JPS5983953A - Preparation of parent material of optical fiber - Google Patents

Abstract

PURPOSE:To prepare a parent material for optical fiber having given transmission properties, preventing cracks during preparation, by blowing a high-temperature gas upon a core part from a nozzle for blowing the high-temperature gas set between a burner for core and a burner for clad. CONSTITUTION:The base material 2 is dropped close to the bottom of the reactor 1. A combustible gas and a raw material gas for forming glass for core are fed to the burner 3 for core, respectively, and the raw material gas for forming glass is hydrolyzed in fire produced by burning the combustible gas. The formed soot 11 for core is attached to the bottom of the base material 2 and gorwn to give the porous preform 12 for core. The preform 12 is pulled up while being rotated, it is heated and shrinked by the jetting gas 13 from the nozzles 4 and 5 for blowing the high-temperature gas, to give the porous preform 14 having the lessened diameter. A combustible gas and a raw material gas for forming glass for clad are then fed to the burner 6 for clad, respectively, the prepared soot 15 is attached to the peripheral surfaces of the perform 12 and 14 to give a clad part, so that the porous preform 16 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing an optical fiber preform, which is a material that is spun into an optical fiber.As one of the methods for manufacturing a zero-element fiber preform, the present invention uses a vapor phase coaxial method ( V
AD) is known, but this VAD is a burner for burning combustible gas containing oxygen and hydrogen, such as an oxyhydrogen burner.
5iC14, GeCl4, POCl3 and BBrs
By supplying volatile glass-forming raw materials such as This is a method of obtaining a substantially cylindrical optical fiber base material by depositing and growing the soot in the axial direction. Since this optical fiber base material is usually an unfinished product in the form of a porous preform, it can be made into a finished optical fiber base material by heating and making it transparent.

As a further development of this VAD, a core burner for synthesizing the glass-forming fine particles constituting the core portion of the optical fiber base material is placed near the growth end of the porous preform, and a cladding portion is formed. A cladding burner for synthesizing glass-forming fine particles is placed above the core burner, and the core and cladding parts are integrated by adhering and growing cladding soot on the circumferential surface of the core porous (N preform). A method for synthesizing
No. 4136 (7 proposed).

However, in the above-mentioned core-clad integral synthesis method, (1) the core soot and the cladding soot are mixed in space, and the oil refractive index distribution near the boundary between the core and cladding is Since the shape differs from the desired shape, the desired transmission characteristics cannot be obtained.

(2) The cladding is formed immediately after the core is formed, and the core is not shrunk during the process, so the core diameter can be adjusted to the cladding diameter, as in the production of single mode fibers. If the ratio is made small, the diameter of the porous preform after manufacture will become too large. For this reason, when the temperature is lowered or heated, there is a large temperature difference between the axial center and the peripheral surface of the porous preform, and there is a risk that the porous brief O 11 may crack due to the difference in shrinkage or expansion. As the performance increases, the overall size of the reaction vessel, heater for transparency, etc. also needs to be increased.

(3) If the core burner and cladding burner are separated from each other in order to prevent soots from mixing with each other, the porous preform cools between them, causing a difference in heat. Therefore, the porous preform tends to collapse due to differences in shrinkage in the M' grooves and l'!I after the cladding soot is attached, and differences in expansion during heating for transparency.

There are some problems.

In order to solve these problems, it is possible to prevent the soot from mixing by providing separate exhaust pipes for the core and for the cladding, and by moving the burners for the core and the cladding closer to each other. A method for reducing the temperature gradient of a porous preform located between burners was disclosed in Japanese Patent Application Laid-Open No. 5
No. 5-25074.

However, even with this method, since the core and cladding burners are attached close to each other, it is still insufficient to prevent the core and cladding soots from mixing, and furthermore, the diameter of the porous preform is too large. There still remains the problem that the cladding cannot be attached very thickly.

On the other hand, an electric furnace or the like is placed between the burner for the C1 core and the burner for the cladding, and a cylindrical porous preform for the core on which glass-forming fine particles are attached and grown is heated in the electric furnace or the like. The diameter of the porous preform for the core is reduced by slightly melting the soots that are fused together to increase the adhesion area between the soots and reducing the space between the soots. JP-A-55-154556 discloses a method of depositing soot for cladding on the outer peripheral surface and then heating it to make it transparent vitrified.
It has been proposed as a number.

According to this method, the cladding portion is bonded after the core porous preform is once shrunk, so there is no problem that the diameter of the finally obtained porous preform is too small.

However, even with this method, the boundary between the core part and the cladding part is still unclear because no measures are taken to prevent the core and cladding soots from mixing, and also because electric furnaces are generally complex and large. In addition, the entire manufacturing equipment has to be separated and becomes large, making it impractical.Furthermore, if there is a furnace material of such a large electric furnace, the furnace material will be eroded by the HCl mist generated by the hydrolysis reaction. There is a high possibility that the products will be mixed into the porous preform as foreign matter, which causes problems such as a decrease in the transmission performance of the optical fiber.

In view of the above-mentioned problems, the present invention prevents mixing of core soot and cladding soot, and prevents mixing of core soot and cladding soot in the vicinity of the boundary between the core and cladding, although it is relatively small and has a simple configuration. Since the refractive index distribution can be made into the desired shape, it is possible to obtain the desired transmission performance, and the temperature gradient of the optical fiber base material during manufacturing can be reduced to prevent cracking.
In addition, since the ratio of the core diameter to the cladding diameter can be made small without increasing the diameter of the resulting optical fiber base material, it is suitable for manufacturing single mode fibers, etc., and it is also possible to make the optical fiber base material by adhering and growing glass-forming particles. There is no need to increase the overall size of the reaction vessel and heater for transparency, and furthermore, the purpose is to form an optical core.

An embodiment of the present invention will be described below with reference to FIGS. 1 and 2.

FIG. 1 shows an example of an optical fiber preform manufacturing apparatus for carrying out the present invention. As shown in FIG. 1, the reaction vessel (1) has a substantially cylindrical shape with a closed upper and lower bottom surface, and is arranged substantially vertically. A substantially cylindrical base material (2) is attached to the approximate center of the upper bottom surface of the reaction vessel (1) by a holder (not shown) that can be moved up and down while rotating.
is retained. Further, near the center of the lower bottom surface, there is provided a core burner (3) having a multi-cylindrical shape in which four cylinders each having a different diameter are arranged concentrically. That is, this core burner (3) includes a center nozzle, a second layer nozzle surrounding this center nozzle, a sixth layer nozzle surrounding this second layer nozzle, and an outermost layer surrounding this sixth layer nozzle. It has a nozzle.

In addition, two cylindrical high-temperature gas blowing nozzles (4) are located near the core burner (3) in the reaction vessel (1).
) (5) and cladding burners (6) having the same structure as the core burner (3) are sequentially arranged at predetermined intervals in the axial direction of the reaction vessel (11).

Furthermore, a high temperature gas blowing nozzle (
4) and the cladding burner (6), two cylindrical exhaust hoods (force (8)) are provided at positions substantially opposite to the cladding burner (6).

In order to manufacture a porous preform of an optical fiber base material using the manufacturing apparatus as described above, the base material (2) is first lowered to near the bottom surface of the reaction vessel (1). Next, a flammable gas and a core glass forming raw material gas such as 5IC14 and GeC14 are respectively supplied to the core burner (3), and the glass forming raw material gas is hydrated in the flame generated by the combustion of the combustible gas. A decomposition reaction is carried out, and the resulting core soot (1υ) is attached and grown on the lower end of the base material (2) to obtain a porous core preform (17J).

The core burner (3) has a multi-cylindrical shape as described above, and this is because the glass forming raw material gas is supplied from the center nozzle, the inert gas such as from the second layer nozzle, and the inert gas from the sixth layer nozzle. This is to inject H2 and 02 from the outermost layer nozzle. Therefore, the inert gas acts as a barrier to prevent the glass forming raw material gas and H2 and 02 from immediately reacting near the outlet of the core burner (3) and clogging the core burner (3). be able to.

After that, the porous preform for the core was pulled up while rotating with a holder (not shown), and the diameter was reduced by heating and shrinking it with the jet gas (131) from the hot gas blowing nozzles (4) and (5). Porous preform for core (obtain 1 piece).

At this time, by supplying halogen gas or halogen compound gas such as C12, 5OC12 to the high temperature gas blowing nozzles (4) and (5), the core porous brifumeme (one low temperature The crystallized GeO2 adhering to the surface is removed by volatilization as eC14.

That is, the temperature of the adhesion growth surface of the core tlυ is highest at the center of the core adhesion growth surface that intersects with the central axis of the core burner (3), and decreases toward the periphery.

GeO2, which is produced by a hydrolysis reaction of GeCl4, which is one of the raw material gases for forming glass, becomes amorphous in the high temperature section.810. It is known that GeO2 adheres as a solid solution with , and in low temperature regions it adheres alone as crystallized GeO2. A large amount of this crystallized GeO2 adheres to the low-temperature area around the growth surface of the pick.

This crystallized Ge02 remains opaque even when the porous preform is heated to make it transparent, and is foamed during heating for spinning, significantly reducing the transmission performance of the optical fiber.

Since crystallized GeO2 has a higher vapor pressure than amorphous GeO2 deposited as a solid solution with SiO□, it is usually removed by volatilization during heating for transparency. However, it is difficult to adhere and grow the soot for the cladding on the peripheral surface of the porous preform for the core, which is called integral growth of the core and the cladding. Therefore, as in this embodiment, it is necessary to volatilize and remove the crystallized G602 before forming the cladding portion.

In this way, the core porous preform side, in which the crystallized GeO2 has been volatilized and removed and whose diameter has become smaller, is pulled up while being further rotated by a holder (not shown). Then, a flammable gas and a glass-forming raw material gas for the cladding mainly composed of 5IC14 are supplied to the cladding burner (6), and the glass-forming raw material gas is hydrated in the flame generated by the combustion of the flammable gas. A decomposition reaction is carried out, and the soot for cladding (19) thus produced is adhered to the circumferential surface of the porous preform for core (13) to form a cladding part, thereby obtaining a porous preform +16.

The reason why the cladding burner (6) has a multi-cylindrical shape like the core burner (3) is due to the same reason as the core burner (3).

As the material (2) is rotated and gradually pulled up in the above manner, a porous preform having a cladding portion formed around the outer periphery of the core portion is gradually formed from the lower end of the base material (2).

When the porous preform (Ili) obtained in this way is heated in a separate heating step, it becomes a transparent optical fiber preform, and when this transparent optical fiber preform is spun into a final optical fiber. becomes.

In addition, in the above-mentioned process for obtaining the porous preform (1, 6), the base material (2) or the porous preform ft.
υ and cladding soot) t15) are immediately evacuated by the exhaust hood (force (8)), respectively.

Comparative examples and examples of the present invention Comparative example 1 [Core burner] Center nozzle 5tc14 = 140 cc 7 minutes, which was carried out using a device substantially similar to the 1q production device for optical fiber base material shown in Fig. 1. G
eCl4 = 40 cc 7 min, POC15 = 2 cc
/min, Ar=360cc/min 2nd layer nozzle/I/ Ar=400cc/min 6th layer nozzle, 71/ H2=3000cc/min outermost layer nozzle #
02=6000cc/min [Burner for cladding] Center nozzle 5ic14=150 cc 7 minutes, PO
CI3 = 2 cc 7 min, Ar = 200 cc 7
min 2nd layer nozzle/l/Ar=500cc/min 6th layer nozzle A/H2=3000cc/min outermost layer nozzle 02=
50 [lOcc/min position 1=80] [High-temperature gas blowing nozzle] Not used [Results] Porous preform (1 (cracks occurred at 9).

However, l = 40 [Results] A porous friform (10) with a diameter of -90rhn and a bulk density of -0.16'i/cm' was obtained.
Example 1 of C [High-temperature gas blowing nozzle] One piece used Ar = 8000 cc/min Temperature immediately after nozzle blowing = 1000°C [Results] Diameter ″==, 80 am, bulk density L=, 0.18 P/z
A porous preform (16) was obtained. Similar to Comparative Example 2, refraction example [high-temperature gas blowing nozzle] 2 used Ar = 4000 cc/min, N2 = 2000 cc/min,
Cl2 = 200 cc Temperature immediately after 7 minutes of nozzle blowing -1100°C [Results] A porous preform with a diameter of -76 curves and a bulk density of -0.19 P/cm' was obtained. When the refractive index distribution was measured in the same manner as in Comparative Example 2, the results shown in FIG. 2C were obtained.

As described below, according to Examples 1 and 2 of the present invention, the means for heat-shrinking the core porous preform (121) is the hot gas blowing nozzle (4) (5).
Compared to electric furnaces and the like, it is relatively small and has a simple configuration.

In addition, by arranging the high temperature gas blowing nozzles (4) and (5) between the core burner (3) and the cladding burner (6), both burners (3) and (6) can be spaced apart, and the high temperature gas Since the ejected gas (13) from the blow-off nozzle (4) (51) is blocked, mixing of the core soot (Ip and Clara h'' soot (1ω) is prevented.Furthermore, the exhaust hood (7) Mixing of (8) with base material (2) or porous preform for core (old core soot that did not adhere to 121 (14)) and cladding soot (151) can also be prevented by immediately exhausting the soot. Therefore, the refractive index distribution near the boundary between the core portion and the cladding portion can be made into a desired shape, making it possible to manufacture an optical fiber base material having desired transmission performance.

Furthermore, even if the core burner (3) and cladding burner (6) are separated as described above, the hot gas blowing nozzle (+4) (5+) disposed between them will emit gas (1
Since ~ is high temperature, the temperature gradient between both burners (3) +6) is small. Therefore, it is possible to prevent the porous preform during manufacture from cracking due to temperature gradients.

Further, the porous core preform (+2) is heated and shrunk by the blowing gas (131) from the high temperature gas blowing nozzles (4) (5) to form a small diameter core porous preform (14). Therefore, the ratio of the core diameter to the cladding diameter can be made small without increasing the diameter of the resulting optical fiber base material, making it suitable for the production of single mode fibers, as well as the overall use of reaction vessels, heaters for transparency, etc. Also, since there is no need for relatively large furnace materials like in electric furnaces, there is less erosion by the mist of HCl generated in the hydrolysis reaction.Therefore, the products of erosion can be treated as foreign matter. There is little risk of contamination with the porous preform, and therefore an optical fiber base material with excellent transmission performance can be manufactured.

Furthermore, C12 is added to the high temperature gas blowing nozzles (4) and (5).
, 5OC12, etc., or a halogen compound gas, the core porous preform (1
Before forming the cladding part, the crystallized Ge02 attached to the
As Ce4, it can be removed once. Therefore, even if the cladding part is Ip,j (attached to IIF), the crystallized Ge
1. O2 will not remain. It is possible to manufacture an optical fiber base material having a transmission signal recorded thereon.

Although the present invention has been explained above with reference to 11 examples, the present invention is not limited to this embodiment, and each
Variations of ``1'' are possible.

For example, in the above-mentioned Example 1, C conveniently uses two high-temperature gas blowing nozzles f4) +5), but the number of nozzles may be six or more, or one may be used in some cases. .

In addition, in the above-mentioned 14 JAIi example, the optical fiber preform obtained by this manufacturing apparatus is separated from the optical fiber 1 soot material manufacturing apparatus N shown in FIG. Although a heating means is required to convert the
If a heating means with a diameter of 1 ball is provided in the chamber, the transparent optical fiber base material can be produced using this manufacturing equipment. can do.

Since the present invention has the configuration as shown in [E] above, it is relatively small and! Although it is a simple (Ip) composition, it prevents the core soot and cladding soot from mixing and allows the refractive index distribution near the boundary between the core and cladding to be shaped into the desired shape, resulting in the desired transmission. In addition, the temperature gradient of the optical fiber base material during manufacturing can be reduced to prevent cracking, and the core diameter can be adjusted to the cladding diameter without increasing the diameter of the resulting optical fiber base material. Since the diameter ratio can be reduced, it is suitable for manufacturing single mode fibers, etc.7, and it is also necessary to increase the overall size of reaction vessels and heaters for transparency, etc., for attaching and growing glass-forming particles to obtain an optical fiber base material. Since there is no risk of foreign matter getting mixed into the optical fiber base material, it is possible to provide an optical fiber base material with excellent transmission performance.Furthermore, the nozzle for blowing out high-temperature gas does not contain halogen gas or halogen compound gas. By supplying this, the glass-forming fine particles that have been crystallized and layered on the porous preform for the core can be volatilized and removed before the cladding part is formed, making it possible to create an optical fiber with excellent transmission performance even with a thick cladding part. A base material can be manufactured.

[Brief explanation of drawings]

FIG. 2 is a schematic vertical cross-sectional view showing an example of a manufacturing apparatus for explaining the present invention. FIG. , B corresponds to Example 1, and c corresponds to Example 2. In addition, in the symbols used in the drawings, (3)
・ Burner for core (4X Ri 1) Nozzle for blowing out high temperature gas ((3)
Burner (1'lr, 14)
Porous preform for core (16) No. 1↓This is the finally obtained porous preform. Agent: Katsutsune Ueya, Yoshi Kamo, Shunsei Sugiura

Claims (1)

[Scope of Claims] 1. A core burner for synthesizing glass-forming fine particles constituting the core portion of an optical fiber preform, and a core burner for synthesizing glass-forming fine particles constituting the cladding portion of the optical fiber preform. A glass-forming raw material gas and a flammable gas are respectively supplied to a cladding burner, and the glass-forming raw material gas is reacted in a flame in which these combustible gases are burned, thereby causing the glass-forming fine particles to adhere and grow. In a method for producing an optical fiber preform, the method comprises obtaining an optical fiber preform comprising the core portion and the cladding portion integrally formed around the core portion, the burner for the core and the cladding portion being integrally formed around the core portion. An optical fiber base material characterized in that a high-temperature gas blowing nozzle is arranged between the burner and the high-temperature gas blowing nozzle blows the high-temperature gas to the core portion! Iq making method. 2. A samurai π characterized in that a halogen gas or a halogen compound gas is supplied to the high temperature gas blowing nozzle.
“1.!! Manufacturing method of the optical fiber base material according to claim 1.