JPH0961643A - Wide band plastic clad optical fiber and optical fiber cord with connector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plastic clad optical fiber of a step index type which has excellent handling quality, workability, easy connector connectability (press bondability), inexpensiveness and coupling property and has a transmission band as wide as 10 to 50MHz.km or above. SOLUTION: This wide band plastic clad optical fiber consists of a core consisting of quartz and a clad composed of a polymer disposed in tight contact with the outer periphery of this core. The refractive index (nc1 ) of the clad and the refractive index (nco ) of the core satisfy 0.25<=(nco <2> -nc1 <2> )<1/2> <=0.34. The clad consists of a fluorine (meth)acrylate resin which has Shore hardness of >=D60 and a coefft. of thermal expansion of 1.0×10<-4> to 2.0×10<-4> at ordinary temp. and is cured by UV rays.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a LAN such as 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 (local area network).

[0002]

2. Description of the Related Art A step index type plastic clad optical fiber (hereinafter referred to as PCF) whose core is made of quartz and whose sheath (clad) is made of plastic is relatively inexpensive and has a relatively low cost. An optical fiber for medium / short-distance transmission because it has excellent translucency, good coupling with a light emitting / receiving element (high numerical aperture of 0.37 to 0.40), and excellent handleability. It is also used as a light guide.

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 resin with high hardness is used as a clad material, which enables the use of a crimp connector,
Excellent workability on site including connector connection.

[0004]

However, although these conventional PCFs are excellent in handleability, workability, simple connector connection (crimping), low cost and bondability, they have a numerical aperture (NA) of 0. Since it is as high as 37 to 0.40, the transmission band is narrow, and as a result, there is a problem that it cannot be sufficiently applied to the broadband information transmission system such as ATM-LAN and high-speed Ethernet.

Further, conventionally known silica-based graded index or single mode type optical fibers for high-speed transmission are unsatisfactory in terms of workability and connector connection work, and cost. .

Therefore, it is an object of the present invention to provide a broadband PCF having long-term reliability in the connector portion accompanying the crimping connector mounting and processing.

[0007]

In order to achieve this object, the PCF of the present invention is a plastic clad optical fiber comprising a core made of quartz and a clad made of a polymer closely attached to the outer periphery of the core. And the refractive index of the clad (n _cl ) and the refractive index of the core (n _co ).
And 0.25 ≦ (n _co ² −n _cl ² ) ^1/2 ≦ 0.34, and the cladding has a Shore hardness of D60 or more and a linear expansion coefficient of 1.0 × 10 at room temperature. ^{-4 to} 2.0
It is characterized in that it is made of an ultraviolet-cured fluorine-based (meth) acrylate resin having × 10 ⁻⁴ .

Further, the clad has a weight of 30 to 45 kg.
/ Mm ² Young's modulus is preferable, and the thickness of the clad is preferably 5 to 30 μm.

The optical fiber of the present invention is 400 k
It has a Weibull average breaking strength of g / mm ² or more.

The optical fiber cord with a connector of the present invention is an optical fiber cord having a polymer coating layer on the outer periphery of the PCF of the present invention, and the polymer coating layer is peeled off at one or both ends thereof. It is characterized by consisting of a connector attached by crimping, the pulling force of the optical fiber from the ferrule inside the connector is 2 kg or more, and the pulling force of 1.0 kg × 1 minute causes the gap between the core and the clad to be pulled out. Pistoning amount is 10μ
m or less.

Plastic clad optical fiber (PC
In order to realize the wide band of F), the refractive index (n _cl ) of the cladding and the refractive index (n _co ) of the core are 0.25 ≦ (n _co ² −n _cl ² ) ^1/2 ( It is necessary to reduce the numerical aperture (NA) of the optical fiber to a level that satisfies n _cl ) ≦ 0.34. That is, in order to use as an optical fiber in a broadband information transmission system, at least the band must be 20 to 50 MHz · km, and the conventional step index type PCF cannot satisfy this band level. If the numerical aperture (NA) is lowered to the above level, at least 20 to 50 MHz · k
The band level of m can be satisfied.

To this end, for example, when the refractive index of the quartz core is 1.458, the refractive index of the cladding is 1.418 to.
A polymer having a relatively high refractive index as compared with the conventional one may be used for the clad so that it becomes 1.436.

Generally, the numerical aperture (N
The lower A) is more preferable, but conversely, the lower the numerical aperture, the larger the increase in light transmission loss when the optical fiber is bent. Therefore, in order to keep the light transmission loss level when the fiber is bent within the allowable range. The numerical aperture (NA) needs to be 0.25 or more. That is, a practical bending loss value (incident NA is 0.2
5. A NA of 0.25 or more is required to keep the bending loss value (measured by injecting light into a 3 m long optical fiber from a light source under full mode excitation conditions) within an allowable range of 0.1 dB or less. is there.

Further, the clad polymer of the broadband plastic clad optical fiber of the present invention is required to have a high hardness of 60 or more by the Shore hardness D method (ASTM-D2240). When the crimping connector is directly crimped to mount the optical fiber, a polymer having a relatively low hardness (for example, Shore hardness D of about 50 to 55 or less) is used as a clad so as not to cause a fracture of the optical fiber or a fatigue fracture due to a crack. However, conversely, it is not possible to sufficiently increase the caulking fixing force between the optical fiber and the ferrule.

However, when a polymer having a high Shore hardness D of 60 or more is used for the clad, the caulking stress can be sufficiently received by the polymer clad portion, so that the polymer clad can be strongly fixed and the optical fiber can be broken. It does not lead to fatigue fracture. Furthermore, when the shore hardness D of the clad polymer is 60 or more, when the optical fiber is cut, the shock propagation of the cutting blade pressed against the optical fiber reaches the core and cuts the quartz core in a mirror-like state. This has the advantage that the optical fiber cross section after cutting the optical fiber can be made very smooth, and connection without the polishing step is possible.

Furthermore, in the optical fiber of the present invention, the coefficient of linear expansion of the cladding polymer is 1.0 × 10 ^{−4 to} 2.0 at room temperature.
It needs to be × 10 ^-4 . If it is less than 1.0 × 10 ⁻⁴ , the polymer is too brittle, so even if the adhesion between the core and the clad is good, the clad is likely to peel off due to mechanical irritation due to thermal shock, bending, etc. is there.
On the other hand, when it exceeds 2.0 × 10 ⁻⁴ , dn _cl / dT (temperature coefficient of refractive index of cladding) is dρ / dT (coefficient of linear expansion).
In the low temperature region, the refractive index of the cladding is large and the NA of the optical fiber is greatly reduced, resulting in an extremely large light transmission loss at low temperatures, which is not suitable.

Therefore, even if the numerical aperture (NA) is set to the above-mentioned low level, the PC satisfies both the mechanical characteristics and the low temperature characteristics.
To obtain F, the coefficient of linear expansion of the clad is 1.0 × 1
It is necessary to set it to 0 ^{−4 to} 2.0 × 10 ⁻⁴ .

The Young's modulus of the clad polymer is preferably 30 to 45 kg / mm ² at 23 ° C. Generally, in a UV-cured fluorine-based (meth) acrylate-based resin used for a clad or the like, the Young's modulus tends to increase as the hardness increases. However, since a resin having a high Young's modulus is difficult to stretch, it is likely to be chipped when the optical fiber is cut, which is one of the causes of deterioration of loss when connecting the optical fiber. Therefore, as described above, it is preferable that the Young's modulus is low even if the hardness is high in order to improve the crimping property. In order to obtain an optical fiber with good connection properties, the Young's modulus (23 ° C.) is 30 to 45 kg / The level of mm ² is preferable.

Furthermore, the clad formed by coating or impregnating the surface of the quartz core and then polymerizing and curing by irradiating with ultraviolet rays has a fluorine-based (from the viewpoint that it is easy to control the refractive index etc. to a desired value). A (meth) acrylate resin may be used.

The thickness of the clad layer is preferably 5 to 30 μm. If the clad thickness is less than 5 μm, the light propagating in the quartz core is likely to leak out of the clad, so that the light transmitting performance is likely to be insufficient. Conversely 3
If it exceeds 0 μm, problems such as an increase in microbend loss of the quartz core due to shrinkage of the clad when left at a low temperature are likely to occur.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a UV-curable fluorine-based (meth) polymer used as a polymer forming a clad.
Examples of acrylate resins include, for example, US Pat. No. 45.
By applying the technique of the composition for clad polymer described in the specification of No. 11209, a main monomer of a fluorinated (meth) acrylate containing a fluorinated alkyl group and a (meth) acrylate-based multifunctional monomer containing an alkyl group are used. A polymer having desired physical properties by optimizing the combination and the mixing ratio thereof can be mentioned. As those monomers, those exemplified below can be used.

Examples of the fluorine-containing (meth) acrylate containing a fluorinated alkyl group include 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 = CHCOOCH 2 (CH} 2) 6 H CH 2 = C (CH 3) COOCH 2 (CH 2) 8 H CH 2 = CHCOOCH 2 (CH 2) 10 H CH 2 = CHCOOCH 2 (CH 2) 12 H _{CH 2 = CHCOOCH 2 C (OH} ) HCH 2 C 8 F 17 CH 2 = CHCOOCH 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 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 ester Neopentyl glycol di (meth) acrylate Bisphenol A di (meth) acrylate pentaerythritol tri (meth) acrylate dipentaerythritol hexa (meth) acrylate pentaerythritol tetra (meth) acrylate trimethylolpropane di (meth) acrylate pentaerythritol monohydroxypenta (meth) acrylate _{CH 2 = CHCOOCH 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.

The monomer composition for the clad polymer used in the present invention is 1 in terms of surface coating on the quartz core.
It is preferably about 0 to 2000 cps, and particularly preferably 15 to 200 cps when applied at room temperature. Further, the monomer composition may be coated on the quartz core while the viscosity is adjusted by heating and cooling.

In addition to the above-mentioned main monomer of fluorine-containing (meth) acrylate containing a fluorine alkyl group and polyfunctional monomer containing a (meth) acrylate containing an alkyl group, the monomer composition is characterized in terms of curing conditions and compatibility. If necessary, various additives may be contained as long as they are within the range allowed by.

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

Particularly, it is desirable to add γ-mercaptotrimethoxysilane. This is because the Shore hardness of the clad can be D60 or more and the adhesion between the core and the clad can be improved, so that the Weibull average breaking strength value can be increased to 400 kg / mm ² or more. This is because high strength reliability can be obtained.

This Weibull breaking strength (average value of Weibull breaking strength) is a value obtained by the following method. 9m
The tensile strength (kg) of a long optical fiber sample is n =
The tensile strength at 100 is measured, and the tensile strength is divided by the core cross-sectional area to obtain the tensile strength at break (kg / mm ² ). The Weibull distribution of this tensile rupture strength is taken, and the cumulative rupture probability at 63.2% is calculated from this Weibull distribution to obtain the Weibull average rupture strength (kg / mm ² ).

Further, it is desirable that the tension when the PCF of the present invention is wound on a bobbin is kept as low as 20 g or less in order to maintain good light transmission loss.

Further, the PCF of the present invention is an optical fiber cord provided with a polymer coating layer on the outer periphery thereof, and the polymer coating layer at one or both ends of the cord is peeled off and a crimp type connector is attached to the optical fiber cord with a connector. It should be a phicode.

According to the present invention, even with such an optical fiber cord with a connector, the pulling force of the optical fiber from the ferrule inside the connector is increased to 2 kg or more and the pulling force is 1.0 kg × 1 minute. At this time, the amount of pistoning between the core and the cladding can be reduced to 10 μm or less.

The pulling force of the optical fiber from the ferrule inside the connector is a value obtained by measuring the force required to pull out the optical fiber from the ferrule inside the connector by attaching a JIS F05 type crimp crimp connector to the optical fiber cord. If the ferrule pulling-out force is less than 2 kg, there is a risk that the optical fiber may drop out from the connector during the wiring between devices, which is not preferable.

The amount of pistening is the amount of pistening generated between the quartz core and the clad polymer when the pulling force of the ferrule is 1.0 kg × 1 minute, and the amount of pistening is 10 μm or less. With this, it is possible to obtain an optical fiber having a high amount of emitted light when the connector is connected, that is, a high connection efficiency, and it is possible to realize high long-term reliability in the workability of the optical fiber of the present invention.

In the optical fiber of the present invention, the diameter of the quartz core is typically 200 μ, but the diameter is not limited to this.

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 for continuously supplying a liquid clad monomer composition, and the solvent is removed if necessary, followed by irradiation with ultraviolet rays. It may be performed by a method of forming a clad layer or the like.

When the curable composition for optical fiber cladding of the present invention is polymerized and cured by an ultraviolet irradiation furnace, the light source is, for example, carbon arc, xenon lamp, medium pressure mercury lamp, ultra high pressure mercury lamp, electrodeless lamp, metal halide lamp. For example, a commercially available light source may be used. Also,
From the viewpoint of increasing the efficiency of polymerization, it is preferable to perform irradiation in an atmosphere of an inert gas such as nitrogen gas.

In this way, the optical fiber having the clad layer formed on the outer circumference of the core is taken out through the roller whose speed is controlled, and if necessary, coated with a resin composition having a protective layer function or the like. Then, it is rolled up.

[0038]

EXAMPLES Optical fiber characteristics in the following examples were measured by the following methods.

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

Ferrule caulking loss (dB): The amount of light transmitted through an 850 nm LED of an optical fiber with a sample length of 3 m, which is attached without adhesion and without caulking, is the initial amount of light. Then attach the connector 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 loss (dB / km): The amount of transmitted light when an optical fiber having a length of 1 km was measured under the environment of 25 ° C. and 50% RH and then left at a low temperature of −60 ° C. From the difference, the transmission loss at a low temperature of −60 ° C. is used.

Example 1 A synthetic quartz base material synthesized by a plasma method was pretreated by flame polishing with an oxyhydrogen flame, and then continuously supplied to a high-purity carbon resistance heating furnace at 2200 ° C. Then, the optical fiber substrate was obtained by melting and thinning so that the core diameter was 200 μm. The substrate was filtered with a 0.1 μm filter of a monomer composition (18 cps) for a cladding polymer, which consisted of trihydroperfluoroundecyl acrylate, trimethylolpropane triacrylate, γ-mercaptotrimethoxysilane and a photosensitizer. Through the supplied clad coat die,
After continuously applying the composition to the surface of the substrate, 360
It was irradiated with light from a 300 W / inch electrodeless lamp having a central wavelength of nm to be cured, pulled by a roller, and wound as an optical fiber having a clad outer diameter of 227 μm. The core / clad eccentricity is 4.0%, and the non-circularity of the quartz core and polymer clad is 0.5% and 0.8, respectively.
The optical fiber had a very high circularity of 100%. The Shore D hardness, Young's modulus (23 ° C.) and linear expansion coefficient of the polymer clad are D68, 39 kg / mm ² , respectively.
It was 1.9 × 10 ⁻⁴ .

When the refractive index of the obtained optical fiber was measured, the refractive indexes of the quartz core and the polymer clad were 1.458 and 1.430, respectively, and the NA (numerical aperture) was 0.
28. The light transmission loss (850 nm) is 3.9.
It was as low as dB / km and the band was as high as 30 MHz · km, which was very excellent in optical characteristics.

The obtained optical fiber was melt-coated with a polymer composed of ethylene / tetrafluoroethylene copolymer to obtain a plastic clad optical fiber having a structure composed of a core / clad and a primary coating layer. The characteristics are as shown in Table 1, and the optical characteristics, terminal processability, and handleability were extremely excellent.

[Examples 2 to 3 and Comparative Examples 1 to 4] Broadband plastic clad optical fibers were obtained under the same conditions as in Example 1 except that the conditions shown in Table 1 were changed, and the same measurements were performed. The characteristics are shown in Table 1.

[0046]

[Table 1]

As can be seen from the results of Table 1, the transmission band can be increased by reducing the NA,
If it is set too low, the bending loss becomes too large and it becomes unsuitable for practical use. Therefore, it is necessary to set the range of NA specified in the present invention.

Further, from the viewpoint of low temperature characteristics, prevention of cut end face chipping and crimping characteristics, etc., 1.0 × 10 ^{−4 to} 2.0 × 10 ^−4.
A clad polymer having a linear expansion coefficient and a Shore D hardness of 60 or more is required.

[0049]

Industrial Applicability The step index type plastic clad capable of widening the transmission band of 20 to 50 MHz · km or more and capable of high-speed and large-capacity optical transmission as an optical transmission medium for medium and short distances. An optical fiber is obtained. Moreover, the connector ferrule has a high pull-out force, a small ferrule caulking loss, a small pistening amount between the quartz and the plastic clad, good on-site workability, and good long-term reliability.

Claims (6)

[Claims] 1. A plastic clad optical fiber comprising 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 refractive index (n _cl ) of the clad and the core Refractive index (n _co )
And 0.25 ≦ (n _co ² −n _cl ² ) ^1/2 ≦ 0.34, and the cladding has a Shore hardness of D60 or more and a linear expansion coefficient of 1.0 × 10 at room temperature. ^{-4 to} 2.0
A broadband plastic clad optical fiber comprising an ultraviolet-cured fluorine-based (meth) acrylate-based resin having × 10 ⁻⁴ . 2. The broadband plastic clad optical fiber according to claim 1, wherein the resin forming the clad has a Young's modulus at 23 ° C. of 30 to 45 kg / mm ² . 3. The broadband plastic clad optical fiber according to claim 1, wherein the clad has a thickness of 5 to 30 μm. 4. The broadband plastic clad optical fiber according to claim 1, wherein the Weibull average breaking strength of the optical fiber is 400 kg / mm ² or more. 5. An optical fiber cord in which a polymer coating layer is provided on the outer periphery of the broadband plastic clad optical fiber according to claim 1, and a connector attached by peeling the polymer coating layer at one end or both ends and crimping the polymer coating layer. An optical fiber cord with a connector, which consists of 6. The pulling force of the optical fiber from the ferrule inside the connector is 2 kg or more, and 1.0 k
6. The optical fiber cord with a connector according to claim 5, wherein the pistening amount between the core and the clad when pulled out with a pulling force of g × 1 minute is 10 μm or less.