JP2013101186A - Optical low-pass filter and imaging equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical low-pass filter and an imaging element that can suppress wavelength dependency of a separation width with simple constitution without generating stray light, and to provide an optical low-pass filter and an imaging element that can develop a two-dimensional quadruple image having wavelength dependency of a separation width suppressed with simple constitution.SOLUTION: An optical low-pass filter includes one or a plurality of inclined structures 31 as a structure formed of an isotropic refractive index material and shaped having two or more inclined surfaces differing in inclination direction, and the two or more inclined surfaces provided to the one or the plurality of inclined structures and differing in inclination direction are arranged in an effective area as an area on which at least luminous flux is made incident so as to separate the incident light into a plurality of light beams utilizing refracting operation for the light beam made incident on the inclined surfaces arranged in the effective area. Further, a cover layer 34 may be provided which covers the inclined surfaces of the inclined structure 31 and is formed on an isotropic refracting material different in refractive index from the inclined structures.

Description

  The present invention relates to an optical low-pass filter and an imaging device having an optical low-pass filter.

  Image sensors such as CCD (Charge Coupled Device) and CMOS (Complementary Metal Oxide Semiconductor) are used in imaging devices such as video cameras and digital cameras, and the amount of light that is input as an external signal for each pixel is charged. In other words, a digital image is generated by performing photoelectric conversion and sequentially processing the electrical signal. Such an image sensor is known to cause distortion due to sampling when capturing an image having a spatial frequency finer than the pixel pitch of the image sensor, and to generate a pattern (moire) or false color different from the original image. It has been.

  In order to prevent such moire and false colors, an imaging device such as a video camera or a digital camera captures an image using an optical low pass filter (OLPF). Specifically, the OLPF has a birefringent plate such as quartz, and separates an incident two-dimensional image by a slight distance in the horizontal direction and / or the vertical direction, thereby entering the imaging element out of the spatial frequency. It has a function of cutting the frequency that overlaps the pixel pitch, that is, the vicinity of the sampling frequency, and has been devised so as not to cause moiré and false color phenomena. The horizontal direction and / or the vertical direction refers to either one or both of the horizontal direction and the vertical direction.

  As such an optical low-pass filter, there is a filter using a birefringent material such as quartz. However, when quartz is used as the birefringent material, the cost is increased, and a film is used to obtain a desired separation width. There is a problem that the thickness increases.

  As an example of an optical low-pass filter that does not use a birefringent material, Patent Document 1 describes a refractive low-pass filter in which prisms are arranged in a stripe shape. Patent Document 1 describes that, for example, when a filter is made of a plastic material, if the distance between separated images is set to 0.08 mm, the influence of chromatic aberration can be practically almost no problem. Yes. Further, it is described that four-point separation is possible when prisms having different apex angles are alternately arranged in a stripe shape.

  Patent Document 2 discloses an MTF (Modulation Transfer Function) characteristic according to wavelength in a phase-type optical low-pass filter (also referred to as a diffraction type using a light diffraction effect) formed by bonding members having different refractive indexes. In order to reduce the difference, it is described that the refractive indices of the c-line, d-line, and g-line of both members satisfy a predetermined conditional expression.

  Further, in Patent Document 3, a large number of lens bodies, which are convex bodies having a substantially regular quadrangular pyramid shape, are arranged two-dimensionally at a constant pitch on the surface of the transparent substrate so as to fill the grooves between the lens bodies. A diffractive optical low-pass filter in which an intermediate having a refractive index different from that of the lens body to be formed is described.

Japanese Unexamined Patent Publication No. 55-38549 Japanese Patent Laid-Open No. 3-191319 JP 2009-163176 A

  Patent Document 1 describes an example of using a low-pass filter in which two types of prisms having different apex angles are alternately arranged in a stripe shape as an example of generating a quadruple image. In addition, the combination of prisms is not limited to two types having different apex angles, and it is described that various types of prisms having different apex angles, such as three types, four types,... ing. However, the quadruple image that can be developed by the method described in Patent Document 1 is a one-dimensional quadruple image in which light is separated only in one direction, and is manifested when prisms are stacked perpendicularly to columns. This is different from a two-dimensional quadruple image in which light is separated in two directions. Further, the method of arranging other types of prisms in combination in a stripe form has a problem that the wavelength separation characteristics cannot be suppressed while maintaining the same separation width.

  The low-pass filter described in Patent Document 2 is a diffractive low-pass filter that utilizes the diffraction effect of light. Therefore, when members having different refractive indexes are bonded, the wavelength of each member is determined by using the dispersion of each member. Even if the difference in MTF characteristics due to the above can be reduced, there is a problem that higher-order diffracted light is generated and becomes stray light.

  Note that the low-pass filter described in Patent Document 3 has the same problem as Patent Document 2 in that it is a diffraction-type low-pass filter.

  Accordingly, an object of the present invention is to provide an optical low-pass filter and an image sensor that can suppress the wavelength dependence of the separation width without generating stray light with a simple configuration. It is another object of the present invention to provide an optical low-pass filter and an imaging device that can express a two-dimensional quadruple image with a simple configuration and suppressing the wavelength dependence of the separation width.

  An optical low-pass filter according to the present invention is an optical low-pass filter that separates incident light into a plurality of lights, and is a structure that is formed of an isotropic refractive index material and has two or more inclined surfaces with different inclination directions. One or a plurality of inclined structures (for example, inclined structures 31) are provided, and the inclination directions provided in one or a plurality of inclined structures are different within at least an effective region where a light beam is incident. The above inclined surfaces are arranged, and the incident light is separated into a plurality of lights by utilizing the refraction action of the light rays incident on the inclined surfaces arranged in the effective region.

  In addition, the optical low-pass filter includes one or a plurality of inclined structures which are structures having four inclined surfaces having different inclination directions, and is provided in the one or more inclined structures at least in the effective region. Four or more inclined surfaces having different inclination directions may be arranged.

  Further, there are a plurality of inclined structures, and the plurality of inclined structures may be periodically arranged at least in the effective region.

  Further, there are a plurality of inclined structures, and the plurality of inclined structures include inclined structures having inclined surfaces having different inclination angles or inclined structures having different numbers of inclined surfaces, and at least in the effective region, the inclined structures are inclined. Inclined structures having inclined surfaces with different angles or inclined structures with different numbers of inclined surfaces may be arranged.

  The optical low-pass filter may include a cover layer (for example, the cover layer 34) that covers the inclined surface of the inclined structure and is formed of an isotropic refractive material having a refractive index different from that of the inclined structure.

  In the optical low-pass filter, the width of the structure forming one inclined surface may be 1 mm or more.

  An imaging device according to the present invention is an imaging device including an imaging device, and includes any one of the above-described optical low-pass filters in an optical path until incident light reaches the imaging device. To do.

  According to the present invention, it is possible to provide an optical low-pass filter and an image sensor that can suppress the wavelength dependency of the separation width without generating stray light with a simple configuration. In addition, according to the present invention, it is possible to provide an optical low-pass filter and an image sensor that can express a two-dimensional quadruple image with a simple configuration and suppressing the wavelength dependence of the separation width.

It is a schematic diagram which shows the principle of the optical low-pass filter 3 of this invention. 3 is an explanatory diagram illustrating a configuration example of an optical low-pass filter 3. FIG. It is explanatory drawing for demonstrating the separation angle in the optical low pass filter. It is explanatory drawing which shows the other structural example of the optical low-pass filter. It is explanatory drawing which shows an example of the combination of the member of the inclination structure 31 and the cover layer. It is explanatory drawing which shows the other example of the optical low-pass filter 3 at the time of dividing | segmenting inclination in an element surface. It is a perspective view which shows the other example of the optical low-pass filter 3 at the time of dividing | segmenting inclination in an element surface. It is explanatory drawing which shows the example of the optical low-pass filter 3 which performs 4-point separation. It is a perspective view which shows the other example of the optical low-pass filter 3 which performs 4-point separation. It is a perspective view which shows the other example of the optical low-pass filter 3 which performs 4-point separation. It is a perspective view which shows the other example of the optical low-pass filter 3 which performs 4-point separation. It is a perspective view which shows the example of the optical low-pass filter 3 in which separation width has in-plane distribution. It is a perspective view which shows the example of the optical low-pass filter 3 in which each isolation | separation has in-plane distribution. It is explanatory drawing which shows the optical low-pass filter 3 of an Example. It is a graph which shows the separation width and refraction angle for every wavelength of the optical low-pass filter 3 of an Example. It is explanatory drawing which shows the optical low-pass filter of a comparative example. It is a graph which shows the separation width and refraction angle for every wavelength of the optical low-pass filter of a comparative example. It is a graph which shows the zero order efficiency and the primary efficiency for every wavelength of the optical low-pass filter of a comparative example.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing the principle of the optical low-pass filter 3 of the present invention. As shown in FIG. 1, the optical low-pass filter 3 of the present invention is located behind the imaging lens 4 and has an inclined surface of a structure made of an isotropic refractive index medium in an incident light beam (light bundle). However, one or more inclined structures 31 that form two or more inclined surfaces in different inclination directions are provided. In such a configuration, light is incident on two or more inclined surfaces having different inclination directions, and the light is separated using the property that the light incident on each inclined surface is refracted in different directions. In FIG. 1, 1 denotes an image sensor, 4 denotes an imaging lens, and 5 denotes a subject. 2 represents the pixel pitch in the image sensor 1. Reference numeral 32 denotes a transparent substrate serving as a base on which the inclined structure 31 is formed.

  FIG. 2 is an explanatory diagram showing a configuration example of the optical low-pass filter 3 shown in FIG. 2A is a perspective view of the optical low-pass filter 3 shown in FIG. 1, and FIG. 2B is a top view of the optical low-pass filter 3 shown in FIG. An optical low-pass filter 3 shown in FIG. 2 is an optical low-pass filter that performs two-point separation, and one inclined structure 31 having inclined surfaces in two different inclination directions is formed on a transparent substrate 32. As shown in FIG. 2, the two inclined surfaces provided in the inclined structure 31 and having different inclination directions are both disposed in an area where a light beam is incident (hereinafter referred to as an effective area). As a result, two inclined surfaces of the structure made of an isotropic refractive index material covering at least the effective region on the transparent substrate 32 and having different inclination directions (in the figure, an inclined surface of the inclination direction 1 and Inclined surface 2 in the inclination direction 2).

  In the present invention, the “inclined surface” refers to a surface formed by a structure made of an isotropic refractive index material and inclined with respect to a plane (XY plane) perpendicular to the direction in which incident light travels. . The “inclination direction” is on the line obtained by projecting the normal of the inclined surface onto the XY plane, and indicates the direction from the higher to the lower inclined surface.

  Further, FIG. 2 exemplifies the frequency in each inclination direction in the case of a 360-degree azimuth with the X direction as a reference. According to FIG. 2, a total of two inclined surfaces are formed: an inclined surface in the inclined direction 1 where the inclination direction is 0 degrees and an inclined surface in the inclined direction 2 where the inclination direction is 180 degrees. It is shown.

  Hereinafter, in the case of one inclined surface, it refers to a plane that is continuous at the same inclination angle with respect to the substrate surface. Here, specifically, the plane refers to a region on the surface where unevenness of a predetermined angle or more, that is, a state without a curve is maintained. That is, for example, when the inclined structure 31 has a conical shape, the present invention does not consider that one inclined surface is formed on the entire surface, and the polygonal shape is such that the bottom surface shape approximates a circle. Assuming that it is a polygonal pyramid, it is considered that a large number of inclined surfaces in the inclination direction of all 360 degrees are formed.

The material of the inclined structure 31 may be an isotropic refractive index material. For example, a resin may be used if it is an organic material. Further, for example, glass, S _i O ₂ , S _i ON, TiO ₂ or the like may be used as long as it is inorganic.

  The inclined structure 31 is formed, for example, by processing an isotropic refractive index material such as a resin applied on the transparent substrate 32 into a desired shape using an imprint molding technique, a photolitho edging technique, or the like. May be.

  By distributing the inclination angle or the inclination direction of the inclination formed by the inclined structure 31 in the plane, the light separation width and the separation direction are controlled.

  Here, when the refractive index of the isotropic refractive index material of the inclined structure 31 is n1, and the refractive index of the medium located at the subsequent stage of the inclined structure 31 with respect to the light traveling direction is n2, the refractive indexes n1 and n2 Control makes it possible to control the chromatic dispersion of the separation width.

FIG. 3 is an explanatory diagram for explaining a separation angle in the optical low-pass filter 3. As shown in FIG. 3, β is a refraction angle, that is, an angle formed by an optical axis of incident light and a direction in which outgoing light travels, d is a height of the inclined structure 31, and W is an angle of the inclined structure 31. In the case of the inclination width of the structure corresponding to the portion forming one inclined surface, the refraction angle is expressed by the following equation (1).
sin β = (n2−n1) · d / w = Δn · d / w Equation (1)

Similarly, the refraction angle of the other inclined surface is also expressed by the following equation (2).
sin β = (n2−n1) · d / w = Δn · d / w Equation (2)

  In the example shown in FIG. 3, since the inclination directions differ by 180 degrees, the inclination angle is refracted in the opposite direction between one inclination and the other inclination, and the incident light beam is separated by 2β.

  Although it has been described here that the inclination width of each other is equal to W, it may be different, and at that time, the refraction angles may be different.

  In Expressions (1) and (2), it is preferable that Δn = (n2−n1) be substantially constant in a desired wavelength band because the separation width can be made constant regardless of the wavelength. For example, the value of Δn of each wavelength included in the desired wavelength band may be within ± 10%, more preferably within ± 5%, compared with Δn of other wavelengths included in the same wavelength band. .

  As a method for realizing such a relationship, for example, as shown in FIG. 4, the inclined surface of the inclined structure 31 may be covered with a cover layer 34 made of an isotropic refractive index material having a refractive index different from that of the inclined structure 31. Good. FIG. 4 is an explanatory diagram showing another configuration example of the optical low-pass filter 3 of the present invention. The cover layer 34 is, for example, dripped with an ultraviolet curable resin for forming the cover layer 34 on the surface of the transparent substrate 32 on which the inclined structure 31 is formed, and superimposed on the transparent substrate 33, and then cured by irradiation with ultraviolet rays. To form. Here, the transparent substrate 33 may be removed to reduce the element thickness. Further, an antireflection film may be formed for the purpose of suppressing light reflection on the light incident surface and the light emitting surface.

  FIG. 5 is an explanatory view showing an example of a combination of members of the inclined structure 31 and the cover layer 34. 5A is a graph showing the relationship between the wavelength and the refractive index of both members (the inclined structure 31 and the cover layer 34), and FIG. 5B is the wavelength in the relationship of FIG. 5 is a graph showing an example of the relationship between the separation width and the separation width. In the example shown in FIG. 5, in the wavelength band 0.4 to 0.8 [μm], by selecting a member having a refractive index where Δn is within a range of ± 5% between the wavelengths, An example in which a separation width of about 4 [μm] is realized is shown. The example shown in FIG. 5 is an example in which a resin is used as the isotropic refractive index material for both members.

  1 and 2, as an example of performing two-point separation, an example in which two inclined surfaces having different inclination directions are formed in a light beam using one inclined structure 31 is formed in the light beam. Two or more inclined surfaces may be provided.

  For example, it is also possible to divide the slope in the element plane and divide it into a plurality of slopes having the same slope direction. Even in the case where two or more inclined surfaces are formed using a plurality of inclined structures 31, if each inclined surface is an inclined surface in one of the two inclined directions defined in advance, the element A refraction effect similar to that in the case where inclined surfaces having two different inclination directions are formed in the surface can be obtained. That is, when two-point separation is performed, the number of inclined surfaces may be any number as long as the number of inclination directions (number of types of inclination directions) in the light flux is two.

  FIG. 6 is an explanatory diagram showing another example of the optical low-pass filter 3 when the inclination is divided in the element plane. 6A is a side view showing an example of the optical low-pass filter 3 in which the inclination is divided in the element plane, and FIG. 6B is a side view of the optical low-pass filter 3 shown in FIG. It is a perspective view. In the optical low-pass filter 3 of this example, three inclined structures 31 having a triangular cross-sectional shape are periodically arranged in the element plane. Each inclined structure 31 has an inclined surface in the inclined direction 1 and an inclined surface in the inclined direction 2. Thereby, in the element surface, inclined surfaces having any one of the two types of inclination directions are formed at a substantially uniform ratio. In the example shown in FIG. 6, the light beam is incident on three of the inclined surfaces, so that the light beams incident on the inclined surfaces having different inclination directions are refracted in different directions, thereby separating the light. ing. In this example, it is only necessary that at least two inclined surfaces having different inclination directions are arranged in the effective region from the inclined surfaces provided on the two or more inclined structures 31.

  Thus, if the number of divisions is increased, the thickness of the element can be reduced, and it is preferable that the inclined width of the structure is 1 mm or more because processing is easy. As shown in FIG. 7, a cover layer 34 may also be provided in this example for controlling the chromatic dispersion of the separation width.

  In addition, the optical low-pass filter in the case of performing two-point separation has been described with reference to FIGS. 1 to 7 as an example, but the optical low-pass filter according to the present invention can easily realize separation of four or more points. .

  FIG. 8 is an explanatory diagram illustrating an example of the optical low-pass filter 3 that performs four-point separation. 8A is a perspective view showing an example of the optical low-pass filter 3 that performs four-point separation, and FIG. 8B is a top view of the optical low-pass filter 3 shown in FIG. 8A. As shown in FIG. 8, in the optical low-pass filter 3 of this example, one inclined structure 31 having inclined surfaces in four different inclination directions is formed on a transparent substrate 32. As shown in FIG. 8, the four inclined surfaces with different inclination directions provided in the inclined structure 31 are all arranged in the effective region. As a result, four inclined surfaces of the structure made of isotropic refractive index material covering at least the effective region on the transparent substrate 32 and having different inclination directions (in the figure, the inclined surfaces in the inclination direction 1). And an inclined surface in the inclined direction 2, an inclined surface in the inclined direction 3, and an inclined surface in the inclined direction 4).

  Note that the slope can be subdivided even when four-point separation is performed. FIG. 9 is a perspective view showing another example of an optical low-pass filter that performs four-point separation. In the optical low-pass filter 3 shown in FIG. 9, twelve quadrangular pyramid-shaped inclined structures 31 are periodically arranged in the element plane. Each inclined structure 31 has an inclined surface in the inclined direction 1, an inclined surface in the inclined direction 2, an inclined surface in the inclined direction 3, and an inclined surface in the inclined direction 4. Thereby, in the element surface, inclined surfaces having any one of the four types of inclination directions are formed at a substantially uniform rate. As shown in FIG. 10, a cover layer 34 may also be provided in this example for controlling the chromatic dispersion of the separation width.

  As another example of the optical low-pass filter that performs four-point separation, as shown in FIG. 11, the inclined structure 31-1 and the inclined structure 31-2 each having a combination of inclined surfaces in different inclination directions are transparent. Alternatively, the substrates 31 and 32 may be formed separately. FIG. 11A is a perspective view illustrating an example of the optical low-pass filter 3 that performs four-point separation by stacking two inclined structures 31 having inclined surfaces in two different inclination directions. Moreover, FIG.11 (b) is a top view of the inclination structure 31-1 and the inclination structure 31-2 in the optical low-pass filter 3 shown to Fig.11 (a).

  When two layers of inclined structures 31 having two inclined surfaces in different inclination directions are stacked to perform four-point separation, the first and second layers are arranged so that the separation directions of the inclined structures are orthogonal to each other. do it.

  Further, when separating into four or more points, the shape of the inclined structure 31 may be determined so that inclined surfaces having different numbers of inclination directions according to the number of separation points are formed in the light flux. As a simple example, an example in which one inclined structure 31 having inclined surfaces in different inclination directions corresponding to the number of separation points is arranged in the light beam can be given.

  The examples described so far are examples in which the separation width and the separation direction are the same in the plane, but the optical low-pass filter 3 according to the present invention can also distribute the separation width and the separation direction in the plane. is there. For example, as shown in FIG. 12, if two or more inclined structures 31 (for example, the inclined structure 31a and the inclined structure 31b) having different inclination angles are arranged in the plane, the separation varies depending on the place where the light beam enters. Light can be separated by width. Moreover, as shown in FIG. 13, if two or more inclined structures (for example, the inclined structure 31a and the inclined structure 31c) having different numbers of inclined surfaces are formed in the plane, depending on the place where the light beam is incident. Light can be separated in different separation directions.

  Thus, the shape of the inclined structure 31 is not limited to a rectangular bottom surface, and the bottom surface is a triangular shape, a parallel square shape, a polygonal shape (for example, a hexagonal shape), a cone shape such as a circle, or a combination thereof. Also good. For example, the shape and arrangement method of the inclined structure 31 may be determined in accordance with the pixel pitch of the image sensor 1. The bottom surface shape of the inclined structure 31 is preferably a shape that can fill the element surface (or at least in the effective region) with the inclined surface. In that case, the bottom surface of each inclined structure 31 may be connected.

  As described above, since the optical low-pass filter of the present invention separates light using the refraction action of light, higher-order diffracted light is not generated and becomes stray light unlike the diffractive optical low-pass filter. . If the refraction action is used, the wavelength dependence of the separation width can be reduced as compared with the case where the diffraction action is used. Further, according to the configuration in which the cover layer 34 is provided, the wavelength dispersion of the separation width can be easily controlled, so that the wavelength dependency of the separation width can be further reduced.

  In addition, since the optical low-pass filter of the present invention uses a refraction function, it does not require fine processing such as setting the inclination width of the structure to 1 to 100 μm in order to develop a diffraction effect, and is easy to process. Furthermore, according to the optical low-pass filter of the present invention, it is possible to easily provide multi-dimensional separation in multiple dimensions and in-plane distribution in the separation width and separation direction.

  Next, an example of the configuration of the present invention will be described in detail using a specific example. FIG. 14 is an explanatory diagram showing the optical low-pass filter 3 of the present embodiment. As shown in FIG. 14, the optical low-pass filter 3 of the present embodiment is an optical low-pass filter for realizing a separation width of about 4 μm at an imaging distance of 3 mm.

  The optical low-pass filter 3 of the present embodiment is an inclined structure 31 having a triangular structure with a rectangular bottom surface and a triangular cross-section as shown in FIG. One inclined structure 31 having a surface is provided. As the isotropic refractive index material of the inclined structure 31, a resin having a refractive index n1 of 1.45 at a wavelength of 450 nm, a refractive index n1 of 1.44 at a wavelength of 546 nm, and a refractive index n1 of 1.43 at a wavelength of 633 nm is used. The height d of the structure forming one inclined surface is 10 μm, and the width W of the structure is 2 mm.

  Although not shown, the optical low-pass filter 3 of this embodiment further includes a cover layer 34. As the isotropic refractive index material for the cover layer 34, a resin having a refractive index n2 of 1.58 at a wavelength of 450 nm, a refractive index n2 of 1.56 at a wavelength of 546 nm, and a refractive index n2 of 1.55 at a wavelength of 633 nm is used.

  FIG. 15 is a graph showing the separation width and the refraction angle for each wavelength of the optical low-pass filter 3 of this example manufactured under the above conditions. As shown in FIG. 15, in the optical low-pass filter 3 of the present embodiment, a desired separation width of 4 μm can be obtained within a range of ± 0.2 μm (within about 5%) over the wavelength band of 0.4 to 0.8 μm. I understand that. Moreover, it turns out that a refraction angle is also substantially uniform over wavelength range 0.4-0.8 micrometer.

[Comparative example]
FIG. 16 is an explanatory diagram showing an example of an optical low-pass filter when a similar separation width is realized using a diffraction grating as a comparative example. As shown in FIG. 16, the optical low-pass filter of the comparative example separates light by a diffractive action expressed by a diffraction grating having a rectangular cross-sectional shape. In this comparative example, assuming that light having wavelengths of 450 nm, 546 nm, and 633 nm is incident, it is designed to satisfy the two conditions of separation width and diffraction efficiency most in the vicinity of the intermediate wavelength.

  As the isotropic refractive index material of the diffraction grating, a resin having a refractive index n1 of 1.51 at a wavelength of 450 nm, a refractive index n1 of 1.50 at a wavelength of 546 nm, a refractive index n1 of 1.49 at a wavelength of 633 nm is used. The grating period of the diffraction grating is 780 μm, and the height of the diffraction grating is 4.4 μm.

  Although not shown, it is assumed that the optical low-pass filter 3 of this comparative example also includes a cover layer. As the isotropic refractive index material of the cover layer, a resin having a refractive index n2 of 1.58 at a wavelength of 450 nm, a refractive index n2 of 1.56 at a wavelength of 546 nm, and a refractive index n2 of 1.55 at a wavelength of 633 nm is used.

  FIG. 17 is a graph showing the separation width and refraction angle for each wavelength of the optical low-pass filter of this comparative example manufactured under the above conditions. As shown in FIG. 17, it can be seen that the diffractive optical low-pass filter of this comparative example has a greater wavelength dependence of the separation width than the optical low-pass filter 3 of the first example.

  FIG. 18 is a graph showing the zero-order efficiency and the first-order efficiency for each wavelength of the optical low-pass filter of this comparative example. As shown in FIG. 18, the diffractive optical low-pass filter of this comparative example also has a large wavelength dependency of efficiency, and ± first-order light at a specific wavelength (in this example, near the intermediate wavelength of 450 nm and 633 nm). It can be seen that even if the diffraction efficiency can be increased, higher-order stray light is generated in other wavelength bands.

  In imaging devices such as video cameras and digital cameras, the present invention can be suitably applied to applications that reduce moiré and false color phenomena.

DESCRIPTION OF SYMBOLS 1 Image pick-up element 2 Pixel pitch 3 Optical low-pass filter 31 Inclined structure 32, 33 Transparent substrate 34 Cover layer 4 Imaging lens 5 Subject

Claims (7)

An optical low-pass filter that separates incident light into a plurality of lights,
One or a plurality of inclined structures which are formed of an isotropic refractive index material and have a shape having two or more inclined surfaces having different inclination directions,
At least two inclined surfaces with different inclination directions provided in the one or more inclined structures are arranged in an effective area that is an area where light flux is incident,
An optical low-pass filter characterized in that incident light is separated into a plurality of lights by utilizing a refracting action of light incident on the inclined surface arranged in the effective region. One or a plurality of inclined structures, which are structures having a shape having four inclined surfaces with different inclination directions,
The optical low-pass filter according to claim 1, wherein at least four inclined surfaces having different inclination directions provided in the one or more inclined structures are arranged in at least the effective region. There are a plurality of inclined structures,
The optical low-pass filter according to claim 1, wherein the plurality of inclined structures are periodically arranged at least in an effective region. There are a plurality of inclined structures, and the plurality of inclined structures include inclined structures having inclined surfaces with different inclination angles or inclined structures with different numbers of inclined surfaces,
4. The inclined structure having inclined surfaces having different inclination angles or inclined structures having different numbers of inclined surfaces are disposed at least in the effective region. 5. Optical low-pass filter. The optical system according to any one of claims 1 to 4, further comprising a cover layer that covers an inclined surface of the inclined structure body and is formed of an isotropic refractive material having a refractive index different from that of the inclined structure body. Low pass filter. The optical low-pass filter according to any one of claims 1 to 5, wherein a pitch of a structure constituting one inclined surface is 1 mm or more. An imaging device including an image sensor,
An image pickup device comprising the optical low-pass filter according to any one of claims 1 to 6 in an optical path until incident light reaches the image pickup device.

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