JP5308141B2 - Optical low-pass filter and manufacturing method thereof - Google Patents

Description

  The present invention relates to an optical low-pass filter and a manufacturing method thereof, and more particularly, to an optical low-pass filter used in a digital camera or the like to prevent moire and a manufacturing method thereof.

  In home video cameras and digital still cameras, CCD area image sensors and CMOS area image sensors are used as imaging means. In these sensors, a large number of light receiving elements are regularly arranged in a lattice pattern on a silicon substrate, and photoelectric conversion is performed. Furthermore, in order to obtain color information, for example, RGB color filters are arranged in stripes or four types of filters in a square mosaic pattern for each light receiving element.

  In such a CCD area image sensor or the like, since the light receiving elements are regularly arranged in a lattice pattern, there may be a problem that a pseudo signal (moire) is generated in the generated image of the subject.

  In order to solve such a problem, an optical low-pass filter that cuts over a specific frequency is used. As such an optical low-pass filter, an optical low-pass filter in which a large number of columnar structures having a refractive index different from that of a matrix are two-dimensionally arranged in a sheet-like matrix and the refractive index periodically changes in the order of 80 nm to 1000 μm. Has been proposed (see Patent Document 1).

JP 2005-242340 A

  Such an optical low-pass filter separates light by diffraction of light, and makes the separated light incident on an adjacent light receiving element, thereby reducing the resolution of a subject having a periodic structure of a specific frequency or more and reducing moire. Generation is suppressed.

However, when such an optical low-pass filter exhibits Bragg diffraction by increasing the thickness, only a specific order of diffracted light is observed, and the subject has a periodic structure with a frequency less than a specific frequency. It is possible to suppress a decrease in resolution. However, when the incident angle is increased, the diffraction efficiency is lowered, and the function of suppressing the generation of moire is lowered.
That is, there is a problem in that the function of suppressing the occurrence of moire deteriorates in the peripheral portion of the optical low-pass filter where the angle of incident light is large.

  The present invention has been made to solve such a problem, and an object of the present invention is to provide an optical low-pass filter in which the function of suppressing the occurrence of moire in the peripheral portion does not deteriorate and a method for manufacturing the same. To do.

According to the present invention,
A method for manufacturing an optical low-pass filter, comprising:
Disposing a photopolymerizable composition containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator on a substrate;
Above the photopolymerizable composition, installing an ND filter whose light transmittance increases exponentially from the center to the outer periphery ;
The photopolymerizable composition is irradiated with parallel light through the ND filter to polymerize and cure the photopolymerizable composition, and is aligned in one direction within the matrix and the sheet-like matrix. comprises the steps of obtaining an optical low-pass filter having multiple refractive index difference between the matrix as the outer peripheral portion is two-dimensionally arranged in a plane orthogonal to the thickness is greater and the columnar structure, a
An optical low-pass filter manufacturing method is provided.

  In the optical low-pass filter manufactured with such a configuration, the refractive index difference between the matrix and the columnar structure increases toward the outer peripheral portion, so that the function of suppressing the occurrence of moire at the outer peripheral portion does not deteriorate.

According to another aspect of the invention,
An optical low-pass filter obtained by photopolymerizing a photopolymerizable composition,
A sheet-like matrix;
A plurality of columnar structures oriented in one direction within the matrix and arranged two-dimensionally in a plane perpendicular to the thickness of the matrix and having a refractive index different from that of the matrix;
The arrangement period of the columnar structures is 80 nm to 1000 μm, and the refractive index difference between the matrix and the columnar structures is larger toward the outer periphery.
An optical low-pass filter is provided.

  In the optical low-pass filter having such a configuration, the difference in the refractive index between the matrix and the columnar structure increases toward the outer peripheral portion, so that the function of suppressing the occurrence of moire in the outer peripheral portion does not deteriorate.

  ADVANTAGE OF THE INVENTION According to this invention, the optical low-pass filter with which the function which suppresses a moire generation | occurrence | production in a peripheral part does not fall and its manufacturing method are provided.

  Hereinafter, an optical low-pass filter according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a perspective view schematically showing the internal structure of an optical low-pass filter 1 according to a preferred embodiment of the present invention.

  The optical low-pass filter 1 includes a sheet or film-like matrix 2 made of a transparent material, and a large number of columnar structures 3 having substantially the same shape and disposed in the matrix 2. Each columnar structure 3 has a refractive index different from that of the matrix 2.

  Each columnar structure 3 is oriented in parallel to each other so as to extend through the sheet or film-like matrix 2 in the thickness direction, and regularly in a hexagonal lattice shape in a plane perpendicular to the thickness of the matrix 2. It is arranged. The hexagonal lattice includes a triangular lattice and a honeycomb lattice.

  Each columnar structure 3 may have a column shape other than a cylinder, for example, an elliptical column or a prism. Further, the arrangement of the columnar structures 3 may be a two-dimensional arrangement other than a hexagonal lattice, for example, a square lattice.

  In this embodiment, the arrangement period (pitch) and diameter of each columnar structure are set such that the refractive index of the optical low-pass filter 1 periodically changes in the order of 80 nm to 1000 μm. Specifically, the diameter of the columnar structure 3 (diameter of the circumscribed circle in the case of a prism) is in the range of 80 nm to 1000 μm, the arrangement period of the columnar structures 3 is 80 nm to 1000 μm, and the refractive index of the optical low-pass filter 1. Is set to periodically change in the order of 80 nm to 1000 μm.

  The arrangement period of the columnar structures 3 is preferably 90 nm to 100 μm, and more preferably 100 nm to 50 μm. The diameter of the columnar structure 3 is preferably 90 nm to 100 μm, and more preferably 100 nm to 50 μm.

The difference in refractive index between the matrix 2 and the columnar structure 3 increases toward the outer periphery.
Specifically, for example, the refractive index difference between the matrix and the columnar structure is such that the arrangement period of the columnar structures is 20 μm, the length of the columnar structures (matrix thickness) is 50 μm, and the light to the optical low-pass filter. In the case where the incident angle is 0 ° to 7 °, if the refractive index difference between the matrix and the columnar structure is Δn, and the incident angle of light to the optical low-pass filter is θ, Δn [unit: dimensionless] and θ [unit] :]] Approximately
Δn = 0.00004θ ² −0.0001θ + 0.0032 Equation 1
It is set so that

Further, when the focal length of the optical system is 20 mm, the following equation is approximately established between the distance D [unit: mm] from the optical low-pass filter center and Δn [unit: dimensionless].
Δn = 0.0003D ² −0.0003D + 0.0032 Equation 2

  In such an optical low-pass filter, the diffraction efficiency is substantially constant regardless of the incident angle in the range of the incident angle of light to the optical low-pass filter from 0 ° to 7 °.

With such a structure, the optical low-pass filter 1 can sufficiently exhibit an interference effect with respect to light in the wavelength range of 350 nm to 2000 nm, and has a high degree of diffraction and deflection in a wavelength range that can be used as an optical low-pass filter. Light control is possible.
Further, in the optical low-pass filter 1 of the present embodiment, six-point separation (three directions) can be performed by a single filter due to the regularity of the arrangement of the columnar structures 3.

Next, a method for manufacturing the optical low-pass filter 1 will be described with reference to FIG.
First, a photopolymerizable composition 5 containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator is applied to the surface of the substrate 4. The substrate 4 can be either circular or rectangular, and preferably has a smooth surface.
The coating thickness of the photopolymerizable composition 5 is appropriately selected according to the thickness of the optical low-pass filter 1 to be manufactured, preferably in the range of 1 μm to 1000 μm, and more preferably in the range of 5 μm to 500 μm.

  Next, the ND filter 6 whose light transmittance increases toward the outer peripheral portion is disposed on the top of the substrate 4 to which the photopolymerizable composition 5 is applied. The ND filter 6 uses the same shape as the substrate 4.

  The relationship between the distance from the center and the light transmittance in the ND filter is selected in consideration of the polymerization reactivity of the resin composition to be used. For example, an ND filter whose light transmittance increases exponentially from the center to the outer periphery is used.

  A photomask 7 is arranged between the substrate 4 coated with the photopolymerizable composition 5 and the ND filter 6, and positional information is inputted at the time of light irradiation, so that the arrangement of the formed columnar structures has high regularity. The photomask 7 has mask holes regularly arranged in a triangular lattice pattern. Further, the mask holes are not limited to the above, and may be arranged in other patterns. For example, a photomask in which mask holes are regularly arranged in a square lattice pattern may be used.

  Next, parallel light L such as ultraviolet rays having a full width at half maximum of 100 nm or less is irradiated from the light source S to the photopolymerizable composition 5 for a predetermined time, and the photopolymerizable composition 5 is cured to some extent by photopolymerization. The light irradiation step is performed (FIG. 2 (a)), and then the photopolymerizable composition 5 is irradiated with ultraviolet rays or the like from the light source S for a predetermined time with the ND filter 6 and the photomask 7 removed. A light irradiation process (FIG. 2B) is performed.

  A large number of columnar structures 3 are formed in the photopolymerizable composition in a hexagonal lattice array with high regularity corresponding to a diffraction pattern reflecting a periodic refractive index change formed at the time of laser beam irradiation. The portion other than 3 becomes the matrix 2. The optical low-pass filter 1 manufactured in this way has a refractive index that periodically changes in the order of 80 nm to 1000 μm.

In order to arrange the columnar structures 3 regularly, the parallel light L to be irradiated preferably has a substantially constant light intensity distribution in a cross section perpendicular to the traveling direction.
As the light source S, for example, 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, or a surface shape such as a surface emitting semiconductor laser (VCSEL). A light source or the like is preferable.

  The parallelism of the light to be irradiated 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, a 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 should be made substantially constant using an appropriate filter or the like. Is preferred.

In order to increase the regularity of the arrangement of the columnar structures 3 in the optical low-pass filter 1, it is preferable to proceed the polymerization reaction uniformly in a plane orthogonal to the film thickness direction of the optical low-pass filter 1, The value of the illuminance distribution given by is preferably 2.0% or less, more preferably 1.0% or less.
Illuminance distribution = (maximum value−minimum value) / (maximum value + minimum value) × 100 Equation 3

  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. Specifically, the full width at half maximum is preferably 100 nm or less, and more preferably 20 nm or less.

  In the optical low-pass filter 1 of the present embodiment, a photopolymerizable composition containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator is 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 3 having a refractive index different from that of the matrix 2 are formed in the matrix 2 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. , 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.

  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.

  Next, an optical system using the optical low-pass filter 1 according to a preferred embodiment of the present invention will be described. FIG. 3 is a schematic diagram schematically showing the configuration of the imaging optical system 8. The imaging optical system 8 includes a solid-state imaging device having pixels with a predetermined pitch, and is used as a digital still camera optical system, a digital camera optical system mounted on a mobile phone, and the like.

  As shown in FIG. 3, the imaging optical system 8 includes a lens 9, an infrared cut filter 10, and a solid-state imaging element 11. The optical low-pass filter 1 is disposed in a state where a gap layer 12 having a predetermined thickness is formed between the optical low-pass filter 1 and the solid-state imaging device 11.

  As the lens 9, a glass lens made of inorganic glass or a plastic lens made of polycarbonate resin, acrylic resin, polystyrene resin, polyolefin resin, or the like is used.

  As the infrared cut filter 10, 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 is used.

  In the present embodiment, the solid-state imaging device 11 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 transferred as signals to the outside by a CCD element or a CMOS circuit. This is an area image sensor that can be used.

  In the present embodiment, the gap layer 12 is made of a polycarbonate resin, an acrylic resin, a polystyrene resin, or a polyimide resin, but may be made of another transparent material such as air.

The thickness of the gap layer 12 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, assuming that 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, the following formula 4 It is expressed as
n ・ Λ ・ sinθ = λ ・ ・ ・ Formula 4

When P / 2 is set as the image blur amount and the pixel pitch P of the image sensor, the thickness L of the gap layer 12 is determined as the following equation 5.
L = P / 2 / tan (sin ⁻¹ (λ / n · Λ)) Equation 5
The thickness L of the gap layer 12 set according to Equation 5 is set in the range of 0.01 μm to 10 mm, preferably in the range of 0.1 μm to 1000 μm, and more preferably in the range of 1 μm to 500 μm.

  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.

  Next, examples of the present invention will be described.

Example 1
NK Ester 14G manufactured by Shin-Nakamura Chemical Co., Ltd .: 50 parts by mass, NK oligo U-2PPA manufactured by Shin-Nakamura Chemical Co., Ltd .: 25 parts by mass, trimethylolpropane triacrylate: 10 parts by mass, phenoxyethyl acrylate: 15 parts by mass 1-hydroxycyclohexyl phenyl ketone: 0.6 parts by mass as a photopolymerization initiator was dissolved to obtain a photopolymerizable composition.

The photopolymerizable composition was dropped on a glass substrate and coated to a thickness of 72 μm using a spin coater. Next, a photomask in which light transmission areas of 10 μmφ are arranged in a square lattice pattern with a pitch of 20 μm is arranged above the photopolymerizable composition, and an ND filter that increases the light transmittance toward the outer periphery is arranged above the photomask. After that, ultraviolet parallel light having a light intensity distribution of approximately 100 nm and a full width at half maximum of wavelength of 1200 mJ / cm ² and a light intensity distribution was irradiated from a direction perpendicular to the glass substrate surface in a nitrogen atmosphere. Thereafter, the photomask is removed, and the photopolymerizable composition is polymerized and cured by irradiating with ultraviolet parallel light having a light intensity distribution of approximately 2400 mJ / cm ² and a full width at half maximum of 100 nm or less. A filter was obtained. At this time, the refractive index difference between the matrix and the columnar structure in the central portion of the optical low-pass filter was 0.0022, and the refractive index difference between the matrix and the columnar structure in the peripheral portion was 0.0034. .

  The light transmittance of the ND filter increases exponentially from the center to the outer periphery, and the light transmittance at the center of the ND filter is 7.5%, but the light transmittance at a distance of 0.7 mm from the center. Is 9.0%, the light transmittance at a distance of 1.4 mm from the center is 27%, and the light transmittance at a distance of 1.75 mm from the center is 90%.

  When the obtained optical low-pass filter was irradiated with a laser beam having a wavelength of 520 nm at an incident angle of 0 ° and the diffraction efficiency was evaluated, the diffraction efficiency in the central portion was 67%, whereas the diffraction efficiency in the peripheral portion was Was 99%. When this diffraction efficiency of 99% was irradiated with laser light having a wavelength of 520 nm at an incident angle of 5 ° and the diffraction efficiency was evaluated, the diffraction efficiency was 66%.

(Example 2)
NK Ester 14G manufactured by Shin-Nakamura Chemical Co., Ltd .: 50 parts by mass, NK oligo U-2PPA manufactured by Shin-Nakamura Chemical Co., Ltd .: 25 parts by mass, trimethylolpropane triacrylate: 10 parts by mass, phenoxyethyl acrylate: 15 parts by mass 1-hydroxycyclohexyl phenyl ketone: 0.6 parts by mass as a photopolymerization initiator was dissolved to obtain a photopolymerizable composition.

The photopolymerizable composition was dropped on a glass substrate, and then coated to a thickness of 72 μm using a spin coater. Next, an ND filter showing the same transmission characteristics as those used in Example 1 and having a higher light transmittance toward the outer periphery is disposed on the photopolymerizable composition, and then the surface of the glass substrate in a nitrogen atmosphere. An optical low-pass filter was obtained by polymerizing and curing the photopolymerizable composition by irradiating with ultraviolet parallel light having a light intensity distribution of approximately 100 nm or less and a full width at half maximum of 100 nm or less at a vertical direction of 1200 mJ / cm ² . . At this time, the refractive index difference between the matrix and the columnar structure in the central portion of the optical low-pass filter was 0.0016, and the refractive index difference between the matrix and the columnar structure in the peripheral portion was 0.0020. .

  When the obtained optical low-pass filter was irradiated with a laser beam having a wavelength of 520 nm at an incident angle of 0 ° and the diffraction efficiency was evaluated, the diffraction efficiency in the central part was 41%, whereas the diffraction efficiency in the peripheral part was Was 58%. When this diffraction efficiency of 58% was irradiated with a laser beam having a wavelength of 520 nm at an incident angle of 5 ° and the diffraction efficiency was evaluated, the diffraction efficiency was 41%.

(Comparative Example 1)
NK Ester 14G manufactured by Shin-Nakamura Chemical Co., Ltd .: 50 parts by mass, NK oligo U-2PPA manufactured by Shin-Nakamura Chemical Co., Ltd .: 25 parts by mass, trimethylolpropane triacrylate: 10 parts by mass, phenoxyethyl acrylate: 15 parts by mass 1-hydroxycyclohexyl phenyl ketone: 0.6 parts by mass as a photopolymerization initiator was dissolved to obtain a photopolymerizable composition.

The photopolymerizable composition was dropped on a glass substrate and coated to a thickness of 72 μm using a spin coater. Next, a photomask in which a 10 μmφ light transmission region is arranged in a square lattice pattern with a pitch of 20 μm is disposed on the photopolymerizable composition, and an ND filter having a uniform light transmittance on the surface is disposed on the photomask. After that, ultraviolet parallel light having a light intensity distribution of approximately 100 nm and a full width at half maximum of wavelength of 1200 mJ / cm ² and a light intensity distribution was irradiated from a direction perpendicular to the glass substrate surface in a nitrogen atmosphere. Thereafter, the photomask is removed, and the photopolymerizable composition is polymerized and cured by irradiating with ultraviolet parallel light having a light intensity distribution of approximately 2400 mJ / cm ² and a full width at half maximum of 100 nm or less. A filter was obtained.
At this time, the refractive index difference between the matrix and the columnar structure in the optical low-pass filter was 0.0022 in both the central portion and the peripheral portion.
When the obtained optical low-pass filter was irradiated with laser light having a wavelength of 520 nm at an incident angle of 0 ° and the diffraction efficiency was evaluated, the diffraction efficiency in the central portion and the peripheral portion was 67%. When this peripheral portion was irradiated with laser light having a wavelength of 520 nm at an incident angle of 5 ° and the diffraction efficiency was evaluated, the diffraction efficiency was 47%.

(Comparative Example 2)
NK Ester 14G manufactured by Shin-Nakamura Chemical Co., Ltd .: 50 parts by mass, NK oligo U-2PPA manufactured by Shin-Nakamura Chemical Co., Ltd .: 25 parts by mass, trimethylolpropane triacrylate: 10 parts by mass, phenoxyethyl acrylate: 15 parts by mass 1-hydroxycyclohexyl phenyl ketone: 0.6 parts by mass as a photopolymerization initiator was dissolved to obtain a photopolymerizable composition.
The photopolymerizable composition was dropped on a glass substrate, and then coated to a thickness of 72 μm using a spin coater. Next, an ND filter having a uniform light transmittance on the surface is disposed on the photopolymerizable composition, and then the full width at half maximum is 100 nm at 1200 mJ / cm ² from the direction perpendicular to the glass substrate surface in a nitrogen atmosphere. An optical low-pass filter was obtained by irradiating with ultraviolet parallel light having a substantially constant light intensity distribution and curing the photopolymerizable composition. At this time, the refractive index difference between the matrix and the columnar structure in the optical low-pass filter was 0.0016 in both the central portion and the peripheral portion.
When the obtained optical low-pass filter was irradiated with laser light having a wavelength of 520 nm at an incident angle of 0 ° and the diffraction efficiency was evaluated, the diffraction efficiency in the central portion and the peripheral portion was 41%. When this peripheral portion was irradiated with laser light having a wavelength of 520 nm at an incident angle of 5 ° and the diffraction efficiency was evaluated, the diffraction efficiency was 29%.

It is a perspective view which shows typically the structure of the optical low-pass filter of preferable embodiment of this invention. It is drawing which shows typically the manufacturing process of the optical low-pass filter of FIG. It is drawing which shows typically the structure of the imaging optical system using the optical low-pass filter of FIG.

Explanation of symbols

1: Optical low-pass filter 2: Matrix 3: Columnar structure 4: Substrate 5: Photopolymerizable composition 6: ND filter 7: Photomask 8: Imaging optical system 9: Lens 10: IR cut filter 11: Solid-state imaging device 12: Gap layer

Claims (2)

A method for manufacturing an optical low-pass filter, comprising:
Disposing a photopolymerizable composition containing a bifunctional or higher polyfunctional monomer or oligomer and a photopolymerization initiator on a substrate;
Above the photopolymerizable composition, installing an ND filter whose light transmittance increases exponentially from the center to the outer periphery ;
The photopolymerizable composition is irradiated with parallel light through the ND filter to polymerize and cure the photopolymerizable composition, and is aligned in one direction within the matrix and the sheet-like matrix. comprises the steps of obtaining an optical low-pass filter having multiple refractive index difference between the matrix as the outer peripheral portion is two-dimensionally arranged in a plane orthogonal to the thickness is greater and the columnar structure, a
An optical low-pass filter manufacturing method characterized by the above. An optical low-pass filter obtained by photopolymerizing a photopolymerizable composition,
A sheet-like matrix;
A plurality of columnar structures oriented in one direction within the matrix and arranged two-dimensionally in a plane perpendicular to the thickness of the matrix and having a refractive index different from that of the matrix;
The arrangement period of the columnar structures is 80 nm to 1000 μm, and the refractive index difference between the matrix and the columnar structures is larger toward the outer periphery.
An optical low-pass filter characterized by that.

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