KR850000908B1 - Method for manufacturing an optical fiber preform - Google Patents

Abstract

The soot-type glass rod is manufactured by the following apparatus. The burner (1) shich has plural concentric nozzles (11) is put on the position accorded with the rotating axis of starting materias. The starting materials are rotated. A first dopant increasing the refractive index of SiO2 glass is transferred from the central nozzle of the burner. The second dopant reducing the refractive index is transferred from the first concentric nozzle.

Description

Method of manufacturing a sales glass lot

1 is a schematic view showing a method for producing a glass (soot) glass lot according to the present invention.

2 is a cross-sectional view of the concentric multiple tube burner.

3 is a refractive index distribution.

4 is a refractive index distribution of the glass lot.

5 and 6 are diagrams showing transmission loss characteristics of a fiber.

The present invention relates to a method of manufacturing a glass rod (rod) used as a material of the glass fiber for light transmission.

The optical fiber for communication is usually composed of a core at the center and a cladding portion having a lower refractive index than the core around the core. Such glass fiber for optical transmission is roughly classified into Step Index type, in which radial refractive index distribution is changing stepwise as core and clad, and Graded Index type which is near parabolic type. have.

The original glass lot, which is made of fiber when thinly pulled out, is called preform, but of course the form is composed of core and clad. One such preform manufacturing method is the method described in Japanese Patent Application Laid-Open No. 49-10056. This method first prepares a cylindrical starting member, and then prepares a particulate glass made of a gas-like glass raw material by flame hydrolysis. Is placed on the surface around the rotating starting member. At this time, in the glass to be laminated, various dopants are applied in addition to the quartz glass to change the refractive index of the glass, and the amount of the dopant is adjusted for each layer so that the finally obtained profile can obtain a predetermined refractive index distribution.

In other words, if the concentration of the dough pant is deposited at least a constant number of times, then the dough pant concentration for suddenly lowering the refractive index is obtained, and a step index type profile is obtained. An index type preform is obtained.

The laminate of the sales glass thus obtained is placed in a high-temperature furnace and made transparent, and then the starting member is removed. As a result, only the synthesized cylindrical glass portion is heated and the hollow portion collapses, forming a preform.

Another method for producing a profile is the method described in Japanese Patent Application No. 51-29953, which first prepares a quartz tube, rotates the quartz tube, and flows a gaseous glass material into the quartz tube. It is heated externally and the glass is laminated several times on the inner surface of the glass tube. In this case as well, the concentration of the dopant for each layer is finally adjusted so that the profile can obtain a predetermined refractive index distribution. Thereafter, it is heated again to a high temperature to collapse the hollow part and form a preform. However, the above two methods each have drawbacks. That is, a part collapses and a preform is formed. However, the above two methods each have drawbacks. That is, the method of Japanese Patent Laid-Open No. 49-10056 has a different thermal expansion coefficient between the starting member and the laminated glass, so it is easy to cause cracks in the laminated glass due to slight temperature change or impact during the process. The method of 51-29953 has limitations in the length, diameter and thickness of the quartz tube that can be used as a starting material, and thus has a weakness in mass production of fibers because large profiles cannot be obtained.

As a method of making a preform that is completely different from the above two methods, there is a Japanese Patent Application No. 49-145338 outside of Fujihara, which is directed toward the surface of the rotating starting base or to one side of the rotating starting member. Glass particles are synthesized by oxidizing or hydrolyzing at a high temperature by ejecting a glass-like glass material of glass by a plurality of nozzles or burners in a direction parallel to the rotation axis or in a direction having an appropriate angle with the rotation axis. The glass lot is obtained by depositing on the starting base or the end portion of the rod-shaped starting member and subsequently laminating the glass particles in the direction of the rotation axis. At this time, the dough pan composition in the glass raw material gas blown out through the plurality of nozzles or burners is a dough pan composition for increasing the refractive index of the glass from the nozzle or burner for laminating the glass to a portion near the rotation axis (center of the lot). And a dopant composition having a lower refractive index than the center of the glass lot synthesized from a nozzle or burner laminated with glass on a part far from the rotation axis, to form a fiber for optical transmission having a core at the center and a clad around the core. You can get the preform of the required structure. This method is not only influenced by the starting element, but also suitable for obtaining large size preforms.

However, fiber optics require two important characteristics in terms of transmission: one, the transmission loss of light is low, and the other is that the pulse wave of the light is twisted during transmission or the pulse width becomes wider. Less work. The latter property means that the band of the baseband frequency that can be transmitted with low loss is wide, and the closer the refractive index distribution of the fiber is to the parabolic formation, the wider the transmission band of the baseband frequency. There are three main factors to increase the transmission loss, the first is the scattering of light due to the difference in refractive index in the axial direction, the second is the absorption of light due to the presence of impurities, and the third is the change in core length in the longitudinal direction. It is scattering based on the method of non-interchangeability.

Regarding the above two transmission characteristics, namely, transmission loss and transmission band of baseband frequency, the method of Japanese Patent Laid-Open No. 49-145338 described above has the following drawbacks. One drawback is that by stacking a plurality of nozzles or burners side by side, even when rotating the base or rod-shaped starting member, at each moment, the distribution of laminated dough pants is not uniform in the circumferential direction. . As an example, consider a case where the burner for synthesizing the glass for cladding is separated from the rotation side with the axis of the burner for synthesizing the glass for the core at a position coinciding with the rotation axis of the starting member. The conventional stacking amount of glass is 20-50 g every hour. If 36 g of glass, that is, 0.01 g / sec of glass is laminated every hour, when it is converted into a fiber having a diameter of 150 µm, a considerable amount of glass is laminated to a fiber of 25 cm per second. In other words, if the base or the starting member is rotated once / second, the fibers will be different in a cycle of 25 cm in refractive index. That is, it is distributed in a spiral form as the clad period.

This is also the same as placing the nozzle for cladding in the position symmetrical to the rotation axis. In short, it is a problem that cannot be solved only by arranging a plurality of nozzles side by side. Therefore, as described above, the axial nonuniformity of the refractive index increases the transmission loss.

In addition, the periodic change of the refractive index distribution spirally also means that the refractive index distribution in the fiber cross section is not circular symmetry. In other words, even if the distribution of any linear refraction through the cross-sectional center of the preform made by side nozzles can not be the same. This results in narrowing the transmission band in the erased index fiber. Another major drawback of using multiple nozzles, or burners, is that the number of gases to be controlled is significantly greater and the device becomes larger and more complex, while maintaining reproducibility.

This invention is made | formed in order to remove the fault of the invention of said Japanese Unexamined-Japanese-Patent No. 49-145338. The point of the present invention is to use only one concentric multi-pipe burner instead of having a plurality of nozzles or a plurality of burners side by side. In addition, although the main object of the present invention is to provide a method for producing a preform for obtaining a graded index fiber having excellent characteristics, it is of course also possible to obtain a preform of a step index type or other refractive index distribution phenomenon. Hereinafter, the specific Example which obtains the graded indeath-type profile is shown. FIG. 1 illustrates a method for generating a sales glass lot 2 for a graded index type profile using a concentric quinine burner 1, and FIG. 2 shows a tip of the concentric quinine burner. This burner is made of quartz glass, and in the center nozzle 11 of the burner, argon gas is used as a carrier gas, and a first glass raw material having a high refractive index is flowed. As the source gas, SiCl ₄ (21) and GeCl ₄ (22) and PoCl ₃ (23) are used as the dough pan gases for increasing the refractive index.

PoCl ₃ increases the refractive index and also achieves the role of adjusting the thermal expansion coefficient and the vitrification temperature of the glass. From the second nozzle 12 of the five-pipe burner, a second glass raw material gas having a lower refractive index than that of the glass synthesized as the first raw material gas is also flown using argon gas as the carrier gas.

As the source gas, SiCl ₄ (24) and BBr ₃ (25) are used as the dough pant gas for lowering the refractive index. SiCl ₄ , GeCl ₄ , PoCl ₃ , and BBr ₃ are placed in the glass containers 31-35 as a liquid phase and are vaporized as argon gas for the carrier. These glass containers 31-35 are put in the thermostat 41-45. The amount of glass raw material gas to be supplied is adjusted according to the temperature of the thermostats 41-45 and the flow rate of the carrier gas. In addition, since the heater 46 is wound around the pipes between the outlets of the raw material containers 31 and 35 and the burner, the temperature is higher than the temperature of the thermostat so that the raw material gas passing through them is not cooled and liquefied. It is becoming. Hydrogen gas is blown out from the fourth nozzle 14 of the five-pipe burner, and oxygen gas is blown out from the fifth nozzle 15. Argon gas is flowed in order to prevent the glass fine particles synthesized from the third nozzle 13 from adhering to the nozzle. When hydrogen is combusted, water is generated, which reacts with the glass raw material gas, and glass fine particles 4 such as SiO ₂ , GeO ₂ , P ₂ O ₅ , and B ₂ O ₃ are synthesized by gas decomposition. The synthesized glass fine particles 4 deposit a mounting commercial glass on the tip of the rotating refractory starting member 3, for example, a quartz glass lot, substantially parallel to the axis of rotation. Subsequently, by continuously supplying the raw materials and growing the glass fine particles in the axial direction, the sales glass lot 2 is formed. When stacking the glass fine particles, the starting member 3 so that the glass stacking surface 5 of the glass stack lot has a constant distance from the tip of the burner in order to keep the outer diameter of the glass stack lot 2 constant. Increase according to the growth rate of sales glass lot. A portion of the first raw material gas ejected from the nozzle 11 and a part of the second raw material gas ejected from the nozzle 12 are mixed after ejecting, so that the dough pan concentration is changed slowly, and the gradient index type It is possible to obtain a sales glass lot to obtain a profile. Therefore, if the degree of mixing is suitable, the refractive index distribution can be made close to the parabolic line. I will explain in more detail why.

The concentration distribution of the sum of the SiCl ₄ is assumed to be maintained almost uniformly by the gas supplied from the nozzle 11 and the nozzle 12, and the diffusion of the dough pan from the nozzle 12 is obtained from two parallel planes. Approximated by the supply of, the doughpan concentration distribution by the gas supplied from the nozzle 11 and the nozzle 12 is represented by the following equation.

(Dough pant concentration distribution by the gas supplied from the nozzle 11)

(Dough pant concentration distribution by the gas supplied from the nozzle 12)

Where r is the distance from the center of the burner

a: radius of the nozzle b: width of the nozzle 12

h: thickness of the partition wall between the nozzle 11 and the nozzle 12 Di, ti,

Cio (i = 12) represents the diffusion coefficient, diffusion time and initial concentration of the dough pans of the nozzle 11 and the nozzle 12, respectively. In the practical range, the dough pan concentration and the refraction are almost proportional to each other, so that the feed gas of the nozzle 11 and the nozzle 12, the refractive index alone, and the total refractive index distribution are shown in the curves (A) and (Fig. B) and (C). By setting the burner dimensions, the composition of the raw materials, and the feed rate appropriately, they can be very close to the parabola.

In the above example, argon gas is used as the carrier gas of the glass raw material gas. However, helium, which is an inert gas, may be used instead of argon, or oxygen or nitrogen may be used. In addition, in order to prevent adhesion of glass, the gas flowing from the nozzle 13 may be nitrogen or helium instead of argon. In addition, the dough pant gas flowing from the nozzle 11 is not limited to GeCl ₄ or PoCl ₃ , and at least one of halogenated gas such as germanium, phosphorus, titanium, aluminum, gallium, or hydrogen compound gas is converted into SiCl ₄ gas. It is good if it is mixed. In addition, the dough pant gas flowing through the nozzle 12 is not limited to BBr ₃ , and at least _one of boric water or a containing gas such as BCl ₃ , SiF ₄ , CF ₄ , CCl ₂ F _2, and the like is added to the SiCl ₄ gas. It is good if it is mixed.

In addition, even when a glass source gas to synthesize SiO ₂ in the foregoing description using the halogenated silane gas of for explanation, but, SiCl ₄ instead of monosilane gas (SiH _4), or SiHCl ₃ in such as the use of SiCl ₄ good. In addition, any combustible gas containing hydrogen such as CH ₃ or C ₂ H ₅ may be used instead of the hydrogen gas for combustion. In principle, the starting member does not need to be rotated. In practice, however, the starting member should be rotated for the purpose of eliminating unevenness in the circumferential direction of the lamination due to eccentricity of the burner nozzle and shaking of the flame.

In the above example, although two glass raw material blowing nozzles of a burner are used, three or more multi-pipe burners may be used. In short, it is advisable to combine the dough pan so that the refractive index decreases sequentially as it goes from the center to the outside raw material supply nozzle. In addition, if the arrangement | positioning of the gas which the 1st source gas which raises the refractive index of glass and the 2nd source gas which makes refractive index lower than that is not mixed, for example, sets it as a burner of a six-pipe, the 2nd source gas May flow through the nozzle of the third layer, and the inert gas may flow through the nozzle of the second layer for the purpose of separating gas.

As described above, the formed glass stack is made transparent while being put in a heating furnace under an inert gas. The heating temperature at this time is preferably 1400-1600 ° C. On the other hand, as described above, when the glass sheet is made into a commercial glass lot and then sintered and laminated, the dough becomes volatilized if the temperature is raised too much as the glass becomes transparent. This is described in Japanese Patent Laid-Open No. 49-99079. In the above example, the glass is synthesized by flame hydrolysis, because the yield of the glass is better than that of oxidizing the raw material gas of the glass by a method other than hydrolysis.

The following shows specific examples and the results.

The used apparatus is shown in FIG. 1, the used burner is a concentric 5-middle burner as shown in FIG. 2, and the outer diameter of the burner is 20 mm. SiCl ₄ , GeCl ₄ and PoCl ₃ were flowed through the nozzle 11, and SiCl ₄ and BBr ₃ were flowed through the nozzle 12 using argon as a carrier gas. In the nozzle 13, argon gas is flowed in order to prevent glass fine particles from adhering to a burner.

The carrier gas flow rates of the gases and the temperatures of the thermostats 41-45 are shown in the first and second tables.

[Table 1]

Gas flow rate

[Table 2]

Temperature of thermostat

Under the above conditions, the glass beads were grown at a rate of 700 mm / hr, and a transparent glass lot of 50 mm × 100 mm was obtained for about 1 hour. This sheet glass lot was sintered at about 1450 ° C. to obtain a transparent glass lot of 25ψ × 100mm. The measured value of the refractive index distribution of this radial direction is shown in FIG. As a result, a distribution close to the parabola is obtained. The preform was pulled down to a diameter of 15.0 mu to form a fiber having a length of 2 km, and transmission characteristics were measured. The wavelength characteristics of the resulting transmission characteristics are shown in FIG. The wavelength at 0.85μ is a very low loss of 3.2dB / km. 6 shows the transmission characteristics of the baseband frequency per kilometer. The frequency at which the transmission loss drops by 6 dB is 1100 MHz, which is a very wide range of fibers. In the example in which we made a sales lot by arranging two burners side by side in the method of Japanese Patent Laying-Open No. 49-145338, and in the example of manufacturing fibers, the transmission band is about 100 M㎐.km, and the transmission band is 10 times by the method of the present invention. I was able to widen over.

Since the kind of gas which flows can be matched with this invention, it is easy to control and the fiber which is very characteristic can be obtained with good reproducibility.

Claims (1)

A first dough pan which has a burner tip including a plurality of concentric nozzles in a position coincident with the axis of rotation of the starting member, rotates the starting member, and increases the refractive index of the SiO ₂ glass from the central nozzle of the tip of the burner. A first raw material gas having a concentration of a second raw material gas having a second dough pant concentration which reduces the refractive index of the SiO ₂ glass from the first concentric nozzle of the burner tip portion which flows the first raw material gas to the starting member. Flowing the combustible gas containing hydrogen and oxygen from the outer concentric nozzle at the tip of the burner surrounding the first concentric nozzle and burning it, and burning it to burn the fine particles of glass by flame hydrolysis. Synthesized at the front end portion and deposited on the terminal portion of the starting member, the burner front end and the deposited glass lot surface front end By removing the starting member from the burner tip so as to maintain a constant distance from the burner tip, a sales glass lot having an annular cross-section is grown on the starting member having a parabolic radial dough pant concentration distribution, and the sales glass lot is heated to A transparent glass body having a parabolic radial dopant concentration distribution.

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