JPH0781973A - Halide glass - Google Patents

Abstract

PURPOSE:To provide the halide glass having excellent stability to devitrification and capable of increasing the difference of the refractive index between the core and the clad in an optical fiber. CONSTITUTION:In the halide glass, 45-60mol.% either one or both of ZrF4 and HfF4 is incorporated in total, 15-30mol.% BaF2 and 0.1-5mol.% BaCl2 is incorporated, but the sum of BaF2 and BaCl2 is 16-32mol%, 0.5-8mol.% either one or both of LuF3 and YbF3 is incorporated in total, 3-12mol.% AlF3 is incorporated and <=18mol.% either one of NaF and CsF is incorporated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared light transmitting fiber for optical communication and medical use, a host glass for a laser glass and an up-conversion laser, an optical glass, and the like. And stable halide glasses.

[0002]

2. Description of the Related Art Fluoride and chloride halide glasses have a transmission loss of 10 ^-2 dB / km or less, which theoretically far exceeds quartz glass in the infrared region, and their phonon energy is small. Since it can be used as a host glass for 1.3 μm band optical amplification, it is attracting attention as a next-generation optical fiber material for communication. There are ZnCl ₂ type glasses, for example, in halide glasses other than fluoride, but this glass is easy to crystallize, and when exposed to the air, it will react immediately with moisture and devitrify from the surface, and the glass transition point is also low. So it has little practical value. Regarding fluoride glass, ZrF ₄ system (Japanese Patent Publication No. 61-24350), AlF ₃ system (Japanese Patent Publication No. 59-34141), GaF ₃ system (Japanese Patent Publication No. 60-137852), InF ₃ The system (Japanese Patent Laid-Open No. 62-171944) has been developed. However, glasses other than the ZrF ₄ type glass are likely to crystallize, and crystallize during the production of the preform or when the fiber is drawn by reheating and the transmission loss increases. Improvements such as adding ZrF ₄ were made in order to increase the stability of the AlF ₃ system glass against devitrification, but the stability against devitrification has not yet reached that of the ZrF ₄ (eg ZBLAN) system, Another problem is that the infrared transmission range is narrower than that of the ZrF ₄ system. On the other hand, in the case of the ZrF ₄ system glass, the crystallization of the glass is considerably improved as compared with the AlF ₃ system. However, in many cases of actual use, it is necessary to increase the difference in refractive index between the core and the clad in order to increase the numerical aperture of the optical fiber, but there is a limit only in the ZrF ₄ system.
As a method of solving this problem, a method of adding PbF ₂ or BiF ₃ to increase the refractive index of the core glass (Japanese Patent Publication No. 1-1678).
(Gazette No. 1) has been considered. However, PbF ₂ and BiF ₃
However, there is a problem in that the stability of the glass against crystallization is extremely deteriorated by the addition of. Regarding the Cl-doped fluoride glass, there is a composition described in JP-A 1-294550, but BaCl ₂ is 5 mol% or more and the total amount of NaF and LiF is 10 mol% or more. However, if the doping amount of Cl exceeds 5 mol% in terms of the content of BaCl ₂ , the critical cooling rate of the glass becomes high, the crystallization tends to occur when the glass melt is cooled, and the viscosity of the glass decreases. However, there is a problem that the moldability becomes poor when the fiber is drawn from the preform. If NaF and LiF are added to the glass in the same amount at the same time, it becomes difficult to adjust the refractive index difference between the core and the clad required for the actual fiber to be large.

[0003]

As described above, the conventional Al
Fluoride glass other than ZrF ₄ system such as F ₃ system has a drawback that stability against devitrification is poor. On the other hand, with ZrF ₄ system fluoride glass, it was difficult to fabricate an optical fiber having a large difference in refractive index between the core and the clad. Further, the generally used means for increasing the refractive index of the core (addition of PbF ₂ etc.) greatly impairs the stability of the glass against devitrification. Further, ZrF ₄ -based fluoride glass doped with a large amount of Cl (Japanese Patent Application Laid-Open No. 1-294550) has a low viscosity and poor moldability, and therefore a problem remains in practical use.

Therefore, the object of the present invention is to eliminate the above-mentioned conventional drawbacks, provide excellent stability against devitrification, and provide a halide glass capable of increasing the difference in refractive index between the core and the clad in an optical fiber. And

[0005]

In order to achieve the above object, the halide glass of the present invention contains one or both of ZrF ₄ and HfF _{4 in} a total amount of 45 to 60 mol%, and contains BaF ₂ .
15-30mol%, BaCl ₂ 0.1-5mol%, but BaF ₂ and Ba
It contains 16 to 32 mol% of Cl ₂ in total, 0.5 to 8 mol% of LuF ₃ and / or YbF ₃ in total, ₃ to 12 mol% of AlF ₃ , and either NaF or CsF. One side to 18
The first feature is that the content is mol% or less. In addition to the above first characteristic, the halide glass of the present invention has a total of 5 mol of any one or more of LaF ₃ , YF ₃ and GdF _3.
The second feature is that the content is not more than%. Further, the third feature of the halide glass of the present invention is that it contains CdF _{2 in an amount} of 8 mol% or less in addition to the first or second feature.

Namely, the present invention is ZrF ₄ - (HfF ₄₎ -BaF part of F ₂ based fluoride glass was replaced with Cl, and also LuF _3, Yb
Is contained F _3, AlF ₃ or the like, which was selectively be contained NaF and CsF, not only increase the stability of the glass against devitrification, it is possible to sufficiently adjust the refractive index of the glass Therefore, the refractive index range of stable glass can be widened, and the difference in the refractive index between the core and the clad can be increased when selecting the glass for the core and the clad of the optical fiber within the glass composition of the present invention.

ZrF ₄ and HfF ₄ are components that form the network skeleton of the present glass, and the total range is 45 to 60 mol%. If it is less than 45 mol% or more than 60 mol%, it tends to be crystallized when the glass melt is cooled and its practical value becomes poor. A lot of ZrF _{4 in the} fiber core,
By selecting HfF ₄ to be small, HfF ₄ to be large in the cladding, and ZrF ₄ to be small, it is possible to greatly adjust the refractive index difference between the core and the cladding.

BaF ₂ plays a role of complementing the network skeleton of the present glass and is an essential component for the present glass. If it is less than 15 mol% or more than 30 mol%, the glass tends to crystallize. Become. BaCl ₂ plays a role similar to BaF ₂ in this glass, and by introducing an appropriate amount of Cl into the glass, the crystallization onset temperature (T
The difference between x) and the glass transition temperature (Tg) becomes large, and the stability of the glass against devitrification is improved. Also, the polarizability of Cl is
Since it is larger than F, it has the effect of increasing the refractive index. However, when BaCl ₂ is less than 0.1 mol%, the effect of increasing the stability against devitrification and the refractive index of glass is small, and when it exceeds 5 mol%, the refractive index is increased, but the critical cooling rate increases. The stability of the glass against devitrification deteriorates, and the viscosity of the glass decreases, so that the moldability of the fiber also deteriorates. If the total of BaF ₂ and BaCl ₂ is less than 16 mol% or more than 32 mol%, the glass tends to crystallize. By selecting a large amount of Cl for the fiber core material and a small amount of Cl for the cladding material, it is possible to greatly adjust the difference in the refractive index between the core and the cladding.

LuF ₃ and YbF ₃ are important components in the present glass, and other rare earth fluorides such as LaF ₃ , YF ₃ ,
Compared with GdF ₃ ), it plays a role of more effectively improving the stability of glass against devitrification. This is because Lu and Yb have heavy atoms in the rare earth metals and have a small ionic radius.
It is considered that this is because the bond with F or Cl is strong, and thus it is difficult to make a transition in the glass network structure. LuF ₃ and YbF ₃ contain 0.5 to 8 mol% of one or both in total,
It is effective in improving the stability of glass against crystallization. If it exceeds 8 mol%, the glass tends to devitrify.
On the other hand, if it is less than 0.5 mol%, the effect of improving the stability of glass is small.

AlF ₃ improves the stability of the glass against devitrification, but if its content is less than 3 mol%, it is less effective.
If it exceeds 12 mol%, the glass tends to devitrify. A part of AlF ₃ may be replaced with InF ₃ , but the replacement amount is 3 mol%
If it exceeds, devitrification tends to occur.

By containing 18 mol% or less of NaF and CsF, respectively, the stability of the glass against devitrification can be increased. NaF lowers the refractive index of glass, and CsF increases the refractive index of glass. That is, NaF
Can improve the stability of the glass against devitrification and reduce the refractive index of the glass.Therefore, CsF should be contained in the glass on the cladding side of the fiber. Since the stability of the glass against devitrification can be improved and the refractive index of the glass can be increased, inclusion in the glass on the core side of the fiber results in a large difference in the refractive index between the core and the clad and stability against devitrification. A good fiber can be obtained. CsF is larger than LiF in R / V (R: molecular refraction,
V: molecular volume), so CsF is in the core and NaF is in the clad
By including the above, LiF in the core and NaF in the clad
It is possible to adjust the refractive index difference of the fiber within a wider range as compared with the one containing NaF and CsF are each preferably in the range of 3 to 16 mol%, and when they exceed 16 mol%, the stability of the glass against devitrification decreases. 3mo again
If it is less than 1%, the stability of the glass against devitrification is reduced, and the effect of adjusting the refractive index is reduced. In any case, NaF
When CsF and CsF exceed 18 mol%, the stability of the glass against devitrification deteriorates and the chemical durability also deteriorates.

LaF ₃ , YF ₃ , and GdF ₃ can improve the stability of the glass against devitrification by containing at least one of them in a total amount of 5 mol% or less. 5 mol
If it exceeds%, the stability of the glass against devitrification deteriorates.

CdF ₂ can increase the glass transition temperature, that is, heat resistance. The appropriate range is 8 mol% or less,
It is preferably 6 mol% or less, and when it exceeds 8 mol%, the stability of the glass against devitrification deteriorates.

[0014]

The halide glass of the first feature of the present invention is made of high-purity ZrF ₄ , HfF ₄ , BaF ₂ , BaCl ₂ LuF ₃ , YbF ₃ and Al.
F ₃ , NaF, CsF are weighed and mixed in an inert gas atmosphere such as Ar gas so as to have a predetermined content, and after melting in the same inert gas atmosphere, at a temperature near the glass transition point. It can be obtained by cooling and solidification including slow cooling.
By changing the content of each component within the indicated content range, the stability of the glass against devitrification is maintained and the refractive index is changed and adjusted within a sufficiently wide range, for example, wider than that of the ZBLAN system. can do. Therefore, it is effective as an optical fiber material for infrared transmission and up-conversion lasers having a core-clad structure. In the halide glass according to the second characteristic, the glass according to the first characteristic further contains LaF ₃ , YF ₃ , and GdF ₃ within a predetermined range, whereby the stability against devitrification of the glass is further improved. In the halide glass according to the third feature, the glass according to the first feature or the glass according to the second feature may further contain CdF ₂ within a predetermined range to improve the heat resistance of the glass.

[0015]

Examples High-purity ZrF ₄ , HfF ₄ , BaF ₂ , BaCl ₂ LuF ₃ , Yb
_{F 3, AlF 3, InF 3} , NaF, CsF, LaF 3, YF 3, GdF 3, CdF 2
, And each of them is weighed and mixed in an Ar gas atmosphere so as to have each composition shown in Nos. 1 to 20, and these are mixed with platinum, gold or a carbon crucible in an Ar gas atmosphere to about 900-
Melted at 1000 ° C. for 1 hour. After that, the glass melt was cast into a metal or carbon mold to be solidified, and gradually cooled at a temperature near the glass transition point to obtain a transparent glass having no foreign matter in appearance. Tables 1 and 2 show the transition point (Tg) and ΔT (crystallization start temperature Tx-glass transition point Tg) of the obtained glass. For comparison, Table 3 shows the measurement results of the glasses having the compositions (Comparative Examples 21 to 28) exceeding the range of the present invention. Tables 1-3
The marks ⊚, ◯, Δ, and × show the appearance that when the glass melt is naturally cooled, the glass is transparent, the glass is mostly transparent, only a small amount is vitrified, and almost crystallized. RE in the table indicates a rare earth metal.

[0016]

[Table 1]

[0017]

[Table 2]

[0018]

[Table 3]

As a result of the examples, in the comparative examples exceeding the range of the present invention, when the glass melt was poured out and quickly press-cooled with a metal plate, it might become glass, but the value of ΔT was small. However, in the case of natural cooling, it will crystallize. On the other hand, within the composition range of the present invention, the glass melt was poured into a mold such as brass heated near the glass transition point (Tg) to easily obtain a transparent glass having a size of 10 × 10 × 6 mm or more. Regarding the refractive index, for example, as is clear from numbers 17 and 18, by increasing the content of BaCl ₂ ,
By increasing the refractive index significantly from 1.497 to 1.508, and replacing the majority of HfF ₄ with ZrF ₄ in Nos. 19 and 20, and including CsF instead of NaF, the refractive index was increased from 1.487.
It is clear that it can be greatly increased to 1.502. That is, the refractive index can be largely changed and adjusted while maintaining the stability of the glass against devitrification.

[0020]

According to the present invention, which has the above-described structure,
According to the halide glass described in (1), the glass is stable against devitrification of the glass, and the refractive index can be easily adjusted and changed in a wide range. Therefore, by using the glass of the present invention, it is possible to manufacture an optical fiber for infrared transmission and up-version laser, which has a large refractive index difference between the core and the clad and has a small transmission loss. According to the halide glass of the second aspect, in addition to the effect of the configuration of the first aspect, the stability of the glass against devitrification can be further improved. According to the halide glass of the third aspect, the heat resistance of the glass can be improved in addition to the effect of the configuration of the first or second aspect.

Claims (3)

[Claims] 1. One or both of ZrF ₄ and HfF ₄ is contained in a total amount of 45 to 60 mol%, BaF ₂ is contained in an amount of 15 to 30 mol%, and BaCl ₂ is contained.
0.1 to 5 mol%, but 16 to 32 mo in total of BaF ₂ and BaCl _2.
1% content, one or both of LuF ₃ and YbF ₃ content of 0.5 to 8 mol%, AlF ₃ content of ₃ to 12 mol%,
A halide glass containing 18 mol% or less of either NaF or CsF. 2. The halide glass according to claim 1, containing at least one of LaF ₃ , YF ₃ and GdF _{3 in} a total amount of 5 mol% or less. 3. The halide glass according to claim 1, which contains CdF _{2 in an amount} of 8 mol% or less.