JP7459483B2 - Optical filter, near-infrared cut filter, and imaging device - Google Patents

Description

The present invention relates to optical filters used in optical devices. In particular, it relates to near-infrared cut filters used as visibility correction filters for solid-state imaging devices such as CCDs (Charge Coupled Devices) and CMOSs (Complementary Metal Oxide Semiconductors) used in digital still cameras and video cameras.

The spectral sensitivity of solid-state imaging devices such as CCDs and CMOSs used in digital still cameras and video cameras is characterized by a stronger sensitivity to light in the near-infrared range than the human visual sensitivity characteristics. Therefore, visual sensitivity correction filters are generally used to match the spectral sensitivity of these solid-state imaging devices to the human visual sensitivity characteristics.

As such a visibility correction filter, Patent Document 1 discloses a near-infrared cut filter glass whose spectral characteristics are adjusted by making Cu ²⁺ ions exist in glass such as fluorophosphate glass or phosphate glass. There is.

In addition, in order to accurately determine and sharpen the transmitted wavelength range, a near-infrared cut filter with excellent properties is known, in which an optical multilayer film is provided on the surface of the near-infrared cut filter glass as described above, in which multiple high-refractive index layers and low-refractive index layers are alternately laminated, and which efficiently transmits visible wavelengths (400 to 600 nm) while sharply cutting near-infrared wavelengths (700 nm) (see, for example, Patent Document 2). In addition, in order to suppress reflection on the glass substrate surface and improve transmittance, an anti-reflection film may be provided on the surface of the near-infrared cut filter glass.

In the case of near-infrared cut filters, the optical multilayer film is, for example, a laminate of high-refractive index layers made of titanium oxide, tantalum oxide, niobium oxide, etc. and low-refractive index layers made of silicon oxide, etc., alternately laminated on a glass substrate. By appropriately setting the constituent materials, thickness, number of layers, etc. of the high-refractive index layers and low-refractive index layers, the optical interference is utilized to selectively transmit light.

In addition, as a near-infrared cut filter that has high transparency in the visible light region and excellent blocking power in the near-infrared region, an optical filter has been proposed in which a resin absorption layer containing a dye or pigment that absorbs infrared light and an optical multilayer film are provided on a substrate (see, for example, Patent Documents 3 and 4).

Japanese Patent Application Laid-Open No. 06-16451 Japanese Patent Application Laid-Open No. 02-213803 JP 2006-301489 A International Publication No. 2014/030628

The optical filters described in Patent Document 3 and Patent Document 4 have excellent optical properties. However, the present inventors have found that the configuration in which a resin layer is provided on an optical multilayer film may adversely affect the optical properties. When providing a resin layer on a substrate or an optical multilayer film, a wet coating method such as spin coating, dipping, or printing is generally used. The thickness of the resin layer formed using these manufacturing methods is quite large compared to the thickness of the optical multilayer film, but is often several tens of μm or less, and in particular, when the thickness approaches the wavelength of light to a few μm or less, it becomes a layer with optical interference properties. In this case, when a resin layer is formed on an optical multilayer film, there is a possibility that the optical properties may be affected unexpectedly. That is, compared to the thickness accuracy of the optical multilayer film, the thickness uniformity and lot-to-lot variation of the resin layer formed by the above wet coating method are large, and it has been found that, in particular, when such a resin layer is present on the optical multilayer film, the optical properties designed by the interference of the optical multilayer film may be significantly deteriorated by the presence of the resin layer. In addition, when the thickness of the resin layer is intentionally changed to obtain the desired optical properties, the design of the optical multilayer film needs to be reviewed each time, and there is also a problem of limited freedom in design.

The present invention was made in consideration of the above problems, and its purpose is to provide an optical filter and a near-infrared cut filter with excellent optical properties.

An optical filter according to the present disclosure includes a substrate, an optical multilayer film provided on the substrate, a matching layer provided on the optical multilayer film, and a transparent filter provided on the matching layer that contains a near-infrared absorbing component. an absorbent layer having a base body. The matching layer suppresses intensity fluctuations in transmittance caused by the absorption layer. The matching layer is composed of a three-layer laminated film in which a high refractive index film having a high refractive index and a low refractive index film having a lower refractive index than the high refractive index film are laminated alternately. The refractive index of the low refractive index film at a wavelength of 500 nm is 1.8 or more, and the refractive index of the low refractive index film at a wavelength of 500 nm is less than 1.6, and the designed center wavelength of the optical multilayer film is the center wavelength. In this case, when the QWOT of the high refractive index film is Q _H and the QWOT of the low refractive index film is Q _L , the matching layer has a width of 3 (aQ _L bQ _H cQ _L ) from the substrate side. composed of layers, a and c are 0.2 or more and less than 0.5, b is 0.07 or more and less than 0.5, and b<a, or a single layer of a medium refractive index film. The medium refractive index film has a refractive index of 1.6 or more and less than 1.8 at a wavelength of 500 nm.

According to the present invention, it is possible to provide an optical filter with excellent optical properties and a near-infrared cut filter.

FIG. 1 is a schematic cross-sectional view of an imaging device according to the present embodiment. FIG. 2 is a schematic cross-sectional view of the optical filter according to the present embodiment. FIG. 3 is a schematic diagram showing an example of the state of reflected light. FIG. 4 is a graph showing transmittance values for each film thickness according to Example 1. FIG. 5 is a graph showing transmittance values for each film thickness according to Comparative Example 1. FIG. 6 is a graph showing transmittance values for each film thickness according to Example 2. FIG. 7 is a graph showing transmittance values for each film thickness according to Example 3. FIG. 8 is a graph showing the transmittance value for each film thickness according to Comparative Example 2.

The following describes in detail a preferred embodiment of the present invention with reference to the attached drawings. Note that the present invention is not limited to this embodiment, and when there are multiple embodiments, the present invention also includes a configuration in which each embodiment is combined.

FIG. 1 is a schematic cross-sectional view of an imaging device according to this embodiment. As shown in FIG. 1, the imaging device 10 according to this embodiment includes a housing 12, a lens 14, an optical filter 16, and an image sensor 18. The housing 12 is a member that holds the lens 14, the optical filter 16, and the image sensor 18. The lens 14, the optical filter 16, and the image sensor 18 are provided in the housing 12 in this order from the side on which the light L is incident. Light L entering from the lens 14 passes through the optical filter 16 and enters the image sensor 18 . The optical filter 16 blocks light in a predetermined wavelength band of the light L incident from the lens 14 , while transmitting light in a wavelength band that is not blocked and makes it enter the image sensor 18 . In this embodiment, the optical filter 16 functions as a near-infrared cut filter that transmits light in the visible wavelength range while blocking light in the near-infrared wavelength range. The image sensor 18 converts the light that has passed through the optical filter 16 into an electrical signal and outputs it as an image signal. By obtaining the image signal in this way, the imaging device 10 images the subject. Note that the image sensor 18 is, for example, a solid-state image sensor such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor). Note that the configuration of the imaging device 10 in FIG. 1 is an example, and the imaging device 10 may have any configuration as long as the light L entering from the lens passes through the optical filter 16 and enters the imaging device 18.

2 is a schematic cross-sectional view of the optical filter according to the present embodiment. As shown in FIG. 2, the optical filter 16 has a substrate 20, an optical multilayer film 22, a matching layer 24, an absorbing layer 26, an auxiliary matching layer 28, and a back layer 30. The optical multilayer film 22 is provided on the surface 20a of the substrate 20. The surface 20a may be referred to as one of the main surfaces of the substrate 20. The matching layer 24 is provided on the surface 22a of the optical multilayer film 22. The surface 22a is the surface of the optical multilayer film 22 opposite the substrate 20, and may be referred to as one of the main surfaces of the optical multilayer film 22. The absorption layer 26 is provided on the surface 24a of the matching layer 24. The surface 24a is the surface of the matching layer 24 opposite the optical multilayer film 22, and may be referred to as one of the main surfaces of the matching layer 24. The auxiliary matching layer 28 is provided on the surface 26a of the absorption layer 26. Surface 26a is the surface of absorbing layer 26 opposite matching layer 24, and may be referred to as one of the main surfaces of absorbing layer 26. Surface 28a of auxiliary matching layer 28 opposite absorbing layer 26 does not have another layer laminated on it, and is exposed to the outside. In other words, surface 28a of auxiliary matching layer 28 is the air-side surface that contacts air. Surface 28a may be referred to as one of the main surfaces of auxiliary matching layer 28.

Back layer 30 is provided on surface 20b of substrate 20. The surface 20b is the surface opposite to the surface 20a, and may also be referred to as the other main surface of the substrate 20. Furthermore, when the surface of the back layer 30 opposite to the substrate 20 is designated as 30a, this surface can be said to be the surface on the air side that comes into contact with the air.

1 and 2, the optical filter 16 is provided in the imaging device 10 so that the auxiliary matching layer 28 and the back layer 30 are on the side of the incident light L (the side of the lens 14). That is, the optical filter 16 is stacked in the order of the auxiliary matching layer 28, the absorption layer 26, the matching layer 24, the optical multilayer film 22, the substrate 20, and the back layer 30 from the incident side of the light L. The optical filter 16 may also be arranged so that the back layer 30 faces the side of the incident light L (the side of the lens 14). By arranging the optical filter 16 in this way, when the absorption layer 26 includes a dye or pigment that has near-infrared absorption characteristics, it is possible to more effectively suppress the influence of the internal turbulence light reflected on the surface of the imaging element 18.

The optical filter 16 has its layers stacked in the above order. The structure of each layer of the optical filter 16 is described in detail below.

(substrate)
The substrate 20 is a plate-shaped member capable of transmitting light in the visible wavelength range. The visible wavelength range generally refers to light in the range of 380 nm to 780 nm, but when considering an optical filter for use as a visibility correction filter for a solid-state imaging device, for example, 420 nm to 650 nm (i.e., 420 nm to 650 nm) is considered as the visible range, and 700 nm and 400 nm are often considered to be near-infrared light and ultraviolet light, respectively, and are often blocked. This is because the visibility of the human eye and the visibility of the solid-state imaging device differ in wavelength dependency, and are determined by the color reproduction method used to construct an image using them, so they cannot necessarily be determined uniquely. Therefore, although it should be considered as a reference, for example, as an optical filter for visibility correction filter use, it is desirable that the transmittance of the green region (generally between 500 nm and 560 nm), which is most important in image construction, is 80% or more.

The substrate 20 preferably has low light in the near-infrared wavelength range. The near-infrared wavelength range generally refers to light in the range of 750 nm to 1.4 μm, but in this specification, it refers to 700 nm to 1000 nm. As mentioned above, the sensitivity characteristics of the solid-state imaging element are greater than those of the human eye, especially in the range of 700 nm or more. Therefore, when the optical filter 16 is used as a visibility correction filter, a blue filter that transmits visible light and absorbs near-infrared light is suitable as the substrate. In this case, the substrate 20 preferably has an average transmittance of 20% or less in the wavelength range of 700 nm to 1000 nm. However, when the transmittance of the wavelength of 700 to 1000 nm is low, the transmittance of visible light also tends to be low, so generally, an optical multilayer film such as an infrared cut filter described later is often used in combination.

The substrate 20 is preferably made of glass or resin. The substrate 20 is required to have strength to support the optical multilayer film, absorption layer, etc., and glass is generally preferable because it has the necessary strength and excellent weather resistance. Cycloolefin resins, etc., which have relatively excellent weather resistance, are preferred. When a resin is used as the substrate 20, it is possible to contain a dye or the like contained in an absorbing layer, which will be described later, in the resin itself.

When the substrate 20 is made of glass, it is preferable to use white plate glass or blue glass as the glass. For white plate glass, silicate glass with high transparency is often used, and borosilicate glass with a low content of alkaline components is more preferable from the viewpoint of weather resistance. It is also preferable that the glass contains little iron, which causes a decrease in visible light transmittance and solarization. Blue glass is glass that has a wide absorption characteristic in the wavelength range of the near-infrared region. Specifically, copper-containing fluorophosphate glass is preferable because it has good weather resistance, visible light transmission, and high near-infrared light absorption. Copper-containing phosphate glass based on phosphate glass that does not contain fluorine components is preferable because it has high near-infrared light absorption.

The fluorophosphates-based glass preferably contains, in cationic % terms, ^P5+ 25-50%, Al3 ⁺ 5-20%, R ⁺ 20-40% (where R ⁺ represents the total amount of Li ⁺ , Na ⁺ , and K ⁺ ), R'2 ⁺ 10-30% (where R'2 ⁺ represents the total amount of Mg2 ⁺ , Ca2 ⁺ , Sr2 ⁺ , Ba2 ⁺ , and Zn2 ⁺ ), Cu2 ⁺ 0.1-15%, and Sb3 ⁺ 0-1%, and, in anionic % terms, ^O2- 30-90%, and ^F- 10-70%. The fluorophosphates-based glass of the above composition is excellent in weather resistance, and contains a copper component, thereby providing spectral characteristics suitable for near-infrared cut filter glass. In addition to the above-mentioned compositions, the fluorophosphate-based glass may be, for example, glass having a composition range or described in the examples disclosed in JP-A-3-83834, JP-A-6-16451, JP-A-8-253341, JP-A-2004-83290, or JP-A-2011-132077. The phosphate glass preferably contains, for example, in mole percent, 50-75% P ₂ O ₅ , 5-22% Al ₂ O ₃ , 0.5-20% R ₂ O (where R ₂ O represents the total amount of Li ₂ O, Na ₂ O, and K ₂ O), 0.1-25% R'O (where R'O represents the total amount of MgO, CaO, SrO, BaO, and ZnO), and 0.1-15% CuO. Phosphate glass of the above composition has high near-infrared absorption ability and has spectral characteristics suitable for near-infrared cut filter glass. In addition to the above-mentioned compositions, the phosphate-based glass may be, for example, glasses having composition ranges or described in the examples disclosed in JP-A-2010-8908, JP-A-2011-121792, JP-A-2012-224491, and JP-A-2015-13773.

To obtain the glass substrate 20, glass raw materials are prepared and melted so as to have the desired glass composition as described above, and then the molten glass is shaped. After producing a glass substrate by processing its outer shape to a predetermined size, the surface of the glass substrate is lapped (ground) and then polished (precision polished) to obtain the substrate 20. Note that in order to obtain the optical filter 16, the optical multilayer film 22, the matching layer 24, the absorption layer 26, and the auxiliary matching layer 28 are formed in this order on the surface 20a of the substrate 20 obtained in this way, and then on the surface 20b of the substrate 20. A back layer 30 is formed. Next, it is cut using a known method (such as scribing, dicing, laser cutting, etc.) to a predetermined product size.

From the viewpoint of making the optical filter 16 thinner, the thickness of the substrate 20 is preferably 0.3 mm or less, more preferably 0.22 mm or less, even more preferably 0.18 mm or less, and most preferably 0.15 mm or less. Further, from the viewpoint of reducing processing costs and reducing strength, the thickness of the substrate 20 is preferably 0.025 mm or more, more preferably 0.03 mm or more, and even more preferably 0.05 mm or more.

(optical multilayer film)
The optical multilayer film 22 is a layer having predetermined optical properties, and in this embodiment, it is configured to transmit light in the visible wavelength range and suppress transmission of light in the near-infrared wavelength range. Ru. For example, the optical multilayer film 22 reflects light with wavelengths in the near-infrared region, thereby suppressing transmission of light with wavelengths in the near-infrared region. That is, the optical multilayer film 22 is an infrared shielding film (also referred to as an InfraRed Cut Filter film or IRCF film). The optical multilayer film 22 preferably has an average transmittance of light in the visible wavelength range of 80% or more, and more preferably 100% or less. Further, it is preferable that the optical multilayer film 22 has an average transmittance of light having wavelengths in the near-infrared region of 10% or less, and more preferably 0% or more.

As the optical multilayer film 22 having such a function, for example, a laminated film in which films with different refractive indices are laminated is used. By being configured in this way, the optical multilayer film 22 can reflect light of wavelengths in the near infrared region and transmit light of wavelengths in the visible region by the interference of light. The optical multilayer film 22 is configured by, for example, arranging a high refractive index film 22A and a low refractive index film 22B having a lower refractive index than the high refractive index film 22A in a plurality of alternating arrangements. As the high refractive index film 22A, for example, at least one metal oxide film selected from ZrO ₂ , Nb ₂ O ₅ , TiO ₂ , and Ta ₂ O ₅ is used. As the low refractive index film 22B, for example, SiO ₂ is used. The film thickness and the number of layers of the high refractive index film 22A and the low refractive index film 22B are appropriately set according to the optical characteristics required for the optical multilayer film 22.

The optical multilayer film 22 is formed on the surface 20a of the substrate 20 using a sputtering method or an ion-assisted vapor deposition method. Films formed by sputtering or ion-assisted vapor deposition have very small changes in spectral characteristics under high temperature and high humidity compared to films formed by vapor deposition that does not use ion assist. It has the advantage that it is possible to realize a non-shift film that does not change. Furthermore, since the films formed by these methods are dense and hard, they are less likely to be scratched and have excellent handling properties in parts assembly processes and the like. Therefore, it is suitable as a method for forming an optical multilayer film of a near-infrared cut filter used as a visibility correction filter for an image sensor.

Further, the optical multilayer film 22 may be formed by a vacuum evaporation method that does not use ion assist. When using this vapor deposition method, the equipment cost is low and manufacturing costs can be suppressed. Moreover, when forming the optical multilayer film 22, a film with less adhesion of foreign matter etc. can be obtained. That is, the method for forming the optical multilayer film 22 is not limited to sputtering, ion-assisted vapor deposition, etc., and may be any method.

(absorbent layer)
Before explaining the matching layer 24, the absorption layer 26 will be explained. The absorption layer 26 is a layer composed of a transparent substrate containing a near-infrared absorption component. The term "transparent" in the transparent substrate means that it is transparent to light in the visible wavelength range.

The transparent substrate of the absorption layer 26 is preferably made of resin or an inorganic material. When the transparent substrate is a resin, examples of the resin include acrylic resin, epoxy resin, ene-thiol resin, polycarbonate resin, polyether resin, polyarylate resin, polysulfone resin, polyethersulfone resin, polyparaphenylene resin, and polyester. Examples include resins, polyimide resins, polyamideimide resins, polyolefin resins, and cyclic olefin resins. In particular, the resin having a high glass transition temperature (Tg) is preferably one or more selected from polyester resins, polycarbonate resins, polyethersulfone resins, polyarylate resins, polyimide resins, and epoxy resins. Furthermore, the resin serving as the transparent substrate is more preferably one or more selected from polyester resins and polyimide resins, and polyimide resins are particularly preferred. As the polyester resin, polyethylene terephthalate resin, polyethylene naphthalate resin, etc. are preferable. Further, when the transparent substrate of the absorption layer 26 is an inorganic material, the inorganic material is preferably, for example, a silicon oxide film.

The near-infrared absorbing component contained in the absorbing layer 26 is composed of an absorbent capable of absorbing light in the wavelength band of the near-infrared region. The absorbing layer 26 is formed by uniformly dissolving or dispersing the absorbent in the transparent substrate, so that the near-infrared absorbing component is contained in the transparent substrate, and the layer transmits light in the wavelength band of the visible region while absorbing light in the wavelength band of the near-infrared region. The absorbent preferably has a maximum absorption wavelength of 600 nm or more and 1200 nm or less, more preferably 600 nm or more and 1000 nm or less, and most preferably 600 nm or more and 850 nm or less when dissolved or dispersed in the transparent substrate. The absorbent may be a dye that absorbs light in the wavelength band of the near-infrared region. If this dye is designated as dye (A), examples of dye (A) include diimonium-based, cyanine-based, phthalocyanine-based, naphthalocyanine-based, dithiol metal complex-based, azo-based, aminium-based, polymethine-based, phthalide, naphthoquinone-based, anthraquinone-based, indophenol-based, pyrylium-based, thiopyrylium-based, squarylium-based, croconium-based, tetradehydocoline-based, triphenylmethane-based, aminium-based dyes, etc. Furthermore, for example, the absorbent may be an inorganic pigment that absorbs light with a wavelength in the near-infrared region. Examples of inorganic pigments include near-infrared absorbing particles containing crystallites of _{A1/nCuPO4 (} wherein A is one or more selected from the group consisting of alkali metals (Li, Na, K, Rb, Cs), alkaline earth metals (Mg, Ca, Sr, Ba) and _NH4 , and n is 1 when A is an alkali metal or _NH4 , and is 2 when A is an alkaline earth metal), and tungsten-containing oxide fine particles.

When the transparent substrate of the absorbing layer 26 is a resin, the transparent substrate in which the absorbent is uniformly dissolved or dispersed is applied to the surface 24a of the matching layer 24 by a coating method such as spin coating or dip coating (dipping), and the transparent substrate is solidified by heat or ultraviolet light, to form the absorbing layer 26. When the transparent substrate of the absorbing layer 26 is an inorganic material, the absorbing layer 26 is formed, for example, by using a sol-gel method. That is, the absorbent is uniformly dissolved or dispersed in a solution that is the raw material for the transparent substrate, and this solution is applied to the surface 24a of the matching layer 24, the solution is converted into a sol, and the sol is converted into a gel, to form the absorbing layer 26.

In this embodiment, the absorption layer 26 is a single layer, but may be composed of multiple layers. The thickness of the absorption layer 26 is preferably 100 nm or more and 5000 nm or less, whether it is composed of a single layer or multiple layers. By making the thickness 5000 nm or less, it is possible to prevent the degree of deterioration of the optical characteristics due to the variation in the film thickness of the absorption layer 26 from becoming too large. In addition, by making the thickness 100 nm or more, it is possible to suppress the absorption ability of the absorption layer 26, i.e., the extinction coefficient, from becoming too high, suppress a sudden increase in the refractive index, and suppress the influence of ripples from becoming too high. In addition, if the thickness is less than 100 nm, it is difficult to form a film by coating, etc., and considering the characteristics of near-infrared absorption, the extinction coefficient k increases, which increases the refractive index n value, and there is a concern that this will be disadvantageous in thin film design. In addition, if the thickness exceeds 5000 nm, it is not preferable because the total thickness of the optical filter increases and the ratio of resin with relatively low weather resistance increases, which may cause deterioration of weather resistance.

Moreover, the absorption layer 26 may contain an ultraviolet absorption component. The ultraviolet absorbing component is composed of, for example, an ultraviolet absorber capable of absorbing light in a wavelength band of the ultraviolet region. Since the ultraviolet absorber is uniformly dissolved or dispersed in the transparent substrate, the ultraviolet absorbing component is contained in the absorbing layer 26. The ultraviolet absorber preferably has a maximum absorption wavelength of 360 nm or more and 415 nm or less when uniformly dissolved or dispersed in a transparent substrate. The ultraviolet absorber is, for example, a dye that can absorb light in the ultraviolet wavelength range. When the dye (U) is a dye that can absorb light in the ultraviolet wavelength range, examples of the dye (U) include oxazole, merocyanine, cyanine, naphthalimide, oxadiazole, oxazine, and oxazolidine. Dyes such as naphthalic acid-based, styryl-based, anthracene-based, cyclic carbonyl-based, and triazole-based dyes may be mentioned.

(matching layer, auxiliary matching layer)
Since it is easier to understand that the matching layer 24 and the auxiliary matching layer 28 are explained together, their functions will be described below.

The matching layer 24 and the auxiliary matching layer 28 are ripple adjustment layers for suppressing the film thickness dependence of the absorption layer 26 as an interference film. As described separately, the thickness of the absorbent layer 26 may vary during the molding process and the like. The matching layer 24 suppresses the influence of this film thickness variation on the optical characteristics of the optical filter.

First, the concept of suppressing intensity fluctuations in transmittance caused by the absorption layer 26 by the matching layer 24 will be explained.

Each structure from the absorption layer 26 to the substrate 20 is composed of the substrate 20, the optical multilayer film 22, the matching layer 24, and the absorption layer 26 in this order. Here, if the absorption layer 26 is considered as an incident medium, the order will be the substrate 20, the optical multilayer film 22, the matching layer 24, and the incident medium (absorption layer 26). For example, if the incident medium is air, it is very common. The structure is the same as that of an optical thin film. The incident medium is a medium that is theoretically considered to exist infinitely on the side into which light enters, and there is no concept of thickness in this respect. Note that in calculations related to optical interference, it is normally assumed that the incident medium has infinite thickness, so the extinction coefficient k value, which is an absorption characteristic, is assumed to be zero.

In the above configuration, a thin film called a ripple adjustment layer has been inserted on the incident medium side of the optical multilayer film 22 in order to minimize the reflectance in the visible region of the spectral waveform created by the optical multilayer film 22 and suppress undulations in the waveform called reflection ripples, transmission ripples, etc., and the matching layer 24 plays the same role as this ripple adjustment layer. In other words, the matching layer 24 is a ripple adjustment layer when the absorption layer 26 is the incident medium. Note that ripple adjustment as described here refers to suppressing intensity fluctuations in the optical characteristics of the visible wavelength band due to changes in the film thickness of the absorption layer 26.

As a guideline, the reflectance in the visible region of the spectral waveform produced by the optical multilayer film 22 is preferably 2% or less, more preferably 1% or less. With this reflectance, intensity fluctuations in spectral characteristics called ripples are also limited.

In regards to the angle of incidence, since the optical filter 16 is actually used in the atmosphere or under a vacuum, the angle of incidence adjusted so that Snell's law holds true is applied as the angle of incidence on the incident medium side, relative to the angle of incidence when air is the medium.

Similarly, the auxiliary matching layer 28 minimizes the reflectance in the visible region and eliminates reflection ripples when the absorption layer 26 is regarded as a substrate and the substrate (absorption layer 26), auxiliary matching layer 28, and incident medium (air) are used. , is a ripple adjustment layer for suppressing waveform undulations called transmission ripples.However, in the above case, since there is only the auxiliary matching layer 28, it is configured as a layer to minimize the reflectance. Since the minimum unit for this is an antireflection film, the auxiliary matching layer 28 may be an antireflection film when the substrate (absorption layer 26), the auxiliary matching layer 28, and the incident medium (air) are used. Of course, as long as the reflectance in the visible region is minimized and ripples are suppressed, a bandpass filter such as an infrared cut filter may be used, but considering the purpose of the present invention, the minimum film thickness, It is most preferable to use an antireflection film having a multilayer structure.

If the absorbing layer 26 is considered as a substrate, with the substrate (absorbing layer 26), auxiliary matching layer 28, and incident medium (air), the target reflectance in the visible region is preferably 2% or less, and more preferably 1% or less. Under these conditions, the intensity fluctuation in the spectral characteristics, known as ripple, is also limited.

In calculations related to optical interference, the extinction coefficient k associated with absorption of the substrate can be considered to be zero, and in terms of optical interference, the thickness of the substrate is considered to be infinite. In other words, like the incident medium, there is no film thickness dependency in the interference design of optical thin films.

When the optical filter 16 is considered based on the absorbing layer 26, the configuration from the absorbing layer 26 to the air side in FIG. 1 is designed so that the absorbing layer 26 can be considered as a substrate, and the configuration from the absorbing layer 26 to the substrate 20 side is designed so that the absorbing layer 26 can be considered as an incident medium. Therefore, even when all the configurations (substrate 20, optical multilayer film 22, matching layer 24, absorbing layer 26, auxiliary matching layer 28, air (incident medium)) are combined, the film thickness dependency of the absorbing layer 26 is very small, and as a result, even if the film thickness fluctuation of the absorbing layer 26 due to the coating process, etc. becomes large, the adverse effect as an optical interference film is suppressed. In order to maintain the reflectance and ripple in the visible region at a minimum when all these configurations are combined, it is preferable that the matching layer 24 is a three-layer structure or a single-layer intermediate refractive index film described later.

Note that with the configuration designed in this manner, the effect of suppressing the influence of the variation in the thickness of the absorption layer 26 on the optical characteristics of the optical filter, which is the objective of the present invention, can be achieved even without the auxiliary matching layer. This is because the absorption layer 26 is a resin layer and therefore has a relatively low surface reflectance, but the presence of the auxiliary matching layer is necessary to obtain better optical characteristics.

In this embodiment, the matching layer 24 is composed of a laminated film of three or more layers, in which a high refractive index film 24A and a low refractive index film 24B are alternately laminated. As described above, the matching layer 24 acts as a ripple adjustment layer for the optical multilayer film 22, and therefore the thickness depends on the configuration of the optical multilayer film 22. Considering the main use of the optical filter 16, for example, the optical multilayer film 22 is an infrared cut filter. Usually, the optical design of these optical multilayer films 22 is basically composed of repetitions of (HL)^n, where the optical thickness QWOT of the high refractive index film is H and the optical thickness QWOT of the low refractive index film is L. Note that (HL)^n represents a configuration in which the high refractive index film 24A and the low refractive index film 24B are repeated n times in this order. In addition, in this case, the high refractive index films 24A to be laminated may have different optical thicknesses. This is also true for the low refractive index film 24B. The matching layer 24 must be made of a film thinner than the optical thickness of the (HL)^n basic repeating structure closer to the matching layer 24 among the repeating structures of the optical multilayer film 22, and is more preferably made of three layers of ( _{aQL bQH cQL} ) described below. From the viewpoint of manufacturing, it is preferable that the film material of the matching layer 24 thus configured is the same as that of the optical multilayer film 22, but it is not necessary that they be made of exactly the same film material as long as the optical thickness satisfies the above conditions.

In addition to the above, the matching layer 24 can also be configured with an intermediate refractive index film, in which case the number of film layers can be reduced. An intermediate refractive index film can be expressed as a three-layer structure of a thinner high refractive index film and a low refractive index film using the concept of an equivalent film, and can therefore exhibit optical characteristics similar to those of the matching layer 24 composed of the above three layers. However, since the equivalent film conditions and the above three-layer structure conditions are different, the performance will be slightly inferior, but it is possible to exhibit the characteristics of the matching layer 24 at a level that does not cause problems in practical use.

The refractive index of the high refractive index film at a wavelength of 500 nm is preferably 1.8 or more and 3 or less, the refractive index of the low refractive index film at a wavelength of 500 nm is preferably 1.4 or more and less than 1.6, and the refractive index of the intermediate refractive index film at a wavelength of 500 nm is preferably 1.6 or more and less than 1.8. Since the present invention is premised on disposing the absorption layer 26 on the optical multilayer film 22, the optical multilayer film 22 determines the basic optical characteristics of the optical filter 16 as an interference multilayer film. Since the film material and refractive index of the matching layer 24 depend on the optical multilayer film 22, the above refractive index range also applies to the optical multilayer film 22, and the above specification of the refractive index is based on the manufacturing requirements for manufacturing, for example, an infrared cut filter.

The configuration of the matching layer 24 will be explained in more detail. As explained above, the matching layer 24 acts as a ripple adjustment layer for the optical multilayer film 22 under specific conditions. Therefore, the central wavelength of the QWOT (Quarter-wave Optical Thickness) in the optical film thickness is determined based on the central wavelength in the film design of the optical multilayer film 22. Specifically, if the optical multilayer film 22 is an infrared cut filter, the central wavelength of the wavelength band cut by the infrared cut filter becomes the central wavelength of the QWOT of the matching layer 24. Note that, if there are multiple wavelength bands cut by the infrared cut filter, the central wavelength of the wavelength band closer to the matching layer 24 is selected. In addition, the central wavelength of the QWOT of the matching layer 24 is preferably 700 nm to 1400 nm.

Here, the QWOT (Quarter-wave Optical Thickness) of the high refractive index film 24A is _QH , and the QWOT of the low refractive index film 24B is _QL . In this case, the matching layer 24 is preferably composed of three layers ( _{aQL bQH cQL} ) from the substrate 20 side (optical multilayer film 22 side) toward the absorption layer 26 side. Here, a, b, and c are coefficients in each basic unit, and represent how many times the physical film thickness of the film in each basic unit is the QWOT. Therefore, _aQL , _bQH , and _cQL indicate the optical film thickness of each film. That is, the matching layer 24 is the film closest to the substrate 20 (optical multilayer film 22 side) is the low refractive index film 24B, and its optical film thickness is _aQL . In the matching layer 24, the film provided on the absorption layer 26 side of the low refractive index film 24B closest to the substrate 20 is the high refractive index film 24A, and its optical thickness is _bQH . In the matching layer 24, the film provided on the absorption layer 26 side of the high refractive index film 24A is the low refractive index film 24B, and its optical thickness is _cQL . In this embodiment, since the matching layer 24 has a three-layer structure, the low refractive index film 24B provided on the absorption layer 26 side of the high refractive index film 24A is the film provided closest to the absorption layer 26. Note that a, b, and c when the matching layer 24 is composed of three layers ( _{aQL bQH cQL} ) are calculated using the respective refractive indices of the high refractive index film 24A and the low refractive index film 24B at the center wavelength of the stop band of the optical multilayer film 22.

Here, a and c are 0.2 or more and less than 0.5, b is 0.07 or more and less than 0.5, and preferably b<a. By setting a, b, and c within such numerical ranges, the matching layer 24 contributes to suppressing the reflectance in the visible region and ripples by suppressing the film thickness dependence of the absorption layer 26.

However, as long as the matching layer 24 is configured to suppress interference of light in the visible wavelength range by the absorption layer 26, it does not have to be configured in such a way that one high refractive index film 24A is provided between two low refractive index films 24B, and the optical film thickness of the high refractive index film 24A and the low refractive index film 24B does not have to have the above-mentioned relationship. For example, the matching layer 24 may have a three-layer configuration in which one low refractive index film 24B is provided between two high refractive index films 24A. In addition, the matching layer 24 may be configured to have a total of four or more layers of high refractive index films 24A and low refractive index films 24B alternately stacked, or a total of two layers stacked. In addition, the matching layer 24 may be configured with one layer having an intermediate refractive index that is a predetermined refractive index, that is, a single layer of the above-mentioned medium refractive index film. The intermediate refractive index is, for example, a value between the refractive index of the high refractive index film 24A and the refractive index of the low refractive index film 24B described above.

Further, the matching layer 24 is formed by laminating the substrate 20, the optical multilayer film 22, the matching layer 24, the absorption layer 26, and the auxiliary matching layer 28 in this order, and the auxiliary matching layer 28 is exposed to the air. It is preferable to suppress the occurrence of ripples in the visible wavelength band of light that enters the auxiliary matching layer 28 from the air side and passes through the substrate 20.

The high refractive index film 24A is, for example, at least one metal oxide film selected from ZrO ₂ , Nb ₂ O ₅ , TiO ₂ , and Ta ₂ O _5. The low refractive index film 24B is, for example, SiO _2. The high refractive index film 24A is preferably made of the same material as the high refractive index film 22A of the optical multilayer film 22, and the low refractive index film 24B is preferably made of the same material as the low refractive index film 22B of the optical multilayer film 22. By using the same material, stacking can be easily performed. However, the high refractive index film 24A and the high refractive index film 22A may be made of different materials, and the low refractive index film 24B and the low refractive index film 22B may be made of different materials.

The matching layer 24 may be formed on the surface 22a of the optical multilayer film 22 in a manner similar to that used to form the optical multilayer film 22. That is, the matching layer 24 may be formed, for example, by sputtering, ion-assisted deposition, vacuum deposition, or the like.

(auxiliary matching layer)
The auxiliary matching layer 28 is a layer that suppresses light in the visible wavelength range that is incident on the auxiliary matching layer 28 from being reflected at the absorption layer 26 (the interface between the auxiliary matching layer 28 and the absorption layer 26). . That is, the auxiliary matching layer 28 is an anti-reflection film (also referred to as an anti-reflection film or an AR film) having an anti-reflection function. In this embodiment, the auxiliary matching layer 28 is an optical multilayer film formed by laminating a plurality of films having different refractive indexes. That is, for the auxiliary matching layer 28, for example, a laminated film in which a plurality of high refractive index films and a plurality of low refractive index films having a refractive index lower than the high refractive index film are arranged alternately is used. As the high refractive index film, for example, a film of at least one metal oxide selected from ZrO ₂ , Nb ₂ O ₅ , TiO ₂ , and Ta ₂ O ₅ is used. For example, SiO ₂ or the like is used as the low refractive index film. The film thicknesses and the number of laminated layers of the high refractive index film and the low refractive index film are appropriately set according to the optical characteristics required of the auxiliary matching layer 28. The auxiliary matching layer 28 may also be formed on the surface 26a of the absorption layer 26 in the same manner as in the formation of the optical multilayer film 22. That is, the auxiliary matching layer 28 may be formed using, for example, a sputtering method, an ion-assisted deposition method, a vacuum deposition method, or the like. Note that the auxiliary matching layer 28 is not limited to such a multilayer film as long as it has an antireflection function, and may be composed of a single layer, an infrared cut filter, an ultraviolet cut filter, etc. . Further, the optical filter 16 may not include the auxiliary matching layer 28.

(Back layer)
The back layer 30 is provided to complement the optical characteristics of the optical filter 16, which is composed of the substrate 20, the optical multilayer film 22, the matching layer 24, the absorption layer 26, and the auxiliary matching layer 28 provided on the substrate 20. Therefore, the back layer 30 may be configured similarly to the optical multilayer film 22, the matching layer 24, the absorption layer 26, and the auxiliary matching layer 28, or may be configured only with the optical multilayer film, or may not be provided. When the optical filter 16 is used as an optical filter for an imaging device, the back layer 30 is assumed to be an infrared cut filter or an anti-reflection film. When the back layer 30 is composed of an optical multilayer film, for example, a laminated film in which a high refractive index film and a low refractive index film having a refractive index lower than that of the high refractive index film are alternately arranged is used. As the high refractive index film, for example, at least one metal oxide film selected from ZrO ₂ , Nb ₂ O ₅ , TiO ₂ , and Ta ₂ O ₅ is used. As the low refractive index film, for example, SiO ₂ is used. The film thickness and number of layers of the high refractive index film and the low refractive index film are appropriately set according to the optical properties required for the rear layer 30. The rear layer 30 may be formed on the surface 20b of the substrate 20 by the same method as that for forming the optical multilayer film 22. That is, the rear layer 30 may be formed by, for example, a sputtering method, an ion-assisted deposition method, a vacuum deposition method, or the like. Note that the rear layer 30 is not limited to such a multilayer film, and may be composed of a single layer, as long as it has an anti-reflection function.

The optical filter 16 has the above configuration. FIG. 3 is a schematic diagram showing an example of the state of reflected light. FIG. 3 shows the difference in the state of reflected light between the optical filter 16x according to the comparative example and the optical filter 16 according to the present embodiment. As shown in FIG. 3, the optical filter 16x according to the comparative example has a substrate 20x, an absorption layer 26x, and an optical multilayer film 22x stacked in this order. That is, in the comparative example, the optical multilayer film 22x is located closer to the incident light L1x than the absorption layer 26x. In this case, out of the incident light L1x, light with unnecessary wavelengths is reflected as reflected light L2x on the surface of the optical multilayer film 22x. The reflected light L2x exists, for example, as stray light inside the casing of the imaging device, and there is a possibility that it may enter the optical filter 16x again. At this time, if stray light enters the optical filter 16x at a wide angle, the stray light cannot be reflected due to the oblique incidence characteristics of the optical multilayer film 22X, and there is a risk that the stray light will pass through the optical filter 16x and reach the image sensor. In this case, the light may be recognized as noise in the captured image, and the quality of the captured image may deteriorate.

On the other hand, in the optical filter 16 according to this embodiment, the absorption layer 26 is located closer to the incident light L1 than the optical multilayer film 22. Note that, in FIG. 3, for convenience of explanation, the auxiliary matching layer 28 and the back layer 30 are omitted. As shown in FIG. 3, the incident light L1 to the optical filter 16 enters the absorption layer 26, and the unnecessary wavelengths of the incident light L1 are absorbed by the absorption layer 26. Then, the unnecessary wavelength light that is not absorbed by the absorption layer 26 is reflected on the surface of the optical multilayer film 22. The light reflected on the surface of the optical multilayer film 22 enters the absorption layer 26 again and is absorbed by the absorption layer 26, and only the light that is not absorbed by the absorption layer 26 enters the housing of the imaging device as reflected light L2. It is emitted. That is, since the reflected light L2 passes through the absorption layer 26 twice, the intensity is lower than that of the reflected light L2x by the amount of absorption during the two passes. Therefore, according to the optical filter 16 according to the present embodiment, even if stray light reaches the image sensor, the intensity of the stray light is reduced, so the influence on the captured image is reduced, and the image quality of the captured image is reduced. suppress. That is, the optical filter 16 according to this embodiment suppresses deterioration of optical characteristics by reducing the intensity of stray light.

However, if the absorption layer 26 is disposed closer to the incident light L1 side than the optical multilayer film 22, as described above, the ripple in the transmittance of the optical multilayer film 22 becomes significant, and the optical characteristics of the optical filter 16 may deteriorate. In contrast, the optical filter 16 according to this embodiment uses the matching layer 24 to suppress interference of light in the visible wavelength range caused by the absorption layer 26, thereby suppressing the ripple in the transmittance of the optical multilayer film 22 and suppressing deterioration of the optical characteristics of the optical filter 16.

As explained above, the optical filter 16 according to the present embodiment includes the substrate 20, the optical multilayer film 22 provided on the substrate 20, the matching layer 24 provided on the optical multilayer film 22, and the matching layer 24. and an absorbing layer 26 having a transparent substrate containing an infrared absorbing component. The matching layer 24 is configured to suppress intensity fluctuations in transmittance caused by the absorption layer 26 . According to this optical filter 16, by suppressing the interference of light in the visible wavelength band by the absorption layer 26 while reducing the intensity of stray light, it is possible to suppress deterioration of the optical characteristics of the optical filter 16.

(Example 1)
Next, Example 1 will be described. In Example 1, the transmittance of the optical filter 16 according to the present embodiment was simulated after changing the film thickness (thickness) of the absorption layer 26. Table 1 describes the configuration of each layer of the optical filter 16 according to Example 1. As shown in Table 1, in Example 1, the high refractive index film of the auxiliary matching layer 28 is made of TiO ₂ , the low refractive index film of the auxiliary matching layer 28 is made of SiO ₂ , and the high refractive index film 24A of the matching layer 24 is made of SiO 2 . and the high refractive index film 22A of the optical multilayer film 22 are made of ZrO ₂ , and the low refractive index film 24B of the matching layer 24 and the low refractive index film 22B of the optical multilayer film 22 are made of SiO ₂ . At a wavelength of 500 nm, the refractive index of _TiO2 is 2.467, the refractive index of _SiO2 is 1.483, and the refractive index of _ZrO2 is 2.058. In Example 1, the optical multilayer film 22, the matching layer 24, and the auxiliary matching layer 28 are configured as shown in Table 1, and the thickness of the absorption layer 26 is varied in the range from 700 nm to 1400 nm. The spectral transmittance of the filter 16 was calculated by simulation. That is, for the optical filter 16 having the configuration shown in Table 1, the transmittance of light emitted from the substrate 20 when light is incident from the auxiliary matching layer 28 was calculated by simulation for each thickness of the absorption layer 26. As shown in Table 1, it can be seen that the matching layer 24 of Example 1 has a three-layer structure (aQ _L bQ _H cQ _L ). In Table 1, the optical multilayer film is on the substrate 20 side, and the auxiliary matching layer is on the air side. In Example 1, the designed center wavelength of the optical multilayer film 22 is 930 nm, a is 0.313, b is 0.131, and c is 0.412. Note that each coefficient was calculated using the refractive index at a wavelength of 930 nm of the high refractive index film 24A and the low refractive index film 24B of the matching layer 24 (ZrO ₂ : 2.025, SiO ₂ : 1.467). In addition, TFCalc (manufactured by Software Spectra) was used as simulation software for calculating the spectral transmittance. Further, the calculation was performed under the condition that the substrate 20 and the absorption layer 26 do not absorb light. Calculations related to optical interference are performed assuming that the extinction coefficient k related to absorption is zero.

Meanwhile, Table 2 shows the configuration of each layer of the optical filter according to Comparative Example 1. In Table 2, the optical multilayer film is on the substrate 20 side, and the auxiliary matching layer is on the air side. The optical filter according to Comparative Example 1 differs from Example 1 in that it does not have a matching layer 24. As with Example 1, for Comparative Example 1, the film thickness of the absorption layer 26 was varied in the range from 700 nm to 1400 nm, and the spectral transmittance of the optical filter 16 was calculated by simulation.

Figure 4 is a graph showing the spectral transmittance value for each film thickness in Example 1. Figure 5 is a graph showing the spectral transmittance value for each film thickness in Comparative Example 1. The horizontal axis of Figures 4 and 5 is wavelength, and the vertical axis is the spectral transmittance of the optical filter 16. Figures 4 and 5 show the calculation results of the transmittance of the optical filter 16 for each film thickness of the absorption layer 26 for each light having a wavelength of 350 nm to 1200 nm. As shown in Figures 4 and 5, in Example 1, the variation in the spectral transmittance value of the optical filter with respect to the change in the film thickness of the absorption layer 26 is smaller than that in Comparative Example 1, and ripples are suppressed, especially when the wavelength of the incident light is 450 nm or more and 750 nm or less (more specifically, 450 nm or more and 650 nm or less). Furthermore, when the variation in the spectral transmittance of the optical filter 16 was examined in detail when the thickness of the absorption layer 26 was changed, the difference between the maximum transmittance and the minimum transmittance in the visible wavelength range (here, wavelengths 450 nm or more and 650 nm or less) was 0.66% or more and 0.89% or less in Example 1, whereas it was 2.60% or more and 7.66% or less in Comparative Example 1.

(Examples 2 and 3)
Next, Examples 2 and 3 will be described. In Example 2, the optical filter 16 according to this embodiment was simulated for transmittance after changing the film thickness (thickness) of the absorption layer 26. Table 3 shows the configuration of each layer of the optical filter 16 according to Example 2. In Table 3, the optical multilayer film is on the substrate 20 side, and the auxiliary matching layer is on the air side. As shown in Table 3, in Example 2, the configuration of the auxiliary matching layer 28 is substantially the same as that of Example 1. On the other hand, the matching layer 24 is different from Example 1 in that it is configured of a single layer of Al ₂ O ₃ as a medium refractive index film. At a wavelength of 500 nm, the refractive index of Al ₂ O ₃ is 1.617. In Example 2, the optical multilayer film 22, the matching layer 24, and the auxiliary matching layer 28 are configured as shown in Table 3, and the film thickness of the absorption layer 26 is changed in the range from 700 nm to 1400 nm, and the spectral transmittance of the optical filter 16 is calculated by simulation. That is, for the optical filter 16 having the configuration shown in Table 3, the transmittance of light exiting the substrate 20 when light is incident on the auxiliary matching layer 28 was calculated for each thickness of the absorption layer 26 using the same simulation software and conditions as in Example 1.

In Example 3, the spectral transmittance of the optical filter 16 according to the present embodiment was simulated after changing the film thickness (thickness) of the absorption layer 26. Table 4 describes the configuration of each layer of the optical filter 16 according to Example 3. In Table 4, the optical multilayer film is on the substrate 20 side, and the absorption layer is on the air side. As shown in Table 4, in Example 3, the configuration of the matching layer 24 is substantially the same as in Example 1. In Example 3, the designed center wavelength of the optical multilayer film 22 is 930 nm, a is 0.313, b is 0.131, and c is 0.412. Note that each coefficient was calculated using the refractive index at a wavelength of 930 nm of the high refractive index film 24A and the low refractive index film 24B of the matching layer 24 (ZrO ₂ : 2.025, SiO ₂ : 1.467). On the other hand, Example 3 differs from Example 1 in that the auxiliary matching layer 28 is not provided. In Example 3, the optical multilayer film 22 and the matching layer 24 are configured as shown in Table 4, and the thickness of the absorption layer 26 is varied in the range from 700 nm to 1400 nm to improve the spectral transmission of the optical filter 16. The rate was calculated by simulation. That is, for the optical filter 16 having the configuration shown in Table 4, the transmittance of light emitted from the substrate 20 when light is incident from the absorption layer 26 was calculated using the same simulation as in Example 1 for each thickness of the absorption layer 26. Calculated using software and conditions.

On the other hand, Table 5 shows the structure of each layer of the optical filter according to Comparative Example 2. In Table 5, the optical multilayer film is on the substrate 20 side, and the absorption layer is on the air side. The optical filter according to Comparative Example 2 differs from Example 1 in that it does not have the matching layer 24 and the auxiliary matching layer 28. In Comparative Example 2, similarly to Example 1, the spectral transmittance of the optical filter 16 was calculated by simulation while varying the thickness of the absorption layer 26.

Figure 6 is a graph showing the spectral transmittance value for each film thickness in Example 2. Figure 7 is a graph showing the spectral transmittance value for each film thickness in Example 3. Figure 8 is a graph showing the spectral transmittance value for each film thickness in Comparative Example 2. The horizontal axis of Figures 6 to 8 is the wavelength, and the vertical axis is the spectral transmittance of the optical filter 16. Figures 6 to 8 show the calculation results of the spectral transmittance of the optical filter 16 for each film thickness of the absorption layer 26 for each light having a wavelength of 350 nm to 1200 nm. As shown in Figures 6 to 8, in Examples 2 and 3, it can be seen that the variation in the transmittance value is small and ripples are suppressed for all wavelengths of light compared to each comparative example, especially when the wavelength of the incident light is 450 nm or more and 750 nm or less (more specifically, 450 nm or more and 650 nm or less). In contrast, in Comparative Example 2, it can be seen that the variation in the transmittance value is large, especially with respect to the variation in the film thickness (thickness) of the absorption layer 26, and ripples are generated. Furthermore, when the variation in the spectral transmittance when the thickness of the absorption layer 26 of the optical filter 16 was changed was examined in detail, the difference between the maximum transmittance and the minimum transmittance in the visible wavelength range (here, wavelengths 450 nm or more and 650 nm or less) was 1.27% or more and 2.38% or less in Example 2, 3.11% or more and 4.72% or less in Example 3, and 1.34% or more and 17.97% or less in Comparative Example 2.

Although the embodiment of the present invention has been described above, the embodiment is not limited to the contents of this embodiment. The above-mentioned components include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-mentioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-mentioned embodiment.

10 Imaging device 16 Optical filter 18 Imaging element 20 Substrate 22 Optical multilayer film 24 Matching layer 26 Absorption layer 28 Auxiliary matching layer 30 Back layer

Claims (7)

A substrate and
an optical multilayer film provided on the substrate;
a matching layer provided on the optical multilayer film;
an absorbing layer provided on the matching layer and having a transparent base containing a near-infrared absorbing component;
The matching layer suppresses intensity fluctuations in transmittance caused by the absorption layer,
The matching layer is
It is composed of a three- layer laminated film in which a high refractive index film having a high refractive index and a low refractive index film having a lower refractive index than the high refractive index film are laminated alternately , and the wavelength of the high refractive index film is 500 nm. The refractive index at a wavelength of 500 nm of the low refractive index film is less than 1.6, and when the designed center wavelength of the optical multilayer film is set as the center wavelength. , where the QWOT of the high refractive index film is QH _and the QWOT of the low refractive index film is _QL , the matching layer is composed of three layers (aQ _L bQ _H cQ _L ) from the substrate side. , a and c are 0.2 or more and less than 0.5, b is 0.07 or more and less than 0.5, and b<a,
Or, it is composed of a single layer of a medium refractive index film , and the refractive index of the medium refractive index film at a wavelength of 500 nm is 1.6 or more and less than 1.8.
An optical filter characterized by: The optical system according to claim 1 , further comprising an auxiliary matching layer provided on the absorption layer and suppressing incident light in a visible wavelength band from being reflected by the absorption layer. filter. The optical filter according to claim 1, wherein the absorption layer has a thickness of 100 nm or more and 5000 nm or less . 4. The optical filter according to claim 1 , wherein the substrate is one of white plate glass, blue glass, and resin. 5. The optical filter according to claim 1, wherein the optical multilayer film has an average transmittance of 80 % or more for light in the visible wavelength range and an average transmittance of 10% or less for light in the near-infrared wavelength range. A near - infrared cut filter comprising the optical filter according to claim 1 . An imaging device comprising the optical filter according to any one of claims 1 to 5 .

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