JPH04300218A - Production of quartz glass doped with rare-earth element - Google Patents

Abstract

PURPOSE:To provide a process for producing quartz glass doped with rare-earth element and useful as a material for optical fiber laser, light amplifier, sensor element, etc. CONSTITUTION:The objective quartz glass doped with rare-earth element is produced by forming silica soot by the flame-hydrolysis of a glass-forming raw material gas in an oxyhydrogen flame, depositing the soot to form a porous glass preform and sintering the preform at a high temperature to obtain transparent glass. In the above process, a sublimable organic rare-earth element compound is supplied in the form of vapor together with a halogen-free raw material gas for glass into the oxyhydrogen flame to effect the deposition of the silica soot containing rare-earth element oxide formed by the flame-hydrolysis and the formed porous glass preform is sintered at a high temperature to obtain transparent glass.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for producing rare earth element-doped quartz glass, particularly for producing rare earth element-doped quartz glass useful for optical fiber lasers, optical amplifiers, sensor elements, etc. It is about the method.

0002

[Prior Art] Rare earth element-doped silica glass has an optical function, so it can be used in optical fiber lasers, optical amplifiers, etc.
It is used as a sensor element, etc. However, the MCVD method has been known for manufacturing this type of quartz glass (see Japanese Patent Application Publication No. 63-501711), but this method involves heating rare earth element oxides to high temperatures and vaporizing them. Since it is supplied to the reaction system, it has the drawbacks that it is difficult to control the supply amount and that it is difficult to obtain a large base material.

On the other hand, in the production of rare earth element-doped quartz glass, a silicon compound as a raw material for glass formation is sent into an oxyhydrogen flame, and silica fine particles produced by the flame hydrolysis are deposited to form a porous glass. There is a method of making a base material, immersing this porous glass base material in a solution of a rare earth element compound to impregnate the porous glass base material with the rare earth element compound, and then sintering this at high temperature to create transparent glass. It has been proposed (see Japanese Patent Publication No. 58-3980),
For this, the amount of dope can be controlled by the concentration of the solution,
Although it has the advantage that it can be applied to compounds with low vapor pressure, this method involves immersing a porous glass base material in a solution of a rare earth element compound, and when drying, the solvent is transferred to the surface of the porous glass base material by capillary action. When the solute moves to the surface, the solute also moves and accumulates near the surface.
There is a problem in that the resulting glass has a dopant concentration distribution, and in extreme cases it can break due to the difference in thermal expansion coefficient between the surface and the inside. There is also the disadvantage that a part of the rare earth element compound is volatilized during the oxidation process, making it impossible to obtain a compound with the desired doping amount.

Therefore, it has been proposed to add a step of oxidizing the dope material in the porous glass matrix in an oxide atmosphere maintained at a temperature below the melting point of the dope material. However, it is difficult to completely convert rare earth element chlorides into oxides by oxidizing them, and a considerable amount of rare earth element chlorides remains even after heat treatment in an oxidizing atmosphere. This volatilizes during the glass process, and even if it is incorporated into the glass without volatilizing, it cannot enter the glass network in its chloride state and separates as microcrystals, causing the glass to become cloudy. state, causing optical transmission loss.
A disadvantage is that the lasing efficiency is also low.

[0005]

[Problems to be Solved by the Invention] Therefore, the method for manufacturing rare earth element-doped quartz glass involves producing fine glass particles by flame hydrolysis of a glass raw material in a vapor phase.
In a method for producing a glass base material for optical fibers, in which a porous glass body is made by laminating these materials and then heated and melted, silicon tetrachloride, trichlorosilane, and monosilane are used as glass raw materials, and organic aluminum and erbium β- A method using a diketone compound has been proposed (see JP-A-2-275724), which makes it possible to synthesize a base material that is larger than the conventional MCVD method and has a uniform concentration distribution of erbium. Although it is possible to
The glass raw material used here is silicon tetrachloride,
It is said to contain a halogen, such as trichlorosilane, and since this halogen-containing silicon compound promotes the decomposition of organic rare earth elements, it is decomposed before it is supplied to the flame. The disadvantage is that its supply becomes difficult.

[0006]

[Means for Solving the Problems] The present invention relates to a method for producing rare-earth element-doped quartz glass that solves the above-mentioned disadvantages. In a method for manufacturing silica glass, in which a porous glass base material obtained by depositing the generated silica particles is sintered at high temperature and turned into transparent glass, a sublimable organic rare earth element compound is used together with a halogen-free glass forming raw material gas. Supplying silica in the gas phase into an oxyhydrogen flame and depositing fine silica particles containing rare earth element compounds produced by this flame hydrolysis to create a porous glass base material, which is then sintered at high temperature to form transparent glass. It is characterized by:

That is, as a result of various studies on effective manufacturing methods for rare-earth element-doped quartz glass, the present inventors found that adding a rare-earth element compound to quartz glass is a method of forming a glass such as a silicon compound that does not contain halogen. During the flame hydrolysis of the raw material in an oxyhydrogen flame, a rare earth element compound is supplied in the gas phase into the oxyhydrogen flame, and the rare earth element compound is flame-hydrolyzed at the same time as the silicon compound, and the rare earth element oxide generated here is converted into a silicon compound. It has been found that the porous glass base material can be formed by depositing it on a carrier together with silica fine particles generated by flame hydrolysis.

[0008] Furthermore, when chlorides such as ErCl3 and NdCl3 are used as the rare earth element compounds used here, since these have high boiling points, it is necessary to heat them to a high temperature and evaporate them before supplying them to the reaction system. However, the controllability of the supply amount can be improved by using a sublimable organic rare earth element compound that can be vaporized at a lower temperature than chloride. In addition, when using a known raw material gas containing halogen such as silicon tetrachloride as a raw material gas for glass formation, the organic rare earth element compound is decomposed before being supplied to the flame as described above. However, the present invention was completed after confirming that this problem could be solved by using a glass raw material gas that does not contain halogen. This will be explained in further detail below.

[0009]

The present invention relates to an improved method for producing rare earth element-doped quartz glass. In the process of producing a porous glass base material by depositing fine silica particles produced by flame hydrolysis of a glass forming raw material, the present invention uses a sublimable organic rare earth element compound in a gas phase together with a halogen-free glass forming raw material gas. The rare earth element oxide generated by flame hydrolysis of this organic rare earth element compound is deposited together with the silica fine particles generated by the flame hydrolysis of a halogen-free silicon compound to form a porous glass containing rare earth element oxide. A base material is created and then sintered at high temperatures to create transparent glass.

[0010] The production of the porous glass preform by flame hydrolysis of the glass forming raw material in the present invention is carried out by the VAD method and the OVD method, which are well known as methods for producing preforms for optical fibers.
It can be done according to the law. However, silicon compounds such as silicon tetrachloride, germanium tetrachloride, which is well known as a dopant for optical fibers, and alumina, which is known to improve optical amplification characteristics, are used as raw materials for forming this glass. If aluminum trichloride, etc. for co-doping is supplied at the same time, it will accelerate the decomposition of organic rare earth element oxides, so this is not recommended for organic silicon compounds, germanium compounds, and aluminum compounds that do not contain halogens. It is necessary to do so.

These halogen-free glass forming raw materials are fed into an oxyhydrogen flame and are hydrolyzed in this flame to become silica, germania, and alumina, and the silica fine particles containing germanium and alumina are made from quartz glass, etc. However, in the present invention, sublimable organic rare earth element compounds are vaporized in the oxyhydrogen flame during flame hydrolysis of this halogen-free glass forming raw material. Since the rare earth element oxide generated by the flame hydrolysis of the rare earth element compound is deposited on the carrier together with the above-mentioned silica fine particles generated by the flame hydrolysis of the glass forming raw material, the rare earth element containing the rare earth element oxide is supplied as a phase. A porous glass matrix is formed.

The organic rare earth element compounds used for this purpose include rare earth elements such as neodymium, europium, and cerium represented by the general formula R-CO-CH=CO-R'.
R and R' are an alkyl group, an allyl group, a fluorine-substituted alkyl group, a heterocyclic group, etc., such as acetylacetonite, trifluoroacetylacetonite, hexafluoroacetylacetonite, dibenzoyltrifluoroacetonite, zine Examples include complexes such as benzoylmethanato, dipivaloylmethanato, thenoyltrifluoroacetylacetonite, and furoyltrifluoroacetylacetonite. These may be stored in an evaporator, heated in an oil bath to vaporize it, and then supplied into the reactor with a carrier gas.

[0013] This sublimable organic rare earth element compound, especially the rare earth element acetylacetonite complex, tends to react with chloride at high temperatures and deposit a gel-like substance in the burner. When supplying glass-forming raw materials to an oxyhydrogen flame, the glass-forming raw materials are non-chloride alkoxy compounds such as tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, and tetramethoxygermanium, and aluminum compounds are also triethyl. Must be an organic compound such as aluminum.

The porous glass base material containing the rare earth element oxide thus obtained is then fired at high temperature to form a transparent glass into rare earth doped quartz glass, and this heating is performed using electricity. In the furnace 1,400-1,000
°C, preferably in an inert gas atmosphere such as helium, but this atmosphere may also be in the presence of a trace amount of halogen gas for the purpose of dehydration, or even for conversion to oxides. In order to make it complete, it may be done in the presence of a trace amount of oxygen gas.

[0015]

[Example] Next, an example of the present invention will be given. Example 1 Hydrogen gas at 5.5 liters/min and oxygen gas at 8.0 liters/min were supplied to a quartz concentric multi-tube burner to form an oxyhydrogen flame, and a tetragonal flame was formed at the center of the burner. Methoxysilane as carrier gas (oxygen gas 0.17 liters/min)
At the same time, trisdipivaloylmethanatoerbium is placed in an evaporator connected to a nozzle outside the nozzle that supplies this tetramethoxysilane, and while the evaporator is heated to 200 °C in an oil bath, a carrier gas (
This organic rare earth element compound was supplied to the burner by blowing argon gas (0.05 liter/min), and the fine particles generated by flame hydrolysis of these gases were deposited and grown in the axial direction of the starting material for 8 hours. As a result, it has an outer diameter of 43 mm, a length of 300 mm, a weight of 150 g, and an average bulk density of 0.
A porous glass preform having a density of 34 g/cm3 was obtained.

[0016] Next, this porous glass base material was placed in an electric furnace and heated at 1,600°C in a helium gas atmosphere to turn it into transparent glass, and quartz glass was obtained.
Analysis of this material using the ICP method revealed that it contained 500 ppm of erbium oxide.

Next, an optical fiber preform with this quartz glass as the core and fluorine-doped quartz glass as the cladding was made, and the optical amplification characteristic of this optical fiber was measured, and it was found to be 1.4. μm pump light 10m
Pumped with W, amplification gain of 1.55 μm signal light is 22
I got dB.

Example 2 A porous glass base material was produced by the VAD method in the same manner as in Example 1, but instead of tetramethoxysilane, tetraethoxysilane was entrained in a carrier gas (argon 0.19 liters/min). At the same time, tetraethoxygermanium was supplied as a carrier gas (argon 0.07 liters/min), and triethylaluminum 0.
．． Furthermore, tristenoyl trifluoroacetinyl acetoerbium was added to the evaporator, and while the evaporator was heated to 200°C in an oil bath, carrier gas (argon 0.05 liter/min) was blown into the organic rare earth. When the elemental compound was supplied to the burner and the obtained silica fine particles were deposited and grown on the starting material for 8 hours,
A porous glass preform having an outer diameter of 38 mm, a length of 300 mm, a weight of 110 g, and an average bulk density of 0.32 g/cm3 was obtained.

[0019] Next, this porous glass base material was placed in an electric furnace and heated at 1,600°C in a helium gas atmosphere to turn it into transparent glass, yielding quartz glass, which was processed using the ICP method. As a result of analysis, it was found to contain 800 ppm of erbium oxide. When this porous glass base material was placed in an electric furnace and heated at 1,600°C in a helium gas atmosphere to make it transparent, quartz glass was obtained, which was analyzed using the ICP method. As a result, it contained 800 ppm of erbium oxide.

Next, an optical fiber preform with this quartz glass as a core and a fluorine-doped quartz glass as a cladding was made, and the optical amplification characteristic of this optical fiber was measured, and it was found that this was 1.4 μm. pump light 10m
Excited with W, amplification gain of 1.55 μm signal light is 35
I got dB.

[0021]

Effects of the Invention The present invention relates to a method for producing rare earth element-doped quartz glass, which involves heating a porous glass base material obtained by depositing fine silica particles produced by flame hydrolysis as described above. In the manufacturing method of quartz glass, which is sintered to make transparent glass, a sublimable organic rare earth element compound is supplied in the gas phase together with a halogen-free glass forming raw material, and the rare earth element oxide obtained by flame hydrolysis is This method involves creating a porous glass base material containing the elements and firing it at a high temperature to turn it into transparent glass. According to this method, the rare earth element compound is supplied as a sublimable organic rare earth element compound, so it can be gasified at a low temperature. can and
This will not be decomposed by the glass forming raw materials,
Since this material becomes rare earth element oxide by flame hydrolysis, quartz glass doped with rare earth element oxide can be easily obtained, and the rare earth element doped quartz glass obtained in this way is Advantages include utility as optical fiber lasers, optical amplifiers, and sensor devices.

Claims (3)

[Claims] [Claim 1] Production of quartz glass by sintering a porous glass base material obtained by depositing silica fine particles produced by flame hydrolysis of a glass forming raw material gas in an oxyhydrogen flame and turning it into transparent glass by sintering it at a high temperature. In this method, a sublimable organic rare earth element compound is supplied in the gas phase into an oxyhydrogen flame together with a glass-forming raw material gas that does not contain halogen, and silica fine particles containing rare earth element oxides produced by this flame hydrolysis are deposited. A method for producing rare earth element-doped quartz glass, which comprises making a porous glass base material, sintering it at high temperature, and turning it into transparent glass. 2. The method for producing rare earth element-doped quartz glass according to claim 1, wherein the sublimable organic rare earth element compound is an acetylacetonate complex of a rare earth element. 3. The method for producing rare earth element-doped quartz glass according to claim 1, wherein the halogen-free glass forming raw material is an organic compound of silicon, germanium, and aluminum.