JP2022041935A - Crystallized glass for optical filter, and optical filter - Google Patents

Abstract

To provide a crystallized glass for optical filter and an optical filter that have both the transmittance required for a conventional optical filter substrate, and a high thermal expansion coefficient that can respond to stress changes caused by an increase in the number of dielectric films formed on the substrate.SOLUTION: Provided is a crystallized glass for optical filter that is characterized by containing, in terms of oxide conversion mass%, SiO2 component by 35.0% to 55.0%, K2O component by 15.0% to 30.0%, Al2O3 component by 10.0% to 25.0%, ZrO2 component by 0% to 10.0%, TiO2 component by 0% to 15.0%, ZrO2 component and TiO2 component total amount over 0% to 15.0%, and having a thermal expansion coefficient at -30 to 70°C of 125 to 155(×10-7/°C).SELECTED DRAWING: None

Description

The present invention relates to crystallized glass for an optical filter and an optical filter.

In recent years, with the steadily increasing spread of communication devices and the rapid development of the Internet, it is required to further increase the scale and capacity of data communication using optical fibers. For data communication using an optical fiber, light in the 1550 nm band, which has a particularly small optical loss in the optical fiber, is used. In addition, the wavelength division multiplexing method (WDM), which further divides this band into a plurality of fine bands, simultaneously transmits a plurality of lights to an optical fiber, and finally separates and extracts the multiplexed optical signals one by one. Used.

Further, WDM is classified into two types according to the density of the light to be multiplexed, a coarse density wavelength division multiplexing (CWDM) and a high density wavelength division multiplexing (DWDM). CWDM has a low density of about 16 wavelengths to be multiplexed. On the other hand, DWDM has a high density because the wavelength to be multiplexed is about 80 to 96. For this reason, DWDM is adopted in applications that require large-capacity communication, such as data communication between operators, nations, and base stations.

In addition, with the full-scale introduction of the 5th generation mobile communication system (5G) and IoT, there is a concern that the data communication capacity limit by WDM will become apparent. As a recent trend, research is underway to overcome the data communication capacity limit by using a new space division multiplexing (SDM) in addition to the conventional wavelength division multiplexing (WDM). ..

By the way, the dielectrics of the low refractive index layer (SiO ₂ and the like) and the high refractive index layer (Ta ₂ O ₅ and the like) are laminated on the optical filter substrate for optical communication to form a film. In order to increase the data communication capacity, it is preferable that the band of the multiplexed light is narrow, and in order to cope with the narrow band of the communication wavelength, it is necessary to increase the number of layers of the film to be formed on the substrate. Therefore, an optical filter substrate having a large coefficient of thermal expansion is required from the viewpoint of adhesion of laminated film formations and in order to cope with stress changes caused by an increase in the number of film formations.

Patent Document 1 describes that the coefficient of thermal expansion at −20 to 70 ° C. is 93 × ^10-7 / ° C. to 130 × ^10-7 / ° C., the Young's modulus is 85 GPa or more, and (a) disilicate is used as the main crystal phase. Disclosed are glass ceramics for optical filters comprising lithium and (b) at least one selected from α-quarts, α-quarts solid solution, α-cristobalite, and α-cristobalite solid solution. However, the problem that the maximum value of the average coefficient of thermal expansion exists in the vicinity of 100 ° C. has not been achieved.

Further, Patent Document 2 contains an Al ₂ O ₃ component and an R ₂ O component (R is at least one selected from Li, Na, and K), and the main crystal phase is calcilite, −30 ° C. Disclosed are inorganic compositions having a coefficient of thermal expansion of 95 × ^10-7 / ° C to 121 × ^10-7 / ° C in the temperature range of −70 ° C. However, no inorganic composition having a coefficient of thermal expansion exceeding 125 × 10 ^-7 / ° C. is disclosed.

Japanese Unexamined Patent Publication No. 2001-318222 Japanese Unexamined Patent Publication No. 2007-031180

Therefore, the present invention maintains the transmittance required for a conventional optical filter substrate, and changes in stress caused by an increase in the number of film formations required for a substrate for a DWDM apparatus in order to cope with an increase in information communication volume in recent years. It is an object of the present invention to obtain a crystallized glass for an optical filter and an optical filter having a high thermal expansion coefficient corresponding to the above.

As a result of intensive test and research to solve the above problems, the present inventors have improved the expansion characteristics by adjusting the network former component and the alkali metal oxide component and crystallizing the glass, and the _ZrO2 component or By controlling the particle size of the precipitated crystal by adjusting the TiO ₂ component, the glass composition and composition of the crystallized glass for an optical filter having a desired thermal expansion coefficient while maintaining the transmittance were found, and the present invention was completed. I arrived.
Specifically, the present invention provides the following.

(1) In terms of oxide mass%,
SiO ₂ component 35.0% -55.0%,
_K2O component is 15.0% to 30.0%,
Al ₂ O ₃ component 10.0% to 25.0%,
ZrO2 component from ₀ % to 10.0%,
TiO ₂ component from 0% to 15.0%,
The total amount of ZrO ₂ component and TiO ₂ component is more than 0% to 15.0%,
Contains,
A crystallized glass for an optical filter, characterized in that the coefficient of thermal expansion at −30 to 70 ° C. is 125 to 155 (× 10 ⁻⁷ / ° C.).

(2) In terms of oxide mass%,
Li ₂ O component from 0% to 7.0%,
Na ₂ O component from 0% to 5.0%,
MgO component from 0% to 7.0%,
The crystallized glass for an optical filter according to (1), which comprises.

(3) As a crystal phase
The crystallized glass for an optical filter according to (1) or (2), which contains KAlSiO ₄ or KAlSiO ₄ solid solution.

(4) The crystallized glass for an optical filter according to any one of (1) to (3), wherein the 1 mm thick sample has a spectral transmittance of 90% or more at 1550 nm.

(5) An optical filter formed by forming a dielectric film on the crystallized glass according to any one of (1) to (4).

According to the present invention, it is possible to provide a crystallized glass for an optical filter and an optical filter having an improved coefficient of thermal expansion while maintaining the transmittance required for the optical filter.

The composition range of each component constituting the crystallized glass for an optical filter of the present invention is described below. In the present specification, the content of each component shall be expressed in mass% with respect to the total mass of the oxide equivalent composition unless otherwise specified. Here, the "oxide-equivalent composition" is used when it is assumed that the oxides, composite salts, metal fluorides, etc. used as raw materials for the glass constituents of the present invention are all decomposed at the time of melting and changed to oxides. It is a composition which describes each component contained in a glass, assuming that the total mass number of the produced oxide is 100 mass%.

[Glass component]
In terms of oxide mass%, the SiO ₂ component is 35.0% to 55.0%, the K2O component is 15.0% to 30.0% _, and the _Al2O3 component is 10.0% to ₂₅ %. It contains 0%, ZrO ₂ component 0% to 10.0%, TiO ₂ component 0% to 15.0%, and the total amount of ZrO ₂ component and TiO ₂ component is more than 0% to 15.0%.

[About essential ingredients and optional ingredients]
The SiO ₂ component is a skeleton component of glass and at the same time, an essential component that forms crystals that precipitate by heat treatment of raw glass. In particular, by setting the content of the SiO ₂ component to 35.0% or more, the raw glass can be stably produced.
Therefore, the lower limit of the content of the SiO ₂ component is preferably 35.0% or more, more preferably 37.0% or more, still more preferably 40.0% or more.
On the other hand, by setting the content of the SiO ₂ component to 55.0% or less, an excessive increase in viscosity and deterioration of meltability can be suppressed, so that the content of the SiO ₂ component is preferably 55.0% or less. , More preferably 53.0% or less, more preferably 50.0% or less, still more preferably 45.0% or less.

The Li ₂ O component is an effective component for promoting the melting reaction of the raw material when it is contained in excess of 0%, lowering the melting temperature of the glass and improving the meltability, while it is chemically used when the content is increased. It causes deterioration of durability and change of precipitated crystal phase.
Therefore, the lower limit of the content of the Li ₂ O component is preferably more than 0%, more preferably 0.5% or more, still more preferably 1.0% or more.
On the other hand, by setting the content of the Li ₂ O component to 7.0% or less, deterioration of devitrification due to excessive content, change in the precipitated crystal phase, and deterioration of chemical durability can be suppressed.
Therefore, the content of the Li ₂ O component is preferably 7.0% or less, more preferably 6.0% or less, still more preferably 5.0% or less.

When the Na ₂ O component is contained in an amount of more than 0%, the meltability of the glass is adjusted, and at the same time, the Na 2 O component is a component constituting crystals precipitated by the heat treatment of the raw glass.
Therefore, the lower limit of the content of the Na ₂ O component is preferably more than 0%, more preferably 0.5% or more.
On the other hand, by setting the content of the Na ₂ O component to 5.0% or less, deterioration of chemical durability and change in the precipitated crystal phase can be suppressed.
Therefore, the content of the Na ₂ O component is preferably 5.0% or less, more preferably 3.0% or less, and further preferably 2.0% or less.

_The K2O component is one of the components constituting the crystals precipitated by the heat treatment of the raw glass when the content exceeds 0%, and at the same time, it is an essential component that contributes to the improvement of the meltability of the glass. The _lower limit of the content of the K2O component is preferably 15.0% or more, more preferably 17.0% or more, still more preferably 18.0% or more.
On the other hand, since the deterioration of the chemical durability is suppressed by setting the content of the K ₂ O component to 30.0% or less, the content of the K ₂ O component is preferably 30.0% or less, more preferably. The upper limit is preferably 28.0% or less, and more preferably 26.0% or less.

When the Al ₂ O ₃ component is contained in excess of 0%, it is one of the components constituting the crystals precipitated by the heat treatment of the raw glass, and at the same time, it enhances the chemical durability and mechanical strength of the glass and melted glass. It is an effective component for improving the devitrification resistance of the glass, and is an essential component of the crystallized glass for an optical filter of the present invention.
Therefore, the lower limit of the content of the Al ₂ O ₃ component is preferably 10.0% or more, more preferably 12.0% or more, still more preferably 14.0% or more.
On the other hand, by setting the content of the Al ₂ O ₃ component to 25.0% or less, deterioration of meltability and devitrification due to excessive content can be reduced, so that the content of the Al ₂ O ₃ component is The upper limit is preferably 25.0% or less, more preferably 22.0% or less, still more preferably 19.0% or less.

The P ₂ O ₅ component is an optional component that, when contained in excess of 0%, contributes as a nucleating agent for precipitated crystals, lowers the viscosity of the melt, and contributes to improving the stability of the glass, but is excessively contained. Then, the precipitated crystal phase changes, the glass tends to be devitrified, and vitrification becomes difficult. Therefore, the lower limit is preferably more than 0%, more preferably 0.5% or more.
Further, the upper limit is preferably 5.0% or less, more preferably 3.0% or less, more preferably 2.5% or less, still more preferably 2.0% or less.

The B ₂ O ₃ component is an optional component that, when contained in excess of 0%, contributes to lowering the viscosity of the melt, forms a network structure of glass, and contributes to the stability of glass. On the other hand, the content of the _B2O3 component is preferably _more than 0%, more preferably 0, because the precipitated crystal phase changes or the chemical durability is lowered as the content increases. The lower limit is 5.5% or more.
Further, the upper limit is preferably 5.0% or less, more preferably 3.0% or less, more preferably 2.5% or less, still more preferably 2.0% or less.

When the MgO component is contained in an amount of more than 0%, it is an optional component that contributes to the improvement of the meltability of the glass in addition to improving the meltability of the glass and at the same time preventing the coarsening of the precipitated crystals.
Therefore, the lower limit of the content of the MgO component is preferably more than 0%, more preferably 1.0% or more.
On the other hand, by setting the content of the MgO component to 7.0% or less, devitrification due to excessive content can be reduced.
Therefore, the content of the MgO component is preferably 7.0% or less, more preferably 5.0% or less, more preferably 4.0% or less, still more preferably 3.8% or less, still more preferably 3.2. The upper limit is% or less.

The ZnO component and the SrO component are optional components that contribute to lowering the viscosity of the melt and improving the stability of the glass when each contains more than 0%. On the other hand, excessive content may change the precipitated crystal phase or facilitate devitrification.
Therefore, the ZnO component and the SrO component may or may not be contained, respectively, as long as the physical properties of the material are not impaired. The content can be 0% to 3.0%, respectively.

Since the ZrO ₂ component acts as a nucleating agent when it is contained in an amount of more than 0%, it is a component that not only facilitates the precipitation of crystals but also contributes to the miniaturization of the precipitated crystals and the improvement of mechanical strength. In particular, in the present invention, it is a component capable of adjusting the particle size of crystals.
Therefore, the content of the ZrO2 component is preferably _more than 0%, more preferably 1.0% or more, more preferably 2.0% or more, more preferably 3.0% or more, still more preferably 3.0%. The lower limit is super.
On the other hand, by setting the content of the ZrO ₂ component to 10.0% or less, devitrification and deterioration of meltability due to excessive content of the ZrO ₂ component can be reduced.
Therefore, the content of the ZrO2 component is preferably 10.0% or less, _more preferably 8.0% or less, still more preferably 6.0% or less.

Since the TiO ₂ component acts as a nucleating agent when it is contained in an amount of more than 0%, it is a component that not only facilitates the precipitation of crystals but also contributes to the miniaturization of the precipitated crystals and the improvement of mechanical strength. In particular, in the present invention, it is a component capable of adjusting the particle size of crystals.
Therefore, the content of the TiO ₂ component is preferably more than 0%, more preferably 1.0% or more, more preferably 2.0% or more, more preferably 3.0% or more, and more preferably 4.0%. As mentioned above, more preferably, the lower limit is more than 4.0%.
On the other hand, by setting the content of the TiO ₂ component to 15.0% or less, the decrease in the transmittance can be suppressed.
Therefore, the content of the TiO ₂ component is preferably 15.0% or less, more preferably 12.0% or less, more preferably 9.0% or less, more preferably 8.0% or less, and more preferably 7. The upper limit is 0% or less, more preferably 6.0% or less.

The Sb ₂ O ₃ component is an optional component capable of defoaming the molten glass when it contains more than 0%.
Therefore, the content of the Sb ₂ O ₃ component may be preferably more than 0%, more preferably 0.03% or more as the lower limit.
On the other hand, by setting the content of the Sb ₂ O ₃ component to 1.0% or less, the decrease in the transmittance can be suppressed.
Therefore, the content of the Sb ₂ O ₃ component may be preferably 1.0% or less, more preferably 0.5% or less, and further preferably 0.2% or less as the upper limit.

The Gd ₂ O ₃ component is a component that lowers the moldability and devitrification of the molten glass when it is contained in an amount of 3.0% or more.
Therefore, the content of the Gd ₂ O ₃ component is preferably less than 3.0% and may not be contained.

In addition, La ₂ O ₃ component, Y ₂ O ₃ component, Yb ₂ O ₃ component, Eu ₂ O ₃ component, Dy ₂ O ₃ component, Er ₂ O ₃ component, Tb ₂ O ₃ as long as the physical properties of the material are not impaired. Ingredients, Pr ₆ O ₁₁ Ingredients, Nd ₂ O ₃ Ingredients, Tm ₂ O ₃ Ingredients, Sm ₂ O ₃ Ingredients, Ho ₂ O ₃ Ingredients, CeO ₂ Ingredients, CaO Ingredients, BaO Ingredients, Ta ₂ O ₅ Ingredients, Nb ₂ O ₅ component, WO ₃ component, TeO ₂ component, Bi ₂ O ₃ component, GeO ₂ component, Ga ₂ O ₃ component, and SnO ₂ component may or may not be contained, respectively. The content can be 0% to less than 3.0%, respectively.

The ZrO ₂ component and the TiO ₂ component function as a nucleating agent for the precipitated crystals when the total content exceeds 0%, and also contribute to the miniaturization of the precipitated crystals and the improvement of the mechanical strength of the material. be. In particular, in the present invention, it is a component capable of adjusting the particle size of crystals.
Therefore, the total content of the ZrO ₂ component and the TiO ₂ component is preferably more than 0%, more preferably 5.0% or more, more preferably 7.0% or more, more preferably 9.0% or more, and more. The lower limit is preferably 9.2% or more, more preferably 9.5% or more, still more preferably 9.7% or more.
On the other hand, by setting the total content of the ZrO ₂ component and the TiO ₂ component to 15.0% or less, it is possible to suppress deterioration of the transmittance and sudden changes in physical properties during crystallization.
Therefore, the total content of the ZrO ₂ component and the TiO ₂ component is preferably 15.0% or less, more preferably 12.0% or less.

The ratio of the total content of the Na ₂ O component, the K ₂ O component, and the Mg O component to the content of the SiO ₂ component [(Na ₂ O + K ₂ O + MgO) / SiO ₂ ] is 0.40 or more. The thermal expansion characteristics of crystallized glass can be improved.
Therefore, the upper limit of the ratio [(Na ₂ O + K ₂ O + MgO) / SiO ₂ ] of the total content of the Na ₂ O component, the K ₂ O component, and the Mg O component to the content of the SiO ₂ component is preferably 1. It is 00 or less, more preferably 0.90 or less, more preferably 0.80 or less, still more preferably 0.70 or less. On the other hand, the lower limit is preferably 0.40 or more, more preferably 0.45 or more, still more preferably 0.50 or more.

Crystallized glass by setting the ratio [(Na ₂ O + K ₂ O) / SiO ₂ ] of the total content of the Na ₂ O component and the K ₂ O component to the content of the SiO ₂ component to 0.30 or more. The thermal expansion characteristics of can be improved.
Therefore, the upper limit of the ratio [(Na ₂ O + K ₂ O) / SiO ₂ ] of the total content of the Na ₂ O component and the K ₂ O component to the content of the SiO ₂ component is preferably 0.80 or less. It is more preferably 0.75 or less, still more preferably 0.70 or less. On the other hand, the lower limit is preferably 0.30 or more, more preferably 0.35 or more, still more preferably 0.40 or more.

The ratio of the total content of the Na ₂ O component and the K ₂ O component to the content of the Al ₂ O ₃ component [(Na ₂ O + K ₂ O) / Al ₂ O ₃ ] is set to 1.00 or more. , The thermal expansion characteristics of crystallized glass can be improved.
Therefore, the upper limit of the ratio [(Na ₂ O + K ₂ O) / Al ₂ O ₃ ] of the total content of the Na ₂ O component and the K ₂ O component to the content of the Al ₂ O ₃ component is preferably 1. It is .80 or less, more preferably 1.70 or less, more preferably 1.60 or less, more preferably 1.55 or less, still more preferably 1.50 or less. On the other hand, the lower limit is preferably 1.00 or more, more preferably 1.10 or more, more preferably 1.20 or more, still more preferably 1.30 or more.

Precipitated crystals by setting the ratio of the content of ZrO ₂ component to the total content of ZrO ₂ component and TiO ₂ component [ZrO ₂ / (ZrO ₂ + TiO ₂ )] to 0.10 or more and 0.70 or less. It is a parameter that contributes to the improvement of the transparency of crystallized glass by the miniaturization of.
Therefore, the upper limit of the ratio of the content of the ZrO ₂ component to the total content of the ZrO ₂ component and the TiO ₂ component [ZrO ₂ / (ZrO ₂ + TiO ₂ )] is preferably 0.70 or less, more preferably 0.70 or less. It is 0.65 or less, more preferably 0.60 or less, more preferably 0.58 or less, still more preferably 0.55 or less. On the other hand, the lower limit is preferably 0.10 or more, more preferably 0.15 or more, more preferably 0.20 or more, still more preferably 0.25 or more.

[Production method]
The crystallized glass for an optical filter of the present invention is produced, for example, as follows. That is, a mixture prepared by uniformly mixing raw materials such as oxides, hydroxides, carbonates, nitrates, fluorides, chlorides, and metaphosphate compounds so that each component is within a predetermined content range is obtained. It is put into a platinum crucible, melted in an electric furnace in a temperature range of 1300 to 1600 ° C. depending on the difficulty of melting the glass composition, homogenized by stirring, lowered to an appropriate temperature, cast into a mold, and slowly cooled. As a result, a glass base material was produced.

The crystallization step is not particularly limited, but for example, the glass base material is heated in a temperature range of 500 ° C. to 560 ° C. for 5 hours to form crystal nuclei, and then in a temperature range of 570 ° C. to 800 ° C. 3 Crystallization was performed by heating for an hour. The precipitated crystal phase was identified by analysis by Bruker's X-ray diffractometer D8 DISCOVER.

The precipitated crystal phase of the crystallized glass for an optical filter of the present invention is preferably a KAlSiO ₄ or KAlSiO ₄ solid solution in order to improve the coefficient of thermal expansion. In addition, as the precipitated crystal phase, Rn ₂ MgSiO ₄ (however, Rn is one or more selected from Li, Na, and K) and Rn ₂ SiO ₃ (where Rn is selected from Li, Na, and K). The above), Li ₂ TiO ₃ , K ₂ ZrSi ₂ O ₇ , and the like may or may not be contained.

After wrapping this crystallized glass, it was polished to obtain a crystallized glass substrate for an optical filter. By forming a dielectric multilayer film on the surface of the substrate of the crystallized glass, it can be used as an optical filter for SDM and an optical filter for DWDM.

[Coefficient of thermal expansion]
A line in the temperature range of -30 ° C to 70 ° C using TD5000S manufactured by MacScience, with reference to the Japan Optical Glass Industry Association standard JOBIS-16 (2019) "Measurement method of average linear expansion coefficient near room temperature of optical glass". The expansion coefficient was measured. The sample was processed into a cylinder having a diameter of 4 mm and a length of 20 mm, and the linear expansion coefficient was calculated from the slope of an expansion curve showing the relationship between the temperature and the elongation of the material in the temperature range of −30 ° C. to 70 ° C.
For the optical filter of the present invention, the lower limit of the coefficient of thermal expansion at −30 ° C. to 70 ° C. is preferably 125 (× ^10-7 / ° C.) or more, more preferably 126 (× ^10-7 / ° C.) or more. Most preferably, it is 127 (× 10 ^-7 / ° C.) or higher. The upper limit is preferably 155 ( ^x10-7 / ° C) or less, more preferably 154 ( ^x10-7 / ° C) or less, and even more preferably 153 ( ^x10-7 / ° C) or less. desirable.

[specific gravity]
The specific gravity of the crystallized glass was measured according to the Japanese Industrial Standards JIS Z 8807 (2012) "Method for measuring the density and specific gravity of a solid".
The specific gravity of the optical filter of the present invention is preferably 4.0 or less, more preferably 3.5 or less, still more preferably 3.0 or less.

[Internal transmittance]
With reference to the Japan Optical Glass Industry Association standard JOBIS-17 (2019) "Measuring method of internal transmittance of optical glass", the spectral transmittance including the reflection loss of 10 mm and 1 mm thick face-to-face parallel polished samples was measured, and these were measured. The internal transmittance (spectral transmittance excluding reflection loss) having a thickness of 1 mm was calculated from the spectral transmittance. The optical filter of the present invention has an internal transmittance of preferably 90.0% or more, more preferably 92.0% or more, still more preferably 95.0% or more, and most preferably 98.0% or more at 1550 nm. Is desirable.

[Transmittance]
Using the spectrophotometer U-4100 manufactured by Hitachi, Ltd., the spectral transmittance of a face-to-face parallel polishing sample with a thickness of 1 mm was measured with reference to the Japan Optical Glass Industry Association standard JOBIS-02 (2019) "Method for measuring the degree of coloration of optical glass". Was measured.
As the optical filter of the present invention, the spectral transmittance at 1550 nm is preferably 90.0% or more, more preferably 90.2% or more, further preferably 90.4% or more, and most preferably 90.5% or more. Is desirable.

In the following examples, the present invention will be shown in detail for illustrative purposes. However, it should be noted that these examples are for illustrative purposes only and that many modifications will be made by one of ordinary skill in the art without departing from the spirit and scope of the invention.

As Examples (No. 1 to No. 21) and Comparative Examples 1 and 2, crystallized glasses having various compositions as listed in Tables 1 and 2 were prepared. In each case, high-purity raw materials used for ordinary crystallized glass such as oxides, hydroxides, carbonates, nitrates, fluorides, chlorides, and metaphosphate compounds corresponding to each component are selected and shown in the table. After weighing and mixing so as to have the composition ratio of each example shown in Tables 1 to 2, the glass is put into a platinum pit, and the temperature range is 1300 to 1600 ° C. in an electric furnace depending on the melting difficulty of the glass composition. After melting with, stirring and homogenizing, the temperature was lowered to an appropriate temperature, the glass was cast into a mold or the like, and the glass obtained by slow cooling was further crystallized at a predetermined temperature. Tables 1 and 2 show the results of measuring the coefficient of thermal expansion, the transmittance, the internal transmittance, and the specific gravity of each of the crystallized glasses.

Since the crystallized glass for an optical filter of the embodiment of the present invention has a high coefficient of thermal expansion while maintaining the transmittance, it has been clarified that it is suitable as an optical filter for an SDM device or a DWDM device.

Claims (5)

By mass% in terms of oxide,
SiO ₂ component 35.0% -55.0%,
_K2O component is 15.0% to 30.0%,
Al ₂ O ₃ component 10.0% to 25.0%,
ZrO2 component from ₀ % to 10.0%,
TiO ₂ component from 0% to 15.0%,
The total amount of ZrO ₂ component and TiO ₂ component is more than 0% to 15.0%,
Contains,
A crystallized glass for an optical filter, characterized in that the coefficient of thermal expansion at −30 to 70 ° C. is 125 to 155 (× 10 ⁻⁷ / ° C.). By mass% in terms of oxide,
Li ₂ O component from 0% to 7.0%,
Na ₂ O component from 0% to 5.0%,
MgO component from 0% to 7.0%,
The crystallized glass for an optical filter according to claim 1, wherein the glass contains. As a crystalline phase
The crystallized glass for an optical filter according to claim 1 or 2, wherein the crystallized glass contains KAlSiO ₄ or KAlSiO ₄ solid solution. The crystallized glass for an optical filter according to any one of claims 1 to 3, wherein the spectral transmittance at 1550 nm is 90% or more for a sample having a thickness of 1 mm. An optical filter formed by forming a dielectric film on the crystallized glass according to any one of claims 1 to 4.