JP3530630B2 - Method of manufacturing refractive index distribution type optical fiber and base material thereof - 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), the base material, and a method for manufacturing 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 base material for manufacturing a GI type optical fiber and a method for manufacturing the base material.

[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 a method for producing the GI type optical fiber, a preform therefor, and a method for producing the preform.

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. A base material consisting of different types of substances (b) and having the substances (b) having different concentrations in the radial direction in the fluoropolymer (a) and existing concentrically.

A method for producing a gradient index optical fiber, characterized in that the above-mentioned base material is made into a 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. A long columnar core material composed of the fluoropolymer (a), the material (b), or a mixture thereof is produced by using the substance (b) of the kind, and the fluoropolymer is provided on the surface of the core material. The substance (b) is contained in the fluoropolymer (a), which is characterized in that it is coated with a coating material composed of (a), the substance (b), or a mixture thereof and having a lower refractive index than the core material.
Exist in concentric circles with different concentrations along the radial direction
Of manufacturing a preform for producing a graded index optical fiber.

First, 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 below, and then the above-mentioned base material, its manufacturing method, and the GI type using the base material. The optical fiber will be described.

<Fluoropolymer (a)> As the fluoropolymer, a tetrafluoroethylene resin, a perfluoro (ethylene-propylene) resin, a perfluoroalkoxy resin, a vinylidene fluoride resin, an 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 in comparison 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 fluorine-containing polymer (a) in the molten state is 10 ³ -at a melting temperature of 200 ° C.-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 subjected to cyclopolymerization. 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 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 fluorinated alicyclic structure in its main chain obtained by cyclopolymerization of a fluorinated 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.

[0029]

[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 refractive index difference of 0. 0 when 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 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 a polymer, is a polymer of a monomer forming the above-mentioned fluoropolymer (a), and has a refractive index in comparison with 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 polymers having a ring structure in the main chain as described above, hydrogen atoms such as tetrafluoroethylene, chlorotrifluoroethylene, dichlorodifluoroethylene, hexafluoropropylene and perfluoroalkyl vinyl ether are not contained. 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, a wavelength 700～1,600Nm, can be the transmission loss of 100m is less 100d B. Especially at a similar wavelength in a fluoropolymer having an alicyclic structure in the main chain,
Transmission loss of 100m can be less 50d B. 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.

<Base Material> In the present invention, a base material (preform) is first produced using the above materials, and then the base material is fiberized to produce an optical fiber. The base material has a long columnar shape and is concentrically formed with a material having a high refractive index at the center and a material having a low refractive index at the peripheral portion.
The refractive index distribution does not necessarily have to exist in the base material. That is, the boundary between the central portion and the peripheral portion may be clear and the refractive index may change sharply at the boundary. This is because even if such a base material is used, the substance (b) is not formed when the fiber is formed.
This is because the refractive index distribution can be formed by diffusing. Of course, the refractive index distribution may be formed sufficiently or to some extent in the base material.

Regardless of whether or not there is a refractive index distribution, in the base material, the central portion is made of a material having a high refractive index and the peripheral portion is made of a material having a low refractive index, and these materials are concentrically arranged. The concentric layers having different refractive indexes 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 a layer closer to the central portion, and the substance (b) is
When is a lower refractive index than the fluoropolymer (a),
The substance (b) is present at a higher concentration in the outermost layer or a layer closer to the outermost layer.

Hereinafter, the substance (b) is a fluoropolymer (a).
The present invention will be described by taking a case where the refractive index is higher than that of [the substance (b) is a substance (b ')] as an example. The present invention is not limited to this case as described above, and when the substance (b) has a lower refractive index than the fluoropolymer (a), the present invention can be carried out according to the following. .

<Regarding Preferred Structure of Base Material> The base material is
The substance (b) is a substance (b ') having a higher refractive index than the fluoropolymer (a), and the substance (b') is present in a relatively high concentration in the central portion of the base material. It is preferable to have In this case, the material of the central part consists only of the substance (b ') or the substance (b') and the fluoropolymer (a)
Consisting of a mixture of. Since the mechanical properties and moldability of the substance (b ') are often insufficient, the material of the central portion preferably comprises a mixture of the substance (b') and the fluoropolymer (a). Peripheral material is fluoropolymer (a)
Or a mixture of the fluoropolymer (a) and the substance (b ′) (where the concentration of the substance (b ′) is lower than the concentration in the central part). The peripheral material is a fluoropolymer (a) and a substance having a lower refractive index (b).
It may be a material composed of a mixture of When the base material is composed of a multi-layered structure having three or more layers, the layer closer to the center has a higher concentration of the substance (b ') (however, lower than the concentration in the center) and the outermost layer is closer to the outermost layer. A material having a low concentration of the substance (b ′) is used. 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.

<Manufacturing Method of Base Material> As the base material, a long columnar core material made of a fluoropolymer (a), a substance (b), or a mixture thereof is manufactured. It is preferably produced by a method of coating with a coating material comprising a fluoropolymer (a), a substance (b), or a mixture thereof and having a lower refractive index than the core material. In particular, a core material made of the substance (b ') or a mixture of the substance (b') and the fluoropolymer (a) is produced, and the fluoropolymer (a) or the fluoropolymer is provided on the surface of the core material. (A)
And a substance (b '), and is preferably produced by a method of coating a coating material having a lower refractive index than the core material. The long cylindrical core material serves as the central portion of the base material, and the coating layer serves as a layer other than the peripheral portion and the central portion.

The shape of the long cylindrical core material is not particularly limited. However, if it is too thin, the production efficiency of the optical fiber is low, and if it is too thick, it takes a long time to diffuse the substance (b), and the distribution error of the diffused substance (b) may increase. The preferable diameter of the core material is 0.1 to 50 mm, particularly 1 to 20 mm. Further, a core material that is too short has a low optical fiber production efficiency, and its length is preferably 10 times or more the diameter. There is no particular upper limit on the length of the core material, and a continuous elongated body may be used. However, except for the case where the base material is continuously manufactured, a length of up to about 1000 times the diameter is preferable because of the fear of decreasing the roundness and the complexity of handling. This core material can be manufactured by molding by extrusion molding or the like.

As a method of coating the core material with the coating material,
An extrusion coating method, a solution coating method, a melt coating method or the like can be used. The extrusion coating method is a method of forming a coating layer around a core material while extruding a coating material using an extrusion molding machine, and is widely used in the production of coated electric wires, which is called a so-called electric wire coating method. Is the method. The solution coating method is a method of forming a coating layer by applying a solution of a coating material to a core material by dipping or the like and removing the solvent. The melt coating method is a method of forming a coating layer by applying a melt of a coating material to a core material by dipping or the like and then solidifying the melt by cooling or the like. A multi-layer base material having three or more layers can be manufactured by these methods. An extrusion coating method is preferably used.

The thickness of the coating layer is not particularly limited, but is preferably 0.2 times or more, particularly preferably 0.5 times or more the radius of the core material. When the coating layer has two or more layers, the total thickness thereof is referred to. The upper limit of the thickness of the coating layer is not particularly limited, but the diameter of the base material is preferably about 10 times, especially about 5 times the diameter of the core material.

At the time of manufacturing the base material, the substance (b) may be diffused at the same time. For example, in the extrusion coating molding method in which the core material made of a mixture of the substance (b ') and the fluoropolymer (a) is coated with the coating material made of the fluoropolymer (a), the molding temperature of the coating material is sufficiently high. The substance (b ′) can be diffused from the core material to the coating layer by raising the temperature and heating the core material if necessary.

Like the GI type optical fiber, it is preferable that the base material has a refractive index distribution of a certain degree or more. That is, it is preferable that the substance (b) is concentrically distributed with a concentration gradient along the radial direction from the center of the base material. During spinning of the base material, the substance (b) can be diffused in the fluoropolymer (a) to form a desired concentration distribution, but it is sufficient because the time for diffusing the substance (b) is limited. Diffusing is often difficult. It is easy to solve this problem by forming a concentration distribution above a certain level in the base material.

As a method for forming the concentration distribution of the substance (b) in the base material, it can be carried out at the time of manufacturing the base material as described above, but preferably the base material is heated and held after the base material is manufactured to heat the substance (b). It is preferable to perform a thermal diffusion treatment for diffusing
A GI type optical fiber having a good refractive index distribution can be obtained by diffusing the base material and then fiberizing it. The temperature and time of the thermal diffusion treatment are not particularly limited, but a desired concentration distribution is formed at a temperature at which the substance (b) diffuses and the fluoropolymer (a) is unlikely to deform or the like. Do on time.

<Regarding the method for producing an optical fiber> The fiberizing method for producing an optical fiber using the base material of the present invention is not particularly limited, and a conventionally known method can be adopted. For example, the desired GI optical fiber can be obtained by heat drawing or melt spinning the base material. The conditions such as the heating temperature and the fiberizing rate for heat drawing and melt spinning can be appropriately determined depending on the kind of the material such as the fluoropolymer (a).

[0055]

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] Polymer B having a diameter of 10 m
A core material having a length of m and a length of 400 mm was manufactured, and a coating made of the polymer A was formed on the outside of the core material in the same manner as an electric wire coating, and a base material having a diameter of 22 mm and a length of 400 mm was manufactured. Next, this base material is held in an atmosphere of 300 ° C. for 8 hours for thermal diffusion, and then stretched at 300 ° C. to form a fiber having a diameter of 600 μ
m 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" Diameter of polymer B is 2 m
Polymer A produced by manufacturing a core material having a length of m and a length of 100 mm
This core material was inserted into the center of a cylindrical mold having an inner diameter of 4.4 mm filled with, and kept in that state at 300 ° C. for 30 minutes. Then, it was cooled to obtain a base material having a diameter of 4.4 mm and a length of 100 mm. In the same manner as in Example 1, the base material was stretched at 300 ° C. to be fiberized 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.

[0063]

INDUSTRIAL APPLICABILITY The present invention provides a base material for producing a novel gradient index optical fiber, in which the substance (b) is distributed with a concentration gradient in the radial direction. Those that are present are preferable. This base material can be easily manufactured by coating a core material made of a material having a high refractive index with a material having a low refractive index. The concentration gradient of the substance (b) can be easily produced by thermally diffusing the substance (b).

The graded index optical fiber obtained according to the present invention uses an amorphous fluororesin having no C—H bond to reduce the loss of light from ultraviolet light to near infrared light at an extremely low loss. It became possible to transmit.

In particular, this gradient index optical fiber is flexible and branched even though the fiber diameter is large.
It is a low loss optical fiber that is suitable for short-distance optical communication because it is easy to connect and can be used practically. In addition, this graded index optical fiber is used in an automobile engine room, OA
Withstands harsh usage conditions in equipment, plants, home appliances, etc.
It is characterized by having heat resistance, chemical resistance, moisture resistance, and incombustibility.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C08F 259/08 C08F 259/08 G02B 6/00 366 G02B 6/00 366 6/18 6/18 // B29K 27:12 B29K 27 : 12 (72) Inventor Tokuhide Sugiyama 1150 Hazawa-machi, Kanagawa-ku, Yokohama, Kanagawa Prefecture Central Research Laboratory, Asahi Glass Co., Ltd. (56) Reference JP-A-4-124603 (JP, A) (58) Fields investigated (Int .Cl. ⁷ , DB name) C08F 2/00-2 / 60,16 / 32 C08F 214 / 18,259 / 08 G02B 1 / 04,6 / 00-6/18

Claims (9)

(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. A refractive index distribution type optical fiber comprising at least one kind of substance (b), wherein the substance (b) is present in concentric circles in the fluoropolymer (a) with different concentrations along the radial direction. Base material for manufacturing. 2. The substance (b) is a substance having a higher refractive index than the fluoropolymer (a), and the substance (b) is present in a relatively high concentration in the central portion of the base material. The base material according to claim 1. 3. A method of manufacturing a graded index optical fiber, which comprises forming the base material according to claim 1 into a fiber. 4. The production method according to claim 3, wherein the substance (b) is diffused in the fluoropolymer (a) during fiberizing. 5. 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. Using at least one kind of substance (b), a long columnar core material made of a fluoropolymer (a), a substance (b), or a mixture thereof is produced, and fluorine-containing material is provided on the surface of the core material. A substance (b) in a fluoropolymer (a), characterized in that it is coated with a coating material comprising a polymer (a), a substance (b) or a mixture thereof and having a lower refractive index than the core material. But
Exist in concentric circles with different concentrations along the radial direction
Of manufacturing a preform for producing a graded index optical fiber. 6. 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). A core material is produced, and a coating material which is a fluoropolymer (a) or a mixture of the fluoropolymer (a) and a substance (b) and has a lower refractive index than the core material is produced on the surface of the core material. Coating,
The manufacturing method according to claim 5. 7. The manufacturing method according to claim 5, wherein the coating of the coating material is performed by an extrusion coating molding method. 8. A method of manufacturing a gradient index optical fiber, characterized in that the preform obtained by the manufacturing method according to claim 5, 6 or 7 is made into a fiber. 9. The production method according to claim 8, wherein the substance (b) is diffused in the fluoropolymer (a) during fiberization.