JPH04260008A - Coated optical fiber - Google Patents

Abstract

PURPOSE:To give superior heat resistance and mechanical strength to the coated optical fiber, a cord, and a cable and to facilitate a postprocess such as plating for the coated optical fiber by reducing rubbing flaws in the surface of the coated optical fiber at the time of a terminal process. CONSTITUTION:The optical fiber 2 consisting of a core and a clad is coated with a carbon film 3, and the surface of the optical fiber is coated with a gel obtained by hydrolyzing various metal alkoxide by utilizing a sol-gel method to form a thin layer 4 of metal oxide in glass structure.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an optical fiber core wire that has improved heat resistance and mechanical strength, and can be provided with electrical conductivity or insulation on the surface as desired, and also relates to cords and cables using the fiber core wire. Regarding.

0002

[Prior Art] In order to provide a predetermined mechanical strength to an optical fiber and protect its surface, generally, immediately after drawing the optical fiber, a UV resin such as epoxy acrylate or urethane acrylate, or a nylon resin, which is hardened by ultraviolet irradiation, is applied. This resin prevents scratches on the optical fiber surface. Cables using this optical fiber cannot transmit light under fire-resistant and heat-resistant conditions, so the optical fiber core is held down multiple times with heat-shielding tape to prevent heat transfer to the central optical fiber core. Al(OH)3, Mg(OH) wrapped or in a plastic sheath
2 and other endothermic materials are added. Even after such treatment, resin-coated optical fiber cores have a resistance of 250 to 300
It is only possible to achieve fire and heat resistance conditions of around ℃.

As a countermeasure to this problem, it has been proposed to protect the optical fiber surface with a metal film by plating or dipping.This method suppresses oxidation deterioration and thermal deterioration of the fiber surface in high-temperature environments, and improves the heat resistance of the optical fiber core. properties and mechanical strength can be further increased. In this case, if a metal film is formed directly on the surface of the optical fiber, the optical fiber may cause microbends due to the difference in expansion between the optical fiber and the coated metal, or the optical fiber may absorb hydrogen or moisture due to contact with the plating solution. , there is a drawback that the transmission loss of the optical fiber increases. Such drawbacks can be avoided if the optical fiber immediately after being drawn is coated with a dense carbon film such as amorphous carbon in advance.

0004

[Problems to be Solved by the Invention] Optical fibers coated only with a carbon film have no conductivity because the carbon layer is thin and has a high resistance. is required, and subsequent electroplating generally makes processing equipment expensive and has low productivity. With relatively inexpensive plating,
Electroless plating, which is used in conjunction with electroplating, has a slow deposition rate and lacks productivity, requires strict control of the plating solution to obtain a stable plating layer, and requires wastewater treatment equipment to prevent pollution. Become.

[0005] Furthermore, when inserting a fiber core into the ferrule of a connector during terminal processing, the inner diameter of the ferrule is generally designed to have a clearance of several μm with respect to the outer diameter of the fiber, so the fiber surface The resin or metal coating must be removed. As a result, the bare optical fiber is susceptible to scratches on its surface due to contact with the ferrule, often causing optical fiber breakage. If the thickness of the surface coating layer of the optical fiber is on the order of submicrons, it is not necessary to remove the coating layer when inserting the optical fiber core into the ferrule of the connector. It was virtually impossible to prevent surface scratches.

As a result of various studies regarding the surface coating layer of optical fibers, the present inventors have found that by using the so-called sol-gel method, gels obtained by hydrolyzing various metal alkoxides are coated on the surface of optical fibers. It was discovered that by coating to form a thin layer of metal oxide with a glass structure, the heat resistance and mechanical strength of the optical fiber core can be relatively easily increased, and it is also possible to impart electrical conductivity and insulation properties to the optical fiber core. This is what I did.

Therefore, the present invention aims to provide optical fiber cores, cords, and cables having excellent heat resistance and mechanical strength by forming a thin layer of metal oxide at desired locations on the optical fiber. The purpose is Also,
Another object of the present invention is to provide a coated optical fiber that is less prone to scratches on its surface during terminal processing. Another object of the present invention is to provide a coated optical fiber that facilitates post-processing such as plating.

[0008]

[Means for Solving the Problems] In order to achieve the above object, in the optical fiber core 1 according to the present invention, as shown in FIG. Then, a thin polymer layer 4 of metal oxide is formed by coating with a gel obtained by hydrolyzing metal alkoxide and heat-treating. Also,
In FIG. 2, the entire optical fiber 2 in the optical fiber core 5 is coated with a resin 6, and a metal oxide polymer thin layer 7 is formed at the tip portion from which the resin 6 is removed during terminal treatment.

The carbon film 3 is generally formed by drawing a molten preform and simultaneously coating it with amorphous carbon or the like in a reaction furnace, and has a thickness of about 300 to 1500 angstroms. The metal oxide polymer thin layer 4 may be formed in a separate step from the coating of the carbon film 3, or it may be formed in-line immediately after drawing the molten preform and coating the carbon film 3. In this case, stable fiber strength can be obtained.

To form a thin layer of metal oxide based on the sol-gel method, metal alkoxide M(OR)n[
In the formula, M is a metal atom such as silicon, tin, titanium, etc., R is an alkyl group, and n is 1 to 4], which is mainly polymerized by hydrolysis and further heated to form a hard glass structure. . The metal alkoxide is applied in the form of a gel with a relatively high viscosity as a result of the polymerization reaction of its water-added solution or partially hydrolyzed low-polymerized sol. To coat the metal alkoxide gel, simply apply or dip the surface of the optical fiber.

[0011] The metal alkoxide used is, for example,
Even if the R group is M(OR)n such as a methyl or ethyl group, a part of the OR group may be substituted with another alkyl group, aryl group, or organic functional group. This metal alkoxide may be polymerized by mixing one type or two or more types in an appropriate ratio, and depending on the application, a conductive film such as SnO2, indium tin oxide (ITO),
2. An insulating film such as mullite (SiO2.Al2O3) can be easily selected.

In the optical fiber core shown in FIG. 3, a carbon film 3 is coated on the optical fiber 2, and a thin conductive metal oxide polymer layer 8 is formed on the optical fiber 2, so that it can be coated with ordinary electroplating or the like. Metal plating layer 9 can be easily formed. This metal plating layer can also be formed by electroless plating, and in this case, it has better stability than the electroless plating layer on the carbon layer. The material of this metal plating layer is copper, nickel, aluminum, silver, gold, etc. As shown in FIG. 4, when an optical fiber 2 is coated with a carbon film 3, a metal oxide polymer thin layer 4 is formed, and then a flame-retardant resin 10 is coated, a flame-retardant optical fiber cord or Can be used as a cable.

[0013]

[Function] The optical fiber core 1 according to the present invention has higher heat resistance by protecting the carbon film 3 with a thin layer 4 of an inorganic substance, and can be coated with either a conductive film or an insulating film depending on the application. You can choose. The carbon film 3 has a dense structure that does not allow hydrogen or moisture to pass through, but because it is extremely thin, the surface may be scratched by contact during transportation or storage. To avoid.

[0014] If the optical fiber 2 coated with the carbon film 3 is made conductive, electroplating can be immediately performed. In addition, when inserting a fiber core into a ferrule of a connector during terminal processing, as shown in FIG. 2, if a thin polymer layer 7 of metal oxide is formed after removing the resin 6 at the fiber tip, Since the optical fiber is generally designed to have a clearance of several μm with respect to the outer diameter of the fiber, it can be inserted as is, and compared to a bare optical fiber, it is less likely to cause scratches on its surface even if it comes into contact with the ferrule.

[0015]

EXAMPLES Next, the present invention will be explained based on examples. Example 1 In order to manufacture the optical fiber core 1 shown in FIG.
Using a 5 μm quartz optical fiber 2, a preform is drawn and simultaneously introduced into a reactor (not shown), and its surface is coated with an amorphous carbon film 3 having a thickness of about 500 angstroms. Tetraethoxysilane [Si(OC2H5)4] was pulled onto this carbon-coated fiber by a dipping method at a pulling speed of 1.8 m/mi.
After coating with SiO
A thin polymer layer 4 of 2 is formed.

[0016] This optical fiber core wire 1 is left in an electric furnace at 450° C. for 30 minutes together with the untreated optical fiber, and then its bending strength is measured. As a result, while the fracture curvature radius of the optical fiber core 1 is 3 to 4 mm,
That of untreated optical fiber is 5-6 mm. Also,
When the bending strength of the optical fiber core 1 is measured after being left in an electric furnace at 550°C for 1 minute, the radius of curvature at break of the optical fiber core 1 is 3.
~6 mm, whereas that of untreated optical fiber is 20-30 mm.

If the carbon film 3 coated on the surface of the optical fiber is left exposed, it will be almost completely oxidized and peeled off in a heating environment of 550° C. for 1 minute. On the other hand, if a thin polymer layer 4 of SiO2 is formed on the surface, the carbon film 3 remains in the heating environment, but an additional 3
When heated for 0 minutes, the carbon film 3 is partially peeled off.

Reference Example The two carbon-coated fibers used in Example 1 were
Leave in an electric oven at ℃ for 5 minutes. One of them is coated with tetraethoxysilane by dipping at a pulling speed of 6 m/min, and then dried with hot air to form a thin polymer layer of SiO2. When measuring the bending strength of two carbon-coated fibers, it was found that the radius of curvature at break of the optical fiber coated with a thin polymer layer was 15 to 25 mm.
That of untreated optical fiber is 20-30 mm.

This experiment assumed deterioration of the fusion spliced portion of the optical fiber core in the ferrule of the connector. The carbon film on the surface of the optical fiber is almost completely oxidized and peeled off in the above-mentioned heating environment, so even if a thin SiO2 polymer layer is formed afterwards, there is no difference in bending strength compared to an untreated optical fiber. Not very accurate.

Example 2 Di-n-butoxytin [Sn(n-C4H9O) was added to the carbon-coated fiber used in Example 1 by dipping.
)2] is baked at 400° C. for 10 minutes to form a SnO2 polymer thin layer 4 on the surface.

In the case of nickel plating, this Sn
The O2 film-formed optical fiber is treated in an electrolytic plating bath having the following bath composition at a bath temperature of 50° C. for 1 to 20 minutes to form a metal plating layer 9 with a thickness of 0.5 to 10 μm.
coated with nickel. Nickel sulfamate 300~
700g/l boric acid
30g/l
Additive (brightener)
Appropriate amount

Example 3 The surface of the optical fiber coated with the thin polymer layer obtained in Example 1 was coated with vinyl chloride resin 10 by extrusion molding to an outer diameter of 0.9 mm.

[0023] The length of the obtained optical fiber cord was 300 m.
m was held horizontally, and the tip of a reducing flame with an oxidizing flame length of 130 mm was applied from an alcohol lamp to the lower center of the optical fiber cord for 30 seconds. After the alcohol lamp was removed, the flame of the optical fiber cord disappeared naturally, and although vinyl chloride residue remained attached to the cord surface, no breakage of the optical fiber was observed.

Example 4 The surface of the optical fiber coated with the polymer thin layer obtained in Example 1 was coated with UV-curable acrylic resin, and the outer diameter of the coated optical fiber was 2.
It is 50 μm. The obtained optical fiber cord has a length of 100
Insert into a stainless steel pipe with an outer diameter of 1.2 mm and an inner diameter of 0.8 mm.

[0025] The heat resistance properties of 8 m of optical fiber cords contained in a pipe are tested under the conditions of the fire resistance curve (840° C. in 30 minutes) in the fire resistance/heat resistance test of Fire and Disaster Management Agency Notification No. 10. When the optical fiber cord was pulled out from one end of the pipe after the test, the UV curing resin was missing in the approximately 50 cm area that was hit by the flame, but the optical fiber itself was not broken and the carbon film was protected by the SiO2 layer. It remains.

[0026]

[Effects of the Invention] The optical fiber core according to the present invention protects the carbon film with a thin layer of inorganic material on the surface.
Its heat resistance becomes even higher. Conventionally, optical fibers are coated with resin to give them a certain mechanical strength, and even though this resin prevents the occurrence of scratches on the optical fiber surface, its heat resistance is 250 to 30% because it is an organic material.
The limit is around 0°C. Further, even if the surface is coated with a carbon film, the carbon film oxidizes and peels off at a temperature of around 400°C, so the carbon film alone does not have sufficient heat resistance at high temperatures.

[0027] Although the carbon film in the optical fiber has a dense structure and does not allow hydrogen and moisture to pass through,
Because it is extremely thin, the surface is easily scratched by contact during transportation or storage, and its mechanical strength deteriorates significantly over time. In the present invention, by forming a hard thin layer of inorganic material on the fiber surface, it is possible to avoid surface scratches and obtain stable fiber strength.

In the optical fiber core wire of the present invention, electroplating can be performed immediately by imparting conductivity to the inorganic thin layer on the surface, and electroless plating and metal vapor deposition can be omitted. This metal plating layer suppresses oxidative deterioration and thermal deterioration of the optical fiber surface in high-temperature environments, and further increases the heat resistance and mechanical strength of the optical fiber core. The equipment used for processing the optical fiber core of the present invention is relatively inexpensive, has high productivity, and does not require strict control of plating solution or wastewater treatment equipment.

Further, in the terminal treatment, in the present invention, after removing the resin at the tip of the fiber, a thin metal oxide polymer layer having a thickness of about submicrons is formed. The inner diameter of the ferrule of the connector is generally designed to have a clearance of several μm from the outer diameter of the fiber, so it can be inserted with the thin layer described above formed, and even if it comes into contact with the ferrule, there will be no scratches on its surface. Almost never occurs. Conventionally, when inserting a fiber core into the ferrule of a connector during terminal processing, the resin coating layer on the surface of the fiber must be removed, resulting in the exposed optical fiber causing scratches on its surface due to contact with the ferrule. This is often the cause of optical fiber breakage.

[Brief explanation of the drawing]

FIG. 1 is an enlarged sectional view of a coated optical fiber according to the present invention.

FIG. 2 is a partial side view showing a modification of the present invention.

FIG. 3 is an enlarged sectional view showing another modification of the present invention.

FIG. 4 is an enlarged sectional view showing still another modification of the present invention.

[Explanation of symbols]

1 Optical fiber core 2 Optical fiber 3 Carbon film 4 Metal oxide polymer thin layer 8 Conductive metal oxide polymer thin layer 9 Metal plating layer 10 Flame-retardant resin

Claims (5)

[Claims] Claim 1: A thin polymer layer of a metal oxide is formed by coating an optical fiber consisting of a core and a cladding with a carbon film, and then coating with a gel obtained by hydrolyzing a metal alkoxide and heat-treating the fiber. optical fiber core. 2. An optical fiber coated with resin on an optical fiber consisting of a core and a cladding, in which a thin polymer layer of metal oxide is formed on the tip portion from which the resin is removed during terminal treatment. fiber core. 3. A thin polymer layer of metal oxide is formed by coating an optical fiber consisting of a core and a cladding with a carbon film, further coating with a gel obtained by hydrolyzing metal alkoxide, and heat-treating the fiber. The optical fiber core is then coated with a metal plating layer. 4. A thin polymer layer of metal oxide is formed by coating an optical fiber consisting of a core and a cladding with a carbon film, further coating with a gel obtained by hydrolyzing metal alkoxide, and heat-treating the fiber. Optical fiber core is coated with flame-retardant resin. 5. An optical fiber cord or cable using the optical fiber core according to claim 4.