JPS62143840A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To produce a high-quality optical fiber preform of SiO2 type at high speed and at low temperature, by using a perchloropolysilane of a specific structure as a main raw material gas and piling fine particles formed by oxidation reaction of hydrolysis reaction on a substrate. CONSTITUTION:A Si compound as a main raw material gas and a gas of dopant of compound of B, Ge, P, F, etc., are subjected to oxidation reaction or hydrolysis reaction to form fine particles. These fine particles are fused and piled on a substrate to give an optical fiber preform of SiO2 type. In the above- mentioned method, a perchloropolysilane shown by the general formula SinCl2n+2, preferably Si2Cl6, Si3Cl8 or their mixture is used as the Si compound. Consequently, a high-quality optical fiber preform is formed at high pile speed without requiring a specific high temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method for producing a SiO2 base material used in optical fibers at high speed and with high quality.

[Description of prior art]

The conventional method for manufacturing 5iCh base materials used in optical fibers is the method of thickening (for example, Japanese Patent Publication No. 57-2836).
7), External attachment is based on the law (for example, Special Publication No. 57-15841)
, a method with a gas phase shaft (for example, Japanese Patent Publication No. 54-35217) is known. In all of these methods, SiC2<Y is used as the main raw material as a silicon compound, and this and GeC1a,
A method is used to manufacture optical fiber base materials by oxidizing or hydrolyzing gases such as BBra and Pocts at high temperatures, and depositing the resulting fine particles on a base material by fusing and depositing them on a base material. It is becoming possible to obtain it.

However, in order for optical fibers to be used in larger quantities and become popular, it is necessary to produce high-quality products at low prices and in large quantities. There is a problem that even if two hydrolysis reactions are carried out, the reaction rate is relatively slow. Therefore, the production rate of fine particles and the growth rate of the base material, which is an aggregate of these fine particles, are not sufficiently high (or not), resulting in a small production amount per unit time, which results in high prices.

That is, (i) In the conventional method, in order to increase the growth rate of the base material to χ, the residence time of 5iC64, which is the main raw material gas, in the supply gas is shortened, so 5ict4 passes through the reaction chamber undecomposed. , the basic unit of 5iC24 to obtain a unit weight of optical fiber base material becomes poor (as well as the energy consumption increases, resulting in an energy disadvantage).

(11) In addition, in the conventional method, when attempting to decompose 5iCt4' and r~ at high speed, increasing the supply amount of 5iCt4 and raising the reaction temperature 7, not only the gas phase in which 5iC44 decomposes, but also the substrate on which the generated fine particles are deposited. Inevitably, the temperature will also be raised.Then, the content of OI-1 will increase, or the temperature will be added to increase the refractive index of the optical fiber.
・For example, Qe γ where the decomposition rate of C14 to GeO2 changes and the amount of solid bath of GeO2 to 5i02 also changes.
This makes it extremely difficult to adjust the refractive index, for example, making it difficult to increase the refractive index of the optical fiber in a sharp parabolic manner toward the center.

[Summary of the invention]

It is an object of the present invention to overcome the drawbacks of the prior art and to provide a 75 method for producing a high quality 5i02 optical fiber preform without requiring particularly high temperatures and at a high deposition rate.

However, the inventors of the present invention have made extensive studies in view of these points, and have found that all of these objects can be achieved by using perchloropolysilane as a silicon compound. Completed 'C.

[Detailed disclosure of the invention]

According to the present invention, a silicon compound is used as the main raw material gas, and this is subjected to an oxidation reaction or a hydrolysis reaction with a gas of a compound such as boron, germanium, phosphorus, fluorine, etc. to generate fine particles, and the fine particles are formed into the fine particle base material. Si is fused and deposited.
In the method for producing an O2-based optical fiber base material, the silicon compound has the general formula (11 SinCt2n-+-z (n is an integer of 2 or more) (I
), a method of fabricating an optical fiber preform using perchloropolysilane is provided.

The perchloropolysilane used in the present invention has the general formula SinC
12n+2 (n is an integer of 2 or more) (I).

Examples of such perchloropolysilanes include hexachlorodisilane (SizCt6), octachlorotrisilane (Sis C1g), decachlorotetranane (5
i4CII'o), dodecachloropentacyla7 (S
is C/+2), tetradecachlorohexasilane (S
Ia C1-14), among others, hexachlorodisilane and octachlorotrisilane are preferred in terms of availability and ease of handling. These may be used alone or in mixtures.

Hexachlorodisilane (Si□C, z6
), octachlorotrisilane (SL+C4s), etc. are preferably of high purity, and in particular, it is preferable to use them with metal impurities such as Fe and A7 reduced as much as possible.

However, it is not a particular problem that S i CA4, which is a raw material of the prior art, may be mixed to some extent, for example, up to 200% or less, preferably about 150%, into the verchloropolysilica used in the present invention.

Cholera perchloropolysilane produced by a known method can be used. It is usually obtained by chlorinating particles of alloys of metal and silicon, such as calcium silicon, red sea bream silicon, or ferrosilicon, or by chlorinating silicon particles themselves at high temperatures (for example, in US Pat. Book No. 260'2728, 26
No. 21111).

In the present invention, additives or dopants used together with the main raw material gas include known compound gases such as boron, germanium, phosphorus, fluorine, etc., such as BBr3, GeCl4,
P OCAa, S i F4, CCL 2 F2, CF
4 etc. is used.

These are mainly used to control the refractive index distribution of the base material by increasing or decreasing the refractive index 7, but others are added for the purpose of adjusting the coefficient of linear expansion and reducing scattering loss.

[Preferred form for carrying out the invention] In the present invention, the above-mentioned main raw material gases, perchloropolysilane and dono-kunto gas, are used to prepare an optical fiber base material by a method known per se.

That is, as a preferred embodiment of the present invention, 5i
The main raw material gas such as 2Ct6 or S i B CAB is added with additive compounds such as boron, germanium, phosphorus, and fluorine for the purpose of adjusting the refractive index, contact point, or coefficient of linear expansion, as well as oxygen, air, and rare gases. etc., and introduced into a reaction chamber where the temperature is raised to several hundred to a thousand degrees Celsius by an oxyhydrogen flame or high-temperature gas flow, where it is turned into fine particles by an oxidation reaction or hydrolysis reaction, and then fused and deposited on a substrate. A method may be adopted in which a porous glass body is obtained by heating the porous glass body, which is degassed or solidified, and used as a base material for optical fibers.

More specifically, the method of the present invention using 5i2Cts, 5iaC1B, etc. as a raw material gas is effective in improving the productivity of optical fibers. The shaft attachment can be suitably used in any method such as the method.

Especially when applying 5i2C26 and 5iaCts used in the present invention to the vapor deposition method (VAD), multiple raw material supply nozzles are installed to control the refractive index.
To form a low refractive index (or high refractive index) part mainly composed of the i02 component, 5i2Ct6 or SisCtg of the present invention is supplied, and a high refractive index (or There is also an embodiment in which 5iC24, which has been conventionally used, is supplied to form the low refractive index portion.

In the present invention, as the main raw material gas, S i 2 cz, which is perchloropolysilane, is chemically modified from conventional 5iCt4,
When applied to a known reaction such as VAD using only 5iCtsY or 5isCtsY, in a reaction chamber of the same volume, the temperature is the same, and the amount of oxygen or water vapor supplied per Si is also the same, and 5iC4'a' is used. Compared to the conventional method,
In the method of the present invention, the production rate of fine particles is much faster;
The conversion rate to i02 is high.

Why in the conventionally known method is the main raw material gas required 5iC1
5i2Cts and 5is from < to perchloropolysilane
Although the detailed reason why the rate of production of fine particles increases greatly by simply changing to C1s is unknown, it is likely that (perchloropolysilane is highly oxidized compared to 5iC44 due to its chemical structure). Because it is susceptible to reaction or hydrolysis reaction (i.e., the rate of liquefaction reaction or hydrolysis, which is considered to be a rate-limiting reaction, is extremely slow, it is estimated that 5 in 2 fine particles can be generated easily and at high speed.

As mentioned above, the decomposition reaction rate of perchloropolysilane to 5iOz fine particles is higher than that of 5iCt4, but the adhesion rate at which the generated r,=siO+ fine particles are fused and deposited on the substrate is also lower when perchloropolysilane is used as a raw material. The case is 5iC
It is 1゛ thicker than if it were made from raw materials.

Although the reason for this is not clear, the physical and chemical conditions of the surface of the perchloropolysilane raw material, such as the OH groups present on the surface, may change during the time when the particles are generated by reaction and immediately fused and deposited. , CL groups, or the composition is assumed to be in a state where the fine particles are fused to each other.

Since the reaction rate and the deposition rate are large, it is thought that perchloropolysilane has a very large value compared to 5iCta.

That is, it is considered that the growth rate (=growth rate x silicon raw material supply rate) in the case of perchloropolysilane is much slower than that of 5iC24.

Also, as a matter of course, perchloropolysilane has a higher Si content in the molecule than 5iCt4.

For example, the Si content of 5iCt4 is 165%, and 5iCt4 has a Si content of 165%.
i2Ct6 is 20.8%. That is, 5i2C4s is 1
．． The Si content is 26 times higher. As a result, the amount of 5i02 produced per unit weight is also 1.26 times larger in the case of 5i2C4s, and the amount of SiCh produced from a unit volume is 1634 times higher when specific gravity is taken into account. This is a major advantage of polychlorosilane, which contributes significantly to the downsizing of equipment and reduces the cost of optical fibers.

In addition, the length of the base material produced from the raw material tank of the same volume and the distance of the optical fiber can be longer.

In this way, the superiority of Rutberg chloroborisilane over 5iC24 becomes even clearer when compared using the "growth rate per unit weight", which is an index that takes into account production starting from per unit weight.

Furthermore, optical fibers were produced using the base material produced using the method of the present invention, and compared with optical fibers produced using the base material produced using the conventional method.

It has become clear that the optical loss value, which is the most important item that determines the characteristics of an optical fiber, is overwhelmingly small in the optical fiber manufactured by the method of the present invention from r, -f'l material.

The reason for this cannot be determined exactly, but the reaction temperature is low and the reaction rate is high, so it may take a long time to manufacture the base material. Is it possible to change the distribution of additive components such as Ge, which determines the density refractive index in the base material, in other temperature ranges or by conventional methods? This seems to be due to the fact that it can be made more sharply and accurately compared to when it is manufactured. Furthermore, 5iO24y produced by the method of the present invention! It is also thought that the particles have an affinity for the fine particles of the dopant (easily fused and deposited, preventing the formation of a layer with a uniform composition).

As described above, in the method of the present invention, it is possible to easily increase the deposition rate of fine particles onto a substrate by more than twice that of the conventional method without particularly increasing the reaction temperature. It can be said that it is an extremely superior constant force method in that it is suitable for adjusting the refractive index. For example, in the filling method (MCVD method), is it conventional to diffuse impurities such as OH groups and metals contained in the base material of the starting quartz tube? However, in the method of the present invention, the reaction proceeds sufficiently even at a low temperature of about 700℃, and a high quality base material for SiO2 fibers can be obtained at a high deposition rate. It is.

The present invention will be explained below with reference to Examples.

Examples 1 and 2 A. Apparatus A high-purity quartz glass tube (outer diameter 10H, inner diameter 8J) was installed horizontally in an apparatus that rotates at a constant speed. It was then heated with an oxyhydrogen flame burner moving along the length of the quartz glass tube.

First, silicon compound bubbler and quaternary germanium (
A GeC14) bubbler was prepared and argon was blown in as a carrier gas so that each compound could be supplied to the quartz glass tube.

Separately, a bar cable and argon piping were connected to the above piping in front of the quartz glass tube, and the silicon compound and GeCl4 were mixed and supplied.

Is there exhaust gas treatment equipment on the opposite side of the waste supply port? installed.

B. Experimental method B-1 Synthetic quartz glass of cladding layer W'Y is transmitted 60 times per minute at 12 crn/min.
The mixture was heated to 1600'C using an acid water flame burner moving at

The quartz glass tube was filled with hexachlorodisilane (Si2Ct).
4) 20 d/m of Ar carrier gas was introduced from a bubbler and mixed with 25 QmA/gum of hydrogen and supplied.

A 100μ thick cladding layer was formed.

S i2 C 1610ml/m and GeC in the synthetic silica glass layer of B-2 core layer
1410me/Decoy & Ar carrier gas is used to introduce 500ml of oxygen from a bubbler and mix it with 17ml of oxygen to synthesize the core layer 2. Production of 0 B-3 fiber After the core layer synthesis, oxyhydrogen burner Y1900 The temperature was raised to °C, and a rod was formed by centrifugation.

After that, it is melted and drawn in a carbon resistance furnace to 125μ
fiber was produced.

C1 Measurement Result The rod was analyzed for composition and weighed seven times, and the following items were calculated for the cladding layer (Example 1) and core layer (Example 2).

■Reaction rate (= rate at which the main raw material silicon compound reacts and decomposes into Si02 in the flame hydrolysis reaction) ■ Adhesion rate (= rate at which 5iOz produced by decomposition adheres to the base material [quartz glass tube]) ■ Growth Rate (=reaction rate x adhesion rate) ② Growth rate results per unit weight are shown in Table 1.

In addition, the optical loss value of the fiber is at a wavelength of 1.27μ,
It was 1.4 dB/Km.

Comparative Examples 1 and 2 Experiments were conducted by replacing the silicon compound hexachlorodisilane in Examples 1 and 2 with silicon tetrachloride (5IC14). The amount of Si supplied to the quartz glass tube was kept constant.
) engineering, 5ect44 during cladding layer synthesis in order to
Q, l/am, 5iC4420 chloride/hydrogen was supplied during core layer synthesis.

The results are shown in Table 2.

Comparing Example 1 and Comparative Example 1, and comparing Example 2 and Comparative Example 2, 5i2cz6 is superior to 5IC44 in terms of reaction rate, adhesion rate, growth rate, and growth rate per unit weight. In other words, the growth rate is 1.4 times, and the growth rate per unit weight is 1.
．． It is 8 times more.

Furthermore, the optical loss value of the fiber is 5.5 at a wavelength of 1.27μ. ! l d B / Km and S 12C4
It was found that when used as a 6Y silicon raw material, it was possible to produce a constant collapse fiber with a fairly small loss value.

Table 1 Table 2 Example 5 A. Apparatus A burner is installed to generate SiO2 mimic particles from a silicon compound by flame hydrolysis reaction. A base material of a quartz plate is placed above it, on which fine particles generated from the burner flame are fused and deposited. The quartz plate is pulled upward while rotating. A porous preform grows on the underside of the substrate.

A silicon compound bubbler and a GeC74 bubbler are connected to the burner. A carrier gas is supplied to the bubbler to entrain the silicon compound and GeC44 gas,
Introduce to burner. Further, hydrogen and hydrogen are also introduced into the burner by arrangement of the chambers.

B. Experimental method B-1 Production of porous base material Hexachlorodisilane (5i2CL6) 30 to the burner
7/1111M, GeCA445 ml/+m'!
a; Ar'l was supplied as a carrier gas. In addition, 1 t/decoy of hydrogen and 21/-tfnf of oxygen were supplied.

A porous base material was manufactured under the above conditions.

The reaction temperature was 1100'C.

Preparation of B-2 Fiber The porous base material described above was made into transparent glass in a helium atmosphere to produce a core material. This core material was placed in high-purity quartz for cladding, and melt-drawn to produce a 125 μm fiber.

C0 Results Composition analysis 2 of the porous base material was conducted to determine the reaction rate, adhesion rate, and growth rate per unit weight.

Show the results to Iotsu.

The optical loss value of the fiber is 1.0 dB/f (7j in m) at a wavelength of 1.27 μ.

Comparative Example 6 An experiment was conducted using 5ICt4 instead of 5i2CA6 in Example B.

In order to supply the same amount of Si per unit time instead of S 12C4s 50 m17m in Example 6, 5iC1<6
Porous base material was prepared under the same conditions as in Example 6 except for one using 0 go/decoy. and used it to manufacture optical fibers.

Results 7 are shown in Table 6.

In fact, 5I2ct6 is clearly 5i for Akirero and Hikuchore.
C14 is excellent in each item.

The growth rate is 29 times better, and the growth rate per unit weight is 68 times better.

Also, the optical loss value of the fiber is 6 at a wavelength of 1.27μ.
8d137 Km, and it can be seen that the case where the 5i2C46 silicon raw material is used is clearly superior.

Claims (5)

[Claims] (1) A silicon compound is used as the main raw material gas, and this and boron,
In a method of producing a SiO_2-based optical fiber base material by performing an oxidation reaction or hydrolysis reaction with a gas of a compound such as germanium, phosphorus, or fluorine to generate fine particles, and depositing the fine particles on a base material by fusion, The silicon compound has the general formula (I) Si_nCl_2_n_+_2 (n is an integer of 2 or more) (
I) A method for producing an optical fiber base material characterized by using perchloropolysilane. (2) Perchloropolysilane is hexachlorodisilane (
2. The method according to claim 1, wherein Si_2Cl_6). (3) The method according to claim 1, wherein the perchloropolysilane is octachlorotrisilane (Si_3Cl_8). (4) The method according to claim 1, in which perchloropolysilane is used as a mixture. (5) The method according to claim 4, which uses a mixture of hexachlorodisilane and octachlorotrisilane.