JPH11314935A - Rare earth element doped glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the deposition of a high m.p. material at the time of sintering a porous glass produced by an outside process such as a VAD soln. impregnation method. SOLUTION: When a rare earth element is added to a host glass having an SiO2 -base compsn. to obtain the objective rare earth element doped glass, the host glass is doped with Al and F. A material that increases the refractive index of the host glass or a material that reduces the softening temp. of the host glass is further added to the compsn. of the host glass if necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rare earth element-doped glass, and more particularly to a rare earth element-doped glass suitable for use in an active optical device such as a laser or an optical amplifier in the form of an optical fiber or an optical waveguide. .

[0002]

2. Description of the Related Art As a functional optical fiber containing a rare earth element in a core, a fiber laser utilizing optical amplification by stimulated emission between electron levels of rare earth elements ions [Ref.
2] and optical amplifiers [Reference Documents 3 and 4] have been reported.
Among the optical fibers, Er-doped fibers have been receiving attention as in-line optical amplifiers that do not require photoelectric conversion because they exhibit an optical amplification effect at a wavelength of 1.55 μm band used in optical communication.

Further, there is a technique of co-doping Al with a rare earth element in order to improve the characteristics of a functional rare earth doped fiber. Al co-doping is 2 as shown below.
Has two advantages.

First, in the case of SiO ₂ glass or GeO ₂ —SiO ₂ glass used for general optical fibers, there is a drawback that when a rare earth element of about 0.1 wt% or more is added, so-called concentration quenching occurs. . This is a phenomenon in which the energy of electrons excited by the aggregation (clustering) of rare earth ions in glass tends to be lost through a non-radiative process, and the lifetime and efficiency of light emission are impaired. . Al co-doping overcomes this disadvantage and allows relatively high concentrations of rare earth elements to be doped without clustering [Ref. 5].

When a rare earth element is doped at a high concentration, a sufficient amplification gain can be obtained even if the working length of the excitation light and the rare earth ion is short, so that a small laser or optical amplifier can be realized.

Second, when Al is co-doped, the emission spectrum of rare earth ions may change. In particular, the emission spectrum of the 1.55 μm band of the quartz-based Er-doped glass becomes broad due to Al co-doping, and the wavelength band that can be amplified is expanded. This is a great advantage when used as an optical amplifier in a wavelength division multiplexing transmission system.

As a method for producing an optical fiber co-doped with a rare earth element and Al, there is a solution impregnation method (MCVD solution impregnation method) based on the MCVD method.
Reported by J. Ainslie et al. [Ref. 6].

[0008] First, according to the usual method,
A glass layer serving as a cladding having a relatively low refractive index is deposited inside the starting quartz glass tube, and then a soot-like porous core glass layer is deposited inside at a lower temperature than usual.
Next, a solution containing rare earth ions and Al ions is impregnated into the pores of the porous core glass layer, and after drying and dehydration steps, the porous core glass layer is sintered and made nonporous in a He gas stream. Hereinafter, the procedure returns to the normal procedure, and the collapse is performed to obtain a solid rod-shaped optical fiber preform.

According to this method, the rare earth elements are not clustered in the glass, and the rare earth
t. % Or more.

References 1) CJ Koester and E. Snitzer: App1.0pt., 3.1182 (19
64) .2) SBPoo1e et al .: E1ectron.Lett., 21, P. 738 (198
5) .3) RJMears et al .: Electron.Lett., 23, P. 1026 (198
7) .4) E. Desurvire et al .: 0pt. Lett., 12,888 (1987) .5) K. Arai et al .: J. App1. Phys., 59.3430 (1986). Mater. Lett., 6, 139 (1988).

Incidentally, the above-mentioned solution impregnation method itself has been known for a long time, and in recent years, it has been widely used as a method for doping a quartz optical fiber preform with an element such as a rare earth element or a transition metal which is hardly added by a gas phase method. It has been adopted. V
Of course, it is also possible to produce a doped glass by impregnating a solution into a porous glass (soot) base material produced by an AD method or an external method.

As is well known, in the VAD method or the external method (so-called outside process), a glass base material having a large size, uniformity, and excellent optical characteristics can be easily produced as compared with the MCVD method (internal method). can do.

Therefore, the present inventors have proposed a solution impregnation method (VAD) based on the VAD method as in the MCVD solution impregnation method.
I think that Al doping is also possible with the solution impregnation method)
Production of Al-doped quartz glass was attempted by the methods of Experiments 1 and 2 described below. Note that Experiments 1 and 2 are also Comparative Examples 1 and 2 described later in the present invention, respectively.

(Experiment 1 = Comparative Example 1) A soot base material having a pure quartz composition having an average bulk density of 0.4 to 0.5 g / cm ³ produced by the VAD method was prepared by dissolving various concentrations of aluminum chloride. Impregnation was performed by immersion in a methyl alcohol solution for 12 to 24 hours. After completion of the impregnation, the solvent was evaporated to dryness, and heated to about 950 ° C. in an oxygen stream to oxidize and fix aluminum salts remaining in the soot. The added Al ₂ O _{3 based} on the dry weight of the soot at this time
Has a weight fraction of 0.3 to 3 wt.
%Met.

Next, in an electric furnace having a center temperature of 1500 ° C., He containing 1% of Cl ₂ and 5% of O ₂ by volume ratio.
While maintaining the gas atmosphere, the soot was lowered at a rate of 2 mm per minute to perform sintering.

In any case, the sintered base material was not completely nonporous, and cracks occurred after cooling. Further, in the base material impregnated with Al at a high concentration, "soot" (cavities) were generated inside. As a result of X-ray diffraction, halo peculiar to the glass phase was not recognized, and most of the cristobalite (Si
O ₂ ) and mullite (3Al ₂ O ₃ .2SiO ₂ ) were confirmed to have changed to high melting point crystalline phases.

When impregnated with Er at the same time as Al, no pores were formed, and no transparent glass was obtained.

(Experiment 2 = Comparative Example 2) P _{2 was} measured by the VAD method.
The O ₅ 1.1wt. % Doped, average bulk density 0.4
A quartz soot base material of about 0.5 g / cm ³ was produced. This was impregnated with the same Al solution as in Experiment 1, and dried and dried under the same conditions.
Oxidation and sintering were performed.

This base material did not completely become nonporous, and cracks occurred to a lesser extent than in Experiment 1. The result of X-ray diffraction also showed no halo, and precipitation of a high melting point crystal phase of cristobalite and aluminum phosphate (AlPO ₄ ) was observed.

Even when Er was impregnated with Al, a transparent glass could not be obtained. As shown in FIG. 2, in the base material impregnated with Er at a high concentration, erbium phosphate (ErP
O ₄ ) was also observed.

The reason that no transparent glass was obtained in the above Experiments 1 and 2 is that the sintering temperature is lower in the VAD solution impregnation method in Experiments 1 and 2 than in the above-mentioned MCVD-based method. It was thought to be. That is, it is considered that the precipitation of the high melting point crystal phase hindered the progress of sintering.

According to the Al ₂ O ₃ —SiO ₂ phase diagram, the eutectic point of mullite and cristobalite is 15
87 ± 10 ° C. and a eutectic composition (Al ₂ O ₃ ≒ 8 wt.
%), The liquidus temperature lies between the eutectic point and the melting point of cristobalite, 1726 ± 5 ° C.
Therefore, at the sintering temperature of 1500 ° C. in Experiment 1, the mullite and cristobalite once deposited do not melt. Elimination of these high melting crystalline phases requires temperatures higher than 1587 ° C. to 1726 ° C. depending on their composition.

On the other hand, Al corresponding to the composition of Experiment 2_TwoO_Three
−P_TwoO_Five-SiO_TwoDetailed phase diagrams of the system have been reported.
No, but the situation is assumed to be the same as in Experiment 1.
You. For example, P_TwoO_Five-SiO_TwoP in the system_TwoO_Five= 1.1w
t. % Liquidus temperature (Cristobalite disappears
Is 1700 ° C. or higher. Al_TwoO_Three−P
_TwoO_FiveAl in the system_TwoO_ThreeIs 30 wt. % Above the liquid phase
Linear temperature (AlPO_FourTemperature is 1500 ° C or more.
You.

In an attempt, when the base materials obtained in the above experiments 1 and 2 were ignited and quenched using an oxyhydrogen flame, all became transparent glasses, but many bubbles remained in the glass. However, it was not practical as an optical glass.

From the above, according to the VAD solution impregnation method, M
Al-doped (or co-doped) glass could not be produced as in the CVD solution impregnation method, and it was concluded that the cause was due to insufficient sintering temperature.

[0026]

In order to solve the problem of insufficient sintering temperature by the VAD solution impregnation method, it is conceivable to increase the sintering temperature to 1600 ° C. or 1700 ° C. or more. A high temperature involves technical and equipment difficulties.

First, a quartz glass furnace tube or a jig generally used in a soot base material sintering furnace is softened and deformed at such a high temperature and cannot be used for a long time. To solve this problem, it is conceivable to use a high-melting-point ceramic core tube instead of a quartz glass core tube.In such a case, impurities are volatilized from the core tube and mixed into the base material. As a result, the transmission loss of the fiber increases sharply.
This is a well-known fact in the art.

Second, when sintering is performed at a temperature higher than the liquidus temperature, the base material may be stretched and dropped by its own weight.

These problems are not limited to the VAD solution impregnation method, but are common to the sintering of porous glass produced by a so-called outside process including an external method.

By the way, in the MCVD solution impregnation method, the quartz glass tube of the base material also serves as the reaction tube, which is directly heated by an oxyhydrogen flame. And there is no fear of contamination. Even if crystallized during sintering, the process can immediately proceed to the collapse step at 1900 ° C. or higher without cooling once, so that cracks due to thermal strain do not occur. In addition, the crystal phase is completely melted during the collapse, and a quenching after solidification provides a transparent glass base material.

[0031]

DISCLOSURE OF THE INVENTION The present inventors have studied the improvement of the glass composition in view of various problems when producing a rare earth element + Al co-doped glass using the above-described outside process such as the VAD method. Invented the invention.

An object of the present invention is to provide a rare earth element + Al co-doped glass having a composition capable of obtaining a transparent glass even at a relatively low sintering temperature.

Another object of the present invention is to provide a rare earth element + Al co-doped glass in which light emission characteristics are not impaired even when a high concentration rare earth element is doped.

[0034]

According to the present invention, the rare earth element-doped glass according to claim 1 is a rare earth element-doped glass obtained by adding a rare earth element to a host glass having an SiO ₂ composition. It is one in which Al and F are doped.

The rare earth element-doped glass according to the second aspect of the present invention is obtained by further adding a substance for increasing the refractive index of the glass to the host glass composition of the rare earth element-doped glass according to the first aspect.

The rare earth element-doped glass of the third aspect of the present invention is obtained by further adding a substance for lowering the softening temperature of the glass to the host glass composition of the first aspect.

The rare earth element-doped glass according to claim 4 of the present invention is a rare earth element-doped glass obtained by adding a rare earth element to a host glass having an SiO ₂ composition, wherein Al and F are contained in the host glass. Ge is doped.

The basic glass composition of the rare earth element-doped glass of the present invention is R ₂ O ₃ —Al ₂ O ₃ —SiO ₂ —F (R
Is a rare earth element, and F is doped so as to replace O), and is basically a silica-free and alkali-free quartz glass. For this reason, properties such as an expansion coefficient and a softening temperature are close to those of a silica glass used for a normal optical fiber, and the fusion property with them is good. Accordingly, an optical fiber (or optical waveguide) having a core-cladding structure using a rare earth element-doped glass produced according to the present invention as a core material and a relatively low refractive index glass such as F-doped silica as a cladding material.
Can be easily produced. Further, it also has excellent fusion splicability with a general quartz fiber.

Further, in the rare earth element-doped glass of the present invention, a high concentration of a rare earth element can be added without deteriorating the light emission characteristics due to the coexistence effect of the rare earth element and Al. Since a large amplification gain can be obtained, downsizing of the laser or the optical amplifier can be realized. Further, when the rare earth element is Er, 1.
The glass composition of the present invention is suitable for optical amplifiers because the wavelength band showing optical amplification around 55 μm is widened.

These effects are achieved by the well-known rare earth element + Al
Although it is equivalent to the co-doped quartz glass, the rare earth element-doped glass of the present invention is a novel quartz glass composition characterized by further containing fluorine. The addition of fluorine has a great advantage in the manufacturing process.

Rare-earth elements and Al have the effect of increasing the refractive index of quartz glass, but, on the other hand, reduce fluorine, so that the refractive index of the glass becomes lower than the quartz level depending on the ratio of the doping amount thereof, and the cladding and the cladding have a lower refractive index. May not be sufficiently ensured. In this case, a component having an effect of further increasing the refractive index may be added to the basic glass composition.

Since AlF ₃ sublimes at 1276 ° C., sintering at a temperature higher than this lowers the amount of Al remaining in the glass. In this case, it is preferable to further add a component for lowering the softening temperature of the glass to the basic glass composition. GeO ₂ or P ₂ O ₅ is particularly preferred as such an additive. In both cases, the softening temperature is lowered while increasing the refractive index of the quartz glass. The former has a remarkable effect by increasing the refractive index, and the latter has a remarkable effect by lowering the softening temperature. As is well known, both components can be easily added to the soot by the VAD method and the external method.

[0043]

In order to produce a high silica, alkali-free rare earth element + Al co-doped quartz glass, a solution impregnation method using a porous glass base material is simple, and adjustment of the rare earth element and Al doping concentration is required. It has advantages such as simplicity and is considered to be general. However, when the impregnated base material is sintered without passing through the fluorine doping step in the VAD solution impregnation method, it is difficult to make the pores non-porous because a high melting point crystal phase is precipitated as in the above-mentioned experimental example.

However, if fluorine is further added in addition to the rare earth element and Al, even if the sintering temperature is relatively low at 1500 ° C. or less, nonporous and transparent vitrification can be easily achieved. Although the reason is not clear, (1) the melt viscosity is reduced by adding fluorine to the glass particles of the quartz base material. Therefore, sintering proceeds quickly, and diffusion and homogenization of the rare earth element and Al into the glass are promoted. (2) It is presumed that the rare earth and Al oxides react with fluorine to change to fluorides having a relatively low melting point as shown in Table 1.

[0045]

[Table 1]

When a rare earth element and / or Al is 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 nonporous glass matrix, the glass matrix immediately becomes transparent when heated to a high temperature using an oxyhydrogen flame or the like. At this time, neither cracks nor bubbles remain.

Therefore, when the glass composition of the present invention is used, V
Even with an outside process such as an AD solution impregnation method, a transparent rare earth element + Al co-doped glass product without bubbles can be obtained.

Incidentally, P (P ₂ O ₅ ) is also known as a dopant which greatly lowers the solution viscosity of quartz glass. However, when P is further added in addition to rare earth elements and Al (when fluorine is not contained). Induces the precipitation of high melting point crystals such as aluminum phosphate and erbium phosphate as shown in Experimental Example 2 described above, which is rather the opposite effect.

Next, when manufacturing the rare earth element-doped glass of the present invention, a glass preform (rod) for a rare earth element-doped optical fiber can be manufactured, for example, by a VAD solution impregnation method as follows.

A quartz glass soot base material is prepared by a VAD method, impregnated with a solution containing a rare earth element and Al ions, and then the solvent is evaporated and dried to remove the salt of the rare earth element and Al into the soot base material. Is deposited in the pores. In this case, as a solution raw material, an alcohol solution or an aqueous solution of chloride, hydrated chloride, nitrate, or the like can be used.

The soot base material impregnated with the above solution is desirably subjected to a heat treatment in an oxygen atmosphere prior to sintering. When chloride raw materials are used as the solution raw materials, they are easily evaporated and volatilized even at a relatively low temperature. Therefore, if they are oxidized and stabilized, the reproducibility of the doping amount in the glass is improved. When a nitrate is used as a solution raw material, the nitrate is decomposed into an oxide at a temperature of about 200 ° C., so that it is not necessary to perform an oxidation step.

Also, in the case where the dehydration treatment is performed in an atmosphere containing a gaseous phase of Cl ₂ or another chlorine compound prior to the sintering, excess oxygen gas is preferably added to the atmosphere. desirable. If oxygen gas is not included, during the dehydration process,
This is because the oxide becomes chloride again and easily volatilizes.

Next, the solution-impregnated base material is sintered and nonporous in a fluorine-containing He atmosphere. As a known fluorine source, a gas such as SiF ₄ , SF ₆ or Freon can be used.

In order to process the rare earth element-doped crow rod obtained as described above into an optical fiber, for example, a clad glass layer is formed by an external method, and then this is heated and drawn to spin. Technology is available. In this way, a rare-earth element-doped optical fiber or optical waveguide in which the whole or a part of the light-guiding portion is made of the rare-earth-element-doped glass of the present invention is obtained.

Although the above description has been made on the case where the quartz glass soot base material manufactured by the VAD solution impregnation method is used, it is needless to say that the quartz glass soot base material manufactured by the external method or the sol-gel method can also be used.

According to the rare earth element-doped glass of the present invention,
Thin film optical waveguides can also be manufactured. For the formation of the thin-film-shaped porous quartz-based glass, for example, a flame hydrolysis method, which is an existing technique, can be used. The reaction film formation mechanism at this time is the same as the VAD method or the external attachment method. For this film formation, a thermal CVD method may be used. In this case, a soot-like porous glass film is formed if the substrate temperature is set lower than when a normal silica glass film is deposited.

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

By combining this method with the existing microfabrication technology (channel formation) and the cladding glass layer formation technology, a rare-earth-doped optical waveguide having an arbitrary shape can be manufactured.

[0059]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Example 1) A soot having a pure quartz composition having an average bulk density of 0.4 to 0.5 g / cm ³ produced by a VAD method was mixed with erbium chloride and aluminum of various different concentrations. 12 in the dissolved methyl alcohol solution
Impregnation was performed by soaking for ~ 24 hours. Al / Er in solution
The molar ratio was set at 1-5. After completion of the impregnation, the solvent was evaporated and dried, and heated to about 950 ° C. in an oxygen stream to oxidize and fix the Er and Al salts remaining in the soot.

Next, in an electric furnace having a center temperature of 1000 ° C.,
The soot was lowered at a speed of 3 mm / min to carry out dehydration while maintaining a He gas atmosphere containing 1% Cl ₂ and 10% O ₂ in volume ratio. After completion of the dehydration, the soot was once pulled up to a low temperature part, and the temperature of the electric furnace was raised to 1300 ° C. Subsequently, the atmosphere in the furnace was adjusted to 0.5 vol. % Of SiF ₄ , and the soot was lowered at a speed of 2 mm per minute to perform sintering.

As a result, various concentrations of Er and Al
Is co-doped Er_TwoO_Three-Al _TwoO_Three-SiO_Two−
An F-based glass rod was obtained. Er is about 0.3 wt. %
The glass doped above is devitrified immediately after sintering and
It had an ink-colored opal glass-like appearance. Devitrification
FIG. 3 shows an example of the X-ray diffraction pattern of the base material. From this figure
It is clear that the diffraction angle is centered on the diffraction angle 2θ = 22 °.
Hello is appearing. In addition, the residual crystal phase (mullite and
And unknown phases) are much higher than those in FIGS. 1 and 2.
Small. As is clear from the above, most of the base material is gas
It is a lath phase.

When this base material was heated with an oxyhydrogen flame using a glass working lathe, it immediately became transparent and a glass rod free of residual air 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 this was heated and stretched to have a core diameter of 7.5 μm, an outer diameter of 125 μm, and a numerical aperture of 0. .12 single mode optical fibers were produced.

Table 2 shows an example of the core glass composition and properties of the obtained fiber. For comparison, 0.09 wt. The characteristics of a single mode fiber comprising a core doped with% Er are also shown in Table 2 as 4 (comparison).

[0065]

[Table 2]

The fluorescence lifetime at a wavelength of 1.55 μm is about 0.5 W
t. % Er-doped fiber is about 10 msec
This is comparable to low-concentration pure silica host glass fiber (four comparisons in Table 2). In addition, wavelength 1.
The transmission loss at 1 μm is sufficiently low at 3 to 12 dB / km. From these, it is possible to understand the good nature of the glass composition of the present invention.

Example 2 About 8 mol% of GeO ₂ was doped by the VAD method, and the average bulk density was 0.4 to 0.5.
g / cm ³ of a quartz soot base material was prepared, and this soot was impregnated with various different concentrations of erbium chloride or neodymium chloride and a methyl alcohol solution in which aluminum chloride was dissolved. Drying, oxidation and dehydration treatments were applied. Then, SiF ₄ was added to 3.0 vo.
l. The sintering was performed in a He gas atmosphere containing%. In this example, it was possible to completely eliminate porosity at 1200 ° C.

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

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

In the obtained fiber, the Er concentration in the core = 0. 080 wt. %, Al concentration = 0.091w
t. %, F concentration = 0.97 wt. % (Al / Er atomic ratio = 7.1), the emission spectrum at a wavelength around 1.55 μm was measured (I in FIG. 4). As the excitation light source, a Ti: sapphire laser having a wavelength of 0.98 μm was used. The fiber length is 10 cm and the incident pump power is 3
0 mW. 0.090wt the GeO ₂ -SiO ₂ type host glass for comparison. The spectrum of a single mode fiber consisting of a core doped with% Er is also shown as II in FIG. As shown in the figure, it can be seen that the emission spectrum I of the fiber of this example is considerably broader than II. This indicates that the amplification band is widened.

In this embodiment, about 4 wt. % Rare earth elements and about 3 wt. % Transparent glass rods co-doped with Al are obtained, but this concentration is not the vitrification limit. Even higher concentrations can be produced.

(Comparative Example 1) When a glass was manufactured in exactly the same manner as in Experiment 1, the glass obtained in the present invention was not obtained as a result of Experiment 1.

(Comparative Example 2) A glass was produced in exactly the same manner as in Experiment 2 above. As a result of Experiment 2, the glass obtained in the present invention was not obtained.

[0074]

The rare earth element doped glass of the present invention has the following effects.

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 Al. Due to the coexistence effect of rare earth elements and Al,
A high-concentration rare earth element can be added without deteriorating the light emission characteristics, and a sufficient amplification gain can be obtained even if the action length with the excitation light is short, so that the laser or the optical amplifier can be downsized. Further, when the rare earth element is Er, the glass band of the present invention is suitable for an optical amplifier because the wavelength band showing optical amplification around 1.55 μm is widened due to the coexistence of Al.

Since the rare earth element-doped glass of the present invention basically has a high silica and alkali-free quartz-based composition, its properties such as thermal expansion coefficient and softening temperature are different from those of quartz-based glass used for ordinary optical fibers. Close, good adhesion to them.
Therefore, the rare earth element-doped glass of the present invention as a core material,
An optical fiber (or optical waveguide) having a core-cladding structure can be easily manufactured by using a relatively low refractive index glass such as F-doped silica for the cladding material. Further, it also has excellent fusion splicability with a general quartz optical fiber.

The rare earth element-doped glass of the present invention has a great advantage in the manufacturing process because the rare earth element-doped glass of the present invention further contains fluorine in addition to the rare earth element and Al. When producing a rare earth element + Al co-doped glass from a porous glass base material, if a glass composition to which fluorine is added is used, a sintering temperature of 150 is used.
Even at a relatively low temperature of 0 ° C. or less, nonporous and transparent vitrification can be easily achieved. Although the reason is not clear, (1) the melt viscosity is reduced by adding fluorine to the glass particles of the quartz base material. Therefore, the sintering proceeds quickly, and the diffusion and homogenization of the rare earth element and Al into the glass are promoted. (2) It is presumed that the rare earth and Al oxides react with fluorine to change to fluorides having a relatively low melting point as shown in Table 1. Therefore, V having a relatively low sintering temperature
Even by an outside process such as an AD method, a transparent rare-earth element + Al co-doped crow product without bubbles can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of X-ray diffraction of a glass soot base material in Experiment 1.

FIG. 2 is an explanatory diagram of X-ray diffraction of a glass soot base material in Experiment 2.

FIG. 3 is an explanatory diagram of X-ray diffraction of a glass soot base material of Example 1 of the present invention.

FIG. 4 is an explanatory diagram of an emission spectrum of an Er-doped optical fiber obtained according to Example 2 of the present invention.

Continued on the front page (72) Inventor Yasumasa Sasaki 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Inside Furukawa Electric Co., Ltd.

Claims (4)

[Claims] 1. A rare earth element-doped glass obtained by adding a rare earth element to a host glass having an SiO ₂ composition, wherein the host glass is doped with Al and F. Doped glass. 2. The rare earth element-doped glass according to claim 1, wherein a substance for increasing the refractive index of the glass is further added to the host glass composition. 3. The rare earth element-doped glass according to claim 1, wherein a substance for lowering the softening temperature of the glass is further added to the host glass composition. 4. A rare earth element-doped glass obtained by adding a rare earth element to a host glass having an SiO ₂ composition, characterized in that the host glass is doped with Al, F, and Ge. Rare earth element doped glass.