Bandpass filters, their manufacturing methods, and applications of glass-ceramic composites.

Abstract

This invention provides a glass-ceramic material for optical filters and an optical filter that combines thermal expansion characteristics to avoid refractive index changes in filter components at operating temperatures with mechanical properties that consider durability, resulting in excellent processability. The glass-ceramic material for optical filters of this invention, with a thickness of 1 mm, has an internal transmittance of 0.970 or higher for light with a wavelength of 1550 nm. Based on the mass percentage of oxides, it contains 40.0% to 70.0% SiO2, 11.0% to 25.0% Al2O3, 5.0% to 19.0% Na2O, 0% to 9.0% K2O, 1.0% to 18.0% of one or more selected from MgO and ZnO, 0% to 3.0% CaO, and 0.5% to 12.0% TiO2.

Description

Technical Field

[0001] This invention relates to a glass-ceramic for use in a filter and a filter using the glass-ceramic. Prior Technology

[0002] Optical filters include those that block or allow specific wavelengths to pass through, and those that reduce light intensity regardless of wavelength. Among the former, there are bandpass filters that allow only specific wavelengths to pass through, band-limiting filters that block only specific wavelengths, high-pass filters that allow only wavelengths shorter or longer than a specific wavelength to pass through, and low-pass filters. Among the latter, there are ND (Neutral Density) filters.

[0003] In addition, filters include absorptive and interferometric types. A representative example of absorptive filters is the ND filter, while a representative example of interferometric filters is the bandpass filter. Absorptive filters used in photography can use plastic as the substrate, but for filters using high-intensity lasers, glass is used due to requirements for durability and heat resistance.

[0004] Bandpass filters can be used to form filters on substrates such as glass with dielectric multilayers, which are structures in which dielectric films with high refractive index (H layer) and dielectric films with low refractive index (L layer) are stacked alternately.

[0005] For bandpass filters used in WDM (Wavelength Division Multiplexing) optical communication systems, the temperature stability of the center wavelength becomes a problem when the bandwidth of the pass wavelength is to be narrowed for application with higher wavelength density. That is, because these are sensitive components where even slight temperature changes cause variations in the center wavelength, temperature compensation is necessary. However, space constraints often prevent the practical installation of temperature controllers. As the amount of optical information increases and the bandwidth needs to be narrowed, the importance of the temperature stability of the center wavelength increases.

[0006] Conventional optical glass has poor heat resistance, making it unsuitable as a substrate for bandpass filters. Patent Document 1 discloses a glass-ceramic material as a substrate for bandpass filters. While this glass-ceramic exhibits excellent thermal expansion characteristics and mechanical strength, its high hardness results in poor machinability. [Previous Technical Documents] [Patent Literature]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2001-318222. Summary of the Invention

[0008] [The problem that the invention aims to solve] The purpose of this invention is to eliminate the various drawbacks of the prior art and provide a glass-ceramic filter and a filter that combines thermal expansion characteristics to avoid refractive index changes of filter components at operating temperature with mechanical properties that take into account durability, thereby achieving excellent processability. [Methods used to solve problems]

[0009] Through repeated and dedicated experimental research, the inventors discovered that, in order to solve the above-mentioned problems, a glass-ceramic system with a predetermined composition has excellent light transmittance, thermal expansion characteristics, and mechanical properties, making it suitable for use as a filter. Furthermore, it has appropriate hardness and excellent processability, thus completing this invention. This invention provides the following content. (Component 1) A glass-ceramic material for optical filters, having an internal transmittance of 0.970 or higher for light with a wavelength of 1550 nm when the thickness is 1 mm; and containing, by mass percent of oxides, 40.0% to 70.0% SiO2, 11.0% to 25.0% Al2O3, 5.0% to 19.0% Na2O, 0% to 9.0% K2O, 1.0% to 18.0% of one or more selected from MgO and ZnO, 0% to 3.0% CaO, and 0.5% to 12.0% TiO2. (Component 2) As described in Form 1, the glass-ceramic used for filters has a coefficient of thermal expansion of 70×10⁻⁷ / ℃ to 95×10⁻⁷ / ℃ between -30℃ and +70℃. (Component 3) The glass-ceramic used for filters as described in Configuration 1 or Configuration 2, wherein the Young's modulus is 78 GPa or higher. (Component 4) The glass-ceramic for filters described in any one of Compositions 1 to 3 contains one or more of the following as the main crystalline phase: MgAl2O4, MgTi2O4, MgTi2O5, Mg2TiO4, Mg2SiO4, MgAl2Si2O8, Mg2Al4Si5O18, Mg2TiO5, MgSiO3, NaAlSiO4, FeAl2O4, and solid solutions thereof. (Component 5) A filter is formed by depositing a dielectric film on a glass-ceramic as described in any one of configurations 1 to 4. (Composition 6) A bandpass filter is formed by depositing a dielectric film on a glass-ceramic as described in any one of configurations 1 to 4. [Invention Benefits]

[0010] According to the present invention, a glass-ceramic material for a filter and a filter are provided, which have both thermal expansion characteristics to avoid refractive index changes of filter components at operating temperature and mechanical properties that take into account durability, thereby having excellent processability. Implementation

[0011] The following describes in detail the embodiments and examples of the present invention. However, the present invention is not limited to the following embodiments and examples and can be implemented by appropriate modifications within the scope of the present invention.

[0012] In this specification, unless otherwise specified, the content of each component is expressed as a percentage by mass (%) converted from oxides. Here, "oxide conversion" refers to the assumption that all the constituent components of the glass-ceramic decompose and transform into oxides; it expresses the amount of oxides of each component in the glass-ceramic as of 100% by mass. In this specification, A% to B% indicates A% or more to B% or less. Furthermore, 0% in 0% to C% means a content of 0%.

[0013] The glass-ceramic of the present invention, by mass percentage converted from oxides, contains 40.0% to 70.0% SiO2, 11.0% to 25.0% Al2O3, 5.0% to 19.0% Na2O, 0% to 9.0% K2O, 1.0% to 18.0% of one or more selected from MgO and ZnO, 0% to 3.0% CaO, and 0.5% to 12.0% TiO2.

[0014] The SiO2 component is a glass-forming component that forms the network structure of the glass. The SiO2 content is preferably 45.0% to 65.0%, more preferably 50.0% to 60.0%.

[0015] Al2O3 is a component suitable for improving mechanical strength. The preferred Al2O3 content is 13.0% to 23.0%.

[0016] The Na₂O and K₂O components are those that participate in ion exchange during chemical fortification. The Na₂O content is preferably 8.0% to 16.0%, but may also be 9.0% or more, or 10.5% or more. The K₂O content is preferably 0.1% to 7.0%, more preferably 1.0% to 5.0%.

[0017] MgO and ZnO components contribute to mechanical strength. ZnO is also effective in reducing the viscosity of glass. The content of one or more components selected from MgO and ZnO is preferably 2.0% to 15.0%, more preferably 3.0% to 13.0%, and even more preferably 5.0% to 11.0%. The content of one or more components selected from MgO and ZnO can be MgO alone, ZnO alone, or both, preferably MgO alone.

[0018] CaO is a component that helps stabilize glass. The preferred CaO content is 0.01% to 3.0%, more preferably 0.1% to 2.0%.

[0019] TiO2 is a nucleating agent that can act as a crystallizer. The TiO2 content is preferably 1.0% to 10.0%, more preferably 2.0% to 8.0%.

[0020] The glass ceramic may contain 0.01% to 3.0% (preferably 0.03% to 2.0%, and even more preferably 0.05% to 1.0%) of one or more components selected from Sb2O3, SnO2 and CeO2 as a clarifying agent.

[0021] The above-mentioned quantities can be combined appropriately.

[0022] The total content of SiO2, Al2O3, Na2O, one or more of MgO and ZnO, and TiO2 can be set to 90% or more, preferably 95% or more, more preferably 98% or more, and even more preferably 98.5% or more. The total content of SiO2, Al2O3, Na2O, K2O, one or more selected from MgO and ZnO, CaO, TiO2, and one or more selected from Sb2O3, SnO2, and CeO2 can be set at 90% or more, preferably 95% or more, more preferably 98% or more, and even more preferably 99% or more. These components can also account for 100%.

[0023] The glass-ceramic may contain ZrO2 without compromising the effectiveness of the present invention, or it may not contain ZrO2. The formulation amount may be 0% to 5.0%, 0% to 3.0%, or 0% to 2.0%. Furthermore, the glass-ceramic may contain, without impairing the effectiveness of the present invention, B2O3, P2O5, BaO, FeO, Li2O, SrO, La2O3, Y2O3, Nb2O5, Ta2O5, WO3, TeO2, and Bi2O3, or may not contain any of these components. The formulation amounts may be 0% to 2.0%, 0% to less than 2.0%, or 0% to 1.0%, respectively.

[0024] In the glass-ceramic of the present invention, other components not mentioned above may be added as needed, without impairing the characteristics of the glass-ceramic. For example, the glass-ceramic of the present invention may also be colorless and transparent, or the glass may be colored without impairing the characteristics of the glass-ceramic.

[0025] Furthermore, the use of Pb, Th, Tl, Os, Be, and Se has tended to be controlled in recent years as they are considered harmful chemical substances, so it is better to have virtually no of these components.

[0026] The glass-ceramic of the present invention contains, for example, one or more of ZnAl2O4, Zn2Ti3O8, Zn2SiO4, ZnTiO3, Mg2SiO4, Mg2Al4Si5O18, NaAlSiO4, Na2Zn3SiO4, Na4Al2Si2O9, LaTiO3 and their solid solutions as the main crystalline phase. In this specification, "main crystalline phase" refers to the crystalline phase that is abundant in glass-ceramics, as determined by the peak value of the X-ray analysis pattern.

[0027] When glass-ceramics are used in optical filters, lower light transmittance naturally leads to poor signal extraction (a decrease in the signal-to-noise ratio). Therefore, a higher light transmittance is preferable, with a minimum of 60% or higher. The glass-ceramic of this invention exhibits an internal transmittance of 0.970 or higher for light with a wavelength of 1550 nm when the sample thickness is 1 mm. More preferably, it is 0.980 or higher, more preferably 0.985 or higher, even more preferably 0.990 or higher, and particularly preferably 0.995 or higher. The upper limit is typically below 1.000, for example, below 0.999. Light transmittance can be measured using the method described in the examples.

[0028] Furthermore, as described above, the glass-ceramic used in filters requires temperature stability of the center wavelength of the band, preferably greater than the coefficient of thermal expansion of the film constituent materials. The coefficient of thermal expansion of the glass-ceramic of the present invention from -30°C to +70°C is typically 70 × 10⁻⁷ / °C to 95 × 10⁻⁷ / °C, for example, 73 × 10⁻⁷ / °C to 93 × 10⁻⁷ / °C, or 75 × 10⁻⁷ / °C to 90 × 10⁻⁷ / °C. The coefficient of thermal expansion can be measured using the method described in the examples.

[0029] Furthermore, glass-ceramics used in filters require high strength against mechanical deformation due to harsh operating conditions. Therefore, after forming a film from the substrate, they are processed into tiny fragments, necessitating a high Young's modulus. The glass-ceramics of this invention preferably have a Young's modulus of 78 GPa or higher. More preferably, 79 GPa or higher, and even more preferably 80 GPa or higher. The upper limit is typically 95 GPa or lower, for example, 90 GPa or lower. The Young's modulus can be measured using the method described in the examples.

[0030] The glass-ceramic of this invention preferably has a Vickers hardness (200g weight) of 550 to 700, for example, 580 to 650. The abrasion resistance is preferably 50 to 100, for example, 70 to 95. The glass-ceramic of this invention has neither excessively high hardness nor excessively low abrasion resistance, and exhibits excellent machinability. The Vickers hardness and abrasion resistance can be measured using the methods described in the examples.

[0031] The glass-ceramic of this invention can be manufactured by the following method: raw materials are uniformly mixed and melted to form a raw glass. This raw glass is then crystallized to produce the glass-ceramic. Furthermore, the glass-ceramic can be used as a base material to form a compressive stress layer for strengthening.

[0032] The original glass system undergoes heat treatment to induce crystallization within the glass. This heat treatment can be performed in one stage or at two stages at different temperatures. In the two-stage heat treatment, the nucleation step is first carried out by heat treatment at a first temperature, and after the nucleation step, the crystal growth step is carried out by heat treatment at a second temperature higher than that of the nucleation step. In a single-stage heat treatment, the nucleation and crystal growth steps are carried out continuously at the temperature of that stage. Typically, the temperature is raised to a predetermined heat treatment temperature, held at that temperature for a fixed time, and then cooled down. The first temperature of the two-stage heat treatment is preferably 600°C to 750°C. The holding time at the first temperature is preferably 30 minutes to 2000 minutes, more preferably 180 minutes to 1440 minutes. The second temperature for the two-stage heat treatment is preferably 650°C to 850°C. The holding time at the second temperature is preferably 30 minutes to 600 minutes, more preferably 60 minutes to 300 minutes. When heat treatment is performed at a single-stage temperature, the heat treatment temperature is preferably 600°C to 800°C, more preferably 630°C to 770°C. In addition, the holding time at the heat treatment temperature is preferably 30 minutes to 500 minutes, more preferably 120 minutes to 400 minutes.

[0033] When strengthening a substrate by forming a compressive stress layer, methods such as grinding and polishing are typically used to produce a thin sheet of glass-ceramic. Then, a compressive stress layer is formed on the glass-ceramic substrate.

[0034] Methods for forming a compressive stress layer include, for example, chemical strengthening, which involves exchanging an alkaline component present on the surface layer of a glass-ceramic with an alkaline component whose ionic radius is larger than that of the alkaline component, thereby forming a compressive stress layer on the surface layer. Other methods include thermal strengthening, which involves heating the glass-ceramic and then rapidly cooling it, and ion implantation, which involves implanting ions into the surface layer of the glass-ceramic.

[0035] Chemical strengthening can be implemented, for example, by contacting or impregnating the glass-ceramic substrate with a molten salt containing potassium or sodium (e.g., potassium nitrate (KNO3), sodium nitrate (NaNO3), or a mixture or composite salt thereof). This contact or impregnation with the molten salt (chemical strengthening treatment) can be performed in one stage or in two stages.

[0036] For example, in the case of a two-stage chemical enhancement treatment, in the first step, the patient is contacted or immersed in sodium salt or a mixture of potassium and sodium salt heated to 350°C to 550°C for 1 to 1440 minutes, preferably 90 to 800 minutes. Subsequently, in the second step, the patient is contacted or immersed in potassium salt or a mixture of potassium and sodium salt heated to 350°C to 550°C for 1 to 1440 minutes, preferably 60 to 800 minutes. In the case of a one-stage chemical enhancement treatment, the patient is exposed to or immersed in a potassium or sodium salt, or a mixture thereof, heated to 350°C to 550°C for 1 to 1440 minutes, preferably 60 to 800 minutes.

[0037] Regarding thermal strengthening methods, for example, the glass-ceramic substrate can be heated to 300°C to 600°C and then rapidly cooled by water cooling and / or air cooling, thereby utilizing the temperature difference between the surface and interior of the glass substrate to form a compressive stress layer. Furthermore, by combining it with the aforementioned chemical treatment methods, the compressive stress layer can be formed more effectively.

[0038] Regarding ion implantation, for example, ions are implanted into the surface of a glass-ceramic substrate by colliding it with acceleration energy and voltage that do not damage the substrate surface. Then, if heat treatment is required, a compressive stress layer can be formed on the surface in the same way as other methods.

[0039] The glass-ceramic of the present invention can be used in filters, and is suitable for interference filters with dielectric multilayer films formed on the substrate surface. It is particularly suitable for bandpass filters with a structure in which high-refractive-index dielectric films (H layers) and low-refractive-index dielectric films (L layers) are alternately stacked as dielectric multilayer films.

[0040] The dielectric material is preferably an inorganic oxide such as TiO2, Ta2O2, Nb2O5, or SiO2. Furthermore, in bandpass filters used in wavelength ranges from 950 nm to 1600 nm, the combination of the H / L layer as the dielectric layer is preferably TiO2 / SiO2, Ta2O2 / SiO2, or Nb2O5 / SiO2. The filter of the present invention can be obtained by forming a dielectric thin film on the surface of a glass-ceramic substrate. Methods for forming the film include vapor deposition, RF (Radio Frequency) ion implantation, magnetron sputtering, and plasma ion implantation. Among these, vapor deposition is preferred. [Example]

[0041] Examples 1 to 5 1. Manufacturing of glass and ceramics Select the corresponding oxides, hydroxides, carbonates, nitrates, fluorides, chlorides, metaphosphates, etc., as raw materials for each component of glass ceramics, and weigh and mix these raw materials in the following composition ratio. [Mass conversion of oxides] The composition is 54% SiO2, 18% Al2O3, 12% Na2O, 2% K2O, 8% MgO, 1% CaO, 5% TiO2, and 0.1% Sb2O3.

[0042] Next, the mixed raw materials are added to a platinum crucible and melted. Then, the molten glass is stirred and homogenized before being poured into a mold and slowly cooled to produce the original glass.

[0043] The obtained raw glass was subjected to a one-stage heat treatment (665°C to 760°C, 5 hours) for nucleation and crystallization to produce glass-ceramics. The crystallization temperature was 665°C in Example 1, 705°C in Example 2, 720°C in Example 3, 740°C in Example 4, and 760°C in Example 5. The crystalline phases were determined by the angle of the peaks appearing in the X-ray diffraction pattern using an X-ray diffraction analysis apparatus (manufactured by Bruker, D8Dsicover). The main crystalline phases, MgAl2O4 and MgTi2O4, were identified.

[0044] The manufactured glass-ceramic material is cut and ground, and then subjected to parallel grinding on both sides to a thickness of 1 mm to obtain a glass-ceramic substrate.

[0045] 2. Evaluation of Glass Ceramics The following physical properties were determined for the obtained glass-ceramic. The results are shown in Table 1.

[0046] (1) Internal penetration rate According to the Japan Optical Glass Manufacturers Association standard JOGIS17-2012 "Method for Determination of Internal Transmittance of Optical Glass", the spectral transmittance including reflection loss of the two parallel polished surfaces with a thickness of 1 mm and 10 mm was measured. The internal transmittance of the 1 mm thick surface (spectral transmittance excluding reflection loss) was calculated.

[0047] (2) Coefficient of thermal expansion According to the Japanese Optical Glass Manufacturers Association standard JOGIS16-2003 "Method for Determining the Average Linear Expansion Coefficient of Optical Glass Near Room Temperature", the coefficient is determined by measuring the relationship between temperature and elongation of the sample, which yields the thermal expansion curve.

[0048] (3) Young's modulus The determination was made using ultrasound.

[0049] (4) Vickers hardness The value is expressed as the surface area (mm2) calculated by dividing the load applied when a diamond square hammer indenter with a face angle of 136° forms a pyramidal indentation on the test surface by the length of the indentation. The test was conducted using a microhardness tester MVK-E manufactured by Akashi Seisakusho, with a test load of 200 gf and a holding time of 10 seconds.

[0050] (5) Wear degree The abrasion degree of optical glass was determined according to the Japan Optical Glass Manufacturers Association standard JOGIS10-1994, "Method for Determination of Abrasion Degree of Optical Glass". Specifically, a glass corner plate sample measuring 30mm × 30mm × 10mm was horizontally placed at a fixed position 80mm from the center of a cast iron flat plate (250mmφ) rotating at 60 revolutions per minute. A load of 9.8N (1kgf) was applied vertically while a polishing slurry containing 10g of #800 (average particle size 20μm) abrasive material (alumina A abrasive particles) was uniformly supplied to 20mL of water for 5 minutes for friction. The mass of the sample before and after polishing was measured, and the abrasion mass was calculated. Similarly, the abrasion mass of a standard sample specified by the Japan Optical Glass Manufacturers Association was calculated using the formula: Abrasion Degree = {(Abrasion Mass of Sample / Specific Gravity) / (Abrasion Mass of Standard Sample / Specific Gravity)} × 100.

[0051] Comparative Example 1 The composition of the glass-ceramic was changed to the following, and the crystallization temperature was set to 750°C. Otherwise, the glass-ceramic was manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1. [Mass conversion of oxides] The composition is 76.0% SiO2, 6.4% Al2O3, 2.0% P2O5, 3.0% ZrO2, 0.6% ZnO, 0.5% MgO, 0.3% CaO, 10.0% Li2O, 1.0% K2O, and 0.2% Sb2O3.

[0052] Comparative Example 2 The glass composition was changed to the following, and crystallization was not carried out. Otherwise, the glass was manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1. [Mass conversion of oxides] The composition is 65.0% SiO2, 13.6% B2O3, 2.0% Al2O3, 1.5% ZnO, 3.0% BaO, 7.4% Na2O, 7.0% K2O, and 0.5% Sb2O3.

[0053] [Table 1] Example Comparative Example 1 Comparative Example 2 1 2 3 4 5 Internal penetration rate (τ / 1mmt) 320 0.010 0.010 0.564 0.978 350 0.785 0.786 0.610 0.990 400 0.961 0.961 0.001 0.001 0.001 0.692 0.994 440 0.967 0.968 0.002 0.002 0.002 0.758 0.994 500 0.971 0.972 0.012 0.012 0.012 0.831 0.995 550 0.977 0.977 0.056 0.056 0.056 0.873 0.995 600 0.983 0.984 0.151 0.151 0.151 0.903 0.995 650 0.990 0.990 0.281 0.281 0.281 0.925 0.995 700 0.994 0.994 0.415 0.415 0.416 0.941 0.995 800 0.997 0.998 0.636 0.636 0.637 0.962 0.992 900 0.999 0.999 0.774 0.774 0.775 0.975 0.999 1000 0.999 0.999 0.859 0.859 0.860 0.982 0.999 1200 0.999 0.999 0.939 0.939 0.940 0.990 0.999 1400 0.999 0.999 0.965 0.965 0.966 0.994 0.999 1500 0.999 0.999 0.978 0.978 0.979 0.999 0.999 1550 0.999 0.999 0.980 0.980 0.981 0.996 0.999 1600 0.999 0.999 0.983 0.983 0.985 0.996 0.999 1800 0.999 0.999 0.987 0.987 0.988 0.997 0.999 2000 0.999 0.999 0.990 0.990 0.991 0.997 0.999 2200 0.999 0.999 0.956 0.956 0.957 0.994 0.997 2400 0.999 0.999 0.959 0.959 0.961 0.995 0.990 Coefficient of thermal expansion (10⁻⁷ / ℃) (-30 to +70) 81 79 79 80 85 101 67 Young's modulus (GPa) 80.6 80.6 81.0 83.0 84.3 97.4 76.5 Vickers hardness (200g weight) Hv_200gf 619 626 622 616 621 755 613 Wear Aa 78 - 86 86 - 31 88 All the documents described in this specification and the disclosures (including the specification, drawings, and scope of the patent application) of the Japanese application that form the basis of the Paris priority in this case are incorporated herein by reference.

Claims

1. A bandpass filter formed by depositing a dielectric film on a glass-ceramic substrate; wherein the glass-ceramic substrate has: an internal transmittance of 0.970 or higher for light with a wavelength of 1550 nm at a thickness of 1 mm; and, by mass percent (converted to oxides), contains: 40.0% to 70.0% SiO2, 11.0% to 25.0% Al2O3, 5.0% to 19.0% Na2O, 0% to 9.0% K2O, 1.0% to 18.0% of one or more selected from MgO and ZnO, 0% to 3.0% CaO, and 0.5% to 12.0% TiO2; and contains one or more selected from MgAl2O4, MgTi2O4, and solid solutions thereof as the main crystalline phase; and has a Young's modulus of 78 GPa or higher.

2. The bandpass filter as described in claim 1, wherein the coefficient of thermal expansion of the aforementioned glass ceramic from -30°C to +70°C is 70×10⁻⁷ / °C to 95×10⁻⁷ / °C.

3. The bandpass filter as described in claim 1 or 2, wherein the aforementioned glass-ceramic contains one or more of Mg2TiO4, Mg2SiO4, MgAl2Si2O8, Mg2Al4Si5O18, Mg2TiO5, MgSiO3, FeAl2O4 and solid solutions thereof as the main crystalline phase.

4. An application of a glass-ceramic material for use as a bandpass filter; wherein the aforementioned glass-ceramic material has: an internal transmittance of 0.970 or higher for light with a wavelength of 1550 nm at a thickness of 1 mm; and, by mass percent (converted to oxides), contains: 40.0% to 70.0% SiO2, 11.0% to 25.0% Al2O3, 5.0% to 19.0% Na2O, 0% to 9.0% K2O, 1.0% to 18.0% of one or more selected from MgO and ZnO, 0% to 3.0% CaO, and 0.5% to 12.0% TiO2; and contains one or more selected from MgAl2O4, MgTi2O4, and solid solutions thereof as the main crystalline phase; and has a Young's modulus of 78 GPa or higher.

5. A method for manufacturing a bandpass filter, comprising: forming a dielectric film on a glass-ceramic substrate; wherein the glass-ceramic substrate has an internal transmittance of 0.970 or higher for light with a wavelength of 1550 nm when the thickness is 1 mm; and contains, by mass percent (based on oxides): 40.0% to 70.0% SiO2, 11.0% to 25.0% Al2O3, 5.0% to 19.0% Na2O, 0% to 9.0% K2O, 1.0% to 18.0% of one or more selected from MgO and ZnO, 0% to 3.0% CaO, and 0.5% to 12.0% TiO2; and contains one or more selected from MgAl2O4, MgTi2O4, and solid solutions thereof as the main crystalline phase; and has a Young's modulus of 78 GPa or higher.