JP2011107217A - Method for manufacturing plastic clad optical fiber core wire, and plastic clad optical fiber core wire - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a plastic clad optical fiber core wire having a bending loss resistance ≤0.1 dB/turn with a small bending radius, and to provide the plastic clad optical fiber core wire. <P>SOLUTION: A soot body containing Ge with silica glass as the principal component is sintered and made transparent to form a core preform, with a core part 2 formed by fusing and line-drawing a ground body for which the outer periphery of the core preform is removed for 2% or more in the diameter ratio by grinding. Then, the core part 2 is covered with plastic having a refractive index lower than that of the core part 2 to form a clad part 3, in the method for manufacturing the plastic clad optical fiber core wire 1. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a plastic clad optical fiber core and a plastic clad optical fiber core, and in particular, is used in a USB cable, an HDMI cable (or cord), a mobile phone, etc. used in general homes and offices. The present invention relates to a method for manufacturing a plastic clad optical fiber and a plastic clad optical fiber.

One type of optical fiber is called a hard polymer clad fiber (hereinafter referred to as HPCF core). This HPCF core wire is formed by covering the outer periphery of a core glass made of quartz glass with a fluorine resin having a refractive index lower than that of the glass as a cladding layer. On this HPCF strand, a resin coating layer made of a fluorine-based thermoplastic resin is extrusion-coated to form an HPCF core.
The HPCF core wire is used in the field of short-distance communication such as FA (Factory Automation) because the coupling efficiency between the pulse light source and the light receiver is high and the connection is easy.

  The HPCF core wire is an optical fiber capable of making the relative refractive index difference between the core and the clad larger than that of the all-glass fiber (for example, Patent Document 1). Specifically, Ge is added to make the refractive index higher than that of pure silica, and the refractive index is made lower than that of pure silica by using a fluororesin for the cladding, thereby increasing the relative refractive index difference between the core and the cladding. is doing.

Japanese Patent Laid-Open No. 11-64665

For example, in an optical composite USB cable, a strict standard multimode fiber that has a bending loss resistance of 0.1 dB / turn or less with a small bending diameter of 4φ (bending radius R = 2 mm) is required.
When the HPCF core wire is bent to a small bending diameter as described above, a macrobend loss occurs, resulting in a decrease in signal strength or a large fluctuation, resulting in a code error and a communication error. Are known. In order to prevent this, it is necessary to reduce the macro bend loss as much as possible.

  An object of the present invention is to solve the above-mentioned problems, and a method for producing a plastic-clad optical fiber having a small bending diameter and a bending loss resistance of 0.1 dB / turn or less, and a plastic-clad optical fiber core Is to provide a line.

The configuration of the present invention is as follows.
(1) A soot body containing silica glass as a main component and containing germanium is sintered and transparentized to form a co-appli foam, and the outer periphery of the co-appli foam is ground and removed by at least 2% in diameter ratio to melt and A method for producing a plastic-clad optical fiber, comprising: drawing a core portion; and coating the core portion with a plastic having a lower refractive index than the core portion to form a clad portion.

(2) A plastic-clad optical fiber core comprising a glass core having a refractive index higher than that of pure silica and a plastic cladding having a refractive index lower than that of pure silica,
A plastic clad optical fiber core, wherein the core is a step index, and the refractive index of the core is a substantially constant value including a portion within 2% of the diameter of the core from the outer periphery of the core. line.

  According to the plastic clad optical fiber manufacturing method and the plastic clad optical fiber core of the present invention, it is possible to obtain a bending loss resistance of 0.1 dB / turn or less with a small bending diameter.

It is a schematic sectional drawing which shows an example of the plastic clad optical fiber core wire which concerns on this invention. It is a correlation diagram of the numerical aperture and bending loss of the plastic clad optical fiber core wire which concerns on this invention. It is a conceptual diagram which shows the refractive index distribution of the core profile before and after the external polishing of the plastic clad optical fiber core wire (SI type) according to the present invention. It is a flow which shows the manufacturing process of the plastic clad optical fiber core wire which concerns on this invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a method for producing a plastic-clad optical fiber (hereinafter referred to as a PCF core) according to the present invention and an embodiment of a plastic-clad optical fiber will be described with reference to the drawings.

  As shown in FIG. 1, the PCF core wire 1 is made of a glass core 2 made of quartz glass and an ultraviolet curable fluororesin such as an ultraviolet curable fluorinated acrylate resin which is a resin having a lower refractive index than the glass core 2. A plastic clad layer 3 surrounding the outer peripheral surface of the formed glass core 2 and a plastic clad optical fiber strand (hereinafter referred to as PCF strand) 4 is provided. A resin coating layer 5 made of a fluorine-based thermoplastic resin such as ethylene-tetrafluoroethylene copolymer (ETFE) is formed on the outer periphery of the cladding layer 3.

  The glass core 2 is made from a preform by the VAD method. The refractive index of the glass core 2 is higher than that of pure silica by adding germanium (Ge). The refractive index distribution of the glass core 2 is a step index (SI) type, and the refractive index (or relative refractive index difference) of the core is constant. It should be noted that the refractive index (or relative refractive index difference) of the portion within 2% of the core diameter from the outer periphery of the core (the outer peripheral portion of the core) is not constant in the normal core (the refractive index decreases toward the outer periphery). However, the plastic clad optical fiber of the present invention has a constant refractive index (or relative refractive index difference) up to that portion (see FIG. 3).

  In order to improve the bending resistance of the glass core 2, it is preferable to use a step index (SI) type fiber having a Ge-added core. Presuming from the numerical aperture (NA) and the tendency of bending loss shown in FIG. 2, a 1.0% Ge-added core (a core added with Ge so that the relative refractive index difference of the core with respect to pure silica is 1.0%) ), The NA value is 0.43, the bending loss is improved to 0.05 dB / turn, and the target of 0.1 dB / turn is achieved. However, in reality, the loss becomes larger than 0.1 dB / turn.

  This is due to the collapse of the core profile during the manufacturing process. That is, when preparing a Ge-added SI core, sooting of Ge-added silica is performed, followed by sintering. In this case, Ge is volatilized particularly in the vicinity of the outer surface of the co-appli foam near the furnace, and the specific refraction is performed. A phenomenon occurs in which the rate difference becomes low. As a result, it is considered that the NA value is effectively lowered by the amount corresponding to the lower relative refractive index difference, and the bending loss resistance deviates from the expected value.

  The PCF core wire 1 of the present invention can make the relative refractive index difference of the co-appli foam uniform by removing the outer circumference of the co-appli foam by peripheral grinding at a diameter ratio of 2% or more, preferably about 5%. . That is, as shown in FIG. 3A, an SI type co-appli foam (outer diameter D1) in which the relative refractive index difference Δ is pure silica level (B level) in the outer peripheral portion and uniform (A level) in the central portion. ), The portion where the refractive index decreased due to the volatilization of Ge (grinding amount t) was removed by peripheral grinding to produce a grinding body (outer diameter D2) as shown in FIG. PCF core wire 1 is created from the body. In FIG. 3, the vertical axis represents the relative refractive index difference Δ, and the horizontal axis represents the glass core diameter D.

  For example, when the outer diameter D1 is 80 mm and the grinding amount t is 1.6 mm (2% of the diameter), a ground body having a ground outer diameter D2 of 76.8 mm is obtained. In particular, it is effective for a thin core (core diameter 50 to 80 μm). As a result, the bending loss becomes 0.04 dB / turn, and the target PCF core wire 1 of 0.1 dB / turn or less can be obtained. A USB cable or an HDMI cable including this PCF core wire in a general home or office, etc. Can be used. As in this example, grinding the outer periphery of the co-appli foam by 2% or more in diameter ratio means that the diameter of the co-appli foam after grinding is 2% or more smaller than the diameter before grinding. Say. The diameter of the co-appli foam (grinding body) after grinding is 98% or less of the diameter of the co-appli foam before grinding.

  The refractive index of the plastic cladding layer 3 has a relative refractive index difference of −3.0% or less with respect to pure silica, and the refractive index of the Ge-added core has a relative refractive index difference of + 0.8% with respect to pure silica. The above is preferable.

  The resin of the plastic clad layer 3 has a low refractive index with respect to pure silica, can be cured with active energy rays such as ultraviolet rays, and has a mechanical strength by curing the resin composition. It is necessary that the resin is a resin that is flexible and provides a cured product having excellent transparency.

Such resins include (a) (meth) acrylate monomers or polymers containing fluorine atoms in the molecule, (b) (meth) acrylate monomers or polymers, (c) core materials and chemicals. It is preferable to use a resin composition comprising a coupling agent that forms a bond and (d) a photopolymerization initiator. A desired refractive index can be obtained by changing the number of fluorine atoms in the molecule of the component (a) or the component, or changing the concentration of the component (a) in the resin composition.
As the (meth) acrylate monomer (a1) containing a fluorine atom in the molecule, a substance represented by the following chemical formula (A) or a compound represented by chemical formulas (B1) to (B3) having two or more unsaturated bonds Substances.

Chemical formula (A)

Chemical formula (B1)

Chemical formula (B2)

Chemical formula (B3)

  As a (meth) acrylate polymer (a2) containing a fluorine atom, for example, it has an ester side chain unsaturated bond as shown by the following chemical formula (C) having a number average molecular weight of 50,000 to 5,000,000 (in terms of styrene). Mention may be made of (meth) acrylate copolymers.

Chemical formula (C)

[Wherein, R1 and R2 each represents hydrogen or a methyl group, Rf represents a fluoroalkyl group, and Rx represents a hydrocarbon group having an unsaturated bond. ]
Examples of the Rx group include a vinyl group, an allyl group, an acrylic group, a methacryl group, and an internal olefin.
The Rf _{group, - (CH 2) a- (} CF 2) b-CF 3
[Wherein, a is 1 or 2, and b is 2-6. ]
Can be illustrated.

Examples of the (meth) acrylate monomer (b) include the following compounds as crosslinkable, that is, those having two or more unsaturated bonds:
1,4-butanediol di (meth) acrylate, ethylene glycol di (meth) acrylate, glycerol dimethacrylate, tetraethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, 1,3-butylene glycol di (meth) Acrylate, neopentyl glycol di (meth) acrylate, triethylene glycol di (meth) acrylate, triglycerol diacrylate, 1,6-hexanediol di (meth) acrylate, tripropylene glycol diacrylate, trimethylolpropane tri (meth) Acrylate, pentaerythritol triacrylate, pentaerythritol tetra (meth) acrylate, ditrimethylolpropane tetraacrylate, dipentaerythritol hexa Acrylate.

Examples of the coupling agent (c) include the following compounds:
Trimethoxyvinylsilane, methacryloxypropyltrimethoxysilane, dimethylethoxyvinylsilane, etc.
Examples of compounds having two or more unsaturated bonds in the molecule include the following compounds:
Diethoxydivinylsilane, dimethoxydivinylsilane, dimethacryloxypropyltrimethoxysilane, etc.

The photopolymerization initiator (d) is preferably a compound that easily generates radicals upon irradiation with ultraviolet light, and includes the following compounds:
Benzophenone, acetophenone, benzyl, benzoin, benzoin methyl ether, benzoin isobutyl ether, benzyl dimethyl ketal, α, α'-azobisisobutyronitrile, benzoyl peroxide, 1-hydroxycyclohexyl phenyl ketone, 2,2-dimethoxy-2 -Phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropan-1-one.

  A preferred embodiment is one in which the resin composition having the above-described configuration is used as a resin liquid, and this resin liquid is applied to the core and further irradiated with ultraviolet rays to produce the clad layer 3. The resin liquid is preferably applied by a die coating method.

  The resin coating layer 5 is formed of a resin composition made of a thermoplastic resin having high heat resistance. Examples of the thermoplastic resin include ethylene-tetrafluoroethylene copolymer (ETFE). Alternatively, an ultraviolet curable resin such as a urethane acrylate resin or a resin obtained by blending an urethane acrylate resin with an epoxy acrylate resin or a polyester acrylate resin may be used.

  Next, a method for manufacturing a PCF core wire will be described.

  As shown in FIG. 4, the so-called co-appli foam is sooted containing Ge containing silica glass as a main component by the VAD method (S10). A soot body containing Ge is dehydrated and sintered and then transparentized to obtain a co-appli foam (S11). The co-appli foam is stretched in a resistance furnace (S12).

  Next, the refractive index of the co-appli foam is inspected by the preform analyzer (PA), and the peripheral grinding amount is set (S13). Then, peripheral grinding and smooth finish polishing of the co-appli foam are performed (S14). A portion of 2% to 20% in diameter ratio is ground from the outer periphery of the co-appli foam. During dehydration and sintering, Ge in the outer peripheral portion of the co-appli foam volatilizes and the relative refractive index difference in that portion becomes lower. However, since this portion is ground, the obtained grinding body is also refracted from the central portion in the outer peripheral portion. The rate (specific refractive index difference) is the same. If a portion having a diameter ratio of 2% is ground from the outer periphery, the portion where Ge is volatilized and the refractive index (specific refractive index difference) is reduced can be sufficiently removed. Moreover, even if it grinds 20% or more, an effect is not changed and it is useless just to grind.

  The outer peripheral grinding uses a centerless grinder that can grind to a constant outer periphery, but in order to improve the stability in the length direction of the optical fiber, it is desirable to use an outer peripheral grinder capable of NC control. In this case, if the refractive index profile is measured with a preform analyzer (PA) in the length direction and the numerical aperture (NA) is constant, the outer diameter changes in the length direction. It is more preferable to calculate the grinding amount in each cross section so that the area of the core portion is constant in the position-refractive index profile diagram.

  Next, the co-appli foam is immersed in hydrofluoric acid (HF) and washed (S15). The co-appli form is connected to the dummy bar (S16). The core is formed by melting and drawing the co-appli foam, and a plastic clad layer having a lower refractive index than the core is coated on the outer periphery with a die (S17). Then, a structural inspection is performed to determine whether the core diameter and the clad diameter are as set (S18). Next, a coating layer that is a thermoplastic resin is formed on the outer periphery of the clad by extrusion molding (S19). Finally, a final inspection of the structure and optical properties is performed (S20).

  As described above, according to the PCF core wire manufacturing method of the present embodiment, the outer periphery of the co-appli foam is removed by peripheral grinding at a diameter ratio of 2% or more so that the relative refractive index difference of the co-appli foam is uniform. Can be. Thereby, even with a small bending diameter of about 2 mm, a bending loss resistance of 0.1 dB / turn or less can be obtained.

  According to the PCF core wire of this embodiment, the refractive index of the core (relative refractive index difference) including the portion within 2% of the diameter ratio from the outer periphery is a substantially constant value, and the bending loss is 0.1 dB / turn or less. realizable. Even if the USB cable or HDMI cable including the PCF core wire is bent to a diameter of 4 mm, the bending loss is sufficiently small, so that it can be used at home or in office with peace of mind.

As examples of the PCF core wire of the present invention, Examples 1 to 3 were grinding preforms in which the outer periphery of a core shape having a core diameter of 200 μm, 50 μm, and 100 μm was shaved by 2% to 5% in diameter ratio. On the other hand, a preform without grinding with a core diameter of 80 μm was used as a comparative example. The bending resistance of each of these co-appli foams at a bending radius of 2 mm was measured.
Note that the numerical aperture of each PCF core wire was 0.43. The numerical aperture changes before and after grinding. Therefore, when grinding, NA = 0.43, and when the co-appli foam is not ground, NA <0.43.

  Table 1 shows the bending loss values of the PCF core wires of Examples 1 to 3 and Comparative Example.

  As shown in Table 1, the increase in bending loss when bending to a small diameter of 2 mm is the diameter ratio of the outer periphery of the co-appli foam in which the relative refractive index difference has decreased due to the volatilization of Ge in Examples 1 to 3. It was removed by 5% peripheral grinding. Thereby, the relative refractive index difference of the co-appli foam can be made uniform, and a practically problematic PCF core wire having a bending loss of 0.1 dB / turn or less can be obtained. On the other hand, in the comparative example, the NA value is effectively reduced by the amount that the relative refractive index difference is reduced due to the volatilization of Ge, and the increase in bending loss is 0.1 dB / turn or more, which is not practical. is assumed.

  Further, when the fracture probability of the obtained PCF core wire was determined, the fracture probability was 1 ppm or less when the core diameter was 100 μm or less, but in Example 1 where the core diameter was larger than 100 μm, the fracture probability was greater than 1 ppm. It was. Therefore, it is preferable to use a PCF core wire having a core diameter of 50 μm or less for applications where the required fracture probability is 1 ppm or less.

  In addition, this invention is not limited to embodiment mentioned above, A deformation | transformation, improvement, etc. are possible suitably. In addition, the material, shape, dimension, numerical value, form, number, arrangement location, and the like of each component in the above-described embodiment are arbitrary and are not limited as long as the present invention can be achieved.

  DESCRIPTION OF SYMBOLS 1 ... PCF core wire, 2 ... Core glass, 3 ... Cladding layer, 4 ... PCF strand, 5 ... Resin coating layer

Claims (2)

  A soot body containing silica glass as a main component and containing germanium is sintered and transparentized to form a co-appli foam, and the ground body removed by grinding the outer periphery of the co-appli foam by a diameter ratio of 2% or more is melted and drawn. A method for producing a plastic-clad optical fiber, comprising: forming a core part, and coating the core part with a plastic having a lower refractive index than the core part. A plastic clad optical fiber comprising a glass core having a higher refractive index than pure silica and a plastic clad having a lower refractive index than pure silica,
A plastic clad optical fiber, wherein the core is a step index, and a refractive index of the core is a substantially constant value including a portion within 2% of a diameter of the core from an outer periphery of the core.

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