-coated resin extruder 17: Second-coated layer Dies 18: Water tank 19: Optical fiber precursor 20: First coating layer resin extruder 21: Dies for simultaneous coating of first and second coating layers 22: Extruder for core material 23: Extruder for clad material 24: Core For simultaneously extruding a material, a clad material, and a resin for forming the first and second coating layers 25: a core material and a die for extruding a clad material 26: a water tank 27: an optical fiber

Claims (9)

[Claims] 1. A coated plastic optical fiber having a first coating layer and a second coating layer on an outer periphery of a plastic optical fiber in order from an optical fiber side, wherein the first coating layer is lower than a resin constituting an optical fiber clad portion. A coated plastic optical fiber comprising a resin having a tensile elasticity, wherein the second coating layer is made of a resin having a higher tensile elasticity than the resin constituting the optical fiber clad portion. 2. The coated plastic optical fiber according to claim 1, wherein the plastic optical fiber is a fluoroplastic optical fiber. 3. The coated plastic optical fiber according to claim 1, wherein the plastic optical fiber is a gradient index plastic optical fiber. 4. A coated plastic optical fiber is obtained by melt-spinning a plastic optical fiber precursor having a resin layer for forming a first coating layer and a resin layer for forming a second coating layer. Claim 1,
4. The method for producing a coated plastic optical fiber according to 2 or 3. 5. A coated plastic by simultaneously extruding a clad material and a core material of a plastic optical fiber, a resin for forming a first coating layer, and a resin for forming a second coating layer from an extruder and integrally forming the same. 4. The method for producing a coated plastic optical fiber according to claim 1, wherein an optical fiber is obtained. 6. A coated plastic optical fiber is obtained by simultaneously or separately coating a resin for forming a first coating layer and a second coating layer on the outer periphery of a plastic optical fiber in order from the optical fiber side. The method for producing a coated plastic optical fiber according to claim 1, 2 or 3. 7. The method according to claim 6, wherein the plastic optical fiber is obtained by melt-spinning a plastic optical fiber precursor. 8. A coated plastic optical fiber is obtained by coating a resin for forming a second coating layer around a plastic optical fiber having a first coating layer. A method for producing the coated plastic optical fiber according to the above. 9. The method according to claim 8, wherein the plastic optical fiber having the first coating layer is obtained by melt-spinning a plastic optical fiber precursor having a resin layer for forming the first coating layer. Method.