Image pickup element, image pickup device, and image pickup system

Abstract

To provide an imaging element that acquires linear polarization information necessary for calculating a Stokes parameter.SOLUTION: An imaging element includes a wedge 111 having birefringence, a polarizer array 113 in which a plurality of sets of polarizers having mutually different transmission axis directions, on which light transmitted through the wedge is incident, are arranged in a plane intersecting the light incident direction, and a light-receiving element array 115 in which a plurality of light-receiving elements on which light transmitted through the polarizer array is incident is arranged so as to correspond to the plurality of polarizers of the polarizer array. From among the plurality of polarizers having the same transmission axis direction in the polarizer array, the same phase difference may be generated for light incident on some of the polarizers, and different phase differences may be generated for light incident on the remaining polarizers.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an imaging element, an imaging device, and an imaging system. [Background technology]

[0002] Non-Patent Document 1 states, "The whole setup consists of a bandpass filter for 450 nm wavelength (design wavelength of the retarder array), a nano-optical retarder, and a polarizer array, as well as a microlens array and crosstalk module (see figure 1). ... Each array (polarizer, retarder, microlens + crosstalk) is fabricated on a 0.5 mm thin substrate and is aligned to and placed directly on top of a CMOS sensor with 2560 x 1920 pixels..." (1 Introduction) Furthermore, Non-Patent Document 2 states, "The polarimeter, acting as a polarization camera, utilizes a low dispersion microretarder array on top of a sensor with Bayer filters and wire-grid linear polarizers." (Abstruct)) and also states, "Ideally, when aligning the microretarder array to the Sony color polarization sensor, every pixel should be precisely aligned on top of each designated retarder." (5. DISCUSSION AND CONCLUSION) [Prior art document] [Non-patent literature] [Non-patent document 1] C. Stock et al., EPJ Web of Conferences 238, 06018 (2020).(https: / / doi.org / 10.1051 / epjconf / 202023806018) [Non-patent document 2] X. Tu et al., Appl. Opt. 59, G33 (2020).(https: / / doi.org / 10.1364 / AO.391027) Summary of the Invention

[0003] A first aspect of the present invention provides an imaging element. The imaging element may include a wedge having birefringence. The imaging element may include a polarizer array in which a plurality of pairs of polarizers having different transmission axis directions are arranged in a plane intersecting the incident direction of the light, onto which light transmitted through the wedge is incident. The imaging element may also include a light receiving element array in which a plurality of light receiving elements onto which light transmitted through the polarizer array is incident are arranged to correspond to the plurality of polarizers in the polarizer array.

[0004] The wedge may cause the same phase difference to light incident on some polarizers in the polarizer array, among multiple polarizers with the same transmission axis direction, and cause different phase differences to light incident on the remaining polarizers.

[0005] The wedge may have a thickness that varies linearly along a wedge axis extending in one direction, and may impart a phase difference corresponding to the thickness to light passing through the wedge.

[0006] The wedge may have a wedge-shaped cross section along the wedge axis, a minimum thickness of 1 mm or less in the cross section, and an inclination angle of 5 degrees or less in the cross section.

[0007] The wedge may be arranged such that the wedge axis forms a 45° angle with respect to the alignment direction of the plurality of polarizers in the polarizer array.

[0008] The wedge may be constructed of calcite.

[0009] A second aspect of the present invention provides an imaging device. The imaging device may include any of the imaging elements described above. The imaging device may include an imaging lens unit. The imaging device may be configured so that light is incident on the imaging lens unit, wedge, polarizer array, and light receiving element array in this order, or may be configured so that light is incident on the wedge, imaging lens unit, polarizer array, and light receiving element array in this order.

[0010] The imaging device may further include a bandpass filter that monochromatizes the light incident on the light receiving element array.

[0011] A third aspect of the present invention provides an imaging system. The imaging system may include any one of the imaging devices described above. The imaging system may also include a calculation device that calculates linear Stokes parameters based on polarization information for each direction of the transmission axis acquired by the imaging device.

[0012] The calculation device may calculate the full Stokes parameters based on linear polarization information obtained from light transmitted through polarizers at four orientations of 0 degrees, 45 degrees, 90 degrees, and 135 degrees, contained within a unit area consisting of nine polarizers arranged in a matrix of 3 rows and 3 columns.

[0013] The calculation device may analyze linearly polarized light information from two types of unit areas in which the nine polarizers are arranged differently.

[0014] The calculation device may specify a function that indicates a relationship between the arrangement positions of the plurality of polarizers and a phase difference that occurs in light that transmits through the wedge by performing calibration using light whose full Stokes parameters are known. The calculation device may calculate the full Stokes parameters using the function.

[0015] The above summary of the invention does not list all of the features of the present invention, and subcombinations of these features may also be inventions. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a schematic diagram of an imaging system 10, according to one embodiment. [Figure 2] 1 is a schematic diagram of an image sensor 100, according to one embodiment. [Figure 3] FIG. 1 is a schematic side view of a wedge 111, according to one embodiment. [Figure 4] FIG. 1 illustrates a method for computing full Stokes parameters according to one embodiment. [Figure 5] FIG. 1 illustrates a method for increasing spatial resolution according to one embodiment. [Figure 6] 10 is a diagram for explaining a method for determining a function that indicates the relationship between the arrangement positions of multiple polarizers and the phase difference that occurs in light that passes through the wedge 111, according to one embodiment. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described below through embodiments of the invention, but the following embodiments do not limit the scope of the invention according to the claims. Furthermore, not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0018] 1 is a schematic diagram of an imaging system 10 according to one embodiment. The imaging system 10 includes an imaging device 15, which is a polarization camera capable of acquiring polarization information of a subject, and a personal computer 70 capable of receiving an image signal including the polarization information from the imaging device 15 and displaying the image on a monitor.

[0019] The imaging device 15 includes an imaging lens unit 20 and a camera body 30. The imaging device 15 can be manufactured to be palm-sized, approximately 28 mm × 28 mm × 50 mm, for example. The imaging device 15 is capable of wireless communication with a personal computer 70, and transmits an image signal containing polarization information acquired by capturing an image of a subject to the personal computer 70. Alternatively or additionally, the imaging device 15 may be capable of wired communication with the personal computer 70.

[0020] The imaging lens unit 20 has an optical system inside its lens barrel, and this optical system defines an optical axis 22. The imaging lens unit 20 is detachably attached to the camera body 30. The imaging lens unit 20 may be housed inside the camera body 30 and may extend outward as shown in the figure when in use.

[0021] The imaging lens unit 20 guides the incident subject light beam into the camera body 30. Note that the imaging lens unit 20 shown in Figure 1 includes two lenses and an aperture simply for clarity of explanation, but is not limited to this configuration.

[0022] The camera body 30 has a bandpass filter 35, an imaging unit 40, a board unit 50, and a flexible board 90. The flexible board 90 connects the imaging unit 40 and the board unit 50 together.

[0023] The subject light beam incident on the imaging lens unit 20 is guided by the imaging lens unit 20 to the imaging unit 40 via the bandpass filter 35. The bandpass filter 35 monochromatizes the light incident on the bandpass filter 35. Preferably, the bandpass filter 35 transmits a wavelength band narrow enough that the wavelength dispersion of the phase at the wedge 111 does not affect the image signal.

[0024] The imaging unit 40 includes an imaging element 100, a mounting substrate 120, and a frame 140. The imaging element 100 includes a wedge 111, a polarizer array 113, and a light receiving element array 115. The imaging element 100 according to this embodiment further includes a microlens array 117.

[0025] The wedge 111 has birefringence. In this embodiment, the wedge 111 is made of calcite, for example. Note that the wedge 111 may be made of a birefringent material such as quartz instead of calcite.

[0026] Light monochromatized by the bandpass filter 35 enters the wedge 111. The light that has passed through the wedge 111 enters the polarizer array 113. In this embodiment, the light that has passed through the wedge 111 passes through the microlens array 117 and enters the polarizer array 113. Note that the wedge 111 in this embodiment also functions as a cover glass that protects the light receiving element array 115 and the like inside the imaging device 15.

[0027] The microlens array 117 may also be referred to as an on-chip lens, and is, for example, a plurality of microlenses arranged on a single glass substrate, with light being incident on each of the plurality of microlenses.

[0028] The polarizer array 113 is formed by arranging a plurality of pairs of polarizers, each having a transmission axis oriented in a different direction, in a plane intersecting the direction of incidence of light. The polarizer array 113 may be of a photonic crystal type or a wire grid type. In this embodiment, light converged by each microlens of the microlens array 117 is incident on each polarizer of the polarizer array 113. The light transmitted through the polarizer array 113 is incident on the light receiving element array 115.

[0029] The light receiving element array 115 has a plurality of light receiving elements arranged to correspond to the plurality of polarizers of the polarizer array 113. In this embodiment, light that has passed through each polarizer of the polarizer array 113 is incident on each light receiving element of the light receiving element array 115. Each light receiving element of the light receiving element array 115 is, for example, a CMOS image sensor or a CCD image sensor, and has a rectangular shape in its main plane.

[0030] Each light receiving element of the light receiving element array 115 captures an image of the subject and generates an image signal containing polarization information of the subject. As described above, the light incident on each light receiving element of the light receiving element array 115 is limited to a narrow band centered on a designed wavelength by the band pass filter 35. Note that, as an example, the imaging device 15 may be capable of handling visible light to near infrared light, i.e., a wavelength range of 400 to 900 nm, based on the specifications of the polarizer array 113. In this case, the band pass filter 35 may be one that is specified to limit the wavelength to, for example, 500±2 nm or 600±2 nm.

[0031] The mounting substrate 120 is mounted with the microlens array 117, polarizer array 113, and light receiving element array 115 of the image sensor 100 stacked in this order. More specifically, of these stacked elements, the light emitting surface side of the light receiving element array 115 is fixed to the front surface of the mounting substrate 120. Furthermore, as an example, a connector 80 is mounted on the back surface of the mounting substrate 120.

[0032] A flexible substrate 90 is connected to the connector 80 mounted on the mounting substrate 120. The connector 80 may transmit an image signal to the board unit 50 via the flexible substrate 90, and may also receive a current from the board unit 50 via the flexible substrate 90.

[0033] The image sensor 100 and the mounting board 120 are adhesively fixed to the frame 140. The frame 140 is fixed to the housing of the camera body 30 by, for example, screws, and thus the image sensor 100 and the like are fixed inside the camera body 30.

[0034] The frame 140 has an opening, and the opening is formed, for example, in the center portion in the xy plane of the frame 140. The above-described stack mounted on the mounting substrate 120 is located in the opening, and the opposite side of the opening from the mounting substrate 120 is sealed by the wedge 111.

[0035] In this embodiment, the direction along the optical axis 22 is defined as the z-axis direction. That is, the direction in which the subject light beam is incident on the imaging surface of the light receiving element array 115 is defined as the z-axis direction. Specifically, the direction in which the subject light beam is incident is defined as the negative z-axis direction, and the opposite direction is defined as the positive z-axis direction. The depth direction as viewed from the plane of FIG. 1 is defined as the x-axis direction, and the up-down direction as viewed from the plane of FIG. 1 is defined as the y-axis direction. The x-axis, y-axis, and z-axis form a right-handed Cartesian coordinate system. For convenience of explanation, the positive z-axis direction may be referred to as the front, front side, etc. The negative z-axis direction may be referred to as the rear, back side, etc. The side in the negative z-axis direction may be referred to as the back side, etc.

[0036] The board unit 50 is disposed at a position in the negative z-axis direction of the imaging unit 40. The board unit 50 includes a board 55, and an MPU 51 and a power supply 53 mounted on the board 55. Note that other electronic circuits may also be mounted on the board 55 in addition to or instead of the board 55.

[0037] The MPU 51 is responsible for overall control of the imaging device 15. The MPU 51 receives the image signal output from the light receiving element array 115 via the mounting substrate 120, the connector 80, and the flexible substrate 90. The MPU 51 has a communication function and transmits the image signal from the light receiving element array 115 to the personal computer 70. The MPU 51 may have a memory such as a RAM, and may store the image signal from the light receiving element array 115 in the memory.

[0038] The power supply 53 includes a battery attached to the imaging device 15 and a power supply circuit that supplies the power stored in the battery to each part of the imaging device 15. The power supply 53 supplies current to the light-receiving element array 115 via, for example, the flexible substrate 90, the connector 80, and the mounting substrate 120.

[0039] The personal computer 70 includes a processor and receives the image signal from the image capture device 15, analyzes the polarization information contained in the image signal, and generates image data for display.

[0040] More specifically, the personal computer 70 calculates linear Stokes parameters based on polarization information for each direction of the transmission axis acquired by the imaging device 15. The personal computer 70 generates image data based on the image signal and the linear Stokes parameters. The personal computer 70 may display the generated image data on a monitor.

[0041] The personal computer 70 is an example of a computing device that performs the above-described calculations. The computing device may be integrated with the image capture device 15, i.e., the image capture device 15 may perform the above-described calculations. In this case, the image capture device 15 may include an FPGA (Field Programmable Gate Array) instead of or in addition to the MPU 51, and the FPGA or the like may have the above-described functions of the computing device. In this case, the image capture device 15 may also include a liquid crystal display or the like that displays the generated image data.

[0042] Figure 2 is a schematic diagram of an imager 100, according to one embodiment, which illustrates spacing between components of the imager 100 along the optical axis 22 of the imager 15 for clarity.

[0043] 2, a wedge axis W extending in one direction of the wedge 111 is indicated by a hollow arrow, and a crystal axis T of the wedge 111 is indicated by a hollow arrow. The same applies to the subsequent figures, and redundant explanations will be omitted.

[0044] Also, in Figure 2, in order to show the relationship between the wedge axis W of the wedge 111 and the arrangement direction of the polarizer array 113, etc., the polarizer array 113, etc. is virtually translated along the optical axis 22 and superimposed on the light exit surface of the wedge 111, as shown by the dashed line array A.

[0045] 2, the transmission axis of each polarizer on the polarizer array 113 is indicated by a hollow arrow. As described above, the polarizer array 113 is formed by arranging a plurality of pairs of polarizers, each pair having a transmission axis oriented in a different direction, in a plane intersecting the direction of incidence of light. More specifically, as shown in FIG. 2, the polarizer array 113 has polarizers for four azimuths of 0 degrees, 45 degrees, 90 degrees, and 135 degrees arranged in the order of bottom right, top right, top left, and bottom left when viewed from the positive side of the z axis in a unit matrix of two rows and two columns. The polarizer array 113 is arranged so that the pairs of polarizers for the four azimuths are repeated in the xy plane.

[0046] 2 illustrates the polarizer array 113, the light receiving element array 115, and the microlens array 117 as arrays arranged in a matrix of 4 rows and 4 columns simply for the purpose of clarity of explanation, but other arrangement numbers are also possible. The arrangement numbers of the polarizer array 113 and the microlens array 117 may be the same as the arrangement number of the light receiving element array 115. In other words, the polarizers of the polarizer array 113, the light receiving elements of the light receiving element array 115, and the microlenses of the microlens array 117 may be arranged in the same number, and may be arranged so as to overlap each other in the z-axis direction. This also applies to the following explanations of each, and redundant explanations will be omitted.

[0047] 2, the imaging device 15 according to this embodiment is configured so that light is incident on the wedge 111, the polarizer array 113, and the light receiving element array 115 in this order. More specifically, as shown in FIG. 1, the imaging device 15 according to this embodiment is configured so that light is incident on the imaging lens unit 20, the wedge 111, the microlens array 117, the polarizer array 113, and the light receiving element array 115 in this order. In this way, by disposing the wedge 111 near the light receiving element array 115, the amount of shift of the subject light imaged by the light receiving element array 115 can be reduced.

[0048] Alternatively, light may be incident in the order of wedge 111, imaging lens unit 20, polarizer array 113, and light receiving element array 115. In this case, a cover glass for protecting light receiving element array 115 and the like in image sensor 100 may be additionally disposed at the position of wedge 111 shown in Fig. 1. For example, wedge 111 may be attached at a predetermined angle to the outer surface of the imaging lens unit of a commercially available polarization camera.

[0049] As long as the bandpass filter 35 is located on the optical axis 22 on the light incident side of the light receiving element array 115, calculation of wavelength-dependent full Stokes parameters (described later) can be performed, and therefore the bandpass filter 35 may be located at a position other than that shown in FIG. 1 . However, to reduce crosstalk in the imaging device 15, it is preferable that the polarizer array 113 and the light receiving element array 115 are adjacent to each other. Therefore, it is preferable that the bandpass filter 35 is located on the optical axis 22 on the light incident side of both the light receiving element array 115 and the polarizer array 113. In this case, the imaging lens unit 20, the wedge 111, and the bandpass filter 35 may be located in any order on the optical axis 22. For example, a set of the wedge 111 and the bandpass filter 35 may be attached at a predetermined angle to the outer surface of the imaging lens of a commercially available polarization camera.

[0050] 3 is a schematic side view of a wedge 111 according to one embodiment. In FIG. 3, the above-mentioned wedge axis W is indicated by a hollow arrow, the minimum thickness L0 of the wedge 111 is indicated by an arrow, and the inclination angle α of the inclined surface of the wedge 111 is indicated by a dashed line.

[0051] In this embodiment, the wedge 111 has a thickness that varies linearly along the wedge axis W. That is, the light incident surface and the light exit surface of the wedge 111 are planes that are not parallel to each other. The wedge 111 having such a shape and birefringence generates a phase difference corresponding to the thickness of the wedge 111 in the light that passes through the wedge 111.

[0052] More specifically, as shown in FIG. 3 , the wedge 111 has a wedge-shaped cross section along the wedge axis W. For example, the wedge 111 has a minimum cross-sectional thickness L0 of 1 mm or less and a cross-sectional inclination angle α of 5 degrees or less. The wedge 111 generates a phase difference proportional to the thickness of the wedge 111 for light passing through the wedge 111. The phase difference may be defined by the following equation 1 as a function δ(w) of the coordinate w [nm] on the wedge axis W. In equation 1, Δn is the birefringence determined by the material of the wedge 111. In equation 1, λ [nm] is the wavelength of light, and the phase difference δ(w) generated in the light incident on the light receiving element array 115 is the wavelength of the light monochromatized by the bandpass filter 35.

number

[0053] In the above formula 1, the unit of the minimum thickness L0 is [nm]. In the above formula 1, the thickness L(w) of the wedge 111 may be assumed to be the thickness of the wedge 111 corresponding to the center of a light receiving element having a finite area. The thickness L(w) of the wedge 111 may vary linearly, curvedly, or stepwise partially or entirely along the wedge axis W, or may vary in a combination of these ways.

[0054] 4 is a diagram illustrating a method for calculating full Stokes parameters according to one embodiment. In FIG. 4, an example of a unit area consisting of nine polarizers arranged in a 3-row, 3-column matrix is ​​indicated by a bold frame (I). Three dashed straight lines A, B, and C perpendicular to the wedge axis W are also indicated on the unit area (I).

[0055] 4 and 2, when a plane intersecting the direction of incidence of light on the polarizer array 113, i.e., an xy plane orthogonal to the optical axis 22, is viewed from the positive direction of the z axis, the wedge 111 is arranged so that its wedge axis W forms an angle of 45 degrees with respect to the arrangement direction of the multiple polarizers in the polarizer array 113. The wedge 111 arranged in this manner and having a thickness that varies linearly along the wedge axis W causes the same phase difference to be imposed on light incident on some of the multiple polarizers in the polarizer array 113 that have the same transmission axis directions, and causes different phase differences to be imposed on light incident on the remaining polarizers.

[0056] In other words, the same phase difference occurs between light beams incident on polarizers with the same transmission axis direction that are aligned on a line extending in a direction perpendicular to the wedge axis W, i.e., a 45-degree angle toward the paper surface of FIG. 4. This is because the thickness of the wedge 111 is uniform on that line. On the other hand, different phase differences occur between light beams incident on polarizers with the same transmission axis direction that are aligned on a line extending along the wedge axis W, due to differences in the thickness of the wedge 111.

[0057] For example, the same phase difference occurs between light incident on two polarizers oriented at 135 degrees and located on dashed line A. On the other hand, different phase differences occur between light incident on a polarizer oriented at 135 degrees and located on dashed line B.

[0058] Here, the following equation 2 is known as the definition of the full Stokes parameters S0 to S3 that describe the polarization state of any light. In equation 2, I0, I 45 , I 90 and I 135 are the light intensities of linearly polarized light at four orientations of 0, 45, 90, and 135 degrees, respectively, and I RCP and I LCPare the light intensities of right-handed circularly polarized light and left-handed circularly polarized light, respectively. As shown in Equation 2, the linear Stokes parameters S0 to S2 can be calculated using the light intensities of linearly polarized light, but to calculate the full Stokes parameters including S3, the light intensities of right-handed circularly polarized light and left-handed circularly polarized light are also required.

number

[0059] Furthermore, the light intensity of each polarization is constrained by the following equation 3. Therefore, when calculating the linear Stokes parameters based on linear polarization information from a unit area consisting of polarizers for four azimuths of 0 degrees, 45 degrees, 90 degrees, and 135 degrees, the number of independent variables becomes three, resulting in redundancy.

number

[0060] In contrast, the imaging system 10 according to this embodiment uses an imaging element 100 including a wedge 111 having the above-described configuration, thereby eliminating the need to directly measure the light intensity of right-handed circularly polarized light and left-handed circularly polarized light, and also eliminating the above-described redundancy.

[0061] Specifically, the personal computer 70 according to this embodiment calculates the full Stokes parameters based on linear polarization information obtained from light transmitted through polarizers at four orientations of 0 degrees, 45 degrees, 90 degrees, and 135 degrees, contained within a unit area consisting of nine polarizers arranged in a matrix of 3 rows and 3 columns.

[0062] For example, for a unit area (I) shown in Figure 4, the light intensities measured for linearly polarized light transmitted through polarizers at 0 and 90 degrees orientations located on dashed line C are defined as I with a superscript C and a subscript 0, and I with a superscript C and a subscript 90, respectively. In this case, S0 and S1 are defined by the following equation 4.

number

[0063] Furthermore, for the unit area (I) shown in FIG. 4, the light intensities measured for linearly polarized light transmitted through polarizers at 45-degree and 135-degree orientations located on dashed line A are defined as I with a superscript A and subscript 45, and I with a superscript A and subscript 135, respectively. Furthermore, the light intensities measured for linearly polarized light transmitted through polarizers at 45-degree and 135-degree orientations located on dashed line B are defined as I with a superscript B and subscript 45, and I with a superscript B and subscript 135, respectively. In this case, S2 for light transmitted through the polarizer on dashed line A and S2 for light transmitted through the polarizer on dashed line B are defined by the following equation 5 using S2 and S3, respectively, and the light intensities defined above. In the following equation 5, δ A and δ B are the phase differences, calculated by the above formula 1, that occur in the light incident on the light receiving element corresponding to the polarizer on the dashed line A and the light incident on the light receiving element corresponding to the polarizer on the dashed line B, respectively.

number

number

[0064] From the above equations 5 and 6, the following equation 7 can be derived, and S2 and S3 can be defined using only the intensity and phase difference of linearly polarized light. However, as shown in the denominator on the right side of equation 7, δ B -δ A The thickness of the wedge 111 must be designed so that ≠0 holds.

number

[0065] As described above, the personal computer 70 according to this embodiment can calculate the full Stokes parameters based on linear polarization information acquired from light transmitted through polarizers for four azimuths of 0 degrees, 45 degrees, 90 degrees, and 135 degrees, which are included in a unit area made up of nine polarizers arranged in a 3-row, 3-column matrix, using the above equations 1, 4, and 7. Note that by using a wedge 111 whose thickness varies along the wedge axis W, the denominator on the right-hand side of equation 7 does not become 0, so equation 7 always holds.

[0066] 4 and 2, when the xy plane is viewed from the positive direction of the z axis, the crystal axis of the wedge 111 coincides with the arrangement direction of the multiple polarizers in the polarizer array 113, i.e., coincides with the y-axis direction among the x-axis and y-axis directions. In order to calculate the full Stokes parameters of the subject light as described above, the crystal axis of the wedge 111 is configured to coincide with the arrangement direction of the multiple polarizers in the polarizer array 113 or to form a 45-degree angle with the arrangement direction. When the crystal axis of the wedge 111 forms a 45-degree angle with the arrangement direction, the light intensities in the 0-degree and 90-degree directions can be replaced with the light intensities in the 45-degree and 135-degree directions in the above-described formula for calculating the full Stokes parameters.

[0067] 1 to 3 are merely examples, and other shapes may be used as long as they function to cause the same phase difference to light incident on some polarizers among the multiple polarizers having the same transmission axis direction in the polarizer array 113, and cause different phase differences to light incident on the remaining polarizers. In addition, it is preferable that the light incident surface of the wedge 111 is perpendicular to the optical axis 22.

[0068] Fig. 5 is a diagram illustrating a method for increasing spatial resolution according to one embodiment. In Fig. 5, in addition to the unit area (I) centered on the polarizer oriented at 0 degrees shown in Fig. 4, a unit area (II) centered on the polarizer oriented at 90 degrees is shown.

[0069] Specifically, the personal computer 70 according to this embodiment may analyze linearly polarized light information from two types of unit areas in which the nine polarizers are arranged differently, such as the two unit areas (I) and (II) in Fig. 5. In other words, the personal computer 70 may perform the calculation of the full Stokes parameters described with reference to Fig. 4 on the linearly polarized light information from the two types of unit areas. This allows the personal computer 70 to have the same spatial resolution as when a 2-row, 2-column unit area is used as the minimum unit for polarization analysis.

[0070] FIG. 6 is a diagram illustrating a method for determining a function that indicates the relationship between the arrangement positions of multiple polarizers and the phase difference that occurs in light transmitted through the wedge 111, according to one embodiment. In addition to the imaging device 15 described with reference to FIGS. 1 to 5, FIG. 6 also illustrates a laser diode 201, an ND filter 203, a linear polarizer 205, a liquid crystal depolarizer 207, and a quarter-wave plate 209 as an example of an apparatus configuration for creating a spatial distribution of Stokes parameters. As shown in FIG. 6, the laser diode 201 and other components are arranged in this order on the optical axis 22 of the imaging device 15. In addition, in this embodiment, collimated light, for example, laser light, is used as an illumination source, so the imaging device 15 is used without the imaging lens unit 20.

[0071] In this embodiment, the laser diode 201 outputs monochromatic, linearly polarized laser light. The ND filter 203 adjusts the intensity of the laser light. The linear polarizer 205 increases the degree of polarization of the laser light, for example, from an extinction ratio of approximately 10:1 to an extinction ratio of approximately 1000:1. The liquid crystal depolarizer 207 spatially modulates the angle of linear polarization (AoLP). The quarter-wave plate 209 partially varies the degree of linear polarization (DoLP) of the incident light, creating light with a non-uniform spatial distribution, i.e., light that is a mixture of linearly polarized light, circularly polarized light, etc.

[0072] In this embodiment, the personal computer 70 may perform calibration using light whose full Stokes parameters are known, for example, by using the device configuration shown in Fig. 6, and thereby specify a function that indicates the relationship between the arrangement positions of the multiple polarizers in the polarizer array 113 and the phase difference that occurs in light that passes through the wedge 111, i.e., the above-mentioned Equation 1. The personal computer 70 may calculate the above-mentioned full Stokes parameters using the specified function.

[0073] As described above, the image sensor 100 according to this embodiment includes the wedge 111 having birefringence, the polarizer array 113 in which a plurality of pairs of polarizers having different transmission axis directions are arranged in a plane intersecting the direction of incidence of the light, and on which light transmitted through the wedge 111 is incident, and the light receiving element array 115 in which a plurality of light receiving elements on which the light transmitted through the polarizer array 113 is incident are arranged to correspond to the plurality of polarizers in the polarizer array 113. The image sensor 100 according to this embodiment having such a configuration can acquire linear polarization information required for calculating the full Stokes parameters by arranging the wedge 111 on the light receiving surface side of the polarizer array 113 at a predetermined angle with respect to the polarizer array 113.

[0074] Furthermore, according to the image sensor 100 of this embodiment, the above-described linear polarization information can be obtained by adjusting the relative angle of the wedge 111 with respect to the polarizer array 113. This avoids the difficulty of, for example, aligning a polarizer array with a retarder array in which multiple retarders corresponding to each polarizer in the polarizer array are arranged. Furthermore, according to the image sensor 100 of this embodiment, calibration of both characteristics of such a combination of a polarizer array and a retarder array is unnecessary. Such a retarder array must be manufactured with nanometer-order precision, which increases the manufacturing cost. Therefore, according to the image sensor 100 of this embodiment, costs can be reduced compared to an image sensor using such a combination. Furthermore, according to the image sensor 100 of this embodiment, crosstalk, i.e., a decrease in the extinction ratio, caused by the use of such a retarder array can be avoided.

[0075] Numerical simulations were performed on the imaging system 10 according to the embodiment described above. Specifically, light with known full Stokes parameters was input to the imaging system 10, and it was verified whether the full Stokes parameters could be reconstructed through measurements. Here, the fixed pattern noise inherent in the CMOS sensor was taken into consideration, and it was assumed that the maximum signal amount was incident on the CMOS sensor. As a result, it was found that the imaging system 10 is capable of measuring full Stokes parameters comparable to the input full Stokes parameters. In other words, the actual measurements showed very good agreement with the results of the numerical simulation. It is expected that the accuracy of reproducing the full Stokes parameters of the imaging system 10 can be further improved by characterizing the light receiving element array 115.

[0076] Although the present invention has been described above using embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It will be apparent to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the claims that such modifications and improvements can also be included within the technical scope of the present invention.

[0077] For example, if you want to increase the amount of light at the expense of spatial resolution, you can arrange multiple light receiving elements for a polarizer in one orientation. For example, you can extract polarization information using a process equivalent to binning. However, as with commercially available RGB color cameras, it is preferable that spatially uniform light is incident on multiple light receiving elements corresponding to one polarizer.

[0078] It should be noted that the execution order of each process, such as operations, procedures, steps, and stages, in the devices, systems, programs, and methods shown in the claims, specifications, and drawings is not specifically stated as "before," "prior to," etc., and that the processes can be performed in any order unless the output of a previous process is used in a subsequent process. Even if the operational flow in the claims, specifications, and drawings is described using "first," "next," etc. for convenience, this does not mean that the processes must be performed in this order. [Explanation of symbols]

[0079] 10. Imaging System 15 Imaging device 20 Imaging lens unit 22 Optical axis 30 Camera Body 35 Bandpass Filter 40 Imaging unit 50 PCB Unit 51 MPU 53 Power supply 55 PCB 70 PC 80 Connector 90 Flexible PCB 100 image sensor 111 Wedge 113 Polarizer Array 115 Photodetector array 117 Microlens Array 120 Mounting board 140 frames 201 Laser Diode 203 ND filter 205 Linear Polarizer 207 Liquid Crystal Depolymerizer 209 Quarter Wave Plate

Claims

1. a birefringent wedge; a polarizer array in which a plurality of pairs of polarizers having different transmission axis directions are arranged in a plane intersecting the direction of incidence of the light, on which the light transmitted through the wedge is incident; a light receiving element array in which a plurality of light receiving elements onto which light transmitted through the polarizer array is incident are arranged so as to correspond to a plurality of polarizers of the polarizer array; An imaging element comprising:

2. the wedge generates the same phase difference between light beams incident on some polarizers among the plurality of polarizers in the polarizer array, the polarizers having the same transmission axis directions, and generates different phase differences between light beams incident on the remaining polarizers; The imaging device according to claim 1 .

3. The wedge has a thickness that varies linearly along a wedge axis extending in one direction, and generates a phase difference corresponding to the thickness in light that passes through the wedge. The imaging device according to claim 2 .

4. The wedge has a wedge-shaped cross section along the wedge axis, a minimum thickness of 1 mm or less in the cross section, and an inclination angle of 5 degrees or less in the cross section. The imaging device according to claim 3 .

5. The wedge is arranged such that the wedge axis forms an angle of 45 degrees with respect to the arrangement direction of the plurality of polarizers in the polarizer array. The imaging device according to claim 3 or 4.

6. The wedge is composed of calcite. The imaging device according to claim 1 .

7. The imaging device according to claim 1 , Imaging lens unit Equipped with a configuration in which light is incident on the imaging lens unit, the wedge, the polarizer array, and the light receiving element array in this order, or a configuration in which light is incident on the wedge, the imaging lens unit, the polarizer array, and the light receiving element array in this order; Imaging device.

8. further comprising a bandpass filter for monochromatizing the light incident on the light receiving element array; The imaging device according to claim 7 .

9. an imaging device according to claim 7 or 8; a calculation device that calculates linear Stokes parameters based on polarization information for each direction of the transmission axis acquired by the imaging device; and An imaging system comprising:

10. the calculation device calculates full Stokes parameters based on linear polarization information acquired from light transmitted through polarizers in four directions of 0 degree, 45 degree, 90 degree, and 135 degree, which are included in a unit area made up of nine polarizers arranged in a matrix of 3 rows and 3 columns; The imaging system according to claim 9 .

11. The calculation device analyzes the linear polarization information from two types of unit areas having different arrangements of the nine polarizers. The imaging system according to claim 10.

12. The computing device performing calibration using light whose full Stokes parameters are known, and identifying a function that indicates the relationship between the arrangement positions of the plurality of polarizers and the phase difference that occurs in the light that transmits through the wedge; Calculating the full Stokes parameters using the function. The imaging system according to any one of claims 9 to 11.

Images