JP2003139948A - Glass for optical filter and optical filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide glass for an optical filter having thermal expansion characteristics so as to avoid fluctuation in the refractive index at the use temperature of a filter member formed as a single-layer or multilayer film (by using a substrate material having high thermal expansion coefficient and giving compressive stress to the film to improve the temperature stability of the refractive index of the film) responding to higher accuracy of a band pass filter, having mechanical characteristics while considering durability, and having favorable transmittance for light of the substrate. SOLUTION: The glass has 90×10<-7> to 120×10<-7> / deg.C thermal expansion coefficient in the temperature range from -20 to +70 deg.C, and preferably has >=75 GPa Young's modulus, >=550 Vickers hardness and >=90% transmittance at 950 to 1600 nm wavelength.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a glass for an optical filter. Furthermore, the present invention relates to an optical filter using glass.

[0002]

2. Description of the Related Art Optical filters include those that cut or transmit a specific wavelength and those that reduce the light intensity regardless of the wavelength. The former optical filters include a bandpass filter that passes only specific wavelengths, a notch pass filter that cuts only certain wavelengths, a highpass filter that passes only wavelengths shorter or longer than a certain wavelength, and a lowpass filter. , The latter optical filter is ND
There is a filter.

Optical filters are classified into absorption type and interference type. N is a typical absorption type optical filter.
There is a D filter or the like, and a typical example of the interference type optical filter is a bandpass filter. Although plastic is used as a substrate for absorption type optical filters for photography and the like, the substrate for optical filters that use a strong laser requires durability and heat resistance, so amorphous glass is mainly used. There is.

A bandpass filter is, for example, a dielectric thin film (H layer) having a high refractive index on a substrate material such as glass.
And a dielectric multilayer film having a structure in which dielectric thin films (L layers) having a low refractive index are alternately laminated is used.

WDM (Wavelength Divi)
In a band pass filter used in an optical communication system, when the band width of the passing wavelength is set narrow and it is applied to a higher density wavelength, the temperature stability of the center wavelength of the band is It's a problem. In other words, since it is a sensitive element in which the center wavelength of the band fluctuates even with a slight temperature change, temperature compensation should be performed with a temperature controller in its use, but due to space problems when using it You can't practically turn on the temperature controller. This temperature stability of the central wavelength is important because the bandwidth needs to be narrowed as the amount of optical information increases.

Amorphous glass substrate materials for band-pass filters that have been used conventionally are not sufficiently high in thermal expansion property and low in mechanical strength, so that they are sufficient in terms of compressive stress applied to the film and durability. There wasn't. Furthermore, these materials have low surface hardness and cannot sufficiently meet future requirements for optical filter substrate materials, particularly bandpass filter substrate materials.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to improve the accuracy of the bandpass filter, the operating temperature of the filter member formed with a single layer or a multilayer film. A machine that considers the thermal expansion characteristics and durability in order to avoid the fluctuation of the refractive index in (1) (The substrate material has a high coefficient of thermal expansion, which gives the film compressive stress and improves the temperature stability of the refractive index of the film). It is an object of the present invention to provide a glass substrate material for an optical filter, which has both optical characteristics and a good light transmittance of the substrate material itself.

[0008]

Means for Solving the Problems As a result of extensive studies conducted by the present inventor, the glass having a specific thermal expansion coefficient range, mechanical strength and light transmittance is suitable for solving the above problems. It was discovered that there was something, and the present invention was achieved.

That is, the invention according to claim 1 is -2
Coefficient of thermal expansion at 0 to + 70 ° C is 90 × 10^-7~ 12
0x10^-7/ ° C and the composition of the glass is percentage by weight,
SiO₂, B₂O₃, P₂O_FiveOnly one selected from the ingredients
Or the total amount of two or more kinds is 35-55%, TiO₂, La₂
O₃, ZrO₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂O₃Success
The total amount of one or more selected from the minutes is 20
~ 45%, MgO, CaO, SrO, BaO, ZnO composition
The total amount of one or more selected from the minutes is 3 to
20%, Li₂O, Na₂O, K₂Selected from O ingredients
5 to 30% of the total amount of one or two or more of Sb
₂O₃, As₂O₃1 type or 2 types selected from the ingredients
The total amount is 0 to 1%, containing each component in the range, Young's modulus
Is 75 GPa or more, and SiO₂The upper limit of the component is 41.
It is a glass for optical filters, which is 39%
And the invention according to claim 2 is SiO.₂Ingredients essential
It is contained as a minute, and the upper limit is 41.39%.
The glass for an optical filter according to claim 1, which is characterized in that
According to the invention described in claim 3,₂Lower limit of component is 1
7. 10% according to claim 2, characterized in that
The invention according to claim 4, which is a glass for an optical filter.
Has a thermal expansion coefficient of 90 × 10 at −20 to + 70 ° C.
^-7~ 120 × 10^-7/ ° C and the composition of the glass is 100
SiO in fraction₂, B₂O₃, P₂O_FiveSelected from the ingredients
The total amount of one or two or more of 35 to 55%, TiO
₂, La₂O₃, ZrO₂, Nb₂O_Five, Ta₂O_Five, WO₃，
Y₂O₃The total of one or more selected from the ingredients
20-45%, MgO, CaO, SrO, BaO,
A total of one or more selected from ZnO components
3-20%, Li₂O, Na₂O, K₂In the O component
The total amount of one or two or more selected from 5 to 30%,
Sb₂O₃, As₂O₃1 or 2 selected from the ingredients
The total amount of seeds is 0 to 1%, containing each component in the range of
B ratio is 75 GPa or more, B₂O₃The ingredients are 0-21.
Glass for optical filter characterized by being in the range of 5%
The invention according to claim 5 is -20 to + 70 ° C.
Coefficient of thermal expansion at 90 × 10^-7~ 120 × 10^-7/
℃, the composition of the glass is percentage by weight, SiO₂, B₂
O₃, P₂O_FiveOne or more selected from the ingredients
Total amount of 35-55%, TiO₂, La₂O₃, Zr
O₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂O₃From the ingredients
20% to 45% of the total amount of one or two or more selected,
From the MgO, CaO, SrO, BaO, ZnO components
The total amount of one or more selected is 3 to 20%, L
i₂O, Na₂O, K₂One kind selected from O components
Is 5 to 30% in total of two or more types, Sb₂O₃, As₂O₃
The total amount of one or two selected from the components is 0 to 1.
%, Each Young's modulus is 75 GPa or less.
Above, P₂O_FiveIngredients must be in the range of 0 to 8.60%
7. A glass for an optical filter characterized by:
The invention described in 1., the coefficient of thermal expansion at -20 to + 70 ° C.
Is 90 × 10^-7~ 120 × 10^-7Of the glass
Composition is weight percentage, SiO₂, B₂O₃, P₂O_FiveIngredient
The total amount of one or two or more selected from among is 35 to 5
5%, TiO₂, La₂O₃, ZrO₂, Nb₂O_Five, Ta₂
O_Five, WO₃, Y₂O₃1 or 2 selected from the ingredients
The total amount of seeds or more is 20 to 45%, MgO, CaO, Sr
One or two selected from O, BaO and ZnO components
The total amount of seeds or more is 3 to 20%, Li₂O, Na₂O, K₂
The total amount of one or more selected from O components is
5-30%, Sb₂O₃, As₂O₃Selected from ingredients
The total amount of 1 type or 2 types is 0 to 1%,
Contains, Young's modulus is 75 GPa or more, TiO₂Success
The optical fiber is characterized by an upper limit of 30.00%.
It is a glass for luster, and the invention according to claim 7 is Ti
O₂Ingredients are included as essential ingredients, and the upper limit is 30.0
The optical fiber according to claim 6, which is 0%.
The glass according to claim 8 is a glass for luther.
O ₂The lower limit of the component is 5.00%,
The glass for an optical filter according to claim 7,
The invention described in 9 has a coefficient of thermal expansion at -20 to + 70 ° C.
Is 90 × 10^-7~ 120 × 10^-7Of the glass
Composition is weight percentage, SiO₂, B₂O₃, P₂O_FiveIngredient
The total amount of one or two or more selected from among is 35 to 5
5%, TiO₂, La₂O₃, ZrO₂, Nb₂O_Five, Ta₂
O_Five, WO₃, Y₂O₃1 or 2 selected from the ingredients
The total amount of seeds or more is 20 to 45%, MgO, CaO, Sr
One or two selected from O, BaO and ZnO components
The total amount of seeds or more is 3 to 20%, Li₂O, Na₂O, K₂
The total amount of one or more selected from O components is
5-30%, Sb₂O₃, As₂O₃Selected from ingredients
The total amount of 1 type or 2 types is 0 to 1%,
Contained, Young's modulus is 75 GPa or more, La₂O₃Success
Light whose minutes are in the range of 0 to 17.00%
It is glass for filters, The invention of Claim 10
Has a thermal expansion coefficient of 90 × 10 at −20 to + 70 ° C.
^-7~ 120 × 10^-7/ ° C and the composition of the glass is 100
SiO in fraction₂, B₂O₃, P₂O_FiveSelected from the ingredients
The total amount of one or two or more of 35 to 55%, TiO
₂, La₂O₃, ZrO₂, Nb₂O_Five, Ta₂O_Five, WO₃，
Y₂O₃The total of one or more selected from the ingredients
20-45%, MgO, CaO, SrO, BaO,
A total of one or more selected from ZnO components
3-20%, Li₂O, Na₂O, K₂In the O component
The total amount of one or two or more selected from 5 to 30%,
Sb₂O₃, As₂O₃1 or 2 selected from the ingredients
The total amount of seeds is 0 to 1%, containing each component in the range of
ZrO with a compression rate of 75 GPa or more₂The ingredients are 0-7.
90% range for optical filter gas
The invention according to claim 11 is -20 to +7.
Coefficient of thermal expansion at 0 ℃ is 90 × 10^-7~ 120 × 10
^-7/ ° C, the composition of the glass is percentage by weight, Si
O₂, B₂O₃, P₂O_FiveOne selected from the ingredients or
The total amount of two or more is 35-55%, TiO₂, La
₂O₃, ZrO₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂O₃Success
The total amount of one or more selected from the minutes is 20
~ 45%, MgO, CaO, SrO, BaO, ZnO composition
The total amount of one or more selected from the minutes is 3 to
20%, Li₂O, Na₂O, K ₂Selected from O ingredients
5 to 30% of the total amount of one or two or more of Sb
₂O₃, As₂O₃1 type or 2 types selected from the ingredients
The total amount is 0 to 1%, containing each component in the range, Young's modulus
Is 75 GPa or more, and Nb₂O_FiveIngredient 0 to 7.90
Glass for optical filters characterized by being in the range of
The invention according to claim 12 is -20 to + 70 ° C.
Coefficient of thermal expansion at 90 × 10^-7~ 120 × 10^-7/
℃, the composition of the glass is percentage by weight, SiO₂, B₂
O₃, P₂O_FiveOne or more selected from the ingredients
Total amount of 35-55%, TiO₂, La₂O₃, Zr
O₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂O₃From the ingredients
20% to 45% of the total amount of one or two or more selected,
From the MgO, CaO, SrO, BaO, ZnO components
The total amount of one or more selected is 3 to 20%, L
i₂O, Na₂O, K₂One kind selected from O components
Is 5 to 30% in total of two or more types, Sb₂O₃, As₂O₃
The total amount of one or two selected from the components is 0 to 1.
%, Each Young's modulus is 75 GPa or less.
Above, Ta₂O_FiveIngredient is in the range of 0-7.0%
A glass for an optical filter, which is characterized in that
The invention described in 13 has a thermal expansion at -20 to + 70 ° C.
Coefficient is 90 × 10^-7~ 120 × 10^-7/ ° C, and
The composition of the powder is percentage by weight, and₂, B₂O₃, P₂O_FiveSuccess
The total amount of one or more selected from the minutes is 35
~ 55%, TiO₂, La₂O₃, ZrO₂, Nb₂O_Five, T
a₂O_Five, WO₃, Y₂O₃One selected from the ingredients
Is a total amount of two or more of 20 to 45%, MgO, CaO,
One selected from SrO, BaO and ZnO components
The total amount of two or more kinds is 3 to 20%, Li₂O, Na₂O,
K₂1 type or a total of 2 or more types selected from O components
The amount is 5-30%, Sb₂O₃, As₂O₃Selected from ingredients
The total amount of one or two of the
Content, the Young's modulus is 75 GPa or more, and the WO₃
Light whose content is in the range of 0 to 2.60%
The invention according to claim 14, which is a glass for filters.
Has a thermal expansion coefficient of 90 × 10 at −20 to + 70 ° C.
^-7~ 120 × 10^-7/ ° C and the composition of the glass is 100
SiO in fraction₂, B₂O₃, P₂O_FiveSelected from the ingredients
The total amount of one or two or more of 35 to 55%, TiO
₂, La₂O₃, ZrO₂, Nb₂O_Five, Ta₂O_Five, WO₃，
Y₂O₃The total of one or more selected from the ingredients
20-45%, MgO, CaO, SrO, BaO,
A total of one or more selected from ZnO components
3-20%, Li₂O, Na₂O, K₂In the O component
The total amount of one or two or more selected from 5 to 30%,
Sb₂O₃, As₂O₃1 or 2 selected from the ingredients
The total amount of seeds is 0 to 1%, containing each component in the range of
G rate is 75 GPa or more, and Y₂O₃0 to 5.0 ingredients
Glass for optical filter characterized by being in the range of 0%
The invention according to claim 15 is -20 to +70.
Coefficient of thermal expansion at ℃ 90 × 10^-7~ 120 × 10^-7
/ ° C, the composition of the glass is percentage by weight,₂，
B₂O₃, P₂O_FiveOne or more selected from the ingredients
The total amount above is 35-55%, TiO₂, La₂O₃, Zr
O₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂O₃From the ingredients
20% to 45% of the total amount of one or two or more selected,
From the MgO, CaO, SrO, BaO, ZnO components
The total amount of one or more selected is 3 to 20%, L
i₂O, Na₂O, K₂One kind selected from O components
Is 5 to 30% in total of two or more types, Sb₂O₃, As₂O₃
The total amount of one or two selected from the components is 0 to 1.
%, Each Young's modulus is 75 GPa or less.
Above, the MgO component is in the range of 0 to 1.00%.
2. A glass for an optical filter, characterized in that
The invention described in No. 6 relates to the thermal expansion coefficient at -20 to + 70 ° C.
The number is 90 × 10^-7~ 120 × 10^-7/ ° C, glass
The composition of the₂, B₂O₃, P₂O_Fivecomponent
The total amount of one or more selected from
55%, TiO₂, La₂O₃, ZrO₂, Nb₂O_Five, Ta
₂O_Five, WO₃, Y₂O₃One selected from the ingredients or
The total amount of two or more kinds is 20 to 45%, MgO, CaO, S
one selected from rO, BaO, ZnO components or
The total amount of two or more kinds is 3 to 20%, Li₂O, Na₂O, K
₂Total amount of one or more selected from O components
Is 5 to 30%, Sb₂O₃, As₂O₃Selected from the ingredients
Each component in the range of 0 to 1% in total of 1 or 2
Containing Young's modulus of 75 GPa or more, ZnO composition
Minutes in the range 0-2.00%
The invention according to claim 17 is a glass for filters,
The coefficient of thermal expansion at -20 to + 70 ° C is 90 x 10^-7~
120 x 10^-7/ ° C and the composition of the glass is percentage by weight
And SiO₂, B₂O₃, P₂O_Five1 selected from the ingredients
35% to 55% of the total amount of one kind or two or more kinds, TiO₂，
La₂O₃, ZrO₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂
O₃Total amount of one or more selected from the ingredients
20-45%, MgO, CaO, SrO, BaO, Z
Total amount of one or more selected from nO components
Is 3 to 20%, Li₂O, Na₂O, K₂From the O component
The total amount of one or more selected is 5 to 30%, S
b₂O₃, As₂O₃One or two selected from the ingredients
The total amount of 0 to 1%, containing each component in the range of Young
The ratio is 75 GPa or more, and the BaO component is 0 to 10.0.
Glass for optical filter characterized by being in the range of 0%
The invention according to claim 18 is -20 to +70.
Coefficient of thermal expansion at ℃ 90 × 10^-7~ 120 × 10^-7
/ ° C, the composition of the glass is percentage by weight,₂，
B₂O₃, P₂O_FiveOne or more selected from the ingredients
The total amount above is 35-55%, TiO₂, La₂O₃, Zr
O₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂O₃From the ingredients
20% to 45% of the total amount of one or two or more selected,
From the MgO, CaO, SrO, BaO, ZnO components
The total amount of one or more selected is 3 to 20%, L
i₂O, Na₂O, K₂One kind selected from O components
Is 5 to 30% in total of two or more types, Sb₂O₃, As₂O₃
The total amount of one or two selected from the components is 0 to 1.
%, Each Young's modulus is 75 GPa or less.
Above, the SrO component is in the range of 0 to 14.80%.
A glass for an optical filter, which is characterized in that
The invention described in 19 has a thermal expansion at -20 to + 70 ° C.
Coefficient is 90 × 10^-7~ 120 × 10^-7/ ° C, and
The composition of the powder is percentage by weight, and₂, B₂O₃, P₂O_FiveSuccess
The total amount of one or more selected from the minutes is 35
~ 55%, TiO₂, La₂O₃, ZrO₂, Nb₂O_Five, T
a₂O_Five, WO₃, Y₂O₃One selected from the ingredients
Is a total amount of two or more of 20 to 45%, MgO, CaO,
One selected from SrO, BaO and ZnO components
The total amount of two or more kinds is 3 to 20%, Li₂O, Na₂O,
K₂1 type or a total of 2 or more types selected from O components
The amount is 5-30%, Sb₂O₃, As₂O₃Selected from ingredients
The total amount of one or two of the
Content, the Young's modulus is 75 GPa or more, and Li₂
The upper limit of O component is 8.50%,
The invention according to claim 20 is a glass for filters,
Li₂O component is contained as an essential component, and the upper limit is 8.
20. Light according to claim 19, characterized in that it is 50%.
The invention according to claim 21, which is glass for filters.
Is Li₂Characteristic that the lower limit of O component is 2.00%
The glass for an optical filter according to claim 20,
Therefore, the invention according to claim 22 is in the range of -20 to + 70 ° C.
Thermal expansion coefficient is 90 × 10^-7~ 120 × 10^-7/ ° C
Yes, the composition of the glass is percentage by weight, SiO₂, B
₂O₃, P₂O_FiveOne or more selected from the ingredients
Total amount of 35-55%, TiO₂, La₂O₃, Zr
O₂, Nb₂O_Five, Ta₂O_Five, WO₃, Y₂O₃From the ingredients
20% to 45% of the total amount of one or two or more selected,
From the MgO, CaO, SrO, BaO, ZnO components
The total amount of one or more selected is 3 to 20%, L
i₂O, Na₂O, K₂One kind selected from O components
Is 5 to 30% in total of two or more types, Sb₂O₃, As₂O₃
The total amount of one or two selected from the components is 0 to 1.
%, Each Young's modulus is 75 GPa or less.
Above, Na₂O component is in the range of 0 to 14.10%
It is a glass for optical filters, characterized by
The invention according to Item 23 is the thermal expansion at −20 to + 70 ° C.
Expansion coefficient is 90 × 10^-7~ 120 × 10^-7/ ° C,
The composition of lath is percentage by weight₂, B₂O₃, P₂O_Five
The total amount of one or more selected from the ingredients is 3
5-55%, TiO₂, La₂O₃, ZrO₂, Nb₂O_Five，
Ta₂O_Five, WO₃, Y₂O₃Only one selected from the ingredients
Or the total amount of two or more kinds is 20 to 45%, MgO, Ca
One selected from O, SrO, BaO and ZnO components
Alternatively, the total amount of two or more kinds is 3 to 20%, Li₂O, Na₂
O, K₂One or more selected from O components
5-30% of total amount, Sb₂O₃, As₂O₃From the ingredients
The total amount of one or two selected is in the range of 0 to 1%.
Contains each component, Young's modulus is 75 GPa or more, K
₂Optical component characterized by O component in the range of 0-9%
The invention according to claim 24 is a glass for filters,
The upper limit of the coefficient of thermal expansion at -20 to + 70 ° C is 115
× 10^-7/ ° C. 24.
The glass for an optical filter according to any one of 1.
In the invention of item 25, the lower limit of Young's modulus is 85 GPa.
In any one of Claims 1-24 characterized by being
27. The glass for an optical filter according to claim 26,
The invention according to claim 1 is on the glass according to any one of claims 1 to 25.
An optical filter comprising a dielectric film formed on
The invention described in 27 is such that the glass has a higher heat than the dielectric.
The optical filter according to claim 26, having an expansion coefficient.
It

The reasons for limiting the thermal expansion characteristics, Young's modulus, Vickers hardness, light transmittance and composition of the optical filter glass of the present invention will be described below. In addition, the composition is expressed on the basis of oxides, like the original glass.

First, regarding the thermal expansion characteristics, the temperature stability of the central wavelength of the band is very important as described above, and it is necessary to have a thermal expansion coefficient larger than that of the film constituent material. As a result of the test research conducted by the present inventor, if the thermal expansion coefficient at −20 ° C. to + 70 ° C. is 90 × 10 ⁻⁷ / ° C. or more, in the temperature range used as the bandpass filter,
It has been found that sufficient compressive stress can be applied to the membrane. However, on the other hand, if it exceeds 120 × 10 ^-7 / ° C,
The difference in thermal expansion coefficient from the film becomes too large, and problems such as peeling of the film tend to occur. More preferable range is 95 × 10
^{-7 to} 115 x 10 ^-7 / ° C, more preferably 105 ±
It is in the range of 5 × 10 ⁻⁷ / ° C.

In the bandpass filter, the temperature stability of the central wavelength naturally depends on the temperature coefficient of the refractive index of the dielectric material forming the thin film, but is much more affected by the thermal expansion coefficient of the substrate material. This is because the refractive index is determined by the filling factor of the thin film. That is, the higher the filling factor of the thin film, the smaller the change in the central wavelength with temperature. The filling factor of the thin film is greatly influenced by the thermal expansion coefficient of the optical filter substrate material on which the thin film is formed. That is, the substrate material at the time of film formation becomes about 200 ° C., but the substrate material itself is greatly expanded by the heat, and the thin film is attached to the expanded substrate material, and then the substrate material is cooled. The thin film is subjected to compressive stress due to the difference in the coefficient of thermal expansion. As a result, the filling factor of the thin film is increased and the refractive index is increased. The larger the coefficient of thermal expansion of the substrate material, the greater the compressive stress applied to the formed dielectric thin film, and the smaller the rate of change of the refractive index with temperature at the temperature of use. For this reason, it is desirable to set the coefficient of thermal expansion of glass larger than that of the dielectric thin film.

In addition to the characteristics other than the above, in consideration of severe usage conditions, the strength against mechanical deformation,
That is, Young's modulus and Vickers hardness cannot be ignored.

Next, regarding the Young's modulus, these substrate materials are formed into minute chips (2 mm or less × 2 m) after film formation.
Since it is processed into m or less × 2 mm or less), high Young's modulus and high strength are required. Considering the subsequent processing steps as described above, the Young's modulus is 75 GPa or more and the Vickers hardness is 5
It is preferably 50 or more.

Next, regarding the light transmittance, if the light transmittance is low, it is of course inconvenient for signal extraction (S / N).
It is preferable that the value is large, and the light transmittance needs to be at least 60% or more. Furthermore, the wavelength used by the bandpass filter is 950 nm.
˜1600 nm, and it is necessary that the light transmittance of this wavelength in a material having a plate thickness of 10 mm is 90% or more.
The light transmittance at the above wavelength is preferably 93% or more, more preferably 95% or more.

Next, the reason why the composition range of the raw glass is limited as described above will be described below. SiO ₂ , B ₂ O ₃ , P ₂
The O ₅ component is a glass constituent component, but if the total amount of one or more selected from these components is less than 35%, the chemical durability of the glass is poor and the Young's modulus and Vickers hardness decrease. cause. On the other hand, if it exceeds 55%, it becomes difficult to melt and form the raw glass, and at the same time, it becomes difficult to obtain high expansion characteristics.

TiO ₂ , La ₂ O ₃ , ZrO ₂ , Nb ₂ O ₅ ,
_{Ta 2 O 5, WO 3,} Y 2 O 3 component, a relatively high alkali (Li, Na, K) in the containing glass, high expansion properties and a high Young's modulus, high Vickers hardness properties without impairing the chemical durability However, if the total amount of one or more selected from these components is less than 20%, the above effect cannot be obtained, and 4
If it exceeds 5%, the melting / molding property of glass, particularly the devitrification property during molding, deteriorates.

The Li ₂ O, Na ₂ O and K ₂ O components are components that improve the meltability of glass and at the same time have high thermal expansion characteristics. One or more selected from these components. If the total amount is 5%, these effects cannot be obtained, and if it exceeds 30%, the chemical durability is deteriorated and, at the same time, the Young's modulus characteristic and the Vickers hardness characteristic are also deteriorated.

MgO, ZnO, CaO, BaO, SrO
The components are contained in order to improve the meltability of the glass and at the same time have the high expansion properties while maintaining the high Young's modulus properties, but the total amount of one or more selected from these components is 3%. If less than 20%, these effects cannot be obtained and 20%
If it exceeds, the melting and forming properties of glass will deteriorate.

The Sb ₂ O ₃ and As ₂ O ₃ components may be added as a fining agent during glass melting, but 1% or 2 types selected from these components is sufficient at 1% or less. It is more preferably 0.5% or less.

In addition, SnO,
CuO, CoO, NiO, Fe ₂ O ₃ , CeO and MnO components can be contained up to 5%.

Next, as to the reason why PbO is not substantially contained, since this component is an environmentally unfavorable component, its use should be avoided as much as possible.

Next, in order to manufacture the glass for an optical filter according to the present invention, the glass having the above composition is melted, molded and slowly cooled (annealed if necessary), and then lapped by a conventional method. Then, by polishing, a glass for an optical filter having a surface roughness Ra (arithmetic mean roughness) of 1.0 Å or more and 5.0 Å or less can be obtained.

The glass of the present invention is suitable for an interference type optical filter in which a dielectric multilayer film is formed on the surface of the substrate, and in particular, as the dielectric multilayer film, a dielectric thin film (H layer) having a high refractive index is used. And a dielectric thin film (L layer) having a low refractive index are alternately laminated, which is suitable for a bandpass filter.

As the above-mentioned dielectric, TiO ₂ , Ta
Inorganic oxides such as ₂ O ₂ , Nb ₂ O ₅ and SiO ₂ are preferred.
Furthermore, in the bandpass filter used in the wavelength range of 950 nm to 1600 nm, H layer / L is used as the dielectric layer.
As a combination of layers, TiO ₂ / SiO ₂ , Ta ₂ O ₂ / Si
O ₂ and Nb ₂ O ₅ / SiO ₂ are preferred. The optical filter of the present invention can be obtained by forming a dielectric thin film on the surface of a glass substrate. As a film forming method, there are a vapor deposition method, an RF ion plating method, a magnetron sputtering method, a plasma ion plating method and the like. Among them, the vapor deposition method is preferable.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Next, preferred embodiments of the present invention will be described. Tables 1, 2, and 3 show examples of the glass for optical filters of the present invention (No. 1 to 8) and glass substrates for optical filters that have been conventionally used (comparative examples), in addition to the composition, precipitated crystal phase. , Thermal expansion coefficient, Young's modulus, Vickers hardness, and light transmittance.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

A method for manufacturing the glass of the above embodiment will be described. Raw materials such as oxides, carbonates, and nitrates are mixed, and this is melted at a temperature of about 1250 to 1350 ° C. using a normal melting apparatus and homogenized by stirring, and then a glass molded body is obtained through a molding / cooling step. It was Then the obtained glass is 800 # ~ 2
Lapping was performed for 5 to 30 minutes with a 000 # diamond pellet, and then polishing was performed for 30 to 60 minutes with an abrasive cerium oxide having a particle diameter (average) of 0.02 to 3 μm for finishing.
The surface roughness Ra (center line roughness) of these glasses was 5Å or less.

Comparing Examples 1 to 8 of the present invention with Comparative Example 1, a glass substrate for an optical filter which has been conventionally used has a thermal expansion coefficient of 88 × 10 ⁻⁷ / ° C. The values were not sufficient to give compressive stress, and the Young's modulus was 70 GPa and the Vickers hardness was 480, which was a low strength material. On the other hand, the glass of the present invention has a coefficient of thermal expansion sufficient to give a compressive stress to the formed film, and also has a sufficient value in Young's modulus and Vickers hardness. It was suitable as a substrate material for the.

On the glass substrate obtained in the above embodiment, TiO ₂ / SiO ₂ , Ta ₂ O ₂ / SiO ₂ , Nb ₂ O was added.
_The interference type optical filter formed by forming each ₅ / SiO ₂ multilayer film has very good temperature stability of the center wavelength and is very good as a bandpass filter for optical communication. there were.

[0033]

As described above, according to the present invention, it is possible to provide a glass for an optical filter which is excellent in temperature stability of the central wavelength while eliminating the above-mentioned drawbacks of the prior art. This feature (high light transmittance, high thermal expansion characteristics, high Young's modulus, high Vickers hardness) is suitable for interference type optical filters, especially for bandpass filters, and particularly WDM and DWDM (high density wavelength division) in optical communication systems. It is most suitable for multiplex applications. Further, on the glass substrate for the optical filter, TiO ₂ / SiO ₂ , Ta ₂
A bandpass filter member formed by forming a plurality of dielectric films of O ₂ / SiO ₂ and Nb ₂ O ₅ / SiO ₂ has temperature stability at the central wavelength, which is not found in conventional bandpass filter members. Yes, as well as terrestrial optical communication systems
There is a possibility that it will also be used in a space-based-satellite or the like.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G02B 1/02 G02B 1/02 F term (reference) 2H048 GA04 GA09 GA13 GA33 GA62 4G062 AA04 BB01 BB05 BB08 BB09 DA01 DA02 DA03 DA04 DA05 DA06 DB01 DC01 DC02 DC03 DC04 DC05 DC06 DD01 DD02 DD03 DD04 DD05 DD06 DE01 DE02 DE03 DE04 DF01 EA01 EA02 EA03 EA04 EB01 EB02 EB03 EB04 EC01 EC02 EC03 EC04 ED01 ED02 ED03 ED04 EE01 EE02 EE03 EE04 EF01 EF02 EF03 EF04 EG01 EG02 EG03 EG04 FA01 FB01 FB02 FB03 FB04 FB05 FC01 FC02 FC03 FC04 FC05 FD01 FE01 FF01 FG01 FG02 FG03 FG04 FG05 FH01 FH02 FH03 FH04 FH05 FJ01 FJ02 FJ03 FJ04 FJ05 FK01 FK02 FK03 FK04 FK05 FL01 GA01 GA10 GB01 GC01 GD01 GE01 HH01 HH03 HH05 HH07 HH09 HH11 HH13 HH15 HH17 HH20 JJ01 JJ03 JJ05 JJ07 JJ10 KK01 KK03 KK05 KK07 KK10 MM02 MM04 NN01 NN10

Claims (27)

[Claims] 1. The thermal expansion coefficient at -20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight. SiO ₂ , B ₂ O ₃ , P ₂ O ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of the seeds contains each component in the range of 0 to 1%, the Young's modulus is 75 GPa or more, and the upper limit of the SiO ₂ component is 4
Glass for optical filters, which is 1.39%. 2. A SiO ₂ component is contained as an essential component,
The glass for an optical filter according to claim 1, wherein the upper limit is 41.39%. 3. The glass for an optical filter according to claim 2, wherein the lower limit of the SiO ₂ component is 17.10%. 4. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, the Young's modulus is 75 GPa or more, and the B ₂ O ₃ component is 0 to 2
Glass for optical filters, which is in the range of 1.5%. 5. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight: SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and P ₂ O ₅ component is 0 to
Glass for optical filters, which is in the range of 8.60%. 6. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , and P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
A glass for an optical filter comprising each component in a total amount of 0 to 1%, Young's modulus of 75 GPa or more, and an upper limit of TiO ₂ component of 30.00%. 7. A TiO ₂ component is contained as an essential component,
The glass for optical filters according to claim 6, wherein the upper limit is 30.00%. 8. The glass for an optical filter according to claim 7, wherein the lower limit of the TiO ₂ component is 5.00%. 9. The thermal expansion coefficient at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and La ₂ O ₃ component is 0 to 0%.
A glass for an optical filter, which is in the range of 17.00%. 10. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and ZrO ₂ component is 0 to
Glass for optical filters, which is in the range of 7.90%. 11. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, the Young's modulus is 75 GPa or more, and the Nb ₂ O ₅ component is 0 to
Glass for optical filters, which is in the range of 7.90%. 12. The thermal expansion coefficient at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight: SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and Ta ₂ O ₅ component is 0 to
Glass for optical filters, which is in the range of 7.00%. 13. The thermal expansion coefficient at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and WO ₃ component is 0 to
Glass for optical filters, which is in the range of 2.60%. 14. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight: SiO ₂ , B ₂ O ₃ , P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of the seeds contains each component in the range of 0 to 1%, the Young's modulus is 75 GPa or more, and the Y ₂ O ₃ component is 0 to
Glass for optical filters, which is in the range of 5.00%. 15. The glass composition has a coefficient of thermal expansion at −20 to + 70 ° C. of 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C. and a glass composition of weight percentage of SiO ₂ , B ₂ O ₃ , and P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, the Young's modulus is 75 GPa or more, and the MgO component is 0 to
Glass for optical filters, which is in the range of 1.00%. 16. The thermal expansion coefficient at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., the composition of the glass is percentage by weight, and SiO ₂ , B ₂ O ₃ , and P ₂ O are contained. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and ZnO component is 0 to
Glass for optical filters, which is in the range of 2.00%. 17. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , and P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and BaO component is 0 to 1
Glass for optical filters, which is in the range of 0.00%. 18. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight. SiO ₂ , B ₂ O ₃ , P ₂ O ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and SrO component is 0 to 1
A glass for an optical filter, which is in the range of 4.80%. 19. The glass composition has a coefficient of thermal expansion at −20 to + 70 ° C. of 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C. and a glass composition of SiO ₂ , B ₂ O ₃ , and P ₂ O in percentage by weight. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, the Young's modulus is 75 GPa or more, and the upper limit of the Li ₂ O component is 8.
Glass for optical filters, which is 50%. 20. The glass for an optical filter according to claim 19, which contains a Li ₂ O component as an essential component and the upper limit thereof is 8.50%. 21. The glass for an optical filter according to claim 20, wherein the lower limit of the Li ₂ O component is 2.00%. 22. The coefficient of thermal expansion at −20 to + 70 ° C. is 90 × 10 ^{−7 to} 120 × 10 ⁻⁷ / ° C., and the composition of the glass is percentage by weight, SiO ₂ , B ₂ O ₃ , and P ₂ O. ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and Na ₂ O component is 0 to
Glass for optical filters, which is in the range of 14.10%. 23. The thermal expansion coefficient of -20 to + 70 ° C. is ^{90 × 10 -7 ~120 × 10 -7} / ℃, the glass composition is in weight _{percent, SiO 2, B 2 O 3} , P 2 O ₅ one or more of the total weight selected from among components _{35~55% TiO 2, La 2 O} 3, ZrO 2, Nb 2 O 5, Ta 2 O 5, W
O _3, Y ₂ O ₃ component one or more of the total amount 20 to 45% MgO selected from among, CaO, SrO, BaO, 1 kind or the sum of two or more selected from among ZnO component 3 to 20% Li ₂ O, Na ₂ O, K ₂ O components selected from the total of 5 or 30% Sb ₂ O ₃ and As ₂ O ₃ components. 1 or 2 chosen
The total amount of seeds contains each component in the range of 0 to 1%, Young's modulus is 75 GPa or more, and K ₂ O component is 0 to 9
Glass for optical filters, characterized by being in the range of%. 24. The optical filter glass according to claim 1, wherein the upper limit of the coefficient of thermal expansion at −20 to + 70 ° C. is 115 × 10 ⁻⁷ / ° C. 25. The glass for an optical filter according to claim 1, wherein the lower limit of Young's modulus is 85 GPa. 26. An optical filter obtained by forming a dielectric film on the glass according to claim 1. 27. The optical filter according to claim 26, wherein the glass has a coefficient of thermal expansion larger than that of the dielectric.