JPH08136744A - Refractive index distribution type polymer clad optical fiber and optical fiber cord with connector - Google Patents

Abstract

PURPOSE: To obtain a polymer clad optical fiber with which fast and large- capacity optical transmission for optical communication in medium or short distance is possible, in which connectors can be easily caulked, a mirror surface can be easily obtd. when the fiber is broken by stress fracture, and which has excellent installing property for practical use, reliability for construction and long-term reliability. CONSTITUTION: This refractive index-distribution type polymer clad optical fiber consists of a quartz core having distributed refractive index and a clad comprising a polymer tightly adhering around the core. In this fiber, the clad consists of a hard polymer having 2.05×10-<4> to 2.95×10-<4> /deg coefft. of linear thermal expansion and >=60 Shore hardness, and the clad has 5 to 30μm thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a LAN such as a high-speed and large-capacity data link within a medium distance and a short distance
The present invention relates to a gradient index polymer clad optical fiber suitable for constructing a (local area network).

[0002]

2. Description of the Related Art As a communication optical fiber for constructing a high-speed and large-capacity data link or the like, a refractive index distribution type silica-based multimode optical fiber among silica-based glass fibers using silica-based glass for a core and a clad is used. And quartz single mode optical fibers, and the standards for these optical fiber strands are defined in C6832 and 6835 of the Japanese Industrial Standard (JIS), respectively.

In particular, as the optical fiber for communication between data links, the former graded-index silica optical fiber is widely used from the viewpoint of workability [for example, The Bell System Technical Journal (B. S.T.J) vol.5
2, No. 9, P1563-1578 (1973)].

However, these graded-index silica optical fibers have a large band of about 500 MHz · km and a communicable distance of 2 km or more, which is excellent as an optical fiber for a long-distance data link, but conversely. , The core diameter is 50μ, though not so much as the single mode optical fiber
Since it is very small, about 100 μm, there is a problem in that it requires a high level of technology for joining, and is poor in economic efficiency and versatility.

That is, in the case of joining the graded index type silica optical fibers, a method of directly joining by electric discharge machining or a method of joining by an adhesive type connector having high dimensional accuracy is applied, and both are expensive. Equipment, advanced technology and long time are required for work, and so-called on-site workability is poor.

Further, there is also a problem that the light emitting / receiving element used in this optical fiber is required to have high dimensional accuracy, and the cost of the entire data link becomes high.

By the way, as an optical fiber excellent in field workability, there is a polymer clad optical fiber (US Pat. No. 4,511,209), which has a large diameter (core diameter of 200 μm) and can have a high numerical aperture. There is an advantage that the connector can be easily attached by crimping.

However, since the core of this polymer clad optical fiber is a step index type, its band is small at around 10 MHz · km, and although it can be used in a low speed data link, it can transmit data at high speed, voice, video, etc. There was a limit to the use as an optical transmission fiber in a large capacity data link that simultaneously transmits data.

Under such circumstances, a refractive index distribution type polymer is used as an optical fiber capable of optical transmission in a large capacity and wide band, and having a high numerical aperture for enhancing coupling efficiency with a light emitting and receiving element. A clad optical fiber has been proposed (JP-A-1-261602, JP-A-3-2451).
08 publication).

[0010]

However, the conventional graded index polymer-clad optical fibers proposed in these publications have a bandwidth of about 70 MHz · km, which is raised to a level at which transmission between medium-speed data links is possible. Although the coupling efficiency with the light emitting / receiving element is improved, the connector mounting process is not easy and the site workability is poor, and the long-term reliability of the connector portion due to the connector mounting process is not sufficient.

That is, in order to easily and reliably perform the end processing of the optical fiber and the attachment of the connector on site, the following conditions (1) to (4) must be satisfied, but a dopant such as germanium is contained. These conditions cannot be satisfied in the graded index polymer-clad optical fiber.

Even if the side surface of the optical fiber is directly caulked via the connector ferrule, the optical fiber should not be broken or fatigue broken due to cracks.

The caulking fixing force between the optical fiber and the ferrule is equal to or more than that of the adhesive connector.

In the above situation, the pisting between the optical fiber core and the cladding is at a very low level, which is substantially zero.

The quartz core has a mirror surface and is broken by a cutting blade pressed against the outer circumference of the polymer clad for cutting the fiber.

Therefore, the present invention solves the problems of the prior art as described above, enables high-speed and large-capacity optical transmission for medium-distance and short-distance optical communication, and facilitates crimping and crimping of connectors. Moreover, the main object of the present invention is to provide a graded index polymer-clad optical fiber which can be easily mirror-finished by optical fiber stress rupture and is excellent in site workability, construction reliability, long-term reliability and the like.

[0017]

To achieve this object, a gradient index polymer clad optical fiber according to the present invention has a core having a refractive index profile and made of quartz, and is closely attached to the outer periphery of the core. In a graded index polymer clad optical fiber including a clad made of a polymer, the clad has a linear expansion coefficient of 2.05 × 10 ^{−4 to} 2.95 × 1.
It is characterized by being made of a hard polymer having 0 ⁻⁴ / deg and a Shore hardness of D60 or more, and having a clad thickness of 5 to 30 μm.

In order to achieve the object of the present invention, first of all, the hardness of the clad polymer is the Shore hardness D method (AST
It is necessary for M-D2240) to be 60 or more in order to satisfy the above-mentioned conditions necessary for improving the on-site workability.

It is effective that the hardness and elastic modulus of the polymer of the clad are low in order to prevent the optical fiber from fracture or fatigue fracture due to cracks when the side surface of the optical fiber is directly caulked through the connector ferrule. ,conventionally,
Low hardness polymers having a Shore hardness method D50-55 at the highest have been used. However, such low hardness,
In the case of a clad polymer having a low elastic modulus, the caulking fixing force between the optical fiber and the ferrule is not sufficient, and it is difficult to satisfy the above conditions.

Therefore, as a result of studying the polymer hardness for the clad, even if a polymer having a high hardness of 60 or more by the Shore hardness D method is used for the clad, the caulking stress is relaxed by the plastic deformation of the clad polymer. It has been found that direct propagation to the quartz core is extremely small, and as a result, optical fiber breakage or fatigue breakage does not occur, and it is effective for smoothing the optical fiber cross section after cutting the optical fiber. .

Further, the clad polymer of the present invention has a coefficient of linear expansion of 2.05 × 10 ^{−4 to} 2.95 × 1 at room temperature.
It is also necessary to be 0 ⁻⁴ / deg.

In the prior art, as described in Japanese Patent Laid-Open No. 3-245108, it was considered necessary to have a concentration of 2.0 × 10 ^-4 / deg or less. However, as a result of detailed examination of the above-mentioned hard polymer having a good connector characteristic and a Shore hardness of D60 or more, it is 2.05 × 10 ^{−4, which} is higher than the conventional one.
It has been found that the range of the linear expansion coefficient of 2.95 × 10 ⁻⁴ / deg is optimum as the cladding polymer for the graded index polymer cladding optical fiber.

That is, when the clad is made of a polymer having a Shore hardness of D60 or more and a linear expansion coefficient of 2.05 × 10 ^-4 or more, the hardness is high and there is no brittleness. Therefore, when the optical fiber is cut, it is pressed against the optical fiber. Breaking impact due to stress concentration from the applied cutting edge propagates to the quartz core, and as a result, there is an advantage that the quartz core can be cut without a crack in the clad with a mirror surface. The fiber cross section becomes very smooth, and it can be used without a polishing process.

On the other hand, the coefficient of linear expansion is 2.05 × 10.
If it is less than ^-4 / deg, which is too low, the polymer is brittle, so even if the adhesion between the core and the clad is good, the clad is easily peeled off due to mechanical stimulus such as thermal shock or bending. It is difficult to obtain a clean cut surface or polished surface because the clad is easily chipped during cutting or polishing.

Further, the coefficient of linear expansion is 2.95 × 10 ^-4 / d.
If it exceeds eg, there is a problem that the microbent loss becomes large and the transmission loss becomes inferior, and the caulking fixing force between the optical fiber and the ferrule is insufficient.

From this point of view, the hardness of the polymer clad is
It is necessary that the Shore hardness D is as high as 60 or higher, and a hardness of D68 or higher is more preferable. The linear expansion coefficient at room temperature is 2.05 × 10 ^{−4 to} 2.95 × 10 ⁻⁴ /
deg is required, and further 2.10 × 10 ⁻⁴
˜2.50 × 10 ⁻⁴ / deg is preferable.

The thickness of the polymer clad layer of the present invention must be 5 to 30 μm. If the clad thickness is less than 5 μm, the light propagating in the quartz core is likely to leak out from the clad, resulting in insufficient light transmission performance, and the caulking stress is transmitted directly to the quartz core and cracks. It is easy to cause chipping. On the other hand, when it exceeds 30 μm, the microbend loss of the quartz core increases due to the contraction of the cladding when left at a low temperature, and it is difficult to sufficiently enhance the reliability represented by the low temperature characteristics.

The glass transition temperature of the clad polymer of the present invention is preferably 40 ° C. or higher, more preferably 65 ° C. or higher, and particularly preferably 80 ° C. or higher. Glass transition temperature is 40 ℃
If it is less than the above range, the microbend loss of the quartz core tends to increase due to the shrinkage of the clad when left at a low temperature, and it is difficult to sufficiently enhance the reliability represented by the low temperature characteristics.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION A clad polymer satisfying the values of hardness and linear expansion coefficient described above is disclosed in US Pat.
It is preferably a UV cured polymer, such as the UV curable monomer compositions for cladding polymers described in No. 09 specification. On the other hand, the thermoplastic resin needs to be melt-coated on the outer periphery of the clad, or needs to be dried after being coated as a solution dissolved in a solvent, but the adhesion with the clad is not good, or the wire diameter cannot be stabilized, Problems such as increased microbend loss tend to occur.

As the curable monomer composition for forming the polymer for the clad, specifically, a main monomer of a fluorinated (meth) acrylate containing a fluorinated alkyl group,
Examples thereof include a monomer composition in which an alkyl group-containing (meth) acrylate-based polyfunctional monomer is used in combination at an appropriate mixing ratio. As these monomers, those exemplified below can be used.

Examples of the fluorine-containing (meth) acrylate containing a fluorinated alkyl group include CH ₂ ═CHCOOCH ₂ CF ₃ CH ₂ ═CHCOOCH ₂ CF ₂ CF ₃ CH ₂ ═CHCOOCH ₂ CFHCF ₃ CH ₂ ═C (CH ₃ ) COOCH _{2 CFHCF 3 CH 2 = CHCOOCH 2} CH 2 CF 3 CH 2 = CHCOOCH 2 CF 2 CFHCF 3 CH 2 = CHCOOCH 2 CF (CF 3) CF 3 CH 2 = CHCOOCH (CF 3) 2 CH 2 = C (F) COOCH _{(CF 3) 2 CH 2 =} C (CH 3) COOCH (CF 3) 2 CH 2 = CHCOOCH 2 (CF 2 CF 2) 3 H CH 2 = C (F) COOCH 2 (CF 2 CF 2) 2 H CH ₂ = C (CH ₃ ) COOCH ₂ (CF ₂ CF ₂ ) _{2
H CH 2 = CHCOOCH 2 CF 2} CF 2 CFHCF 3 CH 2 = CHCOOCH 2 CF 2 CF 2 H CH 2 = C (CH 3) COOCH 2 CF 2 CF 2 H CH 2 = C (F) COOCH 2 CF 2 CF 2 _{H CH 2 = CHCOOCH 2 CH 2} C 8 F 17 CH 2 = C (CH 3) COOCH 2 CH 2 C 8 F 17 CH 2 = CHCOOCH 2 CH 2 C 12 F 25 CH 2 = C (CH 3) COOCH 2 CH _{2 C 12 F 25 CH 2 =} CHCOOCH 2 CH 2 C 10 F 21 CH 2 = C (CH 3) COOCH 2 CH 2 C 10 F 21 CH 2 = CHCOOCH 2 CH 2 C 8 F 13 CH 2 = C (CH 3 _{) COOCH 2 CH 2 C 6 F} 13 CH 2 = CHCOOCH 2 CH 2 C 4 F 9 CH 2 = CFCOOCH 2 CH 2 C 6 F 13 CH 2 = CHCOOCH 2 (CH 2) 6 CF (CF 3)
_{2 CH 2 = CHCOOCH 2 (CH} 2) 6 H CH 2 = C (CH 3) COOCH 2 (CH 2) 8 H CH 2 = CHCOOCH 2 (CH 2) 10 H CH 2 = CHCOOCH 2 (CH 2) 12 H _{CH 2 = CHCOOCH 2 C (OH} ) HCH 2 C 8 F 17 CH 2 = CHCOOCH 2 CH 2 N (C 3 H 7) SO 2
_{C 8 F 17 CH 2 = CHCOOCH} 2 CH 2 N (C 2 H 5) COC
₇ F ₁₅ CH ₂ = CHCOO (CH ₂ ) ₂ (CF ₂ ) ₈ CF (C
_{F 3) 2 CH 2 = C} (CH 2 CH 2 C 8 F 17) COOCH 2 CH
₂ C ₈ F ₁₇ may be mentioned, and these fluorine-based (meth) acrylates may be used as a mixture of two or more kinds of compounds having different structures.

As the polyfunctional monomer, ethylene glycol di (meth) acrylate diethylene glycol di (meth) acrylate triethylene glycol di (meth) acrylate polyethylene glycol di (meth) acrylate (number average molecular weight 200 to 1000) propylene glycol di (Meth) acrylate Dipropylene glycol di (meth) acrylate Tripropylene glycol di (meth) acrylate Polypropylene glycol di (meth) acrylate (number average molecular weight 200 to 1000) Neopentyl glycol di (meth) acrylate 1,3-butanediol di (Meth) acrylate 1,4-butanediol di (meth) acrylate 1,6-hexanediol di (meth) acrylate hydroxypivalate ester Neopentyl glycol di (meth) acrylate Bisphenol A di (meth) acrylate pentaerythritol tri (meth) acrylate dipentaerythritol hexa (meth) acrylate pentaerythritol tetra (meth) acrylate trimethylolpropane di (meth) acrylate pentaerythritol monohydroxypenta (meth) acrylate _{CH 2 = CHCOOCH 2 (C 2} F 4) 2 CH 2 OCO
_{CH = CH 2 CH 2 = CHCOOC} 2 H 4 (C 2 F 4) 3 C 2 H 4 O
_{COCH = CH 2 CH 2 = C} (CH 3) COOC 2 H 4 (C 2 F 4) 3 C
_{2 H 4 OCOC (CH 3)} = CH 2 and the like.

The curable monomer composition for the above-mentioned clad polymer is a fluorine-based (meth) -containing fluoroalkyl group as described above.
Acrylic main monomer and alkyl group-containing (meth)
In addition to the acrylate-based polyfunctional monomer, various additives may be contained, if necessary, as long as the curing conditions and the compatibility are within an allowable range.

The additives include antioxidants such as hindered phenols, light resistance improvers, coupling agents for improving adhesion and bondability with the quartz core, and uniform application to the quartz core. Examples of the defoaming agent, leveling agent, surfactant, plasticizer and the like.

The quartz core needs to have a square distribution type refractive index distribution, that is, a refractive index distribution in the cross-sectional direction of the core. This refractive index distribution is obtained by a usual method of doping germanium or the like. To be In order to obtain an optical fiber having a wide transmission band and capable of high-speed and large-capacity optical transmission, the refractive index distribution state of the quartz core has a square distribution coefficient α of 1.0 to 2.2, and further 1.8. It is preferably -2.2.

The refractive index (n _Cl ) of the clad and the refractive index (n ₁ ) at the outermost peripheral portion of the core are values satisfying the following equations. This is preferable in order to obtain an optical fiber that is capable of optical transmission, has a small bending loss, has good workability, and has high reliability.

[0037] When ^{_{0.20 ≦ (n 1 2 -n Cl}} 2) 1/2 ≦ 0.45 That is, the value of ^{_{(n 1 2 -n Cl 2)}} 1/2, less than 0.20, Since bending loss and the like increase, it is difficult to sufficiently enhance the field workability and reliability in medium and short distances. On the other hand, if it is larger than 0.45, the coupling efficiency with the light emitting and receiving element is increased and the communicable distance is improved, but it is difficult to set the transmission band to about 70 MHz · km or more, and high-speed, large-capacity optical transmission is difficult. .

According to the present invention, the optical fiber cord having the polymer coating layer provided on the outer periphery of the graded index polymer clad optical fiber is attached to one end or both ends of the polymer coating layer, and the crimp type connector is attached to the connector by caulking. When using the attached optical fiber cord, the pulling force of the optical fiber from the ferrule inside the connector is as high as 2.0 kg or more, and the amount of pisting when the pulling load of 1.0 kg × 1 minute is applied is 10 μm or less. Can be made smaller.

The pulling force of the optical fiber from the ferrule inside the connector is a value obtained by measuring the force required to pull out the optical fiber from the ferrule inside the connector by attaching a JIS 05 type caulking crimp connector to the optical fiber cord. Is. The above-mentioned pistening amount is the pistening amount generated between the quartz core and the clad polymer when a load of 1.0 kg x 1 minute is applied in the direction of pulling out the optical fiber from the ferrule.

First, since the pulling-out force of the optical fiber of less than 2.0 kg is a pulling-out force smaller than that of the ferrule fixing in the adhesive type connector using the adhesive such as epoxy resin, it is necessary to remove the light from the connector when the wiring between devices is performed. There is a risk that the fiber will fall out, making it difficult to maintain the reliability of the connector.

Further, since the amount of pistening generated between the quartz core and the clad polymer is 10 μm or less under the condition of the drawing load of 1.0 kg × 1 minute, the amount of light emitted when the connector is connected and the connection efficiency are high. Highly reliable optical fiber can be easily implemented.

The core diameter in the present invention is represented by a diameter of 200 μm, which is represented by JIS standard and FDDI (Fiber Distributed Data Interface) standard.
The diameter is not limited to 0 μm.

The optical fiber based on the core-clad structure of the present invention may be provided with one or more polymer coating layers on its outer periphery for the purpose of buffering, mechanical protection and the like. That is, the optical fiber of the present invention is used as an optical fiber core wire, an optical fiber cord, an optical fiber cable, etc., in addition to an optical fiber element wire.

As these polymer coating layers, curable resins such as silicone resins, UV-curable acrylate resins, and polyimide resins that are cured by heat or UV rays are preferably used. In addition, heat-melt type so-called thermoplastic resins are also used. A resin can also be used.

The shore hardness D of the clad polymer referred to in the present invention is a value measured based on the method of ASTM D2240. At that time, the curable monomer composition for forming the clad polymer is used at the time of forming the clad polymer. The method may be a method in which a polymer plate having a thickness of 1 mm is prepared by curing under the same curing conditions as above, and the Shore hardness D of the polymer plate is measured.

The linear expansion coefficient of the clad polymer is ASTM
-It is the value measured based on the method of D696. The glass transition temperature is a value measured under the condition of 10 ° C./min using a measuring instrument “TMA” manufactured by Seiko Denshi KK

[0047]

EXAMPLES Each physical property value in the examples was measured by the following measuring methods.

Bending loss (dB): The amount of transmitted light is measured as an initial amount of light by using an 850 nm LED light source and a silicon diode light receiving element in an optical fiber having a length of 3 m. Then, the amount of transmitted light is measured with the sample being wound once around a mandrel having a radius of 10 mm, and the difference from the initial amount of light is taken as the bending loss.

Loss increase at low temperature (dB): A 498 m portion of the middle part excluding both ends of a 500 m long optical fiber was put in a thermostatic chamber (normal temperature), and an 850 nm LED was provided at one end and a silicon diode was provided at the other end. Connect the light receiving element and measure the amount of transmitted light as the initial amount of light. Next, the temperature of the constant temperature bath is lowered at a rate of 1 ° C./min to −20 ° C., the light transmission loss is measured after standing at that temperature for 1 hour, and the difference from the initial light amount is defined as the loss increase.

Ferrule Caulking Loss (dB): The amount of transmitted light measured with an 850 nm LED for an optical fiber with a sample length of 3 m, which is attached without adhesive and without caulking, is used as the initial amount of light. Next, the connector is attached to the other end by caulking, the amount of transmitted light in that state is measured, and the difference from the initial amount of light is taken as the ferrule caulking loss.

Average mirror surface area ratio (%) of the end face of the optical fiber: After the stress fracture of the optical fiber, the cross-sectional area of the mirror surface portion in the fractured surface of the core is measured by an optical microscope, and this cross-sectional area of the mirror surface portion with respect to the entire core cross-sectional area is measured. Find the ratio.

Example 1 Quartz glass was doped with a Ge element to prepare a gradient index base material having a gradient index distribution coefficient α of 1.98. This base material is stretched to have an outer diameter of 2
A 5 mmφ quartz core base material was used.

The obtained quartz core base material was placed in an electric furnace of carbon resistance heating type and drawn at an electric furnace temperature of 2180 ° C. and a drawing speed of 100 m / min so that the outer diameter of the quartz core was 200 μmφ. The outer diameter of the quartz core was controlled by adjusting the feeding speed of the quartz core base material into the electric furnace and the core drawing speed. The quartz core drawn from the electric furnace was then introduced into an inert gas atmosphere whose temperature and humidity were controlled and cooled, and trihydroperfluoroundecyl acrylate, trimethylolpropane triacrylate, γ-mercaptotrimethoxysilane and A curable monomer composition for a clad polymer composed of a photosensitizer is applied,
The coating composition was photocrosslinked and cured by irradiation of ultraviolet rays from an ultraviolet irradiation device to form a clad.

The outer diameter of the obtained optical fiber clad is 2
The eccentricity of the core and the clad (the value obtained by dividing the difference between the clad thickest part distance and the clad thinnest part distance by the quartz core diameter) was 4.1%. Further, the non-circularity of the quartz core and the polymer clad are 0.5% and 0.
The optical fiber had an extremely high roundness of 8%. Also,
The hardness of the clad polymer was Shore hardness D70, the coefficient of linear expansion was 2.2 × 10 ⁻⁴ / deg, and the glass transition temperature was 90 ° C.

The obtained optical fiber was melt-coated with a polymer composed of ethylene / tetrafluoroethylene copolymer to obtain a graded index polymer-clad optical fiber having a structure composed of a core / clad and a primary coating layer.

The characteristics of the obtained gradient index polymer clad optical fiber are as shown in Table 1, and the transmission band was wide, and the optical characteristics, the terminal processability and the connector fixing property were all excellent.

[Examples 2-5, Comparative Examples 1-5] Except that the composition of the curable monomer composition for the cladding polymer and its coating conditions were changed so that the conditions shown in Tables 1 and 2 were obtained. A gradient index polymer clad optical fiber was prepared in the same manner as in Example 1. The characteristics of the obtained optical fiber are shown in Tables 1 and 2.

As shown in Tables 1 and 2, Examples 2 to 2
In the case of No. 6, as in Example 1, the transmission band was wide, and all of the optical characteristics, terminal processability, and connector fixability were excellent.

On the other hand, in the case of Comparative Example 1 in which the hardness of the clad was too low and the glass transition temperature was low, the mirror-finishing at the time of cutting was insufficient, and the transmission loss at a low temperature was large. In the case of Comparative Example 2 which is a step index type polymer clad optical fiber, the transmission band was narrow. In Comparative Examples 3 and 4 in which the coefficient of linear expansion of the clad was outside the scope of the present invention, mirroring at the time of cutting was insufficient, the transmission loss was large, and the fixing force of the connector was insufficient. Further, in the case of Comparative Example 5 in which the cladding was too thick, the loss at a low temperature was large.

[0060]

[Table 1]

[0061]

[Table 2]

[0062]

[Effect of the Invention] 70M for medium and short distance optical communication
High-speed, large-capacity optical transmission of Hz · km or more is possible,
Moreover, the caulking and crimping connector (ferrule) and the optical fiber have a strong fixing force, the loss due to caulking is small, the amount of pisting between the core and the clad is small, and it is easy to make a mirror surface when the optical fiber stress is broken. Enforceability,
It is possible to obtain a graded-index polymer-clad optical fiber having excellent construction reliability and long-term reliability.

Front page continuation (72) Inventor Seiji Fukuda 2-2-1 Nihombashi Muromachi, Chuo-ku, Tokyo Toray Industries, Inc. Tokyo business site

Claims (7)

[Claims] 1. A graded-index polymer-clad optical fiber comprising a core having a refractive index distribution and made of quartz, and a clad which is in close contact with the outer periphery of the core and is made of a polymer. Coefficient 2.05 × 10 ^-4 ~
It is made of a hard polymer having a hardness of 2.95 × 10 ⁻⁴ / deg and a Shore hardness of D60 or more, and has a clad thickness of 5
A graded-index polymer-clad optical fiber having a thickness of ˜30 μm. 2. The shore hardness of the hard polymer is D68.
The graded index polymer-clad optical fiber according to claim 1, which is the above. 3. The gradient index polymer-clad optical fiber according to claim 1, wherein the hard polymer is a UV-cured fluorine-based (meth) acrylate-based resin. 4. The glass transition temperature of the hard polymer is 4.
The gradient index polymer-clad optical fiber according to claim 1, 2 or 3, wherein the temperature is 0 ° C or higher. 5. The refractive index (n _Cl ) of the clad and the refractive index (n ₁ ) at the outermost peripheral portion of the core are values satisfying the following expressions. 3. The gradient index polymer clad optical fiber according to 3 or 4. _{^{0.20 ≦ (n 1 2 -n Cl}} 2) 1/2 ≦ 0.45 6. The core has a square distribution coefficient α of 1.0.
The gradient index polymer-clad optical fiber according to claim 1, 2, 3, 4, or 5, having a squared refractive index profile of about 2.2. 7. An optical fiber cord comprising one or a plurality of polymer coating layers on the outer circumference of the graded index polymer clad optical fiber according to claim 1, and the polymer coating layer at one or both ends thereof. An optical fiber cord with a connector, which is a crimp crimp type connector that is peeled off and attached, wherein the pulling force of the optical fiber from the ferrule inside the connector is 2.0 kg or more, and 1.0 k
An optical fiber cord with a connector, wherein the amount of pistening between the core and the cladding when a pulling load of g × 1 minute is applied is 10 μm or less.