JP3533263B2 - Method for producing a preform for producing a refractive index distribution type optical fiber - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention is a graded index optical fiber having high transparency and heat resistance, which has been difficult to realize with conventional optical resins (hereinafter sometimes abbreviated as GI type optical fiber). The present invention relates to a method for manufacturing a base material (preform), and a method for directly manufacturing without using the base material.

Since the GI type optical fiber obtained by the present invention is a non-crystalline resin, it does not scatter light and has a very high transparency in a wide wavelength band from ultraviolet light to near infrared light, so that it has various wavelengths. It can be effectively used for optical systems. In particular, the present invention provides an optical transmission body having low loss at wavelengths of 1300 nm and 1550 nm, which are used for trunk silica fibers in the field of optical communication.

Further, the GI type optical fiber obtained by the present invention has heat resistance, chemical resistance, moisture resistance and nonflammability, which can withstand severe use conditions in the engine room of automobiles.

The refractive index distribution in a gradient index optical fiber means that the refractive index in the transverse section of the optical fiber decreases from the center of the fiber in the radial direction in a curve close to a parabola. In the GI type optical fiber, the traveling speed of light is high in the peripheral portion where the refractive index is low,
Since the light having a high refractive index is slow in the central portion, the light traveling in the peripheral portion has a long path, but the speed is high, so that the transmission speed is almost equal to that of the light traveling in the central portion, and the mode dispersion is low.

[0005]

2. Description of the Related Art As a conventionally known resin for a GI type optical fiber, an optical resin represented by a methylmethacrylate resin, a tetrafluoroethylene resin or a vinylidene fluoride resin described in WO94 / 04949 is proposed. Has been done.

The core of the graded-refraction plastic optical fiber is methyl methacrylate resin, styrene resin,
Many proposals have been made to use an optical resin such as a carbonate resin or norbornene resin and to make the clad a fluoropolymer. Further, JP-A-2-244007 proposes using a fluorine-containing resin for the core and the clad. Also, WO94 / 04949 and JP-A-3-8170.
No. 3, JP-A-3-81704, JP-A 5-1
A method of manufacturing a GI type optical fiber is described in Japanese Patent Publication No. 73026 and the like.

[0007]

DISCLOSURE OF THE INVENTION The present invention has a heat resistance required for automobiles, office automation (OA) equipment, home electric appliances, etc., which cannot be reached by optical fibers such as methyl methacrylate resin, carbonate resin and norbornene resin. G with moisture resistance, chemical resistance, and non-combustibility
A method for manufacturing an I-type optical fiber is provided.

Further, the present invention makes it possible to use ultraviolet light (wavelength 200 nm to 400 nm) and near infrared light (wavelength 700 nm to 2500 nm) which cannot be achieved by an optical transmission material such as methacrylate resin, carbonate resin, norbornene resin, Further, the present invention provides a method of manufacturing a GI type optical fiber having a low optical transmission loss in a wide transmission region band. Further, the present invention provides a method for manufacturing a base material for manufacturing a GI type optical fiber.

[0009]

DISCLOSURE OF THE INVENTION The present inventor has found that a C—H bond (that is, a carbon-hydrogen bond) which imparts heat resistance, moisture resistance, chemical resistance, and incombustibility and causes light absorption in near infrared light. It was found that a fluorinated polymer substantially free of C—H bond is optimal for eliminating the above). This fluoropolymer has C—F bonds (that is, carbon-bonds) instead of C—H bonds.
Fluorine bond).

That is, when a substance is irradiated with light, the stretching vibration of a bond between certain atoms and the light having a wavelength that causes resonance vibration with the bending vibration are preferentially absorbed. The polymeric substances used in plastic optical fibers so far are mainly C
It was a compound having a -H bond. In the polymer substance based on this C—H bond, since the hydrogen atom is light and easily vibrates, the basic absorption is in the infrared region on the short wavelength side (3400 n).
appear in m). Therefore, in the near-infrared to infrared region (600 to 1550 nm), which is the wavelength of the light source, relatively low overtone absorption of this C—H stretching vibration appears in abrupt manner, which is a major cause of absorption loss.

Therefore, when hydrogen atoms are replaced with fluorine atoms, the wavelengths of their overtone absorption peaks shift to the long wavelength side, and the absorption amount in the near infrared region decreases. From the theoretical value, in the case of PMMA (polymethylmethacrylate) having a C—H bond, the absorption loss of the C—H bond is estimated to be 105 dB / km at a wavelength of 650 nm, and 10,000 dB at a wavelength of 1300 nm. / Km
That's all.

On the other hand, in a substance in which hydrogen atoms are replaced by fluorine atoms, there is substantially no loss due to absorption at a wavelength of 650 nm, and even at a wavelength of 1300 nm, between 1 and 6 dB between the 6th and 7th tones of the stretching vibration of the C—F bond. It is on the order of km and it can be considered that there is no absorption loss. For that we are C
It is proposed to use compounds with a -F bond. Further, it is desirable to exclude a functional group such as a carboxyl group or a carbonyl group, which is a factor that hinders heat resistance, moisture resistance, chemical resistance, and incombustibility. Further, a carboxyl group absorbs near infrared light, and a carbonyl group absorbs ultraviolet light. Therefore, it is desirable to exclude these groups. Further, in order to reduce the transmission loss due to light scattering, it is important to use an amorphous polymer.

Further, in the case of the graded index optical fiber, multimode light propagates while being reflected at the interface between the core and the clad. Therefore, modal dispersion occurs and the transmission band is reduced. However, in the graded index optical fiber, mode dispersion hardly occurs and the transmission band increases.

The inventor of the present invention, therefore, used as a material for a GI type optical fiber, an amorphous fluoropolymer having substantially no C—H bond, particularly a fluoropolymer having a ring structure in the main chain, and the polymer. We have newly found a GI type optical fiber in which substances having different refractive indices are used as compared with the combination, and the concentration of the substances having different refractive indices has a gradient in a specific direction. The present invention is the following invention relating to the method for producing the GI type optical fiber.

In comparison between the non-crystalline fluoropolymer (a) having substantially no C--H bond and the fluoropolymer (a), the difference in refractive index is at least 0.001 or more. Multi-layer extrusion molding using an inner layer forming material composed of at least one material selected from the substances (b) of type and an outer layer forming material composed of at least one of the above materials and having a lower refractive index than the inner layer forming material. In the method for producing a base material for producing a gradient index optical fiber by the method, a cylindrical flow of the molten inner layer forming material and a flow of the molten outer layer forming material are formed in the extrusion molding device, and then compared with the diameter of the base material. Flow of the layer forming material in a large-diameter multi-layered cylindrical shape, and then the diameter of the flow of the layer forming material of the multi-layered cylindrical shape is reduced to flow of the multi-layered cylindrical or multi-layered cylindrical layer forming material of a smaller diameter. age Extrusion method for producing a preform for gradient index optical fibers for the production, characterized in that to produce a preform having a multilayered cylindrical shape or multilayer cylindrical shape.

In comparison between the non-crystalline fluoropolymer (a) having substantially no C—H bond and the fluoropolymer (a), the difference in refractive index is at least 0.001 or more. Using an inner layer forming material composed of at least one material selected from the substances (b) of a kind, and an outer layer forming material composed of at least one material selected from the above materials and having a lower refractive index than the inner layer forming material, In a method for producing a gradient index optical fiber by multilayer extrusion molding and spinning, a cylindrical molten inner layer forming material flow and a molten outer layer forming material flow are formed in an extrusion molding device, and then a large diameter multilayer cylindrical shape is formed. The streams of the layer-forming material are laminated, and subsequently the diameter of the flow of the layer-forming material having a multilayer cylindrical shape is reduced to form a stream of the layer-forming material having a smaller diameter in the multilayer cylinder or the multilayer columnar shape, and then the fibrous material. Method for producing a graded-index optical fiber, characterized by molding.

Hereinafter, the fluoropolymer (a), the substance (b) and the GI type optical fiber which are the materials for the GI type optical fiber will be described first, and then the base material and the method for producing the GI type optical fiber will be described.

<Fluorine-containing polymer (a)> As the fluorine-containing polymer, tetrafluoroethylene resin, perfluoro (ethylene-propylene) resin, perfluoroalkoxy resin, vinylidene fluoride resin, ethylene-tetrafluoroethylene has hitherto been used. Resins, chlorotrifluoroethylene resins and the like are widely known. However, since these fluorine-containing resins have crystallinity,
Light is scattered and the transparency is not good, which is not preferable as a material for a plastic optical fiber.

On the other hand, the non-crystalline fluoropolymer is excellent in transparency because it does not scatter light due to crystals.
As the fluoropolymer (a) in the present invention, C-H
There is no limitation as long as it is a non-crystalline fluoropolymer having no bond, but a fluoropolymer having a ring structure in its main chain is preferable. The fluorine-containing polymer having a ring structure in the main chain, a fluorine-containing aliphatic ring structure, a fluorine-containing imide ring structure,
A fluoropolymer having a fluorine-containing triazine ring structure or a fluorine-containing aromatic ring structure is preferable. Among the fluoropolymers having a fluorinated aliphatic ring structure, those having a fluorinated aliphatic ether ring structure are more preferable.

The fluorine-containing polymer having a fluorine-containing alicyclic structure has a thermal stretching or melting property which will be described later as compared with a fluorine-containing polymer having a fluorine-containing imide ring structure, a fluorine-containing triazine ring structure or a fluorine-containing aromatic ring structure. It is a more preferable polymer because it is difficult for the polymer molecules to be oriented even when it is made into fibers by spinning, and as a result, light is not scattered.

The viscosity of the fluorinated polymer (a) in the molten state is from 10 ^{3 at} a melting temperature of 200 ° C. to 300 ° C.
10 ⁵ poise is preferred. If the melt viscosity is too high, not only is melt spinning difficult, but it is necessary to form a refractive index distribution.
Diffusion of the substance (b) is less likely to occur, making it difficult to form a refractive index distribution. In addition, if the melt viscosity is too low, there will be a practical problem. That is, when it is used in electronic devices, automobiles, etc., it is exposed to high temperatures and softens, and the optical transmission performance deteriorates.

The number average molecular weight of the fluoropolymer (a) is
It is preferably 10,000 to 5,000,000, more preferably 50,000 to 1,000,000. If the molecular weight is too small, heat resistance may be impaired, and if it is too large, it becomes difficult to form an optical fiber having a refractive index distribution, which is not preferable.

The polymer having a fluorinated alicyclic structure is obtained by polymerizing a monomer having a fluorinated cyclic structure, or a fluorinated monomer having at least two polymerizable double bonds is cyclopolymerized. A polymer having a fluorinated alicyclic structure in the main chain obtained as described above is suitable.

A polymer having a fluorinated alicyclic structure in its main chain, which is obtained by polymerizing a monomer having a fluorinated alicyclic structure, is known from Japanese Patent Publication No. 63-18964. That is, perfluoro (2,2-dimethyl-
1,3-dioxole) and other monomers having a fluorine-containing alicyclic structure are homopolymerized, and this monomer is also radical-polymerizable monomer such as tetrafluoroethylene, chlorotrifluoroethylene, and perfluoro (methyl vinyl ether). A polymer having a fluorinated alicyclic structure in its main chain can be obtained by copolymerizing with.

Further, a polymer having a fluorine-containing aliphatic ring structure in its main chain obtained by cyclopolymerization of a fluorine-containing monomer having at least two polymerizable double bonds is disclosed in JP-A-63-
It is known from JP-A-238111 and JP-A-63-238115. That is, by cyclopolymerizing monomers such as perfluoro (allyl vinyl ether) and perfluoro (butenyl vinyl ether), or by using such monomers as tetrafluoroethylene, chlorotrifluoroethylene, perfluoro (methyl vinyl ether), etc. A polymer having a fluorine-containing alicyclic structure in its main chain can be obtained by copolymerizing with the radical-polymerizable monomer.

Further, perfluoro (2,2-dimethyl-
Monomers having a fluorinated alicyclic structure such as 1,3-dioxole) and perfluoro (allyl vinyl ether)
A polymer having a fluorinated alicyclic structure in its main chain can also be obtained by copolymerizing a fluorinated monomer having at least two polymerizable double bonds such as or perfluoro (butenyl vinyl ether).

Specific examples of the above-mentioned polymer having a fluorinated alicyclic structure include those having a repeating unit selected from the following formulas (I) to (IV). The fluorine atoms in the polymers having these fluorine-containing alicyclic structures may be partially substituted with chlorine atoms in order to increase the refractive index.

[0028]

[Chemical 1]

[In the above formulas (I) to (IV), 1 is 0 to 5, m is 0 to 4, n is 0 to 1, and l + m + n is 1 to 1.
6, o, p and q are 0 to 5, respectively, and o + p + q is 1 to
6, R is F or CF ₃ , R ₁ is F or CF ₃ , R ₂ is F
Or CF ₃ , X ₁ is F or Cl, X ₂ is F or Cl
Is. The polymer having a fluorinated alicyclic structure is preferably a polymer having a ring structure in its main chain, but a polymer containing 20 mol% or more, preferably 40 mol% or more of polymer units having a ring structure is preferable. It is preferable in terms of transparency and mechanical properties.

<Regarding the substance (b)> The substance (b) has a difference in refractive index of 0. 1 as compared with the fluoropolymer (a).
It is at least one kind of substance of 001 or more and may have a higher refractive index or a lower refractive index than the fluoropolymer (a). In the present invention, a substance having a higher refractive index than that of the fluoropolymer (a) is usually used.

The substance (b) is preferably a low molecular weight compound, an oligomer or a polymer containing an aromatic ring such as a benzene ring, a halogen atom such as chlorine, bromine or iodine, and a bonding group such as an ether bond. In addition, the substance (b) is preferably a substance that does not substantially have a C—H bond for the same reason as that of the fluoropolymer (a). The difference in refractive index with the fluoropolymer (a) is preferably 0.005 or more.

The substance (b) which is an oligomer or polymer is a polymer of the monomer forming the above-mentioned fluoropolymer (a), and has a refractive index in comparison with that of the fluoropolymer (a). It may be an oligomer or a polymer having a difference of 0.001 or more. As a monomer,
It is selected from those which form a polymer having a difference in refractive index of 0.001 or more in comparison with the fluoropolymer (a). For example, two kinds of fluoropolymers (a) having different refractive indexes can be used, and one polymer (a) can be distributed as the substance (b) in the other polymer (a).

These substances (b) have a solubility parameter difference of 7 (cal) in comparison with the above matrix.
/ Cm ³ ) ^1/2 is preferable. Here, the solubility parameter is a characteristic value that is a measure of the mixing property between substances, and the solubility parameter is δ, the molecular cohesive energy of the substance is E, and the molecular volume is V. The equation δ = (E / V) ¹ Expressed as ^{/ 2} .

Examples of the low molecular weight compound include halogenated aromatic hydrocarbons containing no hydrogen atom bonded to a carbon atom. Particularly, a halogenated aromatic hydrocarbon containing only a fluorine atom as a halogen atom or a halogenated aromatic hydrocarbon containing a fluorine atom and another halogen atom is preferable from the viewpoint of compatibility with the fluoropolymer (a). It is more preferable that these halogenated aromatic hydrocarbons do not have a functional group such as a carbonyl group or a cyano group.

Examples of such halogenated aromatic hydrocarbons include those represented by the formula Φ _r -Z _b [Φ _r is a b-valent fluorinated aromatic ring residue in which all hydrogen atoms are replaced by fluorine atoms, and Z is fluorine. Halogen atoms other than -Rf, -CO-Rf,-
O-Rf, or -CN. However, Rf is a perfluoroalkyl group, a polyfluoroperhaloalkyl group, or a monovalent Φ _r . b is 0 or an integer of 1 or more. ] There is a compound represented by. The aromatic ring includes a benzene ring and a naphthalene ring. The perfluoroalkyl group or polyfluoroperhaloalkyl group which is Rf preferably has 5 or less carbon atoms. As a halogen atom other than fluorine, a chlorine atom or a bromine atom is preferable.

Specific compounds include, for example, 1,3-
Dibromotetrafluorobenzene, 1,4-dibromotetrafluorobenzene, 2-bromotetrafluorobenzotrifluoride, chloropentafluorobenzene,
Examples include bromopentafluorobenzene, iodopentafluorobenzene, decafluorobenzophenone, perfluoroacetophenone, perfluorobiphenyl, chloroheptafluoronaphthalene, and bromoheptafluoronaphthalene.

As the substance (b) which is a polymer or an oligomer, among the substances having the repeating units (I) to (IV), a fluorine-containing polymer having a refractive index different from that of the fluoropolymer (a) to be combined is used. A compound (for example, a combination of a fluoropolymer containing only a fluorine atom as a halogen atom and a fluoropolymer containing a fluorine atom and a chlorine atom, obtained by polymerizing two or more monomers of different types or different ratios) Combinations of different fluoropolymers) are preferred.

In addition to the fluorine-containing polymer having a ring structure in the main chain as described above, it does not contain hydrogen atoms such as tetrafluoroethylene, chlorotrifluoroethylene, dichlorodifluoroethylene, hexafluoropropylene and perfluoroalkyl vinyl ether. Oligomers composed of monomers, copolymerized oligomers of two or more of those monomers, and the like can also be used as the substance (b). Also, -C
F ₂ CF (CF ₃₎ O- or _{- (CF 2) n O- (} n is 1-3
Perfluoropolyether having a structural unit of (integer of) can also be used. The molecular weight of these oligomers is selected from the range of molecular weight at which they become amorphous, and the number average molecular weight is 300.
~ 10,000 is preferred. Considering the ease of diffusion, a number average molecular weight of 300 to 5000 is more preferable.

The particularly preferred substance (b) is a chlorotrifluoroethylene oligomer because of its good compatibility with the fluoropolymer (a), especially the fluoropolymer having a ring structure in its main chain. Since the compatibility is good, the fluoropolymer (a), particularly the fluoropolymer having a ring structure in the main chain, and the chlorotrifluoroethylene oligomer are easily mixed by heating and melting at 200 to 300 ° C. be able to. Moreover, both can be mixed uniformly by dissolving in a fluorine-containing solvent and mixing and then removing the solvent. A preferred molecular weight of the chlorotrifluoroethylene oligomer is a number average molecular weight of 500 to 1
500.

<About GI type optical fiber> In the cross section of the GI type optical fiber, the substance (b) is distributed in the fluoropolymer (a) with a concentration gradient from the center to the peripheral direction. Preferably, the substance (b) is a substance having a higher refractive index than the fluoropolymer (a), and the substance (b) has a concentration gradient in which the concentration decreases from the center of the optical fiber to the peripheral direction. It is a distributed optical fiber. In some cases, the substance (b) is a substance having a lower refractive index than the fluoropolymer (a), and this substance is distributed with a concentration gradient in which the concentration decreases from the periphery of the optical fiber toward the center. Fiber optics are also useful.
The former optical fiber can be usually manufactured by arranging the substance (b) at the center and diffusing it toward the peripheral direction. The latter optical fiber can be manufactured by diffusing the substance (b) from the periphery toward the center.

The GI type optical fiber obtained by the present invention can have a transmission loss of 100 db or less at 100 m at wavelengths of 700 to 1,600 nm. Especially at a similar wavelength in a fluoropolymer having an alicyclic structure in the main chain,
The transmission loss of 100 m can be 50 db or less. At relatively long wavelengths of 700 to 1,600 nm, such a low level of transmission loss is extremely advantageous. That is, since the same wavelength as that of the quartz optical fiber can be used, connection with the quartz optical fiber is easy, and compared with the conventional plastic optical fiber which has no choice but to use a wavelength shorter than 700 to 1,600 nm, it is an inexpensive light source. It has the advantage of being completed.

<Regarding the Manufacturing Method of the Present Invention> In manufacturing a GI type optical fiber, it is necessary to diffuse the substance (b) in the fluoropolymer (a) in order to form a refractive index distribution. It is preferable to form the refractive index distribution also when the base material (preform) is manufactured. For example, in the case of manufacturing a base material composed of two layers of a central part and a peripheral part, in order to form a refractive index distribution, the substance (b) is diffused from the central part to the peripheral part (the substance (b) is a fluorine-containing polymer). Coalescence (a)
Higher refractive index) or the substance (b) is diffused from the peripheral part to the central part (when the substance (b) has a lower refractive index than the fluoropolymer (a)). Become.
However, since the diffusion speed of the substance (b) is not always sufficiently high, the problem that the base material manufacturing efficiency is restricted tends to occur. It is conceivable to raise the temperature during the production of the base material in order to accelerate the diffusion rate, but the upper limit of the diffusion temperature naturally exists due to the physical properties of the fluoropolymer (a) and the restrictions on the molding conditions.

In the present invention, in order to accelerate the diffusion rate of the substance (b), the contact area between two layers having different concentrations of the substance (b) is expanded to perform diffusion, and then the base material or GI having a desired diameter is used.
Type optical fiber itself. Therefore, when manufacturing a base material having a desired multilayer cylindrical shape or multilayer cylindrical shape by extrusion molding, the flow of the layer forming material is laminated in a multilayer cylindrical shape having a diameter larger than the diameter of the base material. Then, the diameter of the flow of the multi-layered cylindrical layer-forming material is reduced and extruded as a flow of a smaller-diameter multi-layered cylindrical or multi-layered cylindrical layered material to form a base material having a multi-layered cylindrical shape or multi-layered cylindrical shape. To manufacture. The substance (b) diffuses during the large-diameter multi-layered cylindrical shape and until the base material is molded thereafter. In this case, since the contact area between the two layers having a different concentration of the substance (b) while having a larger diameter than that of the base material is large, it is possible to perform extrusion molding of a multilayer cylindrical base material without changing the diameter. In comparison, the substance (b) diffuses faster. Instead of producing the base material, the extruded material may be spun in a molten state or thermally drawn to be fiberized to directly produce the GI type optical fiber itself.

As an example of concrete molding means, a schematic cross-sectional view of a die tip portion of an extrusion molding apparatus is shown in FIGS. 1 and 2. FIG. 1 shows an example of molding means for maintaining the flow of the large-diameter multilayer cylindrical layer-forming material at a certain distance, and FIG. 2 immediately reduces the diameter of the layer-forming material flow by contacting the layers in the large-diameter multilayer cylindrical shape. It is an example of the forming means to do.

In the die 1 shown in FIG. 1, the melted inner layer forming material and the outer layer forming material flow downward in the cylindrical inner layer forming flow path 2 and the cylindrical outer layer forming flow path 3, respectively. The two streams merge to form a large-diameter, multi-layered cylindrical stream. Next, this large-diameter multi-layered cylindrical flow is maintained for a predetermined distance in the large-diameter flow passage 5, after which the diameter of the multi-layered cylindrical flow is reduced in the reduction flow passage 6, and finally the die end opening 7 is formed into a cylindrical multi-layer. The molded body 8 is extruded,
A base material is obtained. A GI type optical fiber can be manufactured by immediately fiberizing the multilayer material extruded from the die tip opening 7.

In the die 10 shown in FIG. 2, the inner layer forming material is introduced from the first inlet 11 and flows downward in the cylindrical inner layer forming flow passage 12, and the outer layer forming material is supplied from the second inlet 13. The diameter of the multi-layered cylindrical flow is reduced in the contraction channel 16 as soon as it is introduced and flows downward in the cylindrical outer layer forming flow channel 14 and these two flows merge at the confluence section 15, and finally the die tip opening The multilayer molded body 18 is extruded in a columnar shape from the portion 17 to obtain a base material.

The flow of the layer forming material needs to be a laminar flow at least in the flow path downstream of the merging portion in the die, and the extrusion conditions and the shape of the die such as the flow path are formed so that turbulent flow does not occur. Need to be adjusted. The thickness of each layer at the time of merging is preferably 0.1 to 2 mm. If the thickness of each layer is too thin, the extrusion pressure may be excessive and molding may be difficult. Moreover, when the thickness of each layer is too thick, the diffusion of the substance (b) may be insufficient. As will be described later, the substance (b) can be further diffused after the base material is manufactured, but if the diffusion is too insufficient, it takes a long time for the subsequent diffusion to reduce the production efficiency. The apex angle of the conical channel in the reduction channel is preferably 10 to 90 degrees. If this angle becomes too small, the tip becomes too thin and it becomes difficult to handle the position adjustment. Further, if the apex angle is too large, turbulent flow is likely to occur at the tip.

The concentric layers having different refractive indexes in the base material or the GI type optical fiber may be present not only in two layers but also in three or more layers. Even in that case, basically, the central portion and the layers near the central portion are made of a material having a higher refractive index than the layers far from the center. As described above, the substance (b) may have a higher refractive index or a lower refractive index than the fluoropolymer (a). Therefore, when the substance (b) has a higher refractive index than that of the fluoropolymer (a), the substance (b) is present at a higher concentration in the central portion or in a layer closer to the central portion, and the substance (b) is contained. When the refractive index is lower than that of the fluoropolymer (a), the substance (b) is present in a higher concentration in the outermost layer or a layer closer to the outermost layer.

As the base material and the GI optical fiber, the substance (b) is a substance (b) having a higher refractive index than the fluoropolymer (a) [hereinafter, this substance (b) is a substance (b ')]. It is preferable that the substance (b ′) is present in the inner layer forming material at a relatively high concentration. In this case, the material for forming the inner layer is composed of only the substance (b ') or a mixture of the substance (b') and the fluoropolymer (a). The material for forming the inner layer is preferably composed of a mixture of the substance (b ') and the fluoropolymer (a), because the mechanical properties and moldability of the substance (b') are often insufficient. The outer layer forming material consists only of the fluoropolymer (a) or a mixture of the fluoropolymer (a) and the substance (b ') (however, the concentration of the substance (b') is lower than the concentration of the inner layer forming material). Consists of. The outer layer forming material may be a material composed of a mixture of the fluoropolymer (a) and a substance (b) having a lower refractive index than that. When the base material is composed of a multi-layer structure with three or more layers, the layer closer to the center has a higher concentration of the substance (b ') (however, the concentration is lower than that of the center)
The outermost layer or a layer closer to the outermost layer has a lower concentration of the substance (b ′). The substance (b) having a refractive index lower than that of the fluoropolymer (a) may be arranged in the outermost layer or a layer close to the outermost layer.

The refractive index distribution in the base material does not necessarily have to have a desired refractive index distribution enough to correspond to the GI type optical fiber. This is because the desired refractive index distribution can be formed by the substance (b) diffusing to some extent during spinning. In some cases, heat diffusion of the substance (b) is also possible after the base material is manufactured, for example, by performing a diffusion treatment in which the base material is heated to thermally diffuse the substance (b) before fiberizing and then spinning is performed. Is.

[0051]

EXAMPLES Next, examples of the present invention will be described more specifically, but it goes without saying that the description does not limit the present invention.

"Synthesis Example 1" 35 parts by weight of perfluoro (butenyl vinyl ether) [PBVE], 1,1,2-
5 parts by weight of trichlorotrifluoroethane (R113), 150 parts by weight of ion-exchanged water, and 0.09 parts by weight of ((CH ₃ ) ₂ CHOCOO) ₂ as a polymerization initiator,
It was placed in a pressure-resistant glass autoclave. After purging the system with nitrogen three times, suspension polymerization was carried out at 40 ° C. as a result,
28 parts by weight of a polymer having a number average molecular weight of about 1.5 × 10 ⁵ (hereinafter referred to as polymer A) was obtained.

The intrinsic viscosity [η] of the polymer A was 0.50 at 30 ° C. in perfluoro (2-butyltetrahydrofuran) [PBTHF]. The glass transition point of the polymer A was 108 ° C., and it was a tough and transparent glassy polymer at room temperature. The 10% thermal decomposition temperature is 465 ° C,
The solubility parameter was 5.3 (cal / cm ³ ) ^1/2 and the refractive index was 1.34.

The polymer A obtained by the above synthesis was treated with PBTHF.
It is dissolved in a solvent, and CTFE having a number average molecular weight of 800
C TFE for the addition of oligomeric (polymeric mixture
The proportion of the oligomer was 30% by weight) to obtain a mixed solution. This mixed solution was desolvated to obtain a transparent mixed polymer (hereinafter referred to as polymer B). The CTFE oligomer had a refractive index of 1.41, and the difference in solubility parameter from the polymer A was 1.4 (cal / cm ³ ) ^1/2 .

Example 1 Using Polymer A and Polymer B, a GI type optical fiber was manufactured by a coextrusion molding apparatus having a die shown in FIG. The diameter of the cylindrical channel forming the outer layer in the die is 20 mm, and the diameter of the cylindrical channel forming the inner layer is 15 mm.
mm, and the thickness of each flow path at the confluence is 0.
The conical flow path downstream from the confluence has a conical height of 13 mm and a discharge port diameter of 2 mm. The molten polymer A was introduced into the outer layer flow passage, the molten polymer B was introduced into the inner layer flow passage, the temperature of the material in the die was adjusted to 200 to 250 ° C., and the contact time of the two layers in the conical flow passage was set to 30 seconds and extruded. ,
Flow down from the tip of the die, take it up into fiber, and diameter 600
A μm GI type optical fiber was manufactured.

The optical transmission characteristics of the obtained optical fiber are 7
280 dB / km at 80 nm, 120 d at 1550 nm
It was B / km, and was an optical fiber capable of favorably transmitting light from visible light to near infrared.

[Example 2] Using Polymer A and Polymer B, a preform for producing a GI type optical fiber was produced by a coextrusion molding apparatus having a die shown in FIG. The diameter of the cylindrical flow path forming the outer layer in the die is 40 mm, the diameter of the cylindrical flow path forming the inner layer is 30 mm, the thickness of each flow path at the confluence is 1.0 mm, and the downstream from the confluence. The conical height of the conical channel was 30 mm, and the diameter of the discharge port was 4 mm. The molten polymer A was introduced into the outer layer flow passage, the molten polymer B was introduced into the inner layer flow passage, the temperature of the material in the die was adjusted to 250 to 300 ° C., and the contact time of the two layers in the conical flow passage was set to 1 minute and extruded. A base material having a diameter of 4 mm was manufactured. Using this base material, a thermal diffusion process was performed and then hot drawing was performed to manufacture a GI type optical fiber having a diameter of 600 μm.

The optical transmission characteristics of the obtained optical fiber are 7
280 dB / km at 80 nm, 120 d at 1550 nm
It was B / km, and was an optical fiber capable of favorably transmitting light from visible light to near infrared.

[0059]

EFFECTS OF THE INVENTION When a graded index optical fiber or a base material thereof is manufactured by an extrusion molding method, the graded index distribution can be efficiently formed by thermal diffusion of the substance (b). In the gradient index optical fiber obtained by the present invention, by using an amorphous fluororesin having no C—H bond, it is possible to transmit light from ultraviolet light to near infrared light with extremely low loss. Became possible.

This graded-index optical fiber is also suitable for short-distance optical communication because it is flexible and easy to branch and connect despite its large fiber diameter.
It is possible to obtain a practically low-loss optical fiber.
Further, the gradient index optical fiber obtained according to the present invention is used in an engine room of an automobile, OA equipment, a plant,
It has heat resistance, chemical resistance, moisture resistance, and nonflammability that can withstand the harsh conditions of use in home appliances.

[Brief description of drawings]

FIG. 1 is a sectional view of a die tip portion of an extrusion molding apparatus.

FIG. 2 is a cross-sectional view of another die tip portion of the extrusion molding apparatus.

[Explanation of symbols]

1 die 2 Inner layer forming channel 3 Outer layer forming flow path 4 confluence section 5 Large diameter flow path 6 reduction channel 7 Tip opening 8 Multi-layer molding 10 dies 11 First inlet 12 Inner layer forming channel 13 Second inlet 14 Outer layer forming flow path 15 Confluence section 16 Reduced flow path 17 Tip start part 18 Multi-layer molding

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification symbol FI G02B 1/04 G02B 1/04 6/18 6/18 (72) Inventor Tokuhide Sugiyama 1150 Hazawa-machi, Kanagawa-ku, Yokohama-shi, Kanagawa Asahi Glass Co., Ltd. Central Research Laboratory (56) Reference JP-A-6-186441 (JP, A) JP-A-6-297596 (JP, A) JP-A-1-265208 (JP, A) JP-A-5-107404 (JP, A) JP-A-1-164904 (JP, A) JP-A-2-33104 (JP, A) JP-A-1-253704 (JP, A) International Publication 94/15005 (WO, A1) International Publication 64/4949 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02B 6/00-6/02 G02B 6/10 G02B 6/16-6/22 G02B 6/44

Claims (5)

(57) [Claims] 1. A difference in refractive index between the non-crystalline fluoropolymer (a) having substantially no C—H bond and the fluoropolymer (a) is 0.001 or more. An inner layer forming material comprising at least one material selected from at least one substance (b) and an outer layer forming material comprising at least one of the above materials and having a lower refractive index than the inner layer forming material In the method of manufacturing a base material for manufacturing a gradient index optical fiber by extrusion molding,
Form a cylindrical flow of molten inner layer forming material and a flow of molten outer layer forming material in an extrusion molding device, and then stack the layer forming material streams into a multilayer cylinder having a diameter larger than the diameter of the base material. Then, the diameter of the flow of the multi-layered cylindrical layer forming material is reduced and extruded as a flow of the multi-layered cylindrical or multi-layered cylindrical layered material having a smaller diameter to form a base material having a multi-layered cylindrical shape or multi-layered cylindrical shape. A method for producing a preform for producing a graded-index optical fiber, which comprises: 2. The substance (b) is a substance having a higher refractive index than the fluoropolymer (a), and is composed of the substance (b) or a mixture of the substance (b) and the fluoropolymer (a). inner layer forming material, and using the outer layer forming material of a low refractive index than the fluoropolymer (a) or the fluoropolymer (a) a mixture in a by and lining material with a substance (b), according to claim 1
The manufacturing method described in. 3. Obtained by the manufacturing method according to claim 1 or 2.
Refractive index distribution type characterized by fiberizing the formed base material
Optical fiber manufacturing method. 4. The difference in refractive index between the non-crystalline fluoropolymer (a) having substantially no C—H bond and the fluoropolymer (a) is 0.001 or more. An inner layer forming material comprising at least one material selected from at least one substance (b), and an outer layer forming material comprising at least one material selected from the above materials and having a lower refractive index than the inner layer forming material. In the method for producing a gradient index optical fiber by multilayer extrusion molding and spinning, a cylindrical molten inner layer forming material flow and a molten outer layer forming material flow are formed in an extrusion molding device, and then a large diameter multilayer cylinder is formed. The layers of the layer forming material are laminated in a circular pattern, and then the diameter of the layer forming material of the multilayer cylindrical shape is reduced to form a multilayer cylindrical or multilayer cylindrical layer forming material of a smaller diameter. A method of manufacturing a graded index optical fiber, which comprises: 5. The substance (b) is a substance having a higher refractive index than the fluoropolymer (a), and is composed of the substance (b) or a mixture of the substance (b) and the fluoropolymer (a). inner layer forming material, and using the outer layer forming material of a low refractive index than the fluoropolymer (a) or the fluoropolymer (a) a mixture in a by and lining material with a substance (b), according to claim 4
The manufacturing method described in.