CN111381303B - Optical filter and near infrared cut-off filter - Google Patents
Optical filter and near infrared cut-off filter Download PDFInfo
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- CN111381303B CN111381303B CN201911349317.5A CN201911349317A CN111381303B CN 111381303 B CN111381303 B CN 111381303B CN 201911349317 A CN201911349317 A CN 201911349317A CN 111381303 B CN111381303 B CN 111381303B
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Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/28—Interference filters
- G02B5/281—Interference filters designed for the infrared light
- G02B5/282—Interference filters designed for the infrared light reflecting for infrared and transparent for visible light, e.g. heat reflectors, laser protection
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/208—Filters for use with infrared or ultraviolet radiation, e.g. for separating visible light from infrared and/or ultraviolet radiation
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B5/00—Optical elements other than lenses
- G02B5/20—Filters
- G02B5/22—Absorbing filters
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Optics & Photonics (AREA)
- Health & Medical Sciences (AREA)
- Toxicology (AREA)
- Optical Filters (AREA)
- Surface Treatment Of Optical Elements (AREA)
Abstract
The invention provides a filter with excellent optical characteristics and a near infrared cut filter. The optical filter (16) is provided with a substrate (20), an optical multilayer film (22) provided on the substrate (20), an integration layer (24) provided on the optical multilayer film (22), and an absorption layer (26) provided on the integration layer (24) and having a transparent matrix containing an infrared absorption component. The integration layer (24) suppresses intensity fluctuations in transmittance caused by the absorption layer (26).
Description
Technical Field
The present invention relates to a filter used in an optical device. In particular, the present invention relates to a near infrared cut filter which can be used as a visibility correction filter for a solid-state imaging element such as a CCD (Charge Coupled Device: charge coupled device) and CMOS (Complementary Metal Oxide Semiconductor: complementary metal oxide semiconductor) used in a digital still camera and a video camera.
Background
The spectral sensitivity of a solid-state imaging device such as a CCD or CMOS used in a digital still camera or video camera has a characteristic of having a higher sensitivity to light in the near infrared region than the human visibility characteristic. Then, a visibility correction filter that can match the spectral sensitivity of these solid-state imaging elements with the human visibility characteristic is generally used.
As such a visibility correction filter, patent document 1 discloses a near infrared ray cut filter glass in which Cu 2+ ions are present in glass such as fluorophosphate glass or phosphate glass, and the spectral characteristics are adjusted.
Further, a near infrared ray cut filter is known: in order to accurately determine and sharpen the transmitted wavelength range, an optical multilayer film in which a plurality of high refractive index layers and low refractive index layers are alternately laminated is provided on the surface of the near infrared cut filter glass, and has excellent characteristics of transmitting the wavelength (400 to 600 nm) in the visible light range efficiently and sharply cutting off the wavelength (700 nm) in the near infrared range (for example, refer to patent document 2). In addition, in order to suppress reflection on the surface of the glass substrate and to improve transmittance, an antireflection film may be provided on the surface of the near infrared cut filter glass.
In the case of a near infrared cut filter, for example, an optical multilayer film is formed by alternately laminating a high refractive index layer made of titanium oxide, tantalum oxide, niobium oxide, or the like and a low refractive index layer made of silicon oxide or the like on a glass substrate, and light is selectively transmitted by interference of light by appropriately selecting constituent materials, thicknesses, the number of layers, or the like of the high refractive index layer and the low refractive index layer.
As a near infrared cut filter having high transparency in the visible light range and excellent blocking performance in the near infrared range, a filter in which a resin absorbing layer containing a pigment or pigment that absorbs infrared rays and an optical multilayer film are provided on a substrate has been proposed (for example, see patent documents 3 and 4).
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open No. H06-16451
Patent document 2: japanese patent laid-open No. Hei 02-213803
Patent document 3: japanese patent laid-open No. 2006-301489
Patent document 4: international publication No. 2014/030628
Disclosure of Invention
Technical problem to be solved by the invention
The filters described in patent documents 3 and 4 have excellent optical characteristics. However, the present inventors have found that the structure in which the resin layer is provided on the optical multilayer film may adversely affect the optical characteristics. In the case of providing a resin layer on a substrate or an optical multilayer film, a wet coating method such as spin coating, dip coating, printing, or the like is generally used. The resin layer formed by these manufacturing methods has a thickness much larger than that of the optical multilayer film, but most of the resin layers are layers having optical interference characteristics by having a film thickness of several tens of micrometers or less, particularly several micrometers or less, near the wavelength of light. In this case, when the resin layer is formed on the optical multilayer film, there is a possibility that unexpected influence may be exerted on the optical characteristics. That is, when compared with the film thickness accuracy of the optical multilayer film, the uniformity of the film thickness and the variation between batches of the resin layer formed by the wet coating method are large, and particularly when such a resin layer is present on the optical multilayer film, it is found that the designed optical characteristics may be greatly deteriorated by the presence of the resin layer due to the interference of the optical multilayer film. In addition, when the film thickness of the resin layer is to be changed in order to obtain desired optical characteristics, there is a problem in that the optical multilayer film needs to be redesigned every time, and the degree of freedom in design is small.
The present invention has been made in view of the above-described problems, and an object thereof is to provide a filter having excellent optical characteristics and a near infrared cut filter.
Technical proposal adopted for solving the technical problems
In order to solve the above technical problems and achieve the object, an optical filter of the present disclosure includes: the optical multilayer film comprises a substrate, an optical multilayer film provided on the substrate, an integration layer provided on the optical multilayer film, and an absorption layer provided on the integration layer and having a transparent base containing a near infrared ray absorption component, wherein the integration layer suppresses intensity fluctuation of transmittance caused by the absorption layer.
The integration layer is preferably composed of a plurality of high refractive index films having a high refractive index and a low refractive index film having a lower refractive index than the high refractive index films, or is preferably composed of a single layer of a medium refractive index film, wherein the high refractive index film has a refractive index of 1.8 or more at a wavelength of 500nm, the low refractive index film has a refractive index of less than 1.6 at a wavelength of 500nm, and 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.
When the center wavelength of the optical multilayer film is designed as the center wavelength, the integration layer is formed of three layers of (aQ LbQHcQL) 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 is preferable when the QWOT of the high refractive index film is Q H and the QWOT of the low refractive index film is Q L.
Preferably, the light-absorbing layer further includes an auxiliary integration layer provided on the absorption layer and suppressing reflection of light in a wavelength band of an incident visible light region by the absorption layer.
The thickness of the absorption layer is preferably 100nm to 5000 nm.
The substrate is preferably any one of white glass, blue glass, and resin.
The optical multilayer film preferably has an average transmittance of 80% or more in a wavelength band of visible light and an average transmittance of 10% or less in a wavelength band of near infrared light.
In order to solve the above-described technical problems and achieve the object, the near infrared cut filter of the present disclosure preferably has the above-described filter.
Effects of the invention
According to the present invention, a filter having excellent optical characteristics and a near infrared cut filter can be provided.
Drawings
Fig. 1 is a schematic cross-sectional view of an image pickup apparatus of the present embodiment.
Fig. 2 is a schematic cross-sectional view of the filter of the present embodiment.
Fig. 3 is a schematic diagram showing an example of a state of reflected light.
Fig. 4 is a graph showing the transmittance values of the respective film thicknesses of example 1.
Fig. 5 is a graph showing the transmittance values of the respective film thicknesses of comparative example 1.
Fig. 6 is a graph showing the transmittance values of the respective film thicknesses of example 2.
Fig. 7 is a graph showing the transmittance values of the respective film thicknesses of example 3.
Fig. 8 is a graph showing the transmittance values of the respective film thicknesses of comparative example 2.
Symbol description
10. Image pickup apparatus
16. Optical filter
18. Image pickup device
20. Substrate board
22. Optical multilayer film
24. Integration layer
26. Absorbent layer
28. Auxiliary integration layer
30. A back layer.
Detailed Description
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiment, and, in the case where there are a plurality of embodiments, the invention is also included in which the embodiments are combined.
Fig. 1 is a schematic cross-sectional view of an image pickup apparatus of the present embodiment. As shown in fig. 1, the imaging device 10 of the present embodiment includes a housing 12, a lens 14, a filter 16, and an imaging element 18. The housing 12 is a member for holding the lens 14, the filter 16, and the image pickup element 18. The lens 14, the filter 16, and the image pickup device 18 are disposed in this order in the housing 12 from the side where the light L is incident. The light L incident from the lens 14 is incident on the image pickup element 18 through the filter 16. The filter 16 blocks light in a predetermined wavelength band among the light L incident from the lens 14, transmits light in an unblocked wavelength band, and makes the light incident on the image pickup element 18. In the present embodiment, the filter 16 functions as a near infrared cut filter that transmits light in the wavelength band of the visible light range and blocks light in the wavelength band of the near infrared range. The image pickup device 18 converts light incident through the filter 16 into an electrical signal and outputs the electrical signal as an image signal. By obtaining the image signal in this way, the imaging device 10 images the subject. The image pickup device 18 is a solid-state image pickup device such as a CCD (charge coupled device) or a CMOS (complementary metal oxide semiconductor). The configuration of the image pickup device 10 in fig. 1 is an example, and the image pickup device 10 may be configured so that light L incident from a lens is incident on the image pickup element 18 through the filter 16.
Fig. 2 is a schematic cross-sectional view of the filter of the present embodiment. As shown in fig. 2, the filter 16 has a substrate 20, an optical multilayer film 22, an integration layer 24, an absorption layer 26, an auxiliary integration layer 28, and a back layer 30. An optical multilayer film 22 is disposed on the surface 20a of the substrate 20. The surface 20a may also be referred to as one main surface of the substrate 20. The integration layer 24 is disposed on the surface 22a of the optical multilayer 22. The surface 22a is a surface of the optical multilayer 22 opposite to the substrate 20, and may be alternatively referred to as one main surface of the optical multilayer 22. The absorbent layer 26 is disposed on the surface 24a of the conforming layer 24. The surface 24a is a surface of the integration layer 24 on the opposite side of the optical multilayer film 22, and may also be referred to as one main surface of the integration layer 24. The auxiliary integration layer 28 is disposed on the surface 26a of the absorbent layer 26. The surface 26a is a surface of the absorbent layer 26 on the opposite side of the integration layer 24, and may be referred to as the one main surface of the absorbent layer 26. The auxiliary integration layer 28 is not laminated with other layers on the surface 28a on the opposite side to the absorbent layer 26, so to speak, exposed to the outside. That is, the surface 28a of the auxiliary integration layer 28 can be said to be the air-side surface that is in contact with air. The surface 28a may also be referred to as one major surface of the auxiliary integration layer 28.
The back layer 30 is disposed on the surface 20b of the substrate 20. The surface 20b is the surface opposite to the surface 20a, and may be referred to as the other main surface of the substrate 20. In addition, in the case where the surface of the back surface layer 30 on the opposite side from the substrate 20 is denoted as 30a, the surface may be referred to as an air-side surface that contacts air.
As shown in fig. 1 and 2, the filter 16 is provided on the image pickup device 10 in such a condition that the auxiliary integration layer 28 of the auxiliary integration layer 28 and the back surface layer 30 becomes the incident light L side (lens 14 side). That is, in the filter 16, the auxiliary integration layer 28, the absorption layer 26, the integration layer 24, the optical multilayer film 22, the substrate 20, and the back surface layer 30 are laminated in this order from the incident side of the light L. The filter 16 may be disposed so that the back surface layer 30 faces the incident light L side (the lens 14 side). If the filter 16 is disposed in this manner, when a pigment or pigment having the absorption property of near infrared rays is contained in the absorption layer 26, the influence of internal scattered light reflected on the surface of the image pickup element 18 can be more effectively suppressed.
The layers in the filter 16 are laminated in the above order. The structure of each layer of the filter 16 will be specifically described below.
(Substrate)
The substrate 20 is a plate-like member that transmits light in a wavelength band in the visible light range. The wavelength band in the visible light region generally represents light of 380nm or more and 780nm or less in many cases, but when a filter is used as a visibility correction filter for a solid-state imaging element, for example, 420nm to 650nm (that is, 420nm or more and 650nm or less) is often regarded as the visible light region, and 700nm or more and 400nm or less are regarded as near infrared light and ultraviolet light, respectively, and are the blocking targets. This is because the visibility of the eyes of a person is different from the wavelength dependence of the visibility of the solid-state imaging element and is determined by a method of color reproduction when an image is formed using them, and thus cannot always be uniquely determined. Therefore, for reference, for example, as a filter for use as a visibility correction filter, it is desirable that the transmittance of a green region (usually between 500nm and 560 nm) which is most important in terms of image formation is 80% or more.
The substrate 20 preferably has low transmittance of light in a wavelength band of the near infrared region. The wavelength band in the near infrared region generally means light of 750nm to 1.4 μm, but in the present specification means 700nm to 1000nm. As described above, the sensitivity characteristics of the solid-state imaging device, particularly the visibility characteristics of 700nm or more, are larger than those of the human eye. Therefore, in the case where the filter 16 is used as the visibility correction filter, a blue filter that transmits visible light and absorbs near infrared light is preferably used as the substrate. In this case, the average transmittance of the substrate 20 in the wavelength range of 700nm to 1000nm is preferably 20% or less. However, when the transmittance at a wavelength of 700 to 1000nm is low, the transmittance of visible light tends to be low, so that an optical multilayer film such as an infrared cut filter described below is often used together in many cases.
The substrate 20 is preferably glass or resin. Strength for supporting an optical multilayer film, an absorbing layer, or the like is required for the substrate 20, and glass generally has strength and excellent weather resistance required for them, and is therefore preferable; as the resin, cycloolefin resins and the like which are relatively excellent in strength, transparency and weather resistance are preferable. When a resin is used as the substrate 20, the resin itself may contain a dye or the like contained in an absorbing layer described below.
In the case where the substrate 20 is made of glass, it is preferable to use white glass or blue glass as the glass. As the white plate glass, silicate glass having high transparency is often used, and borosilicate glass having a low content of alkali component is more preferable from the viewpoint of weather resistance. In addition, glass having a small content of iron components and the like that cause a decrease in the transmittance of visible light and a negative effect is also preferable. Blue glass is glass having a wide absorption characteristic in a wavelength region of a near infrared region. Specifically, copper-containing fluorophosphate glass is preferable because it has good weather resistance, high visible light transmittance, and near infrared light absorption. In addition, copper-containing phosphate glass based on phosphate glass containing no fluorine component is preferable because it has high near infrared light absorption.
The fluorophosphate glass is preferably, for example, the following glass: expressed as cation%, contains 25 to 50% P 5+, 5 to 20% Al 3+, 20 to 40% R + (wherein R + represents the total amount of Li +、Na+ and K +), 10 to 30% R '2+ (wherein R' 2+ represents the total amount of Mg 2+、Ca2+、Sr2+、Ba2+ and Zn 2+), 0.1 to 15% Cu 2+, 0 to 1% of Sb 3+, and 30 to 90% of O 2- and 10 to 70% of F - are expressed as anion%. The fluorophosphate glass having the above composition is excellent in weather resistance, and the near infrared cut filter glass has suitable spectral characteristics by containing a copper component. In addition to the above-described composition, for example, the fluorophosphate glass may be a glass described in the composition range or 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 is preferably, for example, the following glass: expressed in mole%, contains 50 to 75% P 2O5, 5 to 22% Al 2O3, 0.5 to 20% R 2 O (where R 2 O represents the total amount of Li 2O、Na2 O and K 2 O), 0.1 to 25% R 'O (where R' O represents the total amount of MgO, caO, srO, baO and ZnO), and 0.1 to 15% CuO. The phosphate glass having the above composition has high near infrared absorption capacity and has suitable spectral characteristics. In addition to the above-described composition glasses, for example, the composition ranges and examples disclosed in japanese patent application laid-open publication No. 2010-8908, japanese patent application laid-open publication No. 2011-121792, japanese patent application laid-open publication No. 2012-224491, and japanese patent application laid-open publication No. 2015-13773 can be used as phosphate glass.
In order to obtain the glass substrate 20, glass raw materials are prepared and melted under the conditions for forming the desired glass composition as described above, and then the melted glass is molded. Next, after the glass substrate is manufactured by forming a predetermined size and processing the outer shape, the surface of the glass substrate is polished, and then polished (precision polishing) to obtain the substrate 20. In order to obtain the optical filter 16, an optical multilayer film 22, an integration layer 24, an absorption layer 26, and an auxiliary integration layer 28 are sequentially formed on the surface 20a of the substrate 20 thus obtained, and a back surface layer 30 is formed on the surface 20b of the substrate 20. Next, cutting is performed by a known method (scribing, cutting, laser cutting, etc.) so as to form a predetermined product size.
The thickness of the substrate 20 is preferably 0.3mm or less, more preferably 0.22mm or less, further preferably 0.18mm or less, and most preferably 0.15mm or less, from the viewpoint of thinning the filter 16. In addition, from the viewpoint of suppressing the processing cost and suppressing the decrease in strength, the thickness of the substrate 20 is preferably 0.025mm or more, more preferably 0.03mm or more, and still more preferably 0.05mm or more.
(Optical multilayer film)
The optical multilayer film 22 is a layer having predetermined optical characteristics, and in the present embodiment, is configured to transmit light in a wavelength band in the visible light region and to suppress transmission of light in a wavelength band in the near infrared region. For example, the optical multilayer film 22 can suppress light transmission of wavelengths in the near infrared region by reflecting light of wavelengths in the near infrared region. That is, the optical multilayer film 22 is an infrared shielding film (InfraRed Cut Filter film, also referred to as IRCF film). The optical multilayer film 22 preferably has an average transmittance of light in a wavelength band of the visible light region of 80% or more and 100% or less. The optical multilayer film 22 preferably has an average transmittance of light having a wavelength in the near infrared region of 10% or less and 0% or more.
As the optical multilayer film 22 having such a function, for example, a laminated film obtained by laminating films having different refractive indexes can be used. The optical multilayer film 22 is configured in such a manner that light having a wavelength in the near infrared region is reflected by interference of light, and light having a wavelength range in the visible region is transmitted. The optical multilayer film 22 is configured by alternately disposing a plurality of high refractive index films 22A and low refractive index films 22B having a lower refractive index than the high refractive index films 22A, for example. As the high refractive index film 22A, for example, at least 1 kind of metal oxide film selected from ZrO 2、Nb2O5、TiO2 and Ta 2O5, or the like can be used. As the low refractive index film 22B, for example, siO 2 or the like can be used. The film thicknesses and the number of layers of the high refractive index film 22A and the low refractive index film 22B can be appropriately set according to the optical characteristics required for the optical multilayer film 22.
The optical multilayer film 22 may be formed on the surface 20a of the substrate 20 by using a sputtering method or an ion-assisted evaporation method. The film formed by the sputtering method or the ion-assisted vapor deposition method has the following advantages over the film formed by the vapor deposition method without using the ion assist: a drift-free (non-shift) film having very little change in spectral characteristics at high temperature and high humidity and substantially no spectral change can be realized. Further, the film formed by these methods is dense and has high hardness, so that it is not easily damaged, and the workability in the component mounting process and the like is also excellent. Therefore, the method is suitable for forming an optical multilayer film used as a near infrared cut filter of a sensitivity correction filter of an image pickup device.
The optical multilayer film 22 may be formed by a vacuum vapor deposition method without ion assist. In the case of using this vapor deposition method, the device cost is low, and the manufacturing cost can be suppressed. In addition, when the optical multilayer film 22 is formed, a film with less adhesion of foreign matter or the like can be obtained. That is, the method of forming the optical multilayer film 22 is not limited to the sputtering method, the ion-assisted vapor deposition method, or the like, and may be any method.
(Absorption layer)
Before the description of the integration layer 24, the absorption layer 26 is described. The absorbing layer 26 is a layer composed of a transparent substrate containing a near infrared ray absorbing component. "transparent" of the transparent substrate means having transparency to light in a wavelength band of the visible light region.
The transparent matrix of the absorber layer 26 is preferably a resin or an inorganic material. In the case where the transparent substrate is a resin, examples of the resin include an acrylic resin, an epoxy resin, an alkylene thiol resin, a polycarbonate resin, a polyester resin, a polyacrylate resin, a polysulfone resin, a polyether sulfone resin, a polyparaphenylene resin, a polyester resin, a polyimide resin, a polyamideimide resin, a polyolefin resin, and a cyclic olefin resin. In particular, the resin having a high glass transition temperature (Tg) is preferably 1 or more selected from polyester resins, polycarbonate resins, polyethersulfone resins, polyacrylate resins, polyimide resins, and epoxy resins. The resin used as the transparent substrate is more preferably 1 or more selected from polyester resins and polyimide resins, and particularly preferably polyimide resins. As the polyester resin, polyethylene terephthalate resin, polyethylene naphthalate resin, and the like are preferable. In the case where the transparent substrate of the absorption layer 26 is an inorganic material, for example, a silicon oxide film is preferable as the inorganic material.
The near-infrared ray absorbing component contained in the absorbing layer 26 is made of an absorber capable of absorbing light in a wavelength band in the near-infrared region. The absorbing layer 26 is formed by uniformly dissolving or dispersing an absorber in a transparent substrate, and has a structure in which a near infrared absorbing component is contained in the transparent substrate, so that light in a wavelength band in the visible light region is transmitted and light in a wavelength band in the near infrared region is absorbed. The absorption maximum wavelength of the absorbent when the absorbent is dissolved or dispersed in the transparent substrate is preferably 600nm or more and 1200nm or less, more preferably 600nm or more and 1000nm or less, and most preferably 600nm or more and 850nm or less. The absorber may be a pigment that absorbs light of a wavelength in the near infrared region. When the dye is referred to as dye (A), examples of the dye (A) include diimmonium, cyanine, phthalocyanine, naphthalocyanine, dithiol metal complexes, azo, ammonium, polymethine, phthalein, naphthoquinone, anthraquinone, indophenol, pyranClass, thiopyran/>Class, squaric acid/>Pigments such as, for example, ketone acids, tetradehydrocholines (Japanese TECHO コ), triphenylmethane, and ammonium. The absorber may be, for example, an inorganic pigment that absorbs light having a wavelength in the near infrared region. Examples of the inorganic pigment include near infrared absorbing particles or fine particles of tungsten-containing oxide, which contain crystallites of a 1/nCuPO4 (wherein a is 1 or more selected from alkali metals (Li, na, K, rb, cs), alkaline earth metals (Mg, ca, sr, ba) and NH 4, n is 1 when a is an alkali metal or NH 4, and 2 when a is an alkaline earth metal).
In the case where the transparent substrate of the absorption layer 26 is a resin, the transparent substrate in which the absorbent is uniformly dissolved or dispersed is coated on the surface 24a of the integration layer 24 by a coating method such as spin coating or dip coating (dipping), and the transparent substrate is cured by heat, ultraviolet light, or the like, thereby forming the absorption layer 26. In the case where the transparent substrate of the absorption layer 26 is an inorganic material, the absorption layer 26 is formed by, for example, a sol-gel method. That is, the absorbent is uniformly dissolved or dispersed in a solution that is a raw material of the transparent substrate, and the solution is applied to the surface 24a of the integration layer 24 to cause the solution to be gelled, thereby forming the absorbent layer 26.
In the present embodiment, the absorbent layer 26 is a single layer, but may be formed of multiple layers. When the absorption layer 26 is formed of a single layer or a plurality of layers, the thickness is preferably 100nm or more and 5000nm or less. By setting the thickness to 5000nm or less, the optical characteristics of the absorption layer 26 can be reduced to a degree that is not excessively large due to uneven film thickness. Further, by setting the thickness to 100nm or more, the absorption capacity of the absorption layer 26, that is, the extinction coefficient, can be suppressed from becoming excessively high, the rapid increase in refractive index can be suppressed, and the influence of the ripple can be suppressed from becoming large. In addition, when the thickness is less than 100nm, it is difficult to form a film by coating or the like, and if characteristics such as near infrared absorption are taken into consideration, the extinction coefficient k increases and the refractive index n value increases, so that there is a possibility that there is a disadvantage in the thin film design. In addition, when the thickness exceeds 5000nm, the total thickness of the optical filter increases, and the resin ratio having low weather resistance increases, which may cause deterioration in weather resistance, and thus is not preferable.
The absorbing layer 26 may contain an ultraviolet absorbing component. The ultraviolet absorbing component is composed of, for example, an ultraviolet absorber capable of absorbing light in a wavelength band of an ultraviolet region. The ultraviolet absorber is uniformly dissolved or dispersed in the transparent substrate, so that the ultraviolet absorbing component is contained in the absorbing layer 26. The ultraviolet absorber preferably has a maximum absorption wavelength of 360nm to 415nm when uniformly dissolved or dispersed in the transparent substrate. The ultraviolet absorber is, for example, a dye capable of absorbing light in a wavelength band of an ultraviolet region. When the pigment capable of absorbing light in the wavelength region of ultraviolet rays is referred to as a pigment (U), examples of the pigment (U) includeAzoles, merocyanines, cyanines, naphthalimides,/>Diazoles,/>Oxazines,/>Pigments such as oxazolidines, naphthalenedicarboxylic acids, styryl, anthracene, cyclic carbonyl, and triazole.
(Integration layer, auxiliary integration layer)
Since the description of the integration layer 24 and the auxiliary integration layer 28 is made at the same time to be understood easily, their roles are described below.
The integration layer 24 and the auxiliary integration layer 28 are each a ripple adjusting layer for suppressing the film thickness dependence of the absorption layer 26 as an interference film. As described elsewhere, the absorption layer 26 may have a film thickness that varies during the forming process or the like. The integration layer 24 suppresses the influence on the optical characteristics of the filter caused by the film thickness variation.
First, an idea of suppressing the variation in the transmittance intensity caused by the absorption layer 26 by the integration layer 24 will be described.
The respective components from the absorption layer 26 to the substrate 20 are constituted in the order of the substrate 20, the optical multilayer film 22, the integration layer 24, and the absorption layer 26. Here, when the absorption layer 26 is regarded as an incident medium, the order of the substrate 20, the optical multilayer film 22, the integration layer 24, and the incident medium (absorption layer 26) is changed, and for example, when the incident medium is air, the structure is the same as that of a very general optical film. The incident medium is considered to be a medium that theoretically exists indefinitely on the side where light is incident, at which point the concept of thickness does not exist. In addition, in the calculation regarding optical interference in general, since the incident medium is assumed to be infinitely thick, the extinction coefficient k value as the absorption characteristic is regarded as zero.
In the above-described configuration, in order to minimize the reflectance in the visible light region of the spectral waveform caused by the optical multilayer film 22 and to suppress the waviness of the waveform called reflection ripple, transmission ripple, or the like, a thin film called a ripple adjusting layer has been conventionally inserted on the incident medium side of the optical multilayer film 22, but the integration layer 24 functions in the same manner as the ripple adjusting layer. That is, the integration layer 24 is a ripple adjusting layer when the absorption layer 26 is an incident medium. The ripple adjustment described here is to suppress the variation in the intensity of the optical characteristics of the absorption layer 26 in the wavelength band of the visible light region due to the film thickness variation.
The standard of reflectance in the visible light region of the spectral waveform produced by the optical multilayer film 22 is preferably 2% or less, more preferably 1% or less. If the reflectance is such, intensity variation in spectral characteristics called ripple is also limited.
In addition, since the filter 16 in actual use is used in the atmosphere or under vacuum, the incidence angle adjusted so that the snell's law is satisfied is used as the incidence angle on the incidence medium side with respect to the incidence angle when air is used as the medium.
Similarly, the auxiliary integration layer 28 is a ripple adjusting layer for minimizing the reflectance in the visible light range and suppressing ripples of waveforms called reflection ripples and transmission ripples when the absorption layer 26 is regarded as a substrate and is formed as a substrate (absorption layer 26), the auxiliary integration layer 28, and the incident medium (air), but in the above case, only the auxiliary integration layer 28 is formed as a layer for minimizing the reflectance, and thus the minimum unit for this purpose is an antireflection film, and therefore the auxiliary integration layer 28 may be an antireflection film when the substrate (absorption layer 26), the auxiliary integration layer 28, and the incident medium (air) are formed. Of course, since the reflectance in the visible light range is minimum and the ripple can be suppressed, it is preferable to form an antireflection film having a structure of minimum film thickness and number of layers in view of the object of the present invention, even a band-pass filter such as an infrared cut filter or the like may be used.
The reflectance in the visible light range when the absorption layer 26 is regarded as a substrate, and is formed as a substrate (absorption layer 26), an auxiliary integration layer 28, and an incident medium (air) is preferably 2% or less, more preferably 1% or less. If this condition is used, the intensity variation in spectral characteristics called ripple is also limited.
For the substrate, the extinction coefficient k related to absorption can be calculated as zero in calculation concerning optical interference, and the thickness of the substrate can be regarded as infinite in optical interference. That is, the optical thin film has no film thickness dependence in the interference design of the optical thin film, as in the case of the incident medium.
In the filter 16, when the absorption layer 26 is used as a reference, the structure from the absorption layer 26 to the air side in fig. 1 may be designed by taking the absorption layer 26 as a substrate, and from the absorption layer 26 to the substrate 20 side may be designed by taking the absorption layer 26 as an incident medium. Therefore, even in a state where all the components (the substrate 20, the optical multilayer film 22, the integration layer 24, the absorption layer 26, the auxiliary integration layer 28, and air (incident medium)) are combined together, the film thickness dependence of the absorption layer 26 is very small, and as a result, even if the film thickness variation of the absorption layer 26 due to the coating process or the like is large, adverse effects as an optical interference film can be suppressed. In a state where all the above components are combined, the integration layer 24 is preferably a three-layer structure or a single-layer intermediate refractive index film described below in order to maintain the state of minimizing the reflectance and ripple in the visible light region.
In addition, if the structure is designed in this way, even if the auxiliary integration layer is not provided, the effect of suppressing the influence on the optical characteristics of the filter caused by the film thickness variation of the absorption layer 26, which is the object of the present invention, can be obtained. This is because the absorption layer 26 is a resin layer, so its surface reflectance is small, but in order to obtain better optical characteristics, an auxiliary integration layer needs to be present.
In the present embodiment, the integration layer 24 is a laminated film including three or more layers of alternately laminated high refractive index films 24A and low refractive index films 24B. As described above, the integration layer 24 functions as a ripple adjusting layer of the optical multilayer film 22, and thus the film thickness depends on the composition of the optical multilayer film 22. Considering the main use of the filter 16, the optical multilayer 22 is an infrared cut filter, for example. In general, the optical design of these optical multilayer films 22 is basically constructed in a repetition of (HL) ≡n when the optical film thickness QWOT of the high refractive index film is denoted as H and the optical film thickness QWOT of the low refractive index film is denoted as L. Further, (HL)/(n) represents a structure in which the high refractive index film 24A and the low refractive index film 24B are repeated n times in this order. In this case, the optical film thicknesses of the high refractive index films 24A to be laminated may be different. In this regard, the same applies to the low refractive index film 24B. The integration layer 24 is required to be composed of a thin film of optical film thickness (HL) n, which is closer to the integration layer 24 than the basic repetition configuration (HL) n, more preferably, of the three layers of (aQ LbQHcQL) described below, of the repetition configurations of the optical multilayer film 22. The film material of the integration layer 24 thus constituted is preferably the same as that of the optical multilayer film 22 in terms of production, but the film material need not be the same as that of the optical multilayer film as long as the above conditions are satisfied.
In addition to the above, the integration layer 24 may be formed of an intermediate refractive index film, and in this case, the number of film layers can be reduced. Based on the concept of an equivalent film, the intermediate refractive index film can be represented by a three-layer structure of a thinner high refractive index film and low refractive index film because it can exhibit optical characteristics close to those of the integration layer 24 constituted by the three layers described above. However, since the equivalent film conditions are different from those in the three-layer structure described above, the performance is slightly inferior, but the characteristics as the integration layer 24 can be exhibited at a level that is not problematic in practical use.
The refractive index of the high refractive index film at a wavelength of 500nm is 1.8 or more and 3 or less, the refractive index of the low refractive index film at a wavelength of 500nm 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 500nm is preferably 1.6 or more and less than 1.8. The present invention is premised on the placement of the absorber layer 26 on the optical multilayer film 22, so that the basic optical properties of the filter 16 as an interference multilayer film are determined by the optical multilayer film 22. The film material and refractive index of the integration layer 24 depend on the optical multilayer film 22, and thus the above-described range of refractive indices is also applicable to the optical multilayer film 22, and the above-described specification of refractive index depends on, for example, manufacturing conditions required for manufacturing an infrared cut filter.
The composition of the integration layer 24 is described in more detail. As previously described, the integration layer 24 functions as a ripple adjusting layer under specific conditions with respect to the optical multilayer film 22. Thus, the center wavelength of QWOT (Quarter-wave Optical Thickness: quarter-wave optical thickness) in the optical film thickness is determined by taking the center wavelength on the basis of the film design in the optical multilayer film 22. Specifically, in the case where the optical multilayer film 22 is an infrared cut filter, the center wavelength of the wavelength band cut by the infrared cut filter is the center wavelength of the QWOT of the integration layer 24. When the number of wavelength bands cut by the infrared cut filter is plural, the center wavelength of the wavelength band located near the integration layer 24 is selected. In addition, the center wavelength of QWOT of the integration layer 24 is preferably 700nm to 1400nm.
Here, QWOT (Quarter-wave Optical Thickness: quarter-wave optical thickness) of the high refractive index film 24A is denoted as Q H, and QWOT of the low refractive index film 24B is denoted as Q L. In this case, the integration layer 24 is preferably composed of three layers of (aQ LbQHcQL) from the substrate 20 side (optical multilayer film 22 side) toward the absorption layer 26 side. Here, a, b, and c are coefficients of the respective basic units, and the physical film thickness of the film of each basic unit is expressed as how many times QWOT. Thus, aQ L、bQH、cQL refers to the optical film thickness of each film. That is, the film of the integration layer 24 closest to the substrate 20 side (optical multilayer film 22 side) is a low refractive index film 24B, and the optical film thickness thereof is aQ L. Next, in the integration layer 24, the film on the absorption layer 26 side of the low refractive index film 24B closest to the substrate 20 side is the high refractive index film 24A, and the optical film thickness thereof is bQ H. In the integration 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 the optical film thickness thereof is cQ L. In the present embodiment, the integration layer 24 is configured of three layers, and therefore 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 side. The refractive indices a, B, and c of the integration layer 24 formed of three layers of (aQ LbQHcQL) are calculated by 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, it is preferable that 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. By setting a, b, and c within such a numerical range, the integration layer 24 contributes to suppression of reflectance and ripple in the visible light range by suppressing the film thickness dependence of the absorption layer 26.
However, if the integration layer 24 is configured to suppress interference of light in the wavelength band of the visible light region caused by the absorption layer 26, the optical film thicknesses of the high refractive index film 24A and the low refractive index film 24B may not have the above-described relationship even if 1 high refractive index film 24A is not provided between 2 low refractive index films 24B. For example, the integration layer 24 may be a three-layer structure in which 1 low refractive index film 24B is provided between 2 high refractive index films 24A. The integration layer 24 may be, for example, a total of 4 or more layers of high refractive index films 24A and low refractive index films 24B alternately stacked, or a total of 2 layers may be stacked. The integration layer 24 may be formed of 1 layer having a predetermined refractive index (i.e., intermediate refractive index), that is, a single layer of the intermediate 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.
Furthermore, the integration layer 24 is preferably composed of: the substrate 20, the optical multilayer film 22, the integration layer 24, the absorption layer 26, and the auxiliary integration layer 28 are laminated in this order, and when the auxiliary integration layer 28 is exposed to air, generation of a ripple in a wavelength band of a visible light region of light incident to the auxiliary integration layer 28 from the air side and transmitted through the substrate 20 can be suppressed.
In addition, as the high refractive index film 24A, for example, at least 1 kind of metal oxide film selected from ZrO 2、Nb2O5、TiO2 and Ta 2O5, and the like can be used. Further, as the low refractive index film 24B, for example, siO 2 or the like can be used. The high refractive index film 24A is preferably 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 the same material as the low refractive index film 22B of the optical multilayer film 22. Lamination can be easily performed by using the same material. But the high refractive index film 24A and the high refractive index film 22A may be different materials, and the low refractive index film 24B and the low refractive index film 22B may be different materials.
The integration layer 24 may be formed on the surface 22a of the optical multilayer film 22 by the same method as the formation of the optical multilayer film 22. That is, the integration layer 24 may be formed using, for example, a sputtering method, an ion-assisted vapor deposition method, a vacuum vapor deposition method, or the like.
(Auxiliary integration layer)
The auxiliary integration layer 28 is a layer that suppresses reflection of light of a wavelength band incident to the auxiliary integration layer 28 by the absorption layer 26 (interface of the auxiliary integration layer 28 and the absorption layer 26). That is, the auxiliary integration layer 28 is an antireflection film (also referred to as an Anti-Reflection film or an AR film) having an antireflection function. In the present embodiment, the auxiliary integration layer 28 is an optical multilayer film formed by laminating a plurality of films having different refractive indices. That is, for example, a laminated film in which a plurality of high refractive index films and low refractive index films having a lower refractive index than the high refractive index films are alternately arranged may be used as the auxiliary integration layer 28. As the high refractive index film, for example, at least 1 kind of metal oxide film selected from ZrO 2、Nb2O5、TiO2 and Ta 2O5, and the like can be used. As the low refractive index film, for example, siO 2 or the like can be used. The film thickness or the number of layers of the high refractive index film and the low refractive index film can be appropriately set according to the optical characteristics required for the auxiliary integration layer 28. The auxiliary integration layer 28 may also be formed on the surface 26a of the absorption layer 26 by the same method as the formation of the optical multilayer film 22. That is, the auxiliary integration layer 28 may be formed using, for example, a sputtering method, an ion-assisted vapor deposition method, a vacuum vapor deposition method, or the like. The auxiliary integration layer 28 is not limited to such a multilayer film, and may be formed of a single layer, or may be an infrared cut filter, an ultraviolet cut filter, or the like if it has an antireflection function. In addition, the filter 16 may not be provided with the auxiliary integration layer 28.
(Back layer)
The back layer 30 is provided to complement the optical characteristics of the optical filter 16, and the optical filter 16 includes a substrate 20, and an optical multilayer film 22, an integration layer 24, an absorption layer 26, and an auxiliary integration layer 28 provided on the substrate 20. Accordingly, the back layer 30 may have the same structure as the optical multilayer film 22, the integration layer 24, the absorption layer 26, and the auxiliary integration layer 28, may be composed of only the optical multilayer film, or may not be provided with the back layer 30. When the filter 16 is used as a filter for an imaging device, an infrared cut filter or an antireflection film is assumed as the back surface layer 30. In the case where the back surface layer 30 is made of an optical multilayer film, for example, a laminated film in which a plurality of high refractive index films and low refractive index films having lower refractive index than the high refractive index films are alternately arranged may be used. As the high refractive index film, for example, at least 1 kind of metal oxide film selected from ZrO 2、Nb2O5、TiO2 and Ta 2O5, and the like can be used. As the low refractive index film, for example, siO 2 or the like can be used. The film thickness or the number of layers of the high refractive index film and the low refractive index film can be appropriately set according to the optical characteristics required for the back surface layer 30. The back layer 30 may also be formed on the surface 20b of the substrate 20 by the same method as the formation of the optical multilayer film 22. That is, the back surface layer 30 may be formed using, for example, a sputtering method, an ion-assisted vapor deposition method, a vacuum vapor deposition method, or the like. The back surface layer 30 is not limited to such a multilayer film as long as it has an antireflection function, and may be formed of a single layer.
The filter 16 has the above-described structure. Fig. 3 is a schematic diagram showing an example of a state of reflected light. Fig. 3 shows the difference between the state of the reflected light of the filter 16x of the comparative example and the state of the reflected light of the filter 16 of the present embodiment. As shown in fig. 3, the filter 16x of the comparative example is laminated in the order of the substrate 20x, the absorption layer 26x, and the optical multilayer film 22 x. That is, in the comparative example, the optical multilayer film 22x is located closer to the incident light L1x side than the absorption layer 26 x. In this case, light of an unnecessary wavelength among the incident light L1x is reflected as reflected light L2x at the surface of the optical multilayer film 22 x. The reflected light L2x may be incident on the filter 16x again because it is present as stray light in the housing of the imaging device, for example. At this time, if the stray light is incident on the filter 16X at a wide angle, the stray light cannot be reflected due to the oblique incidence characteristic of the optical multilayer film 22X, and may pass through the filter 16X and reach the image pickup element. In this case, the light is recognized as noise in the captured image, which may cause degradation in the image quality of the captured image.
On the other hand, the absorption layer 26 of the filter 16 of the present embodiment is located closer to the incident light L1 side than the optical multilayer film 22. In fig. 3, the auxiliary integration layer 28 and the back surface layer 30 are omitted for convenience of explanation. As shown in fig. 3, the incident light L1 entering the filter 16 enters the absorption layer 26, and light of an unnecessary wavelength in the incident light L1 is absorbed by the absorption layer 26. In addition, light of an undesired wavelength that is not absorbed by the absorption layer 26 is reflected at the surface of the optical multilayer film 22. The light reflected on the surface of the optical multilayer film 22 is again incident on the absorption layer 26, is absorbed by the absorption layer 26, and only the light not absorbed by the absorption layer 26 is emitted as reflected light L2 into the housing of the image pickup device. That is, the reflected light L2 passes through the absorption layer 26 twice, and thus is absorbed in the transmission twice, the intensity of which is lower than that of the reflected light L2 x. Therefore, according to the filter 16 of the present embodiment, even if stray light reaches the image pickup device, the intensity of the stray light is reduced, so that the influence on the picked-up image is reduced, and the degradation of the image quality of the picked-up image is suppressed. That is, the filter 16 of the present embodiment suppresses a decrease in optical characteristics by decreasing the intensity of stray light.
However, when the absorption layer 26 is disposed closer to the incident light L1 than the optical multilayer film 22, as described above, the ripple of the transmittance of the optical multilayer film 22 becomes remarkable, and there is a possibility that the optical characteristics of the optical filter 16 may be degraded. In contrast, the filter 16 of the present embodiment suppresses the interference of light in the wavelength band of the visible light region by the absorption layer 26 by the integration layer 24, thereby suppressing the ripple of the transmittance of the optical multilayer film 22 and suppressing the reduction of the optical characteristics of the filter 16.
As described above, the optical filter 16 of the present embodiment includes the substrate 20, the optical multilayer film 22 provided on the substrate 20, the integration layer 24 provided on the optical multilayer film 22, and the absorption layer 26 provided on the integration layer 24 and having a transparent base containing an infrared absorbing component. The integration layer 24 is configured to suppress intensity fluctuations in transmittance caused by the absorption layer 26. According to the filter 16, by reducing the intensity of stray light and suppressing interference of light in the wavelength band of the visible light region caused by the absorption layer 26, it is possible to suppress degradation of the optical characteristics of the filter 16.
Example 1
Next, example 1 will be described. In example 1, a simulation experiment of transmittance was performed on the filter 16 of the present embodiment, with the film thickness (thickness) of the absorption layer 26 being changed. Table 1 shows the structures of the layers of the filter 16 of example 1. As shown in table 1, in example 1, tiO 2 was used for the high refractive index film of the auxiliary integration layer 28, siO 2 was used for the low refractive index film of the auxiliary integration layer 28, zrO 2 was used for the high refractive index film 24A of the integration layer 24 and the high refractive index film 22A of the optical multilayer film 22, and SiO 2 was used for the low refractive index film 24B of the integration layer 24 and the low refractive index film 22B of the optical multilayer film 22. At a wavelength of 500nm, the refractive index of TiO 2 is 2.467, the refractive index of SiO 2 is 1.483, and the refractive index of ZrO 2 is 2.058. Next, in example 1, as the optical multilayer film 22, the integration layer 24, and the auxiliary integration layer 28, the spectral transmittance of the optical filter 16 was calculated by simulation experiments by varying the film thickness of the absorption layer 26 in the range of 700nm to 1400nm as shown in table 1. That is, when light enters the optical filter 16 having the structure shown in table 1 from the auxiliary integration layer 28, the transmittance of light emitted from the substrate 20 was calculated by a simulation experiment for each film thickness of the absorption layer 26. As shown in table 1, the integration layer 24 of example 1 was formed of three layers of (aQ LbQHcQL). In table 1, the optical multilayer film is the substrate 20 side and the auxiliary integration layer is the air side. In example 1, the optical multilayer 22 was designed to have a center wavelength of 930nm, a of 0.313, b of 0.131, and c of 0.412. In addition, each coefficient was calculated by using the refractive index (ZrO 2:2.025、SiO2:1.467) of the high refractive index film 24A and the low refractive index film 24B of the integration layer 24 at the wavelength of 930 nm. Also, TFCalc (manufactured by Software spectroscopy corporation) was used as simulation Software for calculating spectral transmittance. The substrate 20 and the absorption layer 26 were calculated without light absorption. The calculation related to optical interference is performed by regarding the extinction coefficient k related to absorption as zero.
TABLE 1
(Table 1) example 1
On the other hand, table 2 shows the structures of the layers of the filter of comparative example 1. In table 2, the optical multilayer film is the substrate 20 side and the auxiliary integration layer is the air side. The filter of comparative example 1 differs from example 1 in the point that it does not have the integration layer 24. In comparative example 1, the spectral transmittance of the optical filter 16 was calculated by a simulation experiment by varying the film thickness of the absorption layer 26 in the range of 700nm to 1400nm in the same manner as in example 1.
TABLE 2
(Table 2) comparative example 1
Fig. 4 is a graph showing the values of spectral transmittance of each film thickness in example 1. Fig. 5 is a graph showing the values of spectral transmittance of each film thickness of comparative example 1. The horizontal axis of fig. 4 and 5 is wavelength, and the vertical axis is spectral transmittance of the filter 16. Fig. 4 and 5 show the calculation results of the transmittance of the filter 16 at each film thickness of the absorption layer 26 for each light having a wavelength of 350nm to 1200 nm. As shown in fig. 4 and 5, in example 1, particularly when the wavelength of the incident light is 450nm or more and 750nm or less (further, 450nm or more and 650nm or less), it is found that the variation in the spectral transmittance value of the optical filter with respect to the film thickness of the absorption layer 26 is small and the ripple is suppressed as compared with comparative example 1. Further, as a result of confirming in detail the variation in spectral transmittance of the optical filter 16 when the film thickness of the absorption layer 26 was varied, the difference between the maximum transmittance and the minimum transmittance in the wavelength band of the visible light region (here, the wavelength is 450nm or more and 650nm 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.
Example 2, example 3
Next, example 2 and example 3 will be described. In example 2, with respect to the filter 16 of the present embodiment, a simulation experiment of transmittance was performed with the film thickness (thickness) of the absorption layer 26 being changed. Table 3 shows the structures of the layers of the filter 16 of example 2. In table 3, the optical multilayer film is the substrate 20 side and the auxiliary integration layer is the air side. As shown in table 3, in embodiment 2, the constitution of the auxiliary integration layer 28 is substantially the same as that of embodiment 1. On the other hand, the intermediate refractive index film of the integration layer 24 is composed of a single layer of Al 2O3, which is different from example 1 in this point. At a wavelength of 500nm, the refractive index of Al 2O3 is 1.617. Next, in example 2, the optical multilayer film 22, the integration layer 24, and the auxiliary integration layer 28 were configured as shown in table 3, and the film thickness of the absorption layer 26 was varied in the range of 700nm to 1400nm, and the spectral transmittance of the optical filter 16 was calculated by simulation. That is, when light enters the optical filter 16 having the structure shown in table 3 from the auxiliary integration layer 28, the transmittance of light emitted from the substrate 20 was calculated for each film thickness of the absorption layer 26 by using the same simulation experiment and conditions as those in example 1.
TABLE 3
(Table 3) example 2
In example 3, a simulation experiment of spectral transmittance was performed on the filter 16 of the present embodiment, with the film thickness (thickness) of the absorption layer 26 being changed. Table 4 shows the structures of the layers of the filter 16 of example 3. In table 4, the optical multilayer film is on the substrate 20 side and the absorbing layer is on the air side. As shown in table 4, in example 3, the composition of the integration layer 24 was substantially the same as that of example 1. In example 3, the optical multilayer 22 was designed to have a center wavelength of 930nm, a of 0.313, b of 0.131, and c of 0.412. In addition, each coefficient was calculated by using the refractive index (ZrO 2:2.025、SiO2:1.467) of the high refractive index film 24A and the low refractive index film 24B of the integration layer 24 at the wavelength of 930 nm. In addition, embodiment 3 is different from embodiment 1 in the point that the auxiliary integration layer 28 is not provided. Next, in example 3, the optical multilayer film 22 and the integration layer 24 were structured as shown in table 4, and the film thickness of the absorption layer 26 was varied in the range of 700nm to 1400nm, and the spectral transmittance of the filter 16 was calculated by simulation. That is, when light enters the optical filter 16 having the structure shown in table 4 from the absorption layer 26, the transmittance of light emitted from the substrate 20 was calculated for each film thickness of the absorption layer 26 by using the same simulation experiment and conditions as those in example 1.
TABLE 4
(Table 4) example 3
On the other hand, table 5 shows the structures of the layers of the filter of comparative example 2. In table 5, the optical multilayer film is on the substrate 20 side and the absorbing layer is on the air side. The filter of comparative example 2 is different from example 1 in the point that the integration layer 24 and the auxiliary integration layer 28 are not provided. In comparative example 2, the spectral transmittance of the filter 16 was calculated by simulation experiments by varying the film thickness of the absorption layer 26 in the same manner as in example 1.
TABLE 5
(Table 5) comparative example 2
Fig. 6 is a graph showing the values of spectral transmittance of each film thickness in example 2. Fig. 7 is a graph showing the values of spectral transmittance of each film thickness in example 3. Fig. 8 is a graph showing the values of spectral transmittance of each film thickness of comparative example 2. The horizontal axis of fig. 6 to 8 is wavelength, and the vertical axis is spectral transmittance of the filter 16. Fig. 6 to 8 show the calculation results of the spectral transmittance of the optical filter 16 at each film thickness of the absorption layer 26 for each light having a wavelength of 350nm to 1200 nm. As shown in fig. 6 to 8, in example 2 and example 3, particularly when the wavelength of the incident light is 450nm or more and 750nm or less (further, 450nm or more and 650nm or less), it is clear that the fluctuation of the transmittance value is small and the ripple is suppressed in all the wavelengths of light as compared with each comparative example. In contrast, in comparative example 2, it is found that the fluctuation of the transmittance value is large with respect to the fluctuation of the film thickness (thickness) of the absorption layer 26, and the ripple is generated. Further, as a result of confirming in detail the variation in spectral transmittance when the film thickness of the absorption layer 26 of the filter 16 was varied, the difference between the maximum transmittance and the minimum transmittance in the wavelength band of the visible light region (here, the wavelength was 450nm or more and 650nm 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.
The embodiments of the present invention have been described above, but the embodiments are not limited to the above embodiments. The above-described components include components which can be easily conceived by those skilled in the art from the components, and components which are substantially identical to the components, i.e., components within the equivalent range. The above-described components can be appropriately combined. Various omissions, substitutions, and changes in the constituent elements may be made without departing from the technical ideas of the above-described embodiments.
Claims (7)
1. An optical filter, comprising, in order:
A back surface layer,
A substrate (substrate),
An optical multilayer film disposed on the substrate,
An integration layer disposed on the optical multilayer film,
An absorber layer provided on the integration layer and having a transparent substrate containing a near infrared absorbing component, and
An auxiliary integration layer disposed on the absorption layer and suppressing reflection of light of a wavelength band of an incident visible light region by the absorption layer,
The integration layer suppresses intensity variation of transmittance caused by film thickness variation of the absorption layer,
The integration layer is formed by laminating a plurality of high refractive index films with high refractive index and low refractive index films with lower refractive index than the high refractive index films, or is formed by a single layer of medium refractive index films,
The high refractive index film has a refractive index of 1.8 or more at a wavelength of 500nm, the low refractive index film has a refractive index of less than 1.6 at a wavelength of 500nm, and 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.
2. The optical filter according to claim 1, wherein the auxiliary integration layer is an optical multilayer film formed by laminating a plurality of films having different refractive indexes, and wherein the auxiliary integration layer minimizes the reflectance in the visible light range and suppresses waves of a waveform called reflection waves or transmission waves when the incident medium is air.
3. The filter according to claim 1, wherein when QWOT of the high refractive index film is denoted as Q H and QWOT of the low refractive index film is denoted as Q L with a designed center wavelength of the optical multilayer film as a center wavelength,
The integration layer is composed of three layers of (aQ LbQHcQL) from the substrate side, a and c are more than 0.2 and less than 0.5, b is more than 0.07 and less than 0.5, and b < a.
4. The filter according to claim 1 or 2, wherein the thickness of the absorption layer is 100nm or more and 5000nm or less.
5. The filter according to claim 1 or 2, wherein the substrate is any one of white glass, blue glass, and resin.
6. The optical filter according to claim 1 or 2, wherein the optical multilayer film has an average transmittance of light in a wavelength band of a visible light region of 80% or more and an average transmittance of light in a wavelength band of a near infrared region of 10% or less.
7. A near infrared cut filter comprising the filter according to any one of claims 1 to 6.
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| JP2019203783A JP7459483B2 (en) | 2018-12-28 | 2019-11-11 | Optical filter, near-infrared cut filter, and imaging device |
| JP2019-203783 | 2019-11-11 |
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| US20080206533A1 (en) * | 2005-08-16 | 2008-08-28 | Asahi Glass Co., Ltd. | Laminated glass for vehicle window |
| JP2016142750A (en) * | 2015-01-29 | 2016-08-08 | 京セラ株式会社 | Optical filter, and package for optical element |
| CN107076895A (en) * | 2015-04-23 | 2017-08-18 | 旭硝子株式会社 | Optical filter and camera device |
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| JP6383980B2 (en) * | 2014-09-26 | 2018-09-05 | Ａｇｃ株式会社 | Near-infrared cut filter |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US20080206533A1 (en) * | 2005-08-16 | 2008-08-28 | Asahi Glass Co., Ltd. | Laminated glass for vehicle window |
| JP2016142750A (en) * | 2015-01-29 | 2016-08-08 | 京セラ株式会社 | Optical filter, and package for optical element |
| CN107076895A (en) * | 2015-04-23 | 2017-08-18 | 旭硝子株式会社 | Optical filter and camera device |
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