JPS6096538A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To prevent the damage of an optical fiber preform at the weld part between the starting material and the drawing substrate, by changing the composition of the optical fiber only at a definite region near the starting end, and varying the expansion coefficient of the preform gradually toward the end part. CONSTITUTION:At the initial stage of the deposition of the soot 6 on the starting substrate 1 in the production of an optical fiber preform, the soot 6 such as SiO2 is deposited without addition of a dopant. Thereafter, the addition of a dopant is started, and the rate of addition of the dopant is varied gradually to the ultimate target content to form the main part 8B of the preform. The buffering zone 9 having a thermal expansion coefficient varying continuously along the longitudinal direction and produced by the above process is not used as the optical fiber. On the other hand, a zone 8A having varying outer diameter is formed near the end of the preform 8, and the zone cannot be used as the optical fiber and is used as the thermal expansion coefficient buffering zone 9. The porous preform prepared by this process is sintered at a high temperature to collaspse the spaces between the soot particles and obtain a transparent preform.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a method for manufacturing an optical fiber base material using a vapor phase axial method, in which transparency occurs during heat treatment such as during slow cooling of the optical fiber base material after transparentization or during stretching of the base material. This invention relates to preventing damage to an optical fiber base material.

One of the manufacturing methods for optical fiber base material is the vapor phase axial method (V
AD) is known, but this gas phase shafting method uses 5iO14r Ge (J4, POCj13 and B
Volatile glass-forming raw materials such as Br3 are supplied, and these glass-forming raw materials are subjected to a hydrolysis reaction in a flame to generate glass-forming fine particles (hereinafter referred to as "soot"), and rod-shaped A substantially cylindrical porous optical fiber base material is obtained by growing the soot in the axial direction from the tip of the starting profiteer, and then a transparent optical fiber base material is obtained by heat-treating at a high temperature. be. The transparent optical fiber preform thus produced is usually heated and drawn in a glass lathe to a target diameter, forming a portion corresponding to the core of the optical core. This transparent optical fiber matrix is Ge02yP205. to adjust the refractive index of the core. B2O3
It is a silica-based glass to which oxides such as As a result, a structure is obtained in which doped quartz glass is fused to the tip of the silica glass bale. Doped quartz glass containing oxides such as G602+P2O5tB203 has a larger coefficient of thermal expansion than pure quartz glass, so stress due to distortion occurs in the fused portion, and as a result, it becomes very susceptible to breakage.

When hot-stretching a transparent optical fiber preform on a glass lathe, there is a method of directly grasping the end of the transparent optical fiber preform;
One possible method is to grip the stretching base material and fuse it to the end of the transparent optical fiber preform, but this method of directly gripping it is not practical because the gripped portion cannot be stretched. Therefore, it is appropriate to separately grasp a quartz glass bale as a base material for stretching and fuse the tip of the quartz rod to the end of the transparent optical fiber base material, but as described above, pure quartz glass and doped quartz Stress is generated due to distortion due to the difference in the thermal expansion coefficient of the glass, making it more likely to break. One way to prevent the stress caused by this strain is to change the pure quartz glass rod for starting and drawing to doped quartz glass having the same expansion coefficient as the transparent optical fiber base material. Quartz glass is generally not commercially available, and even if it is specially made, it is expensive and difficult to put into practical use.

As described above, in the conventional technology, it is practical to use commercially available quartz glass rods as the starting base material and the drawing base material, but since the target optical fiber base material is doped quartz glass, There is a drawback that stress is generated due to distortion at the fused portion with the silica glass bale, making it easy to break. In particular, when the purpose is to create a large numerical aperture fiber with a high refractive index in the core of the optical fiber, dopant oxides must be added to increase the refractive index, resulting in the formation of a transparent optical fiber base material. The coefficient of expansion also becomes very large, making it more likely to break at the fused portion with the quartz glass rod.

The present invention has been made in view of the problems in the prior art, and its purpose is to provide a method for producing an optical fiber matrix using a vapor phase axis method, in which a transparent optical fiber matrix is used as a starting base material and A method for preventing breakage at the fused part with the stretching base material is to gradually change the expansion coefficient of the transparent optical fiber base material in the axial direction toward the stretched end to minimize stress caused by strain. It is something. That is, soot is first grown as a layer on the tip of the starting substrate with a composition equal to the expansion coefficient of the starting substrate, and then the composition is gradually adjusted to the target optical fiber matrix composition. If a second base material is bonded to the end of the base material and then stretched, after growing a cylindrical optical fiber matrix to the target length, the composition is gradually adjusted so that the coefficient of expansion becomes equal to the expansion coefficient of the base material for stretching. This is the method to exit after adjusting.

According to the method of the present invention, since the expansion coefficients of the starting base material and the drawing base material are adjusted to become gradually equal at the starting end and ending end of the transparent optical fiber preform, stress due to strain is alleviated. As a result, almost no damage occurs during transparentization or heating stretching, making it possible to improve the manufacturing efficiency of the optical fiber base material.

The present invention will be explained below based on the drawings. FIG. 1 is a conceptual diagram of a method for producing a porous optical fiber base material by the vapor phase axis method, in which a cylindrical base material 11, for example, a pure quartz glass ball, is rotated and moved in and out by a drive mechanism not shown. A burner λ is arranged towards the
+ Ge O114+ P OO4113+ B B
A volatile glass forming raw material such as r3 is supplied. Also,
The burner λ is supplied with hydrogen gas and oxygen gas through another conduit '1ZB4Q, respectively. As a result, Soo) J is produced by a flame hydrolysis reaction in the flame J produced by the reaction of oxyhydrogen gas, and the soot O at the mouth is based on the base 4.
, 1'/ in the axial direction. Base+
, t/ are rotating during this time and are continuously moving backward in the direction of arrow 7 at a speed corresponding to the above-mentioned deposition speed, and the deposited soot 6 forms a cylindrical porous hole on the tip of the base material l. A solid base material g is gradually generated. And in the method according to the invention, the above soot 6 is converted into a starting group 4) l' l
As the glass is deposited on top of the substrate, the initial glass composition is the same as that of the base material L, that is, in the above example, the glass is produced by supplying only 5i (J4) to the burner 2 without adding any dopant material. 5102 soot 6 is deposited on the substrate l;
Thereafter, the addition of a predetermined dopant substance, for example Gecx4, is started and its addition amount is continuously increased, and the supply amount of Ge0A4 is set so that the targeted CEO2 content of the optical fiber spinning is, for example, 75% by weight. Then, the main body portion B of the base material is formed. The buffer zone of the thermal expansion coefficient whose composition is gradually changed in the axial direction of the base material is a part that cannot be used as an optical fiber. Near the tip, an unsteady part A that gradually expands from the outer diameter of the base material generally occurs over a length of approximately 60 to 70% of the outer diameter of the parent phase, and this outer diameter unsteady part is used as an optical fiber. Since it is a portion that is not molded, it is convenient to use this outer diameter unsteady portion JA as the aforementioned thermal expansion coefficient buffer zone 9.

That is, it is desirable to gradually change the composition over substantially the entire length of the portion JA.

The porous matrix obtained as described above is then sintered at a high temperature to fill the voids between the soots and form a transparent matrix. This transparent glass preform can be sent to the next crund layer formation and fiber spinning process as the glass material that forms the core of the optical fiber, or it can be heated and drawn as follows to reach an outer diameter convenient for fiber spinning. Be made thinner.

That is, as shown in the figure, a porous base material L produced by soot deposition on a starting base material (first base material) L is gradually heated to a high temperature from the end side with a sintering burner 10 to form transparent glass. After completion of transparent vitrification over the entire length, a tip of a cylindrical drawing base material (second base material) made of, for example, pure quartz is placed at the end of the produced transparent glass base material //. This second base material II is chucked in a glass lock and pulled in the axial direction while rotating at the same speed and in the same direction as the first base material II to give the transparent glass base material II a predetermined outer diameter. Heat and stretch until

In the above, in the second invention of the present application, when generating a porous base material zone, as shown in FIG. By gradually changing the composition in the axial direction in the steady portion gc and finally making it the same as the composition of the second base material 12, a thermal expansion coefficient buffer zone 9 similar to that of the starting end is formed. For example, 5i-G
If it is e-glass, GeCl4 to soot generation burner λ
Gradually reduce the supply amount of 5iCI! at the end of the base material where the second base material 12 is joined. The 5i02 soot produced by supplying only 4 is deposited. As a result, the soot composition at the starting and ending outer diameter unsteady portions JA and rc of the porous base material g is such that the content of GeO2 is, for example, doped in the axial direction toward the ends as shown in the graph of FIG. It gradually decreases from tS% to 0%, and the tip consists of 8102 single composition soot, which is the same as 12 to the base material. Therefore, when the above-mentioned λ base material 12 for stretching is joined to the end portion of the base material that has been transparently vitrified by high-temperature sintering, the thermal expansion coefficient α of the transparent glass base material // is the same as that of the seventh base material / and the second base material. material l
The coefficient of thermal expansion α2 (Ge02/j%,
5i02Jj%te/7X10-7) Since there is a smooth transition to the duck, both base materials/S/
The stress caused by strain due to the difference in thermal expansion coefficient between the transparent glass base material ii and the transparent glass base material ii is alleviated, and damage to the base material is prevented.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a front view showing the production process of a porous base material, and a graph showing the concentration of the dopant substance and the distribution of the coefficient of thermal expansion in the same base material. It is a front view which shows the process of extending|stretching after a porous base material is sintered at high temperature and made into transparent glass. l...First base material λ...Soot generation burner 3.
...Raw material supply device IIA...Raw material supply conduit 41B...Hydrogen gas conduit +C...Acid-free gas conduit! ...Flame 6...Soot Z...Porous base material fA, 10...Outer diameter unsteady part T...Thermal expansion coefficient buffer (I¥ (composition changing part) //...Transparent Glass base material 12...Second base material No. 1 Figure 2 Procedures Amendment f Case description (p-:sc(Jn2) 2 Name of the invention Method for manufacturing optical fiber base material 3 Relationship to the case of the person making the amendment Patent applicant address Address g, Hiro-chome, Doshomachi, Higashi-ku, Osaka-shi, Osaka Prefecture Name
(1100) Nobu Saiga, Representative of Nippon Sheet Glass Co., Ltd.
Sponsored by Yubutsu's agent 6 Description and drawings subject to amendment 7 Contents of amendment (1) Page 9 of the specification, line 1 to line 1/: ``In other words, as shown in Figure 2... ” should be amended to the following sentence. [In other words, the tip of a cylindrical drawing base material (second base material) /J made of pure quartz is bonded to the end of the transparent glass base material ti obtained by sintering the porous base material. , this λth
The base material 12 is chucked in a glass lock, and the transparent base material // is heated and softened with a heating burner lO, and the second base material 12 is rotated at the same speed and in the same direction as the first base material l while the axis line The large-diameter transparent base material // is stretched by pulling in the direction to form a transparent base material LLA having a predetermined outer diameter. ”(2)
On page 9, line 11 of the specification, there is l”5i-Gel.
Correct as 5io2-Ce02J. (3) The reference numbers in Figure 2 of the drawings are corrected as shown in the attached sheet.

Claims (3)

[Claims] (1) Glass fine particles obtained by reacting volatile glass-forming raw materials in a flame are grown on the tip of a rotating rod-shaped base material to create a cylindrical porous base material. In a method for manufacturing an optical fiber base material in which a base material is heated and sintered to produce transparent glass, the glass composition near the starting end of the porous base material is changed from the joining point to the base material in the axial direction. 1. A method for producing an optical fiber base material, characterized in that the composition is gradually changed from approximately the same composition to a predetermined optical fiber composition. \1 (2) The method for manufacturing an optical fiber preform according to claim 1, wherein the region whose composition is changed is a portion of the porous preform whose outer diameter is unsteady. (3) A rod-shaped first rotating glass particle obtained by reacting a repellent glass-forming raw material in a flame.
After creating a cylindrical porous base material by adhering and growing on the tip of the base material, this porous base material is heated and sintered to become a transparent glass base material, and a rod-shaped second group is attached to the end of the transparent glass base material. In the method for manufacturing a Hikari 7 Aipah base material, the glass composition near both ends of the porous base material is , the production of an optical fiber preform characterized in that the composition is gradually changed in the axial direction from the joining point with the first and second base materials from approximately the same composition as each of the base materials to a predetermined optical fiber composition. Method.