JPH0777969B2 - Optical fiber preform base material manufacturing equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to an optical fiber preform manufacturing apparatus, and in particular to a large-sized single-mode optical fiber with a small variation in structural characteristics, low loss, and few disconnections. The present invention relates to a device for stably and easily manufacturing a preform.

[Prior Art] Conventionally, in a method of manufacturing an optical fiber preform, a rod composed of a core or a core and a clad layer is horizontally installed, and this is rotated to reciprocate a gaseous glass raw material left and right. Introduced into the oxyhydrogen flame burner, the glass particles produced by the flame hydrolysis are deposited on the rod,
A so-called external method is used to form a porous glass layer, which is then heated and melted to form a transparent glass. This method is easy to work, workability of a burner, and easy to deposit fine glass particles. Therefore, normally, as shown in FIG. 4, the rod 21 is horizontally arranged in the reaction vessel 23, the burner is arranged toward the rod, and the oxyhydrogen flame burner is repeatedly moved in the horizontal direction 26. Rod flame from 24
It is carried out by an apparatus in which fine glass particles are applied to 21 and deposited as a porous glass base material 22 there.

[Problems to be Solved by the Invention] However, in a method for manufacturing an optical fiber preform using such a horizontal device, when the target preform becomes long and large, the rod is straightened in advance. Even after processing, the rod will always bend when it is laid down so that center deviation occurs at both ends and in the center, resulting in a difference in the deposited thickness. There is a problem that there is a difference in the thickness of the clad in the longitudinal direction. In addition, this has the drawback that the porous glass preform is destroyed by repeated bending while glass particles are deposited on the rod, and in this conventional device, the burner moves left and right. Since the large opening 25 is provided, the outside air flows in easily, and dust easily enters. As a result, the preform contains foreign matter and air bubbles, which has a disadvantage of causing fiber breakage and transmission loss.

Therefore, regarding the manufacturing apparatus of this optical fiber preform, the glass microparticles produced by flame hydrolysis of the gaseous glass raw material are deposited on the outer periphery of the glass rod for core by the external method to manufacture the porous glass preform for cladding. , In an apparatus for producing an optical fiber preform by heating it to form a transparent glass, a glass rod for core is installed in a vertical direction,
A method of rotating this and repeating it up and down is also being studied, but in this case, although it is necessary to accurately install the glass rod for the core, this axis alignment is very complicated. It takes a long time, and since the core glass is usually fixed at one point at the upper end, it becomes difficult to maintain this state when the porous body becomes large, and the finished preform tends to be eccentric. The problem arises.

[Means for Solving the Problems] The present invention relates to an apparatus for manufacturing an optical fiber preform that solves such disadvantages, which is formed on the outer periphery of a glass rod for core by flame hydrolysis of a gaseous glass raw material. In the device for producing the optical fiber preform by depositing the above glass fine particles by an external method to produce a porous glass preform for clad, and heating it to produce transparent optical fiber preform, the porous glass preform for clad is produced. The manufacturing device is characterized in that it has a device for vertically mounting a glass rod for a core, and a device for fixing both ends thereof, and b a vertically movable integral frame for fixing the glass rod for a core. It is a thing.

That is, the present inventors have conducted various studies on a method of stably and easily obtaining a single mode optical fiber preform that is large in size and has no dimensional change in the longitudinal direction. If you install the fixing devices at the upper and lower ends correctly, you can easily align the shaft with the glass rod for the core, and since this is fixed at the top and bottom, it will not move during the working process. The present invention has been completed by confirming that the finished optical fiber preform preform has almost no eccentricity.

This will be described in detail below.

[Operation] The optical fiber preform base material manufacturing apparatus of the present invention is provided with the above-mentioned porous glass base material manufacturing apparatus having the above-mentioned a. Core glass rod fixing device and b. Integrated frame. This will be described with reference to the attached FIGS. 1 to 3.

1 and 2 are vertical cross-sectional views of a porous glass preform manufacturing apparatus according to the present invention, and FIG. 3 is a vertical cross-sectional view of an apparatus for fixing a core glass rod to a drive shaft. Figure 1,
As shown in FIG. 2, a glass rod 1 for core for depositing silica fine particles is provided in the reaction vessel 3 so as to be vertically, rotatable, and vertically reciprocally movable. The oxyhydrogen flame burner 6 for depositing is fixed. In addition, an inert gas is supplied to the container 3 as needed. The inert gas may be clean air that has passed through a filter, nitrogen, helium, argon, or the like. The gas is introduced from the gas inlets 11 provided at the upper and lower parts, and the exhaust port 12 is provided at the center of the reaction vessel.

In the apparatus of the present invention, the gaseous glass raw material is introduced into the oxyhydrogen flame burner 6 and the glass particles are formed by this flame hydrolysis, which may be performed by a known method.
Therefore, it is sufficient to use a gasifiable silicon compound containing silicon tetrachloride, trichlorosilane, etc. as the gaseous glass raw material, and as the burner, supply the gaseous glass raw material from the center and from its surroundings. Oxygen gas,
It is sufficient to use a concentric ring-shaped one that supplies hydrogen gas.

Since the optical fiber preform obtained by using the apparatus of the present invention is dimensionally stable in the longitudinal direction, the glass rod 1 for core on which glass particles are deposited is a core portion previously designed as an optical fiber for single mode, or A glass rod consisting of a part of the clad is used as a starting material and straight-centered. As shown in FIG. 3, the glass rod for core 1 was vertically installed on an integral type frame 4 which can be moved up and down, and its both ends were fixed by a chuck 5 to uniformly deposit fine glass powder during operation. To let
It is rotated at 5-80 rpm by a drive shaft 14 having a bearing 9 to which a motor 10 is connected, and after confirming that there is no bowing, twisting or bending over the entire length, glass fine powder is evenly distributed over the entire length of the glass rod 1. The frame 4 is repeatedly moved up and down repeatedly by the vertically movable device 7 for attachment.

Moreover, since the fine glass powder is sprayed onto the glass rod 1 more uniformly and accurately over the entire length of the glass rod, the fine glass powder is repeatedly moved up and down as described above. However, the oxyhydrogen flame burner 6 was placed horizontally at a right angle to the glass rod so that the fine glass powder could be blown directly from the side of the glass rod.
Is fixed, which may be two auxiliary burners 13 arranged one above the other.

The glass rod for core 1 is produced by spraying the glass particles.
Is used as the clad porous glass base material 2, and the amount of deposition in the porous glass base material 2 may be controlled by the load cell 8 fixed to the frame 4.

The clad porous glass preform thus obtained is then heated and dehydrated to obtain an optical fiber preform by vitrification, which can be performed by a known method. According to this, since the porous glass base material has no center deviation, the deposition thickness is uniform, and no foreign matter or bubbles are contained, the optical fiber preform produced from this has little variation in structural characteristics and low loss. This gives the advantage of less breaking.

[Examples] Next, examples of the present invention will be described.

Example As the reaction vessel 3 shown in FIG. 1, the inner diameter of the reaction part is 280 mm.
Prepare a φ Pyrex chamber, horizontally fix the quadruple quartz burner 6 on the side of the center of the Pyrex chamber, and at the opposite part, exhaust port with an inner diameter of 100 mm φ 12
A quartz tube with an outside diameter of 98 mmφ was inserted into this, and it was in contact with the outside air exhaust duct.

The glass rod 1 for core has an outer diameter of 17.7 mmφ and a length of 620 mm,
17mmφ × 200mmL quartz dummy glass is welded to both ends, and 15mmφ × 800mmL quartz rod is fixed on the upper part.
This was pierced through the center of the reaction vessel 3 while keeping it vertical, and the upper and lower parts were fixed to the drive shaft 14 by the chuck 5. This core glass rod 1 is designed as an optical fiber core for single mode in the 1.3μ band, has a refractive index difference of 0.34% due to germanium doping, and the ratio of the core diameter to the clad layer made of silica glass is 0.205. Rod outer diameter ± 100μ
It is finished to m or less. Further, this glass rod 1 is mounted on the rotating part of a vertical pulling machine having a weight weighing function through a quartz glass dummy, which is rotated at 50 rpm and the central axis of the rod is eccentric and vertically moved. It is designed to move within ± 0.5 mm.

After this glass rod for core 1 was attached to the reaction vessel 3, clean air was blown from near the upper and lower openings to prevent the inflow of outside air, and then the entire length of the glass rod 1 was exposed to the oxyhydrogen flame from the auxiliary burner 13. Fire-polished.

Next, silicon tetrachloride is fed from the quadruple burner 6 together with the oxyhydrogen flame using oxygen gas as a carrier, and silica glass fine particles are blown onto the glass rod 1 at this time.
Was rotated at 50 rpm and repeatedly moved up and down at a speed of 150 mm / min, and silica glass fine particles were deposited one by one while controlling the deposition amount by the load cell 8. At this time, the amount of oxyhydrogen and the amount of silicon tetrachloride are 20 g / min of SiCl ₄ and H ₂
It was set to 50 l / min and O ₂ 25 l / min. This reaction is continued for 12 hours, the total length is repeated about 130 times to adhere the particles, and the deposited amount of silica fine particles is measured by the load cell 8. After this reaches a target value, the reaction is stopped and the obtained porous glass body is removed. When examined, this product had an outer diameter of 109.0 mmφ, a total weight of 4,114 g, and an average density of soot was 0.496 g / cc.

Then, when this porous glass body was zone-melted with an electric furnace body heated to 1,500 ° C. through which a mixed gas of helium and chlorine was passed, it was transparent with an outer diameter of 58.1 mmφ and had bubbles,
Since a glass ingot free of foreign matter was obtained, it was heat-processed to an outer diameter of 30 mmφ, and the steady part was drawn with a wire drawing machine to a diameter of 125 mm.
As a glass fiber of μm, we investigated the structural variation over its entire length. The fluctuation of the clad part was measured by changing the designed cutoff wavelength (λ _c ), mode field diameter (ω), and eccentricity (ε) with a fiber of 120 km for about 10 k.
When cut into m and examined 10 points, the average was λ _c = 1.215μ, the deviation (difference between maximum and minimum values) was 30 nm, and the eccentricity was 0.25 μm on average.

Comparative Example Using the horizontal external device shown in FIG. 4, silica glass fine particles were deposited on the quartz rod for core used in the example to form a porous glass body, which was treated in the same manner as in the example. and a glass ingot, was prepared an optical fiber, the average value lambda _c of the cut-off wavelength of this compound 1.177μ
m, deviation 154 nm, eccentricity average 0.62 μm, maximum 1.7
was μm.

In addition, in this horizontal external device, the opening 25 required for moving the burner 24 has a width of 40 mm and a length of 800 mm, and the hydrochloric acid gas inside leaked out and the odor drifted inside the room. When the exhaust gas was intensified, the burner flame fluctuated greatly, the soot deposition time took more than 15 hours, and many bubbles were generated in the transparent glass ingot after vitrification.

[Effects of the Invention] The present invention relates to an optical fiber preform base material manufacturing apparatus, and more particularly to a porous glass base material manufacturing apparatus for manufacturing an optical fiber preform.
A device for vertically fixing the core glass rod at both ends, b.
It is characterized by having an integrally movable frame that fixes the glass rod for core and can move up and down, according to which there is no bending or bending due to gravity on the glass rod for core without complicated processes. Since glass particles can be deposited with a uniform thickness, the advantage of being able to stably and easily obtain a single-mode type optical fiber preform preform with little variation in structural characteristics, low loss, and minimal disconnection. Given.

[Brief description of drawings]

1 and 2 are longitudinal sectional views of an optical fiber preform preform manufacturing apparatus of the present invention, FIG. 3 is a longitudinal sectional view of an apparatus for fixing a glass rod for a core to a drive shaft, and FIG. 2 is a vertical sectional view of the optical fiber preform base material manufacturing apparatus of FIG. 1,21… glass rod for core, 2,22… porous glass base material, 3,23
… Reaction vessel, 4… Integrated frame, 5… Chuck, 6,24
... oxyhydrogen flame burner, 7 ... vertical moving device, 8 ... load cell, 9 ... bearing, 10 ... motor, 11 ... gas inlet, 12, 25 ... exhaust outlet, 13 ... auxiliary burner, 14 ... drive shaft.

Claims (1)

[Claims] 1. A porous glass base material for a clad is manufactured by depositing glass fine particles produced by flame hydrolysis of a gaseous glass raw material on the outer periphery of a glass rod for a core by an external addition method. In an apparatus for producing an optical fiber preform by vitrification, an apparatus for producing the porous glass preform for clad is a device for vertically installing a glass rod for a core and fixing both ends of the glass rod, and b. An apparatus for manufacturing an optical fiber preform preform, which has an integrally movable frame for fixing a rod.