JP2009015032A - Optical low pass filter and manufacturing method thereof and imaging optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact optical low pass filter which is manufactured easily and easily positioned to an optical system. <P>SOLUTION: This optical low pass filter 1 comprises a glass substrate 10, a matrix 14, and a sheet-type refractive index modulation type phase grating 12 which has a different refractive index from the matrix and has a plurality of columnar structures 16 arranged in the matrix like a grating so as to extend in the thickness direction. The glass substrate and the refractive index modulation type phase grating are joined so that the glass substrate contacts one end side of the plurality of columnar structures of the refractive index modulation type phase grating. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an optical low-pass filter and an imaging optical system including the optical low-pass filter, and more particularly, to an optical low-pass filter used for preventing moire in a digital camera or the like mounted on a mobile phone or the like. The present invention relates to an imaging optical system.
The present invention also relates to a method for manufacturing an optical low-pass filter.

  The increase in the size and size of an image sensor using a solid-state image sensor such as a CCD or CMOS is remarkable. In recent years, such image sensors have been widely used in optical devices such as mobile phones or in-vehicle digital cameras. In these applications, there is an increasing demand for further increase in the number of pixels and miniaturization of the optical device. For this reason, the imaging optical system including the image sensor is being made more compact.

  A packaging technique called Wafer Level Chip Size Package (WL-CSP) is attracting attention as a method for manufacturing a sensor suitable for downsizing. In WL-CSP, rewiring and protection layers / terminals are formed in a wafer state, so that the package mounting area is the same as that of a semiconductor chip. Therefore, WL-CSP has a feature that the package can be significantly reduced in size compared with a general package in which a wafer is divided into individual pieces and then molded with a resin or the like to form terminals.

By the way, in an image pickup optical system using an image pickup device such as a CCD or CMOS, the image pickup devices are regularly arranged in a lattice pattern, so that a pseudo signal (moire) is generated in the generated subject image. Inconvenience in color reproduction may occur. In order to solve such a problem, an optical low-pass filter that cuts wavelengths above a specific frequency is used.
As such an optical low-pass filter, those using the birefringence of quartz and those using diffraction of a phase grating (see Patent Documents 1 and 2) are known, but an imaging optical system including an image sensor is known. As the size of the optical low-pass filter increases, there is an increasing demand for miniaturization of these optical low-pass filters.

JP 2002-156608 A JP 2007-34260 A

  The optical low-pass filter using the birefringence of quartz adopts a structure in which two quartz plates are arranged on both sides of a quarter-wave plate or a combination of three quartz plates, so the thickness is 1 mm or more. Thus, there is a problem that it is extremely difficult to satisfy the demand for downsizing. Further, the optical low-pass filter using the birefringence of quartz has a problem that the quartz of the material is expensive.

  In addition, the optical low-pass filter of Patent Document 1 has a concavo-convex phase grating formed on one side of a substrate, but in a region having a size suitable for a wafer size of 8 inches or more necessary for WL-CSP. There is a problem that it is extremely difficult to form a concavo-convex phase grating uniformly.

  Furthermore, in an optical low-pass filter using phase grating diffraction, such as the optical low-pass filter of Patent Document 2, when used in an imaging optical system, solid-state imaging is performed based on the pitch of the diffraction grating and the pixel pitch of the solid-state imaging device. Although the optimum distance between the element and the optical low-pass filter must be determined, there is a problem in that it is difficult to position the optical low-pass filter when mounted and it takes time and effort to incorporate it into the imaging optical system.

  The present invention has been made to solve such problems, and provides an optical low-pass filter or the like that is small in size and easy to manufacture and can be easily positioned with respect to an optical system. Objective.

According to the present invention,
A glass substrate;
A sheet-like refractive index modulation type phase grating having a matrix and a plurality of columnar structures arranged in a lattice shape in the matrix so as to extend in the thickness direction and have a refractive index different from that of the matrix. ,
The glass substrate and the refractive index modulation type phase grating are bonded so that the glass substrate is in contact with one end surfaces of the plurality of columnar structures of the refractive index modulation type phase grating.
An optical low-pass filter is provided.

  According to such a configuration, it is small and easy to manufacture, and can be easily positioned with respect to the optical system.

According to another preferred aspect of the present invention, the glass substrate and the refractive index modulation type phase grating are integrally joined by a silane coupling agent.
According to such a configuration, the glass substrate and the refractive index modulation type phase grating can be easily and firmly bonded.

  According to a preferred embodiment of the present invention, the matrix and the columnar structure constitute a refractive index modulation type phase grating, and the diffraction efficiency of the refractive index modulation type phase grating is 10% or more.

According to a preferred embodiment of the present invention, the columnar structure has an aspect ratio of 10 or more.
According to such a configuration, the diffraction efficiency can be increased.

According to a preferred embodiment of the present invention, the glass substrate has infrared cut performance.
According to such a configuration, the visibility can be corrected, so that it can be suitably used for an imaging optical system using a CCD.

According to the present invention, in an imaging optical system comprising the optical low-pass filter and a solid-state imaging device,
The optical low-pass filter is arranged such that the surface on the glass substrate side faces the solid-state image sensor,
A gap layer is provided between the optical low-pass filter and the solid-state image sensor,
An imaging optical system is provided.

  According to such a configuration, the optical low-pass filter can be easily positioned based on the glass substrate. Further, since the glass can be used as a protective glass for the imaging optical system, the imaging optical system can be reduced in size, and the process can be simplified to increase productivity.

According to the present invention, an optical low-pass filter manufacturing method in which a glass substrate and a refractive index modulation type phase grating are joined,
Applying a photopolymerizable composition onto the glass substrate to form a mold; and
Placing a photomask between a light source and the mold;
A first irradiation step of irradiating the mold with parallel light having a full width at half maximum of 100 nm or less and having a uniform light intensity distribution from the light source through the photomask;
A second irradiation step of removing the photomask, and further irradiating the mold with parallel light having a full width at half maximum of 100 nm or less and having a uniform light intensity distribution from the light source. ,
An optical low-pass filter manufacturing method is provided.

  According to such a configuration, an optical low-pass filter that is small in size and can be easily positioned with respect to the optical system can be easily manufactured.

According to a preferred embodiment of the present invention, the photopolymerizable composition includes a silane coupling agent.
According to such a configuration, an optical low-pass filter in which the glass substrate and the refractive index modulation type phase grating are integrally joined can be manufactured with fewer steps.

  According to the present invention, an optical low-pass filter and the like that are small in size and easy to manufacture and can be easily positioned with respect to the optical system are provided.

  Hereinafter, an optical low-pass filter 1 according to a preferred embodiment of the present invention and an imaging optical system using the same will be described with reference to the accompanying drawings. FIG. 1 is a drawing schematically showing a configuration of an imaging optical system 2 using an optical low-pass filter 1.

The imaging optical system 2 according to the present embodiment is an imaging apparatus that captures an image using a solid-state imaging device having pixels arranged at a predetermined pitch, such as an optical system of a small digital camera mounted on a digital still camera, a cellular phone, or the like. Used as an optical system or the like.
As shown in FIG. 1, the imaging optical system 2 includes an optical low-pass filter 1, a solid-state imaging device 4, and a lens 6.

  In the imaging optical system 2 of the present embodiment, the solid-state imaging device 4 is a two-dimensional arrangement of a large number of light receiving elements on a silicon substrate, and charges generated by each light receiving element are detected by a CCD element or a CMOS circuit. This is an area image sensor that can be transferred to the outside as a signal.

In the present embodiment, the optical low-pass filter 1 is attached to the light receiving surface of the solid-state imaging device 4 with the adhesive layer 8 through a predetermined gap layer. The adhesive layer 8 may use any adhesive, but preferably has a sufficient hardness so that the thickness of the gap layer can be appropriately maintained.
In order to increase the positioning accuracy of the optical low-pass filter 1 with respect to the solid-state imaging device 4, an adhesive with a small change in thickness before and after curing is more preferable. The thickness of the gap layer, that is, the thickness of the adhesive layer is not particularly limited, but is preferably in the range of 0.1 μm to 1000 μm, more preferably in the range of 1 μm to 100 μm.

  The lens 6 is a glass lens made of inorganic glass or a plastic lens made of polycarbonate resin, acrylic resin, polystyrene resin, polyolefin resin, or the like.

  The optical low-pass filter 1 includes a glass substrate 10 and a refractive index modulation type phase grating 12 in the form of a sheet or film integrally bonded to the surface of the glass substrate 10.

  The glass substrate 10 is not particularly limited as long as it is a generally used inorganic glass or the like. However, when a visibility correction is required, such as when a CCD or the like is used for the solid-state imaging device 4, the near-infrared region is used. More preferably, it has a function of cutting light. The thickness of the glass substrate 10 is, for example, 50 to 1000 μm, and preferably 100 to 500 μm.

  FIG. 2 is a perspective view schematically showing the internal structure of the refractive index modulation type phase grating 12. The refractive index modulation type phase grating 12 includes a matrix 14 made of a photopolymerizable composition and a number of columnar structures 16 made of a photopolymerizable composition disposed in the matrix 14. Both the matrix 14 and the columnar structure 16 have translucency, and the columnar structure 16 and the matrix 14 have different refractive indexes.

  Each columnar structure 16 extends within the matrix 14 in the thickness direction of the sheet or film-like refractive index modulation type phase grating 12, and the upper and lower ends thereof are the upper surface of the sheet or film-like refractive index modulation type phase grating 12. And oriented so as to constitute a part of the lower surface, and further arranged in a lattice pattern along the surface of the refractive index modulation type phase grating 12 in the form of a sheet or film.

The diameter of the columnar structure 16 (in the case of a prismatic shape, the diameter of a circumscribed circle) is 80 nm to 1000 μm, preferably 90 nm to 100 μm, more preferably 100 nm to 50 μm.
In the present embodiment, the arrangement period of the columnar structures 16 is set to 80 nm to 1000 μm, preferably 90 nm to 100 μm, more preferably 100 nm to 50 μm.

  Thus, by setting the diameter or the arrangement period of the columnar structures 16 within this range, the interference effect with respect to light in the wavelength range of 350 nm to 2000 nm can be sufficiently exhibited, and the wavelength usable as an optical low-pass filter. High-level light control such as diffraction and deflection is possible in the range.

  The sheet or film-like refractive index modulation type phase grating 12 having such a configuration is attached to the surface of the glass substrate 10 so that one end surface of the columnar structure 16 is in contact with the surface of the crow substrate 10. They are joined together.

  The refractive index modulation type phase grating 12 of the present embodiment is formed by irradiating light to a photopolymerizable composition and polymerizing and curing it. As the photopolymerizable composition, one containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator is used.

  The bifunctional or higher polyfunctional monomer is not particularly limited as long as it is a monomer having two or more polymerizable carbon-carbon double bonds in the molecule, but includes a (meth) acryloyl group. Those containing (meth) acrylic monomers, vinyl groups, allyl groups and the like are particularly preferred.

  Specific examples of such a bifunctional or higher polyfunctional monomer include triethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, 1,4-butanediol di ( (Meth) acrylate, 1,6-hexanediol di (meth) acrylate, hydrogenated dicyclopentadienyl di (meth) acrylate, ethylene oxide modified bisphenol A di (meth) acrylate, trimethylolpropane tri (meth) acrylate, penta Erythritol tetra (meth) acrylate, tetramethylolmethane tetra (meth) acrylate, pentaerythritol hexa (meth) acrylate, polyfunctional epoxy (meth) acrylate, polyfunctional urethane (meth) acrylate Examples include divinylbenzene, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diallyl chlorendate, N, N′-m-phenylene bismaleimide, diallyl phthalate, and the like alone or in combination of two or more. Can be used as a mixture.

  When a polyfunctional monomer having three or more polymerizable carbon-carbon double bonds in the molecule is used, the density of the crosslinking density due to the difference in the degree of polymerization is likely to increase, and a columnar structure is likely to be formed.

  Particularly preferred polyfunctional monomers having three or more polymerizable carbon-carbon double bonds are trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, tetramethylolmethanetetra (meth) acrylate, penta There is erythritol hexa (meth) acrylate.

  When two or more polyfunctional monomers or oligomers are used as the photopolymerizable composition, it is preferable to use those having different refractive indexes of the respective homopolymers, and those having a large difference in refractive index are combined. Is more preferable. In order to obtain functions such as diffraction, deflection, and diffusion with high efficiency, it is necessary to increase the refractive index difference, and the refractive index difference is preferably 0.01 or more. More preferably. When the monomer diffuses during the polymerization process, the difference in refractive index increases, so it is preferable to combine those having a large difference in diffusion constant.

  In addition, when using 3 or more types of polyfunctional monomers or oligomers, the refractive index difference between at least any two of the respective homopolymers may be within the above range. Further, by changing the weight ratio of the two monomers or oligomers having the largest refractive index difference of the homopolymer, the refractive index between the columnar structure 16 of the refractive index modulation type phase grating 12 and the matrix 14 can be adjusted. It is possible to adjust optical characteristics such as diffraction efficiency, deflection, and diffusion. In order to obtain functions such as high-efficiency diffraction, deflection, and diffusion, the weight ratio is preferably 10:90 to 90:10.

  In the present embodiment, a monofunctional monomer or oligomer having one polymerizable carbon-carbon double bond in the molecule may be used as the photopolymerizable composition together with the polyfunctional monomer or oligomer as described above. Good.

  As such a monofunctional monomer or oligomer, those containing a (meth) acryl monomer containing a (meth) acryloyl group, a vinyl group, an allyl group or the like are particularly preferable. Each homopolymer is particularly preferably one having a large difference in refractive index from that of a polyfunctional monomer or oligomer, and the difference in refractive index is preferably 0.01 or more, preferably 0.05 or more. Is more preferable.

  Specific examples of the monofunctional monomer include, for example, methyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, ethyl carbitol (meth) acrylate, dicyclopentenyloxyethyl (meth) acrylate, isobornyl (meth) acrylate, phenyl Carbitol (meth) acrylate, nonylphenoxyethyl (meth) acrylate, 2-hydroxy-3-phenoxypropyl (meth) acrylate, (meth) acryloyloxyethyl succinate, (meth) acryloyloxyethyl phthalate, phenyl (meth) acrylate , Cyanoethyl (meth) acrylate, Tribromophenyl (meth) acrylate, Phenoxyethyl (meth) acrylate, Tribromophenoxyethyl (meth) acrylate, Ben (Meth) acrylate, p-bromobenzyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, trifluoroethyl (meth) acrylate, 2,2,3,3-tetrafluoropropyl (meth) ) (Meth) acrylate compounds such as acrylates; vinyl compounds such as styrene, p-chlorostyrene, vinyl acetate, acrylonitrile, N-vinylpyrrolidone, vinylnaphthalene; allyl compounds such as ethylene glycol bisallyl carbonate, diallyl phthalate, diallyl isophthalate Etc.

  These monofunctional monomers or oligomers are used for imparting flexibility to the refractive index modulation type phase grating 12 and for adjusting the refractive index difference between the columnar structure 16 and the matrix 14. The amount of the monofunctional monomer or oligomer is preferably in the range of 10 to 99% by mass, more preferably in the range of 10 to 50% by mass, of the total amount with the polyfunctional monomer or oligomer.

  Further, as the photopolymerizable composition, a homogeneous solution mixture containing the polyfunctional monomer or oligomer and a compound having no polymerizable carbon-carbon double bond can be used. Examples of the compound having no polymerizable carbon-carbon double bond include polymers such as polystyrene, polymethyl methacrylate, polyethylene oxide, polyvinyl pyrrolidone, polyvinyl alcohol, and nylon, toluene, n-hexane, cyclohexane, acetone, and methyl ethyl ketone. , Low molecular weight compounds such as methyl alcohol, ethyl alcohol, ethyl acetate, acetonitrile, dimethylacetamide, dimethylformamide, and tetrahydrofuran, organic halogen compounds, organosilicon compounds, plasticizers, additives such as stabilizers, and the like.

  These compounds having no polymerizable carbon-carbon double bond are used for reducing the viscosity of the photopolymerizable composition and improving the handleability when producing the refractive index modulation type phase grating 12, or for polymers or inorganic compounds. Is used to improve the curability by reducing the monomer component ratio, and the amount used is preferably in the range of 1 to 99% by mass of the total amount with the polyfunctional monomer or oligomer, and the handleability is also good. In order to form a columnar structure having a regular arrangement while improving, a range of 1 to 50% by mass is more preferable.

  In this embodiment, the photopolymerization initiator used in the photopolymerizable composition is not particularly limited as long as it is used in normal photopolymerization in which polymerization is performed by irradiating active energy rays such as ultraviolet rays. Absent. For example, benzophenone, benzyl, Michler's ketone, 2-chlorothioxanthone, benzoin ethyl ether, diethoxyacetophenone, pt-butyltrichloroacetophenone, benzyldimethyl ketal, 2-hydroxy-2-methylpropylphenone, 1-hydroxycyclohexyl phenyl ketone, Examples include 2-benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, dibenzosuberone and the like.

  The amount of the photopolymerization initiator used is preferably in the range of 0.001 to 10 parts by weight with respect to 100 parts by weight of the other photopolymerizable composition, and the transparency of the optical low-pass filter 1 is not deteriorated. For this purpose, the content is more preferably 0.01 to 5 parts by weight.

  Next, a manufacturing method for joining the refractive index modulation type phase grating 12 integrally with the glass substrate 10 will be described. A silane coupling agent is used for bonding the refractive index modulation type phase grating 12 and the glass substrate 10. The compound used for bonding is a reaction site that binds to an inorganic component such as glass, that is, a site that generates a silanol group by hydrolysis, and a site that reacts with an organic component, such as a (meth) acryloyl group, an epoxy group, vinyl. The compound is not particularly limited as long as it is a compound having both a group and a functional group such as an amino group.

  The silane coupling agent may be used by directly coating on the glass substrate 10, or the photopolymerizable composition may be mixed with the silane coupling agent to form a mixture of the photopolymerizable composition and the silane coupling agent. It may be used. The use of a photopolymerizable composition containing a silane coupling agent is preferable because the process can be simplified as compared with the case where the glass substrate 10 is directly applied and surface-treated.

  First, the above-mentioned photopolymerizable composition 18 is applied on the glass substrate 10. The coating thickness of the photopolymerizable composition is not particularly limited, but is preferably in the range of 1 μm to 1000 μm, and more preferably in the range of 5 μm to 500 μm.

  On the applied photopolymerizable composition 18, a transparent cover 22 made of a material having a small optical absorptance with respect to the wavelength of the irradiation light source 20 is placed to form a mold 24 (FIG. 3). The obtained mold 24 is arranged so that the transparent cover 22 side faces the irradiation light source 20 side. When the transparent cover member is not used, the mold 24 is disposed so that the glass substrate 10 side of the mold 24 faces the irradiation light source 20.

  In order to determine the arrangement of the columnar structures 16 in the matrix 14, tiling is performed. Tiling is a method for realizing high regularity by giving in advance positional information of regular structures to be formed. Tiling can be performed by using a photomask, or by scanning and irradiating radiation such as laser light, X-rays, and γ rays in a visible or ultraviolet wavelength band.

  In the tiling of this embodiment, a photomask 26 is used. A photomask 26 is disposed between the mold 24 and the irradiation light source 20 so as to be substantially parallel to the upper surface of the mold. In order to control the diameter and pitch of the columnar structure 16 more precisely, it is preferable to set the gap between the mold 24 and the photomask 26 to 100 μm or less.

  As the photomask 26, one that is generally used in a photolithography method can be used. The mask hole pattern and the size, pitch and shape of the hole diameter are not particularly limited, but when the mask hole is a circular hole, the hole diameter is preferably 80 nm to 10 μm, and the pitch is 120 nm to 15 μm. Is preferred.

  In this embodiment, a photomask 26 (FIG. 4) in which the mask holes 28 are regularly arranged in a triangular lattice pattern is used. Depending on the performance required for the optical low-pass filter, other mask holes may be used. A pattern can be appropriately selected. For example, as shown in FIG. 5, a photomask 30 in which the mask holes 28 are regularly arranged in a square lattice pattern may be used.

  Next, parallel light is irradiated from the irradiation light source 20 through the photomask 26 toward the photopolymerizable composition 18 of the mold 24. The parallelism of the irradiated light is preferably such that the beam divergence angle is ± 0.03 rad or less, more preferably ± 0.001 rad or less. Moreover, it is preferable that the intensity distribution of parallel light is substantially constant in a vertical cross section orthogonal to the traveling direction of the parallel light. In order to reduce wavelength dependency, it is preferable to use a parallel light whose full width at half maximum of wavelength is 100 nm or less. Here, the laser beam is a preferable light source in terms of parallelism, but since the light intensity distribution has a Gaussian distribution, the light intensity distribution is used with a substantially constant light using an appropriate filter or the like. It is preferable.

  Specifically, the irradiation light source 20 is, for example, a light emitted from a point light source or a rod-shaped light source, converted into parallel light having a substantially uniform light intensity distribution (hat distribution) by a mirror, a lens, or the like, a surface emitting semiconductor laser (VCSEL) A planar light source such as) is preferable.

In order to arrange the columnar structures 16 in the matrix 14 with high regularity, it is preferable to proceed the polymerization reaction uniformly in a plane orthogonal to the film thickness direction of the photopolymerizable composition 18. It is preferable that the light intensity distribution of the irradiated parallel light is substantially uniform within the irradiation range. As shown in FIG. 6, the irradiation area 32 is divided into a plurality of regions (9 regions in the present embodiment), the light intensity of the points 42a to 42i in each region is measured, and the illuminance distribution given by Expression (1) is calculated. The value is preferably 2.0% or less, and more preferably 1.0% or less.
Illuminance distribution = (maximum value−minimum value) / (maximum value + minimum value) × 100 (1)

  Irradiation is performed in two stages. In the first light irradiation step, light is irradiated until the parallel light irradiation site of the photopolymerizable composition 18 is cured into a gel. Thereby, the formation position of the columnar structure 16 is fixed in the matrix 14. In order to achieve both the high regularity of the columnar structure 16 and the high diffraction efficiency of the refractive index modulation type phase grating 12, light is irradiated until the degree of cure of the light irradiation region is within a range of 10% to 60%. It is more preferable to irradiate light until it falls within the range of 20% to 50%. The degree of cure is measured by the photo DSC method by measuring the heat of curing reaction of the photopolymerizable composition 18. The polymerization reaction of the photopolymerizable composition 18 is completely completed. Therefore, the degree of cure in a state where no further heat is generated upon irradiation with light is 100%.

  After the first light irradiation step, as shown in FIG. 7, the photomask 26 is removed, and parallel light under the same conditions as in the first light irradiation step is further irradiated. The light intensity of the parallel light to be used may be different between the first irradiation step and the second irradiation step. Light is irradiated until the total curing degree of the photopolymerizable composition 18 reaches 100%. Since the entire photopolymerizable composition 18 is irradiated with light, and the whole is polymerized and cured, a columnar phase separation structure composed of the columnar structure 16 and the matrix 14 whose formation positions are determined in the first light irradiation step. Molded in the film thickness direction, a difference in refractive index occurs between the matrix 14 and the plurality of columnar structures 16.

  As described above, by performing the irradiation in two stages, the cross-linking density difference between the columnar structure 16 and the matrix 14 occurs due to the polymerization self-promoting effect of the columnar structure 16, and the columnar structure 16 and the matrix 14. As a result of the reaction diffusion between the columnar structure 16 and the matrix 14, a significant refractive index difference can be provided. Therefore, the refractive index modulation type phase grating 12 which shows a clear refractive index change at the boundary between the matrix 14 and the columnar structure 16 is formed.

  By releasing the transparent cover 22 from the completely cured photopolymerizable composition 18, the optical low-pass filter 1 in which the refractive index modulation type phase grating 12 and the glass substrate 10 are integrally bonded can be obtained.

  According to the aspect of the present invention, it is possible to form the columnar structure 16 having a high aspect ratio that extends substantially parallel to the film thickness direction, the columnar structure has an aspect ratio of 10 or more, and diffraction of the refractive index modulation type phase grating 12. An optical low-pass filter having an efficiency of 10% or more can be produced. Further, by performing tiling, the structure and arrangement of the columnar structures can be controlled with high accuracy, so that an optical low-pass filter having desired optical performance can be easily manufactured.

  The present invention is not limited to the above embodiments, and various modifications are possible within the scope of the invention described in the claims, and these are also included in the scope of the present invention. Needless to say.

  KBM5103 (3-acryloxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd.) was diluted in a 2.0% acetic acid aqueous solution to prepare a dilute aqueous solution of a silane coupling agent. The aforementioned silane coupling agent was applied to the surface of a glass substrate having a diameter of 200 mmφ and a thickness of 500 μm to obtain a glass substrate that had been subjected to a silane coupling treatment. On this glass substrate, 100 μm of a photopolymerizable composition obtained by dissolving 0.6 part by mass of 1-hydroxycyclohexyl phenyl ketone in a mixture consisting of 30 parts by mass of phenoxyethyl acrylate and 70 parts by mass of trimethylolpropane trimethacrylate. It applied by thickness. On the photopolymerizable composition, a polyethylene terephthalate film was placed as a transparent cover member and sealed to obtain a mold.

Next, a photomask in which a light passage area of 2 μmφ, that is, holes are arranged in a hexagonal lattice shape (triangular lattice shape) at a pitch of 5 μm, is placed on the upper part of the mold, and light is irradiated from the direction perpendicular to the surface of the mold Ultraviolet parallel light having a substantially uniform intensity distribution was irradiated at 480 mJ / cm ² . The degree of cure of the photopolymerizable composition after irradiation was 25%. Thereafter, the photomask was removed, and the mold was irradiated with parallel ultraviolet light at 2400 mJ / cm ² to further polymerize and cure the photopolymerizable composition. After the photopolymerizable composition was completely cured, the transparent cover member was peeled from the photopolymerizable composition to obtain an optical low-pass filter in which the refractive index modulation type phase grating and the glass substrate were integrally bonded.

  This optical low-pass filter was installed on the solid-state image sensor via an adhesive layer. An optical low-pass filter can be easily obtained by obtaining an optimal distance between the solid-state imaging device and the optical low-pass filter that does not cause moiré in advance and making the thickness of the adhesive layer the same as that distance. Was able to be positioned.

  When the circular zone plate was photographed using the imaging optical system thus produced, it was confirmed that moire was suppressed in a region including a high spatial frequency component.

It is drawing which shows schematically the structure of the imaging optical system using the optical low-pass filter of the preferable embodiment of this invention. It is a perspective view which shows typically the structure of the refractive index modulation type | mold phase grating used for the optical low-pass filter of the preferable embodiment of this invention. It is drawing for demonstrating the optical low-pass filter manufacturing method of the preferable embodiment of this invention. It is a top view of the photomask used with the optical low-pass filter manufacturing method of the preferable embodiment of this invention. It is a top view of the other photomask used with the optical low-pass filter manufacturing method of the preferable embodiment of this invention. It is drawing for demonstrating the determination method of the illumination distribution of the light source in the optical low-pass filter manufacturing method of preferable embodiment of this invention. It is drawing for demonstrating the optical low-pass filter manufacturing method of the preferable embodiment of this invention.

Explanation of symbols

1: Optical low-pass filter 2: Imaging optical system 4: Solid-state imaging device 6: Lens 10: Glass substrate 12: Refractive index modulation type phase grating 14: Matrix 16: Columnar structure

Claims (8)

A glass substrate;
A sheet-like refractive index modulation type phase grating having a matrix and a plurality of columnar structures arranged in a lattice shape in the matrix so as to extend in the thickness direction and have a refractive index different from that of the matrix. ,
The glass substrate and the refractive index modulation type phase grating are bonded so that the glass substrate is in contact with one end surfaces of the plurality of columnar structures of the refractive index modulation type phase grating.
An optical low-pass filter characterized by that. The glass substrate and the refractive index modulation type phase grating are integrally bonded with a silane coupling agent,
The optical low-pass filter according to claim 1. The diffraction efficiency of the refractive index modulation type phase grating is 10% or more.
The optical low-pass filter according to claim 1. The columnar structure has an aspect ratio of 10 or more.
The optical low-pass filter according to claim 1. The glass substrate has infrared cut performance,
The optical low-pass filter according to claim 1. An imaging optical system comprising: the optical low-pass filter according to any one of claims 1 to 5; and a solid-state imaging device.
The optical low-pass filter is arranged such that the surface on the glass substrate side faces the solid-state image sensor,
A gap layer is provided between the optical low-pass filter and the solid-state image sensor,
An imaging optical system characterized by the above. A method of manufacturing an optical low-pass filter in which a glass substrate and a refractive index modulation type phase grating are bonded,
Applying a photopolymerizable composition onto the glass substrate to form a mold; and
Placing a photomask between a light source and the mold;
A first irradiation step of irradiating the mold with parallel light having a full width at half maximum of 100 nm or less and having a uniform light intensity distribution from the light source through the photomask;
A second irradiation step of removing the photomask, and further irradiating the mold with parallel light having a full width at half maximum of 100 nm or less and having a uniform light intensity distribution from the light source. ,
An optical low-pass filter manufacturing method characterized by the above. The photopolymerizable composition includes a silane coupling agent.
The manufacturing method of the optical low-pass filter of Claim 7.

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