JPH01160838A - Method for manufacturing base material for dispersion-shifted optical fiber - Google Patents

Abstract

PURPOSE:To produce the subject preform having a prescribed refractive index profile shape formed with a high accuracy, by pretreating and heating a specific composite rod for a core in an atmosphere of chlorine (compound gas) and collapsing the resultant rod. CONSTITUTION:A pure SiO2 rod 1 for an inner core is inserted into an SiO2 glass pipe 2 containing F added thereto for an outer core, set in a furnace core tube 4 of an electric furnace 3, pretreated, heated at 1000-1300 deg.C in an atmosphere of chlorine (compound gas) and collapsed to provide a composite rod for the core, which is then inserted into an SiO2 glass pipe containing F added thereto for a clad, heated and integrated at 1800-1900 deg.C in the same atmosphere as that described above to afford the aimed dispersion-shift optical fiber preform having a stepped refractive index profile.

Description

[Detailed Description of the Invention] [Industrial Application Field] The invention relates to a method for manufacturing a base material for a single-stranded optical fiber having a zero dispersion wavelength in the 1.5 μm band and reduced transmission loss. . 1 manufactured from the base material of the present invention,
It is suitable for use in 5 μm band foreign shifted single mode fibers as a source of communication lines with long distance and large transmission capacity.

[Conventional technology]

For quartz (S10□) based fiber, the original wavelength is 1.5~
Since the transmission loss is minimum in the 1.6 μm'18jl range (1.5 μm band), optical transmission in this wavelength range provides the maximum repeating interval and enables long-distance communication at 0T. On the other hand, to obtain a large transmission capacity of 1tt, single-mode fiber is used, which has a much wider transmission band than multi-mode fiber and enables extremely high transmission speeds. There is a need to minimize the dispersion effect.

Therefore, as a silica-based fiber for long distances and large transmission capacity, the fiber structure was designed so that the sum of material dispersion and structural dispersion was zero in the 1.55 μm band (1.55 μm dispersion shifted single mode). 7 fiber (hereinafter referred to as dispersion-shifted fiber) is being developed.

By the way, in order to shift the zero dispersion wavelength from the usual 1.5 μm band to the 1.5 μm band in a single mode fiber, it is necessary to make the diameter of the fiber much thinner and to increase the relative refractive index difference Δn between the core and the cladding. be. G602 1 as core? iS quartz (G e 02-8
It is a well-known problem that when using G e O2 (abbreviated as iO2), if the addition of G e O2 is increased in order to increase Δn, the transmission loss also increases. Therefore, 1.
It has two cores of pure quartz (Pure 3102), which has a minimum transmission loss of 69 at 55 μm, and is excellent in principle in terms of radiation resistance, hydrogen resistance, initial transmission loss, etc. A number of fiber structures are being studied using 8102 (abbreviated as 8102) as a cladding.

The non-inventor, etc., has made the inner core 21 pure S as shown in FIG.
Consisting of iO2, the outer core 22 is located to the right of the inner core 21 (
%) low refractive index n, fluorine-8102, cladding 25
A dispersion-shifted fiber structure having a step-like refractive index distribution made of fluorine-8102 (Δ, 〉Δ2) with a refractive index n2 lower than that of the outer core 22 by Δ2 (relative) was already developed in 1986.
This is proposed in the specification of No. 0-220189. In this case, Δ is preferably a ratio of 0.6 to 0.8, and Δ2 is preferably a ratio of 0.1 to 0.5. In one fiber with an outer diameter of 125 μm, the inner core diameter is approximately 4 μm, and the outer core diameter is 6 μm. .5 μm 1 clad diameter/inner core diameter (ratio) is approximately 506 degrees.

In addition, in order to fabricate the entire fiber base material with the structure shown in Figure 2,
After collapsing the rod for the inner core into the pipe for the outer core and heating it from the outside with an oxyhydrogen burner to obtain the glass body for the core,
This was done by collapsing the cladding pipe again. The reason why the glass base material is produced by collapsing using the rod-in-tube method is that the soot body made of pure SiO2 on the inside and 5in2 of fluorine on the outside is created by the VAD method with multiple burners all around. This is because fluorine diffuses into the inner core, and the step-type refractive index distribution structure as shown in FIG. 2 cannot be agglomerated. Such a step-type profile t- has 1
The 5 μm band dispersion shifted source fiber has all the advantages of having a large mode field and being usable on the long wavelength side without being affected by lateral pressure.

[Problem that the invention seeks to solve]

In the method of collapsing using an oxy-hydrogen burner like the above conventional method, local heating can be easily carried out, so there is no leaving of bubbles in the base material, but since a large number of OH groups are generated from the burner, the base material It is considered that the water system (H) may have an influence on the water, which is not preferable. In addition, because fluorine-8102 is exposed to high temperature H2O and fluorine volatilizes, the fourth
As shown in the figure, there is also the problem that the shape of the refractive index distribution fluctuates and the weight decreases. Furthermore, heating with an oxyhydrogen burner can only collapse a core diameter of about 4.5 III at most, and even if a glass rod with a large diameter was made, the diameter was purposely stretched to be thinner to accommodate this. It was necessary to do so.

In view of this current situation, the uninvention is to improve 1. of the structure shown in Figure 2.
This is an improved base material for 5p+m band zero-dispersion shifted fibers, which has been developed for all purposes, and is capable of forming a predetermined refractive index distribution shape with high accuracy, and is capable of producing nine-shaped base materials. This provides a method with high productivity.

[Means to solve all problems]

The invention is characterized by a core part having an inner core part made of pure SiO2 and an outer core part made of fluorine-doped SiO2 glass on the outer periphery of the inner core part, and the outer core part made of fluorine-doped SiO2 glass. A base material for a dispersion-shifting fiber with a stepped refractive index distribution having a cladding part made of fluorine-doped SiO2 glass with a lower refractive index than the outer core part on the outer periphery of the core part is used as a pure SiO20 gold outer core for the inner core. Manufactured by housing the core composite rod in a fluorine-added SiO2 glass pipe for cladding and heating and integrating it, and then housing the core composite rod in a fluorine-added SiO2 glass pipe for cladding and heating and integrating it. In the method of
This is a method for producing a base material for a dispersion-shifted fiber, which is characterized by heating within a temperature range of 51,900°C.

In the present invention, instead of collapsing using a conventional oxyhydrogen burner, collapsing is performed by heating in an electric furnace 5 as shown in Fig. 5g1. First, as shown in Fig. 1, the glass rod 1 is inserted into the glass pipe 2 and set in the furnace core tube 4 of the electric furnace 5, and the atmosphere in the furnace is set to contain chlorine or chlorine compounds, and the temperature is set at 1000 to 1300°C. Perform pretreatment by heating within the temperature range. Next, 1800 in the same atmosphere
The glass rod 1 and the glass pipe 2 are integrated by heating to 51,900°C. The chlorine or chlorine compound contained in the furnace atmosphere at this time is, for example, at2. cat4
．． 5oar2 etc. are mentioned. Note that although a resistance furnace was used as the electric furnace in the embodiment, a high frequency furnace may also be used. 3
Collapse the iO2 pipe and the configuration shown in ff1g1 as described above to obtain a composite rod for the core. Next, similarly collapse the composite rod for the inner core and the F-8102 pipe that will become the cladding, and then
A base material for a dispersion-shifted fiber consisting of an outer core/fluorine-8iO□ cladding is obtained.

The glass rod made of pure SiO2 in the present invention has 1
．． Any manufacturing method may be used as long as it is of a quality that can be used as a core material for a zero-dispersion single mode fiber for a 5 μm band, but usually a rod made of a transparent pure SiO2 soot body manufactured by a known VAD method is used.

For the outer core or cladding pipe made of fluorine 5i02, a SiO2 stub body produced by the fiVAD method is dehydrated and made of, for example, SF6. SiF4゜CC/2F2
A designed amount of F (fluorine) is added to the soot body by heating in an atmosphere containing a fluorine compound such as,
This is made transparent to obtain an 8in2 transparent glass body, and then a hole is punched in the center using an ultrasonic perforator.

In addition, the inner surface of the porcelain pipe was prepared with SF6 before collapsing.
By etching the inner surface with No. 2 gas,
This is preferable in terms of preventing the generation of bubbles in the base material after collapse and reducing transmission loss.

A method is known in which a pipe-shaped soot body is produced by depositing soot on the outer periphery of a mandrel using an external deposition method. Although it is also possible to produce a fluorine-8102 pipe using this method, it is difficult to remove the mandrel. This can easily cause damage to the inner surface of the pipe.

The rod for the inner core is pure 810□ as mentioned above,
As a pipe for the outer core, use Δ in the $1 diagram.

It is preferable to add 2.7 to 5.5% by weight of fluorine so that the amount of SiO2 becomes 0.6 So and 8%. In addition, as a cladding pipe, Δ2 in Fig. 1 is 0.1 to 0.5.
S containing 0.5 to 1% by weight of fluorine so that the
iO2 is preferred. Further, it is preferable that the diameter ratio of the inner core and the outer core is about 0.4 to 0.8 (inner core diameter/outer core diameter). The above limitations apply to a 1.5 μm band zero dispersion shifted single mode fiber, and '! This is to make it less susceptible to bending loss (lateral pressure).

[Effect]

A method of collapsing using an electric furnace has been attempted in the past, but it was impractical and impractical due to the problems of residual foxing in the base material and deformation of the base material. The inventors have found that even if an electric furnace is used, 100
It was confirmed through experiments that the pretreatment performed at a temperature range of 0 to 1300°C can prevent bubbles from remaining in the base material.

As a result of further research, after this pretreatment, a core diameter of 10s + sφ was obtained by collapsing using an electric furnace at 1800°C to 1900°C in an atmosphere containing chlorine or chlorine compounds as described above.
This makes it possible to manufacture large base materials such as 6011Iφ in outer diameter. This can be said to have made it possible to produce a very large base material compared to conventional oxyhydrogen burners, which could only properly collapse materials with a core diameter of 4.5mmφ and an outer diameter of 22m1φ. .

Due to inventiveness, for example, the outer diameter is 8 on the first collapse.
~12mmφ inner core rod and outer diameter 40550mφ
For the second time, extend the integrated core rod obtained above to an outer diameter of 8 to 121 alφ, and integrate it again with a Talarado pipe with an outer diameter of 40 to 50 alφ. In the end, a core diameter/core diameter (ratio) of about 50 times is obtained. The size of this base material is about 10% of that of the large diameter fiber base material made using the conventional method using an oxyhydrogen burner.
It reaches 0 times (fiber equivalent length).

Furthermore, by using an electric furnace, the present invention can eliminate the adverse effects caused by oxyhydrogen flame, particularly the problems of fluctuations in refractive index distribution and decrease in filtration. When glass is exposed to high temperatures in an oxyhydrogen flame, the H2O from the flame is removed, 2 S, FO,, 5 + H20 → 25 in2 + 2 HF
...(1)SiO+ 4)IF i"! 5IF
J +2820...(2) Above +13, (2
The following reactions occur, and the surface fluorine (Fl is HF, S
It volatilizes as iF4, and the refractive index distribution becomes -J.
7! As shown in Figure J4, the weight of the base material decreases at the same time as it changes.

On the other hand, in the collapse using the electric furnace of the present invention, since the above-mentioned high-temperature H2O is not present, the reactions of equations (1) and (2) hardly occur, and therefore, the changes in the refractive index distribution, This decrease can be suppressed.

Furthermore, the method of the present invention is a simple method in which the valley rods and pipes are manufactured separately and then integrated one after another by repeating the rod-in-tube method. This is advantageous in that a refractive index distribution structure can be realized.

〔Example〕

Example 1 A pure SiO2 glass rod produced by the VAD method was stretched using an electric resistance furnace to have an outer diameter of 12111@φ and a length of 7.
Next is the rod for the inner core of 00 parrot. Separately, a porous base material made of pure SiO2 produced by the VAD method was dehydrated, F-added, and made transparent to produce fluorine-810 containing 2% by weight of fluorine.
A rod made of 2 glass and having an outer diameter of 50 mm was obtained. A hole with an inner diameter of 12 mφ is penetrated in the center of this fluorine-8 inch 20 piece using an ultrasonic drilling machine, and a fluorine-3 inch hole for the outer core is made.
, used as pipe material.

The above-mentioned fluorine-8iO□ pipe for the outer core was attached to the same resistance furnace as shown in FIG. 1 and 9, and the inner wall of the pipe was etched under the conditions shown in Table 1 below.

After inserting a pure 5 inch 20 piece for the inner core into the hollow part of the pipe and pre-treating it under the conditions shown in Table 1, the f
A glass rod consisting of an inner core and an outer core of i7 was drawn to an outer diameter of 8.5 Wφ using a resistance furnace to obtain a composite core rod.

According to the above method for producing the outer core pipe by the '/AD method, a fluorine-8iO□ glass rod for the cladding with an outer diameter of 50mm and containing 2.5% by weight of fluorine was separately obtained, and the inner diameter was also The page was passed through a hole of 8 mm diameter, and the inner surface was etched under the conditions shown in Table 1.
A 102 glass pipe was obtained. Fluorine for the cladding
O.

Galanupive and the composite core rod were collapsed and integrated under the conditions shown in Table 1 in the same manner as described above.

The preform obtained above has a refractive index distribution structure shown in FIG. 5, where Δ1 is 0.6%, Δ2 is o, 1s
ratio, the refractive index distribution was normal, and there was no weight change. 'E7t, draw a line and the outer diameter is 12
5μm 1 inner diameter core diameter 4μm.

1 having the desired refractive index distribution with an outer core diameter of 6.5 μm,
A 55 μm dispersion shifted fiber was obtained.

Comparative Example 1 A 5io20 glass tube for the inner core, a 2% by weight fluorine-810 glass tube for the outer core, and a 2.5 weight percent fluorine-8102 glass tube for the cladding were used in Example 1, respectively.
A sample was prepared in the same manner as in the case of , but an oxyhydrogen burner was used instead of the resistance furnace, and etching, pretreatment, and collapse of the inner surface of the nozzle tube were performed under the conditions shown in Table 2. The outer diameter of the rod for the composite core is 4.5 IIφ, and the bike diameter for the cladding is 25IIlφ.
I made it.

Table 2 The obtained preform had a modified refractive index distribution structure as shown in FIG. 4, and its weight was reduced by 10%. Naturally, from this preform, core ino having the desired refractive index distribution could not be obtained.

From the results of Example 1 and Comparative Example 1 above, it is clear that the method of the present invention using a resistance furnace overcomes the problem of the adverse effects caused by oxyhydrogen flame in the conventional method.

〔Effect of the invention〕

As explained above and as follows, the uninvented method for manufacturing the base material for the dispersion-shifted fiber is performed by pre-heating and collapsing in an atmosphere containing chlorine or chlorine compound gas in an electric furnace. By eliminating this, a base material with a normal desired refractive index distribution structure and no weight loss can be obtained. In addition, it is possible to produce a larger base material than in the conventional oxyhydrogen flame method, resulting in a physiologically It is an industrially advantageous invention that improves the quality of the product and opens the way to mass production.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram illustrating an embodiment of the present invention, FIG. 2 is a diagram showing a refractive index distribution of a dispersion-shift source fiber having a stepped refractive index distribution, and FIG. Diagram showing the refractive index distribution of the base material for the nine-dispersion shifted source fiber, No. 4
The figure is a diagram showing the refractive index distribution of a base material for a 99 fiber obtained by a conventional method (comparative example).

Claims (1)

[Claims] A core part having an inner core part made of pure SiO_2 and an outer core part made of fluorine-doped SiO_2 glass on its outer periphery, and a fluorine-doped SiO_2 glass on the outer periphery of the outer core part having a lower refractive index than the outer core part. A base material for a dispersion-shifted optical fiber with a step-like refractive index distribution having a cladding part is housed in a fluorine-doped SiO_2 glass pipe for an inner core and a pure SiO_2 rod for an outer core, and heated and integrated to form a composite rod for the core, Next, in a manufacturing method in which the core composite rod is housed in a fluorine-added SiO_2 glass pipe for cladding and heated and integrated, the heating and integration is performed in an electric furnace under an atmosphere containing chlorine or chlorine compounds at a temperature of 1000 to 1300°C. After pretreatment heating within the temperature range of ℃ 1800 ~ 190℃ under the above atmosphere
A method for producing a preform for a dispersion-shifted optical fiber, the method comprising heating within a temperature range of 0°C.