Imaging element and imaging device

Abstract

This imaging element (3) includes a pixel array (40) in which a plurality of pixels (41) including a photoelectric conversion element are arranged in a two-dimensional array, and a spectroscopic element array in which spectroscopic elements having periodic arrangements of a plurality of fine structures for focusing incident light on different positions on the pixel array (40) according to the polarization direction and the wavelength component of the incident light are arranged in a two-dimensional array. The arrangement period of the plurality of fine structures is shorter than the wavelength of light to be received by the pixel array (40), and all or a part of the plurality of fine structures has a line symmetry axis, and has a surface that is shaped so as to differ in length between the direction of the line symmetry axis and the direction orthogonal to the line symmetry axis as a surface on which the incident light is incident. The line symmetry axis and the structure are modulated according to the position in the spectroscopic element.

Description

Image sensor and image pickup device

[0001] The present invention relates to an imaging element and an imaging device.

[0002] In recent years, there has been active research and development into polarization color imaging devices that enable the acquisition of polarization color images, which are images that contain polarization information in addition to color information. Conventional polarization color imaging devices acquire polarization and color information of the imaged object by stacking microlenses, light-absorbing polarization filters, and color filters on the pixels.

[0003] However, in the above configuration, the light incident on the sensor passes through the polarizing filter and color filter before reaching each pixel, so the total amount of light received is inevitably limited to a maximum of about 1 / 6 of the amount of incident light, limiting the light receiving sensitivity.

[0004] Therefore, in recent years, it has been proposed to achieve high sensitivity in imaging elements by using a light-transmitting polarization separation element with a fine structure pattern instead of a polarizing filter (see, for example, Non-Patent Document 1). It has also been proposed to achieve high sensitivity in imaging elements by using a light-transmitting color separation element with a fine structure pattern instead of a color filter (see, for example, Non-Patent Document 2). The imaging sensitivity of a polarization color imaging element can be improved by using either of the above methods in combination with a filter.

[0005] E. Arbabi, S. M. Kamali, A. Arbabi, and A. Faraon, "Full-Stokes Imaging Polarimetry Using Dielectric Metasurfaces," ACS Photonics 5, 3132-3140 (2018).Masashi Miyata, Naru Nemoto, Kota Shikama, Fumihide Kobayashi, and Toshikazu Hashimoto, "Full-color-sorting metalenses for high-sensitivity image sensors," Optica 8, 1596-1604 (2021).

[0006] However, in order to obtain polarized color images using techniques that use microstructures, it is necessary to use a polarizing filter or a color filter in combination, which poses a problem from the perspective of cost.

[0007] The present invention has been made in view of the above, and has an object to provide an imaging element and an imaging apparatus that can achieve cost reduction.

[0008] In order to solve the above-mentioned problems and achieve the object, an imaging element according to the present invention includes a pixel array in which a plurality of pixels, each including a photoelectric conversion element, are arranged in a two-dimensional array, and a dispersing element array in which a plurality of dispersing elements, each having a periodic arrangement of microstructures that condenses incident light to different positions on the pixel array depending on the polarization direction and wavelength component of the incident light, are arranged in a two-dimensional array. The arrangement period of the microstructures is shorter than the wavelength of light to be received by the pixel array, and all or some of the microstructures have a surface, on which the incident light is incident, that has an axis of linear symmetry and a shape whose length differs in a direction perpendicular to the axis of linear symmetry, and the axis of linear symmetry and the structure are modulated depending on the position on the dispersing element.

[0009] According to the present invention, costs can be reduced.

[0010] FIG. 1 is a side view showing a schematic configuration of an imaging device according to an embodiment. FIG. 2 is a diagram schematically showing an example of a portion of a cross section of a pixel array and a polarization wavelength separation array of an imaging element according to an embodiment. FIG. 3 is a diagram schematically showing an example of a plane of a polarization wavelength separation lens in a polarization wavelength separation lens array of an imaging element according to an embodiment. FIG. 4 is a diagram schematically showing an example of polarization separation and wavelength separation characteristics of a polarization wavelength separation lens of an imaging element according to an embodiment. FIG. 5 is a plan view showing an example of a microstructure constituting a polarization wavelength separation lens according to embodiment 1. FIG. 6 is a side view of a microstructure constituting a polarization wavelength separation lens according to embodiment 1. FIG. 7 is a side view of a microstructure constituting a polarization wavelength separation lens according to embodiment 1. FIG. 8 is a diagram showing an example of a side view of a microstructure constituting a polarization wavelength separation lens according to embodiment 1. FIG. 9 is a view taken in the direction of arrow C in FIG. 8. FIG. 10 is a view taken in the direction of arrow C in FIG. 10. FIG. 12 is a diagram showing calculation results of phase delay characteristics of the microstructures shown in FIGS. 8 and 9. FIG. 13 is a diagram showing calculation results of phase delay characteristics for the microstructures shown in FIGS. 10 and 11 . FIG. 14 is a diagram showing calculation results of phase delay characteristics for a microstructure in which the axis of symmetry of the microstructures shown in FIGS. 8 and 9 is rotated by 45°. FIG. 15 is a diagram showing calculation results of phase delay characteristics for a microstructure in which the axis of symmetry of the microstructures shown in FIGS. 10 and 11 is rotated by 45°. FIG. 16 is a plan view schematically showing another example of a polarized wavelength separation lens according to embodiment 1. FIG. 17 is a diagram schematically showing a portion of a cross section taken along line XVII-XVII shown in FIG. 16 . FIG. 18 is a diagram showing an example of a phase delay spatial distribution realizing the polarized wavelength separation lens according to embodiment 1. FIG. 19 is a diagram showing an example of a phase delay spatial distribution realizing the polarized wavelength separation lens according to embodiment 1. FIG. 20 is a diagram showing an example of a phase delay spatial distribution realizing the polarized wavelength separation lens according to embodiment 1. FIG. 21 is an enlarged view of the region of FIG. 16 in the polarized wavelength separation lens according to embodiment 1.FIG. 22 is a diagram illustrating an example of a wavelength spectrum showing the relationship between the received light intensity and wavelength of each pixel when linearly polarized light in the 0° direction is incident on the image sensor according to the first embodiment. FIG. 23 is a diagram illustrating an example of a light intensity distribution on the pixel array when light of different polarization states and wavelength combinations is perpendicularly incident on the image sensor according to the first embodiment. FIG. 24 is a diagram illustrating an example of a light intensity distribution on the pixel array when light of different polarization states and wavelength combinations is perpendicularly incident on the image sensor according to the first embodiment. FIG. 25 is a diagram illustrating another example of the top surface shape of a microstructure in a polarized wavelength separation lens according to the first embodiment. FIG. 26 is a diagram schematically illustrating a portion of a cross section of another example configuration of the image sensor according to the first embodiment. FIG. 27 is a diagram schematically illustrating a portion of a cross section of another example configuration of the image sensor according to the first embodiment. FIG. 28 is a diagram schematically illustrating a portion of a cross section of another example configuration of the image sensor according to the first embodiment. FIG. 29 is a side view illustrating a schematic example of a microstructure according to the first embodiment. FIG. 30 is a diagram schematically illustrating another example of an arrangement of pixels in a pixel array of the image sensor according to the embodiment. FIG. 31 is a diagram schematically showing another example of pixel arrangement in a pixel array of an image sensor according to an embodiment. FIG. 32 is a plan view schematically showing another example of an image sensor according to Embodiment 1. FIG. 33 is a diagram schematically showing a portion of a cross section taken along line XXXIII-XXXIII shown in FIG. 32. FIG. 34 is a diagram for explaining the angle of incidence of light incident on the image sensor shown in FIGS. 32 and 33. FIG. 35 is a plan view schematically showing another example of an image sensor according to Embodiment 1. FIG. 36 is a diagram schematically showing a portion of a cross section taken along line XXXVI-XXXVI shown in FIG. 35. FIG. 37 is a diagram schematically showing a portion of a cross section of an image sensor according to Embodiment 2. FIG. 38 is a diagram schematically showing a portion of a cross section of an image sensor according to Embodiment 3. FIG. 39 is a diagram schematically showing a portion of a cross section of an image sensor according to Embodiment 4.

[0011] The best mode for carrying out the present invention will be described in detail below with reference to the drawings. Note that in the following description, each drawing merely shows a schematic representation of the shape, size, and positional relationship to the extent that the contents of the present invention can be understood, and therefore the present invention is not limited to only the shape, size, and positional relationship exemplified in each drawing.

[0012] [Embodiment] [Image Capture Apparatus] First, an image capture apparatus according to an embodiment of the present invention will be described. Fig. 1 is a side view showing a schematic configuration of an image capture apparatus according to an embodiment.

[0013] 1, an imaging device 1 according to the embodiment includes a lens optical system 2, an imaging element 3, and a signal processing unit 4. The signal processing unit 4 processes an electrical signal output from the imaging element 3 to generate an image signal.

[0014] The lens optical system 2 is an example of an imaging optical system, and forms an optical image on the imaging surface of the imaging element 3. Light such as natural light or illumination light is irradiated onto an object, and the light is reflected, scattered, or transmitted by the object, or light emitted from the object, and the lens optical system 2 forms an optical image on the imaging surface of the imaging element 3.

[0015] The lens optical system 2 is composed of a lens group consisting of a plurality of lenses arranged along the optical axis in order to correct various optical aberrations, but in FIG. 1 it is shown as a single lens for the sake of simplicity.

[0016] The image sensor 3 is an image sensor using a metasurface, and outputs an electrical signal containing information for each pixel corresponding to the polarization direction and wavelength component based on light incident on the imaging surface by the lens optical system 2. The signal processing unit 4 processes the electrical signal output from the image sensor 3 to generate an image signal, and outputs the generated image signal to the outside.

[0017] The image signal is, for example, a polarized color image signal including polarization information and wavelength information. The polarized color image signal is a signal of an image for each combination of the polarization direction and wavelength component to be separated, but is not limited to this example.

[0018] The imaging device 1 may include known components such as an infrared-blocking optical filter, an electronic shutter, a viewfinder, a power source (battery), a flashlight, etc., but a description of these components is omitted as they are not particularly necessary for understanding the present invention. Furthermore, the above configuration is merely an example, and in the embodiment, known components can be used in appropriate combination as components other than the lens optical system 2, the imaging element 3, and the signal processing unit 4.

[0019] [Image capture element 3] Next, an overview of the image capture element 3 according to the embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram schematically illustrating an example of a part of a cross section of a pixel array and a polarization wavelength separation array of the image capture element 3 according to the embodiment.

[0020] As shown in Fig. 2, the image sensor 3 according to the embodiment has a transparent substrate 10, a polarized wavelength separation lens array 20, a transparent layer 30, and a pixel array 40. In the example shown in Fig. 2, the transparent layer 30, the polarized wavelength separation lens array 20, and the transparent substrate 10 are stacked in this order on the pixel array 40. The polarized wavelength separation lens array 20 is an example of a spectroscopic element array. Fig. 2 corresponds to a cross-sectional view taken along line II-II in Fig. 3, which will be described later.

[0021] In the example shown in Figure 2, the polarized wavelength separation lens array 20 faces the pixel array 40 via the transparent layer 30, and the polarized wavelength separation lens array 20 is arranged on the side where light from the lens optical system 2 is incident.

[0022] The transparent substrate 10 is made of, for example, SiO ２ However, the present invention is not limited to such examples. The polarized wavelength separation lens array 20 includes a plurality of polarized wavelength separation lenses 21 arranged in a two-dimensional array on the bottom surface of the transparent substrate 10. Fig. 2 shows a portion of one of the plurality of polarized wavelength separation lenses 21. The polarized wavelength separation lens 21 is an example of a spectroscopic element.

[0023] Each polarized wavelength separation lens 21 has a periodic arrangement of multiple microstructures that separate incident light according to its polarization direction and wavelength component, and focus the incident light at different positions on the pixel array 40 according to the polarization direction and wavelength component of the incident light. This allows the polarized wavelength separation lens 21 to focus light from the object O to be imaged as incident light at different pixels on the pixel array 40 according to the polarization direction and wavelength component of the incident light.

[0024] The transparent layer 30 is an air layer or SiO ２ However, the transparent layer 30 is not limited to this example. For example, the transparent layer 30 may be made of a material such as glass, or may have a laminated structure made of multiple materials, as long as the refractive index of the material of the polarized wavelength separation lens 21 is lower and the loss with respect to the wavelength of the incident light is low. In FIG. 2, an air layer is shown as the transparent layer 30.

[0025] The pixel array 40 has a plurality of pixels 41 each including a photoelectric conversion element arranged in a two-dimensional array, and a wiring layer 42 that transmits electrical signals generated in each pixel 41 to the signal processing unit 4 and transmits control signals to each pixel 41 to control the operation of the pixel 41.

[0026] For ease of explanation, an xyz Cartesian coordinate system is set in several drawings including Fig. 2. In the xyz Cartesian coordinate system, the direction perpendicular to the pixel array surface of the pixel array 40 is the z-axis, the array direction of the four pixels 41 shown in Fig. 2 is the x-axis, and the direction perpendicular to the x-axis is the y-axis. The pixel array surface is the xy plane, which is the two-dimensional array direction of the pixels 41 in the pixel array 40. Furthermore, an angle θ is set with respect to the x-axis on the xy plane, which is parallel to the pixel array surface of the pixel array 40.

[0027] 3 is a diagram schematically illustrating an example of a plane of a polarization wavelength separation lens 21 in the polarization wavelength separation lens array 20 of the image sensor 3 according to the embodiment. While one polarization wavelength separation lens 21 is shown in FIG. 3, a plurality of polarization wavelength separation lenses 21 are arranged in a two-dimensional array in the x and y directions in the polarization wavelength separation lens array 20.

[0028] 3, the polarization wavelength separation lens 21 has a periodic arrangement of a plurality of microstructures 211. As described above, the plurality of microstructures 211 separate the incident light according to the polarization direction and wavelength component, and condense the incident light to different positions on the pixel array 40 according to the polarization direction and wavelength component of the incident light. The microstructures 211 are made of SiN or TiO, which has a refractive index higher than that of the transparent layer 30. ２ The period P in the periodic arrangement of the microstructures 211 is shorter than the wavelength of the transmitted light, thereby suppressing unnecessary diffracted light.

[0029] The microstructures 211 in the polarization wavelength separation lens 21 shown in FIG. 3 have an incident surface, which is a surface having a shape with a line symmetry axis and a shape with different lengths in the direction of the line symmetry axis and a direction perpendicular to the line symmetry axis, onto which incident light is incident. In the example shown in FIG. 3 , each microstructure 211 has, as its line symmetry axis, an axis parallel to the x-axis or y-axis, or an axis parallel to an axis tilted 45° from the x-axis or y-axis. The polarization wavelength separation lens 21 includes microstructures 211 having, as their line symmetry axis, an axis parallel to the x-axis or y-axis, and microstructures 211 having, as their line symmetry axis, an axis parallel to an axis tilted 45° from the x-axis or y-axis. The shape of the incident surface is, for example, a rectangular shape having a longitudinal direction and a lateral direction, a cross shape having a longitudinal direction and a lateral direction, an elliptical shape having a longitudinal direction and a lateral direction, or the like, and has a shape with different lengths in the direction of the line symmetry axis and a direction perpendicular to the line symmetry axis.

[0030] In the polarized wavelength separation lens 21 shown in Figure 3, the axis of linear symmetry and structure of the microstructure 211 are modulated depending on the position on the polarized wavelength separation lens 21, which allows the polarized wavelength separation lens 21 to more appropriately focus incident light onto pixels 41 at different positions on the pixel array 40 depending on the polarization direction and wavelength component of the incident light.

[0031] The structure of the microstructure 211 is modulated by modulating the area of ​​the upper surface of the microstructure 211 onto which incident light is incident, the shape of the microstructure 211, the volume of the microstructure 211, etc. The structure of the microstructure 211 is modulated so that the phase delay characteristic of the microstructure 211 is modulated. In the polarization wavelength separation lens 21 shown in Fig. 3, the structure of all of the multiple microstructures 211 is modulated, but the present invention is not limited to this example, and the structure may be modulated only for some of the multiple microstructures 211.

[0032] 3, a plurality of microstructures 211 are arranged in each of the x and y directions, and the axis of line symmetry of a microstructure 211 differs by 45° from the axis of line symmetry of adjacent microstructures 211 in the x and y directions, which are the arrangement directions of the periodic array. This allows the polarized wavelength separation lens 21 to change the polarization direction in small incident area units, and to more appropriately focus incident light on pixels 41 at different positions on the pixel array 40 depending on the polarization direction and wavelength components of the incident light.

[0033] The polarization directions separated by the polarized wavelength separation lens 21 are, for example, four or more, and the wavelength components separated by the polarized wavelength separation lens 21 are, for example, two or more, but are not limited to these examples.

[0034] For example, the polarization directions separated by the polarized wavelength separation lens 21 are the x-axis direction (θ=0°), the y-axis direction (θ=90°), the θ=45° direction, and the θ=-45° direction, but may also include, for example, right-handed circularly polarized components and left-handed circularly polarized components.

[0035] The wavelength components separated by the polarized wavelength separation lens 21 are, for example, a red (R) wavelength component, a green (G) wavelength component, a blue (B) wavelength component, and a near-infrared light (N) wavelength component.

[0036] FIG. 4 is a diagram schematically showing an example of the polarization separation and wavelength separation characteristics of the polarization wavelength separation lens 21 of the image sensor 3 according to the embodiment.

[0037] The polarized wavelength separation lens 21 shown in FIG. 4 separates light into four polarization directions, namely, the x-axis direction (θ=0°), the y-axis direction (θ=90°), the θ=45° direction, and the θ=−45° direction, and four wavelength components of red (R), green (G), blue (B), and near-infrared light (N) in each polarization direction.

[0038] In the pixel array 40, incident light, which has been spatially separated into four wavelength components in each of the four polarization directions by the polarizing wavelength separation lens 21, is received by 16 pixels 41. In the pixel array 40, 16 pixels 41 are formed as a unit structure for each polarizing wavelength separation lens 21.

[0039] Light of different combinations of polarization directions and wavelength components is collected on the 16 pixels 41 corresponding to the polarization wavelength separation lens 21. In FIG. 4, the polarization directions and wavelength components collected on these 16 pixels 41 are R ｈ , R ｖ , R ４５ｈ , R ４５ｖ , G ｈ , G ｖ , G ４５ｈ , G ４５ｖ , B ｈ , B ｖ , B ４５ｈ , B ４５ｖ , N ｈ , N ｖ , N ４５ｈ , N ４５ｖ is shown.

[0040] "R" indicates that the wavelength component is red (R), "G" indicates that the wavelength component is green (G), "B" indicates that the wavelength component is blue (B), and "N" indicates that the wavelength component is near-infrared light (N). ｈ " indicates that the polarization direction is the x-axis direction (θ=0°). ４５ｈ " indicates that the polarization direction is θ=45°, and " ｖ " indicates that the polarization direction is the y-axis direction (θ=90°). ４５ｖ " indicates that the polarization direction is θ=−45°.

[0041] The polarization direction and wavelength components separated by the polarized wavelength separation lens 21 are not limited to the example shown in Fig. 4, and the polarization direction and wavelength components separated can be changed arbitrarily depending on the configuration of the polarized wavelength separation lens 21. Furthermore, the arrangement, shape, size, etc. of the pixels 41 are not limited to the example shown in Fig. 4.

[0042] As described above, the image sensor 3 according to the embodiment includes a polarized wavelength separation lens 21 in which dispersive elements, each having a periodic arrangement of microstructures 211 that condense incident light to different positions on the pixel array 40 depending on the polarization direction and wavelength components of the incident light, are arranged in a two-dimensional array. The period P of the periodic arrangement of the microstructures 211 is shorter than the wavelength of the transmitted light. Furthermore, all or some of the microstructures 211 have a surface, onto which the incident light is incident, that has a linear symmetry axis and a shape whose length varies in the direction of the linear symmetry axis and in a direction perpendicular to the linear symmetry axis, and the linear symmetry axis and the structure are modulated depending on the position on the polarized wavelength separation lens 21. This allows the image sensor 3 to separate the polarization direction and wavelength of the incident light without using a color filter or a polarizing filter, thereby reducing the number of components and achieving cost reduction.

[0043] Furthermore, since the image sensor 3 does not use a color filter or a polarizing filter, it is possible to maximize light utilization efficiency and improve imaging sensitivity compared to conventional image sensors that use color filters and polarizing filters. Furthermore, since the above functions can be achieved using only a single layer of microstructure elements that can be easily fabricated, it is possible to provide an image sensor 3 with superior productivity compared to conventional technologies.

[0044] The present embodiment will be described in more detail below with reference to the drawings.

[0045] [Embodiment 1] An imaging device 1 according to embodiment 1 has a lens optical system 2, an imaging element 3, and a signal processing unit 4, similar to the configuration shown in Fig. 1. The imaging element 3 according to embodiment 1 also has a transparent substrate 10, a polarization wavelength separation lens array 20, a transparent layer 30, and a pixel array 40, similar to the configuration shown in Fig. 4.

[0046] The incident light that enters the image sensor 3 is separated into its polarization direction and wavelength components by the polarizing wavelength separation lens 21, and as described above, the separated light is focused at different positions on the pixel array 40 depending on the combination of polarization direction and wavelength components.

[0047] In the pixel array 40, photoelectric conversion is performed by the photoelectric conversion element in each pixel 41, and each unit structure outputs 16 electrical signals corresponding to different combinations of polarization direction and wavelength component.

[0048] The signal processing unit 4 performs image processing such as demosaic processing, color correction processing based on matrix operations, and polarization correction processing based on matrix operations on the 16 electrical signals for each unit structure output from the pixel array 40, thereby generating a polarized color image according to the polarization direction and wavelength components, and outputs a signal of the generated polarized color image.

[0049] The polarized color images are, for example, images obtained by multiplying the number of polarization directions to be separated by the number of wavelength components to be separated, and are images for each combination of the polarization directions to be separated and the wavelength components, but are not limited to this example. In the pixel array 40, the above-mentioned unit structures form an array on a two-dimensional plane, so that the signal processing unit 4 can obtain two-dimensional spatial information about the polarization component information and wavelength component information of the object imaged on the image sensor 3.

[0050] [Polarized Wavelength Separating Lens 21] As described above, the polarized wavelength separating lens 21 includes a periodic arrangement of a plurality of microstructures 211. Each microstructure 211 is a structure formed of a plurality of or a single columnar shape, but may also be a structure composed of a plurality of or a single hole shape, or may be a structure composed of a columnar shape and a hole shape.

[0051] The interval between the microstructures 211 is shorter than the wavelength of the light to be received, that is, shorter than the wavelength of the light to be received by the pixel array 40. For example, the shortest central wavelength of the light receiving wavelength band, which is the wavelength band of the light to be received, is λ ｍｉｎ Then, the interval between the microstructures 211 is λ ｍｉｎ / n ０ It is set to less than n０ is the refractive index of the transparent layer on the transmission side. The interval between the microstructures 211 is the above-mentioned arrangement period P, and this arrangement period P satisfies the following relationship: P<λ ｍｉｎ / n ０ It is defined as follows.

[0052] Here, an example will be described in which the polarization wavelength separation lens 21 is formed by a plurality of microstructures 211 formed on the bottom surface of the transparent substrate 10. Fig. 5 is a plan view showing an example of the microstructures 211 that form the polarization wavelength separation lens 21 according to embodiment 1. Figs. 6 and 7 are side views of the microstructures 211 that form the polarization wavelength separation lens 21 according to embodiment 1. The microstructures 211 shown in Figs. 5 to 7 are structures formed in a columnar shape.

[0053] The polarized light wavelength separation lens 21 is configured by arranging a plurality of columnar microstructures 211 as shown in Figures 5 to 7. Each microstructure 211 has a refractive index n ０ A refractive index n １ The thickness of the structure, i.e., the length h in the z-axis direction, is constant.

[0054] As shown in FIG. 5, the top and bottom surfaces of the microstructure 211 have a width w １ , width in the y-axis direction w ２ The microstructure 211 operates as an optical waveguide that confines and propagates light within the structure due to the difference in refractive index between the structure and the material or space surrounding the structure.

[0055] Therefore, when light is incident on one side (for example, the top surface) of the microstructure 211 as an incident surface, the light is tightly confined within the structure and propagates. At this time, the light incident on the microstructure 211 is propagated through the effective refractive index n ｅｆｆ The light propagates while being subjected to a phase delay effect determined by and is finally output from the other side of the structure (for example, the bottom surface). In this case, when the phase of light propagated through the material or space around the microstructure 211 for a distance h that is the thickness of the microstructure 211 is used as a reference, the amount of phase delay φ caused by the microstructure 211 is expressed by Equation (1), where λ is the wavelength of the light in a vacuum.

[0056]

[0057] As is clear from the above formula (1), the phase delay amount φ due to the microstructure 211 varies depending on the wavelength λ of the light, so that the microstructure 211 having the same structure can give different phase delay amounts to the light depending on the wavelength region. ｅｆｆ The refractive index n ｅｆｆ The degree of phase delay largely depends on the dimensions of the top surface shape of the microstructure 211. Therefore, by using microstructures 211 with various top surface shapes, it is possible to set various combinations of the phase delay amount φ according to the wavelength λ of light.

[0058] Then, depending on the position on the plane including the upper surface of each microstructure 211, an appropriate width w １ , w ２ By arranging the upper surfaces of the microstructures 211 having the above-mentioned structures, it is possible to give an arbitrary spatial distribution of phase delay to light of each wavelength, and as a result, it becomes possible to control the optical wavefront of light of each wavelength arbitrarily.

[0059] Furthermore, as shown in the above formula (1), the refractive index n ｅｆｆ is a function of the structure dimensions, and it is known that a strong polarization dependency occurs depending on the structure shape. In the case of a columnar microstructure 211, when the structure cross section is made rectangular as shown in FIGS. 6 and 7, different refractive indices n ｅｆｆ can be given independently.

[0060] Here, the phase delay amount of the microstructure 211 with respect to the polarization component in the horizontal direction (x-axis direction) in FIG. 5 is φ ｈ , the phase delay amount of the microstructure 211 for the polarization component in the vertical direction (y-axis direction) in FIG. 5 is φ ｖ The effective refractive index of the microstructure 211 for the polarization component in the horizontal direction (x-axis direction) is n ｅｆｆｈ , the effective refractive index of the microstructure 211 for the polarization component in the vertical direction (y-axis direction) is n ｅｆｆｖ In this case, the refractive index n ｅｆｆｈ and refractive index n ｅｆｆｖ The width w １ and width w２ It is known that these can be controlled by combining ０ <n ｅｆｆｈ <n １ , and n ０ <n ｅｆｆｖ <n １ It takes the value of

[0061] Therefore, from equation (1), the phase delay amount φ ｈ and the phase delay amount φ ｖ The width w １ and width w ２ That is, in the examples shown in FIGS. 5 to 7, the width w of the microstructure 211 can be arbitrarily controlled by combining the １ and width w ２ By designing the phase delay amount φ for each polarization direction, ｈ and the phase delay amount φ ｖ It is possible to set the above as desired.

[0062] Furthermore, by rotating the axis of linear symmetry of the upper surface of the microstructure 211, the corresponding polarization direction can be changed. In the example shown in Fig. 5, the axis of linear symmetry of the upper surface of the microstructure 211 is an axis parallel to the x-axis or an axis parallel to the y-axis. By rotating the upper surface of the microstructure 211 by 45° and rotating the axis of linear symmetry, the phase delay amount φ for the polarization component of θ = ±45° can be changed. ４５ｈ and the phase delay amount φ ４５ｖ and the phase of the light of the polarization component of θ=±45° can be defined as a phase delay amount φ ４５ｈ and the phase delay amount φ ４５ｖ and can be modulated respectively.

[0063] From the above, the image sensor 3 has an appropriate width w depending on the position on the x-axis and y-axis plane. １ , w ２ By arranging a plurality of microstructures 211 each having an axis of linear symmetry, the polarization wavelength separation lens 21 can provide an arbitrary spatial distribution of phase delay for each polarization direction. As a result, it becomes possible to perform arbitrary wavefront control for each polarization direction.

[0064] In addition, the phase delay amount φ ｈ and the phase delay amount φ ｖSince, as described above, λ is also a function of the wavelength λ of light, by combining the phase modulation function according to the polarization direction and the phase modulation function according to the wavelength, it is possible to realize a polarized wavelength separation lens 21 having different focusing positions depending on the polarization direction and wavelength region of light.

[0065] In order to perform arbitrary wavefront control, it is preferable that the variable range of the phase delay amount for each polarization direction by the microstructure 211 is equal to or greater than 0 to 2π. Also, from the viewpoint of the manufacturing method and manufacturing cost, it is preferable that the length h of the microstructure 211 in the z-axis direction is as thin as possible. Therefore, from equation (1), the length h of the microstructure 211 in the z-axis direction is given by h = λ / (n １ -n ０ ), but is not limited to this example.

[0066] Here, a specific example of the microstructure 211 of the polarization wavelength separation lens 21 will be further described. Fig. 8 is a diagram showing an example of a side view of the microstructure 211 constituting the polarization wavelength separation lens 21 according to the first embodiment. Fig. 9 is a view taken along arrow C in Fig. 8. As shown in Figs. 8 and 9, for example, the microstructure 211 is formed on the bottom surface of the transparent substrate 10. In the microstructure 211 shown in Fig. 9, the shape of the upper surface, which is the incident surface, is formed into a rectangular shape, and the axis of linear symmetry of the upper surface of the microstructure 211 is, for example, an axis parallel to the x-axis or y-axis.

[0067] Fig. 10 is a diagram showing another example of a side view of the microstructure 211 constituting the polarization wavelength separation lens 21 according to embodiment 1. Fig. 11 is a view taken along arrow C in Fig. 10. As shown in Figs. 10 and 11, for example, the microstructure 211 is formed on the bottom surface of the transparent substrate 10. In the microstructure 211 shown in Figs. 10 and 11, the shape of the upper surface, which is the incident surface, is formed in a cross shape, and the axis of linear symmetry of the upper surface of the microstructure 211 is, for example, an axis parallel to the x-axis or an axis parallel to the y-axis.

[0068] Fig. 12 is a diagram showing the calculation results of the phase delay characteristics of the microstructure 211 shown in Fig. 8 and Fig. 9. Fig. 13 is a diagram showing the calculation results of the phase delay characteristics of the microstructure 211 shown in Fig. 10 and Fig. 11. The material of the microstructure 211 is, for example, SiN(n １ =2.03), and the material constituting the transparent layer 30 (see FIG. 2) between the microstructures 211 and below the microstructures 211 is air (n ０ = 1.0), but as will be described later, the microstructure 211 may be embedded in a single transparent layer.

[0069] 8 to 11, the height (length in the z-axis direction) of the microstructure 211 is h=1250 nm, and the arrangement period of the microstructure 211 is 350 nm. The calculation of the phase delay characteristics is based on the strict coupling theory, and the phase delay amount φ when each plane wave with a wavelength λ=450, 540, or 640 nm is incident from the transparent substrate 10 side is ｈ and the phase delay amount φ ｖ and width w １ and w ２ was calculated as a function of .

[0070] In FIG. 12, the width w in the x-axis direction of the microstructure 211 shown in FIGS. １ and the width in the y-axis direction w ２ 10 and 11. In FIG. 13, the width w of the microstructure 211 in the x-axis direction shown in FIG. 10 and FIG. 11 is expressed as a heat map in which the value of the phase delay amount for each combination is expressed as a shade. １ and the width in the y-axis direction w ２ A heat map in which the value of the phase delay amount for each combination of is expressed by shading is shown as the calculation result of the phase delay characteristics.

[0071] 12(a) and 13(a) show the phase delay amount φ when a plane wave with a wavelength λ=450 nm is incident on the microstructure 211 shown in FIGS. 8 and 9. ｈ 12(b) and 13(b) are heat maps of the phase delay amount φ when a plane wave with a wavelength λ=450 nm is incident. ｖ This is a heat map.

[0072] 12(c) and 13(c) show the phase delay amount φ when a plane wave with a wavelength λ=540 nm is incident. ｈ 12(d) and 13(d) are heat maps of the phase delay amount φ when a plane wave with a wavelength λ=540 nm is incident. ｖ 12(e) and 13(e) are heat maps of the phase delay amount φ when a plane wave with a wavelength λ=640 nm is incident. ｈ 12(f) and 13(f) are heat maps of the phase delay amount φ when a plane wave with a wavelength λ=640 nm is incident. ｖ This is a heat map.

[0073] As shown in FIGS. 12 and 13, the width w １、 w ２ , and various phase delay amounts φ ｈ and the phase delay amount φ ｖ 12 and 13, the microstructure 211 can realize a combination of the phase delay amount φ ｈ and the phase delay amount φ ｖ It can be seen that there is a large wavelength dependence on the

[0074] Therefore, using the calculation results shown in Figures 12 and 13, the shape and arrangement of the microstructure 211 can be determined to match the phase delay spatial distribution suitable for any optical wavefront control, including polarization separation function, wavelength separation function, and focusing function at θ = 0°, 90°.

[0075] Fig. 14 is a diagram showing the calculation results of the phase delay characteristics of the microstructure 211 obtained by rotating the axis of line symmetry of the microstructure 211 shown in Fig. 8 and Fig. 9 by 45°. Fig. 15 is a diagram showing the calculation results of the phase delay characteristics of the microstructure 211 obtained by rotating the axis of line symmetry of the microstructure 211 shown in Fig. 10 and Fig. 11 by 45°.

[0076] As shown in FIGS. 14 and 15, the width w １、 w ２ , and various phase delay amounts φ ｈ and the phase delay amount φ ｖ14 and 15, the microstructure 211 can realize a combination of the phase delay amount φ ｈ and the phase delay amount φ ｖ It can be seen that there is a large wavelength dependence on the

[0077] Therefore, using the calculation results shown in Figures 14 and 15, the shape and arrangement of the microstructure 211 can be determined to match a phase delay spatial distribution suitable for any optical wavefront control, including polarization separation function, wavelength separation function, and focusing function at θ = ±45°.

[0078] Fig. 16 is a plan view schematically showing another example of the polarization wavelength separation lens 21 according to the first embodiment, and Fig. 17 is a view schematically showing a portion of the cross section taken along line XVII-XVII shown in Fig. 16. The polarization wavelength separation lens 21 shown in Fig. 16 and Fig. 17 can be realized by using a microstructure 211 whose calculation results are shown in Figs. 12 to 15 and designing a phase distribution with a different focal point for each combination of the polarization direction of θ = 0°, 45°, 90°, and -45° and each central wavelength in the wavelength range of λ = 450, 540, and 640 nm.

[0079] 18 to 20 are diagrams showing examples of the phase delay spatial distribution that realizes the polarization wavelength separation lens 21 according to embodiment 1. Fig. 18 shows an example of the phase delay spatial distribution when 450 nm light is incident, Fig. 19 shows an example of the phase delay spatial distribution when 540 nm light is incident, and Fig. 20 shows an example of the phase delay spatial distribution when 640 nm light is incident.

[0080] 18 to 20, a different spatial distribution of phase delay depending on the wavelength component and polarization direction can be formed to realize the polarized wavelength separation lens 21. Note that a similar design can be applied to other numbers of wavelength divisions and other numbers of polarization directions.

[0081] Parameters used in the design include, for example, pixel size, focal length, polarization direction to be separated, and center wavelength of each wavelength region to be separated. The pixel size is 1.05 μm × 1.05 μm, the focal length is 5.5 μm, the polarization direction to be separated is, for example, θ = 0°, 45°, 90°, -45°, and the center wavelength of each wavelength region to be separated is, for example, 450 nm, 540 nm, 640 nm, but is not limited to such examples. The focal length is, for example, the distance in the z-axis direction between the polarization wavelength separation lens 21 and the pixel 41.

[0082] Here, an example of the phase distribution of the polarization wavelength separation lens 21 can be expressed by the following equation (2).

[0083]

[0084] In the above formula (2), "x" is the position in the x-axis direction, "y" is the position in the y-axis direction, and "x ｆ " is the focal position in the x-axis direction, and "y ｆ " is the focal position in the y-axis direction, and "z ｆ " is the focal position in the z-axis direction. In addition, in the above formula (2), "φ(x, y)" is the phase delay amount at the position x, y, "λd" is the center wavelength of the wavelength region to be separated, and "n ０ " is the refractive index of the transparent layer 30 on the transmission side, and "C" is a constant.

[0085] For example, when designing a polarized wavelength separation lens 21 with 12 combinations of polarization directions and wavelength components (see, for example, FIG. 16), the focusing position x ｆ , y ｆ , z ｆ is set at the center of each of 16 pixels 41 (see FIG. 16, for example) corresponding to a combination of polarization direction and wavelength component.

[0086] Furthermore, for each combination of polarization direction and center wavelength, the phase distribution boundary regions of the polarized wavelength separation lens 21 are set so that they are symmetrical in each of the x-axis and y-axis directions with the phase distributions of adjacent polarized wavelength separation lenses 21 in each of the x-axis and y-axis directions around the focusing position.

[0087] Furthermore, the constant C may be optimized so as to minimize the error in the phase distribution for each combination of polarization direction and wavelength component. Furthermore, in the phase delay spatial distributions shown in Figures 18 to 20, the phase delay amount φ calculated by the above formula (2) is converted so as to fall within the range of 0 to 2π. For example, -0.5π is converted to 1.5π, and 2.5π is converted to 0.5π.

[0088] The polarized wavelength separation lens 21 can be obtained by selecting and arranging the microstructures 211 having the structure that best matches the above-mentioned 12 (= 4 (polarization directions) × 3 (wavelength components)) phase distributions at each position based on the phase delay amount at each wavelength that the composition structure of the microstructures 211 has. The structure that best matches the phase distribution is, for example, a structure that minimizes the phase error, but is not limited to this example.

[0089] Fig. 21 is an enlarged view of region 21a in Fig. 16 in the polarization wavelength separation lens 21 according to embodiment 1. Polarized light is expressed by two orthogonal polarization directions, and therefore, as shown in Fig. 21, in the polarization wavelength separation lens 21, microstructures 211a and microstructures 211b are arranged so as to be switched depending on the position.

[0090] The microstructure 211a is a microstructure 211 that is responsible for separating the polarization direction of θ=0°, 90° and separating the wavelength components of RGB (red, green, blue), and the microstructure 211b is a microstructure 211 that is responsible for separating the polarization direction of θ=45°, -45° and separating the wavelength components of RGB (red, green, blue).

[0091] 21, in region 21a of polarization wavelength separation lens 21, microstructures 211a and microstructures 211b are alternately arranged in each of the x-axis direction (left-right direction) and the y-axis direction (up-down direction), which are periodic arrangement directions. The microstructures 211a and the microstructures 211b have axes of linear symmetry that differ by 45° from each other, and in region 21a, the microstructures 211a and the microstructures 211b whose axes of linear symmetry differ by 45° are alternately arranged.

[0092] This allows the polarized wavelength separation lens 21 to change the polarization direction in small incident area units, and to more appropriately focus incident light onto pixels 41 at different positions on the pixel array 40 depending on the polarization direction and wavelength components of the incident light. The region in which the microstructures 211a and the microstructures 211b, whose axes of linear symmetry differ by 45°, are alternately arranged is the entire region of the polarized wavelength separation lens 21, but may also be a partial region of the polarized wavelength separation lens 21.

[0093] 22 is a diagram showing an example of a wavelength spectrum showing the relationship between the wavelength and the light intensity of each pixel 41 when linearly polarized light in the 0° direction is incident on the image sensor 3 according to the first embodiment. In (a) of FIG. 22, the combination of the polarization direction and the wavelength component is R ｈ , R ｖ , R ４５ｈ , R ４５ｖ 10 shows the relationship between the received light intensity and wavelength in four pixels 41 corresponding to the four pixels 41, and the spectral peaks are present in the R (Red) wavelength region corresponding to these pixels 41.

[0094] In FIG. 22(b), the combination of polarization direction and wavelength component is G ｒｈ , G ｒｖ , G ｒ４５ｈ , G ｒ４５ｖ The relationship between the light intensity and wavelength at each pixel 41 is shown, and the peak of the spectrum is G ｒ In FIG. 22(c), the combination of polarization direction and wavelength component is G ｂｈ , G ｂｖ , G ｂ４５ｈ , G ｂ４５ｖ The relationship between the light intensity and wavelength at each pixel 41 is shown, and the peak of the spectrum is G ｂ It exists in the wavelength region of (Green-Blue).

[0095] In FIG. 22(d), the combination of polarization direction and wavelength component is B ｈ , B ｖ , B ４５ｈ , B ４５ｖ10 shows the relationship between the received light intensity and wavelength in each pixel 41, and the peak of the spectrum exists in the wavelength region of B (Blue) to which these pixels 41 correspond.

[0096] As shown in (a) to (d) of FIG. 22, it can be seen that the polarized wavelength separation lens 21 in the image sensor 3 has a wavelength separation function.

[0097] Furthermore, it can be seen that, in the pixel group of the same wavelength component, the 0° pixel 41 corresponding to the incident polarized light has the highest light intensity, and the 90° pixel 41 which is perpendicular to the incident polarized light has the lowest light intensity. Therefore, it can be confirmed that the polarized wavelength separation lens 21 has a polarization separation function. The 0° pixel 41 has R ｈ , G ｒｈ , G ｂｈ , B ｈ The pixel 41 at 90° is R ｖ , G ｒｖ , G ｂｖ , B ｖ Each pixel 41 in the image is a pixel 41.

[0098] Furthermore, the peak of the received light intensity at pixel 41 corresponding to the combination of polarization direction and wavelength component exceeds 0.625 (= 1 / 16), which is the upper limit of the peak of the received light intensity when a filter array with a similar pixel arrangement is used, and an increase in the amount of received light can be confirmed.

[0099] Furthermore, the average transmittance of the polarized wavelength separation lens 21 across the visible light band (400 to 700 nm) is approximately 77%, which is higher than the approximate transmittance of 15 to 20% of a two-layer filter array in which a color filter and a polarized filter are stacked. This also confirms that the polarized wavelength separation lens 21 increases the amount of light received by the pixel 41.

[0100] 23 and 24 are diagrams showing examples of light intensity distributions on the pixel array 40 when light having different polarization states and wavelength combinations is incident perpendicularly on the image sensor 3 according to the first embodiment.

[0101] When light having a polarization direction of θ=0° and a wavelength of 450 nm is incident, as shown in FIG. ｈWhen light having a polarization direction of θ=0° and a wavelength of 540 nm is incident, as shown in FIG. ｒｈ , G ｂｈ When light having a polarization direction of θ=0° and a wavelength of 640 nm is incident, as shown in (c) of FIG. ｈ The light is focused on the pixel 41.

[0102] When light having a polarization direction of θ=90° and a wavelength of 450 nm is incident, as shown in FIG. ｖ When light having a polarization direction of θ=90° and a wavelength of 540 nm is incident, as shown in (e) of FIG. ｒｖ , G ｂｖ When light having a polarization direction of θ=90° and a wavelength of 640 nm is incident, as shown in (f) of FIG. ｖ The light is focused on the pixel 41.

[0103] When light with a polarization of θ=−45° and a wavelength of 450 nm is incident, as shown in FIG. ４５ｖ When light having a polarization angle of θ=−45° and a wavelength of 540 nm is incident, as shown in FIG. ｒ４５ｖ , G ｂ４５ｖ When light having a polarization direction of θ=−45° and a wavelength of 640 nm is incident, as shown in FIG. ４５ｖ The light is focused on the pixel 41.

[0104] When light with a polarization of θ=45° and a wavelength of 450 nm is incident, as shown in FIG. ４５ｈ When light having a polarization angle of θ=45° and a wavelength of 540 nm is incident, as shown in (e) of FIG. ｒ４５ｈ , G ｂ４５ｈ When light having a polarization direction of θ=45° and a wavelength of 640 nm is incident, as shown in (f) of FIG. ４５ｈ The light is focused on the pixel 41.

[0105] In this way, it can be confirmed that the polarized light wavelength separation lens 21 can condense light onto the pixel 41 corresponding to the combination of polarization direction and wavelength component.

[0106] As described above, the imaging device 1 equipped with the imaging element 3 according to the embodiment has the signal processing unit 4, and image quality improvement processing is performed in the signal processing unit 4. In the imaging element 3 described above, one unit structure is formed by 16 pixels 41, so there is a risk of degradation in spatial resolution compared to a monochrome image sensor with a pixel unit and a color image sensor with a four-pixel unit, but the signal processing unit 4 performs demosaic processing, which makes it possible to suppress degradation in spatial resolution.

[0107] 22 to 24, depending on the spectral performance of the polarization wavelength separation lens 21, crosstalk of polarization components and crosstalk of wavelength components may occur between the pixels 41. Crosstalk of polarization components between the pixels 41 may lower the low polarization extinction ratio, and crosstalk of wavelength components between the pixels 41 may cause color mixing. Therefore, the signal processing unit 4 corrects the value of the electrical signal output from the pixel array 40 based on the polarization characteristics and light reception spectrum characteristics of each pixel 41, thereby performing processing to suppress color mixing and a decrease in the polarization extinction ratio.

[0108] For example, in the case of mixed colors, the signal processing unit 4 creates a color correction matrix based on the light receiving spectral characteristics of each pixel 41, and performs matrix operations on the pixel values ​​of the image after demosaicing (e.g., three channels in the case of three colors), thereby enabling more appropriate color correction processing.

[0109] Furthermore, in the case of a decrease in the polarization extinction ratio, the signal processing unit 4 creates a polarization correction matrix based on the polarization characteristics of each pixel 41, and performs matrix operations on the pixel values ​​of the image after demosaicing (for example, four channels in the case of four polarization directions), thereby enabling more appropriate polarization correction processing.

[0110] In the above-described example, the shape of the upper surface of the microstructure 211, which is the incident surface, is rectangular or cross-shaped, but the shape of the upper surface of the microstructure 211 is not limited to rectangular or cross-shaped. Fig. 25 is a diagram showing another example of the shape of the upper surface of the microstructure 211 in the polarization wavelength separation lens 21 according to embodiment 1.

[0111] 25(a) to (x), the top surface shape of the microstructure 211 can be formed into various shapes such as a shape with an opening, a shape composed of multiple top surfaces arranged at intervals, a shape with an elliptical outer edge, etc. Furthermore, the above-mentioned rectangular microstructure 211, the cross-shaped microstructure 211, and the microstructures 211 shown in FIG. 25(a) to (x) have top surface shapes with two-fold rotational symmetry axes having line symmetry axes, but are not limited to such examples.

[0112] Furthermore, when the microstructure 211 has a columnar shape, the columnar shape is not limited to a columnar shape having a uniform cross-sectional shape in a direction perpendicular to the z-axis direction, but may have a structure in which part or all of the cross-sectional shape is different.

[0113] The image sensor 3 according to the first embodiment is not limited to the configuration shown in Fig. 17. Figs. 26 to 28 are diagrams schematically showing a part of a cross section of other configuration examples of the image sensor 3 according to the first embodiment. As shown in Fig. 26, the polarization wavelength separation lens 21 is formed on the upper part of the transparent layer 30 above the pixel array 40 or on the SiO ２ Alternatively, the transparent layer may be formed inside the transparent layer made of the material.

[0114] The image sensor 3 shown in FIG. 26(a) has a transparent layer 30 made of SiO ２ The image sensor 3 shown in FIG. 26(b) is a layer made of a material such as SiO 2 , and the microstructure 211 is disposed above the transparent layer 30, and does not have a transparent substrate 10. ２ The image sensor 3 shown in FIG. 26(c) is a layer made of a transparent layer 30 of the same material as the transparent layer 30 and the transparent substrate 10, and a microstructure 211 is disposed inside the transparent layer 30. ２The microstructure 211 is disposed above the transparent layer 30 and does not have a transparent substrate 10.

[0115] In the above example, the microstructure 211 is made up of one layer, but may be made up of two or more layers. For example, in the image pickup device 3 shown in (a) to (e) of Figure 27, each microstructure 211 is formed across two layers. For example, in the image pickup device 3 shown in (a) of Figure 27, the transparent layer 30 is made of SiO ２ The layer is made of materials such as SiO ２ A first layer of a plurality of microstructures 211 is disposed on the upper surface of a transparent layer made of a material such as SiO ２ The second layer of the plurality of microstructures 211 is covered with a transparent layer made of a material such as silicon dioxide.

[0116] The image sensor 3 shown in FIG. 27(b) has a transparent layer 30 made of SiO ２ The image sensor 3 shown in (c) of FIG. 27 is a layer made of a material such as SiO ２ A plurality of microstructures 211 are formed on the top and bottom surfaces of a transparent layer made of a material such as silicon dioxide.

[0117] The image sensor 3 shown in FIG. 27(d) has a transparent layer 30 made of SiO ２ 27(e) differs from the image sensor 3 shown in Fig. 27(a) in that the transparent layer 30 is made of a layer made of a material such as SiO ２ 27(b) in that it is formed of a layer made of a material such as silicon dioxide and an air layer.

[0118] In the image pickup device 3 shown in (a) to (e) of Figure 28, each microstructure 211 is formed across three layers. For example, in the image pickup device 3 shown in (a) of Figure 28, the transparent layer 30 is made of SiO ２ The first layer of the plurality of microstructures 211 is made of SiO ２ The second and third layers of the plurality of microstructures 211 are covered by the transparent layer.

[0119] The image sensor 3 shown in FIG. 28(b) has a transparent layer 30 made of SiO ２ The image sensor 3 shown in FIG. 28(c) has a first and third layers of the plurality of microstructures 211 made of SiO. ２ The second layer of the microstructure 211 is disposed on the transparent layer.

[0120] The image sensor 3 shown in FIG. 28(d) has a transparent layer 30 made of SiO ２ 28(a) in that the imaging element 3 shown in FIG. 28(e) is formed of a layer made of a material such as silicon dioxide and an air layer. The imaging element 3 shown in FIG. 28(e) is formed of a first layer and a second layer of a plurality of microstructures 211 made of SiO ２ The microstructures 211 are disposed inside a transparent layer made of a material such as a silicon dioxide particle, and a third layer of the microstructures 211 is disposed on the bottom surface of the transparent layer.

[0121] 26 to 28 has a back-illuminated structure that receives light from the side opposite to the wiring layer 42, but is not limited to such a structure, and the imaging element 3 may have a front-illuminated structure that receives light from the side of the wiring layer 42. Also, although not shown in figures such as FIGS. 26 to 28, the imaging element 3 may have a SiN or TiO ２ 26 to 28 are fabricated by known semiconductor manufacturing techniques.

[0122] Fig. 29 is a side view showing a schematic example of a microstructure 211 according to embodiment 1. The microstructure 211 shown in Fig. 29(a) has a side surface similar to that of the microstructure 211 shown in Fig. 6. The microstructure 211 shown in Fig. 29(b) is formed across two layers and has microstructure pieces 2111 and 2112 that have the same center line and the same shape.

[0123] The microstructure 211 shown in (c) of Fig. 29 is formed across two layers and has microstructure pieces 2111 and 2112 that have the same center line but different shapes. The microstructure 211 shown in (d) of Fig. 29 is formed across two layers and has microstructure pieces 2111 and 2112 that have different center lines and different shapes. The side shape of the microstructure 211 is not limited to the example shown in Fig. 29.

[0124] Furthermore, in the above-described pixel array 40, four pixels 41 of the same wavelength component are arranged adjacently in the x-axis direction and the y-axis direction, thereby grouping the four pixels 41 of the same wavelength component together. In the pixel array 40 arranged in this manner, crosstalk between wavelength components can be reduced, but the arrangement of the pixels 41 corresponding to the combination of polarization direction and wavelength component is not limited to the above-described example.

[0125] 30 and 31 are diagrams schematically illustrating other examples of the arrangement of pixels 41 in a pixel array 40 of an image sensor 3 according to an embodiment. In the pixel array 40 illustrated in FIGS. 30 and 31, four pixels 41 having the same polarization direction are arranged together by being adjacent to each other in the x-axis direction and the y-axis direction. In this way, in the pixel array 40 illustrated in FIGS. 30 and 31, four pixels 41 having the same polarization direction are arranged together, thereby making it possible to reduce crosstalk in the polarization direction between the pixels 41.

[0126] In the above example, the incident light is incident in a direction perpendicular to the incident surface of the image sensor 3, but the image sensor 3 is not limited to a normal incidence compatible image sensor. In a normal incidence compatible image sensor, if the incident light is incident obliquely to the incident surface of the image sensor 3, the main light incident angle may differ between the center and the edge of the pixel array 40.

[0127] Therefore, in a normal incidence compatible imaging element, if incident light is incident obliquely with respect to the incidence surface of the imaging element 3, the light may not be incident on the appropriate pixel 41, which may cause image degradation. Therefore, in the first embodiment, when incident light is incident in a direction perpendicular to the incidence surface of the imaging element 3, an oblique incidence compatible imaging element that is an imaging element that is compatible with oblique incidence depending on the position of the pixel array 40 is used as the imaging element 3.

[0128] Fig. 32 is a plan view schematically showing another example of the image sensor 3 according to embodiment 1, and Fig. 33 is a diagram schematically showing a portion of a cross section taken along line XXXIII-XXXIII shown in Fig. 32. Fig. 34 is a diagram for explaining the angle of incidence θ of light incident on the image sensor 3 shown in Figs. 32 and 33. Fig. 35 is a plan view schematically showing another example of the image sensor 3 according to embodiment 1, and Fig. 36 is a diagram schematically showing a portion of a cross section taken along line XXXVI-XXXVI shown in Fig. 35.

[0129] 32 and 33 is an image sensor that supports oblique incidence, in which the polarized wavelength separation lens 21 is disposed at a position shifted in the x-axis direction and the y-axis direction with respect to the unit structures (16 pixels 41) of the pixel array 40. Since the light-collecting position of the polarized wavelength separation lens 21 shifts for incident light with an incident angle θ (see FIG. 34) that has an inclination angle in the x-axis direction and the y-axis direction, it is possible to support oblique incidence by shifting the position of the polarized wavelength separation lens 21 in the x-axis direction and the y-axis direction so as to cancel out this shift.

[0130] The image sensor 3 shown in Figures 35 and 36 is an oblique incidence compatible image sensor, and similar to the image sensor 3 shown in Figure 3, the polarization wavelength separation lens 21 and the unit structure (16 pixels 41) of the pixel array 40 are arranged in opposing positions.

[0131] 35 and 36, the polarization wavelength separation lens array 20 is designed so that incident light incident at an incident angle θ (see FIG. 34) is perpendicularly incident on the pixel 41 directly below, and the polarization wavelength separation lens array 20 is positioned according to the position of the pixel array 40. The following equation (3) is an equation for the phase distribution of a lens that guides light having an incident angle θ to the center of the pixel 41 directly below, and the polarization wavelength separation lens array 20 of the image sensor 3 shown in FIGS. 35 and 36 can be designed by performing a design similar to that when using the above-mentioned equation (2).

[0132]

[0133] In the above formula (3), "x" is the position in the x-axis direction, "y" is the position in the y-axis direction, and "x ｆ " is the focal position in the x-axis direction, and "y ｆ " is the focal position in the y-axis direction, and "z ｆ " is the focal position in the z-axis direction. In addition, in the above formula (2), "φ(x, y)" is the phase delay amount at the position x, y, "λd" is the center wavelength of the wavelength region to be separated, and "n ｉｎ " is the refractive index of the material on the incident side, and "n ｏｕｔ " is the refractive index of the material on the exit side and "C" is a constant.

[0134] [Embodiment 2] Next, embodiment 2 will be described. Fig. 37 is a diagram schematically showing a part of a cross section of an image sensor according to embodiment 2. As shown in Fig. 37, an image sensor 3A according to embodiment 2 differs from the image sensor 3 according to embodiment 1 in that it has a color filter 50 above the pixel array 40.

[0135] The color filter 50 is disposed between the polarized wavelength separation lens array 20 and the pixel array 40, more specifically, between the pixel array 40 and the transparent layer 30. The color filter 50 is a filter that transmits wavelength components (e.g., color regions) corresponding to the pixels 41 and cuts light of other wavelength components (e.g., color regions), and is provided, for example, for each pixel 41 or for multiple pixels 41. The color filter 50 is made of resin or the like, and is realized by known technology.

[0136] Light incident on the image sensor 3A is wavelength-separated by the polarizing wavelength separation lens 21, and then incident on the color filter 50 directly above the pixel array 40 and filtered. The transmission wavelength components of the color filter 50 match the wavelength components corresponding to the pixels 41 directly below, and the color filter 50 transmits light of the wavelength components corresponding to the pixels 41 directly below.

[0137] As described above, the image sensor 3A is provided with the color filter 50, which allows light to be guided to the photoelectric conversion elements of the pixels 41 while cutting out components other than the desired wavelength component. Therefore, the image sensor 3A can significantly reduce crosstalk of wavelength components between the pixels 41 while achieving the same function as the image sensor 3 of the first embodiment.

[0138] The image sensor 3A, which uses both the polarizing wavelength separation lens 21 and the color filter 50, can maintain high light utilization efficiency. This is because filtering by the color filter 50 is performed after color separation (wavelength separation) by the polarizing wavelength separation lens 21, so there is almost no reduction in the total amount of light that reaches the pixel array 40.

[0139] [Embodiment 3] Next, embodiment 3 will be described. Fig. 38 is a diagram schematically showing a part of a cross section of an image sensor according to embodiment 3. As shown in Fig. 38, an image sensor 3B according to embodiment 3 differs from the image sensor 3 according to embodiment 1 in that it has a polarizing filter 60 above the pixel array 40.

[0140] The polarizing filter 60 is disposed between the polarized light wavelength separation lens array 20 and the pixel array 40, more specifically, between the pixel array 40 and the transparent layer 30. The polarizing filter 60 is a filter that transmits light of a polarization direction corresponding to the pixel 41 and cuts light of other polarization directions, and is provided, for example, for each pixel 41 or for multiple pixels 41. The polarizing filter 60 is formed of a metal wire grid, a photonic crystal, or the like, and is realized by known technology.

[0141] The light incident on the image sensor 3B is wavelength-separated by the polarizing wavelength separation lens 21, and then incident on the polarizing filter 60 directly above the pixel array 40 and filtered. The transmission polarization axis of the polarizing filter 60 coincides with the polarization direction corresponding to the pixel 41 directly below, and the polarizing filter 60 transmits light having the polarization direction corresponding to the pixel 41 directly below.

[0142] By providing the polarizing filter 60 as described above, the image sensor 3B can guide light to the photoelectric conversion elements of the pixels 41 while cutting out components other than the desired polarization component. Therefore, the image sensor 3B can achieve the same function as the image sensor 3 of the first embodiment, while also significantly eliminating crosstalk in the polarization direction between the pixels 41 and improving the polarization extinction ratio.

[0143] The image sensor 3B, which uses both the polarization wavelength separation lens 21 and the polarization filter 60, can maintain high light utilization efficiency. This is because the polarization separation by the polarization wavelength separation lens 21 is followed by filtering by the polarization filter 60, so there is almost no reduction in the total amount of light that reaches the pixel array 40.

[0144] [Fourth Embodiment] Next, a fourth embodiment will be described. Fig. 39 is a diagram schematically showing a part of a cross section of an image sensor according to the fourth embodiment. As shown in Fig. 39, the image sensor 3C according to the fourth embodiment differs from the image sensor 3 according to the first embodiment in that it has a color filter 50 and a polarizing filter 60 above the pixel array 40.

[0145] The color filter 50 is disposed between the polarized wavelength separation lens array 20 and the pixel array 40, more specifically, between the pixel array 40 and the transparent layer 30. The color filter 50 is a filter that transmits wavelength components (e.g., color regions) corresponding to the pixels 41 and cuts light of other wavelength components (e.g., color regions), and is provided, for example, for each pixel 41 or for multiple pixels 41. The color filter 50 is made of resin or the like, and is realized by known technology.

[0146] The polarizing filter 60 is disposed between the polarized wavelength separation lens array 20 and the pixel array 40, more specifically, between the pixel array 40 and the transparent layer 30, directly above the color filter 50. The polarizing filter 60 is a filter that transmits light of a polarization direction corresponding to the pixel 41 and cuts light of other polarization directions, and is provided, for example, for each pixel 41 or for multiple pixels 41. The polarizing filter 60 is formed of a metal wire grid, a photonic crystal, or the like, and is realized by known technology. The arrangement of the polarizing filter 60 is not limited to the example shown in FIG. 39 , and the polarizing filter 60 may be disposed between the color filter 50 and the pixel array 40.

[0147] The light incident on the image sensor 3C is wavelength-separated by the polarizing wavelength separation lens 21, and then incident on the polarizing filter 60 directly above the pixel array 40, where it is polarized and separated. The transmission polarization axis of the polarizing filter 60 coincides with the polarization direction corresponding to the lower pixel 41, and the polarizing filter 60 transmits light having a polarization direction corresponding to the lower pixel 41.

[0148] The light transmitted through the polarizing filter 60 is incident on the color filter 50 directly above the pixel array 40 and filtered. The transmission wavelength component of the color filter 50 matches the wavelength component corresponding to the pixel 41 directly below, and the color filter 50 transmits light of the wavelength component corresponding to the pixel 41 directly below.

[0149] As described above, the image sensor 3C is provided with the polarizing filter 60 and the color filter 50, so that it can guide light to the photoelectric conversion elements of the pixels 41 while cutting out components other than the desired color component and the desired polarization component. Therefore, the image sensor 3C can achieve the same function as the image sensor 3 of the first embodiment, while significantly reducing crosstalk in the polarization direction between the pixels 41 and crosstalk in the wavelength component between the pixels 41.

[0150] The image sensor 3C, which uses the polarizing wavelength separation lens 21, color filter 50, and polarizing filter 60 in combination, can maintain high light utilization efficiency. This is because filtering by the polarizing filter 60 and color filter 50 is performed after polarization separation and wavelength separation (e.g., color separation) by the polarizing wavelength separation lens 21, so there is almost no reduction in the total amount of light that reaches the pixel array 40.

[0151] The above-described first to fourth embodiments are merely preferred specific examples of the present invention, and the present invention is not limited to these, and various modifications are possible.

[0152] For example, the pixel size, focal length, number and type of polarization directions to be separated, number and type of wavelength components to be separated, etc. are not limited to the examples described above, and can be changed depending on the lens design, the required spatial resolution, etc.

[0153] In the first to fourth embodiments, the polarized light wavelength separation lens 21 is made of SiN or TiO ２ For example, when the imaging elements 3, 3A, 3B, and 3C are used in the visible light to near-infrared region with a light wavelength ranging from 380 nm to 1000 nm, the material of the polarization wavelength separation lens 21 may be SiN, SiC, TiO ２ Materials such as GaN and SiC are suitable because they have a high refractive index and little absorption loss. When the imaging elements 3, 3A, 3B, and 3C are used in the near-infrared region with wavelengths ranging from 800 to 1000 nm, the polarization wavelength separation lens 21 is made of materials with low loss for this light, such as Si, SiC, SiN, and TiO. ２ Furthermore, when the imaging elements 3, 3A, 3B, and 3C are used in the near-infrared region of a long wavelength band (such as 1.3 μm or 1.55 μm, which are communication wavelengths), in addition to the above-mentioned materials, InP or the like can be used as the material for the polarization wavelength separation lens 21.

[0154] Furthermore, when forming the microstructure 211 of the polarized wavelength separation lens 21 by pasting and coating, examples of materials include polyimides such as fluorinated polyimide, BCB (benzocyclobutene), photocurable resins, UV epoxy resins, acrylic resins such as PMMA, and polymers such as general resists.

[0155] In the first to fourth embodiments, the transparent layer 30 is made of SiO. ２ Although an example in which an air layer is assumed has been shown, the transparent layer 30 is not limited to such an example. ２ , an air layer, or the like, as long as its refractive index is lower than that of the material of the polarized wavelength separation lens 21 and has low loss with respect to the wavelength of the incident light. The transparent layer 30 may also be a transparent layer having a laminated structure made of multiple materials.

[0156] In the first to fourth embodiments, the polarization components separated by the polarization wavelength separation lens 21 are linearly polarized light oriented at 0°, 45°, 90°, and −45° relative to any one axis. However, this is not limiting. Depending on the design of the microstructure pattern of the polarization wavelength separation lens 21, separation of circularly polarized light components or elliptically polarized light components is also possible, and a configuration that combines separation of linearly polarized light components and circularly polarized light components may be possible. As an example, an imaging element may be configured with three polarization units (two for separating linearly polarized light components and one for separating circularly polarized light components) that have the functions of separating linearly polarized light oriented at 0°, 45°, 90°, and −45°, and right-handed and left-handed circularly polarized light components. With an imaging element of this configuration, all Stokes parameters describing the polarization state can be derived, making it possible to completely acquire the polarization state of the imaging target.

[0157] Furthermore, in the first to fourth embodiments, the light in the three wavelength regions supported by the polarized wavelength separation lens 21 is light of the three primary colors of R, G, and B, or one of the four wavelength regions supported by the polarized wavelength separation lens 21 is infrared light with a wavelength other than that of the three primary colors, but the present invention is not limited to such examples. For example, the wavelengths that can be separated by the polarized wavelength separation lens 21 may be light with a wavelength other than that of the three primary colors (for example, infrared light or ultraviolet light) in at least one of the three wavelength regions, or light with a wavelength other than that of the three primary colors (for example, infrared light or ultraviolet light) in at least two of the four wavelength regions.

[0158] As described above, the image sensors 3, 3A, 3B, and 3C according to the embodiments include a pixel array 40 in which a plurality of pixels 41, each including a photoelectric conversion element, are arranged in a two-dimensional array, and a polarization wavelength separation lens array 20 in which a plurality of polarization wavelength separation lenses 21, each having a periodic arrangement of a plurality of microstructures 211 that condense incident light to different positions on the pixel array 40 depending on the polarization direction and wavelength components of the incident light, are arranged in a two-dimensional array. The polarization wavelength separation lens array 20 is an example of a spectroscopic element array, and the polarization wavelength separation lens 21 is an example of a spectroscopic element. The arrangement period P of the plurality of microstructures 211 is shorter than the wavelength of light to be received by the pixel array 40. All or some of the plurality of microstructures 211 have a surface, on which incident light is incident, that has a linear symmetry axis and a shape whose length differs in the direction of the linear symmetry axis and in the direction perpendicular to the linear symmetry axis, and the linear symmetry axis and the structure are modulated depending on the position on the polarization wavelength separation lens 21. As a result, the image sensor 3 can separate the polarization direction and wavelength of incident light without using a color filter or a polarizing filter, which reduces the number of parts required and reduces costs. Furthermore, the image sensor 3, 3A, 3B, 3C can increase imaging sensitivity by using the polarized wavelength separation lens array 20, thereby reducing the cost of the image sensor with increased imaging sensitivity.

[0159] Furthermore, the axis of line symmetry of all or some of the multiple microstructures 211 differs by 45° from the axis of line symmetry of adjacent microstructures 211 in the arrangement direction of the periodic array. This allows the image pickup elements 3, 3A, 3B, and 3C to vary the polarization direction in small incident area units, and to more appropriately focus incident light on pixels 41 at different positions on the pixel array 40 depending on the polarization direction and wavelength component of the incident light.

[0160] Furthermore, the multiple microscopic structures 211 have the same length in a direction perpendicular to the pixel array surface of the pixel array 40. This makes it possible to easily create the multiple microscopic structures 211.

[0161] Furthermore, the plurality of microstructures 211 are configured across a plurality of layers, which allows for greater freedom in designing the microstructures 211 in the imaging elements 3, 3A, 3B, and 3C.

[0162] The present invention has been described above based on specific embodiments, but it goes without saying that the present invention is not limited to the above embodiments and can be modified in various ways without departing from the spirit of the invention.

[0163] REFERENCE SIGNS LIST 1 Imaging device 2 Lens optical system 3, 3A, 3B, 3C Imaging element 4 Signal processing unit 10 Transparent substrate 20 Polarized wavelength separation lens array 21 Polarized wavelength separation lens 30 Transparent layer 40 Pixel array 41 Pixel 42 Wiring layer 50 Color filter 60 Polarizing filter 211, 211a, 211b Microstructure

Claims

1. An imaging device comprising: a pixel array in which a plurality of pixels, each including a photoelectric conversion element, are arranged in a two-dimensional array; and a spectroscopic element array in which spectroscopic elements, each having a periodic arrangement of a plurality of microstructures that focus incident light to different positions on the pixel array depending on the polarization direction and wavelength components of the incident light, are arranged in a two-dimensional array; the arrangement period of the microstructures is shorter than the wavelength of light that is to be received by the pixel array; and all or some of the microstructures have a surface, on which the incident light is incident, that has an axis of linear symmetry and a shape whose length differs in the direction of the axis of linear symmetry and in the direction perpendicular to the axis of linear symmetry, and the axis of linear symmetry and the structure are modulated depending on the position on the spectroscopic element.

2. The imaging element according to claim 1, characterized in that the axis of symmetry of all or some of the plurality of microstructures differs by 45° from the axis of symmetry of adjacent microstructures in the arrangement direction of the periodic array.

3. An imaging element according to claim 1 or 2, characterized in that the plurality of microstructures have equal lengths in a direction perpendicular to the pixel array surface of the pixel array.

4. An imaging element according to claim 1 or 2, characterized in that the plurality of microstructures are configured across a plurality of layers.

5. The imaging element according to claim 1 or 2, characterized in that the spectroscopic element array focuses the incident light that is obliquely incident onto the pixel array.

6. The imaging device according to claim 1 or 2, characterized in that at least one of a color filter and a polarizing filter is provided between the spectroscopic element array and the pixel array.

7. An imaging device comprising: an imaging element according to claim 1 or 2; an imaging optical system for forming an optical image on the imaging surface of said imaging element; and a signal processing unit for processing the electrical signal output by said imaging element and generating an image according to the polarization direction and wavelength components.

8. The imaging device according to claim 7, wherein the signal processing unit corrects the value of the electrical signal based on the polarization characteristics and the light reception spectrum characteristics of each pixel.

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