Eye tracking device reduced in size and thickness

Abstract

To provide a light irradiation device that is thin and capable of projecting an optical pattern, and a sensor using the light irradiation device.SOLUTION: A light irradiation device has a light emitting element having a plurality of light emitting portions in a plane and a liquid crystal optical element. The liquid crystal optical element has an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound, and the optically anisotropic layer has a liquid crystal orientation pattern in which the direction of an optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and when the length of a 180° rotation of the direction of the optical axis derived from the liquid crystal compound in the plane is defined as one period, the liquid crystal optical element has regions in which the length of one period is different in the liquid crystal orientation pattern.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to miniaturizing and thinning an eye tracking device for sensing the position and gaze direction of the eyes. [Background technology]

[0002] Eye tracking is a sensing technology that detects the position and movement of the eyes to determine the state of a person's eyes and where they are looking, and has recently begun to be used in many devices. Examples include applications to prevent drivers of vehicles such as cars, trains, and airplanes from looking away or falling asleep, and applications such as tracking the gaze of the wearer in a head-mounted display (HMD) for augmented reality and virtual reality, as described in Patent Document 1.

[0003] Known devices include those that irradiate the eye with an infrared light source directly or using a light guide plate, as in Patent Document 2 and Patent Document 3. Also known is a method of performing eye tracking by irradiating the eye with multiple point light sources, as in Patent Document 4. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2023-512166 [Patent Document 2] Japanese Patent Application Publication No. 2020-81449 [Patent Document 3] Special Publication No. 2023-509305 [Patent Document 4] Special Publication No. 2022-523306 Summary of the Invention [Problem to be solved by the invention]

[0005] However, these devices require a distance between the light source and optical components for eye detection, which raises concerns that the device will become larger and thicker. Particularly in the case of HMDs, if the distance between the eyes and the components becomes too great, the entire device will easily shift due to gravity, causing fatigue and inconvenience to the wearer.

[0006] In view of these considerations, an object of the present invention is to provide a small, thin eye tracking device. [Means for solving the problem]

[0007] In order to solve this problem, the optical element of the present invention has the following configuration. [1] A light guide plate; a light source and a sensor for detecting the position and movement of the eye, which are arranged at the end of the light guide plate; The liquid crystal display device includes at least a liquid crystal optical element 1 and a liquid crystal optical element 2, The liquid crystal optical element 1 is a reflective liquid crystal diffraction element, and is placed on the surface of the light guide plate on the extension of the line of sight. The liquid crystal optical element 2 is an eye tracking device in which a plurality of transmissive liquid crystal diffraction elements are arranged in a circumferential pattern and is disposed between the light source and the end of the light guide plate. [2] An eye tracking device according to [1], wherein the liquid crystal optical element 2 is arranged on the light guide plate surface on the side opposite to the liquid crystal optical element 1, on an extension of the line of sight. [3] An eye tracking device according to [1] or [2], in which the liquid crystal optical element 2 has regions in which the length of one period in the liquid crystal orientation pattern varies when the length of the optical axis direction derived from the liquid crystal compound rotates 180° in-plane is taken as one period, and the one period gradually becomes shorter in one direction. [4] An eye tracking device according to any one of [1] to [3], wherein the light source is infrared light, and a retardation plate with a wavelength of λ / 4 relative to the wavelength of the light source is disposed between the liquid crystal diffraction element 1 or the liquid crystal diffraction element 2 and the observer. [Effects of the Invention]

[0008] According to the present invention, a thin and compact eye tracking device can be provided. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram conceptually illustrating an example of an eye tracking device of the present invention. [Figure 2] FIG. 2 is a diagram conceptually showing the details of the light source and the liquid crystal diffraction element 2 in FIG. [Figure 3] FIG. 3 is a diagram showing another example of an eye tracking device of the present invention. [Figure 4] FIG. 4 is a top view of FIG. [Figure 5] FIG. 5 is a conceptual diagram showing an example of a reflective liquid crystal diffraction element. [Figure 6] FIG. 6 is a plan view conceptually showing the liquid crystal layer of the reflective liquid crystal diffraction element shown in FIG. [Figure 7] FIG. 7 is a conceptual diagram for explaining the function of the liquid crystal layer of the reflective liquid crystal diffraction element shown in FIG. [Figure 8] FIG. 8 is a conceptual diagram showing an example of a transmissive liquid crystal diffraction element. [Figure 9] FIG. 9 is a plan view conceptually showing the liquid crystal layer of the transmissive liquid crystal diffraction element shown in FIG. [Figure 10] FIG. 10 is a conceptual diagram for explaining the function of the liquid crystal layer of the transmissive liquid crystal diffraction element shown in FIG. [Figure 11] FIG. 11 is a conceptual diagram for explaining the function of the liquid crystal layer of the transmissive liquid crystal diffraction element shown in FIG. [Figure 12] FIG. 12 is a plan view conceptually illustrating another example of the liquid crystal layer of the transmissive liquid crystal diffraction element shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0010] The eye tracking device of the present invention will be described in detail below.

[0011] 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. In this specification, "identical" includes a generally accepted margin of error in the technical field. Furthermore, in this specification, when referring to "all," "any," "entire," etc., it includes not only 100% but also a generally accepted margin of error in the technical field, such as 99% or more, 95% or more, or 90% or more.

[0012] In this specification, visible light refers to electromagnetic waves with wavelengths visible to the human eye, in the wavelength range of 380 to 780 nm, while invisible light refers to light with wavelengths shorter than 380 nm and longer than 780 nm. In addition, although not limited thereto, among visible light, light in the wavelength range of 420 to 490 nm is blue light, light in the wavelength range of 495 to 570 nm is green light, and light in the wavelength range of 620 to 750 nm is red light. Furthermore, although not limited thereto, among invisible light, ultraviolet light (ultraviolet light) is light in the wavelength range of less than 380 nm and not less than 200 nm, and infrared light (infrared light) is light in the wavelength range of more than 780 nm and not more than 12,000 nm.

[0013] FIG. 1 shows a conceptual diagram of an example of an eye tracking device of the present invention. The eye tracking device shown in FIG. 1 has at least a light source (10), a light receiving sensor (11), a light guide plate (12), a liquid crystal diffraction element 1 (13), and a liquid crystal diffraction element 2 (14). The liquid crystal diffraction element 2 is an element made up of multiple transmissive liquid crystal diffraction elements, and can convert light from a light source into multiple circular point light sources. The liquid crystal diffraction element 1 is a reflective liquid crystal diffraction element, and deflects the guided light from the light source toward the viewer's eyes.

[0014] As described above, by appropriately performing refraction, focusing, and reflection using a liquid crystal diffraction element so that the light from the light source becomes a circular point source at the position of the eye, multiple circular point sources can be formed around the cornea of ​​the eye, which is necessary for eye tracking.

[0015] Furthermore, these point light sources reflected by the surface of the cornea of ​​the eye are diffracted again by the liquid crystal diffraction element 1, and are sensed by the light-receiving sensor. The data is then processed appropriately, enabling eye tracking.

[0016] FIG. 2 is a conceptual diagram showing the details of the configuration of the light source and the liquid crystal diffraction element 2 in FIG. By arranging the liquid crystal diffraction element 2 on the output side of the light source, it is possible to form a plurality of circular point light sources. If necessary, an optical element for collimating the light from the light source may be disposed between the light source and the liquid crystal diffraction element 2. By collimating the light from the light source, the light incident on the liquid crystal diffraction element 2 is efficiently refracted or focused, thereby increasing the brightness of the point light source and improving the detection sensitivity. Examples of optical elements include, but are not limited to, lenses and louvers.

[0017] A single light source or multiple light sources may be used, but it is preferable that each transmissive liquid crystal diffraction element of the liquid crystal diffraction element 2 acts as a convex lens as described below, because even a single light source can form multiple circular point light sources after passing through the liquid crystal diffraction element 2.

[0018] 2, the light receiving sensor is located at the same end as the light source, but this is not limiting and it may be located at the other end. In this case, the liquid crystal diffraction element 1 may be provided with a layered diffraction element for receiving light reflected from the eye. Since the optical rotation of circularly polarized light changes when it is reflected by the eye, by placing a liquid crystal diffraction element that diffracts circularly polarized light with different optical rotation, only the light reflected from the eye can be diffracted and sensed toward the light receiving sensor without interfering with the diffraction of the LED light.

[0019] Furthermore, the liquid crystal diffraction element 1 may change the diffraction angle depending on the location in accordance with the emission angle of the light source, so that the light entering the liquid crystal diffraction element 2 becomes nearly parallel. By making the light nearly parallel, the detection sensitivity can be increased, as described above.

[0020] Furthermore, if the light-receiving sensor is located at the same end as the light source, a retardation plate may be placed between the liquid crystal diffraction element 1 or 2 and the observer. Specifically, a λ / 4 plate may be used to change the light emitted from the liquid crystal diffraction element from circularly polarized light to linearly polarized light. In the case of circularly polarized light, the optical rotation state changes (right to left or left to right) when reflected and diffracted again by the liquid crystal diffraction element 1, resulting in low diffraction efficiency and reduced detection sensitivity at the light-receiving sensor.

[0021] The wavelength of the light source is not limited as long as it allows for eye detection, but it is preferably invisible light, and in consideration of safety, it is preferably infrared light. An example of a liquid crystal diffraction element will be described below.

[0022] 3 and 4 are another example of an eye tracking device of the present invention. The light from the light source is guided by the liquid crystal diffraction element 1 and deflected toward the viewer's eye, just as in Figure 1, and multiple circular point light sources can be formed at the cornea of ​​the eye by the liquid crystal diffraction element 2. The arrangement of other light sources and light-receiving sensors can be determined appropriately according to the application, just as above.

[0023] (Reflective liquid crystal diffraction element) An example of a reflective diffractive element is a reflective liquid crystal diffractive element having a cholesteric liquid crystal layer formed by cholesterically aligning a liquid crystal compound as an optically anisotropic film. In this reflective liquid crystal diffractive element, the cholesteric liquid crystal layer preferably has a liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in one direction. In this reflective diffraction element, the length by which the optical axis derived from the liquid crystal compound rotates 180° in one direction is the in-plane pitch a, and this in-plane pitch a is one period (one period Λ) in the periodic structure of the diffraction element. In the case of a reflective diffraction element, the in-plane pitch a [nm] is determined from the following formula for first-order diffracted light, and based on that, the photo-alignment film can also be subjected to interference exposure as appropriate, for example, using an exposure device described later. n×a×(sinβ+sinγ)=λ Here, n is the environmental refractive index on the incident light side that comes into contact with the reflective diffraction element (liquid crystal diffraction element), γ is the angle between the light incident on the reflective diffraction element and the normal to the surface of the reflective diffraction element, β is the angle between the reflected diffracted light at the reflective diffraction element and the normal to the surface of the reflective diffraction element, and λ is the wavelength of the incident light [nm]. Therefore, in a reflective diffraction element (reflective liquid crystal diffraction element), the in-plane pitch a should be set so as to obtain a desired reflection angle α.

[0024] In a reflective diffraction element (reflective liquid crystal diffraction element), the optically anisotropic film, i.e., the cholesteric liquid crystal layer, has a cholesteric orientation in the thickness direction. Here, the film thickness d [nm] of the cholesteric liquid crystal layer can be adjusted appropriately according to the required reflection efficiency. For example, to improve light utilization efficiency, the thickness of the liquid crystal can be adjusted to be at least seven times the helical pitch of the cholesteric orientation (the thickness over which the orientation of the liquid crystal molecules changes from 0° to 360° in the thickness direction). In addition, in the cholesteric liquid crystal layer, the wavelength range of the circularly polarized light that is selectively reflected varies depending on the helical pitch, and the longer the helical pitch, the longer the wavelength of the light that is selectively reflected (the selective reflection center wavelength). Therefore, the helical pitch of the cholesteric liquid crystal layer can be appropriately selected depending on the wavelength to be separated.

[0025] (Cholesteric structure formation) In addition, to obtain cholesteric alignment with a desired helical pitch in the thickness direction, the amount of chiral agent added described in WO 2021 / 256413 may be appropriately adjusted. The cholesteric liquid crystal layer may be formed by a known method. For example, a liquid crystal composition containing a liquid crystal compound and a chiral agent is prepared, the liquid crystal composition is applied to an alignment film (photo-alignment film), the applied layer is dried and heated for cholesteric alignment, and then, if necessary, light irradiation (ultraviolet irradiation) is performed to harden the liquid crystal compound (polymerize the liquid crystal compound). In this case, the liquid crystal compound is preferably a polymerizable liquid crystal compound, and the liquid crystal composition preferably contains a polymerization initiator.

[0026] An example of a reflective diffraction element having a cholesteric liquid crystal layer as an optically anisotropic film will be described in detail below. An example of a reflective liquid crystal diffraction element having a cholesteric liquid crystal layer as an optically anisotropic film is conceptually shown in Figures 5 and 6. Figures 5 and 6 show an example in which the liquid crystal compound constituting the cholesteric liquid crystal layer is a rod-shaped liquid crystal compound. As conceptually shown in Fig. 5, the reflective diffraction element has a support 30, an alignment film 32, and a cholesteric liquid crystal layer 34 that exhibits the function of a diffraction element. Fig. 6 is a schematic diagram showing the alignment state of the liquid crystal compound in the plane of the main surface of the cholesteric liquid crystal layer 34. In the following description, the principal surface of the cholesteric liquid crystal layer 34 is defined as the XY plane, and the cross section perpendicular to the XY plane is defined as the XZ plane. In the following description, the cholesteric liquid crystal layer will also be simply referred to as a liquid crystal layer.

[0027] 5 has a support 30, an alignment film 32, and a liquid crystal layer 34, but the present invention is not limited to this. The reflective diffraction element may have only the alignment film 32 and the liquid crystal layer 34, with the support 30 peeled off. Alternatively, the reflective diffraction element may have only the liquid crystal layer 34, with the support 30 and alignment film 32 peeled off.

[0028] <Support> The support 30 supports the alignment film 32 and the liquid crystal layer 34 . The support 30 can be made of various sheet-like materials (films, plates) as long as it can support the alignment film 32 and the liquid crystal layer 34. Examples include glass and resin films such as triacetyl cellulose (TAC) film and polyethylene terephthalate (PET) film. The support 30 preferably has a transmittance of 50% or more for the light to be separated, more preferably 70% or more, and even more preferably 85% or more.

[0029] <Alignment film> In the reflective diffraction element, an alignment film 32 is formed on the surface of a support 30 . The alignment film 32 is an alignment film for aligning the liquid crystal compound 40 in a predetermined liquid crystal alignment pattern when the liquid crystal layer 34 is formed. The liquid crystal layer 34 has a liquid crystal orientation pattern in which the direction of the optical axis 40A (see FIG. 6) derived from the liquid crystal compound 40 changes while continuously rotating along one in-plane direction. Therefore, the alignment film 32 is formed so that the liquid crystal layer 34 can form this liquid crystal orientation pattern.

[0030] The alignment film 32 may be of various known types. Among these, a photo-alignment film using a photo-alignable material is preferably used as the alignment film 32. That is, in a reflective diffraction element, a photo-alignment film formed by applying a photo-alignment material onto the support 30 is preferably used as the alignment film 32.

[0031] Examples of the photo-alignment material include azo compounds described in JP-A Nos. 2006-285197 and 2007-76839, aromatic ester compounds described in JP-A No. 2002-229039, maleimide and / or alkenyl-substituted nadiimide compounds having a photo-alignment unit described in JP-A Nos. 2002-265541 and 2002-317013, and the like. Preferred examples include the photocrosslinkable silane derivatives described in Japanese Patent Application Laid-Open No. 2003-520878 and Japanese Patent Application Laid-Open No. 2004-529220, and the photodimerizable compounds, particularly cinnamate compounds, chalcone compounds, and coumarin compounds, described in Japanese Patent Application Laid-Open No. 9-118717 and Japanese Patent Application Laid-Open No. 10-506420.

[0032] There is no limitation on the method for forming the alignment film 32, and various known methods can be used depending on the material for forming the alignment film 32. One example is a method in which a composition containing a photoalignment material is applied to the surface of the support 30 and dried, and then the alignment film 32 is exposed to laser light to form an alignment pattern. An example of an exposure apparatus that performs this exposure is the exposure apparatus shown in FIG. 3 of International Publication No. 2021 / 256413, which will be described later.

[0033] <Liquid crystal layer (cholesteric liquid crystal layer)> In the reflective diffraction element, a liquid crystal layer 34 is formed on the surface of an alignment film 32 . The liquid crystal layer 34 is a cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase. The liquid crystal layer 34 is also a cholesteric liquid crystal layer having a liquid crystal orientation pattern in which the optical axis (direction of the optical axis) derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane.

[0034] As conceptually shown in FIG. 5, the liquid crystal layer 34 has a helical structure in which liquid crystal compounds 40 are spirally twisted and stacked, similar to a typical cholesteric liquid crystal layer formed by fixing a cholesteric liquid crystal phase. The liquid crystal layer 34 has a structure in which the liquid crystal compound 40 is stacked in a spiral shape with one helical pitch (pitch P) being defined as a configuration in which the liquid crystal compound 40 is stacked in a spiral shape with one rotation (360° rotation).

[0035] 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 selectively reflected light is right-handed or left-handed circularly polarized depends on the twist direction (sense) of the helix of the cholesteric liquid crystal phase. The cholesteric liquid crystal layer selectively reflects circularly polarized light in a specific wavelength range depending on the length of the helical pitch. The longer the helical pitch, the longer the wavelength of the selectively reflected light (selective reflection center wavelength). The direction of rotation and the length of the helical pitch of the cholesteric liquid crystal phase can be adjusted by the type of liquid crystal compound forming the cholesteric liquid crystal layer, the type of chiral dopant added, and the amount of chiral dopant added.

[0036] As shown in FIG. 6, in the XY plane of the liquid crystal layer 34, the liquid crystal compounds 40 are aligned along multiple alignment axes D parallel to each other in the XY plane, and on each alignment axis D, the orientation of the optical axis 40A of the liquid crystal compounds 40 changes while continuously rotating toward one direction in the plane along the alignment axis D. In the illustrated example, the alignment axis D is oriented in the X direction. In addition, in the Y direction, the liquid crystal compounds 40 having the same optical axis 40A are aligned at equal intervals.

[0037] In the liquid crystal layer 34, the length (distance) of one period Λ of the liquid crystal orientation pattern is defined as the length of one period Λ in the direction of the alignment axis D, along which the optical axis 40A of the liquid crystal compound 40 rotates continuously in the plane. In the following description, this length of one period Λ is also referred to as "one period Λ." This one period Λ is the in-plane pitch a in the formula for the first-order diffracted light described above. The liquid crystal orientation pattern of the liquid crystal layer 34 repeats this one period Λ in one direction in which the direction of the arrangement axis D, i.e., the direction of the optical axis 40A, continuously rotates and changes. As described above, in the reflective diffraction element, this one period Λ is the period of the diffraction structure.

[0038] On the other hand, the liquid crystal compound 40 forming the liquid crystal layer 34 has the same orientation of the optical axis 40A in a direction perpendicular to the direction of the alignment axis D (Y direction in Figure 5), i.e., in the Y direction perpendicular to the direction in which the optical axis 40A continuously rotates.

[0039] The diffraction effect of the liquid crystal layer 34 that constitutes the reflective diffraction element will be described below. A typical cholesteric liquid crystal layer specularly reflects incident light, so 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 liquid crystal layer 34 reflects incident light at an angle tilted toward the direction of the array axis D relative to specular reflection. Therefore, for example, when light is incident on the liquid crystal layer 34 from the normal direction, the light is reflected in a direction tilted relative to the normal direction. This will be described below with reference to FIG. 7.

[0040] As an example, the liquid crystal layer 34 is a cholesteric liquid crystal layer that selectively reflects left-handed circularly polarized light in a specific wavelength range. Therefore, when light is incident on the liquid crystal layer 34, the liquid crystal layer 34 reflects only the left-handed circularly polarized light in the specific wavelength range and transmits other light. That is, when unpolarized light in a specific wavelength range is incident on the liquid crystal layer 34, the liquid crystal layer 34 reflects left-handed circularly polarized light and transmits right-handed circularly polarized light.

[0041] In the liquid crystal layer 34, the optical axis 40A of the liquid crystal compound 40 changes while rotating along the direction of the alignment axis D (one direction). The liquid crystal orientation pattern of the liquid crystal layer 34 is a periodic pattern in the direction of the alignment axis D. Therefore, left-handed circularly polarized light L incident on the liquid crystal layer 34 from the normal direction is reflected (diffracted) in a direction according to the period of the liquid crystal orientation pattern, as conceptually shown in Fig. 7, and the reflected left-handed circularly polarized light L is reflected (diffracted) in a direction tilted toward the alignment axis D with respect to the normal direction.

[0042] In the liquid crystal layer 34, the direction of the arrangement axis D, which is one direction in which the optical axis 40A rotates, can be appropriately set to adjust the direction of light reflection. 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 40A of the liquid crystal compound 40, which faces the alignment axis D. In Figures 5 and 6, the rotation direction of the optical axis 40A, which faces the alignment axis D, is clockwise, and left-handed circularly polarized light L is reflected with an inclination toward the alignment axis D. However, by changing this to counterclockwise, the left-handed circularly polarized light L is reflected with an inclination in the opposite direction to the alignment axis D. 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 40, that is, the rotation direction of the reflected circularly polarized light.

[0043] As described above, in this reflective diffraction element, one period Λ, which is the length of a 180° rotation of the optical axis of the liquid crystal compound in the liquid crystal orientation pattern of the liquid crystal compound in the liquid crystal layer, is the period (one period) of the diffraction structure. Furthermore, the direction in which the optical axis of the liquid crystal compound changes while rotating in the liquid crystal layer (direction of the arrangement axis D) is the periodic direction of the diffraction structure. This one period Λ corresponds to the in-plane pitch a in the first-order diffraction formula described above. In a reflective diffraction element, there is no limitation on the length of one period Λ of the diffraction element, and it may be set appropriately depending on the angle of incidence of light on the light guide plate 10, the desired reflection angle, and the like.

[0044] Here, in a reflective diffraction element (reflective liquid crystal diffraction element) having a liquid crystal orientation pattern, the shorter the period Λ, the larger the angle of the reflected light relative to the incident light. In other words, the shorter the period Λ, the more the reflected light can be reflected at a greater inclination relative to the incident light. For example, when light is incident from the normal direction, the shorter the period, the larger the angle between the normal direction and the reflected light. Furthermore, in a liquid crystal layer having this liquid crystal orientation pattern, the angle of reflection (diffraction angle) of light varies depending on the wavelength of the reflected light. Specifically, the longer the wavelength of light, the larger the angle of the reflected light relative to the incident light. Therefore, by selecting the length of one period Λ (in-plane pitch a) in the liquid crystal layer 34 according to the wavelength of the light to be separated, i.e., the light to be selectively reflected, the diffraction element 11 can reflect the incident light at the desired reflection angle α.

[0045] In a reflective diffraction element using a cholesteric liquid crystal layer, the cholesteric liquid crystal layer may be one layer or multiple layers. For example, when the incident light to be separated is light of a narrow band only around a typical infrared wavelength (850 nm, 940 nm), the cholesteric liquid crystal layer may be a single layer. Furthermore, when the incident light to be separated is white light (all visible light), the device may have three cholesteric liquid crystal layers: a cholesteric liquid crystal layer that selectively reflects red light, a cholesteric liquid crystal layer that selectively reflects green light, and a cholesteric liquid crystal layer that selectively reflects blue light. Furthermore, the cholesteric liquid crystal layer may have a so-called pitch gradient structure in which the helical pitch varies in the thickness direction to broaden the selective reflection wavelength band.

[0046] (Transmissive liquid crystal diffraction element) An example of a transmissive liquid crystal diffraction element is a transmissive liquid crystal diffraction element having an optically anisotropic film formed using a composition containing a liquid crystal compound, the film having a predetermined liquid crystal orientation pattern in which the direction of the optical axis derived from the liquid crystal compound rotates in one direction in the plane. In the case of a transmissive liquid crystal diffraction element, as will be described later, the liquid crystal material and film thickness can be selected appropriately so that Δnλ×d, which is expressed as the product of the refractive index anisotropy Δnλ at a wavelength λ [nm] of the optically anisotropic film and the film thickness d [nm] of the liquid crystal layer, becomes λ / 2.

[0047] Furthermore, the in-plane pitch a [nm] can be determined from the following formula for first-order diffracted light, and the optical alignment film can also be subjected to appropriate interference exposure based on this. n×a×(sinβ-sinγ)=λ Here, the in-plane pitch a is the distance between the liquid crystal molecules that change continuously from 0 to 180° in the plane. Also, n is the environmental refractive index on the incident light side that contacts the liquid crystal diffraction element, γ is the angle between the light incident on the liquid crystal diffraction element and the normal to the surface of the liquid crystal diffraction element, β is the angle between the transmitted diffracted light and the normal to the surface of the liquid crystal diffraction element, and λ is the wavelength of the incident light [nm]. As in the reflective liquid crystal diffraction element, in the transmissive liquid crystal diffraction element, this in-plane pitch a corresponds to one period Λ in the liquid crystal orientation pattern described above.

[0048] An example of a transmission type diffraction element having the above-mentioned optically anisotropic film will now be described in detail. An example of a transmission type diffraction element (transmission type liquid crystal diffraction element) having an optically anisotropic film having the above-mentioned liquid crystal orientation pattern is conceptually shown in Figures 8 and 9. Figures 8 to 9 show an example in which the liquid crystal compound constituting the optically anisotropic film is a rod-shaped liquid crystal compound. Fig. 8 is a diagram conceptually showing the layer structure of a transmission diffraction element. As conceptually shown in Fig. 6, the transmission diffraction element has a support 30, an alignment film 32, and an optically anisotropic film that exhibits the function of a diffraction element, i.e., a liquid crystal layer 36. Fig. 9 is a schematic diagram showing the orientation state of liquid crystal compounds in the plane of the main surface of the liquid crystal layer 36. In the following description, the principal surface of the liquid crystal layer 36 is defined as the XY plane, and the cross section perpendicular to the XY plane is defined as the XZ plane.

[0049] Furthermore, the transmission type diffraction element is not limited to the layer structure shown in FIG. That is, the transmissive liquid crystal diffraction element may have a support 30, an alignment film 32 and a liquid crystal layer 36 as in the illustrated example, or may have only an alignment film 32 and a liquid crystal layer 36, or may be composed of only the liquid crystal layer 36.

[0050] 8 and 9 has a support 30, an alignment film 32, and a liquid crystal layer 36 as an optically anisotropic film. The support 30 and the alignment film 32 are the same as those described above. As shown in FIG. 9, the liquid crystal layer 36 of the transmissive diffraction element has a liquid crystal orientation pattern in which the optical axis 40A of the liquid crystal compound 40 rotates continuously along the alignment axis D, similar to the (cholesteric) liquid crystal layer 34. However, as shown in Figure 8, in a transmissive diffraction element, the liquid crystal compound 40 forming the liquid crystal layer 36 is not helically aligned in the thickness direction. Such a liquid crystal layer can be formed in the same manner as the above-mentioned cholesteric liquid crystal layer, using a liquid crystal composition to which no chiral dopant is added. As will be described later, when the liquid crystal compound is to be helically aligned in the thickness direction, a chiral dopant is added to the liquid crystal composition according to the desired twist angle.

[0051] As described above, the liquid crystal layer 36 has a liquid crystal alignment pattern in which the direction of the optical axis 40A derived from the liquid crystal compound 40 changes while continuously rotating in the direction of the alignment axis D, ie, the X direction, within the plane. On the other hand, the liquid crystal compounds 40 forming the liquid crystal layer 36 are arranged at equal intervals in the Y direction perpendicular to the X direction, i.e., in the Y direction perpendicular to the arrangement axis D, which is one direction in which the optical axis 40A continuously rotates.

[0052] In the liquid crystal layer 36, the liquid crystal compounds aligned in the Y direction have the same angle between their optical axes 40A and the X direction. A region R is defined as a region where the liquid crystal compounds 40, whose optical axes 40A and alignment axis D form the same angle, are arranged in the Y direction. In this case, the in-plane retardation (Re) value in each region R is preferably half the wavelength, i.e., λ / 2. That is, the liquid crystal layer 36 (transmissive diffraction element) preferably functions as a half-wave plate. These in-plane retardations are calculated by multiplying the refractive index difference Δn associated with the refractive index anisotropy of region R by the thickness of the optically anisotropic film.

[0053] When circularly polarized light enters such a liquid crystal layer 36, the light is refracted and the direction of the circularly polarized light is changed. This effect is conceptually shown in Figures 10 and 11. It is assumed that the liquid crystal layer 36 has a product of the refractive index difference of the liquid crystal compound and the thickness of the optically anisotropic film of λ / 2. As shown in Figure 10, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the optically anisotropic film is λ / 2, when left-handed circularly polarized light L enters the liquid crystal layer 36, the incident light L is given a phase difference of 180° as it passes through the liquid crystal layer 36, and the transmitted light R is converted into right-handed circularly polarized light. Furthermore, because the liquid crystal orientation pattern formed in the liquid crystal layer 36 is a periodic pattern in the direction of the array axis D, the transmitted light R travels in a direction different from that of the incident light L. In this way, the incident light L, which is left-handed circularly polarized, is converted into transmitted light R, which is right-handed circularly polarized and tilted at a certain angle in the direction of the array axis D with respect to the incident direction.

[0054] On the other hand, as shown in Figure 11, when the product of the refractive index difference of the liquid crystal compound in the liquid crystal layer 36 and the thickness of the optically anisotropic film is λ / 2, when right-handed circularly polarized incident light R enters the liquid crystal layer 36, the incident light R is given a phase difference of 180° as it passes through the liquid crystal layer 36 and is converted into left-handed circularly polarized transmitted light L. Furthermore, because the liquid crystal orientation pattern formed in the liquid crystal layer 36 is a periodic pattern in the direction of the array axis D, the transmitted light L travels in a direction different from that of the incident light R. In this case, the transmitted light L travels in a different direction from the transmitted light R, that is, in the opposite direction from the array axis D relative to the incident direction. In this way, the incident light R is converted into left-handed circularly polarized transmitted light L that is tilted at a certain angle in the opposite direction from the array axis D relative to the incident direction.

[0055] As with the (cholesteric) liquid crystal layer 34 described above, the liquid crystal layer 36 can also adjust the angles of diffraction of the transmitted light R and the transmitted light L by changing the period Λ of the formed liquid crystal orientation pattern. Specifically, in the liquid crystal layer 36, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between lights that have passed through adjacent liquid crystal compounds 40, and therefore the greater the diffraction (refracting) of the transmitted light R and the transmitted light L. Furthermore, in the liquid crystal layer 36 having this liquid crystal orientation pattern, the diffraction angle (refraction angle) of transmitted light varies depending on the wavelength of the reflected light. Specifically, the longer the wavelength of light, the larger the angle of the transmitted light with respect to the incident light. Therefore, by selecting the length of one period Λ (in-plane pitch a) according to the wavelength of the incident light, the diffraction angle (refraction angle) of the transmitted light passing through the diffraction element 20 is adjusted, and the right-handed circularly polarized light I R1 and left-handed circularly polarized light I reflected by the diffraction element 11 and transmitted through the diffraction element 20. L3 The light can be made into parallel light.

[0056] In the transmissive diffraction element, the diffraction direction of transmitted light can be reversed by reversing the rotation direction of the optical axis 40A of the liquid crystal compound 40, which rotates along the direction of the array axis D. That is, in the examples shown in Figures 8 to 11, the rotation direction of the optical axis 40A facing the direction of the array axis D is clockwise, but by changing this rotation direction to counterclockwise, the diffraction direction of transmitted light can be reversed.

[0057] (Formation of twisted structure) In addition, in a transmission type diffraction element, it is preferable that the orientation of the liquid crystal compound in the thickness direction of the liquid crystal layer changes continuously from one interface side to the other interface side, that is, that the liquid crystal layer (optically anisotropic film) has a twist structure in which the liquid crystal compound is helically oriented in the thickness direction. The liquid crystal layer having a twisted structure is preferable in terms of increasing the efficiency of diffracted light and maintaining polarization. In this case, the twist angle of the liquid crystal compound is not limited, but is preferably 5 to 359°, more preferably 30 to 180°. To obtain a twisted structure in the thickness direction, the amount of chiral agent added to the liquid crystal composition forming the liquid crystal layer, as described in WO 2021 / 256413, may be appropriately adjusted.

[0058] (Formation of in-plane alignment pattern) In such a liquid crystal diffraction element, there is no limitation on the method for forming an in-plane orientation pattern required for diffraction on the orientation film, and various known methods can be used. As a suitable example, interference exposure using circularly polarized light can be used, as in the exposure apparatus shown in Figure 3 of WO 2021 / 256413. To obtain the in-plane pitch required for the separation angle, the optical elements of the exposure apparatus can be positioned so that the absolute values ​​of the angles of incidence of each interference exposure are the same relative to the normal direction of the photo-alignment film surface. Furthermore, by adjusting this angle of incidence (the intersection angle of the interfering light), the period Λ (in-plane pitch a) of the liquid crystal alignment pattern can be adjusted.

[0059] In the liquid crystal optical element shown in FIGS. 8 to 11, the optical axis 40A of the liquid crystal compound 40 in the liquid crystal alignment pattern of the optically anisotropic layer rotates continuously only along the direction of the arrow X. However, the present invention is not limited to this, and various configurations can be used as long as the optical axis 40A of the liquid crystal compound 40 rotates continuously along one direction in the optically anisotropic layer.

[0060] One example is an optically anisotropic layer 34 having a concentric pattern of liquid crystal orientation in which the direction of the optical axis of the liquid crystal compound 40 changes while continuously rotating, concentrically from the inside to the outside, as conceptually shown in the plan view of Fig. 12. In other words, the liquid crystal orientation pattern of the optically anisotropic layer 34 shown in Fig. 12 is a liquid crystal orientation pattern in which the direction of the optical axis of the liquid crystal compound 30 changes while continuously rotating, is provided radially from the center of the optically anisotropic layer 34.

[0061] As in FIG. 9, FIG. 12 also shows only the liquid crystal compound 40 on the surface of the alignment film, but as mentioned above, the optically anisotropic layer 34 has a structure in which the liquid crystal compound 40 is stacked from the liquid crystal compound 40 on the surface of the alignment film, as shown in FIG. 8.

[0062] In the optically anisotropic layer 34 shown in FIG. 12, the optical axis (not shown) of the liquid crystal compound 40 is in the longitudinal direction of the liquid crystal compound 40. In the optically anisotropic layer 34, the direction of the optical axis of the liquid crystal compound 40 changes while continuously rotating along multiple directions from the center of the optically anisotropic layer 34 toward the outside, for example, the direction indicated by arrow A1, the direction indicated by arrow A2, the direction indicated by arrow A3, etc. The absolute phase of circularly polarized light incident on the optically anisotropic layer 34 having this liquid crystal orientation pattern changes in each local region where the optical axis of the liquid crystal compound 40 is oriented differently. At this time, the amount of change in each absolute phase differs depending on the optical axis of the liquid crystal compound 40 into which the circularly polarized light is incident.

[0063] The optically anisotropic layer 34 having such a concentric liquid crystal orientation pattern, i.e., a liquid crystal orientation pattern in which the optical axis changes by continuously rotating radially, can transmit incident light as divergent or convergent light depending on the rotation direction of the optical axis of the liquid crystal compound 40 and the direction of the incident circularly polarized light. That is, by forming the liquid crystal alignment pattern of the optically anisotropic layer into a concentric circle, the liquid crystal optical element of the present invention can function as, for example, a convex or concave lens.

[0064] Here, when the liquid crystal orientation pattern of the optically anisotropic layer is concentric and the liquid crystal optical element acts as a convex lens, it is preferable to gradually shorten one period Λ, in which the optical axis rotates 180° in the liquid crystal orientation pattern, from the center of the optically anisotropic layer 34 toward the outside in one direction in which the optical axis continuously rotates. As mentioned above, the angle of refraction of light with respect to the incident direction increases as the period Λ of the liquid crystal orientation pattern shortens. Therefore, by gradually shortening the period Λ of the liquid crystal orientation pattern from the center of the optically anisotropic layer 34 outward in one direction in which the optical axis continuously rotates, the light focusing power of the optically anisotropic layer 34 can be further improved, and the performance as a convex lens can be improved.

[0065] In the present invention, depending on the application of the liquid crystal optical element, for example, when it is used as a concave lens, it is preferable to rotate one period Λ, in which the optical axis rotates by 180° in the liquid crystal orientation pattern, from the center of the optically anisotropic layer 34 in the opposite direction to the direction in which the optical axis continuously rotates, and gradually shorten it toward the outside in one direction. As mentioned above, the angle of refraction of light relative to the incident direction increases as the period Λ of the liquid crystal orientation pattern shortens. Therefore, by gradually shortening the period Λ of the liquid crystal orientation pattern from the center of the optically anisotropic layer 34 outward in one direction in which the optical axis continuously rotates, the light divergence power of the optically anisotropic layer 34 can be further improved, thereby improving the performance as a concave lens.

[0066] In the present invention, for example, when the liquid crystal optical element is a concave lens, it is also preferable to reverse the rotation direction of the incident circularly polarized light.

[0067] In the present invention, when the liquid crystal optical element is made to function as a convex or concave lens, it is preferable that the following formula be satisfied. Φ(r)=(π / λ)[(r 2 +f 2 ) 1 / 2 -f] Here, r is the distance from the center of the concentric circle, and is expressed as follows: r=(x 2 +y 2 ) 1 / 2 where x and y represent the position in the plane, and (x, y) = (0, 0) represents the center of the concentric circles. Φ(r) represents the angle of the optical axis at distance r from the center, λ represents the wavelength, and f represents the desired focal length.

[0068] Conversely, in the present invention, one period Λ of the concentric liquid crystal alignment pattern may be gradually lengthened from the center of the optically anisotropic layer 34 outward in one direction in which the optical axis continuously rotates. Furthermore, depending on the application of the liquid crystal optical element, for example, when it is desired to provide a light intensity distribution in transmitted light, it is also possible to use a configuration in which the period Λ is not gradually changed in one direction in which the optical axis continuously rotates, but rather has regions in which the period Λ is partially different in one direction in which the optical axis continuously rotates. In addition, the liquid crystal optical element of the present invention may have an optically anisotropic layer in which the period Λ is uniform throughout, and an optically anisotropic layer having regions in which the period Λ is different.

[0069] (phase plate) In this configuration, a retardation plate may be provided, which is preferable because it can make it difficult for polarization changes to occur due to reflection or the like. There are no limitations on the material for forming the retardation plate, and any known material used for various retardation plates, such as polymers, liquid crystal materials, and inorganic materials, can be used.

[0070] As shown in the table above, a light irradiation device having a light-emitting element having multiple light-emitting portions in its plane and a liquid crystal optical element, wherein the liquid crystal optical element has an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound, and the optically anisotropic layer has a liquid crystal orientation 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, and when the length of one period is defined as the length of a 180° rotation of the direction of the optical axis derived from the liquid crystal compound in the plane, a light irradiation device having regions with different lengths of one period in the liquid crystal orientation pattern is thin and can project an optical pattern. From the above results, the effects of the present invention are clear. [Industrial Applicability]

[0071] The present invention can be suitably used in various applications that project optical patterns, such as sensors. [Explanation of symbols]

[0072] 10 light source 11 Sensors 12 Light guide plate 13 Liquid crystal diffraction element 1 14 Liquid crystal diffraction element 2 30 Support 32 Alignment film 34 Optically anisotropic layer 36 Optically anisotropic layer 40 Liquid crystal compounds 40A optical axis R Right circular polarization L Left circular polarization

Claims

1. a light emitting element having a plurality of light emitting portions in a plane; A light irradiation device having a liquid crystal optical element, the liquid crystal optical element comprises an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound; The optically anisotropic layer has a liquid crystal orientation pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating along at least one direction in the plane, and when the length of one period is defined as the length of the rotation of the optical axis derived from the liquid crystal compound by 180° in the plane, the optically anisotropic layer has regions in which the length of one period in the liquid crystal orientation pattern is different.

2. The light irradiation device described in claim 1, wherein one period of the liquid crystal orientation pattern gradually becomes shorter toward the one direction in which the direction of the optical axis derived from the liquid crystal compound in the liquid crystal orientation pattern changes while continuously rotating.

3. 3. The light irradiation device according to claim 1, wherein the liquid crystal orientation pattern of the optically anisotropic layer is a concentric pattern having the one direction in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating, in a concentric pattern extending from the inside to the outside.

4. The light irradiation device according to any one of claims 1 to 3, wherein a lens array in which small regions having a lens function are arranged two-dimensionally is disposed between the optical path of the light emitted from the light-emitting element and the liquid crystal optical element.

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