Optical Filters

Abstract

To provide an optical filter that excels in the capability of sealing 400 to 680 nm visible light and the transmissivity of a near infrared ray in wavelength of 800 nm and onward, and which has reliability and exhibits a black color.SOLUTION: Provided is an optical filter comprising a base material and a dielectric multilayer film that is laminated as an outermost layer on at least one principal plane side of the base material. The dielectric multilayer film is a laminate composed of a low refractive index film and a high refractive index film that are laminated one on another, the extinction coefficient k600 in 600 nm wavelength of at least one of the low and high refractive index films being 0.12 or greater, the minimum extinction coefficient k800-1570MIN in a wavelength region of 800 to 1570 nm being 0.01 or less, or the spin density being 5.0×1010 (pcs. / (nm*cm2)) or greater, the optical filter satisfying all of specific spectral characteristics (ii-1) to (ii-3), the nano-indentation hardness at a measurement load of 1 mN being 5.5 GPa or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] In order to increase the sensitivity of the sensor, covers for remote sensor modules that use near-infrared light, such as light detection and ranging (LiDAR) sensors, use optical filters that transmit near-infrared light of 800 nm and above and block visible light that can cause disturbances. For vehicle-mounted covers, it is preferable that the optical filter have low transmittance for light in the visible region of 400 to 680 nm, both from the viewpoint of making it difficult to see inside the sensor from the outside and from the viewpoint of achieving an attractive black cover appearance.

[0003] Known examples of optical filters include reflective filters in which dielectric thin films with different refractive indices are alternately stacked on one or both sides of a transparent substrate (dielectric multilayer film), and the filters utilize optical interference to reflect light that is to be blocked.

[0004] As an optical filter, an absorption type filter using optically absorbing materials as a multilayer film is also known. For example, Patent Document 1 describes an optical filter having a dielectric multilayer film in which high-refractive index layers and low-refractive index layers are alternately stacked, where the high-refractive index layers are silicon hydride layers having an extinction coefficient k of less than 0.0005 in the wavelength range of 800 to 1100 nm. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] U.S. Patent No. 9,354,369 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with a reflective filter that blocks visible light by reflecting it, it is difficult to ensure aesthetic appeal because the exterior has a mirror finish. Furthermore, in the case of absorption-type optical filters, while visible light transmittance and visible light reflectance can be reduced by utilizing visible light absorption properties, materials that absorb visible light also tend to absorb light in the near-infrared region, so if only the visible light absorption properties are strengthened, it is difficult to maintain near-infrared transmittance.

[0007] Furthermore, when using an optical filter as a cover for a sensor module, reliability is required: specifically, the surface of the optical filter must be highly hard to prevent cracks or scratches during installation and use.

[0008] Although the optical filter described in Patent Document 1 uses a visible light-absorbing material, the high refractive index layer has a small extinction coefficient in the 800 to 1100 nm range, and therefore it is presumed that the extinction coefficient in the 600 to 680 nm range, which includes the visible region, is also small, i.e., the transmittance in this wavelength range is also high. Furthermore, if the reflectance in this range is increased in order to compensate for the blocking ability in the 600 to 680 nm range with the reflectivity of the multilayer film, the reflected color will appear red, which will degrade the design.

[0009] An object of the present invention is to provide an optical filter that is reliable, exhibits excellent shielding properties for visible light in the range of 400 to 680 nm, and transmits near-infrared light of 800 nm or more, and is black in color. [Means for solving the problem]

[0010] An optical filter according to one aspect of the present invention is an optical filter used as a cover for a remote sensor module that uses near-infrared light, the optical filter comprising a substrate and a dielectric multilayer film provided on at least one main surface of the substrate and including at least two or more different films stacked together, the dielectric multilayer film having a spin density of 5.0×10 10 (pcs / (nm*cm) 2 )) or more, and the nanoindentation hardness on the surface on the dielectric multilayer film side is 5.5 GPa or more at a measurement load of 1 mN, the maximum transmittance at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm is 6% or less, the maximum reflectance at an incident angle of 5 degrees in the wavelength range of 400 to 680 nm is 20% or less, and the average transmittance at an incident angle of 0 degrees in at least one 50 nm wavelength width range included in the wavelength range of 800 to 1580 nm is 90% or more. Another aspect of the present invention provides an optical filter that is used as a cover for a remote sensor module that uses near-infrared light, the optical filter comprising a substrate and a dielectric multilayer film that is provided on at least one main surface of the substrate and that has at least two or more different layers stacked together, the dielectric multilayer film having an extinction coefficient k 600 is 0.12 or more and the minimum extinction coefficient k in the wavelength range of 800 to 1570 nm 800-1570MIN The nanoindentation hardness of the surface on the dielectric multilayer film side is 5.5 GPa or more at a measurement load of 1 mN, the maximum transmittance at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm is 6% or less, the maximum reflectance at an incident angle of 5 degrees in the wavelength range of 400 to 680 nm is 20% or less, and the average transmittance at an incident angle of 0 degrees in at least one 50 nm wavelength width range included in the wavelength range of 800 to 1580 nm is 90% or more. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an optical filter that is reliable, exhibits excellent blocking properties for visible light in the range of 400 to 680 nm, and transmits near-infrared light of 800 nm or more, and is black in color. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating an example of an optical filter according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view schematically showing another example of the optical filter according to the embodiment. [Figure 3] FIG. 3 is a diagram showing the spectral transmittance curve of the optical filter of Example 2 at an incident angle of 0 degrees. [Figure 4] FIG. 4 is a diagram showing the spectral reflectance curve of the optical filter of Example 2 at an incident angle of 5 degrees. [Figure 5] FIG. 5 is a graph showing the relationship between the spin density and the extinction coefficient k600. DETAILED DESCRIPTION OF THE INVENTION

[0013] In this specification, for example, a transmittance of 90% or more in a specific wavelength range means that the transmittance is not less than 90% across the entire wavelength range, i.e., the minimum transmittance is 90% or more across the wavelength range. Similarly, for example, a transmittance of 1% or less in a specific wavelength range means that the transmittance is not more than 1% across the entire wavelength range, i.e., the maximum transmittance is 1% or less across the wavelength range. The average transmittance in a specific wavelength range is the arithmetic mean of the transmittances per 1 nm in the wavelength range. Unless otherwise specified, the refractive index refers to the refractive index for light with a wavelength of 1550 nm at 20°C.

[0014] The spectral characteristics can be measured using a spectrophotometer. The extinction coefficient can be calculated by measuring the reflectance, transmittance and film thickness of a single layer film formed on a quartz substrate and using optical thin film calculation software. The visible reflectance is the visual reflectance Y value based on the CIE color system. Nanoindentation hardness can be measured using a hardness tester under a measurement load of 1 mN in accordance with ISO14577. In this specification, the use of "to" to indicate a range of values ​​includes the upper and lower limits.

[0015] Spin density can be measured using an electron spin resonance spectrometer. The spin density that can be measured with an electron spin resonance spectrometer includes not only dangling bonds of silicon, but also dangling bonds of silica films and transition metal ions in glass, so sample processing before measurement and peak separation after measurement are required. To process the sample, the optical filter containing the multilayer film is cut appropriately, and then the substrate glass on which the multilayer film is applied is polished to remove as much of it as possible. This reduces the influence of the spin signal from the substrate glass. Furthermore, peak separation after measurement is possible, 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. This parameter is obtained as the result of peak separation by curve fitting using a linear combination of a Gaussian function and a Lorentzian function with the same linewidth. The linewidth here refers to the difference in magnetic field between the peak top and bottom of the electron spin resonance spectrum obtained in the differential form. The spin density can also be calculated from the extinction coefficient, since it is correlated with the extinction coefficient. For example, the spin density of amorphous silicon is calculated from the extinction coefficient k 600 Based on this, it can be calculated using the approximate formula in Figure 5.

[0016] <Optical filters> An optical filter according to one embodiment of the present invention (hereinafter also referred to as "this filter") is an optical filter comprising a substrate and a dielectric multilayer film laminated as an outermost layer on at least one main surface side of the substrate.

[0017] An example of the configuration of the present filter will be described with reference to the drawings. Figures 1 and 2 are cross-sectional views that schematically show an example of an optical filter according to an embodiment. 1 is an example in which a dielectric multilayer film 30 is provided on one main surface side of a substrate 10. Note that "having a specific layer on the main surface side of the substrate" does not only mean that the layer is provided in contact with the main surface of the substrate, but also includes a case in which another functional layer is provided between the substrate and the layer.

[0018] The optical filter 1B shown in FIG. 2 is an example in which the substrate 10 has a dielectric multilayer film 30 on both main surfaces thereof.

[0019] When mounting the optical filter of the present invention, in the case of a filter having a dielectric multilayer film on only one side, it is preferable that the dielectric multilayer film side be the external side and the opposite side be the sensor side. In the case of a filter having a dielectric multilayer film on both sides, it is preferable that the dielectric multilayer film side that satisfies the specific spectral characteristics described below be the external side and the other dielectric multilayer film side be the sensor side.

[0020] <Dielectric multilayer film> In this filter, the dielectric multilayer film is laminated as the outermost layer on at least one of the main surfaces of the substrate.

[0021] The dielectric multilayer film is designed to have wavelength selectivity, and at least one of the dielectric multilayer films is a visible light absorbing layer that blocks visible light mainly by absorption and transmits near-infrared light. When the dielectric multilayer film is laminated on both sides of the substrate, both of the dielectric multilayer films may be visible light absorbing layers, or only one of the dielectric multilayer films may be a visible light absorbing layer. When one of the dielectric multilayer films is a visible light absorbing layer, the other dielectric multilayer film may be designed as a layer having another purpose, such as an antireflection layer.

[0022] A dielectric multilayer film is a laminate of low-refractive index films and high-refractive index films. By laminating thin films with different refractive indices, the reflectance can be increased or decreased by utilizing the interference of light. The higher the reflectance, the lower the transmittance. The low-refractive index films and high-refractive index films may be laminated alternately. The extinction coefficient or spin density also differs depending on the materials that make up the multilayer film. The larger the extinction coefficient, the greater the light absorption and the lower the transmittance. The higher the spin density, the greater the light absorption. In the present invention, an optical filter having a desired spectral characteristic is designed by taking into consideration the refractive index and extinction coefficient or spin density of each multilayer film.

[0023] In the present invention, either the high refractive index film or the low refractive index film satisfies the following spectral characteristic (i-1) and also satisfies the following spectral characteristic (i-2): Alternatively, in the present invention, either the high refractive index film or the low refractive index film has a spin density of 5.0×10 10 (pcs / (nm*cm) 2 ))That's all. (i-1) Extinction coefficient k at a wavelength of 600 nm 600 is 0.12 or more (i-2) Minimum extinction coefficient k in the wavelength range of 800 to 1570 nm 800-1570MIN is 0.01 or less

[0024] The spectral characteristic (i-1) is a characteristic that defines the absorption of red light with a wavelength of 600 nm. Regarding the spectral characteristic (i-1), the k 600 By setting k to 0.12 or more, red light in the vicinity of 600 nm can be blocked by absorption rather than reflection. This eliminates the need to increase the reflectance in the vicinity of 600 nm, resulting in an optical filter in which the reflected color is less likely to be red. 600 is preferably 0.18 or more and preferably 1.00 or less.

[0025] High or low refractive index film 600 In order to make k fall within the above range, for example, amorphous silicon that is not doped with hydrogen, or amorphous silicon that is doped with hydrogen at a doping rate of 20 sccm or less, can be used as the high refractive index film material. 600 can be controlled.

[0026] The spectral characteristic (i-2) is a characteristic that defines the absorbance of light in the near-infrared region from 800 nm onwards. Regarding the spectral characteristics (i-2), the minimum extinction coefficient k in the wavelength range of 800 to 1570 nm 800-1570MINWhen the value is 0.01 or less, it means that the absorption of near-infrared light in the 800 to 1570 nm region is small.

[0027] High or low refractive index film 800-1570MIN In order to make k fall within the above range, for example, amorphous silicon that is not doped with hydrogen, or amorphous silicon that is doped with hydrogen at a doping rate of 20 sccm or less, can be used as the high refractive index film material. 800-1570MIN can be controlled.

[0028] Extinction coefficient k 600 , minimum extinction coefficient k 800-1570MIN By using a high refractive index film or a low refractive index film in which the refractive index is in the above-mentioned specific range, a dielectric multilayer film having high visible light absorption and low near-infrared light absorption can be obtained.

[0029] The spin density represents the amount of dangling bonds in the film. In the present invention, the spin density of either the high refractive index film or the low refractive index film is 5.0×10 10 (pcs / (nm*cm) 2 )) or more, the specific extinction coefficient k 600 In other words, a dielectric multilayer film with high visible light absorption can be obtained. The spin density of either the high refractive index film or the low refractive index film is preferably 1.0×10 12 (pcs / (nm*cm) 2 ))That's all.

[0030] In order to set the spin density of either the high refractive index film or the low refractive index film within the above range, for example, amorphous silicon that is not doped with hydrogen, or amorphous silicon that is doped with hydrogen at a doping rate of 20 sccm or less, can be used as the high refractive index film material.

[0031] In the present invention, the high refractive index film preferably has a refractive index of 3.0 or more, more preferably 4.0 or more. Examples of materials for the high refractive index film include silicon (Si), Ge, ZnSe, Ta2O5, TiO2, Nb2O5, and SiN. Among these, silicon is preferred, and amorphous silicon is particularly preferred, from the viewpoint of easily achieving the above-mentioned specific extinction coefficient or spin density.

[0032] Also, for silicon, k 600 or the spin density is 5.0×10 10 (pcs / (nm*cm) 2 From the viewpoint of achieving the above, silicon that is not doped with hydrogen or silicon that is doped with a reduced amount of hydrogen is more preferred. Hydrogen can be doped by a known method, and the doping amount is preferably 20 sccm or less, with undoped silicon being particularly preferred.

[0033] The low refractive index film may be a film having a refractive index lower than that of the high refractive index film. Examples of the material for the low refractive index film include SiO2, SiO x N y Examples of such materials include Ta2O5, TiO2, and SiO2, and it is possible to use a combination of these with a material having a lower refractive index than the high refractive index film material. When using a combination of low refractive index film materials, a film with a relatively high refractive index may be used as a medium refractive index film, and a film with a low refractive index may be used as a low refractive index film. The low refractive index film preferably has a refractive index of 2.5 or less, more preferably 1.5 or less. From the viewpoint of productivity, SiO2 is preferred.

[0034] When the dielectric multilayer film is designed as a visible light absorption layer, the total number of layers in the dielectric multilayer film is, from the viewpoint of light blocking properties in the visible light region, preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more. However, since a large total number of layers can cause warping or an increase in film thickness, the total number of layers is preferably 70 or less, more preferably 60 or less, and even more preferably 50 or less.

[0035] From the viewpoint of productivity, the thickness of the dielectric multilayer film is preferably 1.5 μm or less, more preferably 1.0 μm or less. When there are two or more dielectric multilayer films, the total thickness of the films is preferably 2.0 μm or less. In the present invention, the visible light region can be sufficiently blocked even if the number of layers or thickness of the dielectric multilayer film is small. This is because the dielectric multilayer film in the present invention has a large extinction coefficient in the visible light region and can block visible light by absorption.

[0036] The dielectric multilayer film of the present invention preferably has an outermost layer that is an oxide layer having a specific density. This allows for an optical filter with high hardness to be obtained. The outermost layer of the dielectric multilayer film is more preferably a low-density SiO2 layer, and particularly preferably an SiO2 layer having an outermost layer density of 2.20 g / cc or less.

[0037] The outermost layer of the dielectric multilayer film can be made to be an oxide layer of a specific density by, for example, subjecting the dielectric multilayer film to a surface treatment during or after laminating the high refractive index film and the low refractive index film. Examples of the surface treatment method include a method of heating the dielectric multilayer film and a method of irradiating the dielectric multilayer film with ions.

[0038] After the above surface treatment, the outermost layer of the dielectric multilayer film becomes less dense and harder. It is believed that the density of a non-oxide dielectric film such as Si decreases when the outermost layer is oxidized, and that the film changes to SiO2, which has high hardness, resulting in an increase in hardness. It is believed that the density of an oxide dielectric film such as SiO2 decreases when weakly bonded OH moieties are broken and H is released, and that the bond group moieties become strong Si-O bonds, resulting in an increase in hardness.

[0039] The density of the outermost layer can be calculated by measuring the X-ray reflectivity (XRR) of the surface of the dielectric multilayer film.

[0040] When the dielectric multilayer film is heated as a surface treatment, the heating conditions are specifically preferably 300°C or higher, more preferably 550°C or higher, and preferably 700°C or lower, and also preferably 3 minutes or longer, and preferably 3 hours or shorter. The heating step may be carried out during or after the formation of the dielectric multilayer film. The heating atmosphere may be either air or nitrogen.

[0041] As a surface treatment method, a dielectric multilayer film may be irradiated with ions by, for example, applying a voltage to a rare gas such as Ar in a vacuum environment during or after the formation of the dielectric multilayer film to ionize it. Ionization can be promoted by applying high frequency waves. ECR, ICP, RF, etc. are used as a method for generating high frequency waves. Ion generation and irradiation are electrically controlled, and constant voltage control is preferred. In the present invention, specific ion irradiation conditions are preferably such that the ion species is Ar, and the applied voltage is preferably 1000 V or higher, more preferably 2000 V or higher, and preferably 3000 V or lower.

[0042] The dielectric multilayer film can be formed by, for example, a dry film formation process such as a CVD method, a sputtering method, or a vacuum deposition method, or a wet film formation process such as a spray method or a dipping method, etc. Among these, a dry film formation process is preferred from the viewpoint that a high refractive index film with a controlled thin film layer can be easily obtained.

[0043] In the present invention, the above-mentioned surface treatment is carried out during or after lamination of the dielectric multilayer film.

[0044] The dielectric multilayer film may have a predetermined spectral characteristic with one layer, or may have a predetermined spectral characteristic with two or more layers. When there are two or more layers, the dielectric multilayer films may have the same or different configurations. When two dielectric multilayer films are provided, one may be a visible light absorbing layer that transmits near-infrared light and blocks visible light, and the other may be a visible / near-infrared light transmitting layer that transmits both near-infrared and visible light.

[0045] When a dielectric multilayer film is designed as an antireflection layer, it is obtained by laminating dielectric films with different refractive indices, as in the visible light absorption layer. Note that the antireflection layer may be formed from an intermediate refractive index medium, a moth-eye structure in which the refractive index changes gradually, or the like, in addition to a dielectric multilayer film.

[0046] <Base material> The substrate in the present filter may have a single-layer structure or a multi-layer structure. The material of the substrate is not particularly limited, and may be an organic or inorganic material as long as it is a transparent material that transmits near-infrared light. A combination of different materials may also be used.

[0047] As the transparent inorganic material, glass or crystalline material is preferred. Examples of glass include soda lime glass, borosilicate glass, alkali-free glass, quartz glass, and aluminosilicate glass. The glass may be chemically strengthened glass obtained by ion exchange at a temperature equal to or lower than the glass transition point to exchange alkali metal ions (e.g., Li ions, Na ions) having a small ionic radius present on the main surface of the glass plate with alkali ions having a larger ionic radius (e.g., Na ions or K ions for Li ions, and K ions for Na ions).

[0048] Examples of the crystalline material include birefringent crystals such as quartz, lithium niobate, and sapphire.

[0049] The shape of the substrate is not particularly limited, and may be a block, plate, or film. The thickness of the substrate is preferably 0.1 to 5 mm, more preferably 2 to 4 mm, from the viewpoints of reducing warpage during the formation of the dielectric multilayer film, reducing the height of the optical filter, and preventing cracks.

[0050] <Optical filter characteristics> The optical filter of the present invention, which comprises the above-mentioned substrate and dielectric multilayer film, functions as an IR bandpass filter that blocks visible light and transmits near-infrared light.

[0051] The optical filter satisfies all of the following spectral characteristics (ii-1) to (ii-3). (ii-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm 400-680(0deg)MAX is 6% or less (ii-2) Maximum reflectance R at an incident angle of 5 degrees in the wavelength range of 400 to 680 nm 400-680(5deg)MAX is 20% or less (ii-3) Average transmittance T at an incident angle of 0 degrees in the wavelength range of X to Y nm X-Y(0deg)AVE is 90% or more (where X=800~1530nm, Y=850~1580nm, YX=50nm)

[0052] The spectral characteristic (ii-1) means low transmittance in the visible light region of 400 to 680 nm, and the spectral characteristic (ii-2) means low reflectance in the visible light region. By satisfying the spectral characteristics (ii-1) and (ii-2), both the transmitted color and the reflected color become black, and an optical filter with high designability can be obtained. The spectral characteristic (ii-1) can be obtained, for example, by adjusting the extinction coefficient k 600 This can be achieved by using a high-refractive index film or a low-refractive index film that has a specific or higher refractive index or a specific or higher spin density, i.e., a high absorption in the visible light region. The spectral characteristic (ii-2) can be achieved by designing a dielectric multilayer film to have a desired visible light reflectance. As shown in the spectral characteristic (ii-1), the low transmittance in the visible light region allows sufficient blocking of the visible light region without increasing the reflectance, as shown in the spectral characteristic (ii-2). Maximum transmittance T 400-680(0deg)MAX is preferably 5% or less. Maximum reflectance R 400-680(5deg)MAX is preferably 10% or less.

[0053] The reflectance of characteristic (ii-2) is a value measured from the side of a dielectric multilayer film having a high refractive index film or a low refractive index film that satisfies the above-mentioned spectral characteristics (i-1) and (i-2) or has the above-mentioned spin density of a specific value or higher.

[0054] The spectral characteristic (ii-3) means that the average transmittance in any 50 nm wavelength range within the near-infrared range of 800 to 1580 nm is good. By satisfying the spectral characteristic (ii-3), the sensitivity of the sensor can be increased when an optical filter is implemented. T shown in characteristic (ii-3) X-Y(0deg)AVEIn order to set the value in the above range, for example, the minimum extinction coefficient k 800-1570MIN is a specific value or less, that is, by using a high refractive index film or a low refractive index film that has little absorption in the near-infrared light region, and designing the reflectance in the wavelength region of X to Y nm to be low.

[0055] Any 50 nm wavelength range (X to Y nm) can be selected depending on the sensor sensitivity. In addition, the dielectric multilayer film may be designed so that near-infrared ranges outside of X to Y nm can be shielded by reflection as necessary. X to Y nm are preferably 1305 to 1355 nm or 1525 to 1575 nm. That is, it is preferable that the optical filter further satisfies the following spectral characteristic (ii-3A) or the following spectral characteristic (ii-3B). (ii-3A) Average transmittance T at an incident angle of 0° in the wavelength range of 1525 to 1575 nm 1525-1575(0deg)AVE Over 90% (ii-3B) Average transmittance T at an incident angle of 0° in the wavelength range of 1305 to 1355 nm 1305-1355(0deg)AVE Over 90%

[0056] The spectral characteristic (ii-3A) means that the transmittance in the near-infrared region of 1525 to 1575 nm is excellent. The spectral characteristic (ii-3B) means that the transmittance in the near-infrared region of 1305 to 1355 nm is excellent. By satisfying the spectral characteristics (ii-3A) or (ii-3B), the sensitivity of the sensor can be increased when an optical filter is implemented.

[0057] Average transmittance T 1525-1575(0deg)AVE is more preferably 95% or more. Average transmittance T 1305-1355(0deg)AVE is more preferably 92% or more.

[0058] The optical filter preferably further satisfies the following spectral characteristic (ii-4). (ii-4) Luminous reflectance Y is 5% or less By satisfying the spectral characteristic (ii-4), the reflectance in the visible light region is further reduced, resulting in a black reflected color, and an optical filter with excellent design properties can be obtained. The luminous reflectance Y is preferably 4% or less.

[0059] The optical filter of the present invention preferably further satisfies the spectral characteristics (ii-5) and (ii-6). (ii-5) Reflection color a* is within ±30 (ii-6) Reflection color b* is within ±30 By satisfying the spectral characteristics (ii-5) and (ii-6), it is easy to obtain an optical filter with a black reflected color and excellent design. The color index used is L*a*b* based on JIS Z 8781-4:2013. The reflected color a* is more preferably within ±10. The reflected color b* is more preferably within ±10.

[0060] The optical filter of the present invention satisfies the above-mentioned spectral characteristics and is also highly reliable. Specifically, the optical filter of the present invention has a nanoindentation hardness of 5.5 GPa or more. Nanoindentation hardness is an index of indentation hardness, and in the present invention, it is a value measured at a measurement load of 1 mN. When the nanoindentation hardness is within the above range, the surface of the optical filter has sufficient hardness, and it is possible to prevent the occurrence of cracks or scratches on the surface of the optical filter when it is mounted on a sensor or during use. The nanoindentation hardness is preferably 7 GPa or more. Furthermore, from the viewpoint of making the optical filter less likely to become brittle and chip, the nanoindentation hardness of the optical filter is preferably 20 GPa or less. The nanoindentation hardness is measured from the dielectric multilayer film side.

[0061] The above-mentioned specific nanoindentation hardness can be achieved, for example, by subjecting the dielectric multilayer film to the above-mentioned surface treatment.

[0062] According to the embodiment described above, an optical filter that is excellent in the shielding property of the visible range and the transmittance of near-infrared light, has reliability, and exhibits a black color can be obtained.

[0063] Furthermore, the LiDAR sensor of the present invention includes the optical filter of the present invention, thereby providing a sensor with excellent sensitivity and appearance.

[0064] As described above, this specification discloses the following optical filters and LiDAR sensors. [1] An optical filter comprising a substrate and a dielectric multilayer film laminated as an outermost layer on at least one main surface side of the substrate, the dielectric multilayer film is a laminate in which a low refractive index film and a high refractive index film are stacked, Either the low-refractive-index film or the high-refractive-index film satisfies the following spectral characteristics (i-1) and (i-2), The optical filter satisfies all of the following spectral characteristics (ii-1) to (ii-3), An optical filter having a nanoindentation hardness of 5.5 GPa or more at a measurement load of 1 mN. (i-1) Extinction coefficient k at a wavelength of 600 nm 600 is 0.12 or more (i-2) Minimum extinction coefficient k in the wavelength range of 800 to 1570 nm 800-1570MIN is 0.01 or less (ii-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm 400-680(0deg)MAX is 6% or less (ii-2) Maximum reflectance R at an incident angle of 5 degrees in the wavelength range of 400 to 680 nm 400-680(5deg)MAX is 20% or less (ii-3) Average transmittance T at an incident angle of 0 degrees in the wavelength range of X to Y nm X-Y(0deg)AVE is 90% or more (where X=800~1530nm, Y=850~1580nm, YX=50nm) [2] An optical filter comprising a substrate and a dielectric multilayer film laminated as an outermost layer on at least one main surface side of the substrate, the dielectric multilayer film is a laminate in which a low refractive index film and a high refractive index film are stacked, Either the low refractive index film or the high refractive index film has a spin density of 5.0×10 10 (pcs / (nm*cm) 2 ))That's all, The optical filter satisfies all of the following spectral characteristics (ii-1) to (ii-3), An optical filter having a nanoindentation hardness of 5.5 GPa or more at a measurement load of 1 mN. (ii-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm 400-680(0deg)MAX is 6% or less (ii-2) Maximum reflectance R at an incident angle of 5 degrees in the wavelength range of 400 to 680 nm 400-680(5deg)MAX is 20% or less (ii-3) Average transmittance T at an incident angle of 0 degrees in the wavelength range of X to Y nm X-Y(0deg)AVE is 90% or more (where X=800~1530nm, Y=850~1580nm, YX=50nm) [3] The optical filter according to [1] or [2], which further satisfies the following spectral characteristic (ii-4): (ii-4) Luminous reflectance Y is 5% or less [4] The optical filter according to any one of [1] to [3], which further satisfies the following spectral characteristic (ii-3A): (ii-3A) Average transmittance T at an incident angle of 0° in the wavelength range of 1525 to 1575 nm 1525-1575(0deg)AVE Over 90% [5] The optical filter according to any one of [1] to [4], wherein the dielectric multilayer film has a total thickness of 2.0 μm or less. [6] The optical filter according to any one of [1] to [5], wherein the high refractive index film is a silicon film, and the low refractive index film is a silicon oxide film. [7] The high refractive index film is a silicon film, and the spin density of the high refractive index film is 5.0 × 10 10 (pcs / (nm*cm) 2 )) or more. The optical filter according to any one of [1] to [6]. [8] A LiDAR sensor equipped with the optical filter according to any one of [1] to [7]. [Example]

[0065] Next, the present invention will be described in more detail by way of examples. The extinction coefficient of the dielectric film was calculated by measuring the reflectance, transmittance and film thickness of a single layer film formed on a quartz substrate and using optical thin film calculation software. The spin density of the dielectric film was calculated based on the extinction coefficient using the approximate formula shown in Figure 5. The approximate formula shown in Figure 5 was calculated from the extinction coefficients and spin densities of several Si single-layer films formed on quartz substrates with different amounts of introduced hydrogen and dangling bonds. The extinction coefficient of the Si single-layer film was calculated using the above method, and the spin density was measured using an electron spin resonance spectrometer (EMX-nano, manufactured by Bruker). The spectral characteristics were measured using a spectrophotometer (Shimadzu Corporation, Solid Spec-3700). Regarding spectral characteristics, unless the angle of incidence is specifically stated, the values ​​are measured at 0° (perpendicular to the main surface of the optical filter). The chromaticity evaluation in the visible wavelength region was measured using a KONICA MINOLTA CM-26d. The color index was evaluated using L*a*b* based on JIS Z 8789:2000. The visible reflectance was the luminous reflectance Y value based on the CIE color system. The nanoindentation hardness was measured using an ESF-5000plus manufactured by ELIONIX.

[0066] A soda glass plate (Wideye (registered trademark) manufactured by AGC Corporation) measuring 100 mm in length, 100 mm in width, and 3.3 mm in thickness was used as the transparent glass substrate.

[0067] The dielectric multilayer film was formed using Si (amorphous silicon not doped with hydrogen) with a refractive index of 3.5 as the high-refractive-index film material and SiO2 with a refractive index of 1.47 as the low-refractive-index film material. SiO2 was deposited by reactive sputtering in an oxygen gas atmosphere using a Si target.

[0068] <Optical filters> (Example 1) A dielectric multilayer film (S1-1) was formed on one main surface of a transparent glass substrate by DC magnetron sputtering, with 23 layers of Si and SiO2 alternately stacked, with SiO2 as the initial layer and SiO2 as the outermost layer. Next, a dielectric multilayer film (S2-1) was formed on the other main surface of the transparent glass substrate by DC magnetron sputtering, with an initial layer of SiO2 and an outermost layer of SiO2, and 11 layers of Si and SiO2 alternately stacked. Subsequently, a heat treatment was carried out at 600°C for 3 minutes. As a result of the above, the optical filter of Example 1 was obtained.

[0069] (Example 2) An optical filter of Example 2 was obtained in the same manner as in Example 1, except that the heat treatment conditions were changed to 300° C. and 3 minutes.

[0070] (Example 3) An optical filter of Example 3 was obtained in the same manner as in Example 1, except that no heat treatment was performed and Ar ion irradiation (LIS-Ar) was performed in a vacuum environment during the deposition of each dielectric multilayer film. Ion irradiation conditions: The applied voltage was 2500 V under constant voltage control.

[0071] (Example 4) An optical filter of Example 4 was obtained in the same manner as in Example 3, except that the ion irradiation conditions were such that the applied voltage was 1250 V under constant voltage control.

[0072] (Example 5) An optical filter of Example 5 was obtained in the same manner as in Example 1, except that neither heat treatment nor Ar ion irradiation was carried out.

[0073] The characteristics of the optical filters of the above examples and the characteristics of the high refractive index film (Si layer) are shown in the table below. The nanoindentation hardness of the optical filters is a measurement value on the multilayer film S1 side. The spectral transmittance curve (incident angle 0 degrees) of the optical filter obtained in Example 2 is shown in Figure 3, and the spectral reflectance curve (incident angle 5 degrees) is shown in Figure 4. The reflection characteristics are measured on the multilayer film S1 side. Examples 1 to 4 are working examples, and Example 5 is a comparative example.

[0074] [Table 1]

[0075] The above results show that the optical filters of Examples 1 to 4, which have a dielectric multilayer film that has been surface-treated by heat treatment or ion irradiation, have higher nanoindentation hardness than the optical filter of Example 5, which has not been surface-treated. Furthermore, it can be seen that the optical filters of Examples 1 to 4, which have a dielectric multilayer film that satisfies a specific extinction coefficient, are optical filters that have excellent near-infrared light transmittance in the 1525 to 1575 nm range and exhibit a black color with low transmittance and reflectance for visible light. [Industrial Applicability]

[0076] The optical filter of the present invention has excellent near-infrared light transmittance, visible light blocking properties, and also excellent reliability and design properties, and is therefore useful for applications in information acquisition devices such as cameras and sensors for transportation aircraft, particularly LiDAR sensors, which have become increasingly high-performance in recent years. [Explanation of symbols]

[0077] 1A, 1B... optical filter, 10... substrate, 30... dielectric multilayer film

Claims

1. The dielectric multilayer film is provided on at least one main surface of the substrate and has at least two or more different layers stacked thereon, An optical filter used as a cover for a remote sensor module that uses near-infrared light, the dielectric multilayer film has a film having a spin density of 5.0×10 10 (pieces / (nm*cm 2 )) or more; the nanoindentation hardness of the surface on the dielectric multilayer film side is 5.5 GPa or more under a measurement load of 1 mN; The maximum transmittance at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm is 6% or less, The maximum reflectance at an incident angle of 5 degrees in the wavelength range of 400 to 680 nm is 20% or less, An optical filter having an average transmittance of 90% or more at an incident angle of 0 degrees in at least one 50 nm wavelength width region included in the wavelength region of 800 to 1580 nm.

2. The dielectric multilayer film is provided on at least one main surface of the substrate and has at least two or more different layers stacked thereon, An optical filter used as a cover for a remote sensor module that uses near-infrared light, the dielectric multilayer film has an extinction coefficient k 600 of 0.12 or more at a wavelength of 600 nm and a minimum extinction coefficient k 800-1570MIN of 0.01 or less in a wavelength region of 800 to 1570 nm; the nanoindentation hardness of the surface on the dielectric multilayer film side is 5.5 GPa or more under a measurement load of 1 mN; The maximum transmittance at an incident angle of 0 degrees in the wavelength range of 400 to 680 nm is 6% or less, The maximum reflectance at an incident angle of 5 degrees in the wavelength range of 400 to 680 nm is 20% or less, An optical filter having an average transmittance of 90% or more at an incident angle of 0 degrees in at least one 50 nm wavelength width region included in the wavelength region of 800 to 1580 nm.

3. An optical filter as described in claim 1 or 2, having a visual reflectance Y of 5% or less.

4. An optical filter as described in claim 1 or 2, having an average transmittance of 90% or more at an incident angle of 0° in the wavelength range of 1525 to 1575 nm.

5. 3. The optical filter according to claim 1, wherein the total thickness of the dielectric multilayer film is 2.0 [mu]m or less.

6. The optical filter according to claim 1, wherein the film having a spin density of 5.0×10 10 (pieces / (nm*cm 2 )) or more is a silicon film.

7. The optical filter according to claim 2, wherein the film having an extinction coefficient k 600 of 0.12 or more at a wavelength of 600 nm and a minimum extinction coefficient k 800-1570MIN of 0.01 or less in a wavelength region of 800 to 1570 nm is a silicon film.

8. A LiDAR sensor comprising the optical filter according to claim 1 or 2.

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