JPH03265537A - Rare-earth element-doped glass and its production - Google Patents

Abstract

PURPOSE:To obtain a glass doped with a high-purity rare-earth element and Al, excellent in transprency and used for a functional optical fiber or an optical waveguide at a relatively low sintering temp. by adding a rare-earth element into an SiO2-based host glass doped with Al and F. CONSTITUTION:The rare-earth element-doped glass is obtained by the following method. Namely, a preform of quartz-based porous glass having connected open cells is dipped in a soln. contg. rare-earth element ion and aluminum ion to impregnate the preform in the doping stage, the doped base material is dried to deposit the rare-earth element and aluminum salt in the cell of the preform or further the deposited salt is oxidized and stabilized in the drying stage, and the dried preform is sintered and made nonporous in the sintering stage to produce the rare-earth element-doped glass. In this process, a fluorine doping stage for heat-treating the preform in a fluorine-contg. atmosphere is interposed between the drying stage and the sintering stage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to rare earth element doped glasses, particularly rare earth element doped glasses suitable for use in active optical devices such as lasers and optical amplifiers in the form of optical fibers or optical waveguides. This invention relates to element-doped glass and its manufacturing method.

(Prior Art) As functional optical fibers containing rare earth elements in their cores, fiber lasers [Reference 1.2] and optical amplifiers [Reference 1.2] and optical amplifiers [Reference 1.2] utilize optical amplification by stimulated emission between electronic levels of rare earth element ions.
Reference 3.4] has been reported. Among the optical fibers mentioned above, Er-doped fibers are used for optical communications1.
Since it exhibits an optical amplification effect at wavelengths in the 55 μm band, it is attracting attention as an in-line optical amplifier that does not require photoelectric conversion.

Furthermore, in order to improve the characteristics of the functional rare earth doped fiber, there is a technique of co-doping A2 at the same time as the rare earth element. β-codoping has two advantages as shown below.

First, the amount of Si, glass, or Ge0z-5iOa glass used in general optical fibers is approximately 0.1w.
Addition of t% or more of rare earth elements has the disadvantage of causing so-called concentration quenching.

This is a phenomenon in which the energy of excited electrons is easily lost through non-radiative processes when rare earth ions aggregate (cluster) together in the glass.
The lifespan and efficiency of light emission are impaired. /l co-doping overcomes this drawback and allows relatively high concentrations of rare earth element doping without clustering [Reference 5].

When rare earth elements are doped at a high concentration, sufficient amplification gain can be obtained even if the action length between the excitation light and the rare earth ions is short, so a compact laser or optical amplifier can be realized.

Second, codoping with Aβ may change the emission spectrum of rare earth ions. In particular, the emission spectrum in the 1.55 μm band of quartz-based Er-doped glass is AI2I2
- The wavelength band that can be amplified is expanded. This is a major advantage when used as an amplifier in a wavelength division multiplexing transmission system.

Conventionally, as a method for manufacturing an optical fiber co-doped with a rare earth element and /l, there is a solution impregnation method (MCVD solution impregnation method) based on the M (': V D method).
J, A1n5lie et al. [Reference 6].

The method involves first depositing a glass layer to serve as a cladding with a relatively low refractive index on the inside of a starting quartz glass tube according to the usual method, and then forming a soot-like porous layer on the inside of the cladding at a lower temperature than usual. 1. Next, a solution containing rare earth ions and AI2 ions is impregnated into the pores of the porous core glass layer, and after a drying and dehydration process, the porous core glass layer is sintered in a He gas flow. It becomes solid and non-porous. below,
Return to the normal procedure and collapse to obtain a solid rod-shaped optical fiber preform. According to this method, it is said that 3 wt.% or more of rare earth elements can be added without clustering of rare earth ions in the glass.

References 1) C, J, Koester and E, 5ni
tzer: Appl, Opt.

3, 1182 f19641.

2) S.B. Poole et al.: El
ectron, Lett, 21°P, 738 f1
9851.

3) R.J., Mears et al.
: Electron, Lett, 23°P,
1026 (19871.

4) E. Desurvire et al.: O
ot, Lett,, 12.888f19871.

5) K. Arai et al.: J. App.
I, Phys., 59.3430 (19861.

6) B, J, A1n5lie et al.:
Mater, Lett, 6.139 (19881).

By the way, the above-mentioned solution impregnation method itself is a method that has been known for a long time, and in recent years it has been widely adopted as a method for doping silica-based optical fiber base materials with elements that are difficult to add using the vapor phase method, such as rare earths and transition metals. It became so. Of course, it is also possible to produce doped glass by impregnating a porous glass (soot) base material produced by the VAD method or the external method with a solution.

As is well known, the VAD method or external process (so-called outside process) makes it easier to produce a glass base material that is large, homogeneous, and has excellent optical properties compared to the MCVD method (filling process). be able to.

Therefore, the present inventors developed V
Solution impregnation method based on AD method (VAD solution impregnation method)
However, we thought that Aj2 doping might be possible, and attempted to produce AI2 doped silica glass using the methods of Experiment 1 and Experiment 2 shown below. Note that Experiment 1 and Experiment 2 are also Comparative Example 1 and Comparative Example 2, respectively, which will be described later in the present invention.

(Experiment 1 = Comparative Example 1) Average bulk density 0.4 to 0-5 g/
cm" of pure quartz composition was impregnated by immersing it in a methyl alcohol solution in which various concentrations of aluminum chloride were dissolved for 12 to 24 hours. After the impregnation, the solvent was evaporated and dried. at approximately 950°C in an oxygen stream.
The aluminum salts remaining in the soot were oxidized and fixed. At this time, the weight fraction of the added Al2,0 m to the dry weight of the soot (hereinafter referred to as impregnation concentration) was 0.3 to 3 wt.%.

Next, the soot was lowered at a rate of 2 mm per minute for sintering while maintaining a He gas atmosphere containing 1% CI2x and 5% 0□ by volume in an electric furnace with a center temperature of 1500°C. I did it.

In all cases, the base material after sintering did not become completely non-porous, and cracks occurred after cooling. In addition, the base material impregnated with Aβ at a high concentration had cavities inside. As a result of X-ray diffraction, no halo peculiar to the glass phase was observed, and it was confirmed that most of the material had changed to high melting point crystal phases of cristobalite (SiO,l) and mullite (3AJ2a03.2SiOzl) as shown in Figure 1. Ta.

Even when Er was impregnated at the same time as Al1, no porosity was achieved and no transparent glass was obtained.

(Experiment 2 = Comparative Example 2) Doped with 1.1 wt% P2O5 by VAD method,
A quartz-based soot base material having an average bulk density of 0.4 to 0.5 g/cm' was prepared. This was impregnated with the same Aβ solution as in Experiment 1, and dried, oxidized, and sintered under the same conditions.

This base material was not completely made non-porous, and cracks occurred, although to a lesser extent than in Experiment 1. The results of X-ray diffraction also showed no halo, and precipitation of high melting point crystal phases of cristobalite and aluminum phosphate (AJ2P04) was observed.

Even when Er was impregnated together with A2, transparent glass was still not obtained. In the base material impregnated with high concentration of Er, the second
As shown in the figure, precipitation of erbium phosphate (ErPO,l) was also observed.

The reason why transparent glass could not be obtained in Experiments 1 and 2 above is thought to be that the sintering temperature was lower in the VAD solution impregnation method in Experiments 1 and 2 than in the MCVD-based method. Ta. That is, it was considered that the precipitation of a high melting point crystal phase inhibited the progress of sintering.

By the way, according to the Aβ103-sio□ system phase diagram, the eutectic point of mullite and cristobalite is 1587±1O℃
In a composition with higher silica than the eutectic composition (Al1.03: 8wt, %), the liquidus temperature is between the eutectic point and the cristobalite melting point of 1726±5°C. Therefore, at the sintering temperature of 1500° C. in Experiment 1, the mullite and cristobalite that have once precipitated do not melt. In order to eliminate these high melting point crystal phases, 1587
Temperatures above 1726°C are required.

On the other hand, Aff corresponding to the composition of Experiment 2, O, -P-0-
-5in, although the detailed phase diagram of the system has not been reported, it is assumed that the situation is similar to that in Experiment I.0 For example, P
, O, -5iO- system, P2O5 = 1.1wt, liquid phase in %, II hot water temperature, temperature at which cristopalite disappears)
is 1700°C or higher. Also AI2. O, -P, O@
In the system, when A 12 zOl exceeds 30 wt.%, the liquidus temperature (disappearance temperature of AI2PO4) becomes 1500° C. or higher.

As an attempt, we ignited and rapidly cooled the base materials obtained in Experiments 1 and 2 above using an oxyhydrogen flame, and both became transparent glass, but many bubbles remained in the glass, making it difficult to use for optical purposes. It could not be put to practical use as glass.

From the above, the VAD solution impregnation method cannot produce Aβ-doped (or co-doped) glass like the MCVD solution impregnation method, and it is believed that the cause is the insufficient sintering temperature. Problems to be Solved by the Invention) In order to solve the problem of insufficient sintering temperature due to the VAD solution impregnation method, it is conceivable to increase the sintering temperature to 1600°C or 1700°C or higher, but such Raising the temperature involves technical and equipment difficulties.

First, the quartz glass furnace core tubes and jigs commonly used in soot base material sintering furnaces soften and deform at such high temperatures and cannot withstand long-term use. One possible solution to this problem is to use a high melting point ceramic furnace core tube instead of a quartz glass furnace core tube, but in that case, impurities would volatilize from the furnace core tube and get mixed into the base material. As a result, fiber transmission loss increases rapidly. This is a well-known fact in the industry.

Second, if sintering is performed at a temperature higher than the liquidus temperature, the base material may stretch and fall due to its own weight.

These problems are not limited to the VAD solution impregnation method.
This is a common problem in the sintering of porous glass produced using e-process.

By the way, in the MCVD solution impregnation method, the quartz glass tube used as the base material also serves as the reaction tube, and since it is directly heated with an oxyhydrogen flame, it can be easily heated to the high melting point crystal phase disappearance temperature. There is no need to worry about contamination with impurities. In addition, even if crystallization occurs during sintering, the process can be immediately transferred to the collab process at temperatures above 1900℃ without first cooling, so no cracks will occur due to thermal strain.Moreover, the crystalline phase will completely melt during collapse, forming a solid solid. A transparent glass base material is obtained by rapid cooling after curing.

[Purpose of the invention]

The present inventors have considered improvements to the glass composition in view of the problems encountered when producing a rare earth element + AI2 co-doped glass using an outside process such as the VAD method as described above, and have arrived at the present invention.

An object of the present invention is to provide a glass co-doped with rare earth elements + and β, which has a composition that allows a transparent glass to be obtained even at a relatively low sintering temperature.

Another object of the present invention is to create a rare earth element + AI which does not impair its luminescent properties even when doped with a high concentration of rare earth element.
An object of the present invention is to provide a dual-doped glass.

Still another object of the present invention is to produce the rare earth element + AI2 co-doped glass, particularly the rare earth element + AI2 co-doped glass with high purity and excellent transparency for functional optical fibers or guiding waveguides, by an outside process such as VAD method. The purpose is to provide a method that can also be manufactured by.

(Means for Solving the Problems) The rare earth element-doped glass according to claim 1 of the present invention comprises:
A rare earth element is added to a host glass having a composition of Sin co-doped with AI2 and F.

The rare earth element-doped glass according to claim 2 of the present invention includes:
A substance that increases the refractive index of the glass is further added to the host glass composition according to the first aspect of the present invention.

The rare earth element-doped glass according to claim 3 of the present invention includes:
A substance that lowers the softening temperature of the glass is further added to the host glass composition according to the first aspect of the present invention.

The rare earth element doped glass according to claim 4 of the present invention is 1
．． A rare earth element is added to a host glass having a composition of GeO□SiO co-doped with l and F.

A method for producing rare earth element-doped glass according to claim 5 of the present invention is to immerse a base material made of silica-based porous glass having connected open pores in a solution containing rare earth element ions and aluminum ions. A doping process in which rare earth elements and aluminum are impregnated into the material, and a base material after the beaving process is dried to deposit rare earth element and aluminum salts in the pores of the base material, or further, the deposited salts are oxidized. In a method for producing rare earth element-doped glass comprising a drying step for stabilization and a sintering step for sintering and making the base material non-porous after the drying step, the sintering step is performed after the drying step is finished. The process is characterized in that a fluorine doping process is performed during the process, in which the base material is heat treated in a fluorine-containing atmosphere.

The method for producing rare earth element-doped glass according to claim 6 of the present invention is characterized in that the fluorine doping step in claim 5 is carried out at a temperature lower than 1276°C, which is the sublimation temperature of aluminum fluoride, preferably at a temperature of 1000°C or lower. It is characterized by the fact that it is carried out in

The seventh aspect of the present invention provides a method for producing rare-earth element-doped glass, in which (1) or other This method is characterized by intervening a step of performing dehydration treatment in an atmosphere containing a gas phase of a chlorine compound and O2.

The basic glass composition of the present invention is R, O, -AugOz S
It is a tOzF-based glass (R is a rare earth element, F is doped to replace O), and is basically a high-silica, alkali-free silica-based glass. Therefore, properties such as expansion coefficient and softening temperature are close to those of quartz glass used in ordinary optical fibers, and the fusion properties with them are good. By using glass with a relatively low refractive index as the cladding material, an optical fiber (or optical waveguide) having a core-clad structure can be easily produced.

Furthermore, it has excellent fusion splicability with general silica fibers.

Furthermore, in the rare earth element-doped glass of the present invention, a high concentration of rare earth elements can be added without impairing the luminescence characteristics due to the coexistence effect of rare earth elements and Al, and sufficient amplification gain can be achieved even if the interaction length with excitation light is short. Therefore, it is possible to downsize the laser or optical amplifier. Further, when the rare earth element is Er, the wavelength band exhibiting optical amplification around 1.55 μm is widened due to the coexistence of A2, so the glass composition of the present invention is suitable for use in optical amplifiers.

These effects are equivalent to the known rare earth element + AI2 doped silica glass, but the rare earth element doped glass of the present invention is a new silica glass composition characterized by further containing fluorine. . The addition of fluorine has significant advantages in terms of the manufacturing process, as shown in the (effects) section below.

Rare earth elements and Al have the effect of increasing the refractive index of quartz glass, but fluorine conversely lowers it, so depending on the doping ratio of these elements, the refractive index of the glass will be lower than the quartz level, and the refractive index of the cladding will be lower. The difference may not be sufficiently secured. In this case, a component having the effect of further increasing the refractive index may be added to the basic glass composition.

Furthermore, since Al2F sublimes at 1276° C., sintering at a higher temperature reduces the amount of Al2 remaining in the glass. In this case, it is also possible to add a component that lowers the softening temperature of the glass to the basic glass composition to give preferable results. Such additives include G e
02 or p, o5 are particularly preferred. Both of them increase the refractive index of quartz glass and at the same time lower the softening temperature.

The former has a remarkable effect on increasing the refractive index, and the latter has a remarkable effect on lowering the softening temperature.As is well known, in the VAD method and the external method, both components can be easily added to the soot.

(Function) To produce a high-silica, alkali-free rare earth element + Aβ co-doped quartz glass, a hot liquid impregnation method using a porous glass matrix is simple, and the rare earth element and Aβ doping concentration is It has advantages such as easy adjustment, and is considered to be general. However, in the VAD solution impregnation method, if the impregnated base material is sintered without going through the fluorine doping step, a high melting point crystal phase precipitates as in the above-mentioned experimental example, making it difficult to make the material non-porous.

However, if fluorine is added in addition to rare earth elements and AP, it can be easily made non-porous and transparent glass even at a relatively low sintering temperature of 1500° C. or lower. Although the reason for this is not clear, (1) Melt viscosity is reduced by adding fluorine to the glass particles of the quartz-based base material. Therefore, sintering progresses quickly, and diffusion and homogenization of rare earth elements and AP into the glass is also promoted. ■Rare earths and A
This is presumed to be because the oxide of P reacts with fluorine and changes into a fluoride with a relatively low melting point as shown in Table 1.

If rare earth elements and/or Al1 are impregnated at a high concentration, diffusion and homogenization may be insufficient and devitrification may occur. However, since a small amount of fine particles are dispersed in a completely non-porous glass matrix, it immediately becomes transparent when heated to a high temperature using an oxyhydrogen flame or the like. At this time, no cracks occur or bubbles remain.

Therefore, if the glass composition of the present invention is used, a transparent, bubble-free rare earth element +/l co-doped glass product can be obtained even by an outside process such as a VAD solution impregnation method.

Incidentally, P (P, O,) is also known as a dopant that greatly reduces the solution viscosity of quartz glass, but when P is added in addition to the rare earth element and Al2 (when fluorine is not included), the above-mentioned As shown in Experimental Example 2, this induces the precipitation of high melting point crystals such as aluminum phosphate and erbium phosphate, which has the opposite effect.

Next, according to the method for producing rare earth element-doped glass of the present invention, a glass base material (lot) for a rare earth element-doped optical fiber can be produced, for example, by a VADi18 liquid impregnation method as follows.

A quartz glass soot base material is prepared by the VAD method, and is impregnated with a solution containing rare earth elements and Aβ ions.The solvent is then evaporated and dried to release rare earth element and AP salts into the pores of the soot material. to be deposited. In this case, as the solution raw material, an alcohol solution or an aqueous solution of chloride, hydrated chloride, nitrate, etc. can be used.

In addition, it is desirable that the soot base material impregnated with the above solution be heat-treated in an oxygen atmosphere prior to sintering.If chloride raw materials are used as the solution raw materials, they should be heated at relatively low temperatures. However, it easily evaporates and volatilizes, so if it is stabilized by oxidation, the reproducibility of the amount of dope into the glass will be improved. When nitrate is used as a solution raw material, the nitrate is 200
Since it decomposes into an oxide at a temperature of about 1000 yen, there is no need to carry out any particular oxidation step.

Further, prior to the sintering, CI2.
Also, when performing dehydration treatment in an atmosphere containing the gas phase of other chlorine compounds, it is desirable to add excess oxygen gas to the atmosphere. This is because the oxide becomes a chloride again and becomes easily volatilized.

Next, the solution-impregnated base material is sintered and made non-porous in a He atmosphere containing fluorine. As is well known, Si is a fluorine source.
Gases such as F, SF, and Freon can be used.

Therefore, according to the method for producing rare earth element-doped glass of the present invention, a rare earth element+AI2 co-doped glass rod that is transparent and free of residual bubbles can be obtained.

In order to process the rare earth element-doped glass rod obtained in this way into an optical fiber, for example, existing techniques such as forming a clad glass layer using an external method and then heating and drawing and spinning this are used. can be used. In this way, it is possible to obtain a rare earth element doped optical fiber or a guiding waveguide in which the entire or part of the light guiding portion is made of the rare earth element doped glass according to claims 1 to 4 of the present invention.

The above description is based on the case where a quartz glass soot base material manufactured by the VAD solution impregnation method is used, but of course, a quartz glass soot base material manufactured by the external method or sol-gel method can also be used.

According to the method for producing rare earth element-doped glass of the present invention, it is also possible to produce a thin film guided waveguide. For example, a flame hydrolysis method, which is an existing technique, can be used to form a thin film of porous quartz glass. The reaction film formation mechanism at this time is the same as the VAD method and the external method. A thermal CVD method may be used for this film formation. In this case, if the substrate temperature is set lower than when depositing a normal silica glass film, a soot-like porous glass film will be formed. .

Hereafter, in the same manner as in the case of manufacturing the glass base material for the rare earth element-doped optical fiber, solution impregnation drying, oxidation and sintering in a fluorine atmosphere are performed to obtain the rare earth element +! A co-doped glass thin film is obtained.

By combining this method with existing microfabrication techniques (channel formation and clad glass layer formation techniques), it is possible to fabricate a rare earth-doped optical waveguide of any shape.

(Example 1) Average bulk density 0.4 to 0.5 g produced by VAD method
Impregnation was carried out by immersing a soot with a pure quartz composition of 1/cm" in a methyl alcohol solution in which various concentrations of erbium chloride and aluminum were dissolved for 12 to 24 hours.

The AQ/Er molar ratio in the solution was set to 1-5. After the impregnation, the solvent is evaporated and dried, and the Er remaining in the soot is removed by heating to about 950°C in an oxygen stream.
and A9 salts were oxidized and fixed.

Next, dehydration treatment was performed by lowering the soot at a rate of 3 mm per minute while maintaining a He gas atmosphere containing 1% C20 and 10% 02 by volume in the electric furnace with a center temperature of 1000°C. Ta. After the dehydration was completed, the soot was once raised to the low temperature section, and the temperature at the center of the electric furnace was raised to 1300°C. Subsequently, the atmosphere in the furnace was changed to He gas containing 0.5 vo[,% SiF4, and the soot was lowered at a rate of 2 mm per minute for sintering.

As a result, Er203-AAzO3-5iOz-F glass rods co-doped with Er and Aβ at various different concentrations were obtained. The glass doped with approximately 0.3 wt.% or more of Er was devitrified immediately after sintering and had a pink opal glass-like appearance. An example of the X-ray diffraction pattern of the devitrified base material is shown in FIG. 3. As is clear from this figure, a clear halo centered at the diffraction angle 2θ=22° appears. Furthermore, as is clear from the fact that the diffraction intensity of the residual crystal phases (mullite and unknown phases) is much smaller than 0 or more compared to FIGS. 1 and 2, most of the base material is a glass phase.

When this base material was heated with an oxyhydrogen flame using a glass processing lathe, it immediately became transparent and a glass rod without residual bubbles was obtained.

Next, a cladding layer of fluorine-doped silica glass was formed on the outer periphery of these glass rods by an external method, and then heated and stretched to obtain a core diameter of 7.5% m, an outer diameter of 125 μm,
A single mode optical fiber with a numerical aperture of 0.12 was fabricated.

Table 2 shows an example of the core glass composition and properties of the obtained fiber.
0.09W for pure silica host glass as shown in
The characteristics of a single mode fiber consisting of a core doped with t,% Er are also shown in Table 2 as 4 (comparison).

The fluorescence lifetime at a wavelength of 155 μm is approximately 0.5wt.

% of Er doped fiber is about 10 m5ec, which is no inferior to the low concentration pure silica host glass fiber (4 comparisons in Table 2). Also, the wavelength is 1.1L
The transmission loss in Lm is sufficiently low at 3-12dB/km. From these, the merits of the glass composition of the present invention can be understood.

(Example 2) A quartz-based soot base material with an average bulk density of 0.4-0.45 g/cm3 doped with about 801% G e O2 by the VAD method was prepared, and various different concentrations were added to this soot. After impregnating a methyl alcohol solution in which erbium chloride or neodymium chloride and aluminum chloride were dissolved,
Drying, oxidation, and dehydration treatments were performed in the same manner as in Example 1.

Subsequently, sintering was performed in a He gas atmosphere containing 3.0% of sIF. In this example, it was possible to make it completely non-porous at 1200°C.

A cladding layer of fluorine-doped silica glass is formed on the outer periphery of these various glass rods with different compositions, and this is heated and stretched to a core diameter of 4 to 6 μm and an outer diameter of 125 μm.
A single mode optical fiber with a numerical aperture of 0.18 and a numerical aperture of 0.18 was fabricated.

The fluorescence lifetime and loss characteristics of these fibers were as good as in Example 1.

Among the obtained fibers, Er concentration in the core = 0.08
0wt, %, A℃ concentration = 0.091wt, %, F concentration =
The emission spectrum of a 0.97 wt, % (Aj2/Er atomic ratio = 7.1) fiber at a wavelength of around 1.55 μm was measured (I in Figure 4).
An 8 μm Ti:sapphire laser was used. The fiber length was 10 cm, and the incident pump power was 30 mW.

For comparison, Ge0z 5ift type host glass was used.
As shown in Figure 6, which also shows the spectrum of a single mode fiber consisting of a core doped with 90wt% Er, as II in Figure 4, the emission spectrum ■ of the fiber of this example is considerably different from II. The fact that the signal becomes broad indicates that the amplification band is widening.

In this example, about 4 wt, up to % rare earth elements and about 3
Although we obtained transparent glass rods codoped with A2 up to w t %, this concentration is not the vitrification limit. Even higher concentrations can be produced.

(Comparative Example 1) When glass was manufactured in exactly the same manner as in Experiment 1,
As shown in the results of Experiment 1, the glass desired by the present invention could not be obtained.

(Comparative Example 2) Glass was produced in exactly the same manner as in Experiment 2, and
As shown in the results of Experiment 2, the glass intended by the present invention could not be obtained.

(Effects of the Invention) The rare earth element-doped glass and the manufacturing method thereof of the present invention have the following effects.

(1) The rare earth element-doped glass of the present invention has a quartz-based composition doped with fluorine in addition to the rare earth element and AI2. Due to the coexistence effect of rare earth elements and AI2, it is possible to add a high concentration of rare earth elements without impairing the emission characteristics, and sufficient amplification gain can be obtained even if the interaction length with the excitation light is short. The amplifier can be made smaller. Furthermore, when the rare earth element is Er, A! The coexistence of the above widens the wavelength band exhibiting optical amplification around 1.55 μm, so the glass composition of the present invention is suitable for use in optical amplifiers.

(2) Since the rare earth element-doped glass of the present invention basically has a high-silica, alkali-free quartz-based composition, its thermal expansion coefficient, softening temperature, and other properties are comparable to those of the quartz-based glass used for ordinary optical fibers. It is close and has good fusion with them. Therefore, by using the rare earth element-doped glass of the present invention as a core material and a relatively low refractive index glass such as F-doped silica as a cladding material, an optical fiber (or guiding waveguide) having a core-clad structure can be easily produced. be able to. Furthermore, it has excellent fusion splicability with general silica-based optical fibers.

(3) Since the rare earth element-doped glass of the present invention further contains fluorine in addition to the rare earth element and AI2,
It has great advantages and advantages in the manufacturing process. When producing β-codoped glass with rare earth element + from a porous glass base material, if the glass composition of the present invention is used, the sintering temperature can be reduced to 1.
It can be easily made non-porous and transparent glass even at a relatively low temperature of 500°C or less.

Although the reason for this is not clear, (1) the addition of fluorine to the glass particles of the quartz-based matrix lowers the melt viscosity.

Therefore, sintering progresses rapidly, and rare earth elements and 89. Diffusion and homogeneity in the glass is also promoted. (2) It is presumed that this is because oxides of rare earth elements and AI2 react with fluorine and change into fluorides with relatively low melting points as shown in Table 1. Therefore, even by an outside process such as the VAD method, which uses a relatively low sintering temperature, a transparent, bubble-free rare earth element + AI2 co-doped glass product can be obtained. (4)
According to the method for producing rare earth element-doped glass of the present invention,
Rare earth elements in the form of rods or films with high purity and excellent transparency, suitable for use in functional optical fibers and optical waveguides.
AJ2 doped glass can be easily produced.

(Margin below) Table 1

[Brief explanation of drawings]

Figures 1 and 2 are explanatory diagrams of X-ray diffraction of glass soot base materials in Experiment 1 and Experiment 2, respectively, and Figure 3 is Example 1 of the present invention.
FIG. 4 is an explanatory diagram of the X-ray diffraction of the glass soot base material.

Claims (7)

[Claims] (1) A rare earth element-doped glass characterized in that a rare earth element is added to a host glass having a SiO_2 composition co-doped with Al and F. (2) A rare earth element-doped glass, characterized in that a substance that increases the refractive index of the glass is further added to the host glass composition of claim 1. (3) A rare earth element-doped glass, characterized in that a substance that lowers the softening temperature of the glass is further added to the host glass composition of claim 1. (4) GeO_2-SiO_2 co-doped with Al and F
A rare earth element-doped glass characterized in that a rare earth element is added to a host glass having a composition of the same type. (5) A doping step in which a base material made of silica-based porous glass having connected open pores is immersed in a solution containing rare earth element ions and aluminum ions to impregnate the rare earth elements and aluminum into the base material; After the doping step, the base material is dried to deposit rare earth element and aluminum salts into the pores of the base material, or further, the deposited salts are oxidized and stabilized, and the base material after the drying step is sintered. Conclusion/
In the method for producing rare earth element-doped glass, which includes a sintering step to make the glass non-porous, the base material is heated in an atmosphere containing fluorine between after the drying step and before the sintering step. 5. The method for producing rare earth element-doped glass according to claim 1, wherein a fluorine doping step of heat treatment is interposed. (6) A method for producing rare earth element-doped glass, characterized in that the fluorine doping step according to claim 5 is carried out at a temperature lower than 1276° C., which is the sublimation temperature of aluminum fluoride, preferably at a temperature of 1000° C. or lower. (7) In claims 5 and 6, the dehydration treatment is performed in an atmosphere containing Cl_2 or other chlorine compound gas phase and O_2 between after the drying step and before the sintering step. 1. A method for producing rare earth element-doped glass, which includes an intervening step.