JPH08239247A - Optical fiber and its production - Google Patents

Abstract

PURPOSE: To obtain an optical fiber restrained from increasing transmission loss over a long period due to hydrogen diffusion by providing a specific silica glass layer as the outermost layer of the clad portion of a quartz-based single mode fiber followed by forming a carbon film thereon. CONSTITUTION: This optical fiber has a silica glass layer as the outermost layer of the clad portion and a carbon film outside the layer. The silica glass layer contains at least one element, except Si and O, selected from Al, B and P, each belonging to groups other than group XIV in the periodic table and differing in valence from Si and has a thickness >=0.5 times the radius of the fiber. This optical fiber is obtained by using a glass preformed material which is made by sintering a glass fine particle build-up body 4 with a diameter of 100mm prepared by depositing glass fine particles on a starting rod composed of chore portion consisting of GeO2 -contg. SiO2 and clad portion of SiO2 so as to be 1mmHg in the partial pressure of AlCl3 as an additive element (compound) in a sintering oven where a heater 1 having the AlCl3 inside is brought to 100 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber and a method for manufacturing the same, and particularly to a quartz single mode optical fiber and a method for manufacturing the same.

[0002]

2. Description of the Related Art In a silica-based optical fiber, hydrogen is diffused into the optical fiber by contact with hydrogen, and the transmission loss increases due to absorption by hydrogen molecules and absorption of hydroxyl groups generated by the reaction of hydrogen. It is known to end up. The absorption peak of the hydrogen molecule appears at a wavelength of 1.24 μm, and the absorption peak of the hydroxyl group appears at a wavelength of 1.38 μm.
Such an absorption peak is not preferable because it increases absorption at 1.30 μm and 1.55 μm, which are communication wavelengths of a normal optical fiber. Therefore, JP-A-3-15
As proposed in Japanese Patent No. 3549, there has been adopted a method of coating a carbon film on the surface of an optical fiber by a chemical vapor deposition method (CVD method) to suppress the diffusion of hydrogen into the optical fiber. The optical fiber obtained by this method is
It is possible to suppress the diffusion of hydrogen into the fiber.

[0003]

However, the carbon-coated optical fiber manufactured by the conventional method has a certain diffusion coefficient of hydrogen into the carbon film, which is not zero but smaller than that of silica glass. Therefore, with time, hydrogen passes through the carbon film, diffuses in the glass, and reaches the core part.
There is a drawback that the transmission loss gradually increases due to absorption of hydroxyl groups generated by the reaction with iO ₂ . Therefore,
It is an object of the present invention to provide an optical fiber having a novel structure and a method for manufacturing the same, which can solve the above-mentioned drawbacks of conventional products and can suppress an increase in transmission loss due to diffusion of hydrogen for a long period of time.

[0004]

As a means for solving the above problems, the present inventors have thought of providing a layer capable of trapping hydrogen molecules that have penetrated into a carbon film, and further manufacturing an optical fiber capable of realizing this structure. I was able to develop a method. That is, the present invention relates to a silica-based single-mode fiber, in which the outermost layer of the cladding portion is a silica glass layer containing an element other than Si and O and belonging to a group other than Group 14 of the periodic table and having a valence different from Si. And a carbon film on the outside thereof. In the above optical fiber of the present invention, the thickness of the quartz glass layer as an outermost layer of the clad portion is a layer other than Si and O, which belongs to a group other than Group 14 of the periodic table and contains an element having a valence different from Si. Is the optical fiber radius of 0.5
It is mentioned as a particularly preferable embodiment that it is not more than double. Further, in the optical fiber of the present invention, one element selected from Al, B and P other than Si and O and belonging to a group other than Group 14 of the periodic table and having a valence different from Si is selected. Alternatively, a plurality thereof is mentioned as a particularly preferred embodiment. Further, according to the present invention, glass particles are deposited on the outer circumference of a starting rod having a core portion made of SiO ₂ containing a refractive index adjusting dopant and a cladding portion made of SiO ₂ , and then the glass particle deposition portion is sintered. In a method for producing an optical fiber in which a glass base material is coated and a carbon film is coated on the surface of the optical fiber by a thermal CVD reaction when the glass base material is drawn and then drawn, sintering is performed in the sintering step of the glass fine particle deposition portion. S for furnace atmosphere gas
There is provided a method for producing the above optical fiber, which is characterized by introducing a compound of an element other than i and O, which belongs to a group other than Group 14 of the periodic table and has a valence different from Si. Still further, according to the present invention, glass fine particles are deposited on the outer periphery of a starting rod having a core portion made of SiO ₂ containing a refractive index adjusting dopant and a clad portion made of SiO ₂ , and then the glass fine particle deposition portion is sintered. As a glass base material, and after stretching the glass base material, the outside of the stretched body is covered with a pipe made by hollowing out the inside of the glass rod to make a glass base material by collapsing, and the glass base material is drawn. In the method of manufacturing an optical fiber in which a carbon film is coated on the surface of the optical fiber by a thermal CVD reaction, the sintering furnace atmosphere gas other than Si and O in the periodic table is used. The present invention provides a method for producing an optical fiber, which comprises introducing a compound of an element belonging to a group other than Group 14 and having a different valence from Si. In the manufacturing method of the present invention, a compound of an element other than Si and O introduced into the sintering furnace atmosphere gas, which belongs to a group other than Group 14 of the periodic table and has a valence different from Si, is Al, One or more selected from the compounds of B or P is mentioned as a particularly preferred embodiment.

The reason why hydrogen molecules can diffuse in the optical fiber is due to the long bond distance between Si (silicon) and O (oxygen) which compose the glass, so it is difficult to lower the diffusion coefficient itself in the glass. Is. However, in the fiber of the present invention, elements other than Si and O are present in the outermost layer of the clad layer, and hydrogen that has penetrated into the fiber reacts with and is adsorbed by the elements present in the glass to diffuse into the core. Can be suppressed. That is, the VAD method or O
By adding an element different from the intended Si and O to the glass particulate deposit synthesized by the VD method, unnecessary impurities can be prevented from entering, and as a result, hydrogen molecules that have penetrated into the carbon film can be prevented. It is possible to obtain an optical fiber having a layer capable of trapping.

It is essential that the element to be introduced is an element other than O, and belongs to a group different from Si in the periodic table and has a valence different from Si, and particularly preferably an element of Group 13 or Group 15 is preferable. More specifically, it is particularly desirable that one or more selected from Al, B or P be used. The reason for this is that these elements are likely to form bonds with hydrogen that has entered the glass, so that even a small amount of entered hydrogen can be suppressed from diffusing to the core in the fiber. Hydrogen can be suppressed by applying only the carbon coat, but since the diffusion coefficient of hydrogen in the carbon coat is not 0, hydrogen gradually penetrates into the fiber. Since the fiber according to the present invention has a layer capable of trapping hydrogen molecules inside the carbon film, a small amount of hydrogen molecules passing through the carbon film are trapped there, so that hydrogen is diffused as compared with the conventional carbon-coated optical fiber. The increase in transmission loss can be suppressed for a long time.

Specific examples of the compound of the element to be added according to the present invention include aluminum halides, boron halides, phosphorus halides, alkali halides and the like, but it is not necessary to be a halide, and an oxide is required. , Nitride, etc. may be used. However, as will be described later, in the case of a manufacturing method in which these elements are introduced into the outermost layer of the cladding in the sintering step, a halide pressure is particularly desirable because it requires a vapor pressure to some extent in the atmosphere of the sintering furnace.

Belongs to a group other than group 14 of the periodic table and has S
The amount of addition of elements (excluding O) whose valence is different from i is 50
˜2000 ppm is desirable, and if it exceeds 2000 ppm, it is not preferable because crystallization of glass or the deterioration of strength occurs, and if it is less than 50 ppm, the amount of hydrogen that can be trapped is small, which is not preferable.

The thickness of the cladding outermost layer containing the additive element other than Si or O is preferably 0.5 times or less the fiber radius. This is because it causes a loss of transmitted light and a decrease in fiber strength. On the other hand, the lower limit of the thickness is 0.05 times, and if it is less than 0.05 times, the amount of hydrogen that can be captured is small, which is disadvantageous.

To add an element to the outermost clad layer,
By introducing a compound containing the target element into the atmosphere of the sintering furnace during the sintering of the glass particle deposit, the element can be introduced into the glass surface layer. According to this method, only the desired element can be added in a necessary amount. That is, the amount of addition of the element in the glass can be controlled by changing the partial pressure of the compound of the element to be added in the sintering furnace atmosphere or the sintering conditions.

[0011] More specifically, the core unit and SiO ₂ containing the refractive index adjusting dopants such as GeO ₂ in SiO ₂
A desired element (compound of the element) can be added to obtain a preform for an optical fiber when the glass particle deposit body in which glass particles are deposited on a starting rod having a clad portion made of is sintered. Also for the base material sintered in the conventional sintering furnace, the outer circumference of the base material for optical fiber is shaved off to reduce the outer diameter as necessary, and elements (or elemental compounds) other than silicon and oxygen are introduced to the outside. The optical fiber preform can also be obtained by collapsing a glass pipe made of the sintered and sintered glass material.

The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

【Example】

[Example 1] Core part made of GeO ₂ -containing SiO ₂ and S
A glass particle deposit body having a diameter of 100 mm, in which glass particles were deposited on a starting rod having a cladding portion made of iO _2, was sintered using the apparatus shown in FIG. Aluminum chloride (AlCl ₃ ) was used as the substance to be added.
The additive element (compound) 2 is placed inside the heater 1 and the heater 1 is heated to 100 ° C. during the normal sintering process so that the partial pressure of AlCl ₃ in the sintering furnace becomes 1 mmHg. And sintered. In FIG. 1, 3 is a tape heater, 4 is a glass particle deposit, 5 is a heater, and 6 is a purge gas supply device. N ₂ was used as a purge gas.
The thus-obtained sintered body was stretched, the surface was flame-polished, and then the wire was drawn using an apparatus as shown in FIG. The optical fiber preform 7 is melted by the heater 8 and has an outer diameter of 125 μm.
The fiber is spun into the reaction tube 9. Reaction tube 9
Is supplied with chloroform (CHCl ₃ ) as a carbon coating raw material at a flow rate of 0.15 liter / min from the carbon coating raw material supply device 10, reacts with heat of the fiber itself, and has a thickness of 40 μm on the optical fiber. Carbon film is formed. Reference numeral 11 is an exhaust system. Then, the coating die 12 covered the resin to obtain the optical fiber 13. The initial transmission loss of this optical fiber at a wavelength of 1.55 μm was 0.20 dB / km, which was good. Further, this optical fiber was kept in an atmosphere of 80 ° C. and a hydrogen partial pressure of 1 atm, and the wavelength was 1.24 μm every 20 hours.
The change in transmission loss (Δα) was measured. The result is shown in FIG. From these results, no increase in transmission loss due to hydrogen was observed from immediately after drawing until the first 20 hours, and it was confirmed that hydrogen did not reach the core.

[Embodiment 2] SiO ₂ which is a dummy rod
A glass fine particle deposit having a diameter of 100 mm, obtained by depositing glass fine particles on a glass rod (diameter: 10 mm, length: 400 mm), was sintered using the apparatus shown in FIG. AlCl ₃ was used as the substance to be added. When the substance 2 to be added is placed inside the heater 1 and the normal sintering process is performed, the heater 1 is heated to 110 ° C. to heat the Al in the sintering furnace.
Sintering was performed so that the partial pressure of Cl ₃ was ₃ mmHg. After stretching the sintered body thus obtained, punching,
A rod having a core part made of GeO ₂ -containing SiO ₂ and a clad part made of SiO ₂ was inserted into the inside and collapsed to prepare a preform for an optical fiber. On this occasion,
The thickness of the layer added with 200 ppm of aluminum is 6.
It was set to 25 mm, which is 1/2 of the radius (12.5 mm) of the optical fiber preform. This base material was stretched and flame-polished, and then an optical fiber having an outer diameter of 125 μm was drawn under the same conditions as in Example 1 and carbon-coated and resin-coated. The initial transmission loss of the obtained optical fiber at a wavelength of 1.55 μm was 0.21 dB / km, which was good. Further, hydrogen treatment was performed in the same manner as in Example 1, and the change in transmission loss (Δα) at a wavelength of 1.24 μm was examined. The result is shown in FIG. From this result, it was found that the loss did not increase at all during the first 40 hours, and the hydrogen that had infiltrated during this period was adsorbed by the glass layer.

[Comparative Example 1] An optical fiber preform manufactured without any addition of Al (the same as in Example 1 except that aluminum was not added) was used to wire under the same apparatus and conditions as in Examples 1 and 2. An optical fiber was prepared by coating, carbon coating, and resin coating. The initial transmission loss of the obtained optical fiber at a wavelength of 1.55 μm was 0.21 dB / km, which was good. This optical fiber was also subjected to hydrogen treatment under the same conditions as in Example 1, and the change in transmission loss was examined. The results are also shown in FIG. From this result, in the case of this comparative example in which there is no layer capable of adsorbing hydrogen in the fiber, the transmission loss increases even after 20 hours, and the transmission loss increases at a substantially constant pace.

[Embodiment 3] As in Embodiment 2, an optical fiber preform is made from a rod having an Al-added pipe, a core and a clad by collapsing. However, the thickness of the Al-added pipe was set to be 2/3 of the radius of the base material for optical fiber. The base material was stretched and flame-polished, and then the same apparatus and conditions as in Example 1 were used to perform drawing, carbon coating and resin coating in the same manner to prepare an optical fiber. The obtained optical fiber was subjected to hydrogen treatment in the same manner as in Example 1 to give a wavelength of 1.2.
The transmission loss change (Δα) of 4 μm was examined. The result is shown in FIG. From this result, no increase in loss was observed during the first 60 hours, and the hydrogen that had infiltrated during this period was adsorbed by the glass layer, but the wavelength of this optical fiber was 1.55 μm.
The initial transmission loss at 0.20 dB / km is 0.10 dB / km higher than the other examples.

Table 1 collectively shows the initial loss at the wavelength of 1.55 μm of the optical fibers obtained in Examples 1 to 3 and Comparative Example 1. From the results shown in Table 1 and FIG. 3, the optical fiber having the clad outermost layer (hydrogen adsorption layer) having a thickness of ½ or less of the fiber radius has a low loss and can maintain the low loss. It turns out to be preferable.

[0017]

[Table 1]

[Embodiment 4] As in Embodiment 1, GeO ₂
The glass particles deposit 100mm in diameter deposited glass particles on the starting rod having a cladding portion comprising a core portion and SiO ₂ comprising a containing SiO _2, and sintered using the apparatus shown in FIG. Phosphorus pentachloride (PCl ₅ ) was used as the substance to be added. When the added starch (compound) 2 is installed inside the heater 1 and the normal sintering process is performed, the heater 1 is heated to 170 ° C. and PCl in the sintering furnace is heated.
Sintering was performed such that the partial pressure of ₅ was 0.5 mmHg. The thus-obtained sintered body was stretched and flame-polished, and then drawn in the same manner as in Example 1 using an apparatus as shown in FIG. The optical fiber preform 7 is melted by the heater 8, spun into an outer diameter of 125 μm, and guided to the reaction tube 9. Raw material for carbon coating is supplied from the raw material supply device 10 to the reaction tube 9, and the reaction is caused by the heat of the fiber itself to form a carbon film having a thickness of 40 μm on the fiber. Then, the resin was coated to obtain the optical fiber 13. The initial transmission loss of this optical fiber at a wavelength of 1.55 μm was 0.21 dB / km 2, which was good. Further, this optical fiber was kept in an atmosphere of 80 ° C. and a partial pressure of hydrogen of 1 atm, and a change in transmission loss (Δα) at a wavelength of 1.24 μm was measured every 20 hours. The result is shown in FIG. From this result, no increase in transmission loss due to hydrogen was observed at all in the first 20 hours, and it was confirmed that hydrogen did not reach the core portion.

[Embodiment 5] As in Embodiment 1, GeO ₂
The glass particles deposit 100mm in diameter deposited glass particles on the starting rod having a cladding portion comprising a core portion and SiO ₂ comprising a containing SiO _2, and sintered using the apparatus shown in FIG. Boron trichloride (BCl ₃ ) was used as the substance to be added. Since BCl ₃ is a gas at 12.5 ° C. or higher, BCl ₃ gas was directly supplied from the heater 1. During the normal sintering process, sintering was performed so that the partial pressure of BCl ₃ in the sintering furnace was 0.1 mmHg. The thus-obtained sintered body was stretched and flame-polished, and then drawn in the same manner as in Example 1 using an apparatus as shown in FIG. The optical fiber preform 7 is a heater 8
Is melted, spun into an outer diameter of 125 μm, and introduced into the reaction tube 9. A raw material for carbon coating is supplied from the raw material supply device 10 to the reaction tube 9, and the reaction is caused by the heat of the fiber itself to form a carbon film having a thickness of 40 μm on the fiber. Then, the resin was coated to obtain the optical fiber 13. The initial transmission loss of this optical fiber at a wavelength of 1.55 μm was 0.20 dB / km, which was good. Further, this optical fiber was held in an atmosphere of 80 ° C. and a hydrogen partial pressure of 1 atm, and the change in transmission loss (Δα) at a wavelength of 1.24 μm was measured every 20 hours. The result is shown in FIG. From this result, no increase in transmission loss due to hydrogen was observed at all in the first 40 hours, and it was confirmed that hydrogen did not reach the core portion.

[Sixth Embodiment] As in the first embodiment, GeO ₂
The glass particles deposit 100mm in diameter deposited glass particles on the starting rod having a cladding portion comprising a core portion and SiO ₂ comprising a containing SiO _2, and sintered using the apparatus shown in FIG. As the substance to be added, AlCl
₃ and PCl ₅ were used. These additive substances are mixed and installed inside the heater 1, and during the normal sintering process, the heater 1 is heated to 100 ° C. and the partial pressure of AlCl ₃ and PCl ₅ in the sintering furnace is increased. Sum of 1.0mmHg
Sintering was performed so that The thus-obtained sintered body was stretched and flame-polished, and then drawn in the same manner as in Example 1 using an apparatus as shown in FIG. The optical fiber preform 7 is melted by the heater 8, spun into an outer diameter of 125 μm, and guided to the reaction tube 9. Raw material for carbon coating is supplied from the raw material supply device 10 to the reaction tube 9, and the reaction is performed by the heat of the fiber itself to form a carbon film on the fiber. Then, the optical fiber 13 is coated with resin.
I got The initial transmission loss of this optical fiber at a wavelength of 1.55 μm was 0.21 dB / km, which was good. Further, this optical fiber was held in an atmosphere of 80 ° C. and a hydrogen partial pressure of 1 atm, and the change in transmission loss (Δα) at a wavelength of 1.24 μm was measured every 20 hours. The result is shown in FIG.
From this result, no increase in transmission loss due to hydrogen was observed at all in the first 40 hours, and it was confirmed that hydrogen did not reach the core portion.

[0021]

As is clear from the above description and the results of the examples, the present invention is excellent in that it has few bubbles and foreign substances, is excellent in fiber strength, and can suppress an increase in transmission loss due to diffusion of hydrogen from an external environment. Optical fiber, and the manufacturing method of the present invention can realize the optical fiber.

[Brief description of drawings]

FIG. 1 is a schematic view of a sintering apparatus for glass particulate deposits according to the present invention.

FIG. 2 is a schematic view of a drawing device according to the present invention.

FIG. 3 shows a wavelength of 1.24 depending on the hydrogen treatment time (hr) of the optical fibers obtained in Examples 1 to 5 and Comparative Example 1.
It is a graph showing the change of transmission loss in μm.

Claims (6)

[Claims] 1. In a silica-based single-mode fiber, a silica glass layer containing an element other than Si and O, which belongs to a group other than Group 14 of the periodic table and has a valence different from Si, as an outermost layer of a cladding portion. And an carbon fiber on the outside thereof. 2. The outermost layer of the cladding portion is made of Si,
The thickness of the silica glass layer other than O and belonging to a group other than Group 14 of Si in the periodic table and having a valence different from Si is 0.5 times or less the radius of the optical fiber. The optical fiber according to claim 1, which is characterized in that. 3. An element other than Si and O, which belongs to a group other than Group 14 to which Si belongs in the periodic table and has a valence different from Si, is one or more selected from Al, B and P. The optical fiber according to claim 1, wherein the optical fiber is provided. 4. SiO ₂ containing a dopant for adjusting the refractive index
After depositing glass fine particles on the outer periphery of the starting rod having a core part made of and a cladding part made of SiO ₂ , the glass fine particle deposition part is sintered to form a glass base material, and the glass base material is stretched and then drawn. In a method of manufacturing an optical fiber in which a carbon film is coated on the surface of the optical fiber by a thermal CVD reaction when the glass fiber is pulled, a periodic table other than Si and O is used as a sintering furnace atmosphere gas in the sintering step of the glass particle deposition portion 4. The method for producing an optical fiber according to claim 1, wherein a compound of an element belonging to a group other than Group 14 and having a valence different from Si is introduced. 5. SiO ₂ containing a refractive index adjusting dopant
After depositing glass particles on the outer periphery of the starting rod having a core part made of and a cladding part made of SiO ₂ , the glass particle deposition part is sintered to form a glass base material, and the glass base material is stretched, A glass base material is obtained by covering the outside of the stretched body with a pipe made by hollowing out the inside of a glass rod to form a glass base material, and a carbon film is coated on the optical fiber surface by a thermal CVD reaction when the glass base material is drawn. In the method for producing an optical fiber, the sintering furnace atmosphere gas is changed to S
4. A compound of an element other than i and O, which belongs to a group other than Group 14 of the periodic table and has a different valence from Si is introduced. Optical fiber manufacturing method. 6. The S introduced into the atmosphere gas of the sintering furnace.
a compound of an element other than i and O, which belongs to a group other than Group 14 of the periodic table and has a different valence from Si, is one or more selected from the compounds of Al, B or P. The method for manufacturing an optical fiber according to claim 4 or 5.