Optical filter and near-infrared light sensor module

Abstract

The present invention relates to an optical filter comprising: a substrate; and a dielectric multilayered film that is provided on at least one main surface side of the substrate and in which a plurality of dielectric films having different refractive indexes are layered, wherein the dielectric multilayered film has a dielectric film A that has an extinction coefficient k600 at a wavelength of 600 nm of 0.12 or greater and has a minimum extinction coefficient k1530-1570MIN in the wavelength range 1530-1570 nm of 0.01 or less, and the optical filter satisfies all of specific spectral properties (i-1) to (i-4).

Description

Optical filters and near-infrared light sensor modules

[0001] The present invention relates to an optical filter that blocks visible light and transmits near-infrared light.

[0002] To enhance the sensitivity of the sensor module, the cover of a sensor module using near-infrared light employs an optical filter that transmits light in the near-infrared wavelength range from 800 nm upwards and blocks light in the visible range. Furthermore, from the viewpoint of concealing the inside of the sensor from external view and giving the cover an aesthetically pleasing black appearance, it is preferable that the optical filter has a low transmittance of light in the visible range of 400 to 680 nm.

[0003] Examples of optical filters include reflective filters that utilize light interference to reflect light to be blocked, such as a dielectric multilayer film, which is a stack of dielectric thin films with different refractive indices on one or both sides of a transparent substrate.

[0004] Patent Document 1 describes an optical filter having a dielectric multilayer film in which a high refractive index layer and a low refractive index layer are stacked, which blocks visible light and transmits near-infrared light.

[0005] Japanese Patent Application Publication No. 2022-103034

[0006] Patent Document 1 discloses that the extinction coefficient at a wavelength of 600 nm and the minimum extinction coefficient in the wavelength range of 1530 to 1570 nm are within a specific range, resulting in excellent transmittance of near-infrared light from 800 nm onward and excellent shielding of visible light from 400 to 680 nm. Generally, when utilizing reflective properties, such as in dielectric multilayer films, there is concern that the spectral characteristics change when the angle of incidence of light is large, and optical filters with low dependence on the angle of incidence are required. In this respect, the optical filter described in Patent Document 1 had room for improvement in its spectral characteristics when the angle of incidence is large. In particular, for optical filters that transmit near-infrared light around a wavelength of 1550 nm, it is required that the change in reflected color (L*a*b*) is small even when the angle of incidence is large.

[0007] In view of the above, the present invention aims to provide an optical filter that is excellent in transmitting near-infrared light and shielding visible light, and that shows little change in reflected color even with light at a large angle of incidence.

[0008] The present invention provides an optical filter having the following configuration: an optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface side of the substrate, wherein a plurality of dielectric films with different refractive indices are laminated thereon, wherein the dielectric multilayer film has an extinction coefficient k at a wavelength of 600 nm ６００ An optical filter having a dielectric film A whose minimum extinction coefficient k1530-1570MIN in the wavelength region 1530-1570 nm is 0.01 or less, wherein the optical filter satisfies all of the following spectral characteristics (i-1) to (i-4). (i-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength region 400-680 nm ４００－６８０ＭＡＸ (i-2) Average reflectance R at an incident angle of 6 degrees in the wavelength range of 400-680 nm ４００－６８０ＡＶＥ (i-3) Reflectance R at an incident angle of 15 degrees at a wavelength of 400 nm, which is 10% or less. ４００ It transmits more than 10% of light in the (i-4) wavelength range of 1530-1570 nm.

[0009] According to the present invention, an optical filter can be provided that exhibits excellent transmittance of near-infrared light and shielding of visible light, and shows little change in reflected color even with light at a large angle of incidence.

[0010] Figure 1 is a schematic cross-sectional view of an optical filter according to one embodiment. Figure 2 is a schematic cross-sectional view of an optical filter according to another embodiment. Figure 3 is a diagram showing the spectral transmittance curve of the optical filter of Example 1. Figure 4 is a diagram showing the spectral reflectance curve of the optical filter of Example 1. Figure 5 is a diagram showing the spectral transmittance curve of the optical filter of Example 2. Figure 6 is a diagram showing the spectral reflectance curve of the optical filter of Example 2. Figure 7 shows the spin density and extinction coefficient k ６００ This diagram shows the relationship.

[0011] In this specification, for a particular wavelength range, a transmittance of, for example, 90% or more means that the transmittance does not fall below 90% across the entire wavelength range, i.e., the minimum transmittance in that wavelength range is 90% or more. Similarly, for a particular wavelength range, a transmittance of, for example, 1% or less means that the transmittance does not exceed 1% across the entire wavelength range, i.e., the maximum transmittance in that wavelength range is 1% or less. The average transmittance in a particular wavelength range is the arithmetic mean of the transmittance for every 1 nm in that wavelength range. Furthermore, in this specification, the "~" indicating a numerical range means that the values ​​described before and after it are included as the lower and upper limits.

[0012] Optical properties can be measured using a spectrophotometer, or calculated using simulation software for optical thin film analysis. The extinction coefficient can be calculated from the reflectance, transmittance, and film thickness of a single-layer film deposited on a quartz substrate using optical thin film analysis software. Spin density can be measured using an electron spin resonance spectrometer, or calculated using the approximate formula described later.

[0013] <Optical Filter> An optical filter according to one embodiment of the present invention (hereinafter also referred to as "this filter") comprises a substrate and a dielectric multilayer film provided on at least one main surface side of the substrate, wherein two or more films with different refractive indices are laminated together.

[0014] An example of the configuration of this filter will be explained using the drawings. Figures 1 and 2 are schematic cross-sectional views showing an example of an optical filter according to one embodiment.

[0015] The optical filter 1A shown in Figure 1 has a dielectric multilayer film S1 on one main surface side of the substrate 10. Note that "having a specific layer on the main surface side of the substrate" is not limited to cases where the layer is in contact with the main surface of the substrate, but also includes cases where another functional layer is provided between the substrate and the layer.

[0016] The optical filter 1B shown in Figure 2 has a dielectric multilayer film S1 on one main surface side of the substrate 10 and a dielectric multilayer film S2 on the other main surface side.

[0017] <Substrate> The substrate for this filter is not particularly limited and can be any transparent material that transmits near-infrared light, whether organic or inorganic.

[0018] Preferred transparent inorganic materials include silicon, glass, crystallized glass, and crystalline materials. Examples of glass include soda-lime glass, borosilicate glass, alkali-free glass, quartz glass, and aluminosilicate glass. Furthermore, chemically strengthened glass may also be used as the glass.

[0019] Examples of crystalline materials include birefringent crystals such as quartz, lithium niobate, and sapphire.

[0020] The base material may have a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, it may have a structure in which two or more base materials are joined together, and the composite materials may be the same or different.

[0021] The shape of the substrate is not particularly limited and may be in the form of a block, plate, or film. Furthermore, the thickness of the substrate is preferably 0.1 mm to 5 mm, and more preferably 2 to 4 mm, from the viewpoint of reducing warping during dielectric multilayer film formation, reducing the height of optical elements, and suppressing cracking.

[0022] <Dielectric Multilayer Film> In this filter, the dielectric multilayer film is laminated on at least one main surface side of the substrate. The dielectric multilayer film is designed to have wavelength selectivity, and preferably at least one dielectric multilayer film blocks visible light and transmits near-infrared light. The dielectric multilayer film is made up of multiple dielectric films with different refractive indices, and its reflectivity can be increased or decreased by utilizing the interference effect of light. The dielectric multilayer film more preferably includes two or more films from a low refractive index film, a medium refractive index film, and a high refractive index film. In this specification, the terms "low refractive index," "medium refractive index," and "high refractive index" do not refer to a specific numerical range of refractive index, but rather refer to the relationship of relative refractive indices among the films included in the dielectric multilayer film of the optical filter. Therefore, the low refractive index film is a film with a lower refractive index than the medium refractive index film, and the medium refractive index film is a film with a lower refractive index than the high refractive index film.

[0023] In this filter, the dielectric multilayer film has an extinction coefficient k at a wavelength of 600 nm. ６００has an extinction coefficient at a wavelength of 600 nm of 0.12 or more and a minimum extinction coefficient k1530-1570MIN in the wavelength range of 1530 to 1570 nm of 0.01 or less (hereinafter also referred to as "dielectric film A"). The extinction coefficient is an index of light absorptivity, and varies depending on the material of the dielectric film. The larger the extinction coefficient, the higher the light absorptivity and the lower the transmittance.

[0024] The extinction coefficient k at a wavelength of 600 nm ６００ being 0.12 or more enables blocking of red light around the wavelength of 600 nm. In addition, since red light can be blocked by absorption rather than reflection, there is no need to increase the reflectance around 600 nm, and an optical filter with high designability in which the reflected color is less likely to appear red can be obtained. k ６００ is preferably 0.18 or more, and is preferably 1.00 or less.

[0025] When the minimum extinction coefficient k1530-1570MIN in the wavelength range of 1530 to 1570 nm is 0.01 or less, near-infrared light around 1530 to 1570 nm can be sufficiently transmitted. k1530-1570MIN is preferably 0.002 or less.

[0026] Extinction coefficient k ６００ To obtain the dielectric film A in which the extinction coefficient k and the minimum extinction coefficient k1530-1570MIN fall within the above ranges, for example, in the case of a high refractive index film, amorphous silicon is preferable; amorphous silicon not doped with hydrogen (a-Si) or amorphous silicon with a hydrogen doping amount of 20 sccm or less is more preferable, and amorphous silicon not doped with hydrogen is particularly preferable. The extinction coefficient can also be adjusted by changing the film formation method for the dielectric film.

[0027] The dielectric film A preferably has a minimum extinction coefficient k800-1000MIN in the wavelength range of 800 to 1000 nm of 0.0005 or more. When k800-1000MIN is 0.0005 or more, the value of k ６００ can be appropriately increased, and red light around 600 nm can be blocked by absorption rather than reflection. k800-1000MIN is more preferably 0.001 or more, and is preferably 0.1 or less.

[0028] Furthermore, the dielectric film A preferably has a spin density of 5.0E+10 or more (spins / (nm*cm) ２ )), more preferably 1.0E+11 or more (pieces / (nm*cm) ２ )), more preferably 5.0E+11 or more (pieces / (nm*cm) ２ )), particularly preferably 6.0E+11 or higher (pieces / (nm*cm) ２ ))). Here, spin density represents the amount of dangling bonds in the film. The above specific extinction coefficient is easily achieved when the spin density of dielectric film A is within the specified range. Furthermore, in order to set the spin density of the high refractive index film within the above range, for example, amorphous silicon (a-Si) that is not doped with hydrogen or amorphous silicon with a hydrogen doping amount of 20 sccm or less can be used.

[0029] Spin density can be measured using an electron spin resonance (EMR) spectrometer. Since the spins measurable by an EMR include not only silicon dangling bonds but also silica film dangling bonds and transition metal ions in glass, sample preparation before measurement and peak separation after measurement are necessary. Sample preparation involves appropriately cutting the optical filter containing the dielectric multilayer film, and then removing as much of the substrate glass to which the dielectric multilayer film is applied as possible by polishing. This reduces the influence of spin signals originating from the substrate glass. Peak separation after measurement can be achieved, for example, by curve fitting. The signal from silicon dangling bonds is observed as an isotropic signal with g = 2.004–2.007 and a linewidth of 4–8 Gauss. These parameters are obtained as a result of peak separation by curve fitting using a linear combination function of Gaussian and Lorentz functions with matching linewidths. Here, linewidth refers to the difference in magnetic fields between the peak top and peak bottom of the electron spin resonance spectrum obtained in differential form.

[0030] From the viewpoint of design flexibility, the dielectric film A is preferably a high refractive index film. Furthermore, when dielectric multilayer films are present on both sides of the substrate, such as when dielectric multilayer films S1 and S2 are present, it is preferable that at least one of the dielectric multilayer films S1 and S2 is dielectric film A.

[0031] Examples of materials for high refractive index films include silicon (Si), germanium (Ge), and silicon-germanium (SiGe). In other words, the high refractive index film may be a silicon film, a germanium film, or a silicon-germanium film. Among the above materials, the extinction coefficient k ６００ From the viewpoint of having a specific range and high visible light absorption capacity, amorphous silicon is preferred, and hydrogen-undoped amorphous silicon (a-Si) is more preferred. The refractive index of the high refractive index film is preferably 3.0 or higher, more preferably 4.0 or higher. In this specification, unless otherwise specified, "refractive index" refers to the refractive index for light with a wavelength of 550 nm at 20°C. The silicon film preferably contains silicon as its main component, more preferably contains 60% by mass or more of silicon, even more preferably contains 80% by mass or more, particularly preferably contains 90% by mass or more, and most preferably contains 95% by mass or more.

[0032] The medium refractive index film is preferably a metal compound, more specifically, one or more metal oxides, nitrides, oxynitrides, and fluorides. Examples of the metal elements include Ta, Nb, Ti, Zr, Hf, Al, etc. An example of a medium refractive index film material is Ta ２ O ５ Nb ２ O ５ ,TiO,ZrO ２ , HfO ２ SiO, Al ２ O ３ These are some examples. Of these, Nb is chosen because it has a significant effect in suppressing reflectivity for near-infrared light at high incidence angles and because it has high reproducibility of optical constants. ２ O ５ Ta ２ O ５ Nb is preferred. ２ O ５ This is more preferable. The refractive index of the intermediate refractive index film may preferably be 1.6 to 3.0, more preferably 1.8 to 2.5.

[0033] Low refractive index films are preferably metal compounds, and more specifically, they may contain one or more metal oxides, nitrides, oxynitrides, and fluorides. Examples of the metal elements include Si and Al. An example of a material for a low refractive index film is SiO ２ SiO ｘ N ｙ , SiO, SiN, Al ２ O ３ These include SiO2, which is inexpensive and easy to handle. ２ This is preferable. The refractive index of the low refractive index film may be preferably 2.0 or less, more preferably 1.5 or less.

[0034] The total number of layers of dielectric multilayer films is preferably 10 or more, more preferably 15 or more, and even more preferably 20 or more, from the viewpoint of increasing the transmittance of near-infrared light and keeping the reflectance of near-infrared light low even at high incident angles. Furthermore, from the viewpoint of suppressing warping and film thickness increase, the total number of layers is preferably 40 or less, and more preferably 30 or less. The total number of layers of dielectric multilayer films can be appropriately determined from the viewpoints of improving the selective transmittance of near-infrared light, suppressing the reflection of visible light, preventing deterioration of productivity due to layer switching, and preventing a decrease in film thickness controllability due to an increase in the number of films.

[0035] Furthermore, the total number of layers of high refractive index films in a dielectric multilayer film may preferably be 1 to 15. The total number of layers of medium refractive index films in a dielectric multilayer film may preferably be 2 to 8. Furthermore, the total number of layers of low refractive index films may preferably be 3 to 15. The total number of layers for each type of film in a dielectric multilayer film can also be appropriately determined from the viewpoint of improving the selective transmittance of near-infrared light, suppressing the reflection of visible light, preventing deterioration of productivity due to layer switching, and preventing a decrease in film thickness controllability due to an increase in the number of films.

[0036] Furthermore, the total thickness of the dielectric multilayer film is preferably 2000 nm or less, more preferably 1800 μm or less, and particularly preferably 1600 nm or less, from the viewpoint of productivity. It is also preferably 300 nm or more, more preferably 500 nm or more, and even more preferably 1000 nm or more.

[0037] Furthermore, when dielectric multilayer films are present on both sides of the substrate, such as when dielectric multilayer films S1 and dielectric multilayer films S2 are present, it is preferable that the total number of layers and total film thickness of dielectric multilayer films S1 and S2 are within the above range.

[0038] This filter can sufficiently block visible light even with a small number of dielectric multilayer layers and a small film thickness. This is because the dielectric multilayer has a dielectric film A that has a large extinction coefficient in the visible light region and can block visible light through absorption.

[0039] For forming dielectric multilayer films, dry deposition processes such as CVD, sputtering, and vacuum deposition, as well as wet deposition processes such as spraying and dipping, can be used.

[0040] Furthermore, this optical filter may have components other than the substrate and dielectric multilayer film, as needed. For example, the dielectric multilayer film may have an anti-fouling film on its surface to make it easier to remove dirt from the surface of the optical filter, an anti-glare film to scatter ambient light and improve visibility, a water-repellent film to make it easier to remove water from the surface of the optical filter, or a protective layer to improve resistance to saltwater corrosion. In addition, a conductive film may be provided on the surface of the dielectric multilayer film or on the side facing the substrate to provide the optical filter with a heater function or electromagnetic interference (EMI) countermeasures.

[0041] <Optical Filter> The optical filter of the present invention, comprising the above substrate and dielectric multilayer film, has all of the following spectral characteristics (optical characteristics): (i-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm ４００－６８０ＭＡＸ (i-2) Average reflectance R at an incident angle of 6 degrees in the wavelength range of 400-680 nm ４００－６８０ＡＶＥ (i-3) Reflectance R at an incident angle of 15 degrees at a wavelength of 400 nm, which is 10% or less. ４００ It transmits more than 10% of light in the (i-4) wavelength range of 1530-1570 nm.

[0042] The optical filter possesses characteristic (i-1), which enhances its ability to block visible light and improves the functionality of sensors and other devices. The maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400-680 nm. ４００－６８０ＭＡＸ The amount is preferably 2% or less, more preferably 1% or less, even more preferably 0.5% or less, and particularly preferably 0.3% or less.

[0043] The optical filter possesses characteristic (i-2), which makes it less likely for visible light to be reflected. Furthermore, due to characteristics (i-1) and (i-2), visible light is less likely to be transmitted and less likely to be reflected, so the color of the optical filter is easily perceived as black, improving the aesthetic appeal of the optical filter. Average reflectance R at an incident angle of 6 degrees in the wavelength range of 400 to 680 nm. ４００－６８０ＡＶＥ It is preferably 7% or less, and more preferably 5% or less. Also, the average reflectance R at an incident angle of 6 degrees in the wavelength range of 400 to 680 nm. ４００－６８０ＡＶＥ There is no specific lower limit, but 1.0% or more is preferred, and 2.0% or more is more preferred. Regarding the reflection characteristics of the optical filter, the incident direction is on the dielectric film A side, and reflection from the back surface is also included.

[0044] For an optical filter to satisfy characteristics (i-1) and (i-2), for example, one can use a dielectric multilayer film that includes the aforementioned dielectric film A, i.e., a dielectric film with high absorption of light at a wavelength of 600 nm, and is designed to have low reflectivity in the visible light region.

[0045] The optical filter possesses characteristic (i-3), which allows for minimal change in reflected color even at large incident angles. In particular, for optical filters transmitting near-infrared light around 1550 nm, the change in reflected color (L*a*b*) can be minimized even at large incident angles. Generally, as the incident angle increases, the spectral reflectance curve shifts to shorter wavelengths. Ideally, designing a dielectric multilayer film to flatten the spectral reflectance curve would reduce the incident angle dependence. However, such design is difficult in practice, and the reflectance tends to be higher at longer wavelengths. It is thought that by deliberately increasing the reflectance at shorter wavelengths to counteract the reflection at longer wavelengths (600-700 nm) in the visible light region, the incident angle dependence can be reduced. Reflectance R at an incident angle of 15 degrees at a wavelength of 400 nm. ４００ The reflectance R is 10% or more, preferably 11% or more, more preferably 12% or more. It is also preferably 20% or less. ４００ To make it 10% or more, for example, when designing the film, use optical thin film calculation software to determine the film material to be used (Si, Nb ２ O ５ SiO ２ ) and the optical constants of those materials (refractive index and extinction coefficient) are input, and the target value of the optical filter is "reflectance R ４００ Based on the results obtained by setting the threshold to "≥10%" (thickness of each film and number of layers), the film can be deposited using methods such as sputtering.

[0046] By having the characteristic (i-4), an optical filter with excellent transmittance of near-infrared light around a wavelength of 1550 nm can be obtained. In specific (i-4), "transmits" means that the minimum transmittance at an incident angle of 0 degrees in the wavelength range of 1530 to 1570 nm is 75% or more.

[0047] The optical filter preferably satisfies the following spectral characteristics (i-5): (i-5) Minimum transmittance T at an incident angle of 0 degrees in the wavelength range of 1530 to 1570 nm. １５３０－１５７０ＭＩＮ The characteristic (i-5) is a preferred embodiment of characteristic (i-4) with a transmittance of 90% or more. Minimum transmittance T １５３０－１５７０ＭＩＮ The transmittance is more preferably 95% or more, even more preferably 98% or more, and particularly preferably 99% or more. Minimum transmittance T１５３０－１５７０ＭＩＮ To achieve the above range, for example, one can use a dielectric multilayer film that includes the aforementioned dielectric film A, i.e., a dielectric film with low absorption in the wavelength region of 1530 to 1570 nm, and is designed to have low reflectivity in the wavelength region of 1530 to 1570 nm.

[0048] This optical filter preferably satisfies the following spectral characteristics (i-6): (i-6) Reflectance R at a wavelength of 1550 nm and an incident angle of 60 degrees. １５５０ The optical filter has a characteristic (i-6) of 2% or less, which allows the reflectance of near-infrared light around 1550 nm to be kept low even at large incident angles, resulting in an optical filter with excellent transmittance of near-infrared light around 1550 nm. １５５０ It is more preferably less than 1.75%, and even more preferably 1.5% or less. Reflectance R １５５０ To set the above range, for example, when designing the film, use optical thin film calculation software to determine the film material to be used (Si, Nb ２ O ５ SiO ２ ) and the optical constants of those materials (refractive index and extinction coefficient) are input, and the target value of the optical filter is "reflectance R １５５０ One example is setting the value to "0.0%" and then using the results obtained (thickness of each film and number of layers) to deposit the film using sputtering or other methods.

[0049] This optical filter is color E at an incident angle of 6 degrees. ６ And, color E at an incident angle of 45 degrees ４５ Color difference ΔE ６－４５ It is preferable that this is 10 or less. This makes it possible to obtain an optical filter in which the change in reflected color (L*a*b*) is small even when the angle of incidence is large. ΔE ６－４５ It is more preferably 7.5 or less, and even more preferably 5.0 or less. Color difference ΔE ６－４５ ΔE ６－４５ = [(L ＊ ４５ -L ＊ ６ ) ２ + (a ＊ ４５ -a ＊ ６ ) ２ + (b ＊４５ -b ＊ ６ ) ２ ０．５ can be calculated by the formula. Lightness L ＊ , chromaticity a ＊ , chromaticity b ＊ can be calculated in accordance with CIE Technical Report Colorimetry, 4th Edition, based on spectral reflectance measured using a spectrophotometer (for example, model number: Cary 7000 manufactured by Agilent Technologies).

[0050] The present optical filter has a color E at an incident angle of 6 degrees ６ and a color E at an incident angle of 60 degrees ６０ and the color difference ΔE ６－６０ is preferably 15 or less. This makes it possible to obtain an optical filter in which the change in reflected color (L*a*b*) is small even when the incident angle is large. ΔE ６－６０ is more preferably 12.5 or less, and still more preferably 10.0 or less.

[0051] In an optical filter, to bring ΔE ６－４５ and ΔE ６－６０ within the above ranges, for example, designing the dielectric multilayer film such that the present optical filter satisfies the above characteristic (i-3), that is, such that the reflectance R ４００ is 10% or more can be mentioned.

[0052] The present optical filter has a property of selectively transmitting near-infrared light, more specifically, a property of blocking visible light and transmitting near-infrared light. The optical filter can be used as a cover, for example, in a sensor module that detects return light reflected after irradiating an object with near-infrared light such as near-infrared laser light. Such a sensor module is suitably used for light detection and ranging (LiDAR) sensors, particularly in-vehicle LiDAR sensors.

[0053] As described above, the following matters are disclosed in the present specification. [1] An optical filter comprising: a base material; and a dielectric multilayer film provided on at least one main surface side of the base material and formed by laminating a plurality of dielectric films having different refractive indices, wherein the dielectric multilayer film has an extinction coefficient k at a wavelength of 600 nm ６００ ​comprises a dielectric film A having a refractive index n of 0.12 or more and a minimum extinction coefficient k1530-1570MIN of 0.01 or less in the wavelength range of 1530 to 1570 nm, wherein the optical filter satisfies all of the following spectral characteristics (i-1) to (i-4): ４００－６８０ＭＡＸ (i-1) a maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm ４００－６８０ＡＶＥ is 6% or less; (i-2) an average reflectance R at an incident angle of 6 degrees in the wavelength range of 400 to 680 nm ４００ is 10% or less; (i-3) a reflectance R at an incident angle of 15 degrees at a wavelength of 400 nm ４００ is 10% or more; (i-4) transmits light in the wavelength range of 1530 to 1570 nm. [2] The optical filter according to [1], wherein the optical filter satisfies the following spectral characteristic (i-5): １５３０－１５７０ＭＩＮ (i-5) a minimum transmittance T at an incident angle of 0 degrees in the wavelength range of 1530 to 1570 nm is 90% or more. [3] The optical filter according to [1] or [2], wherein a total film thickness of the dielectric multilayer film is 2.0 µm or less. [4] The optical filter according to any one of [1] to [3], wherein the dielectric film A has a spin density of 5.0E+10 spins / (nm*cm ２ ) or more. [5] The optical filter according to any one of [1] to [4], wherein the dielectric film A is a silicon film containing silicon as a main component. [6] The optical filter according to any one of [1] to [5], wherein a color difference ΔE between a color at an incident angle of 6 degrees and a color at an incident angle of 45 degrees ６－４５ is 10 or less. [7] The optical filter according to any one of [1] to [6], wherein a color difference ΔE between a color at an incident angle of 6 degrees and a color at an incident angle of 60 degrees ６－６０ is 15 or less. [8] The optical filter according to any one of [1] to [7], wherein the optical filter satisfies the following spectral characteristic (i-6): (i-6) a reflectance R at a wavelength of 1550 nm and an incident angle of 60 degrees １５５０ is 2% or less. [9] The optical filter according to any one of [1] to [8], which is used as a cover for a sensor module using near-infrared light.

[10] A near-infrared light sensor module comprising the optical filter according to any one of [1] to [9].

[0054] The present invention will be described in more detail below using examples, but the present invention is not limited to these. Note that Example 1 is a comparative example, and Example 2 is an example.

[0055] The spectral transmittance and spectral reflectance curves of the optical filter were calculated using optical thin film calculation software. The extinction coefficient of the amorphous silicon film was calculated using optical thin film calculation software by measuring the reflectance, transmittance, and film thickness of a single layer film deposited on a quartz substrate. The spin density of the amorphous silicon film is calculated using the extinction coefficient k. ６００ Based on this, the values ​​were calculated using the approximation formula in Figure 7. The lightness L*, chromaticity a*, and chromaticity b* of the optical filter were measured using a spectrophotometer (model: Cary 7000) manufactured by Agilent Technologies.

[0056] (Example 1) A dielectric multilayer film S1 was formed on one main surface of a 3.9 mm thick borosilicate glass, and a dielectric multilayer film S2 was formed on the other main surface, both by sputtering, to obtain the optical filter of Example 1. Both the dielectric multilayer film S1 and the dielectric multilayer film S2 were made of Si (hydrogen-undoped amorphous silicon) (refractive index 4.5) as a high refractive index film and Nb as a medium refractive index film. ２ O ５ (Refractive index 2.3), SiO as a low refractive index film ２ (Refractive index 1.5) is included. Table 1 shows the details of dielectric multilayer film S1 and dielectric multilayer film S2.

[0057] (Example 2) An optical filter of Example 2 was obtained in the same manner as in Example 1, except that the dielectric multilayer films S1 and S2 were configured as shown in Table 1.

[0058] Table 2 below shows the spectral characteristics of the optical filters in Examples 1 and 2 above, as well as the extinction coefficient and spin density of the amorphous silicon film. Figures 3 and 5 show the spectral transmittance curves (incident angle 0 degrees) and Figures 4 and 6 show the spectral reflectance curves (incident angles 6, 15, 30, 45, and 60 degrees) of the optical filters in Examples 1 and 2, respectively. The spectral reflectance curves were measured from the dielectric multilayer film S1 side.

[0059]

[0060]

[0061] As described above, the reflectance R at a wavelength of 400 nm and an incident angle of 15 degrees is ４００ The optical filter in Example 2, where is 10% or more, has a color difference of ΔE ６－４５ If the color difference is 10 or less, then the color difference ΔE ６－６０ It was found that the reflectance R was 15 or less, indicating that the dependence of the reflected color on the incident angle was small. On the other hand, the reflectance R at a wavelength of 400 nm and an incident angle of 15 degrees ４００ The optical filter in Example 1, where is less than 10%, has a color difference of ΔE ６－４５ When the color difference ΔE exceeds 10, ６－６０ The value exceeded 15, indicating a large dependence of the reflected color on the angle of incidence.

[0062] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2025-038751, filed on 11 March 2025, the contents of which are incorporated herein by reference.

[0063] 1A, 1B Optical filter 10 Substrate S1, S2 Dielectric multilayer film

Claims

1. An optical filter comprising: a substrate; and a dielectric multilayer film provided on at least one main surface side of the substrate, wherein a plurality of dielectric films with different refractive indices are laminated thereon, wherein the dielectric multilayer film has an extinction coefficient k at a wavelength of 600 nm. ６００ An optical filter having a dielectric film A whose minimum extinction coefficient k1530-1570MIN in the wavelength region 1530-1570 nm is 0.01 or less, wherein the optical filter satisfies all of the following spectral characteristics (i-1) to (i-4). (i-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength region 400-680 nm ４００－６８０ＭＡＸ (i-2) Average reflectance R at an incident angle of 6 degrees in the wavelength range of 400-680 nm ４００－６８０ＡＶＥ (i-3) Reflectance R at an incident angle of 15 degrees at a wavelength of 400 nm, which is 10% or less. ４００ It transmits more than 10% of light in the (i-4) wavelength range of 1530-1570 nm.

2. The optical filter according to claim 1, wherein the optical filter satisfies the following spectral characteristics (i-5): (i-5) Minimum transmittance T at an incident angle of 0 degrees in the wavelength range of 1530 to 1570 nm １５３０－１５７０ＭＩＮ over 90% 3. The optical filter according to claim 1, wherein the thickness of the dielectric multilayer film is 2.0 μm or less.

4. The dielectric film A has a spin density of 5.0E+10 or more (spins / (nm*cm) ２ The optical filter according to claim 1, wherein the optical filter is as described in claim 1.

5. The optical filter according to claim 1, wherein the dielectric film A is a silicon film containing silicon as the main component.

6. The color difference ΔE between the color at an incident angle of 6 degrees and the color at an incident angle of 45 degrees. ６－４５ The optical filter according to claim 1, wherein the value is 10 or less.

7. The color difference ΔE between the color at an incident angle of 6 degrees and the color at an incident angle of 60 degrees. ６－６０ The optical filter according to claim 1, wherein the value is 15 or less.

8. The optical filter according to claim 1, wherein the optical filter satisfies the following spectral characteristic (i-6): (i-6) the reflectance R at a wavelength of 1550 nm and an incident angle of 60 degrees １５５０ is 2% or less 9. The optical filter according to claim 1, used as a cover for a sensor module that uses near-infrared light.

10. A near-infrared light sensor module comprising the optical filter described in any one of claims 1 to 9.

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