JP2006178102A - Plastic primary coated optical fiber and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the refractive index of a clad in a plastic primary coated optical fiber (POF) without depending on material. <P>SOLUTION: An outer tube 12 with a large number of fine pores 33 is formed. A core polymer is put in the outer tube 12 to constitute a core material 30 by rotational polymerization, and a preform 21 is prepared composed of the outer tube 12 and the core material 30. The POF is obtained by heating and drawing the preform 21. A large number of fine pores 33 of the outer tube 12 are dispersed through the heating and drawing, so that a number of micro pores are formed in the clad of the POF. The size of the micro pores is set to 1-1,000 μm, and the quantity thereof is set 1-70 vol%. The refractive index of the clad is reduced by these micro pores. Even if the same material as the outer core material is used for the clad, a clad having a lower refractive index than the outer core can be obtained, thereby expanding the selectivity of the base material for the clad. Thus, the POF having a superior affinity, a high NA and a high transmission rate can be obtained. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a plastic optical fiber and a method for manufacturing the same.

  An optical fiber is an optical transmission body composed of a core through which light passes and a clad covering the outer periphery of the core, and is used in various fields because it can perform high-speed transmission and large-capacity information transmission. Among these optical fiber strands, plastic optical fiber strands that have excellent properties such as moldability, flexibility, and impact resistance, are safe and inexpensive, and have low transmission loss ( Attention has been focused on Plastic Optical Fiber (POF).

Recently, a graded index (GI type) POF in which a refractive index distribution is provided in the core of this POF has attracted attention. This GI POF has a structure in which the refractive index continuously increases toward the center of the core. Thus, if the refractive index is continuously changed, light can be gradually refracted and confined in the core. Also, by utilizing the fact that the speed of light in the medium is inversely proportional to the refractive index, the light speed increases as the distance from the center increases, so that light traveling diagonally and light traveling straight are one end of the optical fiber. Since the time required to reach the other end can be made the same, the transmission waveform can be made difficult to collapse.

The GI-type POF is composed of a core obtained by mixing and polymerizing a highly transparent optical resin and an additive (for example, a dopant) having a refractive index different from that of the optical resin, and a clad having a refractive index lower than that of the core. At this time, when the components having different refractive indexes are mixed and polymerized like the optical resin and the dopant, the glass transition temperature (Tg) of the main component (in this case, the optical resin) is lowered, As a result, the heat resistance is reduced. In particular, in an optical fiber, when an additive having a refractive index that is not so high is added to the optical resin and polymerized, the Tg decreases and the numerical aperture (index of transmission capability of the optical fiber) ( NA) decreases. In addition, since the additive is only dispersed in the optical resin and is not fixed, it diffuses and moves when exposed to high temperatures, and the refractive index distribution changes or the additive aggregates. As the light scattering increases, there arises a problem that the light transmission capability changes. In response to such problems, even when an additive is added to an optical resin to produce POF, a GI POF that can realize low optical transmission loss without lowering the heat resistance inherent in the optical resin. Has been proposed (see, for example, Patent Document 1).
JP 2001-91758 A

  In the method described in Patent Document 1, the refractive index distribution is expressed in the core using a metal chelate compound, so that even if an additive is added to the optical resin, the Tg of the optical resin is suppressed from being lowered, and low. A GI POF capable of realizing optical transmission loss can be manufactured. However, including the GI type POF, the POF needs to form a core having a higher refractive index than the clad. However, when a low refractive index component is used for the core, the clad has a higher refractive index than the core. Since a component having a lower refractive index has to be used, there is a problem that components that can be used for the cladding are limited. However, no method has been proposed so far that can solve the problems relating to the component that forms this POF, including the method described in Patent Document 1.

  An object of the present invention is to provide a POF having a refractive index distribution, realizing high NA and high-speed transmission, and a method for manufacturing the same, by selecting materials constituting the core and the clad without limitation. To do.

  The plastic optical fiber in the present invention is a plastic optical fiber having a core and a clad disposed on the outer periphery of the core, and is characterized in that a large number of fine holes are provided in the clad. The size of the micropores is preferably 1 nm or more and 1000 nm or less, and the amount of the micropores is preferably 1 vol% or more and 70 vol% or less. In addition, it is preferable that the material which comprises the said core contains the same material as the material which comprises the said clad. Further, it is preferable that the core has a refractive index distribution in which the refractive index gradually increases as it goes toward the center in the radial direction.

  Further, in the method for producing a plastic optical fiber according to the present invention, a tube having pores is formed, and a polymer for a core is put into the tube and polymerized to obtain a preform for the plastic optical fiber, A plastic optical fiber is produced by heating and stretching to form a clad having fine pores in which the pores are dispersed. In addition, it is preferable to comprise the said pipe | tube from the multilayer pipe | tube arrange | positioned concentrically.

  According to the present invention, since many fine holes are provided in the clad, the refractive index of the clad can be lowered regardless of the material constituting the clad. As a result, even if the same material is used as the material constituting the core and the clad, the refractive index of the clad can be lowered, so a POF with high affinity and high NA or high coupling efficiency is manufactured. can do. Further, when the same material is used as the material constituting the core and the clad, the number of materials used for manufacturing the POF can be reduced, so that the cost can be reduced.

  Embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments. FIG. 1 is a manufacturing process diagram of POF. Each process will be described in detail later, and only the flow of the process will be described here.

First, in the outer tube manufacturing step 11, a tube-shaped outer tube 12 is manufactured. As shown in FIG. 2, the outer tube 12 forms an outer shell portion of the preform 21 that is a base material of the POF 25 (see FIG. 4). After the preform 21 is heated and stretched, the outer tube 12 has a predetermined diameter. It becomes the clad. In the present invention, the outer tube 12 is a multilayer tube in which a plurality of tubes having a large number of pores are arranged concentrically. The material constituting the outer tube 12 and the method for forming the material will be described later.

  Next, the preform 21 is produced by forming the core material 30 in the hollow portion of the outer tube 12 (see FIG. 2). In the present embodiment, the core material 30 having a double structure is formed. In the following description, the outer side, that is, the portion that contacts the inner surface of the outer tube 12 is referred to as the outer core material 31, and the inner portion, that is, the portion that is formed so as to contact the inner surface of the outer core material 31 is referred to as the inner core material 32.

  After producing the outer tube 12, first, in the first injection step 13, a polymerizable compound (hereinafter referred to as an outer core material monomer) for generating the outer core material 31 is injected into the hollow portion of the outer tube 12. To do. Next, as the outer core material generation step 15, the injected outer core material monomer is polymerized to generate the outer core material 31 so that the center of the circular cross section becomes a cavity. However, when an interfacial gel polymerization reaction, which is a kind of bulk polymerization in which a predetermined reaction proceeds, occurs when the polymer swells or dissolves when the polymerizable compound comes into contact with the polymer and soaks into the polymer, The previously formed polymer may be dissolved. Therefore, for example, due to the generation reaction of the inner core material 32 described later, the outer core material 31 previously formed may be integrated with the inner core material 32 and the outer core material 31 may not be recognized.

  Next, as the second injection step 17, a polymerizable compound (hereinafter referred to as an inner core material monomer) for generating the inner core material 32 is injected inside the outer core material 31. Subsequently, as the inner core material generation step 20, the polymerizable compound is polymerized to generate the inner core material 32. In this way, the preform 21 in which the core material 30 composed of the outer core material 31 and the inner core material 32 is formed inside the outer tube 12 is produced. In the present invention, the monomer for the outer core material and the monomer for the inner core material are not limited to monomers, but various polymers as described below in addition to dimers and trimers. And a polymerizable compound for forming.

  The produced preform 21 is subjected to a drawing step 22 and drawn by a predetermined method to become a plastic optical fiber strand (POF) 25. In the stretching step 22, the columnar preform 21 is stretched in the longitudinal direction while being heated. At this time, when the preform 21 is stretched, the outer tube 12 is also stretched at the same time, so that the pores 33 are stretched and dispersed, and as shown in FIG. A clad 40 having a large number of fine holes 44 whose arrangement is controlled is obtained. Similarly, in the core material 30 constituting the preform 21, the inner core 43 is formed from the inner core material 32, and the outer core 42 is formed from the outer core material 31. Furthermore, in the covering step 26, the outer periphery of the POF 25 is covered with a covering material, so that a plastic optical cable 27 having a protective layer formed on the outer periphery can be produced. The POF 25 that has undergone the coating process 26 is called a plastic optical fiber core or a plastic optical fiber cord (both are plastic optical code). In the present invention, this fiber core wire remains as one and is further coated if necessary, and is referred to as a single fiber cable. On the other hand, a plurality of fiber core wires are combined with a tension member or the like. The one covered with the further covering material is referred to as a multi-fiber cable, and the plastic optical cable 27 includes both the single fiber cable and the multi-fiber cable.

  FIG. 2A shows a transverse cross-sectional view cut in the diameter direction of the preform 21 in the present invention, and FIG. 2B shows a longitudinal cross-sectional view cut in the axial direction of the preform 21. The preform 21 includes an outer tube 12 and a core material 30, and the core material 30 includes an outer core material 31 and an inner core material 32. Further, both the outer tube 12 and the core material 30 are tubular in which the outer diameter and inner diameter are constant in the longitudinal direction and the thickness is uniform. Therefore, the inner diameter of the outer tube 12 is equal to the outer diameter of the outer core 31, and the inner diameter of the outer core material 31 is equal to the inner diameter of the inner core material 32.

  In the present embodiment, the core material 30 has a two-layer structure of the outer core material 31 and the inner core material 32, but the present invention is also applicable to other structures. As another structure of the core material 30, for example, there is no boundary between the outer core material 31 and the inner core material 32, and the refractive index is continuous from the inner periphery of the outer tube 12 toward the center of the core material 30. Or the structure which becomes high in steps, and the structure of three or more layers can be mentioned.

As shown in FIG. 2 (A), the outer tube 12 of the preform 21 is a multi-layer tube (3 in this embodiment) in which a tube having a large number of pores 33 is formed of a polymer, and a plurality of these are arranged concentrically. ). However, the present invention is not limited to this with respect to the number of tubes constituting the multilayer tube. In addition, as shown in FIG. 2B, a large number of pores 33 are provided in the diameter direction and the longitudinal direction of the outer tube 12. The shape, arrangement, quantity and the like of the pores 33 are not particularly limited, and the pores 33 may be adjusted so as to express a predetermined refractive index in the POF 25 obtained after the preform 21 is heated and stretched.

  FIG. 3 shows a schematic view of the pore 33. In the present embodiment, the form in which the through-hole 35 as shown in FIG. 3A is the pore 33 is shown (see FIG. 2), but the shape of the pore 33 is not limited to this. For example, a semicircular recess 37 as shown in FIG. 3B may be provided in the outer tube 37, or a bubble 39 as shown in FIG. 3C may be provided in the outer tube 38. In any shape as shown in FIGS. 3 (A) to 3 (C), when the preform 21 is stretched to form POF 25, the pores 33 become finer due to dispersion by stretching. It becomes a hole 44. The method for forming the various pores 33 will be described later. In addition, the dimension of the pores 33 is a value that is appropriately determined according to the type of each pore 33. For example, in the case of the through-hole 35 as shown in FIG. 3A, the diameter is D1, the depth is D2, and in the case of the recess 37 as shown in FIG. Let D3 and the depth be D4. In the case of the bubble 39 as shown in FIG. 3C, the maximum diameter of each bubble may be D5.

The method of forming the pores 33 in the outer tube 12 is not particularly limited. For example, when forming the through-hole 35 (see FIG. 3A), the outer tube 12 is formed of a desired material. After that, a large number of fine through holes 35 may be formed on the peripheral surface. At this time, as a method of forming the through-hole 35, a method in which a thin tube formed of a polymer is bundled and fused to make the pore 33, or a gas such as CO ₂ is dissolved in the polymer in advance. A method of obtaining the pores 33 by reducing the pressure is exemplified, and actually, these various methods are performed singly or in combination. Alternatively, immediately after forming the tube, a large number of through holes 35 may be formed by contacting rollers or pulleys having a large number of hole forming protrusions. Further, the recess 37 (see FIG. 3B) is formed in the same manner as the through hole 35. In the case of the bubbles 39 (see FIG. 3C), when the tube forming the outer tube 12 is extruded, it may be formed by mixing fine bubbles 39 in the molten polymer. The formation method is not particularly limited.

  As described above, the outer tube 12 of the present invention is composed of a tube having a large number of pores 33. In the present embodiment, the outer tube 12 is a multilayer tube produced by using three tubes and concentrically arranging them. In FIGS. 2 (A) and 2 (B), the boundary lines of the respective tubes are shown in order to make this easier to understand. In practice, however, a plurality of tubes used when forming a multilayer tube. Are bonded by fusion bonding or an adhesive, the boundary line is often not confirmed (the same applies to FIGS. 4A and 4B described later). In the case of fusing, it is preferable that the pipes are bonded in close contact so that no gap is formed at the interface formed by the pipes. However, the temperature at the time of fusion may be appropriately determined according to the polymer material to be formed, and is not particularly limited. Moreover, when bonding with an adhesive, a commercially available adhesive can be used, but a PMMA adhesive is preferably used. At this time, it is preferable to select and use an adhesive formed of components that are as similar as possible to the materials constituting the outer tube 12 and the core material 30 because adhesion can be made with higher adhesion.

4A shows a cross-sectional view of the POF 25 cut in the diameter direction, and FIG. 4B shows a vertical cross-sectional view of the POF 25 cut along the axis. The POF 25 includes a clad 40 and a core 41. The clad 40 and the core 41 are formed by heating and stretching the outer shell 12 and the core material 30 constituting the preform 21, respectively. As shown in FIG. 4A, the cladding 40 of the POF 25 has a large number of fine holes 44. This is because the fine pores 33 provided in the outer tube 12 which is the base material of the clad 40 are dispersed and made fine by stretching at the time of heating and stretching. The fine holes 44 conform to the arrangement of the fine holes 33 in the outer tube 12 of the preform 21 and are formed in large numbers in the diameter direction and the longitudinal direction of the cladding 40 as shown in FIG. . 4A and 4B show a state in which the fine holes 44 are regularly arranged in the clad 40. As described above, the fine holes 44 are stretched by the pores 33 at the time of stretching. In practice, however, the arrangement is not particularly a problem in the present invention. However, it is preferable to form the fine holes 44 as similar to the clad 40 as possible from the viewpoint of optical characteristics and the like.

  FIG. 5 shows a schematic diagram regarding the refractive index distribution of the POF 25. In FIG. 5, the range indicated by the symbol (A) on the horizontal axis is the refractive index of the cladding 40 in FIG. 4A, and the range indicated by the symbol (B) is the outer core 42 in FIG. 4B. The range indicated by the symbol (C) is the refractive index of the inner core 43.

As described above, the clad 40 of the present invention is characterized by having a plurality of fine holes 44. The size of the fine holes 44 is preferably 1 nm or more and 1000 nm or less. More preferably, it is 10 nm or more and 100 nm or less. A low transmission loss can be realized when the size of the fine hole 44 is 1/10 or less of the wavelength used. For this reason, when the size of the fine hole 44 is larger than 1000 nm, the transmission loss is increased. On the other hand, when the fine hole 44 is smaller than 1 nm, it is not suitable because it is difficult to manufacture in terms of work. The amount of the fine holes 44 is preferably 1 vol% or more and 70 vol% or less when the cross-sectional area of the POF 25 is 1. More preferably, it is 10 vol% or more and 50 vol% or less. At this time, when the amount of the fine holes 44 is larger than 70 vol%, a high NA value can be obtained, but the strength is weakened, so that it is easily deformed. On the other hand, when the amount of the fine holes 44 is less than 1 vol%, the NA value cannot be increased.

  The outer core 42 has a lower refractive index than the inner core 43, and the inner core 43 has a higher refractive index continuously from the boundary with the outer core 42 toward the center. The clad 40 is made of the same material as that for forming the core 41, but has a lower refractive index than the outer core 42 because a large number of fine holes 44 are provided. In the radial direction of the circular cross section, the difference between the maximum value and the minimum value of the refractive index is preferably 0.001 or more and 0.3 or less. When the structure of the POF 25 expresses such a refractive index, it functions as a GI type optical transmitter. In FIG. 4A, the boundary between the outer core 42 and the inner core 43 is shown for convenience of explanation. However, the clarity of the boundary differs depending on manufacturing conditions and the like, and may not necessarily be confirmed. .

Although the outer core 42 of this embodiment showed the aspect in which the refractive index was substantially constant (refer FIG. 5), the refractive index may become large, so that the inner core 43 is approached. As described above, the change in the refractive index may be stepwise or continuous, and is not particularly limited.

The POF 25 in the present invention is not particularly limited as long as it has a structure in which the refractive index of the core 41 is higher than that of the clad 40. In the present embodiment, the GI POF is shown in which the refractive index increases continuously as it goes toward the center of the core. However, the step index type (Step Step type) in which the refractive index of the clad 40 and the core 41 changes stepwise. Index: SI type). FIG. 6A shows a cross-sectional view of the SI type POF 125. The GI POF 25 has a multi-layer structure composed of a clad 40 and a two-layer core 41 composed of an outer core 42 and an inner core 43, whereas an SI type POF 125 has a clad 140 and a core 141 each having 1 layer. It has a two-layer structure consisting of layers. FIG. 6B shows a schematic diagram regarding the refractive index distribution of the SI type POF 125. In FIG. 6B, the range indicated by the symbol (A) on the horizontal axis is the refractive index of the cladding 140, and the range indicated by the symbol (B) is the refractive index of the core 141. The method for manufacturing the SI-type POF 125 is the same as the method for manufacturing the (GI-type) POF 25 described above, and a description thereof will be omitted.

In the present invention, the material constituting the clad 40 is not particularly limited, but preferably includes the same material as that constituting the core 41. That is, the material constituting the outer tube 12 that becomes the clad 40 includes the same material as the material that constitutes the core material 30 that becomes the core 41. Examples of the material constituting the core material 30 include the following materials, and in this way, when the preform 21 having the outer tube 12 formed using the same material as the core material 30 is heated and stretched. Can produce POF25 excellent in affinity and optical and mechanical properties. However, the outer tube 12 and the core material 30 are most preferably formed using the same material, but a POF 25 having relatively high affinity can be produced even if formed using a similar material. Is preferable. Details of materials used for the outer tube 12 and the core material 30 will be described later.

  The material of the outer tube 12 and the core material 30 is preferably an amorphous polymer so as not to cause light scattering, and is made of a polymer having excellent adhesion to each other, which has excellent mechanical properties such as toughness. More preferably, the heat and moisture resistance is also excellent. Moreover, it is preferable that the outer tube 12 and / or the core material 30 are made of a fluororesin. Details regarding the polymer used for the outer tube 12 and the core material 30 will be described later.

  Examples of materials constituting the core material 30 include (meth) acrylic acid esters (fluorine-free (meth) acrylic acid ester (a), fluorine-containing (meth) acrylic acid ester (b)), styrenic compounds ( c), vinyl esters (d), main chain cyclic fluorinated polymer forming monomers (e), Teflon (registered trademark) amorphous fluoropolymer (Teflon (registered trademark) AF), AVA resin, norbornene-based resin (for example, ZEONEX) (Registered trademark: manufactured by Nippon Zeon Co., Ltd.)), functional norbornene resin (for example, ARTON (registered trademark: manufactured by JSR), etc.) Polymerized by using bisphenol A, which is a raw material for polycarbonates, as a polymerizable compound Can be. As the clad forming polymer, polyvinylidene fluoride (PVDF) is also preferable. Examples include homopolymers obtained by polymerizing each of these as raw materials, copolymers obtained by combining two or more of these, and mixtures of various combinations of the above homopolymers and copolymers. it can. In the case of using a mixture, the boiling point Tb is defined as the lowest temperature among the boiling points of a plurality of raw material compounds constituting the mixture, or the temperature after the boiling point is lowered when the boiling point is lowered by forming an azeotropic mixture. . In the case of a copolymer and a blend polymer obtained using a mixture as a raw material, the glass transition point of each copolymer or blend polymer is defined as Tg. And among these, what contains (meth) acrylic acid esters or a fluorine-containing polymer as a component is more preferable when comprising an optical transmission body. Next, the above example will be described in more detail.

  As the above (a) fluorine-free methacrylic acid ester and fluorine-free acrylic acid ester, methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, tert-butyl methacrylate, benzyl methacrylate, phenyl methacrylate, methacrylic acid Examples thereof include cyclohexyl, diphenylmethyl methacrylate, tricyclo [5 · 2 · 1 · 02,6] decanyl methacrylate, adamantyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, methyl acrylate, ethyl acrylate, acrylic acid- Examples include tert-butyl and phenyl acrylate.

(B) As fluorine-containing acrylic ester and fluorine-containing methacrylate ester, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3,3 -Pentafluoropropyl methacrylate, 1-trifluoromethyl-2,2,2-trifluoroethyl methacrylate, 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate, 2,2,3, Examples include 3,4,4-hexafluorobutyl methacrylate.

(C) Styrene compounds include styrene, α-methylstyrene, chlorostyrene, bromostyrene, etc. (d) vinyl esters include vinyl acetate, vinyl benzoate, vinyl phenyl acetate, vinyl chloroacetate, etc. (E) As main chain cyclic fluorinated polymer forming monomers, a polymer having a cyclic structure as a monomer or forming a fluorinated polymer having a cyclic structure in an amorphous main chain by cyclopolymerization is formed. Monomers forming a polymer having an alicyclic ring or a heterocyclic ring in the main chain exemplified in JP-A-8-334634 and polyperfluorobutanyl vinyl ether known as CYTOP (registered trademark) And Japanese Patent Application No. 2004-186199 And the like. Of course, the present invention is not limited to these, and the refractive index of a polymer composed of a polymerizable compound alone or a copolymer may have a predetermined refractive index distribution in the molded body when molded into an optical transmission body. In addition, it is preferable to determine the type and composition ratio.

  Moreover, as a material which comprises the outer tube | pipe 12, the following are mentioned other than said various compounds. For example, there is a copolymer of methyl methacrylate (MMA) and a fluorinated (meth) acrylate such as trifluoroethyl methacrylate (FMA) or hexafluoroisopropyl methacrylate. In addition, a copolymer of MMA and an alicyclic (meth) acrylate such as (meth) acrylate having a branch such as tert-butyl methacrylate, isobornyl methacrylate, norbornyl methacrylate, tricyclodecanyl methacrylate, etc. is there. Furthermore, polycarbonate (PC), norbornene resin (for example, ZEONEX (registered trademark: manufactured by ZEON CORPORATION)), functional norbornene resin (for example, ARTON (registered trademark: manufactured by JSR)), fluorine resin ( For example, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), or the like) can be used. In addition, a fluororesin copolymer (for example, PVDF copolymer), tetrafluoroethylene perfluoro (alkyl vinyl ether (PFA) random copolymer, chlorotrifluoroethylene (CTFE) copolymer, or the like may be used. it can.

  In addition, when these polymers contain a hydrogen atom (H), it is preferable that the hydrogen atom is substituted with a deuterium atom (D), thereby reducing transmission loss, particularly in the near infrared region. It is possible to reduce the transmission loss at the wavelength.

  Furthermore, in order to use POF25 for near-infrared light, absorption loss due to the C—H bond constituting the polymer occurs, which is described in Japanese Patent No. 3332922 and Japanese Patent Application Laid-Open No. 2003-192708. By using a polymer in which C—H bond hydrogen atoms are replaced with deuterium atoms or fluorine, the wavelength range causing this transmission loss can be lengthened, and the loss of transmission signal light can be reduced. can do. Examples of such polymers include deuterated polymethyl methacrylate (PMMA-d8), polytrifluoroethyl methacrylate (P3FMA), polyhexafluoroisopropyl 2-fluoroacrylate (HFIP 2-FA), and the like. it can. In addition, in order not to impair the transparency after polymerization of the compound as a raw material, it is desirable that impurities and foreign substances serving as scattering sources are sufficiently removed before polymerization.

  In the present invention, a polymerization initiator is used when a polymerizable compound is polymerized to obtain a polymer. As the polymerization initiator, for example, there are various types that generate radicals. For example, benzoyl peroxide (BPO), tert-butylperoxy-2-ethylhexanate (PBO), di-tert-butyl peroxide (PBD), tert-butylperoxyisopropyl carbonate (PBI) ) And peroxide compounds such as n-butyl-4,4-bis (tert-butylperoxy) valerate (PHV). 2,2′-azobisisobutyronitrile, 2,2′-azobis (2-methylbutyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (2-methylpropane), 2,2′-azobis (2-methylbutane), 2,2′-azobis (2-methylpentane), 2,2′-azobis (2,3-dimethylbutane), 2,2 '-Azobis (2-methylhexane), 2,2'-azobis (2,4-dimethylpentane), 2,2'-azobis (2,3,3-trimethylbutane), 2,2'-azobis (2 , 4,4-trimethylpentane), 3,3′-azobis (3-methylpentane), 3,3′-azobis (3-methylhexane), 3,3′-azobis (3,4-dimethylpentane), 3,3'-azobis 3-ethylpentane), dimethyl-2,2′-azobis (2-methylpropionate), diethyl-2,2′-azobis (2-methylpropionate), di-tert-butyl-2,2 ′ -Azo compounds such as azobis (2-methylpropionate). In addition, a polymerization initiator is not limited to these, Moreover, you may use 2 or more types together.

  In order to keep various physical property values such as mechanical properties and thermophysical properties uniform when used as a polymer, it is preferable to adjust the degree of polymerization. A chain transfer agent can be used to adjust the degree of polymerization. About a chain transfer agent, according to the kind of polymerizable monomer used together, a kind and addition amount can be selected suitably. The chain transfer constant of the chain transfer agent for each monomer can be referred to, for example, Polymer Handbook 3rd edition (edited by J. BRANDRUP and EH IMMERGUT, published by JOHN WILEY & SON). The chain transfer constant can also be obtained by experiment with reference to Takayuki Otsu and Masaaki Kinoshita "Experimental Method for Polymer Synthesis", Kagaku Dojin, published in 1972.

  Examples of the chain transfer agent include alkyl mercaptans (for example, n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, tert-dodecyl mercaptan), thiophenols (thiophenol, m-bromothio). Phenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.) are preferably used. In particular, it is preferable to use an alkyl mercaptan such as n-octyl mercaptan, n-lauryl mercaptan, and tert-dodecyl mercaptan. A chain transfer agent in which a hydrogen atom of a C—H bond is substituted with a deuterium atom or a fluorine atom can also be used. Of course, the chain transfer agent is not limited to these, and two or more of these chain transfer agents may be used in combination.

  About each addition amount of the polymerization initiator mentioned above, a chain transfer agent, and a refractive index regulator, a preferable range can be suitably determined according to the kind etc. of the polymeric compound which is a polymer for cores to be used. In this embodiment, although the polymerization initiator is added so that it may become 0.005-0.050 mass% with respect to the polymeric compound of the core material 30, this addition rate is 0.010-0. More preferably, the content is 0.020% by mass. Moreover, although the said chain transfer agent is added so that it may become 0.10-0.40 mass% with respect to the polymeric compound of the core material 30, this addition rate is 0.15-0.30 mass. % Is more preferable.

  In addition, other additives can be added to the outer tube 12 and the core material 30 or a part thereof within a range that does not deteriorate the optical transmission performance. For example, a stabilizer can be added to the core material 30 or a part thereof for the purpose of improving weather resistance, durability and the like. Further, for the purpose of improving optical transmission performance, a stimulated emission functional compound for optical signal amplification can be added. By adding the compound, the attenuated signal light can be amplified by the excitation light, and the transmission distance can be improved. For example, it can be used as a fiber amplifier in a part of the optical transmission link. These additives can also be contained in the outer tube 12, the core material 30, or a part of them by adding to the various polymerizable compounds as the raw material and then polymerizing.

  In the outer core material 31 that forms the outer core 42 and the inner core material 32 that forms the inner core 43, a predetermined amount of a refractive index adjusting agent (hereinafter referred to as a dopant) is added to at least one of the polymers. Mix. As this dopant, a non-polymerizable compound is preferable. When the dopant is added only to the inner core material 32, the addition ratio is preferably 0.01% by weight or more and 25% by weight or less with respect to the polymer as the main component of the inner core material 32. % To 20% by weight or less is more preferable. This makes it easier to control the refractive index distribution coefficient in the radial direction of the circular cross section within the preferred range as described above.

  In this embodiment, a low molecular compound having a high refractive index, a large molecular volume, not participating in polymerization, and having a predetermined diffusion rate in a molten polymer is used as a dopant. The refractive index in the radial direction is changed. The dopant is not limited to a monomer, and may be an oligomer (including a dimer and a trimer). Therefore, in the monomer state, even if it has polymerization reactivity with the monomer for the inner core material or the inner core material 32, when it becomes an oligomer, such an oligomer is used as a dopant. be able to.

  Specific examples of the dopant include benzyl benzoate (BEN), diphenyl sulfide (DPS), triphenyl phosphate (TPP), benzyl-n-butyl phthalate (BBP), diphenyl phthalate (DPP), diphenyl ( DP), diphenylmethane (DPM), tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO) and the like. Among these, BEN, DPS, TPP, and DPSO are preferable. By adjusting the concentration and distribution of the dopant in the core material 30, the refractive index of the POF 25 can be changed to a desired value.

In the present embodiment, the inner core material 32 is produced by a rotating gel weight as will be described later so that the refractive index continuously increases from the outside of the circular cross section toward the center (see FIG. 5). Applying law. The monomer for the inner core material is MMA or all-deuterated methyl methacrylate (MMA-d8), and the outer core material 31 and the inner core material 32 after polymerization are composed mainly of PMMA or all-deuterated polymer. Methyl methacrylate (PMMA-d8). In FIG. 2, the boundary between the two is shown for convenience of explanation, but as described above, the boundary may not be clear. For example, in the preform 21, when a rotating gel polymerization reaction or the like occurs, it may not be clear or the interface may disappear.

  A method for manufacturing the preform 21 will be described in detail with reference to FIGS. FIG. 7 is a cross-sectional view of the polymerization vessel, FIG. 8 is a schematic perspective view of a rotary polymerization apparatus, FIG. 9 is an explanatory view of a polymerization reaction by the polymerization apparatus, and FIG. It is sectional drawing of the superposition | polymerization container at the time of a start. However, the present invention is not limited to the embodiment shown here.

  As shown in FIG. 7, the polymerization container 50 includes a tubular container body 50a and lids 50b that close both ends of the container body 50a. The material may be selected in consideration of heat resistance and the like, and is not particularly limited. In this embodiment, SUS is used. The inner diameter of the polymerization vessel 50 is slightly larger than the outer diameter of the outer tube 12, and the outer tube 12 can be rotated together with the rotation of the polymerization vessel 50 described later. .

First, one end of the outer tube 12 is closed with a plug 51 made of a predetermined material. When generating the outer core material, the outer tube 12 is accommodated in a polymerization vessel 50 as shown in FIG. The plug 51 is made of a material that does not dissolve in the polymerizable compound forming the core material 30, and does not include a compound that elutes a plasticizer or the like. An example of such a material is polytetrafluoroethylene (PTFE). After one end is closed with the stopper 51, the outer core material raw material including the outer core material monomer is injected into the outer tube 12. Then, after the other end is also closed with the stopper 51, the outer core material monomer is polymerized while being rotated to generate the outer core material 31 (see FIG. 2). A support member that supports the outer tube 12 may be provided inside the polymerization vessel 50 so that the outer tube 12 can respond to the rotation of the polymerization vessel 50 as described above.

  The outer core material generation step 15 (see FIG. 1) is performed by setting the polymerization container 50 as described above in a rotary polymerization apparatus 52 as shown in FIG. The rotation polymerization device 52 detects a temperature inside the device main body 53, a plurality of support rotating members 54 inside the device main body 53, a drive unit 55 outside the device main body 53, and the internal temperature according to the detection result. And a temperature controller 56 for controlling.

  The support rotation member 54 has a cylindrical shape, and the longitudinal directions thereof are generally parallel to each other and substantially horizontal so that at least one polymerization vessel 50 can be supported by two peripheral surfaces. One end of each support rotation member 54 is rotatably attached to the side surface of the apparatus main body 53 and is driven to rotate by the drive unit 55 under independent conditions. The drive unit 55 is provided with a controller (not shown), and the drive of the drive unit 55 is controlled by this controller. Then, at the time of a predetermined polymerization reaction, as shown in FIG. 9, the polymerization container 50 is placed on the valley formed by the peripheral surface of the adjacent support rotation member 54, and according to the rotation of the support rotation member 54. Rotate. In FIG. 9, the rotation axis of the support rotation member 54 is denoted by reference numeral 54a. In this embodiment, as shown in FIG. 9, the rotation of the polymerization vessel 50 is a surface drive type, but this rotation method is not limited.

  In the present embodiment, as shown in FIG. 9, the lids 50 b at both ends of the polymerization vessel 50 are provided with magnets 50 c, respectively, and below the space formed by the two adjacent rotating members 54. The magnet 57 is also provided. This prevents the polymerization vessel 50 from floating from the support rotation member 54 during rotation. As a method for preventing the polymerization container 50 from floating from the support rotation member 54, in addition to the above method using a magnet, a rotation means similar to the support rotation member 54 is further provided so as to contact the upper part of the set polymerization container 50. It may be provided and rotated in the same manner, thereby preventing the polymerization vessel 50 from floating. Further, for example, there is a method of applying a predetermined load to the polymerization vessel 50 by providing a pressing means or the like on the polymerization vessel 50, but the present invention does not depend on the floating prevention method.

  Then, the production | generation method of the outer core material 31 is demonstrated. The outer core material 31 exists between the outer tube 12 and the inner core material 32 and is also involved in the polymerization reaction of the inner core material monomer. However, the outer core material 31 may not be necessary depending on the generation conditions of the inner core material 32, and when the inner core material 32 is integrated with the inner core material 32 and disappears as described above. There is also. It is preferable to use the raw material for the outer core part such as the monomer to be used after sufficiently removing the polymerization inhibitor, moisture, impurities and the like by filtration or distillation. Furthermore, after mixing a monomer and a polymerization initiator, it is preferable to remove dissolved gas and volatile components from the mixture by ultrasonic treatment. In addition, before and after the first injection step 13 (see FIG. 1), the outer tube 12 and the injection may be reduced by a known pressure reduction device, if necessary.

  Thereafter, when the polymerization vessel 50 loaded with the outer tube 12 is rotated (horizontal rotation) with the longitudinal direction thereof being set in a substantially horizontal state, the outer core material 31 is generated. Thus, the outer core material 31 is produced by rotational polymerization in which polymerization is performed with the circular tube axis of the outer tube 12 as the rotational center. Prior to the rotation polymerization, pre-polymerization may be performed with the outer tube 12 in an upright state. At the time of this pre-polymerization, the circular shaft of the outer tube 12 is rotated by a predetermined rotation mechanism as necessary. Rotate as the center of rotation. In such rotational polymerization, the outer core material 31 is easily formed on the entire inner surface of the outer tube 12 because the outer tube 12 is rotated while keeping the longitudinal direction thereof generally horizontal. In the present invention, at the time of polymerization of the outer core material 31, it is most preferable to make the longitudinal direction of the outer tube 12 horizontal in order to form the outer core material 31 on the entire inner surface of the outer tube 12, but substantially horizontally. If it is preferable, the allowable angle of the rotating shaft is generally within 5 ° with respect to the horizontal.

  After the outer tube 12 on which the outer core material 31 has been formed as described above is taken out from the rotary polymerization apparatus 52, in this embodiment, a heating process for a predetermined time is performed by a heating means such as a thermostat set to a predetermined temperature. I am doing.

  Next, the inner core material 32 is generated. FIG. 10 is a cross-sectional view of the polymerization vessel 50 at the start of the production of the inner core material 32. Since this polymerization container 50 is the same as that used when the outer core material 31 is produced, the same reference numerals are used. The inner core material 58 including the inner core material monomer is injected into the hollow portion of the outer core material 31. Thereafter, the inlet is closed with a stopper 51, the longitudinal direction of the outer tube 12 on which the outer core material 31 is formed is set to a substantially horizontal state, and the reaction is carried out while rotating so that the center of the cross-sectional circle of the outer tube 12 is the rotation axis. When the polymerization is started and the polymerization proceeds, the inner core material 32 is generated.

  For the polymerization of the inner core material monomer, the longitudinal direction of the outer tube 12 is substantially horizontal as in the case of the outer core material 31 generation, using the rotary polymerization device 52 (see FIG. 8) used in the outer core material generation step 15. The polymerization vessel 50 is rotated so as to be rotated.

  When the inner core material monomer starts to be polymerized, the inner wall of the outer core material 31 is swollen by the inner core material monomer, and a swelling layer is formed in the initial stage of polymerization. This swelling layer is in a gel state, and therefore the polymerization rate is accelerated (referred to as gel effect). From this phenomenon, in this specification, while rotating a tubular member prepared in advance, a swelling layer is formed by a reaction between the tubular member and the injected polymerizable compound, thereby polymerizing the polymerizable compound. This reaction is called a rotational gel polymerization method. In this polymerization reaction, it is more preferable that the longitudinal direction of the tubular member is horizontal as in this embodiment. Then, the polymerization starts from the inner surface of the outer core material 31 and proceeds toward the center of the outer tube 12 having a circular cross section. At this time, since the compound having a smaller molecular volume enters the inside of the swelling layer preferentially, as the polymerization proceeds, a dopant having a larger molecular volume is pushed out from the swelling layer toward the center as compared with other coexisting compounds. It is. As a result, the preform 21 having a high refractive index dopant concentration at the center portion of the formed inner core material 32 and a gradually increasing refractive index toward the center in the radial direction of the circular section is obtained. Can do.

  In the present embodiment, the outer core material 31 and the inner core material 32 have a clear boundary between the outer core material 31 and the inner core material 32 because the preform 21 is produced while forming a swelling layer. It is not a thing. Further, in the rotating gel polymerization method of the present invention, the outer core material 31 has a thickness smaller than that before the inner core material 32 is generated, in addition to the case where the outer core material 31 disappears as described above due to the formation of the gel layer. In some cases.

In the present embodiment, the core material 30 is formed using a rotational gel polymerization method. At this time, when the polymerization is performed, the polymerization container 50 is rotated while being held substantially horizontal, but the rotation method is not limited to this mode. As another method, for example, polymerization may be performed while rotating the polymerization vessel 50 in a suspended state.

  In the rotating gel polymerization method as described above, the reaction temperature is preferably a temperature not higher than the boiling point of the polymerizable compound to be used. When MMA or MMA-d8 is used as the polymerizable compound as in this embodiment, the reaction temperature is preferably 30 to 100 ° C, and more preferably 40 to 80 ° C. If the reaction temperature is higher than a predetermined upper limit, there are problems such as boiling and generation of bubbles. On the other hand, if it is lower than the predetermined lower limit value, the time required for the reaction becomes longer, so that the responsiveness of the polymer production state to the volume shrinkage in the polymerization is deteriorated, and air is entrapped inside the polymer. Problems such as being rare may occur. This may sometimes cause bubbles in the POF 25 after stretching.

  The reaction time is preferably 0.5 to 20 hours, more preferably 1.5 to 3 hours. If it is longer than 20 hours, there is a problem in production efficiency, and if it is shorter than 0.5 hours, the degree of polymerization becomes non-uniform, bubbles are generated, or the polymer is in a wavy state and becomes non-uniform. Problems such as density occur.

  About a rotational speed, it is preferable to set it as 500-4000 rpm, and it is more preferable to set it as 1500-3500 rpm. A speed higher than 4000 rpm is not preferable because an operation load on the apparatus increases, an electric cost required for the apparatus operation increases, and an improvement in the apparatus design against the occurrence of vibration may be required. On the other hand, if the rotation speed is lower than 500 rpm, it may be difficult to control the polymerization reaction so that the rotation axis is the center. For example, even if it is desired to form a hollow portion, a good hollow portion may be formed. It cannot be formed, or the uniformity of the polymer is impaired.

  By using the above method, the outer tube 12 and the core material 30 are made of plastic, and the outer tube 12 having the pores 33 and the core material 30 have a double structure of the outer core material 31 and the inner core material 32. A preform 21 that is a cylindrical light transmission body can be produced. Moreover, by using the obtained preform 21 for the stretching step 22, it is possible to obtain a POF 25 including the clad 40 having the fine holes 44 and the core 41 including the inner core 41 and the outer core 42.

  As a stretching method of the preform 21, various stretching methods described in JP-A-07-234322 can be applied, whereby a POF 25 having a desired diameter, for example, 200 μm or more and 1000 μm or less is obtained.

  POF25 according to the present invention is improved by bending, weather resistance, suppression of performance degradation due to moisture absorption, improvement of tensile strength, imparting stepping resistance, imparting flame resistance, protection from chemical damage, preventing noise from external rays, coloring, etc. For the purpose of improving the commercial value and the like, the surface is usually coated with one or more protective layers.

  In the present embodiment, the plastic optical cable 27 is shown in which the outer periphery of the POF 25 is coated with a coating material. However, the plastic optical cable 27 may be referred to as a bundle of POFs 25 that are covered as they are. Therefore, as a form of coating, there are a contact type coating in which the interface between the coating material and the POF 25 is in contact with the entire circumference, and a loose type coating having a fine hole at the interface between the coating material and the POF 25. is there. In loose type coating, for example, when the protective layer is peeled off at the connection portion with the connector, moisture may enter through the fine holes on the end face and diffuse in the longitudinal direction. When compared with the coating, it is usually preferable to use a close-contact coating.

However, in the case of loose type coating, since the coating material and the POF 25 are not in close contact with each other, most of the stress applied to the plastic optical cable 27 and damage such as heat can be alleviated by the protective layer. Therefore, since damage to the POF 25 can be reduced, it can be preferably used depending on the application. As for the propagation of moisture, moisture propagation from the end face can be prevented by filling the fine pores with a gel-like semi-solid or powder having fluidity. Moreover, a coating with higher performance can be formed by imparting functions different from the prevention of moisture propagation, such as heat resistance and improvement of mechanical functions, to these semi-solids and granular materials. In order to produce a loose-type coating, a fine layer can be produced by adjusting the position of the extrusion nipple of the crosshead die and further adjusting the pressure reducing device.

  In the POF 25 according to the present invention, if necessary, the protective layer may be a primary protective layer, and a secondary (or multilayer) protective layer may be further provided on the outer periphery. When the primary protective layer has a sufficient thickness, thermal damage can be reduced by the presence of the primary protective layer, so the limitation on the curing temperature in the material of the secondary protective layer is Compared with the case where the primary protective layer is coated, it can be relaxed. As described in the covering material, additives such as a flame retardant, an ultraviolet absorber, an antioxidant, a radical scavenger, and a lubricant may be introduced into the secondary protective layer.

  Moreover, in order to give the plastic optical cable 27 a plurality of other functions, a coating layer as a functional layer may be further laminated as appropriate. For example, in addition to the above-mentioned flame retardant layer, there are a barrier layer for suppressing moisture absorption of POF 25, a moisture absorbing material layer for removing moisture contained in POF 25, and the like. As a method for applying such a hygroscopic material layer, for example, there is a method of providing a hygroscopic tape or a hygroscopic gel in a predetermined coating layer or between coating layers. As other functional layers, there are a flexible material layer for relaxing stress at the time of flexibility, a foam material layer as a buffer material for buffering external stress, and a reinforcing layer for improving rigidity. . As a structural material (covering material) of the plastic optical cable 27, a material in which a thermoplastic resin contains a fiber having a high elastic modulus (a so-called tensile fiber) and / or a metal wire having a high rigidity other than a resin is used. The use of such a material is preferable because the mechanical strength of the obtained cable can be reinforced.

  Examples of the tensile strength fibers include aramid fibers, polyester fibers, and polyamide fibers. Examples of the metal wires include stainless steel wires, zinc alloy wires, and copper wires, but are not limited thereto. In addition, a metal tube exterior for protection, an aerial support line, and a mechanism for improving workability during wiring can be incorporated in the outer peripheral portion of the plastic optical cable 27. The shape of the plastic optical cable 27 is a collective type in which the optical fiber core wires are concentrically arranged, a tape type in which the optical fiber core wires are arranged in a line, or a type in which the optical fiber cable 27 is gathered by a presser winding or a wrap sheath. The form is selected according to the application.

  Since the plastic optical cable 27 obtained from the preform 21 of the present invention has a higher tolerance for the axial deviation than the conventional one, it can be used even if joined by butt, more preferably, the end portion thereof. It is preferable to provide an optical connector for connection to each other and securely fix the connecting portions. As the connector, various commercially available connectors such as PN type, SMA type, and SMI type that are generally known can be used. Furthermore, various light emitting elements, light receiving elements, optical switches, optical isolators, optical integrated circuits, optical signal processing apparatuses including optical components such as optical transmission / reception modules, and the like are suitably used in combination. In this case, you may combine with another optical fiber strand etc. as needed. Any known technique can be applied as a technique related to them. For example, the basic and actual of plastic optical fiber (published by NTS Corporation), Nikkei Electronics 2001.1.2.3, pp. 110-127 “Printed Wiring You can refer to "This time, optical components are mounted on the board." Combined with various technologies described in the above documents, internal wiring in computers and various digital devices, internal wiring in vehicles and ships, optical terminals and digital devices, optical links between digital devices, general households and housing complexes・ Suitable for optical transmission systems suitable for short distances such as high-speed, large-capacity data communications and control applications that are not affected by electromagnetic waves, including optical LANs in factories, offices, hospitals, schools, etc. Can be used.

  Further, IEICE TRANS. ELECTRON. , VOL. E84-C, No. 3, MARCH 2001, p. 339-344 “High-Uniformity Star Coupler Using Diffused Light Transmission”, Journal of Japan Institute of Electronics Packaging, Vol. 3, No. 6,2000, pages 476 to 480, which are described in “Interconnection by Optical Sheet Bus Technology”, and the arrangement of light emitting elements on the waveguide surface described in Japanese Patent Application Laid-Open No. 2003-152284; , JP-A-2002-90571, JP-A-2001-290055, and the like; JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968 , JP 2001-318263, JP 2001-31840, etc .; optical branch couplers described in JP 2000-241655, etc .; optical star couplers described in JP 2000-241655, etc .; Optical signals described in Japanese Patent Laid-Open Nos. 2002-101044 and 2001-305395 Optical signal bus system; optical signal processing apparatus described in JP-A No. 2002-23011; optical signal cross-connect system described in JP-A No. 2001-86537; optical described in JP-A No. 2002-26815 Multi-function system described in each publication such as JP 2001-339554 A and JP 2001-339555 A; various optical waveguides, optical splitters, optical couplers, optical multiplexers, optical demultiplexers, etc. In combination, it is possible to construct a more advanced optical transmission system using multiplexed transmission and reception. In addition to the above light transmission applications, it can also be used in the fields of illumination (light guide), energy transmission, illumination, and sensors.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to these examples.

Using PMMA, PMMA tubes in which through holes having a diameter D1 of 0.5 mm and a depth D2 of 0.2 mm were formed as pores 33 were arranged concentrically in a triple layer, and then fused together to form an inner diameter. A multi-layer tube having a hollow portion of 20 mm in length and 60 cm in length was produced as the outer tube 12. In this hollow part, as a monomer for the outer core material, 204.1 g of fully deuterated polymethyl methacrylate (PMMA-d8, Tg; 80 ° C. to 115 ° C.) and dimethyl 2,2′- A mixture of azobis (2-methylpropionate, trade name: V-601, manufactured by Wako Pure Chemical Industries, Ltd., half-life time at 70 ° C .; 5 hours) and n-lauryl mercaptan as a chain transfer agent Each was injected after adjusting to a predetermined temperature. The addition rates of dimethyl 2,2′-azobis (2-methylpropionate) and n-lauryl mercaptan with respect to MMA-d8 were 0.012 mol% and 0.2 mol%, respectively.

  The outer tube 12 into which the outer core material monomer has been injected is accommodated in a polymerization vessel 50, which is set in the rotation polymerization device 52 so that the longitudinal direction is horizontal, and is rotated at 500 rpm in an atmosphere of 60 ° C. The outer core material 31 having a hollow portion was formed by performing heat polymerization for 2 hours, then rotating at 3000 rpm for 16 hours in an atmosphere of 60 ° C., and further rotating at 3000 rpm for 4 hours in an atmosphere of 90 ° C.

  A monomer for the inner core material was injected into the hollow portion of the outer core material 31 under normal temperature and normal pressure. As the monomer for the inner core material, 81.7 g of MMA-d8 from which moisture was removed to 400 ppm or less, dimethyl 2,2′-azobis (2-methylpropionate; V-601) as a polymerization initiator, chain A mixture obtained by mixing n-lauryl mercaptan as a transfer agent and diphenyl sulfide (DPS) as a dopant was used. Next, after setting the outer tube 12 in the rotation polymerization apparatus 52 so that the longitudinal direction is horizontal, the rotation speed is 2000 rpm, and the rotation is performed in an atmosphere of 70 ° C. for 5 hours. The preform 21 was obtained by heating and polymerizing at 90 ° C. for 5 hours while rotating as follows. Finally, the preform 21 was stretched in the stretching step 22 to produce POF 25 having an outer diameter of 316 μm.

Preform 21 and POF 25 were manufactured using the same manufacturing method and manufacturing conditions as in Example 1. However, as the outer tube 12 forming the preform 21, a tube prepared using an amorphous fluororesin and provided with the same pores 33 as in Example 1 was manufactured as the outer tube 12.

  Preform 21 and POF 25 were manufactured using the same manufacturing method and manufacturing conditions as in Example 1. However, a PMMA tube having an outer diameter of 20 mm and a length of 60 cm manufactured using PMMA was used as the outer tube 12 inside the glass tube. In Example 3, the outer tube 12 was not provided with the pores 33.

  Using PMMA, PMMA tubes in which through holes having a diameter D1 of 0.5 mm and a depth D2 of 0.2 mm were formed as pores 33 were arranged concentrically in a triple, and then fused to each other. A multi-layer tube having a hollow portion of 20 mm in length and 60 cm in length was produced as the outer tube 12. In this hollow part, 200 g of methyl methacrylate (MMA) as a monomer for core material and dimethyl 2,2′-azobis (2-methylpropionate, trade name; V-601, Wako Pure) as a polymerization initiator A mixture of Yakuhin Co., Ltd., half-life time at 70 ° C .; 5 hours) and n-lauryl mercaptan as a chain transfer agent was adjusted to a predetermined temperature and then injected. The addition ratio of dimethyl 2,2′-azobis (2-methylpropionate) and n-lauryl mercaptan to MMA was 0.012 mol% and 0.2 mol%, respectively. The outer tube 12 into which the monomer for core material has been injected is accommodated in a polymerization vessel 50, set in the rotation polymerization apparatus 52 so that the longitudinal direction is horizontal, and rotated at 500 rpm under an atmosphere of 60 ° C. Heat polymerization was performed for 16 hours in an atmosphere at 60 ° C. for 16 hours while rotating at 3000 rpm for 4 hours, and then for 4 hours in an atmosphere at 90 ° C. while rotating at 3000 rpm to form a core material having a hollow part. This PF was heated and stretched, and the hollow portion formed inside was crushed to obtain an SI type POF125 having a fiber diameter of 500 μmφ.

〔Evaluation methods〕
The refractive index and numerical aperture of the outer tube 12 on the fracture surface of the POF 25 produced in each example were measured, and the values were evaluated. At this time, a POF having a numerical aperture (NA value) larger than 0.4 is defined as dominant (◯), a value larger than 0.3 is standard (Δ), and a value less than 0.3 is inferior (×). evaluated.

  The evaluation results and execution conditions in each example are shown in Table 1.

  In Example 1, the multilayer tube formed by arranging the PMMA tubes having the pores 33 in triplicate was used as the outer tube 12 to form the preform 21, and this was heated and stretched to produce the POF 25. At this time, the refractive index of the cladding 40 of the POF 25 was n = 1.40, and the NA value was 0.51. In Example 2, a POF 25 was produced in the same manner as in Example 1 using the fluororesin pipe having the pores 33 as the outer pipe 12. At this time, the refractive index of the cladding 40 of the POF 25 was n = 1.27, and the NA value was 0.43. In Example 3, POF 25 was produced in the same manner as in Example 1 except that the PMMA tube without the pores 33 was used as the outer tube 12. At this time, the refractive index of the cladding 40 of the POF 25 was n = 1.48, and the NA value was 0.17. Further, while Examples 1 to 3 produced GI-type POF, in Example 4, the PMMA tube having the pores 33 having the same shape and dimensions as those of Examples 1 and 2 was used as the outer tube 12, and the hollow An SI-type POF 125 having a single layer core 141 formed on the part was produced. At this time, the refractive index of the cladding 140 of the POF 125 was n = 1.42, and the NA value was 0.45.

  In Examples 1, 2 and 4, although the constituent materials and the types of the optical fiber strands are different, a clad having a large number of fine holes 44 is formed. As a result, n = 1.40 in Example 1, n = 1.27 in Example 2, and n = 1.42 in Example 4. Usually, PMMA is about n = 1.49, and fluororesin is about n = 1.34. Therefore, it can be said that both of them can lower the value of the refractive index of the material conventionally. On the other hand, in Example 3, the PMMA tube was used to form the clad 40 in the same manner as in Example 1, but n = 1.49, which was the same as the value conventionally possessed by PMMA. Therefore, it was confirmed that the refractive index can be lowered by providing the fine holes 44 in the clad regardless of the constituent material and the POF type.

  When paying attention to the NA value, the NA values in Examples 1, 2, and 4 were 0.51, 0.43, and 0.45, respectively, and all showed high NA values of 0.4 or more. On the other hand, in Example 3, the NA values were 0.17 and less than 0.3. From these results, it was confirmed that the NA can be further increased by providing the fine hole 44 in the clad regardless of the constituent material and the POF type.

It is the schematic which shows the manufacturing process of the plastic optical fiber strand in this invention. (A) is a cross-sectional view of the preform, and (B) is a vertical cross-sectional view thereof. It is sectional drawing which shows an example of the pore formed in an outer tube | pipe. (A) is a transverse sectional view of POF, and (B) is a longitudinal sectional view thereof. It is the schematic which shows the refractive index distribution of POF. (A) is a cross-sectional view of POF, and (B) is a schematic diagram showing a refractive index distribution. It is sectional drawing of a superposition | polymerization container. It is a schematic perspective view of a rotation polymerization apparatus. It is explanatory drawing about the polymerization reaction by a superposition | polymerization apparatus. It is sectional drawing of the superposition | polymerization container at the time of an inner core material production | generation start.

Explanation of symbols

12 Outer tube 21 Preform 25 Plastic optical fiber (POF)
30 Core Material 31 Outer Core Material 32 Inner Core Material 33 Fine Hole 35 Through Hole 40 Cladding 41 Core 42 Outer Core 43 Inner Core 44 Fine Hole

Claims (7)

In a plastic optical fiber having a core and a clad disposed on the outer periphery of the core,
A plastic optical fiber strand comprising a plurality of fine holes in the clad.   2. The plastic optical fiber according to claim 1, wherein the size of the micropore is 1 nm or more and 1000 nm or less.   3. The plastic optical fiber according to claim 1, wherein the amount of micropores is 1 vol% or more and 70 vol% or less.   4. The plastic optical fiber according to claim 1, wherein the material constituting the core includes the same material as the material constituting the clad.   5. The plastic optical fiber according to claim 1, wherein the core has a refractive index distribution in which a refractive index gradually increases as it goes toward a center in a radial direction. Forming a tube with pores,
The core polymer is placed in the tube and polymerized to form a plastic optical fiber preform, and the preform is heated and stretched to form a clad having fine pores formed by dispersing the pores. A method for producing a plastic optical fiber, characterized by producing an optical fiber. 7. The method of manufacturing a plastic optical fiber according to claim 6, wherein the tube is composed of a plurality of multi-layer tubes arranged concentrically.

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