TWI846612B - Optical Filter - Google Patents

Abstract

The present invention provides a filter that can appropriately cut off infrared light and has low dependency on the incident angle. The present invention is a filter that has a first infrared absorbing glass plate having an average transmittance of 80% or more for light with a wavelength of 400 nm to 550 nm, and a second infrared absorbing glass plate having an average transmittance of 80% or more for light with a wavelength of 400 nm to 550 nm, wherein when the transmittance of the first infrared absorbing glass plate at a wavelength of 700 nm is set as _Ta and the transmittance of the second infrared absorbing glass plate at a wavelength of 700 nm is set as _Tb , the absolute value ΔT of the difference between _Ta and _Tb is between 10% and 90%.

Description

Optical Filter

The present invention relates to a filter such as an infrared cut-off filter.

Infrared cut-off filters can cut off light with wavelengths in the infrared region (hereinafter referred to as "infrared light") and allow visible light to pass through. Therefore, they are widely used in devices such as solid-state imaging devices or sensors.

Generally, an infrared cutoff filter is formed by providing an optical multilayer film having high refractive index layers and low refractive index layers alternately on a substrate such as a transparent substrate (Patent Document 1). [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Publication No. 2006-60014

[The problem the invention is trying to solve]

As machines have become smaller and thinner in recent years, various devices in the machine have gradually been arranged in a closer state. Therefore, devices with infrared cut-off filters tend to allow light to enter at a wide angle.

However, it is known that the optical multilayer film of the infrared cut filter has an incident angle dependency. Therefore, the conventional infrared cut filter having the optical multilayer film has a problem that the optical characteristics vary according to the incident angle of light.

Furthermore, in a machine in which a device having an infrared cutoff filter (hereinafter referred to as an "infrared cutoff device") is arranged in close proximity to a device that radiates infrared rays (hereinafter referred to as an "infrared radiating device"), if the function of the infrared cutoff filter to cut off infrared light is insufficient, there is a possibility that the infrared cutoff device may malfunction.

For example, an ambient light sensor is installed in a smart phone or a portable game console to detect the ambient light around the device. By using the ambient light sensor to detect the ambient light, the brightness of the display of the device can be appropriately adjusted. However, since the ambient light sensor has an infrared cutoff filter, if an infrared radiating device is arranged near the ambient light sensor, there is a risk that the infrared light from the infrared radiating device will cause the ambient light sensor to malfunction.

Due to such problems, in recent years, expectations have been growing for infrared cut filters that can significantly suppress the angle dependence of optical characteristics and appropriately cut infrared light.

The present invention is completed in view of this background. The purpose of the present invention is to provide a filter that can appropriately cut off infrared light and whose optical properties are basically independent of the incident angle of the light. [Technical means to solve the problem]

In the present invention, a filter is provided, which comprises: a first infrared absorbing glass plate, the average transmittance of light with a wavelength of 400 nm to 550 nm of which is 80% or more; a second infrared absorbing glass plate, the average transmittance of light with a wavelength of 400 nm to 550 nm of which is 80% or more; and when the transmittance of the first infrared absorbing glass plate at a wavelength of 700 nm is set as _Ta , and the transmittance of the second infrared absorbing glass plate at a wavelength of 700 nm is set as _Tb , the absolute value ΔT of the difference between _Ta and _Tb is between 10% and 90%. [Effects of the Invention]

In the present invention, a filter can be provided which can appropriately cut off infrared light and whose optical properties are substantially independent of the incident angle of the light.

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In one embodiment of the present invention, a filter is provided, which comprises: a first infrared absorbing glass plate, whose average transmittance of light with a wavelength of 400 nm to 550 nm is greater than 80%; and a second infrared absorbing glass plate, whose average transmittance of light with a wavelength of 400 nm to 550 nm is greater than 80%; and when the transmittance of the first infrared absorbing glass plate at a wavelength of 700 nm is set to _Ta , and the transmittance of the second infrared absorbing glass plate at a wavelength of 700 nm is set to _Tb , the absolute value ΔT of the difference between _Ta and _Tb is greater than 10% and less than 90%.

Here, in this case, the average transmittance of light with a wavelength of 400 nm to 550 nm of the glass plate is also specifically referred to as "average visible light transmittance".

In one embodiment of the present invention, the optical filter comprises a plurality of infrared absorbing glass plates. In addition, in the optical filter of one embodiment of the present invention, each infrared absorbing glass plate contains an infrared absorbing component.

Therefore, in one embodiment of the present invention, unlike the infrared cut-off filter that reflects infrared light by using the interference of light generated by the optical multi-layer film structure, infrared light can be absorbed by the infrared absorption component. Therefore, in the filter of one embodiment of the present invention, the influence of the incident angle of light on the optical characteristics can be significantly suppressed.

Furthermore, if a filter is simply constructed by stacking a plurality of infrared absorbing glass plates, the transmittance in the visible light region may be significantly reduced.

However, in one embodiment of the present invention, both the first and second infrared absorbing glass plates have a characteristic of having an average visible light transmittance of 80% or more. Therefore, in one embodiment of the present invention, even if the first and second infrared absorbing glass plates are overlapped, it is not easy to cause a significant decrease in the transmittance in the visible light region.

Furthermore, in the optical filter of one embodiment of the present invention, each infrared absorbing glass plate is selected in such a manner that when the transmittance of the first infrared absorbing glass plate at a wavelength of 700 nm is set as _Ta and the transmittance of the second infrared absorbing glass plate at a wavelength of 700 nm is set as _Tb , the absolute value of the difference between _Ta and _Tb (hereinafter represented by "ΔT") becomes 10% or more and 90% or less. Thus, the transmittance of the optical filter at a wavelength of about 700 nm, where a large change in transmittance is required, is substantially the same as the optical characteristics of one of the infrared absorbing glass plates, and the design of the optical filter becomes easy. In addition, the transmittance of the optical filter in the infrared region can be significantly reduced.

With the above features, in the filter of one embodiment of the present invention, infrared light can be significantly reduced while significantly suppressing the decrease in transmittance in the visible light region.

Hereinafter, referring to FIG. 1 , the features of the optical filter according to one embodiment of the present invention will be described in more detail.

FIG. 1 schematically shows an example of optical characteristics of the first and second infrared absorbing glass plates included in the filter according to an embodiment of the present invention.

In FIG1 , the horizontal axis is wavelength and the vertical axis is transmittance. Curve A schematically represents the transmittance characteristics of the first infrared absorbing glass plate, and curve B schematically represents the transmittance characteristics of the second infrared absorbing glass plate. Furthermore, curve C is a combination of curve A and curve B, that is, it represents the transmittance characteristics of a filter when the first infrared absorbing glass plate and the second infrared absorbing glass plate are combined.

As shown in FIG. 1 , in the filter of one embodiment of the present invention, the first infrared absorbing glass plate and the second infrared absorbing glass plate both have an average visible light transmittance exceeding 80% in the visible light region.

In this case, as shown by curve C, even if two infrared absorbing glass plates are combined, a relatively high transmittance can be maintained in the visible light region. When both the first infrared absorbing glass plate and the second infrared absorbing glass plate have an average visible light transmittance of less than 80% in the visible light region, the transmittance characteristic of the visible light of the filter is reduced, and thus it is not good. It is better that both the first infrared absorbing glass plate and the second infrared absorbing glass plate have an average visible light transmittance of more than 81% in the visible light region, and more preferably have an average visible light transmittance of more than 82%.

For example, the filter of one embodiment of the present invention has an average visible light transmittance of 76% or more. If the filter has an average visible light transmittance of less than 76%, if the filter is used in a photo sensor, the amount of light received by the sensor may be reduced, which is not preferred. The filter preferably has an average visible light transmittance of 78% or more, and more preferably has an average visible light transmittance of 80% or more.

Furthermore, the first infrared absorbing glass plate has a transmittance _Ta at a wavelength of 700 nm, and the second infrared absorbing glass plate has a transmittance _Tb at a wavelength of 700 nm. The two infrared absorbing glass plates are selected so that the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb is 10% or more. In other words, one of the two infrared absorbing glass plates has a transmittance greater (or less) than the other infrared absorbing glass plate at a wavelength of 700 nm by 10% or more.

In this case, the infrared absorbing glass plate with higher transmittance at a wavelength of 700 nm (the first infrared absorbing glass plate in the case of FIG. 1 ) has a wavelength at which transmittance is significantly reduced compared to the infrared absorbing glass plate with lower transmittance at a wavelength of 700 nm (the second infrared absorbing glass plate in the case of FIG. 1 ), which exists on the high wavelength side.

For example, in the example shown in FIG. 1 , if the wavelength on the high wavelength side when the transmittance of the infrared absorbing glass plate becomes 50% is expressed as the half-value wavelength T ₅₀ , the half-value wavelength T ₅₀ of the first infrared absorbing glass plate is higher than the half-value wavelength T ₅₀ of the second infrared absorbing glass plate.

In this case, as shown by curve C, the transmittance in the infrared region obtained when the infrared absorbing glass plates are overlapped becomes sufficiently small. Here, if the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb is less than 10%, the transmittance characteristics of the light at a wavelength of 700 nm as a filter become low, which is not desirable. If the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb exceeds 90%, the transmittance at a wavelength of 700 nm of one of the infrared absorbing glass substrates (the one with the lower transmittance at a wavelength of 700 nm) must be lowered, and there is a risk that the average transmittance of visible light will decrease, which is not desirable. The two infrared absorbing glass plates are preferably selected so that the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb is 15% or more, more preferably 20% or more. Furthermore, the two infrared absorbing glass plates are preferably selected so that the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb is 89% or less, more preferably 88% or less.

For example, in the optical filter of one embodiment of the present invention, the average value of the optical concentration in the wavelength range of 850 nm to 950 nm is greater than 2.5. The average value of the optical concentration in the wavelength range of 850 nm to 950 nm is preferably greater than 3.0, and more preferably greater than 3.5.

Thus, in the optical filter of one embodiment of the present invention, the transmittance in the infrared region can be significantly reduced while maintaining the transmittance in the visible light region at a relatively high value.

Furthermore, in the optical filter of one embodiment of the present invention, since the infrared light cutoff function generated by the optical multilayer film is not utilized, the angle dependency of the incident light that affects the transmittance can be significantly suppressed.

(Optical filter of one embodiment of the present invention) Next, referring to FIG. 2, the structure of the optical filter of one embodiment of the present invention is described in detail.

FIG2 schematically shows a cross section of an optical filter (hereinafter referred to as "first optical filter") according to an embodiment of the present invention.

As shown in FIG2 , the first filter 100 is formed by laminating a first infrared absorbing glass plate 110 and a second infrared absorbing glass plate 130. The outer surface of the first infrared absorbing glass plate 110 becomes a first side 102 of the first filter 100, and the outer surface of the second infrared absorbing glass plate 130 becomes a second side 104 of the first filter 100.

Furthermore, in the present case, "infrared absorbing glass plate" means a glass plate containing 0.05 cation % or more of an infrared absorbing component. Moreover, examples of infrared absorbing components include iron and copper. Moreover, as a glass plate, as long as it is a glass containing the above-mentioned infrared absorbing component, the glass composition system is not particularly limited. Examples of glass compositions include phosphate glass, fluorophosphate glass, silicophosphate glass, sulfurphosphate glass, sodium calcium glass, borosilicate glass, alkali-free glass, and aluminum silicate glass.

The first infrared absorbing glass plate 110 has an average visible light transmittance of 80% or more. Also, the second infrared absorbing glass plate 130 has an average visible light transmittance of 80% or more.

Furthermore, when the transmittance of the first infrared absorbing glass plate 110 at a wavelength of 700 nm is set to _Ta and the transmittance of the second infrared absorbing glass plate 130 at a wavelength of 700 nm is set to _Tb , the first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130 are selected so that the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb becomes 10% or more and 90% or less.

In the following description, it is assumed that _Ta > _Tb for convenience.

In the first optical filter 100, as described above, the transmittance in the visible light region can be maintained at a relatively high value while significantly reducing the transmittance in the infrared region. In addition, the first optical filter 100 can significantly suppress the angle dependency of the incident light that affects the transmittance.

Hereinafter, each component constituting the first filter 100 will be described in more detail.

(First infrared absorbing glass plate 110) As described above, the first infrared absorbing glass plate 110 has an average visible light transmittance of 80% or more. The average visible light transmittance is preferably 81% or more, and more preferably 82% or more.

Furthermore, the first infrared absorbing glass plate 110 has an infrared absorbing component of 0.05 cation % or more. The infrared absorbing component may be, for example, iron and/or copper.

Furthermore, the first infrared absorbing glass plate 110 may have any composition as long as the above-mentioned relationship between _Ta and _Tb is satisfied between the first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130 .

However, when the first infrared absorbing glass plate 110 is an outer surface of the first filter 100, that is, when one surface of the first infrared absorbing glass plate 110 is exposed, the first infrared absorbing glass plate 110 may also have fluorine. In this way, the weather resistance of the first filter 100 can be improved at least on the side of the first infrared absorbing glass plate 110.

The thickness of the first infrared absorbing glass plate 110 is not particularly limited. However, when the first filter 100 is used in a small device such as an ambient light sensor, in order to reduce the thickness of the first filter 100, the thickness is preferably in the range of 0.05 mm to 2 mm.

(Second infrared absorbing glass plate 130) The second infrared absorbing glass plate 130 is the same as the first infrared absorbing glass plate 110 except for the composition.

The second infrared absorbing glass plate 130 has an infrared absorbing component of 0.05 cation % or more. The infrared absorbing component may be copper, for example.

The second infrared absorbing glass plate 130 may have any composition as long as the above-mentioned relationship of _Ta and _Tb is satisfied between the second infrared absorbing glass plate 130 and the first infrared absorbing glass plate 110 .

However, when the second infrared absorbing glass plate 130 is an outer surface of the first filter 100, that is, when one surface of the second infrared absorbing glass plate 130 is exposed, the second infrared absorbing glass plate 130 may also have fluorine. In this way, the weather resistance of the first filter 100 can be improved at least on the side of the second infrared absorbing glass plate 130.

(Others) Although not shown in FIG. 2 , the first filter 100 may further include an anti-reflection film on the first side 102 and/or the second side 104. By providing the anti-reflection film, the loss of light incident on the first filter 100 can be significantly suppressed.

The anti-reflection film may be formed by alternately laminating low refractive index layers and high refractive index layers. The low refractive index layers are preferably layers having a refractive index of 1.7 or less, and may include, for example, SiO ₂ , MgF ₂ , Al ₂ O ₃ , etc. On the other hand, the high refractive index layers are preferably layers having a refractive index of 2.0 or more, and may include, for example, TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , etc.

Furthermore, there is no particular limitation on the method of bonding the first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130 .

The first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130 may be bonded together by, for example, interposing an adhesive layer therebetween.

As the bonding layer, it is preferable that the refractive index is close to that of the first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130. As the bonding layer, for example, acrylic resin or epoxy resin can be used.

Alternatively, the first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130 may be joined by fluorine bonding (joining by melting the surfaces using fluorine), optical contact, activation using etching, joining by interposing a metal film (formed by sputtering), activation using plasma, anodic bonding, joining by interposing glass material, and joining by melting the surfaces using laser.

(Another embodiment of the optical filter of the present invention) Next, referring to FIG. 3, the structure of another embodiment of the optical filter of the present invention is described in detail.

FIG3 schematically shows a cross section of an optical filter (hereinafter referred to as a "second optical filter") according to another embodiment of the present invention.

As shown in FIG. 3 , the second filter 200 includes a first infrared absorbing glass plate 210 , a second infrared absorbing glass plate 230 , and a transparent glass plate 270 disposed therebetween.

In the second filter 200 , the outer surface of the first infrared absorbing glass plate 210 becomes the first side 202 of the second filter 200 , and the outer surface of the second infrared absorbing glass plate 230 becomes the second side 204 of the second filter 200 .

In the second filter 200, the first infrared absorbing glass plate 210 and the second infrared absorbing glass plate 230 may be constructed by referring to the description of the first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130 in the first filter 100. Therefore, no further explanation is given here.

On the other hand, the transparent glass plate 270 is not an infrared absorbing glass plate, but is made of transparent glass that does not contain infrared absorbing components.

The transparent glass plate 270 is provided in the second filter 200 in order to suppress the separation between the first infrared absorbing glass plate 210 and the second infrared absorbing glass plate 230. That is, when the average thermal expansion coefficient of the first infrared absorbing glass plate 210 at 25°C to 250°C is set to _αa , the average thermal expansion coefficient of the second infrared absorbing glass plate 230 at 25°C to 250°C is set to _αb , and the average thermal expansion coefficient of the transparent glass plate 270 at 25°C to 250°C is set to _αc , the transparent glass plate 270 is selected so that _αc becomes between _αa and _αb .

By providing such a transparent glass plate 270, it is possible to suppress the separation between the first infrared absorbing glass plate 210 and the second infrared absorbing glass plate 230 due to temperature change.

In the second filter 200, the first infrared absorbing glass plate 210 and the second infrared absorbing glass plate 230 are also selected so that the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb is greater than 10% and less than 90%.

Therefore, in the second filter 200, the transmittance in the infrared region can be significantly reduced while maintaining the transmittance in the visible light region at a relatively high value. In addition, the second filter 200 can significantly suppress the angle dependency of the incident light that affects the transmittance.

Furthermore, although not shown in FIG. 3 , the second filter 200 may further include an anti-reflection film on the first side 202 and/or the second side 204 .

Furthermore, the transparent glass plate 270 included in the second filter 200 may also have the following features.

(Transparent glass plate 270) The transparent glass plate 270 may have any composition as long as it does not hinder the function of the second filter 200. Examples of glass compositions include phosphate glass, fluorophosphate glass, silicophosphate glass, sulfuric phosphate glass, sodium calcium glass, borosilicate glass, alkali-free glass, and aluminosilicate glass.

The transparent glass plate 270 has an average visible light transmittance of 80% or more, preferably 81% or more, and more preferably 82% or more.

The transparent glass plate 270 may have a thickness of, for example, 0.05 mm to 2 mm.

Furthermore, as described above, the transparent glass plate 270 does not substantially contain infrared absorbing components. However, there is a case where the transparent glass plate 270 contains less than 0.01 mass % of infrared absorbing components as unavoidable impurities during the manufacturing process.

(Another embodiment of the optical filter of the present invention) Next, referring to FIG. 4, the structure of another embodiment of the optical filter of the present invention is described in detail.

FIG4 schematically shows a cross section of an optical filter according to another embodiment of the present invention (hereinafter referred to as the "third optical filter").

As shown in FIG. 4 , the third filter 300 includes a second infrared absorbing glass plate 330 , a first infrared absorbing glass plate 310 , and a third infrared absorbing glass plate 350 in sequence.

Here, the third infrared absorbing glass plate 350 has the same composition as the second infrared absorbing glass plate 330. Therefore, the third filter 300 has a structure in which the first infrared absorbing glass plate 310 is sandwiched by the second infrared absorbing glass plates 330 on both sides.

In the third filter 300 , the outer surface of the second infrared absorbing glass plate 330 becomes the first side 302 of the third filter 300 , and the outer surface of the third infrared absorbing glass plate 350 becomes the second side 304 of the third filter 300 .

In the third filter 300 , the first infrared absorbing glass plate 310 and the second infrared absorbing glass plate 330 may be configured by referring to the description of the first infrared absorbing glass plate 110 and the second infrared absorbing glass plate 130 in the first filter 100 .

Furthermore, in the third optical filter 300, the second infrared absorbing glass plate 330 and the third infrared absorbing glass plate 350 preferably contain fluorine, thereby improving the weather resistance of the third optical filter 300.

In the third filter 300, the first infrared absorbing glass plate 310 and the second infrared absorbing glass plate 330 are also selected so that the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb is 10% or more and 90% or less. When three infrared absorbing glass plates are used as in the third filter 300, the transmittance characteristic when two infrared absorbing glass plates having substantially the same glass composition or transmittance characteristic are overlapped is defined as transmittance _Ta or transmittance _Tb . For example, in the third filter 300, the transmittance _Tb is defined using the transmittance characteristic when the second infrared absorbing glass plate 330 and the third infrared absorbing glass plate 350 having the same composition are overlapped.

Therefore, in the third filter 300, the transmittance in the infrared region can be significantly reduced while maintaining the transmittance in the visible light region at a relatively high value. In addition, the third filter 300 can significantly suppress the angle dependency of the incident light that affects the transmittance.

Furthermore, although not shown in FIG. 4 , the third filter 300 may further include an anti-reflection film on the first side 302 and/or the second side 304 .

(Another embodiment of the optical filter of the present invention) Next, referring to FIG. 5 , the structure of another embodiment of the optical filter of the present invention is described in detail.

FIG5 schematically shows a cross section of an optical filter according to another embodiment of the present invention (hereinafter referred to as the "fourth optical filter").

As shown in Fig. 5, the fourth filter 400 has a structure in which a transparent glass plate is provided between each infrared absorbing glass plate in the third filter 300. That is, the fourth filter 400 has a structure in which the second infrared absorbing glass plate 430, the first transparent glass plate 470, the first infrared absorbing glass plate 410, the second transparent glass plate 480, and the third infrared absorbing glass plate 450 are stacked in order.

In the fourth filter 400 , the outer surface of the second infrared absorbing glass plate 430 becomes the first side 402 of the fourth filter 400 , and the outer surface of the third infrared absorbing glass plate 450 becomes the second side 404 of the fourth filter 400 .

In the fourth filter 400, the first, second and third infrared absorbing glass plates 410, 430 and 450 may be constructed in accordance with the description of the first, second and third infrared absorbing glass plates 310, 330 and 350 in the third filter 300. Furthermore, the first transparent glass plate 470 may be constructed in accordance with the description of the transparent glass plate 270 in the second filter 200.

On the other hand, the second transparent glass plate 480 is not an infrared absorbing glass plate, but is made of glass that does not contain infrared absorbing components.

Furthermore, the second transparent glass plate 480 is provided in the fourth filter 400 in order to suppress the separation between the first infrared absorbing glass plate 410 and the third infrared absorbing glass plate 450 .

That is, when the average thermal expansion coefficient of the first infrared absorbing glass plate 410 at 25°C to 250°C is set to _αa , the average thermal expansion coefficient of the third infrared absorbing glass plate 450 at 25°C to 250°C is set to _αb ' ( _αb ' is equal to the average thermal expansion coefficient _αb of the second infrared absorbing glass plate 430 at 25°C to 250°C), and the average thermal expansion coefficient of the second transparent glass plate 480 at 25°C to 250°C is set to _αd , the second transparent glass plate 480 is selected in such a way that _αd becomes between _αa and _αb '.

By providing such a second transparent glass plate 480, the separation between the first infrared absorbing glass plate 410 and the third infrared absorbing glass plate 450 can be significantly suppressed.

In the fourth filter 400, the first infrared absorbing glass plate 410 and the second infrared absorbing glass plate 430 are selected so that the absolute value ΔT of the difference between the transmittance _Ta and the transmittance _Tb is greater than 10% and less than 90%. Since the fourth filter 400 uses three infrared absorbing glass plates like the third filter 300, the transmittance Tb is defined by using the transmittance characteristics when the second infrared absorbing glass plate 430 and the third infrared absorbing glass plate 450 having the same composition are overlapped as described _above .

Therefore, in the fourth filter 400, the transmittance in the infrared region can be significantly reduced while maintaining the transmittance in the visible light region at a relatively high value. In addition, the fourth filter 400 can significantly suppress the angle dependency of the incident light that affects the transmittance.

Furthermore, although not shown in FIG. 5 , the fourth filter 400 may further include an anti-reflection film on the first side 402 and/or the second side 404 .

In the above, the filter of one embodiment of the present invention is described with reference to FIGS. 2 to 5. However, the above configuration is only an example, and it is obvious that the filter of one embodiment of the present invention can have any configuration as long as it has the first and second infrared absorbing glass plates as described above and can obtain the above-described effects. [Example]

Hereinafter, examples 1 to 6 are examples of embodiments, and examples 11 and 12 are comparative examples.

(Example 1) A filter including two infrared absorbing glass plates as shown in FIG. 2 above (referred to as "filter of Example 1") was constructed and its characteristics were evaluated.

As the first infrared absorbing glass plate, a glass plate having the composition of "Glass A" shown in Table 1 below was used. The thickness was 1.06 mm.

As the second infrared absorbing glass plate, a glass plate having the composition of "Glass B" in Table 1 was used. The thickness was 0.38 mm. Therefore, the total thickness of the filter of Example 1 was 1.44 mm.

[Table 1] Glass A Glass B Glass C Glass D Glass E Glass F Cation (%) P 62.2 43.9 43.1 63.5 45.3 45.2 B 0.0 0.0 0.0 2.4 0.0 0.0 Al 16.2 9.2 9.1 10.3 9.5 9.5 Li 2.6 24.4 24.0 0.0 25.2 25.2 Na 2.6 0.0 0.0 15.6 0.0 0.0 K 1.8 0.0 0.0 0.0 0.0 0.0 Mg 2.2 3.3 3.3 0.0 3.4 3.4 Ca 0.0 4.5 4.4 0.0 4.7 4.7 Sr 0.0 5.6 5.5 0.0 5.8 5.8 Ba 1.1 5.8 5.7 1.9 6.0 6.0 Zn 3.8 0.0 0.0 0.0 0.0 0.0 Cu 0.0 3.2 5.0 6.3 0.1 0.2 Fe 7.6 0.0 0.0 0.0 0.0 0.0 Total cations 100.0 100.0 100.0 100.0 100.0 100.0 Anion(%) O 100.0 85.4 85.3 100.0 85.8 85.8 F 0.0 14.6 14.7 0.0 14.2 14.2 Total anions 100.0 100.0 100.0 100.0 100.0 100.0 Thermal expansion coefficient (50～250℃) [×10 ^-7 /℃] 76 129 129 106 129 129 The average visible light transmittance of the first infrared absorbing glass plate is 84.4%, and the transmittance _Ta at a wavelength of 700 nm is 61.0%. The wavelength on the long wavelength side where the transmittance becomes 50%, that is, the half-value wavelength _T50 , is 724 nm.

On the other hand, the average transmittance of visible light of the second infrared absorbing glass plate is 87.3%, the transmittance _Tb at a wavelength of 700 nm is 7.1%, and the half-value wavelength _T50 is 614 nm.

Therefore, the absolute value of the transmittance difference between the two at a wavelength of 700 nm, ΔT (= | _Ta - _Tb |), is 53.9%.

The column "Example 1" in Table 2 below summarizes the structure and ΔT of the filter of Example 1.

[Table 2] example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 11 1st infrared absorbing glass plate Type A A A A D D C Thickness(mm) 1.06 1.37 1.32 1.43 0.45 0.51 0.63 Average visible light transmittance (%) 84.4 82.5 82.8 82.1 86.2 85.6 75.8 Transmittance at 700 nm _Ta (%) 61.0 54.1 55.2 52.8 4.5 3.0 0.1 T ₅₀ (nm) 724 708 710 705 614 609 579 Second infrared absorbing glass plate Type B C B C F E - Thickness(mm) 0.38 0.23 0.27 0.17 0.87 0.10 - Average visible light transmittance (%) 87.3 85.2 88.4 86.7 90.0 90.9 - Transmittance T _b (%) at 700 nm 7.1 8.0 15.0 15.6 64.2 89.0 - T ₅₀ (nm) 614 616 629 630 793 - - ΔT(%) 53.9 46.1 40.2 37.2 59.7 86.0 - Next, the optical properties of the filter of Example 1 were evaluated using the following method.

First, the transmittance characteristics of the first infrared absorbing glass plate and the second infrared absorbing glass plate were actually measured using V-570 manufactured by JASCO Corporation.

Next, based on the obtained measurement results, the transmittance characteristics when two infrared absorbing glass plates are laminated are calculated. Here, it is assumed that the interface reflection between each infrared absorbing glass plate is zero. In addition, it is assumed that there is a bonding layer at the interface between each infrared absorbing glass plate, and it is assumed that the transmittance loss of the bonding layer is 0.1%.

The transmittance characteristics of the filter of Example 1 calculated by this method are shown in Fig. 6. In Fig. 6, the transmittance characteristics of the first infrared absorbing glass plate and the transmittance characteristics of the second infrared absorbing glass plate are shown together.

As can be seen from FIG. 6 , the filter of Example 1 maintains a sufficiently high transmittance in the visible light region.

Furthermore, for the filter of Example 1, the average value of the optical concentration OD _ave in the wavelength range of 850 nm to 950 nm was calculated, and the result was OD _ave = 3.72. Therefore, it can be seen that the filter of Example 1 can significantly suppress the transmittance in the infrared region, especially in the wavelength range of 850 nm to 950 nm.

(Example 2) The light filter is constructed by the same method as Example 1 (referred to as "light filter of Example 2").

However, in Example 2, the thickness of the first infrared absorbing glass plate (glass A) is set to 1.37 mm. In addition, as the second infrared absorbing glass plate, a glass plate having the composition of "glass C" in Table 1 is used. The thickness is 0.23 mm. Therefore, the total thickness of the filter of Example 2 is 1.60 mm.

The column "Example 2" in Table 2 above summarizes the structure and ΔT of the filter of Example 2.

Next, the optical properties of the filter of Example 2 were evaluated using the above method.

The transmittance characteristics of the obtained filter of Example 2 are shown in Fig. 7. In Fig. 7, the transmittance characteristics of the first infrared absorbing glass plate and the transmittance characteristics of the second infrared absorbing glass plate are shown together.

As can be seen from FIG. 7 , the filter of Example 2 maintains a sufficiently high transmittance in the visible light region.

Furthermore, for the filter of Example 2, the average value of the optical concentration OD _ave in the wavelength range of 850 nm to 950 nm was calculated, and the result was OD _ave = 4.23. Therefore, it can be seen that the filter of Example 2 can significantly suppress the transmittance in the infrared region, especially in the wavelength range of 850 nm to 950 nm.

(Example 3) The optical filter is constructed by the same method as Example 1 (referred to as "the optical filter of Example 3").

However, in Example 3, the thickness of the first infrared absorbing glass plate (glass A) is set to 1.32 mm. Furthermore, the thickness of the second infrared absorbing glass plate (glass B) is set to 0.27 mm. Therefore, the total thickness of the filter in Example 3 is 1.59 mm.

The column "Example 3" in Table 2 above summarizes the structure and ΔT of the filter of Example 3.

Next, the optical properties of the filter of Example 3 were evaluated using the above method.

The transmittance characteristics of the obtained filter of Example 3 are shown in Fig. 8. In Fig. 8, the transmittance characteristics of the first infrared absorbing glass plate and the transmittance characteristics of the second infrared absorbing glass plate are shown together.

As can be seen from FIG. 8 , the filter of Example 3 maintains a sufficiently high transmittance in the visible light region.

Furthermore, for the filter of Example 3, the average value of the optical concentration OD _ave in the wavelength range of 850 nm to 950 nm was calculated, and the result was OD _ave = 3.57. Therefore, it can be seen that the filter of Example 3 can significantly suppress the transmittance in the infrared region, especially in the wavelength range of 850 nm to 950 nm.

(Example 4) The optical filter is constructed by the same method as Example 1 (referred to as "the optical filter of Example 4").

However, in Example 4, the thickness of the first infrared absorbing glass plate (glass A) is set to 1.43 mm. In addition, as the second infrared absorbing glass plate, a glass plate having the composition of "glass C" in Table 1 is used. The thickness is 0.17 mm. Therefore, the total thickness of the filter of Example 4 is 1.60 mm.

The column "Example 4" in Table 2 above summarizes the structure and ΔT of the filter of Example 4.

Next, the optical properties of the filter of Example 4 were evaluated using the above method.

The transmittance characteristics of the obtained filter of Example 4 are shown in Fig. 9. In Fig. 9, the transmittance characteristics of the first infrared absorbing glass plate and the transmittance characteristics of the second infrared absorbing glass plate are shown together.

As can be seen from FIG. 9 , the filter of Example 4 maintains a sufficiently high transmittance in the visible light region.

Furthermore, for the optical filter of Example 4, the average optical concentration OD _ave in the wavelength range of 850 nm to 950 nm was calculated, and the result was OD _ave = 3.79. Therefore, it can be seen that the optical filter of Example 4 can significantly suppress the transmittance in the infrared region, especially in the wavelength range of 850 nm to 950 nm.

(Example 5) The light filter is constructed by the same method as Example 1 (referred to as "light filter of Example 5").

However, in Example 5, as the first infrared absorbing glass plate, "Glass D" in Table 1 was used. The thickness was 0.45 mm. Also, as the second infrared absorbing glass plate, a glass plate having the composition of "Glass F" in Table 1 was used. The thickness was 0.87 mm. Therefore, the total thickness of the filter in Example 5 was 1.32 mm.

The column "Example 5" in Table 2 above summarizes the structure and ΔT of the filter of Example 5.

Next, the optical properties of the filter of Example 5 were evaluated using the above method.

The transmittance characteristics of the obtained filter of Example 5 are shown in Fig. 10. In Fig. 10, the transmittance characteristics of the first infrared absorbing glass plate and the transmittance characteristics of the second infrared absorbing glass plate are shown together.

As can be seen from FIG. 10 , the filter of Example 5 maintains a sufficiently high transmittance in the visible light region.

Furthermore, for the optical filter of Example 5, the average value of the optical concentration OD _ave in the wavelength range of 850 nm to 950 nm was calculated, and the result was OD _ave = 4.06. Therefore, it can be seen that the optical filter of Example 5 can significantly suppress the transmittance in the infrared region, especially in the wavelength range of 850 nm to 950 nm.

(Example 6) The light filter is constructed by the same method as Example 1 (referred to as "light filter of Example 6").

However, in Example 6, as the first infrared absorbing glass plate, "Glass D" in Table 1 was used. The thickness was 0.51 mm. Also, as the second infrared absorbing glass plate, a glass plate having the composition of "Glass E" in Table 1 was used. The thickness was 0.10 mm. Therefore, the total thickness of the filter in Example 6 was 0.61 mm.

The column "Example 6" in Table 2 above summarizes the structure and ΔT of the filter of Example 6.

Next, the optical properties of the filter of Example 6 were evaluated using the above method.

The transmittance characteristics of the obtained filter of Example 6 are shown in Fig. 11. In Fig. 11, the transmittance characteristics of the first infrared absorbing glass plate and the transmittance characteristics of the second infrared absorbing glass plate are shown together.

As can be seen from FIG. 11 , the filter of Example 6 maintains a sufficiently high transmittance in the visible light region.

Furthermore, for the optical filter of Example 6, the average value of the optical concentration OD _ave in the wavelength range of 850 nm to 950 nm was calculated, and the result was OD _ave = 4.37. Therefore, it can be seen that the optical filter of Example 6 can significantly suppress the transmittance in the infrared region, especially in the wavelength range of 850 nm to 950 nm.

(Example 11) A filter was made using a single infrared absorbing glass plate (referred to as "the filter of Example 11"). In Example 11, "Glass C" in Table 1 was used as the single infrared absorbing glass plate. The thickness was 0.63 mm.

The optical properties of the filter of Example 11 were evaluated.

FIG. 12 shows the transmittance characteristics of the filter of Example 11 that were actually measured.

For the filter in Example 11, the average optical concentration OD _ave in the wavelength range of 850 nm to 950 nm was calculated, and the result was OD _ave = 5.41.

Furthermore, according to FIG. 12 , it can be seen that the transmittance of the filter in Example 11 in the visible light region is not very high.

The characteristics of the optical filters of various examples are summarized in Table 3 below.

[table 3] example 1 Example 2 Example 3 Example 4 Example 5 Example 6 Example 11 Example 12 Optical Filter Thickness(mm) 1.44 1.60 1.59 1.60 1.32 0.61 0.63 0.29 Average visible light transmittance (%) 80.6 76.9 80.1 78.2 85 85.2 75.8 79.3 Transmittance at 700nm (%) 4.7 4.8 9.1 9.0 3.1 2.9 0.1 4.3 T ₅₀ (nm) 609 609 620 620 609 609 579 609 Average optical density (OD _ave ) 3.72 4.23 3.57 3.79 4.06 4.37 5.41 6.86 Furthermore, Table 3 also shows the characteristics of the filter of Example 12 below.

(Example 12) An optical multilayer film (an infrared reflection film formed by alternately laminating TiO ₂ and SiO ₂ (40 layers in total)) was laminated on an infrared absorbing glass plate to produce a filter (referred to as "the filter of Example 12"). However, in Example 12, "Glass C" in Table 1 was used as the infrared absorbing glass plate. The thickness was 0.29 mm.

Next, using the filter of Example 12, the effect of the incident angle of light on the optical properties was evaluated using optical thin film simulation software (TFCalc, manufactured by Software Spectra).

Fig. 13 shows the transmittance characteristics of the filter of Example 12. The incident angles of light are set to 0°, 30°, and 40°.

As shown in FIG. 13 , the filter of Example 12 generates transmission ripples (transmittance variations) in the visible light wavelength region as the incident angle of light increases, and the average transmittance of visible light decreases.

Next, using the filters of Examples 1 to 6, the light incident angle dependence of the optical properties was evaluated using optical thin film simulation software (TFCalc, manufactured by Software Spectra).

FIG. 14 shows the transmittance characteristics of the filter of Example 1 at various incident angles.

FIG. 15 shows the transmittance characteristics of the filter of Example 2 at various incident angles.

FIG. 16 shows the transmittance characteristics of the filter of Example 3 at various incident angles.

FIG. 17 shows the transmittance characteristics of the filter of Example 4 at various incident angles.

FIG. 18 shows the transmittance characteristics of the filter of Example 5 at various incident angles.

FIG. 19 shows the transmittance characteristics of the filter of Example 6 at various incident angles.

In these figures, the incident angles of light are set to 0°, 30°, and 40°.

As shown in Figures 14 to 19, it can be seen that in the optical filters of Examples 1 to 6, even if the incident angle of light changes, the transmittance characteristics hardly change. In other words, it can be said that the optical filters of Examples 1 to 6 significantly suppress the generation of transmission ripples (transmittance changes) in the visible light wavelength region, and the optical characteristics are basically independent of the incident angle of light.

It is considered that the difference in transmittance characteristics (incident angle of light) between the filter of Example 12 and the filters of Examples 1 to 6 is caused by the following reasons.

That is, the optical filter of Example 12 exhibits optical characteristics by the combination of the infrared absorbing glass plate and the optical multilayer film, and is therefore affected by the characteristic change caused by the incident angle of light of the optical multilayer film using the interference effect of light. In contrast, it is considered that the optical filters of Examples 1 to 6 are less likely to have characteristic changes due to the incident angle of light because they exhibit optical characteristics by the infrared absorbing glass plate.

100: 1st filter 102: 1st side 104: 2nd side 110: 1st infrared absorbing glass plate 130: 2nd infrared absorbing glass plate 200: 2nd filter 202: 1st side 204: 2nd side 210: 1st infrared absorbing glass plate 230: 2nd infrared absorbing glass plate 270: Transparent glass plate 300: 3rd filter 302: 1st side 304: 2nd side 310: 1st infrared absorbing glass plate 330: 2nd infrared absorbing glass plate 350: 3rd infrared absorbing glass plate 400: 4th filter 402: 1st side 404: Second side 410: First infrared absorbing glass plate 430: Second infrared absorbing glass plate 450: Third infrared absorbing glass plate 470: First transparent glass plate 480: Second transparent glass plate

FIG. 1 is a schematic diagram for explaining the features of a filter in one embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing the structure of a filter in one embodiment of the present invention. FIG. 3 is a cross-sectional view schematically showing the structure of a filter in another embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing the structure of a filter in another embodiment of the present invention. FIG. 5 is a cross-sectional view schematically showing the structure of a filter in another embodiment of the present invention. FIG. 6 is a graph showing the transmittance characteristics of the filter in Example 1 combined with the transmittance characteristics of the first infrared absorbing glass plate and the second infrared absorbing glass plate. FIG. 7 is a graph showing the transmittance characteristics of the filter of Example 2 combined with the transmittance characteristics of the first infrared absorbing glass plate and the second infrared absorbing glass plate. FIG. 8 is a graph showing the transmittance characteristics of the filter of Example 3 combined with the transmittance characteristics of the first infrared absorbing glass plate and the second infrared absorbing glass plate. FIG. 9 is a graph showing the transmittance characteristics of the filter of Example 4 combined with the transmittance characteristics of the first infrared absorbing glass plate and the second infrared absorbing glass plate. FIG. 10 is a graph showing the transmittance characteristics of the filter of Example 5 combined with the transmittance characteristics of the first infrared absorbing glass plate and the second infrared absorbing glass plate. FIG. 11 is a graph showing the transmittance characteristics of the filter of Example 6 combined with the transmittance characteristics of the first infrared absorbing glass plate and the second infrared absorbing glass plate. FIG. 12 is a graph showing the transmittance characteristics of the filter of Example 11. FIG. 13 is a graph showing the transmittance characteristics (dependence on the incident angle of light) of the filter of Example 12. FIG. 14 is a graph showing the transmittance characteristics (dependence on the incident angle of light) of the filter of Example 1. FIG. 15 is a graph showing the transmittance characteristics (dependence on the incident angle of light) of the filter of Example 2. FIG. 16 is a graph showing the transmittance characteristics (dependence on the incident angle of light) of the filter of Example 3. FIG. 17 is a graph showing the transmittance characteristics (dependence on the incident angle of light) of the optical filter of Example 4. FIG. 18 is a graph showing the transmittance characteristics (dependence on the incident angle of light) of the optical filter of Example 5. FIG. 19 is a graph showing the transmittance characteristics (dependence on the incident angle of light) of the optical filter of Example 6.

100: 1st filter

102: Side 1

104: Side 2

110: No. 1 infrared absorbing glass plate

130: Second infrared absorbing glass plate

Claims (7)

A filter, which has a first infrared absorbing glass plate and a second infrared absorbing glass plate; the average optical concentration in the wavelength range of 850nm~950nm is greater than 2.5; the average transmittance of light with a wavelength of 400nm~550nm is greater than 76%; and the first infrared absorbing glass plate and the second infrared absorbing glass plate each independently contain at least one selected from the group consisting of phosphate glass, fluorophosphate glass, silicophosphate glass, sulfurphosphate glass, sodium calcium glass, borosilicate glass, alkali-free glass, and aluminosilicate glass. For example, the average optical concentration of the filter in claim 1 within the wavelength range of 850nm~950nm is above 3.0. A filter as claimed in claim 1 or 2, wherein the first infrared absorbing glass plate and the second infrared absorbing glass plate contain copper or iron. A filter as claimed in claim 1 or 2, wherein the first infrared absorbing glass plate contains iron and the second infrared absorbing glass plate contains copper. A filter as claimed in claim 1 or 2, wherein the transmittance of the first infrared absorbing glass plate and the second infrared absorbing glass plate at a wavelength of 700nm are different. A filter as claimed in claim 1 or 2, wherein the second infrared absorbing glass plate is provided on both sides of the first infrared absorbing glass plate. The filter of claim 1 or 2 has an anti-reflection film on at least one outer surface.

Images