JPH061625A - Production of quartz base optical fiber - Google Patents

Abstract

PURPOSE:To provide a production method for a quartz optical fiber having sufficient reliability over a long period by securing high mechanical property and ability of preventing permeability of water. CONSTITUTION:An inorganic coating layer 4 is formed on the circumferential surface of the optical fiber after drawing and after that, is irradiated with combination energy to form a compound layer 5 between the optical fiber 3 and the inorganic coating layer 4. As a result, the quartz base optical fiber capable of satisfying reliability over a long period including mechanical property, transmission property, ability of preventing permeability of water is obtained by forming the compound layer 5 between the optical fiber 1 and the inorganic coating layer 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silica-based optical fiber used in the fields of communication and optics.

[0002]

2. Description of the Related Art In the case of a silica-based optical fiber, for example, an optical fiber used for optical communication, mechanical characteristics and transmission characteristics change (deteriorate) with time during long-term use. It may damage.

Such deterioration with time is caused by minute scratches on the surface of the optical fiber during manufacture of the optical fiber and handling at the time of connection, and when this is laid in an environment containing water for a long period of time, ambient moisture, This is because the tension at the time of laying acts on the minute scratches and grows them. In particular, in a hot and humid environment, the action of water on the minute scratches becomes remarkable, so that the strength deterioration of the optical fiber progresses further, and in addition, when hydrogen molecules penetrate to the vicinity of the core of the optical fiber. Since an absorption peak appears near the wavelength of 1.24 μm, the transmission characteristics in this wavelength range deteriorate.

As a countermeasure against this, a hermetic coating such as a carbon coating is formed on the outer peripheral surface of the optical fiber, and a resin coating is performed on the hermetic coating. The hermetic coating has a high-density composition and a high degree of non-transparency that is not found in resin coatings, so that the reliability of the optical fiber is guaranteed within that range.

[0005]

Generally, the following points have been pointed out for hermetic coatings.
One of the reasons is that the hermetic coating has a brittle property, so that when the resin coating layer is removed during optical fiber connection, the coating surface is easily damaged. The other is that the silica-based optical fiber and the hermetic coating are made of different materials, so that the relative adhesion between them is weak, and the hermetic coating is easily separated from the optical fiber. In addition, the other is that, in the case of a carbon coating containing many graphite crystals with a dense atomic arrangement, the elongation strain leading to coating breakage is smaller than that of an optical fiber, so the initial strength is lower than that of a normal resin-coated optical fiber. It is to be. Therefore, an optical fiber having a hermetic coating is not easy to handle as compared with an optical fiber only having a resin coating, and breakage accidents frequently occur during terminal processing and connection work of the optical fiber.

In view of the above technical problems, the present invention intends to provide a method for producing a silica-based optical fiber which can secure high mechanical properties and moisture permeation inhibiting ability and can satisfy long-term reliability. It is what

[0007]

In order to achieve the intended object, a method for manufacturing a silica-based optical fiber according to the present invention draws an optical fiber by drawing a silica-based optical fiber preform by a heating and drawing means. After the drawing, after the drawing, the outer peripheral surface of the optical fiber is coated with an inorganic material to form an inorganic coating layer on the outer peripheral surface of the optical fiber, and after the formation, the inorganic coating layer is irradiated with compounding energy to form an optical fiber. It is characterized in that these compound layers are formed with the inorganic coating layer.

[0008]

According to the method of the present invention, not only the inorganic coating layer (hermetic layer) is formed on the outer peripheral surface of the silica-based optical fiber, but also an ion beam,
Energy such as a laser beam or an electron beam is applied to generate a compound layer between them, and the optical fiber and the inorganic coating layer are combined (integrated) via the compound layer.
The inorganic coating layer thus formed has a high resistance to brittle fracture and thus has a high toughness, is resistant to surface scratches, and has a dense structure, which is also excellent in water permeation inhibiting ability. Particularly, since the optical fiber and the inorganic coating layer are integrated with each other through these compound layers, they are unlikely to be separated from each other. An optical fiber with such an inorganic coating layer may be used during handling or after installation.
It exhibits stable mechanical and transmission characteristics over a long period of time without causing harmful situations such as surface scratches, breakage, and penetration of hydrogen molecules.

[0009]

EXAMPLES A method for manufacturing a silica-based optical fiber according to the present invention will be described with reference to the illustrated examples. In the case of the optical fiber manufacturing means illustrated in FIG. 1, a drawing device 11 for an optical fiber and a primary coating device 21 for coating an inorganic material.
The compound energy irradiation device 41, the secondary coating device 51 for resin coating, the resin curing device 61, and the winding device 71 for optical fiber are arranged in tandem.

The optical fiber drawing device 11 is a combination of an elevator (not shown) for supporting the optical fiber preform 7 so that it can be moved up and down, and a ring-shaped drawing furnace 12 composed of an electric heater. A ring-shaped non-contact type outer diameter measuring instrument 13 is disposed below the drawing furnace 12.

As the optical fiber preform 7, a well-known quartz system having a core glass and a clad glass is used.

Primary coating device 2 for inorganic material coating
Although any device such as a thermal CVD device, a sputtering device, and a plasma device is adopted as 1, the primary coating device 21 illustrated in the drawing is a thermal CVD device for carbon film formation. That is, the primary coating device 21 in the illustrated example is a combination of a CVD reaction tube 22 made of pure carbon, a ring-shaped heating furnace 27 made of an electric heater, and a source gas supply system 28. The CVD reaction tube 22 has an inlet 23 and an outlet 24 on the upper and lower surfaces thereof, a gas inlet 25 on the upper outer periphery thereof, and a gas outlet 26 on the lower outer periphery thereof, and A heating furnace 27 is attached to the outer circumference of the reaction tube 22. By the way, in the reaction tube 22, a mixed gas of a hydrocarbon-based source gas such as acetylene (C ₂ H ₂ ) and a diluent gas such as He, Ar, and N ₂ is used as a source gas for carbon film formation. Supply from the gas inlet 25. Primary coating device 21
For example, by adopting one of the above-mentioned thermal CVD apparatus, sputtering apparatus, and plasma apparatus having a predetermined specification, it is possible to form only amorphous carbon or only graphite crystal. In addition to these, the primary coating device 21 includes Ti, Zr, V, Nb, Ta, Cr, and M.
carbon-based materials including o, W, silicide-based materials, boride-based materials,
Nitride thin film, alumina, mullite, zeolite,
Thin films containing magnesia, sialon, etc. can be made.

The compound energy irradiation device 41 is, for example,
It is provided with means for generating a predetermined compound energy and means for irradiating the target with the compound energy. Specifically, an irradiation device of an inert gas ion such as argon, an excimer laser irradiation device, an electron beam irradiation device, or the like is adopted as the compound energy irradiation device 41.

Secondary coating device 51 for resin coating
Consists of a die-type coating device, in which a synthetic resin having any of these properties such as thermoplasticity, room temperature curing property, thermosetting property, and ultraviolet curing property is stored in a liquid state. There is.

The resin curing device 61 is selected based on the material of the resin used in the secondary coating device 51. For example, the curing device for thermosetting resin has a heating means, and the curing device for ultraviolet curable resin. Is equipped with ultraviolet irradiation means. In the case of a thermoplastic resin or a room temperature curable resin, such a curing device is not particularly required.

The optical fiber winding device 71 is electrically driven by a motor, and a coated optical fiber winding bobbin (not shown) is detachably attached to the winding device 71.

As shown in FIG. 2, the coated optical fiber manufactured by the method of the present invention has a silica-based optical fiber 3 having a core 1 and a cladding 2 which is primarily coated with an inorganic coating layer 4 and which has a cladding 2. The inorganic coating layer 4 and the inorganic coating layer 4 are integrated via these compound layers 5, and the outer periphery of the inorganic coating layer 4 is secondarily coated with the resin coating layer 6.

In the method of the present invention, when the coated optical fiber shown in FIG. 2 is manufactured through the means shown in FIG. 1, it is as follows.

First, the silica-based optical fiber preform 7 is inserted into the drawing furnace 12 of the drawing apparatus 11 at a low speed, and the drawing furnace 12 is inserted.
The lower end of the base material 7 softened inside is taken out at high speed to form the optical fiber 3. The optical fiber 3 thus drawn passes through the outer diameter measuring device 13 and then enters the reaction tube 22 of the primary coating device 21.

In the primary coating device 21, each gas such as a hydrocarbon-based raw material (C ₂ H ₂ ) and a diluent gas (He) is sent from the pipe 33 into the high temperature reaction tube 22 through the gas inlet 25. In the reaction tube 22 into which the above gases are introduced, fine particles of graphite crystals and fine particles of amorphous carbon are generated by the thermal oxidation reaction of these gases,
Since these carbon fine particles adhere to the outer peripheral surface of the optical fiber 3, the inorganic coating layer 4 described in FIG. 2 is formed on the outer peripheral surface of the optical fiber 3. When only fine particles of graphite crystals or only fine particles of amorphous carbon are produced in the primary coating device 21, a raw material gas of such a component may be introduced into the reaction tube 22 to carry out the same reaction as described above. . The optical fiber 3 after the primary coating with the inorganic coating layer 4 reaches the next compound energy irradiation device 41.

The compound energy irradiation device 41 irradiates the inorganic coating layer 4 with an argon ion beam, for example. Inorganic coating layer 4 that has received such compounding energy
Is excited by the molecules of it and the cladding 2 of the optical fiber 3
Compound with. That is, a part of the clad (silicon) 2 and the inorganic coating layer (eg, carbon) 4 are Si—C bonded to form the compound layer 5 of FIG. In the case of this compound layer 5, since a part thereof has a diamond-like crystal structure, the hardness is extremely high. After the compound layer 5 is formed between the cladding 2 and the inorganic coating layer 4, the primary coating optical fiber 3 enters the secondary coating device 51 for resin coating.

The secondary coating device (die type coating device) 51 contains, as an example, an ultraviolet curable liquid resin therein. Therefore, when the optical fiber 3 after the primary coating passes through the inside of the secondary coating device 51, the resin coating layer 6 described in FIG. 2 is formed of the UV resin on the outer peripheral surface of the inorganic coating layer 4. The resin coating layer 6 is cured by being irradiated with ultraviolet rays from a resin curing device 61 arranged next to the secondary coating device 51.

The optical fiber 3 thus primary-coated and secondary-coated is wound up by the winding device 71.

Optical fiber (specific example) according to the method of the present invention,
When the mechanical properties of the conventional optical fibers (Comparative Examples 1 and 2) were evaluated, the results shown in FIG. 3 were obtained. In the sample of the specific example, the optical fiber has an outer diameter of 125 μm.
φ quartz type, inorganic coating layer is made of graphite crystal with a film thickness of 200Å, resin coating layer is made of UV resin with an outer diameter of 400 μm φ, and a compound layer is formed by combining the optical fiber (a part of the clad) and the inorganic coating layer. Is formed. The sample of Comparative Example 1 has the same specifications as the sample of the specific example, except that the optical fiber (a part of the clad) and the inorganic coating layer are not combined, that is, the compound layer is not formed. The sample of Comparative Example 2 has the same specifications as the sample of the specific example, except that the inorganic coating layer including the compound layer is not formed. The sample length of each example is 40 cm, and the resin coating is removed by 10 cm in the middle portion. In the measurement for evaluation, a tensile load is applied to the optical fiber while dropping the aluminum powder of 400 grain size on the portion of the optical fiber where the resin coating is not applied.
% Tensile strain was applied.

As is apparent from FIG. 3, the optical fiber of the specific example has a good strength distribution, a small number of low strength parts, and a breaking strength of 2.2 GPa at a break probability level of 50%.
Is over. On the other hand, the optical fibers of Comparative Examples 1 and 2 have a wide strength distribution, and the breaking strength at a level with a breaking probability of 50% is considerably lower than that of the specific example.

Structural analysis of the inorganic coating layer of the optical fiber of the specific example by electron beam diffraction and Raman spectroscopic analysis confirmed the presence of graphite crystallites and confirmed that Si--C was present.
Presence of compound layer due to binding was also observed. It can be said that the optical fiber of the specific example has improved mechanical properties due to the formation of the inorganic coating layer containing such a compound layer, and is not damaged in the evaluation measurement test.

[0027]

According to the present invention, an inorganic coating layer is formed on the outer peripheral surface of an optical fiber after drawing, and then the inorganic coating layer is irradiated with compounding energy so that the inorganic coating layer is exposed between the optical fiber and the inorganic coating layer. Since a compound layer for chemically unifying is formed, a silica-based optical fiber that can satisfy long-term reliability including mechanical characteristics as well as transmission characteristics and water permeation blocking ability is provided. can get.

[Brief description of drawings]

FIG. 1 is a sectional view schematically showing an embodiment of the method of the present invention.

FIG. 2 is a sectional view of an optical fiber manufactured in one embodiment of the method of the present invention.

FIG. 3 is an explanatory diagram showing measurement results for evaluating mechanical properties of an optical fiber.

[Explanation of symbols]

 3 Quartz Optical Fiber 4 Inorganic Coating Layer 5 Compound Layer 7 Quartz Optical Fiber Base Material 11 Optical Fiber Drawing Device 12 Drawing Furnace 21 Primary Coating Device 22 Reaction Tube 27 Heating Furnace 41 Chemical Energy Irradiation Device

Claims (1)

[Claims] 1. An optical fiber is produced by drawing a quartz optical fiber preform by a heating and drawing means, and after the drawing,
The outer peripheral surface of the optical fiber is coated with an inorganic material to form an inorganic coating layer on the outer peripheral surface of the optical fiber, and after the formation, the inorganic coating layer is irradiated with compounding energy so as to form a gap between the optical fiber and the inorganic coating layer. A method for manufacturing a silica-based optical fiber, characterized in that these compound layers are formed on.