JP2012027493A - Optical low-pass filter and imaging optical system having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical low-pass filter which is cheap, whose thickness is restricted, and which can be used in an optical system which needs the shortening of the optical length.SOLUTION: An optical low-pass filter according to the present invention which is obtained by photopolymerization of a photopolymerizable composition has a matrix 12 and a plurality of columnar structures 14 arranged in one direction in the matrix. The columnar structures have a different refraction factor from that of the matrix, are arranged in a grid manner in the surface orthogonal to the arrangement direction, and have a structure with high regularity in which the refraction factor changes in the order of 80 nm to 1000 μm.

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 in a digital camera or the like attached to a mobile phone or the like to prevent moire and the like. The present invention relates to an imaging optical system.

  2. Description of the Related Art In recent years, home video cameras and digital still cameras with remarkable performance improvements have used CCD area image sensors and CMOS area image sensors as imaging means. These sensors have a configuration in which photoelectric conversion is performed by a large number of light receiving elements arranged two-dimensionally on a silicon substrate, and charges generated by each light receiving element are transferred to the outside by a CCD element or a CMOS circuit. Yes. In these sensors, the image sensors are regularly arranged in a grid pattern. Further, in order to obtain color information for each light receiving element (pixel), for example, RGB color filters are arranged in a stripe pattern or four types of filters in a square mosaic pattern on each pixel.

  As described above, in the CCD area image sensor and the like described above, since the image pickup elements and the like are regularly arranged in a grid pattern, color reproduction such as generation of a pseudo signal (moire) in the generated image of the subject is performed. Inconvenience may occur. In order to solve such a problem, an optical low-pass filter (OLPF) that cuts over a specific frequency is used. As such an optical low-pass filter, a quartz OLPF utilizing the birefringence of quartz is most often used.

On the other hand, besides the method using birefringence, a method of using an optical low-pass filter by diffraction using a phase grating has been proposed. There are two types of phase gratings, a surface irregularity type and a refractive index change type.
As the surface uneven mold, a regular uneven structure is formed by mechanical cutting on the surface of the transparent medium, a stamper method for pressing the mold, or vapor deposition or ion etching. Attempts have been made to use it for optical applications (for example, Patent Document 1).

  On the other hand, as a refractive index change type, an attempt is made to form a one-dimensional or two-dimensional regular structure on a plastic film or sheet and use it for optical applications such as a light control plate. For example, as a method for forming a two-dimensional regular structure, it has been proposed that block polymers are arranged and arranged in a plane perpendicular to the thickness direction of the film (Non-Patent Document 1).

  In order to form a one-dimensional regular structure, an ultraviolet curable composition maintained in a film shape is irradiated with ultraviolet rays from a specific direction, and then an ultraviolet curable composition is formed into a film shape on the obtained cured film. It has been proposed to form a layered structure in a direction perpendicular to the thickness direction of the sheet by repeatedly irradiating ultraviolet rays from another direction (for example, Patent Document 2).

JP-A-9-263932 Japanese Unexamined Patent Publication No. 63-309902

Maclomoecules 2003, 36, 3272-3288

However, the quartz OLPF has a structure in which two quartz plates are arranged on both sides of a quarter-wave plate or a structure in which three quartz plates are combined. There is a problem that the optical system cannot be used for an optical system that is required to shorten the optical length.
Further, the crystal OLPF has a problem that it is expensive.

In addition, the ordered structure described in Non-Patent Document 1 can only be given a very fine regularity on the order of nm, and thus cannot be used for general optical applications such as OLPF that requires regularity of about 80 nm to 1000 μm. It was. Further, the method of Patent Document 1 has a problem that the manufacturing method is complicated and expensive.
On the other hand, although the regular structure described in Patent Document 2 has regularity on the order of submicrons, the degree of regularity is low, so that it is not suitable for optical applications such as OLPF that requires high-level light control. Had a point.

  The present invention has been made to solve such a problem, and is an optical low-pass that can be used in an optical system that is inexpensive, has a suppressed thickness, and is required to shorten an optical length. An object is to provide a filter and an optical system including the same.

  Another object of the present invention is to provide a method for manufacturing an optical low-pass filter that can be used in an optical system that is inexpensive, has a suppressed thickness, and is required to shorten the optical length.

  According to the present invention, an optical low-pass filter obtained by photopolymerizing a photopolymerizable composition, comprising: a matrix; and a plurality of columnar structures arranged in one direction within the matrix, The columnar structure has a refractive index different from that of the matrix, is arranged in a lattice shape in a plane orthogonal to the orientation direction, and has a highly regular structure in which the refractive index changes periodically in the order of 80 nm to 1000 μm. An optical low-pass filter is provided.

  According to such a configuration, the optical low-pass filter is thin due to a highly regular structure in which the refractive index changes periodically in the order of 80 nm to 1000 μm, which is arranged in a lattice shape in a plane orthogonal to the alignment direction. Although it is a structure, it is possible to effectively prevent the occurrence of moire. Furthermore, it is less expensive than an optical low-pass filter made of quartz.

According to another preferred embodiment of the present invention, the columnar structure has a diameter of 80 nm to 1000 μm.
According to another preferred embodiment of the present invention, the arrangement period of the columnar structures is 80 nm to 1000 μm.

  According to another aspect of the present invention, there is provided an optical low-pass filter obtained by photopolymerizing a photopolymerizable composition, a matrix, and a plurality of columnar structures arranged in one direction within the matrix. The columnar structure has a refractive index different from that of the matrix, is arranged in a lattice shape in a plane orthogonal to the orientation direction, and has a regularity in which the refractive index changes periodically in the order of 80 nm to 1000 μm. An imaging optical system is provided, in which an optical low-pass filter or the like characterized by having a high structure is disposed on a light receiving surface of a solid-state imaging device via a gap layer.

  According to such a configuration, the optical low-pass filter is thin due to a highly regular structure in which the refractive index changes periodically in the order of 80 nm to 1000 μm, which is arranged in a lattice shape in a plane orthogonal to the alignment direction. Although the structure can effectively prevent the generation of moire, the thickness of the entire optical system can be suppressed.

  According to another aspect of the present invention, there is provided a method for manufacturing an optical low-pass filter, the step of disposing a transparent resin constituting a gap layer on a light receiving surface of an imaging device, and a polyfunctional or more functional bilayer on the transparent resin. Disposing a photopolymerizable composition containing a functional monomer or oligomer and a photopolymerization initiator; irradiating the photopolymerizable composition with parallel light; polymerizing and curing the photopolymerizable composition; Forming on the gap layer an optical low-pass filter comprising a number of columnar structures oriented in one direction and regularly arranged in the matrix. A method for manufacturing a low-pass filter is provided.

  According to such a configuration, the generation of moire can be effectively prevented by a large number of columnar structures oriented in one direction and regularly arranged, so that the thickness of the entire optical system can be reduced. Since the optical low-pass filter that can suppress this problem can be built directly on the solid-state imaging device, the work process is simplified, and the manufacturing cost and labor are reduced.

  According to another aspect of the present invention, there is provided a method for manufacturing an optical low-pass filter, the step of disposing a transparent resin constituting a gap layer on a smooth substrate such as glass, and a bifunctional or more functional group on the transparent resin. Disposing a photopolymerizable composition containing a polyfunctional monomer or oligomer and a photopolymerization initiator; irradiating the photopolymerizable composition with parallel light; polymerizing and curing the photopolymerizable composition; And an optical low-pass filter having a plurality of columnar structures oriented in one direction and regularly arranged in the matrix on the gap layer. A method of manufacturing a static low pass filter is provided.

  According to such a configuration, the generation of moire can be effectively prevented by a large number of columnar structures oriented in one direction and regularly arranged, so that the thickness of the entire optical system can be reduced. Since the optical low-pass filter that can suppress this problem can be built directly on the solid-state imaging device, the work process is simplified, and the manufacturing cost and labor are reduced.

  According to the present invention, an optical low-pass filter that can be used in an optical system that is inexpensive, has a suppressed thickness, and is required to shorten an optical length, and an optical system including the optical low-pass filter are provided.

  Furthermore, according to the present invention, there is provided a method for manufacturing an optical low-pass filter that is inexpensive, has a suppressed thickness, and can be used in an optical system that is required to shorten the optical length.

It is drawing which shows typically the structure of the imaging optical system using the optical low-pass filter of one Embodiment of this invention. It is the perspective view which showed the structure of the optical low-pass filter typically. It is a perspective view which shows typically arrangement | positioning of the columnar structure in an optical low-pass filter. It is drawing for demonstrating the determination method of the illumination distribution at the time of manufacturing an optical low-pass filter. It is drawing which shows typically the structure of the optical system for evaluation for performing the function evaluation of an optical low-pass filter. 6 is a schematic drawing of a photomask used in the evaluation optical system of FIG. 5. 6 is a schematic drawing of a diffraction grating used in the evaluation optical system of FIG. It is drawing which shows the picked-up image when the photomask of FIG. 6 is projected on a screen. It is drawing which shows the moire image produced with the photomask of FIG. 6, and the diffraction grating of FIG. 10 is a drawing showing a projected image when an optical low-pass filter is inserted into the optical system in which the moire image of FIG. 9 is generated. It is drawing which shows the circular zone plate used for moire evaluation. It is drawing which shows the image which image | photographed the circular zone plate of FIG. 11 with the small camera which is not equipped with an optical low-pass filter. FIG. 12 is a diagram illustrating an image captured by the circular zone plate of FIG. 11 with a small camera equipped with the optical low-pass filter of Example 2. FIG. It is drawing which shows the image which image | photographed the circular zone plate of FIG. 11 with the small camera which is not equipped with an optical low-pass filter. 12 is a diagram showing an image obtained by photographing the circular zone plate of FIG. 11 with a small camera equipped with the optical low-pass filter of Example 3. FIG.

  Hereinafter, an optical system using an optical low-pass filter 1 according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an imaging optical system 2 that captures an image with a solid-state imaging device having pixels of a predetermined pitch, such as an optical system for a digital still camera, an optical system for a digital camera mounted on a mobile phone, or the like. Used as.

  As shown in FIG. 1, in the imaging optical system 2, the optical low-pass filter 1 is disposed on the light receiving surface of the solid-state imaging device 4 via a gap layer 6 having a predetermined thickness. The imaging optical system 2 of the present embodiment further includes a lens 8 and an infrared cut filter 10.

  In the present embodiment, the solid-state imaging device 4 is a device in which a large number of light receiving elements are two-dimensionally arranged on a silicon substrate, and charges generated by each light receiving element are transferred as signals to the outside by a CCD element or a CMOS circuit. This is an area image sensor that can be used.

The gap layer 6 is made of a polycarbonate resin, an acrylic resin, a polystyrene resin, or a polyimide resin, but is not particularly limited as long as it is a transparent material.
The thickness of the gap layer 6 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 thickness of the gap layer 6 is set so that the amount of image blur caused by diffraction becomes a finite amount equal to or smaller than the pixel pitch of the image sensor. When the diffraction angle θ of the diffracted light is considered only when the diffraction order is the first order, when the period of the regular structure is Λ, the wavelength of the light is λ, and the refractive index of the medium of the gap layer is n (1) ).
n ・ Λ ・ sinθ = λ (1)

When P / 2 is set with respect to the pixel pitch P of the image sensor as the image blur amount, the thickness L of the gap layer 6 is determined as in equation (2).
L = P / 2 / tan (sin ⁻¹ (λ / n · Λ)) (2)
The thickness L of the gap layer 6 set by the equation (2) is set in the range of 0.01 μm to 10 mm, preferably in the range of 0.1 μm to 1000 μm, more preferably in the range of 1 μm to 500 μm.

  The lens 8 is composed of 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 infrared cut filter 10 includes a glass filter made of inorganic glass, or a plastic filter made of polycarbonate resin, acrylic resin, polystyrene resin, or polyolefin resin to which an organic dye is added.

  FIG. 2 is a perspective view schematically showing the internal structure of the optical low-pass filter 1. The optical low-pass filter 1 includes a sheet or film matrix 12 and a large number of columnar structures 14 arranged in the matrix 12. The columnar structures 14 have a refractive index different from that of the matrix 12, are oriented in one direction (thickness direction of the matrix 12), and are regularly arranged. In this embodiment, the arrangement period of the columnar structures 14 is set to 80 nm to 1000 μm, preferably 90 nm to 100 μm, more preferably 100 nm to 50 μm.

The diameter of the columnar structure 14 (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.
Thus, by setting the diameter or arrangement period of the columnar structures 14 within this range, an optical product can sufficiently exhibit an interference effect with respect to light in the wavelength range of 350 nm to 2000 nm, and can be used as an optical low-pass filter. Sophisticated light control such as diffraction and deflection can be performed in a possible wavelength range.

  Accordingly, the optical low-pass filter 1 has a highly regular structure in which the refractive index periodically changes in the order of 80 nm to 1000 μm.

  The optical low-pass filter 1 of this embodiment is formed by irradiating light to a photopolymerizable composition and curing it. As the photopolymerizable composition, those containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator are used.

  By including a bifunctional or higher monomer in the composition, the degree of polymerization (crosslink density) is likely to occur in a plane perpendicular to the thickness direction of the photopolymerizable composition during polymerization and curing. A portion having a high degree of polymerization (crosslinking density) has a higher refractive index than a portion having a low degree of polymerization. When the refractive index can be increased or decreased, a portion with a high refractive index becomes a waveguide mode, and more light passes through the portion with a high refractive index.

  For this reason, under the region where the degree of polymerization (crosslinking density) is dense and the refractive index is high, it is considered that the photoreaction of the photocurable composition proceeds with more emphasis on the degree of polymerization (crosslinking density). It is considered that a large number of columnar structures 14 having a refractive index different from that of the matrix 12 are formed in the matrix 12 by such a phenomenon.

  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, for example, (meth) acryloyl group, vinyl Those containing a group, an allyl group or the like are particularly preferable.

  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-phenylenebismaleimide, 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 degree of polymerization (crosslink density) tends to be larger and columnar structures are more 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 are erythritol hexa (meth) acrylate, polyfunctional epoxy (meth) acrylate, and polyfunctional urethane (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 0.0001 or more. More preferably.

  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. Also, the two monomers or oligomers having the largest refractive index difference of the homopolymer should be used in a weight ratio of 10:90 to 90:10 in order to obtain highly efficient functions such as diffraction, deflection, and diffusion. Is preferred.

In this 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 (meth) acryloyl group, vinyl group, allyl group and the like are particularly 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 acrylate; vinyl compounds such as styrene, p-chlorostyrene, vinyl acetate, acrylonitrile, N-vinyl pyrrolidone, vinyl naphthalene; 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 optical low-pass filter. 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 dissolution 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. , Methyl alcohol, ethyl alcohol, ethyl acetate, acetonitrile, dimethylacetamide, dimethylformamide, low molecular compounds such as tetrahydrofuran, organic halogen compounds, organic silicon compounds, plasticizers, additives such as stabilizers, and the like.

  The amount of the compound having no polymerizable carbon-carbon double bond is used to reduce the viscosity of the photopolymerizable composition and improve the handleability when producing an optical low-pass filter. Alternatively, it is preferably in the range of 1 to 99% by mass of the total amount with the oligomer, and more preferably 1 to 50% by mass in order to form a columnar structure having a regular arrangement while improving the handleability. It is a range.

  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, 2-Benzyl-2-dimethylamino-1- (4-morpholinophenyl) -butanone-1, dibenzosuberone and the like.

  The amount of these photopolymerization initiators 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 so as not to deteriorate the transparency of the optical low-pass filter. Therefore, it is more preferable to use 0.01 to 5 parts by weight.

  As described above, in the optical low-pass filter 1 of this embodiment, a large number of columnar structures 14 having a refractive index different from that of the matrix 12 are arranged in one direction in the matrix 12. The columnar structures 14 are arranged with two-dimensional regularity in a plane perpendicular to the alignment direction. Examples of the columnar structure 14 include a columnar shape, an elliptical columnar shape, and a prismatic shape.

  In the optical low-pass filter 1 according to the present embodiment, the columnar structures 14 are regularly arranged so as to form the hexagonal lattice shown in FIG. 3, and by this regularity, six-point separation (three directions) is performed. This can be done with a single filter. The hexagonal lattice includes a triangular lattice and a honeycomb lattice.

Next, a method for manufacturing the optical low-pass filter 1 will be described. The optical low-pass filter 1 of the present embodiment is manufactured on the gap layer 6 disposed on the surface of the solid-state imaging device 4.
First, a transparent resin plate made of a polycarbonate resin or the like constituting the gap layer 6 is disposed on the light receiving surface of the solid-state imaging device 4. Such a transparent resin plate may be fixed on the solid-state imaging device with an adhesive or the like, and a photocurable resin composition is formed on the solid-state imaging device by a spin coating method or the like, and diffused light, etc. What hardened | cured with the ultraviolet-ray may be sufficient. Alternatively, a film-like product may be used in which a solution obtained by dissolving a thermoplastic resin or the like in a solvent is used to form a coating film by spin coating or the like, and the solvent is evaporated to solidify.

  Next, a photopolymerizable composition containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator is applied onto the substrate on the transparent resin plate. The coating thickness of the photopolymerizable composition is not particularly limited, but is preferably in the range of 1 μm to 1000 μm, more preferably in the range of 5 μm to 500 μm.

  Further, the photopolymerization composition is irradiated with parallel light such as ultraviolet rays having a full width at half maximum of 100 nm or less. By this irradiation, the columnar structure 14 of the order of 80 nm to 1000 μm has a highly regular hexagonal lattice structure corresponding to a diffraction pattern reflecting a periodic refractive index change formed at the time of laser beam irradiation. Formed inside. The portion other than the columnar structure 14 of the photopolymerization composition becomes the matrix 12.

Since the irradiated parallel light regularly arranges the columnar structures 14, it is preferable that the light intensity distribution in the cross section orthogonal to the traveling direction is substantially constant.
The light source is not particularly limited. For example, the light from a point light source or a rod-shaped light source is converted into parallel light having a substantially constant light intensity distribution (hat distribution) by a mirror, a lens, or the like, a surface emitting semiconductor A planar light source such as a laser (VCSEL) is preferable.

  The degree of 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, from the viewpoint of forming a regular array of columnar structures. . 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.

In order to increase the regularity of the arrangement of the columnar structures of the optical low-pass filter, it is preferable to carry out the polymerization reaction uniformly in a plane perpendicular to the film thickness direction of the optical low-pass filter. As shown, the light intensity at a plurality of points (I to IX) in the irradiation area is measured, and the illuminance distribution value given by the following formula (1) is preferably 2.0% or less, preferably 1.0% or less. Is more preferable.
Illuminance distribution = (maximum value−minimum value) / (maximum value + minimum value) × 100 Equation 1

Further, in order to obtain a regular arrangement of the columnar structures, it is preferable that the wavelength width of the irradiation light is narrow, and therefore the full width at half maximum is 100 nm or less, more preferably 20 nm or less.
As a layer in which the columnar structure of the optical low-pass filter is formed, the photopolymerizable composition is sealed in a film shape in a glass cell having a predetermined thickness, and parallel light such as ultraviolet rays is irradiated in the same manner as described above. Irradiation is performed to polymerize and cure the photopolymerizable material to prepare a film in which a columnar structure is formed, and this film may be fixed to a transparent resin plate as a gap layer.

  Without being limited to the above-described embodiment of the present invention, various changes and modifications can be made within the scope of the technical idea described in the claims.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely according to an Example, this invention is not limited to these Examples.

Example 1
A photopolymerization initiator is added to a mixture comprising 50 parts by mass of trimethylolpropane triacrylate having a refractive index of 1.535 as well as 50 parts by mass of methyl methacrylate having a refractive index of 1.489 as a single polymer. As a result, 1 part by mass of 1-hydroxycyclohexyl phenyl ketone was dissolved to obtain a photopolymerizable composition. The obtained photopolymerizable composition was encapsulated in a film shape in a glass cell of 50 mm × 50 mm and a thickness of 0.1 mm. Next, from the direction perpendicular to the surface of the upper cover 15 of the glass cell, the beam divergence angle is ± 0.001 rad or less, and the illuminance distribution in the light intensity distribution in the vertical cross section with respect to the light traveling direction is 2. The photopolymerizable composition was polymerized and cured by irradiating with ultraviolet rays of 0% or less to obtain a plastic film. As a light source, a parallel light ultraviolet irradiation device using an ultra-high pressure mercury lamp was used, and monochromatic light having a center wavelength of 365 nm and a full width at half maximum of 10 nm was extracted and irradiated by an interference filter.

The obtained plastic film had a cylindrical structure with a diameter of 2 μm having a refractive index different from that of the matrix in a plane perpendicular to the internal film thickness direction and arranged in a hexagonal lattice pattern with a period of 7 μm.
This plastic film was evaluated for the function of the optical low-pass filter 1 using an evaluation optical system as shown in FIG.

  The evaluation optical system includes a helium neon laser 16, a photomask 18, a diffraction grating 20, a screen 22, a camera 24, and a magnifying lens system 26. The CCD solid-state imaging device mounted on the camera 24 has a pixel size of 3.1 μm and a pixel interval of 5 μm, and the photomask 18 schematically shown in FIG. 6 has the same size as the CCD solid-state imaging device. . The period of the diffraction grating 20 schematically shown in FIG. 7 is 5 μm. Further, the irradiation light 28 from the helium neon laser 16 is 630 nm monochromatic light.

Using such an evaluation optical system, the performance of the optical low-pass filter was evaluated.
FIG. 8 shows a photographed image when the photomask 18 shown in FIG. 6 is projected onto the screen 22.

  FIG. 9 shows a moire image generated by the photomask shown in FIG. 6 and the diffraction grating shown in FIG. Further, FIG. 10 shows a projection image when the internal refractive index modulation type optical low-pass filter 1 having a period of 7 μm is inserted on the photomask 18 shown in FIG. 6 through a gap layer having a thickness of 17 μm. In FIG. 10, it can be confirmed that the moire image observed in FIG. 9 disappears and the function of the optical low-pass filter 1 is developed.

(Example 2)
As a photopolymerizable composition, 40 parts by mass of trimethylolpropane triacrylate having a refractive index of a single polymer of 1.535 and polybutylene glycol dimethacrylate 40 having a refractive index of a single polymer of 1.523 are used. A mixture of 20 parts by weight of U-2PPA, which is a polyfunctional urethane acrylate mixture manufactured by Shin-Nakamura Chemical Co., Ltd., having a refractive index of 1.547, which is also a single polymer, is used as a photopolymerization initiator. 1 part by mass of cyclohexyl phenyl ketone was dissolved to obtain a photopolymerizable composition.
The obtained photopolymerizable composition was encapsulated in a film form in a glass cell having a size of 50 mm × 50 mm and a thickness of 0.06 mm. A transparent gap layer was obtained by irradiating with ultraviolet diffused light using a chemical lamp through the upper cover glass of the cell.

  50 parts by mass of trimethylolpropane triacrylate having a refractive index of a single polymer of 1.535, 10 parts by weight of polybutylene glycol dimethacrylate having a refractive index of a single polymer of 1.523, and 20 parts by weight of EO-modified bisphenol A dimethacrylate having a polymer refractive index of 1.572, and a polyfunctional urethane acrylate mixture made by Shin-Nakamura Chemical Co., Ltd. having a refractive index of a single polymer of 1.557 As a photopolymerization initiator, 0.6 part by mass of 1-hydroxycyclohexyl phenyl ketone was dissolved in a mixture composed of 20 parts by weight of -6HA to obtain a photopolymerizable composition.

  The obtained photopolymerizable composition was encapsulated in a film form in a cell of 5 mm × 6 mm and thickness 0.2 mm using the gap layer as a base film (0.06 mm). Through the upper cover glass of the cell, the beam divergence angle is ± 0.001 rad or less from the direction perpendicular to the cover glass surface, and the illuminance distribution in the light intensity distribution in the vertical section with respect to the light traveling direction is 2 The photopolymerizable composition was polymerized and cured by irradiating ultraviolet rays of 0.0% or less to obtain an optical low-pass filter. As a light source, a parallel light ultraviolet irradiation device using an ultrahigh pressure mercury lamp was used, and monochromatic light having a center wavelength of 365 nm and a full width at half maximum of 10 nm was extracted and irradiated by an interference filter.

  The plastic film on the transparent gap layer constituting the obtained optical low-pass filter is a hexagonal structure having a 2 μm diameter cylindrical structure having a refractive index different from that of the matrix in a plane perpendicular to the internal film thickness direction and a period of 11 μm. They were arranged in a grid.

  This optical low-pass filter is arranged on the imaging sensor part (3.4 mm × 4.3 mm) of a CMOS sensor having 1.3 million pixels, and the side surface of the optical low-pass filter and the surface of the CMOS sensor are bonded with an epoxy resin, An imaging sensor was produced.

  A small camera module incorporating the CMOS image sensor with the optical low-pass filter was fabricated. For comparison, a small camera module was manufactured using a CMOS image sensor without an optical low-pass filter. For each camera, the circular zone plate shown in FIG. 11 was photographed, and the state of occurrence of moire was compared and examined.

  As shown in FIG. 12, in a camera using a CMOS image sensor without an optical low-pass filter, a large number of moire was observed (only the lower left quarter of the captured image is shown). On the other hand, in the photographed image of the small camera module incorporating the CMOS image sensor with the optical low-pass filter shown in FIG. 13, the moire disappears and is reduced (portions illustrated by i, ii, iii, iv, and v) and is optical. It can be confirmed that the function of the low-pass filter 1 is exhibited.

(Example 3)
As a photopolymerizable composition, 40 parts by mass of trimethylolpropane triacrylate having a refractive index of a single polymer of 1.535 and polybutylene glycol dimethacrylate 40 having a refractive index of a single polymer of 1.523 are used. A mixture of 20 parts by weight of U-2PPA, which is a polyfunctional urethane acrylate mixture manufactured by Shin-Nakamura Chemical Co., Ltd., having a refractive index of 1.547, which is also a single polymer, is used as a photopolymerization initiator. 1 part by mass of cyclohexyl phenyl ketone was dissolved to obtain a photopolymerizable composition. Except that a 0.04 mm thick glass cell was used, ultraviolet diffused light was applied in the same manner as in Example 2 to obtain a transparent gap layer.

50 parts by mass of trimethylolpropane triacrylate having a refractive index of a single polymer of 1.535, 10 parts by weight of polybutylene glycol dimethacrylate having a refractive index of a single polymer of 1.523, and 20 parts by weight of EO-modified bisphenol A dimethacrylate having a refractive index of 1.572 and a polyfunctional urethane acrylate mixture made by Shin-Nakamura Chemical Co., Ltd. having a refractive index of 1.557. As a photopolymerization initiator, 0.6 part by mass of 1-hydroxycyclohexyl phenyl ketone was dissolved in a mixture composed of 20 parts by weight of -6HA to obtain a photopolymerizable composition.
The obtained photopolymerizable composition was polymerized and cured in the same manner as in Example 2 except that the thickness of the base film as a gap layer was 0.04 mm. A low pass filter was obtained.

  The plastic film on the transparent gap layer constituting the obtained optical low-pass filter is a hexagonal structure having a 2 μm diameter cylindrical structure having a refractive index different from that of the matrix in a plane perpendicular to the internal film thickness direction and a period of 11 μm. They were arranged in a grid.

  This optical low-pass filter is arranged on the imaging sensor part (3.4 mm × 4.3 mm) of a CMOS sensor having 1.3 million pixels, and the side surface of the optical low-pass filter and the surface of the CMOS sensor are bonded with an epoxy resin, An imaging sensor was produced.

  A small camera module incorporating the CMOS image sensor with the optical low-pass filter was fabricated. For comparison, a small camera module was fabricated using a CMOS image sensor without an optical low-pass filter. For each camera, the circular zone plate shown in FIG. 11 was photographed, and the state of occurrence of moire was compared and examined.

  As shown in FIG. 14, moiré is reduced between the image of a small camera using a CMOS image sensor without an optical low-pass filter and the photographed image of a small camera incorporating a CMOS image sensor with an optical low-pass filter shown in FIG. However, it can be confirmed that the function of the optical low-pass filter 1 is manifested (portion shown by Vi).

1: Optical low-pass filter 2: Imaging optical system 4: Solid-state imaging device 6: Gap layer 12: Matrix 14: Columnar structure

Claims (3)

An optical low-pass filter obtained by photopolymerizing a photopolymerizable composition,
Matrix,
A number of columnar structures arranged in one direction within the matrix;
The columnar structures have a refractive index different from that of the matrix, and are arranged in a lattice shape in a plane orthogonal to the orientation direction;
Having a highly regular structure in which the refractive index changes periodically in the order of 80 nm to 1000 μm,
An optical low-pass filter characterized by that.   An imaging optical system, wherein the optical low-pass filter according to claim 1 is disposed on a light receiving surface of a solid-state imaging device via a gap layer. A method for manufacturing an optical low-pass filter, comprising:
Arranging a transparent resin constituting the gap layer on the light receiving surface of the solid-state imaging device;
Disposing a photopolymerizable composition containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator on the transparent resin;
The photopolymerizable composition was irradiated with parallel light, the photopolymerizable composition was polymerized and cured, and provided with a matrix and a number of columnar structures that were oriented in one direction and regularly arranged in the matrix. Forming an optical low-pass filter on the gap layer.
An optical low-pass filter manufacturing method characterized by the above.

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