JPS6350340A - Production of base material for functional quartz optical fiber - Google Patents

Abstract

PURPOSE:To prevent the dissipation of a trace component and to easily obtain a base material for a functional optical fiber contg. the trace component in a high concn. by preliminarily forming a porous body by a VAD method and subjecting the same to a dehydration treatment, heat treatment, etc., then adding the high melting point trace component thereto. CONSTITUTION:The porous glass body is produced by the VAD method and is subjected to the dehydration treatment preferably at <=1,400 deg.C in an inert gaseous atmosphere contg. a gas for dehydration (e.g.; gaseous chlorine). After said body is subjected to the heat treatment preferably at <=1,400 deg.C in the inert gaseous atmosphere, the porous body is vitrified to transparent glass in the inert gaseous atmosphere contg. the high boiling point trace component (e.g.; NdCl3), by which the trace component is added to the porous body and the objective base material for the functional quartz optical fiber is obtd. The base material for the functional quartz optical fiber having high performance is thereby easily produced and since the porous body is produced by the VAD method, the large-sized base material is easily produced.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for manufacturing a functional quartz optical fiber base material, and more particularly, to a method for manufacturing a functional quartz optical fiber base material, which can be used for optical fiber lasers, optical isolators, etc., and which is free from unnecessary impurities. The present invention relates to a method for producing a high-performance functional quartz optical fiber base material with little contamination.

[Technical background of the invention]

Conventionally, this method has been used to manufacture highly functional quartz glass that contains rare earth elements and some transition metal elements (such as Cr), and has very low levels of impurities such as Fe and Cu, and OH groups, which are on the same level as quartz optical fibers. is the MCVD method (R
ef, S, B, Pool et al, Electo
r.

n Lett, νol 21 pp737~ (1985
), M, WATANABE et al, pH ~, 1
00C-ECOCprce, (1985)) and the PCVD method (11, NAMIKAWA, J
JAP, Vo123, ppL409 (1984)
) etc. are known.

For example, in the MCVD method, as shown in FIG.
A raw material such as eCl4 is introduced from one open end of the quartz tube 1, and a glass thin film is deposited on the inner surface of the quartz tube 1 by a thermal oxidation reaction to form a synthetic layer 2. After that, the auxiliary burner 5 is operated to
C1+, ErCl3, etc.) are vaporized and incorporated into the deposited glass thin film. An optical fiber preform is manufactured by depositing a synthetic core layer 3 containing Il component raw material.

In such a method, most of the conventional manufacturing methods for optical fiber preforms can be used, so low 011 group concentration,
It has the advantage that glass base materials with impurity concentrations can be easily produced, but on the other hand, large glass base materials or rod-shaped base materials (
The drawback is that it is difficult to obtain a pure silica glass layer (not containing a pure silica glass layer around the base material).

On the other hand, according to the PCVD method shown in FIG.
I4 (glass raw material) is guided to the trace component raw material holding tube 19 using Ar gas as a carrier, and the trace raw material (for example, NdC) in the trace component raw material boat 12 vaporized by the heating furnace 8 is
13) into the reaction chamber through the nozzle 9. The raw material gas causes an oxidation reaction by the plasma flame 10 generated by the plasma gas inlet 11 and the plasma teacher RF coil 17, and synthesizes Nd-added quartz 14 on the quartz rod 13. The remaining source gas passes through the heat exchanger 18 and is exhausted from the exhaust pipe 15.

In such a method, since the temperature of the plasma flame 10 (said to be several thousand degrees to tens of thousands of degrees) is extremely high, sublimation of the synthesized oxide glass is avoided in order to deposit the base material. It is necessary to precisely control the positional relationship between the plasma flame 10 and the target.

Another drawback is that it is necessary to stabilize the flow of raw materials and working gas within the plasma torch in order to stabilize the plasma flame.

On the other hand, VA, which is one of the typical manufacturing methods for optical fibers,
Let us consider the synthesis of the base material in method D.

In the VAD method, 5iCI4 in a gas phase is supplied into an oxyhydrogen flame, and gas particles generated in the flame are deposited on the end face of a rotating seed rod, thereby growing a porous glass body in the axial direction of the seed rod. In this method, an optical fiber preform is produced by placing the obtained porous preform under transparent glass in an inert atmosphere containing a dehydrating agent.

When synthesizing a base material containing rare earth elements or some transition elements using this VAD method, the melting point of the rare earth chloride or transition gold mud chloride material used is high, so in order to obtain a sufficient artistic pressure, it is necessary to It is necessary to maintain the raw material at a high temperature above °C (for example: flmlIIt (the temperature of NdCl3 that gives a saturated vapor pressure of g is 1048 °C). As a result,
When synthesizing the base material using the VAD method, it is necessary to keep all the piping at a temperature of about 1000° C., making it difficult to synthesize the base material in practice.

As a method to solve this problem, a method is known in which a porous base material is synthesized using the VAD method, and then added by vapor phase diffusion by processing in an electric furnace in an atmosphere of rare earth chloride raw materials during transparent vitrification treatment. (Patent application 1983-0835)
No. 05). However, in this invention, since the dehydration treatment is performed after the diffusion treatment, the added rare earth element volatilizes again as chloride, so there is a drawback that it is difficult to add it at a high concentration.

[Summary of the invention]

The present invention has been made in view of the above points, and solves the drawbacks of adding high melting point trace components (such as rare earth elements or some transition metals) by the VAD method, and furthermore
It is an object of the present invention to provide a method for manufacturing a functional quartz optical fiber preform that enables the production of large-sized preforms that cannot be synthesized by CVD or PCVD methods.

Therefore, the method for manufacturing a functional quartz optical fiber preform according to the present invention heat-treats a porous body manufactured by the VAD method,
In the 'W manufacturing method of optical fiber base material in which trace component raw materials are added, the porous body is treated in an inert gas atmosphere containing a dehydrating gas, then heat treated in an inert gas atmosphere, and finally It is characterized by transparent vitrification in an inert gas atmosphere containing trace component raw materials.

According to the method for manufacturing a functional quartz optical fiber preform according to the present invention, a porous body is formed in advance by the VAD method, and after this porous body is dehydrated, trace component raw materials are added. The trace component raw material does not volatilize (this has the advantage that a base material to which a high concentration of trace components is added can be produced. Also, in order to produce a porous body by the VAD method, the base material is not volatilized). It also has the advantage of being able to be made larger.

C Detailed Description of the Invention] According to the method for manufacturing a functional quartz optical fiber preform according to the present invention, first, a porous glass body is manufactured by the VAD method.

This porous glass body is not fundamentally limited in the present invention, and any porous glass body for a quartz optical fiber base material produced by the VAD method may be used.

This porous glass body is treated in an inert gas atmosphere containing a dehydrating gas, and then heat treated in an inert glass atmosphere.

Conventionally, the addition of trace component raw materials has been carried out through the following steps: formation of a porous body, addition of trace component raw materials, (oxidation), water introduction, and vitrification.

In the present invention, synthesis of a porous body--water treatment, heat treatment--
Because it is done through the process of adding trace ingredient raw materials and vitrification,
There is no need to worry about volatilization of trace component raw materials.

That is, to explain the addition of Nd2O3 as an example, after first diffusing NdCIa<gas) into the porous body,
In the next dehydration process, the Nd2O3 added into the porous body through oxidation reacts with C1g, which is commonly used as a dehydrating agent, and the Nd2O3 formed becomes KM.
Shishishi 2 mau. This is shown by the reaction formula below.

Nd2O3 (s) → -3C1g (g) 2 NNdC13 () +3 /202 (g) As a result, it becomes impossible to add rare earths at high concentrations,
This was also confirmed through experiments conducted by the present inventors.

On the other hand, according to the method of the present invention, the dehydration treatment is performed prior to the addition of the rare earth element, so the problem of the loss of the rare earth element due to the above reaction does not occur.

This dehydration treatment can effectively use dehydration methods used in conventional techniques of this type. For example, it can be carried out by heating in an atmosphere containing a dehydrating agent, such as a halogen-containing gas.

The temperature of this dehydration treatment and subsequent heat treatment in an inert gas atmosphere is preferably 1400°C or less. 6 when dehydrated and heat treated at temperatures exceeding 1400°C.
This is because, as is clear from Example 4 below, the bulk density of the porous body becomes unsuitably high for the diffusion addition of trace component raw materials, resulting in a structure in which trace component raw materials cannot be added.

Following this dehydration treatment, heat treatment is performed in an inert gas atmosphere in the present invention.

This heat treatment step is performed to replace the dehydrating agent with an inert gas and to control the partial pressure of the dehydrating agent in the transparent vitrification step. Therefore, by changing the time during this heat treatment, the amount of the trace component added can be adjusted. That is, if the partial pressure of the dehydrating agent (for example, chlorine) is high, it will easily volatilize and the amount added will be small, and if the partial pressure of the dehydrating agent is low, the amount added will be large (see Example 2).

The trace components are added to the porous body which has been subjected to the dehydration treatment and heat treatment in this manner by exposing the porous body to an inert gas atmosphere containing the trace component raw material.

As trace component raw materials, Nds Ers Yb, Ice
and compounds of some transition elements such as Cr (for example, halides such as chlorides).

this? ! In the step of adding the it component, the amount of the minor component added can be adjusted by adjusting the temperature of the aforementioned minor component raw material (Example 1).

Example 1 FIG. 3 is a schematic diagram of an apparatus for carrying out the method of the invention. As is clear from this figure, this device consists of a quartz furnace tube (but with a gas inlet and an outlet) 2 equipped with an electric heater 20 and a seed rod 21 that rotates and can move up and down.
It has a configuration with 2.

A porous material 23 is deposited on the seed rod 21 of this quartz furnace tube 22, and N2 is deposited on the bottom of the quartz furnace tube 22.
dC] A boat 24 containing 3 is installed.

Moreover, the temperature distribution in the quartz furnace tube 22 is shown on the right side of FIG.

First, a pure quartz porous base material was produced by the VAD method. The conditions for producing this porous base material were as follows: 5iC14 (40°C, total carrier gas 100 cc) was supplied to an oxyhydrogen burner (・11°2.91/min, 026.0j!/min), and the growth rate was 42 mm/min. It was time.

This porous base material was attached to the electric furnace soaking section of the quartz furnace tube 22. The NdCl3 raw material was placed in a quartz boat 24 placed at the bottom of the quartz furnace tube, and the temperature of the NdCl3 was adjusted by changing the vertical position of the boat 24. That is, according to the temperature distribution shown in the third canvas, there is a portion at the bottom of the furnace tube 22 where the temperature changes in the vertical direction. Therefore, the temperature of NdCl3 can be changed by moving the boat 24 up and down in response to this temperature change portion.

Next, while flowing He gas at 5 A/min into the furnace core tube 22, the furnace temperature was raised to 1000°C. Next, He(5
1/min) and CI2 (70 CC/min) at 1000°C, and after salting for 1 hour, it was further held for 48 hours under an atmosphere of 1ie (5 L/min).

Finally, the temperature was raised to 1500° C. in an atmosphere of 1 le (57!/min). The temperature increase rate is 500℃ from 0 to 1ooo℃.
°C/hour, 1000-b.

FIG. 4 shows the relationship between the NdC13 temperature and the amount of Nd added. As is clear from FIG. 4, it was found that the added concentration of Nd3° ions could be uniquely controlled by adjusting the NdC1a temperature.

Example 2 The same apparatus as in Example 1 was used, and the temperature of the electric furnace was controlled by the program shown below.

Table 1 Note that the temperature of the NdC1:+ raw material was kept constant at 1400°C. FIG. 5 shows the relationship between the heat treatment time and the amount of Nd added.

As is clear from Fig. 5, after C12 tax water treatment, H
It was found that the concentration of Nd'' ions added after vitrification could be changed by adjusting the time for holding the glass at 1000° C. in an atmosphere of e.g.

Example 3 First, a pure quartz porous base material having an outer diameter of 20 mmφ and a length of 30 cm was synthesized by the VAD method. Next, Nd addition vitrification treatment was performed by holding for 2 hours using the method shown in Example 2. The base material after vitrification has a diameter of 10 mm and a length of 17
cm, the concentration of Nd" ions added was 100 ppm. After forming a porous layer (pure quartz) to serve as an external cladding on this base material by a method, it was heated in an electric furnace.
F-added transparent vitrification was performed in an SFe mixed atmosphere. The relative refractive index difference between the core and cladding was 0.3%. Next, using a graphite resistance furnace, a cutoff wavelength of 0.85 μ
A line was drawn so that it became m.

FIG. 6 shows the loss wavelength characteristics of the produced optical fiber. 1
At wavelengths shorter than μm, the loss is 1000 dB/Km, but at 1.0 to 1.3 μm, the loss is 4 dB/Km.
It was found that a sufficiently low loss of about m was achieved, and that a high quality Nd-added base material could be manufactured by the method according to the present invention.

Example 4 A porous base material produced under the same conditions as in Example 1 was used, and dehydration, Nd addition, and transparent vitrification treatment were performed using the same electric furnace. However, the following method was used for dehydration treatment.

First, the porous base material is placed in the electric furnace soaking section, and
He (5I!/min) up to 00'C, C1g (70
cc/min) dehydration treatment was performed under a mixed atmosphere. The temperature increasing conditions are 500°C/hour for 0 to 1000°C, 1000°C
~1400°C, the rate was 200°C/hour.

Next, at 1400℃ under l1e (5j2/min) atmosphere,
After holding for 8 hours, NdCl3 and 1ie (5β・min)
Heat treatment was performed in a mixed atmosphere at a heating rate of 200°C/hour up to 1500°C. Note that the temperature of NdCl3 is 1
The temperature was 400°C.

As a result of quantitative chemical analysis of the amount of Nd added after treatment, it was found that Nd was at the detection limit (1 ppm or less). This shows that if dehydration and heat treatment are performed at a temperature exceeding 1400°C, the bulk density of the base material increases to a value that is inappropriate for the diffusion addition of Nd.

〔Effect of the invention〕

As explained above, according to the method for manufacturing a functional quartz optical fiber preform according to the present invention, the process of synthesizing a porous preform in the conventional VAD method, dehydrating the porous preform, and adding a dopant material that imparts functionality. By separating the additions, there is an advantage that materials with high melting points (rare earth elements and transition metals) can be easily added. Furthermore, since a porous base material is used, there is also the advantage that sufficient dehydration can be performed.

[Brief explanation of drawings]

Figure 1 is a schematic diagram showing the main parts of a conventional base material synthesis apparatus using the MCVAD method, Figure 2 is a schematic diagram of a conventional base material synthesis apparatus using the PCVAD method, and Figure 3 is a diagram for implementing the method of the present invention. Fig. 4 is a diagram showing the Nd ion addition concentration of the base material manufactured in Example 1 and the dependence on the temperature of the NdCl3 raw material, and Fig. 5 shows the Nd'' ion addition concentration and FIG. 6 is a diagram showing the relationship with processing time, and FIG. 6 is a diagram showing the loss wavelength characteristics of the optical fiber in Example 3. 1...Support quartz gap, 2...Synthetic rad bottom,
3...Synthetic core layer, 4...To trace component raw material channel 5...Sub-burner, 6...Main burner, 7.
...Sudulator, 8 ...Minor component raw material heating furnace, 9
... Raw material blowing nozzle, 10 ... Plasma flame, 11
...Glass inlet for plasma, 12...Minor component raw material boat, 13...Quartz loft, 14...Synthetic quartz (addition of trace components), 15...Exhaust pipe, 16...Temperature Articulator, 17... RF coil for plasma generation, 18
... Heat exchanger, 19 ... Trace component raw material holding tube, 21
... Electric furnace heater, 21 ... Seed rod, 22 ... Quartz furnace tube, 23 ... Porous base material, 24 ... NdC13
Raw material port. Applicant's agent Masaki Amemiya Figure 3 Uta-mi (pm) Figure 6

Claims (4)

[Claims] (1) In a method for producing an optical fiber base material in which a porous body produced by the VAD method is heat-treated and a trace component with a high melting point is added, the porous body is treated in an inert gas atmosphere containing a dehydrating gas. A method for producing a functional quartz optical fiber preform, which is then heat-treated in an inert gas atmosphere, and finally transformed into transparent vitrification in an inert gas atmosphere containing trace component raw materials. (2) The method for manufacturing a functional quartz optical fiber preform according to claim 1, wherein the temperature of the dehydration treatment and the heat treatment in an inert gas atmosphere is 1400° C. or lower. (3) Functional quartz according to claim 1 or 2, characterized in that the heat treatment time in an inert gas atmosphere after dehydration treatment is changed in order to control the concentration of trace components added. A method for manufacturing an optical fiber base material. (4) In order to control the added concentration of the trace component, the temperature of the trace component raw material is changed in the process of vitrification treatment in an atmosphere containing the trace component raw material. A method for producing a functional quartz optical fiber base material according to any one of Items 1 to 3.