JPH10293215A - Production of preform and polymer optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obviate the occurrence of scattering factors even if polymers of different kinds are used in producing a preform by a interfacial, gel polymn. method, etc., by forming a buffer layer on the inner peripheral surface of a hollow body. SOLUTION: The buffer layer B is formed on the inner peripheral surface of the hollow body D by using a resin material which has the same or nearly the same refractive index as the refractive index of the polymer by a monomer and is adjusted to the viscosity to the extent of not substantially dissolving the polymer of the hollow body D based on the fundamental that the monomer is polymerized within the hollow body D formed of the polymer. The polymn. of the monomer is effected within the hollow body D formed with the buffer layer B. Such buffer layer B imparts an interfacial gel effect to monomer polymerized in the hollow body D and prevents the dissolution of the polymer in the hollow body D, thereby functioning to prevent the occurrence of the scattering factors.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a preform for a polymer optical fiber, and more particularly to a method for producing a preform obtained by polymerizing a monomer in a hollow body formed of a polymer, and a method for producing the preform. The present invention relates to a polymer optical fiber.

[0002]

BACKGROUND OF THE INVENTION One method of producing a preform for a polymer optical fiber is an interfacial gel polymerization method. In the interfacial gel polymerization method, for example, a monomer for a core is polymerized in, for example, a hollow body for a clad formed of a polymer, and in this polymerization, refraction is performed by utilizing a gel effect at an interface between the hollow body and the monomer for the core. A rate distribution is formed to produce a preform. Such an example is disclosed in, for example,
No. 73025, Japanese Patent Laid-Open No. 5-173026 or WO
93/08488.

[0003] In the case of a preform produced by such an interfacial gel polymerization method, the type of the polymer (homopolymer or copolymer) forming the hollow body and the polymer obtained by polymerizing inside the hollow body are determined. It is common to have the same or otherwise the same or similar refractive index. Equalizing the refractive index of each polymer in this way relates to transparency. In other words, when the interfacial gel effect is used, for example, the polymer for the clad dissolves (swells) in the monomer for the core being polymerized, so that the clad and the core have different refractive indices due to different types of polymers. Finally, polymers having different refractive indices are mixed around the core. Then, this becomes a scattering factor, and the transparency decreases depending on the degree of difference in the refractive index of each polymer.

[0004] A low molecular weight material having no reactivity with respect to the polymer is added to the polymer for the matrix, for example, as disclosed in WO 93/08488,
In the case of a dopant type in which a refractive index distribution is obtained by forming a concentration gradient by diffusion of the low-molecular substance, that is, the dopant accompanying polymerization of the polymer, the same polymer, for example, PMMA (polymethyl methacrylate) is used for each of the core and the clad. select. In the case of the dopant type, by making the polymer of the core and the clad the same, it is possible to provide the core and the clad with almost the same transparency as the inherent transparency of this polymer.

Further, Japanese Patent Application Laid-Open Nos.
As disclosed in US Pat. No. 5,730,026, copolymerization of obtaining a refractive index distribution by forming a concentration gradient in one monomer by utilizing a difference in reactivity ratio between two monomers when copolymerizing two types of monomers. Also in the case of the type, a polymer having the same refractive index as the base polymer in the core is used for the clad. However, in the case of a copolymer type, generally,
The core is formed of a copolymer of one polymer and another polymer having a higher refractive index than the polymer, and the cladding is formed of a homopolymer. Therefore, polymers having different refractive indices (copolymer and homopolymer) are slightly mixed at the interface between the core and the clad.
However, in the copolymer at the periphery of the core, the ratio of the other polymer having the higher refractive index is small, and therefore, by making the base polymer and the clad polymer the same in the core, the refractive index difference of each polymer in the periphery of the core is reduced. Can be made extremely small. For this reason, although the transparency is reduced due to the mixture of different kinds of polymers, the degree is small.

[0006] However, there are cases in which useful advantages can be obtained by changing the type of polymer in the core or clad. For example, in the case of the dopant type disclosed in WO 93/08488, there is one example. That is, in the case of the dopant type, there is a problem that the dopant lowers the heat resistance of the optical fiber due to its plastic effect, but it is necessary to increase the refractive index difference Δn in the refractive index distribution as much as possible in order to reduce bending loss. is there. In other words, in terms of heat resistance, there is a contradictory problem that it is necessary to minimize the amount of the dopant to be added and to increase the amount of the dopant to secure Δn. Therefore, it is conceivable that a polymer having a smaller refractive index than that of the polymer in the core is used for the clad to secure a large Δn as a result, thereby improving the heat resistance by reducing the amount of dopant added.

Another example is the use of PMMA in which all or part of the hydrogen atoms have been converted to deuterium atoms in place of general polymers such as general PMMA. That is, a general polymer has large absorption in a wavelength region frequently used as signal light due to its absorption characteristics at hydrogen atoms, which causes a decrease in transparency. On the other hand, a deuterated polymer in which a hydrogen atom is replaced with a deuterium atom has higher transparency than a general polymer because the absorption characteristics of deuterium are different from those of hydrogen. Therefore, the transmission distance can be greatly improved by using a deuterated polymer, for example, deuterated PMMA. For example, even when general PMMA is about 100 m, deuterated PMMA
In the case of MA, it can be about 300 to 400 m. However, in the case of PMMA, the material price of deuterated PMMA is several hundred times higher than that of general PMMA, leaving a problem in cost performance. Therefore, it is not directly involved in the propagation of signal light, but uses the characteristics of the cladding that the volume ratio in the entire fiber is relatively large, and uses a general polymer for the cladding,
By using the deuterated polymer only for the core, it is conceivable to improve the cost performance of the deuterated polymer type polymer optical fiber.

In the case where the kinds of polymers in the core and the clad are intentionally made different from each other as described above, it is necessary to use different kinds of polymers for the first time without causing dissolution between these different kinds of polymers. Advantages can be effectively utilized.

[0009]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a preform manufactured by an interfacial gel polymerization method or the like which does not cause scattering factors even when different types of polymers are used. On offer. Another object of the present invention is to provide a polymer optical fiber whose performance can be improved by using such a method.

[0010]

For this purpose, the present invention provides a method for manufacturing a preform by polymerizing a monomer in a hollow body formed of a polymer. A layer is formed, and the buffer layer prevents the occurrence of scattering factors. Such a buffer layer functions to prevent the occurrence of scattering factors by preventing the polymer in the hollow body from dissolving while giving an interfacial gel effect to the monomer polymerized in the hollow body. Therefore, the buffer layer is provided with a refractive index of a polymer obtained by polymerizing the monomer so that the buffer layer does not cause a scattering factor even when dissolved in the monomer, or minimizes the scattering factor. It is formed of a resin material having the same or substantially the same refractive index as the solidified state. The viscosity of the resin material is adjusted to a level that does not substantially dissolve the hollow polymer. As a resin material capable of providing such a viscosity, a prepolymer, a mixed solution of a monomer and a polymer in which an appropriate amount of a polymer is dissolved in a monomer, or a heated melt of a polymer can be used.

Therefore, the method for producing a preform according to the present invention is based on the fact that a monomer is polymerized in a hollow body formed of a polymer, and a solidified material having the same or substantially the same refractive index as that of the polymer by the monomer. Having, and forming a buffer layer on the inner peripheral surface of the hollow body using a resin material adjusted to a viscosity that does not substantially dissolve the polymer of the hollow body,
Causing the monomer to polymerize in the hollow body in which the buffer layer is formed.

One of the polymer optical fibers according to the present invention is a dopant type obtained by the above-described interfacial gel polymerization method. This polymer optical fiber has a core and a clad, and in the core, a refractive index distribution is formed by a concentration gradient of a low-molecular substance having no reactivity with the polymer in a polymer having a certain refractive index. Have been. The cladding is formed using a polymer having a smaller refractive index than the polymer. By using a polymer having a smaller refractive index than the polymer of the core for the clad, a large Δn can be secured as a result. Thus, the amount of the low-molecular substance added can be reduced, and thus the heat resistance can be improved.

In the case where polymers having different refractive indices are used for the core and the clad as described above, the preform is formed by the above-described manufacturing method, so that the scattering factor caused by the difference in the refractive index of each polymer is reduced. It can be substantially eliminated or greatly reduced. As a result, the above-described advantages of different core and clad polymers can be more effectively utilized.

Another type of the polymer optical fiber according to the present invention is a copolymer type obtained by the above-described interfacial gel polymerization method. The polymer optical fiber has a core and a clad, and the core has a polymer in which a polymer having a certain refractive index and another polymer having a higher refractive index than this polymer are copolymerized at different ratios. By having a concentration gradient, a refractive index distribution is formed. The cladding is formed using one polymer, that is, a polymer having a smaller refractive index than the base polymer. Also in this case, similarly to the above, a large Δn can be secured as a result. That is, Δn larger than Δn that can be obtained by a practically usable combination of polymers can be realized, and thus the bending loss can be further reduced.

In the case of this copolymer type as well, by forming a preform by the above-mentioned production method, it is possible to substantially eliminate or greatly reduce the scattering factor caused by the difference in the refractive index of each polymer. Can be. As a result, the above-described advantages of different core and clad polymers can be more effectively utilized.

Still another one of the polymer optical fibers according to the present invention is a type in which a deuterated polymer is a polymer material, and a deuterated polymer in which some or all of the hydrogen atoms are deuterium atoms is used as a core. Only used for. That is, a deuterated polymer having excellent transparency but high material cost is used only for the core, and the clad is formed of a general polymer. As a result, cost performance can be improved.

Also in this case, by forming the preform by the above-described manufacturing method, it is possible to substantially eliminate or greatly reduce the scattering factor caused by the difference in the refractive index of each polymer. As a result, the advantage of using the deuterated polymer only for the core can be more effectively utilized.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS At least two types of preforms can be produced by the method of the present invention. One is a dopant type and the other is a copolymerization type. To produce a dopant type preform,
First, a polymerization tube is formed as a hollow body for a clad, and then a buffer layer is formed on the inner peripheral surface of the polymerization tube. Then, a preform is produced by polymerizing a core monomer in the polymerization tube. Hereinafter, these steps will be described by taking as an example the case of a polymer optical fiber in which the clad is formed of a copolymer having a smaller refractive index than the polymer of the core.

Preparation of polymerization tube (FIG. 1): A sufficiently rigid hollow container T having an inner diameter corresponding to the outer diameter of a preform to be used is used. A predetermined amount of a monomer solution for cladding is poured into the hollow container T, and first, prepolymerization is performed. Heat for 2 hours at 70 ° C. with shaking. Next, the hollow container is set on the rotating device S, and the rotation speed is set to 2000 to 3000 rpm.
The polymerization is performed by heating at 70 ° C. for 24 hours while rotating at a speed of m. When the polymerization is completed, the polymerization tube is taken out of the hollow container and subjected to a heat treatment at 90 ° C. for 24 hours.
The monomer solution for cladding is prepared by mixing a monomer for base, a monomer for lowering the refractive index, a polymerization initiator, and a chain transfer agent. MMA as base monomer
(Methyl methacrylate; refractive index 1.492), and 3FMA (2,2,2-trifluoroethyl methacrylate, refractive index 1.420) is used as a monomer for lowering the refractive index. As an initiator, BPO (benzoyl peroxide) is used at 0.5 wt% based on MMA, and as a chain transfer agent, n-BM (normal methyl mercaptan) is used at 0.3 wt% based on MMA.

Formation of buffer layer (FIG. 2): A buffer layer B is formed on the inner peripheral surface of the polymerization tube D obtained above. The buffer layer is in a range necessary to prevent the influence of the core monomer solution described below from reaching the polymerization tube, that is, in a range necessary to prevent swelling of the polymerization tube by the monomer solution, It is preferable to form as thin as possible. Such a thickness is, for example, about 0.5 to 2 mm. In order to form such a buffer layer, a resin material is applied by the same rotation method as in the case of forming the polymerization tube. As the resin material for the buffer layer, a prepolymer obtained by prepolymerizing the same monomer as the matrix monomer in the core described below,
A mixed solution obtained by dissolving a polymer obtained by polymerizing the monomer in the monomer for the matrix or a heated melt of a polymer obtained by polymerizing the monomer for the matrix can be used. These resin materials are adjusted to have a viscosity that facilitates application by heating or the like during the above-described application, and to maintain a high viscosity, for example, a viscosity of about 1000 to 10000 cps at the initial stage of polymerization of the core monomer described below.

Production of preform (FIG. 3): A polymerization solution for a core is filled in the polymerization tube D on which the buffer layer B has been formed as described above, and after sealing, the mixture is filled with an oil bath or the like.
Polymerize for 24 hours while heating at ° C. The monomer solution is prepared by mixing a monomer for a matrix, a low molecular compound (dopant), a polymerization initiator, and a chain transfer agent. MMA is used as a monomer, and DPSO (diphenylsulfoxide) is used as a low molecular compound. D
The amount of PSO added is 12.5 wt% with respect to MMA. DBPO (di-t-butyl peroxide) as an initiator
Is used in an amount of 0.23 wt% based on the monomer, and n-BM is used as a chain transfer agent in an amount of 0.27 wt% based on the monomer.

FIG. 4 shows the refractive index distribution of the polymer optical fiber obtained by subjecting the preform obtained as described above to hot drawing by a generally used hot drawing apparatus.
It was like. The refractive index distribution curve has a stepped portion, which is affected by a relatively thick buffer layer of 2 mm. For comparison, the dotted line also shows the refractive index distribution in the polymer optical fiber when the same polymer is used for the core and the clad for comparison. From this comparison, it can be understood that Δn is significantly increased by using the method of the present invention without lowering the transparency. For reference, FIG. 5 shows the refractive index distribution in the polymer optical fiber when the buffer layer is 1 mm. In this case, there is no step portion as in the case of FIG.

In the case of the copolymer type, the preform can be produced basically in the same manner as described above. Therefore, the description is omitted.

Next, a deuterated polymer, specifically, a deuterated PMMA is used for the core, and a general PM is used for the cladding.
An example of a polymer optical fiber using MA will be described. However, the production of the preform in this case is basically the same as the above except that the monomer used for the production is different, so that the details are omitted. FIG. 6 shows the refractive index distribution in the polymer optical fiber according to this example. In the refractive index distribution curve, there is a portion where the refractive index slightly decreases at the boundary between the core and the refractive index, but this portion is affected by the buffer layer.

[0025]

As described above, according to the present invention, by using different kinds of polymers for the core and the clad, for example, it is possible to reduce the bending loss by increasing Δn or to use the polymer for a deuterated polymer. Or lowering of the transparency that occurs when improving the cost performance of the apparatus can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a process for producing a polymerization tube for a preform.

FIG. 2 is an explanatory view of a process of forming a buffer layer on a polymerization tube.

FIG. 3 is an explanatory view of a preform manufacturing process.

FIG. 4 is a refractive index distribution diagram of an optical fiber according to one embodiment.

FIG. 5 is a refractive index distribution diagram of an optical fiber according to another example.

FIG. 6 is a refractive index distribution diagram of an optical fiber according to another embodiment.

Claims (4)

[Claims] 1. A method for producing a preform for a polymer optical fiber by polymerizing a monomer in a hollow body formed of a polymer, wherein the same or substantially the same refractive index as that of the polymer by the monomer is solidified. Forming a buffer layer on the inner peripheral surface of the hollow body using a resin material having a state and having a viscosity adjusted so as not to substantially dissolve the polymer of the hollow body; and Allowing the monomer to polymerize in the hollow body in which the layer is formed. 2. A refractive index distribution having a core and a clad, wherein the core has a concentration gradient in a polymer having a certain refractive index and a low molecular weight material having no reactivity with the polymer. 2. A polymer optical fiber, wherein the cladding is formed using a polymer having a lower refractive index than the polymer, and the preform obtained by the method according to claim 1 is drawn. . 3. A polymer having a core and a clad, wherein a polymer in which one polymer having a certain refractive index and another polymer having a higher refractive index than the polymer are copolymerized at different ratios is provided with a concentration gradient with respect to the ratio. In the polymer optical fiber having a refractive index distribution formed by having, the cladding is formed using a polymer having a smaller refractive index than the one polymer, and the preform manufactured by the method according to claim 1 A polymer optical fiber obtained by drawing. 4. A polymer optical fiber obtained from the preform manufactured by the method according to claim 1, wherein a deuterated polymer in which some or all of the hydrogen atoms are deuterium atoms is used only for the core. Polymer optical fiber.