JP6556529B2 - Optical filter and optical device provided with optical filter - Google Patents

Optical filter and optical device provided with optical filter Download PDF

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JP6556529B2
JP6556529B2 JP2015133961A JP2015133961A JP6556529B2 JP 6556529 B2 JP6556529 B2 JP 6556529B2 JP 2015133961 A JP2015133961 A JP 2015133961A JP 2015133961 A JP2015133961 A JP 2015133961A JP 6556529 B2 JP6556529 B2 JP 6556529B2
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filter
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JP2017015999A5 (en
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内山 真志
真志 内山
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キヤノン電子株式会社
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  The present invention relates to an optical filter having a fine structure that exhibits a reflection reducing function, and an optical device including the optical filter.

  The aperture stop is provided to control the amount of incident light on a solid-state image sensor such as a silver salt film or a CCD or CMOS sensor, and the aperture is further reduced as the field becomes brighter. It has become. Therefore, when photographing a clear or high-brightness scene, the diaphragm is in a so-called small-aperture state, and is susceptible to the effects of light diffraction and the like, which may degrade image performance.

  As a countermeasure against this, even if the brightness of the object field is the same, the amount of light is controlled by disposing an ND (Neutral Density) filter in the vicinity of the stop. The device is designed to make the aperture opening larger.

  In recent years, as the sensitivity of the image sensor increases, the density of the ND filter is increased to further reduce the light transmittance, and even when a highly sensitive image sensor is used, the aperture of the diaphragm becomes too small. Improvements have been made to prevent it. However, when the density of the ND filter is high, for example, the difference in the amount of light between the light beam that has passed through the ND filter and the light beam that has not passed through, or the difference in light amount between the light beam that has passed through the high density region and the light beam that has passed through the low density region is significantly different. As a result, there may be a problem that the image deteriorates. In order to solve this problem, there is a need for an ND filter having a gradation density gradient (hereinafter referred to as gradation ND filter) having a configuration in which the density of the ND filter is continuously changed. Here, the density D is a value obtained from the transmittance T by D = log 10 (1 / T).

  In such an ND filter used in an imaging optical system or the like, a phenomenon occurs in which a part of light transmitted through the filter is reflected by another member and is incident on the filter again from the light emission surface of the filter. There is. In such a case, if the ND filter has a reflection in the wavelength region of the incident light, the incident light is reflected again by the filter, which may cause problems such as image degradation. Therefore, further enhancement of the antireflection function in the ND filter is strongly desired.

  Furthermore, even with a gradation ND filter in which the density is continuously changed by continuously changing the film thickness, the film thickness laminated at each density in the same filter as the accuracy of the image sensor and the like increases. Due to this difference, there may be a problem that a phase difference occurs and the image deteriorates.

  As a countermeasure against such reflection, Patent Document 1 discloses a method for reducing the reflectance of an optical filter by using a fine structure having a pitch equal to or smaller than the wavelength size of visible light for an ND filter. 2 and Patent Document 3 disclose methods for reducing the above-described phase difference in the ND filter.

JP 2009-122216 A Japanese Patent Laid-Open No. 06-265971 JP 2007-178822 A

  The fine structure having a reflection reducing effect as shown in Patent Document 1 has a low reflection compared with an antireflection film produced by stacking a single thin film or a plurality of layers by a vacuum film formation method or the like. The ratio can be easily realized, and it is relatively easy to expand the antireflection wavelength region, etc., and it has various advantages such as a small difference in spectral reflectance depending on the incident angle. By making it gentle, reflection can be further reduced.

  Moreover, in patent document 2, the light which permeate | transmits a ND filter and the light which does not permeate | transmit a ND filter by comprising and controlling so that a filter edge part may not be exposed to the opening of a ND filter provided with the transparent part. There has been proposed a method for suppressing image degradation and the like by reducing the phase difference between the two.

  However, with the method disclosed in Patent Document 2, it is difficult to reduce the phase difference caused by the film thickness difference in the density gradient region of the gradation ND filter formed by continuously changing the film thickness. Furthermore, it is not possible to simultaneously achieve reflection reduction and phase difference reduction in the density gradient region of the gradation ND filter with only the countermeasures disclosed in Patent Documents 1 and 2, and It is also very difficult to achieve this by combining the configurations.

  Therefore, in Patent Document 3, the authors have disclosed the film thickness distribution of the concentration gradient region on the back side of the substrate facing the region where the concentration gradient region is arranged in the gradation ND filter formed by continuously changing the film thickness. A method of forming an antireflection film having a multilayered film structure with an inversely tapered film thickness distribution was proposed. With the technology at that time, it was possible to obtain a sufficient reflection reduction effect even with these methods and reduce the phase difference due to the film thickness difference, but in order to meet the recent demand for higher accuracy, There is a need to further reduce reflection while reducing the phase difference.

  Similarly, in other optical filters having a plurality of film thickness regions, such as a multi-concentration type ND filter having a stepwise density change and an IR cut filter having a transparent region, reflection in the entire region of the plurality of film thickness regions is similarly performed. It is desired to reduce the phase difference.

  The present invention provides an optical filter and an optical device that reduce phase difference while reducing reflection with respect to incident light.

The optical filter of the present invention includes a transparent substrate that transmits light in a visible wavelength region, and a functional film provided on the transparent substrate, and the functional film is a film thickness provided on the transparent substrate. An optical film in which a plurality of regions differing from each other and a fine structure in which a plurality of fine structures are formed at a pitch shorter than the wavelength size of light provided on the optical film, The structure is characterized in that the microstructure has a different shape in each of the plurality of regions.
The optical filter of the present invention includes a transparent substrate that transmits light in the visible wavelength region, and a functional film provided on the transparent substrate, and the functional film is a film provided on the transparent substrate. An optical film in which a plurality of regions having different thicknesses are formed, and a fine structure formed from a plurality of fine structures at a pitch shorter than the wavelength size of light provided on the optical film, The structure has a microstructure having a different shape according to a change in the thickness of the optical film.

  According to the present invention, in an optical filter having a plurality of film thickness regions on a substrate, such as a gradation ND filter formed by continuously changing the film thickness, the phase difference is reduced in accordance with the film thickness of each region. By disposing a fine structure having a high reflection reduction effect with the structural shape adjusted, it is possible to reduce the phase difference while obtaining a sufficient reflection reduction effect. Furthermore, by mounting such an optical filter, it is possible to obtain an optical device that can improve the accuracy and improve defects such as image degradation.

Explanatory drawing of a fine periodic structure of a pillar array shape. FIG. 3 is a cross-sectional view of an ND filter manufactured in the first embodiment. Schematic of the film-forming jig described in Examples 1 and 2. FIG. The lamination block diagram of the ND filter produced in the present Examples 1 and 2. FIG. Sectional drawing of the ND filter produced in the present Example 2. FIG. Sectional drawing of the structural example of ND filter as described in this Example 3. FIG. Explanatory drawing of the external shape of the microstructure described in the third embodiment. FIG. 6 is an explanatory diagram of a light quantity diaphragm device described in the fourth embodiment. FIG. 6 is an explanatory diagram of an imaging optical system in the fourth embodiment.

  The fine structure according to the present invention is constituted by an infinite number of fine structures having a reflection reducing effect, which are arranged on a substrate, for example, as shown in FIG. 1 and arranged at a pitch shorter than the wavelength size of light. Is done. The optical filter according to the present invention includes an optical film that exhibits predetermined optical characteristics in addition to the above-described substrate and microstructure.

  The substrate for forming the microstructure or the optical film may be any substrate having the strength and optical characteristics of the microstructure or the optical film as the substrate, and a substrate that can function as a substrate is used. As such a substrate, a substrate made of a glass-based material such as BK7 or SFL-6, or PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PES (polyethersulfone), PC (polycarbonate), PO ( A substrate made of a resin material selected from polyolefin, PI (polyimide), PMMA (polymethylmethacrylate), TAC (triacetylcellulose), and the like can be used. A substrate made of a composite material of a glass substrate and a resin layer, an organic-inorganic hybrid substrate in which an organic material and an inorganic material are mixed, and the like can also be used.

  On the substrate as described above, a gradation type ND film having a plurality of different film thickness regions, for example, having a concentration gradient region in which the concentration is changed by changing the film thickness, and formed of a multilayer thin film is formed. To do. Such ND films include a type in which organic dyes or pigments that absorb light are mixed into a substrate and kneaded, and a type in which these are applied. There is a fatal defect that the wavelength dependence is too large. Therefore, a multilayer film is formed on a transparent substrate such as plastic or glass by a vacuum film formation method such as an evaporation method or a sputtering method, or a film formation method such as a sol-gel method, and the concentration gradient region is a multilayer including an absorption layer. It was set as the structure which changes the film thickness of the whole film | membrane continuously. Further, an optical film other than the ND film, such as an IR cut film or a UV cut film having a transparent region, may be used. These optical films may also be formed by a vacuum film formation method such as an evaporation method or a sputtering method, or a film formation method such as a sol-gel method. Thus, a multilayer film is formed on a transparent substrate such as plastic or glass.

  A fine structure that exhibits a reflection reduction effect is formed on the optical film such as the ND film as described above, and a functional film in which the optical film and the fine structure are combined is formed on the transparent substrate. When light is incident on a material, reflection called Fresnel reflection occurs on the surface of the material due to the difference in refractive index between the materials before and after the incidence. Such reflection can be reduced by reducing the difference in refractive index between materials. As one method for reducing this difference in refractive index, various methods using the structure of a substance have been proposed. Microstructures are being manufactured with recent improvements in microfabrication technology, and these microstructures with a concavo-convex structure typified by moth-eye have a continuous structure shape between two substances. In this way, the refractive index between substances is continuously changed to reduce reflection. The fine structure in the present invention is the above-described structure having a reflection reducing function, and has a concavo-convex shape arranged at a pitch shorter than the wavelength of visible light. As one type of such a fine structure, refraction from the atmosphere or an adjacent medium is caused by randomly formed protrusions such as needle-like bodies and columnar bodies, and protrusions or depressions of a concavo-convex structure finely formed in a staircase shape. What reduced the rate difference may be included, and what was arbitrarily selected according to the objective from the well-known fine structure can be used.

  Such a fine structure can be manufactured with good reproducibility using a method such as a thermal nanoimprint method or an optical nanoimprint method.

  Furthermore, in the case of the configuration according to the present invention, an interface is formed on the outermost layer of the multilayer film that forms the microstructure and the optical film, or between the microstructure and the substrate, but the microstructure has an effect of reducing reflection. In order to reduce the reflection as a whole of the optical filter, it is necessary to reduce the interface reflection between these different substances. Therefore, it is desirable to make the difference in refractive index between the two substances forming the interface as small as possible.

  Hereinafter, the optical filter and the optical device of the present invention will be specifically described based on examples.

Example 1
Regarding an embodiment in which a gradation type ND film having a concentration gradient region composed of a multilayer thin film is formed on a transparent substrate, and a fine structure is formed on the outermost layer portion of the ND filter, which is directly above the ND film. Is described in detail.

  First, in the configuration shown in FIG. 2, a BK-7 glass having a thickness of 1.0 mm is used as the substrate 10, and a uniform concentration region having a constant film thickness and a film thickness continuously change on one side of the substrate 10. The gradation ND film 11 composed of a multilayer thin film having a concentration gradient region is formed by a normal EB vapor deposition method that does not add any assist, and the other side of the substrate is turned upside down. On the surface, an antireflection film 14 composed of a multilayer thin film was produced by the same ordinary EB vapor deposition method. Such a vacuum deposition method has the advantages that the film thickness can be controlled relatively easily, the scattering in the visible light wavelength region is very small, and the wavelength dependence of the spectral transmittance can be controlled to a small value. Have. However, the film formation method is not limited to the EB vapor deposition method, and it is possible to form a film in a film formation method such as a sputtering method, an IAD method, an IBS method, an ion plating method, a cluster vapor deposition method, or a sol-gel method. A wet film forming method may be used, and the most appropriate film forming method may be selected in consideration of the purpose and conditions. Moreover, as an optical characteristic of the board | substrate 10 used for the ND filter 15 which is an optical filter like a present Example, 89% or more of the total light transmittance in a visible light wavelength range is preferable, and 91% or more is further more preferable.

As a thin film material constituting the gradation ND film 11, a dielectric layer such as SiO 2 or Al 2 O 3 and Ti, Nb, Ta, Zr, Ni, Cr, W, Mo, Au, Ag, Cu, Mg, Al In addition to light absorption layers composed of simple metals such as these, or alloys and metal compounds thereof, it is possible to use MgF 2 or SiO 2 with a relatively low refractive index for the purpose of reducing reflection particularly for the outermost layer. However, in this example, a laminated structure as shown in FIG. 4A was used, and the outermost layer was an SiO 2 layer. However, the present invention is not limited to this, and in addition to the MgF 2 listed above, for example, Al 2 O 3 , a material with a changed acid value such as SiO, SiN or the like, a metal compound of Si, Al, or Mg, or a mixture thereof. A layer or the like can be appropriately selected. Similarly, metal compounds such as Ti, Nb, Ta, Zr, Ni, Cr, W, Mo, Au, Ag, and Cu may be used. Similarly, various thin film materials can be used for the antireflection film 14. In the first embodiment, as shown in FIG. 4B, the outermost layer is made of SiO 2, and SiO 2 and TiO 2 are alternately made 5. Although the layered structure is used, the present invention is not limited to this, and can be selected as appropriate.

Here, in such a film configuration of the gradation ND film 11, in this embodiment, the SiO 2 layer which is the outermost layer of the ND film 11, and substances such as an adhesion layer and a fine structure formed thereon are formed. Reflection at the interface was ignored, and reflection at the other interface was canceled by the light interference effect, so that the total reflection at the other interface was made as small as possible. This is for the following reason.

  For example, consider a case where the fine structure 12 is formed directly on the gradation ND film 11. First, by reducing the difference in refractive index between the outermost layer of the gradation ND film 11 and the fine structure 12, the reflection at this interface is reduced as much as possible, and the reflection reduction effect of the fine structure is utilized. Reflection from the medium (air) to the outermost layer of the gradation ND film 11 is ideally reduced. Next, after the outermost layer toward the substrate 10 in the gradation ND film 11, reflection is reduced by the optical interference effect at the interface other than the interface between the outermost layer SiO 2 and the fine structure 12. And the reflection as the ND filter 15 whole is reduced by combining these two reflection reduction structures. In the optical filter formed of an optical film having a multilayer structure, the authors reflect at the interface between the outermost layer and the incident medium having a large refractive index difference between the outermost layer such as air, among all the interfaces. It has the greatest effect on the reflection as an optical filter, and it is possible to reduce the reflection formed by the optical interference effect by sufficiently reducing the reflection of this part and further canceling the reflection of all other interfaces. For example, the present inventors have found that the overall reflection as an optical filter can be further reduced. Therefore, with such a configuration, the reflection of the ND filter 15 can be significantly reduced. Here, the case where the fine structure 12 is formed immediately above the gradation ND film 11 has been described as an example, but the same concept is also applied when the fine structure 12 is formed on the gradation ND film 11 via the adhesion layer 13. Is possible. In this case, for example, the interface reflection between the gradation ND film 11 and the adhesion layer 13 is reduced, and the interface reflection between the adhesion layer 13 and the fine structure 12 is reduced, so that the reflection reduction effect of the fine structure is utilized. It ’s fine. As another method, the adhesion layer 13 is considered as the outermost layer of the gradation ND film 11, and after determining the multilayer film structure of the gradation ND film 11 with the same concept as described above, the adhesion layer as the outermost layer of the gradation ND film 11 is determined. By reducing the difference in refractive index between the fine structure 11 and the fine structure 12, reflection at this interface can be reduced, and reflection of the ND filter 15 as a whole can be reduced.

  A fine structure 12 was formed on the gradation ND film 11 produced as described above via an adhesion layer 13. Various manufacturing methods have been proposed for the microstructure, but in this example, an optical nanoimprint method using a UV (ultraviolet) curable resin was selected.

  First, in order to improve the adhesion between the outermost layer of the gradation ND film 11 and the fine structure 12, a primer treatment was performed, and an adhesion layer 13 was provided at the interface between them. As an example of such a primer solution, a solution containing TEOS added for the purpose of adding an appropriate amount of IPA, nitric acid or the like based on a silane coupling agent and further strengthening the adhesion is used. This is dropped onto a substrate through a 0.2 μm PTFE (polytetrafluoroethylene) filter, applied to form an ultrathin film by spin coating, and then subjected to a drying process or the like under predetermined conditions, whereby an adhesion layer 13 is formed. Form. Furthermore, in the range that does not have any adverse effect on other layers such as the substrate 10 and the gradation ND film 11, in order to more uniformly apply the primer solution, hydrophilic treatment with UV ozone or the like before applying the primer solution. May be applied. It is also possible to limit the coating area by applying masking when applying such a process, or changing the film formation process to the inkjet method, gravure method, micro contact printing method, etc. is there.

At this time, as described above, when a higher reflection reduction effect is required, the refractive index difference at the adjacent interface is preferably adjusted to 0.1 or less, and more preferably 0.05 or less. In Example 1, the refractive index at a wavelength of 540 nm of the adhesion layer 13 is adjusted to 1.47, and the outermost layer SiO 2 of the gradation ND film 11 serving as an interface layer with the gradation ND film 11. Since the refractive index of 1.46 and the refractive index of the microstructure 12 is 1.51, the refractive index difference at each interface is set to 0.01 and 0.04.

  Next, the fine structure 12 in Example 1 is formed in a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure is a bell-shaped moth-eye shape, and the period of the structure is about 250 nm. Furthermore, with regard to the arrangement of the protrusion structures, a square arrangement, a three-way (hexagonal) arrangement, and the like are conceivable. For this reason, a three-way array was used in this example.

Further, as shown in Figure 2, although the uniform density region is a microstructure 12 is substantially the same overall height, so that the film thickness of the gradation ND film 11 becomes higher thin Ihodo structure height with a gradient region Configured. This is for the purpose of reducing the phase difference due to the film thickness difference of the gradation ND film 11, and the optimum fine structure height varies greatly depending on the refractive index of the structure and the constituent material of the gradation ND film 11. At the same time, since the fine structure 12 is expected to have a reflection reducing effect, a structure height capable of sufficiently suppressing reflection of light in the visible wavelength region is particularly necessary. In the configuration of this embodiment, the structure is approximately 250 nm or more. Needed. As described above, in this embodiment, the structure height is about 250 nm in the uniform concentration region and the structure height is about 250 nm to 500 nm in the concentration gradient region.

  First, an appropriate amount of a UV curable resin was dropped on a substrate through a 0.2 μm PTFE filter, and then the UV curable resin was applied to the entire surface of the substrate so as to have a predetermined film thickness by spin coating. After that, the quartz mold that has been subjected to mold release processing is pressed against the designed hole array by reversing the desired shape, taking into account the curing shrinkage of the resin, and this state is maintained for a short time. In this state, the resin was cured by irradiating UV light, and the fine structure 12 was produced. Various kinds of materials can be used for such a UV curable resin. In this embodiment, an acrylic UV curable resin is used. However, a fluorine resin, a resin obtained by adding a fluorine component to an acrylic resin, and others. A material mainly composed of the above resin may be used, and depending on the imprint process, an inorganic material such as SOG or an organic-inorganic hybrid type material may be used.

  Here, in the case of a filter having absorption in the entire visible wavelength region such as an ND filter, it often has absorption in the ultraviolet region. Therefore, depending on the wavelength of the UV light to be used, when light is irradiated from the substrate side of the filter, the ND filter absorbs at least part of the light, and sufficient light may not reach the resin. Therefore, in such a case, it is necessary to irradiate UV light from the mold side, and it is necessary to select a mold made of a material that sufficiently transmits the wavelength of the necessary UV light.

  The ND filter 15 manufactured as described above is fine with a high reflection reduction effect by adjusting the structure height so as to reduce the phase difference caused by the film thickness difference in the density gradient region in accordance with the film thickness of the gradation ND film 11. By forming a structure and forming a five-layer antireflection film on the back side of the substrate, it is possible to sufficiently reduce reflection and reduce the phase difference at the same time in the entire area of the filter.

(Example 2)
In the configuration of the first embodiment, details will be described below with respect to an embodiment in which another fine structure having a reflection reducing effect is formed on the surface opposite to the surface on the substrate on which the gradation ND film and the fine structure are formed. .

  In addition, a stabilizer such as an antioxidant or an ultraviolet absorber may be dispersed in the colloidal crystal layer. These stabilizers have the effect of reducing changes over time in the spectral and physical properties of the optical filter. Especially when a plastic substrate such as PC that is weak against ultraviolet rays is used, a light absorber such as a dye is added to the colloidal crystal layer. It is effective when added. Antioxidants include phenol, binderd phenol, amine, binderd amine, sulfur, phosphoric acid, phosphorous acid, etc. UV absorbers include benzophenone, benzotriazole Benzoate and the like, but are not limited thereto. These antioxidants and ultraviolet absorbers may be used alone or in combination.

  In the configuration shown in FIG. 5, first, a gradation film ND composed of a multilayer thin film having a uniform density portion and a density gradient region on one side of the substrate 20 using a PET film having a thickness of 0.075 mm as the substrate 20. A film 21 was formed. In forming the concentration gradient region, in this embodiment, a method of forming a film by installing a mask as shown in FIG. 3 on the film forming surface side on each film forming substrate was selected. Such a gradation ND film 21 has a laminated structure as shown in FIG.

  Here, in the film configuration of the gradation ND film 21, in this embodiment, in the configuration shown in FIG. 5, the adhesion layer 24 is regarded as the outermost layer of the gradation ND film 21, and the interface between the adhesion layer 24 and the fine structure 22. The film configuration is such that the reflection at each interface between the other multilayer films constituting the gradation ND film 21 is canceled by the light interference effect.

  A fine structure 22 was formed on the gradation ND film 21 produced as described above via an adhesion layer 24, and a second fine structure 23 was also formed on the other surface of the substrate. For the production of the fine structure, the photo nanoimprint method using a UV curable resin was selected in this example.

  First, in order to improve the adhesion between the outermost layer of the gradation ND film 21 and the fine structure 22, primer treatment was performed, and an adhesion layer 24 was provided at the interface between them. As an example of such a primer solution, a solution obtained by adding an appropriate amount of IPA, nitric acid or the like based on a silane coupling agent and further adding TEOS was used. This is dropped on a substrate through a 0.2 μm PTFE filter, applied to form an ultrathin film by spin coating, and then subjected to a drying process or the like under predetermined conditions to form the adhesion layer 24.

At this time, in order to obtain a higher reflection reduction effect, in Example 2, the refractive index at the wavelength 540 nm of the adhesion layer 24 is adjusted to 1.47, and the interface with the gradation ND film 21 is adjusted. Since the refractive index of the outermost layer SiO 2 of the gradation ND film 21 to be a layer is 1.46 and the refractive index of the fine structure 22 is 1.51, the refractive index difference at each interface of the adhesion layer is 0 0.01, 0.04, and 0.05 or less.

  The fine structure 22 and the second fine structure 23 in Example 2 have a pillar array shape in which protrusion structures as shown in FIG. 1 are periodically arranged, and the structure has a bell-shaped moth-eye shape. The body period was about 250 nm. Further, the protrusion structure was arranged in a three-way arrangement.

  Further, as shown in FIG. 5, the fine structures 22 have substantially the same structural height in the uniform concentration region, but in the concentration gradient region, the structure height increases as the film thickness of the gradation ND film 21 increases. . More specifically, the structure height is about 250 nm in the uniform concentration region, and the structure height is about 250 nm to 500 nm in the concentration gradient region. Further, the second fine structure 23 formed on the other surface of the substrate has the same structural height of 250 nm in the entire region.

  First, an appropriate amount of a UV curable resin was dropped on a substrate through a 0.2 μm PTFE filter, and then the UV curable resin was applied to the entire surface of the substrate so as to have a predetermined film thickness by spin coating. After that, the quartz mold that has been subjected to mold release processing is pressed against the designed hole array by reversing the desired shape, taking into account the curing shrinkage of the resin, and this state is maintained for a short time. In this state, the resin was cured by irradiating UV light, and the fine structure 22 was produced.

  Thereafter, the front and back of the substrate were reversed, and a second microstructure 23 was produced on the other surface of the substrate by the same method. At this time, in this embodiment, the second microstructure 23 is formed directly on the substrate 20, but an adhesion layer may be inserted at this interface.

  The ND filter 25 manufactured as described above is fine with a high reflection reduction effect by adjusting the structure height so as to reduce the phase difference caused by the film thickness difference in the density gradient region in accordance with the film thickness of the gradation ND film 21. By forming the structure 22 and further forming the second microstructure 23 having a high reflection reduction effect on the other surface of the substrate, the reflection can be sufficiently reduced in the entire region within the filter, and at the same time. It is possible to reduce the phase difference.

  In Example 2, the nanoimprint process was repeated twice to form fine structures on both sides of the substrate. However, after applying the resin to the front and back of the substrate by spin coating or dip coating, both sides were simultaneously coated. A similar microstructure can be formed by UV nanoimprinting.

Example 3
Details of other configuration examples other than those described in the first and second embodiments illustrated in FIGS. 6A to 6B will be described below. In Example 3, a 0.075 mm PET film is used as the substrate, and the ultrathin adhesive layer used in Examples 1 and 2 is used at the interface between the ND film and the fine structure. Is provided. On the other hand, when the fine structure is directly formed on the substrate, the adhesion layer is not provided, but it is possible to insert the adhesion layer as necessary at each interface.

(Example 2)
FIG. 6A is based on the configuration of the second embodiment. In the ND filter 37, in addition to a uniform density region having a constant film thickness and a density gradient region in which the film thickness continuously changes, a transparent region is added. This is a configuration example in which the reflection of the incident light and the phase difference of the region including the transparent region of the ND filter 37 are simultaneously reduced by adjusting the structure height of the fine structure 33. By adopting such a configuration, it is possible to apply the configuration of the present invention to a ND filter having a transparent portion.

  FIG. 6B shows the uniform density region of the gradation ND film 31 and the structure height of the fine structure 33 provided on the concentration gradient region, and the concentration of the second fine structure 34 formed on the back surface of the substrate. This is a configuration example in which the structural height in the gradient region is adjusted, thereby reducing the reflection and phase difference of incident light in the ND filter 37 at the same time.

Further, in addition to changing the structural height of the fine structure 33 provided on the concentration gradient region of the gradation ND film 31, the structure height in the concentration gradient region of the second fine structure 34 formed on the back surface of the substrate. May be adjusted . This is a configuration example in which reflection and phase difference with respect to incident light in the entire area of the ND filter 37 are simultaneously reduced. With such a configuration, the structure height necessary for reducing the phase difference can be divided on the front and back of the substrate, so that the structure height in one fine structure can be set low. Become. By reducing the height of the structure, the rigidity of the formed microstructure is increased, and the productivity in the formation process of the microstructure such as the nanoimprint process described in Example 1 and Example 2 is further increased. Can do.

Change the structural height of the Gradient ND film 31 of the density gradient regions on the provided microstructure body 33 not only further overall height of the microstructure 33, with respect to the substrate 30, the height from the substrate 30 You may form so that a position may also differ . This is a configuration example in which reflection and phase difference with respect to incident light in the entire area of the ND filter 37 are simultaneously reduced. With such a configuration, the range of phase difference adjustment in the fine structure is expanded, and the effect of reducing the phase difference by the fine structure can be further increased.

The board both surfaces, and the thickness is constant uniform density region has a concentration gradient region where the film thickness varies continuously, the gradation ND film 31 composed of a multilayer thin film and the second gradient film 32 Further, the boundary position between the uniform density region and the density gradient region may be arranged so as to be substantially the same on both surfaces of the substrate . This is a configuration example in which reflection and phase difference in the entire area of the ND filter 37 are simultaneously reduced.

As a modification of the configuration described in the previous paragraph, a gradation ND composed of a multilayer thin film having a uniform concentration region with a constant film thickness and a concentration gradient region with a continuously changing film thickness on both surfaces of the substrate. The film 31 and the second gradation film 32 may be configured, and the boundary position between the uniform density region and the density gradient region may be arranged to be different on both surfaces of the substrate . This is a configuration example in which reflection and phase difference in the entire area of the ND filter 37 are simultaneously reduced. With the configuration described in the previous paragraph, it is possible to produce a gradation ND filter that is divided and arranged on both sides of the substrate. For example, the spectral reflectance characteristics on both sides of the substrate can be adjusted to a closer dispersion shape. In addition, it is possible to cope with a high-density ND filter.

Further, the with multiple density regions within the same filter, it is also possible to stepwise applied to the ND filter of the multi-density type of concentration change. Basically, the thicker the film thickness is, the higher the concentration is, and the structure height of the fine structure 33 is adjusted so as to reduce the phase difference in accordance with the film thickness in each concentration region of the multi-concentration ND film 39 . Concentration region can function as multi-density type of ND filter be two or more.

  In addition, the present invention is not limited to these configurations, and the configurations of the first and second embodiments may be included, and a configuration in which two or more portions each characterized by the configuration are combined may be used. The optimal configuration is appropriately selected. It is possible.

  Furthermore, in the first to third embodiments, the method of reducing the phase difference was selected by adjusting the height of the fine structure. However, the present invention is not limited to this. For example, in FIGS. As shown, the phase difference can be reduced by adjusting the outer shape of the fine structure, and these elements including the height can be combined and reduced.

  The basic configuration as shown in the first to third embodiments can be applied to other optical filters. For example, an IR cut filter or a UVIR cut filter used for a surveillance camera having a mechanism for inserting and removing the filter can be used. In the case of such an IR cut filter, an optical path difference occurs in the optical system depending on the presence or absence of the filter, and the image sensor may be deteriorated because the arrangement position and the focal position of the image sensor are changed. In order to reduce the optical path difference (phase difference), a transparent filter such as transparent glass or film may be inserted as a dummy. However, with an IR cut film composed of a multilayer thin film or the like, it is difficult to improve even the phase difference caused by the film thickness difference between the IR cut filter and the transparent filter. Therefore, a microstructure having a reflection reducing effect is formed on the substrate of the transparent filter and has a reflection reducing effect constituted by countless microstructures arranged at a pitch shorter than the wavelength of light, and the structural height of the microstructure is further increased. By adjusting the fine structure shape so as to reduce the phase difference that occurs when the incident light is transmitted through the IR cut film, the reflection by the transparent filter and the position of the IR cut filter and the transparent filter are adjusted. It is possible to reduce the phase difference. In this case, in the IR cut filter, it is also possible to adjust the phase difference by forming a fine structure having a reflection reducing effect on the IR cut film.

  Furthermore, the functions of an IR cut filter and a transparent filter are formed on a single substrate, that is, an IR cut region having an IR cut film and a transparent region having no IR cut film are provided on the same substrate. Furthermore, a fine structure having a reflection reducing effect constituted by a fine structure arranged innumerably at a pitch shorter than the wavelength size of light, between the light that passes through the IR cut film and the light that does not pass through the IR cut film. It is possible to simultaneously reduce reflection and phase difference of the IR cut filter by adjusting and arranging the fine structure shapes in the IR cut region and the transparent region so as to reduce the phase difference generated in FIG.

  As described above, in an optical filter having a plurality of regions having different film thicknesses or an optical device using a plurality of optical filters having different film thicknesses, light having a reflection reducing effect on each region or a film forming each filter. Forming a fine structure composed of countless fine structures arranged at a pitch shorter than the wavelength size of the light, and further reducing the phase difference due to the respective film thicknesses against incident light By adjusting the shape, it is possible to reduce the phase difference while reducing the reflection of the optical filter, and it is possible to achieve high accuracy.

(Example 5)
Next, an embodiment in which the ND filter produced in the first to third embodiments is applied to a light quantity diaphragm device will be described with reference to FIG.

  FIG. 8 shows a light quantity diaphragm device. A diaphragm of a light amount diaphragm device suitable for use in an imaging system such as a video camera or a digital still camera is provided for controlling the amount of light incident on a solid-state imaging device such as a CCD or CMOS sensor. As the field of view becomes brighter, the diaphragm blades 41 are controlled so as to be further narrowed down. At this time, as a countermeasure against image performance degradation that occurs in a small aperture state, an ND filter 44 is arranged in the vicinity of the aperture so that the aperture of the aperture can be made larger even if the brightness of the object field is the same. ing. Incident light passes through the light amount diaphragm device 43 and reaches a solid-state imaging device (not shown), whereby it is converted into an electrical signal and an image is formed.

  The ND filter produced in the first to third embodiments is disposed in the light quantity diaphragm device 43. Furthermore, it is also possible to arrange the ND filter 44 so as to be fixed to the diaphragm blade support plate 42. In this case, although it depends on the position where the ND filter is disposed and the mechanical mechanism of the light quantity diaphragm device 43, it may be assumed that the required outer shape is different from the filter produced in this embodiment, but the optimum shape is selected. Just choose.

(Example 6)
Next, an embodiment applied to a photographing apparatus such as a video camera provided with the optical filter produced in the first to third embodiments will be described with reference to FIG.

  FIG. 9 shows a photographing apparatus such as a video camera. Light rays that have passed through the photographing optical system 51 including the diaphragm blades 55 and the lens units 51 </ b> A to 51 </ b> D are restricted by the ND filter 54 according to the characteristics of the solid-state imaging device 52. And it is supposed to obtain a proper image. Reference numeral 51 denotes a photographing optical system having lens units 51A to 51D. A solid-state image sensor 52 such as a CCD receives the images of the light rays a and b formed by the photographing optical system 51 and converts them into electric signals. 53 is an optical low-pass filter. The imaging optical system 51 includes a light amount diaphragm device including the ND filter 54, the diaphragm blades 55 and 56, and the ground plane 57 shown in FIG.

  At the position of the ND filter 54, the ND filter 54 manufactured in the first to third embodiments is disposed. These filters can be driven in and out freely. More specifically, the ND filter 54 is driven by determining the amount of light that has passed through the photographing optical system 51 and formed on the image sensor 52. When the amount of incident light is excessive for normal photographing, the ND filter 54 is moved so as to cover the solid-state image sensor 52. Conversely, when the amount of light is insufficient, the solid-state imaging device 52 is retracted out of the optical path. Depending on the presence or absence of the ND filter 54, an optical path difference may occur in the light beam to be imaged, and the image may deteriorate. In such a case, a base material made of the same material as the base material of the optical filter is used as a dummy. As shown in FIG. 6A, or by providing a transparent portion in the ND filter 54 as shown in FIG. 6A and using this area, image degradation can be suppressed.

  The imaging device thus manufactured can remarkably reduce inconveniences such as reflection of the filter with respect to incident light and image degradation due to the phase difference.

  Not only this but also other optical devices, by using the ND filter as produced in Examples 1 to 3, it is possible to remarkably reduce problems on the device due to the reflection and phase difference of the filter. It is possible to achieve higher accuracy than this.

10, 20, 30. Substrates 11, 21, 31. Gradation ND film 32. Second gradation ND films 12, 22, 33. Microstructures 23, 34. Second microstructures 13, 24, 35, 36. Adhesion layers 14, 38. Antireflection film 15, 25, 37. ND filter 39. Multi-concentration ND film

16. Mask 17. Shield

41. Diaphragm blade 42. Diaphragm blade indicating plate 43. Light amount diaphragm device 44. ND filter

51. Shooting optical system 52. Solid-state image sensor 53. Optical low-pass filter 54. ND filter 55. Diaphragm blade 56. Diaphragm blade 57. Ground plane

Claims (10)

  1. A transparent substrate that transmits light in the visible wavelength region;
    A functional film provided on the transparent substrate,
    The functional film includes an optical film having a plurality of regions having different film thicknesses provided on the transparent substrate, and a plurality of microstructures at a pitch shorter than the wavelength size of light provided on the optical film. A formed microstructure, and
    The optical filter according to claim 1, wherein the microstructure has a shape different from that of the plurality of regions.
  2.   The optical filter according to claim 1, wherein the fine structure has a fine structure including a plurality of convex portions having different heights in the plurality of regions.
  3.   The optical filter according to claim 1, wherein a reflection reducing structure is formed on the other surface side opposite to the one surface side of the transparent substrate on which the fine structure is formed.
  4.   The optical filter according to claim 3, wherein the reflection reducing structure has another fine structure formed with a plurality of pitches shorter than the wavelength size of light.
  5. In order to reduce the phase difference of incident light in the plurality of regions,
    The shape of the other fine structure is changed, respectively,
    The optical filter according to claim 4.
  6. The shape of the other microstructure is characterized by a structure height of the other fine structures,
    The optical filter according to claim 5.
  7.   The optical filter according to claim 3, wherein a multilayer thin film including an optical attenuation film that attenuates transmitted light in a visible wavelength region is formed on the other surface side of the transparent substrate. .
  8.   The optical filter according to claim 1, wherein a transparent region not having the functional film is provided on the transparent substrate.
  9. A transparent substrate that transmits light in the visible wavelength region;
    A functional film provided on the transparent substrate,
    The functional film includes an optical film provided with a plurality of regions having different thicknesses provided on the transparent substrate, and a plurality of microstructures at a pitch shorter than a wavelength size of light provided on the optical film. A formed microstructure, and
    The optical filter, wherein the fine structure has a fine structure having a different shape according to a change in the thickness of the optical film.
  10.   An optical device comprising the optical filter according to claim 1.
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