JP2001192233A - Optical fiber and method for manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical fiber having a desired refractive index profile which can be manufactured stably, which is an optical fiber having a ring type structure in which a central core portion is doped with an F element, and a method for manufacturing the same. . SOLUTION: A central core region 11 made of quartz glass and doped with an F element, a ring core region 13 doped with GeO ₂ , and an inner clad region 1 doped with an F element.
And a central core region 11
Decreasing towards the boundary, in either or buffer layer 12 or the radial direction GeO ₂ concentration of SiO ₂ of both is added as SiO ₂ or P or Cl additive-free between the ring core region 13 as A concentration gradient region.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber having a ring core and a preferred method for manufacturing the same.

[0002]

2. Description of the Related Art A dispersion-shifted optical fiber has a zero-dispersion wavelength at which the chromatic dispersion value becomes zero at around 1.55 μm. As one type, there is a ring-type structure in which a high refractive index ring core region and a low refractive index cladding region are provided concentrically around a central core region. A dispersion-shifted optical fiber having such a ring-shaped refractive index profile is manufactured by drawing an optical fiber preform having a similar refractive index profile.

[0003] The refractive index profile of this optical fiber preform is based on the fact that quartz glass is used as a main component, and that the F (fluorine) element is added to the central core to be the central core region of the optical fiber, and the ring core to be the ring core region. GeO ₂
(Germanium dioxide). Then, an optical fiber having a desired refractive index profile can be obtained by subjecting the optical fiber preform to melt spinning, that is, drawing.

[0004]

However, when the optical fiber preform is drawn, the optical fiber preform is heated,
At this time, the F element added to the central core portion diffuses to the peripheral region, while the Ge added to the ring core portion diffuses to the central core portion and the outer cladding region. Due to this mutual diffusion, transmission loss increases. Also, when Ge and F are mixed, GeF ₄ and GeO are generated in the heating and integrating process to generate bubbles, and the quality of the manufactured optical fiber is deteriorated. As a result, there is a problem that desired fiber characteristics cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problem, and is an optical fiber having a ring structure having a region to which F element is added and a region to which Ge is added. It is an object to provide an optical fiber having a possible desired refractive index profile and a method for manufacturing the same.

[0006]

In order to solve the above-mentioned problems, an optical fiber according to the present invention is made of quartz glass and has a central core region to which F element is added and a ring core region to which GeO ₂ is added. An optical fiber, wherein an undoped SiO 2 is provided between the central core region and the ring core region.
₂ Si containing either (silicon dioxide) or P (phosphorus) or Cl (chlorine) or both
It is characterized by having a buffer layer made of O ₂ .

The optical fiber of the present invention can be manufactured by drawing an optical fiber preform having a cross-sectional profile similar to that of the optical fiber. In other words, the optical fiber preform also has a buffer layer made of SiO ₂ either or both its SiO ₂ or P or Cl no additives are added between the central core region and the ring core region. When this optical fiber is drawn, the interdiffusion of F and Ge between the ring core region and the central core region is suppressed by the presence of the buffer layer. The presence of the buffer layer in the obtained optical fiber means that the effect of suppressing the mutual diffusion functions sufficiently and the fiber characteristics are maintained.

The thickness of the buffer layer is 0.01 μm or more and 5 μm or more.
It is preferably not more than μm. If the thickness of the buffer layer is thinner than this, Ge and F may diffuse beyond the buffer layer. On the other hand, if the thickness of the buffer layer is larger than this, the bending loss that occurs when the optical fiber is bent increases, which is not preferable.

[0009] Alternatively, the optical fiber of the present invention is made of quartz glass, and has a central core region arranged concentrically, a ring core region doped with germanium dioxide, and an inner clad region doped with elemental fluorine. in the fiber, between the ring core region and inner cladding region, characterized in that one or both of the SiO ₂ or P or Cl with no additive is provided with a buffer layer made of SiO ₂ being added.

Also in this case, the interdiffusion of F and Ge between the ring core region and the inner cladding region when an optical fiber is formed by drawing an optical fiber preform having a similar structure is suppressed by the presence of the buffer layer. Is done. The fact that the buffer layer is present in the obtained optical fiber means that the effect of suppressing the interdiffusion sufficiently functions and the fiber characteristics are maintained.

In this case, the thickness of the buffer layer is 0.01 μm
It is preferable that it is above. This is because if the thickness of the buffer layer is smaller than this, Ge and F may be interdiffused beyond the buffer layer. On the other hand, the change in bending loss caused by bending the optical fiber due to the thickness of the buffer layer is smaller than when the buffer layer is formed between the ring core region and the central core region, so that the buffer layer is further thickened. You may.

Alternatively, the optical fiber of the present invention is made of quartz glass, and has a central core region to which an F element is added;
an optical fiber having a ring core region to which eO ₂ is added, wherein the radius of the central core region is a [μm], and the Ge of the ring core region at the position of the radius r [μm] from the center.
If the concentration of O ₂ is C _G (r) [wt%]

(Equation 5) The concentration gradient y _G1 [wt% · μm ² ] of GeO _{2 at} the boundary between the ring core region and the central core region defined by
00 wt% · μm ² or less, or radius r from the center
If the concentration of the F element in the central core region at the position of [μm] is C _F (r) [wt%]

(Equation 6) Concentration gradient y _F1 [wt%] of the elemental fluorine at the boundary between the central core region and the ring core region defined in
[Μm ² ] is 18 wt% · μm ² or less.

Alternatively, the optical fiber of the present invention is made of quartz glass, and has a central core region arranged concentrically,
In an optical fiber having a ring core region doped with eO ₂ and an inner cladding region doped with an F element,
The radius of the ring core region is b [μm], and the radius is r from the center.
If the concentration of GeO ₂ in the ring core region at the position of [μm] is C _G (r) [wt%]

(Equation 7)Boundary between the ring core region and the inner cladding region defined in
Concentration gradient of germanium dioxide in the part y_G2[Wt
% ・ Μm^TwoIs 180 wt% · μm^TwoLess than or centered
Of the inner cladding region at a radius r [μm] from
The concentration of F element is C _F(R) [wt%]

(Equation 8) Concentration gradient of elemental fluorine at the boundary between the inner cladding region and the ring core region defined by the formula y _F2 [wt% · μm
² ] is 30 wt% · μm ² or less.

The diffusion speed of the interdiffusion of F and Ge generated during the above-described drawing is caused by the concentration gradient at the boundary between the region where F element is added and the region where GeO ₂ is added. According to the findings of the present inventors, the radial distribution of the added amount of GeO ₂ or the added amount of F element in each region is determined by the weighted concentration gradient y _G1 at the boundary defined by the equations (1) to (4), y _F1 ,
By setting y _G2 and y _{F2 to} be equal to or less than predetermined values,
The diffusion speed of the mutual diffusion of F and Ge is reduced, and the mutual diffusion is suppressed. For this reason, desired fiber characteristics can be reliably obtained.

On the other hand, the method for manufacturing an optical fiber according to the present invention comprises:
(1) a step of forming a quartz glass pipe having a layer to which germanium dioxide is added at least on the inner peripheral side;
(2) generating a buffer layer by depositing SiO ₂ either or both its SiO ₂ or P or Cl additive-free into the quartz glass pipe is added, the inner (3) a buffer layer A step of inserting a quartz glass rod to which the element F is added and then heating and integrating to form an intermediate preform; and (4) a step of melt-spinning an optical fiber preform containing the intermediate preform. It is characterized by being. According to this manufacturing method, it is possible to suitably manufacture the optical fiber having the above-described buffer layer.

Alternatively, the method for manufacturing an optical fiber according to the present invention comprises: (1) a step of forming a quartz glass pipe having a layer to which GeO ₂ is added at least on the inner peripheral side; and (2) heating the quartz glass pipe. (3) evaporating GeO ₂ on the inner surface to remove at least a part thereof; and (3) inserting a quartz glass rod to which the element F is added into the inside of the quartz glass pipe, followed by heating and integration to form an intermediate mother And (4) a step of melt-spinning an optical fiber preform including an intermediate preform. According to this manufacturing method, it is possible to preferably manufacture an optical fiber in which the concentration of germanium dioxide near the boundary of the ring core region is reduced.

The method of manufacturing an optical fiber having an inner cladding region according to the present invention is the following three methods. The first method includes (1) a step of producing a quartz glass pipe having a layer to which at least the F element is added on the inner peripheral side, and (2) a step of forming a non-added SiO ₂ or P or Cl inside the quartz glass pipe. Depositing SiO ₂ to which either or both of them are added to form a buffer layer; (3)
Forming a glass layer to which GeO ₂ is added on the inner periphery thereof to form an intermediate pipe; and (4) inserting a quartz glass rod inside the intermediate pipe, heating and integrating to form an intermediate base material. And (5) a step of melt-spinning the optical fiber preform including the intermediate preform.

The second method is as follows: (1) Concentrically forming a quartz layer, a layer to which GeO ₂ is added, a layer to which neither P nor Cl or both are added, from the center of the axis. To produce a quartz glass rod,
(2) a step of forming a quartz glass pipe having a layer to which at least the F element is added on the inner peripheral side; and (3) inserting a quartz glass rod into the quartz glass pipe, followed by heating and integration to form an intermediate base material. And (4) a step of melt-spinning the optical fiber preform including the intermediate preform.

In the third method, (1) and (2) are common to the first method. (3) A quartz glass rod having a quartz layer around the axis and a layer to which germanium dioxide is added around the quartz layer is used. Forming, (4) inserting a quartz glass rod inside the buffer layer, heating and integrating to form an intermediate preform, and (5) melt-spinning an optical fiber preform containing the intermediate preform. And a process. Either method can suitably manufacture the optical fiber according to the present invention having a buffer layer between the inner cladding region and the ring core region.

In the step of producing these quartz glass pipes, an opening penetrating the axial center is formed by plastically deforming a quartz glass rod having a layer to which elemental fluorine or germanium is added at least on the inner peripheral side at a high temperature. It may be made into a glass pipe. According to this, a required quartz glass pipe can be suitably produced.

Alternatively, another method of manufacturing an optical fiber according to the present invention comprises the steps of (1) forming a quartz glass rod having a quartz layer on the axial center side and a ring-shaped layer doped with germanium dioxide on the outside thereof. (2) a step of forming a quartz glass pipe by opening a quartz glass rod along an axis; and (3) inserting a quartz glass rod added with elemental fluorine into the inside of the quartz glass pipe, followed by heating and integration. (4) a step of melt-spinning an optical fiber preform including the intermediate preform. According to this manufacturing method, it is also possible to suitably manufacture an optical fiber having the above-described buffer layer.

[0022]

Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. To facilitate understanding of the description, the same reference numerals are given to the same constituent elements in each drawing as much as possible, and duplicate description will be omitted.

FIG. 1 is a diagram showing a cross-sectional structure of an optical fiber according to a first embodiment of the present invention, and FIG. 2 shows a refractive index profile thereof.

The optical fiber according to the first embodiment is a quartz glass.
It is made of lath and, as shown in FIGS.
Center core region 11 (outer diameter 2a), inner buffer layer 12 (thickness
T ₁), Ring core region 13 (outer diameter 2b, thickness t)_b),
Outer buffer layer 14 (thickness t_Two), Inner cladding region 15
(Outer diameter 2c, thickness t_c), Outer cladding region 16 is concentric
They are arranged in a circle. Of which, inside and outside
The two buffer layers 12, 14 and the outer cladding region 16 on the
Pure quartz with almost no additives, whose refractive index is n
₀And elemental fluorine is added to the central core region 11.
And its refractive index is n₀Lower n₁And the ring core
The region 13 is doped with germanium dioxide.
Refractive index is n₀Higher n_TwoAnd the inner cladding region 15
Has a fluorine element added and has a refractive index of n₀And n₁
N between_ThreeThe addition amount is adjusted so that
You.

The outer diameter 2a of the central core region 11 is several μm, and the outer diameter 2b of the ring core region 13 is several μm to 10 μm.
about [mu] m is (thickness t _b is about several [mu] m), the outside diameter 2c of the inner cladding region 15 is several μm~ several tens [mu] m approximately (a thickness t _C about several Myuemu～10myuemu), external cladding region The outer diameter of 16 is usually 125 μm. The thicknesses t ₁ and t ₂ of the buffer layers 12 and 14 are 0.01 to 5 respectively.
It is about μm. Further, the relative refractive index difference Δn ^{− of} the central core region 11 with reference to the refractive index n ₀ of the outer cladding region 16 =
(N ₁ −n ₀ ) / n ₀ is −0.2% to −0.7%, and similarly, the relative refractive index difference Δn ^{+ of} the ring core region 13 based on the refractive index n ₀ of the outer cladding region 16. = (N ₂ -n
₀ ) / n ₀ is about 0.5 to 1.5%.

Next, two of the methods for manufacturing this optical fiber are described.
A description will be given by exemplifying different types of manufacturing methods. FIG. 3 is a flowchart showing the first manufacturing method, and FIG. 4 is a cross-sectional view showing an intermediate product in each step.

First, in step S11, a starting glass tube 10 made of quartz glass to which element F is added is prepared (FIG. 4A). The starting glass tube 10 is to be an inner cladding region 15 having a low refractive index of an optical fiber, and is, for example, a tube having an inner diameter of 14 mm, an outer diameter of 25 mm, and a length of 300 mm. Here, the concentration of the added F element is 0.4
It is preferable that the content be in the range of wt% to 1.5 wt%.

In step S12, the starting glass tube 1
0 any or CVD of SiO ₂ added with both the inner peripheral surface of the additive-free SiO ₂ or P or Cl in
The outer buffer layer 14 is formed by depositing a thickness of about 0.06 mm by a method (FIG. 4B). By adding P or Cl, the viscosity difference between the layers formed on both sides of the buffer layer 14 can be adjusted, and the drawing at the time of manufacturing the optical fiber can be stably performed. Subsequently, in step S13, and the GeO ₂ was added to the inner peripheral surface of the outer buffer layer 14 Si
O ₂ is deposited by a CVD method to a thickness of about 1.7 mm,
The ring core region 13 is formed (FIG. 4C). Here, the concentration of GeO ₂ to be added is 10 wt% to 30 w%.
It is preferable to be about t%. Thereby, the ring core region 13 has a high refractive index. Further, in step S14, the non-added Si is added to the inner peripheral surface of the ring core region 13.
SiO ₂ to which O ₂ or P and / or Cl is added is 0.04 mm thick by CVD.
To form an inner buffer layer 12 (FIG. 4).
(D)). As a result, a multilayer glass tube 10 having an inner diameter of about 12.2 mm is obtained.

By adding P or Cl to the quartz glass forming the buffer layers 12 and 14, the viscosities of the respective layers at the time of heating and melting can be adjusted, and the heating wire described later can be easily and reliably performed.

In step S15, the central core region 1 is placed inside the multilayer glass tube 10 thus formed.
The F element-added quartz glass rod 11a that becomes 1 is inserted (FIG. 4E). Here, the F element concentration in the central core region 11 is about 0.5 wt% to 2.5 wt%. At this time, a gap may be generated between the multilayer glass tube 10 and the quartz glass rod 11a. However, in order to obtain an optical fiber in which the ellipticity of the core region is small, it is preferable that the gap is small. Before insertion, both or one of the multilayer glass tube 10 and the quartz glass rod 11a may be heated and stretched to an appropriate diameter, or may be surface-treated with an HF solution. When the quartz glass rod 11a is stretched by heating using an oxygen / hydrogen flame, a surface treatment with an HF solution is indispensable in order to remove moisture adhering to the surface of the quartz glass rod 11a.

In step S16, the multilayer glass tube 10 in which the quartz glass rod 11a is inserted is heated under reduced pressure to integrate them, thereby obtaining a multilayer quartz glass rod 20 (FIG. 4 (f)). ). This heating integration step is performed in an atmosphere of Cl ₂ gas or a mixed gas of Cl ₂ gas and O ₂ gas.

In step S17, the multilayer quartz glass rod 20 is inserted inside the pure quartz glass tube 16a (FIG. 4 (g)). This pure quartz glass tube 16a
Is to be the lower refractive index outer cladding region 16 of the optical fiber. Before insertion, the multilayer quartz glass rod 20 may be heated and stretched to an appropriate diameter,
Further, the surface may be treated with an HF solution. When the multilayer quartz glass rod 20 is heated and stretched using an oxygen / hydrogen flame, it is essential to perform a surface treatment with an HF solution in order to remove moisture adhering to the surface.

Then, in step S18, the quartz glass tube 16a with the multilayer quartz glass rod 20 inserted therein is heated under reduced pressure to integrate the two (FIG. 4).
(H)). In order to increase the equivalent fiber length, an outer cladding may be further provided outside the outer cladding by a known VAD method or OVD method. Through the above steps, an optical fiber preform is obtained. The optical fiber preform manufactured in this way is shown in FIG.
Has a refractive index profile similar to the refractive index profile of the optical fiber shown in FIG.

In step S19, the optical fiber preform is heated and drawn by a known method to obtain an optical fiber having a desired refractive index profile. By using the optical fiber preform having such a refractive index profile, when drawing a heating wire, the Ge atoms from the ring core region 13 to the central core region 11 and the inner cladding region 15 and the F atoms in the opposite direction. Is prevented by the presence of both buffer layers 12, 14. That is,
The inflow of F atoms into the ring core region 13 and the outflow of Ge atoms from this region are suppressed. As a result, an optical fiber can be manufactured while the ring core region 13 is maintained in a high refractive index state. Therefore, an optical fiber having good characteristics as a dispersion-shifted fiber can be obtained.

Next, the second manufacturing method will be described with reference to FIGS. FIG. 5 is a flowchart showing the second manufacturing method, and FIG. 6 is a cross-sectional view showing an intermediate product in each step.

First, in step S21, GeO ₂
A quartz glass tube 10a to which is added is prepared (FIG. 6).
(A)). The quartz glass tube 10a is to be a ring core region 13 having a high refractive index of an optical fiber, and has, for example, an inner diameter of about 15 mm, an outer diameter of about 24 mm, and a length of 30 mm.
It has a tubular shape of about 0 mm. And the GeO ₂ concentration is 10 wt% to 30 wt%.

In step S22, on the inner peripheral surface of the quartz glass tube 10a, unadded SiO _{2 and /} or SiO _{2 to} which either or both of P and Cl are added.
₂ is deposited by a CVD method to a thickness of about 0.3 mm to form an inner buffer layer 12 (FIG. 6B).

In step S23, a quartz glass rod 11a to which the element F is added, which becomes the central core region 11, is inserted inside the quartz glass tube 10a on which the buffer layer 12 is formed (FIG. 6C). The F element concentration of the quartz glass rod 11a is 0.5 wt% to 2.5 wt%. At this time,
A gap may be formed between the quartz glass tube 10a and the quartz glass rod 11a. However, in order to obtain an optical fiber in which the ellipticity of the core region is small, it is preferable that the gap is small. Before insertion, both or one of the quartz glass tube 10a and the quartz glass rod 11a may be heated and stretched to an appropriate diameter, or may be surface-treated with an HF solution. When the quartz glass rod 11a is stretched by heating using an oxygen / hydrogen flame, a surface treatment with an HF solution is indispensable in order to remove moisture adhering to the surface of the quartz glass rod 11a.

In step S24, the quartz glass rod 1
The quartz glass tube 10a in the state where 1a is inserted is heated to integrate them (FIG. 6D). This heating integration step is performed in an atmosphere of Cl ₂ gas or a mixed gas of Cl ₂ gas and O ₂ gas. Thus, the multilayer quartz glass rod 2
0a is obtained.

In step S25, the multilayer quartz glass rod 20a is moved to the region 15 to which F atoms are added on the inner peripheral side.
And a quartz glass tube 21 having a pure quartz region on both sides thereof (FIG. 6E). Here, the F atom added region becomes the inner cladding region 15, the outer pure quartz region becomes the outer cladding region 16, and the inner pure quartz region becomes the outer buffer layer 14. The region to be the outer buffer layer 14 is
It may contain phosphorus or chlorine or both. Prior to insertion, the multilayer quartz glass rod 20a may be heated and stretched to an appropriate diameter, or may be surface-treated with an HF solution. In the case where the multilayer quartz glass rod 20a is heated and stretched using an oxygen / hydrogen flame,
In order to remove moisture adhering to the surface, a surface treatment with an HF solution is essential.

In step S26, the quartz glass tube 21 in which the multilayer quartz glass rod 20a is inserted is heated to integrate them (FIG. 6 (f)). Further, an external cladding may be provided outside the outer cladding using a known VAD method or OVD method. Through the above steps, an optical fiber preform is obtained. The optical fiber preform manufactured in this manner has a refractive index profile similar to that of the optical fiber shown in FIG.

In step S27, the optical fiber preform thus obtained is heated and drawn by a known method to obtain an optical fiber having a desired refractive index profile. The optical fiber preform obtained up to step S26 corresponds to step S18 of the first manufacturing method whose flowchart is shown in FIG.
The configuration is the same as that of the optical fiber preform obtained up to this point, and the same effect as the first manufacturing method can be obtained in the second manufacturing method. That is, an optical fiber having excellent characteristics as a dispersion-shifted fiber can be obtained.

Next, a third manufacturing method will be described with reference to FIGS. FIG. 7 is a flowchart showing the third manufacturing method, and FIG. 8 is a cross-sectional view showing an intermediate product in each step.

First, in step S31, a multiple quartz glass tube 20b is prepared (FIG. 8A). The multiple quartz glass tube 20b is to be a region of the ring core region 13 of the optical fiber having a high refractive index and the buffer layers 12 and 14 on the inner and outer circumferences.
3, the inner circumference is set to 15 mm, the outer circumference is set to 24 mm, and the entire outer circumference is set to, for example, 30 mm. Details of the method of manufacturing the multiple quartz glass tube will be described later.

In step S32, a quartz glass rod 11a to which the element F is added, which becomes the central core region 11, is inserted inside the quartz glass tube 20b (FIG. 8).
(B)) In step S33, both are heated and integrated in the inserted state (FIG. 8 (c)). The details of these steps are the same as those in steps S23 and S24 described above, and a description thereof will be omitted.

In step S34, the outer peripheral surface of the integrated quartz glass rod 30 is removed by grinding or etching with an HF solution.
The outer diameter of 0 is processed to about 1.1 times the outer diameter of the ring core region 13 (FIG. 8D).

In step S35, the quartz glass rod 30 thus processed is inserted into the inside of the quartz glass tube 21 having the region 15 to which F atoms are added on the inner peripheral side and the pure quartz region outside the region 15 (FIG. 8 ( e)), Step S3
In step 6, both are heated in this inserted state to be integrated (FIG. 8 (f)). In addition, a known V
An external cladding may be provided using the AD method or the OVD method. Details of these steps are described in steps S25 and S25 described above.
26, the description is omitted. Through the above steps, an optical fiber preform is obtained. The optical fiber preform manufactured in this manner has a refractive index profile similar to that of the optical fiber shown in FIG.

In step S37, the optical fiber preform thus obtained is heated and drawn by a known method to obtain an optical fiber having a desired refractive index profile. The optical fiber preform obtained up to step S36 is shown in FIG.
It has the same configuration as the optical fiber preform obtained by the first and second manufacturing methods shown in the flowchart of FIG.
In the manufacturing method described above, the same effects as those of the first and second manufacturing methods can be obtained. That is, an optical fiber having excellent characteristics as a dispersion-shifted fiber can be obtained.

Here, various methods can be used for manufacturing various quartz glass tubes used in each manufacturing method. For example, a glass tube can be produced by depositing a soot body on the outer periphery of a quartz glass rod to produce a multilayer glass rod, and then removing the inner glass rod by drilling or the like. In addition, the known VAD method, OVD
After a glass rod is prepared by the method, a glass tube can be prepared by removing the inner glass rod by drilling or the like.

In addition, a quartz glass tube can be manufactured by using piercing. Hereinafter, a manufacturing method thereof will be described with reference to FIGS. FIG. 9 is a longitudinal sectional view of an intermediate product in each step of this manufacturing method. here,
An example in which a two-layer glass tube is manufactured will be described, but the present invention is also applicable to the manufacture of a single-layer glass tube or a multilayer glass tube having three or more layers.

First, a glass rod 22 'having a region 22a near the axis center and an outer peripheral region 22b surrounding it is manufactured by using a known VAD method, OVD method or the like (FIG. 9A). Next, the glass rod 22 'is heated in an inert gas atmosphere to a softening temperature of 1500 which is slightly lower than the melting point.
After heating to at least ℃, the glass rod 22 ′ is plastically deformed by inserting a rod 30 made of a heat-resistant material, for example, tungsten, alumina or carbon, along the central axis as shown in FIG. 9 (b). Thus, an opening is formed along the central axis (piercing) to obtain a quartz glass tube 22 as shown in FIG. 9C.

Thereafter, the surface of the quartz glass pipe was melted using a 5% to 50% HF solution, or
The quartz glass pipe is heated to 000 ° C. or higher, and then processed by vapor phase etching using SF ₆ gas or the like, so that the inner peripheral surface is removed by at least 10 μm or more and smoothed. As a result, a quartz glass pipe 22 having an inner surface roughness of 10 μm or less after the treatment and having less deviation of the boundary between the inner region 22a and the outer region 22b in the axial direction is obtained. The inner peripheral surface of the quartz glass pipe was S
An iO ₂ -GeO ₂ glass layer may be deposited and the opening may be enlarged by inserting a rod 30 into the pipe.

The present inventors made optical fibers having different thicknesses of the buffer layer, and conducted experiments for comparing the effects of the thickness of the buffer layer. The results will be described below.

First, the influence of the thickness of the inner buffer layer was examined.
The optical fiber produced based on the above-mentioned first manufacturing method was used in this comparative experiment, and its basic structure is shown in Table 1.

[Table 1] FIG. 10 summarizes the change in transmission loss of each type of optical fiber with respect to the thickness of the inner buffer layer. The abscissa represents the variable thickness of the inner buffer layer, and the ordinate represents the transmission loss at a wavelength of 1.55 μm. Is shown. As the inner buffer layer becomes thicker, the transmission loss is reduced, and the inner buffer layer thickness becomes 1 μm.
When m exceeds m, the difference in transmission loss almost disappeared even when the F element concentration on the other side of the inner buffer layer was different. On the basis of only the transmission loss, it was found that the thicker the inner buffer layer, the more preferable it was, and it was preferable that the thickness be at least 0.01 μm or more.

Table 2 shows that 1.55 wavelengths of five type 2 optical fibers having different thicknesses of the inner buffer layer were used.
FIG. 11 shows the results obtained by summarizing the transmission characteristics at μm.
Is a graph showing the change in bending loss at a wavelength of 1.55 μm with respect to the thickness of the buffer layer when these optical fibers are bent at a diameter of 20 mm.

[Table 2] It can be seen that the bending loss increases as the thickness of the inner buffer layer increases. In this regard, it is preferable that the thickness of the inner buffer layer be within 5 μm. From the above results, it was found that the thickness of the inner buffer layer is preferably 0.01 μm to 5 μm.

Next, the influence of the thickness of the outer buffer layer was examined.
The optical fiber produced based on the above-mentioned first manufacturing method is also used in this comparative experiment, and its basic structure is shown in Table 3.

[Table 3] FIG. 12 is a graph summarizing the change in transmission loss at a wavelength of 1.55 μm of each type of optical fiber with respect to the thickness of the outer buffer layer. The transmission loss at 0.55 μm is shown.
As in the case of the inner buffer layer, as the outer buffer layer becomes thicker, the transmission loss is reduced, and the outer buffer layer has a thickness of 1 μm.
When m exceeds m, the difference in transmission loss almost disappeared even when the F element concentration on the other side of the outer buffer layer was different. On the basis of only the transmission loss, the thicker the outer buffer layer is, the more preferable it is, and it is found that the thickness is preferably at least 0.01 μm or more.

Table 4 shows that the wavelengths of the 1.55 optical fibers of the type 5 optical fibers having different thicknesses of the outer buffer layer were 1.55.
FIG. 13 shows the results obtained by summarizing the transmission characteristics at μm.
Is a graph showing the change in bending loss at a wavelength of 1.55 μm with respect to the thickness of the outer buffer layer when these optical fibers are bent at a diameter of 20 mm. In the case of the outer buffer layer, unlike the case of the inner buffer layer described above, when the buffer layer is thickened, the dispersion value increases, but no deterioration such as bending loss is observed. Therefore, the thickness of the outer buffer layer is 0.01
It was found that the thickness may be as long as it is at least μm.

[Table 4]

Next, a second embodiment of the optical fiber according to the present invention will be described. FIG. 14 is a diagram showing the cross-sectional structure, and FIG. 15 shows the refractive index profile.

The optical fiber according to the second embodiment is made of quartz glass, and as shown in FIGS.
From the center to the central core region 11 (outer diameter 2a), ring core region 13 (outer diameter 2b, thickness t _b ), inner cladding region 15
(Outer diameter 2c, the thickness t _c), the outer cladding region 16 is configured by concentrically arranged. The difference from the first embodiment shown in FIGS. 1 and 2 is that the buffer layers 12 and 14 in the first embodiment do not exist, and the radial distribution of the refractive index of the ring core region 13 is uniform. Instead, the distribution has a maximum value n ₂ in the middle part. This is realized by changing the GeO ₂ concentration distribution in the ring core region 13 in the radial direction so as to lower the concentration at the boundary between the central core region 11 and the inner cladding region 15 and increase the concentration at the intermediate portion. .

Here, the GeO ₂ concentration distribution is expressed by the following equation (1) where the GeO ₂ concentration at a position of a radius r from the center of the ring core region 13 is C _G (r) [wt%].

(Equation 9)With the central core region 11 of the ring core region 13 defined in
GeO at the boundary _TwoConcentration gradient y_G1[Wt% ・ μ
m^Two] Is 100wt% ・ μm^TwoIs set to be
Expression (3)

(Equation 10) Inner cladding region 15 of the ring core region 13 defined by
GeO ₂ concentration gradient y _G2 at the boundary portion between the [wt%
[Μm ² ] is preferably set to 180 wt% · μm ² or less. Here, y _G1 = 0, y _G2 = 0
Means that there is a 1 μm thick buffer layer at each boundary.

Next, an example of a method for manufacturing the optical fiber will be described. FIG. 16 is a flowchart showing this manufacturing method, and FIG. 17 is a cross-sectional view showing an intermediate product in each step.

First, in step S41, GeO ₂
A starting glass tube 13b made of quartz glass to which is added is prepared (FIG. 17A). The starting glass tube 13b becomes the ring core region 13. G in this glass tube 13b
The eO ₂ concentration distribution is uniform and its concentration is 10 wt%
４０40 wt%.

Next, in step S42, the starting glass tube 13b is heated to evaporate GeO ₂ from the inner and outer peripheral surfaces, and remove GeO ₂ from the region near the inner and outer peripheral surfaces. Thus, a ring core region 13 having a refractive index profile as shown in FIG. 15 is obtained (FIG. 17B).

In step S43, the starting glass tube 1
A quartz glass rod 23 to which the element F is added is inserted into the inside of 3b (FIG. 17 (c)). By heating this in step S44, the two are integrated to form a multilayer glass rod 24. (FIG. 17D).

Steps S45 to S47 (FIG. 17)
(E) and (f)) correspond to steps S25 to S25 shown in FIG.
This is the same step as each step of S27 (FIGS. 6E and 6F), and the description thereof is omitted. Thus, an optical fiber preform having a refractive index profile shown in FIG. 15 is obtained, and an optical fiber is obtained by drawing this optical fiber preform.

In the present embodiment, the diffusion of Ge atoms from the ring core region 13 to the central core region 11 and the inner cladding region 15 during the heating wire draws a small concentration gradient of GeO ₂ at the boundary between the _two. Therefore, the diffusion speed is suppressed by suppressing the diffusion speed. At the same time, the inflow of F atoms in the reverse direction is also suppressed. As a result, an optical fiber can be manufactured while maintaining the ring core region 13 in a high refractive index state. Therefore, an optical fiber having good characteristics as a dispersion-shifted fiber can be obtained.

Of course, the ring core region 13 may be formed by changing the concentration of GeO ₂ added in the radial direction by using a known VAD method or OVD method. Further, the concentration gradient region may be formed by depositing glass on the inner peripheral surface and the outer peripheral surface of the glass tube to which the added GeO ₂ concentration is uniform while changing the GeO ₂ concentration. Alternatively, using a known MCVD method, the concentration gradient region is changed by changing the added GeO ₂ concentration when depositing a synthetic glass layer on the inner surface of a pure quartz glass or a fluorine-added quartz glass pipe from small to large to small. It may be formed.

The present inventors made optical fibers having different concentration gradients y _G1 and y _G2 of GeO _{2 at} the boundary portions on both sides of the ring core region 13 and performed a comparative experiment for comparing the effects of the concentration gradients. The results are reported below.

First, the influence of the concentration gradient y _G1 of GeO _{2 at} the boundary between the ring core region 13 and the central core region 11 was examined. The optical fiber produced based on the above-mentioned manufacturing method was used for this comparative experiment. Table 5 shows the basic structure.

[Table 5] FIG. 18 summarizes the results of the comparative experiment, in which the GeO at the inner interface of the ring core region 13 whose abscissa is variable.
_The vertical axis indicates the transmission loss at a wavelength of 1.55 μm on the value of the concentration gradient y _G1 of ₂ . Concentration gradient y _G1 is 100wt%
When the value exceeds μm ² , there is no difference in the transmission loss, but as the concentration gradient y _G1 is reduced to 100 wt% · μm ² or less, the transmission loss decreases. From this, it was found that the concentration gradient y _G1 of the inner interface of GeO _{2 at} the inner interface of the ring core region 13 is preferably 100 wt% · μm ² or less.

Next, the influence of the concentration gradient y _G2 of GeO _{2 at} the boundary between the ring core region 13 and the inner cladding region 15 was examined. The optical fiber similarly used for this comparative experiment was produced based on the above-mentioned manufacturing method. Table 6 shows the basic structure.

[Table 6] FIG. 19 summarizes the results of the comparative experiment, in which the GeO at the outer interface of the ring core region 13 in which the horizontal axis is variable is shown.
_The vertical axis indicates the transmission loss at a wavelength of 1.55 μm on the value of the concentration gradient y _G2 of ₂ . As in the case of the concentration gradient y _G1 described above, the concentration gradient y _G2 is equal to or more than a certain value, in this case, 18
When it exceeds 0 wt% · μm ² , there is no difference in the transmission loss, but as the concentration gradient y _G2 becomes smaller at 180 wt% · μm ² or less, the transmission loss becomes smaller. From this, it was found that the concentration gradient y _G2 of GeO _{2 at} the outer interface of the ring core region 13 is preferably set to 180 wt% · μm ² or less.

In the above two embodiments, a buffer layer or a concentration gradient region is provided in both the ring core region and the central core region, a ring core region and the central core region, and both a ring core region and the internal cladding region. Although the embodiment in which is provided has been described,
One of them may be provided with a buffer layer and the other may be provided with a concentration gradient region.

Next, a third embodiment of the optical fiber according to the present invention will be described. The cross-sectional structure of this embodiment is shown in FIG.
20 is the same as that of the second embodiment shown in FIG. 4, but has a refractive index profile shown in FIG. In other words, the radial distribution of the refractive index of the ring core region 13 is made uniform, and instead, the radial distribution of the refractive index of the central core region 11 is not uniform, but has a minimum value n ₁ at the center. Are different. That is, the concentration gradient region exists only inside the ring core region 13. This is realized by gradually decreasing the F concentration in the central core region 11 from the central portion toward the boundary with the ring core region 13. Then, this concentration distribution is expressed by the following equation (2) where the F concentration at a position of a radius r from the center of the central core region 13 is C _F (r) [wt%].

[Equation 11] F concentration gradient y _F1 [wt% · μm ² ] at the boundary between the central core region 11 and the ring core region 13 defined by
Is preferably set to be 18 wt% · μm ² or less.

In this optical fiber, a region outside the ring core region 13 excluding the center core region 11 is formed as a multiple quartz glass tube, and a quartz glass rod having a high F-doped concentration in the center portion is inserted therein. It can be manufactured by drawing an optical fiber preform manufactured by heat integration.

The present inventors have determined that the outer boundary of the central core region 11
Concentration gradient of element F in the boundary region y _F1Are different
Create a density gradient y_F1Experiments to compare the effects of
The results are reported below.

Table 7 shows the basic structure of the optical fiber used in the comparative experiment.

[Table 7] FIG. 21 summarizes the results of the comparative experiment, in which the horizontal axis represents the value of the variable concentration gradient y _F1 and the vertical axis represents the transmission loss at a wavelength of 1.55 μm. It was found that the transmission loss was reduced as the concentration gradient y _F1 was reduced, and the reduction effect was large when the concentration gradient was 18 wt% · μm ² or less. Therefore, the concentration gradient y _F1 is preferably 18 wt% · μm ² or less.

Next, a fourth embodiment of the optical fiber according to the present invention will be described. The cross-sectional structure of this embodiment is shown in FIG.
4 is the same as the second embodiment shown in FIG. 4, but is different in that it has a refractive index profile shown in FIG. That is, the radial distribution of the refractive index of the ring core region 13 is made uniform, and instead, the radial distribution of the refractive index of the inner cladding region 15 is not uniform, and the local minimum n ₃
The difference is that the distribution takes the following. That is, the concentration gradient region exists only outside the ring core region 13. This is realized by gradually increasing the F concentration in the inner cladding region 15 outward from the boundary with the ring core region 13. And
This concentration distribution is expressed by the following equation (4) where the F concentration at a position of radius r from the center of the central core region 13 is C _F (r) [wt%].

(Equation 12) Ring core region 13 of inner cladding region 15 defined in
Concentration gradient y _F2 [wt% · μm
² ] is preferably set to 30 wt% · μm ² or less.

In this optical fiber, a region inside the ring core region 13 is formed as a multiple quartz glass rod, and this is made of a quartz glass pipe having an F-doped region inside, and a concentration distribution of which is reduced toward the inside. It can be manufactured by drawing an optical fiber preform manufactured by inserting into the inside and heating and integrating.

The present inventors have made optical fibers having different concentration gradients y _F2 of the F element in the inner boundary portion of the inner cladding region 15 and conducted a comparative experiment for comparing the effects of the concentration gradients y _F2. , And report on the results.

Table 8 shows the basic structure of the optical fiber used in the comparative experiment.

[Table 8] FIG. 23 summarizes the results of the comparative experiment, in which the horizontal axis indicates the value of the variable concentration gradient y _F2 and the vertical axis indicates the transmission loss at a wavelength of 1.55 μm. It was found that the transmission loss was reduced as the concentration gradient y _F2 was reduced, and the reduction effect was large when the concentration gradient was 30 wt% · μm ² or less. Therefore, it is preferable that the concentration gradient y _F2 is 30 wt% · μm ² or less.

By combining the above embodiments with the buffer layers formed on both sides of the ring core region 13 or the concentration gradient region, various types of optical fibers can be manufactured.

Further, as shown in FIG. 1 and FIG.
The number of core regions 13 is not limited to one.
As shown in FIGS. 4 (a) and 4 (b), a high refractive index ring
The area 13 may be provided in multiple layers. In this case,
GeO in the ring core region _TwoWith high refractive index
Between the region 13 and the low refractive index region 11 to which the F element is added,
Providing opposing layers 12, 14 or providing a concentration gradient region
Is preferred.

[0082]

As described above, according to the present invention,
Since a buffer layer or a concentration gradient region doped with pure quartz or P or Cl is provided at at least one boundary between the ring core region and the central core region, and between the ring core region and the inner cladding region, the ring core region and the central core region during heating are drawn. , Ge and F between the ring core region and the inner cladding region
Are suppressed, the ring core region is maintained at a high refractive index, and characteristics suitable as a dispersion-shifted optical fiber can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a structure of an optical fiber according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a refractive index profile of the optical fiber of FIG. 1;

FIG. 3 is a flowchart of a first manufacturing method for manufacturing the optical fiber of FIG. 1;

4 is a cross-sectional view showing an intermediate product in each step of the first manufacturing method shown in FIG.

FIG. 5 is a flowchart of a second manufacturing method for manufacturing the optical fiber of FIG. 1;

6 is a cross-sectional view showing an intermediate product in each step of the second manufacturing method shown in FIG.

FIG. 7 is a flowchart of a third manufacturing method for manufacturing the optical fiber of FIG. 1;

8 is a cross-sectional view showing an intermediate product in each step of the third manufacturing method shown in FIG.

FIG. 9 is a longitudinal sectional view showing each step of a method for manufacturing a quartz glass tube.

FIG. 10 is a graph showing the relationship between the thickness of the inner buffer layer and the transmission loss of the optical fiber.

FIG. 11 is a graph showing the relationship between the thickness of the inner buffer layer and the bending loss of the optical fiber.

FIG. 12 is a graph showing the relationship between the thickness of an outer buffer layer and the transmission loss of an optical fiber.

FIG. 13 is a graph showing the relationship between the thickness of the outer buffer layer and the bending loss of the optical fiber.

FIG. 14 is a cross-sectional view showing a structure of an optical fiber according to a second embodiment of the present invention.

FIG. 15 is a diagram showing a refractive index profile of the optical fiber of FIG. 14;

16 is a flowchart of a method for manufacturing the optical fiber of FIG.

17 is a cross-sectional view showing an intermediate product in each step of the manufacturing method shown in FIG.

FIG. 18 shows GeO _{2 at} the inner boundary of the ring core region.
5 is a graph showing a relationship between a concentration gradient y _G1 and a transmission loss of an optical fiber.

FIG. 19: GeO _{2 at} the outer boundary of the ring core region
6 is a graph showing a relationship between a concentration gradient y _G2 and a transmission loss of an optical fiber.

FIG. 20 is a diagram showing a refractive index profile of a third embodiment of the optical fiber according to the present invention.

FIG. 21 is a graph showing the relationship between the F element concentration gradient y _{F1 at} the outer boundary of the central core region and the transmission loss of the optical fiber.

FIG. 22 is a diagram showing a refractive index profile of a fourth embodiment of the optical fiber according to the present invention.

FIG. 23 is a graph showing the relationship between the F element concentration gradient y _{F2 at} the inner boundary of the inner cladding region and the transmission loss of the optical fiber.

FIG. 24 is a diagram showing a refractive index profile of another embodiment of the optical fiber according to the present invention.

[Explanation of symbols]

11: central core region, 12: inner buffer layer, 13: ring core region, 14: outer buffer layer, 15: inner cladding region, 16: outer cladding region.

Continuation of the front page (72) Inventor Yoshio Yokoyama 1 Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa F-term (reference) in Yokohama Works, Sumitomo Electric Industries, Ltd. 2H050 AB05X AB10X AC15 AC16 AC28 AC36 AC76 4G021 BA02 BA03 BA04 HA01 4G062 AA06 AA07 BB02 LA03 LA06 LA08 LA10 NN01

Claims (15)

[Claims] 1. An optical fiber comprising quartz glass and having a central core region to which elemental fluorine is added and a ring core region to which germanium dioxide is added, wherein an optical fiber is provided between the central core region and the ring core region. An optical fiber comprising a buffer layer made of silicon dioxide to which additional silicon dioxide and / or phosphorus or chlorine are added. 2. The optical fiber according to claim 1, wherein said buffer layer has a thickness of 0.01 μm or more and 5 μm or less. 3. An optical fiber made of quartz glass having a central core region to which elemental fluorine is added and a ring core region to which germanium dioxide is added, wherein the radius of the central core region is a [μm], and Radius r
Assuming that the concentration of germanium dioxide in the ring core region at the position of [μm] is C _G (r) [wt%], Concentration gradient y of germanium dioxide at the boundary between the ring core region and the central core region defined by
An optical fiber, wherein _G1 [wt% · μm ² ] satisfies 100 wt% · μm ² or less. 4. An optical fiber made of quartz glass and having a central core region to which elemental fluorine is added and a ring core region to which germanium dioxide is added, wherein a radius of the central core region is a [μm], and a distance from the center is a [μm]. Radius r
Assuming that the concentration of the elemental fluorine in the central core region at the position of [μm] is C _F (r) [wt%], The concentration gradient y _{F1 of the} elemental fluorine at the boundary between the central core region and the ring core region defined in
An optical fiber, wherein [wt% · μm ² ] satisfies 18 wt% · μm ² or less. 5. An optical fiber comprising quartz glass and having a central core region arranged concentrically, a ring core region doped with germanium dioxide, and an inner clad region doped with elemental fluorine, wherein the ring core region And between the inner cladding region,
An optical fiber, comprising: a buffer layer made of silicon dioxide to which no additive, or one or both of phosphorus and chlorine are added. 6. The optical fiber according to claim 5, wherein said buffer layer has a thickness of 0.01 μm or more. 7. An optical fiber comprising quartz glass and having a concentrically arranged central core region, a ring core region to which germanium dioxide is added, and an inner cladding region to which elemental fluorine is added, wherein the ring core region Is the radius of b [μm] and the concentration of germanium dioxide in the ring core region at the position of the radius r [μm] from the center is C _G (r) [wt%]. Concentration gradient y of germanium dioxide at the boundary between the ring core region and the inner cladding region defined by
_G2 [wt% · μm ^2] is an optical fiber and satisfies the 180wt% · μm ² or less. 8. An optical fiber made of quartz glass and having a concentrically arranged central core region, a ring core region to which germanium dioxide is added, and an inner cladding region to which elemental fluorine is added, wherein the ring core region Is the radius of b [μm] and the concentration of the elemental fluorine in the inner cladding region at the position of the radius r [μm] from the center is C _F (r) [wt%]. Elemental fluorine concentration gradient y _F2 [wt at the boundary between the inner cladding region and the ring core region defined by
% · Μm ² ] satisfies 30 wt% · μm ² or less. 9. A step of producing a quartz glass pipe having a layer to which germanium dioxide is added at least on the inner peripheral side; and a step of adding no or one or both of phosphorus and chlorine to the inside of the quartz glass pipe. Depositing silicon dioxide to form a buffer layer, and inserting a quartz glass rod to which elemental fluorine is added inside the buffer layer, and then heating and integrating to form an intermediate base material, Melt-spinning an optical fiber preform containing an intermediate preform. 10. A step of forming a quartz glass pipe having a layer to which germanium dioxide is added at least on the inner peripheral side, and heating the quartz glass pipe to evaporate germanium dioxide from an inner surface to form germanium dioxide on a surface layer. Removing a quartz glass rod to which an elemental fluorine is added, and then heating and integrating the quartz glass rod inside the quartz glass pipe to form an intermediate preform; and an optical fiber preform including the intermediate preform. And a step of melt-spinning the fiber. 11. A step of producing a quartz glass pipe having a layer to which fluorine is added at least on the inner peripheral side, and a step of making no addition to the inside of the quartz glass pipe or adding one or both of phosphorus and chlorine to the inside of the quartz glass pipe. Depositing silicon dioxide to form a buffer layer, further forming a glass layer to which germanium dioxide is added on the inner periphery thereof to form an intermediate pipe, and forming quartz glass inside the intermediate pipe. After inserting the rod,
A method for producing an optical fiber, comprising: a step of heating and integrating to form an intermediate preform; and a step of melt-spinning an optical fiber preform containing the intermediate preform. 12. A quartz glass rod is formed by concentrically forming a quartz layer, a layer to which germanium dioxide is added, a layer to which either or both of phosphorus and chlorine or both are added from the axis center side. And a step of preparing a quartz glass pipe having a layer to which fluorine is added at least on the inner peripheral side. After inserting the quartz glass rod into the quartz glass pipe, heat and integrate to form an intermediate base material. A method for producing an optical fiber, comprising: a step of melt-spinning an optical fiber preform including the intermediate preform. 13. A step of producing a quartz glass pipe having a layer to which fluorine is added at least on the inner peripheral side, wherein no addition or addition of either or both of phosphorus and chlorine is performed inside the quartz glass pipe. Depositing silicon dioxide to form a buffer layer; forming a quartz glass rod having a quartz layer at the center of the axis and a layer to which germanium dioxide is added around the quartz layer; and After inserting the quartz glass rod,
A method for producing an optical fiber, comprising: a step of heating and integrating to form an intermediate preform; and a step of melt-spinning an optical fiber preform containing the intermediate preform. 14. The step of forming the quartz glass pipe includes forming an opening penetrating the center of the shaft by plastically deforming a quartz glass rod having a layer to which fluorine or germanium dioxide is added at least on the inner peripheral side at a high temperature. And forming a glass pipe.
3. The method for manufacturing an optical fiber according to any one of items 3. 15. A step of forming a quartz glass rod having a quartz layer on the axis center side and a ring-shaped layer to which germanium dioxide is added on the outside thereof, and opening the quartz glass rod along the axis to form a quartz glass rod. A step of forming a glass pipe; a step of inserting a quartz glass rod to which elemental fluorine is added into the inside of the quartz glass pipe; and a step of heating and integrating to form an intermediate base material; and an optical fiber base including the intermediate base material. Melt-spinning a material.