JPH06122532A - Fluoride glass fiber - Google Patents

Abstract

PURPOSE:To provide a fluoride glass capable of producing a fiber having high NA value. CONSTITUTION:The subject glass fiber has a core consisting of a glass composed of ZrF4, BaF2, LaF3, YF3, AlF3, NaF and PbF2 and satisfying the formula 0.65<=R<=1.45 wherein R is ratio of the contents of PbF2, YF3 and AlF3 and defined by the formula R=[PbF2]/{[AlF3]+[YF3]}.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a fluoride glass used for a fiber for optical communication.

[0002]

2. Description of the Related Art Fluoride glass, which transmits light in the visible to mid-infrared region, has been attracting attention as a host for optical communication fibers, optical amplification, upconversion, and fiber lasers. In particular, research on praseodymium (Pr ^{3 +} )-doped fluoride glass fiber amplifier for the purpose of signal amplification in the 1.3 μm band, which is a communication wavelength, is very active. In addition, some researches on various measurements such as radiation temperature measurement, gas analysis and liquid analysis using fluoride glass fiber have been reported.

Of great importance in these applications are:
It is the opening angle (NA) of the fiber. For example, when the fiber is used for measurement, it is necessary to change the NA according to the measured area, and in some cases, NA of 0.3 or more may be required. Further, in the case of a fiber used for an optical amplifier installed at a relay point of a fiber for optical communication, it is needless to say that it is a single mode, and in order to increase amplification efficiency, NA is increased and core diameter is decreased. Is required.

As means for making a difference in refractive index between the core and the clad with a fluoride glass fiber, (1) an additive for increasing the refractive index in the core (for example, P
bF ₂ ) is added (2) A part of ZrF ₄ of the clad is replaced with HfF ₄ (3) A part of NaF of the clad is replaced with LiF (4) Four methods of doping the core with chlorine are well known. ing.

The method (1) is the simplest means, but when PbF ₂ is added to a conventionally known fluoride glass composition, not only the stability against crystallization of glass is lost, The softening point of glass is relatively lower than that of the clad, making spinning difficult.

Although the methods (2) and (3) can change only the refractive index without significantly changing the thermal properties of the glass, the refractive index difference (Δn) between the core and the clad obtained is obtained. Was at most 1.6% (NA-0.27).

In the case of the method (4), a large Δn can be obtained by adding a small amount of chlorine, but as in the case of the method (1), the addition of chlorine lowers the softening point and the chemical durability of the glass. There was a problem.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a fluoride glass capable of obtaining a fiber having a high NA.

[0009]

[Means for Solving the Problems] The above-mentioned objects are as follows: the constituent components are ZrF ₄ , BaF ₂ , LaF ₃ , YF ₃ , AlF ₃ ,
NaF and PbF ₂ , and PbF ₂ , YF ₃ ,
Ratio R of content of AlF ₃ (R = [PbF ₂ ] / {[Al
F ₃ ] + [YF ₃ ]}) is achieved by using glass with 0.65 ≦ R ≦ 1.45 for the core.

That is, the previously reported ZrF
_The refractive index is increased by adding PbF ₂ to _4- BaF ₂ —LaF ₃ —YF ₃ —AlF ₃ —NaF glass, but at that time, the value of R should be within the above-mentioned limited range. For example, it is possible to obtain a crystal-free homogeneous glass. If R is out of the above-mentioned limited range, the glass melt may become cloudy or fine crystals such as AlF ₃ and YF ₃ may be precipitated.

The range of the composition of the core glass will be described in more detail. 37 ≤ ZrF ₄ ≤ 54 mol%, 12
≤ BaF ₂ ≤ 24 mol%, 0 ≤ LaF ₃ ≤ 5 mol%, 1 ≤ YF ₃ ≤ 10 mol%, 3 ≤ AlF ₃
≤ 10 mol%, 10 ≤ NaF ≤ 20 mol%, 4.
5 ≦ PbF ₂ ≦ 18 mol%, and PbF ₂ ,
The ratio R of the contents of YF ₃ and AlF ₃ (R = [PbF ₂ ] /
It is sufficient that {[AlF ₃ ] + [YF ₃ ]}) satisfies 0.65 ≦ R ≦ 1.45.

The content of ZrF ₄ and BaF ₂ is in the above-mentioned limited range, preferably 42 ≦ ZrF ₄ ≦ 48 mol%, 14 ≦ B.
If it is out of the range of aF ₂ ≦ 23 mol%, a homogeneous melt may be obtained, but the melt may become emulsion during cooling.

LaF ₃ may not necessarily be contained, but the above-mentioned limited range, preferably 1.5 ≦ LaF ₃ ≦
Addition in the range of 3.5 mol% increases the stability of the resulting glass against devitrification.

YF ₃ and AlF ₃ are essential components of this glass, and when the content is lower than the lower limit of the above-mentioned limited range, the crystallization rate during cooling becomes remarkably high. In addition, LaF ₃ , AlF
_{When 3} is more than the upper limit of the above-mentioned limited range, the heat resistance and water resistance of the glass are improved, but fine crystals of both may be precipitated.

NaF is also an essential component of this glass,
If the content is out of the above range, the melt may become turbid during cooling, and if the content is more than the upper limit of the range, the water resistance is extremely low even if glass is obtained.

PbF ₂ is an essential component for increasing the refractive index of glass. Even when the content of PbF ₂ is lower than the lower limit of the above-mentioned limited range, a glass which is sufficiently stable against crystallization can be obtained, but the above ZrF ₄ / HfF ₄ substitution,
No superiority is recognized as compared with the means such as NaF / LiF substitution or chlorine doping. In addition, the content of PbF ₂ is
If it is higher than the upper limit of the above-mentioned limited range, the melt may become an emulsion during cooling although it may become a homogeneous melt.
Further, even if the content of PbF ₂ is within the above-mentioned limited range, the ratio R of the content of YF ₃ and the content of AlF ₃ is 0.65 ≦
If R ≦ 1.45 is not satisfied, then the melt becomes turbid during cooling, and a homogeneous glass cannot be obtained.

[0017]

EXAMPLE 1 The present invention will be described in more detail with reference to examples.

As shown in Table 1, the composition of the obtained glass is ZrF ₄ : 46% and BaF ₂ : 22 in mol.
%, LaF ₃ : 2%, YF ₃ : 2%, AlF ₃ : 4.5
%, NaF: 18.5%, PbF ₂ : 5%, and the total amount of 50 g was weighed and melted at 900 ° C. for 2 hours in an inert gas atmosphere using a platinum crucible.

Thereafter, the obtained melt was treated with a diameter of 40 mm,
It was poured into a mold having a depth of 10 mm, placed in an electric furnace at 300 ° C., and gradually cooled. The obtained compound of the above composition is a colorless transparent substance, and has a glass transition point (272
C.), a crystallization starting point of 351.degree. C. was observed, and only a halo pattern peculiar to amorphous appeared even in X-ray diffraction, and thus the obtained compound was determined to be glass.

The refractive index (n _d ) of the obtained glass at Na-d line was measured, and as shown in Table 1, n _d =
It was 1.511. Therefore, the obtained glass is used as a core, and PbF ₂ -free glass, for example, ZrF ₄ : 47%, BaF ₂ : 20%, La in composition expressed in mol.
_{F 3: 3%, YF 3} : 3%, AlF 3: 6%, NaF:
If 21% glass is used for the cladding, a fiber with NA = 0.23 is obtained because the glass has an n _d of 1.494.

[0021]

[Examples 2 to 5] A total of 50 g of raw material was weighed so that the composition shown in Table 1 was obtained, and a platinum crucible was used in the same manner as in Example 1 under an inert gas atmosphere at 900 ° C for 2 hours. After melting, the mixture was poured into a mold having a diameter of 40 mm and a depth of 10 mm, put in an electric furnace at 300 ° C., and gradually cooled. The obtained compound having the above composition was a colorless transparent substance, and the glass transition point and the crystallization starting point having the values shown in Table 1 were observed in the differential thermal analysis. Since only a halo pattern appeared, the obtained compound was determined to be glass.

When the n _d of the obtained glass was measured,
The values shown in Table 1 are shown. For example, the composition is expressed in mol,
ZrF ₄ : 47%, BaF ₂ : 20%, LaF ₃ : 3
%, YF ₃ : 3%, AlF ₃ : 6%, NaF: 21%,
It was found that when the glass of No. 2 is used for the clad, a fiber having NA = 0.27 to 0.38 can be obtained because the n _{d of the} glass is 1.494.

[0023]

[Comparative Example 1] As shown in Table 2, the composition of the obtained glass is ZrF ₄ : 47% and BaF ₂ : 22 in mol.
%, LaF ₃ : 2%, YF ₃ : 2%, AlF ₃ : 4%,
A total of 50 g was weighed so that NaF was 20% and PbF _{2 was} 3%, and melting was performed at 900 ° C. for 2 hours in an inert gas atmosphere using a platinum crucible.

Thereafter, the obtained melt was treated with a diameter of 40 mm,
It was poured into a mold having a depth of 10 mm, placed in an electric furnace at 300 ° C., and gradually cooled. The obtained compound having the above composition is a colorless transparent substance, and has a glass transition point (271) in a differential thermal analysis.
C.), a crystallization start point of 353.degree. C. was observed, and only a halo pattern peculiar to amorphous was revealed by X-ray diffraction, and thus the obtained compound was determined to be glass.

However, when the n _d of the obtained glass was measured, it was found that n _d = 1.503 as shown in Table 2. For example, the composition was expressed in mol, ZrF ₄ : 47%, BaF ₂ :
20%, LaF ₃ : 3%, YF ₃ : 3%, AlF ₃ : 6
%, NaF: 21%, the NA of the resulting fiber is 0.16 because the glass has an n _d of 1.494. This is ZrF ₄ / H
No superiority is recognized as compared with the means such as fF ₄ substitution, NaF / LiF substitution and chlorine doping.

[0026]

[Comparative Examples 2 to 5] A total of 50 g of raw materials were weighed so that the compositions shown in Table 2 were obtained, and a platinum crucible was used in the same manner as in Example 1 under an inert gas atmosphere at 900 ° C. for 2 hours. After melting, the mixture was poured into a mold having a diameter of 40 mm and a depth of 10 mm, put in an electric furnace at 300 ° C., and gradually cooled. But,
In any of the materials, the content of glass constituents or the value of R was out of the range of the present invention, so that slight precipitation of fine crystals or complete devitrification was observed.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

As can be seen from the above embodiments according to the present invention, since fluoride glass of the present invention has a high refractive index and yet stable to crystallization, ZrF ₄ which it has been known
By using a system glass as a clad, a fiber having a higher NA than before can be obtained, and it is suitable for a fiber for optical communication, particularly a rare earth ion-doped fiber for a fiber amplifier.

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[Procedure amendment]

[Submission date] February 2, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Claim 2

[Correction method] Change

[Correction content]

Claims (2)

[Claims] 1. The core glass is ZrF ₄ , BaF ₂ , La.
_{F 3, YF 3, AlF 3} , NaF and consists PbF _2, and PbF _2, YF _3, the ratio R of the content of AlF ₃
(R = [PbF ₂ ] / {[AlF ₃ ] + [YF ₃ ]})
Is 0.65 ≦ R ≦ 1.45, a fluoride glass fiber characterized by the following: 2. The composition of the core glass is 37 ≦ ZrF ₄ ≦ 54 mol%, 12 ≦ BaF ₂ ≦
24 mol%, 0 ≤ LaF ₃ ≤ 5 mol%, 1 ≤ Y
F ₃ ≤ 10 mol%, 3 ≤ AlF ₃ ≤ 10 mol%,
10 ≤ NaF ≤ 20 mol%, 4.5 ≤ PbF ₂ ≤
18 mol%, and PbF ₂ , YF ₃ , AlF ₃
Content ratio R (R = [PbF ₂ ] / {[AlF ₃ ] +
[YF ₃ ]}) is 0.65 ≦ R ≦ 1.45, The fluoride glass fiber according to claim 1.