JPH01164740A - Production of optical fiber preform - Google Patents

Abstract

PURPOSE:To obtain the title preform having a low content of oxygen and having excellent resistance to hydrogen, etc., by heating, dehydrating, and reducing the deposit of fine pure quartz glass particles for a core at a specified temp. in an inert gas contg. a dehydrating and reducing gas, and then vitrifying the deposit. CONSTITUTION:The deposit of fine pure quartz glass particles for a core is formed by VAD, etc., to obtain the optical fiber preform having a core of pure quartz glass. The deposit 25 is then placed in the furnace core tube 22 of a soaking pit, the inert gas (e.g., He) contg. a dehydrating and reducing gas (e.g., gaseous mixture of CCl4 and O2) is introduced from an inlet 28 and heated by a heater 24 to 900-1100 deg.C, hence gaseous CO2 is generated by the reaction shown by the formula, and the deposit 25 is dehydrated and reduced. The deposit 25 is then vitrified, and a reliable optical fiber preform is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The invention relates to a method for manufacturing a base material for a base fiber, and more particularly, a method for manufacturing a base material for a core of a base fiber whose core is substantially pure quartz glass. This is about the method.

[Conventional technology]

Original fibers whose cores are comprised of substantially pure quartz (S10□) glass are less susceptible to the presence of additives than original fibers whose cores contain additives (most commonly Ge02) to adjust their refractive index. Because there is little increase in transmission loss induced by radiation or hydrogen, it is highly reliable and useful for optical fiber cables that can be used in radiation environments or environments where there is a risk of hydrogen diffusion. . Furthermore, even in the initial state without exposure to radiation or hydrogen, by not including any additives in the core, Sileyl scattering can be suppressed to a low level, and a low-loss original fiber can be realized.

A specific example of the structure of such a pure quartz core fiber is shown in Table 1. Fluorine-treated quartz glass as cladding (
By using F-3iO□ glass) or low refractive index resin, original fibers with various structures can be constructed.

[Problem that the invention seeks to solve]

Conventionally, as a highly productive means of synthesizing the core part of this type of original fiber, the VAD method has been used to synthesize a deposit of 5in2 glass particles using a flame hydrolysis reaction of a glass raw material, followed by heating. There are methods of dehydration and heating to make it transparent.

However, in a pure quartz (hereinafter also referred to as pure 5102) core fiber using a core base material produced by this method, a problem sometimes arises in that absorption at a wavelength of 0.65 μm becomes large. This wavelength is different from the original wavelength for transmission, but the absorption at 0.65 μm is caused by so-called NOI Bridging Oxy
gen associatedHal! e Cente
This is thought to be due to the presence of r: NBOHO), which deteriorates the hydrogen resistance properties of the original fiber and leads to a decline in the long-term stability and reliability of the fiber, so it is difficult to put the original fiber into practical use. This was a serious problem.

The present invention has been made with the intention of providing a method for producing a core base material with a small amount of defects.

[Means for solving problems]

The present inventors have conducted repeated research on the method for producing the base material for the core, and have found that there is a close relationship between the amount of defects and the composition of the atmospheric gas during the heating dehydration treatment of the glass fine particle deposit for the core. .

In other words, when 5102 glass is drawn with high tension, it is 0.65 μm.
A large absorption occurs. Although this mechanism is still unclear, a leading theory is that =Si-0-0-3i in the base material
There is a theory that the = bond is broken, creating a -=Si-0 defect, which appears as 0.63 μm absorption. Therefore, the present inventors calculated = 5i-0-0- in the core material.
8i; He came up with the idea of creating a core material (pure 5102 glass fine particle deposit) using the VAD method to reduce bonding, and creating a reducing atmosphere to reduce the oxygen content in the glass during dehydration and transparency treatment. invention has been achieved.

That is, the present invention involves dehydrating the pure silica glass fine particle deposit for the core in the process of making it transparent by heating when producing a base material for the original fiber having a core of substantially pure quartz glass.・Regarding a method for producing a base material for an original fiber, which is characterized by being made transparent after dehydration and reduction treatment by heating within a temperature range of 900 to 1100°C in an inert gas atmosphere containing a reducing agent gas. .

The dehydrating/reducing agent gas in the present invention includes a gas consisting of Cat4 and 02, a gas consisting of Cat0 and 02, a gas consisting of Cat4 and Cat02, and a gas consisting of Cat4 and Cat02,
Cl2,82CI! It is particularly preferred to use 2. Further, in the case of gases consisting of CC/4 and 02, it is necessary to use gases in which the molar concentration ratio of both is within the range of 0.5≦027 GOla<1. Moreover, it is preferable to use He gas as the inert gas.

In the present invention, the glass particle deposit body (soot body) created by the VAD method or other known technology is heated in a temperature range of 900 to 1100°C in an atmosphere containing a reducing gas and a dehydrating agent gas. Dehydrate the soot body. This coexistence atmosphere of reducing gas and dehydrating gas is GCl4
The atmosphere consists of either 02, CO, 02,5OCl2 or 82G/2, and an inert gas such as He or Ar, preferably He. In the case of aCt4 and 02, the concentrations of both are adjusted within the range of 0.5≦027GCl4<1, and the reason for this will be explained in the section on effects.

The time required for the dehydration treatment can be appropriately selected depending on the size of the soot body. The heating means may be either a soaking furnace or a zone furnace.

After the above dehydration treatment, the soot body is heated to a high temperature of about 1600° C. to make it transparent, thereby obtaining a transparent glass body for the core (base material for the core). The atmosphere at this time may be the same as the atmosphere during the dehydration treatment, or may be an atmosphere containing only an inert gas such as He.

Figure 1 (shows the case where a soaking furnace is used for Al, the furnace core tube 2
A soot body 25 is housed inside the soot body 2, and is heated by a heater section 24 having a length spanning the entire length of the soot body. Atmospheric gas is supplied through the inlet 28, and the flow meter 26,
The air is exhausted through a valve 27 and an outlet 29 . 21 is a support rod, and 25 is a furnace.

When using a zone furnace, the soot body 25 housed in the furnace core tube 22 is pulled up or down at a predetermined speed as shown in FIG. The introduction and discharge of atmospheric gas are the same as in the case of Al shown in Fig. 1.

[Effect]

The effect of atmospheric gas in the dehydration process of the present invention is Do/4
The case of an atmosphere consisting of and 02 will be explained as an example. aC
When t4 and 02 are introduced into the heating furnace, cat4++ 02
→C0+2012-.-<11 CO gas, which becomes a reducing agent, is generated as shown in equation +11 above. At this time, the ratio between Cat4 and Cat02 is preferably within the range of the following formula (2) in terms of flow rate ratio.

0.5≦027 CO/4 < 1...
- (2) When o27aa14<0.5, a reaction occurs as shown in equation (3) below, and C (carbon) is precipitated and deposited on the soot.

(2+n)ccz4+02-)2 (lo+2(2-1
-n) O/2+n-C- (3) Conversely, 02/GO/4)
1, a reaction occurs as shown in equation (4) below, resulting in an excessive amount of 02 in the atmosphere.

CCl4+(1+n)02-+002+2C;/2+n
O2・+41 By dehydrating and making the glass transparent in an atmosphere where at2 gas, which has a dehydrating effect, and CO gas, which has a reducing effect, coexist, the oxygen content in the glass is reduced, and the conventional product is also It is considered that an original fiber with a small amount of defects was obtained.

〔Example〕

Example 1 A core shaft SiO2 glass particle pellet produced by the VAD method was heat-treated in a zone furnace as shown in Fig. 1+81 under the conditions shown in Table 2, with the oxygen flow rate x (007 minutes) set at a constant rate. did.

Table 2 The obtained pure 51o2 glass base material for the core was heated in an electric resistance furnace.
It was heated to 900°C and stretched to 10 μm.

This base material was used as a starting material 1 having the structure shown in FIG. 2, and a porous glass body 2 consisting only of 8102 was formed on its outer peripheral portion. 6 is a synthesis burner.

This porous glass body part 2 was subjected to dehydration, gradual addition of fluorine, and heat treatment for transparency under the conditions shown in Table 3 to form transparent glass.

Table 3 The obtained transparent glass body was tested again at IQ+m in an electric resistance furnace.
It was stretched to φ and sooted in the same manner as above, and then subjected to dehydration reduction, fluoridation, and transparency treatments again under the conditions shown in Table 5. The resulting transparent glass body consisting of a pure quartz core and a fluorine-added cladding was drawn into a fiber having an outer diameter of 125 am at a sonic velocity of 100 m for 7 minutes and a tension of fO/. The refractive index distribution of the fiber was as shown in FIG. In addition, the relationship between the absorption amount Δα at 0.63 μm of each fiber and the 02 flow rate X ((X:;7 minutes) during core dehydration was investigated, and the result was as shown in Figure 4, and CC/4102 It can be seen that when Δα exceeds 1, Δα increases rapidly.

In addition, the absorption amount Δα (dB /Km
) is pure 5102 without defects as shown in Figure 5.
This is the amount of increase in the transmission loss A of the fiber from the transmission loss port in the case of .

Example 2 Dehydration and transparency of a glass fine rice grain deposit for a core prepared in the same manner as in Example 1 was performed using 5oG122000c/min instead of "CCl4 and 02" as a reducing treatment agent, and other conditions were as shown in Table 2. I did the same thing.

A base material for the original fiber was prepared in the same manner as in Example 1, and the fiber was made into a fiber. The obtained fiber has Δa = 1.
OclB/Km.

Example 6 Dehydration and transparency of a core glass particle deposit prepared in the same manner as in Example 1 was carried out using “CGl!4 and 02” as a reducing treatment agent.
”, cosoac 7 minutes, Cl2600cc
/min, and the other conditions were the same as in Table 2.

Below, a base material for the original fiber was prepared in the same manner as in Example 1 and made into a fiber, and the Δa of this material was 1.5 dB.
/kff+.

Example 4 Same as Example 2.5, 1 CCl4 and 0 among the conditions in Table 2
A fiber was obtained in the same manner as in Example 1 except that only 2'' was replaced with 52G12200 cc/min. The Δα of this fiber was very low at 0.7 dB/-.

Comparative Example 1 A fiber was obtained in the same manner as in Example 1 except that at2600cc1 was used in place of "CCl4 and 02" in Table 2. The Δα of this product was as high as 506B/KnI.

Comparative Example 2 A fiber was obtained in the same manner as in Example 1 except that Cl26000c/min and 02600cc/min were used instead of "act4 and 02" in Table 2.

The Δα of this product was extremely high at 606 B/km.

As described above, the fibers of Examples 1 to 4 using the core base material subjected to the reduction and dehydration treatment according to the present invention all have reduced absorption at 0°63 μm, but compared to the conventional at
2/ Comparative Example 1 using a He atmosphere has a high absorption at 0°65 μm, and Comparative Example 2, which is subjected to dehydration treatment in an oxidizing atmosphere, has a very high absorption at 0.65 μm.

From these results, it is clear that the method of the present invention can produce an original fiber base material with a small amount of defects.

〔Effect of the invention〕

Since the present invention dehydrates the pure 5102 glass particle deposit for the core by heating it in a reducing atmosphere, there is an advantage that the amount of oxygen in the glass is reduced and the absorption at 0.65 μm can be reduced. As a result, the present invention can produce a reliable base material for original fibers with excellent hydrogen resistance properties.

[Brief explanation of the drawing]

Figure 1 (1! and (Bl) are schematic cross-sectional views for explaining embodiments of the present invention, in which Figure 1 (A) shows the case of a soaking furnace, and CB+ shows the case of a zone furnace. The figure is a schematic explanatory diagram of the process of sooting the cladding part in an example of the present invention, and FIG. 5 is a diagram showing the refractive index distribution structure of the fiber obtained in Example 1. In the dehydration/reduction treatment process of the core base material in Example 1, the amount of oxygen (XCC/min) was changed to 027CC/4
Absorption f at 0.65 μrn when changing the ratio
This is a diagram showing changes in t(Δα), and FIG. 5 is 0.65 μ
It is a figure explaining the amount of absorption (Δα) in m.

Claims (6)

[Claims] (1) When producing an optical fiber base material having a core of substantially pure quartz glass, in the step of making the pure silica glass particle deposit for the core transparent by heating, the deposit is dehydrated and treated with a reducing agent. Under an inert gas atmosphere containing gas,
1. A method for producing an optical fiber preform, characterized in that the preform is made transparent after being subjected to dehydration and reduction treatment by heating within a temperature range of 900 to 1100°C. (2) The dehydration/reducing agent gas consists of CCl_4 and O_2, and the molar concentration ratio of both is 0.5≦O_2/CCl_4
The method for manufacturing a core preform for an optical fiber according to claim 1, wherein the preform is within the range of <1. (3) The method for manufacturing an optical fiber preform according to claim 1, wherein the dehydrating/reducing agent gas is composed of CO and Cl_2. (4) The method for manufacturing an optical fiber preform according to claim 1, wherein the dehydrating/reducing agent gas is SOCl_2. (5) The method for manufacturing an optical fiber preform according to claim 1, wherein the dehydration/reducing agent gas is S_2Cl_2. (6) A method for manufacturing an optical fiber preform according to any one of claims 1 to 5, wherein the inert gas is He.