JP2003146680A - Method of manufacturing optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing an optical fiber that can make a refractive index profile definite within the same clad region formed through a process repeated several times. SOLUTION: A glass rod to be a core part is prepared, a clad part is formed on the outer circumference of the glass rod, thereby a first glass intermediate is produced. A tubular heaped body of fine glass particles is formed in which fluorine is added in the concentration of not less than 0.01 wt.% but not more than 0.4 wt.%. On this tubular body, dehydrating and vitrification treatments are performed using chlorine to obtain a first glass pipe. The first glass intermediate is inserted into the first glass pipe to make a second glass intermediate by a collapse method. On the outer circumference of the second glass intermediate, fine glass particles are heaped, with the dehydrating and the vitrification treatments performed on the heaped fine glass particles to produce a preform for an optical fiber. This preform is drawn by a tensile force not less than 80 MPa but not more than 280 MPa to manufacture the optical fiber.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for manufacturing an optical fiber.

[0002]

2. Description of the Related Art An optical fiber is manufactured by drawing an optical fiber preform having a core portion and a clad portion provided on the outer periphery of the core portion. Here, the optical fiber preform is configured so that the manufactured optical fiber achieves desired light propagation characteristics. For example, in an optical fiber preform for manufacturing a single mode optical fiber or a dispersion compensating optical fiber, the outer diameter of the optical fiber preform is relatively larger than the diameter of the core portion.

[0003]

When manufacturing an optical fiber preform having an outer diameter that is relatively larger than the diameter of the core portion, the cladding portion is generally formed by a plurality of steps. For example, the core portion and the first portion provided on the outer periphery of the core portion
A clad part and a second clad provided on the outer periphery of the first clad part
In the case of producing an optical fiber preform having a clad portion, first, the first portion is formed on the outer circumference of the glass rod to be the core portion.
The clad portion is formed, and the second clad portion is formed on the outer periphery of the first clad portion. Further, the second cladding portion is often formed by two steps. In this case, in the first step, the glass pipe manufactured through the vapor phase synthesis method is collapsed with respect to the outer circumference of the first cladding portion to form the inner circumference portion of the second cladding portion. And in the second step,
Glass fine particles are deposited on the outer circumference of the inner peripheral portion by a vapor phase synthesis method, and the deposited glass fine particles are made into transparent glass to form the outer peripheral portion.

When the glass pipe for forming the inner peripheral portion is produced, since a large amount of water is contained in the glass fine particle deposit obtained by the vapor phase synthesis method, dehydration treatment using chlorine gas or the like is performed. To be done. Further, also when forming the outer peripheral portion, dehydration treatment using chlorine gas or the like is performed on the glass fine particles deposited by the vapor phase synthesis method. By the way, when chlorine remains in the glass fine particles during the dehydration treatment, the remaining chlorine is added to the inside of the second cladding, and the refractive index of the second cladding becomes higher than a desired value. In particular, since the residual chlorine concentration does not necessarily match between the inner peripheral portion and the outer peripheral portion, it is difficult to match the refractive index of both. For example, when the outer peripheral portion has a higher refractive index than the inner peripheral portion, the bending loss of the optical fiber tends to increase. When the refractive index of the inner peripheral portion is higher than that of the outer peripheral portion, there is a problem that the cutoff wavelength becomes longer than a desired value and single mode transmission cannot be performed. Further, when the chlorine content in the inner peripheral portion is higher than that in the outer peripheral portion, when the optical fiber preform is drawn, the viscosity of the glass at the drawing temperature becomes lower in the inner peripheral portion than in the outer peripheral portion. Therefore, the stress generated by the tension during drawing is concentrated in the inner peripheral portion, and the refractive index in the inner peripheral portion is higher than that in the outer peripheral portion. As a result, the cutoff wavelength is further increased, and there is a problem that single mode transmission cannot be realized.

Therefore, an object of the present invention is to provide a method of manufacturing an optical fiber which can make the refractive index distribution within the same clad region formed by a plurality of steps constant.

[0006]

In the method of manufacturing an optical fiber according to the present invention, (1) a glass rod to be a core portion is prepared, and (2) at least one clad portion is formed on the outer circumference of the glass rod. To produce the first glass intermediate, (3)
Fluorine-added glass fine particles are deposited on the starting rod to form a glass porous body, and the glass porous body is dehydrated using a gas containing chlorine, and the dehydrated glass porous body is made into transparent vitrification. To obtain a glass body, provide a through hole along the central axis of the glass body, and add 0.01% fluorine.
A first glass pipe containing a concentration of not less than wt% and not more than 0.4 wt% is produced, and (4) the first glass intermediate is inserted into the first glass pipe, and the first glass pipe is inserted into the first glass pipe. A second glass intermediate is prepared by collapsing the glass intermediate, and (5) glass particles are deposited on the outer periphery of the second glass intermediate, and the deposited glass particles are dehydrated and dehydrated. The obtained glass fine particles are made into transparent glass to produce an optical fiber preform, and (6) the optical fiber preform is drawn with a tension of 80 MPa to 280 MPa to produce an optical fiber.

In the above manufacturing method, the first glass pipe is manufactured through a deposition step of depositing glass particles to which fluorine (F) has been added. The fine glass particles are subjected to dehydration treatment using a gas containing chlorine (Cl). When Cl used for this dehydration treatment mixes into the first glass pipe, Cl causes the refractive index of the glass pipe. Will increase above the desired value. However, since F which is a refractive index lowering agent is added to the first glass pipe, the increase in the refractive index due to Cl can be compensated by F. Moreover, such an optical fiber preform is 80MP
Since it is drawn with a tension of a or more and 280 MPa or less, the F concentration of the first glass pipe is 0.01 wt% or more and 0.4 or less.
When the content is less than or equal to wt%, it is possible to compensate for the change in refractive index caused by stress concentration due to the difference in viscosity difference. Can be manufactured.

Further, glass fine particles are deposited on the starting rod to form a second glass porous body, and a second porous glass pipe is obtained based on the second glass porous body. The glass pipe is dehydrated, the dehydrated second porous glass pipe is made into a transparent glass, a second glass pipe is produced, and a second glass intermediate is inserted into the second glass pipe. The second glass pipe can be collapsed with respect to the second glass intermediate to produce an optical fiber preform. Also in this way, it is possible to manufacture an optical fiber in which the difference in the refractive index between the inner peripheral portion and the outer peripheral portion of the clad portion is reduced.

Further, in the above-mentioned deposition step, it is preferable to add fluorine to the glass fine particles by using carbon tetrafluoride gas. Thereby, the F concentration of the first glass pipe is easily adjusted to fall within the above range.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of an optical fiber manufacturing method according to the present invention will be described below with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

In this embodiment, an optical fiber preform having a core portion, a first cladding portion provided on the outer periphery of the core portion, and a second cladding portion provided on the outer periphery of the first cladding portion is manufactured. . The second cladding portion is roughly formed by two steps.

FIG. 1 is a flow chart for explaining the optical fiber manufacturing method according to the present embodiment. As shown in FIG. 1, first, a core rod to be the core portion of the optical fiber preform is prepared (S101). This core rod is, for example, VA
It is made of quartz glass added with germanium oxide (GeO ₂ ) prepared by using the D (Vapor-phase Axial Deposition) method. Next, a first cladding glass pipe to be the first cladding portion of the optical fiber preform is prepared. The first cladding glass pipe may be, for example, a quartz glass pipe containing fluorine (F) produced by using the VAD method. Then, the core rod is inserted into the first cladding glass pipe. Then, the glass pipe is collapsed with respect to the core rod to produce a glass intermediate (S102).

Subsequently, the glass intermediate is heated and drawn. As a result, the ratio between the outer diameter of the glass intermediate and the core diameter is set to a desired value. After the drawing, the glass intermediate was treated with hydrofluoric acid (H
F) Immersing in an aqueous solution and chemically grinding the outer peripheral portion of the glass intermediate. Thereby, the ratio of the outer diameter of the glass intermediate body to the diameter of the core portion is adjusted to a value suitable for obtaining the chromatic dispersion value that the optical fiber as the final product should have. For convenience of explanation, the glass intermediate obtained in the steps so far is referred to as a first glass intermediate.

Next, a preferable example will be described with respect to the production of the first glass pipe to be the inner peripheral layer of the second cladding portion. The first glass pipe is preferably made by using the VAD method. That is, the glass raw material gas is supplied to a glass synthesis burner, the glass raw material gas is hydrolyzed by an oxyhydrogen flame emitted from this burner, and glass fine particles produced by the hydrolysis are deposited on an arbitrary starting rod, A porous body is obtained. At this time, not only the glass raw material gas but also carbon tetrafluoride (CF ₄ ) gas is supplied to the burner to add fluorine (F) to the glass fine particles. The amount added was such that the F concentration in the first glass pipe after completion was 0.
It is adjusted to be not less than 01 wt% and not more than 0.4 wt%.

The F-added glass porous body obtained as described above is placed in an appropriate heating furnace, and Cl ₂ gas is supplied into the heating furnace to perform dehydration treatment. As the gas used for the dehydration treatment, in addition to Cl ₂ gas, a gas containing chlorine such as SiCl ₄ or GeCl ₄ gas can be used. The dehydration treatment removes water or OH groups contained in the porous glass body. Subsequently, the temperature of the heating furnace is raised to a predetermined temperature to sinter the glass porous body and to make it a transparent glass. Next, a through hole is provided along the central axis of this transparent glass body by using a glass processing machine to obtain a first glass pipe.
(S103).

Next, the first glass pipe is placed in the first glass pipe.
By inserting the glass intermediate body and heating the first glass pipe from the outside thereof, the first glass pipe is collapsed with respect to the first glass intermediate body. Thereby, the core portion, the first clad portion provided on the outer periphery of the core portion, and the first
A second glass intermediate body having an inner peripheral portion of the second cladding portion provided on the outer periphery of the cladding portion is obtained (S104).
This inner peripheral portion contains F at a concentration of 0.01 wt% or more and 0.4 wt% or less.

After that, glass particles are deposited on the outer periphery of the second glass intermediate by a vapor phase synthesis method. At this time, the thickness of the deposited layer made of glass fine particles can be set to a thickness suitable for realizing the wavelength dispersion characteristics that the optical fiber manufactured by drawing the optical fiber preform should have. The second glass intermediate body on which the glass particles are deposited is placed in a predetermined heating furnace, and a gas containing chlorine is supplied into the heating furnace to remove water contained in the glass particles. Then, the temperature of the heating furnace is raised to sinter the glass fine particles and make them vitrified. As described above, the optical fiber preform having the core part, the first clad part, and the second clad part provided on the outer periphery of the first clad part is obtained (S105).

Subsequently, the optical fiber preform is attached to a predetermined drawing device, the lower end of the optical fiber preform is heated and drawn with a tension in the range of 80 MPa or more and 280 MPa or less. An optical fiber having one clad region and a second clad region around the first clad region is manufactured (S106).

As described above, in the optical fiber manufacturing method of this embodiment, first, the optical fiber preform is manufactured. That is, the first cladding glass pipe is collapsed on the glass rod to be the core portion, and the first glass intermediate body is manufactured. Next, on the outer periphery of the first cladding portion, VA
The first glass pipe manufactured by using the D method is collapsed to form the inner peripheral portion of the second cladding portion. continue,
Glass fine particles are deposited on the outer circumference of the inner circumference to produce an optical fiber preform. The first glass pipe has F of 0.
It is contained at a concentration of 01 wt% or more and 0.4 wt% or less.
Therefore, when drawing is performed with a tension in the range of 80 MPa or more and 280 MPa or less due to the balance between the increase in the refractive index due to the stress concentration generated during drawing and the action of the decrease in the refractive index due to fluorine, the inner and outer clad portions of the cladding of the optical fiber It is possible to prevent a difference in refractive index. Even if Cl is taken into the glass during the dehydration treatment during the production of the first glass pipe, the increase in the refractive index due to Cl is compensated.
Therefore, the inner peripheral portion formed from the first glass pipe,
The refractive index of the outer peripheral portion formed on the outer periphery can be substantially matched. Further, since the optical fiber preform thus manufactured is drawn with a tension in the range of 80 MPa or more and 280 MPa or less, it is possible to prevent the residual stress generated in the inner peripheral portion from increasing. Therefore, it is possible to prevent an increase in the refractive index due to an increase in residual stress.

Next, the effect of the optical fiber manufacturing method according to the present embodiment will be explained. FIG. 2A is a schematic diagram for explaining the difference in refractive index between the inner peripheral portion and the outer peripheral portion of the second cladding portion of the optical fiber preform. FIG. 2B is a schematic diagram for explaining the difference in refractive index between the inner peripheral portion and the outer peripheral portion in the second cladding region of the optical fiber. In the following description, the relative refractive index difference is a value with respect to the outer peripheral portion of the inner peripheral portion of the second cladding portion in the case of the optical fiber base material, and is the value of the inner peripheral portion of the second cladding region in the case of the optical fiber. It is a value for the outer peripheral part of the part. According to the knowledge of the present inventors, the concentration of Cl remaining in the glass fine particles after the dehydration treatment is 100 to 1
It is about 000 wtppm. Therefore, Cl having such a concentration is mixed in the optical fiber preform. In addition, the residual chlorine concentration in the inner peripheral portion of the second clad portion of the optical fiber preform is 900 wtp at the maximum compared to the outer peripheral portion.
It may be as high as pm. If there is such a density difference, the relative refractive index difference Δ ₁ between the inner peripheral portion and the outer peripheral portion is +0.0
It will be about 1%. This state is shown in FIG.

Further, when the residual chlorine concentration in the inner peripheral portion is higher than that in the outer peripheral portion, the viscosity of the glass at the drawing temperature becomes lower in the inner peripheral portion when the optical fiber preform is drawn. Therefore, the stress generated by the tension during drawing is concentrated in the inner peripheral portion, and the refractive index in the inner peripheral portion increases. As a result, as shown in FIG. 2B, in the manufactured optical fiber, a relative refractive index difference Δ ₂ is further generated in addition to the relative refractive index difference Δ ₁ generated in the optical fiber preform. The present inventors have found that the relative refractive index difference Δ caused by drawing
And ₂ were examined for the relationship between the residual chlorine concentration difference at an inner peripheral portion and outer peripheral portion. FIG. 3 shows how the relative refractive index difference Δ ₂ changes from the inner peripheral portion to the outer peripheral portion in response to the change in the residual chlorine concentration difference between the inner peripheral portion and the outer peripheral portion of the second cladding region of the optical fiber. It is a graph which shows whether. In FIG. 3, open circles are the results when the drawing tension is 240 MPa. Further, in FIG. 3, the triangles show the results in the case of 160 MPa. From Figure 3, the drawing tension is 240MP
It is understood that, when the residual chlorine concentration in the inner peripheral portion is higher than that in the outer peripheral portion by about 900 wtppm, the relative refractive index difference Δ ₂ between the inner peripheral portion and the outer peripheral portion is about + 0.08%. .

From the above, the drawing tension is 240 MPa.
In the case of, the relative refractive index difference Δ from the inner peripheral portion to the outer peripheral portion is
Difference in relative refractive index due to difference in concentration of residual chlorine Δ ₁ = 0.01
% And the relative refractive index difference Δ ₂ = 0.
The total amount (08%) (0.09%) is higher than that of the outer peripheral portion.

In the method of manufacturing the optical fiber according to the present embodiment, since F is added to the inner peripheral portion of the second cladding portion, the increase in the refractive index of the inner peripheral portion is compensated. Below, F
The appropriate addition amount of is explained. FIG. 4 is a graph for explaining the effect of adding F to the inner peripheral portion of the second cladding portion. In order to explain the effect of adding F, the figure shows the case where no Cl remains at the inner and outer peripheral portions of the second cladding portion. Further, in the figure, line A shows the relationship between the F concentration in the optical fiber preform and the relative refractive index difference. Furthermore, line B
Shows the relationship between the F concentration in the inner peripheral portion of the cladding region and the relative refractive index difference in the optical fiber produced by drawing the optical fiber preform with a tension of 240 MPa. In the optical fiber preform, the relative refractive index difference Δ _M decreases as the F concentration in the inner peripheral portion increases (line A). On the other hand, in the optical fiber, the relative refractive index difference increases as the amount of F added to the inner peripheral portion increases (line B). This is because as the F concentration in the inner peripheral portion increases, the viscosity of the inner peripheral portion at the time of drawing decreases and the stress concentrates on the inner peripheral portion. Considering the results represented by the lines A and B, the net change in the relative refractive index difference in the optical fiber due to the change in the F concentration is represented by the line C.

As described above, the relative refractive index difference Δ caused by the difference in residual chlorine concentration is about 0.09%. Referring to FIG. 4, in order to compensate for the relative refractive index difference Δ of about 0.09%, the concentration of F added to the inner peripheral portion of the second cladding portion should be set to 0.3 wt%. I understand. F concentration is 0.
When it is lower than 3 wt%, the refractive index of the inner peripheral part of the second cladding part becomes higher than that of the outer peripheral part. Therefore, the cut-off wavelength of the light propagating through the manufactured optical fiber becomes longer, and single mode operation in a desired signal wavelength band may be impossible. Therefore, the F concentration is preferably 0.3 wt% or more. Further, when the F concentration is increased from 0.3 wt%, the relative refractive index difference decreases, but the relative refractive index difference is -0.0.
If it is lower than 2%, the bending loss of the manufactured optical fiber increases. Referring to FIG. 4, the F concentration is 0.4
When it is wt%, the change in the relative refractive index difference caused by the addition of F is about -0.11%. Therefore, the relative refractive index difference between the inner peripheral portion of the second cladding region and the outer peripheral portion of the optical fiber is −0.
It can be seen that the F concentration should be 0.4 wt% in order to achieve 02% or more.

The suitable concentration of F has been described above in the case of drawing an optical fiber preform having a residual chlorine concentration difference of about 900 wtppm between the inner peripheral portion and the outer peripheral portion of the second cladding portion with a tension of 240 MPa. Drawing tension of 240M
The reason for setting Pa is that the breaking life of the manufactured optical fiber is sufficiently secured and the optical transmission loss is sufficiently reduced. However, the tension at the time of drawing the optical fiber preform may be adjusted in consideration of the optical transmission characteristics of the optical fiber to be manufactured. According to the knowledge of the present inventors, in a dispersion compensating fiber or the like in which Ge is added at a high concentration, the transmission loss is suppressed to a level at which there is no practical problem.
The drawing tension is preferably 80 MPa or more. Also,
As a result of the same consideration as above, it was found that the preferable F concentration in this case is 0.01 wt% or more and 0.04 wt% or less. If it is less than 0.01 wt%, the cut-off wavelength of the light propagating through the manufactured optical fiber becomes long, and therefore single mode operation in the desired signal wavelength band may be impossible. If it is higher than 0.04 wt%, the relative refractive index difference Δ becomes lower than −0.02%,
The bending loss of the manufactured optical fiber increases. As a result of repeating similar considerations, the inventors have found that a preferable range of the F concentration added to the inner peripheral portion of the second cladding portion of the optical fiber preform is 0.01 wt% or more and 0.4 wt%, It is considered that the preferable range of the drawing tension is 80 MPa or more and 280 MPa or less.

(Embodiment 1) Next, the method for producing an optical fiber according to the present invention will be described in more detail with reference to embodiments. FIG. 5 shows the optical fiber 1 manufactured in Example 1.
It is a figure explaining the refractive index profile of. As shown in the figure, the optical fiber 1 includes a core region 10 having an outer diameter of 2a and a maximum refractive index of n ₀ , and a core region 10 surrounding the core region 10 having an outer diameter of 2b and a refractive index of n ₁ . It has a first cladding region 11 and a second cladding region 12 which surrounds the first cladding region 11 and has an outer diameter of 2c (125 μm) and a refractive index of n ₂ . The magnitude relation of the refractive index of each region is n ₁ <n ₂ <n ₀ .

First, the production of the optical fiber preform will be described. First, a core rod to be the core portion of the optical fiber preform was prepared. This core rod is made of GeO ₂ -doped quartz glass produced by the VAD method. Also, the relative refractive index difference Δ of this core rod with respect to pure quartz is
_c has a maximum value of 1.5% on its central axis, and is distributed toward the outer circumference so as to be approximated by the relationship represented by Δ _c = 1.5 × [1- (r / a) ² ] (%) is doing. Here, r is the distance from the central axis of the core rod (r ≦ a), and a is the radius of the core rod. Since the core rod has such a relative refractive index difference distribution, the refractive index profile of the core region of the optical fiber 1 can be as shown in FIG.

Next, a glass tube for the first cladding, which is the first cladding portion of the optical fiber preform, was prepared. This glass pipe was made of F-containing quartz glass and was manufactured by using the VAD method. That is, first, a glass porous body containing 0.04 wt% of fluorine (F) was prepared by the VAD method. Next, this glass porous body was heated to a predetermined temperature to form a transparent glass. Subsequently, a through hole was provided along the central axis of this glass body to obtain a first cladding glass pipe.

Subsequently, the first cladding glass pipe was attached to a heating furnace for carrying out the collapse, the etching gas was supplied into the glass pipe, and the glass pipe was heated to etch the inner surface thereof. By this etching, the inner diameter of the first cladding glass pipe was set to a predetermined value, and then the core rod was inserted therein. Then, the first glass pipe was collapsed on the core rod to obtain a glass intermediate.

Then, the glass intermediate was heated and stretched, and the ratio of the outer diameter of the glass intermediate and the diameter of the core was set to a desired value.
Further, the glass intermediate is immersed in an aqueous solution of hydrofluoric acid (HF), the outer peripheral portion of the glass intermediate is chemically ground, and the ratio of the outer diameter to the core diameter is measured as the final product. It was adjusted to a value suitable for obtaining the chromatic dispersion value that the fiber should have.

Next, the glass which becomes the inner peripheral layer of the second cladding portion
A pipe was produced. That is, glass raw material gas and C
F_FourGas is supplied to the glass synthesis burner,
The glass material gas and CF due to the flame emitted from_Fourgas
Pyrolytically decomposes the generated glass particles into any starting glass
By depositing on a rod, a porous glass body was obtained. This and
F concentration in the second glass pipe to be manufactured is 0.3w
CF to be t% _FourThe amount of gas supplied was adjusted. Next
Then, the glass porous body is placed in a predetermined heating furnace, and
Cl in the heating furnace₂Gas is flowed and contained in the glass porous body
Water was removed. Next, change the temperature of the heating furnace to the specified temperature.
The glass porous body to sinter and
Bright glass. Columnar glass body thus obtained
A hole is mechanically drilled along the center axis of the
I got an ip. Measure the concentration of residual chlorine in this glass pipe
When determined, the concentration was about 900 ppm.

A glass pipe to be the inner peripheral portion of the second clad portion was attached to a heating furnace and its inner surface was etched using a predetermined etching gas. After the etching, the above glass intermediate was inserted into this glass pipe, and the glass pipe was heated from the outside to collapse the glass pipe with respect to the glass intermediate to obtain a second glass intermediate. .

Next, glass particles were deposited on the outer periphery of the second glass intermediate by the VAD method. At this time, the thickness of the deposited layer composed of glass fine particles was set to a thickness suitable for realizing a desired wavelength dispersion characteristic in an optical fiber having an outer diameter of 125 μm produced by drawing an optical fiber preform. The second glass intermediate body on which the glass particles were deposited was placed in a predetermined heating furnace, and chlorine gas was caused to flow in the heating furnace to perform dehydration treatment. Then, the temperature of the heating furnace was raised to sinter the glass fine particles and make them vitrified. As described above, the optical fiber preform having the core part, the first clad part, and the second clad part provided on the outer periphery of the first clad part was obtained. The concentration of chlorine remaining on the outer periphery of the second clad was about 150 ppm.

After this, the optical fiber preform was attached to a predetermined drawing device, the lower end of the optical fiber preform was heated and drawn with a tension of 240 MPa to produce an optical fiber 1 having an outer diameter of 125 μm. About the optical fiber 1,
As a result of measuring the refractive index distribution by the RNFP method, the relative refractive index difference between the inner peripheral portion and the outer peripheral portion of the second cladding portion was −0.
It was 01%. Then, the optical transmission characteristics of the optical fiber 1 were measured. As a result, the chromatic dispersion value at a wavelength of 1.55 μm was about −47 ps / nm / km, and the dispersion slope was about −0.06 ps / nm ² / km. When the cutoff wavelength was measured by bending the optical fiber 1 with a radius of curvature of 2 m, it was 780 nm.
I got the result. From this result, the transmission band of 1.
It was confirmed that single mode transmission is realized in the 55 μm band. Furthermore, when the optical fiber 1 was wound into a coil having a diameter of 20 mm and measured, the bending loss was 2 dB.
It was found to be a sufficiently low value of about / m.

(Example 2) As Example 2, except that the concentration of F in the second glass pipe was set to 0.03 wt% in the production of the optical fiber preform, the same conditions and procedures as in Example 1 were used. An optical fiber was manufactured. When manufacturing this optical fiber, the refractive index distribution of the optical fiber preform was measured using a preform analyzer. As a result, the relative refractive index difference between the inner peripheral portion and the outer peripheral portion of the second cladding portion was 0. It was 002%. Further, when the refractive index distribution of the manufactured optical fiber was measured by the RNFP method, the relative refractive index difference between the inner peripheral portion and the outer peripheral portion of the second cladding region was 0.05%. This optical fiber has a diameter of 2
When the cutoff wavelength was measured by bending with a curvature of m, the cutoff wavelength was 1600 nm. When a signal light with a wavelength of 1.55 μm is propagated in this optical fiber,
Since the wavelength of the signal light is shorter than the cutoff wavelength above,
Not only the fundamental mode light but also the higher order mode light will propagate in this optical fiber. However, even in such a situation, if the optical fiber is sufficiently long, the higher-order mode light is attenuated, so that this optical fiber can be used substantially as a single-mode optical fiber.

The method for manufacturing an optical fiber according to the present invention has been described above with reference to the embodiments and examples.
The present invention is not limited to these. For example, second
The outer peripheral portion of the clad portion can be formed similarly to the inner peripheral portion thereof. That is, first, a glass porous body is formed by the VAD method, a glass porous body is formed by the VAD method, and the glass porous body is subjected to dehydration treatment using chlorine gas for sintering and transparent vitrification. To do. Next, a through hole is provided along the central axis of the cylindrical glass body to obtain a glass pipe. Then, the second glass intermediate body can be inserted into the glass pipe, and the glass pipe can be collapsed with respect to the second glass intermediate body to form the outer peripheral portion.

Further, in the above-mentioned embodiments and examples, the second glass pipe which is the inner peripheral portion of the second cladding portion is manufactured by the VAD method, but the present invention is not limited to this. For example, an OVD (Outside
After depositing glass fine particles by the Vapor Deposition method, the starting rod may be pulled out to form a cylindrical glass porous body, and dehydration treatment and transparent vitrification may be performed to produce the second glass pipe.

Furthermore, the method for producing an optical fiber according to the present invention can also be applied when producing an optical fiber having three or more cladding regions. In this case, first, in the same manner as the procedure (S102) of forming the first cladding portion on the outer periphery of the core rod, a plurality of cladding portions that sequentially surround the outer periphery of the core rod are formed. Next, the procedure of forming the inner peripheral portion and the outer peripheral portion of the second cladding portion in the above embodiment (S1
03 to S105) to form the outermost clad portion, and produce an optical fiber preform. Then, if this optical fiber preform is drawn with the above drawing tension, an optical fiber having three or more cladding regions is manufactured.

[0039]

As described above, according to the optical fiber manufacturing method of the present invention, it is possible to make the refractive index distribution within the same cladding region formed by a plurality of steps uniform. A method of making a fiber is provided.

[Brief description of drawings]

FIG. 1 is a flow chart illustrating a method of manufacturing an optical fiber according to the present embodiment.

FIG. 2 (a) is a schematic diagram for explaining a difference in refractive index between an inner peripheral portion and an outer peripheral portion in a second cladding portion of an optical fiber preform. FIG. 2B is a schematic diagram for explaining the difference in refractive index between the inner peripheral portion and the outer peripheral portion in the second cladding region of the optical fiber.

FIG. 3 shows how the relative refractive index difference between the inner peripheral portion and the outer peripheral portion with respect to the change in the residual chlorine concentration difference between the inner peripheral portion and the outer peripheral portion of the second cladding region of the optical fiber. It is a graph which shows whether it changes.

FIG. 4 is a graph illustrating the effect of adding F to the inner peripheral portion of the second cladding portion.

FIG. 5 is a diagram illustrating a refractive index profile of the optical fiber 1 manufactured in this example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical fiber, 10 ... Core area | region, 11 ... 1st cladding area, 12 ... 2nd cladding area.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) // C03C 13/04 C03C 13/04 (72) Inventor Masaaki Hirano 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Sumitomo Electric Industries Yokohama factory F term (reference) 2H050 AC14 4G021 BA04 EA03 EB18 EB19 EB24 4G062 AA07 BB02 CC01 DA08 LB08 NN01

Claims (3)

[Claims] 1. A glass rod to serve as a core portion is prepared, and at least one clad portion is formed on the outer periphery of the glass rod to prepare a first glass intermediate body, and glass fine particles to which fluorine is added are prepared. A glass porous body is formed by depositing on a starting rod, the glass porous body is dehydrated using a gas containing chlorine, and the dehydrated glass porous body is transparentized to obtain a glass body, A through hole is provided along the central axis of the glass body, and contains fluorine in a concentration of 0.01 wt% or more and 0.4 wt% or less.
Of the glass pipe, the first glass intermediate is inserted into the first glass pipe, the first glass pipe is collapsed with respect to the first glass intermediate, and the second glass intermediate is inserted. A glass intermediate is prepared, glass fine particles are deposited on the outer periphery of the second glass intermediate, the deposited glass fine particles are subjected to dehydration treatment, and the dehydrated glass fine particles are converted into transparent vitreous to obtain an optical fiber. A method for producing an optical fiber, which comprises producing a preform and drawing the optical fiber preform with a tension of 80 MPa or more and 280 MPa or less to produce an optical fiber. 2. A glass rod is deposited on a starting rod to form a second glass porous body, a second porous glass pipe is obtained based on the second glass porous body, and the second glass porous body is obtained. A porous glass pipe is dehydrated, and the dehydrated second porous glass pipe is made into transparent glass to produce a second glass pipe, and the second glass intermediate is placed in the second glass pipe. The method for producing an optical fiber according to claim 1, wherein a body is inserted, and the second glass pipe is collapsed with respect to the second glass intermediate body to produce an optical fiber preform. 3. The method for producing an optical fiber according to claim 1, wherein in the depositing step, fluorine is added to the glass fine particles using carbon tetrafluoride gas.