JP2012137645A - Optical filter - Google Patents

Abstract

The generation of unnecessary light can be reduced, and the thickness and cost can be reduced.
SOLUTION: A light absorbing structure 3 made of an organic thin film formed by dispersing a dye having absorption in a desired wavelength region in a resin binder on a transparent substrate 2 is formed. On the upper layer of the light absorbing structure 3, a light reflecting structure 4a made of an inorganic thin film formed by laminating a plurality of vapor deposition films so as to reflect near infrared light is formed. On the opposite surface of the transparent substrate 2, a light reflecting structure 4b made of an inorganic thin film is provided.
The light reflecting structures 4a and 4b have a transition wavelength region that transitions from a light transmission wavelength region to a transmission limited wavelength region, and at least a part of the absorption wavelength region of the light absorption structure 3 overlaps the transition wavelength region. .
[Selection] Figure 1

Description

  The present invention relates to an optical filter that restricts light transmission in a predetermined wavelength region.

  As an optical filter of a type that transmits only light in a specific wavelength or wavelength region and limits light in an unnecessary wavelength region, a band pass filter, an edge filter, or the like is generally widely known. Examples of such filters include dichroic filters, near-infrared cut filters (IR cut filters), ultraviolet cut filters (UV cut filters), ultraviolet infrared cut filters (UVIR cut filters), fluorescent filters, laser line filters, and excitation filters. Can be mentioned.

  These optical filters have an absorption type in which a material having absorption in the limited region is kneaded into the base material of the optical filter or coated on the base material in order to limit transmission in a desired wavelength range, and the base material Two or more types of thin films with different refractive indexes are stacked on top of each other, and a reflection type that reflects using the interference of the thin film, and further, a dielectric film and a material that has absorption in a partial wavelength region such as a metal film or colored glass. Broadly divided into a combined reflection / absorption hybrid type.

  These optical filters are structurally transitioned from a transmission wavelength region that transmits light, a transmission limitation wavelength region that limits light transmission, and from a transmission wavelength region to a transmission limitation wavelength region, or from a transmission limitation wavelength region to a transmission wavelength region. It has a transition wavelength region. Since the transition wavelength region cannot ideally be set to 0 nm, the transmittance is changed to a desired value between certain wavelength regions such as about 20 nm.

  In the light of the wavelength corresponding to the transition wavelength region described above, a part of the light is transmitted through the optical filter, and a part of the light is reflected by some member arranged at the back, and is incident on the optical filter from the back side again. There is a phenomenon that will be done. At this time, a part of the re-incident light is reflected again by the optical filter, and the unnecessary light becomes noise, which may cause various problems such as deterioration of image / image quality and deterioration of color reproducibility.

  In a simple way of thinking, the (incident light transmittance) / (re-incident light reflectance) at each wavelength is the intensity of unnecessary light in the optical filter. More simply, (incident light transmittance in the optical filter) / (incident light reflectance) is a measure of the intensity of unnecessary light.

  Therefore, for example, in the case of a reflection type ultraviolet infrared cut filter made only of a dielectric material, the intensity of such unnecessary light is maximum near the half-value wavelength on the ultraviolet light side and the half-value wavelength on the near infrared light side. Become.

  The influence of such unnecessary light varies depending on, for example, the type of an optical system such as an imaging optical system and a scanning optical system, the arrangement position of an optical filter, and the like. However, in principle, the reflection type optical filter has a greater influence than the absorption type optical filter. For this reason, the problem of unnecessary light that becomes noise is gradually becoming apparent due to the recent high precision of various electronic devices such as videos, cameras, microscopes, projectors, etc., in which reflection type optical filters are used.

  In order to reduce this, various countermeasures have been proposed, such as placing the optical filter tilted with respect to the optical axis or depositing a thin film on a curved substrate. However, there are some other problems such as a large space on the optical path, a film thickness error within the same optical filter, and a significant reduction in productivity.

  Therefore, when such unnecessary light becomes a problem, it is more preferable to use an optical filter with absorption, and various types of absorption optical filters are proposed. Has been.

  For example, Patent Document 1 proposes a method in which a dye or the like having a property of absorbing light of a specific wavelength is dispersed in a resin.

  Patent Document 2 proposes a method of absorbing light of a specific wavelength by dispersing a metal complex or the like in a substrate such as glass or resin.

  Further, Patent Documents 3 and 4 propose a hybrid configuration of a light reflection structure using an inorganic film and a light absorption structure using an organic film.

JP 2005-99820 A JP-A-11-160529 JP 2006-301894A JP 2008-51985 A

  However, in the case of a configuration in which a dye or the like is dispersed in a resin as in Patent Document 1, in order to limit the transmittance over the entire transmission limited region desired only by the absorption component, the required transmission wavelength region At the same time, the transmittance is lowered. In addition, there is a problem that a large ripple is generated in a transmission wavelength region where a rapid change is generally small and a continuous change is desired.

  In addition, as in Patent Document 2, in the case of a configuration in which a metal complex or the like is dispersed in a substrate, the absorption layer needs to have a corresponding thickness. In particular, when the absorbent is dispersed in the substrate, a thickness of about 0.3 to 0.5 mm or more is necessary, and it is extremely difficult to achieve the demand for thinning and downsizing in recent years. And there is a problem that the product cost becomes high.

  Furthermore, as disclosed in Patent Documents 3 and 4, even in a hybrid configuration of an absorption layer composed of an organic film and a reflection layer composed of an inorganic film, the transmittance in the transmission wavelength region is configured to be high. There is a case. In this case, it is not possible to obtain large absorption in the transition wavelength region, particularly in the vicinity of the half-value wavelength in the spectral characteristics formed by the inorganic film, and the reflection in this region cannot be greatly reduced. It is extremely difficult to reduce the above.

  As described above, in an optical filter having a transition wavelength region, unnecessary light is generated due to the reflectance of the optical filter in the transition wavelength region, which becomes noise and causes problems such as image degradation in various optical systems. There is a fear.

  In addition, in the case of a type of filter that has absorption by a metal film or colored glass, the wavelength region that can be absorbed is extremely limited, and it is difficult to apply to a wide variety of optical filters.

  An object of the present invention is to provide an optical filter that can eliminate the above-mentioned problems, reduce the generation of unnecessary light, and realize a reduction in thickness and cost.

  To achieve the above object, an optical filter according to the present invention includes a light absorption structure formed of a resin layer and having a predetermined absorption wavelength region on a transparent substrate, and at least one light reflection layer in which a plurality of inorganic thin films are laminated. And the at least one light reflecting structure has a transition wavelength region that transitions from a light transmission wavelength region to a light transmission limited wavelength region, and at least a part of the absorption wavelength region of the light absorption structure Overlaps with the transition wavelength region.

  According to the optical filter of the present invention, it is possible to reduce the amount of unnecessary light that becomes noise even when part of the transmitted light re-enters from the back surface, and to significantly reduce problems caused by multiple reflections. Can do. Furthermore, since it is less necessary to combine a plurality of absorbing materials in order to obtain desired absorption characteristics, ripples in the transmission wavelength region can be reduced, and costs can be reduced. In addition, since it is not necessary to tilt the optical filter and the like, the optical system can be made thinner, and further, since it can be manufactured on a flat substrate, productivity is not impaired.

2 is a configuration diagram of an optical filter according to Embodiment 1. FIG. FIG. 3 is a graph showing the spectral transmittance of the light reflecting structure of Example 1. 3 is a graph of spectral absorptance of the light absorption structure of Example 1. FIG. 3 is a graph showing the spectral transmittance of the optical filter manufactured according to Example 1. FIG. It is a graph of the spectral transmittance of the optical filter of a conventional example. 6 is a configuration diagram of an optical filter of Example 2. FIG. It is a graph of the spectral transmittance of the light reflecting structure of Example 2. It is a graph of the spectral absorptance of the light absorption structure of Example 2. 6 is a graph showing the spectral transmittance of an optical filter manufactured according to Example 2. FIG. FIG. 6 is a configuration diagram of an optical device according to Example 3. FIG. 6 is a configuration diagram of an optical device according to Example 4.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 shows a configuration diagram of an optical filter 1 of Example 1 that functions as an infrared cut filter that restricts transmission of light in the near-infrared light region.

  In this optical filter 1, a light absorption structure 3 made of an organic thin film formed by dispersing a dye having absorption in a desired wavelength region in a resin binder is formed on a transparent substrate 2. A light reflecting structure 4a made of an inorganic thin film formed by laminating a plurality of vapor deposition films so as to reflect near infrared light is formed on the upper layer of the light absorbing structure 3. Further, on the opposite surface of the transparent substrate 2, a light reflecting structure 4b made of an inorganic thin film is provided.

  The transparent substrate 2 is made of, for example, an Arton (product name) film made of synthetic resin, which is a norbornene-based material having a thickness of 0.1 mm. The Arton film has a high glass transition temperature (Tg), a high flexural modulus, and can reduce cracks and undulations of the transparent substrate 2.

  In Example 1, an Arton film is used, but in addition to this, a polyimide resin film or the like is also a suitable material. Furthermore, as long as it has transparency in the visible wavelength region, for example, use of polyester type represented by PET, PEN, acrylic type, aramid type, PC (polycarbonate), polyvinyl chloride, PVA (polyvinyl alcohol), etc. Is possible.

  The light absorbing structure 3 is formed by applying a resin layer in which a pigment is dispersed, for example, by a spin coating method. An acrylic resin is used for the resin binder constituting the light absorbing structure 3, and this acrylic resin is an acrylic resin partially containing styrene from the viewpoint of adhesion between the transparent substrate 2 and the resin layer. Styrene copolymer resin is selected.

  In addition to acrylic, the resin may be polystyrene, polyester, polyurethane, fluorine, PC, polyimide, styrene, polyolefin, or the like if the translucency is high in the visible wavelength region. These resins may be used alone or in admixture of two or more, or may be used as a copolymer. In other words, any material that has a small absorption in the visible wavelength region may be used. A resin binder may be selected.

  More preferably, the resin binder has a small refractive index difference from the transparent substrate 2. When the transparent substrate 2 and the light-absorbing structure 3 are adjacent to each other, the refractive index difference is reduced, so that reflection at the interface between the transparent substrate 2 and the resin layer is reduced. It is possible to reduce the influence of. For the same reason, even when a functional film layer such as an adhesive layer or a stress relaxation layer is inserted between the transparent substrate 2 and the light absorbing structure 3, the transparent substrate 2, the functional film layer, the light absorbing structure It is more preferable that the three members of the body 3 have similar refractive indexes.

  The stress caused by curing shrinkage that occurs when the resin layer of the light absorption structure 3 is dried can be reduced by reducing the film thickness of the light absorption structure 3. At this time, in order to maintain the desired absorption characteristics, it is necessary to adjust the concentration of the dye and, for example, the coating process such as the rotation speed in the case of the spin coating method.

  In the case of the light-absorbing structure 3 composed of an organic thin film, the dye component is weak in moisture, so even if dispersed in a resin binder, the resin absorbs water notably from the surrounding environment such as temperature and humidity. In some cases, the optical properties of the pigment component may change due to the influence of the pigment component. For this reason, the light reflecting structure 4 a is arranged on the surface layer side of the light absorbing structure 3.

  Each of the light reflecting structures 4a and 4b is formed by laminating at least two kinds of inorganic thin films, and the light reflecting structures 4a and 4b function as one thin film laminated structure, and transmit light in a certain wavelength region. Is limiting.

  When a synthetic resin material is used for the transparent substrate 2, a heat problem due to the film forming process of the light reflecting structures 4a and 4b occurs. In the case of a resin transparent substrate having an extremely low glass transition temperature compared to a glass transparent substrate, the warp of the transparent substrate 2 due to the difference in the linear expansion coefficient between the transparent substrate 2 and the film, and the film accompanying this warp The occurrence of cracks on the surface can be considered. Therefore, it is necessary to take measures against heat generated during film formation. Specifically, it is conceivable to select a material having a high glass transition temperature as the transparent substrate 2 or to lower the temperature of the film formation process.

  In film formation of the light reflecting structures 4a and 4b, a method for removing heat generated in the transparent substrate 2 during film formation by a radiation cooling effect by selecting a heat absorption mechanism in the film formation apparatus was selected. At that time, it is necessary to measure in advance the maximum temperature on the transparent substrate 2 reached in the film forming process and select a material that can withstand that temperature. In Example 1, in consideration of the stability of the film forming process, a certain allowable value is added to the maximum temperature reached in the experiment, and the glass transition temperature is used as a parameter for determining the suitability. The transparent substrate 2 having is selected.

  In addition, since the temperature during the film formation of the light reflecting structures 4a and 4b is lower than the normal film formation temperature, film density such as a sputtering method in which some assistance is added or a film is formed with a relatively high energy. It is highly desirable to select processes that increase Specifically, any film forming method capable of relatively accurately controlling the film thickness, such as a sputtering method, an IAD method, an ion plating method, an IBS method, and a cluster vapor deposition method, to obtain a highly reproducible film. Good. It may be formed by a physical or chemical film formation method other than vapor deposition, or may be a wet process such as a sol-gel method. From the required film properties and the constraints of each material including the transparent substrate 2, etc. An optimal method may be selected.

  FIG. 2 is a graph showing the spectral transmittance characteristics of the reflection type optical filter when only the light reflecting structures 4a and 4b are formed on the transparent substrate 2 made of an Arton film having a thickness of 0.1 mm. This optical filter has a high transmittance in the visible wavelength region, a first blocking wavelength region W1 for preventing transmission of wavelengths in the region from the ultraviolet wavelength region to the visible wavelength region, and a wavelength region in the visible wavelength region to the near infrared wavelength region. Has a second blocking wavelength region W2. Further, the third blocking wavelength region W3 is provided in the wavelength region from the second blocking wavelength region W2 to the near-infrared wavelength, and is constituted by three blocking wavelength regions W1 to W3. The blocking wavelength regions W1 and W2 are formed by the light reflecting structure 4a, and the blocking wavelength region W3 is formed by the light reflecting structure 4b.

  The thin film laminated structure of the light reflecting structures 4a and 4b is formed by sequentially laminating a plurality of inorganic dielectric films by the IAD method. Generally, in such a multilayer film, the film stress becomes very large, and if the thickness of the transparent substrate 2 is reduced from the viewpoint of reducing the thickness of the optical system, the transparent substrate 2 may be warped. As a countermeasure, when the light reflecting structures 4a and 4b are respectively formed on both surfaces of the transparent substrate 2 as shown in FIG. 1, the same material, film thickness and film quality are laminated on both surfaces of the transparent substrate 2. The stress can be reduced.

  However, in this case, it is difficult to design the structure of the film, and if the film design is performed so that the number of stacked layers is the same as that in the case of designing on one side of the transparent substrate 2, the optical characteristics may be greatly sacrificed. In addition, in order to satisfy both the optical characteristics and the relaxation of the film stress at the same time, the number of layers increases, which increases the number of steps for manufacturing the filter. When warping of the transparent substrate 2 due to film stress becomes a problem, it is preferable to divide and arrange the thin film laminated structure on both surfaces of the transparent substrate 2 as shown in FIG.

  In the above description, the light reflecting structures 4a and 4b are arranged on both surfaces of the transparent substrate 2 for stress balance. In addition, in Example 1, the light absorbing structure 3 and the light reflecting structures 4a and 4b are arranged. It is also necessary to balance the stress. For that purpose, it is preferable to balance the stresses on both sides of the transparent substrate 2 by measuring each stress in advance and optimizing the arrangement on both sides of the transparent substrate 2.

Therefore, in Example 1, first, the light absorption structure 3 is formed on the transparent substrate 2, and a 29-layer thin film of the light reflection structure 4 a is formed on the upper layer. A 21-layer thin film is formed by the reflective structure 4b. Such light reflecting structure 4a, a dielectric film made of 4b material, TiO ₂ in the high refractive index material, the low refractive index material using SiO _2, laminating TiO ₂ and SiO ₂ alternately did.

In addition, although it depends on the film forming method, generally Nb ₂ O ₅ , ZrO ₂ , Ta ₂ O ₅ or the like is used for the high refractive index material, and MgF ₂ is used for the low refractive index material. In some cases. For reasons of design and film formation, Al ₂ O ₃ or the like, which is an intermediate refractive index material, may be used in some layers, but an optimal combination of materials may be selected as appropriate.

  Moreover, in the case of a hybrid type filter like the optical filter 1 of Example 1, the absorption by the organic thin film and the reflection by the inorganic thin film are taken into consideration so that the desired wavelength becomes the half-wavelength of infrared light in advance. It may be necessary to adjust.

  FIG. 3 shows spectral characteristics having a predetermined absorption wavelength region when the cyanine dye of the light absorption structure 3 is dispersed in an acrylic resin binder, and the concentration of the dye and the dye so as to obtain a desired absorption. It is formed by adjusting the film thickness and coating it into a film. The dye dispersed in this way is half the infrared light spectral transmittance in the transition wavelength region in which the near-infrared light formed by the light reflecting structures 4a and 4b transmits from the transmission wavelength region to the transmission limited wavelength region. It has an absorption band near the wavelength including the wavelength.

  At this time, it is common to add a solvent such as methyl ethyl ketone (MEK), toluene, methyl isobutyl ketone (MIBK) to the resin binder and volatilize it through a drying process after coating. What is necessary is just to select the optimal solvent suitably from relationships, such as a construction method. For example, the solvent is not limited to ketones, but hydrocarbons such as cyclohexane and toluene, esters such as methyl acetate and ethyl acetate, ethers such as diethyl ether and tetrahydrofuran, alcohols such as methanol and ethanol, dimethylformamide, etc. The amine solvent or water may be selected so as to be an optimum combination as a single substance or a mixture of two or more kinds in consideration of the solubility and volatility of the pigment / resin binder. In Example 1, a solvent obtained by mixing methyl ethyl ketone (MEK) and methyl isobutyl ketone (MIBK) at a ratio of 1: 9 (weight ratio) is used, and a desired spectrum can be obtained by spin coating the coating solution. A film was formed to a thickness, and dried and cured in a drying oven.

  In addition, by adding an antioxidant to the light absorption structure 3, deterioration of the pigment may be reduced in some cases. Examples of the antioxidant include phenol-based, binderd phenol-based, amine-based, binderd amine-based, sulfur-based, phosphoric acid-based, phosphorous acid-based and the like.

  FIG. 4 is a graph showing the spectral transmittance characteristics of the optical filter 1 manufactured by the above-described method, and combines the spectral characteristics of the light reflecting structures 4a and 4b shown in FIG. 2 and the light absorbing structure 3 shown in FIG. Will be. The intensity of unnecessary light in the infrared cut filter is simply a value calculated by (spectral transmittance of infrared cut filter) / (spectral reflectance of infrared cut filter). When the optical filter is composed of only an inorganic thin film, the intensity of unnecessary light is maximized at the half-wavelength of infrared light, and assuming that the transmittance is 50% and the reflectance is 50%, the value is approximately 25%.

  Practically, it is necessary to reduce the intensity of unnecessary light to at least about 15 to 16%. Therefore, for example, in order to reduce the strength to 16% or less, when the light absorption structure 3 is combined, the light absorption structure 3 described above is at least 40% transmittance and 40% reflectance. The absorptance at the half-wavelength of infrared light needs to be about 20% or more.

  In a simple calculation, the maximum intensity of unnecessary light by only the light reflecting structures 4a and 4b is about 25% as described above, whereas unnecessary light in the transition wavelength region of the optical filter 1 manufactured in Example 1 is used. The maximum strength is 8% or less. The effect of unnecessary light varies depending on the sensitivity characteristics of the image sensor, the total value of unnecessary light generated from the transition wavelength region to the transmission limited wavelength region, and the like. However, the optical filter 1 manufactured in Example 1 reduces the maximum intensity in the transition wavelength region by 30% or more, and can reduce unnecessary light in many optical systems.

  After the light absorption structure 3 and the light reflection structures 4a and 4b described above are formed on the entire surface of the transparent substrate 2, the optical filter 1 is processed into a 10 mm square shape by punching into a desired shape. The same optical filter 1 can be produced by a method in which a mask is formed on the transparent substrate 2 at the time of film formation, and a desired range is partially formed and then cut out after film formation.

  FIG. 5 is a graph showing the spectral transmittance of an optical filter of a comparative example produced based on Patent Document 4 for comparison. FIG. 5A is a graph of an organic thin film layer, FIG. 5B is a graph of two inorganic thin film layers arranged on both sides of the substrate, and FIG. 5C is an organic thin film layer and an inorganic thin film. Fig. 2 shows a graph produced by layers.

  It can be seen from FIG. 5B that the half-wavelength of infrared light formed by the inorganic thin film layer is a wavelength around 650 nm. Moreover, even if it is a case where an organic thin film layer and an inorganic thin film layer are comprised from FIG.5 (c), an infrared-light half value wavelength is 650 nm vicinity, and has become the wavelength similar to FIG.5 (b). I understand. Further, from the characteristics of the organic thin film layer shown in FIG. 5 (a), the absorption rate in the transition wavelength region of the organic thin film layer presented in Patent Document 4, particularly the absorption rate at the half-wavelength of infrared light is However, it is expected to be an extremely small value of about 10%.

  In the transmission wavelength region and the transmission limited wavelength region, either the transmittance or the reflectance approaches 0. Therefore, as described above, the intensity of unnecessary light is simply calculated by changing the transmittance and the reflectance in the transition wavelength region as described above. The multiplied value becomes dominant. Therefore, when sufficient absorption cannot be obtained in this transition wavelength region, if the transmittance is low, the reflectance is high, and if the reflectance is low, the transmittance is high, thereby reducing the intensity of unnecessary light. Is extremely difficult.

  Although the influence of unnecessary light is slightly different depending on the configuration of the entire optical system, such as the sensitivity characteristics of the image pickup device and the arrangement position of the filter, the unnecessary light is not used in the optical characteristics shown in FIG. It is difficult to reduce sufficiently.

  FIG. 6 shows a configuration diagram of the optical filter 11 of Example 2 that functions as a fluorescent filter that transmits light only in a part of the visible wavelength region and restricts transmission in the wavelength region in the vicinity thereof.

  In this optical filter 11, a light absorption structure 13 made of an organic thin film formed by dispersing a dye having absorption in a desired wavelength region in a resin binder is formed on a transparent substrate 12. On the light absorbing structure 13, a light reflecting structure 14a made of an inorganic thin film formed by laminating a plurality of vapor deposition films is formed. Further, a light reflecting structure 14b made of an inorganic thin film is formed on the opposite surface of the transparent substrate 12 in the same manner.

  As the transparent substrate 12, for example, BK7 having a thickness of 0.5 mm is used. The transparent substrate 12 may be a synthetic resin substrate as long as it has transparency in a desired wavelength region, and the resin film described in Example 1 can be used.

  The light absorption structure 13 is formed by applying a resin layer in which a pigment is dispersed, for example, by spin coating. An acrylic resin is used for the resin binder constituting the light absorption structure 13, but other resins mentioned in Example 1 can be used.

  For the same reason as in the first embodiment, the light reflecting structure 14 a is arranged on the surface layer side of the light absorbing structure 13. Each of the light reflecting structures 14a and 14b is formed by laminating at least two kinds of inorganic thin films, and the light reflecting structures 14a and 14b function as one thin film laminated structure, and transmit a certain wavelength region. Is limiting.

  When a synthetic resin material is used for the transparent substrate 12, heat generated during film formation, such as selecting a material having a high glass transition temperature as in Example 1 or reducing the temperature of the film formation process. It is necessary to take measures.

  FIG. 7 is a graph showing the spectral transmittance characteristics of the reflection type optical filter when only the light reflecting structures 14 a and 14 b are formed on the transparent substrate 12. This optical filter has a high transmittance in a desired visible wavelength region, and has a first blocking wavelength region W11, a second blocking wavelength region W12, and a third blocking wavelength region W13 that limit transmission from the ultraviolet wavelength region to the transmission wavelength region. It is composed of three blocking wavelength regions W11 to W13. A blocking wavelength region W13 is formed by the light reflecting structure 14a, and blocking wavelength regions W11 and W12 are formed by the light reflecting structure 14b.

  The thin film laminated structure of the light reflecting structures 14a and 14b is formed by sequentially laminating a plurality of layers of inorganic dielectric films by sputtering.

  In Example 2, the light absorbing structure 13 is first formed on the transparent substrate 12, a 20-layer thin film is formed on the upper layer by the light reflecting structure 14 a, and then light is reflected on the opposite surface of the transparent substrate 12. A 25-layer thin film is formed by the structure 14b.

  FIG. 8 shows spectral characteristics having a predetermined absorption wavelength region when the phthalocyanine dye of the light absorption structure 13 is dispersed in an acrylic resin binder, and the concentration of the dye so as to obtain a desired absorption. In addition, the film thickness is adjusted and the film is applied to form a film. The pigment dispersed in this manner has an absorption band in the vicinity of the wavelength including the half-value wavelength of the spectral transmittance in the transition wavelength region formed by the light reflecting structures 14a and 14b.

  FIG. 9 is a graph showing the spectral transmittance characteristics of the optical filter 11 manufactured by the above-described method, and combines the spectral characteristics of the light reflecting structures 14a and 14b shown in FIG. 7 and the light absorbing structure 13 shown in FIG. Will be.

  Fluorescence is faint light, so even a little unnecessary light causes image quality degradation. Therefore, it is important to reduce unnecessary light as much as possible, thereby reducing the influence as noise.

  In a simple calculation, the maximum intensity of unnecessary light with only the light reflecting structures 14a and 14b is about 25% as described above, whereas, for example, in the transition wavelength region of the optical filter 11 produced in Example 2. The maximum intensity of unnecessary light is about 8.3%. The effect of unnecessary light also varies depending on the sensitivity characteristics of the image sensor, the total value generated from the transition wavelength region to the transmission limited wavelength region, and the like. However, the optical filter 11 manufactured in Example 2 reduces the maximum intensity in the transition wavelength region by about 30%, and the optical filter 11 maintains the high transmittance in the transmission wavelength region and also has an influence of noise. Can be reduced.

  Here, in Examples 1 and 2, the light-absorbing structure was applied by spin coating, but is not limited thereto, dip coating, gravure coating, spray coating, kiss coating, die coating, knife A similar film can be formed by a coating method, a blade coating method, a bar coater method, or the like. That is, an optimum film formation method may be selected in consideration of a film thickness, shape, productivity, and the like that satisfy a desired spectrum.

  For the light absorbing structure 13, cyanine-based pigments were used in Example 1, and phthalocyanine-based pigments were used in Example 2. However, the present invention is not limited to this. For example, azo dyes, phthalocyanine dyes, naphthalocyanine dyes, diimonium dyes, polymethine dyes, anthraquinone dyes, naphthoquinone dyes, triphenylmethane dyes, aminium dyes, pyrylium dyes, squarylium dyes may be used alone or in combination. it can. However, a dye that has low absorption in the transmission wavelength region and whose transmittance in the transmission wavelength region is flat or continuously changed is preferable.

  In Examples 1 and 2, a thermosetting method is used as a method for curing the light absorbing structures 3 and 13 after film formation. However, other active energy rays such as visible light, electron beam, plasma, infrared rays, and ultraviolet rays are used. Etc. may be used. The irradiation amount of active energy rays should just be an energy amount which the hardening of a resin composition advances, and what is necessary is just to add a photoinitiator and antioxidant as needed.

  Examples of the photopolymerization initiator include benzophenone, benzyl, 4,4-dimethylaminobenzophenone, 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzoin ethyl ether, diethoxyacetophenone, benzyldimethyl ketal, 2-hydroxy-2- Examples include, but are not limited to, methylpropiophenone, 1-hydroxycyclohexyl phenyl ketone, tetramethylthiuram monosulfide, tetramethylthiuram disulfide, hydrazone, α-acyloxime ester. It may be used.

  Examples of electron beam curing initiators include benzophenone, 2-ethylanthraquinone, 2,4-diethylthioxanthone, methyl orthobenzoylbenzoate, isopropylthioxanthone, diethoxyacetophenone, benzyldimethyl ketal, 1-hydroxycyclohexyl-phenyl ketone, benzoin methyl ether, Benzoin ethyl ether, benzoin isopropyl ether, benzoin isobutyl ether, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, bis-phenylphosphine oxide, methylbenzoylformate, 1,7-bisacridinylheptane, 9-phenylacridine, etc. However, it is not limited to these, You may use individually or in plurality.

  Thermal polymerization initiators include benzoyl peroxide, t-butyl perbenzoate, cumene hydroperoxide, diisopropyl peroxydicarbonate, di-n-propyl peroxydicarbonate, di (2-ethoxyethyl) peroxydicarbonate. , T-butyl peroxyneodecanoate, t-butyl peroxybivalate, (3,5,5-trimethylhexanoyl) peroxide, dipropionyl peroxide, diacetyl peroxide, 2,2-azobisisobutyro Nitrile, 2,2-azobis (2-methylbutyronitrile), 1,1-azobis (cyclohexane-1-carbonyl), 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2-azobis (2,4-dimethyl-4-methoxyvaleronitrile), dimethyl 2 2- azobis (2-methyl propionate), 4,4-azobis (4-cyanovaleric acid) and others as mentioned, not limited to these, may be used singly or a plurality.

  FIG. 10 is a simple configuration diagram of an image pickup apparatus according to a third embodiment in which the optical filter 1 manufactured in the first embodiment is used for a video camera or the like. An objective lens 21, a light quantity diaphragm 23 having diaphragm blades 22, lenses 24 to 26, an optical filter 27, and a solid-state imaging device 28 including a CCD or CMOS sensor are arranged along the optical path.

  The field light transmitted through the imaging optical system 29 including the objective lens 21, the light amount diaphragm 23, and the lenses 24 to 26 is limited by the optical filter unit 27 in accordance with the characteristics of the solid-state imaging device 28, and an appropriate image is obtained. It is like that.

  For example, by disposing the optical filter 1 in the optical filter unit 27 and incorporating it into the image pickup device, it blocks ultraviolet rays and infrared rays, and reduces unnecessary light that adversely affects noise and realizes high image accuracy. it can. Further, when the optical filter 1 is arranged in the optical filter unit 27, the position of the light absorption structure 3 with respect to the light reflection structure 4a is set so that unnecessary light due to reflection of the optical filter 1 can be further reduced. It is preferable to be on the side close to.

  Specifically, the amount of light transmitted through the imaging optical system 29 and imaged on the solid-state imaging device 28 is determined, and the optical filter unit 27 is driven by the driving member. When the amount of light in the object field is sufficient for normal shooting, the optical filter unit 27 is moved so as to cover the solid-state image sensor 28, and when the amount of light is insufficient, the optical element is not applied to the solid-state image sensor 28. The filter unit 27 is retracted out of the optical path.

  Depending on the presence or absence of the optical filter 1 in the optical filter unit 27, an optical path difference may occur in the light beam to be imaged, and the image may deteriorate. In such a case, the same material as the transparent substrate 2 of the optical filter 1 is used. By inserting the transparent substrate 2 as a dummy, image deterioration can be reduced.

  Further, in the past, in order to reduce such unnecessary light, the optical filter was sometimes tilted with respect to the optical path. However, in Example 3, the unnecessary light is reduced by the optical filter 1, An inclined arrangement is not necessary, and it is possible to cope with downsizing of the photographing optical system.

  FIG. 11 is a simple configuration diagram of the observation apparatus of Example 4 in which the optical filter 11 that is a fluorescence filter manufactured in Example 2 is mounted on a fluorescence microscope apparatus.

  The fluorescent material absorbs excitation light having a specific wavelength, and has a characteristic of releasing energy as light when returning from the excited state to the ground state. Various types of fluorescent materials have been developed according to the purpose, and the wavelength band covers a wide range from ultraviolet light to near infrared light. The fluorescence microscope apparatus is for observing a fluorescent material having such characteristics.

  In FIG. 11, an excitation filter 32 that is a bandpass filter and a dichroic mirror 33 are disposed along the optical path in the emission direction of the light source 31, and the dichroic mirror 33 is disposed in an oblique direction with respect to the optical path of the light source 31. . A measurement sample S made of a fluorescent material is arranged in the reflection direction of the dichroic mirror 33, and an optical filter 11 that functions as a fluorescence filter is provided on the opposite side of the measurement sample S from the dichroic mirror 33.

  Light emitted from the light source 41 is extracted by the excitation filter 32 only for light necessary for excitation of the fluorescent substance, and proceeds to the dichroic mirror 33. The dichroic mirror 33 reflects only light of a specific wavelength and transmits light of other wavelengths. Excitation light is reflected in the direction of the measurement sample S by the dichroic mirror 33, and fluorescence emitted from the measurement sample S passes through the dichroic mirror 33 and proceeds to the optical filter 11.

  The optical filter 11 efficiently transmits the fluorescence emitted from the measurement sample S by removing other unnecessary light. The leakage of scattered light and excitation light from the optical system becomes unnecessary light and appears as noise in the image. Therefore, in order to obtain a clearer image, the optical filter 11 needs to further reduce unnecessary light.

DESCRIPTION OF SYMBOLS 1, 11 Optical filter 2, 12 Transparent substrate 3, 13 Light absorption structure 4a, 4b, 14a, 14b Light reflection structure 21 Objective lens 22 Diaphragm blade 23 Light quantity diaphragm part 27 Optical filter part 28 Solid-state image sensor 29 Imaging optical system 31 Light source 32 Excitation filter 33 Dichroic mirror S Measurement sample

Claims (6)

A light absorption structure formed of a resin layer and having a predetermined absorption wavelength region on a transparent substrate;
Having at least one light reflecting structure in which a plurality of inorganic thin films are laminated,
The at least one light reflecting structure has a transition wavelength region that transitions from a light transmission wavelength region to a transmission limited wavelength region, and at least a part of the absorption wavelength region of the light absorption structure overlaps the transition wavelength region. An optical filter characterized by the above.   2. The optical filter according to claim 1, wherein the light absorption structure is formed of a resin layer in which a dye having the absorption wavelength region is dispersed in a part of the wavelength of the near infrared wavelength region.   The optical filter according to claim 1, wherein the light reflecting structure is laminated on both surfaces of the transparent substrate.   The optical filter according to any one of claims 1 to 3, wherein the light reflection structure is formed in an upper layer of the light absorption structure.   An optical device equipped with the optical filter according to claim 1.   6. The optical filter according to claim 5, wherein when the optical filter is disposed in front of the solid-state imaging device, the light absorption structure of the optical filter is positioned closer to the solid-state imaging device than the light reflecting structure. An optical device equipped with an optical filter.

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