JP2005321686A - Multi-step index type plastic optical fiber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-step index type plastic optical fiber which has satisfactory productivity and excellent transmission performance, and broadens the bandwidth particularly corresponding to GI-POF (graded-index plastic optical fiber). <P>SOLUTION: The multi-step index type plastic optical fiber has a core part composed of three or more layers concentrically arranged and a clad part formed on the outer periphery. Therein, each of the three or more layers is made of non-crystalline polymer composition which has not substantially C-H bonds and the three or more layers are arranged such that the refractive index of the core part become smaller toward the outer periphery from the center. In the multi-step index type plastic optical fiber, it is preferable that every difference of refractive indexes between adjacent layers in the core part is substantially the same and the refractive index of the core part approximates the G-power distribution. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the technical field of plastic optical members, and in particular, a multi-step having a multi-step refractive index distribution capable of broadening the band according to a refractive index distribution type plastic optical fiber (sometimes abbreviated as GI-POF). It belongs to the technical field of index type plastic optical fiber (may be abbreviated as MSI-POF).

  Plastic optical members have advantages such as easy manufacture and processing and low cost compared to quartz optical members having the same structure. In recent years, optical fibers and optical lenses, Various applications such as waveguides have been attempted. Among these optical members, plastic optical fibers (sometimes abbreviated as POF) are good, although they have a disadvantage that transmission loss is slightly larger than that of quartz system because all the strands are made of plastic. It has the advantages of being flexible, lightweight, easy to process, easy to manufacture as a fiber having a large diameter compared to quartz optical fiber, and capable of being manufactured at low cost. Therefore, various studies have been made on optical communication transmission media for short distances where the magnitude of transmission loss is not a problem.

  A plastic optical fiber generally has a refractive index different from that of a core made of an organic compound having a polymer matrix (referred to herein as a “core part”) (generally a low refractive index). And an outer shell made of an organic compound (referred to herein as a “cladding portion”). In particular, a gradient index plastic optical fiber having a core having a distribution of refractive index from the center to the outside can increase the bandwidth of an optical signal to be transmitted. Recently, it has been attracting attention as an optical fiber (see Patent Documents 1 and 2). As one of the methods for producing such a refractive index distribution type optical member, an optical member base material (referred to as “preform” in the present specification) is prepared by utilizing interfacial gel polymerization. A method of stretching is proposed.

  The problem with GI-POF is low productivity. Since the preform rod using the interfacial gel polymerization forms a refractive index distribution by utilizing the diffusion state of the dopant molecules in the core polymerization step, there is a limit to the thickness and length of the rod. From this point of view, MSI-POFs mainly composed of polymethyl methacrylate (sometimes abbreviated as PMMA) have been proposed (see, for example, Patent Documents 3, 4 and 5). However, MSI-POF has a problem that its transmission capacity is lower than that of GI-POF.

JP-A-61-130904 WO93 / 08488 JP-A-10-111414 JP-A-10-133303 JP-A-11-52146 JP 2002-31254 A

  The present invention has been made in view of the above-mentioned problems, and maintains a superior productivity of the conventional MSI-POF, has a good transmission performance, and in particular a multi-band capable of widening according to GI-POF. It is an object of the present invention to provide a step index type plastic optical fiber.

Means for solving the problems are as follows.
[1] A multi-step index type plastic optical fiber having a core portion composed of three or more layers arranged concentrically and a cladding portion on the outer periphery thereof, each of the three or more layers being substantially C A multi-step index type plastic light comprising an amorphous polymer composition having no —H bond, and wherein the three or more layers are arranged so that the refractive index of the core portion decreases from the center toward the outer periphery; fiber.
[2] The multi-step index type of [1], wherein the refractive index difference between adjacent layers in the core part is substantially the same, and the refractive index of the core part approximates a G-th power distribution. Plastic optical fiber.
[3] A multi-step index type plastic optical fiber having a core portion composed of two or more layers arranged concentrically and a cladding portion on the outer periphery thereof, each of the two or more layers being substantially C Each of the layers is arranged so that the refractive index of the core portion decreases from the center toward the outer periphery, and the refractive index of the clad portion is made of the amorphous polymer composition having no —H bond. A multi-step index type plastic optical fiber having a refractive index of 3% or more lower than the refractive index of the outermost layer.
[4] The multi-step index type plastic optical fiber according to any one of [1] to [3], wherein the amorphous polymer having substantially no CH bond is a deuterated polymer or a fluorinated polymer. .

  According to the present invention, there is provided a multi-step index type plastic optical fiber having a good optical transmission capability and capable of widening the bandwidth according to GI-POF while maintaining the excellent productivity of conventional MSI-POF. can do.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention will be described in detail.
The multi-step index type plastic optical fiber (MSI-POF) of the present invention has a core part composed of a plurality of layers arranged concentrically and a clad part on the outer periphery thereof. Each of the layers constituting the core portion is composed of a composition containing an amorphous polymer having substantially no C—H bond. In the present invention, since each of the plurality of layers is formed using a polymer having no C—H bond, optical transmission loss due to the C—H bond can be greatly reduced. Furthermore, since an amorphous polymer is used, scattering loss can be greatly reduced.

  The amorphous polymer is preferably selected from (A) deuterated polymer or (B) fluorinated polymer. The former (A) is a polymer in which C—H bonds are mainly replaced with C—D bonds, and the latter (B) is a polymer in which C—H bonds are mainly replaced with C—F bonds. Of course, polymers having both a CD bond and a CF bond belonging to both (A) and (B) can also be used.

  First, the former (A) deuterated polymers will be described. The deuterated polymer (A) may be basically any type of polymer as long as the C—H bond hydrogen atom in the polymer is substituted with a deuterium atom. In addition, the polymer used for this invention is a polymer which does not have C-H bond substantially, It is preferable that the deuterated substitution rate of (A) deuterated polymers is 95% or more. (A) A part of fluorine atoms may be mixed in the polymer, that is, a C—F bond may be present. For example, examples of the polymer include poly (meth) acrylic acid esters, polycarbonates, polyesters, and norbornene polymers. Among these, poly (meth) acrylic acid esters are most preferable. Specific examples of the monomers include deuterated methyl (meth) acrylate, t-butyl (meth) acrylate, benzyl (meth) acrylate, phenyl (meth) acrylate, and (meth) acrylic. Norbornyl acid, isobornyl (meth) acrylate, (meth) acrylic acid (bicyclo-2,2,1-heptyl-2), (meth) acrylic acid-1-adamantyl, (meth) acrylic acid-2-adamantyl, ( (Meth) acrylic acid-3-methyl-1-adamantyl, (meth) acrylic acid-3,5-dimethyl-1-adamantyl, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3 methacrylate , 3, -pentafluoropropyl, 2,2,3,3-tetrafluoropropyl methacrylate, hexafluoro-2-propyl methacrylate Perfluorohexylmethyl methacrylate, perfluoro-t-butyl methacrylate, and the like, each of which is deuterated methyl methacrylate, t-butyl methacrylate, benzyl methacrylate, phenyl methacrylate, norbornyl methacrylate, methacrylic acid Isobornyl, 2,2,2-trifluoroethyl methacrylate, 2,2,3,3 methacrylate, 3-pentafluoropropyl, 2,2,3,3-tetrafluoropropyl methacrylate, hexafluoro-2 methacrylate -Propyl is particularly preferred.

  Next, the latter (B) fluorinated polymers will be described. (B) Fluoropolymers may basically be any type of polymer as long as hydrogen atoms in the polymer are substituted with fluorine atoms. In addition, it is preferable that the polymer used for this invention is a polymer which does not have C-H bond substantially, and a fluorination substitution rate is 90% or more. The lower limit of the substitution rate is smaller than the deuteration substitution rate because the adverse effect of the C—F bond on the transmission loss is smaller than the C—D bond. (B) The C—H bonds remaining in the fluorinated polymers are preferably converted to C—D bonds. For example, the polymer type is at least one selected from fluorine-containing polyether, fluorine-containing aromatic polyester, fluorine-containing aromatic polycarbonate, and fluorine-containing polyimide, and a fluorine-containing polymer having a ring structure in the polymer main chain. preferable. Examples of the polymer include those described in JP-A No. 2002-311254.

  The amorphous polymer can be prepared by polymerizing a polymerizable monomer by a known polymerization method. Any of solution polymerization, suspension polymerization, and bulk polymerization can be used, but from the viewpoint of transmission loss, the bulk polymerization system is most preferable. Among these, polymerization is preferred. The molecular weight of the non-crystalline polymer is not particularly limited. However, when drawing into a POF form by drawing by stretching, the mechanical properties at the time of stretching are within a desired range, which contributes to improvement in productivity. From this viewpoint, the molecular weight is preferably 10,000 to 2,000,000, more preferably 30,000 to 1,000,000. The molecular weight of the polymer can be adjusted to a desired range by controlling the polymerization rate and degree of polymerization of the polymerizable monomer with a polymerization initiator and an optionally added chain transfer agent.

  The polymerization of the polymerizable monomer is preferably advanced by a polymerization initiator. As a polymerization initiator, it can select suitably according to the monomer and polymerization method to be used, but benzoyl peroxide (BPO), t-butylperoxy-2-ethylhexanate (PBO), di-t-butylperoxide. Peroxide compounds such as oxide (PBD), t-butyl peroxyisopropyl carbonate (PBI), n-butyl 4,4, bis (t-butylperoxy) valerate (PHV), or 2,2′-azobis Isobutyronitrile, 2,2'-azobis (2-methylbutyronitrile), 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), 3,3′-azobis (3-methylpentane), 3,3′-azobis (3,4-dimethylpentane), 3,3′-azobis (3-ethylpentane) , Dimethyl-2,2′-azobis (2-methylpropionate), diethyl-2,2′-azobis (2-methylpropionate), di-t-butyl-2,2′-azobis (2-methyl) And azo compounds such as propionate). Two or more kinds of polymerization initiators may be used in combination.

  The polymerizable monomer is preferably polymerized in the presence of a chain transfer agent. The chain transfer agent is mainly used for adjusting the molecular weight of the polymer. When polymerization is performed in the presence of a chain transfer agent, the polymerization rate and degree of polymerization of the polymerizable monomer can be further controlled by the chain transfer agent, and the molecular weight of the polymer can be adjusted to a desired molecular weight. For example, when a cylindrical tube formed by concentrically laminating a plurality of layers made of the polymer is sometimes drawn, and then drawn by drawing to form an optical transmission body, the molecular weight is adjusted to adjust the molecular weight. The mechanical characteristics can be set within a desired range, which contributes to improvement of productivity. About the said 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.

  As chain transfer agents, alkyl mercaptans (n-butyl mercaptan, n-pentyl mercaptan, n-octyl mercaptan, n-lauryl mercaptan, t-dodecyl mercaptan, etc.), thiophenols (thiophenol, m-bromothiophenol, p-bromothiophenol, m-toluenethiol, p-toluenethiol, etc.) are preferably used, and among them, alkyl mercaptans such as n-octyl mercaptan, n-lauryl mercaptan, and t-dodecyl mercaptan are preferably used. 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. In addition, the said chain transfer agent may use 2 or more types together.

  The core portion of the MSI-POF of the present invention has a structure in which a plurality of layers having different refractive indexes are arranged concentrically and the refractive index decreases from the center toward the outside. With this structure, a refractive index gradient is formed stepwise in the fiber from the inner layer toward the outer layer. The core part is preferably composed of three or more layers. A more excellent effect can be obtained by stacking three or more layers having different refractive indexes in three steps or more, that is, by changing the refractive index stepwise. As the number of layers constituting the core portion increases, the gradient of the refractive index becomes smoother, and an effect close to that of a GI type fiber can be obtained. On the other hand, when the number of layers is increased, the manufacturing cost increases and the GI type increases. It becomes the same level as the fiber. In order to obtain an MSI-POF having a good balance between performance and cost, the core portion is preferably composed of about 3 to 20 layers, more preferably about 5 to 10 layers.

In the core portion of the MSI-POF of the present invention, a plurality of layers are concentrically arranged so that the refractive index gradually decreases from the center of the core portion toward the outside. The refractive index of the core part is preferably made so as to change along a so-called G-th power distribution. This G-th power distribution shows that when Nc is the refractive index of the core center, δN is the refractive index difference between the core center and the outermost periphery of the core, and Rcore is the core radius, the refractive index at the radius R from the core center is the following. formula:
N = [Nc × 1-2δN (R / Rcore) ^G ] ^1/2
The distribution is a value approximated by. In general, in order to manufacture an MSI-POF that realizes a wide band, the value of G is about 2, and the refractive index of each layer positioned at R from the core center indicates the refractive index N derived from the above formula. Similarly, it is preferable to adjust the refractive index of each layer.

In the MSI-POF of the present invention, it is preferable that the refractive index of the core portion approximates a G-th power distribution, and the refractive index difference between adjacent layers in the core portion is substantially the same. For example, the core portion is n (n proviso that 3 or more is a natural number) if composed of layers, x from the inside (where natural number satisfying 2 ≦ x ≦ n) th layer n _x and its neighboring (x- 1) It is preferable that the refractive index difference between the _first layer _nx-1 and the refractive index difference between the xth layer _nx and the adjacent (x + 1) th layer _{nx + 1} are equal. Note that “substantially equal” means a range of the value ± 0.0005.

Conventionally, it has been common to design the core portion so that the constituent layers have the same thickness ΔR and the refractive index decreases from the center to the outside in a G-power distribution. However, in the MSI-POF of the present invention, it is not essential that the thickness (ΔR) of the constituent layers is the same. As described above, an embodiment in which the refractive index difference between adjacent layers in the core part is substantially the same is preferable.
FIG. 1 shows a schematic diagram of a refractive index distribution in an aspect in which the refractive index difference between adjacent layers in the core portion is substantially the same, and a schematic diagram of the cross-sectional shape below the refractive index distribution. FIG. 2 shows a schematic diagram of the refractive index distribution in a mode in which the thicknesses of the layers constituting the core portion are substantially the same, and a schematic diagram of the cross-sectional shape of the fiber below. In both cases, the refractive index is distributed to the G power. However, in the MSI-POF shown in FIG. 2, the constituent layers have the same thickness ΔR, while the MSI-POF shown in FIG. ΔN is the same. The embodiment of FIG. 1 is preferable, and with the MSI-POF of this embodiment, it is possible to obtain a band of about 1 GHz · 100 m and several GHz · 100 m.

  Next, FIGS. 3 to 5 show results obtained by computer simulation of the band of the MSI-POF of the present invention. FIG. 3 shows a three-layered structure, FIG. 4 shows a five-layered structure, and FIG. 5 shows a 10-layered MSI-POF band (vertical axis) by changing the G value (horizontal axis) in Equation 1 above. The results are obtained by simulation. In any simulation, the NA (numerical aperture) of the incident system was 0.3, the intensity distribution of incident light was a Gaussian distribution, and the total length of the fiber was 100 m. The solid lines in each graph indicate that the refractive index differences ΔN between adjacent layers are the same at 0.0075, 0.005, 0.0025, and 0.00125, respectively, and the refractive index approximates the G-th power distribution. The band of the MSI-POF model assumed to be arranged was determined by changing the value of G. The refractive index difference ΔN between adjacent cores is a value obtained by dividing the refractive index difference δN between the core center and the core outermost periphery by the number of steps. On the other hand, the broken line represents the band of the MSI-POF model assuming that the layers forming the core portion have the same thickness and the refractive index approximates the G-th power distribution. The results are obtained by changing the values.

  As shown in FIGS. 3 to 5, the maximum values of the bands were about 3 GHz · 100 m, about 5 GHz · 100 m, and about 7 GHz · 100 m in the configurations of the number of steps (number of layers) 3, 5 and 10, respectively. It can also be seen that the band does not change much even if the value of G changes. Furthermore, the band of MSI-POF with a constant thickness ΔR indicated by a broken line is about 1 GHz · 100 m at maximum, whereas the band of MSI-POF with a constant refractive index difference ΔN indicated by a solid line is It can be seen that the frequency can be about several GHz · 100 m, and the bandwidth can be increased up to the band of GI-POF.

In order to produce the core part having the above structure, a method for adjusting the refractive index of each layer constituting the core part to a desired value is required. For example, there are the following two kinds of methods.
First, the first method is a method in which a refractive index of each layer is set to a desired value by using a copolymer of a plurality of types of monomers as an amorphous polymer and adjusting the copolymerization ratio. Specifically, as the amorphous polymer for each layer, copolymers of a plurality of types of monomers and having different copolymerization ratios are used. Since the copolymer has a different refractive index due to a difference in copolymerization ratio, a difference also occurs in the refractive index of the layer formed from the composition containing each copolymer.
The second method uses, as a layer forming material, a composition containing a non-crystalline polymer and a refractive index adjusting agent (sometimes referred to as a dopant) having a refractive index difference of 0.001 or more from the polymer. In this method, the refractive index of each layer is adjusted to a desired value by adjusting the concentration of the dopant. Specifically, as the composition that is a raw material of each layer, a composition containing an amorphous polymer and a dopant and having different dopant concentrations is used. Since the composition has a different refractive index due to a difference in dopant concentration, a difference also occurs in the refractive index of a layer formed from each composition. The amorphous polymer used when this method is used may be a homopolymer or a copolymer. It is preferable that the refractive index adjusting agent also has substantially no C—H bond.

  Examples of amorphous copolymers utilized in the first method include deuterated copolymers such as methyl methacrylate and benzyl methacrylate, methyl methacrylate and trifluoroethyl methacrylate. The refractive index of the copolymer can be increased by increasing the relative proportion of deuterated benzyl methacrylate for the former copolymer and methyl methacrylate for the latter copolymer. By using a plurality of types of copolymers having different relative copolymerization ratios and adjusted relative ratios, a core portion having a desired refractive index distribution structure can be produced.

The dopant used in the second method may be either a low molecular substance or an oligomer. The dopant preferably has a difference in solubility parameter within 7 (cal / cm ³ ) ^1/2 in comparison with the above polymer. Here, the solubility parameter is a characteristic value that is a measure of the mixing property between substances, where the solubility parameter is δ, the molecular cohesive energy of the substance is E, the molecular volume is V, and the formula δ = (E / V) ^Expressed in ^half .

  When the amorphous polymer is selected from (A) deuterated polymers, examples of the dopant include benzyl benzoate (BEN), diphenyl sulfide (DPS), triphenyl phosphate (TPP), and benzyl phthalate. Examples include n-butyl (BBP), diphenyl phthalate (DPP), biphenyl (DP), diphenylmethane (DPM), tricresyl phosphate (TCP), diphenyl sulfoxide (DPSO), sulfurized diphenyl derivatives, and dithian derivatives. The sulfurized diphenyl derivative and dithiane derivative are appropriately selected from the compounds specifically shown below. Among these, BEN, DPS, TPP, DPSO and sulfurized diphenyl derivatives are preferable. In addition, the compound which substituted the hydrogen atom which exists in these compounds with the deuterium atom is preferable.

  On the other hand, when the non-crystalline polymer is selected from (B) fluorinated polymers, examples of the dopant include 1,3-dibromotetrafluorobenzene, 1,4-dibromotetrafluorobenzene, 2-bromotetra Low molecular weight compounds such as fluorobenzotrifluoride, chloropentafluorobenzene, bromopentafluorobenzene, iodopentafluorobenzene, decafluorobenzophenone, perfluoroacetophenone, perfluorobiphenyl, chloroheptafluoronaphthalene, bromoheptafluoronaphthalene and chlorotrifluoro An ethylene oligomer is mentioned. The preferred molecular weight of the chlorotrifluoroethylene oligomer is 500-1500 in number average molecular weight.

The dopant may be added to the amorphous polymer in a molten state, or may be added to a solution of the amorphous polymer. Moreover, you may make it mix in an amorphous polymer by polymerizing a polymerizable monomer in presence of the said dopant. In terms of ease of preparation, it is preferable to polymerize a polymerizable monomer in the presence of the dopant to obtain an amorphous polymer mixed with the dopant.
By increasing the relative proportion of the dopant, the refractive index can be increased. By using a plurality of types of compositions having different content concentrations, in which the relative proportions of the dopants are adjusted, a core portion having a desired refractive index distribution structure can be produced.

As a specific example of a preferable combination of an amorphous polymer and a dopant,
A combination of a deuterated methyl methacrylate homopolymer with deuterated bromobenzene (sometimes referred to as BB-d5); and poly (perfluorobutenyl vinyl ether) and 1,3-dibromotetrafluorobenzene; A combination of
Can be mentioned. Of course, the combination is not limited to the above.

In the plastic optical fiber of the present invention, the standard of the difference in refractive index is that the refractive index n _d for sodium D-line is 0.003 or more, preferably 0.005 or more at a temperature of 20 ° C. More preferably, it is 0.01 or more. Further, the difference in refractive index between adjacent layers varies depending on the number of layers to be formed, etc., but when forming about 5 to 10 layers, the refractive index varies between adjacent layers by about 0.001 to 0.03. It is preferable.

  Furthermore, the MSI-POF of the present invention has a clad portion (sometimes referred to as a clad layer) outside the core portion composed of the plurality of layers. The clad layer contributes to the improvement of the mechanical strength of POF. The refractive index of the cladding layer is preferably lower than the refractive index of the outermost layer of the core part, and specifically, it is preferably at least 3% lower than the refractive index of the outermost layer of the core part. When the refractive index difference between the cladding layer and the outermost layer of the core is within the above range, the numerical aperture can be increased.

  For the formation of the cladding layer, a resin having a refractive index of about 1.3 to 1.44 can be used. Select by paying attention to the refractive index of the resin in the outermost layer of the core. Of course, adhesion with the resin is also an important point in selection. Examples of the resin for the cladding layer include, but are not limited to, vinylidene fluoride and tetrafluoroethylene copolymer, vinylidene fluoride and hexafluoropropene copolymer, and fluoroalkyl methacrylate copolymer. For the formation of the cladding layer, a commercially available product may be used. For example, a commercially available pellet-shaped resin may be melted and used. The thickness of the cladding layer is preferably 5 to 50 μm.

  Next, the manufacturing method of the multi-step index type plastic optical fiber (MSI-POF) of this invention is demonstrated. There are two types of manufacturing methods. (1) A method of forming a preform by successively laminating layers composed of polymers having different refractive indexes, and (2) simultaneously preparing a plurality of polymers or polymer compositions having different refractive indexes, which are produced in advance. There is a method of forming a preform by molding. MSI-POF can be produced by stretching these preforms.

First, the method (1) will be described.
The method (1), that is, a method for sequentially producing each layer, is further divided into two types, a method for sequentially producing layers from the outside to the inside, and a method for sequentially producing them in the opposite direction. The former is preferred because of its simplicity. The former will be described. An outer frame made of a first resin having a refractive index n ₁ is first prepared, and a melt or solution of a second resin having a refractive index n ₂ higher than n ₁ or a second resin can be formed inside the outer frame. A second composition is provided by supplying an adhesive composition (which may be a low-viscosity polymer sol), heating while rotating, melt diffusion or desolvation, or polymerization. This is a method of producing by repeating this operation. Although the operation is somewhat troublesome, there is a possibility that optical performance close to GI may be obtained. The latter uses a dip coating method, a CVD method, a solution coating / drying method, or the like.
In the former method, for example, a cladding layer of a cylindrical tube may be prepared in advance, and each layer of the core portion may be sequentially formed inside the cladding layer, or the core portion may be sequentially formed from the outside toward the inside. Then, finally, only the clad layer may be formed by a dip coating method, a CVD method, a solution coating / drying method, or the like. In the latter method, the clad portion can be finally formed by a dip coating method, a CVD method, a solution coating drying method, or the like.

Next, the method (2), that is, a method for producing an MSI-POF at a time will be described.
There are mainly two types of method (2). One is a method in which a melt of a resin having a plurality of different refractive indexes is supplied to, for example, a multilayer composite spinning die, melt extruded to obtain a preform, and continuously stretched as it is to obtain a fiber. On the other hand, resin pipes designed to have a desired refractive index distribution with a plurality of different refractive indexes are overlapped (however, the central portion is a polymer rod having the highest refractive index) and overlapped. In this method, a pipe is heated and melted and drawn to obtain a fiber. Among these, from the viewpoints of performance and economy, continuous polymerization is performed to obtain a plurality of types of resins having different refractive indexes as they are, and they are supplied as they are in a molten state, for example, to a multilayer composite spinning die and melt extruded. Further, it is preferable to further stretch to obtain the MSI-POF of the present invention. For the production, for example, a multilayer composite spinning die described in FIG. 2 of JP-A-10-133303 can be used.
In addition, as a manufacturing method of a clad part, one layer may be added to the above-mentioned multilayer composite spinning die, and it may be manufactured integrally with the inner multilayer structure, or only the inner multilayer structure. After manufacturing with the multilayer composite spinning die, the clad layer resin may be coated by a crosshead die or a coating method.

  In the present invention, it is preferable that the refractive index of each layer decreases in a second-order distribution from the inner layer to the outer layer of the fiber. In this specification, “secondary distribution” does not mean only a secondary distribution in a strict sense, but is used in a broad sense including various distributions that approximate a secondary distribution, and is stepwise. Of course, distributions based on changes are also included. The distribution in which the refractive index decreases substantially symmetrically with increasing distance from the center, where the vertical axis is the magnitude of the refractive index and the horizontal axis is the distance from the center of the cross section is It shall be included in the “two-dimensional distribution”.

  FIG. 6 schematically shows the relationship between the refractive index of MSI-POF and the distance from the center. The vertical axis is the refractive index, and the horizontal axis is the distance from the center. In general, as shown in FIG. 6A, the refractive index of each layer of MSI-POF is uniform. However, the MSI-POF of the present invention is not limited to this embodiment, and as shown in FIGS. 6B and 6C, the refractive index in each layer is not uniform and may be inclined. For example, in the manufacturing method described above, the concentration of the refractive index adjusting agent is not uniformly contained in the amorphous polymer but polymerized so that the concentration is inclined; A refractive index distribution structure in each layer as shown in FIG. 6 (B) or (C) can be formed by diffusing the refractive index adjusting agent by operation and inclining its concentration.

  The plastic optical fiber of the present invention having the core part and the clad part can be used in various forms as it is. Further, for the purpose of protection and reinforcement, it can be used for various applications in a form having a coating layer on the outside, a form having a fiber layer, and / or a form in which a plurality of fibers are bundled. In the coating process, for example, in the case where a coating is provided on a fiber strand, the fiber strand is passed through opposing dies having holes through which the fiber strand passes, and the coating resin melted between the opposing dies is filled. Can be obtained by moving between the dies. In order to protect the coating layer from stress to the internal fiber when it is flexible, it is desirable that the coating layer is not fused with the fiber. Further, at this time, since the fiber strand is thermally damaged by being in contact with the molten resin, it is desirable to select a resin that can be stretched at a moving speed or low temperature that suppresses damage as much as possible. At this time, the thickness of the coating layer depends on the physical properties of the coating material, the wire drawing speed, and the cooling temperature of the coating layer.

  By coating the strand, a plastic optical fiber cable can be manufactured. At that time, as a form of the coating, a contact type coating in which the interface between the coating material and the plastic optical fiber is in contact with the entire circumference, and a loose having a gap at the interface between the coating material and the plastic optical fiber There is a mold coating. In the loose type coating, for example, when the coating layer is peeled off at the connection portion with the connector, for example, moisture may enter from the gaps at the end face and diffuse in the longitudinal direction. However, in the case of a loose-type coating, since the coating and the strands are not in close contact, most of the damage such as stress and heat applied to the cable can be mitigated by the coating layer, and the damage to the strands can be reduced. Since it can be reduced, it can be preferably used depending on the purpose of use. As for the propagation of moisture, by filling the voids with fluid semi-solid or powdery particles, moisture propagation from the end face can be prevented, and heat and A coating with higher performance can be formed by having functions different from moisture propagation prevention such as improvement of mechanical functions. In order to produce a loose type coating, the void layer can be formed by adjusting the position of the extrusion nipple of the crosshead die and adjusting the pressure reducing device. The thickness of the gap layer can be adjusted by pressurizing / depressurizing the nipple thickness and the gap layer.

Furthermore, you may provide a coating layer (secondary coating layer) further in the outer periphery of a coating layer (primary coating layer) as needed. Flame retardants, UV absorbers, antioxidants, radical scavengers, photosensitizers, lubricants, etc. may be introduced into the secondary coating layer, and as long as moisture permeation resistance is satisfied, Introduction is possible.
In addition, some flame retardants contain halogen-containing resins such as bromine, additives, and phosphorous. However, metal hydroxides are becoming mainstream as flame retardants in terms of safety such as reduction of toxic gases. . Since the metal hydroxide has moisture as crystal water inside, and the attached water cannot be completely removed during the manufacturing process, the flame retardant coating by the metal hydroxide is the moisture-permeable coating of the present invention. It is desirable to provide as an outer layer coating (secondary coating layer) of (primary coating layer).
Moreover, in order to provide a plurality of functions, coatings having various functions may be laminated. For example, in addition to flame retardancy as in the present invention, a barrier layer for suppressing moisture absorption of the wire and a moisture absorbing material for removing moisture, such as a moisture absorbing tape or moisture absorbing gel, are provided in the coating layer or between the coating layers. In addition, a flexible material layer for relaxing stress at the time of flexibility, a cushioning material such as a foam layer, a reinforcing layer for increasing rigidity, and the like can be selected and provided depending on the application. In addition to the resin, if the thermoplastic resin contains a fiber having a high elastic modulus (so-called tensile fiber) and / or a highly rigid metal wire, the mechanical strength of the resulting cable can be reinforced. It is preferable because it is possible.
Examples of the tensile strength fiber include aramid fiber, polyester fiber, and polyamide fiber. Examples of the metal wire include stainless steel wire, zinc alloy wire, copper wire and the like. None of these are limited to those described above. In addition, a metal tube exterior for protection, an aerial support line, and a mechanism for improving workability during wiring can be incorporated.

  In addition, depending on the type of use, the cable shape is a collective cable in which the strands are concentrically arranged, an aspect called a tape core wire arranged in a row, and a collective cable in which they are gathered together with a presser roll or wrap sheath You can choose according to.

  An optical fiber as an optical member of the present invention and a system for transmitting an optical signal using an optical fiber cable include various light emitting elements, light receiving elements, other optical fibers, an optical bus, an optical star coupler, and an optical signal processing device. It consists of an optical connector for connection. Any known technique can be applied as a technique related to them. For example, in addition to the basic and actual plastic optical fiber (issued by NTS), JP-A-10-123350, JP-A-2002-90571, JP-A-2001-290055, etc., optical buses, JP-A-2001-74971, JP-A-2000-329962, JP-A-2001-74966, JP-A-2001-74968, JP-A-2001-318263, The optical branching and coupling device described in Japanese Laid-Open Patent Application No. 2001-31840, the optical star coupler described in Japanese Patent Application Laid-Open No. 2000-241655, Japanese Patent Application Laid-Open No. 2002-62457, Japanese Patent Application Laid-Open No. 2002-101104, Japanese Patent Application Laid-Open No. 2001-2001. No. 305395 and the like, an optical signal transmission device and an optical data bus system, The optical signal processing apparatus described in the gazette of JP-A-2-23011, the optical signal cross-connect system described in the gazette of JP-A-2001-86537, the optical transmission system described in the publication of JP-A-2002-26815, etc. Reference can be made to multifunction systems described in Japanese Laid-Open Patent Publication Nos. 2001-339554 and 2001-339555.

  The present invention will be described more specifically with reference to the following examples. The materials, reagents, ratios, operations, and the like shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the specific examples shown below.

[Example 1]
A multi-step index type plastic optical fiber having a seven-layer structure was manufactured using a multilayer composite spinning die having the same structure as that shown in FIG. In FIG. 7, 1 to 7 are resin receiving ports, and 8 is a guide pipe. Deuterium-substituted methyl methacrylate (MMA-d8) and deuterium-substituted phenyl methacrylate (PheMA-d10) were used as purification raw material monomers. Di-t-butyl peroxide (PBD), n-lauryl mercaptan (n-LM) ) Was used to obtain a polymer. The deuterium substitution rates of both monomers were 99.6% and 99.4%.

The polymerization apparatus consists of a 7-stage complete mixing polymerization reactor, followed by a devolatilizing extruder and a gear pump. From each of the polymer supply series, a polymer in which the copolymerization ratio of the two kinds of monomers was adjusted was obtained and supplied to the supply port of the multilayer composite spinning die. The composition and refractive index of each polymer are as shown in Table 1. The melt flow index of the polymer was in the range of 1-6 g / 10 min at 230 ° C. While maintaining the temperature of the polymer in the process at 200 to 220 ° C., the strand discharged from the outlet of the multi-layer composite spinning die was stretched and stretched to obtain a core portion of a plastic optical fiber having a diameter of 0.50 mm. Further, a cladding resin was coated on the outside of the core portion through a crosshead die. As the cladding resin, PVDF resin having a refractive index of 1.423 was used.
The refractive index of each layer was measured with a transmission interference microscope (manufactured by Mizoji Optical).

The clad resin coating layer had a thickness of 20 μm, and the final optical fiber had a diameter of 0.54 mm. As shown in Table 1 below, the obtained MSI-POF is composed of an amorphous MMA-d8 / PheMA-d10 copolymer in which each layer of the core portion has substantially no CH bond. Each layer had a different refractive index due to the difference in copolymer composition, and the refractive index difference ΔN between adjacent layers was 0.002 and the same. That is, the obtained MSI-POF had a refractive index distribution shown in FIG.
Next, the produced optical fiber was coated with black polyethylene (thickness 0.8 mm) to obtain a cable, and the transmission loss was measured. As a result, it was 90 dB / km at 650 nm and 170 dB / km at 850 nm.
Next, a bending loss test was performed on the coated fiber. A bending test was carried out by the experimental method described in JP-A-7-244220. The experimental conditions were a mandrel diameter of 60 mm, and the fiber was wound around the mandrel once every 90 degrees to measure the loss. The maximum increase in loss was 0.1 dB. The transmission band was 2.1 GHz · 100 m.

[Example 2]
MSI-POF was produced in the same manner as in Example 1 except that the copolymer composition ratio of the copolymer in each layer of the core portion was changed to the copolymer composition ratio shown in Table 2.
The thickness of the resulting POF cladding layer was 20 μm, and the final optical fiber diameter was 0.54 mm. As shown in Table 2 below, the obtained MSI-POF is composed of an amorphous MMA-d8 / PheMA-d10 copolymer in which each layer of the core part has substantially no CH bond, Each layer had a different refractive index due to the difference in copolymer composition, and the refractive index difference between adjacent layers was not the same. However, the thicknesses ΔR of the constituent layers were the same. That is, the obtained MSI-POF had a refractive index distribution shown in FIG.
This optical fiber was covered with black polyethylene (thickness 0.8 mm) to obtain a cable, and the transmission loss was measured. As a result, it was 92 dB / km at 650 nm and 3800 dB / km at 850 nm. Next, as a result of conducting a bending loss test on the coated fiber by the same method as in Example 1, the maximum increase in loss was 0.1 dB. The transmission band was 0.5 GHz · 100 m.

[Example 3]
As a raw material of each layer of the core part, all-deuterated polymethyl methacrylate (deuterated substitution rate 99.6%) PMMA-d8 and the refractive index adjuster shown below with the contents shown in Table 3 are contained. A MSI-POF having a 7-layer structure was produced using a multilayer composite spinning die in the same manner as in Example 1 except that the composition was used.

The thickness of the resulting POF cladding layer was 20 μm, and the final optical fiber diameter was 0.54 mm. As shown in Table 3 below, the obtained MSI-POF is composed of a composition in which each layer of the core part contains amorphous PMMA-d8 which has substantially no CH bond, The refractive index was different depending on the difference in the content of the refractive index adjusting agent contained in the composition, and the refractive index difference ΔN between adjacent layers was 0.002 and the same. That is, the obtained MSI-POF had a refractive index distribution shown in FIG.
This optical fiber was covered with black polyethylene (thickness 0.8 mm) to obtain a cable, and the transmission loss was measured. As a result, it was 78 dB / km at 650 nm and 90 dB / km at 850 nm. Next, as a result of performing a bending loss test on the coated fiber in the same manner as in Example 1, the maximum increase in loss was 0.1 dB. The transmission band was found to be 2.2 GHz · 100 m.

Furthermore, poly (perfluorobutenyl vinyl ether) (refractive index 1.34) as a core polymer, 1,3-dibromotetrafluorobenzene (refractive index 1.52) as a dopant, and Teflon AF1600 (registered) as a cladding polymer. As a result of performing the same test as in Example 2 using the trademark, the refractive index of 1.3), similarly good transmission performance results were obtained.
A coated fiber was prepared in the same manner as in Example 1 except that poly t-butyl methacrylate (refractive index: 1.46) was used as the resin for the cladding layer. Since the outermost layer of the core portion of this fiber is made of PMMA and has a refractive index of 1.492, the difference in refractive index between the outermost layer of the core portion and the cladding layer was less than 3%. When the bending loss test was performed in the same manner as in Example 1, the maximum value of the increase in loss was 1.0 dB, and it was found that the mechanical characteristics were inferior to those in Example 1.

It is the schematic which shows the basic refractive index distribution characteristic of the core part of an example of the multistep index type plastic optical fiber of this invention, and the cross-sectional shape of the optical fiber. It is the schematic which shows the basic refractive index distribution characteristic of the core part of an example of a multistep index type plastic optical fiber, and the cross-sectional shape of the optical fiber. It is a graph which shows the result of having calculated | required the zone | band of the multistep index type plastic optical fiber of this invention by the computer simulation about the case where the number of steps of a core refractive index is 3. FIG. It is a graph which shows the result of having calculated | required the zone | band of the multistep index type plastic optical fiber by this invention by computer simulation about the case where the number of steps of a core refractive index is five. It is a graph which shows the result of having calculated | required the zone | band of the multistep index type plastic optical fiber by this invention by the computer simulation about the case where the number of steps of a core refractive index is ten. It is the figure which showed partially the relationship between the refractive index of a core part, and the distance from a center partially about several aspects of the multistep index type plastic optical fiber of this invention. In an Example, it is a cross-sectional schematic diagram of the multilayer composite spinning die used for preparation of a core part.

Explanation of symbols

1-7 Resin receiving port 8 Guide pipe

Claims (4)

A multi-step index type plastic optical fiber having a core part composed of three or more layers arranged concentrically and a cladding part on the outer periphery thereof, each of the three or more layers being substantially C—H coupled. A multi-step index type plastic optical fiber comprising a non-crystalline polymer composition having no core and having the three or more layers disposed so that the refractive index of the core portion decreases from the center toward the outer periphery. The multi-step index plastic according to claim 1, wherein the refractive index difference between adjacent layers in the core part is substantially the same, and the refractive index of the core part approximates a G-th power distribution. Optical fiber. A multi-step index type plastic optical fiber having a core part composed of two or more layers arranged concentrically and a cladding part on the outer periphery thereof, wherein each of the two or more layers is substantially C—H bond. Each layer is arranged such that the refractive index of the core portion decreases from the center toward the outer periphery, and the refractive index of the cladding portion is the highest in the core portion. Multi-step index type plastic optical fiber that is 3% or more lower than the refractive index of the outer layer The multi-step index type plastic optical fiber according to any one of claims 1 to 3, wherein the amorphous polymer having substantially no CH bond is a deuterated polymer or a fluorinated polymer.

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