JPH0193433A - Production of preform for optical fiber - Google Patents

Abstract

PURPOSE:To obtain preform for optical fiber having small transmission loss, by inserting a rod for core comprising SiO2 glass into a hallow part of a specific pipe for clad and heating the pipe using hydrogen-containing flame as a heating source. CONSTITUTION:In production of perform for optical fiber by inserting a rod for core comprising SiO2 glass into a pipe for clad having difference in specific refractive index >=0.5 smaller than that of the SiO2 glass and heating to fuse and to integrate both the rod and the pipe, a fluorine-containing SiO2 glass pipe having <=50mm outer diameter is used as the pipe for the clad, hydrogen- containing flame is used as a heating source in heating and the core diameter A and the clad diameter B after fusing and integration are made to satisfy conditions of A>=2mm, B/A>=6 and 1/2(B-A)>=7mm. H2/O2 flame or hydrocarbon/O2 flame such as natural gas/O2 flame, methane/O2 and propane/O2 are preferable as the hydrogen-containing flame with respect to supply of easy flame with strong heating power.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to a method for manufacturing a base material for an original fiber, and more particularly to a method for manufacturing a base material for a fiber, particularly for a single-mode fiber, particularly a dispersion-shifted single-mode fiber that has zero dispersion in the 1.55 μm wavelength band. The present invention relates to a method for manufacturing a base material.

[Conventional technology]

As shown in Fig. 2, one of the conventional original fiber manufacturing techniques is to insert the glass rod 4 for the core into the hollow part of the glass pipe 5 for the entire cladding, and then weld them together by heating (referred to as collapse). A method of producing a core/clad structure 7 and drawing the structure 7 as a source fiber using a high-temperature furnace is known as the rod-in-tube method.

In recent years, the development of single-mode fibers such as dispersion-shifted fibers has progressed, but this fiber has a large refractive index difference between the core and cladding, a small core diameter, and a large cladding diameter/core diameter (ratio). A large structure is required.

To produce a single mode fiber base material with a small core diameter and a large cladding diameter/core diameter ratio using the rod-in-tube method described above, repeat the operation in Collapse 1 or as shown in Fig. 5. A method of forming a soot body 8 for cladding by further adding glass fine particles (sue) 10 synthesized in the flame of a burner 9 to the outer periphery of the core/cladding structure 7 (e.g. Publication No.)
etc. are known.

[Problem that the invention seeks to solve]

However, due to the above-mentioned conventional technology, the refractive index distribution of a single mode fiber, especially the cross section of the fiber, as shown in Figure 1 (
In the structure shown in aJ or (bl), core 1 is made of pure quartz (S1
0□) Made of glass, cladding 2 is made of quartz containing 7 elements (
F-8102) When a dispersion-shifted single mode fiber made of glass and having a relative refractive index difference of 0.5% or more between the core and the cladding is manufactured, there is a problem that a fiber with small transmission loss cannot be obtained.

The present invention is a single mode fiber, especially a core single mode fiber, and has a low transmission loss.
This was done with the aim of manufacturing by fully utilizing the rod-in-tube method.

[Problem t-Means and effects for solving] The present invention has 8
102 A core rod made of glass whose relative refractive index difference is 51o2 is inserted into the hollow part of a cladding pipe that is smaller than 0.5% and heated to weld and integrate the two elements. In the method for manufacturing a fiber base material, the cladding pipe has an outer diameter of 5
Using a SiO□ glass pipe containing 7 elements with less than 0 deception,
A method for producing an optical fiber base material, characterized in that a flame containing hydrogen is used as a heating source for the heating, and the core diameter A and the cladding diameter B after welding and integration satisfy the above conditions. 91. This has excellent transmission characteristics.
This makes it possible to manufacture a 55 μm band zero dispersion shifted single mode fiber using an efficient rod-in-tube method.

The present invention will be described in detail below, starting with the circumstances that led to the invention.

If the core is 8102 and the cladding is F-3iO2 glass, it has a refractive index distribution structure shown in Figure 1 (al or (bl), and the relative refractive index difference between the core and cladding is 0, such as a dispersion shift type.
．． If you try to make a whole fiber with a large core diameter of 5μ or more and a small core diameter of about 5μ, the fluorine CF in the cladding
) It is necessary to have a large m addition, and it is also necessary to form a large clad diameter/core diameter ratio.

By the way, SiO□ with fluorine CF)? Add F-81
02, its physical properties are different from those of 5in2, but the viscosity in particular changes greatly, and the viscosity of SiO□ is greatly reduced by the addition of F. This is particularly noticeable in single mode fibers with a large Fti addition.

A small diameter 51o2 core, which is the object of the present invention, by the collapse method,
When attempting to fabricate a structure consisting of large-diameter F-3iO2 cladding, the cladding glass becomes softer during heating, and this cladding glass is welded to the core glass at low temperatures, causing the core glass surface to become softer. They are integrated before they reach a smooth state (without any cracks) due to sufficient heating. Ninth, there is a large degree of crackling left on the core-clad interface, which is a major factor contributing to the deterioration of the transmission loss of the 7-IPA.

In addition, in F-8102 glass, the diffusion rate of gold ions, etc. is greater at high temperatures than in 5in2 glass.
especially? In highly concentrated glass, impurities such as metals and OH groups that enter from the outside and are harmful to the transmission characteristics of the original fiber are more likely to diffuse into the vicinity of the core during heating processes such as collapse or drawing. This also greatly reduces the transmission loss of the optical 7-aiper.

Therefore, the inventors of the present invention have conducted detailed studies and repeated experiments to determine the heating source in the heating process, the size of the core and cladding, etc. in order to minimize the influence of the above-mentioned differences in physical properties.

As a result, if the refractive index value is 0.5% or more smaller than the relative refractive index difference compared to 310□ glass for the F-3iO2 glass pipe that becomes the cladding, the pipe metal weight is smaller than 501 m in outer diameter, and the heating source When collapsing is carried out using a flame of hydrogen, and the core diameter after collapsing is t As cladding diameter 'fr:B, the following A≧2, B/A≧6, H(s-A)27 Conditions for the edition? If it is filled, you can collapse even more, and impurities,
In particular, it has been found that a dispersion-shifted single mode fiber with an SxO2 core can be obtained in which the influence of residual moisture is negligible for a practical fiber.

The pipe for cladding made of F -SiO
By the method proposed in Specification No. 97, etc., it is possible to produce a relatively high-purity quartz glass base material in which 2 is added relatively uniformly in the radial direction. A desired pipe can be obtained by this method. The outer diameter of the clad pipe is preferably 501!11 or less, and the wall thickness is preferably 20% or less. This is because if these values are exceeded, it becomes difficult to raise the core surface to a sufficiently high temperature.

Core 810. The glass rod contains Ge in the raw material gas.
An 8102 soot body was prepared without introducing dopants such as O, and this was used as CI! After sufficiently dehydrating with a chlorine-based gas such as No. 2, the desired glass rod can be exploded by further heating to make it transparent.

As described above, with the 5zO2 rod for the core inserted into the hollow part of the F-8102 pipe for rad, the pipe is heated from the outside with a flame containing hydrogen and collapsed.

Examples of the flame containing hydrogen used in the present invention include H
2102 flame, natural gas 102 flame, hydrocarbon 10□ flame such as methane 102 or propane 102 flame, etc. are preferable because they are easy to use and can provide strong heat.

Regarding the core diameter A and the crund diameter B after collapse, it is preferable that A≧2IrlI.If the diameter is smaller than this, the core will tend to meander during the collapse process, causing air bubbles to be drawn around the core, or the core This is because if the eccentricity is large, it becomes sharp and a good collapsed body cannot be obtained.

Further, the conditions of a/A≧6 and 3A(B-A)≧70 are based on the reason that the residual water content, which greatly affects the transmission loss of the obtained fiber, is limited to a predetermined value.

The relative refractive index difference between the core and the crand is 0.5%, and the core diameter is 5.
Fiber k having the structure shown in Fig. 1 ta+ with an outer diameter of 125 μm, collapse by H2/O2 flame,
It was synthesized by combining the soot deposition methods shown in Figure @3. At this time, when B after collapse is kept at a constant value of 241111, the value of the core rod outer diameter A is mainly changed, and the cladding diameter/core diameter, that is, BZA, is changed.
．． Changes in transmission loss at 38 μm were investigated. 1.38
The transmission loss at 11 m can be estimated as the residual OH view. This result is shown in the graph of FIG. 4 as b5, and it can be seen that the transmission loss decreases rapidly when a/A is 6 or more, which is within the range of the present invention.

〔Example〕

Examples and Comparative Examples A high-purity S-02 glass rod was synthesized by the VAD method, and it was heated using a resistance furnace with a carbon heater.
It was stretched to a predetermined outer diameter. On the other hand, the relative refractive index difference is 8102
F-containing 8102 with a refractive index 0.7% lower than glass
Glass rods were synthesized by the VAD method, a hole was punched in the center of the rods, and the rods were then stretched to produce a cladding pipe of a predetermined size.

Table 1 shows the combinations of rods and pipes. 41 to A3 are products of the present invention (examples), and A4 to A6 are comparative products (comparative examples).

Insert the above glass rod into the hollow part of the glass pipe for cladding, and place it at the interface between the two (3123o).

H while introducing ee/min and SF6500007 min.
The core rod and the clad pipe were welded and integrated by heating the pipe to about 1800 DK with a 2102 flame burner and shrinking the pipe from one end.
(see figure). The obtained structure was stretched, and the outer periphery of the stretched body was subjected to a VAD method having the configuration shown in FIG. 3'), S102
Deposited soot. The thickness of the SiO2 soot layer was set to a predetermined thickness such that the core diameter would be 5 μm when a fiber having an outer diameter of 125 μm was drawn after the preform was made into a wire drawing preform by adding fluorine and making it transparent.

The soot body was dehydrated under the conditions of the first step in Table 1, and
Fluorine is added under the conditions of the first step, and the fiber is made transparent under the conditions of the third step, which is then drawn to form a fiber with an outer diameter of 125 μm.
I got a fiber with m1 core 5μm.

The loss (αtJ8) of each of the nine obtained fibers at a wavelength of 1.38 μm was measured. These results are shown in Table 2.

From the results in Table 2, it is clearly seen that when the core diameter A and the cladding diameter B satisfy the range and conditions defined by the present invention, a single mode fiber with excellent transmission loss characteristics is obtained.

Table 1 [Effects of the Invention] As is clear from the above explanation and the results of Examples and Comparative Examples, the present invention has the advantage that a 7-eyeper with small transmission loss cannot be obtained by the conventional method using rod-in-tube collapse. In addition, it is possible to manufacture a single-mode fiber with a refractive index distribution shown in Figure 1 (al, (bl) with a SiO2 core/v-s1o2 cladding with low transmission loss, and in particular, it is possible to manufacture a single-mode fiber with a small transmission loss. This is extremely advantageous in that it can achieve small losses.

[Brief explanation of the drawing]

Figure 1 (al and (bl) are diagrams for explaining the refractive index distribution structure and glass composition of a single mode fiber according to the present invention. Figures 2 and 3 are diagrams for explaining embodiments of the present invention. , Figure 2 shows the collumpus process, and Figure 3 shows the soot deposition process. Figure 4 shows the cladding diameter/core diameter ratio: B/A and the wavelength 1.58.
It is a chart showing the relationship of transmission loss (dB/Km) in /JH.

Claims (1)

[Claims] A core rod made of SiO_2 glass is inserted into a hollow part of a cladding pipe whose relative refractive index difference is 0.5% or more smaller than that of SiO_2 glass, and the two are welded and integrated by heating. In the method for manufacturing an optical fiber base material, the cladding pipe has an outer diameter of 50 mm.
Using a fluorine-containing SiO_2 glass pipe of mm or less,
For the above heating, a flame containing hydrogen is used as a heating source, and the core diameter A and cladding diameter B after welding and integration are {A≧2mm B/A≧6 1/2 (B-A)≧7mm}. A method for producing an optical fiber base material, characterized in that it satisfies the above conditions.