JPH08114714A - Production of plastic optical fiber preform - Google Patents

Abstract

PURPOSE: To provide a process for easily producing a plastic optical fiber preform having sufficiently large differences in refractive indexes and smooth refractive index distribution. CONSTITUTION: A core part is formed in a process for producing the core part by polymerizing a liquid mixture composed of a monomer and a refractive index increasing agent on a core central part 302 to form multiple layers having the successively decreasing refractive indices to form a first core part 305 and further, polymerizing a liquid mixture composed of the monomer and a refractive index decreasing agent thereon to form multiple layers having the successively decreasing refractive indices to form a second core 307 part. The plastic optical fiber preform 126 may be produced by further forming a clad part 308 thereon by polynm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a base material for a plastic optical fiber.

[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 and is low cost, so that its transmission loss is not a problem. It is often used as a short-distance optical transmission line. A plastic optical fiber having such characteristics is used in a LAN (local
area network), ISDN (integrated service digit)
In the concept of next-generation communication networks such as al networks), their importance is increasing.

FIG. 10 shows a plastic optical fiber.
As schematically shown in FIG. 1, a step index type (SI type) fiber having a refractive index distribution which changes stepwise has already been put into practical use. This SI type fiber can be used for transmission over an extremely short distance, for transmission between components inside an electronic device, and the like, but since it has a small transmission capacity, it is not necessarily suitable for communication.

It is possible to send a large amount of information per unit time (large transmission capacity) as compared with the above SI type fiber,
As an optical fiber having more suitable characteristics as an optical transmission line for communication, a graded index (GI) type optical fiber having a core refractive index distribution that changes in the radial direction is proposed, as schematically shown in FIG. ing.

In order to produce a GI type plastic optical fiber, a method of producing a plastic optical fiber preform having a refractive index distribution in advance and drawing this can easily produce a fiber with a small bending loss. . And
As a method for producing such a base material, Japanese Patent Application Laid-Open No. 2-1
As described in 6504, there is a method of concentrically extruding a laminate of two or more kinds of polymerizable mixtures having different refractive indexes.

[0006]

However, since the method disclosed in the above-mentioned patent is a lamination extrusion method, it is possible to form only about 10 layers having different refractive indexes. Therefore, the refractive index distribution has a stepwise shape, and in such a method, a base material having a smooth refractive index distribution that descends radially outward from the central portion as shown in FIG. 11 is produced. I can't.

There is also a method of obtaining a continuous and smooth refractive index distribution by diffusing a monomer between each layer after extrusion using such a method, but in this case, the number of steps is increased, As a result, productivity is impaired.
Further, in this case, the difference in refractive index between the core portion and the clad portion cannot be made sufficiently large. Therefore, even if the base material manufactured by this base material manufacturing method is drawn, a fiber having excellent bending characteristics cannot be obtained.

Therefore, the present invention provides a method for easily producing a plastic optical fiber preform having a sufficiently large difference in refractive index between the core portion and the clad portion and a smooth refractive index distribution with high productivity. To aim.

[0009]

In order to realize a method of manufacturing a plastic optical fiber preform which solves the above problems, the present inventor has found that a rod made of a polymer having a high refractive index has a gradually decreasing refractive index. It was considered to manufacture the plastic optical fiber preform by using the method of forming the layer of. Then, as a result of repeated experiments and trial production, it is extremely effective to provide a manufacturing method that achieves the above object, by adopting a polymerization method of polymerizing a monomer for forming each layer in such a method. I found it.

Therefore, according to the method for producing a base material for a plastic optical fiber of the present invention, (1) a core is made of a polymer having a substantially cylindrical portion and having a refractive index n; A plurality of first core-forming molds (M (1) to M (i)) each having a substantially cylindrical shape.
And the inner diameter is larger than the diameter of the core central portion and 1 <a ≦ i for a number a (inner diameter of M (a-1))
The first core manufacturing mold (M (1) to M (i)) having a relationship of ≦ (inner diameter of M (a)), and (b) the first number i of the refractive index raising agent added to the monomer. The number of the monomer refractive index raising agent mixed liquids (S (1) to S (i)), and the refractive index when polymerized is 1 <a ≦ i and n ≧ for the number a.
Monomer refractive index raising agent mixed liquid (S (1) to S) having a relationship of (refractive index of S (a-1)) ≧ (refractive index of S (a))
(I)) is used to arrange a member including the core center portion in the center of the hollow portion of the first core manufacturing mold M (x) for the number x of 1 ≦ x ≦ i, and One core part manufacturing mold M (x) is charged with a monomer refractive index raising agent mixed liquid S (x) into a space defined between the molds and polymerized to form an xth layer. 1 to i in order to form a first core portion on the side surface of the core center portion, the first core portion having a first number i of layers and having a refractive index distribution in which the refractive index decreases radially outward. And (2) one member on which the first core portion is formed, (c) a plurality of second core portion molds (N (1 ) -N (j)) and with respect to the inner diameter:
The diameter is larger than the diameter of the outermost layer of the 1st 000000th part and 1 <b ≦ j for the number b (inner diameter of N (b-1)) ≦
The second core manufacturing mold (N (1) to N (j)) having a relationship of (inner diameter of N (b)), and (d) a second number j of the refractive index lowering agent added to the monomer. The number of the monomer refractive index lowering agent mixed liquids (T (1) to T (j)), and the refractive index when polymerized is 1 <b ≦ j with respect to the number b (T
(B-1) refractive index) ≧ (T (b) refractive index), the monomer refractive index lowering agent mixed liquid (T (1) to T
(J)) is used for the number y of 1 ≦ y ≦ j
A member including a core part is disposed in the center of the hollow part of the second core part manufacturing mold N (y), and the monomer refraction is performed in the space defined between the member and the second core part manufacturing mold N (y). The operation of adding the rate-lowering agent mixed liquid T (y) and polymerizing the mixture to form the y-th layer is sequentially performed for the number y from 1 to j, and the second core layer is formed on the side surface of the outermost layer of the first core portion. Forming a second core portion having a refractive index profile in which the refractive index decreases radially outward and has a number j of layers.

According to this method, a mixed liquid in which a refractive index raising agent is added to a monomer is filled and polymerized, and the refractive index gradually decreases toward the outside on the core central portion having a sufficiently high refractive index. After forming one core part, the mixture is filled with a mixed liquid in which a refractive index lowering agent is added to the monomer and polymerized, and the refractive index gradually decreases toward the outside, and the core outermost part has a sufficiently low refractive index. By forming the second core portion having a shell, it becomes possible to obtain a plastic optical fiber preform having a sufficiently large refractive index difference between the core center portion and the core outermost shell and having a smooth refractive index distribution. . In addition, workability is good because each layer is formed by using a polymerization method that is simple and relatively short in reaction time, and does not use CVD or solution coating drying method, which has poor workability and requires a long reaction time. Thus, it becomes possible to manufacture the plastic optical fiber preform in a time-saving manner.

Further, among the refractive index lowering agents, a fluorine compound which has an effect of remarkably lowering the refractive index is rare and therefore expensive, but it is not used for a thick clad portion, but a thin layer as in the present invention. The second core part is formed by using it so that the refractive index distribution is such that the refractive index of the outermost core of the core is lower than that of the clad part, so that the difference in refractive index is sufficient without consuming a large amount of rare substances. Mass production of large plastic optical fiber preforms becomes possible.

In the present invention, the core portion made of the polymer to which the refractive index raising agent is added is the first core portion, and the core portion made of the polymer to which the refractive index lowering agent is added is the second core portion and the first core portion. The inner portion of the first core portion formed on the outer side thereof is referred to as the core central portion. Further, the columnar shape refers to a cylindrical shape having no hollow portion.

Further, in the method for manufacturing a plastic optical fiber preform according to the present invention, the first step has an inner diameter smaller than the diameter of all the first core part manufacturing molds (M (1) to M (i)). A core center part having a refractive index n is prepared by charging a mixture containing a monomer and a refractive index raising agent into a hollow part of a core molding mold having a hollow and substantially cylindrical shape, and polymerizing the mixture. It may be characterized by including a manufacturing operation.

Further, in the method for producing a plastic optical fiber preform according to the present invention, the core portion is disposed at the center of the hollow portion of the hollow mold having a substantially cylindrical shape having an inner diameter larger than the diameter of the core portion. It may be characterized in that it further comprises a third step of introducing a monomer into a space defined between the mold and the clad manufacturing mold to polymerize the monomer to form a clad on the cylindrical side surface of the core.
Alternatively, the core part is arranged in the center of the hollow part of the hollow clad part manufacturing mold having an inner diameter larger than the diameter of the core part, and the space is defined between the core part and the clad part manufacturing mold. , A monomer refractive index raising agent mixed liquid in which a refractive index raising agent is added to a monomer at a ratio that makes the refractive index smaller than the refractive index n ₁ when polymerized and polymerized to form a clad portion on the cylindrical side surface of the core portion. It may be characterized by further including a third step of

In the method of manufacturing a plastic optical fiber preform according to the present invention, the first core part manufacturing mold after the injection in any of the first step, the second step or the first step and the second step. The second core part manufacturing mold or the first core part manufacturing mold and the second core part manufacturing mold may be rotated about the longitudinal axis of the hollow part to perform polymerization. The longitudinal axis in the present invention means the axis of rotation of a cylinder or a cylinder when viewed as a rotating body.

Further, the method for producing a plastic optical fiber preform according to the present invention is characterized in that, in the third step, polymerization is carried out by rotating the mold for producing the clad part about the longitudinal axis of the hollow part after the injection. Good.

The method for producing a plastic optical fiber preform according to the present invention may be characterized in that the monomer contains methyl methacrylate.

The present invention will be described in more detail below.

(Monomer or polymer obtained by polymerizing such a monomer) Known transparent polymers can be used without particular limitation. For example, a homopolymer of methyl methacrylate (polymethyl methacrylate), 2,2-bis (4 −
Polycarbonate produced by transesterification reaction of (hydroxyphenyl) propane and phenyl ester,
In addition, a transparent copolymer of methacrylic acid and the other monomers listed below can be preferably used. The other monomer is, for example, monofunctional (meth) acrylic acid,
Alkyl (meth) acrylate, polyfunctional acrylic acid, acrylic acid such as methacrylic acid, styrene, chloride of styrene and the like can be used. More preferred materials are polymethylmethacrylate (refractive index n = 1.490) and polycarbonate (refractive index n = n = 1.490) produced by transesterification reaction of 2,2-bis (4-hydroxyphenyl) propane with phenylstel. 1.59).

(Refractive Index Raising Agent) In the present invention, an additive that gives a higher refractive index than the refractive index of a polymer containing only a monomer when a mixture added to such a monomer is polymerized is called a refractive index raising agent. . The molecular weight of the refractive index raising agent is not particularly limited as long as it gives a desired refractive index distribution and can coexist stably with the above-mentioned polymer. Further, the refractive index raising agent itself may have a polymerizable functional group (for example, a functional group having an unsaturated bond such as a vinyl group). That is,
The refractive index raising agent may be a monomer or a mixture thereof, or may be an oligomer or a polymer. When methyl methacrylate (refractive index n = 1.490) is used as a monomer, polymethyl methacrylate to which a refractive index raising agent as described below is added is preferably used for the core part. This refractive index raising agent includes, for example, butyl phthalate phthalate (refractive index n = 1.53).
6), 2-phenylethyl acetate (n = 1.51), dimethyl phthalate (n = 1.515), diphenyl sulfide (n = 1.635), vinyl benzoate (n = 1.57).
7), benzyl methacrylate (n = 1.568), diallyl phthalate (n = 1.518) and the like can be preferably used. In the above, vinyl benzoate, benzyl methacrylate and diallyl phthalate are refractive index raising agents having a polymerizable functional group.

(Refractive index lowering agent) In the present invention, an additive that gives a lower refractive index than the refractive index of a polymer containing only a monomer when a mixture added to such a monomer is polymerized is called a refractive index lowering agent. . As in the case of the refractive index raising agent, the molecular weight of the refractive index lowering agent is not particularly limited, as long as it gives a desired refractive index distribution and can coexist stably with the above polymer. Further, the refractive index lowering agent itself may have a polymerizable functional group (for example, a functional group having an unsaturated bond such as a vinyl group). That is, the refractive index lowering agent may be a monomer or a mixture thereof, or an oligomer or a polymer. When methyl methacrylate (refractive index n = 1.490) is used as a monomer, polymethyl methacrylate to which a refractive index raising agent as described below is added is preferably used for the core part.
This refractive index lowering agent includes, for example, 2,2,2-trifluoroethyl methacrylate, (refractive index n = 1.36.
1), hexyl acetate (n = 1.408), bis (3,5,5-trimethylhexyl phthalate) (n = 1.47)
8), bis (2-methylhexyl) phthalate (n = 1.
486) and the like can be preferably used. In the above description, 2,2,2-trifluoroethyl methacrylate is a polymerizable material.

(Molecular Weight of Base Material) In the present invention, from the viewpoint of workability (prevention of disconnection during drawing, or hardness during heating of the base material) at the time of drawing the optical fiber base material, GPC (gel permeati
on chromatography), the weight average molecular weight is 10,
000 or more and 300,000 or less,
Furthermore, 30,000 or more and 250,000 or less (especially 5
It is preferably from 2,000 to 200,000.

The weight average molecular weight of the polymer constituting the core portion and the cladding portion of the optical fiber preform can be measured, for example, as follows.

(Measurement Method of Weight Average Molecular Weight) The entire plastic optical fiber preform whose average molecular weight is to be measured is dissolved in tetrahydrofuran (THF) to a concentration of 0.1.
Use a THF solution of about mg / ml.

The THF solution thus obtained is passed through a membrane filter (for example, a membrane filter manufactured by Millipore), if necessary, and then introduced into a GPC measurement system to perform GPC analysis. The weight average molecular weight of the optical fiber preform is obtained based on the analysis result. This G
For PC analysis, for example, the following measurement conditions are preferably used.

GPC device: Tosoh Corporation, trade name: HLC-8020 GPC column: Tosoh Corporation, trade name: TSK gel 4000HXL TSK gel 2500HXL TSK gel 2000HXL (3 connected) (inner diameter 7.8 mm x length 300 mm ( Column bath temperature: 40 ° C. Mobile phase: THF Flow rate: 1.0 ml / min Detector: RI (refractive index) Data processing device: Tosoh Corporation, trade name: CP-8000 The molecular weight of the base material that can be formed is not particularly limited, but from the viewpoint of workability during wire drawing of the optical fiber base material (prevention of disconnection during drawing, or hardness during heating of the base material), the core part is formed. The weight average molecular weight (M _R ) of the polymer is 1
It is preferably from 2,000 to 300,000. The weight average molecular weight (M _D ) of the polymer constituting the clad portion is also preferably 10,000 or more and 300,000 or less. The weight average molecular weight of the core portion or the clad portion can be measured in the same manner as the weight average molecular weight of the whole base material described above.

From the standpoint of workability during the drawing of the optical fiber preform (prevention of disconnection during drawing or hardness during heating of the preform), the ratio M _D / M _R of the above M _R and M _D Is preferably about 0.8 to 1.2, and more preferably about 0.9 to 1.1.

In the present invention, the method for obtaining the above-mentioned molecular weight is not particularly limited, but for example, in the presence of a polymerization initiator and / or a chain transfer agent which terminates the polymerization reaction, the polymerization of the core part and / or the clad part. By doing
Furthermore, the specific molecular weight described above can be obtained by adjusting the amounts of the polymerization initiator and / or the chain transfer agent.

(Polymerization reaction) For example, when methyl methacrylate is used as a monomer, radical polymerization using a peroxide having an OO bond or an azo compound as an initiator is preferably used. This initiator includes benzoyl peroxide,
So-called mesophilic initiators that effectively dissociate radicals at about 40 ° C to about 100 ° C, such as lauroyl peroxide, can be preferably used. Therefore, when such a mesophilic initiator is used, the temperature condition of the polymerization reaction is preferably about 40 ° C to about 10 ° C.
0 ° C. The polymerization reaction rate is such that cracks or the like do not occur in the polymer during or after the polymerization reaction due to expansion and contraction due to the reaction heat or the reaction itself, and that the methyl methacrylate monomer does not boil during the reaction due to the reaction heat. It has to be adjusted, which can be adjusted by a combination of the polymerization temperature and the amount of initiator added. The amount of the initiator added is about 0.001 to 10% by weight, more preferably about 0.
It may be about 01 to 0.3% by weight (particularly about 0.05 to 0.15% by weight). For example, when 0.1% by weight of benzoyl peroxide is added to methyl methacrylate and a polymerization reaction is carried out at 70 ° C., a polymer can be produced without causing cracks and boiling of the monomer. In addition to such bulk polymerization using heat energy, bulk polymerization using light energy and the like can also be used. Even when a monomer other than methyl methacrylate is used, it is possible to control the polymerization reaction rate in the same manner by combining the input energy amount such as temperature and the concentration.

The chain transfer agent, which is optionally used in the polymerization of the clad portion and the core portion, is a weight average molecular weight of 10,000 to 300, which is the above-mentioned plastic base material.
There is no particular limitation as long as 000 is given, and it is possible to appropriately select and use from known chain transfer agents. Examples of such known chain transfer agents include aromatic hydrocarbons such as benzene and isopropylbenzene; chloroform,
Examples thereof include halides such as carbon tetrachloride; and mercapto compounds (compounds having a -SH group) such as butyl mercaptan.

(Manufacturing device and number of revolutions) As long as the device is capable of rotating the plastic optical fiber preform and the mold integrally and has a heating means having a temperature control function,
It can be preferably used in the present invention regardless of the form. However, in the polymerization reaction, the progress of the reaction may be hindered by oxygen in the air. Therefore, when the base material is inserted into the mold and set, both ends of the base material must be sealed.

When the base material and the mold are rotated during the polymerization reaction, the rotation speed is preferably about 10,000 rpm or less (particularly, about 100 rpm to about 5,000 rpm).

(Mold) The mold used for manufacturing each of the first core portion, the second core portion, the clad portion, and the core central portion may have a hollow cylindrical shape, and various materials such as glass can be used. is there. For the first core part manufacturing mold and the second core part manufacturing mold, it is necessary to use a large number of molds having different inner diameters corresponding to the formation of a large number of layers. In addition, the mold having the maximum inner diameter among the second core part manufacturing molds is made of a polymer material forming the core part and having a suitable refractive index for the clad part, and the mold after the formation of the second core part is completed. It may be used as a clad portion by performing a collapse as it is without demolding.

(Drawing Method) Next, a method of drawing the optical fiber preform into the optical fiber will be described.

A description will be given with reference to the schematic sectional view (longitudinal sectional view) of FIG. 9 which can be used for drawing a base material manufactured by the method of the present invention. It should be noted that, in the following drawings, a scale slightly different from the actual scale may be used for convenience of description.

As shown in FIG. 9, a drawing apparatus 910 for a plastic optical fiber according to this embodiment has a drawing furnace 912.
An outer diameter monitor 914 and a winding means 916.

The drawing furnace 912 has a metal cover 920.
And a housing composed of an upper cylinder 928 and a lower cylinder 932 which are respectively arranged above and below the cover 920. The wire drawing furnace 912 includes the housing, a circular tube-shaped furnace core tube 922 arranged inside the housing, and a heater 924 arranged outside the furnace core tube 922.

When a cylindrical plastic optical fiber preform 926 is drawn by using the drawing device 910 having the above-mentioned structure, the preform 926 is formed by a neck-down portion 92 described later.
7 with its tip end to give 7
It is inserted inside the furnace core tube 922 so as to be directed downward from No. 8 and is arranged in the drawing furnace 912.

By winding a part of the drawn base material (that is, the optical fiber) by the winding means 916, the optical fiber base material 926, as shown in FIG. It will be arranged in the drawing furnace 912 with 927 facing down.

The plastic optical fiber preform 926
Is normally not completely surrounded by the cover 920, and a part thereof remains in a state of protruding above the upper cylinder 928. In order to maintain the airtightness inside the drawing furnace 912, the upper surface of the upper cylinder 928 is sealed by a ring 930 having a hole having a size substantially equal to the outer diameter of the plastic optical fiber preform 926. On the other hand, a metal shutter 934 is provided on the lower surface of the lower cylinder 932, and a small opening is provided near the center of the shutter 934 so that a drawn fiber can pass through.

When the above-described drawing apparatus of FIG. 9 is used, the plastic optical fiber preform 926 is heated by the heater 924, while the inert gas is supplied into the drawing furnace 912 through the ring 930. Then, it flows in the furnace core tube 922 along the arrow 929 and comes into contact with the base material 926. The heated and melted base material 926 is spun at a predetermined speed to form a plastic optical fiber 938, and the shutter 9
After passing through the opening of 34, passing through the outer diameter monitor 914 and measuring the outer diameter, it is wound by the winding means 916.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

[0044]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail with reference to the accompanying drawings, if necessary, with reference to the accompanying drawings. In the description of the accompanying drawings, the same elements are denoted by the same reference numerals, and duplicate description is omitted.

FIG. 1 is a perspective view of an apparatus for manufacturing a plastic optical fiber preform which is preferably used in the present invention. FIG.
As shown in FIG. 3, the manufacturing apparatus 100 includes a base 102 and a mold housing unit 104. The mold accommodating portion 104 includes two mold assemblies 108a and 108b.
Are housed and connected to the motors 106a and 106b, respectively, and are in a rotatable state. The mold accommodating portion 104 having no bottom portion is installed on a portion of the base 102 that does not have an upper surface. A heater 110 (illustrated by a dotted line) is arranged on the bottom surface of the base 102 below the mold housing portion 104. Therefore, there is no obstacle between the heater 110 and the mold assembly 108a, 108b, and the mold assembly 10
8 a and 8 b are directly heated by the heater 110. The heater 110 has a temperature control function.

Of the left and right mold assemblies 108a and 108b having the same structure, 108a will be described below.

FIG. 2 is a sectional view of the mold assembly 108. As shown in FIGS. 1 and 2, the mold assembly 108 includes a cylindrical glass mold 120.
And one cylindrical Teflon chuck 12 on each side
2, 123 and covers 124, 125, and includes a base material 126 inside. Mold assembly 108
Are held in the mold container as follows. The chuck 122 at one end of the mold assembly 108 engages with a support cylinder 132 fixed to a shaft 128 for transmitting the drive of the motor 106, and the chuck 123 at the other end engages with a shaft 129 inserted in a bearing 130. Fixed support cylinder 1
Engage with 33. That is, the mold assembly 108 is
The motor is driven by the motor 106 and supported by both ends of the motor 106 to be held in the mold housing portion 104.

As shown in FIG. 2, the chucks 122 and 123 respectively have recesses 134 and 135 having the same diameter as the base material 126 at the center of one bottom surface, and the base material 126 engages with the recesses 134 and 135. Are combined. Further, the mold 120 is held so as to have the same center as the centers of the chucks 122 and 123 by being inserted into the covers 124 and 125 fixed to the chucks 122 and 123, respectively. Therefore, the mold 120 and the base material 12
6 is fixed in the mold assembly 108 so as to have the same central axis. That is, by installing the base material 126 in such a mold assembly 108,
A cylindrical space 140 having a uniform thickness is formed between the mold 120 and the base material 126.

As shown in FIG. 2, chucks 122 and 123 have injection vent openings (shown in dotted lines) 142 and 143 to communicate with space 140 when assembled.
Are formed. Before the assembly 108 is installed in the housing portion 104, a monomer or the like is injected through one of the openings, and at the same time, the air in the space 140 is pushed out through the other opening, so that the space 140 is filled with the monomer or the like.

Example 1 FIG. 3 is a process drawing of the plastic optical fiber according to the present embodiment, and is a side view of the plastic optical fiber preform in each manufacturing process. Note that the thickness scale is exaggerated from the actual scale in FIG. 3 in order to express changes in each process in an easy-to-understand manner. In this example, the apparatus for producing a plastic optical fiber preform shown in FIGS. 1 and 2 was used, using methyl methacrylate as a monomer, butyl benzyl phthalate as a refractive index raising agent, and hexyl acetate as a refractive index lowering agent. G
An I-type plastic optical fiber preform was prepared. FIG.
The plastic optical fiber preform manufacturing apparatus shown in 1 is used in all the examples and comparative examples.

In this example, a plastic optical fiber preform was manufactured as follows. Referring to FIGS. 1 and 3,
The process will be described. First, a diameter of 5 m composed of polymethylmethacrylate containing butylbenzyl phthalate
A cylindrical rod 302 of m was prepared (see FIG. 3A). The refractive index of this rod was 1.51. This rod 302 is used as the core center. In addition, 20 first core manufacturing molds M (1) to M (20) having different inner diameters for manufacturing the first core portion and three second core manufacturing portions having different inner diameters for manufacturing the second core portion are manufactured. Mold N (1) ~
N (3) and a cladding part manufacturing mold for manufacturing the cladding part were prepared. These molds were all glass hollow cylinders. The numbers given to these molds, that is, the numbers 1 to 20 for the first core portion and the numbers 1 to 3 for manufacturing the second core portion are given in ascending order of inner diameter.

The first core portion was formed as shown below. According to FIGS. 1 and 2, a base material 126 (in the examples of the present specification, those having at least a core center portion is collectively referred to as a base material) was installed in the mold assembly 108. That is, the base material 126 (in this case, the core center portion 30
2) was inserted into the first core manufacturing mold M (1) 120, chucks 122 and 123 were engaged with both ends of these, and covers 124 and 125 were arranged to form the mold assembly 108. At this time, the base material 126 and the mold 1
A cylindrical space 140 having a constant width is formed between the hollow space 20 and the space 20. Then, in this space 140, methyl methacrylate 100
To 70 parts by weight of butyl benzyl phthalate (part by weight, the same shall apply hereinafter) to S (1), 0.1% by weight of benzoyl peroxide based on the weight of methyl methacrylate in the mixture. Are mixed and injected to fill the space 140. After the injection is completed, the mold assembly 108 is installed in the manufacturing apparatus 100, the heater 110 is set to a temperature of 70 ° C. and operated, and at the same time, the motor 106 is operated to rotate the mold assembly 108 at about 1000 rpm. . In this state, heating and rotation were continued to form the first layer 304 of the first core portion on the core central portion of the base material (see FIG. 3B.
See 1)). After the polymerization reaction for forming the first layer is completely completed, that is, after the curing is completed, this is removed from the manufacturing apparatus, and the base material on which the first layer 304 of the first core portion is formed is removed from the mold. Base material for the first core manufacturing mold M (2)
It is installed in the mold assembly 108 of the manufacturing apparatus so as to be arranged in the hollow central part of the. Then, a small amount of methyl methacrylate was added to the mixed solution S (1) of methyl methacrylate and butylbenzyl phthalate described above to slightly dilute it, and the newly prepared mixed solution S (2) was added to the mixed solution S (1). 0.1% by weight of benzoyl peroxide with respect to the weight of methyl acid is mixed and injected into the space formed between the base material and the mold, and heated and rotated to polymerize as in the previous case. went. The same operation as this is performed for the first core part manufacturing molds M (3) to M (20) using the gradually diluted mixed solutions S (3) to S (20) one by one in order.
The third layer to the twentieth layer were formed in this order on the layer in the order of decreasing refractive index to form the first core portion 305 (see FIG. 3Bi, in this example, i = 20). First
The refractive index of the 20th layer of the core portion, that is, the outermost shell of the first core portion is
1.49.

Next, the second core portion was formed in the same manner as the above-mentioned formation method of the first core portion. That is, as shown in FIG. 2, the base material 126 is attached to the second core manufacturing mold N (1) 12.
0 and insert chucks 122 and 123 at their ends.
Were engaged with each other to produce the mold assembly 108. That is, a cylindrical space having a constant width is formed between the rod 126 and the mold 120 in the circumferential direction and the longitudinal direction. A mixed solution T obtained by adding hexyl acetate to 100 parts of methyl methacrylate in a space formed between the base material 126 and the second core part manufacturing mold N (1).
To (1), 0.1% of benzoyl peroxide was added to the weight of methyl methacrylate and the mixture was injected. After the injection is complete
The manufacturing apparatus is heated to 70 ° C., and the mold assembly 108
Was rotated at about 1000 rpm. In this state, about 12
The polymerization reaction was completed by continuing heating and rotation for a period of time to form the first layer 306 of the second core portion on the first core portion 305 (see FIG. 3 (c1)). Then, hexyl acetate was added to this mixed solution of methyl methacrylate and hexyl acetate to gradually dilute the mixed solutions T (2) to T (3) and N (2).
To N (3), the second core part manufacturing molds are sequentially used one by one, and the second layer to the third layer are formed in the order in which the refractive index gradually decreases, similarly to the formation of the second core part first layer. The second core portion 307 was manufactured by forming the layers (see FIG. 3 (cj)).
In this embodiment, j = 3). 2nd core part 3rd layer, ie, 2nd
The outermost shell of the core had a refractive index of 1.41. In this way, the first part of the core having the inner diameter of 5 mm is radially moved toward the center part.
The diameter of the core part formed by forming the core part and the second core part was 40 mm.

Then, on the core portion composed of the core center portion 302, the first core portion 305 and the second core portion 307 thus formed, the clad is formed by the same method as the formation of each layer of these core portions. The part 308 was formed. That is, the base material on which the core portion is formed is installed in the mold assembly 108 of the manufacturing apparatus, and the clad manufacturing mold is placed outside the base material so that the base material is located in the hollow central portion of the mold. .
Then, 0.1% by weight of benzoyl peroxide was added to methyl methacrylate and injected into the space formed between the base material and the mold, the mixture was heated to a temperature of 70 ° C., and the mold assembly was rotated at a rotation speed of 4000 rpm. 108 was rotated and superposition | polymerization was performed and the clad part 308 was formed (refer FIG.3 (d)). The diameter of the base material after forming the clad portion was 50 mm. Here, the manufacturing process of the plastic optical fiber preform is completed.

The refractive index distribution of the plastic optical fiber preform formed as described above was measured by the preform analyzer method (measurement device: manufactured by York, trade name: P-101, hereinafter,
When this method and apparatus were used in the measurement of the refractive index distribution of all the examples and comparative examples, it was revealed that the refractive index distribution had a smooth refractive index distribution as shown in FIG.

Further, when the whole base material was dissolved in tetrahydrofuran (THF) and GPC analysis was carried out and the weight average molecular weight of the base material was determined based on the GPC analysis result, the molecular weight was 50,000.

Then, this plastic optical fiber preform was drawn by using the drawing device shown in FIG.
A 0 μm plastic optical fiber was produced. This plastic optical fiber is wound around a mandrel having a diameter of 10 mm and is sprinkled (measurement device name: AQ-
6315B Optical spectrum analyzer (manufactured by Ando Electric Co., Ltd., hereinafter, this method and apparatus were used to measure bending loss in all Examples and Comparative Examples). The value of bending loss at this time was 0.6 dB.

By the same operation as in Example 1, the number of layers when forming the first core portion and the second core portion was 3 layers for the first core portion and 2 layers for the second core portion. The example with 5 layers in total,
For comparison, the base material produced in this case had a stepwise refractive index distribution as shown in FIG.

Example 2 FIG. 6 is a cross-sectional view of the mold assembly 108 shown in FIG. 2, showing a state before filling in the step of forming the core central portion of this example. In this example, the apparatus for producing a plastic optical fiber preform shown in FIGS. 1 and 2 was used, using methyl methacrylate as a monomer, butyl benzyl phthalate as a refractive index raising agent, and hexyl acetate as a refractive index lowering agent. Through the process shown in FIG. 3, the core central part, the first core part, the second core part, and the clad part were all formed by polymerization to produce a GI type plastic optical fiber preform.

With reference to FIGS. 1, 2, 3, and 6, the core center portion was manufactured as follows. First, as shown in FIG. 6, the mold assembly 108 was produced by engaging both ends of the glass core center mold 120 having an inner diameter of 5 mm with the chucks 122 and 123. At this time, the base material 126 does not exist inside the core center manufacturing mold 120, and thus the inside of the core center manufacturing mold 120 is a hollow cavity 141. Into this cavity, 0.1% of benzoyl peroxide was added to the mixed solution in which 70 parts of butylbenzyl phthalate was added to 100 parts of methyl methacrylate, and the mixture was injected. Then, after the injection is completed, the mold assembly 1
08 is installed in the manufacturing apparatus 100, and the heater 110 is set to 70 ° C.
The mold assembly 108 was rotated at about 1000 rpm by operating the motor 106 and the motor 106 at the same time. Continue heating and rotating in this state, diameter 5m
A cylindrical core center portion of m was formed (see FIG. 3A).

Then, the steps shown in FIGS. 3B to 3D are performed in exactly the same manner as the method for forming the first core portion and the second core portion of the first embodiment, and the first core portion is formed on the core central portion. The core portion, the second core portion, and the clad portion are formed by polymerization to have a diameter of 5
A 0 mm plastic optical fiber preform was prepared.

Examination of the refractive index distribution of the plastic optical fiber preform thus formed revealed that it has a smooth refractive index distribution as shown in FIG. The weight average molecular weight measured in the same manner as in Example 1 was 80,000.

Then, this plastic optical fiber preform was drawn using the apparatus shown in FIG.
A μm plastic optical fiber was produced. The bending loss was measured while the plastic optical fiber was wound around a mandrel having a diameter of 10 mm. The value of bending loss at this time was 0.6 dB.

Example 3 In this example, the apparatus for producing a plastic optical fiber preform shown in FIGS. 1, 2 and 6 was used. Methyl methacrylate was used as the monomer, butyl benzyl phthalate phthalate was used as the refractive index raising agent, and the refractive index was used. Using 2,2,2-trifluoroethyl methacrylate as the depressant, the process shown in FIG.
All of the core central part, the first core part, the second core part, and the clad part were formed by polymerization to prepare a GI type plastic optical fiber preform.

In this Example, as in Example 2, benzoyl peroxide was added to a mixed solution of 70 parts of butylbenzyl phthalate and 100 parts of methyl methacrylate to add benzoyl peroxide, and the cavity of the mold for producing the core center part was added. Pouring into 70 ℃
Polymerization was carried out under the conditions of 1000 rpm and 1000 rpm (see FIG. 3 (a)). After that, under the same number of layers as in Examples 1 and 2 and polymerization conditions such as temperature and rotation speed, as shown in FIG.
The steps shown in (b) to (d) are performed to polymerize a mixed solution of methyl methacrylate and butylbenzyl phthalate phthalate to form a first core portion, on which methyl methacrylate and 2,2 are added. , A mixture of 2-trifluoroethylmethacrylate is polymerized to form a second core portion to form a core portion, and then a methyl methacrylate is further polymerized thereon to form a clad portion, thereby forming a base material. Was produced.

When the refractive index distribution of the plastic optical fiber preform formed as described above was examined, it was revealed that it had a smooth refractive index distribution as shown in FIG. The weight average molecular weight measured in the same manner as in Example 1 was 100,000.

Then, this plastic optical fiber preform was drawn by using the apparatus shown in FIG.
A μm plastic optical fiber was produced. The bending loss was measured while the plastic optical fiber was wound around a mandrel having a diameter of 10 mm. The bending loss value at this time was 0.5 dB.

Example 4 In this example, using the plastic optical fiber preform manufacturing apparatus shown in FIGS. 1 and 2, methyl methacrylate was used as the monomer, 2-phenylethyl acetate was used as the refractive index raising agent, and the refractive index lowering agent was used. By using hexyl acetate, the first core portion, the second core portion and the clad portion are polymerized on the core central portion made of methyl methacrylate and 2-phenylethyl acetate prepared in advance by the process shown in FIG. To form a GI type plastic optical fiber preform.

In this example, as in Example 1, a rod made of methyl methacrylate and 2-phenylethyl acetate having a diameter of 5 mm was prepared, and this rod was used as the center of the core (see FIG. 3 (a)). . Then, the steps shown in FIGS. 3 (b) to 3 (d) are performed under the same number of layers as in Examples 1 to 3 and polymerization conditions such as the number of rotations and the number of rotations, to obtain methyl methacrylate and 2-phenylethyl acetate. The first core portion is formed by polymerizing the mixed solution, the mixture of methyl methacrylate and hexyl acetate is polymerized on the first core portion to form the second clad portion, and then the methyl methacrylate is further polymerized on it. To form a clad portion to produce a base material having a diameter of 50 mm.

Examination of the refractive index distribution of the plastic optical fiber preform thus formed revealed that it has a smooth refractive index distribution as shown in FIG. The weight average molecular weight measured in the same manner as in Example 1 was 150,000.

Then, this plastic optical fiber preform was drawn using the device shown in FIG.
A μm plastic optical fiber was produced. The bending loss was measured while the plastic optical fiber was wound around a mandrel having a diameter of 10 mm. The value of bending loss at this time was 0.6 dB.

Example 5 In this example, using the plastic optical fiber preform manufacturing apparatus shown in FIGS. 1 and 2, methyl methacrylate was used as the monomer, butyl benzyl phthalate phthalate was used as the refractive index raising agent, and the refractive index lowering agent was used. 2,2,2-trifluoroethylmethacrylate is used for the first core part, the first core part and the second core part on the core center part made of methyl methacrylate and butylbenzyl phthalate phthalate prepared in advance by the process shown in FIG. Two core parts and clad parts were formed by polymerization to prepare a GI type plastic optical fiber preform.

In this example, similarly to Example 1, a rod having a diameter of 5 mm made of methyl methacrylate and butylbenzyl phthalate was prepared, and this rod was used as the center of the core. Then, the steps shown in FIGS. 3B to 3D are performed under the same number of layers as in Examples 1 to 4 and the polymerization conditions such as the temperature and the number of rotations to obtain methyl methacrylate and butyl benzyl phthalate phthalate. The mixed solution is polymerized to form a first core portion, and a mixture of methyl methacrylate and 2,2,2-trifluoroethyl methacrylate is polymerized on the first core portion to form a second core portion. As an outermost shell layer, a refractive index lowering agent that polymerizes by itself to form a polymer 2,2,2
-Secondarily by polymerizing trifluoroethyl methacrylate
The core part was formed. Further, a mixed solution prepared by adding butyl benzyl phthalate phthalate to methyl methacrylate in an addition amount that gives a refractive index lower than that of the central part of the core is polymerized to form a clad part. A material was produced.

Examination of the refractive index distribution of the plastic optical fiber preform thus formed revealed that it has a smooth refractive index distribution as shown in FIG. The weight average molecular weight measured in the same manner as in Example 1 was 130,000.

Then, this plastic optical fiber preform was drawn using the apparatus shown in FIG.
A μm plastic optical fiber was produced. The bending loss was measured while the plastic optical fiber was wound around a mandrel having a diameter of 10 mm. The bending loss value at this time was 0.5 dB.

Comparative Examples 1 to 3 For comparison with the method for manufacturing the plastic optical fiber preform according to Examples 1 to 5 described above, the core portion and the clad portion are formed by forming a multilayer by polymerization. A method, using a refractive index raising agent or a refractive index lowering agent alone, that is, a method of forming only one of the first core portion or the second core portion outside the core central portion, Three examples of producing a plastic optical fiber preform will be given.

FIG. 7 is a process drawing in Comparative Examples 1 to 3, and is a side view of the plastic optical fiber preform in each manufacturing process. In this comparative example, the plastic optical fiber preform manufacturing apparatus shown in FIGS. 1 and 2 was used, methyl methacrylate was used as the monomer, and butyl benzyl phthalate phthalate was used as the refractive index raising agent.
Either the first core portion or the second core portion and the clad portion were formed by polymerization to produce a GI type plastic optical fiber preform 700.

In Comparative Example 1, a rod having a diameter of 5 mm made of methyl methacrylate and butyl benzyl phthalate (refractive index increasing agent) was prepared, and this was used as the core center portion 70.
And 2. Then, under the same polymerization conditions as in the case of forming the first core portion of Example 1, the steps shown in FIGS. 7B to 7C are performed to polymerize a mixed solution of methyl methacrylate and butylbenzyl phthalate phthalate. The first layer 703
After forming the first core portion 704, butyl benzyl phthalate phthalate is added to methyl methacrylate in an amount such that the refractive index is lower than the refractive index of the outermost shell of the first core portion. The clad portion 706 is formed by polymerizing the added mixed liquid, and the base material 70 having a diameter of 50 mm is formed.
0 was produced.

In Comparative Example 2, a rod having a diameter of 5 mm made of methyl methacrylate and hexyl acetate (refractive index lowering agent) was prepared and used as the core central portion 702. And
Under the same polymerization conditions as in the case of forming the second core portion of Example 1, the steps shown in FIGS. 7B to 7C are performed to polymerize a mixed solution of methyl methacrylate and hexyl acetate to give a core. After forming the second core portion 704 on the central portion 702, a mixture of methyl methacrylate and hexyl acetate added in an amount such that the refractive index is lower than the refractive index of the outermost shell of the second core portion. A clad portion 706 was formed by polymerizing the liquid, and a base material 700 having a diameter of 50 mm was produced.

In Comparative Example 3, the steps shown in FIGS. 7 (a) to 7 (c) were performed under the same polymerization conditions as in the formation of the core central portion and the formation of the first core portion in Example 2 to carry out methacrylic acid. By polymerizing a mixed solution of methyl and butylbenzyl phthalate, the core center 702 and the first
After forming the core portion 704, polymerizing a mixed solution in which methyl methacrylate is added with butylbenzyl phthalate phthalate in an addition amount such that the refractive index is lower than the refractive index of the outermost shell of the first core portion. A clad portion 706 was formed by using the above to prepare a base material 700 having a diameter of 50 mm.

FIG. 8 is a graph showing the refractive index distribution of the three plastic optical fiber preforms produced in Comparative Examples 1 to 3 as described above. The weight average molecular weight measured in the same manner as in Example 1 was 200,
000, 80,000 in Comparative Example 2 and 14 in Comparative Example 3.
It was 000.

The bending loss of each of the optical fibers having a diameter of 650 μm drawn under the same conditions as in Examples 1 to 5 was measured while being wound around a mandrel having a diameter of 10 mm. The bending loss values at this time were 2.6 dB in Comparative Examples 1 and 3, and 2.5 dB in Comparative Example 2.

Regarding the bending loss of the drawn optical fiber,
Examples 1, 2, 3 and 5 in which phthalic acid butylbenzyl ester was used as the refractive index raising agent, and Comparative Examples 1 and 3 in which phthalic acid butylbenzyl ester was also used as the refractive index raising agent.
These results are summarized in Table 1 for comparison with.
According to Table 1, the bending loss of the optical fibers according to Comparative Examples 1 and 3 in which only the step of forming the first core portion using the refractive index raising agent on the core central portion in forming the core portion is 2.
In contrast to 6 dB, Examples 1, 2, 3 and 5 of the present invention include the step of forming the second core portion using a refractive index lowering agent in addition to the step of forming the first core portion.
The bending loss of the optical fiber is 0.5 to 0.6 dB.
And, it is remarkably improved. Further, comparing FIGS. 4 and 8, in Examples 1, 2, 3 and 5 of the present invention including the step of forming the first core portion and the step of forming the second core portion, smooth refraction is performed. It was shown that a plastic optical fiber preform having a refractive index distribution and a large difference in refractive index was produced.

[0084]

[Table 1]

Similarly, in order to compare Examples 1, 2 and 4 using hexyl acetate as a refractive index lowering agent with Comparative Example 2 using hexyl acetate as a refractive index lowering agent, the results are shown in Table 1. 2 shows. According to Table 2, the bending loss is 2.5 dB in Comparative Example 2 including only the step of forming the second core portion.
In contrast, in Examples 1, 2 and 4 including the step of forming the first core portion performed before the step of forming the second core portion, the bending loss is remarkably 0.5 to 0.6 dB. Has improved. Further, comparing FIGS. 4 and 8, in Examples 1, 2 and 4 of the present invention including the step of forming the first core portion and the step of forming the second core portion, a smooth refractive index distribution is obtained. It was shown that a plastic optical fiber preform having a large refractive index difference was produced.

[0086]

[Table 2]

[0087]

As described above in detail, for the formation of the core portion, the step of forming the first core portion using the refractive index raising agent and the formation of the second core portion using the refractive index lowering agent. According to the method for producing a plastic optical fiber preform of the present invention including the step of, a plastic optical fiber preform having a smooth refractive index and a large refractive index difference can be easily produced with good productivity, A plastic optical fiber having a low bending loss can be easily manufactured from the base material manufactured in this manner.

[Brief description of drawings]

FIG. 1 is a perspective view of a plastic optical fiber preform manufacturing apparatus preferably used in the present invention.

FIG. 2 is a vertical cross-sectional view of a mold assembly of a plastic optical fiber preform manufacturing apparatus preferably used in the present invention, showing a state in which the preform is contained inside.

FIG. 3 is a process drawing of Examples 1 to 5, showing a state of a plastic optical fiber preform in each process.

FIG. 4 is a graph showing the radial direction refractive index distribution of the plastic optical fiber preforms produced in Examples 1 and 2.

5 is a graph showing the radial direction refractive index distribution of the plastic optical fiber preform manufactured in Example 1. FIG.

FIG. 6 is a vertical cross-sectional view of a mold assembly of a plastic optical fiber preform manufacturing apparatus preferably used in the present invention, showing a state before forming a core central portion in Example 2.

FIG. 7 is a process chart of Comparative Examples 1 to 3, showing a state of a plastic optical fiber preform in each process.

FIG. 8 is a graph showing a radial direction refractive index distribution of plastic optical fiber preforms manufactured in Comparative Examples 1 and 3.

FIG. 9 is a vertical cross-sectional view of a wire drawing device that can be used for wire drawing of a base material manufactured according to the present invention.

FIG. 10 is a graph showing a refractive index distribution of a step index (SI) type fiber.

FIG. 11 is a graph showing a refractive index distribution of a graded index (GI) type fiber.

[Explanation of symbols]

100 ... Manufacturing apparatus, 102 ... Stand, 104 ... Mold receiving section, 106a, b ... Motor, 108a, b ... Mold assembly, 110 ... Heater, 120a, b ... Mold,
122a, b, 123 ... Chuck, 124a, b, 12
5 ... Cover, 126 ... Base material, 128a, b, 129a,
b ... Shaft, 130a, b ... Bearing, 132a, b, 133
... Supporting cylinders, 134, 135 ... Dimples, 140 ... Space, 1
41 ... Cavity, 142, 143 ... Injection vent port, 302 ...
Core part, 304 ... 1st core part 1st layer, 305 ... 1st
Core part, 306 ... Second core part first layer, 307 ... Second core part, 308 ... Clad part, 700 ... Base material, 702 ... Core center part, 703 ... First layer, 704 ... First core part or Two
Core part, 706 ... Clad part, 910 ... Wire drawing device, 91
2 ... Wire drawing furnace, 914 ... Outer diameter monitor, 916 ... Winding means,
920 ... Cover, 922 ... Between cores, 924 ... Heater, 9
26 ... Base material, 927 ... Neck down part, 928 ... Upper cylinder, 929 ... Arrow, 930 ... Ring, 932 ... Lower cylinder, 934 ... Shutter, 938 ... Plastic optical fiber.

Claims (7)

[Claims] 1. A method for producing a base material for a plastic optical fiber having a substantially cylindrical portion, which has a core portion composed of a core center portion, a first core portion, and a second core portion, wherein: ) Production of (a) a plurality of first core parts of a plurality of first numbers i, which are hollow and have a substantially cylindrical shape, with respect to one core central portion made of a polymer having a substantially cylindrical portion and having a refractive index n. Molds (M (1) to M (i)), wherein the inner diameter is larger than the diameter of the core center and 1 <a ≦ i for a number a ((inner diameter of M (a-1)) ≦ (Inner diameter of M (a)), which has a relationship of (M (1))
To M (i)) and (b) the refractive index raising agent is added to the monomer in the first number i of monomer refractive index raising agent mixtures (S (1) to S (i)), Regarding the refractive index when polymerized, n ≧ (S (a−
(1) refractive index) ≧ (refractive index of S (a)) and a monomer refractive index raising agent mixed liquid (S1 to Si),
For a number x of 1 ≦ x ≦ i, a member including the core center portion is arranged in the center of the hollow portion of the first core manufacturing mold M (x), and the member and the first core manufacturing mold M (x). )
The monomer refractive index raising agent mixed liquid S (x) is charged into the space defined between and to polymerize to form the x-th layer in order from 1 to i for several x, A first step of forming, on the side surface of the core central part, a first core part consisting of the first number i layers and having a refractive index distribution in which the refractive index decreases outward in the radial direction; and (2) (C) A plurality of second core part molds (N (1 )
˜N (j)), the inner diameter being larger than the diameter of the outermost layer of the first core portion and 1 <b ≦ j for the number b ((inner diameter of N (b-1)) ≦ (N (B) inner diameter), and the second core manufacturing mold (N (1) to N
(J)) and (d) a mixture of liquids (T (1) to T (j)) of the refractive index lowering agent of the second number j in which the refractive index lowering agent is added to the monomer, Regarding the refractive index at the time of carrying out, a monomer refractive index lowering agent mixed liquid having a relationship of (refractive index of T (b-1)) ≧ (refractive index of T (b)) with respect to the number b of 1 <b ≦ j (T (1) to T (j)), the member having the first core portion formed is subjected to the second core manufacturing mold N (y) for the number y of 1 ≦ y ≦ j.
Is placed in the center of the hollow part of the above, and the monomer refractive index lowering agent mixed liquid T (y) is charged into a space defined between the member and the second core part manufacturing mold N (y) to polymerize the mixture. To form the y-th layer in the order of 1 to j with respect to the number y, and is formed by the second number j layers on the side surface of the outermost layer of the first core portion and is bent outward in the radial direction. And a second step of forming a second core portion having a refractive index distribution with a reduced index. 2. The first step includes all the first steps.
A core and a refractive index raising agent are contained in the hollow portion of the core core manufacturing mold having a substantially cylindrical shape having an inner diameter smaller than the diameter of the core manufacturing mold (M (1) to M (i)). The method for producing a plastic optical fiber preform according to claim 1, further comprising a core center manufacturing operation of manufacturing the core center having the refractive index n by introducing a mixture and polymerizing the mixture. 3. The core part is disposed at the center of the hollow part of the clad part manufacturing mold having a hollow cylindrical shape having an inner diameter larger than the diameter of the core part, and between the core part and the clad part manufacturing mold. 3. The method according to claim 1, further comprising a third step of forming the clad portion on the cylindrical side surface of the core portion by introducing and polymerizing the monomer into the space defined by the above. A method for producing a plastic optical fiber preform as described. 4. The core part is disposed at the center of the hollow part of the clad part manufacturing mold having a hollow cylindrical shape having an inner diameter larger than the diameter of the core part, and between the core part and the clad part manufacturing mold. The monomer refractive index raising agent mixed liquid in which the refractive index raising agent is added to the monomer in such a ratio that the refractive index becomes smaller than the refractive index n ₁ when polymerized is charged into the space defined by The method for producing a plastic optical fiber preform according to claim 1 or 2, further comprising a third step of forming a clad portion on the surface of the cylindrical side surface. 5. In the first step, the second step, or the first step and the second step, the first core part manufacturing mold and the second core part after the charging. The manufacturing mold or the first core part manufacturing mold and the second core part manufacturing mold are rotated about the longitudinal axis of the hollow part to perform the polymerization. Manufacturing method of plastic optical fiber preform. 6. The method according to claim 3, wherein, in the third step, the polymerization is performed by rotating the mold for producing a clad part around the longitudinal axis of the hollow part after the charging. The method for producing a plastic optical fiber preform according to any one of claims. 7. The method for producing a plastic optical fiber preform according to claim 1, wherein the monomer contains methyl methacrylate.