JPH09222526A - Wide-band plastic clad optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wide-band PCF(plastic clad optical fiber) which is a plastic clad optical fiber provided with a core consisting of quartz and clads consisting of polymers disposed in tight contact with the outer periphery of this core, is made wider in the band, suppresses the disadvantages (connection loss by a simple crimping connector, bending loss and further the degradation in the light transmission loss according to a temp. change) increasing accordingly and is adequate for an ATMA-LAN and high-speed Ethernet. SOLUTION: The clads have the two-layered structures consisting of the different polymers. The refractive index (nc0 ) of the core, the refractive index (nc L1 ) of the first clad disposed in tight contact with the outer periphery of the core and the refractive index (nc L2 ) of the second clad disposed in tight contact with the outer periphery of the first clad simultaneously satisfy 0.21<=(nco <2> -nc L1 <2> )<1/2> <0.30 and nc L2 <nc L1 . More particularly, the first clad and second clad are preferably of the specific values in Shore hardness, coefft. of thermal expansion, Young's modulus, etc. The outer periphery of the clads is preferably provided with a stress relieving layer and coating layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an LA for a high-speed and large-capacity data link in a medium-range or short-range range.
The present invention relates to a broadband plastic clad optical fiber suitable for constructing an N (local area network).

[0002]

2. Description of the Related Art A step index type plastic clad optical fiber (hereinafter referred to as PCF) in which a core is made of quartz and a sheath (cladding) is made of plastic is relatively inexpensive and compared with a plastic optical fiber. It is used as a medium / short-distance transmission optical fiber or light guide because of its excellent translucency, good coupling with light receiving and emitting elements, and excellent handling.

For example, a PCF having a core made of pure quartz and a clad made of an ultraviolet-curable fluororesin described in Japanese Patent Application Laid-Open No. 5-271350 is used for communication in equipment, between equipment, mobile communication, and building communication. Is possible. Further, in this PCF, a fluorine-based resin having high hardness is used as a clad material, and a crimp connector can be used, so that the PCF is excellent in on-site workability including connector connection.

[0004]

However, these conventional PCFs are excellent in handling, workability, simple connector connection (crimping), low cost, and coupling, but have a high numerical aperture (NA). Since the transmission band is high, such as 0.37 to 0.40, the transmission band is narrow, and as a result, there is a problem that the transmission band cannot be sufficiently applied to a wide band information transmission system such as ATM-LAN or high-speed Ethernet.

[0005] In addition, for a high-speed transmission, conventionally known silica-based graded-index and single-mode optical fibers have a high transmission band, but processing and connector connection work are complicated. In addition, there is a problem that the cost is not easily reduced due to the complicated coating configuration.

[0006] Therefore, in an inexpensive PCF which is easy to process and connect a connector, and easy to design and coat a base material, it is possible to achieve a wider band and to increase the demerits associated therewith. It is a main object of the present invention to provide a broadband PCF capable of suppressing connection loss, bending loss, and deterioration of light transmission loss due to temperature change.

[0007]

In order to achieve this object, a PCF of the present invention is a plastic clad optical fiber having a core made of quartz and a clad made of a polymer provided in close contact with the outer periphery of the core. Wherein the clad has a two-layer structure made of different polymers, and has a refractive index (n _CO ) of a core, a refractive index (n _CL1 ) of a first clad provided in close contact with the outer periphery of the core, and Refractive index (n _CL2 ) of second clad provided on outer periphery of first clad
Is 0.21 ≦ (n _CO ² −n _CL1 ² ) ^1/2 <0.30,
And n _CL2 <n _CL1 is satisfied at the same time.

The first cladding has a Shore hardness of D60 or more and a linear expansion coefficient of 1.0 × 10 ^{−4 to} 2.0 × 10 at room temperature.
UV cured fluorine-based having ^-4 consist (meth) acrylate resin, and a second cladding Shore hardness D
60 or more and a coefficient of linear expansion at normal temperature of 1.0 × 10 ⁻⁴ or more
It is preferred to be made of an ultraviolet-cured fluorine (meth) acrylate resin having 2.3 × 10 ⁻⁴ .

A polymer forming the first cladding; and
The Young's modulus of each of the polymers constituting the second cladding at 23 ° C. is 30 to 65 kg / mm ² , and 15 to 60 kg / mm ² .
It is preferably kg / mm ² .

Further, the thickness (D1) of the first clad and the thickness (D2) of the second clad are 10 μm ≦ D1 +
D2 ≦ 20 μm, 5 μm ≦ D1 and 5 μm ≦ D2
Is preferably satisfied at the same time.

Further, the second clad is coated with an ultraviolet-curable composition which does not substantially contain a polymer produced by polymerization,
It is preferably a layer formed by UV-curing, and further, the UV-curing composition for the first clad applied to the glass core is UV-cured to a curing degree of 50 to 90%, and then the UV-curing for the second clad. It is preferable to apply the functional composition and cure the composition with ultraviolet rays.

Furthermore, it is preferable that a stress buffer layer made of an energy-hardened polymer is provided in close contact with the outer periphery of the clad, and a coating layer is further provided on the outer periphery of the stress buffer layer. For the layer, it is desirable to use an ultraviolet curable resin having a 90 ° peel force of 45 g / cm or less.

Further, the outer diameter of the second cladding (DCL2
), The outer diameter (DS) of the stress buffer layer, and the outer diameter (DB) of the coating layer are 0.3≤ (DS-DCL2) / (DB
It is desirable to satisfy −DCL2) ≦ 0.7.

Plastic clad optical fiber (PC
In order to realize broadband in F), the numerical aperture of the optical fiber ^{_{(NA = n CO 2 -n CL1}} 2) it is necessary to be lowered, therefore, the present invention, the refractive index of the first cladding ( n _CL1 ) and the refractive index (n _CO ) of the core are 0.
21 ≦ (n _CO ² −n _CL1 ² ) ^1/2 <0.30.

That is, in order to use as an optical fiber in a wide band information transmission system, the band in the transmission length of 100 to 200 m must be at least 156 Mbps, which is a conventional step index type PCF.
Then, this band level cannot be satisfied. But,
Bandwidth levels of at least 156 Mbps (100-200 m) can be achieved by lowering the numerical aperture (NA) to said level.

To this end, for example, when the refractive index of the quartz core is 1.458, the refractive index of the clad is 1.427 to.
A polymer having a higher refractive index than that of the conventional PCF may be used for the clad so that the cladding has a thickness of about 1.443.

However, the light propagating in the core of the low numerical aperture step index type optical fiber is easily converted into a radiation mode when the optical fiber is bent. Therefore, when the numerical aperture (NA) of the PCF is reduced as described above, the bending The problem of increased loss arises, which is a major limitation for practical use. Therefore, in the PCF in which the clad is composed of only one layer, the bending loss value (incident NA) practically allowed by the conventional PCF (high numerical aperture of 0.37 to 0.40).
Using an LED light source of 0.30, a level equivalent to the level of the amount of light decrease from the initial amount of light generated when light is incident on a 3 m long optical fiber and wound around a 5 mmR mandrel 15 times (0.35 dB). In order to maintain
Even if the numerical aperture (NA) of CF was reduced, the limit was 0.36 or more. That is, the bending characteristic of such a PCF is P
It is affected not only by the refractive index of the cladding that determines the numerical aperture (NA) of CF, but also by the physical properties of the polymer used for the cladding and the variation in the coating state in the longitudinal direction.
If the numerical aperture (NA) is less than 0.36, in addition to lowering the numerical aperture, their effects cannot be ignored, and the stable bending properties required for practical use cannot be sufficiently satisfied. Therefore, to obtain stable bending characteristics, P
Even if the numerical aperture (NA) of CF was reduced, the limit was 0.36 or more.

However, on the outer periphery of the first cladding, n
_If the second clad satisfying the refractive index of _CL2 <n _CL1 is provided, the numerical aperture of the first clad is 0.21 ≦ NA <0.3.
Bending loss can be suppressed even when the value is considerably reduced to 0. This is considered to be because when the optical fiber is bent, the radiation mode once generated at the interface between the core and the first cladding can be totally reflected again at the interface between the first cladding and the second cladding. . That is, when n _CL2 ≧ n _CL1 , the light cannot be totally reflected and the emitted light is radiated out of the optical fiber and is lost. Furthermore, (n _CO ² −n _CL2 ² ) ^1/2 ≧
Be a ^{_{[(n CO 2 -n CL 1}} 2) 1/2 +0.03], preferred for the total reflection at the interface between the first and second cladding. Further, n _CL2 / n _CL1 is preferably 0.95 or more at the lowest.

Similarly, widening the band of the PCF by reducing the numerical aperture (NA) of the PCF has a problem of increasing the caulking loss when the crimping connector is attached by caulking the caulking member on the outer periphery of the cladding. It is also required for practical use to suppress the connector connection loss to the same level as the conventional PCF (high numerical aperture of 0.37 to 0.40) (0.5 dB or less). However, in the case of a PCF comprising only one clad, a caulking loss value (incident NA) of 0.5 dB or less, which is comparable to that of a conventional PCF, regardless of the composition and physical properties of the clad, variations in its longitudinal direction, and the type of crimp connector. Is 0.20, and the numerical aperture (NA) of the PCF is at least 0.3 in order to maintain the full-mode excitation condition).
6 or more was the limit. That is, if it is less than 0.36, the influence of the difference in the composition and physical properties of the clad and the variation in the longitudinal direction cannot be ignored, and it is difficult to obtain a stable caulking characteristic, so that it cannot be put to practical use.

However, if the second clad having a refractive index within a specific range is provided to form a double clad, the numerical aperture of the first clad may be 0.21 ≦ NA <0.30 to reduce the caulking loss. Can be done.

Providing the second cladding having a refractive index smaller than that of the first cladding is very effective not only for reducing bending loss and caulking loss but also for broadening the bandwidth of the PCF. is there.

That is, if the second clad having a refractive index within a specific range is provided, the leaked light leaked from the core in the low order mode is transmitted through the first clad and then the first clad and the second clad. Is reflected at the interface of. On the other hand, in the case of the higher-order mode, the light leaked through the first clad and reaching the second clad is attenuated by a large loss with respect to the light of the second clad, and the light reflected at the outer peripheral interface of the second clad is Reflection at the interface between the first clad and the second clad adds to the attenuation. Therefore, the conventional PCF
Transmission loss in the lower-order mode can be reduced, and the filter characteristics in the higher-order mode can be improved, and as a result, the broadband transmission can be made longer. is there.

The polymer forming the first clad and the second clad of the broadband plastic-clad optical fiber of the present invention has a hardness after hardening according to the Shore hardness D method (ASTM-D2).
240) and preferably has a high hardness of 60 or more.

When the optical fiber side surface is directly caulked via the connector ferrule to attach the crimp connector, the cladding polymer preferably has a relatively low hardness so as not to cause breakage of the optical fiber or fatigue breakage due to cracks. However, when the Shore hardness D is about 50 to 55 or less, the caulking fixing force between the optical fiber and the ferrule cannot be sufficiently increased, and the probability that the cut surface of the quartz core can be mirror-finished when the optical fiber is cut decreases.

On the other hand, when a polymer having a Shore hardness D of 60 or more, preferably D60 to 85, is used, the caulking stress can be sufficiently received by the polymer clad portion, and the polymer can be firmly fixed. Moreover, with such a high hardness, there is no breakage of the optical fiber or fatigue breakage,
Furthermore, when cutting the optical fiber, there is an advantage that the shock propagation of the cutting blade pressed against the optical fiber reaches the core and the quartz core can be cut with a mirror surface. Can be made very smooth and can be connected without a polishing step.

The polymer used for the first clad of the optical fiber of the present invention has a linear expansion coefficient of 1.0 × 10
^{-4 to} 2.0 x 10 ^-4 is preferred, and the second
The polymer used for the cladding has a linear expansion coefficient of 1.
It is preferably 0 × 10 ^{−4 to} 2.3 × 10 ⁻⁴ .
When it is less than 1.0 × 10 ⁻⁴ , the polymer is too brittle, so that even if the adhesion between the core and the clad is good, the clad is easily peeled off by mechanical stimulation such as thermal shock or bending.

On the contrary, when the linear expansion coefficient of the polymer of the first cladding exceeds 2.0 × 10 ^-4 , dn _CL / dT (temperature coefficient of refractive index of the cladding) is proportional to dρ / dT (linear expansion coefficient). Therefore, the refractive index of the cladding is increased in the low temperature region, and the NA of the optical fiber is greatly reduced. As a result, the light transmission loss at the low temperature is likely to be extremely large. Also, the second
When the coefficient of linear expansion of the polymer of the clad exceeds 2.3 × 10 ⁻⁴ , the microbend loss tends to increase due to the polymer shrinkage at a low temperature, and the light transmission loss at a low temperature tends to increase.

Accordingly, a broadband PCF having a low numerical aperture (NA) and a two-layered polymer clad structure as described above.
In P, P satisfying both mechanical properties and low-temperature properties
In order to obtain CF, the linear expansion coefficient of the first clad is 1.
The coefficient of linear expansion of the second cladding is preferably set to 0 × 10 ^{−4 to} 2.0 × 10 ⁻⁴ and 1.0 × 10 ^{−4 to} 2.3 × 10 ⁻⁴ .

Each of the polymer of the first clad and the polymer of the second clad has a Young's modulus (23 ° C.) of 3
It is desirably 0 to 65 kg / mm ² and 15 to 60 kg / mm ² . UV-cured fluorine (meth) acrylate resins commonly used for cladding, etc.
As the hardness increases, the Young's modulus also tends to increase, but resins with a higher Young's modulus than the above range are less likely to stretch,
Chipping easily occurs when the optical fiber is cut, which is a factor in an increase in optical fiber connection loss. Therefore, as described above, it is preferable that the Young's modulus is low even with high hardness in order to improve the caulking characteristics. In order to obtain an optical fiber having good overall connection characteristics, the level of the Young's modulus is preferably This is preferable, and as a result, connection without a polishing step due to mirror surface breakage of the quartz core is also possible. If the Young's modulus is lower than the above range, the probability that the cut end face can be mirror-finished at the time of cutting the optical fiber is low even if the hardness is high.

By satisfying the values of the Shore hardness, the coefficient of linear expansion and the Young's modulus described above, the double band clad plastic clad optical fiber having a wide band should have good crimping characteristics, caulking characteristics, mechanical characteristics and low temperature characteristics. Is possible.

The first clad and the second clad formed on the surface of the quartz core are made of a fluorine-based (meth) acrylate-based resin cured by ultraviolet rays because the refractive index and the like can be easily controlled to desired values. Preferably, in this case,
It is formed by applying or impregnating an ultraviolet-curable fluorine-based (meth) acrylate-based composition on the surface of a quartz core, and then irradiating ultraviolet rays to polymerize and cure the composition.

The thickness of the cladding layer according to the present invention is such that the thickness (D1) of the first cladding and the thickness (D2) of the second cladding are 10
It is preferable that μm ≦ D1 + D2 ≦ 20 μm is satisfied, and both the thickness (D1) of the first clad and the thickness (D2) of the second clad are 5 μm or more.

When the thickness of each clad layer is less than 5 μm, it is difficult to keep the degree of eccentricity between the quartz core and each clad within a good range, and when the optical fiber is broken, each clad is chipped or peeled. It is easy to occur and it is difficult to obtain a good mirror surface. Furthermore, if the eccentricity is poor, stress is easily applied non-uniformly when the crimping connector is caulked and attached, and the caulking loss tends to be worse.

If the sum of the thickness (D 1) of the first clad and the thickness (D 2) of the second clad is less than 10 μm, the crimping force when the crimping connector is crimped cannot be sufficiently received. Since the optical fiber is broken or fatigued, it is difficult to obtain a sufficient fixing force. On the other hand, if the sum of the thickness (D1) of the first cladding and the thickness (D2) of the second cladding exceeds 20 μm, when left at low temperature, the shrinkage of the cladding causes an increase in microbend loss of the quartz core. Easy to occur.

[0035]

BEST MODE FOR CARRYING OUT THE INVENTION Quartz forming the core of the optical fiber of the present invention is typified by pure quartz, and is a multi-component type in which a doping agent is added to this or an alkali metal is contained. May be.

In the present invention, the polymer constituting the first clad or the second clad is selected from the group consisting of UV-curable polymers because of the work efficiency such as ease of coating and the fact that the curing speed is high and suitable for high-speed production of fibers. It is preferably a mold resin. Further, from the viewpoint of easily controlling the refractive index or the like to a desired value, it is more preferable to be constituted by a fluorine-based (meth) acrylate-based resin cured by ultraviolet rays. As the UV-cured fluorine (meth) acrylate resin suitably used in this case, for example, US Pat.
No. 09, No. 09, by applying the technology of the polymer precursor composition for cladding, a main monomer of a fluorinated alkyl group-containing fluorine (meth) acrylate and an alkyl group-containing (meth) acrylate monofunctional monomer And polymers having desired physical properties by optimizing a combination with a polyfunctional monomer and a mixing ratio thereof.

The following examples can be used as monomers for forming these polymers. As the main monomer of a fluorinated alkyl group-containing fluorinated (meth) acrylate, CH ₂ ═CHCOOCH ₂ CF ₃ CH ₂ ═CHCOOCH ₂ CF ₂ CF ₃ CH ₂ ═CHCOOCH ₂ CFHCF ₃ CH ₂ ═C (CH ₃ ) COOCH _{2 CFHCF 3 CH 2 = CHCOOCH 2} CH 2 CF 3 CH 2 = CHCOOCH 2 CF 2 CFHCF 3 CH 2 = CHCOOCH 2 CF (CF 3) CF 3 CH 2 = CHCOOCH (CF 3) 2 CH 2 = C (F) COOCH _{(CF 3) 2 CH 2 =} C (CH 3) COOCH (CF 3) 2 CH 2 = CHCOOCH 2 (CF 2 CF 2) 3 H CH 2 = C (F) COOCH 2 (CF 2 CF 2) 2 H CH ₂ = C (CH ₃ ) COOCH ₂ (CF ₂ CF ₂ ) _{2
H CH 2 = CHCOOCH 2 CF 2} CF 2 CFHCF 3 CH 2 = CHCOOCH 2 CF 2 CF 2 H CH 2 = C (CH 3) COOCH 2 CF 2 CF 2 H CH 2 = C (F) COOCH 2 CF 2 CF 2 _{H CH 2 = CHCOOCH 2 CH 2} C 8 F 17 CH 2 = C (CH 3) COOCH 2 CH 2 C 8 F 17 CH 2 = CHCOOCH 2 CH 2 C 12 F 25 CH 2 = C (CH 3) COOCH 2 CH _{2 C 12 F 25 CH 2 =} CHCOOCH 2 CH 2 C 10 F 21 CH 2 = C (CH 3) COOCH 2 CH 2 C 10 F 21 CH 2 = CHCOOCH 2 CH 2 C 8 F 13 CH 2 = C (CH 3 ) COOCH ₂ CH ₂ C ₆ F ₁₃ CH ₂ ＣＨCHCOOCH ₂ CH ₂ C ₄ F ₉ CH ₂ ＣＦCFCOOCH ₂ CH ₂ C ₆ F ₁₃ CH ₂ ＣＨCHCOOCH ₂ (CH ₂ ) ₆ CF (CF ₃ )
₂ CH ₂ ＣＨCHCOOCH ₂ C ₁₀ F ₂₀ H CH ₂ ＣC (CH ₃ ) COOCH ₂ C ₁₀ F ₂₀ H CH ₂ ＣＨCHCOOCH ₂ C ₁₂ F ₂₄ H CH ₂ C (CH ₃ ) COOCH ₂ C ₁₂ F ₂₄ H CH ₂ ＣＨCHCOOCH ₂ C (OH) HCH ₂ C ₈ F ₁₇ CH ₂ ＣＨCHCOOCH ₂ CH ₂ N (C ₃ H ₇ ) SO _{2
C 8 F 17 CH 2 = CHCOOCH} 2 CH 2 N (C 2 H 5) COC
₇ F ₁₅ CH ₂ ＣＨCHCOO (CH ₂ ) ₂ (CF ₂ ) ₈ CF (C
_{F 3) 2 CH 2 = C} (CH 2 CH 2 C 8 F 17) COOCH 2 CH
₂ C ₈ F _17. These fluorine-based (meth) acrylates may be used as a mixture of two or more compounds having different structures.

As the alkyl group-containing (meth) acrylate monofunctional monomer, CH ₂ ＣＨCHCOOCH ₂ (CH ₂ ) ₆ H CH ₂ ＣC (CH ₃ ) COOCH ₂ (CH ₂ ) ₈ H CH ₂ ＣＨCHCOOCH ₂ (CH ₂ ) ₁₀ H CH ₂ ＣＨCHCOOCH ₂ (CH ₂ ) ₁₂ H.

As the polyfunctional monomer, ethylene glycol di (meth) acrylate diethylene glycol di (meth) acrylate triethylene glycol di (meth) acrylate polyethylene glycol di (meth) acrylate (number average molecular weight 200 to 1000) propylene glycol di (Meth) acrylate dipropylene glycol di (meth) acrylate tripropylene glycol di (meth) acrylate polypropylene glycol di (meth) acrylate (number average molecular weight 200 to 1000) neopentyl glycol di (meth) acrylate 1,3-butanediol di (Meth) acrylate 1,4-butanediol di (meth) acrylate 1,6-hexanediol di (meth) acrylate hydroxypivalate Neopentyl glycol di (meth) acrylate bisphenol A di (meth) acrylate pentaerythritol tri (meth) acrylate dipentaerythritol hexa (meth) acrylate pentaerythritol tetra (meth) acrylate trimethylolpropane tri (meth) acrylate pentaerythritol monohydroxypentane (Meth) acrylate CH ₂ ＣＨCHCOOCH ₂ (C ₂ F ₄ ) ₂ CH ₂ OCO
CH = CH ₂ CH ₂ = CHCOOC ₂ H ₄ (C ₂ F ₄ ) ₃ C ₂ H ₄ O
_{COCH = CH 2 CH 2 = C} (CH 3) COOC 2 H 4 (C 2 F 4) 3 C
_{2 H 4 OCOC (CH 3)} = CH 2 and the like.

Curable Polymer Composition for Clad Polymer Used in the Present Invention (Clad Polymer Precursor Composition)
Is 10 to 2 in terms of surface coating on the quartz core.
It is desirable to have a viscosity of about 000 cps, and particularly 15 to 200 cps is desirable in the case of application at room temperature. The monomer composition for the clad polymer may be coated on the optical fiber core while adjusting the viscosity by heating or cooling.

This curable monomer composition contains, in addition to the above-mentioned fluorine-based alkyl group-containing fluorine-based (meth) acrylate main monomer and alkyl group-containing (meth) acrylate-based polyfunctional monomer, curing conditions and phase. If necessary, various additives may be contained as long as the solubility and the like allow.

For example, an antioxidant such as a hindered phenol type, a light resistance improver, a silane coupling agent for improving the adhesion and bondability with the quartz core, and a defoaming agent for uniform application to the quartz core. Agents, leveling agents, surfactants and the like can be appropriately mixed.

Examples of the coupling agent include silane-based, titanium-based, and zirco-aluminate-based coupling agents such as γ-aminopropyltriethoxysilane, γ-methacryloxypropylmethoxysilane, and γ-acryloxypropylmethyltrimethylsilane. Silanes such as methoxysilane and γ-mercaptopropyltrimethoxysilane are preferred.

Examples of the photopolymerization initiator include benzophenone, acetophenone, benzoin, benzoin ethyl ether, benzoin isobutyl ether, benzyl methyl ketal, azobisisobutyronitrile,
Hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one and the like may be used at a ratio of 0.1 to 5% by weight. These photopolymerization initiators may be used in combination with a photosensitizer such as an amine compound or a phosphorus compound, if necessary.

In particular, a coupling agent such as γ-mercaptopropyltrimethoxysilane is preferably added to the first cladding composition, whereby the adhesion between the core and the clad is improved and the average Weibull break strength is improved. Value 4
It can be as high as 00 kg / mm ² or more, and a PCF having high strength reliability can be obtained. The addition amount is preferably less than 5%, but 0.1 to 3.0.
% Is more preferred.

This clad composition, especially the second clad composition, preferably contains a monomer component as described above and substantially no polymerization product polymer, and the composition is usually It has a viscosity of about 10 to 100 cps. The polymer product refers to an oligomer (dimer or more) or a polymer produced by vinyl polymerization of the above-mentioned monomer component.

When the polymer precursor composition for cladding substantially containing no polymerized polymer is used, application of the composition, ultraviolet curing, application of the composition, and ultraviolet curing are repeated in this order. The adhesion between the clad layers formed when a plurality of clad layers are formed is increased, and the problems of interface peeling and edge chipping during processing can be sufficiently reduced. This effect is particularly effective when a fluorine-containing monomer is used as the cladding.

Further, in order to enhance the effect, after the polymer precursor composition for the first cladding is continuously applied to the surface of the core substrate, when the ultraviolet ray is irradiated with an ultraviolet ray by an ultraviolet ray irradiator, the composition is cured. It is preferable to control the degree of curing to 50 to 90% by controlling the intensity of ultraviolet irradiation, the amount of ultraviolet irradiation, and the flow rate of nitrogen purge gas for promoting curing. That is, it is possible to keep a high residual ratio of the residual monomer component in the first cladding, which is necessary to enhance the adhesiveness with the second cladding that is subsequently formed, and to improve the adhesiveness with the second cladding component. Is more promoted. It is considered that this is because an extremely thin mixed polymer layer is formed at the interface between the first clad and the second clad.

Further, the polymer precursor composition for a clad, which does not substantially contain a polymer product, is effective for improving the transparency and mechanical properties of the clad.

In the optical fiber having the clad thus formed, a coating layer is formed on the outer periphery. The polymer that forms the coating layer is nylon 1 for thermoplastic resin.
For example, a polyamide resin such as 1, 12 or the like, a fluorine resin such as ethylene / tetrafluoroethylene copolymer, or a hard urethane acrylate resin can be used as an ultraviolet curable resin.

When the above-mentioned ultraviolet-cured fluorine-based (meth) acrylate-based resin is used as the clad, the transmission loss may vary greatly due to the temperature change of the use environment. In this case, it is effective to provide a stress buffer layer made of an energy-cured polymer in close contact with the outer periphery of the clad between the clad and the coating layer.

The polymer forming the stress buffer layer may be either thermoplastic or UV-curable, but a soft polymer having a Shore hardness of less than A80 is preferable, and a UV-curable silicone resin or urethane acrylate-based polymer is particularly preferable. Resin or the like is preferable.

Further, the polymer preferably has a 90 ° peeling force of 45 g / cm or less, particularly preferably 25 to 45 g / cm. This is because, when the stress buffer layer is stripped and the crimp connector is attached, if the adhesion between the cladding and the stress buffer layer is too strong, it is difficult to completely remove the stress buffer layer even if it is stripped, and a part of it will adhere to the clad. Since it remains as it is, the workability of fitting the PCF and the connector ferrule is liable to deteriorate. Further, since the strength of the adhesive force greatly affects the light transmission loss, particularly the loss due to a temperature change in the use environment, in order to improve the low-temperature characteristics, a polymer having a low peeling force is used as described above. Is preferred. However, if the adhesion is too weak, P
Since the problem such as the protrusion of the bare fiber portion from the end face of the CF (pistoning) is likely to occur, it is particularly preferable to set the value to at least 25.

The 90 ° peel force of the polymer is a value determined by the following method. A polymer or a curable composition is applied to another component glass so as to have a thickness of 200 μm and solidified, or cured by irradiation with 200 mJ of ultraviolet light to form a film. The film is peeled in a direction of 90 °, and the resistance value (g / cm) at the time of peeling is measured.

In the case where a stress buffer layer is provided, the outer diameter (DS) and the outer diameter (DB) of the coating layer must be 0.3 ≦ 0.3.
It is preferable that (DS-DCL) / (DB-DCL) ≤ 0.7 (cladding outer diameter: DCL, coating layer outer diameter: DB). If it is less than 0.3, it is difficult to sufficiently prevent the shrinkage stress of the coating layer from adversely affecting the bare fiber portion.
If the thickness exceeds, the thickness of the coating layer becomes too thin, and the original function of the coating layer of preventing transmission of lateral pressure and external force to the bare fiber portion becomes insufficient.

The presence of this stress buffer layer is apt to appear even when the coefficient of linear thermal expansion of the polymer between the clad and the coating layer is greatly different, especially when the numerical aperture (NA) is made small, and microbending loss at low temperature or the like. Can be sufficiently suppressed.

Such an optical fiber can be manufactured by a usual method. That is, after the quartz base material for the core material is pre-treated by flame polishing or hydrofluoric acid, it is melted and thinned in a high-frequency heating furnace, an electric resistance carbon furnace, or an oxyhydrogen flame to obtain an optical fiber substrate. Then, the optical fiber substrate is continuously applied to the surface of the optical fiber substrate through a clad coating die that continuously supplies a liquid clad composition, and the solvent is removed if necessary, followed by irradiation with ultraviolet rays. Then, the first clad is formed by a method of polymerizing and curing to form a clad layer, and subsequently,
The second cladding may be formed by the same method. When the third cladding and the stress buffer layer are formed on the outside of the sled, those layers may be formed by the same method after the formation of the second cladding.

The light source for polymerizing and curing the curable composition for cladding of the present invention in an ultraviolet irradiation furnace is, for example, a carbon arc, a xenon lamp, a medium-pressure mercury lamp, an ultra-high-pressure mercury lamp, an electrodeless lamp, a metal halide lamp and the like. Usually, a commercially available light source may be used. From the viewpoint of increasing the efficiency of polymerization, it is preferable to perform the irradiation in an atmosphere of an inert gas such as nitrogen gas. In this way, a clad layer composed of at least the first clad and the second clad is formed on the outer periphery of the core, taken off via a speed-controlled roller, and a stress relaxation layer is formed as necessary,
If necessary, it is wound after being covered with a resin composition having a protective layer function.

[0059]

【Example】

Example 1 After a synthetic quartz preform synthesized by a plasma method was subjected to a flame polishing pretreatment with an oxyhydrogen flame, a 220
It was continuously supplied into a high-purity carbon resistance heating furnace at 0 ° C. and melted and thinned so that the core diameter became 200 μm to obtain an optical fiber substrate. A first clad polymer precursor composition (18 cps) consisting of the following composition A was filtered through a 0.1 μm filter, supplied to a clad coat die, and continuously coated on the surface of the substrate, after which the center wavelength was set to 360 nm. A UV-curable fluoroacrylate resin (refractive index 1.440) that is cured by irradiation with light from a 300 W / inch electrodeless lamp having a curing rate of 75%.
A clad (outside diameter 216 μm) was formed.

Composition A: 2- (perfluorooctyl) ethyl acrylate 30 parts by weight 2,2,3,3-tetrafluoropropyl acrylate 40 parts by weight trimethylolpropane triacrylate 30 parts by weight γ-mercaptopropyltrimethoxysilane 1 part by weight Parts photopolymerization initiator (2-hydroxy-2-methyl-1-phenylpropan-1-one) 0.48 parts by weight

Subsequently, a polymer precursor composition for a second clad (18 cps) having the following composition B is applied and cured by the same method as described above to obtain an ultraviolet-curable fluorine acrylate resin (refractive index: 1.409). A second clad (outside diameter 230 μm) was formed.

Composition B: 1,1,1-trihydroperfluoroundecyl acrylate 65 parts by weight 2,2,3,3-tetrafluoropropyl acrylate 10 parts by weight Trimethylolpropane triacrylate 25 parts by weight Photopolymerization initiator ( Same as above) 0.50 parts by weight

Subsequently, a stress buffer layer (outer diameter: 330 μm) made of a UV-curable urethane acrylate resin (refractive index: 1.438) was formed by the same method, and then ethylene / tetrafluoroethylene copolymer was formed. A polymer layer is melt-coated to form a coating layer (outer diameter 500 μ
m) was formed and wound as an optical fiber.

When the refractive index of the obtained optical fiber was measured, the refractive indexes of the quartz core and the first cladding were 1.458 and 1.440, respectively, and the NA (numerical aperture) was 0.
23. The core-cladding eccentricity is 4.
The non-circularity of the quartz core and the polymer clad was 0.5% and 0.8%, respectively.

The Shore D hardness, Young's modulus (23 ° C.) and linear expansion coefficient of the first cladding are D65 and 4 respectively.
8 kg / mm ² , 1.8 × 10 ⁻⁴ , and the Shore D hardness, Young's modulus (23 ° C.) and linear expansion coefficient of the second cladding are D77, 45 kg / mm ² , 2.0 × 10, respectively.
^-4 . Further, the stress buffer layer has a Shore A hardness of A
The 60,90 ° peel force was 30 g / cm.

The light transmission loss of the obtained optical fiber was 8 wavelengths.
5.6 dB / km at 50 nm, 7.9 at 650 nm
The transmission speed of dB / km and 200 m was 180 Mbps, which was very excellent in optical characteristics.

The crimping loss when the crimp connector was attached was as small as 0.42 dB, which was favorable. Bending loss is 0.28d when wound 10 times around a mandrel with a radius of 5mm.
B was as small as the conventional PCF (numerical aperture of 0.35 to 0.40) and good bending characteristics were obtained. In addition, the low-temperature characteristic is 1.27 dB compared to 25 ° C. at -20 ° C., which is the conventional PCF
And the good low temperature characteristics were obtained.

Furthermore, a CT-2 cutter (SpecTr
an Specialty Optics Compa
When the cross section of the optical fiber (n = 100) cut by ny) was confirmed with a microscope, the ratio of mirror fracture was 99.
%, Which was extremely high, and none of the clads had chipping.

Each physical property value was measured by the following methods.

Bending loss (dB): Light was made to enter a 3 m long optical fiber from a light source under the full mode excitation condition with an incident NA of 0.25, and the amount of transmitted light was measured using a silicon photomal light receiving element. , And the initial amount of light. Next, the sample is wound 10 times around a mandrel having a radius of 5 mm, the transmitted light amount is measured, and the difference from the initial light amount is defined as bending loss.

Caulking loss (dB): 85 of an optical fiber with a sample length of 3 m attached to a connector without adhesion and without caulking
The amount of light transmitted through the 0 nm LED is defined as the initial amount of light. Next, a connector is attached to one end by caulking, the amount of transmitted light at that time is measured, and the difference from the initial amount of light is taken as the ferrule caulking loss.

Low temperature characteristics (dB): From the difference in the amount of transmitted light when an optical fiber having a length of 200 m was measured in the environment of 25 ° C. and 50% RH and then left at a low temperature of −20 ° C. , And a transmission loss at a low temperature of −20 ° C.

[Examples 2 to 6 and Comparative Examples 1 to 3] The wire drawing condition and the first condition were set so that the conditions shown in Tables 1 and 2 were obtained.
An optical fiber was produced in the same manner as in Example 1 except that the types of the clad, the second clad, the stress buffer layer and the coating layer were changed. Various evaluation measurements were also performed according to the method described in Example 1. The results are shown in Tables 1 and 2. In Comparative Example 2, the second clad was not provided.

As can be seen from the results of Tables 1 and 2, the invention of claim 1 provides a high transmission rate,
Moreover, the bending loss and the caulking loss were small, and a highly practical broadband PCF could be obtained.

On the other hand, Comparative Example 1 has large bending loss, Comparative Example 2 has large bending loss and caulking loss, and
In Comparative Example 3, the bending loss, the caulking loss, and the low temperature characteristics were poor, and all were unsuitable for practical use.

In the case of Examples 3 to 6, the clad chipping and peeling, the mirror surface property of the cut end surface, etc.
There were some points that were less than 2.

[0077]

[Table 1]

[0078]

[Table 2]

[0079]

[Table 3]

[0080]

[Table 4]

Example 7 An optical fiber was produced in the same manner as in Example 1 except that the composition of the second cladding polymer precursor composition was changed to the following composition C. Further, measurement and evaluation were performed by the method described in Example 1, and the results are shown in Table 3 in comparison with the results of Example 1.

Composition C: 1,1,1-trihydroperfluoroundecyl acrylate 45.5 parts by weight 2,2,3,3-tetrafluoropropyl acrylate 7.0 parts by weight trimethylolpropane triacrylate 17.5 parts by weight Parts Polymer component obtained by polymerizing the above acrylate component (molecular weight 800 to 1000) 30 parts by weight Photopolymerization initiator (same as above) 0.50 parts by weight

The obtained optical fiber was almost satisfactory in transmission loss and transmission speed, but the bending loss and the caulking loss were slightly inferior, and further, cracking and peeling of the clad were likely to occur and the cut end face had a mirror surface property. Was insufficient.

[0084]

[Table 5]

[0085]

As described above, the transmission speed in 100 to 200 m is 1
It can be a plastic clad optical fiber suitable for ATM-LAN or high-speed Ethernet, which is a high-bandwidth information transmission method of 56 Mbps or more, and has a small bending loss and caulking loss. A broadband PCF having good practical characteristics such as connector connection workability can be obtained.

Further, it is possible to provide the characteristics that the transmission characteristics at a low temperature are good, chipping and peeling at the cut end surface can be prevented, and the cut end surface has excellent mirror surface property.

Claims (10)

[Claims] 1. A plastic clad optical fiber having a core made of quartz and a clad made of a polymer provided in close contact with the outer periphery of the core, wherein the clad has a two-layer structure made of a different polymer, and Refractive index (n _CO ) of the core, the first
The refractive index (n _CL1 ) of the clad and the refractive index (n _CL2 ) of the second clad provided in close contact with the outer periphery of the first clad are 0.21 ≦ (n _CO ² −n _CL1 ² ) ^{1 / 2} <
0.30 and n _CL2 <n _CL1 are satisfied at the same time, a broadband plastic clad optical fiber. 2. The Shore hardness of the first cladding is D
60 or more and the coefficient of linear expansion at room temperature is 1.0 × 10 ^-4
A UV-cured fluorine-based (meth) acrylate-based resin having a viscosity of about 2.0 × 10 ⁻⁴ , and the second
The clad is made of an ultraviolet-cured fluorine-based (meth) acrylate resin having a Shore hardness of D60 or more and a linear expansion coefficient at room temperature of 1.0 × 10 ^{−4 to} 2.3 × 10 ^−4. The broadband plastic clad optical fiber according to claim 1, wherein: 3. The first cladding comprises a polymer having a Young's modulus at 23 ° C. of 30 to 65 kg / mm ² , and the second cladding has a Young's modulus at 23 ° C. of 15 to 65 kg / mm ^2.
Broadband plastic clad optical fiber according to claim 1, characterized in that it consists of 60 kg / mm ² of the polymer. 4. The thickness (D1) of the first cladding and the thickness (D2) of the second cladding are: 10 μm ≦ D1
+ D2 ≦ 20 μm, 5 μm ≦ D1, and 5 μm ≦
2. The broadband plastic clad optical fiber according to claim 1, wherein D2 is simultaneously satisfied. 5. The second clad is a layer formed by applying an ultraviolet curable composition that does not substantially contain a polymer produced by polymerization and curing the composition with ultraviolet light. Broadband plastic clad optical fiber as described. 6. The refractive indices (n _CO , n _CL1 and n _CL2 ) of the core, the first cladding and the second cladding are (n _CO ²
−n _CL2 ² ) ^1/2 ≧ [(n _CO ² −n _CL1 ² ) ^1/2 +0.
03] is satisfied, the broadband plastic clad optical fiber according to claim 1. 7. An ultraviolet curable composition for a first cladding, which is applied to a glass core, is ultraviolet-cured to a curing degree of 50 to 90%, and an ultraviolet-curable composition for a second cladding is applied, and is ultraviolet-cured. 6. The broadband plastic clad optical fiber according to claim 5, which has a clad formed by. 8. A stress buffer layer made of an energy-cured polymer which is in close contact with the outer periphery of the clad, and a coating layer is further provided on the outer periphery of the stress buffer layer. Broadband plastic clad optical fiber as described. 9. The stress buffer layer has a 90 ° peel force of 4
9. The broadband plastic clad optical fiber according to claim 8, which is made of an ultraviolet curable resin having a weight of 5 g / cm or less. 10. The outer diameter of the second cladding (DCL2
), The outer diameter (DS) of the stress buffer layer, and the outer diameter (DB) of the coating layer are 0.3≤ (DS-DCL2) / (DB
9. The broadband plastic clad optical fiber according to claim 8, wherein -DCL2) ≤0.7 is satisfied.