JP3258478B2 - High viscosity synthetic quartz glass tube for thermal CVD method and quartz glass preform for optical fiber using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention has a high softening point high viscosity synthetic quartz glass tube, in particular a high viscosity synthetic quartz glass tube for a thermal CVD method, and the synthetic quartz glass tube pre quartz glass for optical fiber had use a follower And a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a method of manufacturing a silica glass based optical fiber includes a soot manufacturing method such as a vapor phase axial method (hereinafter referred to as a VAD method) or an external gas phase method (hereinafter referred to as an OVD method). Manufacturing method using a quartz glass tube such as an internal CVD method (hereinafter referred to as an MCVD method) for forming a glass layer on the inner surface of a quartz glass tube or a plasma CVD method (hereinafter referred to as a PCVD method) in which a heating source is plasma. Is known and has been put to practical use.

[0003] As a raw material for the above silica glass based optical fiber
Is the natural quartz glass obtained from natural quartz was used, impurities in the natural quartz glass, foreign material, there is contained the bubbles, reduction of the breaking strength of the fiber according to variations in characteristics, fluctuations in fiber characteristics And so on.

[0004] In recent years, there has been a demand for the improvement of the characteristics of optical fibers, and for that purpose, the raw materials of optical fibers have rapidly shifted to synthetic quartz glass, and all synthetic quartz vitrification has already been completed by the VAD method and the OVD method. are doing. However, in the above-mentioned MCVD method and PCVD method (hereinafter referred to as thermal CVD method), the vitrification of all synthetic quartz is significantly delayed, and natural quartz glass tubes are still used. It largely depends on the softening point of the synthetic quartz glass tube. Synthetic quartz glass tubes have the disadvantage that, even with anhydrous synthetic quartz glass dehydrated and vitrified, the softening point is lower than that of conventional natural quartz glass for optical fibers, and the temperature condition setting width of the CVD reaction is narrow, making it difficult to use. For this reason, a natural quartz glass tube has been used as a quartz glass tube for the thermal CVD method despite the drawbacks, and has reached the present.

[0005]

SUMMARY OF THE INVENTION The above-mentioned thermal CVD method is so-called
This method is excellent in productivity and attractive because the clad portion having a large volume ratio can be manufactured using an optical fiber with a high productivity as compared with the VAD method or the OVD method via a wire. For this thermal CVD method, the quartz glass tube is a reaction vessel for the glass raw material to react, and also shuts off the reaction gas inside the quartz glass tube from the outside, prevents air, foreign matter, moisture and other disturbances, and keeps the gas concentration constant. It is also a flow reaction tube for keeping the flow rate stable. Further, the quartz glass tube is also a heat transfer medium for thermally reacting the glass raw material. The heat for the thermal reaction is supplied by external heat, but transfers the heat to the reaction gas through the quartz glass. In order to deposit a uniform glass film over the entire length of the quartz glass, the entire length is repeatedly heated with a single heat source. High temperature heating is required, and the surface of the quartz glass tube is required to have a higher temperature. On the other hand, the inner surface of the quartz glass tube is a substrate for depositing quartz glass for a waveguide (substrate). The deformation of the diameter and thickness of the quartz glass tube and the variation of the heat transfer coefficient are related not only to the abnormality in that portion but also to the pressure, gas flow, and temperature distribution in the flow reaction tube, so that a uniform glass film cannot be obtained. The quartz glass tube is also a part of the optical fiber. Because it has a deposition rate that is at least sufficiently larger than the core of the optical fiber, its physical property values, such as impurities that affect transmission loss, OH groups, alkali ions related to strength, bubbles, foreign matter, devitrification, or at the time of drawing The properties such as spinnability, melt breaking property, tensile properties at around normal temperature, long term creep and water resistance must not be inferior to other quartz glass.

Although many of the above-mentioned characteristics are required for a quartz glass tube for an optical fiber, synthetic quartz glass is almost satisfied. However, at present, the synthetic softening glass obtained from any of the production methods has a lower thermal softening point than natural quartz glass. That is, the synthetic quartz glass tube has substantially the same thermophysical property values as the quartz glass synthesized and deposited therein, and has substantially the same softening point. In order to obtain a good quality glass film, it is necessary to dissolve the precipitated glass particles at a sufficiently high temperature. However, this requires heating the synthetic quartz glass tube to a higher temperature, which promotes the deformation of the synthetic quartz glass tube.

[0007] As described above, synthetic quartz glass tubes have excellent properties, and methods for avoiding high temperatures have been tried to take advantage of the advantages. However, if the temperature is lowered to such an extent that the synthetic quartz glass is not deformed, a reduction in productivity due to a decrease in the reaction rate, a change in the composition of the deposited glass, and an abnormality in the deposited glass film cause deterioration in transmission loss. Also,
Incorporation of a reaction catalyst or a reaction aid to promote the reaction of the raw material gas also increases the transmission loss of the optical fiber. further,
There is a method of mixing the MCVD method and the plasma CVD method to reduce the external heat temperature (AT & T method) and a low-pressure plasma method (Philips method) as a method other than the external heat. Preform for optical fiber
I can't get it. In addition to the above, even if a synthetic quartz glass tube is used ignoring some deformation, the yield of the obtained product is not practically small. That is, the low OH-based synthetic quartz glass, the low OH-based synthetic quartz glass by the chlorine dehydration method, or the vacuum-dissolved low OH-based synthetic quartz glass all have an OH group of several ppm or less, and
The viscosity was higher than that of the direct synthetic quartz glass having ppm. But still Heralux WG (Heralux WG)
(ux WG Tube, manufactured by Heraus) glass. Fused quartz glass was produced by using synthetic crystallized quartz glass as a powder, but a trace amount of a crystallization agent remained, causing deterioration in the strength of the glass fiber.

It is expected that the demand for optical fibers will be greatly increased in the future, and it has become essential to synthesize a large amount of glass in a short time due to the demand for cost reduction. All of the conditions for high-speed deposition, such as thickening, thickening, and increasing the amount of raw material gas, require the supply of even stronger heat energy, and the heat resistance of the synthetic quartz glass tube is higher than that of heat CV.
It can be said that it holds the key to the future trend of the D method.

In view of the above-mentioned situation, the present inventors have made intensive studies and found that a dopant having a specific viscosity increasing effect is contained in synthetic quartz glass to improve the thermal softening point of the synthetic quartz glass tube. As a result, it has been found that quartz glass exhibiting a high softening point substantially equal to or higher than Heralux WG manufactured from natural quartz or the like can be obtained, and the present invention has been completed. Ie

An object of the present invention is to provide a high-viscosity synthetic quartz glass tube suitable for a thermal CVD reaction.

Further, the present invention provides a high-temperature suitable for thermal CVD reaction.
It is an object of the present invention to provide a high-quality quartz glass preform for optical fibers using a viscous synthetic quartz glass tube .

Still another object of the present invention is to provide a method for producing the above-mentioned quartz glass preform for an optical fiber.

[0013]

According to the present invention, there is provided a high-viscosity method for a thermal CVD method comprising at least one selected from the group consisting of a carbon element, an aluminum element, a zirconium element and a compound thereof. low OH groups if <br/> formed quartz glass tube, the synthetic quartz glass tube for optical fiber quartz glass pre follower used - beam, and the optical fiber of quartz glass pre follower - according to the method of manufacturing the beam.

The above synthetic quartz glass is disclosed in, for example,
90837 JP, are produced by external methods such as JP-A-64-9821, carbon element during its manufacture, aluminum
Elemental zirconium and their compounds?
It is produced by adding at least one member selected from the group consisting of: As the carbon element source, a carbon atom-containing organic sila
Compounds including silicon, hydrocarbons, alcohols
Coexistence reaction with aluminum, ester, etc.
Aluminum chloride (AlCl ₃ ) is used as a source
Is convenient. These compounds can be easily vaporized as low molecular weight compounds, or can be dispersed in a liquid and vitrified after adsorption and drying in a liquid phase. In particular, the addition in the gas phase rather than the liquid phase using the dispersion medium is more suitable for maintaining the purity of the optical fiber. This carbon element, aluminum element, zirconia
The choice of elemental metals and their compounds depends on the field of use of the optical fiber and should be selected for long-distance transmission, short-distance or measurement optical fibers. And this carbon element, aluminum element
It is presumed that the addition of trace amounts of elemental and zirconium elements and their compounds to synthetic quartz glass increases the softening point independently of the OH group content and chlorine content.

The above carbon element, aluminum element, zircon
At least one selected from the elemental elementium and their compounds
As one kind of addition method, various well-known methods can be used. That is, a glass material is reacted in the gas phase to produce a porous quartz glass, which is then carbonized in the gas or liquid phase.
Element, aluminum element, zirconium element and its Re
A method of adsorbing at least one selected from the above compounds into a glass, a raw material gas and a carbon element, an aluminum element
Selected from elemental and zirconium elements and their compounds
Flame oxidation or oxidative hydrolysis of at least one of them in the gas phase, or a method using both. carbon
Element, aluminum element, zirconium element and it
The concentration of at least one selected from these compounds is desirably uniform throughout, but it is also possible for the concentrations to differ concentrically. However, an excessive change in concentration or localized distribution is not preferable. This carbon element, aluminum element
Selected from elemental and zirconium elements and their compounds
The synthetic quartz glass tube containing at least one
Less thermal deformation even at high temperatures of 0 ° C or higher.

Elemental carbon, elemental aluminum, zirconium
At least one element selected from the group consisting of
If the amount of the seed added is high or if there is a locally high-concentration portion, foaming occurs at the time of vitrification, fiber breakage occurs, and transmission loss occurs.

The carbon element, aluminum element, di
Small number of elements selected from ruconium elements and their compounds
Heat C using synthetic quartz glass tube containing at least one kind
The VD method refers to an MCVD method in which the internal CVD method is improved or a PCVD method using a heating source as plasma. These manufacturing methods are described in, for example, Japanese Patent Publication No. 55-22423 as a method for manufacturing a quartz glass preform for an optical fiber.

At least one selected from the group consisting of carbon, aluminum, zirconium and compounds thereof
It is possible to coexist an additive for lowering the refractive index or an additive for increasing the refractive index in the synthetic low OH-based quartz glass tube containing the seed. In an optical fiber called a depressed type or a segment type, additives may be mixed in addition to the core. Examples of the additive for lowering the refractive index include fluorine and boron, and additives for increasing the refractive index include germanium, phosphorus, aluminum, titanium,
There are elements such as tellurium. These additives are used in large amounts as compared to at least one selected from the group consisting of carbon element, aluminum element, zirconium element and compounds thereof.
The addition is performed in the same manner as the addition of at least one element selected from zirconium elements and their compounds. However, doping agents such as fluorine, boron and phosphorus significantly lower the viscosity of quartz glass, and can be improved by at least one selected from carbon, aluminum, zirconium and their compounds. .

The synthetic quartz glass preform for an optical fiber using the synthetic quartz glass tube of the present invention is, for example, MCVD.
When using the method, first, a liquid glass raw material (SiCl ₄ )
Further, an additive for controlling the refractive index, for example, germanium tetrachloride is vaporized and introduced into the synthetic quartz glass tube of the present invention. The synthetic quartz glass tube is set on a glass lathe and rotated at a constant speed. The synthetic quartz glass tube is heated to about 1600 ° C. or more while reciprocating a heating source in the axial direction from the outside, and the temperature in the glass tube is raised to 1400 ° C. The temperature is controlled to １1600 ° C. to generate glass fine particles, to be melted and vitrified to form a uniform glass layer on the inner surface of the synthetic quartz glass tube. If necessary
Carbon, aluminum, zirconium and
The ratio of at least one selected from these compounds and the glass raw material is changed. When each glass layer is formed to a predetermined thickness, the synthetic quartz glass tube is collapsed and preformed.
To form In the PCVD method, an optical fiber preform is formed in the same manner as in the MCVD method except that the heating source is plasma. The preform obtained in this way
The fiber is drawn by a drawing machine and drawn into an optical fiber.

[0020]

EXAMPLE AlCl ₃ was evaporated at 200 ° C. and flame-hydrolyzed together with a vapor-phase glass material, which was dehydrated and vitrified. The glass was clear and free of air bubbles. The amount of carbon was very small, and although it was impossible to quantitatively detect and identify it by a general combustion method, it contained about 5 ppm of aluminum. Table 1 shows the results of examining the softening point while changing the temperature. The softening point is measured by a beam bending method.
A temperature of 7.65 was indicated as the softening point. The concentration of OH groups contained in the synthetic quartz glass was determined by infrared spectrophotometry at 2.7 μm absorption, and the concentration of chlorine was determined by silver nitrate turbidimetry.

As reference examples for the synthetic quartz glass of the present invention, the physical properties of Heraux WG (natural quartz glass), dehydrated synthetic quartz glass, non-dehydrated synthetic quartz glass, and direct synthetic quartz glass are also shown in the table.

[0022]

[Table 1]

Examples 1 and 2 of Table 1 and Reference Examples 1 to
A quartz glass tube having a diameter of 25 mmφ and a thickness of 3 mm was prepared using the quartz glass of No.
The sample was heated to over ℃ and its thermal deformation was examined. Two-color pyrome
The temperature was raised to the deformation temperature of the dehydrated synthetic quartz glass of Reference Example 2 while observing the temperature with a tar. The quartz glass tubes of Examples 1 and 2 and Reference Example 1 had no deformation, but other Reference Example 2
The quartz glass tubes No. to No. 4 were deformed. As a result, although the use temperature in the MCVD method was higher than the softening point of quartz glass, the glass of the present invention was found to be advantageous because the practical deformation temperature started from a temperature lower than the softening point by about 50 ° C. or more. Further, an optical fiber preform is manufactured by the MCVD method using the quartz glass tube of the above-mentioned Example 1, and the optical fiber is drawn by an optical fiber drawing machine at 2,000 ° C. and linear variation at 100 m / min to 300 m / min. The cutting performance was examined, and it was confirmed that the cutting performance was better than that of the preform manufactured using the tube of Reference Example 1, and the same as in Reference Example 2. Furthermore, outer diameter 125μ
After surface coating as an mφ tube fiber, a tensile test was performed, but it was not different from the optical fiber manufactured by the MCVD method using the synthetic quartz glass tube of Reference Example 2.

[0024]

The synthetic quartz glass tube of the present invention is an excellent synthetic quartz glass tube having a heat softening temperature as high as that of a natural quartz glass tube and having the same uniformity as dehydrated synthetic quartz glass. By drawing an optical fiber preform made using this synthetic quartz glass tube , the filter transmission characteristics can be improved.
An excellent high quality optical fiber can be obtained .

Continuation of front page (56) References JP-A-2-74534 (JP, A) JP-A-62-191432 (JP, A) JP-A-61-219724 (JP, A) JP-A-2-283015 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C03B 8/04 C03B 37/018

Claims (4)

(57) [Claims] At least one selected from the group consisting of a carbon element, an aluminum element, a zirconium element and a compound thereof.
High viscosity low O for thermal CVD characterized by containing seeds
H-based synthetic quartz glass tube. 2. The thermal CVD method according to claim 1, further comprising at least one selected from the group consisting of fluorine, boron, germanium, titanium, aluminum, phosphorus, tellurium and compounds thereof. High viscosity
Low OH group synthetic quartz glass tube. 3. A quartz glass preform for an optical fiber manufactured by using the high-viscosity low-OH-based synthetic quartz glass tube for a thermal CVD method according to claim 1. 4. At least one selected from the group consisting of carbon, aluminum, zirconium and compounds thereof.
An optical fiber characterized in that a high-viscosity low OH-based synthetic quartz glass tube containing seeds is used as a substrate and a thermal CVD method is performed to form a glass layer on the inner surface of the substrate and collaps the glass layer. For manufacturing quartz glass preforms