JPH1053429A - Preform for optical fiber and method of manufacturing the same - Google Patents

Abstract

(57) [Summary] An object of the present invention is to provide a core and a club by a VAD method or an OVAD method.
A porous glass base material having a head portion, with low loss,
Especially in the 1.38 μm or 1.55 μm band by hydrogen
Preform that can provide optical fiber with little loss increase and its stability
Of a manufacturing method. [Solution] GeO_TwoCore containing as a dopant
And a porous material comprising a clad having a lower refractive index than the core portion.
In the glass base material, the average bulk density of the core is 0.18.
g / cm^Three~ 0.26g / cm^ThreeLight characterized by being
Fiber preform and core by VAD or OVD method
A part and a clad part are synthesized, and GeO_TwoThe dopant and
And a clad having a lower refractive index than the core
Method for producing a porous glass preform consisting of
The core has a bulk density of 0.1 g / cm ^Three~ 0.26g /
cm^ThreeSynthesis while adjusting the bulk density so that
A method for producing a preform for an optical fiber, characterized in that:

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preform for an optical fiber capable of providing an optical fiber having a low loss, particularly a small loss in the 1.38 μm or 1.55 μm band due to hydrogen, and a method for producing the same.

[0002]

2. Description of the Related Art When hydrogen enters glass of an optical fiber,
Hydrogen reacts with the defects generated in the glass at the time of fiber production to generate OH groups, and the signal transmission wavelength band (1.3 μm
Alternatively, it is known to increase the transmission loss of 1.38 μm close to 1.55 μm). GeO ₂ especially in the core
This phenomenon is prominent in the case of an optical fiber doped with. On the other hand, in the production of a conventional optical fiber preform, the chlorine concentration in the core glass is regulated as proposed in Japanese Patent Application Laid-Open No. 62-083333, or proposed in Japanese Patent Application Laid-Open No. 62-270441. Thus, the hydrogen characteristics of the optical fiber have been improved by means such as reducing the alkali metal ion concentration.

[0003] On the other hand, in recent years, the productivity has increased due to the enlargement of the base material.
The core refractive index distribution (Prof.
Ile) is being stepped. Especially for profiles
As a method of proceeding with stepping, a method of increasing the refractive index
In order to prevent the volatilization of Ge, which is a punt,
As proposed in JP-A-63-47931, the core /
In simultaneous cladding synthesis, the refractive index profile of the core
In order to make a step, the bulk density around the core is 0.5 g / cm
^ThreeLess than and 0.2 g / cm ^ThreeGreater than
To increase the bulk density around the core
Has been used to increase the core bulk density as a whole.
Was. Also, for example, in Japanese Patent Application Laid-Open No. 62-162641,
When simultaneously synthesizing core cladding in the VAD method,
Number of clad burners each intersects the center axis of the porous matrix.
Do not insert each clad burner in the radius direction of the porous base material.
The bulk density of the cladding
Means to make the bulk density of the porous base material uniform
Proposed.

[0004]

The above-mentioned measures, such as the regulation of the chlorine concentration and the reduction of the alkali metal ion concentration, could not completely suppress the increase in the hydrogen loss, but also increased the size of the base material and the profile. As a result of the progress of steps, it has become difficult to manage hydrogen characteristics with conventional measures. In particular, according to the above, it was found that the stepping of the refractive index distribution was very good, but the hydrogen characteristics were sometimes worse than before. In particular, such a phenomenon also depends on conditions for synthesizing glass particles, for example, a burner structure in a gas phase synthesis method. When the burner shown in FIG. 4B is used for synthesizing the core, there is a problem that the hydrogen characteristic is liable to be deteriorated, although it is excellent in that the refractive index distribution is stepped. The present invention contemplates a large optical fiber preform having good hydrogen characteristics and a step-type refractive index distribution, and a method for manufacturing the same.

[0005]

Means for Solving the Problems As means for solving the above problems, the present invention provides (1) a porous glass base material comprising a core portion containing GeO ₂ as a dopant and a clad having a lower refractive index than the core portion. , the average bulk density of the core portion to provide a preform for an optical fiber, which is a ^{0.18g / cm 3 ~0.26g / cm 3} . Furthermore, the present invention
(2) glass particles produced by a hydrolysis reaction or an oxidation reaction of a gaseous glass material in a flame are grown in the axial direction from the tip of a rotating starting rod,
A core part and a clad part are synthesized by radially growing the outer circumference of the starting rod to produce a porous glass base material including a core part containing GeO ₂ as a dopant and a clad having a lower refractive index than the core part. In the above method, the core has an average bulk density of 0.18 g / cm ^{3 to} 0.26 g.
And a method for producing a preform for an optical fiber, characterized in that the composition is performed while adjusting the bulk density so as to be / cm ³ . Also, the present invention provides (3) adjusting the bulk density, when synthesizing the core portion, by monitoring the surface temperature of the glass fine particle deposition surface, so that the surface temperature becomes constant, hydrogen gas, oxygen gas, The method for producing an optical fiber preform according to the above (2) is provided by controlling at least one parameter among the burner positions.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have surprisingly found that the hydrogen characteristic of an optical fiber having a step-shaped profile is affected by the core bulk density of a porous glass preform at the time of producing a preform for an optical fiber. They have found the facts and have reached the present invention. In the present invention, the bulk density is “weight per unit volume including pores [g / cm ³ ]” and represents hardness. That is, in the present invention, glass material, fuel gas, and auxiliary gas are ejected from the burner, and the glass material is subjected to a hydrolysis reaction or an oxidation reaction in a flame to generate glass fine particles, and this is used as a target (starting rod). The bulk density of the core portion is adjusted to be in the range of 0.18 to 0.26 g / cm ³ when depositing and manufacturing a porous glass preform for optical fiber (hereinafter abbreviated as porous preform). .

Here, an increase in transmission loss at 1.38 μm due to OH groups generated by hydrogen intrusion is represented by Δα _1.38 ,
When Δα _1.38 showing this hydrogen characteristic exceeds 0.2 dB / km, not only the loss at 1.38 μm but also 1.44 μm,
Absorption due to glass defects occurs at 1.52 μm or the like, increasing the loss of signal wavelength. This phenomenon is remarkably observed when GeO ₂ is used as a dopant. Results of study of the present inventors, by setting the average value of the bulk density of the core portion to 0.26 g / cm ³ or less, △ alpha _{1. 38} ≦
It was found that an optical fiber satisfying 0.2 dB / km and having a small increase in hydrogen loss can be obtained. Also, △ α
_In order to obtain good characteristics when _1.38 becomes 0.1 dB / km or less, it is preferable to make it 0.24 g / cm ³ or less.
Furthermore, the bulk density is required to be 0.18 g / cm ³ or more from the viewpoint of making the shape of the refractive index distribution closer to the step shape and preventing the porous base material from cracking to ensure stable production. In order to completely prevent cracking in consideration of manufacturing variations, the amount is preferably 0.2 g / cm ³ or more.

As a method for producing the porous base material in the present invention, a general VAD method (gas phase shafting method) or an OVD method (external method) shown in FIGS. 1 and 2 can be used. The porous base material obtained by synthesizing while adjusting the bulk density of the core portion as described above is heated in an atmosphere containing chlorine or a chlorine compound gas to dehydrate water contained in the porous base material. After that, it is further heated and sintered at a high temperature to obtain a transparent glass base material.

In the VAD method, as shown in FIG.
A glass material such as Cl ₄ and a Ge dopant material Ge
A core burner that supplies a fuel gas such as Cl ₄ or hydrogen and a combustion-promoting gas such as oxygen and an inert gas to synthesize a core portion, a clad material for forming a clad, a dopant material for a clad, a fuel gas and a fuel-burning agent An inert gas, an inert gas, or the like is supplied, and a clad burner for synthesizing a clad is provided on the outer periphery of the core to synthesize a porous base material. Although FIG. 1 shows one burner as the clad burner, a plurality of burners may be used. The obtained porous base material is dehydrated by heating in a dehydrating atmosphere, and then heated and sintered to form a transparent glass body.

In the OVD method, as shown in FIG. 2, a glass raw material, a dopant raw material, a fuel gas, and a combustible gas are ejected from a burner, glass fine particles formed in the flame are adhered to the outer periphery of a starting rod, and a core is formed. A porous glass layer and a clad porous glass layer are sequentially laminated, a starting rod is pulled out after synthesizing a porous glass preform for an optical fiber, a dehydration treatment,
Performs transparent vitrification.

The glass raw material used in the present invention includes, for example, Si chloride such as SiCl ₄ and SiHCl ₃ , and the dopant raw material includes GeCl ₄ . As a fuel gas for forming a flame, for example, CH ₄ gas, C ₂ H ₆ gas, C ₃ H besides H ₂ gas
It is also preferable to use a hydrocarbon compound gas such as _eight gases. O ₂ is preferably used as the combustion supporting gas, but a gas containing O ₂ such as air may be used.

FIGS. 4A and 4B show an example of a core synthesis burner particularly commonly used in the VAD method. FIG.
(A) is a concentric multi-tube burner, which has been frequently used in the VAD method. Generally, a glass source gas and a second port 42 are provided at the central ejection port 42.
H ₂ gas, an inert gas for combustion control through the third port 43, and an O ₂ gas through the fourth port 44. Inert gas, H ₂ gas, inert gas,
A double flame burner in which another flame is formed on the outside by providing an O ₂ gas ejection port can also be used. The dopant material is a central port or a second port,
Alternatively, it is supplied to the center port and the second port.

On the other hand, the burner shown in FIG. 4B is a burner which has a high thermal power, can make the bulk density distribution of the core relatively uniform, and is considered to be effective for stepping the core profile. In this burner, a glass source gas flows through a central port 45, H ₂ gas flows through a second port 46, and an inert gas flows through a third port 47 on the outer periphery thereof. Further, H ₂ gas flows from the outer port 48.
A plurality of small-diameter ports 49 are provided in 8, from which O ₂ gas flows. Outside this, an inert gas ejection port 50 and an O ₂ gas ejection port 51 are further provided. The dopant material is supplied to the center port or the second port, or the center port and the second port.

In both burners, Ar, N ₂ and helium are generally used as inert gases. In particular, in the present invention, when the flow rate of the O ₂ gas flowing through the fourth port is insufficient in the concentric multiple tube burner, particularly the double flame burner,
For example, a flow ratio O ₂ / H ₂ with H ₂ gas flowing through the second port
Is 1 or less, or a burner using a burner of the type shown in FIG.

The burner used for synthesizing the clad has almost the same structure as the burner for synthesizing the core, and a burner as shown in FIG. 4 is used. Particularly, a double flame burner is preferably used.

In the present invention, the bulk density relating to the H ₂ characteristic is the bulk density of the core portion, and the bulk density of the clad can be freely selected. For example, the bulk density of the core is 0.22 g /
cm ³ , the bulk density of the cladding is 0.2-0.45 g / c
m ³ is common. If the bulk density of the clad is too small, the base material is easily broken, and if it is too hard, bubbles and cracks are caused.

In the present invention, the adjustment of the bulk density during the synthesis of the porous base material is performed by monitoring the surface temperature of the surface of the core glass particle deposit (deposition surface), and adjusting the fuel gas so that the monitor temperature becomes constant. At least one of three parameters, that is, a flow rate, an auxiliary gas flow rate, and a burner position is controlled. This enables stable production. For example, increasing the surface temperature can be realized by increasing the amount of fuel gas such as H ₂ , reducing the flow rate of a supporting gas such as O ₂ to increase the flame temperature, or bringing the burner closer to the deposition surface.

[0018]

【Example】

 [Embodiment 1] The VAD method having the structure shown in FIG.
The average bulk density was varied as shown in Table 1 to
Were synthesized simultaneously. Fig. 4 as a burner for core synthesis
Using the structure of (b), a burner for cladding synthesis
A double flame burner was used. Glass material is SiCl
_FourAnd H_TwoGas, O_TwoCombustion gas, combustion assisting gas
Used as Ar was used as an inert gas. Ma
The core port of the core burner is GeO_TwoAs a raw material
GeCl_FourShed. Each flow rate is SiCl_Four 
500cc / min, GeCl_Four180cc / min,
H_Two 12000cc / min, O_Two 40000cc
/ Min, Ar 8000 cc / minj. Kula
The burner is SiCl_Four7000cc / min, H_Two 
150,000cc / min, O_Two 190000cc
/ Min, Ar 27000cc / min
Was. Adjustment of the bulk density is achieved by adjusting the core burner H_TwoAdjust gas flow
I went. The core outer diameter of each base material is 30mm ± 2
mm, and the cladding outer diameter was 140 mm ± 3 mm. Profit
Cl for each porous matrix_TwoIn atmosphere (Cl_Two
5% containing He atmosphere) at 1100 ° C.
Traverse at a speed of 5 mm / min and dehydrated
Then, at a speed of 8 mm / min in a He atmosphere at 1600 ° C.
The sintering was made transparent by traversing at. That
After that, the outer periphery of each glass base material is further SiO _TwoGala consisting of
Layer that has a clad / core outer diameter ratio
After adjusting according to the properties, it was drawn and the outer diameter was 125 μm.
An optical fiber having a resin coating diameter of 250 μm was manufactured. This light
Fiber at room temperature for 1 week_TwoProcessing (H_Two100% atmosphere
Exposure inside) and then H_TwoCompare loss increase with initial value
evaluated. Average Bulk Density of Porous Base Material Core and Light Obtained
Fiber H_TwoTable 1 and Fig. 3 show the loss increase by the test.
Show. The vertical axis in FIG._TwoLoss increase (dB / km), horizontal
The axis represents the core average bulk density.

[0019]

[Table 1]

As is clear from the results in Table 1 and FIG.
The H ₂ characteristic △ alpha _1.38 is △ alpha satisfy _1.38 ≦ 0.2dB / km, the average bulk density is required 0.26 g / cm ³ or less. Further, it can be seen that the average bulk density needs to be 0.24 g / cm ³ or less to satisfy Δα _1.38 ≦ 0.1 dB / km.

[0021]

As described above, according to the present invention, V
In both cases of the AD method and the OVD method, by limiting the average bulk density of the core, a preform for an optical fiber having a low loss, in particular, a small increase in loss in the 1.38 μm or 1.55 μm band due to hydrogen is obtained. be able to.

[Brief description of the drawings]

FIG. 1 is a schematic explanatory view showing an example of producing a porous base material by a VAD method in the present invention.

FIG. 2 is a schematic explanatory view showing an example of producing a porous base material by an OVD method in the present invention.

FIG. 3 is a graph showing the relationship between the bulk density of an optical fiber preform core portion as a material of each optical fiber obtained in an example of the present invention and an increase in hydrogen loss.

FIG. 4 is a cross-sectional view schematically showing a structure of a burner used in the present invention.

[Explanation of symbols]

41 central spout, 42 second port, 43
3rd port, 44 4th port, 45 center port, 46 2nd port, 47 3rd port,
48 Outer peripheral port, 49 Small diameter port, 50 Inert gas ejection port, 51 O ₂ gas ejection port.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Tatsuhiko Saito 1st Taya-cho, Sakae-ku, Yokohama-shi, Kanagawa Prefecture Inside the Sumitomo Electric Industries, Ltd. Yokohama Works

Claims (3)

[Claims] 1. A porous glass base material comprising a core portion containing GeO ₂ as a dopant and a clad having a lower refractive index than the core portion, the core portion having an average bulk density of 0.18.
g / cm ³ ~0.26g / cm optical fiber preform, which is a ^3. 2. A method in which glass particles produced by a hydrolysis reaction or an oxidation reaction of a gaseous glass material in a flame are deposited and grown in the axial direction from the tip of a rotating starting rod, or the starting rod outer periphery. The core and cladding are synthesized by depositing and growing in the radial direction on
In a method for producing a porous glass base material including a core portion containing eO ₂ as a dopant and a clad portion having a lower refractive index than the core portion, the core portion has an average bulk density of 0.1%.
8g / cm ³ ~0.26g / method of manufacturing an optical fiber preform, characterized in that the synthesis while adjusting the bulk density such that the cm ^3. 3. The method of controlling the bulk density is to monitor the surface temperature of the glass particle deposition surface when synthesizing the core portion, and adjust the positions of hydrogen gas, oxygen gas, and burner so that the surface temperature becomes constant. 3. The method according to claim 2, wherein at least one of the parameters is controlled.