JPH08304640A - Plastic optical fiber - Google Patents

Abstract

PURPOSE: To provide a plastic optical fiber capables of realizing a desired refractive index with low transmission loss by a simple method. CONSTITUTION: This plastic optical fiber consists of a fiber core and a clad part formed around the core. The fiber core is formed by adhering surroundingly plural resin layers having different refractive indices in the other of higher refractive index from the center axis to the outside in the radial direction so that the refractive index distribution shows steplike decrease from the center corresponding to the resin layers. The clad layer has a lower refractive index than the refractive index in the center part of the core.

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 that has been put into practical use is a step index type (SI type) plastic optical fiber having a refractive index distribution that 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. 4 is more suitable for communication applications such as LAN, and the transmission band of the fiber can be 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 to obtain a sufficient transmission capacity even with a stepwise refractive index distribution as shown in FIG. You can

In Japanese Patent Publication No. 5-808488, a plastic light having a refractive index distribution that smoothly changes from the center to the outside in one step by an interfacial gel polymerization method is added with a dopant that changes the refractive index of the plastic. An aspect is disclosed in which a GI type plastic optical fiber is obtained by producing a fiber preform and drawing it. The interfacial gel polymerization method has the property that the polymer diffuses into the monomer,
It is a polymerization method that causes the distribution of the composition in a polymer by utilizing the property that a monomer selectively diffuses into a polymer phase (gel phase). Review by Koike (Chemical Industry, 199)
The details are described in the January 2 issue, pp. 14-23).

[0005]

Since the plastic optical fiber of the above-mentioned document is produced by the interfacial gel polymerization method, it is necessary to gradually proceed the polymerization reaction from the outside of the core to the center side. In the case of producing a large base material, it takes a long time for the polymerization. In the interfacial gel polymerization, the polymerization conditions for obtaining a smooth refractive index distribution are limited, and the refractive index difference in the core cannot be increased so much. In addition, there is a problem that if the polymerization time is shortened to increase the productivity, the refractive index distribution tends to be SI type distribution.

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

[0007]

In the plastic optical fiber of the present invention, 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. , A fiber-shaped core having a refractive index distribution in which the refractive index drops in a stepwise manner corresponding to the resin layer from the center toward the outside in the radial direction, and is coated on the outside of the core, and And a cladding portion having a low refractive index.

Further, in the plastic optical fiber of the present invention, the resin layer is composed of the refractive index raising agent for raising the refractive index and the polymer, and the ratio of the refractive index raising agent decreases from the center toward the outer side in the radial direction. The resin layer may be formed in this order to form the core to form the resin layer.

The plastic optical fiber of the present invention may be characterized in that the refractive index raising agent is a non-polymerizable compound having no polymerizable functional group.

In the plastic optical fiber of the present invention, the resin layer is composed of a refractive index lowering agent for lowering the refractive index and a polymer, and the ratio of the refractive index lowering agent increases from the center toward the outer side in the radial direction. The resin layer may be formed in this order to form the core to form the resin layer.

The plastic optical fiber of the present invention may be characterized in that the refractive index lowering agent is a non-polymerizable compound having no polymerizable functional group.

The plastic optical fiber of the present invention may be characterized in that each resin layer forming the core contains a polymer obtained by polymerizing the same monomer.

The plastic optical fiber of the present invention may be characterized in that each resin layer forming the core contains a polymer obtained by polymerizing the same or different monomer for each resin layer.

Further, the plastic optical fiber of the present invention may be characterized in that the polymer monomer forming the clad portion is the same as the polymer monomer forming one resin layer of the core.

Further, the plastic optical fiber of the present invention may be characterized in that the polymer monomer constituting the clad portion is different from all polymer monomers constituting the core resin layer.

Further, the plastic optical fiber of the present invention may be characterized in that the outermost refractive index of the core is lower than the refractive index of the clad portion.

Further, the plastic optical fiber of the present invention may be characterized in that the core is composed of a resin layer containing a refractive index raising agent and a resin layer containing a refractive index lowering agent.

The plastic optical fiber of the present invention may be characterized in that the monomer has acryloyl or methylacryloyl.

Further, the plastic optical fiber of the present invention may be characterized in that the monomer is methyl methacrylate.

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

The plastic optical fiber of the present invention can be easily obtained by heating and melting a base material composed of a plurality of resin layers in the order of increasing refractive index from the inside and heating and melting the base material by a known method. .

As the resin monomer constituting the plastic optical fiber of the present invention, the compounds exemplified below may be used as the first monomer.
The compound may be a second compound which is one of these halogen compounds: methyl acrylate (methyl acrylate), methyl methacrylate (methyl methacrylate), ethyl acrylate, ethyl methacrylate, propyl acrylate, methacrylic acid. Propyl, butyl acrylate, butyl methacrylate, tertiary butyl acrylate, tertiary butyl methacrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate, hexyl methacrylate, cyclohexyl acrylate, cyclohexyl methacrylate, isobornyl acrylate, Isobornyl methacrylate, adamantyl acrylate (acrylic adamantane), adamantyl methacrylate (methacryl adamantane). A second halogenated version of such a first compound
When the compound (1) is used as a monomer, the refractive index of the homopolymer can be changed by changing the halogen substitution number of the monomer.

In the present invention, an additive that gives a higher refractive index when the mixture added to the monomer is polymerized than that of the monomer-only polymer is called a refractive index raising agent. It is sufficient that the refractive index raising agent can stably coexist in the polymer in the core. Examples of the refractive index raising agent include butylbenzyl phthalate (butylbenzyl phthalate) (refractive index n = 1.536, the same applies hereinafter), 2-phenylethyl acetate (n = 1.51), dimethyl phthalate. (N = 1.515), diphenyl sulfide (1,1′-thiobis [benzene]) (n = 1.63)
5) etc. can be used conveniently. However, the refractive index raising agent that can be used in the present invention does not include a compound having an unsaturated bond such as a vinyl group. This is because when the resin layer forming the core contains a copolymer, transmission loss is deteriorated due to light scattering, and it is necessary to prevent this.

In the present invention, an additive which gives a refractive index lower than that of a polymer obtained by polymerizing a mixture added to a monomer is called a refractive index lowering agent.
Examples of the refractive index lowering agent include hexyl acetate (n =
1.408), bis (3,5,5-trimethylhexyl) phthalate (n = 1.478), bis (2-methylhexyl) phthalate (n = 1.486) and the like can be preferably used. . However, like the refractive index raising agent, the refractive index lowering agent that can be used in the present invention does not include a compound having an unsaturated bond such as a vinyl group. This is because when the resin layer forming the core contains a copolymer, transmission loss is deteriorated due to light scattering, and it is necessary to prevent this.

The molecular weight of the plastic optical fiber of the present invention is such that the weight average molecular weight of the polymer constituting the core and the clad by GPC is 10,000 or more and 300,00.
It is preferably 0 or less, and more preferably 30,000 or more and 250,000 or less (further 50,000 or more and 200,
000 or less) is preferable.

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. Since the plastic optical fiber can be obtained by drawing the base material, if the resin constituting the base material has the above-mentioned molecular weight, a plastic optical fiber formed of a resin having the same molecular weight can be obtained.

A known polymerization reaction can be used for the polymerization reaction of the monomer for producing the core and the clad portion of the present invention, but a peroxide or an azo compound having an OO bond is used as an initiator. Radical polymerization is preferred. Here, the initiator of the reaction radical polymerization reaction is, for example, benzoyl peroxide, lauroyl peroxide, or the like at about 40 ° C. to about 1 ° C.
So-called medium temperature initiators that effectively generate radicals at 00 ° C can be preferably used. Therefore, when such a mesophilic initiator is used, the temperature condition of the polymerization reaction is preferably about 4
It is 0 degreeC-about 100 degreeC. 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 0.001 to 0.001 with respect to the entire system with respect to the condition of the polymerization reaction initiation of about 40 ° C to about 100 ° C.
It may be about 10% by weight, more preferably about 0.01 to 0.3% by weight (particularly about 0.05 to 0.15% by weight).
In addition to such bulk polymerization by heat energy,
Bulk polymerization or the like using light energy 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.

When the core or clad portion of the plastic optical fiber preform is manufactured by a polymerization reaction initiated by heating, the manufacturing apparatus used for manufacturing the core or clad part rotates the preform or the following mold. As long as it is a device that has a heating means capable of controlling temperature, it can be suitably used in the present invention regardless of its form. However,
Since the progress of the reaction may be hindered by oxygen in the air in this polymerization reaction, it is preferable to have a function of sealing both ends of the base material when the base material is inserted into the mold and set.

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.

The mold used for producing the clad portion of the base material may be a hollow cylindrical shape, and various materials such as glass can be used. The clad portion of the base material may be polymerized while rotating as described above, or may be formed by making a hole in the rod. In the production of the core, the polymerization may be performed up to the center of the core, or the polymerization may be terminated halfway and then collapsed.

[0031]

The core of the plastic optical fiber of the present invention is composed of a plurality of resin layers in order of increasing refractive index from the inside, and the refractive index distribution has a stepwise shape from the center toward the outside in the radial direction. . Therefore, the mode dispersion can be made smaller than that of the SI type plastic optical fiber, and the level of transmission band required for high-speed communication can be realized. Moreover, since the polymerization of each resin layer is a simple polymerization reaction, a core having a refractive index distribution can be manufactured in a short manufacturing time without quality variations. Therefore, it becomes possible to manufacture the plastic optical fiber applicable to high-speed communication applications with high productivity.

Further, the core of the plastic optical fiber of the present invention uses the refractive index raising agent or the refractive index lowering agent to obtain the refractive index distribution. Therefore, by changing the ratio of these to the polymer, the desired refractive index can be obtained. The distribution can be easily obtained.

In the embodiment in which the refractive index raising agent or the refractive index lowering agent does not contain a polymerizable functional group, each resin layer is formed of a resin containing no copolymer, so that light scattering due to blocking is prevented. It never happens.

In a mode in which a homopolymer in which the refractive index is changed by changing the molecular weight of the monomer is used in the resin layer, the refractive index can be further changed in combination with the refractive index raising agent or the refractive index lowering agent. A desired refractive index distribution can be easily obtained.

Further, in the mode in which the refractive index of the outermost core is lower than that of the cladding, it is easy to increase the difference (Δn) in the refractive index between the central part of the core and the outermost part of the core. Has a greater effect of confining light. Therefore, it is possible to obtain a plastic optical fiber with a small bending loss.

[0036]

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 perspective view of an apparatus for manufacturing a plastic optical fiber preform that can be used in the present invention. As shown in FIG. 1, the manufacturing apparatus 100 includes a table 102 and a stacking unit accommodating unit 104. The overlapping portion accommodating portion 104 accommodates two overlapping portion assemblies 108a and 108b, which are connected to the motors 106a and 106b and are rotatable. The overlapping portion accommodating portion 104 having no bottom portion is used for the base 10
2 is installed on the part without the upper surface. Overlap section accommodation section 1
A heater 110 (illustrated by a dotted line) is arranged on the bottom surface of the base 102 below 04. Therefore, there is no obstruction between the heater 110 and the overlapping portion assemblies 108a and 108b, and the overlapping portion assemblies 108a and 108b are directly heated by the heater 110. The heater 110 has a temperature control function.

Hereinafter, the left and right overlapping portion assemblies 1 having the same structure are provided.
08a and b will be described with respect to 108a, and the subscript a will be omitted in the following description.

FIG. 2 is a cross-sectional view of the superposition section assembly 108 in a state where the base material in the process of manufacturing is installed. As shown in FIG. 1 and FIG. 2, the overlapping portion assembly 1 in the base material manufacturing process
Reference numeral 08 denotes a columnar Teflon (registered trademark) chuck 122, 123 and covers 124, 12 one on each side.
5 and includes a base material 126 which is being manufactured.
The chuck 122 at one end of the overlapping portion assembly 108 is engaged with a support cylinder 132 fixed to a shaft 128 that transmits the drive of the motor 106, and the chuck 123 at the other end is a shaft inserted into a bearing 130. Support cylinder 1 fixed to 129
33 is engaged. That is, the overlapping portion assembly 108 is horizontally supported by both ends of the overlapping portion assembly 108 and is contained in the overlapping portion accommodating portion 104 while being rotatable by the driving of the motor 106.

As shown in FIG. 2, the chucks 122 and 123 each have a base material 126 at the center of one bottom surface.
It has cylindrical recesses 134 and 135 of the same diameter as that of which the base material 126 is engaged.

(Embodiment 1) FIG. 3 is a process drawing of the manufacturing process of the plastic optical fiber preform in this embodiment,
It is an external view of the plastic optical fiber preform in each process of manufacture. In this example, first, the plastic optical fiber preform manufacturing apparatus shown in FIGS. 1 and 2 was used, methyl methacrylate was used as a monomer, and butyl benzyl phthalate phthalate was used as a refractive index raising agent. G having a stepwise refractive index distribution due to multi-layer formation
An I-type plastic optical fiber preform was prepared. Next, this base material was drawn using a known drawing device to obtain a plastic optical fiber. Then, the transmission loss and bending loss of the obtained plastic optical fiber were measured.

In this example, a plastic optical fiber preform was manufactured as follows. The process will be described with reference to FIGS. First, a cylinder 126 made of a polymer of methyl methacrylate and having an inner diameter of 40 mm and an outer diameter of 50 mm was prepared (see FIG. 3A). This cylinder 126 was used as a clad portion for the base material.

The core portion was formed inside the clad portion 126 as follows. As shown in FIGS. 1 and 2, both ends of a base material (hereinafter, those having at least a clad portion are collectively referred to as “plastic optical fiber base material” or “base material”) 126 are chucks 122 and 12.
3, the covers 124 and 125 were arranged to form the overlapping portion assembly 108. The superposition section assembly 108 was installed in the manufacturing apparatus 100. Next, methyl methacrylate 100
25 parts of butyl benzyl phthalate was added to 20 parts of the monomer refractive index raising agent mixed solution S (1), and 0.1% of benzoyl peroxide was mixed to prepare a mother solution. Material 126 (that is, FIG. 3A at this point)
(Equal to the cladding 302 as shown in FIG. 3). Then, the heater 110 was set to a temperature of 70 ° C. and operated, and at the same time, the motor 106 was operated to rotate the superposition section assembly 108 at a rotational speed of about 1,000 rpm. The injected monomer refractive index raising agent mixture S (1) is rotated by rotating the polymerization unit assembly 108.
Exists on the inner surface of the base material 126 (in this case, the clad portion 302) with a substantially uniform thickness in the circumferential direction and the longitudinal direction of the clad portion due to the centrifugal force. In this state, heating and rotation were continued, and the core portion first layer 304 was formed inside the cladding portion 302 (see FIG. 3 (b1)).
After the polymerization reaction for forming the first layer is completely completed, butyl benzyl phthalate phthalate is added little by little to the monomer refractive index raising agent mixed solution S (1) to sequentially increase the refractive index. While preparing S (2) to S (8), the same operation is performed by sequentially using each of them from S (2) to S (8), and the same operation is performed from the core layer second layer (S (2)) The core portion 306 was formed up to the eighth layer (S (8)) and the refractive index gradually increased toward the inner side (see FIG. 3Bi, i = 8 in this example). Here, the plastic optical fiber preform 126 including the clad portion 302 and the core portion 306 was produced. The time required for the polymerization reaction to form each of the above resin layers is 3 per layer.
It was 0 minutes to 1 hour. If a similar process is performed using the interfacial gel polymerization method, a smooth GI type refractive index distribution can be obtained, but a polymerization time of 10 to 12 hours or more is required for each layer. Therefore, it was revealed that the productivity is remarkably improved if the stepwise GI type plastic optical fiber preform is manufactured without using the interfacial gel polymerization method as in this example.

The refractive index distribution of this plastic optical fiber preform is measured by the interferometric method (measuring device: P-101, manufactured by Yoke Co., Ltd., and the method and the device are used for measuring the refractive index distributions of all the examples and comparative examples. ), It became clear that it has a stepwise GI type refractive index profile as shown in FIG.

Next, this plastic optical fiber preform was drawn into a plastic optical fiber having a diameter of 650 μm using a known drawing device. The conditions for drawing at this time were that the temperature of the core tube was 240 ° C. and the drawing speed was 2 m / min. Met. The transmission loss of the plastic optical fiber immediately after being drawn is measured by the cutback method (measurement device: AQ-6315).
B, manufactured by Ando Electric Co., Ltd., and this method and apparatus are used in the measurement of transmission loss in all of the Examples and Comparative Examples below, and the measured value is 200 dB / km at a wavelength of 650 nm.
Met. In addition, it was confirmed that the obtained plastic optical fiber had a stepwise refractive index distribution that dropped from the center toward the outside in the radial direction, as shown in FIG.

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 2.5 dB.

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.

As described above, according to the present invention, methyl methacrylate is used as a monomer and butyl benzyl phthalate phthalate is used as a refractive index raising agent according to the present invention. It was shown that a plastic optical fiber can be easily produced with good productivity by forming an increased number of 8-layer cores, and it was further confirmed that this plastic optical fiber has good transmission loss and bending loss.

It should be noted that this embodiment can be modified. For example, in the production of the base material, in addition to the method of using the rotating cylinder described above, a plurality of materials having different addition rates of the refractive index raising agent or the refractive index lowering agent can be used. The pellet-shaped polymethylmethacrylate was obtained in advance by polymerization, and was extruded using a die in which the die was concentrically arranged, and was composed of a plurality of layers similar to those produced in this example. A base material including a core whose refractive index changes stepwise may be manufactured.

Example 2 A plastic optical fiber preform was prepared in the same manner as in Example 1 except that hexyl acetate was used as a refractive index lowering agent, and this was drawn into a plastic optical fiber. The transmission loss and bending loss of the obtained plastic optical fibers were compared.

In this embodiment, a cylinder having an inner diameter of 40 mm and an outer diameter of 50 mm, which is made of a polymer obtained by adding hexyl acetate to methyl methacrylate, is used as the clad portion, and the inside of the clad portion is formed by using the apparatus shown in FIGS. 1 and 2. Hexyl acetate was gradually added to methyl methacrylate in a reduced amount and dissolved to dissolve the monomer refractive index lowering agent mixed liquids T (1) to T (8) (the addition ratio of hexyl acetate is all higher than that of the clad portion). Low)
Was sequentially used to form a core portion composed of 8 layers in the order in which the refractive index was gradually increased by the process shown in FIG. 3 to fabricate a plastic optical fiber preform. When the refractive index distribution of the produced plastic optical fiber preform was measured, it became clear that it showed a stepwise GI type refractive index distribution as shown in FIG.

Then, this plastic optical fiber preform was drawn under the same drawing conditions as in Example 1 using a drawing device.
A plastic optical fiber with a diameter of 650 μm was drawn.
The transmission loss of the plastic optical fiber immediately after being drawn was measured and found to be 190 dB / wavelength at a wavelength of 650 nm.
It was km.

Next, 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 2.8 dB.

As described above, in this example, according to the present invention, methyl methacrylate was used as a monomer and hexyl acetate was used as a refractive index lowering agent, and the refractive index lowering agent was gradually decreased from the outside toward the center. It was shown that a plastic optical fiber can be easily produced with good productivity by forming an 8-layer core, and it was further confirmed that this plastic optical fiber has good transmission loss and bending loss.

Example 3 Except that a homopolymer of ethyl methacrylate was used for the clad, ethyl methacrylate was used as the core monomer, and butyl benzyl phthalate was used as the refractive index raising agent. By the same operation, a plastic optical fiber preform was prepared and drawn to a plastic optical fiber, and the transmission loss and bending loss of the obtained plastic optical fiber were compared. That is,
A plastic optical fiber having a stepwise refractive index distribution was produced by using polymers of different monomers for the core polymer and the clad polymer.

In this example, a cylinder made of a polymer of ethyl methacrylate and having an inner diameter of 40 mm and an outer diameter of 50 mm was used as a clad portion, and the inside of the clad portion was made of ethyl methacrylate by using the apparatus shown in FIGS. Using the monomer refractive index raising agent mixed liquids S (1) to S (8) in which phthalic acid butylbenzyl ester was gradually added in an increased amount and dissolved, the refractive index was gradually increased by the process shown in FIG. A plastic optical fiber preform was manufactured by forming a core portion composed of eight layers in the ascending order. When the refractive index distribution of the produced plastic optical fiber preform was measured, it became clear that it showed a stepwise GI type refractive index distribution as shown in FIG.

Then, this plastic optical fiber preform was drawn under the same drawing conditions as in Example 1 using a drawing device.
A plastic optical fiber with a diameter of 650 μm was drawn.
The transmission loss of the plastic optical fiber immediately after being drawn was measured and found to be 180 dB /
It was km.

Next, 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 2.5 dB.

As described above, in the present embodiment, according to the present invention, the monomer of the clad portion is different from the monomer of the core, and the core of eight layers in which the refractive index increasing agent is sequentially increased from the outside to the center is used. It was shown that the plastic optical fiber can be easily produced with good productivity by forming the above-mentioned material. Further, it was confirmed that this plastic optical fiber has good transmission loss and bending loss.

Example 4 Methyl methacrylate was polymerized in the same manner as in the core to prepare a clad portion, and then a methacrylic acid alkyl ester was used as a core monomer and a butyl phthalate phthalate ester was used as a refractive index raising agent. A core composed of 8 layers of homopolymer was formed in the same manner as in Example 1 in the order of the alkyl having the largest number of carbon atoms and the amount of addition of the refractive index increasing agent was increased to prepare a plastic optical fiber preform. did. This was drawn on a plastic optical fiber, and the transmission loss and bending loss of the obtained plastic optical fiber were compared.

In this example, as the means for increasing the refractive index, the addition amount of the refractive index increasing agent and the change of the monomer were used together to increase the refractive index synergistically. When methacrylic acid alkyl ester is used as the monomer,
Increasing the carbon number of the alkyl increases the refractive index of the polymer.

First, a mold for manufacturing a clad portion of a glass hollow cylinder having an inner diameter of 50 mm and an outer diameter of 60 mm was placed in the apparatus shown in FIG. 1, and methyl methacrylate added with 0.1% benzoyl peroxide was clad. It was supplied to the surface of the hollow part of the partial mold. And the mold is 4,000 rp
Polymerization is carried out by heating while rotating at m.
A clad portion, which is a hollow cylinder of mm, was produced.

Next, using the apparatus shown in FIG. 1 and FIG. 2, 25 parts by weight of butylbenzyl phthalate phthalate was added to and dissolved in ethyl methacrylate to prepare a monomer refractive index raising agent mixed solution S ( 1) was used to form the core first layer 304 by the process shown in FIG. Next, the core second layer was similarly formed by using the monomer refractive index raising agent mixed liquid S (2) in which butyl benzyl phthalate phthalate was added to propyl methacrylate at a larger addition rate than S (1). Thereafter, using the monomer refractive index raising agent mixed liquids S (3) to S (7) in which the carbon number of alkyl was increased and the addition ratio of butylbenzyl phthalate was sequentially increased, the core third layer to A seventh layer of the core was formed to produce a plastic optical fiber preform. Here, the content of each monomer refractive index raising agent mixed liquid is
S (3) is butyl methacrylate, S (4) is pentyl methacrylate, S (5) is hexyl methacrylate, S
(6) was heptyl methacrylate, and S (7) was octyl methacrylate. Further, the addition ratio of the refractive index raising agent was adjusted so that S (i) <= S (i + 1) (i = 1 to 7).

When the refractive index distribution of the plastic optical fiber preform manufactured as described above was measured, it was found that the same GI type refractive index distribution with 7 steps as shown in FIG. 4 was exhibited. It was revealed.

Then, this plastic optical fiber preform was drawn under the same drawing conditions as in Example 1 using a drawing device.
A plastic optical fiber with a diameter of 650 μm was drawn.
The transmission loss of the plastic optical fiber immediately after being drawn was measured and found to be 180 dB /
It was km.

Next, 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 2.5 dB.

As described above, in the present embodiment, the number of carbon atoms of the alkyl of the methacrylic acid alkyl ester, which is the core monomer, was increased from the outer side toward the center, and the refractive index raising agent was sequentially increased. It was shown that the plastic optical fiber can be easily produced with high productivity by forming the core of the layer, and it was further confirmed that the plastic optical fiber has good transmission loss and bending loss.

(Embodiment 5) In this embodiment, as shown in FIG. 5, it has a lower refractive index than the cladding portion, rises stepwise toward the center, and has a 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. Using a homopolymer of methyl methacrylate for the clad,
In the core portion adjacent to the clad portion, a refractive index lowering agent is used to make the refractive index lower than that of the clad portion, and a plurality of particles are formed by the same operation as in Example 1 so that the addition rate of the refractive index lowering agent decreases in order. Layers were formed. Next, a homopolymer layer of methyl methacrylate is formed on the inside thereof, and a plurality of layers having a refractive index higher than that of the clad portion by using a refractive index raising agent are further added on the inside thereof. The plastic optical fiber preforms were manufactured by forming the plastic optical fiber preforms in the order of increasing amount by the same operation as in Example 1. The core of this plastic optical fiber consists of a total of 16 layers. This was drawn into a plastic optical fiber, and the transmission loss and bending loss of the obtained plastic optical fiber were measured. In this example, methyl methacrylate was used as the core monomer, hexyl acetate was used as the refractive index lowering agent, and butyl benzyl phthalate phthalate was used as the refractive index raising agent.

First, a hollow cylinder made of a homopolymer of methyl methacrylate and having an inner diameter of 40 mm and an outer diameter of 50 mm was used as a clad portion, and using the apparatus shown in FIGS. 1 and 2, methyl methacrylate was added to hexyl acetate. A monomer refractive index lowering agent mixture T (1) in which was dissolved was injected together with 1.0% benzoyl peroxide, and the apparatus was rotated and heated to polymerize to form a core first layer. Then, the monomer refractive index lowering agent mixed liquids T (2) to T (7) in which the addition rate of the refractive index lowering agent to methyl methacrylate is successively reduced are used one by one in order, and the core second layer to the core seventh layer are used. A resin layer was sequentially formed up to the layer. Here, regarding the addition ratio of hexyl acetate, T (i)> = T (i + 1), i = 1 to 7.

Next, the core eighth layer of a homopolymer of methyl methacrylate was formed inside the core seventh layer by the same method for forming the layer as in Example 1.

Further, a monomer refractive index raising agent mixture S (1) in which butyl benzyl phthalate is added to methyl methacrylate is injected into the inner side of the eighth layer of the core, and heated in the same manner while rotating to give the core first layer. Nine layers were formed. Then, the monomer refractive index lowering agent mixed liquids S (2) to S (8) in which the addition rate of the refractive index lowering agent to methyl methacrylate is sequentially increased are used one by one in order, and the core tenth layer to the core sixteenth layer are used. A plastic optical fiber preform was manufactured by sequentially forming resin layers up to the layers. Here, regarding the addition ratio of butyl benzyl phthalate, S (i) <= S (i + 1), i = 1
Was ~ 8.

When the refractive index distribution of the plastic optical fiber preform manufactured as described above was measured, it was found that it showed a stepwise GI type refractive index distribution with a large Δn as shown in FIG. Became.

Next, this plastic optical fiber preform was drawn into a plastic optical fiber having a diameter of 650 μm using the same drawing apparatus as in Example 1 and under the same drawing conditions as in Example 1. The refractive index distribution of the drawn plastic optical fiber exhibited a stepwise GI type distribution with a large Δn, as shown in FIG. When the transmission loss of the plastic optical fiber immediately after being drawn was measured, it was 170 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 0.5 dB.

As described above, this Example shows that a plastic optical fiber having a large Δn can be manufactured by using the refractive index lowering agent and the refractive index raising agent according to the present invention. It was confirmed to have good transmission loss and bending loss. In particular, it has been shown that such a plastic optical fiber having a core with a large Δn can obtain a very advantageous result in bending characteristics and can be easily manufactured with high productivity.

It should be noted that this embodiment can be modified. For example, the type of the monomer to be used is further changed for each resin layer of the core, and the addition amounts of the refractive index lowering agent and the refractive index raising agent are the same as in the present embodiment. It is possible to further increase Δn by changing to. As a method of changing the kind of the monomer, for example, as in Example 4, the number of carbon atoms of the alkyl of the methacrylic acid alkyl ester may be changed.

Comparative Examples 1 to 3 In order to further clarify the effectiveness of the present invention shown by Examples 1 to 5 made according to the present invention, the following three examples not according to the present invention are shown as Comparative Example 1. ~ 3. In common with these Comparative Examples 1 to 3, it was attempted to obtain a GI type refractive index distribution by utilizing a one-step interfacial gel polymerization method for forming a core.

The following procedure was carried out in common with these three comparative examples. First, a cylinder made of a polymer of methyl methacrylate having an inner diameter of 40 mm and an outer diameter of 50 mm was prepared and used as a clad portion. Then, by using the apparatus shown in FIGS. 1 and 2, the hollow portion of the clad portion is filled with a mixed liquid of a monomer and a refractive index raising agent, and gently heated while rotating to form a core of a base material. did. That is, in Comparative Examples 1 to 3, the core of the base material is not formed of a plurality of layers as in the present invention, but a composition distribution is provided by an interfacial gel polymerization method in one layer, and the refractive index gradually increases. I tried to get the core.

In Comparative Example 1, methyl methacrylate was used as the core monomer and butyl benzyl phthalate was used as the refractive index raising agent. In Comparative Example 2, methyl methacrylate was used as the core monomer and diphenyl sulfide was used as the refractive index raising agent. In Comparative Example 3, methyl methacrylate was used as the core monomer, and triphenyl phosphate (triphenyl phosphate) was used as the refractive index raising agent.

When the refractive index distributions of the respective plastic optical fiber preforms obtained in Comparative Examples 1 to 3 thus conducted were investigated, it was found that the refractive index distributions were SI as shown in FIG. It was revealed that it had a type distribution.

Further, in Comparative Examples 1 to 3, in common, although the core had one layer, the time required for producing the base material in Example 1 was twice as long.

[0082]

As described in detail above, since the plastic optical fiber of the present invention has a stepwise refractive index distribution, it has sufficient transmission loss and bending loss to be applied to communication applications. Very easy to manufacture and high in productivity.

Therefore, it is possible to provide a practical plastic optical fiber that can be used for high speed communication.

[Brief description of drawings]

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

FIG. 2 is a vertical cross-sectional view of a superposition section assembly in an example of a plastic optical fiber preform manufacturing apparatus preferably used in the present invention.

FIG. 3 is a perspective view of a plastic optical fiber for each step, showing the steps in Examples 1-5 and Comparative Examples 1-3.

FIG. 4 is a graph showing a refractive index distribution of a graded index (GI) type plastic optical fiber having a stepwise refractive index distribution.

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 with a large Δn.

FIG. 6 is a graph showing a refractive index distribution of a step index (SI) type plastic optical fiber.

[Explanation of symbols]

100 ... Manufacturing apparatus, 102 ... Stand, 104 ... Mold accommodation section, 106a, b ... Motor, 108a, b ... Mold assembly, 110 ... Heater, 122a, b, 123 ... Chuck, 124a, b, 125 ... Cover, 126 ... Base material, 128a, b, 129a, b ... Shaft, 130a, b ...
Bearings, 132a, b, 133 ... Support cylinders, 134, 1
35 ... Dimple, 302 ... Clad part, 304 ... Core 1st
Layer, 306 ... Core.

Claims (13)

[Claims] 1. A plurality of resin layers having different refractive indexes are formed so as to closely surround a resin layer having a higher refractive index from the central axis toward the outer side in the radial direction. A fiber-like core having a refractive index distribution in which the refractive index drops in a stepwise manner corresponding to the layers, and a cladding portion which 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. A plastic optical fiber comprising: 2. The resin layer is composed of a refractive index raising agent that raises the refractive index and a polymer, and the ratio of the refractive index raising agent decreases from the center toward the outer side in the radial direction. The plastic optical fiber according to claim 1, wherein the resin layer is formed to form the core. 3. The plastic optical fiber according to claim 2, wherein the refractive index raising agent is a non-polymerizable compound having no polymerizable functional group. 4. The resin layer is composed of a refractive index lowering agent for lowering the refractive index and a polymer, and the ratio of the refractive index lowering agent increases from the center toward the outer side in the radial direction in the order of the resin layers. The plastic optical fiber according to claim 1, wherein the resin layer is formed to form the core. 5. The plastic optical fiber according to claim 4, wherein the refractive index lowering agent is a non-polymerizable compound having no polymerizable functional group. 6. The plastic optical fiber according to claim 1, wherein each of the resin layers forming the core contains a polymer obtained by polymerizing the same monomer. 7. The plastic optical fiber according to claim 1, wherein each of the resin layers forming the core contains a polymer obtained by polymerizing the same or different monomer for each resin layer. 8. The plastic optical fiber according to claim 1, wherein a polymer monomer forming the clad portion is the same as a polymer monomer forming one resin layer of the core. 9. The plastic optical fiber according to claim 1, wherein the monomer of the polymer forming the clad portion is different from all the monomer of the polymer forming the resin layer of the core. 10. The refractive index of the outermost portion of the core is lower than the refractive index of the clad portion.
9. The plastic optical fiber according to any one of 9 above. 11. The plastic optical fiber according to claim 10, wherein the core comprises a resin layer containing the refractive index raising agent and a resin layer containing the refractive index lowering agent. 12. The monomer according to claim 1, wherein the monomer comprises acryloyl or methylacryloyl.
10. The plastic optical fiber according to any one of 10. 13. The plastic optical fiber according to claim 12, wherein the monomer is methyl methacrylate.