Optical filter

Abstract

To provide a black optical filter excellent in shielding property for visible light of 400-680 nm and in transmissivity of near infrared light of 800 nm or more even at high incident angle.SOLUTION: The optical filter comprises a substrate, and a dielectric multilayer film formed by laminating a low refractive index film and a high refractive index film on at least one principal surface of the substrate. The dielectric multilayer film includes four or more high refractive index films with film thickness of 15 nm or less, the high refractive index film has minimum film thickness of 1.5-5 nm and maximum film thickness of 100 nm or less. The high refractive index film has extinction coefficient k600 of 0.12 or more at wavelength of 600 nm, minimum extinction coefficient k800-1570MIN of 0.01 or less in 800-1570 nm, and spin density of 5.0×1010(piece / (nm*cm2)) or more. Further, the optical filter satisfies all of specific spectral characteristics (ii-1)-(ii-4).SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] For the cover of a remote sensor module that uses near-infrared light, such as a light detection and ranging (LiDAR) sensor, an optical filter that transmits near-infrared light of 800 nm or more and blocks visible light that is a disturbance factor is used to enhance the sensitivity of the sensor. In addition, as a vehicle-mounted cover, from the viewpoint of making it difficult to visually recognize the inside of the sensor from the outside and from the viewpoint of making the appearance of the cover a highly designed black color, it is preferable that the transmittance of light in the visible region of 400 to 680 nm in the optical filter is low.

[0003] As an optical filter, for example, a reflective filter that alternately stacks dielectric thin films with different refractive indices (dielectric multilayer film) on one or both sides of a transparent substrate and reflects the light to be blocked using light interference is known. [[ID=]18]

[0004] As an optical filter, an absorption-type filter using a material having optical absorbency as a multilayer film is also known. For example, 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 alternately stacked. Here, the high refractive index layer is a hydrogenated silicon layer having an attenuation 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

Summary of the Invention

Problems to be Solved by the Invention

[0006] <( However, with reflective filters that block visible light by reflecting it, it is difficult to ensure aesthetic appeal because the surface becomes mirror-like. Furthermore, in the case of absorption-type optical filters, while visible light absorption characteristics can reduce visible light transmittance and visible light reflectance, materials that absorb visible light also tend to absorb near-infrared light. Therefore, if only the visible light absorption characteristics are enhanced, it becomes difficult to maintain near-infrared transmittance.

[0007] Furthermore, since scanning over a wide angle range is required within the sensor, it is also necessary to ensure transmission in the near-infrared region at high incidence angles (wide-angle incidence).

[0008] Furthermore, although the optical filter described in Patent Document 1 uses a visible light absorbing material, the extinction coefficient in the high refractive index layer at 800-1100 nm is small, which suggests that the extinction coefficient in the 600-680 nm range, including the visible region, is also small, meaning that the transmittance in this wavelength range is high. In addition, if the reflectance in this range is increased to compensate for the shielding ability in the 600-680 nm range with the reflectivity of the multilayer film, the reflected color will be red, reducing the aesthetic appeal.

[0009] The present invention aims to provide an optical filter that exhibits excellent shielding properties for visible light in the 400-680 nm range, as well as excellent transmittance of near-infrared light beyond 800 nm, even at high incidence angles, and that is black in color. [Means for solving the problem]

[0010] An optical filter according to one aspect of the present invention comprises a substrate and a dielectric multilayer film provided on at least one main surface side of the substrate, wherein at least two or more different films are laminated together, and is used as a cover for a remote sensor module using near-infrared light, wherein the dielectric multilayer film has a spin density of 5.0 × 10 10 (pcs / (nm*cm) 2 The film has four or more layers with a spin density of 5.0 × 10⁻¹⁰ or higher, and the spin density is 5.0 × 10⁻¹⁰. 10 (pcs / (nm*cm) 2 For films meeting the above criteria, the minimum film thickness is 1.5 to 5 nm, the maximum transmittance at an incident angle of 0 degrees in the 400 to 680 nm wavelength range is 6% or less, the maximum reflectance at an incident angle of 5 degrees in the 400 to 680 nm wavelength range is 20% or less, the average transmittance at an incident angle of 0 degrees in at least one 40 nm wavelength range included in the 800 to 1570 nm wavelength range is 90% or more, and the average transmittance at an incident angle of 60 degrees in at least one 40 nm wavelength range included in the 800 to 1570 nm wavelength range is 90% or more. Furthermore, an optical filter according to another aspect of the present invention comprises a substrate and a dielectric multilayer film provided on at least one main surface side of the substrate, wherein at least two or more different films are laminated, and is used as a cover for a remote sensor module that uses near-infrared light, wherein the dielectric multilayer film has an extinction coefficient k at a wavelength of 600 nm. 600 The minimum extinction coefficient k is 0.12 or greater and in the wavelength range of 800-1570 nm. 800-1570MIN The film has four or more layers in which the extinction coefficient k at a wavelength of 600 nm is 0.01 or less. 600 The minimum extinction coefficient k is 0.12 or greater and in the wavelength range of 800-1570 nm. 800-1570MIN A film in which the value is 0.01 or less has a minimum film thickness of 1.5 to 5 nm, a maximum transmittance of 6% or less at an incident angle of 0 degrees in the wavelength region of 400 to 680 nm, a maximum reflectance of 20% or less at an incident angle of 5 degrees in the wavelength region of 400 to 680 nm, an average transmittance of 90% or more at an incident angle of 0 degrees in at least one 40 nm wavelength width region included in the wavelength region of 800 to 1570 nm, and an average transmittance of 90% or more at an incident angle of 60 degrees in at least one 40 nm wavelength width region included in the wavelength region of 800 to 1570 nm. [Effects of the Invention]

[0011] According to the present invention, an optical filter can be provided that exhibits excellent shielding properties for visible light in the 400-680 nm range and excellent transmittance of near-infrared light beyond 800 nm, even at high incidence angles, and is black in color. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1 is a schematic cross-sectional view showing an example of an optical filter according to one embodiment. [Figure 2] Figure 2 is a schematic cross-sectional view showing another example of an optical filter according to one embodiment. [Figure 3] Figure 3 shows the spectral transmittance curves of the optical filters in Example 2 and Example 3 at an incident angle of 0 degrees. [Figure 4] Figure 4 shows the spectral transmittance curves of the optical filters in Example 2 and Example 3 at an incident angle of 60 degrees. [Figure 5] Figure 5 shows the spectral reflectance curves of the optical filters in Example 2 and Example 3 at an incident angle of 5 degrees. [Figure 6] Figure 6 shows the relationship between spin density and the extinction coefficient k600. [Modes for carrying out the invention]

[0013] In this specification, for a specific 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 specific 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 specific wavelength range is the arithmetic mean of the transmittances for every 1 nm in that wavelength range. Unless otherwise specified, the refractive index refers to the refractive index for light at a wavelength of 1550 nm at 20°C.

[0014] Spectroscopic characteristics can be measured using a spectrophotometer. The attenuation coefficient can be calculated using optical thin film calculation software by measuring the reflectance, transmittance, and film thickness of a single-layer film formed on a quartz substrate. The visible reflectance is the visual sense reflectance Y value based on the CIE color system. In this specification, the "~" representing a numerical range includes the upper and lower limits.

[0015] The spin density can be measured using an electron spin resonance apparatus. The spin density that can be measured by the electron spin resonance apparatus includes, in addition to the dangling bonds of silicon, the dangling bonds of the silica film and transition metal ions in the glass. Therefore, processing of the sample before measurement and peak separation after measurement are necessary. For sample processing, after appropriately cutting an optical filter including a multilayer film, the substrate glass with the multilayer film is removed by polishing as much as possible. Thereby, the influence of the spin signal derived from the substrate glass can be reduced. Also, peak separation after measurement can be performed, for example, by curve fitting. The signal of the silicon dangling bond is observed as an isotropic signal with g = 2.004 to 2.007 and a line width of 4 to 8 gauss, and this parameter is obtained as a result of peak separation by curve fitting using a linear combination function of a Gaussian function and a Lorentz function with the line widths aligned. Here, the line width means the difference in magnetic field between the peak top and the peak bottom of the electron spin resonance spectrum obtained in differential form. Since the spin density also has a correlation with the attenuation coefficient, it can also be calculated from the attenuation coefficient. For example, the spin density of amorphous silicon can be calculated using the approximate formula in FIG. 6 based on the attenuation coefficient k 600

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

[0017] A configuration example of this filter will be described using the drawings. FIGS. 1 to 2 are cross-sectional views schematically showing an example of an optical filter according to an embodiment. ​The optical filter 1A shown in Figure 1 is an example in which a dielectric multilayer film 30 is provided 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.

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

[0019] When mounting the optical filter of the present invention, if the filter has a dielectric multilayer film on only one side, it is preferable to have the dielectric multilayer film side as the exterior side and the opposite side as the sensor side. If the filter has dielectric multilayer films on both sides, it is preferable to have the dielectric multilayer film side that satisfies the specific film thickness and spectral characteristics described later as the exterior side and the other dielectric multilayer film side as the sensor side.

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

[0021] The dielectric multilayer film is designed to have wavelength selectivity, with at least one layer being a visible light absorbing layer that primarily blocks visible light by absorption and transmits near-infrared light. Furthermore, when the dielectric multilayer film is laminated on both sides of the substrate, both films may be visible light absorbing layers, or only one may be a visible light absorbing layer. Also, if one film is a visible light absorbing layer, the other dielectric multilayer film may be designed as a layer serving other purposes, such as an anti-reflective layer.

[0022] A dielectric multilayer film is a laminate in which a low refractive index film and a high refractive index film are stacked. By stacking thin films with different refractive indices, the reflectivity can be increased or decreased by utilizing the interference effect of light. The higher the reflectivity, the lower the transmittance. The low refractive index film and the high refractive index film may be stacked alternately. Furthermore, the extinction coefficient or spin density differs depending on the materials that make up the multilayer film. A larger extinction coefficient results in greater light absorption and lower transmittance. A larger spin density results in higher light absorption. In this invention, an optical filter having the desired spectral characteristics is designed by considering the refractive index and extinction coefficient or spin density of each multilayer film.

[0023] Furthermore, the spectral characteristics of the entire multilayer film change depending on the thickness of the low-refractive-index and high-refractive-index films. From the viewpoint of suppressing visible light reflectivity (improving visible light absorption), increasing the thickness of the absorbing dielectric film is advantageous. However, since light absorption characteristics are generally continuous, the overall absorption capacity, including not only visible light but also near-infrared light, may improve, potentially reducing near-infrared transmittance. In this invention, as described later, by controlling the thickness of the high-refractive-index film, which is also a visible light absorbing material, we design an optical filter that achieves both suppression of visible light reflectivity and high transmittance of near-infrared light even at high incidence angles.

[0024] In the present invention, the high refractive index film satisfies the following spectral characteristics (i-1) and also satisfies spectral characteristics (i-2). Alternatively, in the present invention, the high 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 higher (i-2) Minimum extinction coefficient k in the wavelength region of 800~1570 nm 800-1570MIN is 0.01 or less

[0025] Spectral characteristic (i-1) is a characteristic that defines the absorption of red light at a wavelength of 600 nm. Regarding spectral characteristic (i-1), the k of a high refractive index film 600 When k is 0.12 or higher, red light around 600 nm can be blocked by absorption rather than reflection. This eliminates the need to increase the reflectance around 600 nm, resulting in an optical filter that is less likely to exhibit a red color in its reflections. 600 It is preferably 0.18 or higher, and also preferably 1.00 or lower.

[0026] High refractive index film k 600To achieve the above range, for example, amorphous silicon that is not hydrogen-doped, or amorphous silicon with a hydrogen doping amount of 20 sccm or less, can be used as the high refractive index film material. Furthermore, the method of forming the multilayer film also affects k 600 It can be controlled.

[0027] Spectral characteristics (i-2) are characteristics that define the absorption of light in the near-infrared region from 800 nm onward. Regarding the spectral characteristics (i-2), the minimum extinction coefficient k in the wavelength range of 800-1570 nm. 800-1570MIN A value of 0.01 or less indicates low absorption of near-infrared light in the 800-1570 nm region.

[0028] High refractive index film k 800-1570MIN To achieve the above range, for example, amorphous silicon that is not hydrogen-doped, or amorphous silicon with a hydrogen doping amount of 20 sccm or less, can be used as the high refractive index film material. Furthermore, the method of forming the multilayer film also affects k 800-1570MIN It can be controlled.

[0029] Extinction coefficient k 600 , minimum extinction coefficient k 800-1570MIN By using a high refractive index film within the specific range mentioned above, a dielectric multilayer film can be obtained that has high absorption of visible light and low absorption of near-infrared light.

[0030] Spin density represents the amount of dangling bonds in a film. In this invention, the spin density of the high refractive index film is 5.0 × 10⁻⁶. 10 (pcs / (nm*cm) 2 )) or more, the above specific extinction coefficient k 600 This is easily achieved. In other words, a dielectric multilayer film with high visible light absorption can be obtained. The spin density of the high refractive index film is preferably 1.0 × 10⁻⁶. 12 (pcs / (nm*cm) 2 That's all.

[0031] To achieve the spin density of a high refractive index film within the above range, for example, amorphous silicon that is not hydrogen-doped, or amorphous silicon with a hydrogen doping amount of 20 sccm or less, can be used as the high refractive index film material.

[0032] The high refractive index film preferably has a refractive index of 3.0 or higher, and more preferably 4.0 or higher. Examples of materials for the high refractive index film include silicon (Si), Ge, ZnSe, Ta2O5, TiO2, Nb2O5, and SiN. Of 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.

[0033] Also, as for silicon, k 600 From the perspective of setting the value to 0.12 or higher, or the spin density to 5.0 × 10⁻⁶ 10 (pcs / (nm*cm) 2 From the above viewpoint, undoped silicon or silicon with a reduced amount of hydrogen doping is even more preferred. Hydrogen can be doped by known methods, and the amount of doping is preferably 20 sccm or less, with undoped silicon being particularly preferred.

[0034] A low refractive index film can be any film with a refractive index lower than that of the high refractive index film mentioned above. Examples of materials for low refractive index films include SiO2 and SiO2. x N y Examples include Ta2O5, TiO2, and SiO2, and a combination of materials with a lower refractive index than the high refractive index film material can be used from among these. When using a combination of low refractive index film materials, a film with a relatively high refractive index may be used as the medium refractive index film, and a film with a low refractive index may be used as the low refractive index film, and these can be laminated together. The low refractive index film preferably has a refractive index of 2.5 or less, and more preferably 1.5 or less. From the viewpoint of productivity, SiO2 is preferred.

[0035] The dielectric multilayer film in the present invention comprises four or more layers of high refractive index films with a thickness of 15 nm or less. By including a specific amount of high refractive index films of a specific thickness, an optical filter with low reflectivity in the visible light region can be obtained. Furthermore, it is preferable to include one or more layers of high refractive index films with a thickness of 5 nm or less. If the optical filter of the present invention comprises two or more dielectric multilayer films, it is preferable that at least one of the dielectric multilayer films satisfies the above requirements.

[0036] The high refractive index film in the present invention has a minimum film thickness of 1.5 to 5 nm. Because the minimum film thickness of the high refractive index film falls within this range, an optical filter with high transmittance in the near-infrared region can be obtained even at high incidence angles. The minimum film thickness is preferably 1.5 to 3.0 nm. Furthermore, if the optical filter of the present invention comprises two or more dielectric multilayer films (two or more layers of a single group of dielectric multilayer films), it is preferable that the high refractive index films in the dielectric multilayer film, which include four or more layers of high refractive index films with a film thickness of 15 nm or less, satisfy the above requirements.

[0037] The maximum thickness of the high refractive index film in this invention is 100 nm or less. This range of maximum thickness allows for the acquisition of an optical filter with high transmittance in the near-infrared region, even at high incidence angles. The maximum thickness is preferably 90 nm or less, and preferably 30 nm or more from the viewpoint of transmission characteristics in the near-infrared region. Furthermore, if the optical filter of this invention comprises two or more dielectric multilayer films, it is preferable that the high refractive index films in the dielectric multilayer film, which include four or more layers of high refractive index films with a thickness of 15 nm or less, satisfy the above requirements.

[0038] When designing a dielectric multilayer film as a visible light absorbing layer, the total number of layers of the dielectric multilayer film is preferably 10 or more, more preferably 20 or more, and even more preferably 30 or more, from the viewpoint of light shielding in the visible light region. However, as the total number of layers increases, warping and other issues may occur, and the film thickness may increase, so the total number of layers is preferably 70 or less, more preferably 60 or less, and even more preferably 50 or less.

[0039] Furthermore, the thickness of the dielectric multilayer film is preferably 1.5 μm or less, and more preferably 1.0 μm or less, from the viewpoint of productivity. When there are two or more dielectric multilayer films, the total thickness of the films is preferably 2.0 μm or less. In this invention, the visible light region can be sufficiently shielded even with a small number of layers and a small film thickness of dielectric multilayer films. This is because the extinction coefficient of the dielectric multilayer film in this invention is large in the visible light region, allowing for shielding of visible light through absorption.

[0040] 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. Among these, dry deposition processes are preferred from the viewpoint of easily obtaining high refractive index films with controlled thin film layers.

[0041] A dielectric multilayer film may provide predetermined spectral characteristics with a single layer or with two or more layers. When there are two or more layers, each dielectric multilayer film may have the same or different configuration. 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.

[0042] When designing a dielectric multilayer film as an anti-reflective layer, it can be obtained by stacking dielectric films with different refractive indices, similar to visible light absorption layers. In addition to dielectric multilayer films, the anti-reflective layer may also be formed from an intermediate refractive index medium, a moth-eye structure with a gradually changing refractive index, or the like.

[0043] <Base material> The substrate in this filter may have a single-layer or multi-layer structure. Furthermore, the material of the substrate is not particularly limited; it may be an organic or inorganic material, as long as it is a transparent material that transmits near-infrared light. A combination of multiple different materials may also be used.

[0044] Glass and crystalline materials are preferred as transparent inorganic materials. Examples of glass include soda-lime glass, borosilicate glass, alkali-free glass, quartz glass, and aluminosilicate glass. As the glass, chemically strengthened glass may be used, obtained by ion exchange at a temperature below the glass transition temperature, in which alkali metal ions with small ionic radii (e.g., Li ions, Na ions) present on the main surface of the glass plate are replaced with alkali ions with larger ionic radii (e.g., Na ions or K ions for Li ions, and K ions for Na ions).

[0045] Examples of crystalline materials include birefringent crystals such as quartz, lithium niobate, and sapphire.

[0046] 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 to 5 mm, and more preferably 2 to 4 mm, from the viewpoint of reducing warping during dielectric multilayer film deposition, lowering the height of the optical filter, and suppressing cracking.

[0047] <Characteristics of optical filters> The optical filter of the present invention, comprising the above-mentioned substrate and dielectric multilayer film, functions as an IR bandpass filter that blocks visible light and transmits near-infrared light.

[0048] The optical filter satisfies all of the following spectral characteristics (ii-1) to (ii-4). (ii-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400~680 nm 400-680(0deg)MAX less than 6% (ii-2) Maximum reflectance R at an incident angle of 5 degrees in the wavelength range of 400~680 nm 400-680(5deg)MAX less than 20% (ii-3) Average transmittance T at an incident angle of 0 degrees in the wavelength range of X~Ynm X-Y(0deg)AVE Over 90% (however, X=800~1530nm, Y=840~1570nm, YX=40nm) (ii-4) Average transmittance T at an incident angle of 60 degrees in the wavelength range of X~Ynm X-Y(60deg)AVEOver 90% (however, X=800~1530nm, Y=840~1570nm, YX=40nm)

[0049] Spectral characteristic (ii-1) means low transmittance in the visible light region from 400 to 680 nm, and spectral characteristic (ii-2) means low reflectance in the visible light region. By satisfying spectral characteristics (ii-1) and (ii-2), both the transmitted and reflected colors become black, resulting in an optical filter with a high aesthetic appeal. Spectral characteristic (ii-1) is, for example, defined by the extinction coefficient k as described in characteristic (i-1) above. 600 This can be achieved by using a high refractive index film with a specific or specific spin density, i.e., a high absorption in the visible light region. Spectral characteristics (ii-2) can be achieved by designing a dielectric multilayer film to have the desired visible light reflectance. As shown in spectral characteristics (ii-1), the low transmittance in the visible light region allows for sufficient shielding of the visible light region without increasing the reflectance, as shown in spectral characteristics (ii-2). Maximum transmittance T 400-680(0deg)MAX It is preferably 5% or less. Maximum reflectance R 400-680(5deg)MAX It is preferably 10% or less.

[0050] Note that the reflectance of characteristic (ii-2) is the value measured from the dielectric multilayer film side having a high refractive index film that satisfies the spectral characteristics (i-1) and (i-2) described above, or a high refractive index film whose spin density is above a specified level as described above.

[0051] Spectral characteristics (ii-3) to (ii-4) indicate that the average transmittance in any 40 nm wavelength range within the near-infrared region of 800 to 1570 nm is good even at high incidence angles. By satisfying spectral characteristics (ii-3) to (ii-4), the sensitivity of the sensor can be increased even when light with a high incidence angle is incident when an optical filter is implemented. T shown in characteristic (ii-3) X-Y(0deg)AVE To achieve the above range, for example, the minimum extinction coefficient k shown in the above characteristic (i-2) is used for the dielectric multilayer film. 800-1570MINThis can be achieved by using a high refractive index film where the absorption in the near-infrared region is below a certain level, and by designing it to have low reflectivity in the wavelength region of X to Y nm. The T shown in characteristic (ii-4) X-Y(60deg)AVE To achieve the above range, for example, this can be accomplished by using a dielectric multilayer film with a controlled film thickness of the high refractive index film described above.

[0052] Any 40nm wavelength range (X~Ynm) can be selected according to the sensor sensitivity. Furthermore, the dielectric multilayer film may be designed to shield the near-infrared region outside of X~Ynm by reflection as needed. X~Ynm is preferably 1310~1350nm or 1530~1570nm. In other words, it is preferable that the optical filter further satisfies all of the following spectral characteristics (ii-3A) to (ii-4A), or all of the following spectral characteristics (ii-3B) to (ii-4B). (ii-3A) Average transmittance T at an incident angle of 0° in the wavelength region of 1530~1570nm 1530-1570(0deg)AVE over 90% (ii-4A) Average transmittance T at an incident angle of 60° in the wavelength region of 1530~1570nm 1530-1570(60deg)AVE over 90% (ii-3B) Average transmittance T at an incident angle of 0° in the wavelength region of 1310~1350nm 1310-1350(0deg)AVE over 90% (ii-4B) Average transmittance T at an incident angle of 60° in the wavelength region of 1310~1350nm 1310-1350(60deg)AVE over 90%

[0053] The spectral characteristics (ii-3A) to (ii-4A) indicate excellent transmittance in the near-infrared region of 1530 to 1570 nm, even at high incidence angles. The spectral characteristics (ii-3B) to (ii-4B) indicate excellent transmittance in the near-infrared region of 1310-1350 nm, even at high incidence angles. By satisfying the spectral characteristics (ii-3A) to (ii-4A) or (ii-3B) to (ii-4B), the sensitivity of the sensor can be increased even when light with a high incidence angle is incident when an optical filter is implemented.

[0054] Average transmittance T 1530-1570(0deg)AVE It is more preferably 95% or more. Average transmittance T 1530-1570(60deg)AVE It is more preferably 92% or higher. Average transmittance T 1310-1350(0deg)AVE It is more preferably 92% or higher. Average transmittance T 1310-1350(60deg)AVE It is more preferably 94% or higher.

[0055] The optical filter is further preferably satisfied with the following spectral characteristics (ii-5). (ii-5) Luminous reflectance Y is 5% or less By satisfying the spectral characteristics (ii-5), the reflectance in the visible light region is further reduced, resulting in a black reflected color and an optical filter with superior aesthetic appeal. The luminous reflectance Y is preferably 4% or less.

[0056] The optical filter of the present invention preferably further satisfies spectral characteristics (ii-6) and (ii-7). (ii-6) Reflected color a* is within ±30 (ii-7) Reflected color b* is within ±30 By satisfying spectral characteristics (ii-6) and (ii-7), it is easier to obtain an optical filter with a highly aesthetic design that has a black reflected color. The color index used is L*a*b*, based on JIS Z 8781-4:2013. Reflected color a* is within ±10 more. Reflected color b* is within ±10 more.

[0057] According to the embodiments described above, an optical filter is obtained that exhibits excellent shielding properties in the visible range and transmission of near-infrared light, and is black in color. In the present invention, the extinction coefficient k 600A large value indicates high absorption in the visible region, and the minimum extinction coefficient k is large. 800-1570MIN By using multilayer film materials with low near-infrared absorption or with a specific spin density, and by controlling the thickness of the multilayer film, we achieved both suppression of visible light reflectance due to optical interference and securing of near-infrared light transmittance.

[0058] Furthermore, the LiDAR sensor of the present invention is equipped with the optical filter of the present invention described above. This results in a sensor with excellent sensitivity and appearance.

[0059] In other words, this specification discloses the following optical filters, etc. [1] An optical filter comprising a substrate and a dielectric multilayer film laminated as the 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. The dielectric multilayer film comprises four or more layers of high refractive index films with a thickness of 15 nm or less. The minimum film thickness of the aforementioned high refractive index film is 1.5 to 5 nm. The maximum thickness of the aforementioned high refractive index film is 100 nm or less. The aforementioned high refractive index film satisfies the following spectral characteristics (i-1) and (i-2): The optical filter is an optical filter that satisfies all of the following spectral characteristics (ii-1) to (ii-4). (i-1) Extinction coefficient k at a wavelength of 600 nm 600 is 0.12 or higher (i-2) Minimum extinction coefficient k in the wavelength region of 800~1570 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 400~680 nm 400-680(0deg)MAX less than 6% (ii-2) Maximum reflectance R at an incident angle of 5 degrees in the wavelength range of 400~680 nm 400-680(5deg)MAX less than 20% (ii-3) Average transmittance T at an incident angle of 0 degrees in the wavelength range of X~Ynm X-Y(0deg)AVEOver 90% (however, X=800~1530nm, Y=840~1570nm, YX=40nm) (ii-4) Average transmittance T at an incident angle of 60 degrees in the wavelength range of X~Ynm X-Y(60deg)AVE Over 90% (however, X=800~1530nm, Y=840~1570nm, YX=40nm) [2] An optical filter comprising a substrate and a dielectric multilayer film laminated as the 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. The dielectric multilayer film comprises four or more layers of high refractive index films with a thickness of 15 nm or less. The minimum film thickness of the aforementioned high refractive index film is 1.5 to 5 nm. The maximum thickness of the aforementioned high refractive index film is 100 nm or less. The aforementioned high refractive index film has a spin density of 5.0 × 10⁻⁶ 10 (pcs / (nm*cm) 2 ))That's all, The optical filter is an optical filter that satisfies all of the following spectral characteristics (ii-1) to (ii-4). (ii-1) Maximum transmittance T at an incident angle of 0 degrees in the wavelength range of 400~680 nm 400-680(0deg)MAX less than 6% (ii-2) Maximum reflectance R at an incident angle of 5 degrees in the wavelength range of 400~680 nm 400-680(5deg)MAX less than 20% (ii-3) Average transmittance T at an incident angle of 0 degrees in the wavelength range of X~Ynm X-Y(0deg)AVE Over 90% (however, X=800~1530nm, Y=840~1570nm, YX=40nm) (ii-4) Average transmittance T at an incident angle of 60 degrees in the wavelength range of X~Ynm X-Y(60deg)AVE Over 90% (however, X=800~1530nm, Y=840~1570nm, YX=40nm) [3] An optical filter according to [1] or [2], which further satisfies the following spectral characteristics (ii-5). (ii-5) Luminous reflectance Y is 5% or less [4] An optical filter according to any of [1] to [3], which further satisfies the following spectral characteristics (ii-3A) and (ii-4A). (ii-3A) Average transmittance T at an incident angle of 0° in the wavelength region of 1530~1570nm 1530-1570(0deg)AVE over 90% (ii-4A) Average transmittance T at an incident angle of 60° in the wavelength region of 1530~1570nm 1530-1570(60deg)AVE over 90% [5] The optical filter according to any one of [1] to [4], wherein the total thickness of the dielectric multilayer film is 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 The optical filter described in any of [1] to [6] above. A LiDAR sensor equipped with an optical filter as described in any of [8], [1], to [7]. [Examples]

[0060] Next, the present invention will be described in more detail with reference to examples. The extinction coefficient of the dielectric film was calculated by measuring the reflectance, transmittance, and film thickness of a single layer film deposited on a quartz substrate, and then using optical thin film calculation software. The spin density of the dielectric film was calculated using the extinction coefficient and the approximate formula shown in Figure 6. The approximate formula in Figure 6 was derived from the extinction coefficients and spin densities of multiple Si monolayer films deposited on a quartz substrate, each with different hydrogen introduction amounts and dangling bond characteristics. The extinction coefficient of the Si monolayer film was calculated using the method described above, and the spin density was measured using an electron spin resonance spectrometer (Bruker EMX-nano). The spectral characteristics were measured using a spectrophotometer (Solid Spec-3700, manufactured by Shimadzu Corporation). Regarding spectral characteristics, unless otherwise specified, measurements are taken at 0° (perpendicular to the main surface of the optical filter). Chromaticity in the visible wavelength range was measured using a KONICA MINOLTA CM-26d.

[0061] A borosilicate glass plate (Tempax®, manufactured by Schott) measuring 100 mm in length, 100 mm in width, and 3.3 mm in thickness was used as the transparent glass substrate.

[0062] For the formation of the dielectric multilayer film, we used silicon (undoped hydrogen amorphous silicon) with a refractive index of 3.5 and SiO2 with a refractive index of 1.47. The SiO2 film was deposited by reactive sputtering in an oxygen gas atmosphere using a Si target.

[0063] (Example 1) On one main surface of a transparent glass substrate, a dielectric multilayer film (S1-1) with a thickness of 1.8 μm was formed by DC magnetron sputtering, with the initial layer being SiO2 and the outermost layer being SiO2, and 23 layers of Si and SiO2 alternately stacked. The thinnest Si layer was 2.1 nm (second layer from the outermost layer), and further layers with a thickness of 15 nm or less included layers of 6.0 nm (fourth layer from the outermost layer), 5.9 nm (eighth layer from the outermost layer), and 9.4 nm (fourteenth layer from the outermost layer). The thickest Si layer was 89.3 nm (twelfth layer from the outermost layer). Next, on the other main surface of the transparent glass substrate, a dielectric multilayer film (S2-1) with a thickness of 1.1 μm was formed by alternately stacking 11 layers of Si and SiO2, with the initial layer being SiO2 and the outermost layer being SiO2, using the DC magnetron sputtering method. The thinnest Si layer was 8.8 nm (10th layer from the outermost layer), and the thickest Si layer was 35 nm (4th layer from the outermost layer). From the above, we obtained the optical filter for Example 1.

[0064] (Example 2) A dielectric multilayer film (S1-2) with a thickness of 2.0 μm was formed on one main surface of a transparent glass substrate by DC magnetron sputtering, with the initial layer being SiO2 and the outermost layer being SiO2, and 21 layers of Si and SiO2 alternately stacked. The thinnest Si layer was 1.6 nm (2nd layer from the outermost layer), and there were further layers with thicknesses of 5.8 nm (4th layer from the outermost layer), 11.2 nm (8th layer from the outermost layer), and 6.7 nm (14th layer from the outermost layer) with a thickness of 15 nm or less. The thickest Si layer was 71.8 nm (12th layer from the outermost layer). Next, on the other main surface of the transparent glass substrate, a dielectric multilayer film (S2-2) with a thickness of 1.4 μm was formed by alternately stacking 11 layers of Si and SiO2, with the initial layer being SiO2 and the outermost layer being SiO2, using the DC magnetron sputtering method. The thinnest Si layer was 13.4 nm (10th layer from the outermost layer), and the thickest Si layer was 39.8 nm (4th layer from the outermost layer). From the above, we obtained the optical filter for Example 2.

[0065] (Example 3) On one main surface of a transparent glass substrate, a dielectric multilayer film (S1-3) with a thickness of 1.7 μm was formed by alternately stacking 21 layers of Si and SiO2, with the initial layer being SiO2 and the outermost layer being SiO2, using the DC magnetron sputtering method. The thinnest Si layer was 0.9 nm (second layer from the outermost layer), and further layers with a thickness of 15 nm or less included layers of 4.5 nm (fourth layer from the outermost layer) and 9.8 nm (eighth layer from the outermost layer). The thickest Si layer was 80.8 nm (twelfth layer from the outermost layer). Next, on the other main surface of the transparent glass substrate, a dielectric multilayer film (S2-3) with a thickness of 1.3 μm was formed by alternately stacking 11 layers of Si and SiO2, with the initial layer being SiO2 and the outermost layer being SiO2, using the DC magnetron sputtering method. The thinnest Si layer was 4.8 nm (10th layer from the outermost layer), and the thickest Si layer was 47 nm (4th layer from the outermost layer). From the above, we obtained the optical filter for Example 3.

[0066] (Example 4) On one main surface of a transparent glass substrate, a dielectric multilayer film (S1-4) with a thickness of 1.9 μm was formed by DC magnetron sputtering, with the initial layer being SiO2 and the outermost layer being SiO2, and 23 layers of Si and SiO2 alternately stacked. The thinnest Si layer was 2.1 nm (second layer from the outermost layer), and there was an additional layer with a thickness of 6.0 nm (fourth layer from the outermost layer) with a thickness of 15 nm or less. The thickest Si layer was 89.3 nm (twelfth layer from the outermost layer). Next, on the other main surface of the transparent glass substrate, a dielectric multilayer film (S2-4) with a thickness of 1.3 μm was formed by alternately stacking 11 layers of Si and SiO2, with the initial layer being SiO2 and the outermost layer being SiO2, using the DC magnetron sputtering method. The thinnest Si layer was 4.8 nm (10th layer from the outermost layer), and the thickest Si layer was 47 nm (4th layer from the outermost layer). From the above, we obtained the optical filter for Example 4.

[0067] (Example 5) A dielectric multilayer film (S1-5) with a thickness of 1.0 μm was formed on one main surface of a transparent glass substrate by DC magnetron sputtering, with the initial layer being SiO2 and the outermost layer being SiO2, and 14 layers of Si and SiO2 alternately stacked. The thinnest Si layer was 5.2 nm (second layer from the outermost layer), and there was a further layer with a thickness of 13.4 nm (fourth layer from the outermost layer) that was less than 15 nm thick. The thickest Si layer was 266.7 nm (twelfth layer from the outermost layer). Next, on the other main surface of the transparent glass substrate, a dielectric multilayer film (S2-5) with a thickness of 0.7 μm was formed by alternately stacking 14 layers of Si and SiO2, with the initial layer being SiO2 and the outermost layer being SiO2, using the DC magnetron sputtering method. The thinnest Si layer was 4.3 nm (13th layer from the outermost layer), and the thickest Si layer was 152 nm (4th layer from the outermost layer). From the above, we obtained the optical filter for Example 5.

[0068] The spectral characteristics of the optical filters in each of the above examples, and the characteristics of the high refractive index film (Si layer), are shown in the table below. Furthermore, the spectral transmittance curve (incident angle 0 degrees) of the optical filters obtained in Examples 2 and 3 above is shown in Figure 3, the spectral transmittance curve (incident angle 60 degrees) is shown in Figure 4, and the spectral reflectance curve (incident angle 5 degrees) is shown in Figure 5. Note that the reflection characteristics are measured on the multilayer film S1 side. Examples 1 and 2 are examples of actual cases, and Examples 3 to 5 are comparative examples.

[0069] [Table 1]

[0070] From the results above, it can be seen that the optical filters in Example 1 and Example 2 are optical filters that exhibit excellent visible light shielding and near-infrared light transmission in the 1530-1570 nm range even at a high incidence angle of 60 degrees, and that have a black color with low visible light transmittance and reflectance. The optical filters in Examples 3 and 4 had fewer than four layers of high refractive index films with a thickness of 15 nm or less, resulting in high reflectivity in the visible light region. In Example 5, the optical filter had fewer than four layers of high-refractive-index film with a thickness of 15 nm or less, the minimum thickness of the high-refractive-index film exceeded 5 nm, and the maximum thickness of the high-refractive-index film exceeded 100 nm, resulting in low visible light transmittance at an incident angle of 60 degrees. [Industrial applicability]

[0071] The optical filter of the present invention is excellent in both the transmission of near-infrared light and the shielding of visible light, and is therefore useful in applications such as cameras and sensors for transport aircraft, and especially in information acquisition devices such as LiDAR sensors, where performance has been steadily increasing in recent years. [Explanation of symbols]

[0072] 1A, 1B...Optical filters, 10...Substrate, 30...Dielectric multilayer film

Claims

1. The device comprises a substrate and a dielectric multilayer film provided on at least one main surface side of the substrate, wherein at least two different layers of films are laminated together. An optical filter used as a cover for a remote sensor module that uses near-infrared light, The dielectric multilayer film has a spin density of 5.0 × 10⁻¹⁶ as measured using an electron spin resonance spectrometer. １０ (pcs / (nm*cm) ２ )) Having four or more layers of membrane, The aforementioned spin density is 5.0 × 10 １０ (pcs / (nm*cm) ２ For films exceeding )), the minimum film thickness is 1.5 to 5 nm. 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. The average transmittance at an incident angle of 0 degrees in at least one 40 nm wavelength width region included in the wavelength range of 800 to 1570 nm is 90% or more. An optical filter having an average transmittance of 90% or more at an incident angle of 60 degrees in at least one 40 nm wavelength width region included in the wavelength range of 800 to 1570 nm.

2. The device comprises a substrate and a dielectric multilayer film provided on at least one main surface side of the substrate, wherein at least two different layers of films are laminated together. 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 at a wavelength of 600 nm. ６００ The minimum extinction coefficient k is 0.12 or greater and in the wavelength range of 800 to 1570 nm. ８００－１５７０ＭＩＮ The film has four or more layers in which the value is 0.01 or less. The extinction coefficient k at the wavelength of 600 nm ６００ The minimum extinction coefficient k is 0.12 or greater and in the wavelength range of 800 to 1570 nm. ８００－１５７０ＭＩＮ For films where the value is 0.01 or less, the minimum film thickness is 1.5 to 5 nm. 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. The average transmittance at an incident angle of 0 degrees in at least one 40 nm wavelength width region included in the wavelength range of 800 to 1570 nm is 90% or more. An optical filter having an average transmittance of 90% or more at an incident angle of 60 degrees in at least one 40 nm wavelength width region included in the wavelength range of 800 to 1570 nm.

3. The optical filter according to claim 1, comprising four or more layers of a film having a spin density of 5.0×10 １０ (pieces / (nm*cm ２ )) or more and a film thickness of 15 nm or less.

4. Extinction coefficient k at a wavelength of 600 nm for film thickness of 15 nm or less ６００ The minimum extinction coefficient k is 0.12 or greater and in the wavelength range of 800 to 1570 nm. ８００－１５７０ＭＩＮ The optical filter according to claim 2, comprising four or more layers of film having a coefficient of 0.01 or less.

5. The aforementioned spin density is 5.0 × 10 １０ (pcs / (nm*cm) ２ The optical filter according to claim 1, wherein the maximum film thickness of the film having a thickness of 100 nm or less.

6. The extinction coefficient k at the wavelength of 600 nm ６００ The minimum extinction coefficient k is 0.12 or greater and in the wavelength range of 800 to 1570 nm. ８００－１５７０ＭＩＮ The optical filter according to claim 2, wherein the maximum film thickness at which the coefficient of gravity is 0.01 or less is 100 nm or less.

7. The optical filter according to claim 1 or 2, wherein the luminous reflectance Y is 5% or less.

8. The average transmittance at an incident angle of 0° in the wavelength range of 1530-1570 nm is 90% or more. The optical filter according to claim 1 or 2, wherein the average transmittance at an incident angle of 60° in the wavelength range of 1530 to 1570 nm is 90% or more.

9. The optical filter according to claim 1 or 2, wherein the total thickness of the dielectric multilayer film is 2.0 μm or less.

10. The aforementioned spin density is 5.0 × 10 １０ (pcs / (nm*cm) ２ The optical filter according to claim 1, wherein the film is a silicon film.

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

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

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