Imaging system

Abstract

Provided is an imaging system capable of obtaining a captured image having reduced noise. This imaging system has: a light source for emitting infrared rays; an imaging device for imaging an object irradiated with the infrared rays emitted from the light source; and a first polarization filter that is provided between the light source and the object and polarizes the infrared rays emitted from the light source. The imaging device comprises, from the incident side, a lens, a second polarization filter for polarizing the infrared rays, and an image sensor.

Description

Imaging system

[0001] The present invention relates to an imaging system that captures an image of an object using infrared rays, and more particularly to an imaging system that has a polarizing filter that polarizes infrared rays.

[0002] In recent years, in order to increase the functionality of devices and save space, devices have been developed that combine a display element for displaying images and a device for visible light, such as a visible light imaging element used to capture visible light, with an infrared light sensing system.

[0003] For example, Patent Document 1 describes an imaging system for imaging a scene, the imaging system including: a camera having an image sensor for capturing images of the scene in both the visible wavelength region and the infrared wavelength region; at least one light source configured to emit a light beam for selectively illuminating the scene with infrared radiation during image capture by the camera; and an electrically controllable filter configured to transmit infrared wavelength light to the image sensor and to selectively transmit or filter visible light based on a control signal so that the visible light is received by the image sensor. The electrically controllable filter includes a polarizing filter.

[0004] Japanese Patent Application Laid-Open No. 2022-123858

[0005] The imaging system of Patent Document 1 includes a polarizing filter, but the captured image contains noise, and it is desirable to reduce the noise. An object of the present invention is to provide an imaging system that can obtain captured images with reduced noise.

[0006] In order to achieve the above-mentioned object, invention [1] is an imaging system having a light source that emits infrared rays, an imaging device that images an object irradiated with the infrared rays emitted from the light source, and a first polarizing filter that is provided between the light source and the object and that polarizes the infrared rays emitted from the light source, and the imaging device comprises, from the incident side, a lens, a second polarizing filter that polarizes the infrared rays, and an image sensor.

[0007] Invention [2] is the imaging system according to Invention [1], wherein the first polarizing filter includes a first linear polarizer, the second polarizing filter includes a second linear polarizer, and the polarization axis of the first linear polarizer and the polarization axis of the second linear polarizer are orthogonal to each other. Invention [3] is the imaging system according to Invention [1] or [2], wherein the second linear polarizer is an absorptive linear polarizer. Invention [4] is the imaging system according to Invention [2] or [3], wherein the second linear polarizer has an average transmittance of 70% or more for visible light.

[0008] Invention [5] is the imaging system according to Invention [1] or [4], in which the second polarizing filter is an optical element having an absorption axis for infrared light in an in-plane direction, and in which, when linearly polarized infrared light orthogonal to the absorption axis is irradiated from a direction tilted 45° from the normal direction at an azimuth angle orthogonal to the normal direction of the optical element and from a direction tilted 45° from the normal direction, the absorbance is greater than the absorbance when irradiated from the normal direction. Invention [6] is the imaging system according to any one of Inventions [1] to [5], in which the second polarizing filter has a haze of 1 or less. Invention [7] is the imaging system according to any one of Inventions [1] to [6], in which the object is at least one of a vehicle driver and a vehicle occupant, and is used in a vehicle interior occupant monitoring system.

[0009] Invention [8] is an imaging system comprising: a light source that emits infrared rays; an imaging device that images an object irradiated with infrared rays emitted from the light source; and a first polarizing filter that is provided between the light source and the object and that polarizes the infrared rays emitted from the light source; the imaging device comprises, from the incident side, a second polarizing filter that polarizes the infrared rays, a lens, and an image sensor; the second polarizing filter is an optical element that has an absorption axis for infrared rays in an in-plane direction, and that, when linearly polarized infrared light that is orthogonal to the absorption axis is irradiated from a direction tilted 45° from the normal direction at an azimuth angle orthogonal to the absorption axis, has a higher absorbance when irradiated from a direction tilted 45° from the normal direction than when irradiated from the normal direction. Invention [9] is an imaging system including a light source that emits infrared light, an imaging device that images an object illuminated with the infrared light emitted from the light source, and a first circular polarizing filter that circularly polarizes the infrared light emitted from the light source and is disposed between the light source and the object, the imaging device including a second circular polarizing filter that circularly polarizes the infrared light from the incident side, a lens, and an image sensor. Invention

[10] is the imaging system according to Invention [9], in which the second circular polarizing filter includes a linear polarizer and a λ / 4 plate, and the Nz factor of the λ / 4 plate is greater than 0 and less than 1. Invention

[11] is the imaging system according to Invention

[10] , in which the linear polarizer of the second circular polarizing filter is an absorptive linear polarizer. Invention

[12] is the imaging system according to Invention

[10] or

[11] , in which the linear polarizer of the second circular polarizing filter has an average transmittance of visible light of 70% or more. Invention

[13] is the imaging system according to invention [9], wherein the second polarizing filter has a haze of 1 or less.

[0010] According to the present invention, it is possible to provide an imaging system that can obtain captured images with reduced noise.

[0011] FIG. 1 is a schematic diagram showing a first example of an imaging system according to an embodiment of the present invention. FIG. 2 is a schematic diagram showing the polarization axes of a first polarizing filter and a second polarizing filter of the first example of the imaging system according to an embodiment of the present invention. FIG. 3 is a side view showing another example of the second polarizing filter of the imaging system according to an embodiment of the present invention. FIG. 4 is a plan view showing a first layer of another example of the second polarizing filter of the imaging system according to an embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing the first layer of another example of the second polarizing filter of the imaging system according to an embodiment of the present invention. FIG. 6 is a schematic cross-sectional view showing the second layer of another example of the second polarizing filter of the imaging system according to an embodiment of the present invention. FIG. 7 is a schematic perspective view illustrating a state of another example of the second polarizing filter of the imaging system according to an embodiment of the present invention when linearly polarized infrared light orthogonal to the absorption axis for infrared light existing in the in-plane direction is irradiated from the normal direction of the optical element and from a direction tilted 45° from the normal direction at an azimuth angle orthogonal to the absorption axis. FIG. 8 is a schematic diagram illustrating a mechanism by which the S / N ratio is improved for another example of the second polarizing filter of the imaging system according to an embodiment of the present invention. FIG. 9 is a plan view showing another example of the second polarizing filter of the imaging system according to an embodiment of the present invention. FIG. 1 is a cross-sectional view showing another example of a second polarizing filter of an imaging system according to an embodiment of the present invention. FIG. 2 is a schematic perspective view illustrating another example of a second polarizing filter of an imaging system according to an embodiment of the present invention when linearly polarized infrared light orthogonal to the absorption axis for infrared light existing in an in-plane direction is irradiated from a direction tilted by 45° from the normal direction at an azimuth angle orthogonal to the normal direction and the absorption axis of the optical element. FIG. 3 is a schematic diagram illustrating a mechanism by which the S / N ratio is improved for another example of a second polarizing filter of an imaging system according to an embodiment of the present invention. FIG. 4 is a schematic diagram showing a second example of an imaging system according to an embodiment of the present invention. FIG. 5 is a schematic diagram showing an example of a vehicle interior occupant monitoring system in which an imaging system according to an embodiment of the present invention is used. FIG. 6 is a schematic diagram showing an example of the configuration of a vehicle interior occupant monitoring system. FIG. 7 is a schematic diagram showing an imaging system used in examples.

[0012] The imaging system of the present invention will be described in detail below based on the preferred embodiments shown in the accompanying drawings. Note that the drawings described below are merely illustrative for explaining the present invention, and the present invention is not limited to the drawings shown below. Note that in the following, the "to" symbol indicating a range of values ​​includes the values ​​written on both sides. For example, when ε is a value ε α ~Number ε β That is, the range of ε is the number ε α and the number ε β The range includes ε α ≦ε≦ε β "Parallel" includes a generally accepted error range in the relevant technical field unless otherwise specified. Furthermore, the angles, temperatures, and times also include generally accepted error ranges in the relevant technical field unless otherwise specified. Furthermore, "visible light" refers to light with a wavelength of 400 nm or more and less than 700 nm. "Infrared light" refers to light with a wavelength of 700 nm or more and less than 2500 nm. "Ultraviolet light" refers to light with a wavelength of 10 nm or more and less than 400 nm.

[0013] [First Example of Imaging System] FIG. 1 is a schematic diagram showing a first example of an imaging system according to an embodiment of the present invention. The imaging system 10 shown in FIG. 1 includes a light source 12 that emits infrared light, an imaging device 14 that captures an image of an object 13 illuminated with the infrared light emitted from the light source 12, and a first polarizing filter 16 that is disposed between the light source 12 and the object 13 and polarizes the infrared light emitted from the light source 12. The imaging device 14 includes, from the incident side, a lens 20, a second polarizing filter 24 that polarizes the infrared light, a lens 22, and an image sensor 26. The lens 20, the second polarizing filter 24, the lens 22, and the image sensor 26 are arranged spaced apart from each other in the optical axis direction. The two lenses 20, 22, and the second polarizing filter 24 form an optical system 27. The two lenses 20, 22 are, for example, convex lenses. Therefore, light incident on the lens 20 is converted into approximately parallel light between the lens 20 and the lens 22 in the optical axis direction. The lens 22 also converges light onto the image sensor 26. That is, the lens 22 forms an image of the light incident on the lens 22 onto the image sensor 26. For this reason, the light receiving surface (not shown) of the image sensor 26 is disposed at the focal position of the lens 22.

[0014] The imaging system 10 further includes a display control unit 17 connected to the image sensor 26, a control unit 18, and a display unit 19. The control unit 18 controls the light source 12, the image sensor 26, and the display control unit 17. The control unit 18 controls the light intensity of the light source 12 and the on / off of the light source 12. The control unit 18 also controls the on / off of the image sensor 26. The image sensor 26 acquires an image signal carrying information about the object 13, as described below, and this image signal constitutes a captured image. The display control unit 17 displays a captured image based on the image signal acquired by the image sensor 26 on the display unit 19. The display of the captured image on the display unit 19 by the display control unit 17 is controlled by the control unit 18.

[0015] The display unit 19 displays the image captured by the image sensor 26, and may be any of various known displays, such as a liquid crystal display or an organic EL (Electro Luminescence) display.

[0016] The light source 12 emits infrared rays as emitted light Lo. The configuration of the light source 12 is not particularly limited as long as it can emit infrared rays. The light source 12 may be a light-emitting element such as an LED (Light Emitting Diode) or an LD (Laser Diode).

[0017] A first polarizing filter 16 is disposed on the output side of the light source 12. The surface of the first polarizing filter 16 facing the light source 12 is the back surface 16b, and the opposite surface is the front surface 16a. As long as the first polarizing filter 16 can polarize the infrared light emitted from the light source 12 as described above, it may be disposed anywhere between the light source 12 and the object 13. If the light emitted from the light source 12 Lo diverges, it is preferable to dispose the first polarizing filter 16 closer to the light source 12 between the light source 12 and the object 13.

[0018] The imaging device 14 includes, for example, two lenses 20 and 22, each with its optical axis C aligned and spaced apart in the optical axis direction. A second polarizing filter 24 is disposed between the lens 20 and the lens 22. The optical axis direction is the direction in which the optical axis C extends. Polarized output light Lo is incident on the object 13, and reflected light Li reflected by the object 13 is incident on the incident-side lens 20. The reflected light Li is light carrying information about the object 13. Between the lens 20 and the lens 22, the reflected light Li incident on the lens 20 is converted into approximately parallel light and polarized by the second polarizing filter 24. The reflected light Li is then converged by the lens 22 and focused to form an image on the light-receiving surface (not shown) of the image sensor 26. The image sensor 26 obtains an image signal carrying information about the object 13, and this image signal constitutes a captured image.

[0019] The image sensor 26 receives light carrying information about the object 13 via a light-receiving surface, converts the light into an electrical signal through photoelectric conversion, and obtains an image signal carrying the information about the object 13. This results in an image of the object 13. The image sensor 26 has a photoelectric conversion function as described above and includes, for example, a conventionally known photoelectric conversion element. The image sensor 26 may be, for example, a charge-coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor. Preferably, the image sensor 26 is sensitive to visible light as well as infrared light. This allows for the acquisition of both infrared and visible light images. The image signal carrying the information about the object 13 obtained by the image sensor 26 is output to the display control unit 17 as described above and displayed on the display unit 19.

[0020] The imaging system 10 includes, from the incident side, a lens 20, a second polarizing filter 24 that polarizes infrared light, and an image sensor 26. Reflected light Li passing through the lens 20 is polarized by the second polarizing filter 24. Therefore, light that is obliquely incident on the lens 20 is refracted as it passes through the lens 20, reducing the probability that the reflected light Li will be obliquely incident on the second polarizing filter 24. This reduces noise in the captured image, resulting in a noise-reduced captured image. On the other hand, if the second polarizing filter 24 is positioned between the lens 20 and the object 13, for example, at position Pj, light that is at an angle that is misaligned with the polarization axis of the second polarizing filter 24 (e.g., light that is obliquely incident on the second polarizing filter 24) will pass through the second polarizing filter 24. As a result, light that should be blocked by the second polarizing filter 24 will be obliquely incident on the lens 20. This obliquely incident light causes noise in the captured image. On the other hand, in the imaging system, the generation of noise that occurs when the second polarizing filter 24 is placed at the position Pj as described above is suppressed. The position Pj at which the second polarizing filter 24 is placed is referred to as the object-side position.

[0021] In the imaging system 10, the second polarizing filter 24 is disposed between the two lenses 20 and 22 in the optical axis direction, but this is not limiting. For example, the second polarizing filter 24 may be disposed between the image sensor 26 and the lens 22 facing the image sensor 26. The space between the two lenses 20 and 22 in the optical axis direction is referred to as the pupil position. Furthermore, the space between the image sensor 26 and the lens 22 facing the image sensor 26 in the optical axis direction is referred to as the image side position. Regarding the position of the second polarizing filter 24, the pupil position is preferable from the viewpoint of noise reduction because the pupil position is closer to parallel light than the image side position. On the other hand, from the viewpoint of ease of disposing the second polarizing filter 24, the image side position is preferable to the pupil position.

[0022] Furthermore, in the imaging system 10 shown in FIG. 1 , instead of the second polarizing filter 24 described above, the imaging device 14 may be configured to include a second polarizing filter 30 that polarizes infrared light from the incident side, the lens 20, and the image sensor 26. In this case, the second polarizing filter 24 described above is not provided, and the second polarizing filter 30 is disposed on the incident surface 20a side of the lens 20. The second polarizing filter 30 is an optical element that has an absorption axis for infrared light in an in-plane direction, and when linearly polarized infrared light orthogonal to the absorption axis is irradiated from the normal direction of the optical element and from a direction tilted 45° from the normal direction at an azimuth angle orthogonal to the absorption axis, the absorbance when irradiated from a direction tilted 45° from the normal direction is greater than the absorbance when irradiated from the normal direction. The second polarizing filter 30 will be described later with reference to FIG. 8 .

[0023] Furthermore, while the imaging system 10 is configured to include two lenses 20 and 22, the number of lenses is not limited to two. The lenses 20 and 22 are not limited to single lenses. For example, the lenses 20 and 22 may each be a lens group including multiple lenses, or a lens assembly including multiple lenses and optical elements. When the lenses 20 and 22 are configured as a lens group or a lens assembly, the second polarizing filter 24 is disposed between the lens groups or lens assembly in the optical axis direction. Furthermore, the lenses 20 and 22 of the imaging system 10 may be configured to include movable lenses that can move along the optical axis and have an optical magnification or focusing function.

[0024] Next, the first polarizing filter 16 and the second polarizing filter 24 will be described. FIG. 2 is a schematic diagram showing the polarization axes of the first polarizing filter and the second polarizing filter in a first example of an imaging system according to an embodiment of the present invention. FIG. 2 shows the first polarizing filter 16 and the second polarizing filter 24. The first polarizing filter 16 includes, for example, a first linear polarizer 28. The first linear polarizer 28 has a polarization axis D1. In this case, the first polarizing filter 16 is a linearly polarized polarizing filter. The second polarizing filter 24 includes a second linear polarizer 29. The second linear polarizer 29 has a polarization axis D2. In this case, the second polarizing filter 24 is a linearly polarized polarizing filter. The direction of the polarization axes D1 and D2 is the direction of linear polarization. When the first polarizing filter 16 includes the first linear polarizer 28 and when the second polarizing filter 24 includes the second linear polarizer 29, both may be configured to include an optical compensation layer, although not shown.

[0025] 2 , when the first linear polarizer 28 and the second linear polarizer 29 are viewed from the rear surface 16b of the first polarizing filter 16 facing the light source 12 and the rear surface 24b of the second polarizing filter 24 facing the image sensor 26, the polarization axis D1 of the first linear polarizer 28 and the polarization axis D2 of the second linear polarizer 29 are orthogonal to each other. In this case, infrared light emitted from the light source 12 passes through the first linear polarizer 28 and becomes linearly polarized infrared light, and the linearly polarized infrared light, i.e., the output light Lo, is irradiated onto the object 13. The linearly polarized infrared light is reflected by the object 13. The linearly polarized infrared light reflected by the object 13, i.e., the reflected light Li, passes through the lens 20, the second linear polarizer 29, and the lens 22 in this order, and is incident on the image sensor 26. At this time, the second linear polarizer 29 blocks the linearly polarized infrared light reflected by the object 13, that is linearly polarized in the direction of the polarization axis D1 of the first linear polarizer 28. Therefore, the reflected light Li that maintains its linear polarization can be removed. This reduces noise in the captured image. For example, when capturing an image of a human face, the reflected light caused by facial irregularities can be removed, allowing a high-quality captured image of the human face to be obtained. Therefore, the imaging system is suitable for, for example, a driver monitoring system, an eye tracking system, a vein authentication system, and the like. Facial irregularities include eyeglasses and the like.

[0026] When linearly polarized light is used as described above, if the second polarizing filter 24 is placed at position Pj shown in FIG. 1 , light at an angle that is misaligned with the polarization axis of the second polarizing filter 24 passes through the second polarizing filter 24, resulting in reflected light that maintains its linear polarization. This results in noise in the captured image. On the other hand, in an imaging system using linearly polarized light, the second polarizing filter 24 is placed at the pupil position or image-side position described above. Therefore, even if reflected light Li enters the lens 20 from an oblique direction, light at an angle that is misaligned with the polarization axis of the second polarizing filter 24 is prevented from entering the second polarizing filter 24. This suppresses the generation of noise that would occur if the second polarizing filter 24 were placed at position Pj as described above, resulting in a captured image with reduced noise.

[0027] The second linear polarizer 29 is preferably an absorptive linear polarizer. This suppresses reflection in the imaging device 14, thereby further reducing noise in the captured image. The second linear polarizer 29 preferably has an average visible light transmittance of 70% or more. This allows for a clear image in the visible light range to be obtained. The average visible light transmittance is more preferably 80% or more, and even more preferably 90% or more. The upper limit is not particularly limited, and is, for example, 99% or less. The average visible light transmittance is the average value of the transmittances at each wavelength across the entire visible light range, and can be measured using a spectrophotometer. More specifically, the average visible light transmittance of the second linear polarizer is determined by measuring the transmittance of the second linear polarizer at 1-nm intervals in the wavelength range of 400 nm or more and less than 700 nm using a UV-Visible-Near-Infrared Spectrophotometer (e.g., UV-Visible-Near-Infrared Spectrophotometer V-660 (JASCO Corporation)) and calculating the arithmetic average of the transmittances at each wavelength obtained. Furthermore, the second polarizing filter 24 preferably has a haze of 1 or less. This suppresses reflection in the image capture device 14, thereby further reducing noise in the captured image. The lower limit of haze is 0.1. The haze of the second polarizing filter 24 can be measured using a haze meter.

[0028] The imaging system 10 is not limited to a configuration using linearly polarized light, such as the first polarizing filter 16 including the first linear polarizer 28 and the second polarizing filter 24 including the second linear polarizer 29, as described above. For example, circularly polarized light can also be used. In this case, the first polarizing filter 16 includes a first linear polarizer 28 and a λ / 4 plate. The slow axis of the λ / 4 plate is tilted 45°±10° with respect to the polarization axis D1 of the first linear polarizer 28. This results in circularly polarized light. The second polarizing filter 24 includes a second linear polarizer 29 and a λ / 4 plate. The slow axis of the λ / 4 plate is tilted 45°±10° with respect to the polarization axis D2 of the second linear polarizer 29. This results in circularly polarized light. The λ / 4 plate converts the wavelength of incident light to λ / 4 when the output light is λ. In the case of circularly polarized light, the direction of the circular polarization is reversed upon reflection. For this reason, right-handed circularly polarized infrared light that passes through the first polarizing filter 16 becomes left-handed circularly polarized light, reversing its direction, when reflected by the object 13. For this reason, the second polarizing filter 24 must have the same configuration as the first polarizing filter 16 in order to block left-handed circularly polarized light.

[0029] [λ / 4 Plate] As the λ / 4 plate, any retardation element having a phase retardation amount equivalent to a quarter wavelength in a predetermined wavelength range can be used without limitation, including inorganic retardation plates, stretched polymer retardation plates, liquid crystal retardation plates in which a liquid crystal compound or a polymerizable liquid crystal compound is fixed in an oriented state, and metasurface retardation plates. Here, having a phase retardation amount equivalent to a quarter wavelength means that Re(550) is in the range of 120 nm to 160 nm. When acting on visible light beams, it is preferable that the plate exhibits quarter-wave characteristics over a wide band, and its wavelength dispersion preferably exhibits the relationship Re(450)<Re(550)≦Re(650), i.e., so-called reverse wavelength dispersion. The λ / 4 plate may be a single-layer film or sheet, or may exhibit its characteristics by laminating multiple films or sheets. Furthermore, it may be combined with a retardation plate using twisted alignment liquid crystal or hybrid alignment liquid crystal to exhibit the characteristics of a λ / 4 plate only for specific polarized light.

[0030] Furthermore, the λ / 4 plate is a phase difference plate that has the function of converting linearly polarized light of a specific wavelength into circularly polarized light (or circularly polarized light into linearly polarized light). More specifically, it is a plate that exhibits an in-plane retardation Re of λ / 4 (or an odd multiple thereof) at a specific wavelength λ nm. In this example, the λ / 4 plate acts as a λ / 4 plate with respect to infrared light of wavelength λ emitted by the light source 12. Note that the in-plane retardation Re(λ) of the λ / 4 plate may have an error of about 25 nm around the ideal value (λ / 4 nm).

[0031] The λ / 4 plate may be composed of a single retardation layer, or may be composed of two or more retardation layers laminated by lamination, sequential formation, or other methods. The retardation layer referred to here is a layer that exhibits optical anisotropy. Examples of the retardation layer include layers in which at least two of nx, ny, and nz are different. Note that nx represents the refractive index in the direction perpendicular to the thickness direction of the retardation layer (in-plane direction) and giving the maximum refractive index. ny represents the refractive index in the in-plane direction of the retardation layer and perpendicular to the nx direction. nz represents the refractive index in the thickness direction of the retardation layer. The λ / 4 plate may also have a support or the like that supports the retardation layer.

[0032] The material constituting the retardation layer is not particularly limited, and examples thereof include a liquid crystal compound and a polymer. A liquid crystal compound can form a retardation layer by orienting a liquid crystal material to exhibit refractive index anisotropy. A polymer can form a retardation layer by exhibiting refractive index anisotropy through stretching a polymer film obtained by casting, coating, or the like. In terms of thinness, the retardation layer is preferably a layer formed using a liquid crystal compound, and more preferably a layer formed using a liquid crystal compound having a polymerizable group.

[0033] The type of liquid crystal compound is not particularly limited. Generally, liquid crystal compounds can be classified into rod-shaped (rod-shaped liquid crystal compounds) and discotic (discotic liquid crystal compounds) based on their shape. Liquid crystal compounds can also be classified into low-molecular-weight and high-molecular-weight compounds. High-molecular-weight compounds generally refer to compounds with a degree of polymerization of 100 or more (see "Polymer Physics: Phase Transition Dynamics," by Masao Doi, p. 2, Iwanami Shoten, 1992). In the present invention, any liquid crystal compound can be used, but rod-shaped or discotic liquid crystal compounds are preferred, and rod-shaped liquid crystal compounds are more preferred. Two or more rod-shaped liquid crystal compounds, two or more discotic liquid crystal compounds, or a mixture of rod-shaped and discotic liquid crystal compounds may also be used.

[0034] Examples of rod-shaped liquid crystal compounds include those described in claim 1 of JP-A No. 11-513019 and paragraphs 0026 to 0098 of JP-A No. 2005-289980. Examples of discotic liquid crystal compounds include those described in paragraphs 0020 to 0067 of JP-A No. 2007-108732 and paragraphs 0013 to 0108 of JP-A No. 2010-244038.

[0035] The liquid crystal compound preferably has a polymerizable group. In other words, the liquid crystal compound is preferably a polymerizable liquid crystal compound. When the liquid crystal compound has a polymerizable group, the alignment state of the liquid crystal compound can be easily fixed by a curing treatment described later. The type of polymerizable group possessed by the liquid crystal compound is not particularly limited, and a functional group capable of an addition polymerization reaction is preferred, a polymerizable ethylenically unsaturated group or a ring-polymerizable group is more preferred, and a (meth)acryloyl group, a vinyl group, a styryl group, or an allyl group is even more preferred. The number of polymerizable groups possessed by the liquid crystal compound is not particularly limited, but is preferably 2 or more. The upper limit is not particularly limited, but is often 10 or less.

[0036] The liquid crystal compound forming the retardation layer preferably contains a liquid crystal compound represented by the following general formula (1).

[0037]

[0038] In the formula (1), D<linking bond> is independently a single bond, or —CO—, —O—, —S—, —C(═S)—, or —CR 1 R 2 -, -CR 3 =CR 4 -, -NR 5 -, or a divalent linking group formed by a combination of two or more thereof, R 1 ~R 5 each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 12 carbon atoms.

[0039] A 1 and A 2 Each <rigid ring> independently represents an aromatic hydrocarbon ring which may have a substituent, an aromatic heterocycle which may have a substituent, or a divalent alicyclic hydrocarbon group which may have a substituent, provided that one or more -CH2- constituting the alicyclic hydrocarbon group may be substituted with -O-, -S-, or NH-.

[0040] SP 1 and SP 2 Each <flexible chain> independently represents a single bond or a divalent aliphatic hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, provided that one or more of the methylene groups which may have a substituent and which constitute the aliphatic hydrocarbon group may be substituted with -O-, -S-, -NH-, -N(Q)- or CO-. Q represents a substituent.

[0041] L 1 and L 2 Each of the <terminal group> independently represents a monovalent organic group, 1 and L 2 At least one of the groups represents a polymerizable group, and n represents an integer of 0 or more.

[0042] Specific examples of thermotropic liquid crystals are given in paragraphs

[0129] to

[0249] of International Publication No. 2022 / 215757.

[0043] The liquid crystal compound may be a liquid crystal compound that exhibits either forward wavelength dispersion or reverse wavelength dispersion. When a retardation layer that exhibits the characteristics of a wideband λ / 4 plate as a single film is used, a liquid crystal compound that exhibits so-called reverse wavelength dispersion, in which the retardation increases with increasing wavelength, is preferred, and a liquid crystal compound that has two or more polymerizable groups and exhibits reverse wavelength dispersion is more preferred.

[0044] The λ / 4 plate preferably satisfies the following formula: 0.50<Re(450) / Re(550)<1.00

[0045] In addition, when the retardation layer is a layer formed using a liquid crystal composition containing a liquid crystal compound, the liquid crystal composition may contain a surfactant, a polymerization initiator, a crosslinking agent, and other additives in addition to the above-mentioned liquid crystal compound.

[0046] The surfactant is preferably a compound that can function as an alignment control agent that contributes to the stable or rapid alignment of the cholesteric liquid crystal phase. Examples of the surfactant include silicone surfactants and fluorine surfactants. It is also preferable to use a non-fluorine surfactant as the surfactant.

[0047] The non-fluorine-based surfactant preferably contains a siloxane unit or a long-chain alkyl group.

[0048] As described above, the retardation layer is preferably a layer formed using a liquid crystal compound having a polymerizable group, and more preferably a layer formed by fixing the orientation state of a liquid crystal compound having a polymerizable group. The orientation state that a liquid crystal compound having a polymerizable group can assume is not particularly limited, and examples thereof include homogeneous orientation, homeotropic orientation, twisted orientation, cholesteric orientation, hybrid orientation (orientation in which the tilt angle of the liquid crystal compound changes continuously from one surface to the other), and tilted orientation (orientation in which the tilt angle of the liquid crystal compound is constant from one surface to the other). Note that twisted orientation refers to an orientation state in which the liquid crystal compound is twisted around the thickness direction as the rotation axis, and when the liquid crystal compound is twisted and has a predetermined tilt angle (tilt angle greater than 0°), it corresponds to twist hybrid orientation. Note that, in this specification, twisted orientation refers to an embodiment in which the twist angle of the liquid crystal compound is less than 360°, and cholesteric orientation refers to an embodiment in which the twist angle of the liquid crystal compound is 360° or more.

[0049] The "fixed" state is a state in which the alignment of the liquid crystal compound is maintained, which is the most typical and preferred embodiment. However, it is not limited thereto, and specifically, it is more preferred that the layer has no fluidity and the alignment state is not changed by an external field or external force, and the fixed alignment state can be stably maintained, usually in a temperature range of 0 to 50°C, or under more severe conditions in a temperature range of −30 to 70°C.

[0050] The retardation layer formed using a liquid crystal compound may have a plurality of regions in the thickness direction where the liquid crystal compound has different alignment states. For example, the retardation layer may have a region in which the liquid crystal compound is fixed in a homogeneously aligned state and a region in which the liquid crystal compound is fixed in a twisted aligned state, along the thickness direction.

[0051] The thickness of the retardation layer is not particularly limited, but is preferably 0.1 to 10.0 μm, more preferably 0.5 to 5.0 μm.

[0052] The λ / 4 plate may be composed of a single retardation layer or a laminate of two or more retardation layers, for example, a combination of a λ / 4 retardation layer and a λ / 2 retardation layer. Furthermore, other retardation layers such as a positive C plate and a negative C plate may be further added to compensate for the change in retardation due to obliquely incident light.

[0053] Here, the λ / 4 plate preferably has an Nz factor greater than 0 and less than 1, more preferably 0.2 to 0.7, even more preferably 0.3 to 0.6, and even more preferably 0.5. The Nz factor is a value given by Nz = (nx - nz) / (nx - ny), where nx is the refractive index in the in-plane slow axis direction, ny is the refractive index in the direction perpendicular to the in-plane slow axis, and nz is the refractive index in the thickness direction. The refractive index nx in the in-plane slow axis direction, ny is the refractive index in the direction perpendicular to the in-plane slow axis, and nz is the refractive index in the thickness direction, and can be measured using an AxoScan or an Abbe refractometer, for example.

[0054] By setting the Nz factor of the λ / 4 plate to greater than 0 and less than 1, it is possible to compensate for changes in phase difference for light incident from an oblique direction. For example, infrared light diverged by a lens and incident on the λ / 4 plate is incident from a direction approximately perpendicular to the λ / 4 plate near the center (the position where the optical axis of the lens passes through). Therefore, the λ / 4 plate acts to impart an appropriate λ / 4 phase difference to the incident infrared light. In contrast, at positions away from the center, the infrared light is incident from an oblique direction to the λ / 4 plate, i.e., at an angle (polar angle) relative to the perpendicular to the surface of the λ / 4 plate greater than 0°. Therefore, if the Nz factor is 0, the phase difference imparted to the incident infrared light will deviate from λ / 4, and the converted infrared light may become elliptically polarized. Therefore, by setting the Nz factor to greater than 0 and less than 1, it is possible to impart a λ / 4 phase difference to infrared light incident on the λ / 4 plate from an oblique direction, thereby appropriately converting the incident infrared light into circularly polarized light.

[0055] Furthermore, polarizers having cholesteric liquid crystal layers can be used for both the first polarizing filter 16 and the second polarizing filter 24. In this case, the first polarizing filter includes a first cholesteric liquid crystal layer, and the second polarizing filter includes a second cholesteric liquid crystal layer. The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer reflect light with the same rotation direction.

[0056] FIG. 3 is a side view showing another example of the second polarizing filter of the imaging system according to the embodiment of the present invention. FIG. 4 is a plan view showing the first layer of another example of the second polarizing filter of the imaging system according to the embodiment of the present invention. FIG. 5 is a schematic cross-sectional view showing the first layer of another example of the second polarizing filter of the imaging system according to the embodiment of the present invention. Note that FIG. 5 is a cross-sectional view taken along line A-A in FIG. 4. FIG. 6 is a plan view showing the second layer of another example of the second polarizing filter of the imaging system according to the embodiment of the present invention. FIG. 7 is a schematic cross-sectional view showing the second layer of another example of the second polarizing filter of the imaging system according to the embodiment of the present invention. Note that FIG. 7 is a cross-sectional view taken along line A-A in FIG. 6. FIG. 8 is a schematic perspective view illustrating another example of the second polarizing filter of the imaging system according to the embodiment of the present invention when linearly polarized infrared light orthogonal to the absorption axis for infrared light existing in the in-plane direction is irradiated from the normal direction of the optical element and from a direction tilted 45° from the normal direction at an azimuth angle orthogonal to the absorption axis. FIG. 9 is a schematic diagram illustrating a mechanism for improving the S (signal) / N (noise) ratio for another example of the second polarizing filter of the imaging system according to the embodiment of the present invention.

[0057] The second polarizing filter 30 is an optical element having a laminated structure of, for example, a first layer 32 and a second layer 34. As will be described later, the first layer 32 and the second layer 34 contain an infrared-absorbing dichroic material, and the orientation states of the material are different.

[0058] In Fig. 4, direction X and direction Y indicate the orientations of two coordinate axes that are orthogonal to each other on the observation surface. In Fig. 5, direction X and direction Z indicate the orientations of two coordinate axes that are orthogonal to each other on the observation surface. Direction Z is parallel to the thickness direction of the first layer 32. As shown in Figs. 4 and 5, the first layer 32 contains an infrared-absorbing dichroic material N therein. Also, as shown in Figs. 4 and 5, in the first layer 32, the major axes of the infrared-absorbing dichroic material N are aligned along the Y-axis (the vertical direction on the paper surface in Fig. 4). Therefore, the first layer 32 has an absorption axis for infrared light in the in-plane direction of the Y-axis.

[0059] In FIG. 6 , the X and Y directions indicate the orientations of two coordinate axes that are orthogonal to each other on the observation surface. In FIG. 7 , the X and Z directions indicate the orientations of two coordinate axes that are orthogonal to each other on the observation surface. The Z direction is parallel to the thickness direction of the second layer 34. As shown in FIGS. 6 and 7 , the second layer 34 contains an infrared-absorbing dichroic material N therein. Also, as shown in FIGS. 6 and 7 , in the second layer 34, the major axes of the infrared-absorbing dichroic material N are aligned along the Z axis (the vertical direction in the plane of the paper in FIG. 7 ). Therefore, the second layer 34 has an absorption axis for infrared rays in the in-plane Z axis direction (i.e., the thickness direction).

[0060] The second polarizing filter 30 includes a first layer 32 having an absorption axis for infrared light in the in-plane direction and a second layer 34 having an absorption axis for infrared light in the thickness direction. As shown in FIG. 8 , the second polarizing filter 30 has an absorption axis originating from the first layer 32 in the in-plane direction, in the Y-axis direction. That is, the absorption axis is in the direction indicated by the thin black arrow. Next, the characteristics when the second polarizing filter 30 is irradiated with linearly polarized infrared light perpendicular to the absorption axis will be described. First, in the second polarizing filter 30, the direction of the linearly polarized infrared light perpendicular to the absorption axis corresponds to the X-axis direction. In the second polarizing filter 30, light is incident on the surface 34a of the second layer 34 shown in FIG. 8 and exits from the back surface 32b of the first layer 32. As shown in the direction of the white arrow in FIG. 8 , when the linearly polarized light is irradiated from the normal direction of the second polarizing filter 30, the absorption axis of the second layer 34 is parallel to the thickness direction and perpendicular to the absorption axis of the first layer 32, so the light is transmitted with little absorption. In contrast, when linearly polarized infrared light is irradiated from a direction tilted 45° from the normal direction (the direction of the thick black arrow in FIG. 8 ) at an azimuth angle orthogonal to the absorption axis of the second polarizing filter 30 (the azimuth angle indicated by the dashed line in FIG. 8 ), the absorption axis of the first layer 32 and the absorption axis of the second layer 34 intersect in a crossed Nicol configuration, so that light incident from the direction of the thick black arrow is almost entirely absorbed in the second polarizing filter 30 and not transmitted. In other words, the second polarizing filter 30 is an optical element in which the absorbance of light incident from the normal direction is greater than the absorbance of light incident from a direction tilted 45° from the normal direction. Therefore, such a second polarizing filter 30 has the function of efficiently transmitting light incident from the normal direction but not transmitting light incident from an oblique direction.

[0061] Therefore, as described above, the influence of stray light is suppressed by using the second polarizing filter 30, which includes a first layer 32 having an absorption axis for infrared rays in the in-plane direction and a second layer 34 having an absorption axis for infrared rays in the thickness direction. The mechanism is described below with reference to FIG. 9 . As described above, the second polarizing filter 30 has the function of efficiently transmitting light incident from the normal direction but blocking light incident from an oblique direction. Therefore, in the second polarizing filter 30, light reflected from the object 13 and incident on the surface 34a of the second layer 34 at an angle close to the normal direction is transmitted through the back surface 32b of the first layer 32. However, light incident on the surface 34a of the second layer 34 from an oblique direction, i.e., stray light S, is absorbed by the second polarizing filter 30. As a result, the second polarizing filter 30 has a high S / N ratio.

[0062] FIG. 10 is a plan view showing another example of a second polarizing filter of an imaging system according to an embodiment of the present invention. FIG. 11 is a cross-sectional view showing another example of a second polarizing filter of an imaging system according to an embodiment of the present invention. Note that FIG. 11 is a cross-sectional view taken along line B-B in FIG. 10. FIG. 12 is a schematic perspective view illustrating another example of a second polarizing filter of an imaging system according to an embodiment of the present invention when linearly polarized infrared light perpendicular to the absorption axis of the infrared light existing in the in-plane direction is irradiated from the normal direction of the optical element and from a direction tilted 45° from the normal direction at an azimuth angle perpendicular to the absorption axis. FIG. 13 is a schematic diagram illustrating the mechanism by which the S / N ratio is improved for another example of a second polarizing filter of an imaging system according to an embodiment of the present invention. Unlike the second polarizing filter 30 shown in FIG. 3, the second polarizing filter 36 is a single-layer optical element containing an infrared-absorbing dichroic material in a predetermined orientation, as described below. In FIG. 10, the direction X and the direction Y indicate the orientations of two coordinate axes that are orthogonal to each other on the observation surface. In FIG. 11 , directions Y and Z indicate the orientations of two coordinate axes that are orthogonal to each other on the observation surface. Direction Z is parallel to the thickness direction of the second polarizing filter 36. As shown in FIGS. 10 and 11 , the second polarizing filter 36 contains an infrared-absorbing dichroic material N therein. As shown in FIG. 10 , the long axes of the infrared-absorbing dichroic material N are aligned along the Y axis (the vertical direction of the paper in FIG. 10 ) in the in-plane direction of the second polarizing filter 36. Therefore, the second polarizing filter 36 has an absorption axis for infrared light in the Y axis direction in the in-plane direction. As shown in FIG. 11 , the infrared-absorbing dichroic material N is aligned in a disk shape in a cross section along the absorption axis. Therefore, there is no absorption anisotropy for infrared light in a cross section along the infrared absorption axis in the in-plane direction of the second polarizing filter 36.

[0063] As described above, the second polarizing filter 36 is composed of a single layer having an absorption axis for infrared rays in the in-plane direction, and is an optical element that exhibits no absorption anisotropy for infrared rays in a cross section along this absorption axis. As shown in FIG. 12 , this second polarizing filter 36 has an absorption axis in the Y-axis direction, originating from the side surface of the infrared-absorbing dichroic material N arranged in a disk shape. In other words, the absorption axis is in the direction indicated by the thin black arrow. Next, the characteristics of the second polarizing filter 36 when linearly polarized infrared rays perpendicular to the absorption axis are described. First, in the second polarizing filter 36, the direction of the linearly polarized infrared rays perpendicular to the absorption axis corresponds to the X-axis direction. Light enters the second polarizing filter 36 through the front surface 36a shown in FIG. 12 and exits through the back surface 36b.

[0064] As shown by the white arrow in Figure 12 , when the linearly polarized light is irradiated from the normal direction of the second polarizing filter 36, it is perpendicular to the absorption axis and therefore transmits with almost no absorption. In contrast, when linearly polarized infrared light is irradiated from a direction tilted 45° from the normal direction (the direction of the thick black arrow in Figure 12 ) at an azimuth angle perpendicular to the absorption axis of the second polarizing filter 36 (the azimuth angle indicated by the dashed line in Figure 5 ), there is no absorption anisotropy for infrared light in the cross section along the absorption axis, so the light incident from the direction of the thick black arrow is almost absorbed by the infrared-absorbing dichroic material N in the second polarizing filter 36 and is not transmitted. In other words, the second polarizing filter 36 is an optical element in which the absorbance of light incident from the normal direction is greater than the absorbance of light incident from a direction tilted 45° from the normal direction. Therefore, the second polarizing filter 36 has the function of efficiently transmitting light incident from the normal direction but not transmitting light incident from an oblique direction. 13, of the light reflected by the object 13, light that strikes the front surface 36a at an angle close to the normal direction of the second polarizing filter 36 is transmitted through the back surface 36b. However, light that strikes the front surface 36a from an oblique direction, i.e., stray light S, is absorbed by the second polarizing filter 36. As a result, the second polarizing filter 36 has a high S / N ratio.

[0065] The optical element having a higher absorbance for light incident from the normal direction than for light incident from a direction tilted 45° from the normal direction is not limited to the above-described configuration, and may be, for example, an optical element with a limited viewing angle, such as a louver film or a privacy film. In this case, the louver film or privacy film is used not as a standalone film but, for example, provided on the incident side of a linear polarizer.

[0066] [Second Example of Imaging System] FIG. 14 is a schematic diagram illustrating a second example of an imaging system according to an embodiment of the present invention. In the imaging system 11 shown in FIG. 14, components identical to those in the imaging system 10 shown in FIG. 1 are designated by the same reference numerals, and detailed descriptions thereof will be omitted. The imaging system 11 differs from the imaging system 10 shown in FIG. 1 in that, instead of the first polarizing filter 16, a first circular polarizing filter 60 is provided between the light source 12 and the object 13, which circularly polarizes the infrared light emitted from the light source 12. Also, instead of the second polarizing filter 24, the imaging device 14 includes, from the incident side, a second circular polarizing filter 62 that circularly polarizes the infrared light, lenses 20 and 22, and an image sensor 26. Other than these, the imaging system 11 has the same configuration as the imaging system 10 shown in FIG. 1. The first circular polarizing filter 60 that circularly polarizes the infrared light includes, for example, a linear polarizer 63 and a λ / 4 plate 64. In this case, similar to the first polarizing filter 16 described above, the slow axis of the λ / 4 plate 64 is tilted 45°±10° with respect to the polarization axis (not shown) of the linear polarizer 63. The first circular polarizing filter 60 is positioned with the linear polarizer 63 facing the light source 12. The front surface 60a of the first circular polarizing filter 60 is composed of the λ / 4 plate 64, and the back surface 60b is composed of the linear polarizer 63. In the first circular polarizing filter 60, unpolarized infrared light incident on the linear polarizer 63 is converted into circularly polarized light, and the circularly polarized infrared light is emitted from the front surface 60a. The second circular polarizing filter 62, which circularly polarizes the infrared light, includes a linear polarizer 65 and a λ / 4 plate 66, and it is preferable that the Nz factor of the λ / 4 plate 66 is greater than 0 and less than 1. In this case, similar to the second polarizing filter 24 described above, the slow axis of the λ / 4 plate 66 is tilted 45°±10° with respect to the polarization axis (not shown) of the linear polarizer 65. The second circular polarizing filter 62 is disposed with the λ / 4 plate 66 facing the incident surface 20a of the lens 20. The front surface 62a of the second circular polarizing filter 62 is composed of a linear polarizer 65, and the back surface 62b is composed of the λ / 4 plate 66. In the second circular polarizing filter 62, unpolarized infrared light incident on the linear polarizer 65 is converted into circularly polarized light, and the circularly polarized infrared light is emitted from the back surface 62b.Furthermore, the phase difference given to infrared light incident on the λ / 4 plate from an oblique direction can be set to λ / 4, and the incident infrared light can be appropriately converted into circularly polarized light.

[0067] In this case, infrared light emitted from the light source 12 passes through the first circular polarizing filter 60 and becomes circularly polarized infrared light. The circularly polarized infrared light, i.e., the emitted light Lo, is irradiated onto the object 13. The circularly polarized infrared light is reflected by the object 13. The circularly polarized infrared light reflected by the object 13, i.e., the reflected light Li, passes through the second circular polarizing filter 62, the lens 20, and the lens 22 in this order, and is incident on the image sensor 26. At this time, the second circular polarizing filter 62 converts the circularly polarized infrared light reflected by the object 13 into linearly polarized light in the polarization axis direction of the linear polarizer 65, using the linear polarizer 65. The linearly polarized light generated by the linear polarizer 65 is then converted into circularly polarized light by the λ / 4 plate 66. This allows the reflected light Li that maintains its linear polarization to be removed. This reduces noise in the captured image. For example, when capturing an image of a human face, the reflected light caused by the unevenness of the face can be removed, resulting in a high-quality captured image of the human face. 1, the imaging system 11 is suitable for, for example, a driver monitoring system, an eye tracking system, a vein authentication system, etc. The facial irregularities include eyeglasses and the like.

[0068] While the first circular polarizing filter 60 and the second circular polarizing filter 62 are illustrated as including a linear polarizer and a λ / 4 plate, the present invention is not limited thereto and may be configured as a single component as long as they can circularly polarize infrared light. The linear polarizer 65 of the second circular polarizing filter 62 is preferably an absorptive linear polarizer because it is positioned on the incident side. This suppresses reflection on the surface 62a of the second circular polarizing filter 62, thereby further reducing noise in the captured image. The linear polarizer 65 of the second circular polarizing filter 62 preferably has an average visible light transmittance of 70% or more. This allows for the acquisition of clear images in the visible light range. The average visible light transmittance of the linear polarizer is more preferably 80% or more, and even more preferably 90% or more. The upper limit is not particularly limited and may be, for example, 99% or less. Since the average visible light transmittance is as described above, a detailed description thereof will be omitted. Furthermore, the second circular polarizing filter 62 preferably has a haze of 1 or less. This suppresses reflection in the imaging device 14, thereby further reducing noise in the captured image. The lower limit of the haze is 0.1.

[0069] [Application Example of Imaging System] FIG. 15 is a schematic diagram showing an example of a vehicle interior occupant monitoring system using an imaging system according to an embodiment of the present invention. FIG. 16 is a schematic diagram showing an example of the configuration of a vehicle interior occupant monitoring system. In FIGS. 15 and 16, components identical to those in the imaging system 10 shown in FIG. 1 are designated by the same reference numerals, and detailed descriptions thereof will be omitted. FIG. 15 shows the interior of a vehicle 40. Two seats 42 are arranged side by side in the vehicle 40. A driver 43 sits in one seat 42, and an occupant sits in the other seat 42. For example, an imaging system 46 is installed on a dashboard 45 at the front of the vehicle. The imaging system 46 targets at least one of the vehicle driver and the vehicle occupant. In the example shown in FIG. 15, the target is the driver 43. When only the driver 43 is monitored, the system is called a driver monitoring system. Note that the imaging system 46 can also be positioned so that the driver 43 and the occupant 44 are within the field of view.

[0070] 1 , the imaging system 46 has a calculation unit 48, which is connected to the image sensor 26 and the display control unit 17 and controlled by the control unit 18. As described above, the imaging system 46 can remove reflected light caused by unevenness of the face, and therefore can obtain a high-quality image of the face of the driver 43. The calculation unit 48 of the imaging system 46 identifies, for example, the direction of the driver 43's face based on the image signal representing the driver 43's face obtained by the image sensor 26. To identify the direction of the driver 43's face, for example, known image recognition technology and AI (Artificial Intelligence) technology such as machine learning or deep learning are used.

[0071] The calculation unit 48 also stores criteria information in which states such as dozing and looking away are pre-associated with the direction of the driver's face. The identified direction of the driver's face is compared with the criteria information to determine the driver's state. The result of this state determination can be output to the display control unit 17 and displayed on the display unit 19. This allows the driver's state to be visually grasped. For example, known image matching technology and AI technology such as machine learning or deep learning are used to determine the driver's state. The calculation unit 48 can also perform image analysis on the captured image of the driver 43 to extract time-series brightness information and acquire pulse rate information. This allows the driver's physical state to be grasped.

[0072] Furthermore, when the imaging system is applied to eye tracking, the calculation unit 48 may detect the pupil position based on the eye position in the captured image of the face. In this case, the pupil reference position when looking straight ahead is determined in advance. The calculation unit 48 estimates the gaze of the driver 43 or the like based on the difference between the pupil position and the pupil reference position. Note that the pupil position refers to the center position of the pupil relative to the outer and inner corners of the eyes in the captured image of the face. By estimating the driver 43's gaze as described above, it is possible to estimate states such as drowsiness and looking away. When applied to eye tracking, the reflected component from the corneal surface becomes noise when detecting the pupil position. However, as described above, the reflected component from the corneal surface is blocked, and a captured image of the face with less noise can be obtained, thereby enabling the gaze of the driver 43 or the like to be estimated with high accuracy. Identifying the eye position in the captured image and detecting the pupil position can be achieved using, for example, known image recognition technology and AI technology such as machine learning or deep learning.

[0073] Furthermore, since the imaging system 10 can obtain images with little noise as described above, it can be used for vein authentication. In this case, the object is, for example, a palm. In this case, the reflected components from the palm surface also become noise, but as described above, the reflected components from the palm surface are blocked, making it possible to obtain a palm vein image with little noise. The imaging system 10 used in the driver monitoring system, eye tracking, and vein authentication described above may be configured such that the second polarizing filter 30 is disposed on the incident surface 20a of the lens 20, without providing the second polarizing filter 24 as described above. Furthermore, the imaging system 11 shown in FIG. 14 can be used in the driver monitoring system, eye tracking, and vein authentication described above.

[0074] [First Polarizing Filter and First Circular Polarizing Filter] The configuration of the first polarizing filter is not particularly limited as long as it can polarize the infrared light emitted from the light source 12 as described above, but the first polarizing filter and the second polarizing filter have the same polarization form. For example, if the first polarizing filter linearly polarizes light, the second polarizing filter also linearly polarizes light. If the first polarizing filter circularly polarizes light, i.e., in the case of a first circular polarizing filter, the second polarizing filter also circularly polarizes light. In other words, it is a second circular polarizing filter. If the first polarizing filter has a cholesteric liquid crystal layer, the second polarizing filter also has a cholesteric liquid crystal layer.

[0075] [Second Polarizing Filter and Second Circular Polarizing Filter] The second polarizing filter is not particularly limited in configuration as long as it can polarize the infrared light incident on the imaging device as described above. The second circular polarizing filter is not particularly limited in configuration as long as it can circularly polarize the infrared light incident on the imaging device as described above. The second polarizing filter and the second circular polarizing filter may be reflective or absorptive, but are preferably absorptive from the viewpoint of suppressing reflection within the imaging device 14 and suppressing noise in the captured image.

[0076] As described above, the first polarizing filter may include a first linear polarizer, and the second polarizing filter may include a second linear polarizer. Alternatively, as described above, the first circular polarizing filter may include a linear polarizer, and the second circular polarizing filter may include a linear polarizer. In this way, both the first polarizing filter and the second polarizing filter may include a linear polarizer. The linear polarizer will now be described.

[0077] (Linear Polarizer) A linear polarizer has a function of converting unpolarized infrared light into linearly polarized light. Linear polarizers are classified into reflective linear polarizers and absorptive linear polarizers. Examples of reflective linear polarizers include (i) a multilayer linearly polarized light reflector, (ii) a polarizer in which thin films with different birefringence are stacked, (iii) a wire grid polarizer, (iv) a polarizing prism, and (v) a scattering anisotropy polarizer.

[0078] (i) Examples of a multilayer linearly polarized light reflector include those formed by laminating multiple dielectric thin films having different refractive indices. To form a wavelength-selective reflective film, it is preferable to alternately laminate multiple layers of high-refractive-index dielectric thin films and low-refractive-index dielectric thin films, but the number of layers is not limited to two or more, and more than two types may be used. The number of layers is preferably 2 to 20, more preferably 2 to 12, even more preferably 4 to 10, and particularly preferably 6 to 8. If the number of layers exceeds 20, production efficiency may decrease due to multilayer vapor deposition.

[0079] There are no restrictions on the order in which the dielectric thin films are stacked, and it can be selected appropriately depending on the purpose. For example, if the refractive index of the adjacent film is high, a film with a lower refractive index is stacked first. Conversely, if the refractive index of the adjacent layer is low, a film with a higher refractive index is stacked first. The boundary between high and low refractive index is 1.8. Note that whether a refractive index is high or low is not absolute, and even among high refractive index materials, there may be materials with relatively high and low refractive indexes, and these may be used alternately.

[0080] Examples of materials for the high refractive index dielectric thin film include Sb2O3, Sb2S3, Bi2O3, CeO2, CeF3, HfO2, La2O3, Nd2O3, and Pr6O. 11 , ScO, SiO, TaO, TiO, TlCl, YO, ZnSe, ZnS, and ZrO, etc. Among these, BiO, CeO, CeF, HfO, SiO, TaO, TiO, YO, ZnSe, ZnS, and ZrO, etc. are preferred examples, and SiO, TaO, TiO, YO, ZnSe, ZnS, and ZrO, etc. are particularly preferred examples.

[0081] Examples of materials for the low refractive index dielectric thin film include Al2O3, BiF3, CaF2, LaF3, PbCl2, PbF2, LiF, MgF2, MgO, NdF3, SiO2, SiO3, NaF, ThO2, and ThF4. Among them, Al2O3, BiF ３ , CaF2, MgF2, MgO, SiO2, and Si2O3 are preferred examples, and Al2O3, CaF ２Particularly preferred examples include MgF, MgO, SiO, and SiO. The atomic ratio of the material for the dielectric thin film is not particularly limited and can be appropriately selected depending on the purpose, and the atomic ratio can be adjusted by changing the atmospheric gas concentration during film formation.

[0082] The method for forming the dielectric thin film is not limited and can be appropriately selected depending on the purpose. Examples of the film formation method include vacuum deposition methods such as ion plating and ion beam deposition, physical vapor deposition (PVD) methods such as sputtering, and chemical vapor deposition (CVD) methods. Among these, vacuum deposition and sputtering are preferred, with sputtering being particularly preferred. As a sputtering method, direct current (DC) sputtering, which has a high film formation rate, is preferred. In DC sputtering, it is preferable to use a material with high conductivity. Furthermore, methods for forming multilayer films by sputtering include, for example, (1) a single-chamber method in which films are formed alternately or sequentially from multiple targets in one chamber, and (2) a multi-chamber method in which films are formed continuously in multiple chambers. Among these, the multi-chamber method is particularly preferred from the viewpoints of productivity and preventing material contamination. There is no limitation on the thickness of the dielectric thin film, but the thickness is preferably λ / 16 to λ, more preferably λ / 8 to 3λ / 4, and even more preferably λ / 6 to 3λ / 8, on the order of optical wavelength.

[0083] Light propagating through a dielectric deposition layer is partially reflected by each dielectric thin film, resulting in multiple reflections. These reflected lights interfere with each other, allowing only light of a wavelength determined by the product of the thickness of the dielectric thin film and the refractive index of the film to be selectively transmitted. Furthermore, the central transmission wavelength of the dielectric deposition layer is angularly dependent on the incident light, and the transmission wavelength can be changed by changing the incident light.

[0084] (ii) Examples of polarizers in which thin films with different birefringences are laminated include those described in, for example, JP-A-9-506837. Specifically, polarizers can be formed using a wide variety of materials when processed under conditions selected to achieve a refractive index relationship. Generally, one of the first materials must have a refractive index different from that of the second material in a selected direction. This refractive index difference can be achieved by various methods, including stretching, extrusion molding, or coating during or after film formation. Furthermore, it is preferable that the two materials have similar rheological properties (e.g., melt viscosity) so that they can be co-extruded. Commercially available polarizers in which thin films with different birefringences are laminated can be used. Examples of commercially available polarizers include those manufactured by 3M under the trade name DBEF.

[0085] (iii) A wire-grid polarizer is a polarizer that transmits one polarized light and reflects the other polarized light due to the birefringence of thin metal wires. Wire-grid polarizers are composed of periodically arranged metal wires and are primarily used as polarizers in the terahertz wave band. In order for a wire grid to function as a polarizer, the wire spacing must be sufficiently smaller than the wavelength of the incident electromagnetic wave. In a wire-grid polarizer, the metal wires are arranged at equal intervals. Polarized light components polarized in a direction parallel to the longitudinal direction of the metal wires are reflected by the wire-grid polarizer, while polarized light components polarized in a direction perpendicular to the longitudinal direction are transmitted through the wire-grid polarizer. Commercially available wire-grid polarizers can be used. Examples of commercially available wire-grid polarizers include the Wire Grid Polarizing Filter 50x50 and NT46-636 manufactured by Edmund Optics, and WGF (registered trademark) manufactured by Asahi Kasei Corporation. For example, when a wire-grid polarizer and a louver are used in combination, the louver is provided on the incident side of the wire-grid polarizer. The wire grid polarizer is arranged so that its transmission axis is perpendicular to the light blocking axis of the louver, and the light blocking axis of the louver is oriented in a direction that blocks light incident from an oblique direction.

[0086] Examples of absorptive linear polarizers include (i) polarizers in which shape-anisotropic metal nanoparticles are fixed in an array, and (ii) polarizers in which dichroic dyes are fixed in an array. (i) Polarizers in which shape-anisotropic metal nanoparticles are fixed in an array are made by orienting and fixing silver halide particles or silver particles with a large aspect ratio. This type of polarizer is an absorptive linear polarizer that absorbs light whose electric field vibration plane is in the particle alignment direction and transmits light in a direction perpendicular to that. Examples of polarizers that can be used include those described in JP-A-59-083951, JP-A-2-248341, and JP-A-2003-139951.

[0087] (ii) Examples of polarizers with a dichroic dye aligned and fixed include polarizing films prepared by adsorbing iodine to PVA (polyvinyl alcohol) or doping a dichroic dye and stretching the resulting film. To produce polarizers in the infrared region, the film can be partially dehydrated to form polyvinylene. This polarizer absorbs light in the electric field oscillation plane during stretching and transmits light perpendicular to the electric field oscillation plane. The dichroic dye can be aligned by passing a PVA film through a dyeing composition bath containing iodine / iodide or the like to dye the PVA layer and then stretching the film 4 to 6 times. PVA can be converted to polyvinylene using a hydrochloric acid vapor method, as described in U.S. Pat. No. 2,445,555. To improve the stability of this polarizing material, boration can also be performed using an aqueous boration bath containing boric acid and borax. An example of a commercially available near-infrared linear polarizing film manufactured by Edmund Optics Japan is a comparable product.

[0088] There are no limitations on the thickness of the linear polarizer, but it is preferably from 0.05 to 300 μm, more preferably from 0.2 to 150 μm, and even more preferably from 0.5 to 100 μm.

[0089] [Second polarizing filter containing an infrared-absorbing dichroic material] The second polarizing filters 30 and 36 are specific second polarizing filters containing an infrared-absorbing dichroic material, as described above. The infrared-absorbing dichroic material will be described in detail as a component of the composition described below. The second polarizing filters 30 and 36 correspond to the LCF described below.

[0090] The thickness of the second polarizing filter described above is not particularly limited, but since it can be formed by a coating method rather than a louver film, as described in the formation method described below, it can be adjusted to 10 μm or less. The thickness of the second polarizing filter described above is preferably 0.5 to 8.0 μm, more preferably 0.5 to 6.0 μm. In this specification, the thickness of the second polarizing filter refers to the average thickness of the second polarizing filter. The average thickness is determined by measuring the thickness at any five or more locations on the second polarizing filter and calculating the arithmetic average. The thickness of the second circular polarizing filter is the same as the thickness of the second polarizing filter described above, and therefore a detailed description thereof will be omitted.

[0091] In the present invention, because the in-plane absorption characteristics and the thickness absorption characteristics can be adjusted independently, it is preferable that the second polarizing filter has a first layer containing an infrared-absorbing dichroic material and having an absorption axis for infrared light in the in-plane direction, and a second layer containing an infrared-absorbing dichroic material and having an absorption axis for infrared light in the thickness direction, as described above. Furthermore, it is preferable that the second layer has no absorption anisotropy for infrared light in the in-plane direction. Note that "no absorption anisotropy for infrared light in the in-plane direction" means that when linearly polarized infrared light is irradiated from the normal direction of the second polarizing filter over 360° while changing the azimuth angle in 5° increments, the difference between the maximum and minimum absorbance values ​​is within 5% of the maximum value.

[0092] When a visible light image is captured by the image sensor 26, it is preferable that the first layer and the second layer have an average visible light transmittance of 70% or more.

[0093] In the present invention, because coating is completed in a single layer and thinning can be easily achieved, the second embodiment described above is preferred, i.e., the second polarizing filter described above is composed of a single layer containing an infrared-absorbing dichroic material and having an infrared absorption axis in the in-plane direction, and has no infrared absorption anisotropy in a cross section along the absorption axis. Here, "no infrared absorption anisotropy" means that the following relationship is satisfied, where kx is the absorbance of the infrared absorption axis in the in-plane direction, ky is the absorbance of the infrared transmission axis in the in-plane direction, and kz is the absorbance in the thickness direction: kx = kz > ky. Furthermore, the state of "no infrared absorption anisotropy" can be evaluated as "no infrared absorption anisotropy" if there is no phase difference when a cross section along the infrared transmission axis in the in-plane direction is observed through transmission with a polarizing microscope.

[0094] In the second polarizing filter 36 (see FIG. 10 ), when the image sensor 26 captures a visible light image, it is preferable that the infrared-absorbing dichroic material be a material that does not substantially absorb visible light. Here, "a material that does not substantially absorb visible light" refers to a material that, when its transmittance is measured in the visible light region from 400 nm to less than 700 nm, does not exhibit a specific peak in this region and has a transmittance of 80% or more. In the second polarizing filter 36 (see FIG. 10 ), it is preferable that the infrared-absorbing dichroic material be a discotic dye. Note that discotic dyes will be described in detail as components of the composition below.

[0095] From the viewpoint of adjusting the alignment state of the infrared-absorbing dichroic material, the layer structure of the second polarizing filter is preferably a layer formed from a composition containing the infrared-absorbing dichroic material and a liquid crystal compound. Below, the components contained in the composition will be described in detail, and then a method for forming the layer in the second polarizing filter will be described in detail.

[0096] <Liquid Crystal Compounds> The type of liquid crystal compound is not particularly limited, but can be classified into rod-shaped types (rod-shaped liquid crystal compounds) and discotic types (discotic liquid crystal compounds) based on their shape. Each type can further be divided into low-molecular-weight types and high-molecular-weight types. A high-molecular-weight compound generally refers to a compound with a degree of polymerization of 100 or more (see "Polymer Physics / Phase Transition Dynamics," by Masao Doi, page 2, Iwanami Shoten, 1992). Two or more rod-shaped liquid crystal compounds, two or more discotic liquid crystal compounds, or a mixture of a rod-shaped liquid crystal compound and a discotic liquid crystal compound may be used. The liquid crystal compound may be a thermotropic liquid crystal compound or a lyotropic liquid crystal compound.

[0097] The position of the maximum absorption wavelength of the liquid crystal compound is not particularly limited, but it is preferably in the ultraviolet region.

[0098] As the liquid crystal compound, a liquid crystal compound having a polymerizable group (a rod-shaped liquid crystal compound or a discotic liquid crystal compound) is preferred because it can reduce changes in optical properties due to temperature and humidity. The liquid crystal compound may be a mixture of two or more types, and in that case, it is preferable that at least one of the liquid crystal compounds has two or more polymerizable groups. In other words, the layer constituting the second polarizing filter is preferably a layer formed by fixing a liquid crystal compound having a polymerizable group (a rod-shaped liquid crystal compound or a discotic liquid crystal compound) by polymerization or the like. In this case, the layer no longer needs to exhibit liquid crystallinity. The type of the polymerizable group is not particularly limited, and a polymerizable group capable of radical polymerization or cationic polymerization is preferred. As the radical polymerizable group, a known radical polymerizable group can be used, and an acryloyl group or a methacryloyl group is preferred. As the cationic polymerizable group, a known cationic polymerizable group can be used, and specific examples thereof include an alicyclic ether group, a cyclic acetal group, a cyclic lactone group, a cyclic thioether group, a spiro orthoester group, and a vinyloxy group. Among these, an alicyclic ether group or a vinyloxy group is preferred, and an epoxy group, an oxetanyl group, or a vinyloxy group is more preferred. Particularly preferred examples of the polymerizable group include the following.

[0099]

[0100] The content of the liquid crystal compound in the composition is not particularly limited, but is preferably 50% by mass or more, more preferably 70% by mass or more, based on the total solid content of the composition. The upper limit is not particularly limited, but is often 90% by mass or less. The total solid content of the composition does not include the solvent.

[0101] <Infrared-Absorbing Dichroic Substance> The infrared-absorbing dichroic substance is not particularly limited as long as it is a dichroic substance that absorbs infrared light, but is preferably a dichroic dye that absorbs infrared light. The dichroic dye refers to a dye that has different absorbance in the long axis direction of the molecule and in the short axis direction. Examples of infrared-absorbing dichroic substances include diketopyrrolopyrrole dyes, diimmonium dyes, phthalocyanine dyes, naphthalocyanine dyes, azo dyes, polymethine dyes, anthraquinone dyes, pyrylium dyes, squarylium dyes, triphenylmethane dyes, cyanine dyes, aminium dyes, metal complex dyes, boron complex dyes, oxonol dyes, rylene dyes, diphenylamine dyes, triphenylamine dyes, and quinone dyes. The infrared-absorbing dichroic substance may be used alone or in combination of two or more.

[0102] Dichroic dyes can be classified into those whose molecular shape is rod-shaped (hereinafter abbreviated as "rod-shaped dyes") and those whose molecular shape is discotic (hereinafter abbreviated as "discotic dyes"). In the first embodiment of the present invention, it is preferable to use a rod-shaped dye, and in the second embodiment of the present invention, it is preferable to use a discotic dye. Here, a discotic dye has a discotic partial structure in its core, and the discotic structure of the core portion excluding the side chain portion can be defined by the lengths a, b, and c obtained by the following (1) to (4) or the following (1), (2), and (3') to (5'). (1) For the discotic structure of the discotic dye, a molecular structure as close to a plane as possible is constructed. It is preferable to use standard values ​​corresponding to the orbital hybridization for the bond distance and bond angle. The standard values ​​are described in the Chemical Handbook, Revised 4th Edition, Basics, Vol. II, Chapter 15, edited by the Chemical Society of Japan (Maruzen, 1993). (2) Using the structure obtained in (1) above as the initial value, the structure is optimized using molecular orbital methods or molecular force field methods. Gaussian92, MOPAC93, CHARMm / QUANTA, and MM3 can be used as optimization methods. Gaussian92 is particularly preferred. (3) Each atom in the optimized discotic structure is assigned a sphere defined by the van der Waals radius, and the molecular shape is described using this sphere. (4) Let a, b, and c be the three edges of the smallest rectangular parallelepiped into which the discotic structure obtained in (3) above can fit.

[0103] To reduce arbitrariness, it is preferable to perform the following steps (3') to (5') instead of the above steps (3) and (4). (3') The center of gravity of the structure obtained by structural optimization is moved to the origin, and the coordinate axes are set to the principal axes of inertia (principal axes of the inertia tensor ellipsoid). (4') Each atom is assigned a sphere defined by the van der Waals radius, and the molecular shape is described using this. (5') The lengths in each coordinate axis direction on the van der Waals surface are measured, and these are designated as a, b, and c, respectively. When defined using a, b, and c obtained by the above procedure, a preferred discotic structure satisfies the relationships a≧b>c and a≧b≧a / 2. A more preferred discotic structure satisfies the relationships a≧b>c and a≧b≧0.7a. It is also preferable that b / 2>c.

[0104] Rod-shaped dyes are preferably azo dyes, anthraquinone dyes, perylene dyes, or mericianin dyes. For example, examples of azo dyes include those described in JP-A-11-172252, examples of anthraquinone dyes include those described in JP-A-8-067822, examples of perylene dyes include those described in JP-A-62-129380, and examples of mericianin dyes include those described in JP-A-2002-241758. These may be used alone or in combination of two or more. Examples of discotic dyes include polarizers using lyotropic liquid crystals, such as those manufactured by OPTIVA Inc., known as "E-Type polarizers." For example, materials described in JP-A-2002-090547 may be used. Similarly, there are examples of using bis-azo dichroic dyes that utilize a string-like micelle structure as a chemical structure that absorbs light in a discoid shape, such as the materials described in JP-A No. 2002-090526. These may be used alone or in combination of two or more.

[0105] Examples of discotic dyes suitable for use in the second embodiment of the present invention include compounds having a discotic skeleton specific to dyes, such as a porphyrin nucleus, a phthalocyanine nucleus, a formazan nucleus, and a triphenylmethane nucleus, and discotic dye compounds in which rod-shaped dichroic dyes, such as azo dyes, are incorporated as radial side chains into a discotic skeleton described in a discotic liquid crystal molecule, such as a benzene ring or a triphenylene ring. Furthermore, these dyes can be used in combination so as to polarize light in a desired wavelength range. The above-mentioned discotic dyes have been reported in various literatures (porphyrin nucleus: N. E. Kagen et al., J. Amer. Chem. Soc., Vol. 99, p. 5484, 1977; phthalocyanine nucleus: "28th Organic Device Workshop Sample: New Developments in Organic Phthalocyanines" (Kobayashi Nagao, p. 1); and P. A. Stuzhin et al., Inog. Chem., Vol. 37, p. 2655, 1988; formazan nucleus: Chemistry and application of leuco dyes, Plenium Press, New York, 1997, Ch. 7 Daniel S. Daniel, p. 207; and triphenylmethane nucleus: Chemistry and application of leuco dyes, Plenium Press, New York, 1997, Ch. 4 I. J. Fletcher, p. 97).

[0106] In the present invention, the infrared-absorbing dichroic substance preferably has a mesogenic group. When the infrared-absorbing dichroic substance has a mesogenic group, it is easily aligned together with the liquid crystal compound, making it easy to control the predetermined absorption characteristics. A mesogenic group is a functional group that is rigid and has alignment properties. Examples of the structure of the mesogenic group include a structure in which a plurality of groups selected from the group consisting of aromatic ring groups (aromatic hydrocarbon ring groups and aromatic heterocyclic groups) and alicyclic groups are linked together directly or via a linking group (for example, —CO—, —O—, —NR— (R represents a hydrogen atom or an alkyl group), or a group combining these).

[0107] In the present invention, a preferred embodiment of the infrared-absorbing dichroic material is a compound represented by the following formula (1). Compounds having a structure represented by the following formula (1) have low absorption in the visible light region, and the resulting optically absorptive anisotropic film is more suppressed from coloring. Furthermore, since this compound contains a group having a mesogenic group, it is easily oriented together with the liquid crystal compound. In this case, since the group having a mesogenic group is arranged so as to extend laterally from the fused ring moiety containing a nitrogen atom at the center of the compound, the fused ring moiety is easily aligned in a direction perpendicular to the slow axis of the optically absorptive anisotropic film to be formed. In other words, absorption in the infrared region (particularly, wavelengths of 700 to 900 nm) originating from the fused ring moiety is easily obtained in a direction perpendicular to the slow axis of the optically absorptive anisotropic film, and an optically absorptive anisotropic film exhibiting desired properties is easily obtained.

[0108]

[0109] R １１ and R １２ each independently represents a hydrogen atom or a substituent, at least one of which is an electron-withdrawing group; R １１ and R １２ may be bonded to form a ring. Examples of the substituent include an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an amino group, an alkoxy group, an aryloxy group, an aromatic heterocyclic oxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, an aromatic heterocyclic thio group, a sulfonyl group, a sulfinyl group, a ureido group, a phosphoric acid amide group, a hydroxy group, a mercapto group, a halogen atom, a cyano group, a sulfo group, a carboxyl group, a nitro group, a hydroxamic acid group, a sulfino group, a hydrazino group, an imino group, a heterocyclic group, and a silyl group.

[0110] The electron-withdrawing group represents a substituent with a positive Hammett σp value (sigma para value), and examples thereof include a cyano group, an acyl group, an alkyloxycarbonyl group, an aryloxycarbonyl group, a sulfamoyl group, a sulfinyl group, and a heterocyclic group. These electron-withdrawing groups may be further substituted. The Hammett substituent constant σ value will be explained. Hammett's rule is an empirical rule proposed by L. P. Hammett in 1935 to quantitatively discuss the influence of substituents on the reaction or equilibrium of benzene derivatives, and is now widely recognized as valid. The substituent constants calculated by Hammett's rule include σp and σm values, and these values ​​can be found in many general textbooks. For example, see J. A. This is described in detail in, for example, "Lange's Handbook of Chemistry," edited by Dean, 12th edition, 1979 (McGraw-Hill); "Chemical Domain," special edition, No. 122, pp. 96-103, 1979 (Nankodo); and Chem. Rev., Vol. 91, pp. 165-195, 1991. In the present invention, the electron-withdrawing group is preferably a substituent having a Hammett's substituent constant σp value of 0.20 or more. The σp value is preferably 0.25 or more, more preferably 0.30 or more, and even more preferably 0.35 or more. There is no particular upper limit, but it is preferably 0.80 or less. Specific examples include a cyano group (0.66), a carboxyl group (-COOH: 0.45), an alkoxycarbonyl group (-COOMe: 0.45), an aryloxycarbonyl group (-COOPh: 0.44), a carbamoyl group (-CONH ２ : 0.36), alkylcarbonyl group (-COMe: 0.50), arylcarbonyl group (-COPh: 0.43), alkylsulfonyl group (-SO ２ Me: 0.72), and an arylsulfonyl group (—SO ２ In this specification, Me represents a methyl group, and Ph represents a phenyl group. The values ​​in parentheses are the σp values ​​of representative substituents, excerpted from Chem. Rev., 1991, Vol. 91, pp. 165-195.

[0111] R １１ and R １２When R are bonded to form a ring, they form a 5- to 7-membered ring (preferably a 5- or 6-membered ring), and the ring formed is preferably one that is normally used as an acidic nucleus in a merocyanine dye. １１ and R １２ are bonded to each other, a 1,3-dicarbonyl nucleus, a pyrazolinone nucleus, a 2,4,6-triketohexahydropyrimidine nucleus (including thioketones), a 2-thio-2,4-thiazolidinedione nucleus, a 2-thio-2,4-oxazolidinedione nucleus, a 2-thio-2,5-thiazolidinedione nucleus, a 2,4-thiazolidinedione nucleus, a 2,4-imidazolidinedione nucleus, a 2-thio-2,4-imidazolidinedione nucleus, a 2-imidazolin-5-one nucleus, a 3,5-pyrazolidinedione nucleus, a benzothiophen-3-one nucleus, or an indanone nucleus is preferred.

[0112] R １１ is preferably a heterocyclic group. The heterocyclic group is preferably a pyrazole ring group, a thiazole ring group, an oxazole ring group, an imidazole ring group, an oxadiazole ring group, a thiadiazole ring group, a triazole ring group, a pyridine ring group, a pyridazine ring group, a pyrimidine ring group, a pyrazine ring group, a benzo-fused ring group or a naphtho-fused ring group thereof, or a complex of these fused rings.

[0113] R １３ each independently represents a hydrogen atom, an alkyl group, an aryl group, a heteroaryl group, a substituted boron group, or a metal atom; R １１ may be covalently or coordinately bonded to R １３ The substituent of the substituted boron represented by R １１ and R １２ is the same as the substituent described above, and an alkyl group, an aryl group, or a heteroaryl group is preferred. １３ The metal atom represented by the formula (I) is preferably a transition metal atom, a magnesium atom, an aluminum atom, a calcium atom, a barium atom, a zinc atom, or a tin atom, and more preferably an aluminum atom, a zinc atom, a tin atom, a vanadium atom, an iron atom, a cobalt atom, a nickel atom, a copper atom, a palladium atom, an iridium atom, or a platinum atom.

[0114] R １４R each independently represents a group having a mesogenic group. The definition of a mesogenic group is as described above. １４ is preferably a group represented by the following formula (2): * represents a bonding position. Formula (2) *-M １ -(X １ -M ２ ) ｎ -X ２ -P.M. １ represents a substituted or unsubstituted arylene group or a substituted or unsubstituted heteroarylene group. Examples of the arylene group include a phenylene group. X １ and X ２ each independently represents a single bond, —O—, —CO—, or —CH ２ -, -CH=CH-, -C≡C-, -NR ０ -, or a combination thereof (for example, -O-CO- and -CH ２ -CH ２ -) represents. ０ represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms. ２ represents a substituted or unsubstituted arylene group, a substituted or unsubstituted heteroarylene group, or a substituted or unsubstituted cycloalkylene group. n represents 1 to 5, and preferably 2 to 4. P represents a hydrogen atom or a polymerizable group. The definition of the polymerizable group is the same as the definition of the polymerizable group that the liquid crystal compound may have.

[0115] A preferred embodiment of the infrared absorbing dichroic material is an oxonol dye, and the oxonol dye is preferably a compound represented by formula (11).

[0116]

[0117] In formula (11), Y １ and Y ２ each independently represents a non-metallic atomic group forming an aliphatic ring or a heterocyclic ring; M ＋ represents a proton, a monovalent alkali metal cation, or an organic cation; L １ represents a methine chain consisting of 5 or 7 methine groups, and the central methine group of the methine chain has a substituent represented by the following formula A,Ａ -T Ａ Formula (A) In formula (A), S Ａ represents a single bond, an alkylene group, an alkenylene group, an alkynylene group, —O—, —S—, —NR Ｌ１ -, -C(=O)-, -C(=O)O-, -C(=O)NR Ｌ１ -, -S(=O) ２ -, -OR Ｌ２ - or a group formed by combining these, R Ｌ１ represents a hydrogen atom, a halogen atom, an alkyl group, an aryl group, or a heteroaryl group; R Ｌ２ represents an alkylene group, an arylene group, or a divalent heterocyclic group; T Ａ represents a halogen atom, an alkyl group, a cycloalkyl group, an aryl group, a heteroaryl group, a cyano group, a hydroxy group, a formyl group, a carboxy group, an amino group, a thiol group, a sulfo group, a phosphoryl group, a boryl group, a vinyl group, an ethynyl group, a trialkylsilyl group, or a trialkoxysilyl group; S Ａ represents a single bond or an alkylene group, and T Ａ When represents an alkyl group, S Ａ and T Ａ The total number of carbon atoms contained in is 3 or more, and * represents the bonding site with the central methine group of the methine chain.

[0118] As the oxonol dye, a compound represented by formula (12) is more preferred.

[0119]

[0120] In formula (12), M ＋ and L １ is M in formula (11). ＋ and L １ It is the same as R ｍ１ , R ｍ２ , R ｍ３ and R ｍ４ each independently represents a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group, and each X independently represents an oxygen atom, a sulfur atom, or a selenium atom.

[0121] As the oxonol dye, a compound represented by formula (13) is more preferred.

[0122]

[0123] In formula (13), M ＋ , L １ and X is M in formula (11). ＋ , L １ and X. ｎ１ , and R ｎ３ each independently represents a hydrogen atom, an alkyl group, an aryl group, or a heteroaryl group; R ｎ２ , and R ｎ４ each independently represents an alkyl group, a halogen atom, an alkenyl group, an aryl group, a heteroaryl group, a nitro group, a cyano group, or —OR Ｌ３ , -C(=O)R Ｌ３ , -C(=O)OR Ｌ３ , —OC(═O)R Ｌ３ , -N(R Ｌ３ ) ２ , -NHC(=O)R Ｌ３ , -C(=O)N(R Ｌ３ ) ２ , -NHC(=O)OR Ｌ３ , -OC(=O)N(R Ｌ３ ) ２ , -NHC(=O)N(R Ｌ３ ) ２ , -SR Ｌ３ , -S(=O) ２ R Ｌ３ , -S(=O) ２ OR Ｌ３ , -NHS(=O) ２ R Ｌ３ , or -S(=O) ２ N (R Ｌ３ ) ２ represents R Ｌ３ each independently represents a hydrogen atom, an alkyl group, an alkenyl group, an aryl group, or a heteroaryl group; and each n independently represents an integer of 1 to 5.

[0124] A preferred embodiment of the infrared absorbing dichroic substance is a cyanine dye, and the cyanine dye is preferably a compound represented by formula (3) or a compound represented by formula (4).

[0125]

[0126]

[0127] In formula (3), Ar ３ ~Ar ４ each independently represents a heterocyclic group which may have a substituent, R ｃ１ represents a hydrogen atom or a substituent. ３ and Ar ４ At least one of the groups preferably represents a heterocyclic group having a substituent containing a hydrophilic group (hereinafter also referred to as a "specific substituent"). Examples of the hydrophilic group include an acid group or a salt thereof, an onium salt, a hydroxy group or a salt thereof, a sulfonamide group (H ２ N-SO ２ -) or a salt thereof, and a group containing a polyoxyalkylene group are exemplified, and an acid group or a salt thereof is preferred. Examples of the acid group or a salt thereof include a sulfo group (-SO ３ H) or a salt thereof (—SO ３ － M ＋ .M ＋ represents a cation, and a carboxyl group (—COOH) or a salt thereof (—COO － M ＋ .M ＋ represents a cation.) Examples of heterocyclic rings constituting the heterocyclic group include an indolenine ring, a benzoindolenine ring, an imidazole ring, a benzimidazole ring, a naphthoimidazole ring, a thiazole ring, a benzothiazole ring, a naphthothiazole ring, a thiazoline ring, an oxazole ring, a benzoxazole ring, a naphthoxazole ring, an oxazoline ring, a selenazole ring, a benzoselenazole ring, a naphthoselenazole ring, and a quinoline ring, with an indolenine ring, a benzoindolenine ring, a benzothiazole ring, or a naphthothiazole ring being preferred. The specific substituent may be substituted on a heteroatom or a carbon atom in the heterocyclic ring. The heterocyclic group may have one or more (e.g., 2 to 3, etc.) specific substituents.

[0128] r ｃ１ represents an integer of 1 to 7, preferably an integer of 3 to 5.

[0129] Rｃ１ The type of the substituent represented by is not particularly limited, and includes known substituents, preferably an alkyl group which may have a substituent, an aryl group which may have a substituent, or a heteroaryl group which may have a substituent. Examples of the substituent that the alkyl group, aryl group, and heteroaryl group may have include an alkyl group, an alkenyl group, an alkynyl group, an aryl group, an alkoxy group, an aryloxy group, an aromatic heterocyclic oxy group, an acyl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an acyloxy group, an acylamino group, an alkoxycarbonylamino group, an aryloxycarbonylamino group, a sulfamoyl group, a carbamoyl group, an alkylthio group, an arylthio group, an aromatic heterocyclic thio group, a ureido group, a halogen atom, a cyano group, a nitro group, a heterocyclic group (e.g., a heteroaryl group), a silyl group, and a group combining these (hereinafter, these groups are collectively referred to as "substituent W"). The above substituent may be further substituted with a substituent W.

[0130] In formula (4), Ar ５ ~Ar ６ each independently represents a heterocyclic group which may have a substituent, Ar ７ represents a cyclic skeleton having 5 to 7 carbon atoms, and W represents a hydrogen atom, a halogen atom, a methyl group, a phenyl group which may have a substituent, a benzyl group which may have a substituent, a pyridyl group, a morpholyl group, a piperidyl group, a pyrrolidyl group, a phenylamino group which may have a substituent, a phenoxy group which may have a substituent, an alkylthio group which may have a substituent, or a phenylthio group which may have a substituent. ５ and Ar ６Preferably, at least one of the groups represents a heterocyclic group having a specific substituent. Examples of heterocyclic rings constituting the heterocyclic group include an indolenine ring, a benzoindolenine ring, an imidazole ring, a benzimidazole ring, a naphthoimidazole ring, a thiazole ring, a benzothiazole ring, a naphthothiazole ring, a thiazoline ring, an oxazole ring, a benzoxazole ring, a naphthoxazole ring, an oxazoline ring, a selenazole ring, a benzoselenazole ring, a naphthoselenazole ring, and a quinoline ring. An indolenine ring, a benzoindolenine ring, a benzothiazole ring, or a naphthothiazole ring is preferred. Examples of the substituents that the phenyl group, benzyl group, phenylamino group, phenoxy group, alkylthio group, and phenylthio group represented by W may have include the groups exemplified for the substituent W above, hydrophilic groups, and specific substituents. The number of carbon atoms in the alkylthio group represented by W is not particularly limited, but is preferably 1 to 5, and more preferably 1 to 3.

[0131] The compound represented by formula (4) is preferably an intramolecular salt type having a cation and an anion in one molecule, or an intermolecular salt type, and in the case of an intermolecular salt type, examples thereof include organic salts such as halide salts, perchlorate salts, antimony fluoride salts, phosphate fluoride salts, boron fluoride salts, trifluoromethanesulfonate salts, bis(trifluoromethane)sulfonimide salts, and naphthalenesulfonic acid salts. Specific examples thereof include indocyanine green and the water-soluble dyes described in JP-A-63-033477.

[0132] The compound represented by formula (4) is preferably a compound represented by formula (4-1).

[0133]

[0134] In formula (4-1), R ｃ２ ~R ｃ５ R each independently represents a hydrogen atom or a substituent. ｃ２ ~R ｃ５ At least one of the ３ － Substituents having the formula (e.g., —SO ３ －The alkyl group preferably has 1 to 10 carbon atoms.), —COO － Substituents having the formula (e.g., —COO － The alkyl group preferably has 1 to 10 carbon atoms.), —SO ３ － , or -COO － It is preferred that R ｃ R each independently represents a hydrogen atom or a substituent. ｃ Examples of the substituent represented by Ar include the groups exemplified as the substituent W, and an alkyl group is preferred. The number of carbon atoms in the alkyl group is preferably 1 to 5. ｃ１ and Ar ｃ２ each independently represents an aromatic hydrocarbon ring (e.g., a benzene ring or a naphthalene ring), and Ar ７ represents a cyclic skeleton having 5 to 7 carbon atoms; W represents a hydrogen atom, a halogen atom, a methyl group, an optionally substituted phenyl group, an optionally substituted benzyl group, a pyridyl group, a morpholyl group, a piperidyl group, a pyrrolidyl group, an optionally substituted phenylamino group, an optionally substituted phenoxy group, an optionally substituted alkylthio group, or an optionally substituted phenylthio group; r ｃ２ represents an integer of 1 to 3, and r ｃ３ represents an integer of 1 to 3. ｃ２ ~R ｃ５ Examples of the substituent represented by the formula (I) include the groups exemplified as the substituent W and specific substituents. Examples of the substituent that the phenyl group, benzyl group, phenylamino group, phenoxy group, alkylthio group, and phenylthio group represented by W may have include the groups exemplified as the substituent W and specific substituents.

[0135] The content of the infrared absorbing dichroic substance in the composition is not particularly limited, but in terms of achieving better effects of the present invention, it is preferably 5 to 70% by mass, and more preferably 10 to 50% by mass, based on the total mass of the liquid crystal compound.

[0136] <Other Components> The composition described above may contain components other than the liquid crystal compound and infrared-absorbing dichroic material described above. The composition may also contain a polymerization initiator. The polymerization initiator used is selected depending on the type of polymerization reaction, and examples include thermal polymerization initiators and photopolymerization initiators. Examples of photopolymerization initiators include α-carbonyl compounds, acyloin ethers, α-hydrocarbon-substituted aromatic acyloin compounds, polynuclear quinone compounds, and combinations of triarylimidazole dimers and p-aminophenyl ketones. The content of the polymerization initiator in the composition is preferably 0.01 to 20% by mass, more preferably 0.5 to 10% by mass, based on the total solids content of the composition.

[0137] The composition may also contain a polymerizable monomer. Examples of the polymerizable monomer include radically polymerizable or cationically polymerizable compounds. Among these, polyfunctional radically polymerizable monomers are preferred. Examples of the polymerizable monomer include monomers copolymerizable with the liquid crystal compound having the above-mentioned polymerizable group. Examples include the polymerizable monomers described in paragraphs

[0018] to

[0020] of JP-A No. 2002-296423. The content of the polymerizable monomer in the composition is preferably 1 to 50% by mass, more preferably 2 to 30% by mass, based on the total mass of the liquid crystal compound.

[0138] The composition may also contain a surfactant. Examples of surfactants include conventionally known compounds, but fluorine-based compounds are preferred. Examples include the compounds described in paragraphs

[0028] to

[0056] of JP-A No. 2001-330725 and the compounds described in paragraphs

[0069] to

[0126] of Japanese Patent Application No. 2003-295212.

[0139] The composition may also contain a solvent. The solvent is preferably an organic solvent. Examples of organic solvents include amides (e.g., N,N-dimethylformamide), sulfoxides (e.g., dimethyl sulfoxide), heterocyclic compounds (e.g., pyridine), hydrocarbons (e.g., benzene, hexane), alkyl halides (e.g., chloroform, dichloromethane), esters (e.g., methyl acetate, ethyl acetate, butyl acetate), ketones (e.g., acetone, methyl ethyl ketone), and ethers (e.g., tetrahydrofuran, 1,2-dimethoxyethane). Two or more types of organic solvents may be used in combination.

[0140] The composition may also contain various alignment control agents such as a vertical alignment agent and a horizontal alignment agent. These alignment control agents are compounds that can control the alignment of the liquid crystal compound horizontally or vertically on the interface side. Furthermore, the composition may contain an adhesion improver, a plasticizer, and a polymer in addition to the above-mentioned components.

[0141] <Formation Method> The method for forming the second polarizing filter using the above-mentioned composition is not particularly limited, and known methods can be used. Among them, from the viewpoint of easy control of in-plane retardation, a method is preferred in which a composition containing a liquid crystal compound having a polymerizable group (hereinafter also simply referred to as a "polymerizable liquid crystal compound") and an infrared-absorbing dichroic substance is applied to form a coating film, the coating film is subjected to an alignment treatment to align the polymerizable liquid crystal compound, and the resulting coating film is subjected to a curing treatment (irradiation with ultraviolet rays (light irradiation treatment) or heat treatment) to form a light-absorbing anisotropic film. The steps of the above-mentioned method are described in detail below.

[0142] First, a composition is applied to a support to form a coating film, and the coating film is subjected to an alignment treatment to align the polymerizable liquid crystal compound. The composition used contains a polymerizable liquid crystal compound. The definition of the polymerizable liquid crystal compound is as described above.

[0143] The support used is a member that functions as a substrate for applying the composition. The support may be a temporary support that is peeled off after the composition is applied and cured. In addition to a plastic film, a glass substrate may also be used as the support (temporary support). Examples of materials that constitute the plastic film include polyester resins such as polyethylene terephthalate (PET), polycarbonate resins, (meth)acrylic resins, epoxy resins, polyurethane resins, polyamide resins, polyolefin resins, cellulose derivatives, silicone resins, and polyvinyl alcohol (PVA). The thickness of the support may be approximately 5 to 1000 μm, preferably 10 to 250 μm, and more preferably 15 to 90 μm.

[0144] If necessary, an alignment layer may be disposed on the support. The alignment layer generally contains a polymer as its main component. Polymers for alignment layers are described in many literatures, and many commercially available products are available. As the polymer for alignment layers, polyvinyl alcohol, polyimide, or derivatives thereof are preferred. The alignment layer is preferably subjected to a known rubbing treatment. The thickness of the alignment layer is preferably 0.01 to 10 μm, more preferably 0.01 to 1 μm.

[0145] Examples of the method for applying the composition include curtain coating, dip coating, spin coating, print coating, spray coating, slot coating, roll coating, slide coating, blade coating, gravure coating, and wire bar coating. In any case, single-layer application is preferred.

[0146] The coating film formed on the support is subjected to an alignment treatment to align the polymerizable liquid crystal compound in the coating film. The alignment treatment can be performed by drying the coating film at room temperature or by heating the coating film. In the case of a thermotropic liquid crystal compound, the liquid crystal phase formed by the alignment treatment can generally be transitioned by changes in temperature or pressure. In the case of a lyotropic liquid crystal compound, the transition can also be achieved by adjusting the composition ratio, such as the amount of solvent. The conditions for heating the coating film are not particularly limited, but the heating temperature is preferably 50 to 250°C, more preferably 50 to 150°C, and the heating time is preferably 10 seconds to 10 minutes. After heating the coating film, the coating film may be cooled, if necessary, before the curing treatment (light irradiation treatment) described below. The cooling temperature is preferably 20 to 200°C, more preferably 30 to 150°C. The difference between the heating temperature and the cooling temperature of the coating film described above is not particularly limited, but is preferably 40°C or higher. The upper limit is not particularly limited, but may be 150°C or lower. In particular, when the coating film is heated and cooled before the curing treatment, the heating temperature T Ａ is 50 to 250°C, and the cooling temperature T Ｂ is the heating temperature T Ａ ×0.4~Heating temperature T Ａ It is preferable that the range is 0.7×.

[0147] Next, the coating film in which the polymerizable liquid crystal compound has been aligned is subjected to a curing treatment. The method of curing the coating film in which the polymerizable liquid crystal compound has been aligned is not particularly limited, and examples thereof include light irradiation treatment and heat treatment. Among these, from the viewpoint of manufacturability, light irradiation treatment is preferred, and ultraviolet irradiation treatment is more preferred. The irradiation conditions for the light irradiation treatment are not particularly limited, but are preferably 50 to 1000 mJ / cm. ２ The irradiation dose is preferably 1000 ppm or more.

[0148] In the above-mentioned forming method, by adjusting various conditions, it is possible to adjust the arrangement state of the infrared-absorbing dichroic material, and as a result, the optical properties of the light-absorbing anisotropic film. For example, by adjusting the heating temperature when orienting the liquid crystal compound after applying the composition to a support to form a coating film, and the cooling temperature when cooling after heating, it is possible to adjust the arrangement state of the infrared-absorbing dichroic material, and as a result, the optical properties of the light-absorbing anisotropic film. Note that the second circular polarizing filter can be formed by the same forming method as the above-mentioned second polarizing filter, and therefore a detailed description thereof will be omitted.

[0149] The present invention is basically configured as described above. Although the imaging system of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the spirit and scope of the present invention.

[0150] The features of the present invention will be explained in more detail below with reference to examples. The materials, reagents, amounts and proportions of substances, and procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention is not limited to the following examples. In these examples, noise in captured images was evaluated for the imaging systems of Examples 1 to 11 and Comparative Examples 1 and 2 below. The results are shown in Table 1 below.

[0151] The imaging systems of Examples 1 to 11 and Comparative Examples 1 and 2 use the imaging system 10 shown in FIG. 1 , but differ in the type and position of the second polarizing filter. An LED lamp with a wavelength of 850 nm (WindFire Mini IR Lamp Zoomable 5W 850nm / 940nm LED Infrared Flashlight Night Vision) was used as the light source 12. A camera with a lens attached was used as the imaging device 14. The lens used was a Lensation B5M6018 (manufactured by iDS), 6 mm, 1 / 2.5". The camera used was a daA3840-45uc (manufactured by Basler). The imaging systems of Examples 1 to 11 and Comparative Examples 1 and 2 will be described.

[0152] Example 1 In Example 1, a second polarizing filter 24 was arranged at the pupil position of the imaging system 10 shown in FIG. 1. The following LCF was used for the second polarizing filter 24. The LCF had a haze of 0.8. The LCF will be described below. The LCF is an absorptive linear polarizer.

[0153] (LCF) A cellulose acylate film T1 ("TD40UL" manufactured by Fujifilm Corporation) was passed through a dielectric heating roll at a temperature of 60°C to raise the surface temperature of the film to 40°C. Thereafter, an alkaline solution having the composition shown below was applied to one side of the film using a bar coater in an amount of 14 ml / m. ２ The film was then heated to 110°C. The resulting film was then transported under a steam-type far-infrared heater manufactured by Noritake Co., Ltd. for 10 seconds. Next, using the same bar coater, pure water was applied to the surface of the film at a rate of 3 ml / m. ２ Next, the obtained film was washed with water using a fountain coater and then drained with an air knife three times, and then the film was transported to a drying zone at 70°C for 10 seconds and dried, thereby preparing an alkali-saponified cellulose acylate film as a support.

[0154] ---------------------------------------------------------------- (Alkaline solution) ---------------------------------------------------------------- Potassium hydroxide 4.7 parts by mass Water 15.8 parts by mass Isopropanol 63.7 parts by mass Surfactant (C １４ H ２９ O (CH ２ CH ２ O) ２０ H) 1.0 part by mass Propylene glycol 14.8 parts by mass

[0155] An alignment layer coating solution having the following composition was continuously applied to the support using a #14 wire bar. The support on which the coating film was formed was then dried with hot air at 60°C for 60 seconds and then with hot air at 100°C for 120 seconds. The dried coating film was then continuously subjected to a rubbing treatment to form an alignment layer. At this time, the longitudinal direction of the long film was parallel to the transport direction, and the rotation axis of the rubbing roller was at an angle of 45° clockwise relative to the longitudinal direction of the film.

[0156] ------------------------------------------------------------------ (Alignment layer coating liquid) ------------------------------------------------------------------ Modified polyvinyl alcohol (listed below) 10.0 parts by mass Water 371.0 parts by mass Methanol 119.0 parts by mass Glutaraldehyde 0.5 parts by mass Polymerization initiator (Irgacure 2959, manufactured by BASF) 0.3 parts by mass ------------------------------------------------------------------

[0157] Modified polyvinyl alcohol (in the structural formula below, the ratios are molar ratios)

[0158] The following coating liquid for an optically absorptive anisotropic film was prepared. ------------------------------------------------ (Coating liquid for optically absorptive anisotropic film) ------------------------------------------------ - Liquid crystal compound L-1 (shown below) 80 parts by mass - Infrared absorbing dye IR-2 20 parts by mass - Photopolymerization initiator 1 (Irgacure OXE01, manufactured by BASF) 3.0 parts by mass - Photopolymerization initiator 2 (Irgacure 184, manufactured by BASF) 3.0 parts by mass - Fluorine-containing compound F-1 (shown below) 0.2 parts by mass - Cyclopentanone 227.1 parts by mass ------------------------------------------------

[0159] Liquid crystal compound L-1 (a mixture of the following three compounds. The mixing ratio is shown in the upper left corner of the compound.)

[0160] Infrared absorbing dye IR-2

[0161] Fluorine-containing compound F-1

[0162] The coating solution for the optically absorbing anisotropic film was applied onto the alignment layer with a wire bar to form a coating film, which was then heated at 100° C. for 5 minutes and cooled to 60° C. Thereafter, the atmosphere was purged with nitrogen so that the oxygen concentration was 1.0% by volume or less, and a high-pressure mercury lamp was used to irradiate the film with an irradiation dose of 500 mJ / cm. ２ The coating film was irradiated with ultraviolet light of 1000 kJ / cm to prepare an LCF. The thickness of the obtained LCF (excluding the support and the alignment layer) was 5 μm.

[0163] Example 2 Example 2 was the same as Example 1 except that, compared to Example 1, a light-absorbing anisotropic film 1 was provided instead of the LCF. The light-absorbing anisotropic film 1 had a haze of 0.8. The light-absorbing anisotropic film 1 was an absorptive linear polarizer. The light-absorbing anisotropic film 1 will be described below.

[0164] (Lightly absorbing anisotropic film 1) Composition 1 was prepared having the following composition: Composition 1: Rod-like compound I-1 10 parts by mass Infrared absorbing dye IR-1 1 part by mass Water 89 parts by mass

[0165] Rod-shaped compound I-1 (see structural formula below)

[0166]

[0167] Infrared absorbing dye IR-1 (see structural formula below)

[0168]

[0169] The above-prepared composition 1 (5 g) and zirconia beads (20 g) with an average particle size of 2 mm were filled into a 45 mL zirconia container and milled for 50 minutes at 300 rpm (revolutions per minute) using a FRISCH P-7 Classic Line planetary ball mill. The milled composition 1 was applied to a glass substrate as a substrate using a wire bar (movement speed: 100 cm / s) and then air-dried. The resulting composition layer was then immersed in a 1 mol / L aqueous calcium chloride solution for 5 seconds, washed with ion-exchanged water, and blown dry to fix the orientation, thereby producing a 1.2 μm-thick optically absorbing anisotropic film 1.

[0170] Example 3 Example 3 was the same as Example 1 except that, compared to Example 1, the second polarizing filter was positioned closer to the image side. Example 4 Example 4 was the same as Example 2 except that, compared to Example 2, the second polarizing filter was positioned closer to the image side.

[0171] Example 5 Example 5 was the same as Example 1, except that a wire-grid polarizer and a louver were used instead of the LCF of the second polarizing filter. The wire-grid polarizer was a reflective linear polarizer. WGF (registered trademark) manufactured by Asahi Kasei Corporation was used as the wire-grid polarizer. A louver manufactured by 3M was used as the louver. The wire-grid polarizer is denoted as "WG" in Table 1. The combination of the wire-grid polarizer and the louver is denoted as "WG + louver" in Table 1. In Example 5, the lens 20, louver, wire-grid polarizer, and lens 22 were arranged in this order. The transmission axis of the wire-grid polarizer and the light-blocking axis of the louver were arranged orthogonal to each other. The light-blocking axis of the louver was arranged in a direction that cuts off light incident from an oblique direction.

[0172] (Example 6) Example 6 was the same as Example 5, except that a louver was not provided, as compared to Example 5. (Example 7) Example 7 was the same as Example 6, except that a second polarizing filter was positioned on the image side, as compared to Example 6. (Example 8) Example 8 was the same as Example 2, except that light-absorbing anisotropic film 2 was used instead of light-absorbing anisotropic film 1 of the second polarizing filter, as compared to Example 2. Light-absorbing anisotropic film 2 will be described below. Light-absorbing anisotropic film 2 had a haze of 3.

[0173] (Lightly Absorbent Anisotropic Film 2) Lightly absorptive anisotropic film 2 was produced in the same manner as lightly absorptive anisotropic film 1, except that the milling treatment time of lightly absorptive anisotropic film 1 was changed to 5 minutes. Like lightly absorptive anisotropic film 1, lightly absorptive anisotropic film 2 is an absorptive linear polarizer.

[0174] (Example 9) Example 9 was the same as Example 1, except that the second polarizing filter was positioned on the object side, i.e., on the object 13 side of lens 20 shown in FIG. 1 . (Example 10) Example 10 was the same as Example 1, except that the LCF of the second polarizing filter was replaced with a circular polarizing plate, and the circular polarizing plate was positioned on the object side, i.e., on the object 13 side of lens 20 shown in FIG. 1 . The circular polarizing plate corresponds to the second circular polarizing filter. The circular polarizing plate will be described below. The circular polarizing plate is a combination of a linear polarizer and a λ / 4 plate.

[0175] <Preparation of Circular Polarizing Plate> <<Preparation of Linear Polarizer>> Composition 1 having the following composition was prepared: Composition 1 was a composition exhibiting lyotropic liquid crystal properties.

[0176] ―――――――――――――――――――――――――――――――― Composition 1 ―――――――――――――――――――――――――――――――― Dichroic dye III-2 5 parts by mass Water 95 parts by mass ――――――――――――――――――――――――――――――

[0177] Dichroic dye III-2

[0178]

[0179] The above-prepared composition 1 (5 g) and zirconia beads (20 g) having an average particle size of 2 mm were packed into a 45 mL zirconia container, and milled for 50 minutes at a rotation speed of 300 rpm using a FRISCH planetary ball mill P-7 Classic Line.

[0180] The milled composition 1 was applied to a glass substrate using a wire bar (movement speed: 100 cm / s) and then air-dried. The resulting composition layer was then immersed in a 1 mol / L aqueous calcium chloride solution for 5 seconds, washed with ion-exchanged water, and air-dried to fix the orientation, thereby producing a 200 nm-thick light absorption anisotropic film 1 (linear polarizer).

[0181] The produced light absorption anisotropic film 1 acts as an absorptive linear polarizer for light with a wavelength of 940 nm.

[0182] <<Preparation of λ / 4 Plate>> [Preparation of Optically Anisotropic Layer] Composition H1 for forming an optically anisotropic layer was prepared according to the following formulation, heated and dissolved at 50° C. for 3 hours while stirring, and filtered through a 0.45 μm filter.

[0183] Optically anisotropic layer forming composition H1 75.5 parts by mass of the following liquid crystal compound H1 0.8 parts by mass of polymerization initiator IRGACURE 819 (manufactured by BASF) 0.6 parts by mass of the above surfactant F-1 274.5 parts by mass ----------------------------------------------------------------

[0184] Liquid crystal compound H1 (a mixture of the following three compounds. The mixing ratio (mass ratio) is shown in the upper left of the compound.)

[0185] (Preparation of Transparent Support) -Preparation of Core Layer Cellulose Acylate Dope- The following composition was charged into a mixing tank and stirred to dissolve each component, thereby preparing a cellulose acetate solution to be used as a core layer cellulose acylate dope.

[0186] Core layer cellulose acylate dope ------------------------------------------------ Cellulose acetate having an acetyl substitution degree of 2.88: 100 parts by mass Polyester compound B described in the examples of JP-A No. 2015-227955: 12 parts by mass Compound F below: 2 parts by mass Methylene chloride (first solvent): 430 parts by mass Methanol (second solvent): 64 parts by mass

[0187] Compound F

[0188] -Preparation of Outer Layer Cellulose Acylate Dope- 10 parts by mass of the following matting agent solution was added to 90 parts by mass of the above core layer cellulose acylate dope to prepare a cellulose acetate solution to be used as the outer layer cellulose acylate dope.

[0189] Matting agent solution - Silica particles with an average particle size of 20 nm (AEROSIL R972, manufactured by Nippon Aerosil Co., Ltd.) 2 parts by mass - Methylene chloride (first solvent) 76 parts by mass - Methanol (second solvent) 11 parts by mass - The above-mentioned cellulose acylate dope for the core layer 1 part by mass -

[0190] Preparation of Cellulose Acylate Film 1 The core layer cellulose acylate dope and the outer layer cellulose acylate dope were filtered through a filter paper with an average pore size of 34 μm and a sintered metal filter with an average pore size of 10 μm. The core layer cellulose acylate dope and the outer layer cellulose acylate dope on both sides of the core layer cellulose acylate dope were simultaneously cast onto a drum at 20°C through a casting nozzle (band caster). The film was then peeled off while still containing approximately 20% solvent by weight. Both ends of the film in the width direction were fixed with tenter clips, and the film was stretched transversely at a stretch ratio of 1.1 times while being dried. The film was then transported between the rolls of a heat treatment device and further dried to produce a 40 μm-thick optical film (transparent support), designated as Cellulose Acylate Film 1. The in-plane retardation of the resulting Cellulose Acylate Film 1 was 0 nm.

[0191] (Formation of Photo-Alignment Film PA1) A coating liquid PA1 for forming a photo-alignment film, which will be described later, was continuously applied onto the cellulose acylate film 1 using a wire bar. The support on which the coating film was formed was dried with hot air at 140° C. for 120 seconds, and then the coating film was irradiated with polarized ultraviolet light (10 mJ / cm ２ A photo-alignment film PA1 was formed by irradiating the substrate with a 0.5 μm-thick TAC (triacetyl cellulose) film.

[0192] -------------------------------------------------- Coating liquid PA1 for forming photoalignment film -------------------------------------------------- Polymer PA-1 (shown below) 100.00 parts by mass Acid generator PAG-1 (shown below) 8.25 parts by mass Stabilizer DIPEA (shown below) 0.6 parts by mass Xylene 1126.60 parts by mass Methyl isobutyl ketone 125.18 parts by mass --------------------------------------------------

[0193] Polymer PA-1

[0194] Acid generator PAG-1

[0195] Stabilizer DIPEA

[0196] The optically anisotropic layer-forming composition H1 was continuously applied onto the obtained photo-alignment film PA1 using a wire bar to form a coating layer H1. The coating layer H1 was then heated at 100°C for 5 minutes and cooled to 60°C to form a dry film. In the dry film, the liquid crystal compound was in a nematic phase. Then, an LED lamp (center wavelength 365 nm) was used to illuminate the film at an illuminance of 200 mW / cm. ２ The optically anisotropic layer H1 was formed on the photo-alignment film PA1 by irradiating the film with light for 2 seconds under the irradiation conditions of: The thickness of the optically anisotropic layer H1 was 1.9 μm.

[0197] The optically anisotropic layer H1 thus produced acts as a λ / 4 retardation layer for light with a wavelength of 940 nm.

[0198] [Preparation of Positive C Plate] The above-mentioned cellulose acylate film 1 was used as a temporary support. The cellulose acylate film 1 was passed through a dielectric heating roll at a temperature of 60°C to raise the film surface temperature to 40°C, and then an alkaline solution having the composition shown below was applied to one side of the film using a bar coater in an amount of 14 ml / m. ２ The film was heated to 110°C and transported for 10 seconds under a steam-type far-infrared heater manufactured by Noritake Co., Ltd. Next, using the same bar coater, pure water was applied onto the film at a rate of 3 ml / m ２ Next, after repeating washing with water using a fountain coater and removing water with an air knife three times, the film was transported to a drying zone at 70° C. for 10 seconds and dried, thereby preparing an alkali-saponified cellulose acylate film 1.

[0199] ---------------------------------------------------------------- (Alkaline solution) ---------------------------------------------------------------- Potassium hydroxide 4.7 parts by mass Water 15.8 parts by mass Isopropanol 63.7 parts by mass Fluorine-containing surfactant SF-1 (C １４ H ２９ O (CH ２ CH ２Ｏ ) ２０ H) 1.0 part by mass Propylene glycol 14.8 parts by mass

[0200] An alignment layer-forming coating solution 2 having the following composition was continuously coated using a #16 wire bar onto the above-mentioned alkali-saponified cellulose acylate film 1. The cellulose acylate film 1 on which the coating film was formed was dried with hot air at 60°C for 60 seconds and then with hot air at 100°C for 120 seconds to form an alignment layer.

[0201] ------------------------------------------------------------------ (Coating liquid 2 for forming alignment layer) ------------------------------------------------------------------ Polyvinyl alcohol (PVA103, manufactured by Kuraray) 2.4 parts by mass Isopropyl alcohol 1.6 parts by mass Methanol 36 parts by mass Water 60 parts by mass ------------------------------------------------------------------

[0202] The coating solution C1 for forming a positive C plate, which will be described later, was applied onto the alignment layer, and the resulting coating film was aged at 60° C. for 60 seconds, and then irradiated with 70 mW / cm 2 ２ An air-cooled metal halide lamp (manufactured by Eye Graphics Co., Ltd.) was used, and the light intensity was 1000 mJ / cm ２The alignment state was fixed by irradiating the liquid crystal compound with ultraviolet light of 1000 nm to vertically align the liquid crystal compound, thereby producing a TAC film having a positive C-plate C1. The Rth(550) of the obtained positive C-plate C1 was −130 nm.

[0203] ------------------------------------------------ (Coating liquid C1 for forming positive C-plate) -------------------------------------------------- 80 parts by mass of liquid crystal compound L-11 shown below 20 parts by mass of liquid crystal compound L-12 shown below 1 part by mass of vertically aligned liquid crystal compound promoter (S01) shown below 8 parts by mass of ethylene oxide-modified trimethylolpropane triacrylate (V#360, manufactured by Osaka Organic Chemical Industry Ltd.) 3 parts by mass of IRGACURE 907 (manufactured by BASF) 1 part by mass of Kayacure DETX (manufactured by Nippon Kayaku Co., Ltd.) 0.4 parts by mass of compound B03 shown below 170 parts by mass of methyl ethyl ketone 30 parts by mass of cyclohexanone ------------------------------------------------

[0204] Liquid crystal compound L-11 and liquid crystal compound L-12

[0205] Vertically aligned liquid crystal compound promoter (S01)

[0206] Compound B03

[0207] The positive C plate C1 side of the TAC film having the positive C plate C1 prepared above was bonded to the optically anisotropic layer side of the TAC film having the optically anisotropic layer H1 using the UV adhesive composition below, and the alignment layer and cellulose acylate film 1 on the optically anisotropic layer H1 side were removed to obtain a laminate (λ / 4 plate) including a retardation layer (optically anisotropic layer H1 and positive C plate C1).

[0208] (Preparation of UV adhesive composition) The following UV adhesive composition was prepared. ---------------------------------------------------------------- UV adhesive composition ---------------------------------------------------------------- CEL2021P (manufactured by Daicel Corporation) 70 parts by mass 1,4-butanediol diglycidyl ether 20 parts by mass 2-ethylhexyl glycidyl ether 10 parts by mass CPI-100P (described below) 2.25 parts by mass ----------------------------------------------------------------

[0209] CPI-100P

[0210] The refractive indices nx, ny, and nz of the prepared λ / 4 plate were measured using an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd.) with a sodium lamp (λ=589 nm) as the light source. From the measured refractive indices nx, ny, and nz, the Nz factor: Nz=(nx-nz) / (nx-ny) was calculated. Note that the refractive indices nx, ny, and nz were substituted with the respective refractive indices at a wavelength of 550 nm. The Nz factor was 0.5.

[0211] The prepared λ / 4 plate was left to stand for 24 hours under conditions of 20°C and 65% RH (relative humidity) to condition the humidity, and then cut into a size of 200 mm x 15 mm (machine direction (MD) x width direction (TD) when applying composition H1 for forming an optically anisotropic layer), and attached to a testing machine (tensile testing machine "AG-IS" manufactured by Shimadzu Corporation) with a chuck spacing of 100 mm, and subjected to a tensile test at a tension rate of 1000 mm / min under conditions of 20°C and 65% RH, and the tensile modulus was calculated from the ratio of the obtained initial stress to the initial strain. The tensile modulus was 2.0 x 10 3 The pressure was MPa.

[0212] <<Lamination of Linear Polarizer and λ / 4 Plate>> An adhesive (SK-2057, manufactured by Soken Chemical & Engineering Co., Ltd.) was applied to the surface of the λ / 4 plate facing the optically anisotropic layer H1 to form an adhesive layer, and the surface of the linear polarizer (lightly absorptive anisotropic film 1) opposite the glass substrate was attached to the adhesive layer in close contact with the adhesive layer to obtain a circular polarizer. The slow axis of the optically anisotropic layer H1 and the absorption axis of the lightly absorptive anisotropic film 1 were oriented at 45°. In this manner, a circular polarizer was produced.

[0213] Example 11 was the same as Example 1, except that a circular polarizing plate (cholesteric reflective type) was used instead of the LCF of the second polarizing filter, and the second polarizing filter was positioned on the object side, i.e., on the object 13 side of lens 20 shown in Figure 1. The circular polarizing plate will be described below.

[0214] (Formation of Alignment Film) A glass substrate was prepared as a support. The following alignment film forming coating liquid P-1 was applied onto the support by spin coating. The support coated with this alignment film forming coating liquid P-1 was dried on a hot plate at 60°C for 60 seconds to form a coating film.

[0215] Coating liquid P-1 for forming alignment film ----------------------------------- 1.00 parts by mass of the following photoalignment material; Water 16.00 parts by mass; Butoxyethanol 42.00 parts by mass; Propylene glycol monomethyl ether 42.00 parts by mass ---------------------------------------------------

[0216] Material for photo alignment

[0217] (Preparation of Photo-Alignment Film) The resulting coating film was exposed to light to form a 5 μm-thick photo-alignment film P-1. Next, Composition B-3 was applied once onto the photo-alignment film P-1 to prepare an optically anisotropic layer.

[0218] Composition B-3 (coating liquid for forming cholesteric liquid crystal layer) ---------------------------------------------------------------- Rod-shaped liquid crystal compound L-13 described above: 100.00 parts by mass Polymerization initiator (Irgacure OXE01, manufactured by BASF): 1.00 part by mass Chiral agent Ch-1 described below: 4.2 parts by mass Methyl ethyl ketone: 115.72 parts by mass

[0219] Rod-shaped liquid crystal compound L-13 (containing the following structure in the mass ratio shown on the right)

[0220] Chiral agent Ch-1

[0221] The optically anisotropic layer was prepared as follows: First, one layer of Composition B-1 was applied onto the photo-alignment film P-1, and the coating film was heated to 80°C on a hot plate. Thereafter, at 80°C, ultraviolet light having a wavelength of 365 nm was applied at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere. 2 The coating film was irradiated with an irradiation amount of Δn 940 It was confirmed using a polarizing microscope that the film thickness d = Re(940) was 470 nm. The laminate including the prepared optically anisotropic layer was a circular polarizer having a reflective cholesteric liquid crystal layer. The circular polarizer was reflective and reflected and diffracted right-handed circularly polarized light with a wavelength of 940 nm. When light was incident perpendicularly to the surface of the optically anisotropic layer, it reflected right-handed circularly polarized light in a direction of a polar angle of 30° and transmitted left-handed circularly polarized light without diffracting it (0° direction).

[0222] (Comparative Example 1) Comparative Example 1 was the same as Example 2 except that, compared to Example 2, the position of the second polarizing filter was on the object side, i.e., on the object 13 side of lens 20 shown in Figure 1. (Comparative Example 2) Comparative Example 2 was the same as Example 6 except that, compared to Example 6, the position of the second polarizing filter was on the object side, i.e., on the object 13 side of lens 20 shown in Figure 1.

[0223] (Haze Measurement) The absorption anisotropy of the optically absorptive anisotropic films 1 and 2 prepared as second polarizing filters was measured using a haze meter (NDH2000 (manufactured by Nippon Denshoku Industries Co., Ltd.)).

[0224] (Evaluation of Noise in Captured Images) The noise in captured images was evaluated as follows. For the imaging systems of Examples 1 to 11 and Comparative Examples 1 and 2, a mirror 50 was placed directly opposite the mirror 50 as shown in FIG. 17 , and a mirror 52 was placed at an oblique position, and the reflected light from the mirror surface, which caused noise, was photographed. The mirror 50 was positioned so that the optical axis C (see FIG. 1) of the lenses 20 and 22 (see FIG. 1) was perpendicular to the surface 50a. The mirror 52 was positioned so that the optical axis C of the lenses 20 and 22 was tilted with respect to the surface 52a. With the mirrors 50 and 52 positioned as shown in FIG. 17 , images were captured using the imaging systems of Examples 1 to 11 and Comparative Examples 1 and 2, and the shutter speed was adjusted so that the maximum luminance value in the image was constant, thereby obtaining captured images. The average luminance of the captured images was evaluated, and the noise in the captured images of the imaging systems was evaluated as a value relative to the evaluation value (average luminance value) in Example 1. The results are shown in the "Relative Average Luminance Value" column in Table 1 below. Note that the relative average luminance value for Example 1 is "1." A smaller relative average brightness value indicates less noise. The captured images were also evaluated using the following evaluation criteria to evaluate the noise in the captured images of the imaging system. The results are also shown. Specifically, 10 testers were asked to rate each captured image on the following scale from A to D. As a result, the evaluation of the captured image was determined based on the rating given by 8 or more of the 10 testers. Evaluation criteria A: No noise is detected in the captured image. B: Some noise is detected in the captured image. C: Noise is detected in the captured image, but the noise is not noticeable. D: Significant noise is detected in the captured image.

[0225] In Examples 1 to 11 and Comparative Examples 1 and 2, the average transmittance of the second polarizing filter was measured. The results are shown in Table 1 below. Since all of the second polarizing filters were linear polarizers or had linear polarizers, the average transmittance was referred to as the "average transmittance of the second linear polarizer" in Table 1 below. The average transmittance of the second polarizing filter (second linear polarizer) was measured as follows. First, using a V-660 ultraviolet-visible-near-infrared spectrophotometer (JASCO Corporation), the transmittance at wavelengths of 400 nm or more and less than 700 nm was measured. Next, the transmittances at each wavelength obtained were arithmetically averaged to calculate the average transmittance (unit: %) of the second polarizing filter (second linear polarizer).

[0226]

[0227] As shown in Table 1, Examples 1 to 11 provided captured images with lower relative average luminance values ​​and reduced noise compared to Comparative Examples 1 and 2. The relative average luminance values ​​corresponded to the sensory evaluation of noise. From Examples 1 to 11, regardless of the position of the second polarizing filter, among Light Absorbing Anisotropic Film 1, Light Absorbing Anisotropic Film 2, a wire-grid polarizer, a combination of a wire-grid polarizer and a louver, and an LCF, LCF was able to reduce noise the most. From Examples 1 to 11, an absorptive second polarizing filter was able to reduce noise more effectively than a reflective second polarizing filter. From Examples 4 and 8, a second polarizing filter with lower haze was able to reduce noise more effectively. Furthermore, from Examples 1 to 7, a second linear polarizer with an average visible light transmittance of 70% or more was able to reduce noise more effectively. Note that when the second polarizing filter was positioned on the object side as in Example 9, the obliquely incident component increased, but the relative average luminance values ​​and noise were average for Examples 1 to 11. Furthermore, when the second polarizing filter was configured to have a linear polarizer and a λ / 4 plate (second circular polarizing filter) and was placed on the object side as in Example 10, results similar to those of the above-mentioned Examples 1 and 3 were obtained. Furthermore, when the second polarizing filter was configured to have a cholesteric liquid crystal layer (second circular polarizing filter) and was placed on the object side as in Example 11, results similar to those of the above-mentioned Examples 1 and 3 were obtained.

[0228] 10, 46 Imaging system 12 Light source 13 Object 14 Imaging device 16 First polarizing filter 16a, 34a, 36a, 50a, 52a, 60a, 62a Surface 16b, 24b, 32b, 36b, 60b, 62b Back surface 17 Display control unit 18 Control unit 19 Display unit 20, 22 Lens 24 Second polarizing filter 26 Image sensor 27 Optical system 28 First linear polarizer 29 Second linear polarizer 30 Second polarizing filter 32 First layer 34 Second layer 36 Second polarizing filter 40 Vehicle 42 Seat 43 Driver 44 Occupant 48 Computing unit 50, 52 Mirror 60 First circular polarizing filter 62 Second circular polarizing filter 63, 65 Linear polarizers 64, 66 λ / 4 plate C Optical axis D1, D2 Polarization axis Li Reflected light Lo Outgoing light S Stray light X, Y, Z directions

Claims

1. An imaging system comprising: a light source that emits infrared rays; an imaging device that images an object irradiated with the infrared rays emitted from the light source; and a first polarizing filter that polarizes the infrared rays emitted from the light source and is arranged between the light source and the object, wherein the imaging device comprises, from the incident side, a lens, a second polarizing filter that polarizes the infrared rays, and an image sensor.

2. The imaging system of claim 1, wherein the first polarizing filter includes a first linear polarizer, the second polarizing filter includes a second linear polarizer, and the polarization axis of the first linear polarizer and the polarization axis of the second linear polarizer are orthogonal to each other.

3. The imaging system of claim 2, wherein the second linear polarizer is an absorptive linear polarizer.

4. The imaging system according to claim 2 or 3, wherein the second linear polarizer has an average transmittance of visible light of 70% or more.

5. The imaging system of claim 1, wherein the second polarizing filter is an optical element having an absorption axis for infrared light in an in-plane direction, and when linearly polarized infrared light perpendicular to the absorption axis is irradiated from a direction tilted 45° from the normal direction at an azimuth angle perpendicular to the normal direction of the optical element and from a direction tilted 45° from the normal direction, the absorbance is greater than the absorbance when irradiated from the normal direction.

6. The imaging system according to any one of claims 1, 2 and 5, wherein the second polarizing filter has a haze of 1 or less.

7. The imaging system according to any one of claims 1 to 3, wherein the object is at least one of a driver of a vehicle and an occupant of the vehicle, and is used in a vehicle interior occupant monitoring system.

8. An imaging system comprising: a light source that emits infrared rays; an imaging device that images an object irradiated with the infrared rays emitted from the light source; and a first polarizing filter that is arranged between the light source and the object and polarizes the infrared rays emitted from the light source; the imaging device comprises, from the incident side, a second polarizing filter that polarizes the infrared rays, a lens, and an image sensor; and the second polarizing filter is an optical element that has an absorption axis for infrared rays in an in-plane direction and has a higher absorbance when linearly polarized infrared rays orthogonal to the absorption axis are irradiated from a direction tilted 45° from the normal direction than when irradiated from the normal direction at an azimuth angle orthogonal to the absorption axis.

9. An imaging system comprising: a light source that emits infrared rays; an imaging device that images an object irradiated with the infrared rays emitted from the light source; and a first circular polarizing filter that circularly polarizes the infrared rays emitted from the light source and is arranged between the light source and the object, wherein the imaging device comprises, from the incident side, a second circular polarizing filter that circularly polarizes the infrared rays, a lens, and an image sensor.

10. The imaging system of claim 9, wherein the second circular polarizing filter includes a linear polarizer and a λ / 4 plate, and the Nz factor of the λ / 4 plate is greater than 0 and less than 1.

11. The imaging system of claim 10, wherein the linear polarizer of the second circular polarizing filter is an absorptive linear polarizer.

12. The imaging system according to claim 10 or 11, wherein the linear polarizer of the second circular polarizing filter has an average transmittance of visible light of 70% or more.

13. The imaging system according to claim 9, wherein the second circular polarizing filter has a haze of 1 or less.