JPH03228845A - Production of matrix for optical fiber preform - Google Patents

Abstract

PURPOSE:To uniformize the unevennesses on the surface of porous glass matrix and to obtain the matrix for a large-sized optical fiber preform with good productivity by arranging a plurality of pieces of burners in the equiintervals at the same design dimension and successively transferring and dispersing the starting position of reciprocating movement in the case of producing the matrix for the optical fiber preform by an externally fitting method. CONSTITUTION:In a method for producing the matrix for an optical fiber preform by introducing a gaseous glass raw material 6 into an oxyhydrogen flame burner 2 and blowing glass fine particles produced by flame hydrolysis thereof on the outer circumference of a glass rod 1 for a core being rotated and relatively reciprocating and moving the burner 2 or the glass rod 1 parallel to the axial direction and thereby laminating the glass fine particles one layer by one layer on the glass rod 1 for the core to form the porous glass matrix 8 and then heating and dehydrating this matrix 8 to transparently vitrifying it, the following means is adopted. In other words, at least three pieces of burners 2... having the same dimension are arranged oppositely to the glass rod 1 for the core in the specified euqiintervals in a range over the whole length thereof. The glass fine particles are deposited while successively transferring and dispersing the starting position of the reciprocating movement in at least three points.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing an optical fiber preform base material, and particularly a method for manufacturing a large optical fiber preform base material at high speed without deteriorating the structural characteristics of the optical fiber. The present invention relates to a method for manufacturing an optical fiber preform base material that can be produced.

(Prior art) In the early stages of development, optical fiber preforms were manufactured by coating a glass tube with core glass (see Japanese Patent Publication No. 11071/1971), but in recent years With the remarkable improvement in properties and precision and the increase in preform size, gaseous glass raw materials are introduced into an oxyhydrogen flame burner, and the glass particles generated by flame hydrolysis are rotated around the outer periphery of the glass rod for the core. The glass fine particles are sprayed onto the core glass rod by reciprocating either the burner or the core glass rod (to simplify the explanation below, it will be explained by moving the burner) parallel to the axial direction. There has been a transition to a method of laminating layers one by one to form a porous glass base material, which is then heated, dehydrated, and made into transparent glass to produce an optical fiber preform (see Japanese Patent Application Laid-Open No. 49-84258). .

However, regarding the manufacturing method of this type of optical fiber preform, there is a method of continuous deposition in the vertical direction (Japanese Patent Application Laid-Open No.
5-118638)), glass-forming raw materials with different compositions are supplied to the porous glass base material from multiple burners, and eight rods are reciprocated relative to the burners, and each time the glass is A method has also been proposed in which a preform having a desired refractive index distribution in the radial direction is obtained by changing the composition of the forming raw material. A method of applying vibrational motion to the generation of glass particles (JP-A-56-120528, JP-A-5
8-9835), a thin oxyhydrogen flame burner with a width approximately equal to the length of the core glass rod to be manufactured, or a burner in which multiple oxyhydrogen flame burners are arranged horizontally in a row. A method of blowing glass fine particles onto a core glass rod without forming a row and moving them (see Japanese Patent Application Laid-open No. 70449/1989), and a method that controls the amount of gas supplied to multiple burners, although it is not an optical fiber base material. The deposition density of glass particles can be changed along the radial direction by adjusting the distance between the banner surface and the surface on which glass particles are deposited, or by adjusting the rotation speed of the heat-resistant substrate. Method for preventing cracks (Unexamined Japanese Patent Publication No. 64-9
821) is also known.

(Problems to be Solved by the Invention) However, when trying to manufacture an optical fiber preform base material using these conventional known methods,
In the method disclosed in Publication No. 8, since there is only one burner, the deposition rate of glass fine particles is slow, and when manufacturing long and large diameter items, there is insufficient heat, and the deposited silica layer is damaged by the machine. However, the methods disclosed in JP-A-56-120528, JP-A-57-183330, JP-A-58-9835, etc. Although it has the advantage that the core layer and cladding layer can be obtained in one process, both the core layer and cladding layer have low density, making it difficult to handle when increasing the size, requiring larger equipment, and increasing the refractive index of the core. The distribution is unknown and a thick cladding layer is deposited on this, which has the disadvantage that the product deviates from the target value.
Furthermore, with the method disclosed in JP-A-53-70449, it cannot be guaranteed that the gas ejected from the slits of the burners will be under the same conditions over the entire length of the core glass rod. Uneven deposition occurs, and in reality, the accuracy of the deposited thickness of the obtained preform base material deteriorates, but the method disclosed in JP-A No. 64-9821 has a fast deposition rate and can make large-sized products. Although this has the advantage of reciprocating with a constant amplitude in the length direction, the stop point of the burner and the moving part are always repeated at the same position, resulting in uneven deposition, and the resulting deposit has an uneven surface. It cannot be used for manufacturing optical fiber base materials because aluminum as a core material is doped into the silica layer as a metal impurity.

(Means for Solving the Problems) The present invention relates to a method for manufacturing an optical fiber preform base material that solves the above-mentioned disadvantages. Glass fine particles generated by hydrolysis are blown onto the outer periphery of a rotating core glass rod, and the burner or the glass rod is relatively reciprocated in parallel with the axial direction to blow the glass fine particles into the core glass rod. In the method of manufacturing an optical fiber preform base material by laminating layers one layer at a time to form a porous glass base material, which is then heated, dehydrated, and made into transparent glass, the core glass rod is At least three or more burners of the same size are arranged at regular intervals along the entire length, and glass particles are deposited while sequentially dispersing three or more starting positions of the reciprocating movement of the burner row as a single burner row. It is characterized by:

That is, the present inventors have studied various methods for producing large optical fiber preform base materials at high speed without deteriorating the structural characteristics of optical fibers. In this case, uneven deposition of glass particles occurs between each burner and between the burners, and when the burner is moved to alleviate this, uneven accumulation of glass particles occurs at the stop point and the moving point, and the resulting porous glass base material has a rough surface. Therefore, in accordance with the present invention, the plurality of burners used here are specified to have the same general size, and the intervals between the banners are set at equal intervals, and the starting positions of the reciprocating movement of the burners are set at the same distance. By sequentially moving the burners so that they are dispersed to different locations as much as possible without stopping in one position, each burner stop position is also moved sequentially because the moving distance is specified, and the burner dimensions and deposition conditions are kept constant. Therefore, uneven deposition of glass particles between each burner is minimized, and since the burner interval is constant, uneven accumulation of glass particles on the burner moving part is also reduced, and furthermore, if the start position of the reciprocating movement is shifted sequentially Since the stopping point changes each time, the unevenness of deposition between the stopping point and the moving point is averaged out, so the porous glass base material can be made without any unevenness on the surface, and therefore it can be made into transparent glass. The present invention was completed by discovering that a homogeneous optical fiber preform base material can be easily obtained by doing so.

This will be explained in further detail below.

(Function) In the production of the optical fiber preform base material according to the present invention, a porous glass base material is created by depositing glass fine particles produced by hydrolyzing a gaseous glass raw material with an oxyhydrogen flame on a glass rod for a core. In this case, a plurality of burners having the same general dimensions are arranged at equal intervals, and the starting positions of their reciprocating movements are sequentially moved and dispersed.

The production of the optical fiber preform base material in the present invention is basically carried out by a known method. Therefore, this method involves introducing a gaseous glass raw material such as silicon tetrachloride into an oxyhydrogen flame burner, and transferring the glass particles generated by flame hydrolysis here to the moving or rotating burner row and its axis. A porous glass base material is created by blowing the glass particles onto a core glass rod that is relatively reciprocating in parallel to the direction, and depositing the glass particles layer by layer on the core glass rod.
This porous glass base material is then heated to a high temperature to degas it and turn it into transparent glass.

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

In order to increase the deposition rate of the glass particles on the core glass rod, it is necessary to send as much raw material gas as possible.To do this, it is necessary to increase the concentration of the gas, make the burner thicker to send a large amount, or The number of burners may be increased, but since there is a limit to the number of burners made of wood, the present invention adopts a method of using at least three burners. As shown in FIG. 1, these burners 2 are arranged in series facing the core glass rod 1, and these burners are fixed to a burner stand 3 and arranged in a burner row parallel to the core glass rod. Alternatively, either one of the glass rods for the core is reciprocated. This burner 2
As basic gases, gases are fed from a hydrogen gas feed vibrator 4, an oxygen gas feed vibrator 5, and a silicon tetrachloride feed vibro accompanied by a carrier gas (for example, oxygen gas). A flame 7 is formed, and glass particles generated by this flame hydrolysis are deposited on the core glass rod 1 to form a porous glass base material 8. In order to minimize unevenness, the burners 2 used here are all concentric multi-tube burners made of quartz, for example, designed with the same dimensions, and the deposition conditions for each burner are the same. Therefore, it is desirable that each of these burners is equipped with a control mechanism C that can independently control the gas conditions. These burners 2... are preferably installed so that the distance between the burner outlet and the glass particle deposition surface is the same for all burners,
The gaps between each burner are designed to be equally spaced within a range of 1.5 to 2.5 times the spread of the flame 7 on the surface of the stack, in order to reduce the interference effect between adjacent flames. do it. The spread of flame depends on the diameter of the collision surface, the linear velocity of the gas,
It depends on the distance and expands as the deposition progresses, but
Since the deposition efficiency is better with a larger diameter, the burner interval is preferably determined based on the larger deposition diameter. The figure also shows that both end portions of the porous glass base material 8 are heated by the flame lO of the heating burner 9, but this is because the glass particles have a low density at the end portions. Since stress concentration tends to occur in this area, and therefore cracks are likely to occur in this area, it is advisable to constantly heat this area to increase the density.

With such a device, the glass rod for the core is rotated, all the burners are ignited, and the burner row and the glass rod are reciprocated relative to each other, so that the glass fine particles generated by the flame hydrolysis of the gaseous glass raw material are removed from the glass for the core. When depositing on a core glass rod to make a porous glass base material, each bar is of the same size and the deposition conditions are matched, so the amount of glass fine particles deposited on the core glass rod can be adjusted at each location. However, during reciprocating movement, it naturally stops at - and starts moving in the opposite direction, so the amount of accumulation at the stop position inevitably changes compared to the moving part.
When this is repeated at the same position for a long time, the difference becomes quite large, and the result is that the target porous glass base material has irregularities as shown in FIG. 2(a).

In order to solve this disadvantage, the present invention sequentially moves the start position of this reciprocating movement to three or more points. According to this, for example, as shown in FIG. 2(b), the reciprocating movement of the burner group When the starting position of the movement is shifted, the deformation shown in FIG. 2(a) is reduced.

If the deviation of the stopping point is further increased, the result will be as shown in Figure 1,
The part where the deposited thickness fluctuates due to the stoppage of the burner gradually shifts, and if this process is repeated, the changes in the deposited amount will be distributed and averaged out as a whole, and the target porous glass base material will have a smooth surface. It gives you the advantage of becoming.

2. Since the purpose of this invention is to disperse the movement starting points over the entire area, it is preferable that there are many starting points within the distance between two burners. The movement starting point of the present invention is based on a case in one direction as shown in Fig. 1, but Fig. 2(b) and (e
), round trip, zigzag movement, or random movement is possible.

In addition, these may be combined depending on the purpose and conditions, such as moving the starting point several times rather than every time, or changing it as the diameter increases, but in either case, the It is important to schedule the movement so that the number remains essentially constant (Fig. 2, b, c). The starting point of movement is sequentially shifted, but it is desirable that the point shifted to the adjacent burner position is one unit, and the movement is repeated for at least 1 to 3 units. As the unit becomes larger, the surface smoothness becomes better, but the tapered portions at both ends of the entire length become longer in proportion to the number of units, which becomes wasteful (Fig. 3). It is recommended that the amount of adhesion be continuously measured using a weight detection device, etc., and that the stop line be placed at a wide range near the target weight, and that the schedule should be such that there is no excess or deficiency in the number of layers, and the target weight is obtained.

In this way, if the reciprocating distance of the burner is large, the taper part at both ends will increase and the steady part will decrease, so it is best to keep this within a range that does not exceed three times the distance between adjacent burners.
Furthermore, the interval between the start positions of the reciprocating movement of the burners varies depending on the burner interval, the diameter of the core glass rod, the diameter of the deposit, the burner diameter, the thickness of the flame, etc., but if it is large, the effect will be small, and if it is small, it will take a long time. Since the deposited amount, density, etc. in the thickness direction vary and promote deformation, it is preferable to set the burner interval in the range of 172 to 3 mm.

Note that the glass fine particles in the porous glass base material obtained in this way have a low density, and cracks occur in the glass base material, making it difficult to handle. Therefore, if the diameter of the glass particles is large, the average deposition density is set to be large. and at least 0
．． 3 to 1.5 g/cm3, and in order to adjust the deposited weight and density of glass particles in this porous glass matrix, the amount of hydrogen, the amount of oxygen, the amount ratio of gaseous glass raw materials, etc. It is sufficient to control one or more of the following gas conditions, the linear velocity of the burner outlet, the distance between the burner outlet and the deposition surface, the rotational speed of the core glass rod, and the moving speed of the burner flame.

When the burner is moved, the burner, burner stand, piping, etc. are subjected to vibrations due to the movement, generating foreign matter that adheres to the surface of the deposit and causes the generation of bubbles, so it is preferable to use a glass rod to move the burner.

Further, this can be done not only horizontally but also vertically, and when it is done by moving the shaft, there are fewer openings and foreign matter can be blocked from the outside.

It is best to keep this reactor sealed with the exception of the exhaust port, air supply port, burner insertion port, and part of the main rotation transmission part.This prevents dust from adhering to the burner flame and fluctuating the burner flame, and prevents the exhaust gas from can be controlled, giving the advantage that a porous glass base material free of bubbles can be easily obtained.

The porous glass preform obtained in this way is then made into a transparent vitrification by a known method to form an optical fiber preform preform. Chlorine gas, 5OCI2
．． 5iC14, 1,000℃ in an inert gas atmosphere such as helium, argon, or nitrogen gas containing fluorine gas, etc.
The optical fiber preform base material obtained in this way is stretched in a glass lathe or electric furnace, and the profile verification and dimension are confirmed using a preform analyzer. It is considered the final product.

(Example) Next, examples of the present invention will be given.

Example 1 A quartz glass rod with a diameter of 20 mm and a length of 800 mm was attached to a horizontal external device. A four-pipe concentric burner designed with the same dimensions was placed opposite the side of this quartz rod with a center distance of l.
I! Six pieces were arranged at equal intervals with a length of 100 mm, and heating burners were attached to both ends. The central axis of each burner was aligned with the central axis of the quartz glass rod, and the burners were fixed to the burner stand at the same distance. Check the flame of each banner, make sure the flame shape and temperature are the same, and adjust the direction of the burner.
The gas conditions were adjusted.

The external device was rotated at 30 rpm, gas was flowed through the burner row, ignited, and the burner row was reciprocated at 60 mm/min. It was confirmed that the burner would return in the opposite direction after moving 100 mm, and silicon tetrachloride entrained in the carrier gas was flowed from the point at which it stopped at the left end. The raw material was flame-hydrolyzed in the flame to produce silica particles, which were deposited on the surface of the glass rod. The burner row was stopped for 5 seconds after moving 100 mm to the right, and then moved 90 mm to the left at a speed of 60 mm/min. The burner row that had moved to the left will stop 10mm before the initial starting position, but
At this point, each burner stops at 10m+n, so when moving to the left, the deposited layer spreads 100mm and then 10m.
The layers were discontinued by m. Next, after stopping for 5 seconds, start the second time and move 100mm to the right, 10mm from the first time.
I stopped the burner row on the right and moved it 90mm to the left.

This stopping point was shifted 20 mm to the right from the first starting point, and each layer was interrupted by 10 mm. If this is repeated 10 times, a point shifted 100 m+m to the right from the start point becomes the starting point of the movement, which corresponds to the first movement starting point of the second banner, and is one unit. There was a layer shortage of 10 mm per round trip, but 1
In 0 repetitions, 1 layer (100 mm) was missing and 19 layers were deposited, but the burner stopped at 11 points during 1 unit and 100 mm, and the abnormal points where the deposited layer was interrupted were evenly distributed at 10 points. Ta.

Next, shift the starting point of the movement to the left one by one, but the starting point is 1
Starting from the starting point shifted to the right by 00m+m, first 100m
Move further mm to the right. Next when moving to the left 11
01 Move. Then, on the left side of each deposited layer, 1011I11
are deposited one on top of the other. Pause at the left end for 5 seconds, then move 100 degrees to the right.
It moves 110mm to the left after stopping. Repeat this action 10 times to return to the starting point on the far left.

When moving back to the left, 10wn are piled up for each round trip, so when one unit is completed, the number of deposited layers increases by one to 21 layers, making 40 layers in total, including 19 layers when moving to the right.

In this example, there are 4 reciprocations between these units, and 1 moving deposit layer.
Finished with 60 layers.

The gas conditions were increased during the deposition, and changed significantly especially when switching units, and finally reached H228j2/m.
in, 0236 jll/min, SiCj! 424
g/min. All of these positional movements and gas switching were performed by computer.

The created deposit was a uniform white soot with cone portions of approximately 120 mmL at both ends, and the straight body length was approximately 410+.
am, the weight of the diameter 145mmφ deposit is 4.95k
A very smooth soot with no unevenness was obtained at g.

This soot was melted in an electric furnace at 1,520°C while flowing He gas containing 5% chlorine gas.
There was no abnormal diameter variation between m.

Comparative example 1 Using the apparatus used in Example 1, the following three types of experiments were conducted.

In (A), one burner was used to reciprocate the entire length of 600 mUa. In (B), two burners were moved back and forth over a range of 600 mm (400 III 11 in the stationary part). However, in this case, the steady part becomes two layers due to two burner depositions in one movement. In (C), the same six burners as in the example were used to move a fixed point over a distance of 100 m1. The number of layers was 160 for each method. If the number of burners is small, the cooling time will be longer than the deposition time, and the amount of heat will be insufficient, so the amount of oxyhydrogen was increased. These comparative examples are shown in Table 1 along with Example 1.

0 In Comparative Example C, after 3 hours, the deformed portion began to be emphasized and the diameter gradually became uneven, making it difficult to deposit any more, and the deposition efficiency was significantly reduced.

Example 2 A core quartz glass rod for single mode with a diameter of 24.0 mmφ and a length of 620+nmL was prepared, and dummy quartz rods were welded to both ends of the core quartz glass rod. Under these conditions, the entire core was aligned and corrected using a glass lathe so that the variation in the outer diameter of the quartz glass rod for the core was ±200μ (±0.83%) or less. The structural parameters of the core part were measured using Preform Analyzer P101 manufactured by York, UK, and the thickness of the rad required for the completed preform was calculated.

The surface of the quartz glass rod for the core was cleaned with acetone, and the rod was attached vertically to the rotating part of a vertical closed external device.

The rotary drive unit was placed on a weighing platform with the core glass rod attached, and the weighing platform was further fixed to a movable platform of a large lifting machine that could be moved up and down.

The vertically installed core glass rod was rotated to align its axes and then rotated at 30 rpm.

The burner was 8 concentric quadruple tube banners used in Example 1.
They were arranged vertically in series at equal intervals of 100 mm and fixed. The exhaust was installed on the opposite side of the burner, and clean air was introduced from above and below the chamber. The gas conditions were the same as in Example 1. Ignite the gas and raise and lower the pulling machine to a moving speed of 60mm.
/ff1in. Confirm that there are no foreign objects or defects on the glass rod, and then insert it from the bottom end of the quartz glass rod for the core.
5iCrl14 gas was flowed, 100 mm was defined as 1 unit, and the position was shifted by 10 mm+, 20 reciprocations, 4
It returned to its original starting position on the 0th layer. After repeating this four times, the interval between the stopping points was changed to adjust the weight. In the first adjustment, the deviation interval was set to 25 mm, and 20 layers were deposited by moving between 5 points (FIG. 2C). In the second adjustment, the target weight was achieved by moving between 3 points (Fig. 2 b) once for 6 layers and finally moving between 2 points (Fig. 2 a) 4 times. The finished soot has a uniform surface with no irregularities and has 19 layers.
0 layer, suit weight 6.046 kg, time 5.48
It was time. When this was dehydrated and melted at 1,520°C in helium and trichlorine gas, a transparent ingot with a diameter of 78.9 mm was obtained.

The ingot shown in Table 1 was stretched to an outer diameter of 47φ using an electric furnace, and a steady portion was drawn. The characteristic values of this fiber were stable as shown in Table 3, and no fluctuations in the cladding layer were observed.

4゜ (Effects of the Invention) As described above, the method for producing an optical fiber preform base material according to the present invention involves depositing glass particles generated by flame hydrolysis of a gaseous glass raw material on a glass rod to produce a porous glass base material. When doing so, a plurality of burners of the same size are placed at regular intervals across the entire length of the glass rod, and the starting positions of the reciprocating motion are sequentially moved and dispersed. Since the stopping point is shifted, the unevenness on the surface of the porous glass base material obtained after long-term operation is evened out on the average, and the axial movement is performed without deteriorating the structural properties and the reaction chamber is sealed tightly. This also makes it possible to reduce air bubbles, giving the advantage that a large optical fiber pre-firm base material can be easily obtained with good productivity.

[Brief explanation of drawings]

Fig. 1 shows a longitudinal cross-sectional view of the porous glass preform manufacturing apparatus used in the method of the present invention, and Fig. 2 shows the starting position of the reciprocating movement of the burner group in the method of the present invention, which is sequentially moved. FIG. 3 shows the shape of the end of the knife when one unit is enlarged to twice or three times the burner distance.

Claims (1)

[Claims] 1. Introducing a gaseous glass raw material into an oxyhydrogen flame burner,
The glass particles generated by the flame hydrolysis are blown onto the outer periphery of the rotating core glass rod, and the burner or the glass rod is relatively reciprocated in parallel with the axial direction to blow the glass particles into the core glass. In the method of manufacturing an optical fiber preform base material by laminating layers one by one on a rod to form a porous glass base material, which is then heated, dehydrated, and made into transparent glass, the core glass rod is An optical fiber preform motherboard characterized in that at least three or more burners of the same size are arranged at regular intervals over the entire length, and glass fine particles are deposited while sequentially moving and dispersing the starting positions of the reciprocating motion at three or more points. Method of manufacturing wood. 2. The method for manufacturing an optical fiber preform preform according to claim 1, wherein the reciprocating movement distance and the maximum deviation width of the movement start position are in a range of 1 to 3 times the distance between adjacent burners. 3. The method for manufacturing an optical fiber preform base material according to claim 1, wherein the start position of the reciprocating movement is moved by at least 3 mm and within the distance between the burners. 4. Manufacturing the optical fiber preform base material according to claim 1, wherein the movement starting point is sequentially moved or randomly moved, and in either case, the number of deposited layers is substantially the same, and the stopping positions are equally spaced. Method. 5. The method for manufacturing an optical fiber preform preform according to claim 1, wherein the reciprocating movement is performed by a core glass rod.