JP2023007699A - Imaging element, imaging device, and imaging system - Google Patents

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

The present invention relates to an imaging device, an imaging device, and an imaging system.

Non-Patent Document 1 describes "The whole setup consists of a bandpass filter for 450 nm wavelength (design wavelength of the retarder array), nano-optical retarder and polarizer array as well as microlens array and crosstalk module (see figure 1). …Each array (polarizer, retarder, microlens + crosstalk) is fabricated on a 0.5 mm thin substrate and are aligned to and placed directly on top of a CMOS sensor with 2560*1920 pixels …” (1 Introduction) It consists not only of a microlens array and a crosstalk module, but also a bandpass filter for the 450 nm wavelength (the design wavelength of the retarder array), a nano-optical retarder and a polarizer array (see Fig. 1)...each array (polarizer , retarder, microlens+crosstalk) are formed on a 0.5 mm thick substrate 20 and aligned and directly mounted on the top surface of a 2560×1920 pixel CMOS sensor...). there is In addition, Non-Patent Document 2 describes "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." Acting as a camera, it utilizes a low-dispersion microretarder array on top of the sensor with a Bayer filter and a wire-grid linear polarizer. , every pixel should be precisely aligned on top of each designated retarder.” (5. DISCUSSION AND CONCLUSION) , should be precisely aligned on the top surface of each designed retarder.).
[Prior art documents]
[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)

A first aspect of the present invention provides an imaging device. The imaging device may comprise a wedge having birefringence. The imaging device may include a polarizer array in which a plurality of sets of polarizers having different transmission axis directions, on which light transmitted through the wedge is incident, are arranged in a plane intersecting the light incident direction. The imaging element may include a light receiving element array in which a plurality of light receiving elements to which light transmitted through the polarizer array is incident are arranged so as to correspond to the plurality of polarizers of the polarizer array.

Among a plurality of polarizers having the same transmission axis direction in the polarizer array, the wedge causes the light incident on some of the polarizers to have the same phase difference, and the light incident on the remaining polarizers. may be caused to have different phase differences with respect to each other.

The wedge may have a thickness that varies linearly along a unidirectionally extending wedge axis to produce a phase difference corresponding to the thickness for light transmitted through the wedge.

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.

The wedge may be arranged such that the wedge axis forms 45 degrees with respect to the arrangement direction of the polarizers in the polarizer array.

The wedges may be composed of calcite.

In a second aspect of the invention, an imaging device is provided. An imaging device may include any of the imaging elements described above. The imaging device may comprise an imaging lens unit. Light is incident in the order of the imaging lens unit, wedge, polarizer array, and light receiving element array, or configured so that light is incident in the order of the wedge, imaging lens unit, polarizer array, and light receiving element array. may be

The imaging device may further include a bandpass filter that monochromates light incident on the light receiving element array.

In a third aspect of the invention, an imaging system is provided. An imaging system may include any of the imaging devices described above. The imaging system may include a computing device that computes linear Stokes parameters based on the polarization information for each transmission axis direction acquired by the imaging device.

Light transmitted through polarizers in four directions of 0 degrees, 45 degrees, 90 degrees and 135 degrees included in a unit area composed of nine polarizers arranged in a matrix of 3 rows and 3 columns. Full Stokes parameters may be calculated based on the linear polarization information obtained from .

The computing device may analyze the linear polarization information from two types of unit areas in which the arrangement of the nine polarizers is different from each other.

By performing calibration using light with known full-stokes parameters, the arithmetic unit specifies a function that indicates the relationship between the array positions of the multiple polarizers and the phase difference that occurs in the light that passes through the wedge. good too. The computing device may compute the Full Stokes parameters using the function.

It should be noted that the above summary of the invention does not list all the features of the invention. Subcombinations of these feature groups can also be inventions.

1 is a schematic diagram of an imaging system 10, according to one embodiment. FIG. 1 is a schematic diagram of an image sensor 100, according to one embodiment. FIG. FIG. 11 is a schematic side view of wedge 111, according to one embodiment. FIG. 4 is a diagram for explaining a method of computing full Stokes parameters, according to one embodiment; FIG. 4 is a diagram illustrating a method for increasing spatial resolution, according to one embodiment; FIG. 11 is a diagram for explaining a method of specifying a function indicating the relationship between the arrangement positions of a plurality of polarizers and the phase difference occurring in the light transmitted through the wedge 111, according to one embodiment;

Hereinafter, the present invention will be described through embodiments of the invention, but the following embodiments do not limit the invention according to the claims. Also, not all combinations of features described in the embodiments are essential for the solution of the invention.

FIG. 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 polarization information from the imaging device 15 and displaying an image on a monitor.

The imaging device 15 includes an imaging lens unit 20 and a camera body 30 . As an example, the imaging device 15 can be manufactured in palm size of about 28 mm×28 mm×50 mm. Further, the imaging device 15 can wirelessly communicate with the personal computer 70 , and transmits to the personal computer 70 an image signal including polarization information acquired by imaging a subject. Alternatively or additionally, the imaging device 15 may be able to communicate with the personal computer 70 by wire.

The imaging lens unit 20 has an optical system in its lens barrel, and an optical axis 22 is defined by the optical system. The imaging lens unit 20 is detachably attached to the camera body 30 . The imaging lens unit 20 may be housed in the camera body 30 and protrude outward as shown in the drawing when in use.

The imaging lens unit 20 guides the incident subject light flux into the camera body 30 . It should be noted that the imaging lens unit 20 shown in FIG. 1 includes two lenses and a diaphragm for the sake of clarity of explanation, but it is not limited to this configuration.

Camera body 30 has bandpass filter 35 , imaging unit 40 , substrate unit 50 , and flexible substrate 90 . The flexible board 90 connects the imaging unit 40 and the board unit 50 .

The subject light flux incident on the imaging lens unit 20 is guided to the imaging unit 40 via the bandpass filter 35 by the imaging lens unit 20 . The bandpass filter 35 monochromaticizes the light incident on the bandpass filter 35 . Preferably, the bandpass filter 35 transmits a wavelength band so narrow that the phase chromatic dispersion at the wedge 111 does not affect the image signal.

The imaging unit 40 has an imaging element 100 , a mounting board 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 device 100 according to this embodiment further includes a microlens array 117 .

Wedge 111 has birefringence. In this embodiment, the wedge 111 is made of calcite, ie, calcite, as an example. The wedge 111 may be made of a birefringent material such as crystal instead of calcite.

The wedge 111 receives light monochromatic by the bandpass filter 35 . Light transmitted through the wedge 111 enters the polarizer array 113 . In this embodiment, light transmitted through the wedge 111 enters the polarizer array 113 via the microlens array 117 . 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 .

The microlens array 117 can also be referred to as an on-chip lens, and as an example, multiple microlenses are arranged on a single glass substrate, and light is incident on each of the multiple microlenses.

The polarizer array 113 is formed by arranging a plurality of sets of polarizers having different transmission axis directions in a plane intersecting the incident direction of light. The polarizer array 113 may be of the photonic crystal type or of the 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 .

The light receiving element array 115 is formed by arranging a plurality of light receiving elements so as to correspond to the polarizers of the polarizer array 113 . In this embodiment, light transmitted 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 main planar shape.

Each light-receiving element of the light-receiving element array 115 captures an image of a 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 restricted by the band-pass filter 35 to a narrow band around the designed wavelength. Note that, as an example, the imaging device 15 may be capable of handling visible light to near-infrared light, that is, a wavelength range of 400 to 900 nm, based on the specifications of the polarizer array 113. In this case, the bandpass filter 35 For example, a specification that limits the wavelength to 500±2 nm or 600±2 nm may be used.

On the mounting substrate 120, the microlens array 117, the polarizer array 113, and the light receiving element array 115 in the imaging device 100 are stacked in this order and mounted. More specifically, the light emitting surface side of the light receiving element array 115 among these laminates is fixed to the surface of the mounting substrate 120 . Also, as an example, a connector 80 is mounted on the back surface of the mounting board 120 .

A flexible substrate 90 is connected to the connector 80 mounted on the mounting substrate 120 . The connector 80 may transmit image signals to the board unit 50 via the flexible board 90 and may be supplied with current from the board unit 50 via the flexible board 90 .

The imaging element 100 and the mounting substrate 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, thereby fixing the imaging device 100 and the like inside the camera body 30 .

The frame 140 has an opening, and the opening is formed in the frame 140, for example, in the central portion in the xy plane. The laminate mounted on the mounting substrate 120 is positioned in the opening, and the opposite side of the opening from the mounting substrate 120 is sealed by the wedge 111 .

Here, 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 flux 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 flux is incident is defined as the z-axis minus direction, and the opposite direction is defined as the z-axis plus direction. Further, the depth direction toward the paper surface of FIG. 1 is defined as the x-axis direction, and the vertical direction toward the paper surface of FIG. 1 is defined as the y-axis direction. The x-, y-, and z-axes are a right-handed orthogonal coordinate system. For convenience of explanation, the positive direction of the z-axis may be referred to as the front side, the front side, or the like. Also, the negative direction of the z-axis is sometimes referred to as the rear side, the rear side, or the like. Also, the side in the negative direction of the z-axis may be called the rear side or the like.

The board unit 50 is arranged 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 . It should be noted that other electronic circuits may additionally or alternatively be mounted on the substrate 55 .

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

The power supply 53 includes a battery attached to the imaging device 15 and a power supply circuit that supplies power accumulated 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 the flexible substrate 90, the connector 80 and the mounting substrate 120, for example.

The personal computer 70 has a processor. The personal computer 70 receives the image signal from the imaging device 15, analyzes the polarization information included in the image signal, and generates image data for display.

More specifically, the personal computer 70 calculates the linear Stokes parameters based on the polarization information for each transmission axis direction 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 the monitor.

It should be noted that the personal computer 70 is an example of a computing device that performs the computations and the like described above. Note that the arithmetic device may be integrated with the imaging device 15, that is, the imaging device 15 may perform the aforementioned arithmetic operations. In this case, the imaging device 15 may include an FPGA (Field Programmable Gate Array) in place of or in addition to the MPU 51, and the FPGA or the like may have the above-described functions of the arithmetic device. Further, in this case, the imaging device 15 may include a liquid crystal display or the like for displaying the generated image data.

FIG. 2 is a schematic diagram of an image sensor 100, according to one embodiment. In FIG. 2, the components of the imaging device 100 are shown spaced apart along the optical axis 22 of the imaging device 15 for clarity of illustration.

In FIG. 2, the wedge axis W extending in one direction of the wedge 111 is indicated by an outline arrow, and the crystal axis T of the wedge 111 is indicated by an outline arrow. The same applies to subsequent figures, and redundant description is omitted.

In FIG. 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 and the like, the polarizer array 113 and the like are virtually translated along the optical axis 22 so that the wedge 111 Array A of dashed lines indicates a state superimposed on the light exit surface of .

Further, in FIG. 2, the transmission axis of each polarizer is indicated by an outline arrow on the polarizer array 113 . As described above, the polarizer array 113 is obtained by arranging a plurality of sets of polarizers having different transmission axis directions in a plane that intersects the light incident direction. More specifically, as shown in FIG. 2, the polarizer array 113 is arranged in a unit matrix of 2 rows and 2 columns in order of lower right, upper right, upper left, and lower left when viewed from the z-axis plus side. Polarizers for four orientations of 45 degrees, 90 degrees and 135 degrees are arranged. The polarizer array 113 is arranged such that the sets of polarizers corresponding to the four directions are repeated within the xy plane.

2, the polarizer array 113, the light receiving element array 115, and the microlens array 117 are each arranged in a matrix of 4 rows and 4 columns for the purpose of clarifying the description. However, other number of arrays may be used. The number of arrays of the polarizer array 113 and the number of microlens arrays 117 may be the same as the number of arrays of the light receiving element array 115, for example. 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, or may be arranged so as to overlap each other in the z-axis direction. good. The same applies to the subsequent descriptions, and overlapping descriptions are omitted.

As shown in FIG. 2, the imaging device 15 according to this embodiment is configured such 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, in the imaging device 15 according to the present embodiment, light is emitted in the order of the imaging lens unit 20, the wedge 111, the microlens array 117, the polarizer array 113, and the light receiving element array 115. configured for incidence. By arranging the wedge 111 in the vicinity of the light receiving element array 115 in this way, the shift amount of the subject light imaged by the light receiving element array 115 can be reduced.

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

As long as the bandpass filter 35 is arranged on the optical axis 22 on the light incident side of the light receiving element array 115, the calculation of the wavelength-dependent full Stokes parameter described later can be established. may be placed in However, in order 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, the bandpass filter 35 is preferably arranged 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 arranged on the optical axis 22 in random order. For example, the set of wedge 111 and bandpass filter 35 may be attached at a predetermined angle to the outer surface of the imaging lens of a commercially available polarization camera.

FIG. 3 is a schematic side view of 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 straight line.

In this embodiment, the wedge 111 has a thickness that varies linearly along the wedge axis W. FIG. 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 causes a phase difference corresponding to the thickness of the wedge 111 with respect to the light transmitted through the wedge 111 .

More specifically, as shown in FIG. 3, wedge 111 is wedge-shaped in cross-section along wedge axis W. As shown in FIG. As an example, the wedge 111 has a minimum thickness L ₀ of 1 mm or less in cross section and an inclination angle α of 5 degrees or less in cross section. The wedge 111 causes a phase difference proportional to the thickness of the wedge 111 to the light transmitted through the wedge 111 . The phase difference may be defined as a function δ(w) of the coordinate w [nm] on the wedge axis W by Equation 1 below. In Equation 1, Δn is the birefringence determined by the wedge 111 material. In Equation 1, λ [nm] is the wavelength of light, and the phase difference δ(w) occurring in the light incident on the light receiving element array 115 is the wavelength of the light monochromatic by the bandpass filter 35. .

In the above formula 1, the unit of the minimum thickness _L0 is [nm]. In Equation 1 above, the thickness L(w) of the wedge 111 may be assumed to be the thickness of the wedge 111 corresponding to the center of the light receiving element having a finite area. Note that the thickness L(w) of the wedge 111 may change partially or entirely along the wedge axis W linearly, curvilinearly, or stepwise, or may be a combination of these changes. may

FIG. 4 is a diagram illustrating a method of computing full Stokes parameters, according to one embodiment. In FIG. 4, an example of a unit area composed of nine polarizers arranged in a matrix of 3 rows and 3 columns is indicated by a thick frame (I). Also, three dashed straight lines A, B, and C orthogonal to the wedge axis W are shown on the unit area (I).

As shown in FIGS. 4 and 2, when the plane intersecting the direction of incidence of light on the polarizer array 113, that is, the xy plane perpendicular to the optical axis 22 is viewed from the z-axis plus direction, the wedge 111 is along the wedge axis W is arranged to form an angle of 45 degrees with respect to the arrangement direction of the plurality of polarizers in the polarizer array 113 . The wedge 111 arranged in this way and having a thickness that varies linearly along the wedge axis W serves as a polarizer for some of the polarizers having the same transmission axis direction in the polarizer array 113 . The light incident on the polarizers is caused to have the same phase difference, and the light incident on the remaining polarizers is caused to have different phase differences.

In other words, the light beams incident on the polarizers having the same transmission axis directions, which are arranged on a straight line extending in a direction perpendicular to the wedge axis W, that is, in a direction oblique to the plane of FIG. A phase difference occurs. This is because the thickness of the wedge 111 is uniform along the straight line. On the other hand, due to the difference in the thickness of the wedges 111, the lights incident on the polarizers having the same transmission axis direction and arranged on a straight line extending in the direction along the wedge axis W have different phase differences. occur.

For example, light incident on two polarizers having an azimuth of 135 degrees located on the dashed line A have the same phase difference. On the other hand, the light incident on the polarizer with an azimuth of 135 degrees located on the dashed line A and the light incident on the polarizer with an azimuth of 135 degrees located on the dashed line B have different phase differences. occur.

Here, the following equation ₂ is known as the definition of the full _- Stokes parameters S0 to S3 that describe the polarization state of arbitrary light. In Equation 2, I ₀ , I ₄₅ , I ₉₀ and I ₁₃₅ are the light intensities of linearly polarized light in four directions of 0 degrees, 45 degrees, 90 degrees and 135 degrees, respectively, and I _RCP and I _LCP are respectively the right Light intensity of circularly polarized light and light intensity of left-handed circularly polarized light. As shown in Equation ₂ , the linear Stokes parameters from _S0 to S2 can be calculated with the light intensity of linearly polarized light, but in order to calculate the full Stokes parameters including S3 _, right-handed circularly polarized light and left-handed circularly polarized light A polarized light intensity is also required.

In addition, the light intensity of each polarized light is subject to the constraint of Equation 3 below. Therefore, when calculating the linear Stokes parameter based on the linear polarization information from the unit area composed of the polarizers of four orientations of 0 degrees, 45 degrees, 90 degrees and 135 degrees, the independent variable is 3, and the redundancy will exist.

On the other hand, according to the imaging system 10 according to the present embodiment, by using the imaging element 100 including the wedge 111 having the above-described configuration, the light intensities of the right-handed circularly polarized light and the left-handed circularly polarized light are directly measured. It eliminates the need and eliminates the redundancy described above.

Specifically, the personal computer 70 according to the present embodiment has four angles of 0 degrees, 45 degrees, 90 degrees and 135 degrees included in a unit area composed of nine polarizers arranged in a matrix of 3 rows and 3 columns. A full Stokes parameter is calculated based on the linear polarization information obtained from the light transmitted through the azimuthal polarizer.

For example, for the unit area (I) shown in FIG. Defined by a subscript 0 and a superscript C of I and a subscript 90. In this case, S ₀ and S ₁ are defined in Equation 4 below.

上記の式５は、行列の逆演算により、以下の式６のように変形され、すなわちＳ_２およびＳ_３を以下の式６で定義できる。

Furthermore, for the unit area (I) shown in FIG. Defined by a subscript 45 and a superscript A and a subscript 135 of I. Further, the light intensities measured for the linearly polarized light transmitted through the polarizers of each orientation of 45 degrees and 135 degrees located on the dashed line B are respectively the superscript B and subscript 45 of I, and the superscript B and I subscript 135. 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 , _{respectively ,} with S2 and _S3 and the light intensity defined above It is defined by Equation 5 below. In the following formula 5, δ _A and δ _B are respectively the phase difference generated in the light incident on the light receiving element corresponding to the polarizer on the dashed line A and the polarizer on the dashed line B calculated by the above formula 1. It is the phase difference that occurs in the light incident on the corresponding light receiving element.

Equation 5 above is transformed into Equation ₆ below by matrix inversion, that is, S2 and S3 can be defined by Equation ₆ below.

The following equation 7 is derived from the above equations ₅ and ₆ , and S2 and S3 can be defined only by the light intensity and phase difference of the linearly polarized light. However, as indicated by the denominator on the right side of Equation 7, it is necessary to design the thickness of the wedge 111 so that δ _B −δ _A ≠0.

As described above, the personal computer 70 according to the present embodiment uses the above equations 1, 4 and 7 to obtain a 0 degree , 45 degrees, 90 degrees and 135 degrees. Note that Equation 7 above always holds because the denominator of the right side of Equation 7 does not become 0 by using the wedge 111 whose thickness changes along the wedge axis W.

In this embodiment, as shown in FIGS. 4 and 2, when the xy plane is viewed from the z-axis plus direction, the crystal axis of the wedge 111 is aligned with the arrangement direction of the plurality of polarizers in the polarizer array 113, i.e. Of the x-axis direction and the y-axis direction, it matches the y-axis direction. The crystal axis of the wedge 111 is aligned with the arrangement direction of the plurality of polarizers in the polarizer array 113 or at 45 degrees with respect to the arrangement direction in order to calculate the Full Stokes parameter of the subject light as described above. configured to When the crystal axis of the wedge 111 forms an angle of 45 degrees with respect to the arrangement direction, in the above equation for the Full Stokes parameter, the light intensity at the 0-degree and 90-degree azimuths and the light intensity at the 45-degree and 135-degree azimuths are It is sufficient to replace with the light intensity.

The shape of the wedge 111 shown in FIGS. 1 to 3 is only an example, and light incident on some of the plurality of polarizers having the same transmission axis direction in the polarizer array 113 Any other shape may be used as long as the function of generating the same phase difference for the light beams entering the remaining polarizers and different phase difference for the light beams incident on the remaining polarizers is achieved. Also, the light incident surface of the wedge 111 is preferably perpendicular to the optical axis 22 .

FIG. 5 is a diagram illustrating a method for increasing spatial resolution, according to one embodiment. FIG. 5 shows a unit region (II) centered on a polarizer oriented at 90 degrees in addition to the unit region (I) centered on the polarizer oriented at 0 degrees shown in FIG.

Specifically, the personal computer 70 according to the present embodiment can transmit linearly polarized light information from two types of unit areas in which nine polarizers are arranged differently from each other, such as the two unit areas (I) and (II) in FIG. may be analyzed. In other words, the personal computer 70 may perform the calculation of the Full Stokes parameters described with reference to FIG. 4 for the linear polarization information from the two types of unit areas. As a result, the personal computer 70 can have the same spatial resolution as when the unit area of 2 rows and 2 columns is the minimum unit of polarization analysis.

FIG. 6 is a diagram for explaining a method of specifying a function that indicates the relationship between the arrangement positions of multiple polarizers and the phase difference that occurs in the light that passes through the wedge 111, according to one embodiment. FIG. 6 shows, in addition to the imaging device 15 described with reference to FIGS. 1 to 5, a laser diode 201, an ND filter 203, and a linearly polarized Element 205, liquid crystal depolarizer 207 and quarter wave plate 209 are shown. As shown in FIG. 6, the laser diodes 201 and the like are arranged on the optical axis 22 of the imaging device 15 in this order. In addition, in the present embodiment, collimated light such as laser light is used as an illumination source, so that the imaging device 15 is used with the imaging lens unit 20 removed.

In this embodiment, the laser diode 201 outputs monochromatic and linearly polarized laser light. The ND filter 203 adjusts the intensity of laser light. The linear polarizer 205 increases the degree of polarization of the laser beam from, for example, an extinction ratio of approximately 10:1 to an extinction ratio of approximately 1000:1. The liquid crystal depolarizer 207 spatially modulates the AoLP (linear polarization angle). The quarter-wave plate 209 partially changes the DoLP (degree of linear polarization) of the incident light to produce light with uneven spatial distribution, that is, mixed light of linear polarized light and circular polarized light.

In this embodiment, the personal computer 70 performs calibration using light with a known full-stokes parameter, for example, by using the device configuration shown in FIG. , and the phase difference occurring in the light passing through the wedge 111, that is, Equation 1 above may be specified. The personal computer 70 may use the specified function to compute the Full Stokes parameters described above.

As described above, according to the image pickup device 100 according to the present embodiment, a set of the wedge 111 having birefringence and a plurality of polarizers having mutually different transmission axis directions on which the light transmitted through the wedge 111 is incident. , a plurality of polarizer arrays 113 arranged in a plane that intersects the direction of incidence of light, and a plurality of light-receiving elements on which light transmitted through the polarizer array 113 is incident are arranged so as to correspond to the plurality of polarizers of the polarizer array 113. and a light receiving element array 115 arranged in a row. According to the imaging device 100 of the present embodiment having such a configuration, the wedge 111 is arranged on the side of the light receiving surface of the polarizer array 113 at a predetermined angle with respect to the polarizer array 113 to calculate the full Stokes parameters. can obtain the linear polarization information required for

Further, according to the imaging device 100 of the present embodiment, by adjusting the relative angle of the wedge 111 with respect to the polarizer array 113, the linear polarization information can be obtained. Difficulties in aligning the element array and the retarder array in which a plurality of retarders are arranged corresponding to each polarizer of the polarizer array can be avoided. Further, according to the imaging device 100 according to this embodiment, it is possible to eliminate the need for calibration of both characteristics in such a combination of the polarizer array and the retarder array. Such a retarder array needs to be manufactured with nano-order accuracy, and the manufacturing cost is high. Therefore, according to the imaging device 100 according to this embodiment, the cost can be reduced as compared with the imaging device using the combination. Further, according to the imaging device 100 of the present embodiment, it is possible to avoid the occurrence of crosstalk due to the use of such a retarder array, that is, the deterioration of the extinction ratio.

A numerical simulation was performed for the imaging system 10 in the embodiment described above. Specifically, the imaging system 10 was given an input of light with known full Stokes parameters, and it was verified whether the full Stokes parameters could be recovered by measurement. Here, in consideration of the fixed pattern noise of the CMOS sensor, it is assumed that the maximum amount of signal is incident on the CMOS sensor. As a result, it has been found that the imaging system 10 can perform measurements comparable to the input full-stokes parameters. That is, the measured values show very good agreement with the numerical simulation results. In the imaging system 10, characterization of the light receiving element array 115 is expected to further improve the reproduction accuracy of the full Stokes parameters.

Although the present invention has been described above using the embodiments, the technical scope of the present invention is not limited to the scope described in the above embodiments. It is obvious to those skilled in the art that various modifications and improvements can be made to the above embodiments. It is clear from the description of the scope of claims that forms with such modifications or improvements can also be included in the technical scope of the present invention.

For example, when it is desired to increase the amount of light at the expense of spatial resolution, a plurality of light-receiving elements may be arranged with respect to the polarizer in one direction. For example, polarization information may be extracted by a process equivalent to binning. However, as with commercially available RGB color cameras, it is preferable that spatially uniform light is incident on a plurality of light receiving elements corresponding to one polarizer.

The execution order of each process such as actions, procedures, steps, and stages in the devices, systems, programs, and methods shown in the claims, the specification, and the drawings is particularly "before", "before etc., and it should be noted that they can be implemented in any order unless the output of the previous process is used in the subsequent process. Regarding the operation flow in the claims, the specification, and the drawings, even if the description is made using "first," "next," etc. for the sake of convenience, it means that it is essential to carry out in this order. not a thing

10 imaging system 15 imaging device 20 imaging lens unit 22 optical axis 30 camera body 35 bandpass filter 40 imaging unit 50 substrate unit 51 MPU
53 Power supply 55 Substrate 70 Personal computer 80 Connector 90 Flexible substrate 100 Imaging element 111 Wedge 113 Polarizer array 115 Photodetector array 117 Microlens array 120 Mounting substrate 140 Frame 201 Laser diode 203 ND filter 205 Linear polarizer 207 Liquid crystal depolarizer 209 Quarter single wave plate

Claims (12)

a wedge having birefringence;
a polarizer array in which a plurality of sets of polarizers having mutually different transmission axis directions, on which the light transmitted through the wedge is incident, are arranged in a plane intersecting the light incident direction;
An imaging device comprising a light receiving element array in which a plurality of light receiving elements to which light transmitted through the polarizer array is incident are arranged so as to correspond to the plurality of polarizers of the polarizer array. The wedge causes the light incident on some polarizers of the plurality of polarizers having the same transmission axis direction in the polarizer array to have the same phase difference as each other, and is incident on the remaining polarizers. causing different phase differences for the light to be emitted,
The imaging device according to claim 1 . The wedge has a thickness that varies linearly along a wedge axis extending in one direction, and produces a phase difference corresponding to the thickness for light transmitted through the wedge.
The imaging device according to claim 2 . 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. 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. wherein the wedge is composed of calcite;
The imaging device according to any one of claims 1 to 5. An imaging device according to any one of claims 1 to 6;
comprising an imaging lens unit and
Light is incident on the imaging lens unit, the wedge, the polarizer array, and the light receiving element array in this order, or the wedge, the imaging lens unit, the polarizer array, and the light receiving element array configured for sequential incidence of light,
Imaging device. Further comprising a bandpass filter for monochromatic light incident on the light receiving element array,
The imaging device according to claim 7. An imaging device according to claim 7 or 8;
and an arithmetic device that calculates a linear Stokes parameter based on the polarization information for each direction of the transmission axis acquired by the imaging device. The arithmetic device transmitted through polarizers for four orientations of 0 degrees, 45 degrees, 90 degrees and 135 degrees contained in a unit area composed of nine polarizers arranged in a matrix of 3 rows and 3 columns. computing the full-stokes parameters based on the linear polarization information obtained from the light;
An imaging system according to claim 9 . The arithmetic device analyzes the linearly polarized light information from two types of the unit areas in which the nine polarizers are arranged differently.
11. The imaging system of claim 10. The computing device is
By performing calibration using light with a known Full Stokes parameter, 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 is transmitted through the wedge,
using the function to compute the Full Stokes parameter;
12. Imaging system according to any one of claims 9-11.

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