WO2011070922A1 - Gradient-index plastic optical fiber - Google Patents

Abstract

Disclosed is a gradient-index plastic optical fiber which is composed of a core portion and a cladding portion that is arranged around the core portion. The core portion is mainly configured of: a copolymer of a monomer that contains 55-95% by weight of 2,2,2-trifluoroethyl methacrylate (3FMA) and 5-45% by weight of methyl methacrylate (MMA); and a dopant that has a higher refractive index than the copolymer and is compatible with the copolymer. The cladding portion is mainly configured of a polymer of a monomer that contains more than 55% by weight but 100% by weight or less of 3FMA and 0% by weight or more but less than 45% by weight of MMA. The 3FMA content in the polymer is set to be higher than the 3FMA content in the copolymer of the core portion.

Description

Gradient index plastic optical fiber

The present invention relates to a refractive index distribution type plastic optical fiber, and more particularly, has a sufficient light transmission performance to be able to construct an optical transmission link system for a short distance such as an optical transmission link system indoors, especially in a house, and is bent. The present invention relates to a refractive index distribution type plastic optical fiber with low transmission loss and capable of high-speed communication.

In recent years, the spread of the Internet in each home has progressed, and the trend of increasing the amount of communication information such as movie reception and interactive video communication via TV and personal computers has been remarkable, and the speed of the terminal communication network in the home has increased. Is eager. With the spread of fiber-to-the-home (FTTH), the number of households with optical communication has been increasing up to the front of the house, but conventional copper wire communication is common in the home. In addition, wireless communication has been penetrating to some extent for convenience, but in both cases, the communication speed is slow and rate limiting. Furthermore, as the speed of copper wire increases, noise countermeasures need to be strengthened, and there is a concern about information leakage in wireless communication.
Therefore, there is an increasing need to penetrate optical wiring capable of high-speed communication into the home, and a plastic optical fiber (hereinafter sometimes abbreviated as “POF”) is most promising as the medium. POF is generally various in that it has good flexibility, is lightweight, has good workability, is easy to manufacture as a large-diameter fiber, can be manufactured at low cost, and is not subject to electromagnetic noise. Has the advantages of

Conventionally, a POF having a core part made of methacrylic resin such as polymethyl methacrylate (hereinafter sometimes abbreviated as “PMMA”) is known (for example, see Patent Document 1).

Further, for the purpose of increasing the communication speed, a refractive index distribution type (GI type) POF is known in which the refractive index changes continuously or stepwise from the center of the fiber in the radial direction.
In GI-type POF, a method of imparting a difference in refractive index is called a dopant, which is a method of doping a low molecule having a different refractive index and good compatibility with a polymer (see, for example, Patent Document 2), A method of changing the copolymer composition of monomers having different rates (for example, see Patent Document 3) is known. Among them, the former is superior from the viewpoint of maintaining the transparency of the light guide unit that determines the communicable distance.
Further, as a method for imparting a refractive index distribution, a method using a gel effect in polymer polymerization (see, for example, Patent Document 2) or a method of physically laminating layers having different refractive indexes (for example, patents). Document 4) and a method using thermal diffusion of a dopant into a polymer are known (for example, see Patent Document 5).

Until now, GI-type POF using PMMA-based resin as a core portion was considered suitable for high-speed communication, but its adoption was postponed for the following reasons.
In the case of a PMMA fiber, an LED light source having a wavelength of 650 nm is generally used. However, an LD light source compatible with gigabit high-speed communication has a short life and is insufficient for home use. On the other hand, a VCSEL light source of about 660 to 680 nm is considered to have a lifetime, but the transmission loss of the PMMA GI POF in these wavelength regions is about 200 to 330 dB / km (for example, see Patent Document 2). Thus, as the wavelength becomes longer, the loss suddenly increases. Considering the loss of PMMA due to moisture absorption, it cannot be used at a communication distance of 30 m or more, particularly 50 m or more required for home use.

On the other hand, POF capable of achieving high-speed communication with other materials is known. For example, hydrogen atoms in the MMA molecular structure are partially or entirely replaced with deuterium atoms, and C—H bond expansion and contraction is achieved. Absorption wavelength region caused by motion is shifted by a long wavelength, and substantially all of the hydrogen atoms in the polymer molecular structure are replaced with fluorine atoms that have achieved low loss in the above wavelength region (for example, see Patent Document 2). GI type POF (for example, refer to Patent Document 6) and the like in which transmission loss is greatly reduced by doing so.
However, although these POFs can be high-speed communication optical fibers, the cost of raw material monomers is high, and they are expensive compared to PMMA. Therefore, it is difficult to introduce or disseminate them for communication transmission indoors, especially in homes. It is done.
Further, GI-POF made of, for example, polytetrafluoroethyl methacrylate (hereinafter sometimes abbreviated as “P4FMA”) in which hydrogen atoms in the polymer molecular structure are partially substituted with fluorine atoms is transparent. Although the glass transition temperature (Tg) of P4FMA is as low as about 75 ° C., and the dopant is added, the Tg is further lowered, so that the long-term heat resistance is inferior. There was a challenge to deal with it.

In addition, when optical fibers are wired indoors, especially in homes, they are bent several tens of times with a bending radius of about 10 mm by folding them around the corners of the room, from the inner wall to the ceiling, or along the door periphery. Since a location is required, there is a problem that it is necessary to suppress transmission loss at the bent portion.

Under these circumstances, it has sufficient light transmission performance to eliminate the drawbacks of the conventional gradient index plastic optical fiber, and can construct an optical transmission link system indoors, especially in the home, with little transmission loss when bent, and Development of a gradient index plastic optical fiber capable of high-speed communication is desired.

Japanese Patent No. 3576223 Japanese Patent No. 3333292 Patent No. 3010369 Japanese Patent No. 3258605 Japanese Patent No. 3471015 Japanese Patent No. 3487964

In view of the above-mentioned problems of the prior art, the object of the present invention is to have a sufficient light transmission performance for constructing an optical transmission link system indoors, especially in a home, with little transmission loss when bent, and capable of high-speed communication. The object is to provide a gradient index plastic optical fiber.

As a result of intensive studies in order to solve the above problems, the present inventors have formed a core part and a clad part in an optical fiber comprising a core part and a clad part arranged on the outer periphery of the core part. As components, 2,2,2-trifluoroethyl methacrylate (hereinafter sometimes abbreviated as “3FMA”) and methyl methacrylate (hereinafter sometimes abbreviated as “MMA”), respectively, at a predetermined ratio. In the core part, a specific dopant is blended with the specific copolymer, while the clad part contains the 3FMA monomer in the polymer forming the clad part. Refractive index having desired characteristics by adjusting the ratio to be larger than the content ratio of 3FMA monomer in the copolymer forming the core part Found that fabric-type plastic optical fiber is obtained, by their findings, the present invention has been completed.

That is, according to the first aspect of the present invention, there is provided a gradient index plastic optical fiber (GI-type POF) comprising a core portion and a clad portion disposed on the outer periphery of the core portion,
The core has a copolymer of monomers containing 55 to 95% by weight of 2,2,2-trifluoroethyl methacrylate and 5 to 45% by weight of methyl methacrylate, and a refractive index higher than that of the copolymer. And a dopant compatible with the copolymer as a main constituent,
The clad part mainly comprises a polymer of a monomer containing 55 to 100% by weight of 2,2,2-trifluoroethyl methacrylate and 0 to less than 45% by weight of methyl methacrylate, and the polymer There is provided an optical fiber characterized in that the content ratio of 2,2,2-trifluoroethyl methacrylate in is greater than the content ratio of 2,2,2-trifluoroethyl methacrylate in the copolymer of the core part.

According to the second invention of the present invention, in the first invention, the difference in the content ratio of 2,2,2-trifluoroethyl methacrylate in the copolymer of the core part and the polymer of the clad part is different. An optical fiber characterized in that it is 5 to 25% by weight is provided.

According to a third aspect of the present invention, in the first or second aspect, the copolymer of the core portion is 80 to 90% by weight of 2,2,2-trifluoroethyl methacrylate and 10 to 20%. The optical fiber provides that the polymer of the clad portion contains 90% to 100% by weight of 2,2,2-trifluoroethyl methacrylate and 0% to 10% by weight of methyl methacrylate, while the polymer of the clad part contains 90% by weight of methyl methacrylate. Is done.

According to a fourth aspect of the present invention, there is provided an optical fiber according to any one of the first to third aspects, wherein the dopant is dibenzothiophene.

According to a fifth aspect of the present invention, there is provided an optical fiber according to any one of the first to fourth aspects, wherein the outer periphery of the cladding is coated with a plastic mainly composed of polycarbonate. Is done.

Further, according to the sixth aspect of the present invention, there is provided a short-distance optical transmission link system using the optical fiber according to any one of the first to fifth aspects.

Further, according to the seventh aspect of the present invention, there is provided an indoor optical transmission link system using the optical fiber according to any one of the first to fifth aspects.

In the present specification, the core part and the clad part are not limited to the core and clad in the optical sense of the optical fiber (for example, a material discriminated based on the presence or absence of a dopant), respectively. A layer composed of a polymer which is a main component constituting the core is referred to as a core portion, and a layer composed of a polymer which is the main component which constitutes a cladding is referred to as a cladding portion.

The refractive index distribution type plastic optical fiber of the present invention has sufficient light transmission performance to construct a short-distance optical transmission link system such as an optical transmission link system indoors, especially in a home, and has a transmission loss when bent. There are few and high-speed communication is possible.

The optical fiber of the present invention is a refractive index distribution type plastic optical fiber (GI-type POF) comprising a core part and a clad part arranged on the outer periphery of the core part, wherein the core part is 2,2,2-trifluoroethyl methacrylate. And a monomer copolymer (A) containing methyl methacrylate in a specific ratio and a dopant (D) having a higher refractive index than that of the copolymer and compatible with the copolymer. On the other hand, the clad part is mainly composed of 2,2,2-trifluoroethyl methacrylate, or a polymer (B) of a monomer containing methyl methacrylate in a specific ratio, and the polymer The content of 2,2,2-trifluoroethyl methacrylate in the copolymer of the core part is 2,2,2- Characterized in that more than the content ratio of Li fluoroalkyl methacrylate.
Hereinafter, the present invention will be described in detail for each item.

1. Gradient index plastic optical fiber (GI POF)
The GI POF of the present invention is composed of a core part and a clad part arranged on the outer periphery of the core part, and is classified into a graded index (GI) type having a refractive index distribution. Here, the refractive index distribution means that the refractive index changes in a stepwise manner with a constant curve or a curve close to a parabola in the radial direction from the center of the fiber. Among these, those having a refractive index that decreases in the radial direction from the center are preferable. By providing such a refractive index distribution, the communication speed can be improved.

In addition, the refractive index may once decrease in a curvilinear or stepwise manner from the center of the fiber in the radial direction, and then increase in a curvilinear or stepwise manner. In this case, the core part and the outermost layer of the cladding part preferably have a higher refractive index of the core part, but the outermost layer of the cladding part may have a higher refractive index than the core part. The clad part may contain a dopant.

2. Copolymer (A) and polymer (B)
As the copolymer (A) that forms the core of the optical fiber of the present invention, a monomer copolymer containing 2,2,2-trifluoroethyl methacrylate (3FMA) and methyl methacrylate (MMA) is used. . Among them, a copolymer of MMA and 3FMA as a comonomer is suitable.

In general, during copolymerization, the copolymer composition of the resulting polymer gradually changes with the degree of polymerization (polymerization conversion rate), and as a result, the refractive index of the copolymer obtained in the first and second stages of polymerization. Therefore, the resulting polymer that is a mixture of them has a large scattering loss.
However, in the case of copolymerization of 3FMA and MMA, the monomer reactivity ratio was r ₁ = 0.97 for 3FMA and r ₂ = 0.83 for MMA.
The monomer reactivity ratio represents the reactivity of each monomer in copolymerization. For example, considering the copolymerization of monomer 1 and monomer 2, it is a radical that grows at a certain moment (one polymer chain that is undergoing radical polymerization and is growing, and has a radical at its end. ), The terminal is the radical of monomer 1 or monomer 2. When the terminal is a radical of monomer 1, k ₁₁ is the reaction rate constant when monomer 1 is continuously reacted and added to the terminal, and k is the reaction rate constant when monomer 2 is added by reaction. _{If twelve} , then r ₁ = k ₁₁ / k ₁₂ is defined. When the terminal of the growing radical is the monomer 2, similarly, the reaction rate constant when the monomer 2 is continuously added to the terminal is k ₂₂ and the reaction rate constant when the monomer 1 is reacted and added is k _21. Then, r ₂ = k ₂₂ / k ₂₁ is defined. From the combination of r ₁ and r ₂ , it can be theoretically estimated what kind of copolymer composition is obtained. From these results, it was shown that these monomers exhibit good copolymerizability and an almost ideal random copolymer can be obtained.
For the above reasons, in the copolymerization of 3FMA and MMA, it is presumed that the above-mentioned scattering loss is very small even if polymerization is carried out with an arbitrary composition.

The content ratio of 3FMA in the copolymer (A) is in the range of 55 to 95% by weight, preferably 80 to 90% by weight, based on all monomers constituting the polymer. This range is preferable because the transmission loss at a wavelength of 660 to 680 nm is low and the communication distance can be extended.

On the other hand, as the polymer (B) forming the clad part of the optical fiber of the present invention, a 3FMA homopolymer or a monomer copolymer containing 3FMA and MMA is used.
The content ratio of 3FMA in the polymer (B) is in the range of more than 55% by weight to 100% by weight, preferably 90 to 100% by weight, based on all monomers constituting the polymer. Within this range, the refractive index can be reduced as compared with the core portion, and the numerical aperture (NA) can be increased, that is, the bending loss can be reduced, which is preferable.

In the optical fiber of the present invention, the content ratio of 3FMA in the core copolymer (A) and the clad polymer (B) is such that the latter content ratio is larger than the former content ratio. It is necessary to ensure excellent characteristics.
The difference in the content ratio of 3FMA between them is preferably 5 to 25% by weight, more preferably 7 to 15% by weight. When this difference is 5 to 25% by weight, the cladding part has a lower refractive index than the core part, so that a low bending loss is obtained, and when this difference is 7 to 15% by weight, The refractive index of the clad part can be appropriately reduced as compared with the core part, and both a low bending loss and a wide band can be achieved.

The polymer constituting the core part and the clad part of the optical fiber of the present invention can be produced by a method known in the art. For example, a method of subjecting a mixture of monomers constituting the polymer to solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization or the like can be mentioned. From the viewpoint of preventing foreign matters and impurities from being mixed, the bulk polymerization method. Is preferred.
The polymerization temperature at this time is not particularly limited, and is, for example, 80 to 150 ° C. The reaction time can be appropriately adjusted according to the amount and type of monomer, the amount of polymerization initiator and chain transfer agent described later, the reaction temperature, and the like, and is, for example, 20 to 60 hours.
In addition, you may manufacture these polymers simultaneously or continuously, when shape | molding the core part and / or clad part which are mentioned later.

The polymer constituting the core part and / or the clad part preferably does not use any other monomer component in addition to the above-mentioned 3FMA and MMA. May be contained.
Examples of the polymerizable monomer include (meth) acrylic such as ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, methyl acrylate, ethyl acrylate, n-propyl acrylate, and n-butyl acrylate. Acid ester compounds; styrene compounds such as styrene, α-methylstyrene, chlorostyrene, bromostyrene; vinyl esters such as vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate; N-cyclohexylmaleimide, Nn -Maleimides such as butylmaleimide, N-tert-butylmaleimide, N-isopropylmaleimide, N-phenylmaleimide; and deuterium substitutions of these monomers.

In producing the polymer, it is preferable to use a polymerization initiator and / or a chain transfer agent.
Examples of the polymerization initiator include ordinary radical initiators such as benzoyl peroxide (BPO), t-butylperoxy-2-ethylhexanate (PBO), di-t-butyl peroxide (PBD), and t-butyl. Peroxide compounds such as peroxyisopropyl carbonate (PBI) and n-butyl 4,4, bis (t-butylperoxy) valerate (PHV); 2,2′-azobisisobutyronitrile, 2,2 ′ -Azobis (2-methylbutyronitrile), 1,1'-azobis (cyclohexane-1-carbonitrile), 2,2'-azobis (2-methylpropane), 2,2'-azobis (2-methylbutane) 2,2′-azobis (2-methylpentane), 2,2′-azobis (2,3-dimethylbutane), 2,2′-azobis (2-methylhexane) 2,2′-azobis (2,4-dimethylpentane), 2,2′-azobis (2,3,3-trimethylbutane), 2,2′-azobis (2,4,4-trimethylpentane), 3,3′-azobis (3-methylpentane), 3,3′-azobis (3-methylhexane), 3,3′-azobis (3,4-dimethylpentane), 3,3′-azobis (3- Ethylpentane), dimethyl-2,2′-azobis (2-methylpropionate), diethyl-2,2′-azobis (2-methylpropionate), di-t-butyl-2,2′-azobis And azo compounds such as (2-methylpropionate). These may be used alone or in combination of two or more.
The polymerization initiator is suitably used at about 0.01 to 2% by weight based on the total monomers.

The chain transfer agent is not particularly limited, and known ones such as alkyl mercaptans (n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, t-dodecyl mercaptan, etc.), And thiophenols (thiophenol, m-bromothiophenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.), among others, n-butyl mercaptan, n-octyl mercaptan, n- Alkyl mercaptans such as lauryl mercaptan and t-dodecyl mercaptan are preferably used. Further, a chain transfer agent in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or a fluorine atom may be used. These may be used alone or in combination of two or more.

The chain transfer agent is usually used for adjusting to an appropriate molecular weight in terms of molding and physical properties, and it is preferable to appropriately adjust the type and addition amount according to the type of monomer.
The chain transfer constant of the chain transfer agent for each monomer is, for example, Polymer Handbook 3rd edition (edited by J. BRANDRUP and EH IMMERGUT, published by JOHN WILEY & SON) “Experimental Method for Polymer Synthesis” (Takayuki Otsu, Masami Kinoshita Co-authored, Chemistry Dojin, published in 1972), etc., can be obtained by experiments, and the chain transfer agent type and amount added are adjusted as appropriate according to the type of monomer, taking into account the chain transfer constant For example, the addition amount can be 0.1 to 4% by weight based on the total monomers.

The polymer constituting the core part and / or the clad part is preferably a polymer having a weight average molecular weight in the range of 50,000 to 300,000, and more preferably in the range of 100,000 to 250,000. It is preferable for securing the properties and the like. A weight average molecular weight points out the value of polystyrene conversion measured by GPC (gel permeation chromatography) of a polymer, for example.

3. Dopant (D)
In the optical fiber of the present invention, the core portion contains a dopant (D). The dopant is a compound having a refractive index higher than the refractive index of the copolymer constituting the core part, and is compatible with the copolymer, and by using such a compound, the core is used. Therefore, the scattering loss can be suppressed as much as possible, and the communicable distance can be increased.

Dibenzothiophene (hereinafter also referred to as “DBT”) is suitable as the dopant (D). By using DBT, it is possible to suppress a decrease in the glass transition temperature (hereinafter also referred to as Tg) of the core due to the plasticizing effect of the dopant. As the dopant, it is preferable not to use other types, but one type or two or more types may be used in combination as long as the Tg of the obtained core part and the optical fiber characteristics are not impaired.

Examples of the other kind of dopant include a predetermined low molecular weight compound or a compound in which a hydrogen atom present in the compound is substituted with a deuterium atom. Examples of the predetermined low molecular weight compound include diphenyl sulfone and diphenyl sulfone derivatives (for example, diphenyl sulfone such as 4,4′-dichlorodiphenyl sulfone and 3,3 ′, 4,4′-tetrachlorodiphenyl sulfone), diphenyl sulfide (DPS). ), Sulfur compounds such as diphenyl sulfoxide and dithiane derivatives; phosphate compounds such as triphenyl phosphate (TPP) and tricresyl phosphate (TCP); 9-bromophenanthrene (BPT); benzyl benzoate; benzyl n-butyl phthalate Diphenyl phthalate (DPP); biphenyl (DP); diphenylmethane (DPM) and the like. Of these, diphenyl sulfide (DPS), triphenyl phosphate (TPP), and 9-bromophenanthrene (BPT) are preferable.

The addition amount of the dopant in the core part is not particularly limited, but is appropriately adjusted depending on the composition of the copolymer constituting the core part, the intended refractive index, the composition of the polymer constituting the clad part to be used, the kind of dopant to be used, etc. For example, it is 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight with respect to 100 parts by weight of the core part. By setting the amount of dopant within this range, the refractive index of the core part can be adjusted to a suitable value, and can be compatible with the copolymer constituting the core part.

4). Other compounding agents In the polymer constituting the optical fiber of the present invention, compounding agents, for example, heat stabilization aids, processing, and the like, as long as the optical fiber transparency and heat resistance are not impaired. Auxiliaries, heat resistance improvers, antioxidants, light stabilizers and the like may be blended. These can be used alone or in combination of two or more.

Examples of the heat resistance improver include α-methylstyrene type, N-phenylmaleimide type and the like. Examples of the antioxidant include phenolic antioxidants.
Examples of light stabilizers include hindered amines.
Examples of the method of mixing these blends with the monomer or polymer include a hot blend method, a cold blend method, and a solution mixing method.

5. Production method and use of GI-type POF The method for producing the optical fiber of the present invention is not particularly limited, and methods known in the art can be used. For example, interfacial gel polymerization, rotational polymerization, melt extrusion dopant diffusion, composite melt spinning, and rod-in-tube to form one or two or more cladding portions on the outer periphery of one or more core portions Laws can be used. Further, a preform may be formed in advance, and drawing, drawing, and the like may be performed. However, a fiber may be directly formed by the method described above.

Specifically, there is a method in which a hollow clad part is produced and a core part is produced in the hollow part of the clad part. In this case, the monomer constituting the core part is introduced into the hollow part of the cladding part, and the polymer is polymerized while rotating the cladding part to form a core part having a higher refractive index than the cladding part. This operation may be performed only once to form a single-layer core portion, or a multi-layer core portion may be formed by repeating this operation.

As the polymerization vessel to be used, a glass, plastic or metallic cylindrical tube-shaped vessel (tube) having mechanical strength capable of withstanding external force such as centrifugal force due to rotation and heat resistance during heat polymerization can be used.
The rotation speed of the polymerization vessel at the time of polymerization is exemplified by about 500 to 3000 rpm.
Usually, it is preferable to introduce the monomer into the polymerization vessel after filtering the monomer through a filter to remove dust contained in the monomer.

Furthermore, the method of forming a core part and a clad part using two or more melt extruders, two or more multilayer dies and a multilayer spinning nozzle may be used.
That is, the polymer and the like constituting the core part and the clad part are heated and melted, and injected from the individual flow paths to the multilayer die and the multilayer spinning nozzle. A core or a preform can be formed by extruding one or two or more concentric clad portions on the outer periphery of the core and extruding and integrating them with the die and nozzle.

In order to provide a GI-type refractive index distribution in an optical fiber, for example, as described in WO 93/08488, the monomer composition ratio is made constant, a dopant is added, and the monomer is bulk polymerized at the interface of the polymer. Interfacial gel polymerization that gives the dopant concentration distribution by the reaction, or the rotational gel polymerization method in which the reaction mechanism of the interfacial gel polymerization is the rotational polymerization method, and the monomer charge composition ratio with different refractive index is gradually changed In other words, the polymerization rate of the previous layer is controlled (low polymerization rate), the next layer with a higher refractive index is polymerized, and the refractive index distribution gradually increases from the interface with the cladding to the center. Thus, a method such as carrying out rotational polymerization is exemplified.
In addition, after forming the core part and the clad part using two or more melt extruders, two or more layers of multi-layer dies and a multi-layer spinning nozzle, the dopant may be peripherally or centered in the heat treatment zone provided subsequently. A melt-extrusion dopant diffusion method in which a dopant concentration distribution is given by diffusion toward the part, a polymer having a different amount of dopant introduced into two or more melt extruders, and a core part and / or a multilayer structure. A method of extruding the clad part is exemplified.

When an optical fiber preform is formed by the above-described method or the like, a plastic optical fiber can be produced by melt-drawing the preform. Examples of the melt drawing method include a method in which a preform is heated by passing through an interior of a heating furnace or the like, melted, and then drawn and spun. The heating temperature can be appropriately determined according to the material of the preform, and is, for example, about 180 to 250 ° C. The stretching conditions (stretching temperature and the like) can be appropriately adjusted in consideration of the diameter of the preform obtained, the diameter of the desired optical fiber, the material used, and the like.
In addition, when the core part is produced by a rotational gel polymerization method or a rotational polymerization method, since the center part is hollow, it is preferable to stretch the preform while decompressing from the top during stretching.

Also, heat treatment may be performed at an arbitrary stage. This heat treatment allows the dopant to diffuse toward the periphery or center of the optical fiber or preform. The conditions (for example, temperature, time, pressure, atmosphere composition, etc.) at this time are preferably adjusted arbitrarily.

The optical fiber of the present invention can be applied in the form of a core part and a clad part. However, the optical fiber contracts with time in the environment of 60 ° C., which is the highest temperature in the living environment, and transmission loss is caused by microbending. Since it may deteriorate, it is preferable to coat the outer periphery of the clad portion with a resin having a Vicat softening temperature of 90 ° C. or higher.
The covering material (hereinafter may be abbreviated as “over clad material”) is not particularly limited as long as the Vicat softening temperature is 90 ° C. or higher, and polycarbonate resin, methacrylic resin, polyethylene resin, polypropylene resin, nylon Examples of the resin include a polyester resin and a polycarbonate resin, which are excellent in mechanical strength characteristics and can provide sufficient adhesion to the clad portion. In particular, a modified polycarbonate combined with polyester is preferable in terms of excellent chemical resistance and fluidity. The thickness of the over clad coating layer is not particularly limited, but is preferably 50 μm or more and 500 μm or less because it is excellent in long-term heat resistance in a house and satisfies the physical properties necessary for an optical fiber such as flexibility. In this specification, an optical fiber including a coating layer of an overclad material is referred to.

The optical fiber of the present invention can be applied as it is. Moreover, it can apply to various uses, such as an optical fiber cable, by coat | covering the outer periphery with a 1 or several resin layer, a fiber layer, a metal wire, and / or bundling a some fiber.
The resin for coating the optical fiber is not particularly limited, but satisfies the strength, flame retardancy, flexibility, chemical resistance, heat resistance, etc. required for the optical fiber cable, for example, vinyl chloride resin, chlorinated chloride. Vinyl resin, chlorinated polyethylene resin, polyethylene resin, acrylic resin, fluororesin, polycarbonate resin, nylon resin, polyester resin, ethylene-vinyl acetate copolymer, ethylene-vinyl acetate copolymer, vinyl chloride-ethylene-vinyl acetate copolymer Preferred are those composed mainly of a coalesced vinyl acetate-vinyl chloride copolymer. Moreover, what used the composition which added the additive mentioned above to these resin may be used.
Examples of the fiber covering the optical fiber include aramid fiber, polyester fiber, polyamide fiber, and the like.
Examples of the metal wire covering the optical fiber include stainless steel wire, zinc alloy wire, copper wire, and the like.
The method of coating the resin on the outer periphery of the optical fiber is not particularly limited, and examples thereof include a method of coating and extruding the surface layer after forming the optical fiber.

It is preferable that the cable using the optical fiber is securely fixed to the jack portion using a connection optical plug at the end. As the connector constituted by a plug and a jack, various commercially available connectors such as PN type, SMA type, SMI type, F05 type, MU type, FC type, and SC type can be used. In addition, a plug for connection is not used at the end of the cable using an optical fiber, but a plugless connector such as OptoLock (trade name, manufactured by Firecoms) is attached to the connection device side such as a media converter, and the disconnected cable is inserted and connected. It is also possible to do.

Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited to these examples. In addition, the evaluation method used by the Example and the comparative example is as follows.

1. Measurement and evaluation method for optical fiber samples (1) Transmission loss:
Transmission loss at 665 nm was measured using the cutback method.
(2) Transmission band:
For a 30 m fiber, the transmission band at 650 nm was measured by limited mode excitation with a quartz multimode fiber having a core diameter of 50 μm.
(3) Long-term heat resistance:
The transmission loss after leaving the fiber in an oven at 60 ° C. for 3000 hours was measured.
(4) Bending loss:
The increase in loss of 665 nm light in a state bent 180 ° with a bending radius R10 with respect to the state of standing naturally was measured. The loss increase was measured according to JIS 6823.
(5) Winding test:
After winding an optical fiber around a rod having a diameter of 10 mm or 20 mm five times, an increase in loss after release (loss increase after release relative to that before winding) was measured and evaluated as follows.
○: Loss increase is 0.2 dB or less.
Break: No measurement light passes through after release.

[Example 1]
Into a mixture of 80 parts by weight of 3FMA, 20 parts by weight of MMA and 3 parts by weight of DBT as a dopant, di-t-butyl peroxide as a polymerization initiator and n-lauryl mercaptan as a chain transfer agent are added to the total amount of the resin raw material composition. A resin raw material composition was prepared by adding 0.03% by weight and 0.2% by weight, respectively. This resin raw material composition was put in a polymerization vessel, and polymerized over 40 hours while maintaining the temperature of the polymerization vessel at 110 ° C. to obtain a core member rod (outer diameter 30 mm).

Further, in a mixture of 90 parts by weight of 3FMA and 10 parts by weight of MMA, di-t-butyl peroxide as a polymerization initiator and n-lauryl mercaptan as a chain transfer agent are each 0.03 weight per total amount of the resin raw material composition including them. % And 0.2% by weight were added to prepare a resin raw material composition. This resin raw material composition was put into a polymerization vessel and polymerized over 40 hours while maintaining the temperature of the polymerization vessel at 110 ° C. to obtain a clad member rod (outer diameter 30 mm).

The obtained core member rod and clad member rod are formed into a multilayered structure of the core part and the clad part by using separate extruders and a two-layer mold connected to them, and the heating channel is constant. Through the passage of time, the dopant contained in the core portion was diffused into the cladding portion. Further, XYLEX X7300CL (product name, manufactured by SABIC Innovative Plastics, polyester composite polycarbonate (Vicat softening temperature 108 ° C.)) (hereinafter also referred to as “PC”), which is an overcladding material, is obtained by another extruder. It melt | dissolved and it was made to coat | cover to the outermost periphery by making it merge with the flow path along which said core part and clad | crud part melt | dissolution passes using a 2 layer metal mold | die. The molten resin discharged from the mold outlet was taken to obtain a GI POF having a core part diameter, a cladding part diameter, and a fiber outer diameter of 200 μm, 280 μm, and 750 μm, respectively. With respect to the optical fiber sample, predetermined characteristics were measured and an evaluation test was performed. The results are shown in Table 1.

[Examples 2 to 4], [Comparative Examples 1 to 3]
As shown in Table 1, each optical fiber sample was prepared in the same manner as in Example 1 except that the ratio of the monomer component in the core part and the clad part and the addition amount of DBT were changed. And an evaluation test.
The results are shown in Table 1.

[Example 5]
As shown in Table 1, an optical fiber sample was prepared in the same manner as in Example 1 except that 2.2 parts by weight of DPS was added instead of DBT as a dopant, and predetermined characteristics of the sample were measured. An evaluation test was conducted.
The results are shown in Table 1.

[Example 6]
As shown in Table 1, the examples except that the ratio of the monomer component in the core part and the clad part and the addition amount of DBT were changed and the over clad material was changed to methacrylic resin (Vicat 107 ° C.) (referred to as PMMA). An optical fiber sample was prepared in the same manner as in No. 1, and predetermined characteristics of the sample were measured and an evaluation test was performed.
The results are shown in Table 1.

[Example 7]
As shown in Table 1, an optical fiber sample was prepared in the same manner as in Example 6 except that the overcladding material was changed so as not to be coated, and predetermined characteristics of the sample were measured and an evaluation test was performed. .
The results are shown in Table 1.

As a result, as apparent from Table 1, in Examples 1 to 5, since the polymer composition satisfying the requirements defined in the present invention was used for the core part and the clad part, these core part / cladding part An optical fiber made by bonding an overclad PC to the part has sufficient light transmission performance, has low transmission loss at a wavelength of 665 nm, has excellent long-term heat resistance, has low transmission loss when bent, and is further wound There was little transmission loss even after the test.
In Examples 6 to 7, since the polymer composition satisfying the requirements defined in the present invention is used for the core part and the clad part, the obtained optical fibers are excellent as in Examples 1 to 5. However, since PMMA was used instead of PC as the over clad material or no over clad material was used, all of them were defective in the winding test.
On the other hand, in Comparative Example 1, since a polymer composition that does not satisfy the requirements defined in the present invention is used for the core portion, the transmission loss at a wavelength of 665 nm is large, and the long-term heat resistance is clearly inferior. .
Further, in Comparative Example 2, the content ratio of 3FMA in the core copolymer and the clad polymer is the same, and the latter content ratio is not larger than the former content ratio. For this reason, there is a large transmission loss when bent, and a balanced characteristic as an optical fiber cannot be secured.
Furthermore, in Comparative Example 3, since a polymer composition that does not satisfy the requirements defined in the present invention is used for the core portion, transmission loss when bent is large, and balanced characteristics as an optical fiber can be secured. There wasn't.

The refractive index distribution type plastic optical fiber of the present invention has sufficient light transmission performance to construct a short-distance optical transmission link system such as an optical transmission link system indoors, especially in a home, and has a transmission loss when bent. It is useful as a component of an optical fiber and optical fiber cable intended for high-speed communication. In addition, by changing the shape, optical elements such as optical waveguides, still cameras, video cameras, telescopes, glasses, plastic contact lenses, sunlight condensing lenses, concave mirrors, polygons, etc. Since it can be applied as an optical member such as a mirror such as a mirror or a prism such as a pentaprism, its industrial applicability is very large.

Claims (7)

1. A refractive index distribution type plastic optical fiber comprising a core part and a clad part disposed on the outer periphery of the core part,
   The core has a copolymer of monomers containing 55 to 95% by weight of 2,2,2-trifluoroethyl methacrylate and 5 to 45% by weight of methyl methacrylate, and a refractive index higher than that of the copolymer. And a dopant compatible with the copolymer as a main constituent,
   The clad part mainly comprises a polymer of a monomer containing 55 to 100% by weight of 2,2,2-trifluoroethyl methacrylate and 0 to less than 45% by weight of methyl methacrylate, and the polymer 2. An optical fiber, wherein the content ratio of 2,2,2-trifluoroethyl methacrylate in said copolymer is larger than the content ratio of 2,2,2-trifluoroethyl methacrylate in said copolymer of said core part.
2. 2. The optical fiber according to claim 1, wherein the difference in the content of 2,2,2-trifluoroethyl methacrylate in the core copolymer and the clad polymer is 5 to 25% by weight. .
3. The core copolymer comprises 80-90 wt% 2,2,2-trifluoroethyl methacrylate and 10-20 wt% methyl methacrylate, while the clad polymer is 90-100 wt%. The optical fiber according to claim 1 or 2, comprising 2% by weight of 2,2,2-trifluoroethyl methacrylate and 0 to 10% by weight of methyl methacrylate.
4. The optical fiber according to any one of claims 1 to 3, wherein the dopant is dibenzothiophene.
5. The optical fiber according to any one of claims 1 to 4, wherein the outer periphery of the clad is coated with a plastic mainly composed of polycarbonate.
6. 6. A short-distance optical transmission link system using the optical fiber according to claim 1.
7. An indoor optical transmission link system using the optical fiber according to any one of claims 1 to 5.