JPH08313734A - Production of plastic optical fiber - Google Patents

Abstract

PURPOSE: To provide a process for easily producing a plastic optical fiber having low transmission loss with good productivity by embodying desired refractive indices. CONSTITUTION: Plural homopolymers varying in refractive indices are discharged from the plural nozzles arranged on plural concentric circles into an extrusion die 18 of an extrusion molding machine 16 in such a manner that one kind of the homopolyer corresponds to every nozzle on the respective concentric circles, by which the plastic optical fiber 22 consisting of a fiber-like core which is formed by tightly enclosing plural resin layers having the different refractive indices in order of the resins of the higher refractive indices from the central axis toward the outer side of the radial direction and has the refractive index distribution of the refractive indices decreasing from the center toward the outer side of the radial direction and a clad part which is clad on the outer side of the core and has the refractive index lower than the refractive index in the central part of the core. The respective resin layers of the core described above are formed of the resins consisting of one kind of the respective different homopolymers. The extrusion die 18 may be of a form having plural groove-like discharge holes formed to a concentric shape.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to plastic optical fibers.

[0002]

2. Description of the Related Art A plastic optical fiber whose core and clad are both made of plastic is easier to process and handle than a glass fiber, so that the transmission loss of the plastic optical fiber is not so long as a problem. Currently, it is widely used as, for example, transmission and reception of optical signals between electronic devices, but in the future, it may play an important role as a high-speed transmission medium in the concept of next-generation communication networks such as LAN and ISDN. Is expected.

A plastic optical fiber which has been put into practical use is a step index type (SI type) plastic optical fiber having a refractive index distribution which changes stepwise as shown in FIG. Since it is small, it has a small transmission capacity and is not suitable for communications such as high-speed transmission media. A graded index (GI) type plastic optical fiber having a core refractive index distribution that changes in the radial direction as shown in FIG. 5 is more suitable for communication applications such as LAN, and the transmission band of the fiber is widened. Further, the transmission capacity is increased. At this time, in order to increase the transmission capacity, it is ideal to obtain a smooth curved refractive index distribution, but it is possible to obtain a sufficient transmission capacity even with a stepwise refractive index distribution as shown in FIG. it can.

In Japanese Unexamined Patent Publication No. 6-186441, a mixture of a polymer, a monomer and a refractive index raising agent is discharged from the outer and inner discharge holes of a spinneret having double concentric discharge holes to form a rod shape. After that, polymerization and diffusion are performed to produce a plastic optical fiber having a smooth refractive index distribution from the center toward the outer side in the radial direction.

[0005]

However, the manufacturing method of the above-mentioned document has some problems due to the use of the refractive index raising agent. When a compound having a polymerizable functional group is used as the refractive index raising agent, the block polymer tends to be present in the polymer of the produced plastic optical fiber, and in this case, light scattering occurs and the transmission loss decreases. . On the other hand, when a refractive index raising agent that does not have polymerizability is used, such a refractive index raising agent has absorption in the visible light region, and thus the transmission loss is impaired. Also, in the above literature,
In order to obtain a smooth refractive index distribution, the refractive index raising agent is diffused at the time of polymerization, but this significantly extends the polymerization time and is not advantageous from the viewpoint of mass production.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an excellent plastic optical fiber having a desired refractive index and a low transmission loss with high productivity.

[0007]

A method for producing a plastic optical fiber according to the present invention comprises a plurality of homopolymers having different refractive indexes from a plurality of nozzles arranged on a plurality of concentric circles in an extrusion die of an extrusion molding machine. 1 for each concentric nozzle
The homopolymers of the species are ejected so as to correspond to each other, and a plurality of resin layers having different refractive indexes are formed by closely surrounding the resin layers having a higher refractive index from the central axis toward the outer side in the radial direction in the radial direction from the center Each of the resin of the core is composed of a fiber-shaped core having a refractive index distribution in which the refractive index decreases toward the outside, and a clad portion coated on the outside of the core and having a refractive index lower than that of the central portion of the core. The layers are characterized in that they form a plastic optical fiber formed of a resin consisting of different homopolymers.

Further, in the method for producing a plastic optical fiber according to the present invention, a plurality of homopolymers having different refractive indexes are discharged from a plurality of groove-shaped discharge holes formed concentrically in an extrusion die of an extrusion molding machine. Each homopolymer is discharged in a corresponding manner, and a plurality of resin layers having different refractive indexes are formed by closely surrounding and enclosing the resin layers having a higher refractive index from the central axis toward the outer side in the radial direction. From a fiber-shaped core having a refractive index distribution in which the refractive index drops outward in the radial direction, and a clad portion coated on the outside of the core and having a refractive index lower than the refractive index of the central portion of the core. Each of the resin layers may form a plastic optical fiber formed of a resin composed of a different type of homopolymer.

Further, in the method for producing a plastic optical fiber of the present invention, each homopolymer forming each resin layer of the core is
A homopolymer in which hydrogen of the first polymer, which is the same or different homopolymer for each resin layer, is replaced by an atom or a functional group to reduce the ratio of carbon-hydrogen (CH) bonds contained in the molecule. It may be characterized by being a certain second polymer.

Further, the method for producing a plastic optical fiber of the present invention may be characterized in that the atom is halogen.

Further, the method for producing a plastic optical fiber of the present invention may be characterized in that the first polymer is the same for each resin layer.

Further, in the method for producing a plastic optical fiber of the present invention, the halogen is fluorine (F), and the plurality of resin layers are arranged in the second direction from the central axis toward the outer side in the radial direction.
The polymer may be characterized in that the core is formed by closely surrounding the polymer in the ascending order of the fluorine content.

Further, in the method for producing a plastic optical fiber of the present invention, halogen is chlorine (Cl) and bromine (B).
r) and one selected from the group consisting of iodine (I),
Further, the core may be formed by closely surrounding a plurality of resin layers from the central axis toward the outer side in the radial direction in order of increasing halogen content of the second polymer.

Further, in the method for producing a plastic optical fiber of the present invention, halogen is chlorine (Cl) and bromine (B).
r) and two or more selected from the group consisting of iodine (I), and the plurality of resin layers have a large total content of halogens in the second polymer from the central axis toward the outer side in the radial direction. It may be characterized in that the core is formed so as to be closely enclosed in order.

The outermost refractive index of the core may be lower than the refractive index of the cladding.

In the method for producing a plastic optical fiber of the present invention, a resin layer made of a homopolymer in which halogen is fluorine (F), halogen is chlorine (Cl), bromine (Br) and iodine (I). ) And a resin layer made of a homopolymer selected from the group consisting of

Further, the method for producing a plastic optical fiber of the present invention may be characterized in that the first polymer is represented by the general formula:

[0018]

Embedded image

[R ₁ is an atom or a functional group selected from the group consisting of hydrogen and methyl, and R ₂ is methyl and
It is a functional group selected from the group consisting of ethyl, propyl, butyl, tertiary butyl, pentyl, hexyl, cyclohexyl, isobornyl, and adamantyl. ].

Further, the method for producing a plastic optical fiber of the present invention may be characterized in that each resin layer of the core is composed of a second polymer which is a homopolymer represented by the general formula (4):

[0021]

[Chemical 4]

[R ₁ is an atom or a functional group selected from the group consisting of hydrogen and methyl, and R ₂ is 1 to 1 carbon atoms.
20 straight chain alkyl, branched alkyl or cyclic alkyl. ].

Further, in the method for producing a plastic optical fiber of the present invention, a plurality of resin layers are formed by using the second polymer in the order of increasing R ₂ carbon number from the central axis toward the outer side in the radial direction. The core may be formed by.

Further, in the method for producing a plastic optical fiber of the present invention, the homopolymer represented by the general formula (4) is further substituted with hydrogen for fluorine, and the second polymer is directed radially outward from the central axis. The core may be formed of a plurality of resin layers used in the order of increasing fluorine content and in the order of increasing or decreasing carbon number of R ₂ .

Further, in the method for producing a plastic optical fiber of the present invention, the hydrogen of the homopolymer represented by the general formula (4) is further substituted with an atom selected from the group consisting of chlorine, bromine and iodine. The core is formed of a plurality of resin layers in which the second polymer is used from the central axis toward the outer side in the radial direction in descending order of atomic content and in order of increasing or decreasing molecular weight of R _2. Good.

The plastic optical fiber of the present invention will be further described below.

The homopolymer of the resin which constitutes the plastic optical fiber of the present invention may be the second polymer which is a halogen-substituted compound obtained by using the homopolymer of the compounds exemplified below as the first polymer. Good:
Methyl acrylate (methyl acrylate), methyl methacrylate (methyl methacrylate), ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, butyl acrylate, butyl methacrylate, tertiary butyl acrylate, tertiary methacrylic acid Butyl,
Pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, isobornyl methacrylate, adamantyl acrylate (acrylic adamantane), adamantyl methacrylate (methacryl adamantane). When the second compound obtained by halogenating the first compound is used as the monomer, the refractive index of the homopolymer can be changed by changing the halogen substitution number of the monomer. Further, the second polymer may be obtained by polymerizing a halogen-substituted product of the compounds listed here.

The resin monomer constituting the plastic optical fiber of the present invention may be a linear alkyl ester, a branched alkyl ester, or a cyclic alkyl ester of acrylic acid or methacrylic acid. When such a compound is used as a monomer, the refractive index can be changed by changing the carbon number of alkyl. The carbon number of the alkyl may be changed within a range of 1 to 20 in order to obtain a desired refractive index. Considering the manufacturing process and the like, it is preferable to change the carbon number within a range of about 1 to 15.

The "resin composed of a homopolymer" in the present invention includes a resin composed of a homopolymer containing a known additive such as a plasticizer added to plastics.

The molecular weight of the plastic optical fiber of the present invention is determined by the homopolymer GP which constitutes the core and the clad.
Weight average molecular weight by C of 10,000 or more 300,
000 or less, more preferably 30,000
Or more 250,000 or less (more than 50,000 or more 20
It is preferably not more than 2,000).

The weight average molecular weight of the polymer constituting the core is preferably 10,000 or more and 300,000 or less. The weight average molecular weight of the polymer constituting the clad portion is also preferably 10,000 or more and 300,000 or less.

When a homopolymer is obtained by polymerizing monomers to produce the core and clad of the present invention,
A known polymerization reaction can be used for the polymerization reaction.
Radical polymerization using a peroxide having an —O bond or an azo compound as an initiator is preferable. Here, as the initiator of the reaction radical polymerization reaction, so-called medium temperature initiators such as benzoyl peroxide and lauroyl peroxide, which effectively generate radicals at about 40 ° C. to about 100 ° C., can be suitably used. Therefore, when using such a mesophilic initiator,
The temperature condition of the polymerization reaction is preferably about 40 ° C to about 100 ° C.
Is. The polymerization reaction rate is adjusted so that cracks etc. do not occur in the polymer during or after the polymerization reaction due to the heat of reaction or expansion and contraction due to the reaction itself, and that the monomer does not boil during the reaction due to the reaction heat. There is a need, which can be adjusted by a combination of polymerization temperature and initiator concentration. The addition amount of the initiator of the radical polymerization reaction is about 0.001 to 10% by weight with respect to the entire system with respect to the condition for starting the polymerization reaction of about 40 ° C to about 100 ° C.
Furthermore, about 0.01 to 0.3% by weight (especially 0.05 to
About 0.15% by weight). In addition to such bulk polymerization using heat energy, bulk polymerization using light energy and the like can also be used. Also in this case, similarly, the polymerization reaction rate can be adjusted by combining the input energy amount such as temperature and the initiator concentration.

A plastic optical fiber manufacturing apparatus that can be used in the present invention has an extrusion die in which one or more nozzles for discharging resin are arranged on a concentric circle, and one nozzle group is provided on each concentric circle. It is necessary to have a function of extruding different homopolymers for each concentric circle by supplying the homopolymer. In addition, a heating means for heating and melting the homopolymer must be provided for extrusion. The extrusion die may include a plurality of groove-shaped discharge holes formed in a concentric shape.

[0034]

Since the core of the plastic optical fiber of the present invention is composed of a plurality of resin layers in the order of increasing refractive index from the inside, its refractive index distribution exhibits a stepwise shape from the center toward the outside in the radial direction. There is. Therefore, since mode dispersion can be reduced, it is possible to manufacture a plastic optical fiber that realizes a large transmission band required for high-speed communication applications.

Further, in the present invention, since the extrusion method using the homopolymer whose refractive index is adjusted in advance is adopted, the polymerization reaction is not included in the manufacturing process of the plastic optical fiber. Therefore, the reproducibility of the refractive index distribution is high.

Further, since each resin layer is formed of a resin composed of a homopolymer, light scattering due to blocking does not occur.

Since each resin layer contains no dopant having an absorption band in the visible light region, the transmission loss can be reduced.

Further, since a compound having a small ratio of carbon-hydrogen (C—H) bonds is used as a homopolymer monomer constituting each resin layer, absorption in the visible light region is reduced and transmission loss is reduced. The impact is reduced.

The homopolymer constituting each resin layer is the first
The second polymer, in which hydrogen (H) of the polymer of (1) is replaced with an atom or a functional group to reduce the ratio of carbon-hydrogen (CH) bonds contained in the first polymer, is reduced. A GI-type plastic optical fiber having a refractive index distribution can be obtained by using a substituted derivative of a known monomer that can be used for the fiber. This substituted derivative can be relatively easily synthesized by using a known monomer as a starting material, and a homopolymer having a different refractive index can be easily obtained by changing the number of substitutions or the number of substitution atoms or substituents. A desired refractive index distribution can be easily obtained by using a monomer as a raw material.

In the embodiment using the polymer substituted with halogen, the refractive index of the resin can be changed only by changing the halogen content of the polymer, so that the desired refractive index can be easily obtained. When the halogen is fluorine, the fluorine contained in the polymer decreases the refractive index of the homopolymer, and the refractive index tends to decrease as the fluorine content increases. When the halogen is chlorine, bromine and iodine, chlorine, bromine and iodine contained in the polymer increase the refractive index of the homopolymer, and the refractive index tends to increase as the number of substitutions increases. In addition, fluorine and [chlorine /
It is also possible to adjust the refractive index to the desired value by substituting the hydrogen of the polymer in combination with [bromine / iodine]. Therefore, it is possible to obtain a plastic optical fiber having a refractive index distribution as shown in FIG. 5 by forming the homopolymer layer in various layers by changing the refractive index.

Similarly, in a mode in which a homopolymer in which the molecular weight of the functional group is changed to change the refractive index is used in the resin layer, the refractive index of the resin can be changed only by changing the molecular weight of the functional group. The desired refractive index can be easily obtained. In this case, the refractive index rises as the proportion of carbon-hydrogen (CH) bonds contained in the polymer decreases. When the functional group is linear alkyl, branched alkyl or cyclic alkyl, the refractive index increases as the carbon number increases. Therefore, it is possible to obtain a plastic optical fiber having a refractive index distribution as shown in FIG. 5 by forming the homopolymer layer in various layers by changing the refractive index.

Further, using the above polymer, the refractive index near the outermost core is made lower than the refractive index of the clad to increase the refractive index difference (Δn) between the core center and the outermost core. It is easy, and in this case, the light confinement effect becomes large. Therefore, it becomes possible to obtain a plastic optical fiber with a small bending loss.

Therefore, it becomes possible to manufacture a GI type plastic optical fiber having a wide transmission band easily and without quality variations.

[0044]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the accompanying drawings as needed with reference to the accompanying drawings. In the description of the accompanying drawings, the same elements are denoted by the same reference numerals, and duplicated description is omitted. In some cases, the scale is exaggerated for convenience of description.

FIG. 1 is a block diagram of an apparatus for manufacturing a plastic optical fiber that can be used in the present invention. As shown in FIG. 1, a plastic optical fiber manufacturing apparatus 10
Is a polymer pellet supply device 12, a supply pipe 14,
The extrusion device 16 includes an extrusion device 16, an extrusion die 18 installed at the tip of the extrusion device 16, and a winding 20. In the polymer pellet supply device 12, a plurality of types of polymer pellets having different refractive indexes are stored for each refractive index. The polymer pellets are supplied to the extrusion device 16 by the supply pipe 14 for each refractive index. The number of the supply pipes 14 is equal to the number of resin layers of the plastic optical fiber. For example, in FIG. 1, an apparatus for a plastic optical fiber having a total of four layers including a core having three layers having different refractive indexes and a clad. Is shown as an example, and the number of supply pipes in this case is four, that is, 14a, 14b, 14c, and 14d. The polymer pellets supplied to the extrusion device 16 via the supply pipe 14 are extruded in the extrusion device 16 for each polymer pellet having a different refractive index. At this time, each polymer is extruded in a concentric layered manner and at the same extrusion speed of each polymer to form a plastic optical fiber 22 and is wound around the winding 20. The extrusion device 16 contains a heating means for heating and melting the polymer and an extrusion line for the desired number of layers of the plastic optical fiber.

FIG. 2 is a sectional view of the extrusion die 18 at the tip of the extrusion device 16. FIG. 3A shows an extrusion die 18
FIG. 4 is a front view of the discharge die 18 showing the arrangement shape of the discharge holes of the extrusion die 18. As shown in FIG. 2, inside the extrusion die 18, there are provided tubular extrusion nozzles 24 corresponding to the layers having different refractive indexes constituting the plastic optical fiber.
As shown in FIGS. 2 and 3 (a), the extrusion die 18
A large number of discharge holes 26, which are the outlets of the extrusion nozzle 24, are arranged. First, one discharge hole 26 is arranged at the center, and is arranged on three circles concentric with the center. A polymer having the same refractive index is extruded into the concentric ejection holes to fabricate a plastic optical fiber formed of four concentric layers having different refractive indexes. The number of extrusion nozzles 24 is equal to the number of die shown in FIG. Since FIG. 2 is a cross-sectional view, FIG. 2 shows a single extrusion nozzle 24, one for the central layer and the other three layers, one on each side, for a total of seven.

(Embodiment 1) In this embodiment, first, FIG.
Using the plastic optical fiber manufacturing apparatus shown in FIG. 2 and FIG. 3A, a GI type plastic optical fiber having a stepwise refractive index distribution was manufactured. Then, the transmission loss and bending loss of the obtained plastic optical fiber were measured.

In this example, a plastic optical fiber was manufactured as follows. The process will be described with reference to FIGS. 1, 2 and 3A.

FIG. 4 is an external view of the plastic optical fiber 30 produced in this embodiment, and shows the structure of the cross section of the plastic optical fiber 30. First, a polymer for the clad and the core was synthesized. In this example, a homopolymer of methyl methacrylate and a homopolymer of methyl fluoromethacrylate obtained by substituting methyl methacrylate with fluorine were used as the polymer for the clad portion and the core.
In order to make the refractive index different, the number of fluorine substitution of methyl methacrylate was changed for each layer. Referring to FIG. 4, for the clad portion 32, a homopolymer of methyl octafluoromethacrylate in which all the hydrogen of methyl methacrylate was replaced with fluorine was used. Also, the core has three layers, and from the outside,
For the core first layer 34, methyl heptafluoromethacrylate of methyl fluoride, for the core second layer 36, hexafluoromethylmethacrylate of hexafluoride, for the core third layer 38, of methyl methacrylate. A core was formed using each homopolymer. The 6-8 fluoride of methyl methacrylate may be a compound in which hydrogen at any position of methyl methacrylate is replaced with fluorine.
In the following, similarly, the layers forming the core are the core first layer, the core second layer. ． ． Call.

When a compound in which hydrogen of a polymerizable compound is replaced with fluorine (F) is used as a monomer, a compound having a larger fluorine substitution number has a smaller refractive index of its homopolymer.
Therefore, when a fluorine substitution product is used, if a plurality of layers are formed by extruding homopolymers in such a manner that the fluorine substitution number is arranged from the outside in the descending order of the number of fluorine substitutions, the refractive index is lowered toward the outside in the radial direction with the central portion being the maximum. It is possible to obtain a plastic optical fiber having a refractive index distribution.

The above methyl methacrylate homopolymers and methyl methacrylate 6-8 fluoride homopolymers were presynthesized and stored in pellet form for extrusion. Polymerization of methyl methacrylate and a fluoride of methyl methacrylate was carried out by a known bulk polymerization method.

The pellets of the four kinds of homopolymers used for the clad portion and the core are fed into the polymer pellet feeding device 12
Separately, the homopolymer was separately supplied. From the polymer pellet feeder 12, each homopolymer is fed into its respective feed tube 14
The homopolymer is separately fed to the extrusion device 16 via. One kind of homopolymer pellets flows down into each supply pipe. The extruder 16 is also provided with an extrusion line for each homopolymer pellet. In the present example, since there are four types of homopolymer pellets, an extruder equipped with at least four extrusion lines can be used. Each of the four extrusion lines provided in the extrusion device 16 is connected to each of the four supply pipes, and further connected to the nozzle 24 for forming the clad portion of the die 18.

For example, methyl polyoctafluoromethacrylate is supplied only from the supply pipe 14a to the extrusion line for polyoctafluoromethylmethacrylate of the extruding device 16, and from there, the extrusion die 18 for extruding methyloctafluoromethylmethacrylate in the extrusion die 18. Nozzle 24 (in FIG. 2,
8F is displayed above the extrusion nozzle, and in FIG. 3A, it corresponds to 16 discharge holes 26 arranged on the outermost concentric circle.)
Leading to. Then, the clad portion is formed from the nozzle 24 through the discharge hole 26.

In this way, each homopolymer is extruded at the same extrusion rate from the discharge hole 26 of the extrusion die 18, and as shown in FIG. 4, the clad portion 32 and the three-layer core 50 are extruded.
A four-layer plastic optical fiber was prepared. The extrusion conditions were as follows: resin temperature 200 ° C, diameter of plastic optical fiber 650μ.
m.

The refractive index distribution of this plastic optical fiber was measured by an interferometric method (measuring device: P-101, manufactured by York Corporation,
This method and apparatus are used in the measurement of the refractive index distributions of all the examples and comparative examples), and it has a GI type refractive index distribution that descends stepwise from the center as shown in FIG. Became clear. The transmission loss of a plastic optical fiber is measured by the cutback method (measurement device: A
Q-6315B, manufactured by Ando Electric Co., Ltd., and the transmission loss and bending loss of all Examples and Comparative Examples below were measured using AQ-6315B by the cutback method.) When measured, it was 90 dB at a wavelength of 650 nm. It was / km.

Next, this plastic optical fiber was wound around a mandrel having a diameter of 10 mm, and the bending loss was measured by AQ-6315B by the cutback method. The bending loss value at this time was 1.0 dB.

As described above, in this embodiment, the extrusion method according to the present invention was used to use a monomer in which methyl methacrylate was substituted with fluorine, and the number of substitutions was gradually increased from the outer side toward the center. It was shown that a fiber could be made and it was further confirmed that this plastic optical fiber has good transmission and bending losses.

Example 2 Except that a chlorine-substituted methyl methacrylate was used as each monomer forming the core,
A plastic optical fiber was manufactured in the same manner as in Example 1, and the transmission loss and bending loss of the obtained plastic optical fiber were measured.

When a compound in which hydrogen of a polymerizable compound is replaced with chlorine (Cl) is used as a monomer, a compound having a larger chlorine substitution number has a higher refractive index of its homopolymer, contrary to the fluorine-substituted product. Therefore, when a chlorine-substituted product is used, if the homopolymers are extruded so as to be lined in the order of smaller chlorine substitution from the outside to form a plurality of layers, the refractive index is lowered toward the outer side in the radial direction with the central portion being the maximum. It is possible to obtain a plastic optical fiber having a refractive index distribution.

In this example, a homopolymer of methyl methacrylate is provided in the clad portion, and, with respect to the core, from the outside, the core first layer of the homopolymer of methyl monochloromethacrylate, which is a monochloride of methyl methacrylate, methyl methacrylate. Polymer pellet supply device 12, supply pipe so as to become a core second layer of a homopolymer of methyl dichloromethacrylate which is a dichloride of 1, and a core third layer of a homopolymer of methyl octachloromethacrylate that is an octachloride. 1
4, the extrusion device 16 and the extrusion die 18 were set. In addition, each homopolymer was prepared as pellets as in the examples. It should be noted that the 1, 2, and 8 chlorine-substituted compounds may be those in which hydrogen at an arbitrary position of methyl methacrylate is replaced with chlorine.

Next, using the apparatus shown in FIGS. 1, 2 and 3 (a) as in Example 1, each homopolymer was extruded at once to form a plastic optical fiber having a diameter of 650 μm. The refractive index distribution of the plastic optical fiber exhibited a stepwise GI type distribution as shown in FIG. When the transmission loss of the plastic optical fiber was measured, it was 100 dB / km at a wavelength of 650 nm.

Next, this plastic optical fiber was wound on a mandrel having a diameter of 10 mm, and the optical fiber of Example 1 was used.
The bending loss was measured in the same manner as in. The value of bending loss at this time was 1.1 dB.

As described above, in this example, according to the present invention, three homopolymers having different chlorine substitution numbers were used by using a monomer obtained by substituting chlorine for methyl methacrylate, and homopolymers of methyl methacrylate for the clad portion were prepared. It has been shown that a plastic optical fiber containing a core of three layers can be extruded with a polymer, and it was further confirmed that this plastic optical fiber has good transmission and bending losses.

Example 3 A bromine substitution product of methyl methacrylate was used as each core-forming monomer, except that
A plastic optical fiber was produced in the same manner as in Example 1, and the transmission loss and bending loss of the obtained plastic optical fiber were measured.

When a compound in which hydrogen of a polymerizable compound is replaced with bromine (Br) is used as a monomer, a compound having a larger bromine substitution number has a higher refractive index of its homopolymer, like a chlorine substitution product. Therefore, when using a bromine substitution product, if homopolymers are extruded so that the bromine substitution number is arranged from the outside in ascending order, multiple layers are formed. A plastic optical fiber having a rate distribution can be obtained.

In this example, a homopolymer of methyl methacrylate was used for the clad portion, and from the outside, the core first layer of the homopolymer of methyl monobromomethacrylate, which is a monobromine substitution product of methyl methacrylate, methacryl A polymer pellet feeder 12, a feed tube 14, so as to form a core second layer of a homopolymer of methyl dibromomethylmethacrylate of methyl bromide and a core third layer of a homopolymer of methyl octabromomethacrylate of octabromide. The extrusion device 16 and the extrusion die 18 were set. In addition, each homopolymer was prepared as pellets as in the examples. The 1, 2, and 8 bromine-substituted products may be those in which hydrogen at arbitrary positions of methyl methacrylate is replaced by bromine.

Next, using the apparatus shown in FIGS. 1, 2 and 3 (a) as in Example 1, each homopolymer was extruded at once to form a plastic optical fiber having a diameter of 650 μm. The refractive index distribution of the plastic optical fiber exhibited a stepwise GI type distribution as shown in FIG. When the transmission loss of the plastic optical fiber was measured, it was 90 dB / km at a wavelength of 650 nm.

Next, this plastic optical fiber was wound on a mandrel having a diameter of 10 mm, and Example 1 was used.
The bending loss was measured in the same manner as in. The bending loss value at this time was 0.9 dB.

As described above, in this example, the number of bromine substitutions of methyl methacrylate was changed to 3 according to the present invention.
It has been shown that three kinds of homopolymers obtained by polymerizing kinds of monomers can be extruded together with a homopolymer of methyl methacrylate for a clad part to produce a plastic optical fiber including a core composed of three layers. It was confirmed to have good transmission loss and bending loss.

(Example 4) A plastic optical fiber was prepared in the same manner as in Example 1 except that an iodine substitution product of methyl methacrylate was used as each monomer forming the core. The transmission loss and bending loss of the fiber were measured.

When a compound obtained by substituting hydrogen of a polymerizable compound with iodine (I) is used as a monomer, a compound having a larger number of iodine substitutions, like chlorine substitution and bromine substitution,
The refractive index of the homopolymer increases. Therefore, when an iodine-substituted product is used, if a plurality of layers are formed by extruding homopolymers in such a manner that compounds having a smaller iodine substitution number are arranged from the outside, the refractive index is increased toward the outer side in the radial direction with the central portion being the maximum. It is possible to obtain a plastic optical fiber having a falling refractive index profile.

In this example, a homopolymer of methyl methacrylate was used for the clad portion, and, with respect to the core, from the outside, the core first layer of the homopolymer of methyl monoiodomethyl methacrylate, which was a monoiodine-substituted methyl methacrylate, the methacrylic acid was used. Polymer pellet supply device 12, supply pipe, so as to form a core second layer of a homopolymer of methyl diiodomethylmethacrylate of methyl iodide and a core third layer of a homopolymer of methyl octaiodomethylmethacrylate of octaiodide 14,
The extrusion device 16 and the extrusion die 18 were set. In addition, each homopolymer was prepared as pellets as in the examples. In addition, 1,2,8 iodine substitution thing should just be what replaced hydrogen of the arbitrary position of methyl methacrylate with iodine, respectively.

Next, each homopolymer was extruded at once using the apparatus shown in FIGS. 1, 2 and 3 (a) in the same manner as in Example 1 to form a plastic optical fiber having a diameter of 650 μm. The refractive index distribution of the plastic optical fiber exhibited a stepwise GI type distribution as shown in FIG. When the transmission loss of the plastic optical fiber was measured, it was 100 dB / km at a wavelength of 650 nm.

Next, this plastic optical fiber was wound around a mandrel having a diameter of 10 mm, and Example 1 was used.
The bending loss was measured in the same manner as in. The bending loss value at this time was 1.0 dB.

As described above, in the present example, three kinds of homopolymers obtained by polymerizing three kinds of monomers in which the number of iodine substitution of methyl methacrylate was changed were prepared according to the present invention.
It was shown that a plastic optical fiber containing a core consisting of three layers could be produced by extrusion with a homopolymer of methyl methacrylate in the clad part, and it was further confirmed that this plastic optical fiber had good transmission loss and bending loss. .

(Example 5) A plastic optical fiber was prepared in the same manner as in Example 1 except that chlorine and bromine substitution of methyl methacrylate were used as the monomers forming the core. The transmission loss and bending loss of the plastic optical fiber were measured.

When a compound in which hydrogen of a polymerizable compound is replaced with chlorine (Cl) and bromine (Br) is used as a monomer, a compound having a larger total number of chlorine substitutions and bromine substitutions has a higher refractive index of its homopolymer. growing. In addition, since chlorine and bromine differ in the degree of change in the refractive index corresponding to the number of substitutions in the monomer, by selecting the monomer based on the combination of the number of chlorine substitutions and the number of bromine substitutions,
It is possible to obtain a refractive index profile different from the refractive index profile of the core realized by substitution of chlorine alone or bromine only. In the present example, if a plurality of layers are formed by extruding a homopolymer so that the total number of chlorine substitutions and the number of bromine substitutions are arranged in order from the outer side, a plurality of layers are formed. It is possible to obtain a plastic optical fiber having a refractive index distribution in which the index drops.

In this example, a homopolymer of methyl methacrylate for the clad portion, and a core first layer of a homopolymer of methyl monochloromethacrylate, which is a mono-chlorine substitution product of methyl methacrylate, in order from the outside, for the core, A core second layer of a homopolymer of methyl chlorobromomethyl methacrylate, which is a monochlorine monobromine substitution of methyl methacrylate;
2nd chlorine 2nd chlorine 2
A polymer pellet feeding device 12, so as to form a core fourth layer of a homopolymer of dichlorodibromomethylmethacrylate that is a bromine substitute, and a core fifth layer of tetrachlorotetrabromomethylmethacrylate that is a tetrachlorotetrabromide substitute,
The supply pipe 14, the extrusion device 16, and the extrusion die 18 were set. Also, each homopolymer was prepared as pellets as in Example 1. Each of the above methyl methacrylate substitutes may be one obtained by substituting hydrogen at an arbitrary position of methyl methacrylate.

Next, using the apparatus shown in FIGS. 1, 2 and 3 (a) as in Example 1, each homopolymer was extruded at once to form a plastic optical fiber having a diameter of 650 μm. The refractive index distribution of the plastic optical fiber showed a stepwise GI type distribution with five steps in the same profile as shown in FIG. When the transmission loss of the plastic optical fiber was measured, it was 100 dB / km at a wavelength of 650 nm.

Next, this plastic optical fiber was wound on a mandrel having a diameter of 10 mm, and Example 1 was used.
The bending loss was measured in the same manner as in. The bending loss value at this time was 1.0 dB.

As described above, in the present example, according to the present invention, five homopolymers each having a different total number of substitutions were used by using a monomer in which methyl methacrylate was substituted with chlorine and bromine, and methacrylic acid in the clad portion was used. It was shown that a plastic optical fiber containing a core of 5 layers could be extruded with a homopolymer of methyl, and it was further confirmed that this plastic optical fiber had good transmission and bending losses.

Example 6 A plastic optical fiber was produced in the same manner as in Example 1 except that the following compounds were used as the monomers forming the core, and the transmission loss of the obtained plastic optical fiber was measured. And bending loss were measured. Further, in this example, the transmission band of the plastic optical fiber was also measured.

In this example, a chlorine-substituted methacrylic acid alkyl ester was used as the monomer, and the number of chlorine substitutions was increased from the outside and the carbon number (molecular weight) of the ester-bonded alkyl was not decreased ( That is, the cores were produced by selecting monomers such that they are the same or increasing toward the inside) and forming 14 resin layers made of a homopolymer.

Further, in this embodiment, the extrusion die 18 of the plastic optical fiber manufacturing apparatus 10 shown in FIG. 1 has the shape of the discharge hole shown in FIG. 3 (b). As shown in FIG. 3B, which is a front view of the extrusion die 18, in this embodiment, the discharge holes 26 corresponding to the respective resin layers of the intended plastic optical fiber have a plurality of very thin concentric grooves. Therefore, it is necessary to use the extrusion die 18 in which the number of the grooves 26 matches the number of the resin layers of the intended plastic optical fiber. In FIG. 3 (b),
Although an extrusion die 18 for producing a four-layer fiber is shown as in FIG. 3A, an extrusion die having ten concentric groove-shaped ejection holes 26 is used in this example.

As described above, the higher the chlorine substitution number, the higher the refractive index of the homopolymer. Furthermore,
In the case of methacrylic acid alkyl ester, the larger the carbon number of the ester-bonded alkyl, the larger the refractive index of the homopolymer. Therefore, by using the chlorine-substituted methacrylic acid alkyl ester as a monomer, and utilizing the above effects, the monomer is selected according to the combination of the chlorine substitution number and the molecular weight of the alkyl, and a plurality of layers are formed.
It is possible to obtain a plastic optical fiber having a refractive index distribution in which the refractive index drops radially outward with the maximum in the center.

A homopolymer of methyl methacrylate is provided in the clad portion, and a core first layer of a homopolymer of methyl monochloromethacrylate, a core second layer of a homopolymer of ethyl dichloromethacrylate, and a homopolymer of propyl trichloromethacrylate are provided as cores. Polymer core third layer, tetrachlorobutyl methacrylate homopolymer core fourth layer
Layer, pentachlorobutyl methacrylate homopolymer core fifth layer, hexachlorobutyl methacrylate homopolymer core sixth layer, pentachlorobutyl methacrylate homopolymer core seventh layer, octachlorobutyl methacrylate homolayer Polymer pellet feeding device 12 and feeding pipe 1 so as to form the polymer core eighth layer and the homopolymer core ninth layer of tetradecachlorobutyl methacrylate.
4, the extrusion device 16 and the extrusion die 18 were set. Also, each homopolymer was prepared as pellets as in Example 1. Each of the above-mentioned chlorine-substituted methacrylic acid alkyl esters may be one obtained by substituting hydrogen at an arbitrary position of the methacrylic acid alkyl ester with chlorine.

As described above, in the methacrylic acid alkyl ester, the number of carbon atoms of the alkyl was increased from 1 to 5, the number was the same after 5 and the number of chlorine substitution was increased to 1 to 7 and 14 cores of 9 layers. Was simultaneously extruded together with the clad using the apparatus shown in FIGS. 1, 2 and 3 (b) to produce a plastic optical fiber having a diameter of 650 μm. When the refractive index distribution of the plastic optical fiber was measured, a GI having the same shape as that shown in FIG.
It has become clear that it shows a type refractive index distribution. When the transmission loss of the plastic optical fiber was measured, it was 100 dB / km at a wavelength of 650 nm.

The transmission band of this plastic optical fiber was measured by the pulse method. The transmission range of this plastic optical fiber is 100 at a wavelength of 650 nm.
It was MHz · km. It has been revealed that the value of this transmission band is about 10 times wider than that of the standard SI type plastic optical fiber.

Next, this plastic optical fiber was wound around a mandrel having a diameter of 10 mm, and the optical fiber of Example 1 was used.
The bending loss was measured in the same manner as in. The bending loss value at this time was 0.9 dB.

As described above, it was confirmed that the plastic optical fiber of this example had good transmission loss and bending loss, and it was further clarified that it had a wide transmission band.

The present embodiment can be modified, for example, by using a homopolymer of a monomer in which methacrylic acid alkyl ester is substituted with bromine or iodine in place of chlorine, and a plurality of layers are similarly extruded. To form a plastic optical fiber. In addition, using a monomer in which methacrylic acid alkyl ester was substituted with fluorine instead of chlorine, the monomer was selected so that the number of fluorine substitution decreases from the outside to the center, contrary to the case of chlorine described above. You may form a core. Also in the case of the plastic optical fibers of these modified examples, it was possible to obtain the same refractive index distribution, transmission loss, bending loss, and transmission band as in this embodiment.

(Example 7) A plastic optical fiber was produced in the same manner as in Example 1 except that a methacrylic acid alkyl ester was used as each monomer forming the core, and the obtained plastic optical fiber was transmitted. The loss and bending loss were measured.

When the carbon number of the alkyl is changed, the ratio of carbon-hydrogen (CH) bonds in the acrylic acid derivative molecule is changed, so that the refractive index of the homopolymer is changed.
Then, utilizing this, when forming a plurality of homopolymer layers to produce a core having a predetermined refractive index distribution, acrylic acid derivatives are selected from the outside in the order of increasing carbon number of alkyl. By forming a plurality of layers of the homopolymer by extruding the monomer, it is possible to obtain a plastic optical fiber having a refractive index distribution in which the refractive index is lowered toward the outer side in the radial direction with the central portion being the maximum.

Methyl methacrylate in the clad portion, and regarding the core, the first layer of ethyl methacrylate, the second layer of homopolymer of propyl methacrylate, the third layer of homopolymer of butyl methacrylate, and octyl methacrylate. Polymer pellet supply device 12, supply pipe 14, extrusion device 1 so as to form the homopolymer core fourth layer
6 and the extrusion die 18 were set. Also, each homopolymer was prepared as pellets as in Example 1.

Next, using the apparatus shown in FIGS. 1, 2 and 3 (a) as in Example 1, each homopolymer was extruded at once to form a plastic optical fiber having a diameter of 650 μm. The refractive index distribution of the plastic optical fiber was the same as that shown in FIG. 5, and exhibited a stepwise GI type distribution with five steps. When the transmission loss of the plastic optical fiber was measured, it was 120 dB / km at a wavelength of 650 nm.

Next, this plastic optical fiber was wound on a mandrel having a diameter of 10 mm, and Example 1 was used.
The bending loss was measured in the same manner as in. The bending loss value at this time was 1.2 dB.

As described above, according to the present invention, in accordance with the present invention, a monomer group in which the carbon number of the methacrylic acid linear alkyl ester is changed is selected in ascending order of carbon number,
It was shown from the outside that a plastic optical fiber comprising a core consisting of five layers of homopolymer could be produced, and it was further confirmed that this plastic optical fiber has good transmission and bending losses.

(Embodiment 8) In this embodiment, as shown in FIG. 6, the outermost portion has a lower refractive index than the clad portion, and it rises stepwise toward the center to obtain the maximum refractive index of the core. A plastic optical fiber having a core having a refractive index distribution with a large difference (Δn) from the minimum refractive index was produced. A homopolymer of methyl methacrylate without halogen substitution is used for the clad part, and a fluorine (F) substitute that lowers the refractive index is used for the core part close to the clad part so that the number of fluorine substitutions decreases in order. A plurality of methyl methacrylate homopolymer layers inside, and chlorine (C) that increases the refractive index inside the homopolymer layer of methyl methacrylate.
The substitution product of 1) was made into a plurality of layers arranged so that the chlorine substitution number would be large, and these were extruded at once to produce a plastic optical fiber. The core of this plastic optical fiber consists of a total of 11 layers. The transmission loss and bending loss of the obtained plastic optical fiber were measured.

The homopolymer of methyl methacrylate was used for the clad, and the core was composed of a first layer of a homopolymer of methyl octafluoromethacrylate, a second layer of a core of a homopolymer of methyl hexafluoromethacrylate, and a pentafluoromethacrylic acid. Methyl homopolymer core third layer, tetrafluoromethyl methacrylate homopolymer core fourth layer, methyl trifluoromethacrylate homopolymer core fifth layer, methyl difluoromethacrylate homopolymer core sixth layer A core monolayer of a homopolymer of methyl monofluoromethacrylate, a core eighth layer of a homopolymer of methyl methacrylate, a core ninth layer of a homopolymer of monochloromethylmethacrylate which is a monochlorinated methylmethacrylate, Homopoly of methyl dichloromethacrylate Core tenth layer of chromatography, such that the core 11th layer of the homopolymer of octa-chloro methyl methacrylate, polymer pellets feeder 12, feed pipe 14,
The extrusion device 16 and the extrusion die 18 were set. Also, each homopolymer was prepared as pellets as in Example 1. It should be noted that the above-mentioned fluorine compound and chlorine-substituted methyl methacrylate may be those in which hydrogen at arbitrary positions of methyl methacrylate is substituted with fluorine or chlorine.

Each of the above homopolymers was extruded at once using the apparatus shown in FIGS. 1, 2 and 3 (a) to produce a plastic optical fiber having a diameter of 650 μm. When the refractive index distribution of the manufactured plastic optical fiber was measured, it was revealed that it showed a stepwise GI type refractive index distribution with a large Δn, as shown in FIG. When the transmission loss of the plastic optical fiber was measured, it was 100 dB / km at a wavelength of 650 nm.

Next, this plastic optical fiber was wound around a mandrel having a diameter of 10 mm, and the optical fiber of Example 1 was used.
The bending loss was measured in the same manner as in. The value of bending loss at this time was 0.3 dB.

As described above, according to the present invention, according to the present invention, a large Δn is obtained by an extrusion method mainly using a homopolymer of a monomer in which methyl methacrylate is substituted with fluorine and a homopolymer of a monomer in which chlorine is substituted. It was shown that a plastic optical fiber could be made, and it was further confirmed that this plastic optical fiber has good transmission loss and bending loss. In particular, it has been shown that a plastic optical fiber having such a core with a large Δn can obtain a very advantageous result in bending characteristics.

Comparative Examples 1 to 4 Example 1 according to the present invention
In order to further clarify the effectiveness of the present invention shown in FIGS.
Shown as 4. In Comparative Examples 1 to 4, the core is composed of a plurality of layers having different refractive indexes as in Examples 1 to 8,
A polymer layer is formed by using a plurality of homopolymers having different refractive indexes, which are obtained by polymerizing a polymerizable monomer by adding a dopant (refractive index increasing agent) for increasing the refractive index in a different ratio, and
The difference from the above Examples 1 to 8 is that a stepwise refractive index distribution as shown in FIG.

In Comparative Examples 1 to 4, methyl methacrylate was commonly used as the monomer. Furthermore, Comparative Example 1 in which butyl benzyl phthalate was used as the refractive index raising agent,
Comparative Example 2 using diphenyl sulfide as a refractive index raising agent, Comparative Example 3 using triphenyl phosphate as a refractive index raising agent, and Comparative Example 3 using methyl octachloromethacrylate as a refractive index raising agent It was set as Example 4. In Comparative Example 4, the monomer and the refractive index raising agent are copolymerized.

The following procedure was carried out in common with these five comparative examples. The above-mentioned refractive index raising agent was added to methyl methacrylate at an adjusted amount to synthesize a plurality of polymers having different refractive indexes to obtain a pellet form. Then
This was extruded under the same equipment and conditions as in Example 1 to obtain a plastic optical fiber. The plastic optical fibers obtained in Comparative Examples 1 to 5 each exhibited the stepwise GI type refractive index distribution shown in FIG. Then, in the same manner as in Example 1, the transmission loss at a wavelength of 650 nm was measured, and then the bending loss in a state of being wound around a 10 mm mandrel was measured.

In Comparative Example 1 using a polymer obtained by adding butylbenzyl phthalate as a refractive index increasing agent to methyl methacrylate as a monomer, the transmission loss was 150.
dB / km and bending loss were 2.5 dB. In Comparative Example 2 in which a polymer obtained by adding diphenyl sulfide as a refractive index raising agent to methyl methacrylate as a monomer was used, the transmission loss was 160 dB / km and the bending loss was 2.6 d.
It was B. In Comparative Example 3 in which a polymer obtained by adding triphenyl phosphate as a refractive index raising agent to methyl methacrylate as a monomer was used, the transmission loss was 180 dB.
/ Km, and bending loss was 2.8 dB. In Comparative Example 4 in which a polymer obtained by adding methyl octachloromethacrylate as a refractive index increasing agent to methyl methacrylate as a monomer was used, the transmission loss was 300 dB / km and the bending loss was 3.
It was 0 dB.

As described above, the plastic optical fiber of the present invention, which utilizes the difference in the refractive index of the monomer itself in order to obtain the refractive index distribution, is similar to the plastic optical fiber containing the dopant for changing the refractive index. It was shown that even the refractive index distribution is excellent in both transmission loss and bending loss.

[0108]

As described in detail above, the plastic optical fiber of the present invention has a core made of a homopolymer containing no dopant that changes the refractive index.
It has excellent transmission loss and bending loss because it has no light scattering or absorption in the visible light range.

The method for producing a plastic optical fiber of the present invention uses one kind of homopolymer for each layer,
Since the multilayer cores having different refractive indexes are formed inside the clad portion, it becomes possible to easily and highly productively manufacture a plastic optical fiber having a stepwise GI type refractive index distribution.

Therefore, a practical plastic optical fiber that can be used for high-speed communication can be provided with high productivity.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an example of a plastic optical fiber manufacturing apparatus preferably used in the present invention.

FIG. 2 is a cross-sectional view of an extrusion die in an example of a plastic optical fiber manufacturing apparatus preferably used in the present invention.

FIG. 3 is a front view of an extrusion die.

FIG. 4 is an external view of a plastic optical fiber manufactured according to the present invention.

FIG. 5 is a graph showing a refractive index distribution of a graded index (GI) type plastic optical fiber having a stepwise refractive index distribution.

FIG. 6 is a graph showing a refractive index distribution of a graded index (GI) type plastic optical fiber having a stepwise refractive index distribution with a large Δn.

FIG. 7 is a graph showing a refractive index distribution of a step index (SI) type plastic optical fiber.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Plastic optical fiber manufacturing apparatus, 12 ... Polymer pellet supply apparatus, 14 ... Supply tube, 16 ... Extrusion apparatus, 18 ... Extrusion die, 20 ... Winding up, 22 ... Plastic optical fiber, 24 ... Nozzle, 26 ... Discharge hole, 32
... clad, 34 ... core first layer, 36 ... core second layer, 3
8 ... Core third layer, 50 ... Core.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technology display area // B29K 33:00

Claims (15)

[Claims] 1. A plurality of homopolymers having different refractive indexes from one or more nozzles arranged on a plurality of concentric circles in an extrusion die of an extruder, and one kind of homopolymer corresponds to each nozzle on each concentric circle. The plurality of resin layers having different refractive indexes are formed by closely surrounding and enclosing the resin layers having the higher refractive index from the central axis toward the outer side in the radial direction. Consists of a fiber-shaped core having a refractive index distribution that falls, and a clad portion that is coated on the outside of the core and has a refractive index lower than the refractive index of the central portion of the core, and each resin layer of the core is A method for producing a plastic optical fiber, which comprises forming a plastic optical fiber made of a resin composed of different kinds of homopolymers. 2. A plurality of homopolymers having different refractive indexes from a plurality of concentric groove-shaped ejection holes formed in an extrusion die of an extrusion molding machine so that one homopolymer corresponds to each ejection hole. The plurality of resin layers having different refractive indexes are formed by closely surrounding the resin layers having a higher refractive index from the central axis toward the outer side in the radial direction, and the refractive index drops from the center toward the outer side in the radial direction. And a fiber-shaped core having a refractive index distribution and a clad portion that is coated on the outside of the core and has a refractive index lower than the refractive index of the central portion of the core, and the resin layers of the core are respectively A method for producing a plastic optical fiber, which comprises forming a plastic optical fiber made of a resin composed of one different kind of homopolymer. 3. Each of the homopolymers forming each of the resin layers of the core has a carbon atom in which hydrogen of the first polymer, which is a homopolymer which is the same or different in each resin layer, is replaced with an atom or a functional group. The method for producing a plastic optical fiber according to claim 1 or 2, wherein the second polymer is a homopolymer having a reduced ratio of hydrogen (CH) bonds contained in the molecule. . 4. The method of manufacturing a plastic optical fiber according to claim 3, wherein the atom is halogen. 5. The method for producing a plastic optical fiber according to claim 3, wherein the first polymer is the same for each of the resin layers. 6. The halogen is fluorine (F), and the plurality of resin layers are closely surrounded from the central axis toward the outer side in the radial direction in the order of increasing fluorine content of the second polymer. 6. The method for producing a plastic optical fiber according to claim 4, wherein the core is formed by the method. 7. The halogen is selected from the group consisting of chlorine (Cl), bromine (Br) and iodine (I), and the plurality of resin layers are radially outward from a central axis. 6. The production of a plastic optical fiber according to claim 4, wherein the core is formed by closely surrounding the second polymer in order of increasing content of the halogen in the second polymer. Method. 8. The halogen is selected from two or more from the group consisting of chlorine (Cl), bromine (Br), and iodine (I), and the plurality of resin layers are arranged in a radial direction from a central axis. The plastic light according to claim 4 or 5, wherein the core is formed by closely surrounding the second polymer in the order of increasing total content of the halogens toward the outside. Fiber manufacturing method. 9. The method of manufacturing a plastic optical fiber according to claim 1, wherein the outermost refractive index of the core is lower than the refractive index of the clad. 10. A resin layer made of the homopolymer wherein the halogen is fluorine (F), and the halogen is selected from the group consisting of chlorine (Cl), bromine (Br) and iodine (I). The method for producing a plastic optical fiber according to claim 9, wherein the core is formed from a resin layer made of the homopolymer. 11. The method for producing a plastic optical fiber according to claim 5, wherein the first polymer is represented by the general formula of Chemical formula 1. Embedded image [R ₁ is an atom or a functional group selected from the group consisting of hydrogen and methyl, and R ₂ is methyl, ethyl, propyl, butyl,
It is a functional group selected from the group consisting of tertiary butyl, pentyl, hexyl, cyclohexyl, isobornyl, and adamantyl. ] 12. The manufacturing of a plastic optical fiber according to claim 3, wherein each of the resin layers of the core is composed of the second polymer which is a homopolymer represented by the general formula (2). Method. Embedded image [R ₁ is an atom or a functional group selected from the group consisting of hydrogen and methyl, and R ₂ is a linear alkyl, branched alkyl or cyclic alkyl having 1 to 20 carbon atoms. ] 13. The core is formed of a plurality of resin layers, wherein the plurality of resin layers use the second polymer in an order from the central axis toward the outer side in the radial direction in order of the carbon number of R _2. The method of manufacturing a plastic optical fiber according to claim 12, wherein 14. The homopolymer represented by the general formula (2) above, wherein the second polymer in which hydrogen is further substituted with fluorine is used in the order of increasing fluorine content from the central axis toward the outer side in the radial direction. The method for producing a plastic optical fiber according to claim 12, wherein the core is formed of a plurality of resin layers used in the same or larger order of carbon number of R ₂ . 15. The homopolymer represented by the general formula of the chemical formula 2 wherein the hydrogen is further substituted with an atom selected from the group consisting of chlorine, bromine and iodine, the second polymer 13. The core is formed of a plurality of resin layers used in the order of increasing the atomic content and in the order of increasing or decreasing the molecular weight of R _{2 from} 13. Manufacturing method of plastic optical fiber.