JPH0658445B2 - Polymer-clad glass optical fiber and its manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical fiber having a silica glass as a core and a highly transparent polymer having a refractive index lower than that of the core glass as a clad, and a method for producing the same. is there.

[Prior Art] Conventionally, as a material used as a clad in a polymer clad glass optical fiber (PCF), silicone resin (Japanese Patent Publication No. 57-40483), polyfluoroalkyl methacrylate (Japanese Patent Application Laid-Open No. 58-121461), fluorine Vinylidene chloride / tetrafluoroethylene copolymer (Japanese Patent Publication No. 56-41966), polyether ester amide (Japanese Patent Publication No. 56-60402),
Also known are UV-curable fluorinated acrylate compositions (US Pat. No. 4,511,209).

However, in the clad polymer used in the conventional polymer clad glass optical fiber, recently required properties such as low optical transmission loss, simplification of connector attachment by caulking method, and stabilization of loss temperature characteristic are required. It is impossible to deal with sophistication.

For example, since silicone resin has low mechanical properties, particularly mechanical strength, optical transmission loss increases due to caulking type connector attachment. Vinylidene fluoride / tetrafluoroethylene copolymer and polyether ester amide are
Since the scattering and the absorption are large, the light transmittance is inferior, and it is impossible to reduce the loss of the PCF. The fluoroalkyl methacrylate copolymer is highly transparent, but has insufficient adhesion to the core glass. Since the UV-curable fluorinated acrylate composition is cured by UV after being applied on the core glass, loss due to residual stress increases due to control of the cured state, shrinkage of the cladding during curing, and fiber outer diameter. There are problems such as difficult adjustment.

Further, since the core glass is originally superior in light transmissivity to plastic, it is easily affected by a slight difference in transmissivity of the clad. It has been impractical to use a polymer as the cladding of an optical fiber having a glass core, because the transparency of the optical fiber is significantly reduced when impurities are present in the polymer used as the cladding.

[Object of the Invention] It is an object of the present invention to provide a polymer-clad glass optical fiber which solves the above drawbacks and which uses silica glass as a core and a polymer as a clad.

[Structure of the Invention] The gist of the present invention is to provide, on the outside of a core made of silica glass,
Structural formula: [In the formula, X ₁ , X ₂ and X ₃ represent a hydrogen atom or a fluorine atom, and R represents a fluorine-containing alkyl group or a fluorine-containing alicyclic group. ] It exists in the polymer clad glass optical fiber characterized by having the clad of the fluorine-containing polyvinyl ester shown by these.

In the optical fiber of the present invention, the polymer used as the clad has the above structure, but X ₁ , X ₂ and X ₃ are hydrogen atoms and R is a trifluoromethyl group, that is, the clad polymer is polyvinyl trifluoroacetate. Is particularly preferable.

In the optical fiber of the present invention, the silica glass used as the core is generally pure silica glass. However, in the present invention, the silica-based glass used as the core may contain silica as a main component and an additive for adjusting the refractive index. Examples of the additive include titanium oxide, germanium oxide, barium oxide, and the like.

The optical fiber of the present invention can be formed by coating the clad polymer on the core glass by a known extrusion method or solution method. However, it is preferable that the clad polymer is prepared by purifying and polymerizing the fluorine-containing ester monomer in a totally closed system, and the clad polymer is applied to the core glass fiber in a clean inert atmosphere.

Therefore, another aspect of the present invention is to provide a structural formula: [In the formula, X ₁ , X ₂ and X ₃ represent a hydrogen atom or a fluorine atom, and R represents a fluorine-containing alkyl group or a fluorine-containing alicyclic group. ] A method for producing a polymer clad glass optical fiber having a fluorine-containing polyvinyl ester clad represented by: Then, the clad polymer is applied around the core glass and dried or cooled.
By the method of the present invention, a lower loss optical fiber can be obtained.

As the polymerization method, a suspension polymerization method or an emulsion polymerization method can be used. However, since impurities are less mixed into the clad polymer and a fiber with low loss can be supplied, a radical initiation bulk polymerization method or a solution polymerization method is possible. Is preferably used. Examples of the solvent used in the solution polymerization method include tetrahydrofuran. The radical for initiating the polymerization can be generated by irradiation with electron beam or gamma ray, or by a radical initiator such as peroxide or isocyanurate.

The manufacturing method of the present invention can be typically carried out using an apparatus as shown in FIG. The manufacturing apparatus shown in FIG. 1 comprises a monomer distiller 1, a polymerization reactor 2, a clad polymer coating die 3,
3 ', drying or cooling towers 4, 4', core preform 5, heater 6 and clean inert atmosphere area 7.

The clad monomer is distilled and purified in the monomer distiller 1, and then this monomer is polymerized in the polymerization reactor 2 to prepare a clad polymer. This distillation purification and polymerization are carried out in a closed system. If necessary, in the polymerization reactor 2, after removing the unreacted monomer, the clad polymer can be dissolved using a solvent for the clad polymer to prepare a clad polymer solution. Examples of the solvent for the clad include ethers such as tetrahydrofuran and diethyl ether, ketones such as methyl ethyl ketone and acetone, and the like.

The core is formed by drawing the quartz core base material 5 while heating it with the heater 6, and at the same time, the clad polymer is applied around the core by the clad polymer applying die 3. Next, the clad is dried by the drying or cooling tower 4 to remove the solvent and form the clad. The clad polymer may be applied to the core fiber as it is without using a solvent, and then the clad polymer is cooled to form the clad. The drawing of the base material, the coating of the clad, and the drying or cooling are performed in the clean inert area 7 using an inert gas such as nitrogen gas or helium gas. There is another set of clad coating dies 3 ', and a drying or cooling tower 4'to perform coating and drying or cooling of the cladding once again. After the second drying and cooling, the optical fiber is pulled by a pulling machine.

[Advantages of the Invention] The polymer-clad glass optical fiber of the present invention has a mechanical property of the clad polymer superior to that of the conventional silicone resin, so that the increase in loss does not occur even when caulking type connector attachment is performed, and the heat-cycle after thermal cycle There is no protrusion from the connector surface of the core part.

The fluorine-containing polyvinyl ester of the clad polymer is
Since the refractive index is lower than that of silicone resin and the temperature dependence of the refractive index is small, the change in optical transmission characteristics at low temperature due to the increase in the refractive index of the clad polymer is small. Since the numerical aperture of the optical fiber becomes smaller and the optical transmission loss increases, the lower limit of the operating temperature of the conventional polymer clad glass optical fiber using silicone resin or the like as a clad polymer was about -20 ° C. In, a stable optical transmission characteristic can be obtained in a wide temperature range including a lower temperature.

Since the fluorine-containing polyvinyl ester of the clad polymer is amorphous and has excellent light transmittance in the visible to near-infrared region, the optical transmission loss of the optical fiber of the present invention is small.

The clad polymer of the present invention, when applied to the core glass fiber, is already in a polymer state, so unlike the curable polymer, there is no problem associated with control of the cured state and curing shrinkage, and the fiber outer diameter and An optical fiber with stable clad characteristics can be obtained.

[Preferred Aspects of the Invention] Examples are shown below.

Example 1 Polyvinyl trifluoroacetate (refractive index n _D ²⁵ = 1.3) synthesized by an emulsion polymerization method using water as a dispersion medium.
9) was dissolved in tetrahydrofuran to prepare a clad polymer solution having a concentration of 30% by weight. While drawing a core glass fiber having an outer diameter of 200 μm using quartz having a refractive index of 1.45, a clad polymer solution was applied to the periphery of the core fiber using a die and dried at 120 ° C. Repeated times, a polymer-clad glass optical fiber with an outer diameter of 230 μm was obtained.

The optical transmission loss of this fiber is 7 at a wavelength of 800 nm.
It was dB / km, and no increase in loss was observed even if caulking type connector attachment was performed.

Comparative Example 1 A core glass fiber having an outer diameter of 200 μm was drawn using quartz having a refractive index of 1.45, and at the same time, a commercially available silicone resin (XE14-062 manufactured by Toshiba Silicone) was applied around the core fiber and heat cured at 150 ° C. Outside diameter 230
A μm polymer clad glass optical fiber was obtained.

The optical transmission loss of this fiber is 6 at a wavelength of 800 nm.
It was dB / km. A caulking type connector was attached using this optical fiber, and about 1.
A loss increase of 5 dB was observed.

Example 2 Using the apparatus shown in FIG. 1, vinyl trifluoroacetate monomer was subjected to vacuum distillation and purification in a completely closed system in a clean nitrogen gas atmosphere, and then radical initiation was carried out at 60 ° C. using benzoyl peroxide as an initiator. Bulk polymerization was performed. After removing volatile components including unreacted monomer, purified methyl ethyl ketone was added to prepare a clad polymer solution having a concentration of 30% by weight. In a clean nitrogen gas atmosphere, quartz with a refractive index of 1.45 is used and the outer diameter is 200μ.
At the same time as drawing the m core glass fiber, the clad polymer solution was applied around the core fiber and dried at 120 ° C., and this coating and drying operation was repeated once again to obtain a polymer clad glass optical fiber having an outer diameter of 230 μm.

The optical transmission loss of this optical fiber is 4 at a wavelength of 800 nm.
It was dB / km. A caulking type connector was attached using this optical fiber, but no increase in loss was observed.

[Brief description of drawings]

FIG. 1 is a schematic view showing a typical manufacturing apparatus used in the present invention. 1 ... Monomer distiller, 2 ... Polymerization reactor, 3, 3 '... Clad polymer coating die, 4, 4' ... Drying or cooling tower, 5 ... Core base material, 6 ... Heater, 7 ...... Clean, inert atmosphere area.

Claims (5)

[Claims] 1. A structural formula on the outside of a core made of silica glass: [In the formula, X ₁ , X ₂ and X ₃ represent a hydrogen atom or a fluorine atom, and R represents a fluorine-containing alkyl group or a fluorine-containing alicyclic group. ] The polymer clad glass optical fiber which has the clad of the fluorine-containing polyvinyl ester shown by these. 2. The optical fiber according to claim ₁ , wherein in the structural formula, X ₁ , X ₂ and X ₃ are hydrogen atoms and R is a trifluoromethyl group. 3. The optical fiber according to claim 1 or 2, wherein the core is pure silica glass. 4. A structural formula on the outside of a core made of quartz glass: [In the formula, X ₁ , X ₂ and X ₃ represent a hydrogen atom or a fluorine atom, and R represents a fluorine-containing alkyl group or a fluorine-containing alicyclic group. ] A method for producing a polymer clad glass optical fiber having a fluorine-containing polyvinyl ester clad represented by the following method, in which a clad polymer is prepared by purifying and polymerizing a clad monomer in a totally closed system, and then in a clean inert atmosphere. A coating method in which the clad polymer is applied around the core glass and dried or cooled. 5. The method according to claim 4, wherein the clad monomer is polymerized by a radical initiation bulk polymerization method or a solution polymerization method.
The manufacturing method described in paragraph.