JPH0459254B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention provides a method for manufacturing a quartz glass base material for optical transmission;
In particular, the present invention relates to a method for manufacturing a quartz glass base material for optical transmission that does not contain elemental or compound chlorine by an internal MCVAD method.

Various methods are known for manufacturing silica glass base materials for optical transmission, but these require extremely high purity, and furthermore, it is necessary to control the refractive index in the cross-sectional direction. Because of this, the chemical vapor deposition method (CVD method), which uses chemical reactions, is widely used. And this
Regarding the CVD method, there is an internal method (MCVD method) in which silica obtained by oxidizing a silicon compound is formed as a transparent glass film inside a quartz tube, and a method in which silica made by flame hydrolysis of a silicon compound is formed on the outer surface of the core material. Furthermore, the vapor phase attachment method (VAD method) is known, in which silica made by flame hydrolysis of silicon compounds is deposited on rotating refractory materials and made into a rod. However, this external method,
The VAD method differs from the MCVD method in that the reaction is not carried out in a closed system, making it difficult to control the refractive index of the glass base material. The internal MCVD method is preferred because it is easy to use.

However, in the conventional internal MCVD method, silicon tetrachloride (SiCl ₄ ) as a glass forming raw material gas and germanium tetrachloride (GeCl ₄ ) as a dopant to control the refractive index of the glass are supplied from one end of a quartz tube. , phosphorus oxychloride (POCl ₃ ), boron trichloride (BCl ₃ ), etc. are fed together with oxidizing oxygen gas, and an oxide flame burner or electric resistance heating device is installed on the outside of the quartz tube from the gas supply side. Move to the exhaust gas side repeatedly to heat these gases,
Silica containing a dopant produced by the gas phase oxidation reaction is deposited as a transparent glass film in the length direction inside the quartz tube, and then the hollow quartz tube with this glass film layer is solidified to form a quartz glass base material. Because this method is a method of
In addition to the disadvantage that absorption loss occurs in the 1.1 μm wavelength range, this dissolved chlorine also poses the problem of causing foaming in the solidification step or the subsequent spinning step.

In addition, in this internal MCVD method, as mentioned above, the heat necessary for the gas phase oxidation reaction of the raw material gas to occur is supplied from the outside of the quartz tube, and this heating from the outside brings the quartz glass tube to its softening point. As the quartz tube is heated, it tends to twist or bend, which also means that the thicker the glass deposit layer becomes, the worse the heat transfer becomes, and the external heating must be increased accordingly. This deformation will be further exacerbated. And this is especially true when the external heating source is an oxyhydrogen flame, in order to increase the heating temperature it is necessary to increase the amount of hydrogen, which increases the speed of the flame, resulting in this deformation. There was a tendency for this to occur more and more easily. Incidentally, this deformation also had the disadvantage that the thickness of the glass deposited layer was made non-uniform, so that the refractive index distribution of the target quartz glass base material became significantly disordered.

The present invention solves these disadvantages by providing an internal installation.
This article relates to a method for producing a silica glass base material for optical transmission using the MCVD method, which has the general formula R ¹ _o Si (OR ² ) _4-o (where R ¹ is a hydrogen atom, a methyl group, an ethyl group, or ² is a methyl group or ethyl group, n is a positive number from 0 to 4) and an ester silane represented by the formula Ge(OR ³ ) ₄ , B(OR ³ ) ₃ (where R ³ is a monovalent hydrocarbon group) Or a dopant indicated by PH ₃ is heated and burned in a quartz tube, and the resulting silica containing the dopant is laminated as a transparent glass film on the inner wall of the quartz tube, and then the quartz tube is heated and melted. It is characterized by the fact that it becomes solid.

To explain this, the present inventors particularly studied a method for producing a quartz glass base material for optical transmission that does not contain halogen atoms or halogen compounds and has a preferable refractive index distribution, and in this case, the glass forming raw materials and dopant We conducted research focusing on the fact that it is sufficient to use a silane and a doping agent that do not contain halogen atoms in the molecule, and if we use an ester silane represented by the general formula above as the silane, it will be possible to find that the boiling point of the silane is approximately It has a low burning rate at temperatures above 100°C, is easy to handle, and is industrially inexpensive.As for this dopant, if it is germanium, boron, or PH ₃ containing an alkoxy group, it can be used to remove halogen atoms. The use of these raw material gases and dopants ensures that a silica glass matrix that does not contain halogen atoms or halogen compounds and has a good refractive index distribution can be obtained. In addition to being able to obtain materials, this also eliminates the difference in reaction rate depending on the type of gas,
Furthermore, since these gases are more reactive than those of conventional methods, the amount of heat needed to heat the quartz tube from the outside is small; for example, when this external heating source is an oxyhydrogen flame, , since the amount of hydrogen for this heating can be reduced to 1/5 to 1/2 of the conventional amount, the flame can be weakened, and as a result, deformation of the quartz tube is prevented, so it is possible to reduce the amount of hydrogen needed for the desired quartz glass base material. They found that the refractive index distribution becomes better, and after further studies on these various conditions, they completed the present invention.

As mentioned above, the ester silane used as a raw material for forming glass in the method of the present invention is represented by the general formula R ¹ _o Si (OR ² ) _4-o , and includes methyltrimethoxysilane, dimethyldimethoxysilane, Examples include trimethylmethoxysilane, tetramethoxysilane, methyltriethoxysilane, and tetraethoxysilane, but methyltrimethoxysilane and tetramethoxysilane are preferred industrially because they are inexpensive and easy to handle. . This ester silane is a by-product of dimethyldichlorosilane synthesis, which is the main raw material for silicone rubber, silicone varnish, and silicone oil, by the direct reaction of methyl chloride and metal silicon. or by thermally decomposing polymethylpolychloropolysilane or polymethylpolychloropolysiloxane with the general formula (CH ₃ ) _o Si _n Cl _x O _y obtained in the manufacturing process of dimethyldichlorosilane. This tetramethoxysilane can be easily obtained by reacting a mixture of monomethyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, monomethyldichlorosilane, etc., obtained with alcohol. It can be produced by the following formula Si + 4CH ₃ OHNoOCH ₃ ――――――――→ 100-110℃Si(OCH ₃ ) ₄ + 2H ₂ by reacting in the presence of NaOCH ₃ as a catalyst. It can be supplied industrially at low cost, and it can also be easily obtained as a purified product free of impurities by rectification of its raw material, chlorosilane or its ester silane. According to this method, a quartz glass base material with high purity can be obtained.

On the other hand, the dopant used in the method of the present invention has the above-mentioned formula Ge(OR ³ ) ₄ , B(OR ³ ) ₃ , PH ₃ , which includes Ge(OCH ₃ ) ₄ [boiling point 150℃],
Ge(OC ₂ H ₅ ) ₄ [boiling point 190℃], Ge(O-n-C ₃ H ₇ ) ₄
[Boiling point 240°C], Ge(O-n-C ₄ H ₉ ) ₄ [Boiling point 290°C],
B(OCH ₃ ) ₃ [boiling point 68℃], B(OC ₂ H ₅ ) ₃ [boiling point 117
℃], B(O-n-C ₃ H ₇ ) ₃ [boiling point 176℃], B(O-
Examples include n- _C4H9 ) _{3 [} boiling point 227°C],
Among these, those in which the R ³ group is a methyl group or an ethyl group are preferred because they have a relatively low boiling point and can be supplied into the reactor by being entrained in a carrier gas. In addition, this Ge(OR ³ ) ₄ , B
The method for producing (OR ³ ) ₃ is known, and is described, for example, in J.
Amer.Chem.Soc., 1953, 75, P.718, J.Chem.
Soc., 1956, P.4916, Encyclopedia of
It can be easily obtained by the method described in Chemical Technology, 3rd edition, Volume 4, P.111. Also, regarding this PH ₃ (boiling point -88℃),
Among phosphorus compounds, this is a typical compound that does not contain halogens, shows extremely high combustion efficiency even in air or oxygen, and can be easily obtained in high purity by filling it in a cylinder. It is considered optimal for a reason.

In the method of the present invention, a mixed gas of ester silane and a doping agent is conveyed by a carrier gas if necessary, and is fed into a quartz tube together with oxygen gas as an oxidizing agent, and an oxidation reaction is carried out in the quartz tube. This is done by depositing silica containing dopants generated by silica on the inner wall of a quartz tube.
In addition, in the conventionally known internal MCVD method, an oxyhydrogen flame burner is sequentially moved along the inside of the quartz tube in order to uniformly deposit silica generated from the reaction gas introduced into the quartz tube on the inner wall of the quartz tube. ,
Although it was necessary to reciprocate the ester silane and the dopant, in the method of the present invention, both the ester silane and the dopant are flammable substances, and they are burned at the tip of the feed nozzle for feeding into the quartz tube, resulting in the dope being immediately released. In this case, it is preferable to fix the heating source such as an oxyhydrogen flame burner and move the quartz tube itself to reciprocate, since the silica containing the agent is deposited on the wall of the quartz tube. In addition, if the velocity of feeding these raw material gases into the quartz tube is low, there is a risk of flashback occurring, so it is best to inject this into the quartz tube at a sufficient flow rate.
Furthermore, if oxygen gas is not mixed in, the combustion rate may decrease and complete combustion may not be achieved, so it is preferable to mix oxygen immediately before the feed nozzle.

Note that the silica deposited inside the quartz tube is melted by the combustion heat of the raw material gas and external burner or electric heating, and is deposited as a glass film on the inner wall of the quartz tube, but this silica or glass film is not doped. The material contains a doping agent and exhibits a different refractive index depending on the amount of the dopant. Therefore, in carrying out this process, the raw materials must be stacked so that glass films having a predetermined refractive index are sequentially laminated in the inner diameter direction of the quartz tube. It is preferable to sequentially change the dopant concentration in the mixed gas.

In addition, the quartz tube with the glass layer containing the dopant thus obtained laminated on its inner wall is then heated and melted to form a solid quartz glass base material, which is a method known in the art. A collapse process can be applied, for example, using this quartz tube.
The method is to melt the glass by heating it at around 2000 degrees Celsius, and use the viscosity of the molten glass and the surface tension of the glass to crush it into a solid material so that no air remains inside.

Next, the method of the present invention will be explained based on the attached drawings. FIG. 1 is a schematic vertical cross-sectional view of an apparatus for carrying out the method of the present invention, and FIG. 2 is ^a schematic vertical cross-sectional view showing the movement of the quartz tube. ) ₄ containers 2, B (OR ³ ) ₄ containers 3,
The raw material gas dope contained in the PH ₃ container 4 is carried by argon gas as a carrier gas introduced from a pipe 5, and these are combined with oxygen gas sent from a conduit 7 in a mixer 6 to a quartz gas pipe 8.
sent to These gases are injected into the quartz tube from the feed nozzle 9;
is heated from the outside by the oxyhydrogen flame burner 10, so the gas fed there burns at the tip of the feed nozzle 9, and this oxidation reaction turns it into silica containing the dopant, which is then rotated. It is deposited on the inner wall of the quartz tube. This silica is deposited uniformly on the inner wall of the quartz tube as the quartz tube is sequentially moved from one end to the other with respect to the stationary burner. Melts by heating from
A glass layer is laminated on the wall of the quartz tube, and the silica and exhaust gas that have not been formed into a glass film are discharged to the outside from the other end of the quartz tube. Figure 2 shows the movement of this quartz tube, in which the quartz tube 8 is moved from a) to b) with respect to the fixed burner 10, and b) as shown in figure b). It is shown that after moving to the end, the glass film is sequentially formed by immediately returning to the state shown in a).

In this case, as mentioned above, the amount of dopant added to the ester silane is adjusted over time so that the concentration of dopant contained in the glass film laminated on the quartz tube exhibits a predetermined refractive index. When the glass film reaches a predetermined thickness, the supply of raw material gas is stopped, and the hollow quartz tube thus obtained is then treated with the collapse process described above. If realized, the desired quartz glass base material can be obtained.

In summary, the method of the present invention uses an ester silane and a dopant that do not contain halogen atoms or halogen compounds as starting materials, and laminates a glass layer containing a dopant on the inner wall of a quartz tube using the MCVD method. According to this method, a quartz glass base material for optical transmission is manufactured by a method that does not contain any halogen atoms or halogen compounds, and therefore, it is easy to produce a quartz glass base material without light absorption loss due to the presence of halogen components. Furthermore, since this dopant has a good reaction rate at low temperatures, it is easy to obtain a silica glass base material for optical transmission with small changes in the refractive index distribution and a large relative refractive index difference. In this case, the external heating can be made at a lower temperature than in the conventional method, which prevents deformation of the quartz tube, and as a result, it is possible to obtain a quartz glass base material with a favorable refractive index distribution. It has the advantage of being easy.

Next, examples of the present invention will be given.

Example 1 A synthetic quartz tube with an outer diameter of 30 mm and a length of 1000 mm was used to create an apparatus as shown in Figure 1, and methyltrimethoxysilane [CH ₃ Si
(OCH ₃ ) ₃ ], Ge(OC ₂ H ₅ ) ₄ and as dopants
using PH ₃ and transporting these with argon gas,
It was mixed with oxygen gas and supplied into the quartz tube from a feeder nozzle.

This quartz tube will be heated with an oxyhydrogen flame burner, and this burner will be fixed and the quartz tube will be heated.
Assuming that the movement is performed at a speed of 150 mm/min, the raw material gas, dopant,
By varying the amount of oxygen as shown in FIG. 3, 100 layers of glass films having a composition of SiO ₂ --P ₂ O ₅ --GeO ₂ were formed on the inner wall of a quartz tube.

Then, the supply of this raw material gas was stopped, and the temperature of external heating was increased to solidify the quartz tube to form a rod-shaped quartz glass base material.

This quartz glass base material is transparent, and when we measured the refractive index distribution on this cross section, we found that it was a graded index type as shown in Figure 4.
When analyzed with a line microanalyzer, no chlorine atoms were detected, and even when this base material was stretched, no foaming occurred, and there was no absorption loss due to chlorine atoms.

Example 2 Using a synthetic quartz tube with an outer diameter of 30 mm and a length of 1000 mm, an apparatus as shown in Fig. 1 was made, and 100 C.C. of methyltrimethoxysilane (value per minute,
(the same applies hereafter), B (OCH ₃ ) ₃ 200C.C. as a doping agent.
was conveyed with argon gas at 400 C.C., mixed with oxygen gas at 1850 C.C., and sent into the quartz tube.
Thirty layers of glass film having a composition of SiO ₂ -B ₂ O ₃ were formed as a cladding layer on the inner wall of the quartz tube in the same manner as above.

Next, 100C.C. of methyltrimethoxysilane is used as the raw material gas, and 10C.C. of PH ₃ is used as the doping agent.
C. and Ge (OC ₂ H ₅ ) ₄ 30C.C. and Argon gas 300C.C.
After mixing oxygen gas at 1250 C.C., it was fed into a quartz tube and treated in the same manner as in Example 1.
Seventy glass films having a composition of SiO ₂ −P ₂ O ₅ −GeO ₂ were formed as a core layer.

Thereafter, the supply of raw material gas was stopped, and the temperature of the external heating source was raised to solidify the quartz tube to form a rod-shaped quartz glass base material.

When we measured the refractive index distribution in the cross section of the resulting transparent glass body, we found that it was a step index type as shown in Figure 5a. However, no chlorine atoms were detected in this, and the base material did not foam even when stretched, and there was no absorption loss attributable to the presence of chlorine atoms.

Example 3 The apparatus shown in Fig. 1 was made using a synthetic quartz tube with an outer diameter of 30 mm and a length of 1000 mm, and tetramethoxysilane [Si(OCH ₃ ) ₄ ] 100 C.C. was used as a raw material gas, and a doping agent was used. B(OC ₂ H ₅ ) ₃ 200C.C. was transported with argon gas at 200C.C., and oxygen gas at 2900C.C. was mixed with this and sent into the quartz tube, and the same as in Example 1 was carried out. After treatment, 50 glass films having a composition of SiO ₂ -B ₂ O ₃ were formed as cladding layers.

Next, 100C.C. of tetramethoxysilane as this raw material gas and 10C.C. of PH ₃ as a dopant,
Ge(OCH ₃ ) ₄ 35C.C. was transported with argon gas at 300C.C., and oxygen gas was mixed with this and 1000C.C. was sent into the quartz tube and treated in the same manner as in Example 1. SiO ₂ −
Fifty glass layers having a composition of P ₂ O ₅ -GeO ₂ were formed as a core layer.

Thereafter, the supply of raw material gas was stopped, and the temperature of the external heating source was raised to solidify the quartz tube to form a rod-shaped quartz glass base material.

When we measured the refractive index distribution of the obtained transparent glass body, we found that it was a step index type as shown in Figure 5b, and when we analyzed the fiber made from this with an X-ray microanalyzer, we found that it was No chlorine atoms were detected in the sample, and this base material did not foam even when stretched, and there was no absorption loss due to the presence of chlorine atoms.

[Brief explanation of the drawing]

Fig. 1 is a schematic longitudinal cross-sectional view of an apparatus for implementing the method of the present invention, Fig. 2 is a longitudinal cross-sectional view showing movement of the quartz tube, and Fig. 3 is a raw material gas, dopant, and oxygen gas in Example 1. Graphs showing the gas flow rates of FIG. 4 is Example 1, FIG. 5 a and b are Example 2,
3 shows a refractive index distribution map of the quartz glass base material made in Example 3. 1...Ester silane container, 2...Ge (OR ³ ) ₄
Container, 3...B (OR ³ ) ₃ containers, 4...PH ₃ containers,
5, 7... Conduit, 6... Mixer, 8... Quartz glass tube, 9... Feed nozzle, 10... Burner.

Claims (1)

[Claims] 1 General formula R ¹ _o Si(OR ² ) _4-o [wherein R ¹ is a hydrogen atom or a methyl group or an ethyl group, R ² is a methyl group or an ethyl group, and n is 0 to 4 An ester silane with the formula Ge(OR ³ ) ₄ , B(OR ³ ) ₃ [where R ³ is a monovalent hydrocarbon group] or a dopant with the formula PH ₃ is placed in a quartz tube. Heat and burn with
A quartz glass base material for optical transmission characterized by laminating silica containing a doping agent generated by this as a transparent glass film on the inner wall of a quartz tube, and then heating and melting the quartz tube to make it solid. manufacturing method.