Optical sensor

Abstract

The present invention addresses the problem of providing an optical sensor which has a wide opening and receives light coming from various directions by using a small number of sensors. This optical sensor, which has at least a light-guiding base material, a light reception sensor and a reflection-type diffraction element, solves the problem by the light-guiding base material having at least a surface A on which light is incident, a surface B inclined in relation to the surface A, and a surface C, wherein the inclination angle of the surface B in relation to the surface A is 25° or less, the reflection-type diffraction element is located on the surface B, and the light reception sensor is provided on the surface C.

Description

Optical sensor

[0001] The present invention relates to an optical sensor, and more particularly to an optical sensor capable of receiving light incident from various directions with a small number of sensors.

[0002] In recent years, communication that propagates light through space using visible light, infrared light, etc. has begun to be studied. These are called optical wireless communication, free space optical communication, Li-Fi (Light Fidelity), etc.

[0003] In such communications, light is transmitted in various directions, and therefore, optical sensors are required to receive light incident from various directions. For example, Patent Document 1 describes an optical detector in which multiple sensors are arranged, and each sensor is provided with an element for receiving light only from a specific direction. This optical detector can detect light incident from various directions, but requires many sensors. Furthermore, Patent Document 2 describes an optical sensor that uses a lens, a light-guiding substrate, an optical sensor, and a diffraction element to receive light incident from various directions. This optical sensor requires a small number of sensors, but because the location where the incident light hits the sensor changes depending on the angle, the size of the sensor and the diffraction element must be large to receive a wide range of incident light.

[0004] International Publication No. 2018 / 220388 U.S. Patent Application Publication No. 2020 / 0295828

[0005] In view of these considerations, the object of the present invention is to provide an optical sensor that has a wide opening, guides light incident from various directions in one direction, and receives the guided light with a sensor located at the end, thereby being able to receive light from various directions with a small number of sensors.

[0006] The present inventors have found that the above object can be achieved by the following configuration: [1] An optical sensor having at least a light-guiding substrate, a light-receiving sensor, and a reflective diffraction element, wherein the light-guiding substrate has at least a surface A on which light is incident, a surface B inclined with respect to surface A, and a surface C, the inclination angle of surface B with respect to surface A being 25° or less, the reflective diffraction element is disposed on surface B, and the light-receiving sensor is disposed on surface C. [2] The optical sensor according to [1], wherein the light-guiding substrate has one or more surfaces B, and surface B forms at least a part of any one of a pyramid, a truncated pyramid, a cone, a truncated cone, and a spherical crown. [3] The optical sensor according to [1] or [2], wherein the reflective diffraction elements include two to four reflective diffraction elements having different diffraction angles, and the reflective diffraction elements have an in-plane pitch p [nm] that satisfies the following formula (c-1) or formulas (c-1) and (c-2), where Y [°] is the diffraction angle of each reflective diffraction element. n × sin(Y + a) > 1 formula (a) sin(|X1|) = n × sin(X2) formula (b) n × p = λ / {sin(X2 - a) + sin(Y)} formula (c-1) n × p = λ / {sin(X2 + a) + sin(Y)} formula (c-2) Here, the in-plane pitch p [nm] is a value expressed by formula (c-1) or formula (c-2) using formulas (a) and (b). Furthermore, X1 [°] is the angle of incidence of the incident light with respect to the normal to surface A, and its positive and negative values ​​are positive when the light is incident from the opposite side of surface C with respect to the normal to surface A, and negative when the light is incident from the surface C side. X2 [°] is the angle of incidence inside the light guiding substrate, λ [nm] is the wavelength of the light, a [°] is the inclination angle of surface B with respect to surface A, and n is the refractive index of the light guiding substrate. Furthermore, when X1 is positive, formula (c-2) is used, and when X1 is negative, formula (c-1) is used. Furthermore, the in-plane pitch of each reflective diffractive element is calculated by substituting the angle of incidence X1 shown in 1) to 3) below depending on the number of reflective diffractive elements that the optical sensor has.1) When the number of reflective diffractive elements is 2: X1 = -30°, -80° 2) When the number of reflective diffractive elements is 3: X1 = 30°, -30°, -80° 3) When the number of reflective diffractive elements is 4: X1 = 80°, 30°, -30°, -80° [4] The optical sensor according to any one of [1] to [3], wherein the reflective diffractive element is a liquid crystal diffractive element. [5] The optical sensor according to any one of [1] to [4], wherein in the light guiding substrate, surface C is a surface connecting surface A and surface B. [6] The optical sensor according to any one of [1] to [4], wherein in the light guiding substrate, surface A and surface C face each other.

[0007] According to the present invention, it is possible to provide an optical sensor that has a wide opening and receives light incident from various directions with a small number of sensors.

[0008] FIG. 1 is a diagram schematically showing an example of an optical sensor of the present invention. FIG. 2 is a diagram schematically showing a wedge-shaped light-guiding substrate of the optical sensor shown in FIG. 1. FIG. 3 is a diagram schematically showing an example of incident light in the optical sensor shown in FIG. 1. FIG. 4 is a diagram schematically showing an example of reflected diffracted light in the optical sensor shown in FIG. 1. FIG. 5 is a diagram schematically showing another example of an optical sensor of the present invention. FIG. 6 is a diagram schematically showing an example of reflected diffracted light in the optical sensor shown in FIG. 5. FIG. 7 is a diagram schematically showing an example of guiding incident light in the wedge-shaped light-guiding substrate of the optical sensor shown in FIG. 1. FIG. 8 is a diagram schematically showing an example of diffracted light in the optical sensor shown in FIG. 1. FIG. 9 is a diagram schematically showing an example of guiding incident light in the wedge-shaped light-guiding substrate of the optical sensor shown in FIG. 5. FIG. 10 is a diagram schematically showing an example of diffracted light in the optical sensor shown in FIG. 5. FIG. 11 is a diagram schematically showing another example of a light-guiding substrate. FIG. 12 is a diagram schematically showing another example of a light guiding substrate. FIG. 13 is a diagram schematically showing another example of a light guiding substrate. FIG. 14 is a diagram schematically showing another example of a light guiding substrate. FIG. 15 is a diagram schematically showing another example of a light guiding substrate. FIG. 16 is a cross-sectional view of FIG. 15. FIG. 17 is a diagram schematically showing another example of an optical sensor of the present invention. FIG. 18 is a top view schematically showing another example of an optical sensor of the present invention. FIG. 19 is a diagram schematically showing an example of a reflective liquid crystal diffraction element. FIG. 20 is a schematic diagram for explaining the liquid crystal diffraction element shown in FIG. 19. FIG. 21 is a schematic diagram for explaining the action of the liquid crystal diffraction element shown in FIG. 19.

[0009] Hereinafter, preferred embodiments of the optical sensor of the present invention will be described in detail.

[0010] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0011] In this specification, visible light is defined as light with a wavelength of 380 to 780 nm, and infrared light is defined as light with a wavelength of more than 780 nm and not more than 2500 nm. The figures shown below are schematic diagrams for explaining the present invention, and the size, thickness, shape, structure, positional relationship, etc. of each component do not necessarily correspond to the actual ones.

[0012] 1 is a schematic diagram showing an example of an optical sensor according to the present invention. In this optical sensor, the light-guiding substrate has, as an example, a wedge-shaped cross section that is a right-angled triangle. This optical sensor has a wedge-shaped light-guiding substrate 101 to which a first reflective diffractive element 201 and a second reflective diffractive element 202 are bonded, and also has a light-receiving sensor 301.

[0013] FIG. 2 shows surfaces A, B, and C of the wedge-shaped light guiding substrate 101 in the optical sensor shown in FIG. 1 . In the illustrated wedge-shaped light guiding substrate 101, as an example, the surface corresponding to the hypotenuse of the right triangle is surface B, the surface corresponding to the longer of the remaining sides of the right triangle is surface A, and the surface corresponding to the shortest side of the right triangle is surface C. Therefore, surface B corresponding to the hypotenuse of the right triangle is inclined with respect to surface A. Furthermore, surface C connects surfaces A and B. In the present invention, surface A is the surface onto which light is incident, i.e., the opening (light entrance, light entrance surface) of the optical sensor. Furthermore, a first reflective diffractive element 201 and a second reflective diffractive element 202 are arranged on surface B, i.e., the surface corresponding to the hypotenuse of the right triangle. Furthermore, a light-receiving sensor 301 is arranged on surface C, i.e., the surface corresponding to the shortest side of the right triangle.

[0014] In the wedge-shaped light-guiding substrate 101 of the optical sensor of the present invention, surface B, on which the first reflective diffractive element 201 and the second reflective diffractive element 202 are arranged, is inclined with respect to surface A, which is the light incidence surface. Here, in the present invention, the inclination angle a of surface B with respect to surface A is 25° or less. In the following description, the inclination angle a of surface B with respect to surface A will also be simply referred to as the "inclination angle a." In the present invention, by setting the inclination angle a to 25° or less, a wide light incidence surface, i.e., a wide opening, is provided, making it possible to receive light incident from various directions with a small number of sensors. The inclination angle a may be 25° or less, but is preferably 22.5° or less, and more preferably 20° or less.

[0015] FIG. 3 is a schematic diagram illustrating an example of how light is incident on the optical sensor shown in FIG. Incident light 401, incident light 402, and incident light 403 are light of the same wavelength and are shown incident from various directions. Here, the wavelength of the incident light may be visible light or IR light (infrared light). The incident light may be polarized or unpolarized. In the example shown in FIG. 3, incident light 401 is light incident from surface C (the light-receiving sensor 301 side) with respect to the normal to surface A, i.e., the light-incident surface. In the present invention, the angle of incidence of light incident from this direction is considered negative. Therefore, the angle of incidence of incident light 403, which is incident from the opposite side to surface C (the light-receiving sensor 301 side) with respect to the normal to surface A, i.e., the light-incident surface, is positive. For example, when the angles of incidence of the incident light 401 and the incident light 403 are both 30°, the angle of incidence of the incident light 401 is −30° and the angle of incidence of the incident light 403 is 30° (+30°).

[0016] 4 is a schematic example of how incident light incident on the wedge-shaped light guiding substrate 101 is diffracted by the reflective diffraction element or reflected by surface B of the wedge-shaped light guiding substrate 101. After incident light 401 at a negative incident angle enters the wedge-shaped light guiding substrate 101, it is guided inside the wedge-shaped light guiding substrate 101 and enters surface B. The incident light 401 passes through surface B, exits the wedge-shaped light guiding substrate 101, enters the first reflective diffraction element 201, and is reflected and diffracted by the first reflective diffraction element 201 to become diffracted light 501. This diffracted light 501 enters the wedge-shaped light guiding substrate 101 from surface B, is guided inside, enters surface C, passes through surface C, exits from the wedge-shaped light guiding substrate 101, and is sensed by the light receiving sensor 301.

[0017] Incident light 402 incident from the normal direction of surface A enters the wedge-shaped light guiding substrate 101, is guided inside the wedge-shaped light guiding substrate 101, and then enters surface B. The incident light 402 transmits through surface B and exits the wedge-shaped light guiding substrate 101, transmits through the first reflective diffraction element 201 and enters the second reflective diffraction element 202, and is reflected and diffracted by the second reflective diffraction element 202 to become diffracted light 502. This diffracted light 502 transmits through the first reflective diffraction element 201 and enters the wedge-shaped light guiding substrate 101 from surface B, is guided inside, enters surface C, transmits through surface C, exits the wedge-shaped light guiding substrate 101, and is sensed by the light-receiving sensor 301.

[0018] Incident light 403 incident at a positive incident angle enters the wedge-shaped light guiding substrate 101, is guided inside the wedge-shaped light guiding substrate 101, and is incident on surface B. The incident light 403 is reflected on the inside side of surface B of the wedge-shaped light guiding substrate 101 due to the difference in refractive index between the wedge-shaped light guiding substrate 101 and the outside, is guided inside the wedge-shaped light guiding substrate 101, is incident on surface C, transmits through surface C, exits the wedge-shaped light guiding substrate 101, and is sensed by the light-receiving sensor 301.

[0019] As is well known, whether incident light is reflected / diffracted by a reflective diffraction element or transmitted without being reflected / diffracted depends on the relationship between the in-plane pitch of the reflective diffraction element and the angle of incidence of the incident light incident on the reflective diffraction element. In the optical sensor of the present invention, the in-plane pitch of the reflective diffraction element is set by a well-known method using the following well-known formula for the in-plane pitch of a diffraction element, so that the reflective diffraction element does not unnecessarily reflect incident light with an incompatible angle of incidence: n(sin α+sin β)=λ / p In the above formula, n is the refractive index of the light guide plate, α is the angle of incidence, β is the diffraction angle, λ is the wavelength of the incident light, and p is the in-plane pitch of the diffraction element.

[0020] Figure 5 schematically shows an example of another embodiment of the optical sensor of the present invention and an example of the manner in which light is incident on this optical sensor. The example shown in Figure 5 differs from the example shown in Figure 3 in that surface A, i.e., the opening (incident surface) of the optical sensor, is wider. As in the example shown in Figure 5, when surface A of the wedge-shaped light guiding substrate 101 is widened, that is, extended in the tilt direction of surface B, incident light 403 incident at a positive angle of incidence may not be reflected at the interface of surface B depending on the angle of incidence. Correspondingly, the optical sensor shown in Figure 5 has a third reflective diffractive element 203 corresponding to incident light 403, in addition to a first reflective diffractive element 201 corresponding to incident light 401 and a second reflective diffractive element 202 corresponding to incident light 402.

[0021] 6 is an example that schematically illustrates how incident light incident on a wedge-shaped light-guiding substrate 101 with a widened surface A (opening) is diffracted by a reflective diffraction element. As in the example shown in FIG. 3, incident light 401 incident at a negative angle of incidence and incident light 402 incident from a direction approximately normal to surface A enter the wedge-shaped light-guiding substrate 101, are guided inside the wedge-shaped light-guiding substrate 101, and are transmitted through surface B. The incident light 401 that has transmitted through surface B is reflected and diffracted by the first reflective diffraction element 201, and the incident light 402 is reflected and diffracted by the second reflective diffraction element 202, respectively, to become diffracted light 501 and diffracted light 502. The diffracted light 501 and the diffracted light 502 enter the wedge-shaped light guiding substrate 101 , are guided inside, enter the surface C, exit from the wedge-shaped light guiding substrate 101 , and are sensed by the light-receiving sensor 301 .

[0022] On the other hand, incident light 403 incident at a positive angle of incidence enters the wedge-shaped light-guiding substrate 101, is guided inside the wedge-shaped light-guiding substrate 101, and then enters surface B. In a configuration in which surface B is wide, as in the examples shown in Figures 5 and 6, incident light 403 incident at a positive angle of incidence may not be reflected by surface B depending on the angle of incidence. In this case, incident light 403 passes through surface B and exits the wedge-shaped light-guiding substrate 101, passes through the first reflective diffractive element 201 and the second reflective diffractive element 202, enters the third reflective diffractive element 203, and is reflected and diffracted to become diffracted light 503. This diffracted light 502 passes through the second reflective diffraction element 202 and the first reflective diffraction element 201, enters the wedge-shaped light-guiding substrate 101 from surface B, is guided inside, enters surface C, passes through surface C, exits the wedge-shaped light-guiding substrate 101, and is sensed by the light-receiving sensor 301.

[0023] 4 and 6, the incident light is reflected and diffracted so that the diffracted light travels from the reflective diffraction element and surface B directly toward surface C, but the optical sensor of the present invention is not limited to this. As an example, as shown in Figures 8 and 10 described below, in the reflective diffraction element, reflection and diffracting may be performed so that the diffracted light is incident on surface A of the wedge-shaped light-guiding substrate 101, and the diffracted light totally reflected at surface A may be incident on surface C.

[0024] The above-described functions of the light-guiding substrate and the reflective diffraction element are basically the same in the embodiments shown in Figures 12 to 17 described below, in which surface B forms at least a part of any one of the shapes of a pyramid, a truncated pyramid, a cone, a truncated cone, and a spherical cap.

[0025] Examples of reflective diffraction elements include surface relief diffraction elements, volume hologram diffraction elements, and liquid crystal diffraction elements. The diffraction angle in these reflective diffraction elements depends on the in-plane pitch. In other words, the in-plane pitch is one period of the periodic structure in the diffraction element (diffraction grating). In the case of surface relief and volume hologram diffraction elements, the in-plane pitch corresponds to the reciprocal of the number of grooves. On the other hand, in the case of liquid crystal diffraction elements, the in-plane pitch is the length required for the optical axis derived from the liquid crystal compound to rotate 180° in one direction in the plane.

[0026] Examples of reflective diffraction elements include the diffraction elements described above. Among these, a liquid crystal diffraction element is suitable for the optical sensor of the present invention because it can maintain high diffraction efficiency regardless of the diffraction angle and elements having different wavelengths and different diffraction angles can be stacked or adhered together for use.

[0027] The diffraction efficiency and diffraction wavelength of the liquid crystal diffraction element can be adjusted appropriately depending on the application. The diffraction efficiency depends on the film thickness, and the diffraction wavelength depends on the chiral pitch length, so they can be adjusted appropriately depending on the application.

[0028] Furthermore, a reflective liquid crystal diffraction element uses a cholesteric liquid crystal layer in which a cholesteric liquid crystal phase is fixed. As is well known, a cholesteric liquid crystal layer selectively reflects either right-handed or left-handed circularly polarized light. Therefore, when using a liquid crystal diffraction element as a reflective diffraction element, a diffraction element that selectively reflects left-handed circularly polarized light and a diffraction element that selectively reflects right-handed circularly polarized light can be stacked to diffract unpolarized light. As will be described later, the circularly polarized light to be selectively reflected can be selected by appropriately selecting a chiral agent. Furthermore, the diffraction direction can be adjusted to the desired direction by taking into account the diffraction direction of each liquid crystal diffraction element and stacking them by bonding or the like.

[0029] In the present invention, a composite element in which a plurality of liquid crystal diffraction elements are stacked so that they have the same diffraction angle and reflect and diffract both left- and right-handed circularly polarized light is regarded as a single element.

[0030] In addition, the method for stacking the reflective diffraction elements can be selected appropriately taking into consideration the performance required for the system, such as stacking them (with an air layer), bonding them using an adhesive or UV adhesive, or forming another diffraction element directly on top of the diffraction element.

[0031] Furthermore, in order to change the diffraction direction while maintaining the same diffraction angle, the in-plane pitch direction may be stacked in a different direction, or the diffraction direction may be changed depending on the location. Even if the diffraction angle is the same, such an element configuration is considered to be one element in the present invention.

[0032] FIG. 19 is a schematic diagram of an example of a reflective liquid crystal diffraction element. As conceptually shown in FIG. 19, the liquid crystal diffraction element includes a support 50, an alignment film 52, and a cholesteric liquid crystal layer 54, which is a liquid crystal layer that functions as a diffraction element. FIG. 20 conceptually illustrates the orientation state of the liquid crystal compound within the principal surface of the cholesteric liquid crystal layer 54. In the following description, the principal surface of the cholesteric liquid crystal layer 54 is referred to as the X-Y plane, and the cross section perpendicular to this X-Y plane is referred to as the X-Z plane. That is, FIG. 19 corresponds to a schematic diagram of the X-Z plane of the cholesteric liquid crystal layer 54, and FIG. 20 corresponds to a schematic diagram of the X-Y plane of the cholesteric liquid crystal layer 54. As shown in FIG. 19, the cholesteric liquid crystal layer 54 is a layer in which the liquid crystal compound is cholesterically aligned. Furthermore, FIGS. 19 and 20 illustrate an example in which the liquid crystal compound constituting the cholesteric liquid crystal layer is a rod-shaped liquid crystal compound.

[0033] 19 includes a support 50, an alignment film 52, and a cholesteric liquid crystal layer 54, but the present invention is not limited to this. For example, the liquid crystal diffraction element may have only the alignment film 52 and the cholesteric liquid crystal layer 54, with the support 50 peeled off. Alternatively, the liquid crystal diffraction element may have only the cholesteric liquid crystal layer 54, with the support 50 and the alignment film 52 peeled off.

[0034] <Support> The support 50 supports the alignment film 52 and the cholesteric liquid crystal layer 54. As the support 50, various sheet-like materials (films, plates) can be used as long as they can support the alignment film 52 and the cholesteric liquid crystal layer 54.

[0035] <Alignment Film> In the liquid crystal diffraction element, an alignment film 52 is formed on the surface of the support 50. The alignment film 52 is an alignment film for orienting the liquid crystal compound 58 into a predetermined liquid crystal alignment pattern when forming the cholesteric liquid crystal layer 54. As will be described later, in the liquid crystal diffraction element, the cholesteric liquid crystal layer 54 has a liquid crystal alignment pattern in which the orientation of the optical axis 58A (see FIG. 20 ) derived from the liquid crystal compound 58 changes while continuously rotating along one in-plane direction. Therefore, the alignment film 52 is formed so that the cholesteric liquid crystal layer 54 can form this liquid crystal alignment pattern. In the following description, "the orientation of the optical axis 58A rotates" will also be simply referred to as "the optical axis 58A rotates."

[0036] Various known alignment films can be used for the alignment film 52. Examples include a rubbed film made of an organic compound such as a polymer, an obliquely evaporated film of an inorganic compound, a film with microgrooves, and a film formed by accumulating LB (Langmuir-Blodgett) films made of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate by the Langmuir-Blodgett method.

[0037] In addition, in the liquid crystal diffraction element, the alignment film 52 is preferably a so-called photo-alignment film, which is formed by irradiating a photo-alignment material containing a photo-alignment material with polarized or unpolarized light to form the alignment film 52. Various known photo-alignment materials can be used for the alignment film. Suitable photo-alignment materials include azo compounds, photo-crosslinkable polyimides, photo-crosslinkable polyamides, photo-crosslinkable polyesters, cinnamate compounds, and chalcone compounds.

[0038] There are no limitations on the method for forming the alignment film 52, and various known methods can be used depending on the material for forming the alignment film 52. One example is a method in which a photo-alignable alignment film 52 containing a photo-alignment material is applied to the surface of the support 50, dried, and then the alignment film 52 is exposed to laser light to form an alignment pattern. An example of the exposure method in this case is a method in which right-handed circularly polarized light and left-handed circularly polarized light formed by separating laser light are made to interfere with each other, and the photo-alignment film is exposed to this interference light, such as exposure using an exposure apparatus shown in Figure 13 of Japanese Patent No. 7541104.

[0039] <Cholesteric Liquid Crystal Layer> In the reflective liquid crystal diffraction element, a cholesteric liquid crystal layer 54 is formed on the surface of the alignment film 52. The cholesteric liquid crystal layer 54 is a liquid crystal layer formed by fixing a cholesteric liquid crystal phase, and is a cholesteric liquid crystal layer having a liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0040] As conceptually shown in Figure 19, the cholesteric liquid crystal layer 54 has a helical structure in which liquid crystal compounds 58 are spirally wound and stacked, similar to a cholesteric liquid crystal layer formed by fixing a normal cholesteric liquid crystal phase, and has a structure in which liquid crystal compounds 58 spirally wound and stacked at multiple pitches, with one helical pitch (helical pitch P) being defined as a configuration in which liquid crystal compounds 58 are spirally wound and stacked at one rotation (360° rotation).

[0041] As is well known, cholesteric liquid crystal phases exhibit selective reflectivity at specific wavelengths. In a typical cholesteric liquid crystal phase, the selective reflection central wavelength (central wavelength of selective reflection) λ depends on the helical pitch P in the cholesteric liquid crystal phase and follows the relationship λ = n × P with the average refractive index n of the cholesteric liquid crystal phase. Therefore, the selective reflection central wavelength can be adjusted by adjusting this helical pitch P. The longer the helical pitch P, the longer the selective reflection central wavelength of the cholesteric liquid crystal phase.

[0042] The helical pitch P of a cholesteric liquid crystal phase depends on the type and concentration of the chiral dopant used together with the liquid crystal compound when forming the cholesteric liquid crystal layer. Therefore, the desired helical pitch P can be obtained by adjusting these factors. The adjustment of the helical pitch P is described in detail in Fujifilm Research Report No. 50 (2005), pp. 60-63. The sense of helicity and the method for measuring the helical pitch P can be found in "Introduction to Liquid Crystal Chemistry Experiments," edited by the Japanese Liquid Crystal Society, published by Sigma Publishing in 2007, p. 46, and in "Liquid Crystal Handbook," published by the Liquid Crystal Handbook Editorial Committee, Maruzen, p. 196.

[0043] As is well known, cholesteric liquid crystal phases exhibit selective reflection for either left- or right-handed circularly polarized light at a specific wavelength. Whether the reflected light is right-handed or left-handed circularly polarized light depends on the twist direction (sense) of the helix of the cholesteric liquid crystal phase. When the twist direction of the helix of the cholesteric liquid crystal phase is right-handed, right-handed circularly polarized light is reflected, and when the twist direction of the helix is ​​left-handed, left-handed circularly polarized light is reflected. The direction of rotation of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer and / or the type of chiral agent added.

[0044] Furthermore, the half-width Δλ (nm) of the selective reflection band (circularly polarized light reflection band) exhibiting selective reflection depends on the Δn of the cholesteric liquid crystal phase and the helical pitch P, and follows the relationship Δλ = Δn × P. Therefore, the width of the selective reflection band can be controlled by adjusting Δn. Δn can be adjusted by the type and mixing ratio of the liquid crystal compounds forming the cholesteric liquid crystal layer, as well as the temperature during alignment fixation.

[0045] As shown in FIG. 20 , in the X-Y plane of the cholesteric liquid crystal layer 54, the liquid crystal compounds 58 are aligned along multiple alignment axes D parallel to each other in the X-Y plane. On each alignment axis D, the orientation of the optical axis 58A of the liquid crystal compounds 58 changes while continuously rotating in one direction in the plane along the alignment axis D. For the sake of explanation, it is assumed here that the alignment axis D is oriented in the X direction. Furthermore, in the Y direction, liquid crystal compounds 58 having the same orientation of the optical axis 58A are aligned at equal intervals. In the present invention, when the liquid crystal compound 58 is a rod-shaped liquid crystal compound, the optical axis 58A of the liquid crystal compound 58 refers to the molecular long axis of the rod-shaped liquid crystal compound. On the other hand, when the liquid crystal compound 58 is a discotic liquid crystal compound, the optical axis 58A of the liquid crystal compound 58 refers to an axis parallel to the normal to the discotic plane of the discotic liquid crystal compound.

[0046] In the cholesteric liquid crystal layer 54, in the liquid crystal orientation pattern of the liquid crystal compound 58, the length (distance) over which the optical axis 58A of the liquid crystal compound 58 rotates 180° in the direction of the alignment axis D, in which the optical axis 58A continuously rotates and changes in the plane, is the length of one period of the liquid crystal orientation pattern. In the liquid crystal diffraction element, the length over which the optical axis 58A rotates 180° is one period of the periodic structure as a diffraction element (diffraction grating), that is, the in-plane pitch p of the diffraction element. In other words, in the liquid crystal diffraction element, the in-plane pitch p is the distance between the centers of two liquid crystal compounds 58 that are at the same angle with respect to the alignment axis D direction, in the direction of the alignment axis D. Specifically, as shown in FIG. 20 , the in-plane pitch p is the distance between the centers of two liquid crystal compounds 58 whose alignment axis D direction and the direction of the optical axis 58A coincide, in the direction of the alignment axis D.

[0047] On the other hand, the liquid crystal compounds 58 forming the cholesteric liquid crystal layer 54 have the same orientation of the optical axes 58A in the direction perpendicular to the direction of the alignment axis D (the Y direction in FIG. 20 ), i.e., in the Y direction perpendicular to the direction in which the optical axes 58A continuously rotate. In other words, the liquid crystal compounds 58 forming the cholesteric liquid crystal layer 54 have the same angle between the optical axes 58A of the liquid crystal compounds 58 and the alignment axis D (the X direction) in the Y direction.

[0048] The diffraction effect of the cholesteric liquid crystal layer will be described below. In a typical cholesteric liquid crystal layer, the cholesteric liquid crystal phase is specularly reflective. Therefore, for example, when light is incident on the cholesteric liquid crystal layer from the normal direction, the light is reflected in the normal direction. In contrast, the cholesteric liquid crystal layer 54 is a reflective liquid crystal diffraction element that reflects incident light at an angle in the direction of the alignment axis D relative to the specular reflection. The cholesteric liquid crystal layer 54 has a liquid crystal orientation pattern in which the optical axis 58A changes while continuously rotating in-plane along the direction of the alignment axis D (a predetermined direction). The following description will be made with reference to FIG. 21 .

[0049] As an example, the cholesteric liquid crystal layer 54 is configured to polarize right-handed circularly polarized red light R R Therefore, when light is incident on the cholesteric liquid crystal layer 54, the cholesteric liquid crystal layer 54 selectively reflects right-handed circularly polarized red light R R It reflects only light and transmits all other light.

[0050] In the cholesteric liquid crystal layer 54, the optical axis 58A of the liquid crystal compound 58 changes while rotating along the direction of the alignment axis D (one direction). The liquid crystal alignment pattern formed in the cholesteric liquid crystal layer 54 is a periodic pattern along the direction of the alignment axis D. Therefore, the right-handed circularly polarized light R of red light incident on the cholesteric liquid crystal layer 54 R As conceptually shown in FIG. 5, the right-handed circularly polarized light R of the reflected red light is reflected (diffracted) in a direction according to the period of the liquid crystal orientation pattern. R is reflected (diffracted) in a direction tilted toward the alignment axis D direction with respect to the XY plane (the main surface of the cholesteric liquid crystal layer).

[0051] In the cholesteric liquid crystal layer 54, the direction of the alignment axis D, which is one direction in which the optical axis 58A rotates, can be appropriately set to adjust the reflection direction (diffraction direction) of light.

[0052] Furthermore, when reflecting circularly polarized light of the same wavelength and the same rotation direction, the reflection direction of the circularly polarized light can be reversed by reversing the rotation direction of the optical axis 58A of the liquid crystal compound 58 that faces the alignment axis D. For example, in Figures 19 and 20, the rotation direction of the optical axis 58A that faces the alignment axis D is clockwise, and some circularly polarized light is reflected with an inclination toward the alignment axis D. However, by changing this to counterclockwise, some circularly polarized light is reflected with an inclination in the opposite direction to the alignment axis D.

[0053] Furthermore, in liquid crystal layers having the same liquid crystal orientation pattern, the reflection direction is reversed depending on the helical rotation direction of the liquid crystal compound 58, i.e., the rotation direction of the reflected circularly polarized light. For example, if the helical rotation direction is right-handed, right-handed circularly polarized light is selectively reflected, and a liquid crystal layer having a liquid crystal orientation pattern in which the optical axis 58A rotates clockwise along the alignment axis D direction reflects right-handed circularly polarized light with an inclination toward the alignment axis D direction. Also, for example, if the helical rotation direction is left-handed, left-handed circularly polarized light is selectively reflected, and a liquid crystal layer having a liquid crystal orientation pattern in which the optical axis 58A rotates clockwise along the alignment axis D direction reflects left-handed circularly polarized light with an inclination opposite to the alignment axis D direction.

[0054] In a cholesteric liquid crystal layer (reflective liquid crystal diffraction element) having a liquid crystal orientation pattern, the shorter the in-plane pitch p, the greater the angle of the reflected light relative to the incident light. In other words, the shorter the in-plane pitch p, the greater the angle at which the reflected light can be reflected relative to the incident light. For example, when light is incident from the normal direction of the liquid crystal diffraction element, the shorter the in-plane pitch p, the greater the angle between the direction of propagation of the reflected light and the normal direction. Therefore, the length of the in-plane pitch p of the liquid crystal diffraction element can be appropriately set depending on the angle of incidence on the light-guiding substrate, etc., so that the diffracted light reflected by the liquid crystal diffraction element (reflective diffraction element) can enter the light-receiving sensor arranged on surface C. The method for setting the in-plane pitch p of the reflective diffraction element in this invention will be described in detail later.

[0055] Such a cholesteric liquid crystal layer may be formed by a known method, for example, by applying a liquid crystal composition containing a liquid crystal compound and a chiral agent to an alignment film, heating and drying the liquid crystal composition to align the liquid crystal compound, and then curing the liquid crystal compound by irradiation with ultraviolet light or the like, as necessary, to form a cholesteric liquid crystal layer.

[0056] In the optical sensor of the present invention, the light-guiding substrate is not particularly limited, and any known light-guiding plate used in, for example, AR glasses and backlight units in liquid crystal display devices can be used as long as it can guide incident light. The shape of the light-guiding substrate is also not limited, and various shapes can be used, including a wedge shape as shown in FIG. 1 and various shapes described below, as long as it has a surface A serving as a light incident surface, a surface B having an inclination angle (inclination angle a) of 25° or less with respect to surface A and on which a reflective diffraction element can be disposed, and a surface C on which a light-receiving sensor can be disposed.

[0057] Furthermore, in the optical sensor of the present invention, there is no limitation on the light-receiving sensor, and various known optical sensors can be used as long as they can sense (detect) the reception (incidence) of incident light. Examples include a photodiode, a photomultiplier, and a two-dimensional sensor.

[0058] In the optical sensor of the present invention, there are no limitations on the method for attaching the light-receiving sensor and the reflective diffraction element to the light-guiding substrate, and known methods can be used. Examples include a method of bonding using an adhesive that is sufficiently transparent to incident light, a method using a transparent adhesive such as an OCA (Optically Clear Adhesive) or a PSA (Pressure Sensitive Adhesive), and a method using plasma. Examples of adhesives include photocurable adhesives and thermosetting adhesives. Furthermore, when a liquid crystal diffraction element is used as the reflective diffraction element, an alignment film may be formed on the light-guiding substrate and cholesteric liquid crystals may be formed on the surface thereof to form a liquid crystal diffraction element on the light-guiding substrate. The optical sensor of the present invention is not limited to a configuration in which the light-receiving sensor and / or the reflective diffraction element are attached to the light-guiding substrate. That is, the optical sensor of the present invention may be arranged on the light-guiding substrate with a separate support member for supporting the light-receiving sensor and / or the reflective diffraction element, with the reflective diffraction element facing surface B and the light-receiving sensor facing surface C.

[0059] As described above, in the optical sensor of the present invention, surface A of the light-guiding substrate is the light incident surface, a reflective diffraction element is provided on surface B, and a light-receiving sensor is provided on surface C. Here, in the optical sensor of the present invention, an optical member that auxiliary changes the direction of light may be disposed on surface A and / or surface C of the light-guiding substrate, as necessary. Specific examples include optical members such as lenses and prisms that have functions such as light collection and refraction.

[0060] The state of incident light that has entered the wedge-shaped light guiding substrate 101 will now be described.

[0061] FIG. 7 is an example of a more detailed schematic depiction of the incident light 401 incident from the surface C side of the wedge-shaped light-guiding substrate 101 with respect to the normal to the surface A of the wedge-shaped light-guiding substrate 101 in FIG. 3 at an incident angle X1 [°]. As described above, in the present invention, for convenience, the incident angle from this direction is considered negative. When the incident light 401 enters the wedge-shaped light-guiding substrate 101, the incident light 401 is refracted at a refraction angle X2 [°] at the interface (surface A) between air and the wedge-shaped light-guiding substrate 101. That is, the refraction angle X2 is the angle of incidence of the incident light 401 inside the wedge-shaped light-guiding substrate 101. In the following description, the refraction angle X2 will also be referred to as the incident angle X2. When the refractive index of the wedge-shaped light-guiding substrate 101 is n, the incident angle X1 and the incident angle X2 are related by the following formula (b). Furthermore, sin is sine. sin(|X1|)=n×sin(X2) Equation (b) After that, the incident light 401 refracted at the interface (surface A) is incident on the first reflective diffraction element 201 arranged on surface B at an incident angle X2-a, where "a" is the tilt angle a [°], i.e., the angle of surface B relative to surface A.

[0062] FIG. 8 is a schematic diagram showing an example of the state of light after the incident light 401 in FIG. 7 is diffracted by the first reflective diffraction element 201. The diffraction angle [°] of the diffracted light 501 by the first reflective diffraction element 201 is defined as "Y." Here, if the wavelength of the incident light 401 is defined as λ [nm], the in-plane pitch of the diffraction element, i.e., the reciprocal of the number of grooves in a surface relief type diffraction element, and the length over which the optical axis rotates 180° in a liquid crystal diffraction element, are defined as the in-plane pitch p [nm], the angle of incidence X2-a and the angle of diffraction Y are related by the following formula (c-1): n×p=λ / {sin(X2-a))+sin(Y)} Formula (c-1) The diffracted light then strikes surface A at an angle of incidence Y+a. In order for the diffracted light 501 to be totally reflected, the angle of incidence Y+a on surface A must be greater than the critical angle. In other words, the formula (a) must be satisfied. n×sin(Y+a)>1 Formula (a)

[0063] 9 is a schematic example of incident light 403 incident at an incident angle X1 from the side opposite to surface C with respect to the normal to surface A of the wedge-shaped light guiding substrate 101 in FIG. 5. As described above, in the present invention, for convenience, the incident angle from this direction is considered positive. In this example, the relationship between the incident angle X1 and the incident angle (refraction angle) X2 is expressed by formula (b), as in the example shown in FIG.

[0064] Furthermore, when light is not diffracted by the first reflective diffraction element 201 and the second reflective diffraction element 202 arranged on surface B, but is incident on surface B or the third reflective diffraction element 203 at an incident angle of X2+a, the same concept as in FIG. 8 and formula (c-1) can be used. In other words, formula (c-2) is used. n×p=λ / {sin(X2+a))+sin(Y1)} formula (c-2)

[0065] 10 is a schematic diagram assuming that the incident light 403 in FIG. 5 is not totally reflected by surface B, and is a diagram showing a schematic example of the state of the light after being diffracted by the third reflection type diffraction element 203. As described above, the same concept as in FIG. 8 and formula (a) can be used, except that the diffracted light is incident on surface A at an incident angle of Y+a.

[0066] In the optical sensor of the present invention, based on the above-mentioned concept, by determining the in-plane pitch p of the reflective diffractive elements so that incident light at the following angles is totally reflected depending on the number of reflective diffractive elements, it is possible to guide incident light at various angles toward the light-receiving sensor: 1) When the number of reflective diffractive elements is 2: X1 = -30°, -80° 2) When the number of reflective diffractive elements is 3: X1 = 30°, -30°, -80° 3) When the number of reflective diffractive elements is 4: X1 = 60°, 30°, -30°, -80°

[0067] For example, if the number of reflective diffraction elements is two, by setting the in-plane pitch p so that incident light with an incident angle X1 of -30° and -80° is totally reflected, one reflective diffraction element can diffract incident light from -30° to +30°, and the other reflective diffraction element can diffract incident light from -80° to -30°, thereby satisfying the total reflection condition toward the light receiving sensor 301 (surface C). This is because the in-plane pitch for diffracting incident light with an incident angle of -30° and incident light with an incident angle of -80° is the smallest in each range, so light with other incident angles is more diffracted and the total reflection condition is easily satisfied. In addition, in this case, it is assumed that the inclination angle a is such that incident light with an incident angle X1 of +30° to +80° is totally reflected on surface B of the wedge-shaped light guiding substrate 101 even without a reflective diffraction element.

[0068] The same idea applies when the number of reflective diffraction elements is 3 or 4. Furthermore, if the opening (surface A) is made wider, that is, if the inclination angle a is small, this can be addressed by increasing the number of reflective diffraction elements. However, if the number of reflective diffraction elements is 5 or more, the range of incident angles becomes narrower, and diffraction occurs even with other reflective diffraction elements, making it difficult to diffract light in the desired direction. Two, three, or four reflective diffraction elements are sufficient, and the number should be selected appropriately taking into account the area of ​​the opening.

[0069] That is, in the present invention, as shown in Figures 9 and 10, when incident light is reflected and diffracted by a reflective diffraction element, and then the diffracted light is incident on surface A and totally reflected by surface A, thereby causing the diffracted light to be incident on light-receiving sensor 301, i.e., surface C, or when the diffracted light is directly incident on surface C as shown in Figures 4 and 6, by setting the in-plane pitch p [nm] so that the reflective diffraction element satisfies formula (c-2) or so that formulas (c-1) and (c-2), the incident light can be suitably incident on surface C. n x p = λ / {sin(X2 - a) + sin(Y)} formula (c-1) n x p = λ / {sin(X2 + a) + sin(Y)} formula (c-2)

[0070] Specifically, as described above, the range of the diffraction angle Y of a reflective diffraction element that can totally reflect diffracted light by surface A can be determined by the following formula (a): n × sin(Y + a) > 1 Formula (a) As described above, n is the refractive index of the light-guiding substrate, and a is the tilt angle. Note that tilt angle a is the tilt angle of surface B relative to surface A.

[0071] On the other hand, as described above, the relationship between the incident angle X1 of light incident on the wedge-shaped light guiding substrate 101 and the incident angle X2 inside the wedge-shaped light guiding substrate 101, i.e., the diffraction angle at the interface of surface A, is expressed by formula (b): sin(|X1|)=n×sin(X2)

[0072] From the range of diffraction angles Y at which total reflection at surface A is possible, as found in formula (a), a diffraction angle Y at which diffracted light can be incident on surface C by total reflection by surface A or directly by diffraction by the reflective diffraction element is selected as appropriate, and the in-plane pitch p of the reflective diffraction element is calculated using formulas (c-1) and (c-2) and the incident angle X2 calculated using formula (b). n×p=λ / {sin(X2−a)+sin(Y)} formula (c-1) n×p=λ / {sin(X2+a)+sin(Y)} formula (c-2) Note that when the incident angle X1 is positive, formula (c-2) is used, and when the incident angle X2 is negative, formula (c-1) is used to calculate the in-plane pitch p.

[0073] Here, when the optical sensor has two reflective diffraction elements, the incident angle X1 of the incident light corresponding to each reflective diffraction element is set to -30° for one reflective diffraction element and -80° for the other reflective diffraction element. For example, in the example shown in FIGS. 1 to 4, the incident angle X1 of the first reflective diffraction element 201 corresponding to the incident light 401 is set to -80°, and the incident angle X1 of the second reflective diffraction element 202 corresponding to the incident light 402 is set to -30°. Using this incident angle X1 and equation (b), the incident angle X2 at the first reflective diffraction element 201 and the second reflective diffraction element 202 is calculated. Since the incident angle X1 is negative for both, the in-plane pitch p of the first reflective diffraction element 201 and the second reflective diffraction element 202 is calculated using equation (c-1) using the calculated incident angle X2 and the diffraction angle Y set according to each reflective diffraction element. That is, when the number of reflective diffraction elements is two, the in-plane pitch p of the reflective diffraction elements is calculated using only formula (c-1).

[0074] This makes it possible to set an in-plane pitch p such that the first reflective diffraction element 201 reflects and diffracts incident light 401 having an incident angle X1 of −80° to −30°, and the second reflective diffraction element 202 reflects and diffracts incident light 402 having an incident angle X1 of −30° to +30°, and the incident light 402 can be properly incident on the light-receiving sensor 301 (surface C). Note that in this example, as described above, an inclination angle a is assumed such that incident light having an incident angle X1 of +30° to +80° is totally reflected by surface B of the wedge-shaped light guiding substrate 101 even without a reflective diffraction element.

[0075] Furthermore, when the optical sensor has three reflective diffraction elements, the incident angle X1 of the incident light corresponding to each reflective diffraction element is set to -30° for the first reflective diffraction element, -80° for the second reflective diffraction element, and 30° for the third reflective diffraction element. As described above, a configuration in which the optical sensor has three (three or more) reflective diffraction elements corresponds to a case in which, for example, the inclination angle a is reduced in order to enlarge the opening, i.e., surface A, and therefore the positive incident light may not be totally reflected by surface B of the wedge-shaped light guiding substrate 101. For example, in the example shown in FIGS. 5 and 6, the first reflective diffraction element 201 and the second reflective diffraction element 202 are set to -80° and -30° as the incident angle X1, as before, and the third reflective diffraction element 203 is set to 30° as the incident angle X1. Then, for the first reflective diffraction element 201 and the second reflective diffraction element 202, the in-plane pitch p is calculated and set as before. Similarly, the incident angle X2 is calculated using equation (b) for the third reflective diffraction element 203. Since this incident angle X1 is positive, the in-plane pitch p of the third reflective diffraction element 203 is calculated using equation (c-2) using the calculated incident angle X2 and the diffraction angle Y set according to the third reflective diffraction element 203.

[0076] This allows the first reflective diffraction element 201 to reflect and diffract incident light 401 with an incident angle X1 of -80° to -30°, the second reflective diffraction element 202 to reflect and diffract incident light 402 with an incident angle X1 of -30° to +30°, and the third reflective diffraction element 203 to reflect and diffract incident light 403 with an incident angle X1 of +30° to +80°, respectively, and makes it possible to set an in-plane pitch p that allows the light to properly enter the light receiving sensor 301 (surface C).

[0077] Furthermore, when the optical sensor has four reflective diffraction elements, the incident angle X1 of the incident light corresponding to each reflective diffraction element is set as follows: -30° for the first reflective diffraction element, -80° for the second reflective diffraction element, 30° for the third reflective diffraction element, and 80° for the fourth reflective diffraction element. This embodiment corresponds to the configuration shown in FIGS. 5 and 6, for example, in which a fourth reflective diffraction element is further provided. In this case, as an example, the incident angles X1 of -80°, -30°, and 30° are set for the first reflective diffraction element 201 to the third reflective diffraction element 203, as described above, and the incident angle X1 of 80° is set for the fourth reflective diffraction element. Then, the in-plane pitch p is calculated and set for the first reflective diffraction element 201 to the third reflective diffraction element 2032, as described above. Furthermore, for the fourth reflective diffraction element, since the incident angle X1 is positive, the in-plane pitch p is calculated and set using equation (c-2) in the same way as for the third reflective diffraction element.

[0078] The in-plane pitch p may be set in this manner for at least one of the two to four reflective diffraction elements in the optical sensor of the present invention. That is, for example, if the optical sensor of the present invention has two reflective diffraction elements, the in-plane pitch p may be set for only one of the reflective diffraction elements using the above-described method, and the in-plane pitch p for the other reflective diffraction elements may be set using another method. However, in the present invention, it is preferable to set the in-plane pitch p for all two to four reflective diffraction elements using the above-described method. A reflective diffraction element having an in-plane pitch p set using the above-described method can transmit incident light without reflection or diffraction when the incident light has an incompatible incident angle X1. That is, by setting the in-plane pitch of all reflective diffraction elements using the above-described method, even when incident light has an incident angle X1 corresponding to the other reflective diffraction elements, the incident light can be transmitted without reflection or diffraction, thereby preventing the incident light from being diffracted in unwanted directions.

[0079] The above optical sensor is an example in which the light-guiding substrate is wedge-shaped, but the present invention is not limited thereto, and various shapes can be used for the light-guiding substrate. FIG. 11 shows an example. In FIG. 11 , the light-guiding substrate 102 has four faces B, and face B has a shape that forms a part of a quadrangular pyramid. In other words, this light-guiding substrate 102 has a quadrangular pyramid-shaped recess on one of the largest faces of the rectangular parallelepiped-shaped light-guiding substrate, and the side faces of this recess are faces B. Therefore, in this example, there are four faces B and four faces C. Specifically, the largest face of the rectangular parallelepiped that does not have a recess is face A, the four side faces of the quadrangular pyramid are faces B, and the four side faces of the rectangular parallelepiped are faces C.

[0080] Although not shown in the figure, in this case, a reflective diffraction element is disposed on each surface B, and a light-receiving sensor is disposed on each surface C. With this configuration, incident light entering from all four directions can be reflected and diffracted by the reflective diffraction element, and can be made to preferably enter the light-receiving sensor, i.e., surface C. The above points also apply to the embodiments shown in Figures 12 to 18, which will be described later.

[0081] In the embodiment shown in Fig. 11, as shown in two enlarged partial views in Fig. 11, the apex of the quadrangular pyramid formed by surface B may reach surface A, or may not reach surface A, with the light guiding substrate 102 existing between the apex of the quadrangular pyramid and surface A. This point also applies to the embodiments shown in Figs. 12 to 16, which will be described later.

[0082] 11, the light guiding substrate 102 has a rectangular parallelepiped shape with a recess, but the present invention is not limited to this. For example, the light guiding substrate may have a triangular prism shape, with face B constituting a part of a triangular pyramid, that is, a triangular pyramid-shaped recess may be provided on one of the largest faces of the triangular prism. Alternatively, the light guiding substrate may have a hexagonal prism shape, with face B constituting a part of a hexagonal pyramid, that is, a hexagonal pyramid-shaped recess may be provided on one of the largest faces of the hexagonal prism. This configuration can also be applied to the embodiments shown in FIGS. 12 to 16, which will be described later.

[0083] The surface B of the light guiding substrate is not limited to being a part of a quadrangular pyramid. That is, the recess formed on the light guiding substrate to become surface B is not limited to being a quadrangular pyramid. For example, as in the light guiding substrate 103 schematically shown in FIG. 12, the surface B of the light guiding substrate may be a part of a truncated quadrangular pyramid. That is, the recess formed on the light guiding substrate to become surface B may be a truncated quadrangular pyramid. In this case, the four side surfaces of the truncated cone become surface B. Alternatively, as in the light guiding substrate 104 schematically shown in FIG. 13, the surface B of the light guiding substrate may be a part of a cone. That is, the recess formed on the light guiding substrate to become surface B may be a cone. In this case, the side surfaces of the cone become surface B. Furthermore, as in the light guiding substrate 104 schematically shown in FIG. 14, the surface B of the light guiding substrate may be a part of a truncated cone. That is, the recess formed on the light guiding substrate to become surface B may be a truncated cone. In this case, the side surface of the truncated cone becomes surface B. Furthermore, as in the light guiding substrate 104 schematically shown in Fig. 15 , surface B of the light guiding substrate may constitute a part of a spherical crown. That is, the recess formed in the light guiding substrate to become surface B may be a spherical crown. In this case, the spherical surface of the spherical crown becomes surface B.

[0084] In the spherical crown-shaped surface B shown in Fig. 15, the inclination angle a is measured as follows. Fig. 16 is a cross-sectional view of Fig. 15. In this case, the inclination angle a is the inclination of a tangent at a point that is one-third the length (L / 3) of the distance L from the center of the spherical crown to the edge, i.e., the inclination of this tangent to surface A is defined as the inclination angle a of surface B with respect to surface A.

[0085] In all of the above examples, the light guiding substrate has a shape in which surface C is the surface connecting surface A and surface B. However, the present invention is not limited to this, and the light guiding substrate may have a shape in which surface A and surface C oppose each other (face to face). FIG. 17 schematically shows one example. In the example shown in FIG. 17 , the light guiding substrate 107 has a truncated cone shape. In this case, as an example, the larger bottom surface of the truncated cone is surface A, i.e., the light incident surface, the reflective diffraction element is disposed on the side surface of the truncated cone as surface B, and the light receiving sensor is disposed on the smaller bottom surface of the truncated cone as surface C. That is, in this example, by disposing the light receiving sensor on the smaller bottom surface, light enters from the larger bottom surface, is guided through the light guiding substrate 107, and the collected light is received after being diffracted by the reflective diffraction element.

[0086] Fig. 18 is a top view of another example of a wedge-shaped light guiding substrate. That is, Fig. 18 is a view of the wedge-shaped light guiding substrate as viewed from the side of surface A. In the case of a light guiding substrate in which the width narrows from the tip of the wedge toward the light-receiving sensor side, i.e., surface C, as in light guiding substrate 108 shown in Fig. 18, by arranging multiple reflective diffraction elements on surface B so that the diffraction angle remains the same but the diffraction direction changes depending on the location, or by arranging reflective diffraction elements patterned in this way on surface B, diffracted light 604 to 606 can be concentrated on the light-receiving sensor side.

[0087] Although typical embodiments of the present invention have been described above, the present invention is not limited to these and various embodiments that can be understood by those skilled in the art can be applied as long as they fall within the scope of the claims of the present invention.

[0088] 101 Wedge-shaped light-guiding substrate 201 First reflective diffraction element 202 Second reflective diffraction element 203 Third reflective diffraction element 301 Light-receiving sensor 401, 402, 403 Incident light 501, 502, 503, 604, 605, 606 Diffracted light 102, 103, 104, 105, 106, 107, 108 Light-guiding substrate

Claims

1. An optical sensor having at least a light guide substrate, a light receiving sensor, and a reflective diffraction element, wherein the light guide substrate has at least a surface A on which light is incident, a surface B inclined with respect to the surface A, and a surface C, the inclination angle of the surface B with respect to the surface A is 25° or less, the reflective diffraction element is disposed on the surface B, and the light receiving sensor is disposed on the surface C.

2. The optical sensor according to claim 1, wherein the light guide substrate has one or more surfaces B, and the surface B constitutes at least a part of any one of a pyramid, a frustum of a pyramid, a cone, a frustum of a cone, and a spherical crown.

3. The optical sensor according to claim 1 or 2, wherein as the reflective diffraction element, there are 2 to 4 of the reflective diffraction elements having different diffraction angles, and when the diffraction angle Y [°] of each of the reflective diffraction elements is used, the reflective diffraction element satisfies the following formula (c-1), or has an in-plane pitch p [nm] that satisfies formula (c-1) and formula (c-2). n × sin(Y + a) > 1 Formula (a) sin(|X1|) = n × sin(X2) Formula (b) n × p = λ / {sin(X2 - a) + sin(Y)} Formula (c-1) n × p = λ / {sin(X2 + a) + sin(Y)} Formula (c-2) Here, the in-plane pitch p [nm] is a value represented by formula (c-1) or formula (c-2) using formula (a) and formula (b). Also, X1 [°] is the incident angle of the incident light with respect to the normal of the surface A, and its positive or negative sign is positive when the light is incident from the side opposite to the surface C with respect to the normal of the surface A, and negative when the light is incident from the surface C side. X2 [°] is the incident angle inside the light guide substrate, λ [nm] is the wavelength of light, a [°] is the inclination angle of the surface B with respect to the surface A, and n is the refractive index of the light guide substrate. Also, when X1 is positive, formula (c-2) is used, and when X1 is negative, formula (c-1) is used. Also, the in-plane pitch of each of the reflective diffraction elements is calculated by substituting the incident angle X1 shown in the following 1) to 3) according to the number of the reflective diffraction elements included in the optical sensor. 1) When the number of the reflective diffraction elements is 2: X1 = -30°, -80° 2) When the number of the reflective diffraction elements is 3: X1 = 30°, -30°, -80° 3) When the number of the reflective diffraction elements is 4: X1 = 80°, 30°, -30°, -80° 4. The optical sensor according to claim 1 or 2, wherein the reflective diffraction element is a liquid crystal diffraction element.

5. The optical sensor according to claim 1 or 2, wherein in the light guide substrate, the surface C is a surface connecting the surface A and the surface B.

6. The optical sensor according to claim 1 or 2, wherein in the light guide substrate, the surface A and the surface C face each other.

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