JPH0492825A - Production of silica glass and optical waveguide using same silica glass - Google Patents

Abstract

PURPOSE:To obtain the subject silica glass suitable for a fiber-type optic amplifier, etc., by doping a silica glass particle aggregate with Al and Er and sintering in a fluorine atmosphere while lowering the sintering temperature. CONSTITUTION:A silica glass fine particle aggregate (bulk density: preferably within a range of 0.4-0.7g/cm<2>) produced by the gas phase synthesis method is doped with Al and Er and then calcined (1400-1500 deg.C) in a fluorine atmosphere to obtain a silica glass doped with Al, Er and F. In case of producing an optical waveguide using the resultant glass, an inner core body is formed using the above-mentioned silica glass doped with Al, Er and F. An outer core layer composed of a glass material having a high refractive index than that of the above-mentioned silica glass doped with three components is formed on the outer periphery of the above-mentioned inner core body and a clad layer composed of a glass having a lower refractive index than that of the glass constituting the outer core layer is formed on the outer periphery thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing quartz glass suitable for fiber-type optical amplifiers and the like, and a guiding waveguide using the quartz glass obtained thereby.

[Conventional technology]

Erbium-doped optical fibers are known as fiber-type optical amplifiers. However, this erbium-doped optical fiber has a disadvantage that its operating characteristics have a relatively large dependence on wavelength, and the operating gain changes greatly due to slight fluctuations in the wavelength of the communication light source.

Therefore, in recent years, optical fibers doped with both aluminum and erbium have been developed as a solution to the above-mentioned disadvantages due to their small wavelength dependence.

The present inventors have previously proposed Japanese Patent Application No. 2-49100 as a preferable method for producing quartz glass doped with aluminum and erbium.

However, silica glass doped with aluminum has a high melt viscosity (
The sintering temperature must be high when sintering the soot to make it transparent, and in a sintering furnace using a normal quartz muffle, the amount of aluminum added is 0, due to the upper limit of the sintering temperature.
It will be limited to 5 vt% or less. Further, even if the amount of aluminum added is 0.5 wt % or less, the sintering temperature is high as described above, which causes the disadvantage that the life of the quartz matsufuru is shortened.

[Problem to be solved by the invention]

Therefore, an object of the present invention is to provide a manufacturing method that can reduce the sintering temperature when manufacturing quartz glass co-doped with erbium and aluminum.

[Means to solve the problem]

This problem can be solved by doping a quartz glass fine particle aggregate with aluminum and erbium, and then sintering this fine particle aggregate in a fluorine atmosphere.

The present invention will be described in detail below.

First, a silica glass fine particle aggregate to serve as a matrix is prepared. This quartz glass fine particle aggregate can be produced by VAD method, OVD method,
It is obtained by a well-known gas phase synthesis method such as the method, and is made of fine particles made of silicon oxide or a mixed oxide of silicon oxide and a dopant such as germanium oxide or boron oxide synthesized by thermal oxidation reaction or flame hydrolysis reaction. It is a porous body made by depositing.

The shape of this quartz glass fine particle aggregate is a rod-like shape in which quartz glass fine particles are deposited in the axial direction at the tip of a rod-shaped starting base material if the VAD method is used, and a rod-like shape if it is made by the OVD method. The cylindrical shape is obtained by depositing silica glass fine particles on the outer peripheral surface of the starting base material in the radial direction and then pulling out the starting base material, but the present invention is not limited to this.

This quartz glass fine particle aggregate has a bulk density of 0.4 to
The bulk density is preferably in the range of 0.7 g/am', and the bulk density is preferably uniform between the center portion and the surface portion. If the bulk density is less than 0.4 g/cs, the mechanical strength will be insufficient and it will not be able to withstand handling such as permeation with an alcohol solution of aluminum chloride and erbium chloride in the next process, and if it exceeds 0.7 g/cs, the above-mentioned The alcohol solution will not penetrate quickly and sufficiently into the center of the aggregate.If the bulk density is less than 0.4 g/c11, heat treatment in an inert atmosphere such as helium or argon will reduce the It can be increased within the range of .4 to 0.7 g/cm''. The heating temperature for this differs depending on the type of glass constituting the silica glass fine particle aggregate, and is 1200 to 130
In the temperature range of 0°C, glass made of quartz glass with germanium oxide, boron oxide, etc.
Heat treatment is performed in the range of 00 to 1100°C. Through this heat treatment, the surfaces of the glass particles constituting the silica glass particle aggregate are melted, and the gaps between the glass particles are reduced, and the bulk density is also reduced to 0.4 to 0.7 g/am.
``Increases to a certain degree.

In addition, in the case of the silica glass fine particle aggregate obtained by the ordinary VAD method, the bulk density of the central part is high < (0,4
~0.45g/cm”), and the surface area is lower (about 0.45g/cm”).
0.25g/c++"). Therefore, it does not give good results in uniformly penetrating the alcohol solution. For this reason, the bulk density of the silica glass fine particle aggregate tends to be The VAD method is preferable because it can obtain a result with no difference between the surface and the surface.For example, when forming a silica glass particle aggregate, the temperature at the center and the surface of the aggregate at the glass particle deposition site is preferably The temperature difference can be reduced by 1 by using an additional heating burner, etc.
By adopting a method of keeping the temperature within 00°C, a silica glass fine particle aggregate with a uniform bulk density can be obtained. It is also possible to increase the bulk density of only the surface portion of a silica glass fine particle aggregate obtained by a normal VAD method by heating it multiple times for a short period of time at a temperature close to the melting temperature of the glass.

Separately, an alcohol solution in which aluminum chloride and erbium chloride are mixed and dissolved is prepared. As aluminum chloride, an anhydrous trichloride salt or a hydrated salt is used. Further, as erbium chloride, an anhydrous trichloride salt is used. Further, as the alcohol, methanol, ethanol, isopropyl alcohol, butanol, etc. are used, preferably having 2 carbon atoms.
~5 monohydric alcohols are used. The concentration of aluminum chloride and erbium chloride is determined by the amount of dopant added, and is usually about 1 to 30% by weight for aluminum chloride and 0.1 to 1% by weight for erbium chloride, although it is not limited. Alternatively, aluminum chloride and erbium chloride may be dissolved in the same or different alcohols, and the two solutions may be mixed at an appropriate mixing ratio.

Next, the thus obtained mixed alcoholic solution of aluminum chloride and erbium chloride is allowed to permeate into the silica glass fine particle aggregate. The simplest method for this infiltration operation is to immerse the aggregate in a mixed alcohol solution for about 0.5 to 24 hours. It is also possible to drop, apply, or spray the mixed alcohol solution onto the aggregate. Furthermore, before the infiltration operation, the aggregate may be left in a vacuum to suck out and eliminate gas, moisture, etc. in the voids of the aggregate to promote the infiltration of the mixed alcohol solution.

The mass impregnated with the mixed alcohol solution in this way is then heated in an inert gas atmosphere at 70 to 1
The alcohol is thoroughly removed by heating at 00°C for 96 hours or more. Of course, reduced pressure drying can also be used together.

Next, this dried aggregate is heat-treated in a heating furnace such as an electric furnace while flowing chlorine gas to remove moisture (hydroxyl groups) remaining in the aggregate.

Next, this aggregate is heat-treated in a fluorine atmosphere to dope fluorine into the quartz glass particles and melt the quartz glass particles to make transparent glass. A quartz glass body is obtained.

Fluorine compounds for forming a fluorine atmosphere include:
SiFm, CF, SFa, CtCOtF*, etc. are used, and a fluorine atmosphere is created by introducing one or a mixture of these into the heating furnace as is or diluting with an inert gas such as argon or helium. I can do it. A heating temperature in the range of 1,400 to 1,500°C is sufficient, and transparent vitrification is possible even if the temperature does not exceed 1,500°C.

In this method of manufacturing quartz glass, quartz glass fine particle aggregates doped with erbium and aluminum are heat-treated in a fluorine atmosphere to add fluorine to lower the melt viscosity of the glass, making it difficult to make transparent glass. The sintering temperature for this purpose can be lowered.

By the way, the refractive index of the erbium-, aluminum-, or fluorine-doped quartz glass obtained in this way is reduced by fluorine doping in accordance with the doping amount. For this reason, in an optical fiber with a core made of silica glass and a cladding made of fluorine-doped silica glass, it is no longer possible to increase the relative refractive index difference, which is necessary to obtain a high-efficiency, high-gain fiber-type optical amplifier. It becomes difficult to obtain a small mode field diameter (MFD) that is assumed to be small.

Therefore, in the guiding waveguide according to claim (2) of the present invention, in order to solve this problem, the inner core body is formed from quartz glass doped with aluminum, erbium, and fluorine, and the outer periphery of this inner core body is an outer core body made of glass having a higher refractive index than the three-component doped quartz glass, and a cladding body made of glass having a lower refractive index than the glass forming the outer core body around the outer periphery of the outer core body. There is.

Specifically, aluminum obtained as described above,
An erbium- or fluorine-doped quartz glass body is stretched to form a stretched rod, and a glass having a high refractive index, such as pure quartz glass, is provided on the stretched rod by a method or the like.

Next, on this outer core body, a glass having a low refractive index, such as fluorine-doped quartz glass, etc., is provided on the outer core body by a similar method to form a cladding body. This wood is then spun into a fiber using a conventional method.

Figure 1 shows an example of the refractive index distribution of a fiber obtained by such a method, where reference numeral 1 indicates an inner core made of aluminum, erbium, and fluorine-doped silica glass.
Reference numeral 2 indicates an outer core made of pure silica glass, and reference numeral 3 indicates a cladding made of fluorine-doped quartz glass.The relative refractive index difference between the inner core 71 and the outer core 2 is -0,2.
%, and the relative refractive index difference between the outer core 2 and the cladding 3 is -0.7%.

In such a fiber, it is possible to have a large effective relative refractive index difference between the core and the cladding, and a highly efficient and high gain fiber type optical amplifier can be constructed.

A specific example will be shown below.

(Example) The overall bulk density was 0.45 g/cm by the VAD method using a silica glass fine particle deposition burner and a heating burner.
A uniform silica glass particle aggregate (weight 208 g) was obtained.Next, the above-mentioned quartz was added to a solution of 200 g of AσC1!, 20 wt% ethanol solution and 250 g of ErC (lso, 54 wt% ethanol solution). When the glass particle aggregate was immersed, 141 g of the mixed solution was absorbed.Then, the pressure was reduced to about 30 torr at room temperature and left to dry for 3 days.This was placed in a heating furnace.
The inside of the furnace is a helium atmosphere with a chlorine gas concentration of 0.5%9
After heating to 00° C. to dehydrate, the material was heated to 1,500° C. in a helium atmosphere containing 10% concentration of 5iF4, and sintered to obtain a transparent glass body. Er in this transparent glass body is 0.1vt%, and Aff is 2
It was vt%. This transparent glass body is stretched to form a stretched rod, and an external core body made of pure silica glass and a cladding body made of fluorine-doped quartz glass are provided on the stretched wood, and the fibers are spun using a conventional method. A fiber having a refractive index distribution as shown in FIG. 1 was obtained.

Into this fiber, as a pump light, 1.48μ 45mW
When inputting a laser beam of
It was found that optical amplification was performed with a high efficiency of /mW. Further, the gain fluctuation could be suppressed to within 3 dB within a range of 25 n■ centered around 1.552 μl. The gain at this time was 30.5 dB.

(Conventional example) In the example, the atmosphere during transparent vitrification was 10
When carried out in a 0% helium atmosphere, the sintering temperature was 1
Even if the temperature was raised to 550°C (limit temperature of quartz matzuru), a transparent glass body could not be obtained.

(Comparative example) A fluorine-doped quartz glass serving as a cladding body was attached externally directly onto the drawn rod obtained in the example, and this was spun using a conventional method to obtain a fiber having a refractive index distribution as shown in Fig. 2. Obtained. In Fig. 2, reference number 1] indicates the core, and reference number 12 indicates the cladding. When this fiber was operated for optical amplification in the same manner as in the example, the gain was as low as 0.8 dB/mW.

〔Effect of the invention〕

As explained above, the method for manufacturing quartz glass of this invention is as follows:
The silica glass fine particle aggregate obtained by vapor phase synthesis is doped with aluminum and erbium, and then this fine particle aggregate is sintered in a fluorine atmosphere. It is possible to lower the temperature), extend the life of the heating furnace, and increase the amount of aluminum doped.

Furthermore, the waveguide of the present invention has an inner core made of quartz glass doped with aluminum, erbium, and fluorine, and is provided on the outside of this inner core, and has a refractive index higher than that of the quartz glass forming the inner core. It consists of an outer core body made of glass, and a cladding body provided outside the outer core body and having a lower refractive index than the glass forming the outer core body, so that the effective relative refractive index difference can be increased. This makes it possible to perform highly efficient optical amplification.

[Brief explanation of the drawing]

Claims (2)

[Claims] (1) A quartz glass particle aggregate obtained by vapor phase synthesis is doped with aluminum and erbium, and then this particle aggregate is sintered in a fluorine atmosphere to produce quartz glass doped with aluminum, erbium, and fluorine. A method for producing quartz glass characterized by obtaining glass. (2) An inner core made of quartz glass doped with aluminum, erbium, and fluorine, and an outer core made of glass that is provided outside of this inner core and has a higher refractive index than the quartz glass that makes up the inner core. and a cladding body provided outside the outer core body and having a lower refractive index than the glass constituting the outer core body.