Patent Application
20220003896
The present disclosure relates to an optical filter that allows light having wavelengths in the infrared region to pass through.
A solid-state imaging device such as a charge coupled device (CCD) image sensor, a complementary metal oxide semiconductor (CMOS) image sensor, and the like has a strong sensitivity to infrared light as compared to the visual sensitivity characteristic of humans. Therefore, for example, in digital cameras, digital video, and the like, spectral correction is performed with use of an optical filter such as an infrared cut filter.
In an image-capturing device such as a monitoring camera that continuously performs image capturing day and night, the incidence of light having wavelengths in the visible region enables image capturing to be performed during the daytime hours. During the nighttime hours, it may be necessary to take in light having wavelengths in the infrared region due to the dark conditions. Therefore, it may be necessary to perform spectral correction by using an optical filter that allows both light in the visible region and light in the infrared region to pass through.
An optical filter that allows both light in the visible region and light in the infrared region to pass through can be configured by properly designing an optical multilayer film that is arranged on a substrate. That is, the aforementioned optical characteristics can be exhibited by forming an optical multilayer film having a repeating high refractive index layer and low refractive index layer structure.
For example, PTD1 and PTD2 each describe an optical filter capable of passing light in the visible region and light in the infrared region by a repeating high refractive index layer and low refractive index layer structure.
In conventional optical filters, in a case where there is an increased number of layers to be included in an optical multilayer film, the optical filter-to-optical filter variation in optical characteristics tends to increase when mass produced. This is because when the number of layers included in the optical multilayer film is increased, fluctuations in the thicknesses of the respective layers impact the optical characteristics to an extent that cannot be dismissed. In particular, in the infrared region, when the number of layers included in the optical multilayer film is increased, variations might occur in the optical characteristics such as optical transmittance to an extent that cannot be dismissed.
The present disclosure is made in view of such a background and it is an object of the present disclosure to provide an optical filter capable of effectively suppressing variations in the optical characteristics even when there is an increased number of layers included in the optical multilayer film.
In the present disclosure, an optical filter is provided that includes a glass substrate in which an average optical transmittance in a specific visible region defined as a wavelength range of 430 nm to 650 nm is 80% or more and an average optical transmittance in a specific infrared region defined as a wavelength range of 900 nm to 1,000 nm is 25% to 85%,
a first optical multilayer film in which an average optical transmittance in the specific visible region is 80% or more and an average optical transmittance in the specific infrared region is in a range of 45% to 65%, the first optical multilayer film having, between the specific visible region and the specific infrared region, a first blocking band that blocks light, and
a second optical multilayer film in which an average optical transmittance in the specific visible region is 80% or more and an average optical transmittance in the specific infrared region is in a range of 45% to 65%, the second optical multilayer film having, on a side of wavelengths longer than those in the specific infrared region, a second blocking band that blocks light.
According to at least one embodiment of the present disclosure, an optical filter capable of effectively suppressing variations in the optical characteristics even when there is an increased number of layers included in the optical multilayer film can be provided.
Hereinafter, an embodiment of the present disclosure is described with reference to the drawings.
The optical transmittance of a glass substrate and an optical filter in the embodiment of the present disclosure, unless otherwise noted, is a value taking into account a reflection of the interface of the substrate and air. Also, the optical transmittance of an optical multilayer film represents the optical transmittance in a case where the optical multilayer film is provided on super white glass, and this optical transmittance is a value taking into account the reflection of the rear surface side of the white glass where the optical multilayer film is not provided.
In one aspect of the present disclosure, there is provided an optical filter that includes:
a glass substrate in which an average optical transmittance in a specific visible region defined as a wavelength range of 430 nm to 650 nm is 80% or more and an average optical transmittance in a specific infrared region defined as a wavelength range of 900 nm to 1,000 nm is 25% to 85%;
a first optical multilayer film in which an average optical transmittance in the specific visible region is 80% or more and an average optical transmittance in the specific infrared region is in a range of 45% to 65%, the first optical multilayer film having, between the specific visible region and the specific infrared region, a first blocking band that blocks light; and
a second optical multilayer film in which an average optical transmittance in the specific visible region is 80% or more and an average optical transmittance in the specific infrared region is in a range of 45% to 65%, the second optical multilayer film having, on a side of wavelengths longer than those in the specific infrared region, a second blocking band that blocks light.
In the present disclosure, a numerical value range expressed using “to” includes the upper limit value and the lower limit value. In the present disclosure, “specific visible region” refers to a wavelength range of 430 nm to 650 nm, whereas “specific infrared region” refers to a wavelength range of 900 nm to 1,000 nm. Also, as described further below, the wavelength range of 1,100 nm to 1,200 nm is specifically referred to as “second specific infrared region”.
The optical filter according to the embodiment of the present disclosure includes a glass substrate. The glass substrate is unique in that the average optical transmittance in the specific visible region is 80% or more and the average optical transmittance in the specific infrared region is 25% to 85%.
As illustrated in
This glass substrate is also unique in that in the specific infrared region, the optical transmittance drops as compared to the specific visible region, with the average optical transmittance in the specific visible region being in a range of 25% to 85%.
Also, the optical filter according to the embodiment of the present disclosure includes a first optical multilayer film.
The first optical multilayer film has an average optical transmittance that is 80% or more in the specific visible region, and has an average optical transmittance that is in a range of 45% to 65% in the specific infrared region. Also, the first optical multilayer film is unique in that that first optical multilayer film has, between the specific visible region and the specific infrared region, a first blocking band that blocks light.
As illustrated in
In the first optical multilayer film, the first optical transmission band Bt1 has a high transmittance, with the average optical transmittance of the specific visible region being 80% or more, for example.
The second optical transmission band Bt2 has a transmittance that is mid-range or higher, with the average optical transmittance of the specific infrared region being in a range of 45% to 65%, for example.
In contrast to this, the first blocking band Ct1 has a low transmittance, with the average optical transmittance in the wavelength range of 780 nm to 830 nm being 3% or less, for example.
In the first optical multilayer film, the optical characteristics at wavelengths higher than the specific infrared region is not particularly limited. As such, the curved line illustrated in
The optical filter according to the embodiment of the present disclosure also has a second optical multilayer film.
The second optical multilayer film has an average optical transmittance that is 80% or more in the specific visible region, and has an average optical transmittance that is in a range of 45% to 65% in the specific infrared region. Also, the second optical multilayer film is unique in that the second optical multilayer film has, on a side of wavelengths longer than those in the specific infrared region, a second blocking band that blocks light.
As illustrated in
In the second optical multilayer film, the first optical transmission band Bu1 has a high transmittance. For example, the average optical transmittance of the specific visible region is 80% or more.
The second optical transmission band Bu2 has a mid-range transmittance. For example, the average optical transmittance of the specific infrared region is in a range of 45% to 65%.
The second blocking band Cu2 has a low transmittance, with the average optical transmittance being 5% or less in a range of 1,050 nm to 1,200 nm.
In the second optical multilayer film, the optical characteristic between the specific visible region and the specific infrared region is not particularly limited. As such, the curved line illustrated in
Since the optical filter according to the embodiment of the present disclosure has the glass substrate, the first optical multilayer film, and the second optical multilayer film each having the previously-mentioned respective features, the optical characteristics of the optical filter, as a combination of the optical characteristics of the respective members, is as illustrated in
As illustrated in
The optical transmittance curved line of the optical filter according to the embodiment of the present disclosure also includes a first blocking band Ca1 between the first optical transmission band Ba1 and the second optical transmission band Ba2 and a second blocking band Cat on a side of wavelengths longer than those in the second optical transmission band Ba2.
The first optical transmission band Ba1 has a high transmittance, with the average optical transmittance in the specific visible region being 80% or more, for example. Also, the second optical transmission band Ba2 has a mid-range transmittance, with the average optical transmittance in the specific infrared region being in a range of 40% to 90%, for example.
The first blocking band Ca1 has a low transmittance, with the average optical transmittance being 5% or less in a wavelength range of 700 nm to 850 nm, for example. Also, the second blocking band Ca2 has a low transmittance, with the average optical transmittance being 5% or less in a wavelength range of 1,050 nm to 1,200 nm.
In the example illustrated in
However, this is simply one example. As long as the average optical transmittance is 80% or more in the specific visible region, the first optical transmission band Ba1 may exist in a narrower region. Likewise, as long as the average optical transmittance is in a range of 40% to 60% in the specific infrared region, the second optical transmission band Ba2 may exist in a narrower region.
Also, in the example illustrated in
However, this is simply one example. As long as the average optical transmittance is 5% or less in wavelength range of 700 nm to 850 nm, the first blocking band Ca1 may exist in a narrower region.
The same holds true for the second blocking band Ca2 as well.
Here, as is evident from
Also, the glass substrate in the optical filter according to the embodiment of the present disclosure is unique in that the average optical transmittance is 25% to 85% in the specific infrared region.
In a conventional optical filter, there is a tendency for variation in optical characteristics to increase as the number of layers included in the optical multilayer film increases. This is because, as the number of layers included in the optical multilayer film increases, even a slight variation in the thicknesses of the respective layers can impact the optical characteristics to an extent that cannot be dismissed. Particularly, when the number of layers included in the optical multilayer film is increased, the variation in the optical characteristics of the optical transmittance and the like in the specific infrared region is too great to be dismissed.
However, in a case where a glass substrate having the aforementioned features is used as a portion of the optical filter, a portion of the light in the specific infrared region is absorbed. Therefore, the impact on characteristic variation that can occur in the second optical transmission band Bt2 in the first optical multilayer film and in the second optical transmission band Bu2 in the second optical multilayer film can be effectively reduced or eliminated owing to the light absorption characteristics of the glass substrate.
Accordingly, in the optical filter according to the embodiment of the present disclosure, variation in the optical characteristic in the second optical transmission band Ba2 exhibited by the combination of the glass substrate, the first optical multilayer film, and the second optical multilayer film can be effectively suppressed even when there are many layers included in the first optical multilayer film or the second optical multilayer film or both.
In the optical filter according to the embodiment of the present disclosure, due to the light absorption characteristic of the glass substrate, the optical transmittance of the optical filter in the specific infrared region decreases somewhat. This notwithstanding, the optical transmittance of the second optical transmission band Ba2 of the optical filter according to the embodiment of the present disclosure can be maintained in a range of 40% to 60%, for example.
Furthermore, in the optical filter according to the embodiment of the present disclosure, the aforementioned features can also effectively suppress the problem of dependence on angle of light incidence that can arise in the second optical transmission band Ba2.
That is, in a conventional optical filter, a suitable combination of optical multilayer films results in the exhibition of an optical transmission band in the specific infrared region. However, the optical characteristics of such optical multilayer films are problematic in that they change depending on the light angle of incidence.
In contrast to this, in the optical filter according to the embodiment of the present disclosure, the second optical transmission band Ba2 in the specific infrared region decreases to a range of 40% to 60%, for example, owing to the absorption characteristics of the glass substrate. Also, such an absorption characteristic of the glass substrate is unique in that the dependence on angle of incidence is small.
Therefore, in the optical filter according to the embodiment of the present disclosure, the optical characteristic of the second optical transmission band Ba2 is unlikely to be impacted by the angle of light incidence, and thus the problem of angular dependence can be reduced.
(Optical Filter According to the Embodiment of the Present Disclosure)
Next, the embodiment of the present disclosure is described in greater detail with reference to
As illustrated in
The glass substrate 110 has a first main surface 112 and a second main surface 114 opposite to each other. The first optical multilayer film 130 and the second optical multilayer film 160 are both disposed over the first main surface 112 of the glass substrate 110.
In the example illustrated in
The glass substrate 110 has an average optical transmittance that is 80% or more in the specific visible region. Also, the glass substrate 110 has an average optical transmittance in a range of 25% to 85% in the specific infrared region. The glass substrate 110 has optical transmittance characteristics such as those illustrated in
The first optical multilayer film 130 has an average optical transmittance that is 80% or more in the specific visible region. Also, the first optical multilayer film 130 has an average optical transmittance that is in a range of 45% to 65% in the specific infrared region, and the first blocking band has, between the specific visible region and the specific infrared region, the first blocking band that blocks light.
The first optical multilayer film 130 may have optical transmittance characteristics such as those illustrated in
The first optical multilayer film 130 has a repeating “high refractive index layer” and “low refractive index layer” structure. The term “high refractive index layer” refers to a layer that has a refractive index of 2.0 or more at a wavelength of 500 nm, whereas the term “low refractive index layer” refers to a layer that has a refractive index of 1.6 or less at a wavelength of 500 nm.
In the example as illustrated in
In contrast to this, the second optical multilayer film 160 has an average optical transmittance that is 80% in the specific visible region. The second optical multilayer film 160 also has an average optical transmittance in a range of 45% to 65% in the specific infrared region, and has, on a side of wavelengths longer than those in the specific infrared region, the second blocking band that blocks light.
The second optical multilayer film 160 may have optical transmittance characteristics such as those illustrated in
The second optical multilayer film 160 also has a repeating “high refractive index layer” and “low refractive index layer” structure as does the first optical multilayer film 130.
In the example illustrated in
However, as is described further below, the configurations of the second optical multilayer film 160, for example, the thicknesses of the respective layers are different from the first optical multilayer film 130.
In the first optical filter 100 that includes such a configuration, optical transmittance characteristics such as those illustrated in
In the first optical filter 100, as described above, the impact on characteristic variation that can occur in the first optical multilayer film 130 and the second optical multilayer film 160 can be effectively reduced or eliminated owing to the light absorption characteristics of the glass substrate 110.
Accordingly, in the first optical filter 100, variation in the optical characteristic in the second optical transmission band Ba2 can be effectively suppressed even when there are many layers included in the first optical multilayer film 130 or the second optical multilayer film 160 or both.
Also, in the first optical filter 100, dependence on angle of light incidence in the specific infrared region can be effectively suppressed.
(Regarding Each Constituent Member of the Optical Filter)
Next, each optical member to be used in the optical filter according to the embodiment of the present disclosure is described in greater detail.
In the description below, for the sake of clarity, the reference numbers illustrated in
(Glass Substrate 110)
At long as the glass substrate 110 has the features described above, the glass substrate may have any composition.
The glass substrate 110 may be infrared-absorbing glass that contains an infrared-absorbing component.
The infrared-absorbing component may be iron or copper or both, for example. The amount of the infrared-absorbing component may be 0.05 cations or more. Examples of the glass substrate 110 include borosilicate glass containing copper, phosphate glass containing copper, and phosphate glass containing iron, but the glass substrate 110 is not limited to these examples.
The glass substrate 110, as previously described, has an average optical transmittance of 80% or more in the specific visible region. The average optical transmittance in the specific visible region is preferably 81% or more, and more preferably 82% or more.
Also, the glass substrate 110 has an average optical transmittance of 25% to 85% in the specific infrared region. The average optical transmittance in the specific infrared region is preferably in a range of 30% to 80% and more preferably in a range of 35% to 75%.
The thickness of the glass substrate 110 is not particularly limited. However, in a case where the first optical filter 100 is to be used in a compact device, the thickness of the glass substrate 110 is preferably in a range of 0.05 mm to 2 mm to ensure thinness of the first optical filter 100.
The glass substrate 110 may satisfy:
T
glass
<T
t1+t2 Formula (1)
where Tglass (%) is the average optical transmittance in the specific infrared region. Here, Tt1+t2(%) is the average optical transmittance in the specific infrared region and is obtainable by taking the first optical multilayer film 130 and the second optical multilayer film 160 in combination.
In a case where Formula (1) is satisfied, the first optical filter 100 obtains an effect whereby optical transmittance variation associated with mass production can be reduced.
(First Optical Multilayer Film 130)
As long as the first optical multilayer film 130 has the previously-described features, the first optical multilayer film 130 may have any layer configuration.
The first optical multilayer film 130 may have a repeating high refractive index layer and low refractive index layer structure, as described above.
The number of times of repetition is not particularly limited but is, for example, in a range of 1 time to 50 times (that is, the number of layers is 2 to 100). The number of times of repetition is preferably 20 times or less or more preferably 15 times or less.
As described above, variation in the optical characteristics can be effectively suppressed even if the number of times of repetition in the first optical multilayer film 130 of the first optical filter 100 is increased to 20 times or more, for example. Therefore, the number of times of repetition can be effectively increased as compared to conventional technology, and thus optical design of a more precise optical filter can be achieved.
Examples of the high refractive index layer include titanium oxide, tantalum oxide, niobium oxide, and the like. Examples of the low refractive index layer include silicon oxide, magnesium fluoride, and the like. For example, the refractive index layer of titanium oxide at a wavelength of 500 nm is generally in a range of 2.3 to 2.8 depending on the crystalline phase, whereas the refractive index of silicon oxide is generally in a range of 1.4 to 1.5 depending on the crystalline phase.
In the first optical multilayer film 130, the optical transmittance characteristics as illustrated in
(Second Optical Multilayer Film 160)
As long as the second optical multilayer film 160 has the previously-described features, the first optical multilayer film 160 may have any layer configuration.
The second optical multilayer film 160 may have a repeating high refractive index layer and low refractive index layer structure, as described above.
The number of times of repetition is not particularly limited but is, for example, in a range of 1 time to 70 times (that is, the number of layers is 2 to 140). The number of times of repetition is preferably 50 times or less or more preferably 26 times or less.
As described above, in the first optical filter 100, variation in the optical characteristics can be effectively suppressed even if the number of times of repetition in the second optical multilayer film 160 is increased to 20 times or more. Therefore, the number of times of repetition can be effectively increased as compared to conventional technology.
Examples of the high refractive index layer include titanium oxide and the like, whereas examples of the low refractive index layer include silicon oxide and the like.
In the second optical multilayer film 160, the optical transmittance characteristics as illustrated in
(First Optical Filter 100)
The first optical filter 100 has optical transmittance characteristics as illustrated in
The first optical filter 100 may have an average optical transmittance of 80% or more in the specific visible region. The average optical transmittance in the specific visible region is preferably 85% or more and more preferably 90% or more.
The first optical filter 100 has the first optical transmission band Ba1 in the specific visible region. The first optical transmission band Ba1 may exist along the entire wavelength range of 430 nm to 650 nm.
The first optical filter 100 also has the second optical transmission band Ba2 in the specific infrared region. The second optical transmission band Ba2 may exist along the entirety of the wavelength range of 900 nm to 1,000 nm. Also, the central wavelength in the second optical transmission band Ba2 may be in a range of 920 nm to 980 nm. Alternatively, the central wavelength in the second optical transmission band Ba2 may be in a range of 930 nm to 960 nm.
Also, the first optical filter 100 may have an average optical transmittance of less than 3% in a wavelength range of 780 nm to 830 nm. Moreover, the first optical filter 100 may have an average optical transmittance of 2.5% or less in the second specific infrared region.
Here, in the first optical filter 100, the absorption contribution level P of the glass substrate 110 expressed as Formula (2) below may be 32% or more.
Absorption contribution level P (%)=(V1/V2)×100 Formula (2)
Here, V1 is expressed as:
V
1=100(%)−Tglass (%) Formula (3)
And V2 is expressed as:
V
2=100(%)−average optical transmittance (%) in specific infrared region of first optical filter 100 Formula (4)
Also, in the first optical filter 100, second absorption contribution level Q of glass substrate 110 represented by Formula (5) below may be 9% or more:
Second absorption contribution level Q (%)=(W1/W2)×100 Formula (5)
Here, W1 is expressed as:
W
1=100(%)−average optical transmittance (%) in second specific infrared region of glass substrate 110 Formula (6)
Here, W2 is expressed as:
W
2=100(%)−average optical transmittance (%) in second specific infrared region of first optical filter 100 Formula (7)
As described above, the “second specific infrared region” is represented by a wavelength range of 1,100 nm to 1,200 nm.
(Optical Filter According to Another Embodiment of the Present Disclosure)
Next, an optical filter according to another embodiment of the present disclosure is described with reference to
As illustrated in
However, the placement of the first and the second optical multilayer films in the second optical filter 200 is different from that in the previously-described first optical filter 100. That is, in the second optical filter 200, the first optical multilayer film 130 is placed on the side where the first main surface 112 of the glass substrate 110 is, whereas the second optical multilayer film 160 is placed on the side where the second main surface 114 of the glass substrate 110 is.
Even the second optical filter 200 having such a configuration can obtain the optical transmittance characteristics as illustrated in
Also, even in the second optical filter 200, an effect is substantially the same as the effect obtained with first optical filter 100, that is, an effect of effectively suppressing variation in optical characteristics in the second optical transmission band Ba2 even if the number of layers included in the first optical multilayer film 130 or the second optical multilayer film 160 or both is increased, can be obtained.
Moreover, even in the second optical filter 200, dependence on angle of light incidence in the specific infrared region can be effectively suppressed.
In the above, the configuration according to the embodiments of the present disclosure is described using the first optical filter 100 and the second optical filter 200 as examples.
However, in the present disclosure, it is apparent to one skilled in the art that the optical filter can be obtained by other configurations.
For example, in the first optical filter 100 or the second optical filter 200, a third optical multilayer film having a third blocking band in a specific visible region can be provided. In such as case, an optical filter having an optical transmission band (for example, the second optical transmission band Ba2) only in the specific infrared region and not having any optical transmission bands in the specific visible region can be obtained.
The first and second optical filters 100, 200 having such functions can be applied to an image-capturing device or the like. Examples of the image-capturing device include a monitoring camera, a vehicle camera, a web camera, and the like.
Next, the embodiment examples of the present disclosure are described.
In the description below, the first example and the second example are embodiment examples whereas the third example is a comparative example. Also, the simulation calculations were performed using optical thin-film design software (TF Calc developed by Software Spectra, Inc.) Also, there is an anti-reflective film (not illustrated) on the second main surface 114.
An optical filter (hereinafter, referred to as “optical filter according to the first example”) such as that illustrated in
Infrared absorbing glass having a “Glass A” composition in Table 1 indicated below was used in the glass substrate. The thickness of the glass substrate is 0.3 mm.
In
The average optical transmittance Tglass in the specific infrared region of the Glass A is 46.9%. The average optical transmittance in the second specific infrared region of the Glass A is 38.3%.
In Table 2 and Table 3 below, the respective configurations of the first optical multilayer film and the second optical multilayer film that are layered over the glass substrate are illustrated.
The first optical multilayer film has a repeating high refractive index layer and low refractive index layer structure and the number of layers is 22. Also, the second optical multilayer film has a repeating high refractive index layer and low refractive index layer structure and the number of layers is 52. In both the first optical multilayer film and the second optical multilayer film, the high refractive index layers are TiO2 and the low refractive index layers are SiO2.
The first optical multilayer film is layered on the second optical multilayer film. That is, the optical filter according to the first example is formed by layering in order of the glass substrate, the second optical multilayer film, and the first optical multilayer film.
Here, in Table 2 and Table 3, the lower the layer number is, the closer the layer is to the glass substrate. Therefore, in the first example, on one main surface of the glass substrate, the second optical multilayer film is formed, and then the first optical multilayer film is also formed. The second optical multilayer film has a total of 52 layers, with the first layer thereof having a thickness of 26.75 nm, whereas the first optical multilayer film has a total of 22 layers, with the first layer thereof having a thickness of 107.45 nm.
The average optical transmittance Tt1+t2 (%) in the specific infrared region obtained by the combination of the first optical multilayer film and the second optical multilayer film was 79.4%.
The average optical transmittance in the specific visible region of the optical filter according to the first example was 96.9%. Also, the average optical transmittance in the specific infrared region was 40.1% and the average optical transmittance in the second specific region infrared region was 1.0%.
The absorption contribution level P of the glass substrate was obtained based on the aforementioned Formula (2). The result was:
Absorption contribution level P (%)=(V1/V2)×100{(100−46.9)/(100−40.1)}×100=88.6%.
Also, the second absorption contribution level Q of the glass substrate was obtained based on the aforementioned Formula (5). The result was:
Second absorption contribution level Q (%)=(W1/W2)×100{(100−38.3)/(100−1.0)}×100=62.3%.
An optical filter (hereinafter, referred to as “optical filter according to the second example” was formed by the same method as that in the first example.
However, in this second example, an infrared absorption glass having the composition of “Glass B” in aforementioned Table 1 was used as the glass substrate.
The other conditions were the same as those in the first example.
The average optical transmittance Tglass in the specific infrared region of Glass B was 80.0%. Also, the average optical transmittance in the second specific infrared region of Glass B was 84.2%.
The average optical transmittance in the specific visible region of the optical filter according to the second example was 94.3. Also, the average optical transmittance in the specific infrared region was 42.5%, and the average optical transmittance in the second specific infrared region was 1.8%.
The absorption level contribution P and the second absorption contribution level Q of the glass substrate were obtained based on aforementioned Formula (2) and Formula (5), respectively. As the results, the absorption contribution level P was 34.8% and the second absorption contribution level Q was 15.4%.
An optical filter (hereinafter, referred to as “optical filter according to the third example” was formed by the same method as that in the first example.
However, in the third example, commercially-available glass (D263 made by Schott) was used as the glass substrate. This glass substrate is hereinafter referred to as “Glass C”.
The other conditions were the same as those in the first example.
The average optical transmittance Tglass in the specific infrared region of Glass C was 92.0%. Also, the average optical transmittance in the second specific infrared region of Glass C was 92.0%.
The average optical transmittance in the specific visible region of the optical filter according to the third example was 98.0%. Also, the average optical transmittance in the specific infrared region was 74.3% whereas the average optical transmittance in the second specific infrared region was 2.6%.
The absorption contribution level P and the second absorption contribution level Q of the glass substrate were obtained based on aforementioned (2) Formula and (5) Formula, respectively. As the results, the absorption contribution level P was 31.3% whereas the second absorption contribution level Q was 8.2%.
Table 4 below illustrates the main optical characteristics of the respective optical filters according to the first example, the second example, and the third example.
(Evaluation)
In the respective optical filters according to the first example, the second example, and the third example, variation that can occur in optical transmittance characteristics was evaluated using the Monte Carlo simulation under certain assumptions.
As preconditions, when the first optical multilayer film having the configuration illustrated in aforementioned Table 2 and the second optical multilayer film having the configuration illustrated in aforementioned Table 3 (total layer number of 74 layers) are layered over the glass substrate, it is assumed that a variation of 3σ=2.6% in thickness occurs in the respective layers. Moreover, it is also assumed that a variation of ±12 μm in the thickness of the glass substrate occurs.
The optical filter was formed one-hundred (100) times by simulation under the aforementioned preconditions. The extent of the variation in the average optical transmittance in the specific infrared region was evaluated based on the optical transmittance characteristics of the 100 optical filters that were obtained.
The results are illustrated below in Table 5.
As can be seen from Table 5, in a case of the optical filter according to the third example, the standard deviation σ of the average optical transmittance in the specific infrared region was 4.002. In contrast to this, in the case of the optical filter according to the first example and the optical filter according to the second example, the standard deviation σ was under 2.
From this, it is evident that variation in the optical characteristics in the specific infrared region in the optical filters according to the first example and the second example can be effectively suppressed.
This application is a continuation of International Application PCT/JP2020/011524, filed on Mar. 16, 2020 and designated the U.S., which is based on and claims priority to Japanese Patent Application No. 2019-063526 filed on Mar. 28, 2019, with the Japan Patent Office. The entire contents of these applications are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2020/011524 | Mar 2020 | US |
| Child | 17448415 | US |
