JP2000264675A - Glass for optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide optical fiber glass which has a high refractive index (nd) of >=1.640, an excellent light transmittance, and an excellent melting property, has thermal characteristics close to those of clad grass, namely a softening point(SP) of 680-740 deg.C, an average linear expansion coefficient (α) of 85×107/ deg.C to 110×107/ deg.C in a temperature range of 100-300 deg.C, and can easily be spun. SOLUTION: This optical fiber glass comprises 25-34 wt.% of SiO2, 1-8 wt.% of B2O3, 3-10 wt.% of Al2O3, 0.5-7 wt.% of ZrO2, 0-8 wt.% of Ta2O5, 0.1-15 wt.% of ZnO, 5-20 wt.% of CaO, 0-0.1 wt.% of TiO2, 0-<1 wt.% of PbO, 31-52 wt.% of BaO, 0.5-4 wt.% of Li2O, 0-8 wt.% of Na2O, 0-8 wt.% of K2O, 0-1 wt.% of Sb2O3, provided that the total amount of SiO2 and B2O3 is <=35 wt.%. The optical fiber glass has a high refractive index (nd) of >=1.640, a softening point(SP) of 680-740 deg.C, and an average linear expansion coefficient (α) of 85×107/ deg.C to 110×107/ deg.C in a temperature range of 100-300 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a multi-component optical fiber.
It is related to glass for Ivar and has a refractive index (nd).
It has an optical constant of 1.640 or more and a softening point (SP) of 6
80 to 740 ° C. and 100 to 300
Average linear expansion coefficient (α _{100 ~ 300 ° C})
Is 85 to 110 × 10^-7/ ℃ in the range of thermal properties
Especially for endoscope imagescopes and light guides.
High numerical aperture required for applications such as sensors and sensors
(High NA) used as core glass for optical fiber
A glass suitable for use.

[0002]

2. Description of the Related Art In general, an optical fiber is composed of a core glass (core material) having excellent translucency and a clad glass having excellent weather resistance covering the periphery thereof, and the core glass has a higher refractive index than the clad glass. When light is incident on one end face of the optical fiber, the light is transmitted to the other end face while repeating total reflection at the interface between the core glass and the clad glass. Here, when light is incident, the coupling efficiency between the optical fiber and the light source increases as the light receiving angle at the end face of the optical fiber increases. The light receiving angle is expressed as a numerical aperture (NA), where the NA is the refractive index of the core glass n ₁ ,
Assuming that the refractive index of the clad glass is n ₂ , it is represented by the following equation.

NA = (n ₁ ² −n ₂ ² ) ^1/2

Therefore, in order to increase the NA,
The refractive index difference between the core glass and the clad glass may be increased, and considering the case where the refractive index of the clad glass is constant, the NA increases as the refractive index of the core glass increases.
Therefore, a core glass having a refractive index as high as possible is actually demanded as a core glass of a high NA optical fiber.

A multi-component glass optical fiber is not suitable for long-distance transmission because the optical transmission loss is larger than that of a silica glass optical fiber, but it is not possible to increase the diameter of the fiber or change the NA as described above. Since it can be easily formed, it has good coupling efficiency with light sources and sensors, and is used for short-distance transmission, imagescopes for endoscopes, light guides, sensors, and the like.

[0006] In the multi-component glass optical fiber for the above applications, soda lime silicate glass is generally used as a clad glass having excellent weather resistance, and has a higher refractive index than this clad glass and has a sufficient resistance. From the viewpoint of devitrification, the core glass is disclosed in
SiO ₂ -PbO listed in 60310 JP etc.
-R ₂ O-based (R ₂ O is an alkali metal oxide) is often used glass. However, this glass is inferior in light transmittance in a short wavelength region, as shown in FIG.
When the transmission path is long, the transmitted light has a yellow tint, and there is a problem that the color rendering property is reduced. JP-A-2-293346 discloses a glass suitable for the core glass.
iO ₂ —Na ₂ O—K ₂ O—BaO—ZnO—La ₂ O ₃ based glass; Japanese Patent Application Laid-Open No. 62-70245 discloses SiO ₂
-Al ₂ O ₃ -ZrO ₂ -BaO-B ₂ O ₃ -R ₂ O-RO glasses are disclosed, but these glasses have low refractive indices and have a higher NA that has been demanded in recent years. Is insufficient as a glass for optical fibers.

On the other hand, the double crucible method and the rod-in-chu
In the optical fiber spinning process performed by the
Agulhas sufficient devitrification resistance at spinning temperature
Is essential, and the heat of core glass and clad glass
It is required that the target characteristics be as close as possible. Sand
Consisting of the above-mentioned soda-lime-silicate glass
Clad glass has a softening point (SP) of 700 to 770
° C, average linear expansion coefficient (α _{100 ~ 300 ° C}) Is 80-100x
10^-7/ ℃ has a thermal characteristic in the range, optical fiber
-Softening point of core glass due to problems such as temperature control during spinning
(SP) is the same as the softening point (SP) of the clad glass
Or a slightly lower temperature is preferred
No. Also, the average linear expansion coefficient of the core glass
(Α_{100 ~ 300 ° C}) Also structural irregularities and cracks due to differential thermal expansion
It is desirable to be close to that of clad glass for prevention
However, considering the fiber bending strength, etc.
The average linear expansion coefficient (α_{100 ~ 300 ° C}5)
-10 × 10^-7It is preferable that the value be as large as about / ° C
No. However, the preferred softening point (SP) and
Linear expansion coefficient (α_{100 ~ 300 ° C}) And high refractive index
Glass with excellent light transmittance and melting properties
The fact is that it is unknown.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to improve the drawbacks of the above-mentioned conventional glass, and in particular, to improve the high NA.
It has a high refractive index (nd) of 1.640 or more suitable for use as a core glass of an optical fiber, has excellent light transmittance and melting properties, and has thermal properties close to those of clad glass, that is, a softening point. (SP) is 680-740
It can be easily spun by having an average linear expansion coefficient (α _{100 to 300 ° C.} ) in the temperature range of _{100 to 300 ° C.} of 85 to 110 × 10 ⁻⁷ / ° C. It is to provide glass for optical fiber.

[0009]

Means for Solving the Problems In order to achieve the above object, the present inventor has conducted intensive studies and found that SiO ₂ —B ₂ O _{3 of a} specific composition range which has not been specifically disclosed.
—Al ₂ O ₃ —ZrO ₂ —ZnO—CaO—BaO—Li ₂
In an O-based glass, a high refractive index of 1.640 or more (n
d) having excellent light transmittance and melting property, and
The present inventors have found that a glass having the above-mentioned desired thermal characteristics for improving the spinnability with the clad glass can be obtained, and have accomplished the present invention.

That is, the glass for an optical fiber according to the first aspect of the present invention for achieving the above object,
25% to 34% by weight of SiO ₂ , 1 to 8% of B ₂ O ₃ , provided that the total amount of SiO ₂ and B ₂ O ₃ is 35% or less, _{3 to} 10% of Al ₂ O ₃ , and ZrO ₂ . _{5~ 7%, Ta 2 O 5} 0~ 8%, ZnO 0.1~15%, CaO 5~20%, TiO 2 0~0.1%, PbO 0~ less than 1%, BaO 31~52%, Li ₂ O 0.5 to 4%, Na ₂ O 0 to 8%, K ₂ O 0 to 8%, Sb ₂ O ₃ 0 to 1%, each component having a refractive index (nd) of 1. 640 or more and the softening point (S
P) is in the range of 680 to 740 ° C, and 100 to 30
0 average linear expansion coefficient in a temperature range of _{℃ (α 100 ~ 3 00 ℃} ) is being in the range of 85~110 × 10 ^-7 / ℃.

Further, fiber-glass according to claim 2 according to the present invention, in _{weight%, SiO 2 25~34%, B} 2 O 3 1~ 5%, however, the SiO ₂ and B ₂ O ₃ the total amount is 35% or _{less, Al 2 O 3 3~ 8%} , ZrO 2 3~ 7%, Ta 2 O 5 0~ 8%, 0.1~10% ZnO, CaO 5~15%, however, ZnO and the total amount of CaO is more than _{7%, TiO 2 0~0.1%, BaO 40~50} %, Li 2 O 1~ 4%, Na 2 O 0~ 2%, Sb 2 O 3 0~ 1% range Having a refractive index (nd) of 1.640 or more and a softening point (S
P) is in the range of 680 to 740 ° C, and 100 to 30
0 average linear expansion coefficient in a temperature range of _{℃ (α 100 ~ 3 00 ℃} ) is being in the range of 85~110 × 10 ^-7 / ℃.

[0012]

DETAILED DESCRIPTION OF THE INVENTION As described above, the reasons for limiting the composition range of each component are as follows. That is, the SiO ₂ component, which is a glass forming component, needs to be 25% or more in order to maintain the devitrification resistance and chemical durability of glass.
If it exceeds 4%, it becomes difficult to maintain the desired refractive index and softening point (SP).

The B ₂ O ₃ component is a component for adjusting the softening point (SP) and, like the SiO ₂ component, is a glass-forming component. Requires 1% or more. However, it should be up to 8% to maintain the chemical durability of the glass. Further, since the SiO ₂ and B ₂ O ₃ components are components that give a low refractive index particularly in the glass composition system of the present invention, in order to easily obtain a desired refractive index, the B ₂ O ₃ component must be 5 %, And for the same reason, the total amount of both components should be 35% or less.

The Al ₂ O ₃ component is a component which comprehensively improves the chemical durability of the glass. If the amount is less than 3%, the above effect is small, and if it exceeds 10%, the glass tends to be devitrified. Become. Further, since the Al ₂ O ₃ component has a large effect of increasing the softening point (SP), a more preferable range is 3 to 3.
8%.

The ZrO ₂ component is used for the chemical durability of glass,
Particularly, it is a component having a large effect of improving acid resistance. However, if the amount is less than 0.5%, the above effect cannot be obtained, and if it exceeds 7%, the glass tends to rapidly devitrify. Further, in order to obtain particularly excellent chemical durability, the amount is more preferably 3% or more.

Although the Ta ₂ O ₅ component is effective for adjusting the refractive index and improving the devitrification resistance, it is a relatively expensive raw material and should be introduced especially when the above effects are required. In order to obtain the above effect, up to 8% is sufficient.

The ZnO and CaO components coexist by allowing these two components to coexist, as shown in FIG.
This is an important component that has been found to have an effect of lowering the viscosity of the glass in the melting temperature range while keeping the softening point (SP) on the same level as that of conventional glass. By lowering the viscosity, the glass can be melted at a low temperature, the influence of impurity contamination caused by melting of the furnace material etc. into the molten glass due to the high-temperature melting can be suppressed, and a high refractive index glass excellent in light transmittance can be obtained. . The above-mentioned effect is achieved by changing the ZnO and CaO components to 0.1% respectively.
% And 5% or more, and it is more preferable that the total amount of these two components is 7% or more. Further, each component of the ZnO and CaO components,
Above 15% and 20%, respectively, the glass tends to devitrify. Further, in order to obtain a glass having further excellent devitrification resistance, the ZnO component is more preferably set to 10% or less, and in order to more easily maintain the target softening point (SP), the CaO component is preferably used. Is more preferably 15% or less.

The PbO and TiO ₂ components can be arbitrarily added to prevent solarization of the glass. However, the amounts introduced to achieve the above effects are less than 1% and 0.1% or less, respectively. the amount of PbO and TiO ₂ component, respectively, exceeds more than 1% and 0.1%, light transmittance is lowered. In addition, since the effect can be obtained by introducing only one of these components, PbO which requires cost for environmental measures is required.
More preferably, no components are introduced.

The BaO component is an essential component for stabilizing the glass at the time of melting and maintaining the refractive index. However, if it is less than 31%, it is difficult to obtain a target refractive index, and if it exceeds 52%, the glass is devitrified. Easier to do. Further, in order to obtain a glass excellent in devitrification resistance in the spinning temperature range (850 to 1000 ° C.) of the optical fiber, it is more preferable to set the range to 40 to 50%.

The Li ₂ O component is an important component for adjusting the softening point (SP) and the average linear expansion coefficient (α _{100 to 300 ° C.} ). has the effect of increasing the α _{10 0 ~ 300 ℃),} also it has the effect of improving the meltability of the glass. In order to maintain the target average linear expansion coefficient (α _{100 to 300 ° C.} ), it is necessary to make the Li ₂ O component 0.5% or more, but if the amount exceeds 4%, the softening point becomes higher. And it is difficult to maintain the desired 680 ° C.

The components of Na ₂ O and K ₂ O are Li ₂
It has the same effect as the O component and can be arbitrarily added for the purpose of obtaining an auxiliary effect of the Li ₂ O component. Further, when these two components are added in the same amount by weight as the Li ₂ O component, the average linear expansion coefficient (α _{100 to 300 ° C.} )
Is increased similarly to the Li ₂ O component, but the softening point (SP) does not decrease as much as the Li ₂ O component. Therefore, Li ₂
By introducing the O component in combination with the Na ₂ O and / or K ₂ O components, the adjustment of the softening point (SP) and the average coefficient of linear expansion (α _{100 to 300 ° C.} ) can be performed more easily. . However, if the amount of each of the Na ₂ O and K ₂ O components exceeds 8%, the glass tends to be devitrified instead. In addition, among these three components, the K ₂ O component is the component that gives the lowest refractive index to the glass,
In order to obtain a glass having a higher refractive index for the A optical fiber, it is more preferable to use a Na ₂ O component without introducing a K ₂ O component. Furthermore, it has a high refractive index,
In addition, in order to obtain glass having excellent devitrification resistance and chemical durability, the Na ₂ O component is set to 2% or less, and Li ₂
It is more preferable to introduce the O component at 1% or more.

The Sb ₂ O ₃ component can be arbitrarily added as a fining agent when the glass is melted, but an amount of 1% or less is sufficient.

[0023]

EXAMPLES Next, examples of compositions (No. 1 to No. 14) relating to the glass for optical fibers of the present invention are described in Japanese Patent Application Laid-Open Nos. 70245 and JP-A-2-2933
No. 46, comparative examples (No. A to No. C) of glass having the same composition as those of the examples were prepared by comparing the refractive index (nd), softening point (SP), and average linear expansion of the obtained glass. The results are shown in Tables 1 and 2 together with the coefficients (α _{100 to 300 ° C.} ), the degree of coloring and the measurement results of the devitrification test.

[0024] Here, the coloring degree, by Japanese Optical Glass Industrial Standard (JOGIS 02- ^1975), to measure the spectral transmittance of the sample parallel to the thickness 10 ± 0.1 mm was polished face, the transmittance 80 % And 5% are shown in units of 10 nm, rounded to the first integer, and the wavelength (λ80) indicating 80% transmittance and the wavelength (λ5) indicating 5% transmittance are short. The smaller the degree of coloring, the better the light transmittance.

In the devitrification test, 150 g of a glass sample was put into a 50 cc pot made of platinum, and each sample was melted at a temperature of 1250 to 1380 ° C. for 5 hours in an electric furnace according to the degree of melting property of each glass. After cooling, each sample was cooled to 1000
After keeping at 5 ° C. and 900 ° C. for 5 hours, the glass was taken out of the furnace and observed for devitrification by a microscope. As a result, a glass having no devitrification was indicated by a circle.

[0026]

[Table 1] (% by weight)

[0027]

[Table 2] (% by weight)

As can be seen from Tables 1 and 2, the present invention
In any of the glasses of the working composition examples, no devitrification was observed.
Excellent devitrification resistance equivalent to conventionally known core glass
The refractive index (nd) within the range targeted by the present invention,
Point (SP) and average linear expansion coefficient (α_{100 ~ 300 ° C})
Comparative Composition Example No. A SiO_Two-Al_TwoO _Three
-ZrO_Two-BaO-B_TwoO_Three-R_TwoO-RO glass and
And Comparative Composition Example No. C SiO_Two-Na_TwoOK_TwoOB
aO-ZnO-La_TwoO_ThreeRefractive index (nd) is higher than system glass
Even higher, the glass of the working composition of the present invention has a high NA optical filter.
It turns out that it is suitable as a core glass for fiber
You. Further, the glass of the working example of the present invention has a coloring degree of 3.
Comparative composition example N in the range of 1/26 to 33/28
o. B SiO_Two-PbO-R_TwoDegree of coloring than O-based glass
Is small and the light transmittance is much better
You.

FIG. 1 shows an example of the composition No. of the present invention in Table 1 above. 8 and Comparative Composition Example No. 8 in Table 2 above. It is a figure which shows the result of having measured the spectral transmittance of the sample of thickness 10 +/- 0.1mm obtained from the glass of B and which polished the facing surface in parallel. As can be seen in FIG. The spectral transmittance curve shown by the solid line of the glass of Comparative Example No. 8 is Comparative Example No. 8. FIG. 1 also shows that the spectral transmittance curve shown by the dotted line of glass B is shifted to the shorter wavelength side, and the light transmittance in the short wavelength region is superior to the glass of the comparative composition example. I understand.

FIG. 2 is a graph showing Example Composition Example No. of the present invention in Table 1 above. 7 and Comparative Composition Example No. The result of measuring the viscosity (log η) of the glass of C is shown. As can be seen in FIG. The glass of No. 7 has a glass softening point (SP), that is, a temperature at which the viscosity (log η) of the glass shows 7.65 poise (poise), is almost the same as the glass of the comparative composition example.
In the melting temperature range of about 1250 ° C. or higher, the viscosity (log η) is much smaller than the glass of the comparative composition example, and the glass of the embodiment composition example of the present invention has better melting property than the glass of the comparative composition example and has a lower temperature. It turns out that it can be melted.

Each of the glasses of Examples of the present invention shown in Tables 1 and 2 was prepared by mixing raw materials such as oxides, carbonates and nitrates at a predetermined ratio and mixing them in a platinum crucible or the like. Inject, depending on the degree of meltability of the composition, melted at a temperature of 1250-1380 ° C. for 2-4 hours,
After stirring and homogenizing, it can be easily obtained by lowering to an appropriate temperature, casting into a mold or the like, and gradually cooling.

[0032]

As described above, according to the present invention, an optical fiber glass of the present invention is _{SiO 2 -B 2 O 3 -Al 2} O 3 -ZrO 2 -Z
Since it has a specific composition range of nO—CaO—BaO—Li ₂ O, the softening point (SP) is 680 to 740.
Since the average linear expansion coefficient (α _{100 to 300 ° C.} ) in the temperature range of 100 ° C. and _{100 to 300 °} C. is in the range of 85 to 110 × 10 ⁻⁷ / ° C. and the devitrification resistance is excellent, the fiber Spinning can be easily performed. In addition, it has a high refractive index (nd) of 1.640 or more, has low viscosity in a melting temperature range, and can be melted at low temperature, and has excellent light transmittance in a short wavelength range, so that color rendering property is deteriorated. Because it ’s small,
It is suitable as a glass for a high NA optical fiber having a small light transmission loss, and particularly suitable as a core glass.

[Brief description of the drawings]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 8 and Comparative Composition Example No. 8 The figure which shows the result of having measured the spectral transmittance of the glass of B.

FIG. 2 is an example of the composition of the present invention. 7 and Comparative Composition Example No. 7 The figure which shows the result of having measured the viscosity of the glass of C.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H050 AA01 AB29X AC03 AC71 AD06 4G062 AA07 BB01 BB03 DA04 DA05 DB03 DE02 DE03 DE04 DF01 DF02 EA02 EA03 EB01 EB02 EB03 EC01 EC02 EC03 EE03 EE04 EG05 F02F03 F03 FC02 JJ04 MM02 NN02 NN29 NN31

Claims (2)

[Claims] 1. A _{weight%, SiO 2 25~34%, B} 2 O 3 1~ 8%, provided that the total amount of SiO ₂ and B ₂ O ₃ is 35% or less, Al ₂ O ₃ 3~10% _{, ZrO 2 0.5~ 7%, Ta} 2 O 5 0~ 8%, ZnO 0.1~15%, CaO 5~20%, TiO 2 0~0.1%, PbO 0~ less than 1%, BaO _{31~52%, Li 2 O 0.5~ 4} %, Na 2 O 0~ 8%, K 2 O 0~ 8%, made from the components of Sb ₂ O ₃ 0~ 1% of the range, the refractive index ( nd) is not less 1.640 or more, a softening point (SP) is in the range of six hundred eighty to seven hundred and forty ° C., an average linear expansion coefficient in a temperature range of _{100~300 ℃ (α 100 ~ 3 00} ℃) 8
An optical fiber glass having a temperature in the range of 5 to 110 × 10 ⁻⁷ / ° C. 2. A _{weight%, SiO 2 25~34%, B} 2 O 3 1~ 5%, provided that the total amount of SiO ₂ and B ₂ O ₃ is 35% or less, Al ₂ O ₃ 3~ 8% _{, ZrO 2 3~ 7%, Ta} 2 O 5 0~ 8%, 0.1~10% ZnO, CaO 5~15%, provided that the total amount of ZnO and CaO is more than 7%, TiO ₂ 0 to 0. 1%, BaO 40~50%, Li 2 O 1~ 4%, Na 2 O 0~ 2%, made from the components of Sb ₂ O ₃ 0~ 1% of the range, the refractive index (nd) of 1.640 or more, the softening point (SP) is in the range of six hundred eighty to seven hundred forty ° C., an average linear expansion coefficient in a temperature range of _{100~300 ℃ (α 100 ~ 3 00} ℃) 8
An optical fiber glass having a temperature in the range of 5 to 110 × 10 ⁻⁷ / ° C.