JPS62162639A - Production of preform for w-type single mode optical fiber - Google Patents

Abstract

PURPOSE:A soot material which is composed of the core soot, the fluorine-doped first clad and the dope-free second soot is formed by the vapor-phase axis deposition method and sintered whereby the production of the preform is made easy and the prolongation of the product becomes possible. CONSTITUTION:The raw materials for the core glass and oxyhydrogen flame are blown out of the core burner 5 to the target made of, e.g., quartz rod which ascends as it rotates. The hydrolytic reactions form the core soot 8 on the top end of the target and the first fluorine-containing clad soot 9 is formed from the first clad burner 6 by the hydrolysis of the fluorine-containing first clad materials around the outer surface of the core. Further, the second clad soot 10 is formed on the outer surface of the first clad by the second clad burner. The resultant soot material 11 is doped with a fluorine compound by heat treatment in the atmosphere of an inert gas and a fluorine compound mixture and sintered to give the title preform. Only the first clad soot 9 is doped with fluorine, when the soot material is produced, and the production of the soot material 11 is faciliated.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a W-type single-mode optical fiber preform in which the cladding is doped with fluorine, and in particular to a W-type single-mode optical fiber preform that can be lengthened by the VAD method. .

Glumode optical fiber fl! This is how to make it.

[Prior Art] Single-mode optical fibers have low loss and wide bandwidth, and have therefore been used as transmission lines for long-distance transmission systems.

The bandwidth of a single mode optical fiber is indicated by its dispersion. Currently, the refractive index distribution structure of single mode optical fiber is the MatChed clad type (MC type) shown in Figure 4.
The refractive index distribution of the core part 1 and the cladding part 2 is as shown in the figure, and the relative refractive index of the core Δn=0.3% is 1.3IJIR.
It has an atmospheric dispersion wavelength nearby. However, this MC type has a power of 1.55, 15 PS/Ktan in the cm region.
It is impossible to achieve low dispersion in a wide wavelength range of a values.

On the other hand, in the W-type structure shown in FIG. Since it is formed small, an atmosphere dispersion region extending from 1.3/Jllll to 1.51 m can be obtained. This W-type single mode optical fiber has a radius of the core portion 1, a thickness of the first cladding portion 3, tl, and a thickness of the first cladding portion 3 and the second cladding portion 4.
If the thickness of is t2, then t+/a=1, t2/a=7
The first
The cladding part 3 and the second cladding part 4 are doped with fluorine.

[Problems to be Solved by the Invention] However, when conventional W-type single mode optical fiber preforms are manufactured by the MCVD method, the growth rate of the glass film is slow when forming the fluorine-doped glasses of the first and second claddings.
In order to form a predetermined film thickness, it is necessary to perform CvD many times and it takes a long time. Therefore, 01 from the quartz tube
Single group diffusion is likely to occur, making it difficult to stably achieve low loss in the 1.31 JIR band.Furthermore, the first cladding portion 3 has a thin film thickness, which causes fluorine diffusion during carabulation of the quartz tube.
There is a problem that refractive index control is difficult.

[Objective of the Invention 1 The object of the present invention is to eliminate the drawbacks of the prior art described above, and to
It is an object of the present invention to provide a method for manufacturing a W-type single-mode optical fiber preform, which can be easily manufactured using a VAD method.

[Summary of the Invention] In order to achieve the above object, the present invention provides a core glass raw material from a core burner, a first clad glass raw material containing a fluorine compound from a first clad burner, and a second clad raw material from a second clad burner. Each raw material is sequentially supplied to the target, and each raw material is hydrolyzed with an oxyhydrogen flame to form a soot base material of a W-type single mode optical fiber at the tip of the target, and then the soot base material is doped with a fluorine compound. It is sintered, and when forming the soot base material,
By blowing the first cladding glass raw material containing a fluorine compound from the first cladding burner and blowing only the second cladding raw material without a dopant from the second cladding burner, the soot base material can be easily formed. By doping the fiber with a fluorine compound and sintering it, a W-type single mode optical fiber base material can be easily manufactured to any length.

[Example] A preferred example of the method for manufacturing a W-type single mode optical fiber preform according to the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 5 is a core burner, 6 is a first clad burner, and 7 is a second clad burner, each of which is a four ffl'1 quartz burner, and as shown in the figure, a first tallad bar and 6 are arranged above the core burner 5. A second clad burner 7 is disposed above the cladding burner 7, and is disposed so as to eject the raw material and oxyhydrogen toward the target and upwardly of the diagonal mouth.

The core glass raw material and the carrier gas, that is, 5iCQ4, are supplied to the core burner 5 from the first layer inside the core burner 5 at a rate of 0.39/
1llin, GOCi4 is 0.02 g/
min, 8r is supplied at 0.11/sin, and the second
112 from layer is 2J! /1n, the inert gas Ar from the third layer is 0.81/1n, and the 02 from the fourth layer is 4 J
? /Win are supplied respectively.

The first clad burner 6 has a first
The cladding glass raw material, fluorine compound, and carrier gas, namely 5iCJ14, was 21 J/min.

SiF4: 0.2.12/min, Ar: 0.25
J2/min is supplied, and 112 is supplied from the second layer at 4J/min.
n, Ar is IJ/win from the third layer, 02 from the fourth layer
are supplied at [1/min].

The second clad burner 7 has a second layer from the first layer on the inside thereof.
Talatsudo glass raw material and carrier gas, namely 5iC1
14 is supplied at 109/min, ^' is supplied at IJ!/1ain, 112 from the second layer is supplied at 127/sin, Ar from the third layer is supplied at IJ/i+in, and 411th to 02 is supplied at 10J/w.
In is supplied respectively.

In the above, when the core glass raw material and oxyhydrogen flame are supplied from the core burner 5 toward a rotating upward target (not shown) such as a quartz rod, a core soot 8 is formed at the tip of the target by hydrolysis. A first clad soot 9 is formed around the outer periphery of the first cladding glass raw material containing a fluorine compound supplied from the first clad burner 6 by hydrolysis of an oxyhydrogen flame, and a second clad soot 9 is formed around the outer periphery of the first clad soot 9. A second cladding suit 1o of 7 is formed. In this case, a fluorine compound is supplied from the first clad burner 6, and its soot 9
Even if the formation rate is slow, the thickness of the soot 9 to be formed is small, so it can be made the same as the other soot formation rates. Further, since the second clad burner 7 does not contain a fluorine compound, the second clad soot 10 can be formed to have any thickness.

In this way, the core suit 8. 1st clad suit9. The soot base material 11 on which the second clad soot 10 was sequentially formed had an outer diameter of 110III.

Next, this soot base material 11 is placed in an electric furnace 14 consisting of a 6-English chamber 12 and a heating coil 13 shown in FIG.
The soot base material 11 is fed from top to bottom at a rate of 1#lll1/win, and an inert gas, e.g. The soot base material 11 is supplied with CF, discharged from the outlet nozzle 16 as appropriate, and heat-treated at a temperature of 1100°C in the soot base material 11.
Dope 4. Next, move the soot base material 11 from bottom to top.
．． Pull at 5mm/Win, l: Inlet nozzle 1 with gero
IOJ He from 5! /win supply and increase the furnace temperature to 16
The soot base material 11 was sintered at 50° C. and turned into transparent glass. This transparent vitrified base material was heated and stretched, inserted into a quartz glass tube, and simultaneously heated and fused to form a fiber, thereby obtaining the W-type single mode optical fiber illustrated in FIG. 3. still,
In FIG. 3, 17 is a quartz glass tube fused to the outer periphery of the base material, and its refractive index is shown.

The W-type single mode optical fiber obtained in the present invention has a core relative refractive index Δn−0.2%, a first cladding portion Δn−−
0.4%, the second cladding part Δn-0.2%, and the transmission loss at the length 10- is 0.4 dB/1 in the 1.3-band.
m, several PS in the 1.3-1.5/llj band as a result of dispersion measurement
/ Kana+ and low dispersion was confirmed in a wide wavelength range.

Further, in the present invention, when doping fluorine in the electric furnace 14, fluorine is doped uniformly in the radial direction of the soot base material 11, but the first tartar soot 9 is doped with fluorine in advance during soot formation. Therefore, the refractive indices of the first cladding and the second cladding can be adjusted to desired values.

In the embodiment, in doping with fluorine, the first
An example was shown in which 5iC14 and SiF4 are continuously ejected during the formation of the clad soot 9, but this is because, for example, when CI''4 is used as the fluorine compound, the SiO2 and CF4 of the first clad soot 9 that are formed react. (Si02+CF4
→SiF4+CO2) L/ produces SiF4 and reduces the soot yield, so SiF4 was used as the fluorine dope when forming the first cladding soot 9.

In addition to CF4, the fluorine compounds to be doped in the electric furnace 14 include SFa, CCIhh, 5iF.
n, but SiF4. When using SFa, C1 ``,
The thermal decomposition temperature is higher than that of (SFa −-→SF4
SF4.

S F 3zoo convex breasts S F 2. SF decomposes at each temperature), so it is doped with fluorine at the sintering temperature (1650°C), so it is doped with fluorine at the same time as sintering. Decomposes at 5 degrees
Before i02 reacts with fluorine and becomes CO2, C becomes quartz CH1
In order to deposit C,,1, on the upper part of the 1-member 12, when doping C,,1,, it is heat-treated at about 1100.degree. C., which is lower than the sintering temperature, and then sintered.

[Effects of the Invention] As is clear from the detailed description above, the present invention exhibits the following excellent effects.

(1) A core soot, a first clad soot doped with fluorine, and a second clad soot not doped with fluorine are prepared using the vapor phase axial method.
After forming a soot base material consisting of cladding 1~, the base material is doped with fluorine and sintered.
W type single mode optical filter? The fiber base material can be easily made and can be made into a long length.

(2) Soot 1 - Since the soot base material is formed by doping only the first clad soot with fluorine when forming the base material, the soot base material can be easily formed.

(3) The resulting W-type single-mode optical fiber has low loss and low dispersion, similar to fibers formed by other CVD methods, and has low dispersion even in a wide wavelength range of 1.3 to 1.5 wavelengths. You can get something.

[Brief explanation of drawings]

1 and 2 are diagrams showing a method for manufacturing a base material of a W-type single mode optical fiber of the present invention, in which FIG. 1 shows an example of forming a soot base material, and FIG. A diagram showing an example in which the material is doped with fluorine and sintered. FIG. 3 is a diagram showing the refractive index distribution of the J34 W type single mode optical fiber according to the present invention and a conventional example. FIG. 4 is a diagram showing the refractive index distribution of the conventional MC type optical fiber. FIG. 3 is a diagram showing a refractive index distribution of an optical fiber. In the figure, 5 is a core burner, 6 is a first clad burner, 7 is a second clad burner, 8 is a core soot, 9 is a first clad soot, 10 is a second clad soot, 11 is a soot base material, and 14 is an electric furnace. Patent applicant: Hitachi Cable Co., Ltd. 1<, Prisoner BuP
Keishisa 5 Fujihiro Figure 1 Figure 2 Procedures Amendment %f (spontaneous) 5゜1 Incident Display Showa 61 Patent Application No. 3861
7゜2 Name of the invention Manufacturing method of W-type single mode optical fiber base material 3 Name of person making the correction (512) Representative of Hitachi 1st Section Line Co., Ltd.
Hiroharu Hashimoto 4th Director Address: 100
2-1-2 Marunouchi, Chiyoda-ku, Tokyo The full text of the amended specification is as per the attached document. Catalog of Attached Documents Attached Sheet (Corrected Specification) Quantity: Original Specification 1, Title of the Invention Method for manufacturing W-type single mode optical fiber preform 2, Claims (1) Core glass raw material from a core burner In the evening, a first cladding glass raw material containing a fluorine compound was supplied from a first cladding burner, and a second cladding raw material was supplied from a second cladding burner toward 32 tons in the evening, and each raw material was hydrolyzed with an oxyhydrogen flame. A method for manufacturing a W-type single mode optical fiber preform, comprising forming a soot preform in which the first cladding is doped with a fluorine compound, and then sintering the preform. (2) The method for manufacturing a W-type single mode optical fiber preform according to claim 1, wherein SiCg and SiF, i are used as the first clad glass raw material ejected from the first clad burner. (3) The soot base material is placed in a mixed gas of an inert gas and a fluorine compound, and the soot base material is doped with a fluorine compound while being heat-treated, and then sintered. A method for manufacturing a W-type single mode optical fiber according to item 1. (4) The W according to claim 1, characterized in that the soot base material is placed in a mixed gas of SiF or SF6 and an inert gas, and the base material is doped with SiF or SF6 at the same time as sintering. A method for manufacturing single-mode optical fiber preform. 3. Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a method for manufacturing a W-type single mode optical fiber base material in which the cladding is doped with fluorine, and in particular to a W-type single mode optical fiber base material that can be lengthened by the VAD method. The present invention relates to a method of manufacturing a mode optical fiber preform. [Prior Art] Single-mode optical fibers have low loss and wide bandwidth, and have therefore been used as transmission lines for long-distance transmission systems. The bandwidth of a single mode optical fiber is indicated by its dispersion. At present, the refractive index division structure of single mode optical fiber is a matched clad type (MC type) shown in Figure 4, and the refractive index distribution of the core part 1 and clad part 2 is as shown in the figure, and the relative refractive index of the core is △n-Q, 1.3μ at 396
It has a zero dispersion wavelength near m. However, this MC type cannot achieve low dispersion in a wide wavelength range of 15 PS/Kmnm in the 1.55 μm region. On the other hand, in the W-type structure shown in FIG. Since it is formed small, a zero dispersion region is obtained over a range of 1.3 μm to 1.5 μm. In this W-type single mode optical fiber, the radius of the core portion 1 is a1, the thickness of the first cladding portion 3 is tl, and the thickness of the first cladding portion 3 and the second cladding portion 4 is t, then t/a −1 ,t2/a-7
The first
The cladding part 3 and the second cladding part 4 are doped with fluorine. [Problems to be Solved by the Invention] However, when conventional W-type single mode optical fiber preforms are manufactured by the MCVD method, the growth rate of the glass film is slow when forming the fluorine-doped glasses of the first and second claddings.
In order to form a predetermined film thickness, it is necessary to perform CVD many times, which takes a long time. Therefore, OH from the quartz tube
Radical diffusion is likely to occur, making it difficult to stably achieve low loss in the 1.3 μm band.Furthermore, the first cladding portion 3 has a thin film thickness, which causes fluorine diffusion when quartz tubes are coated, making it difficult to control the refractive index. There's a problem. [Object of the Invention] The object of the present invention is to eliminate the drawbacks of the prior art described above, and to
It is an object of the present invention to provide a method for manufacturing a W-type single-mode optical fiber preform, which can be easily manufactured using a VAD method. [Summary of the Invention] In order to achieve the above object, the present invention provides a core glass raw material from a core burner, a first clad glass raw material containing a fluorine compound from a first clad burner, and a second clad raw material from a second clad burner. Each raw material is sequentially supplied to the target, and each raw material is hydrolyzed with an oxyhydrogen flame to form a soot base material of a W-type single mode optical fiber at the tip of the target, and the soot base material is doped with a fluorine compound and sintered. When forming the soot base material, the first cladding glass raw material containing a fluorine compound is blown from the first cladding burner, and only the second cladding raw material without dopants is blown from the second cladding burner. The W-type single mode optical fiber preform can be easily manufactured to any length by doping the soot preform with a fluorine compound and sintering it. [Example] A preferred example of the method for manufacturing a W-type single mode optical fiber preform according to the present invention will be described below with reference to the accompanying drawings. In FIG. 1, 5 is a core burner, 6 is a first clad burner, and 7 is a second clad burner, each of which is a quadruple tube quartz burner, and as shown in the figure, the first clad burner 6 is arranged above the core burner 5, Additionally, the second clad burner 7
are arranged so that the raw material and oxyhydrogen are ejected upward toward the target. The core burner 5 is supplied with a core glass raw material and a carrier gas, that is, S I C&' 4, from the first layer inside the core burner 5 .
3g/akin, GeCΩ4 is 0.02g/ll1in
, Ar is 0. IN/1n is supplied, and H2 is 2 from the second layer.
jl/ll1ins From the third layer, Ar, which is an inert gas, is 0. 02 is supplied from the fourth layer at a rate of 8ff/min at a rate of 4g/[l1in]. The first clad burner 6 has a first
The cladding glass raw material, fluorine compound, and carrier gas, that is, SiCD 4, were fed at 2 g/min. SiF4 is 0.21)/min, Ar is 0.2
5R/min is supplied, and H2 from the second layer is 4Ω/+ni
n, Ar is supplied from the third layer at a rate of IN/min, and O2 is supplied from the fourth layer at a rate of 6Ω/ωin, respectively. The second clad burner 7 has a second layer from the first layer on the inside thereof.
Clad glass raw material and carrier gas, i.e. SiCΩ
4 is supplied at 10 g/min, Ar is supplied at IN/sin, H2 is supplied from the second layer at 12 g/min, and Ar is supplied from the third layer at L9.
/min, and 02 is supplied from the fourth layer at 10R/min, respectively. In the above, when the core glass raw material and oxyhydrogen flame are supplied from the core burner 5 toward a rotating upward target (not shown) such as a quartz rod, a core soot 8 is formed at the tip of the target by hydrolysis. A first clad soot 9 is formed on the outer periphery by hydrolysis of a first clad glass raw material containing a fluorine compound supplied from the first clad burner 6 and an oxyhydrogen flame, and a second clad soot 9 is formed on the outer periphery of the first clad soot 9. A second cladding soot 10 is formed by the burner 7. In this case, a fluorine compound is supplied from the first clad burner 6, and its soot 9
Even if the formation rate is slow, the thickness of the soot 9 to be formed is small, so it can be made the same as the other soot formation rates. Further, since the second clad burner 7 does not contain a fluorine compound, the second clad soot 10 can be formed to have any thickness. In this way, a soot base material 11 having an outer diameter of 110 um was obtained, in which the core soot 8, the first clad soot 9, and the second clad soot 10 were sequentially formed from the center. Next, this soot base material 11 is placed in an electric furnace 14 consisting of a quartz chamber 12 and a heating coil 13 shown in FIG.
The soot base material 11 is fed from top to bottom at a rate of 11/min, and an inert gas such as He is supplied at 101/win% and a fluorine compound such as CF4 is supplied at 0.3N10+in from the inlet nozzle 15 at the bottom of the quartz chamber 12. is appropriately discharged from the outlet nozzle 16, and the temperature inside the furnace 14 is reduced to 110°C.
Heat treatment is performed at 0° C., and the soot base material 11 is doped with CF4. Next, the soot base material 11 is 1.5III from bottom to top.
At the same time as raising the temperature at 1/1lIIn, 1041)/a+in of He was supplied from the inlet nozzle 15, and the temperature inside the furnace was raised to 165
The soot base material 11 was sintered at 0° C. and made into transparent glass. This transparent vitrified base material was heated and stretched, inserted into a quartz glass tube, and simultaneously heated and fused to form a fiber, thereby obtaining the W-type single mode optical fiber illustrated in FIG. 3. In addition, in FIG. 3, 17 is a quartz glass tube fused to the outer periphery of the base material, and its refractive index is shown. The W-type single mode optical fiber that has been smoothed in the present invention is
Core relative refractive index Δn=0.2%, first cladding part Δn−
-0.4%, second cladding part △n--0.2%,
The transmission loss with a length of 10Ka+ is 0 in the 1.3μm band,
4 dB/Ka+, dispersion measurement result 1.3-1.5μ
Low dispersion was confirmed in the m band over a wide wavelength range of several PS/Ka+nm. Further, in the present invention, when doping fluorine in the electric furnace 14, fluorine is doped uniformly in the radial direction of the soot base material 11, but the first clad soot 9 is doped with fluorine in advance during soot formation. Therefore, the refractive indexes of the first cladding and the second cladding can be adjusted to desired values. In the embodiment, in doping with fluorine, the first
When forming the cladding suit 9, S iC,1! 4 and Si
An example of ejecting F4 was shown, but this means that, for example, when CF4 is used as a fluorine compound, 5IO2 of the first clad soot 9 that is formed reacts with CF4 (SiO + CF4).
4-"SiF4+ (:Q2) to produce SiF4 and reduce the soot yield, so SiF4 was used as a fluorine dope during the formation of the first cladding soot 9. Also, fluorine doped in the electric furnace 14 In addition to CF, compounds include SF%CCg2F2 and SiF, but when using SiF%SF6, 2000"K
(decomposes at each temperature as SF SF, SF), so it is doped with fluorine at the sintering temperature (1650°C). In addition, in the case of CF, the sintering salt ff decomposes at 1 degree, and before Si,02 reacts with fluorine and becomes CO2, C is deposited on the upper part of the quartz chamber 12.
Sintering salt when doping with CF! It is doped by heat treatment at about 1100°C, which is lower than 101°C, and then sintered. [Effects of the Invention] As is clear from what has been described in detail above, the present invention exhibits the following excellent effects. (1) A soot base material consisting of a core soot, a first cladding soot doped with fluorine, and a second cladding soot not doped with fluorine is formed by the vapor phase axial mounting method and then sintered, resulting in a W-type single mode optical fiber. The base material can be easily made and can be made into a long length. (2) Since the soot base material is formed by doping only the first clad soot with fluorine when forming the soot base material, the soot base material can be easily formed. (3) The resulting W-type single-mode optical fiber has low loss and low dispersion, similar to fibers formed by other CVD methods, and has low dispersion even in a wide wavelength range of 1.3 to 1.5 μm. is obtained. 4. Brief description of the drawings FIGS. 1 and 2 are diagrams showing a method for manufacturing a base material for a W-type single mode optical fiber of the present invention. FIG. 1 is a diagram showing an example of forming a soot base material, Fig. 2 shows an example in which the soot base material is doped with fluorine and sintered, Fig. 3 shows the refractive index distribution of the W-type single mode optical fiber in the present invention and the conventional example, and Fig. 4 shows the conventional one. FIG. 3 is a diagram showing the refractive index distribution of the MC type optical fiber. In the figure, 5 is a core burner, 6 is a first clad burner, 7 is a second clad burner, 8 is a core soot, 9 is a first clad soot, 10 is a second clad soot, 11 is a soot base material, and 14 is an electric furnace. be.

Claims (4)

[Claims] (1) A core glass raw material is supplied from a core burner, a first clad glass raw material containing a fluorine compound is supplied from a first clad burner, and a second clad glass raw material containing a fluorine compound is supplied from a second clad burner toward a target in order, and each raw material is acidified. A W-type single-mode optical fiber characterized in that a soot base material of a W-type single-mode optical fiber is formed at the tip of a target by hydrolysis with a hydrogen flame, and then the soot base material is doped with a fluorine compound and sintered. Method of manufacturing base material. (2) The method for manufacturing a W-type single mode optical fiber preform according to claim 1, wherein SiCl_4 and SiF_4 are used as the first cladding glass raw material ejected from the first cladding burner. (3) W-type single mode light characterized by placing the soot base material in a mixed gas of an inert gas and a fluorine compound, doping the soot base material with a fluorine compound while heat treating it, and then sintering it. Method for manufacturing fiber base material. (4) A method for manufacturing a W-type single mode optical fiber preform, which comprises placing a soot preform in a mixed gas of SiF_4 or SF_6 and an inert gas, and doping the preform with SiF_4 or SF_6 during sintering. .