JP2622182B2 - Manufacturing method of optical fiber preform base material - Google Patents

Description

The present invention relates to a method for manufacturing an optical fiber preform preform, and more particularly, to a method for producing a large-sized optical fiber preform at high speed without deteriorating the structural characteristics of the optical fiber. The present invention relates to a method for producing an optical fiber preform base material that can be produced.

(Prior Art) In the early stage of development, optical fiber preforms were manufactured by coating a glass for a core with a glass tube (see JP-B-41-11071). The gas glass raw material is introduced into the oxy-hydrogen flame burner with the remarkable improvement in the characteristics and accuracy of the preform and the size of the preform is enlarged, and the glass fine particles generated by the flame hydrolysis are rotated around the outer periphery of the core glass rod. The glass fine particles are sprayed on the core glass rod by reciprocating one of the burner and the core glass rod (hereinafter, described as burner movement for simplicity) in parallel to the axial direction. Are laminated one by one to form a porous glass base material, which is then heated and dehydrated,
The method has been shifted to a method of forming an optical fiber preform by forming a transparent glass (see JP-A-49-84258).

As for the method for producing this type of optical fiber preform, a method of continuously depositing in the vertical direction (Japanese Patent Application Laid-Open
Japanese Patent Application Laid-Open No. 55-116638), glass forming raw materials having different compositions are supplied from a plurality of burners to a porous glass base material, and a core rod is reciprocated relative to the burners to cause the porous glass base material to reciprocate.
There has also been proposed a method of obtaining a preform having a desired refractive index distribution in the radial direction by changing the composition of the glass forming raw material for each movement (Japanese Patent Application Laid-Open No. 57-18 / 1982).
No. 3330), a method in which a core rod is rotated and moved in a longitudinal direction to give an oscillating motion to the production of glass particles (see JP-A-56-120528 and JP-A-58-9835).
A thin oxyhydrogen flame burner having a width approximately equal to the length L of the core glass rod to be manufactured, or a number of oxyhydrogen flame burners are arranged side by side to form a burner row and do not move. (See JP-A-53-70449). Further, the amount of gas supplied to a plurality of burners, which is not an optical fiber preform, is adjusted or the burner surface and glass are blown. A method for preventing cracks in a porous glass base material by adjusting the distance to the surface on which the fine particles are deposited or adjusting the rotation speed of the heat-resistant substrate to change the deposition density of the glass fine particles in the radial direction (Japanese Patent Application Laid-Open (JP-A) No. 2002-110630). See Japanese Patent Application Laid-Open No. 64-9821).

(Problems to be Solved by the Invention) However, if an attempt is made to manufacture an optical fiber preform preform by these conventional methods, the method disclosed in JP-A-49-84258 requires only one burner. For this reason, the deposition rate of glass particles is slow, and when producing long and large diameter particles, the calorific value is insufficient, and the deposited silica layer has low mechanical strength, so that cracks are generated. Yes, JP-A-56-120528, JP-A-57-183330
Although the method disclosed in JP-A-58-9835 has the advantage that the core layer and the cladding layer can be obtained in one step, the core layer and the cladding layer have a low density, so that However, there is a disadvantage that the product becomes out of the target value because a thick cladding layer is attached to the core while the refractive index distribution of the core is unknown. Further, in the method disclosed in JP-A-53-70449, it cannot be guaranteed that the gas ejected from the slits of the burners has the same condition over the entire length of the core glass rod. Deposition unevenness occurs, and the accuracy of the deposition thickness of the obtained preform base material becomes poor in practice.
Although the method disclosed in Japanese Patent Publication No. 21 has the advantage that the deposition rate is high and large-sized ones can be manufactured, the stop point of the burner and the moving part are always the same because the shuttle moves back and forth at a constant amplitude in the length direction. Since the deposition is uneven at the position, the resulting deposit has irregularities on the surface, and there is a defect that aluminum as a core material is doped into the silica layer as a metal impurity in the optical fiber base. Not available for wood production.

(Means for Solving the Problems) The present invention relates to a method for producing an optical fiber preform preform which solves such disadvantages, and introduces a gaseous glass raw material into an oxyhydrogen flame burner, and the flame In a method of manufacturing a porous glass preform for an optical fiber by laminating glass fine particles generated by hydrolysis one by one on the outer periphery of a rotating core glass rod for an optical fiber, three or more pieces having the same size design are manufactured. Using a burner,
This is arranged at equal intervals over the entire length of the glass rod,
To measure the total weight and average outer diameter of the porous glass base material during deposition, detect the predetermined outer diameter and weight set in advance and the difference at that time, and to minimize the difference ,
Feedback control of the total gas supply of all burners, measurement of the deposition diameter of the porous glass base material during deposition over the entire length, and gas supply of each burner to minimize the difference in deposition diameter at each part Is feedback-controlled, and the distance between the burner and the porous glass base material is adjusted in accordance with the optimum deposition distance.

That is, the present inventors have conducted various studies on a method for producing a large-sized optical fiber preform base material at a high speed without deteriorating the structural characteristics of the optical fiber. In the method, unevenness of deposition of glass particles occurs between the burners and between the burners. When the burner is moved to alleviate this, uneven deposition of glass particles occurs at the stopping point and the moving point. The resulting porous glass base material has irregularities on the surface, but according to the present invention, a plurality of burners used here are specified to have the same size, and the burner intervals are set to equal intervals, and The total gas supply amount of all the burners and the gas supply amount of each burner are individually controlled, and the diameter of the porous glass base material separately measured by the outer diameter measuring device, the integrated weight of the glass fine particles during deposition, and By controlling the supply amount of the silicon compound as the gaseous glass raw material supplied to the burner in accordance with the above, a porous glass base material having a uniform outer diameter can be obtained. It has been found that an optical fiber pre-firm preform can be easily obtained, and the present invention has been completed.

 This will be described in more detail below.

(Function) In the production of the optical fiber preform preform according to the present invention, glass fine particles produced by hydrolyzing a gaseous glass raw material with an oxyhydrogen flame are deposited on a glass rod for a core to produce a porous glass preform. At the same time, a plurality of burners of the same design dimensions are arranged at equal intervals, and a porous glass preform made by depositing silica fine particles generated by flame hydrolysis of a gaseous glass material on a core glass rod in the system A device for measuring the diameter of the glass and a device for measuring the weight thereof are provided. Further, a control valve is provided for a plurality of burner rows and a burner base plug portion provided on the device to supply the gaseous glass raw material supplied to the system. It is made to control the amount.

The glass rod for the core used here is a graded intex type or a single glass rod made by a known VAD method, OVD method, MCVD method or the like because it is a core part of the target optical fiber preform base material. It is desirable to have a mode-type profile or the like, a certain cladding layer, and measurement and confirmation of structural parameters such as refractive index and dimensions after vitrification. It is preferable that the entire length of the core glass rod be finished so that the outer diameter variation is 5% or less, and then the surface be cleaned and fire polished.

In order to increase the deposition rate, it is necessary to send as much of the raw material gas as possible to increase the deposition rate. For this purpose, it is necessary to increase the concentration of the gas, perform high-speed injection for large-volume delivery, or use a burner. May be increased or the number of burners may be increased. However, since there is a limit in one burner, a method of using at least three or more burners is adopted in the present invention. As shown in FIG. 1, these burners 2 are arranged in series in opposition to the core glass rod 1, and they are fixed to a burner stand and are arranged in parallel with the core glass rod in a row of burners or One of the core glass rods is reciprocated. Gases from the respective feed pipes, such as hydrogen gas, oxygen gas, and silicon tetrachloride entrained in a carrier gas (eg, oxygen gas), are fed into the burners 2. The glass fine particles generated by the flame hydrolysis are deposited on the core glass rod 1 to form the porous glass preform 4, but the surface of the porous glass preform 4 has a small unevenness. Because the burners 2 used here are all concentric multi-tube burners made of, for example, quartz and designed with the same dimension, the deposition conditions by each burner are the same. Each of these burners is provided with a control mechanism B capable of independently controlling the gas conditions. In order to control the gas supply amount of all these burners, this burner is used. Control mechanism A is provided in the main valve section 5 of the chromatography. Are preferably installed so that the distance between the burner outlet and the glass particle deposition surface is the same for all the burners, but the gap between the burners is set between adjacent flames. In order to reduce the interference effect, the flame 3 may be equally spaced in a range of 1.5 to 2.5 times the spread of the flame 3 on the surface of the deposit. The spread of the flame depends on the diameter of the collision surface, the linear velocity of the gas, and the distance, and expands as the deposition progresses.However, the larger the deposition efficiency, the better the deposition efficiency. It is good to decide as a standard.

With such a device, the core glass rod is rotated, all the burners are ignited, and the burner row and the glass rod are caused to reciprocate relatively, so that the glass fine particles generated by the flame hydrolysis of the gaseous glass raw material are used for the core glass. When the porous glass preform is made by depositing it on a rod, the amount of glass particles deposited on the core glass rod should be approximately the same in each part because each burner has the same dimensions. However, it is difficult to make the dimensional accuracy of each burner and the accuracy of gas conditions exactly the same, and a more detailed examination shows that the direction of air flow in the reactor, the strength, the degree of flame interference, the temperature distribution, Since the difference in heat history due to the position of the glass rod gradually changes as the deposition diameter increases, it affects each other and it is difficult to maintain the deposition conditions uniformly along the entire length to the end,
The shape, diameter, and weight of the obtained porous glass base material differ greatly depending on each part.

Therefore, in the present invention, the diameter of each part of the porous glass base material during the production is measured by moving the diameter measuring device 6 and measuring the weight thereof, and the average apparent specific gravity of each layer is calculated. If the gas supply amount of all the burners is constantly corrected and controlled using the control mechanism A provided in the gas main plug 5 and the control mechanism B attached to each burner, the final diameter of the porous glass base material becomes uniform. It has been found that it is possible to obtain the target weight with the above.

The reactor is preferably sealed except for the exhaust port, air supply port, burner insertion port and a part of the main rotation transmitting section. This prevents dust from adhering, and prevents the burner flame from swaying. Therefore, the advantage that the porous glass base material having no air bubbles can be easily obtained is provided.

The porous glass base material thus obtained is then made into a transparent glass by a known method to obtain an optical fiber preform base material. This transparent vitrification is added as necessary in an electric furnace. Chlorine gas, SOCl ₂ , S
Heating to 1,000 ° C or more in an inert gas atmosphere such as helium, argon, or nitrogen gas containing iCl ₄ , fluorine gas, or the like, dehydration and clear vitrification may be performed. The material is stretched in a glass lathe or an electric furnace, and profile verification and dimension are confirmed by a preform analyzer.

(Examples) Examples of the present invention and comparative examples will be described below.

Examples and Comparative Examples As shown in FIG. 1, a quartz glass rod 1 as a core glass rod having an outer diameter of 24.4 mm and a length of 800 mm L was mounted in a closed reactor having an exhaust port, and a side surface of the quartz rod was used. 6 concentric cylindrical quadruple tube burners 2 having an outer diameter of 40 mm and having the same dimensions were installed at regular intervals of 100 mm. Each of these burners 2 is provided with a mass flow controller (control devices B _{1 to} B _n ) for controlling the supply amount of silicon tetrachloride as a gaseous gas raw material. A large mass flow controller (control device A) for controlling the amount of gas is provided. These burners can reciprocate right and left at the same time, and the distance to the core glass rod 1 can be adjusted. .

The production of the porous glass base material is as follows.
And ignite by flowing gas through the burner rows.
This was accomplished by moving the burner to the left and right at a speed of 100 mm / min over a distance of 100 mm, but the gas supplied to each burner increased with increasing deposition diameter, and ultimately SiCl ₄ 2.9
/ Min, H ₂ 50.4 / min, and the silica fine particles generated by flame hydrolysis of SiCl ₄ as O ₂ 24 / min was deposited on a glass rod for the core.

With respect to the porous glass base material 4 obtained by the deposition of the silica fine particles, the outer diameter over the entire length is measured by the outer diameter measuring device 6 and the average outer diameter is determined, and the total weight is further measured by a weight measuring device (not shown). , A difference between the predetermined outer diameter and the weight set in advance at that time is detected, and in order to minimize the difference, the supply amount of all SiCl ₄ is controlled by the control device A.
In addition, the supply amount of SiCl ₄ in each burner is controlled by the controller B in order to minimize the difference in the deposition diameter in each part, and the burner and the porous glass base material are increased with the increase in the deposition diameter. After synthesizing while adjusting the distance to the deposition distance, a porous glass base material having a uniform outer diameter and a weight of 8.608 kg having a diameter of 162 mm was obtained after 4.26 hours. When heated to 1,550 ° C. for 4 hours in a helium gas atmosphere to form a transparent glass, a single mode optical fiber preform having an outer diameter of 86.6 mm was obtained.

The optical fiber preform obtained in this way is
A single-mode optical fiber having a diameter of 125 μm was drawn by drawing at 1,950 ° C., and cut-off wavelengths (λc) were determined from these 10 places.
c = 1.216 μm, and the maximum variation was 52 nm.

However, in the apparatus shown in FIG. 1 for comparison,
The controller A for controlling the total amount of supplied SiCl ₄ was used, but the controller B for controlling the amount of SiCl ₄ of each burner was not used.
When a 0 mm porous glass preform was manufactured, the outer diameter varied up to 148 to 170 mm over its entire length, and the predicted clad thickness was significantly out of specification. It was unmodifiable as a fiber preform and was unfit for production.

(Effects of the Invention) According to the present invention, the irregularities on the surface of the porous glass preform obtained after long-time operation are averaged uniform, and a large-sized optical fiber prefabricated mother can be obtained without deteriorating the structural characteristics. The advantage is that the material can be easily obtained with good productivity.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a porous glass preform manufacturing apparatus used in the method of the present invention. DESCRIPTION OF SYMBOLS 1 ... Core glass rod, 2 ... Burner 3 ... Burner flame 4 ... Porous glass base material 5 ... Burner base plug 6 ... Diameter measuring device, A, B ... Control device

Claims (1)

(57) [Claims] 1. A gaseous glass raw material is introduced into an oxyhydrogen flame burner, and glass fine particles generated by the flame hydrolysis are laminated one by one on the outer periphery of a rotating optical fiber core glass rod to form an optical fiber porous material. In a method of manufacturing a porous glass preform, three or more burners of the same size and design are used, and the burners are arranged at regular intervals over the entire length of the glass rod, and the total weight of the porous glass preform during deposition is reduced. The average outer diameter is measured, the predetermined outer diameter and weight set in advance and the difference at that time are detected, and the total gas supply amount of all burners is feedback-controlled in order to minimize the difference. At the same time, the deposition diameter of the porous glass base material during deposition is measured over the entire length, and the gas supply amount of each burner is feedback-controlled in order to minimize the difference in the deposition diameter at each location, and The method of manufacturing an optical fiber preform preform, which comprises synthesized for optimal deposition distance the distance between the donor and the porous glass preform.