JP2005352422A - Manufacturing method of refractive index distribution type optical material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method by which a shape of refractive index distribution can optionally be set and refractive index distribution type optical materials having the same refractive index distribution can be stably manufactured with sufficient reproducibility in large quantities without causing optical performance lowering due to thermal degradation. <P>SOLUTION: In the manufacturing method of the refractive index distribution type optical materials, a thermoplastic resin solvent solution (A) with relatively high refractive index and a thermoplastic resin solvent solution (B) with relatively low refractive index are mixed while continuously changing a mixing ratio and the obtained mixture is successively supplied into a cylindrical vessel rotating around a center axis and is dried. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for manufacturing a gradient index optical material.

Gradient index type optical materials are graded index type optical fiber, rod lens, optical waveguide, optical splitter, optical multiplexer, optical demultiplexer, optical attenuator, optical switch, optical isolator, optical transmission module, optical reception module It is useful in a wide range such as a coupler and an optical integrated circuit.

Traditionally, gradient index optical materials have been made of quartz (glass), but recently,
Since light weight is required and low cost is required, thermoplastic resin-based refractive index distribution type optical materials using methyl methacrylate resin, styrene resin, carbonate resin, fluorine resin, etc. have been proposed. (For example, refer to Patent Document 1 and Patent Document 2).
JP-A-2-244007 JP-A-5-173025

Various methods for producing a thermoplastic resin-based refractive index distribution type optical material have also been proposed. For example, a container wall is made of a transparent polymer and is held horizontally and rotated around a central axis. The monomer that dissolves the transparent polymer is gradually supplied, and the monomer is radically polymerized by sequentially moving the gel layer from the container wall toward the inside of the container while dissolving the transparent polymer in the monomer. Thus, a method for producing a synthetic resin optical transmission body having a refractive index gradient continuous in a certain direction (see, for example, Patent Document 3) or an amorphous fluoropolymer having substantially no C—H bond. The difference in refractive index from the fluoropolymer is 0.0 at the center of the melt.
A method for producing a refractive index distribution type optical resin material in which a region where the refractive index continuously changes is formed by injecting a 01 or more substance or a fluoropolymer containing the substance, and molding the substance while diffusing the substance ( For example, see Patent Document 4).
Japanese Patent Laid-Open No. 5-173026 JP-A-8-336911

However, in the above manufacturing method, it is difficult to manufacture a refractive index distribution type optical resin material whose refractive index continuously changes as designed, and it is also possible to manufacture a refractive index distribution type optical resin material with good reproducibility. It was difficult.

Further, homopolymers HP1, HP2,..., And HPn that are respectively produced from two or more types of monomers M1, M2,..., And Mn (n is an integer of 2 or more) and whose refractive index decreases sequentially, and Using a (co) polymer selected from the group consisting of one or more binary copolymers CP of these monomers, a plurality of spinning raw materials having different refractive indexes are prepared, and the refractive index of the outer peripheral portion is reduced. A multi-layer concentric nozzle is fed to reduce and spun from the nozzle, and within and / or after spinning from the nozzle, the polymer is interdiffused between each layer of the fiber, and two ( Both)
A method of producing a gradient index optical fiber for forming a polymer mixed layer (see, for example, Patent Document 5).
) Has been proposed.
Japanese Patent No. 3437848

However, the above-described production method has a problem that optical properties are deteriorated due to thermal deterioration during spinning molding.

In view of the above-described drawbacks, the object of the present invention is to arbitrarily set the shape of the refractive index distribution, and to stably manufacture a large amount of refractive index distribution type optical material having the same refractive index distribution with good reproducibility and without deterioration of optical performance due to thermal degradation It is in providing the method which can be manufactured.

The method for producing a gradient index optical material according to claim 1 comprises a continuous thermoplastic resin solvent solution (A) having a relatively high refractive index and a thermoplastic resin solvent solution (B) having a relatively low refractive index. The mixture is mixed while changing the mixing ratio, and the mixture is supplied and dried in a cylindrical container that sequentially rotates around the central axis.

As the thermoplastic resin, any resin conventionally used as an optical material can be used, but a thermoplastic resin excellent in transparency and heat resistance is preferable, for example, an acrylic resin, a fluororesin, and a carbonate resin. , Aromatic polyester resin, arylate resin, epoxy resin, silicone resin, styrene resin, imide resin and fluorinated product thereof.

Examples of the acrylic resin include polymethyl methacrylate, polybenzyl methacrylate, polyphenyl methacrylate, poly 1-phenylethyl methacrylate, poly 1,1,2-trifluoroethyl methacrylate, polycyclohexyl methacrylate, methyl methacrylate-benzyl methacrylate. Examples thereof include a copolymer, a methyl methacrylate-phenyl methacrylate copolymer, a methyl methacrylate-1,1,2-trifluoroethyl methacrylate copolymer, and a methyl methacrylate-styrene copolymer.

As the fluororesin, an amorphous fluororesin having substantially no C—H bond is preferable. For example, a fluororesin having a main chain having a ring structure such as an aliphatic ring, an imide ring, a triazine ring, or an aromatic ring. Is mentioned.

The combination of the thermoplastic resin solvent solution (A) having a relatively high refractive index and the thermoplastic resin solvent solution (B) having a relatively low refractive index may be determined as appropriate. An example of the refractive index of the resin is as follows.
Polymethyl methacrylate 1.489
Polybenzyl methacrylate 1.568
Polyphenyl methacrylate 1.571
Poly 1-phenylethyl methacrylate 1.549
Poly 1,1,2-trifluoroethyl methacrylate 1.420
Polycyclohexylmethacrylate 1.507
Styrene resin 1.591

Accordingly, a thermoplastic resin having compatibility and a relatively high refractive index and a thermoplastic resin having a relatively low refractive index may be selected from these thermoplastic resins.

The solvent may be any solvent that can dissolve the thermoplastic resin, and examples thereof include ethyl acetate, acetone, toluene, xylene, cyclohexane, tetrahydroxyfuran, dimethylsulfamide, and the like.

In order to obtain the thermoplastic resin solvent solution (A) having a relatively high refractive index and the thermoplastic resin solvent solution (B) having a relatively low refractive index, relative to the thermoplastic resin having a relatively high refractive index. In addition, a common solvent for thermoplastic resins having a low refractive index or a solvent having an approximate solubility parameter SP value is preferable.

The concentration of the thermoplastic resin solvent solution may be determined as appropriate. However, if the solution is thin, a large amount of solvent is required.
-50% by weight is preferred.

In the above production method, the thermoplastic resin solvent solution (A) having a relatively high refractive index and the thermoplastic resin solvent solution (B) having a relatively low refractive index are mixed while continuously changing the mixing ratio, The mixture is fed and dried in a cylindrical container that rotates around a central axis.

That is, at first, the thermoplastic resin solvent solution (B) is made 100% by weight, and supply / drying is started.
By gradually increasing the addition ratio of the thermoplastic resin solvent solution (A), a refractive index distribution type optical material having a lower refractive index at the outer peripheral portion and a higher refractive index and the highest refractive index at the central portion can be obtained. .

In addition, while continuously changing the mixing ratio, mixing means not only that the refractive index is always changing,
Including those that change step by step in a certain range.

The cylindrical container rotates around the central axis, and the supplied solvent solution is dried while being pressed against the inner wall surface by centrifugal force.

For the supply and drying, any conventionally known method may be employed. For example, the supply may be a method using a tube pump, etc. The drying method may be a method of drying with warm air, a method of drying with a heater, or the like. Can be mentioned.

In addition, a thermoplastic resin solvent solution (B) having a relatively low refractive index is supplied and dried in a cylindrical container rotating around the central axis, and after forming a cladding layer, the refractive index is relatively low. A high thermoplastic resin solvent solution (A) and a thermoplastic resin solvent solution (B) having a relatively low refractive index are mixed while continuously changing the mixing ratio, and the mixture is supplied and dried in order, A refractive index distribution type optical material having a cladding layer is obtained.

Furthermore, a cylindrical clad made of a thermoplastic resin having a relatively low refractive index or a thermoplastic resin having a relatively low refractive index, which constitutes the thermoplastic resin solvent solution (B) having a relatively low refractive index. And a refractive index distribution type optical material having a cladding layer on the outer periphery can be obtained by previously fitting the inner surface of a cylindrical container rotating around the central axis.

As the thermoplastic resin constituting the clad, the thermoplastic resin can be used, but a fluorine resin is preferable.
Further, for the production of the cylindrical clad, any conventionally known method may be adopted, for example,
Extrusion molding etc. are mentioned.

The thermoplastic resin solvent solution (A) is 100% by weight, and supply and drying are started. By gradually increasing the addition ratio of the thermoplastic resin solvent solution (B), the thermoplastic resin solvent solution (A) is continuously increased from the central portion toward the outer peripheral portion. Needless to say, a refractive index distribution type optical material having an increased refractive index can be obtained.

Further, a thermoplastic resin film may be produced by selecting three or more types of thermoplastic resins having relatively different refractive indexes.

Although the length and thickness of the obtained gradient index optical material are not particularly limited, the length is preferably 10 to 300 cm, more preferably 50 to 150 cm, for ease of production. The length is preferably 0.5 to 30 cm, more preferably 1 to 15 cm.

The refractive index distribution type optical material is heated and spun to obtain a gradient index optical fiber.

The method for producing a graded index optical material according to claim 4 comprises a thermoplastic resin composition solvent solution (C) comprising a thermoplastic resin and a dopant and having a relatively high refractive index, and the thermoplastic resin alone or thermoplastic. A thermoplastic resin composition solvent solution (D) composed of a resin and a dopant and having a relatively low refractive index is mixed while continuously changing the mixing ratio, and the mixture is sequentially rotated around the central axis in a cylindrical container. It is characterized by being supplied and dried.

  The thermoplastic resin composition and the solvent are as described in the first aspect.

The dopant is a substance having a refractive index different from that of the thermoplastic resin, preferably a substance having a refractive index different by 0.001 or more from the refractive index of the thermoplastic resin, and usually has a higher refractive index than the thermoplastic resin. The substance it has is used.

As the dopant of the thermoplastic resin other than the fluororesin, any conventionally known dopant can be used. For example, benzyl-n-butyl phthalate, di-n-butyl phthalate, diethyl phthalate, diphenyl phthalate Benzyl salicylate, benzyl phenyl ether, dibenzyl ether, 1-methoxyphenyl-1-phenylethane, benzoic anhydride, benzyl benzoate, bromobenzene, o-chlorobenzene, m-chlorobenzene, 1,
2-dibromobenzene, 3-phenyl-1-propanol, diethylene glycol dibenzoate, diphenyl, diphenylmethane, diphenyl ether, diphenyl sulfide, diphenyl sulfoxide, m-phenoxytoluene, phenylbenzoate, 1,2 propanediol dibenzoate, triphenyl phosphate, Examples include tricresyl phosphate and diphenyl sulfide.

Examples of the fluororesin dopant include fluorine-based low-molecular compounds and oligomers.

Examples of the fluorine-based low molecular weight compound include 1,3-dibromotetrafluorobenzene, 1,4-dibromotetrafluorobenzene, 2-bromotetrafluorobenzotrifluoride, chloropentafluorobenzene, bromopentafluorobenzene, and iodopenta. Examples thereof include fluorobenzene, decafluorobenzophenone, perfluoroacetophenone, perfluorobiphenyl, chloroheptafluoronaphthalene, bromoheptafluoronaphthalene and the like.

The fluorine-based oligomer does not contain a hydrogen atom such as a fluororesin oligomer having a ring structure in the main chain, tetrafluoroethylene, chlorotrifluoroethylene, dichlorodifluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, etc. oligomers comprising _{monomers, -CF 2 CF (CF 3)} O- or - (CF ₂₎ n
And an oligomer of perfluoropolyether having a structural unit of O- (n is an integer of 1 to 3).

The molecular weight of these oligomers is preferably selected from a molecular weight range that becomes amorphous,
A number average molecular weight of 300 to 10,000 is preferable, and a number average molecular weight of 500 to 5000 is more preferable.

In the said manufacturing method, similarly to the manufacturing method of Claim 1, the thermoplastic resin composition solvent solution (C) with a relatively high refractive index and the thermoplastic resin composition solvent solution (with a relatively low refractive index) ( D)
Are mixed while continuously changing the mixing ratio, and the mixture is supplied and dried in a cylindrical container that is sequentially rotated around the central axis.

That is, at first, the thermoplastic resin composition solvent solution (D) is set to 100% by weight and supply / drying is started. By gradually increasing the addition ratio of the thermoplastic resin composition solvent solution (C), the outer peripheral portion A refractive index distribution type optical material having a low refractive index and a gradually increasing refractive index and the highest refractive index at the center is obtained.

In addition, a certain amount of thermoplastic resin composition solvent solution (D) consisting of a thermoplastic resin alone or a thermoplastic resin and a dopant and having a relatively low refractive index is supplied and dried in a cylindrical container rotating around the central axis. Then, after forming the clad layer, the thermoplastic resin composition solvent solution (C) having a relatively high refractive index and the thermoplastic resin composition solvent solution (D) having a relatively low refractive index are continuously mixed. A refractive index distribution type optical material having a cladding layer on the outer periphery can be obtained by mixing while changing the ratio, and sequentially supplying and drying the mixture.

Furthermore, consisting of the above thermoplastic resin alone or a thermoplastic resin and a dopant, comprising a thermoplastic resin composition solvent solution (C) having a relatively low refractive index, consisting of a thermoplastic resin alone or a thermoplastic resin and a dopant, A cylindrical clad comprising a thermoplastic resin composition having a relatively low refractive index or a thermoplastic resin alone or a thermoplastic resin and a dopant, and comprising a thermoplastic resin composition having a relatively lower refractive index than the thermoplastic resin composition. Is fitted in advance on the inner surface of a cylindrical container rotating around the central axis, whereby a gradient index optical material having a cladding layer on the outer periphery is obtained.

The method for producing a gradient index optical material according to claim 7 comprises a dopant solvent solution (E) having a relatively high refractive index and a thermoplastic resin alone or a thermoplastic resin and a dopant, and having a relatively refractive index. The low thermoplastic resin composition solvent solution (F) is mixed while continuously changing the mixing ratio, and the mixture is supplied and dried in a cylindrical container that sequentially rotates around the central axis.

The thermoplastic resin composition, the solvent, and the dopant are as described in the first aspect.

In the above production method, as in the production method of claim 1, the solution comprises a dopant solvent solution (E) having a relatively high refractive index and a thermoplastic resin alone or a thermoplastic resin and a dopant. The low thermoplastic resin composition solvent solution (F) is mixed while continuously changing the mixing ratio, and the mixture is supplied and dried in a cylindrical container that sequentially rotates around the central axis.

That is, at first, the thermoplastic resin composition solvent solution (F) is set to 100% by weight and supply / drying is started. By gradually increasing the addition ratio of the dopant solvent solution (E), the refractive index of the outer peripheral portion is lowered As a result, the refractive index gradually increases and a refractive index distribution type optical material having the highest refractive index in the center is obtained.

Also, a certain amount of thermoplastic resin composition solvent solution (F) consisting of a thermoplastic resin alone or a thermoplastic resin and a dopant and having a relatively low refractive index is supplied and dried in a cylindrical container rotating around the central axis. After forming the cladding layer, a dopant solvent solution having a relatively high refractive index (
E) and a thermoplastic resin composition solvent solution (F) having a relatively low refractive index are mixed while continuously changing the mixing ratio, and the mixture is sequentially supplied and dried to have a refractive index having a cladding layer on the outer periphery. A distributed optical material is obtained.

Furthermore, it consists of a thermoplastic resin alone or a thermoplastic resin and a dopant, and comprises a thermoplastic resin composition solvent solution (F) having a relatively low refractive index, consisting of a thermoplastic resin alone or a thermoplastic resin and a dopant, A cylindrical clad made of a thermoplastic resin composition having a low refractive index or a thermoplastic resin alone or a thermoplastic resin and a dopant, and having a refractive index relatively lower than that of the thermoplastic resin composition. A refractive index distribution type optical material having a clad layer on the outer periphery can be obtained by previously fitting the inner surface of a cylindrical container rotating around the central axis.

The gradient index optical material obtained in the present invention is heated and spun to obtain a gradient index optical fiber. The gradient index optical fiber may be further coated with a cladding layer.

Since the structure of the manufacturing method of the refractive index distribution type optical material of the present invention is as described above, the shape of the refractive index distribution can be arbitrarily set and the refractive index distribution type optical resin material having the same refractive index distribution can be reproduced. It can be manufactured stably and in large quantities without degradation of optical performance due to thermal degradation. In addition, the optical fiber formed by stretching the refractive index distribution type optical resin material can achieve a broad band.

Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.

Example 1
An ethyl acetate solution (resin concentration 30% by weight) of methyl methacrylate-benzyl methacrylate copolymer (weight ratio 4: 1) and an ethyl acetate solution of polymethyl methacrylate (resin concentration 30% by weight) were prepared.

A tube pump is placed in a cylindrical container with an inner diameter of 2.5 cm that rotates around a central axis while mixing an ethyl acetate solution of methyl methacrylate-benzyl methacrylate copolymer and an ethyl acetate solution of polymethyl methacrylate in an instantaneous mixer. Supply and dry using, diameter 2
. A gradient index optical material having a length of 5 cm and a length of 45 cm was obtained.

First, supply and dry only the ethyl acetate solution of polymethyl methacrylate, gradually decrease the supply amount of the ethyl acetate solution of polymethyl methacrylate, and acetic acid of the methyl methacrylate-benzyl methacrylate copolymer by the reduced amount. Supply with ethyl solution added
Dried.

That is, in the obtained gradient index optical material, the outer peripheral portion is made of 10 polymethyl methacrylate.
The content of polymethyl methacrylate gradually decreases from that point, the content of methyl methacrylate-benzyl methacrylate copolymer gradually increases, and methyl methacrylate-benzyl methacrylate copolymer in the center. The content of was about 100% by weight.

The obtained gradient index optical material was supplied to a cylindrical heater set at 250 ° C. and heated and stretched to obtain an optical fiber having a diameter of 0.6 mm. The refractive index of the center part of the obtained optical fiber was 1.512, and it became lower toward the periphery, and a clad layer was formed on the outer peripheral part. The refractive index was 1.489.

(Example 2)
An ethyl acetate solution (resin concentration 30 wt%) of polymethyl methacrylate and diphenyl sulfoxide (weight ratio 7: 1) and an ethyl acetate solution of polymethyl methacrylate (resin concentration 30 wt%) were prepared.

While mixing an ethyl acetate solution of polymethyl methacrylate and diphenyl sulfoxide and an ethyl acetate solution of polymethyl methacrylate with a momentary mixer, a cylindrical clad made of polyvinylidene fluoride having a thickness of 0.3 cm was fitted in advance. Supply and dry using a tube pump in a cylindrical container with an inner diameter of 5.0 cm that rotates around, a diameter of 5.0 cm,
A gradient index optical material having a length of 45 cm was obtained.

First, supply and dry only the ethyl acetate solution of polymethyl methacrylate, gradually reduce the supply amount of the ethyl acetate solution of polymethyl methacrylate, and the ethyl acetate solution of polymethyl methacrylate and diphenyl sulfoxide by the reduced amount. Was added and dried.

That is, in the obtained gradient index optical material, the outer peripheral portion excluding the cladding is 100% by weight of polymethyl methacrylate, and the content of polymethyl methacrylate gradually decreases from that point, and the content of diphenyl sulfoxide. The content of diphenyl sulfoxide was about 12.5% by weight in the center.

The obtained gradient index optical material was supplied to a cylindrical heater set at 250 ° C. and heated and stretched to obtain an optical fiber having a diameter of 0.6 mm. The refractive index of the center part of the obtained optical fiber was 1.512, and it became lower toward the periphery, and a clad layer was formed on the outer peripheral part. The refractive index was 1.420.

(Example 3)
An ethyl acetate solution (30% by weight) of diphenyl sulfoxide and an ethyl acetate solution of polymethyl methacrylate (resin concentration: 30% by weight) were prepared.

Supply and dry using a tube pump in a cylindrical container with an inner diameter of 4.0 cm that rotates around the central axis while mixing an ethyl acetate solution of diphenyl sulfoxide and an ethyl acetate solution of polymethylmethacrylate with an instantaneous mixer. A refractive index distribution type optical material having a diameter of 4.0 cm and a length of 45 cm was obtained.

First, supply and dry only the ethyl acetate solution of polymethyl methacrylate, 0.2
The addition of an ethyl acetate solution of diphenyl sulfoxide was started from the stack of 5 cm, and the addition amount was gradually increased to supply and dry.

That is, the obtained gradient index optical material has 100% by weight of polymethyl methacrylate up to a point of 0.25 cm from the outer periphery, and the content of polymethyl methacrylate gradually decreases from that point. The content of sulfoxide gradually increased, and the content of diphenyl sulfoxide was about 12.5% by weight at the center.

The obtained gradient index optical material was supplied to a cylindrical heater set at 250 ° C. and heated and stretched to obtain an optical fiber having a diameter of 0.6 mm. The refractive index of the center part of the obtained optical fiber was 1.512, and it became lower toward the periphery, and a clad layer was formed on the outer peripheral part. The refractive index was 1.489.

Claims (9)

A thermoplastic resin solvent solution (A) having a relatively high refractive index and a thermoplastic resin solvent solution (B) having a relatively low refractive index are mixed while continuously changing the mixing ratio. A method for producing a graded index optical material, comprising: supplying and drying in a cylindrical container rotating around A thermoplastic resin solvent solution (B) having a relatively low refractive index is supplied and dried in a cylindrical container rotating around the central axis, and after forming a cladding layer, heat having a relatively high refractive index. The thermoplastic resin solvent solution (A) and the thermoplastic resin solvent solution (B) having a relatively low refractive index are mixed while continuously changing the mixing ratio, and the mixture is sequentially supplied and dried. Item 2. A method for producing a gradient index optical material according to Item 1. A cylindrical clad made of a thermoplastic resin having a relatively low refractive index or a thermoplastic resin having a relatively low refractive index is previously fitted into the inner surface of a cylindrical container that rotates about a central axis. A method for producing a gradient index optical material according to claim 1. A thermoplastic resin composition solvent solution (C) having a relatively high refractive index composed of a thermoplastic resin and a dopant, and a thermoplastic resin having a relatively low refractive index composed of a thermoplastic resin alone or a thermoplastic resin and a dopant. Mixing composition solvent solution (D) continuously changing the mixing ratio,
A method for producing a gradient index optical material, wherein the mixture is supplied and dried in a cylindrical container that sequentially rotates around a central axis. A thermoplastic resin composition solvent solution (D) consisting of a thermoplastic resin alone or a thermoplastic resin and a dopant and having a relatively low refractive index is supplied and dried in a cylindrical container rotating around a central axis, and dried. After the formation of the cladding layer, the mixing ratio of the thermoplastic resin composition solvent solution (C) having a relatively high refractive index and the thermoplastic resin composition solvent solution (D) having a relatively low refractive index is continuously changed. 5. The method for producing a gradient index optical material according to claim 4, wherein the mixture is mixed while being changed, and the mixture is sequentially supplied and dried. A thermoplastic resin alone or a thermoplastic resin and a dopant, and a relatively low refractive index thermoplastic resin composition or a thermoplastic resin alone or a thermoplastic resin and a dopant,
5. A cylindrical clad made of a thermoplastic resin composition having a refractive index relatively lower than that of the thermoplastic resin composition is preliminarily fitted on an inner surface of a cylindrical container that rotates about a central axis. Or 5. A method for producing a gradient index optical material according to 5. A dopant solvent solution (E) having a relatively high refractive index and a thermoplastic resin composition solvent solution (F) comprising a thermoplastic resin alone or a thermoplastic resin and a dopant and having a relatively low refractive index.
A method for producing a refractive index distribution type optical material, comprising: continuously mixing a mixture at different mixing ratios, and supplying and drying the mixture in a cylindrical container that sequentially rotates around a central axis. A thermoplastic resin composition solvent solution (F) having a relatively low refractive index is supplied and dried in a cylindrical container rotating around the central axis, and after forming a cladding layer, the refractive index is relatively low. A high dopant solvent solution (E) and a thermoplastic resin solvent solution (F) having a relatively low refractive index are mixed while continuously changing the mixing ratio, and the mixture is sequentially supplied and dried. Item 8. A method for producing a gradient index optical material according to Item 7. A thermoplastic resin alone or a thermoplastic resin and a dopant, and a relatively low refractive index thermoplastic resin composition or a thermoplastic resin alone or a thermoplastic resin and a dopant,
8. A cylindrical clad made of a thermoplastic resin composition having a refractive index relatively lower than that of the thermoplastic resin composition is preliminarily fitted on an inner surface of a cylindrical container that rotates about a central axis. Alternatively, a method for producing a gradient index optical material according to 8.