Optical element

Abstract

The present invention addresses the problem of providing an optical element capable of improving the utilization efficiency of split light. The liquid crystal display device includes a liquid crystal diffraction element and a prism having a first surface in direct contact with the liquid crystal diffraction element or in contact with the liquid crystal diffraction element via another layer, and the liquid crystal diffraction element includes an optically anisotropic layer. The optically anisotropic layer has a liquid crystal alignment pattern in which the orientation originating from the optical axis of the liquid crystal compound changes while continuously rotating in at least one direction in the plane, and the prism has a second surface that reflects one of the light separated by diffraction by the liquid crystal diffraction element.

Description

Technical Field

[0001] The invention relates to an optical element which splits incident light by a liquid crystal diffraction element. Background Art

[0002] There are known liquid crystal diffraction elements that diffract and transmit incident light.

[0003] As such a liquid crystal diffraction element, there is known a liquid crystal diffraction element having an optically anisotropic layer formed using a liquid crystal composition containing a liquid crystal compound.

[0004] For example, Patent Document 1 describes a liquid crystal diffraction element (optical element) comprising a plurality of stacked birefringent sublayers such as a liquid crystal sublayer, wherein the liquid crystal sublayer is configured to change the propagation direction of light passing therethrough according to a Bragg condition, and wherein the stacked birefringent sublayer has a local optical axis that changes along each boundary surface between adjacent layers of the stacked birefringent sublayer in a manner that defines each lattice period.

[0005] In the liquid crystal diffraction element, as in reference 1 Figure 2 As shown in , etc., the birefringent sublayer constituting the laminated birefringent sublayer has an orientation pattern of the liquid crystal compound in which the orientation of the rod-like liquid crystal compound, that is, the orientation of the optical axis derived from the liquid crystal compound, continuously rotates in one direction.

[0006] A liquid crystal diffraction element having an orientation pattern of a liquid crystal compound (liquid crystal orientation pattern) as described in Patent Document 1 can diffract (refract) incident light at an angle corresponding to the wavelength. Furthermore, as long as the light has the same wavelength, the light can be diffracted at a constant angle.

[0007] The liquid crystal diffraction element having a liquid crystal orientation pattern can be used for various purposes by utilizing such characteristics. For example, the liquid crystal diffraction element can be preferably used as a spectroscopic element in a hyperspectral camera that separates incident light into multiple wavelength regions and takes pictures.

[0008] Previous technical literature

[0009] Patent Literature

[0010] Patent Document 1: Japanese Patent Application No. 2017-522601 Summary of the invention

[0011] Technical issues to be solved by the invention

[0012] This liquid crystal diffraction element can diffract incident light and split it.

[0013] On the other hand, the liquid crystal diffraction element diffracts the incident light in two different directions according to polarized light. Therefore, in devices such as hyperspectral cameras that use the liquid crystal diffraction element as a spectroscopic element, it is difficult to utilize all the split light, that is, the utilization efficiency of the split light is low.

[0014] An object of the present invention is to solve the problems of the prior art and to provide an optical element that can improve the utilization efficiency of the split light in an optical element that splits incident light using a liquid crystal diffraction element.

[0015] Means for solving technical problems

[0016] In order to solve the problem, the optical element of the present invention has the following structure.

[0017] [1] An optical element comprising a liquid crystal diffraction element and a prism, wherein the prism has a first surface that is in direct contact with the liquid crystal diffraction element or in contact with the liquid crystal diffraction element via another layer,

[0018] The liquid crystal diffraction element includes an optically anisotropic layer having a liquid crystal orientation pattern in which the direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one direction in a plane.

[0019] The prism has a second surface that reflects one of the lights separated by diffraction of the liquid crystal diffraction element.

[0020] [2] The optical element according to [1], wherein:

[0021] In the optically anisotropic layer, the liquid crystal compound is twisted and oriented in a helical shape in the thickness direction.

[0022] [3] The optical element according to [1] or [2], wherein:

[0023] The liquid crystal diffraction element has at least two optically anisotropic layers in which liquid crystal compounds are twisted and oriented in a spiral shape along the thickness direction, wherein the twisting directions of the liquid crystal compounds in the two optically anisotropic layers along the thickness direction are opposite.

[0024] [4] The optical element according to any one of [1] to [3], wherein

[0025] The angle between the first surface and the second surface of the prism is 70 to 110 degrees.

[0026] [5] The optical element according to any one of [1] to [4], wherein

[0027] The light separated by the diffraction of the liquid crystal diffraction element and reflected by the second surface and the light not incident on the second surface are emitted from the same surface of the prism.

[0028] Effects of the Invention

[0029] According to the optical element of the present invention, in the optical element that splits incident light using a liquid crystal diffraction element, it is possible to improve the utilization efficiency of the split light. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram conceptually showing an example of the optical element of the present invention.

[0031] Figure 2 This is a diagram conceptually showing an example of a liquid crystal diffraction element.

[0032] Figure 3 yes Figure 2 A top view of the optically anisotropic layer of the liquid crystal diffraction element is shown.

[0033] Figure 4 Yes means Figure 2 A conceptual diagram showing the effect of the optically anisotropic layer of the liquid crystal diffraction element.

[0034] Figure 5 Yes means Figure 2 A conceptual diagram showing the effect of the optically anisotropic layer of the liquid crystal diffraction element.

[0035] Figure 6 This is a diagram conceptually showing another example of a liquid crystal diffraction element.

[0036] Figure 7 It is a conceptual illustration of Figure 2 FIG. 1 is a diagram showing an example of an exposure device for exposing an alignment film of a liquid crystal diffraction element shown in FIG.

[0037] Figure 8 This is a diagram conceptually showing the function of a liquid crystal diffraction element.

[0038] Fig. 9 This is a diagram conceptually showing an example of a spectroscopic element using the optical element of the present invention.

[0039] Fig.10 This is a diagram conceptually showing another example of the optical element of the present invention.

[0040] Fig.11 This is a diagram conceptually showing an example of a spectroscopic element using the optical element of the present invention.

[0041] Fig.12 This is a diagram conceptually showing another example of the optical element of the present invention.

[0042] Fig.13 It is a conceptual diagram for explaining an embodiment of the present invention.

[0043] Fig.14 It is a conceptual diagram for explaining an embodiment of the present invention. DETAILED DESCRIPTION

[0044] Hereinafter, the optical element of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0045] In the present specification, a numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0046] In this specification, "(meth)acrylate" is used to mean "one or both of acrylate and methacrylate".

[0047] In this specification, "same" includes the error range generally allowed in the technical field. In addition, in this specification, when referring to "all", "all" and "entire surface", etc., in addition to the case of 100%, it includes the error range generally allowed in the technical field, including, for example, the case of 99% or more, 95% or more, or 90% or more.

[0048] In this specification, visible light is light with a wavelength visible to human eyes among electromagnetic waves, and refers to light in the wavelength range of 380 to 780 nm. Invisible light is light in the wavelength range of less than 380 nm and the wavelength range of more than 780 nm.

[0049] Furthermore, although not limited thereto, in visible light, light in the wavelength region of 420 to 490 nm is blue light, light in the wavelength region of 495 to 570 nm is green light, and light in the wavelength region of 620 to 750 nm is red light. Furthermore, although not limited thereto, in non-visible light, ultraviolet light (ultraviolet light) refers to light in the wavelength region of less than 380 nm and more than 200 nm, and infrared light (infrared light) refers to light in the wavelength region of more than 780 nm and less than 12000 nm.

[0050] Figure 1 An example of the optical element of the present invention is conceptually shown in FIG.

[0051] Figure 1 The optical element 10 shown has a liquid crystal diffraction element 12 and a prism 14 .

[0052] As will be described in detail later, the liquid crystal diffraction element 12 has an optically anisotropic layer ( Figure 2 The optically anisotropic layer has 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.

[0053] The optically anisotropic layer having such a liquid crystal orientation pattern, that is, the liquid crystal diffraction element 12 having such an optically anisotropic layer, splits the incident light according to the wavelength when unpolarized light is incident, and diffracts right-handed circularly polarized light R (right-handed circularly polarized light component R) and left-handed circularly polarized light L (left-handed circularly polarized light component L) in opposite directions.

[0054] In other words, the liquid crystal diffraction element 12 (optically anisotropic layer) diffracts incident unpolarized light, separates the unpolarized light into right-handed circularly polarized light and left-handed circularly polarized light, and diffracts (refracts) the light in opposite directions.

[0055] In the optical element 10 of the present invention, the liquid crystal diffraction element 12 is arranged on one surface of the prism 14. The surface on which the prism 14 is arranged is the first surface in the present invention.

[0056] As an example, Figure 1 As shown, the liquid crystal diffraction element 12 diffracts right-handed circularly polarized light R in the incident unpolarized light toward the right in the figure, and diffracts left-handed circularly polarized light L toward the left in the figure.

[0057] Of the light diffracted and separated by the liquid crystal diffraction element 12 (optically anisotropic layer), the light diffracted in the left direction is reflected by the second surface 14 a of the prism 14 .

[0058] The light diffracted to the right by the liquid crystal diffraction element 12 (left-handed circularly polarized light) and the light reflected by the second surface 14a of the prism 14 become parallel light and are emitted in the same direction from the same surface of the prism 14. In addition, the light reflected by the second surface 14a of the prism 14 is converted into left-handed circularly polarized light by reflection.

[0059] Therefore, according to the present invention, the light dispersed by the liquid crystal diffraction element can be used with high efficiency. The above viewpoint will be described in detail later.

[0060] Figure 2 An example of a liquid crystal diffraction element is conceptually shown in FIG.

[0061] The liquid crystal diffraction element 12 shown in the figure includes a support 20 , an alignment film 24 , and an optically anisotropic layer 26 .

[0062] In the liquid crystal diffraction element 12, the optically anisotropic layer 26 is formed using a composition containing a liquid crystal compound 30. In the present invention, the optically anisotropic layer 26 has a predetermined liquid crystal alignment pattern in which the direction of the optical axis derived from the liquid crystal compound 30 continuously changes while rotating in at least one direction.

[0063] In addition, the liquid crystal diffraction element 12 shown in the figure has a support 20, but the liquid crystal diffraction element may not have the support 20. For example, Figure 2The structure shown in FIG. 1 is to peel off the support 20, and only the alignment film 24 and the optical anisotropic layer 26 constitute the liquid crystal diffraction element. Figure 2 In the structure shown, the support 20 and the alignment film 24 are peeled off, and the liquid crystal diffraction element is composed of only the optical anisotropic layer 26 .

[0064] Alternatively, the first surface of the prism 14 described later may be made to function as a support body.

[0065] That is, in the optical element 10 of the present invention, as long as the liquid crystal diffraction element 12 has an optically anisotropic layer formed using a 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 originating from the liquid crystal compound changes while continuously rotating along at least one direction within the plane, various layer structures can be utilized.

[0066] As described above, the liquid crystal diffraction element 12 includes the support 20 , the alignment film 24 , and the optically anisotropic layer 26 .

[0067] In the liquid crystal diffraction element 12 , the support 20 is used to support the alignment film 24 and the optically anisotropic layer 26 .

[0068] The support 20 may be any sheet (film, plate, layer) as long as it can support the alignment film 24 and the optical anisotropic layer 26 and has sufficient transparency to the light of the wavelength to be separated.

[0069] As a support, for example, polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films, polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride and other resin films, glass plates, etc. As cycloolefin polymer films, for example, the trade name "ARTON" manufactured by JSR Corporation and the trade name "ZEONOR" manufactured by ZEON CORPORATION can be exemplified.

[0070] The thickness of the support 20 is not limited, and may be appropriately set to a thickness capable of maintaining the alignment film 24 and the optically anisotropic layer 26 according to the application of the liquid crystal diffraction element 12 and the material of the support 20 .

[0071] An additive such as an ultraviolet absorber may be added to the support 20. Adding an ultraviolet absorber to the support 20 is preferred in that the light resistance of the liquid crystal diffraction element 12 can be improved.

[0072] In the liquid crystal diffraction element 12 , an alignment film 24 is formed on the surface of a support 20 .

[0073] The alignment film 24 is an alignment film for aligning the liquid crystal compound 30 in a predetermined liquid crystal alignment pattern when forming the optically anisotropic layer 26 of the liquid crystal diffraction element 12 .

[0074] Although it will be described later, in the liquid crystal diffraction element 12, the optically anisotropic layer 26 has an optical axis 30A derived from the liquid crystal compound 30 (refer to Figure 3 ) is continuously rotated along one direction in the plane (arrow X direction described later) while changing the liquid crystal orientation pattern. Therefore, the orientation film 24 of the liquid crystal diffraction element 12 is formed in such a way that the optical anisotropic layer 26 can form the liquid crystal orientation pattern.

[0075] In the following description, “rotation of the orientation of the optical axis 30A” is also simply referred to as “rotation of the optical axis 30A”.

[0076] As the alignment film 24 , various known alignment films can be used.

[0077] For example, friction-treated films composed of organic compounds such as polymers, oblique vapor-deposited films of inorganic compounds, films having microgrooves, and films that accumulate LB (Langmuir-Blodgett) films based on the Langmuir-Blodgett method of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride and methyl stearate, etc. can be exemplified.

[0078] An alignment film based on a rubbing treatment can be formed by rubbing the surface of a polymer layer multiple times in a constant direction by paper or cloth.

[0079] Preferred examples of materials used for the alignment film include polyimide, polyvinyl alcohol, polymers having polymerizable groups described in JP-A-9-152509, and materials used for forming alignment films described in JP-A-2005-97377, JP-A-2005-99228, and JP-A-2005-128503.

[0080] In the liquid crystal diffraction element 12, the alignment film 24 is preferably formed by irradiating polarized light or non-polarized light to a photo-alignment material, which is a so-called photo-alignment film. That is, in the liquid crystal diffraction element 12, as the alignment film, it is preferred to use a photo-alignment film formed by coating a photo-alignment material on the support 20.

[0081] Irradiation with polarized light can be performed from a vertical direction or an oblique direction with respect to the photo-alignment film, and irradiation with non-polarized light can be performed from an oblique direction with respect to the photo-alignment film.

[0082] Examples of the photo-alignment material that can be used in the photo-alignment film of the present invention include Japanese Patent Application Publication No. 2006-285197, Japanese Patent Application Publication No. 2007-76839, Japanese Patent Application Publication No. 2007-138138, Japanese Patent Application Publication No. 2007-94071, Japanese Patent Application Publication No. 2007-121721, Japanese Patent Application Publication No. 2007-140465, Japanese Patent Application Publication No. 2007-15 Azo compounds described in Japanese Patent Publication No. 6439, Japanese Patent Publication No. 2007-133184, Japanese Patent Publication No. 2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, and aromatic ester compounds described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 Maleimide and / or alkenyl-substituted nadic imide compounds having photo-alignment units described in Japanese Patent Nos. 4205195 and 4205198, photo-crosslinkable silane derivatives described in Japanese Patent Nos. 2003-520878, 2004-529220, and 4162850, photo-crosslinkable polyimides, photo-crosslinkable polyamides, and photo-crosslinkable esters Preferred examples include compounds capable of photodimerization described in JP-A-9-118717, JP-A-10-506420, JP-A-2003-505561, International Publication No. 2010 / 150748, JP-A-2013-177561, and JP-A-2014-12823, in particular cinnamate compounds, chalcone compounds, and coumarin compounds.

[0083] Among them, it is preferable to use an azo compound, a photo-crosslinkable polyimide, a photo-crosslinkable polyamide, a photo-crosslinkable ester, a cinnamate compound, and a chalcone compound.

[0084] The thickness of the alignment film 24 is not limited, and may be appropriately set to obtain a desired alignment function according to the material forming the alignment film 24. The thickness of the alignment film 24 is preferably 0.01 to 5 μm, more preferably 0.05 to 2 μm.

[0085] The method for forming the alignment film is not limited, and various known methods corresponding to the materials for forming the alignment film can be used. As an example, a method of forming an alignment pattern by coating the alignment film on the surface of the support 20 and drying it, and then exposing the alignment film to a laser beam can be exemplified.

[0086] exist Figure 7An example of an exposure device for exposing the alignment film 24 to form the above-mentioned alignment pattern is conceptually shown in FIG.

[0087] Figure 7 The exposure device 60 shown comprises: a light source 64 having a laser 62; a beam splitter 68 for separating a laser beam M emitted by the laser 62 into two light beams MA and MB; reflectors 70A and 70B respectively arranged on the optical paths of the two separated light beams MA and MB; and λ / 4 plates 72A and 72B.

[0088] Although not shown in the figure, the light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (light beam MA) into right-handed circularly polarized light P R , the λ / 4 plate 72B converts the linear polarized light P0 (light MB) into left-handed circularly polarized light P L .

[0089] The support 20 having the alignment film 24 before the alignment pattern is formed is placed in the exposure section, and two light beams MA and MB are made to intersect and interfere with each other on the alignment film 24, and the interference light is irradiated onto the alignment film 24 for exposure.

[0090] Due to the interference at this time, the polarization state of the light irradiated on the alignment film 24 changes periodically in the form of interference fringes. Thus, in the alignment film 24, an alignment pattern in which the alignment state changes periodically can be obtained.

[0091] In the exposure device 60, the period of the orientation pattern can be adjusted by changing the intersection angle α of the two light beams MA and MB. That is, in the exposure device 60, by adjusting the intersection angle α, in the orientation pattern in which the optical axis 30A originating from the liquid crystal compound 30 continuously rotates in one direction, the length of one period (one period Λ described later) in which the optical axis 30A is rotated 180° in one direction in which the optical axis 30A is rotated can be adjusted.

[0092] By forming an optically anisotropic layer on an alignment film having an alignment pattern in which the alignment state changes periodically, as described later, an optically anisotropic layer 26 having a liquid crystal alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 rotates continuously in one direction can be formed.

[0093] Furthermore, the rotation direction of the optical axis 30A can be reversed by rotating the optical axes of the λ / 4 plates 72A and 72B by 90° respectively.

[0094] In addition, in the liquid crystal diffraction element, the alignment film is preferably provided, but is not an essential component.

[0095] For example, an orientation pattern can be formed on the support 20 by a method of rubbing the support 20, processing the support 20 with a laser beam, etc., and the optically anisotropic layer 26 can be provided with a structure having a liquid crystal orientation pattern in which the direction of the optical axis 30A originating from the liquid crystal compound 30 changes while continuously rotating along at least one direction within the plane.

[0096] In the liquid crystal diffraction element 12 , an optically anisotropic layer 26 is formed on the surface of the alignment film 24 .

[0097] In addition, in the following Figure 4-5 In order to simplify the drawings and clearly show the structure of the liquid crystal diffraction element 12, the optical anisotropic layer 26 only shows the liquid crystal compound 30 (liquid crystal compound molecules) on the surface of the alignment film. Figure 2 As conceptually shown, the optically anisotropic layer 26 has a structure in which aligned liquid crystal compounds 30 are stacked in the thickness direction, similar to a general optically anisotropic layer formed using a composition containing a liquid crystal compound.

[0098] As described above, in the liquid crystal diffraction element 12, the optical anisotropic layer (liquid crystal layer) 26 is formed using a composition containing a liquid crystal compound. When the in-plane retardation value is set to λ / 2, the optical anisotropic layer 26 has a function as a general λ / 2 plate, that is, a function of imparting a phase difference of half a wavelength, i.e., 180°, to two linearly polarized light components orthogonal to each other contained in the light incident on the optical anisotropic layer.

[0099] The optically anisotropic layer 26 has a liquid crystal alignment pattern in which the orientation of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating in one direction indicated by the arrow X in the plane.

[0100] The optical axis 30A derived from the liquid crystal compound 30 is an axis having the highest refractive index, a so-called slow axis, in the liquid crystal compound 30. For example, when the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A is along the rod-shaped long axis direction.

[0101] In the following description, “one direction indicated by arrow X” is also simply referred to as “arrow X direction”. Also, in the following description, the optical axis 30A derived from the liquid crystal compound 30 is also referred to as “optical axis 30A of the liquid crystal compound 30 ” or “optical axis 30A”.

[0102] In the optically anisotropic layer 26, the liquid crystal compound 30 is two-dimensionally arranged in a plane parallel to the arrow X direction and the Y direction perpendicular to the arrow X direction. Figure 2 and the following Figure 4-5 In the figure, the Y direction is the direction perpendicular to the paper surface.

[0103] Figure 3 2 is a conceptual top view of the optically anisotropic layer 26.

[0104] Floor plan Figure 2 2 is a diagram of the liquid crystal diffraction element 12 observed from above, that is, a diagram of the liquid crystal diffraction element 12 observed from the thickness direction (= the stacking direction of each layer (film)). In other words, it is a diagram of the optical anisotropic layer 26 observed from a direction perpendicular to the main surface. In addition, the main surface is the largest surface of the sheet-like object, usually the two sides of the sheet-like object in the thickness direction.

[0105] And, in Figure 3 In order to clearly show the structure of the liquid crystal diffraction element 12, Figure 2 Likewise, the liquid crystal compound 30 shows only the liquid crystal compound 30 on the surface of the alignment film 24. However, as described above, the optically anisotropic layer 26 has a thickness direction such as Figure 2 As shown, the alignment film 24 has a structure in which the liquid crystal compounds 30 are stacked on top of each other.

[0106] The optically anisotropic layer 26 has a liquid crystal alignment pattern in which the direction of the optical axis 30A derived from the liquid crystal compound 30 changes while continuously rotating in the direction of arrow X in the plane.

[0107] The orientation of the optical axis 30A of the liquid crystal compound 30 changes while continuously rotating in the direction of arrow X (a predetermined direction). Specifically, the angle formed by the optical axis 30A of the liquid crystal compound 30 arranged along the direction of arrow X and the direction of arrow X changes from θ to θ+180° or θ-180° along the direction of arrow X depending on the position of the direction of arrow X.

[0108] The difference in angle between the optical axes 30A of the liquid crystal compounds 30 adjacent to each other in the arrow X direction is preferably 45° or less, more preferably 15° or less, and still more preferably a smaller angle.

[0109] On the other hand, among the liquid crystal compounds 30 forming the optically anisotropic layer 26, the liquid crystal compounds 30 having the same optical axis 30A are arranged at equal intervals in the Y direction orthogonal to the arrow X direction, that is, in the Y direction orthogonal to a direction in which the optical axis 30A rotates continuously.

[0110] In other words, among the liquid crystal compounds 30 forming the optically anisotropic layer 26 , the directions of the optical axes 30A of the liquid crystal compounds 30 aligned in the Y direction make the same angle with the arrow X direction.

[0111] In the liquid crystal orientation pattern of the liquid crystal compound 30 of the optically anisotropic layer 26, the length (distance) of the optical axis 30A of the liquid crystal compound 30 rotated 180° in the arrow X direction where the orientation of the in-plane optical axis 30A changes by continuous rotation is set as the length Λ of one period in the liquid crystal orientation pattern. In the following description, the length Λ of one period is also referred to as one period Λ. In other words, one period Λ in the liquid crystal orientation pattern is defined by the distance from θ to θ+180° between the angle formed by the optical axis 30A of the liquid crystal compound 30 and the arrow X direction.

[0112] That is, the distance between the centers of two liquid crystal compounds 30 in the direction of arrow X, which have the same angle with respect to the direction of arrow X, is set to one period Λ. Figure 2 As shown in FIG. 1 , the distance between the centers of two liquid crystal compounds 30 in the direction of arrow X, whose direction of arrow X coincides with the direction of the optical axis 30A, is defined as one period Λ.

[0113] In the liquid crystal diffraction element 12 , the liquid crystal orientation pattern of the optically anisotropic layer repeats the one period Λ in the arrow X direction, that is, in one direction in which the orientation of the optical axis 30A changes by continuous rotation.

[0114] As described above, in the optically anisotropic layer, the angles formed by the optical axis 30A of the liquid crystal compound arranged in the Y direction and the arrow X direction (a direction in which the direction of the optical axis of the liquid crystal compound 30 is rotated) are equal. The region in the Y direction where the liquid crystal compound 30 is arranged with the optical axis 30A and the arrow X direction forming the same angle is defined as region F.

[0115] At this time, the value of the in-plane retardation (Re) in each region F is preferably half a wavelength, that is, λ / 2. These in-plane retardations are calculated by multiplying the refractive index difference Δn accompanying the refractive index anisotropy of the region F by the thickness of the optical anisotropic layer. Here, the refractive index difference accompanying the refractive index anisotropy of the region F in the optical anisotropic layer is a refractive index difference defined by the difference between the refractive index in the slow axis direction in the plane of the region F and the refractive index in the direction perpendicular to the slow axis direction. That is, the refractive index difference Δn accompanying the refractive index anisotropy of the region F is equal to the difference between the refractive index of the liquid crystal compound 30 in the direction of the optical axis 30A and the refractive index of the liquid crystal compound 30 in the direction perpendicular to the optical axis 30A in the plane of the region F. That is, the above-mentioned refractive index difference Δn is equal to the refractive index difference of the liquid crystal compound.

[0116] If circularly polarized light is incident on such an optically anisotropic layer 26, the light is diffracted (refracted), and the direction of the circularly polarized light is converted.

[0117] exist Figure 4This effect is conceptually shown in . In the optically anisotropic layer 26 , the value of the product of the refractive index difference of the liquid crystal compound and the thickness of the optically anisotropic layer is set to λ / 2.

[0118] like Figure 4 As shown, when the value of the product of the refractive index difference of the liquid crystal compound of the optical anisotropic layer 26 and the thickness of the optical anisotropic layer is λ / 2, if left-handed circularly polarized light L is incident on the optical anisotropic layer 26, the left-handed circularly polarized light L passes through the optical anisotropic layer 26, thereby being given a phase difference of 180°, and the transmitted light is converted into right-handed circularly polarized light R.

[0119] Furthermore, the absolute phase of the left-handed circularly polarized light L incident on the optical anisotropic layer 26 changes according to the orientation of the optical axis 30A of each liquid crystal compound 30 when passing through the optical anisotropic layer 26. At this time, since the orientation of the optical axis 30A changes while rotating in the direction of the arrow X, the amount of change in the absolute phase of the left-handed circularly polarized light L varies depending on the orientation of the optical axis 30A. In addition, since the liquid crystal orientation pattern formed in the optical anisotropic layer 26 is a periodic pattern in the direction of the arrow X, as shown in FIG. Figure 4 As shown, a periodic absolute phase Q1 in the arrow X direction corresponding to the direction of the optical axis 30A is given to the left-handed circularly polarized light L passing through the optical anisotropic layer 26. Thus, an equiphase surface E1 inclined in the direction opposite to the arrow X direction is formed.

[0120] Therefore, the right-handed circularly polarized light R transmitted through the optical anisotropic layer 26 is refracted in a manner inclined toward a direction perpendicular to the equiphase plane E1, and travels in a direction different from the traveling direction of the left-handed circularly polarized light L as the incident light. In this way, the left-handed circularly polarized light L incident on the optical anisotropic layer 26 is converted into the right-handed circularly polarized light R, which is inclined at a constant angle in the arrow X direction relative to the incident direction.

[0121] On the other hand, Figure 5 As conceptually shown in FIG. 2 , when the value of the product of the refractive index difference of the liquid crystal compound of the optical anisotropic layer 26 and the thickness of the optical anisotropic layer is λ / 2, if right-handed circularly polarized light R is incident on the optical anisotropic layer 26, the right-handed circularly polarized light R passes through the optical anisotropic layer 26, thereby being given a phase difference of 180° and converted into left-handed circularly polarized light L.

[0122] Furthermore, when the right-handed circularly polarized light R passes through the optical anisotropic layer 26, the absolute phase changes according to the orientation of the optical axis 30A of each liquid crystal compound 30. At this time, since the orientation of the optical axis 30A changes while rotating in the direction of the arrow X, the amount of change in the absolute phase of the right-handed circularly polarized light R varies depending on the orientation of the optical axis 30A. In addition, since the liquid crystal orientation pattern formed in the optical anisotropic layer 26 is a periodic pattern in the direction of the arrow X, as shown in FIG. Figure 5 As shown, the right-handed circularly polarized light R passing through the optical anisotropic layer 26 is provided with periodic absolute phases Q2 in the arrow X directions corresponding to the directions of the optical axes 30A.

[0123] Here, since the incident light is right-handed circularly polarized light R, the periodic absolute phase Q2 in the direction of the arrow X corresponding to the direction of the optical axis 30A is Figure 4 As a result, in the right circularly polarized light R, an isophase plane E2 is formed which is inclined in the direction of the arrow X in the opposite direction to the left circularly polarized light L.

[0124] Therefore, the right-handed circularly polarized light R is refracted in a manner inclined toward a direction perpendicular to the equal phase plane E2, and travels in a direction different from the traveling direction of the right-handed circularly polarized light R. In this way, the right-handed circularly polarized light R incident on the optical anisotropic layer 26 is converted into the left-handed circularly polarized light L, which is inclined at a constant angle relative to the incident direction in the direction opposite to the arrow X direction.

[0125] Therefore, by setting the rotation direction of the optical axis 30A of the liquid crystal compound 30 that rotates in the arrow X direction to the opposite direction, the diffraction direction of the transmitted light can be set to the opposite direction.

[0126] That is, in Figure 2 to Figure 5 In the example shown, the rotation direction of the optical axis 30A toward the direction of arrow X is clockwise. In contrast, if the rotation direction of the optical axis 30A is counterclockwise, when the incident light is left-handed circularly polarized light L, the right-handed circularly polarized light R that becomes transmitted light is refracted in the direction opposite to the direction of arrow X, and when the incident light is right-handed circularly polarized light R, the left-handed circularly polarized light L that becomes transmitted light is diffracted in the direction of arrow X.

[0127] In the optically anisotropic layer 26, the in-plane retardation value of the plurality of regions F is preferably half a wavelength. In particular, the in-plane retardation Re(λ) of the plurality of regions F of the optically anisotropic layer 26 with respect to incident light having a wavelength of λ nm is = Δn λ ×d is preferably within the range defined by the following formula (1). λis the refractive index difference associated with the refractive index anisotropy of the region F when the wavelength of the incident light is λ nm, and d is the thickness of the optically anisotropic layer 26 .

[0128] 0.7×(λ / 2)nm≤Δn λ ×d≤1.3×(λ / 2)nm……(1)

[0129] That is, if the in-plane retardation Re(λ) of the plurality of regions F of the optically anisotropic layer 26 is equal to Δn λ If ×d satisfies the formula (1), a sufficient amount of circularly polarized light components of light incident on the optically anisotropic layer 26 can be converted into circularly polarized light traveling in a direction inclined in the positive direction or in the reverse direction with respect to the arrow X direction.

[0130] In-plane retardation Re(λ) = Δn λ More preferably, ×d is 0.8×(λ / 2)nm≤Δn λ ×d≤1.2×(λ / 2)nm, more preferably 0.9×(λ / 2)nm≤Δn λ ×d≤1.1×(λ / 2)nm.

[0131] Furthermore, the in-plane retardation values ​​of the plurality of regions F in the optically anisotropic layer 26 may be outside the range of the above formula (1). Specifically, by setting Δn λ ×d<0.7×(λ / 2)nm or 1.3×(λ / 2)<Δn λ ×d, it can be divided into light traveling in the same direction as the incident light and light traveling in a direction different from the incident light. λ When ×d is close to 0 nm or λ nm, the component of light traveling in the same direction as the traveling direction of the incident light increases, and the component of light traveling in a direction different from the traveling direction of the incident light decreases.

[0132] Here, by changing one period Λ of the liquid crystal alignment pattern formed in the optically anisotropic layer 26 , the diffraction angle of the transmitted light can be adjusted.

[0133] Specifically, the shorter the period Λ of the liquid crystal orientation pattern, the stronger the interference between the light passing through the adjacent liquid crystal compounds 30, so that the transmitted light can be greatly diffracted. That is, when light is incident from the normal direction of the optical anisotropic layer 26, the shorter the period Λ of the liquid crystal orientation pattern, the larger the angle between the normal direction and the transmitted light (diffracted light).

[0134] In addition, the normal direction refers to a direction perpendicular to a plane such as the main surface of the sheet-like object.

[0135] The optical anisotropic layer 26 can diffract the transmitted light more greatly as the wavelength of the incident light is longer. That is, when light is incident from the normal direction of the optical anisotropic layer 26, the longer the wavelength of the incident light, the larger the angle of the transmitted light (diffracted light) relative to the normal direction.

[0136] Therefore, the optical anisotropic layer 26 (liquid crystal diffraction element 12) can split the incident light according to the wavelength. For example, when white light is incident on the optical anisotropic layer 26 from the normal direction, the angle formed by the normal direction and the transmitted light is the largest for red light, the second largest for green light, and the smallest for blue light. Therefore, the white light can be split into red light, green light, and blue light.

[0137] That is, the angle of diffraction by the optically anisotropic layer 26 (liquid crystal diffraction element 12) is determined by "Λ / λ" from one period Λ and the wavelength λ of the incident light.

[0138] Furthermore, regarding diffraction by the optically anisotropic layer 26 , as long as the wavelengths are equal, the angle of diffraction (refraction) is equal regardless of whether the incident light is right-handed circularly polarized light R or left-handed circularly polarized light L.

[0139] For example, when unpolarized light of a wavelength of 550 nm is incident on the optically anisotropic layer 26 from the normal direction, the angle formed by the transmitted right-handed circularly polarized light R and the normal direction is equal to the angle formed by the transmitted left-handed circularly polarized light L and the normal direction.

[0140] The optically anisotropic layer 26 is formed by curing a liquid crystal composition containing a rod-like liquid crystal compound or a discotic liquid crystal compound, and has a liquid crystal alignment pattern in which the optical axis of the rod-like liquid crystal compound or the optical axis of the discotic liquid crystal compound is aligned as described above.

[0141] The optically anisotropic layer 26 composed of a cured layer of the liquid crystal composition can be obtained by forming an alignment film 24 on the support 20, and applying and curing the liquid crystal composition on the alignment film 24. It is the optically anisotropic layer 26 that functions as a so-called λ / 2 plate, but the present invention includes a mode in which a laminate integrally provided with the support 20 and the alignment film 24 functions as a λ / 2 plate.

[0142] Furthermore, the liquid crystal composition for forming the optically anisotropic layer 26 contains a rod-like liquid crystal compound or a disc-like liquid crystal compound, and may further contain other components such as a leveling agent, an alignment control agent, a polymerization initiator, and an alignment aid.

[0143] The optically anisotropic layer 26 preferably has a broadband with respect to the wavelength of incident light, and is preferably formed using a liquid crystal material having a reversely dispersed birefringence.

[0144] Furthermore, it is also preferred that the optical anisotropic layer be substantially broadband relative to the wavelength of incident light by imparting a twist component to the liquid crystal composition and / or stacking different phase difference plates. For example, in an optical anisotropic layer, a method of realizing a broadband patterned λ / 2 plate by stacking two layers of liquid crystals having different twist directions is shown in Japanese Patent Publication No. 2014-089476, etc., and can be preferably used in the present invention.

[0145] -Rod-like liquid crystal compound-

[0146] As the rod-like liquid crystal compound, preferably used are azomethines, azoxyls, cyanobiphenyls, cyanophenyl esters, benzoates, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolans and alkenylcyclohexylbenzonitriles. Not only the above low molecular weight liquid crystal molecules but also high molecular weight liquid crystal molecules can be used.

[0147] It is more preferable to fix the alignment of the rod-like liquid crystal compound by polymerization. As the polymerizable rod-like liquid crystal compound, there can be used Makromol. Chem., Vol. 190, p. 2255 (1989), Advanced Materials 5, page 107 (1993), U.S. Patent No. 4,683,327, U.S. Patent No. 5,622,648, U.S. Patent No. 5,770,107, International Publication No. 95 / 22586, International Publication No. 95 / 24455, International Publication No. 97 / 00600, International Publication No. 98 / 23580, International Publication No. 98 / 52905, Japanese Patent Application No. 1-272551, Japanese Patent Application No. 6-16616, Japanese Patent Application No. 7-110469, Japanese Patent Application No. 11-80081 and Japanese Patent Application No. 2001-64627. Furthermore, as the rod-like liquid crystal compound, for example, rod-like liquid crystal compounds described in JP-A-11-513019 and JP-A-2007-279688 can also be preferably used.

[0148] -Disc-like liquid crystal compounds-

[0149] As the discotic liquid crystal compound, for example, discotic liquid crystal compounds described in Japanese Patent Application Laid-Open Nos. 2007-108732 and 2010-244038 can be preferably used.

[0150] In addition, when a disc-shaped liquid crystal compound is used in the optically anisotropic layer, the liquid crystal compound 30 stands up in the thickness direction in the optically anisotropic layer, and the optical axis 30A derived from the liquid crystal compound is defined as an axis perpendicular to the disc surface, the so-called fast axis (see Figure 25).

[0151] In the liquid crystal diffraction element 12, the film thickness of the optical anisotropic layer 26 is not limited, but from the viewpoint of thinning the liquid crystal diffraction element 12, it is preferably 20 μm or less, more preferably 15 μm or less, further preferably 10 μm or less, and particularly preferably 5 μm or less.

[0152] exist Figure 2 In the illustrated liquid crystal diffraction element 12 , the liquid crystal compound 30 constituting the optically anisotropic layer 26 is oriented in the same direction as the optical axis 30A in the thickness direction.

[0153] However, the present invention is not limited thereto. In the optical element 10 of the present invention, Figure 6 As conceptually shown in FIG. 1 , the liquid crystal compound 30 constituting the optically anisotropic layer 26 is preferably twisted and oriented in a helical shape along the thickness direction of the optically anisotropic layer 26 .

[0154] In the optically anisotropic layer 26 , the liquid crystal compound 30 is twisted and aligned in the thickness direction, so that the diffraction efficiency of circularly polarized light by the liquid crystal diffraction element 12 can be improved.

[0155] Here, when the liquid crystal compound 30 constituting the optically anisotropic layer 26 is twisted and oriented in a helical shape in the thickness direction, the diffraction efficiency of right-handed circularly polarized light and left-handed circularly polarized light differs depending on the twisting direction of the helix.

[0156] Therefore, when the liquid crystal compound 30 constituting the optically anisotropic layer 26 is twisted and oriented in a spiral shape in the thickness direction, as shown in FIG. Figure 6 As shown in FIG. 1 , it is preferred that two optically anisotropic layers 26 having liquid crystal compounds in different twisting directions be stacked.

[0157] With such a structure, the diffraction efficiency of right-handed circularly polarized light and left-handed circularly polarized light can be improved at the same time, and the diffraction efficiency of right-handed circularly polarized light and left-handed circularly polarized light can be made consistent.

[0158] The number of optically anisotropic layers stacked is not limited to one or two layers, and may be three or more layers as necessary.

[0159] In the optical element 10 of the present invention, the twist angle of the liquid crystal compound 30 in the optically anisotropic layer 26 is not limited.

[0160] From the perspective of appropriately improving the diffraction efficiency, regardless of whether the twisting direction of the liquid crystal compound 30 is right twist or left twist (clockwise or counterclockwise), the absolute value of the twist angle of the liquid crystal compound 30 is preferably 5 to 360°, more preferably 10 to 320°, further preferably 20 to 280°, and particularly preferably 30 to 250°.

[0161] The twist angle of the liquid crystal compound 30 refers to the twist angle of the liquid crystal compound 30 twisted and aligned in the thickness direction in the optically anisotropic layer 26 from the lower surface to the upper surface.

[0162] In the optical element 10 of the present invention, the liquid crystal diffraction element 12 having such an optically anisotropic layer 26 is disposed on one surface of the prism 14 .

[0163] In addition, when the liquid crystal diffraction element 12 has an orientation film 24 and / or a support 20, the optical anisotropic layer 26 may be located on the prism 14 side or on the side opposite to the prism 14 in the liquid crystal diffraction element 12. Furthermore, an anti-reflection film such as a dielectric multilayer film or a moth-eye film may be provided on the interface with air.

[0164] The liquid crystal diffraction element 12 may be a prism 14, for example. Figure 2 The support 20 shown in the figure has an alignment film 24 and an optical anisotropic layer 26 formed on one side of the prism 14 as described above, thereby being directly in contact with the prism 14. In addition, the liquid crystal diffraction element 12 can be directly in contact with one side of the prism 14 by methods such as alignment treatment, coating and polymerization of a liquid crystal composition.

[0165] Alternatively, the liquid crystal diffraction element 12 may be attached to one side of the prism 14 using an adhesive such as an optically transparent adhesive (OCA (Optical Clear Adhesive)), an optically transparent double-sided tape, or an ultraviolet curable resin. Furthermore, the liquid crystal diffraction element 12 may be directly attached to one side of the prism 14 by performing an adhesion strengthening surface treatment such as a plasma treatment. An anti-reflection film or the like may be provided between the prism 14 and the liquid crystal diffraction element 12 as required.

[0166] In the optical element 10 of the present invention, when there is a layer between the optical anisotropic layer 26 and the prisms 14 including the support 20 and the alignment film 24, the layer preferably has a refractive index close to that of the optical anisotropic layer 26 and the prisms 14. That is, the optical anisotropic layer 26 and the prisms 14 are preferably optically in close contact.

[0167] Specifically, when there is a certain layer between the optically anisotropic layer 26 and the prisms 14 , the difference in refractive index between the layer and the optically anisotropic layer 26 and the prisms 14 is preferably ±0.5 or less, and more preferably ±0.3 or less.

[0168] exist Figure 1 In the illustrated optical element 10 , the prism 14 is a triangular prism having a right-angled triangle-shaped base.

[0169] The liquid crystal diffraction element 12 is arranged on a side that forms a right angle in a right triangle. In the optical element 10 of the illustrated example, the side on which the prism 14 is arranged is the first side of the prism in the present invention, and the side that forms a right angle in a right triangle together with the first side is the second side that reflects the light separated by diffraction based on the liquid crystal diffraction element 12. As described above, the light separated by diffraction based on the liquid crystal diffraction element 12 is right-handed circularly polarized light or left-handed circularly polarized light.

[0170] In the present invention, a prism refers to an optical component (optical element) formed of a material such as quartz glass or crystal, that is, a transparent medium, and used to disperse, refract, totally reflect, or double refract light.

[0171] In the present invention, light includes not only visible light but also electromagnetic waves such as the above-mentioned ultraviolet rays and infrared rays.

[0172] As described above, if non-polarized light enters the liquid crystal diffraction element 12 (optically anisotropic layer 26), Figure 8 As conceptually shown in the figure, the incident light is separated by diffraction based on the liquid crystal diffraction element 12, and the component of the right-handed circularly polarized light R is diffracted in the direction of the arrow X (the right direction in the figure), and the component of the left-handed circularly polarized light L is diffracted in the direction opposite to the direction of the arrow X (the left direction in the figure).

[0173] In addition, as described above, the direction of return of the transmitted light is opposite to that of the incident light due to diffraction by the liquid crystal diffraction element 12 .

[0174] The light separated by the liquid crystal diffraction element 12 and diffracted to the left in the figure propagates in the prism 14, is incident on the second surface 14a orthogonal to the first surface of the prism 14 provided with the liquid crystal diffraction element 12, and is regularly reflected. In addition, the rotation direction of the circularly polarized light is reversed by this reflection.

[0175] Here, as described above, the angle of diffraction by the liquid crystal diffraction element 12 is the same angle as long as the wavelength of light is the same.

[0176] Therefore, the light (diffracted light) diffracted in the left direction in the figure and incident on the second surface 14a of the prism 14 which is orthogonal to the first surface, i.e., the main surface of the liquid crystal diffraction element 12 (optically anisotropic layer 26) and is reflected regularly, and the light (diffracted light) diffracted in the direction opposite to the light incident on the second surface 14a by the optically anisotropic layer 26 become parallel light.

[0177] That is, the two lights separated by the liquid crystal diffraction element 12 according to the rotation direction of the circularly polarized light become parallel lights and are emitted from the surface other than the first surface and the second surface 14a of the prism 14. Hereinafter, for convenience, this surface is also referred to as the third surface.

[0178] In addition, Figure 1 and Figure 8 In order to simply illustrate the function of the optical element 10, two separated beams of the same wavelength are used to illustrate the light diffracted by the liquid crystal diffraction element 12. However, as described above, the incident light incident on the optical element 10 of the present invention is split into multiple beams by the liquid crystal diffraction element 12 and diffracted at angles corresponding to the wavelengths. However, in the optical element 10 of the present invention, the incident light may be light of a short wavelength (monochromatic light).

[0179] And, in Figure 1 In the figure, for convenience, the light emitted from the third surface of the prism 14 is shown to go straight and pass through the third surface. However, in reality, the light emitted from the third surface is refracted at the interface between the third surface and the air layer according to the difference in refractive index between the material forming the prism 14 and the air and the incident angle to the third surface, and then emitted. This is also the same in other figures used to explain the optical element of the present invention.

[0180] like Figure 8 As shown, the light diffracted by the liquid crystal diffraction element 12 (optically anisotropic layer 26) is separated according to the rotation direction of the circularly polarized light, and is diffracted in opposite directions, that is, the arrow X direction and the direction opposite to the arrow X.

[0181] Therefore, it is difficult to utilize both of the two beams of light diffracted and separated by the liquid crystal diffraction element 12, and in most cases only one of them can be utilized. That is, the utilization efficiency of the separated light in the optical element using the conventional liquid crystal diffraction element is low.

[0182] Alternatively, by combining a plurality of optical components such as a reflector and a lens, both of the light diffracted and split into two beams by the liquid crystal diffraction element 12 can be used. However, in this case, the optical elements such as the spectroscopic element cannot be avoided from being enlarged and complicated.

[0183] On the other hand, according to the optical element 10 of the present invention, the two lights separated by diffraction by the liquid crystal diffraction element 12 are emitted from the same surface (third surface) of the prism 14 as parallel lights.

[0184] That is, according to the optical element 10 of the present invention, the two beams of light diffracted and separated by the liquid crystal diffraction element 12 are emitted from the same surface (third surface) of the prism 14 in the same direction.

[0185] In addition, in the optical element 10 of the present invention, the liquid crystal diffraction element 12 splits the incident light, but as mentioned above, the diffraction based on the liquid crystal diffraction element 12 has opposite diffraction directions in right-handed circularly polarized light and left-handed circularly polarized light, but as long as the wavelength is the same, the diffraction angle is the same.

[0186] Therefore, if Fig. 9 The solid line, dotted line and dashed line show that the light with the same wavelength Figure 1 Similarly, one of the separated lights is diffracted in the direction of arrow X (right direction in the figure), and the other is regularly reflected by the second surface of the prism 14. As a result, the two lights separated by the diffraction of the liquid crystal diffraction element 12 become parallel lights and are emitted from the third surface of the prism 14.

[0187] exist Fig. 9 ( Fig.11 ), the dotted line is, for example, blue light, the solid line is, for example, green light, and the single-point dashed line is, for example, red light.

[0188] Therefore, the optical element 10 of the present invention can easily utilize the two lights (diffracted lights) separated by the liquid crystal diffraction element 12. As a result, the optical element 10 of the present invention can improve the utilization efficiency of the light separated by the liquid crystal diffraction element 12.

[0189] For example, Fig. 9 As conceptually shown in FIG. 1 , as long as the lenses 16 are arranged opposite to each other on the third surface of the prism 14 and the light is focused, the parallel light is focused at the same position, so that the two beams of light separated by the liquid crystal diffraction element 12 can be easily measured by one detector 18. That is, according to the present invention, the utilization efficiency of the light separated by the liquid crystal diffraction element 12 can be improved.

[0190] And, if Fig. 9 As shown, the optical element 10 of the present invention can constitute, for example, a spectroscopic device with a simple and compact structure in which only one lens 16 and one detector 18 are combined on the optical element 10. That is, the optical element 10 of the present invention can also achieve miniaturization of the optical system.

[0191] In the optical element 10 of the present invention, the material forming the prism 14 is not limited, and all of the various materials used for various prisms can be used.

[0192] Here, in the present invention, the difference in refractive index between the prism 14 and the liquid crystal diffraction element 12 (each layer) is preferably small. Specifically, the difference in refractive index between the prism 14 and the liquid crystal diffraction element 12 is preferably ±0.5 or less, and more preferably ±0.3 or less.

[0193] By adopting such a structure, it is possible to prevent reflection of light between the prism 14 and the liquid crystal diffraction element 12 , thereby further improving the utilization efficiency of the light split by the liquid crystal diffraction element 12 .

[0194] In the optical element 10 of the present invention, the second surface 14 a of the prism 14 , that is, the surface of the prism 14 that reflects one of the lights separated by the liquid crystal diffraction element 12 , preferably totally reflects the light.

[0195] That is, the liquid crystal diffraction element 12 preferably diffracts the incident light so that one of the separated lights is incident on the second surface 14 a of the prism 14 at an angle equal to or greater than the critical angle.

[0196] As described above, the angle of diffraction of circularly polarized light by the liquid crystal diffraction element 12 is determined by one period Λ of the optical anisotropic layer 26 and the wavelength λ of the incident light as “Λ / λ”.

[0197] Therefore, in the optical element 10 of the present invention, it is preferable to determine one period Λ of the optical anisotropic layer 26 according to the wavelength of the light to be spectroscopically analyzed so that the incident angle of the light incident on the second surface 14a of the prism 14 becomes equal to or greater than the critical angle.

[0198] If the incident angle of the light incident on the second surface 14a is too large, the size of the prism 14 increases. Therefore, one period Λ is preferably determined so that the incident angle of the light incident on the second surface 14a does not increase and the size of the prism 14 does not increase.

[0199] Specifically, when the wavelength λ of the light to be spectrally split is 450nm, one period Λ is preferably set to 0.3 to 2μm. Furthermore, when the wavelength λ of the light to be spectrally split is 550nm, one period Λ is preferably set to 0.4 to 3μm. Furthermore, when the wavelength λ of the light to be spectrally split is 700nm, one period Λ is preferably set to 0.5 to 4μm. Furthermore, when the wavelength λ of the light to be spectrally split is 1000nm, one period Λ is preferably set to 0.8 to 5μm.

[0200] In addition, Figure 1 In the example shown, the incident light entering the optical element 10 of the present invention comes from the normal direction of the liquid crystal diffraction element 12, but the present invention is not limited to this.

[0201] That is, the light incident on the optical element 10 (liquid crystal diffraction element 12) of the present invention may be from a direction having an angle with respect to the normal direction of the liquid crystal diffraction element 12. Therefore, in this case, in addition to the wavelength of the light to be split, it is also preferred to determine one period Λ of the optical anisotropic layer 26 based on the incident angle of the incident light to be set so that the incident angle of the light to the second surface 14a of the prism 14 becomes less than the critical angle.

[0202] Alternatively, the incident angle of light onto the optical element 10 (liquid crystal diffraction element 12) of the present invention may be adjusted so that the incident angle of light onto the second surface 14a of the prism 14 becomes equal to or smaller than the critical angle.

[0203] In the optical element 10 of the present invention, light is totally reflected by the second surface 14 a of the prism 14 without being restricted.

[0204] For example, a reflective film such as a dielectric multilayer film or a metal film may be provided on the second surface 14 a of the prism 14 so that light is regularly reflected on the second surface 14 a of the prism 14 .

[0205] However, considering the utilization efficiency of the light separated by the liquid crystal diffraction element 12 , it is preferred that one of the lights separated by the liquid crystal diffraction element 12 is incident at an angle equal to or greater than the critical angle so that the light is totally reflected by the second surface 14 a of the prism 14 .

[0206] As a preferred embodiment, in the optical element 10 shown in the figure, in the prism 14, the first surface on which the liquid crystal diffraction element 12 is disposed is orthogonal to the second surface 14a for reflecting one side of the light diffracted and separated by the liquid crystal diffraction element 12. More specifically, in the optical element 10, the main surface of the liquid crystal diffraction element 12 (optically anisotropic layer 26) is orthogonal to the second surface of the prism 14.

[0207] However, in the optical element of the present invention, the angle formed between the first surface (the main surface of the liquid crystal diffraction element 12 ) and the second surface of the prism 14 can be variously configured other than being orthogonal.

[0208] When the incident angle (incident direction) of light deviates from the normal direction of the first surface of the prism 14, the same effect can be obtained by making the angle formed by the first surface and the second surface 14a deviate from orthogonal, that is, the effect of making the diffracted light from one side of the first surface and the diffracted light from the other side of the first surface reflected by the second surface 14a parallel.

[0209] Furthermore, one direction (arrow X direction) in which the optical axis of the optical anisotropic layer 26 rotates is preferably parallel to the direction of the diffraction vector of the second surface 14a, that is, the repetition direction of the periodic structure of the diffraction element. Furthermore, it is preferred that the normal direction of the second surface 14a is parallel to the arrow X direction. Furthermore, it is preferred that the arrow X direction is included in the plane of the surface orthogonal to the first surface and the second surface 14a. Furthermore, it is preferred that the line (ridge line) formed by the angle between the first surface of the prism 14 and the second surface 14a is orthogonal to the arrow X direction.

[0210] As an example, Fig.10 In the optical element 10A conceptually shown in FIG. 1 , the angle between the first surface and the second surface of the prism 14 can be an obtuse angle.

[0211] By setting it to this structure, Fig.10 As shown, the light diffracted by the liquid crystal diffraction element 12 in the direction of arrow X (right direction) and the light diffracted in the opposite direction and reflected by the second surface 14a of the prism 14 travel in separate directions and are emitted from the third surface.

[0212] According to the optical element, Fig.11 As conceptually shown in FIG. 1 , by arranging lenses 16 facing each other on the third surface of the prism 14 to focus light, and by using a detector 18 to measure light, the intensity of light separated into right-handed circularly polarized light R and left-handed circularly polarized light L can be measured by one detector 18 .

[0213] Alternatively, the angle formed by the first surface and the second surface of the prism 14 may be an acute angle.

[0214] By setting such a structure, the light diffracted by the liquid crystal diffraction element 12 in the direction of arrow X (right direction) and the light diffracted in the opposite direction and reflected by the second surface 14a of the prism 14 move toward the direction close to each other and are emitted from the third surface (reference Fig.14 ).

[0215] That is, by configuring the first surface and the second surface of the prism not to be orthogonal to each other, a polarization separation system that separates light according to polarization can be constructed.

[0216] The angle formed by the first surface (the main surface of the liquid crystal diffraction element 12 ) and the second surface of the prism 14 is preferably 70 to 110°, more preferably 80 to 110°, and further preferably 90°.

[0217] By setting the angle between the first surface and the second surface of the prism 14 to 70 to 110 degrees, the utilization efficiency of the split light can be more reliably improved, and it is preferable in that the split light corresponding to the polarized light can be detected in a close range.

[0218] In addition, in the present invention, the liquid crystal diffraction element 12 is basically arranged parallel to the first surface of the prism 14. Therefore, the above description is for the angle between the first surface of the prism 14 and the second surface 14a, but the most important thing is the angle between the main surface of the liquid crystal diffraction element 12 (optically anisotropic layer 26) and the second surface 14a.

[0219] Furthermore, in the optical element 10 shown in the figure, both of the two beams of light separated by the liquid crystal diffraction element 12 are emitted from the third surface of the prism 14 .

[0220] Therefore, the angle formed by the first surface and the second surface 14 a and the third surface is appropriately set so that the light incident on the third surface can be emitted without being reflected.

[0221] For example, Figure 1 As shown, when the first surface on which the liquid crystal diffraction element 12 is provided is orthogonal to the second surface 14a for reflecting one side of the light separated by the liquid crystal diffraction element 12, the angle formed by the first surface and the third surface which becomes the exit surface of the light from the prism 14 is preferably 5 to 60°, and more preferably 10 to 45°.

[0222] In the present invention, as required, Fig.12 In the optical element 10B conceptually shown in FIG. 1 , a phase difference layer 19 may be provided on a surface of the prism 14 that reflects one of the lights separated by the liquid crystal diffraction element 12 .

[0223] When the prism 14 has the phase difference layer 19 , one of the lights separated by the liquid crystal diffraction element 12 is reflected after the phase is adjusted by the phase difference layer 19 .

[0224] By having such a phase difference layer 19, for example, it is possible to compensate for the phase change caused by total reflection, adjust the phase of the split light, for example, make the polarization of the diffracted light from one side of the first surface and the polarization of the diffracted light from the other side of the first surface reflected by the second surface 14a orthogonal or parallel, etc.

[0225] The phase difference layer 19 is not limited, and various known phase difference layers can be used. In addition, the phase difference provided by the phase difference layer 19 is also not limited.

[0226] Furthermore, the refractive indexes of the prism 14 and the retardation layer 19 are preferably close to each other in order to prevent reflection at the interface between the prism 14 and the retardation layer 19. Specifically, the difference in refractive index between the prism 14 and the retardation layer 19 is preferably ±0.5 or less, and more preferably ±0.3 or less.

[0227] In the optical element 10 of the illustrated example, the prism 14 is a triangular prism, and the light separated by the liquid crystal diffraction element 12 arranged on the first surface is directly emitted on one side and reflected by the second surface 14a on the other side, and both are emitted from the third surface different from the first surface and the second surface 14a.

[0228] However, the present invention is not limited thereto.

[0229] For example, the prism may be formed into a polygonal shape that is larger than a quadrilateral, so that the light separated by the liquid crystal diffraction element 12 and the light reflected by the second surface are parallel, and then the two light beams are reflected by one or more surfaces of the prism, and two light beams (diffracted light) are emitted from outside the configuration area of ​​the liquid crystal diffraction element 12 on the first surface where the liquid crystal diffraction element 12 is configured.

[0230] Alternatively, the light separated by the liquid crystal diffraction element 12 and the light reflected by the second surface may be made parallel and then the two light beams may be reflected by one or more surfaces of the prism so that two light beams (diffracted light) are emitted from the surface of the prism where the light first enters.

[0231] That is, in the optical element of the present invention, as long as one light is reflected from the second surface 14a, the two light beams separated by the liquid crystal diffraction element 12 are made parallel and then the two light beams are reflected from the same surface, the propagation of light in the prism can utilize various structures.

[0232] However, no matter what the structure is, the two beams of light separated by the liquid crystal diffraction element 12 are preferably emitted from the same surface of the prism.

[0233] As mentioned above, the optical element of the present invention has been described in detail, but the present invention is not limited to the above-mentioned examples, and various improvements and changes can be made without departing from the scope of the present invention.

[0234] Example

[0235] The following examples are given to more specifically describe the features of the present invention. The material, reagent, usage amount, amount of substance, ratio, processing content and processing sequence etc. shown in the following examples can be appropriately changed without departing from the gist of the present invention. Therefore, the scope of the present invention should not be interpreted restrictively by the specific examples shown below.

[0236] [Example 1]

[0237] <Fabrication of Liquid Crystal Diffraction Element>

[0238] (Formation of Orientation Film)

[0239] A glass substrate (EAGLE manufactured by Corning Incorporated Co., Ltd.) was prepared as a support. The following coating liquid for forming an alignment film was applied to the support by spin coating. The support having the coating film of the coating liquid for forming an alignment film was dried on a hot plate at 60° C. for 60 seconds to form an alignment film.

[0240] Coating liquid for forming an alignment film

[0241]

[0242]

[0243] Materials for photo-orientation

[0244] [Chemical formula 1]

[0245]

[0246] (Exposure of Alignment Film)

[0247] The formed alignment film was irradiated with polarized ultraviolet light (50 mJ / cm 2 , using an ultra-high pressure mercury lamp), the orientation film was exposed.

[0248] use Figure 7 The exposure device shown in the figure exposes the alignment film to form an alignment film having an alignment pattern. In the exposure device, a device that emits a laser beam with a wavelength (325nm) is used as a laser. The exposure amount based on the interference light is set to 300mJ / cm 2 In addition, the crossing angle (crossing angle α) of the two beams was adjusted so that one period Λ (the length of the optical axis rotated 180°) of the alignment pattern formed by the interference of the two laser beams was 1 μm.

[0249] (Formation of Optically Anisotropic Layer (Liquid Crystal Layer))

[0250] As a liquid crystal composition for forming an optically anisotropic layer, the following composition B-1 was prepared.

[0251] Composition B-1

[0252]

[0253] Rod-like liquid crystal compound L-1 (containing the following structures in the mass ratio shown on the right)

[0254] [Chemical formula 2]

[0255]

[0256] Leveling agent T-1

[0257] [Chemical formula 3]

[0258]

[0259] The optically anisotropic layer was formed by coating the composition B-1 on the oriented film in multiple layers.

[0260] Specifically, after the first layer of composition B-1 is coated on the oriented film, heated, cooled and then UV-cured to prepare a liquid crystal fixing layer, the operation is repeated for the second layer and thereafter: coating is performed by overlapping the coating on the liquid crystal fixing layer, and similarly heating, cooling and then UV-curing is performed.

[0261] First, the composition B-1 was applied on the oriented film as the first layer, and the coating was heated to 80° C. on a hot plate. Then, a high pressure mercury lamp was used at 300 mJ / cm 2 in a nitrogen atmosphere at 80° C. 2 The coating film was irradiated with ultraviolet rays having a wavelength of 365 nm in an irradiation amount, thereby fixing the alignment of the liquid crystal compound.

[0262] For the second layer and later, the liquid crystal fixing layer is overlapped and coated, and then heated and cooled under the same conditions as above, and then ultraviolet curing is performed to produce a liquid crystal fixing layer. In this way, overlapping coating is repeated until the total thickness reaches the desired film thickness, thereby forming an optically anisotropic layer.

[0263] In addition, for the refractive index difference Δn of the cured layer of composition B-1, the retardation Re (λ) and film thickness of the liquid crystal fixed layer obtained by coating composition B-1 on a support with an oriented film prepared separately for retardation measurement, aligning the liquid crystal compound so that the arrow pointing to the liquid crystal compound is horizontal to the substrate, and then irradiating the liquid crystal compound with ultraviolet light to fix the liquid crystal compound, were measured and determined. Δn can be calculated by dividing the retardation Re (λ) by the film thickness. λ The retardation Re (λ) was measured at a target wavelength using Axoscan manufactured by Axometrix, and the film thickness was measured using a SEM (Scanning Electron Microscope).

[0264] Furthermore, the refractive index ne(λ) for extraordinary light and the refractive index no(λ) for normal light were measured using an Abbe refractometer. Furthermore, the refractive index difference Δn(λ) was obtained from the difference between ne(λ) and no(λ). In the notations Re(λ), ne(λ), no(λ), and Δn(λ), λ is the wavelength of the incident light. Hereinafter, the wavelength λ of the incident light is set to 633 nm.

[0265] The final film thickness of the optically anisotropic layer was confirmed to be 1.68 μm using a microscope, and Δn 633×Thickness=Re(633) was 255 nm, and the liquid crystal was periodically oriented. In the optically anisotropic layer, the twist angle of the liquid crystal compound in the thickness direction was 0°.

[0266] In the cross-sectional image obtained by SEM, light and dark lines perpendicular to the lower interface (interface with the support) of the optically anisotropic layer were observed. The light and dark lines were observed in a structure in which liquid crystal compounds were stacked in the same direction in the thickness direction.

[0267] The refractive indexes of the optically anisotropic layer at a wavelength of 633 nm were ne=1.694 and no=1.543.

[0268] In addition, the refractive index was measured by an Abbe refractometer.

[0269] The formed optically anisotropic layer is transferred and bonded to the bottom surface of the prepared triangular prism.

[0270] The triangular prism is made of SCHOTT SK2 type optical glass, and has a refractive index of 1.605 at a wavelength of 633 nm. The prepared triangular prism has an angle of 90°, and the angle of the inclined surface (hypotenuse) of the triangular prism is 20°.

[0271] The optically anisotropic layer was bonded to the surface sandwiched between the right angle of the triangular prism and the angle of 20. The bonding was performed by direct bonding with an adhesion-enhancing surface treatment by plasma treatment.

[0272] The bonding direction of the optical anisotropic layer was set to a direction that changes while the direction of the optical axis of the liquid crystal compound in the optical anisotropic layer rotates, that is, the direction of the diffraction vector in the plane of the optical anisotropic layer (the direction perpendicular to the light and dark lines) was perpendicular to the direction of the straight line formed by the right angles of the prism. In this way, an optical element was produced.

[0273] [Example 2]

[0274] In order to form the first optically anisotropic layer in which the liquid crystal compound was spirally twisted clockwise in the thickness direction and spirally oriented, the following composition B-2 was prepared.

[0275] Composition B-2

[0276]

[0277]

[0278] Chiral reagent Ch-A

[0279] [Chemical formula 4]

[0280]

[0281] The composition B-2 was applied in multiple layers in the same manner as in Example 1 (composition B-1), thereby forming a first optically anisotropic layer on the alignment film.

[0282] The first optically anisotropic layer was confirmed to have a final film thickness of 1.68 μm and a Δn of 1.68 μm using a microscope. 633 ×Thickness=Re(633) was 255 nm, and was periodically oriented. In the first optically anisotropic layer, the twist angle of the liquid crystal compound in the thickness direction was 70° (right twist).

[0283] In the cross-sectional image based on SEM, light and dark lines inclined with respect to the lower interface (interface with the support) of the optically anisotropic layer were observed. The inclined light and dark lines were observed due to the structure in which the liquid crystal compound was twisted and oriented in a spiral shape in the thickness direction.

[0284] Next, in order to form a second optically anisotropic layer in which the liquid crystal compound was spirally twisted to the left in the thickness direction and spirally oriented, the following composition B-3 was prepared.

[0285] Composition B-3

[0286]

[0287]

[0288] Chiral reagent Ch-B

[0289] [Chemical formula 5]

[0290]

[0291] A second optically anisotropic layer was formed on the first optically anisotropic layer in the same manner as in the first optically anisotropic layer except that Composition B-3 was used.

[0292] The final film thickness of the second optically anisotropic layer was confirmed to be 1.68 μm using a microscope, and Δn 633 ×Thickness=Re(633) was 255 nm, and the orientation was periodic. In the first optically anisotropic layer, the twist angle of the liquid crystal compound in the thickness direction was -70° (left-handed).

[0293] Furthermore, in the cross-sectional image based on SEM, light and dark lines tilted relative to the lower interface (interface with the support) of the optical anisotropic layer were observed. The structure of the liquid crystal diffraction element in which the light and dark lines of the first optical anisotropic layer and the light and dark lines of the second liquid crystal were formed with opposite inclination angles and a left-twisted optical anisotropic layer was provided on the right-twisted optical anisotropic layer was observed.

[0294] In this manner, a liquid crystal diffraction element having the first optically anisotropic layer and the second optically anisotropic layer stacked was produced.

[0295] As a result of the measurement in the same manner as above, the refractive index of the first optically anisotropic layer at a wavelength of 633 nm was ne=1.694, no=1.543, and the refractive index of the second optically anisotropic layer at a wavelength of 633 nm was ne=1.694, no=1.543.

[0296] An optical element was produced in the same manner as in Example 1 using the two optically anisotropic layers produced.

[0297] [Example 3]

[0298] As the triangular prism, triangular prisms having vertex angles of 80°, 20°, and 80° were prepared. The triangular prisms were made of SK2 type optical glass produced by SCHOTT, and had a refractive index of 1.605 at a wavelength of 633 nm.

[0299] The angle of 90° in Example 1 was replaced with an angle of 80°, and the optically anisotropic layer prepared in Example 2 was bonded to the surface sandwiched between the angles of 80° and 20° of the prism in the same manner as in Example 1, thereby preparing an optical element.

[0300] [Evaluation 1]

[0301] Using the optical element of Example 1, the following Fig. 9 The spectroscopic system shown.

[0302] like Fig.13 As shown in FIG. 1 , the split target light is collimated and incident from the surface of the optical anisotropic layer. The incident light is set to be non-polarized light.

[0303] Half of the incident light is diffracted by the liquid crystal diffraction element to the right side of the figure, and the other half is diffracted by the liquid crystal diffraction element to the left side of the figure, and then is totally reflected by the second surface of the prism. As a result, the two beams of light separated by the liquid crystal diffraction element become parallel light. Then, the two beams of light are emitted from the inclined surface (hypotenuse) of the prism. The various angles are shown in the table below.

[0304] like Fig. 9 As shown, the spectroscopic system is made by using a line (image) sensor to capture the signal of each wavelength after the emission surface is focused by a focusing lens. The evaluation results show that the 550nm light can be split with a high efficiency of more than 95%. In addition, the 400nm and 700nm can be split with a high efficiency of more than 50%, and the 1000nm can be split with a high efficiency of more than 20%.

[0305] [Table 1]

[0306]

[0307] [Evaluation 2]

[0308] A spectroscopic system was produced in the same manner as in Evaluation 1 using the optical element of Example 3.

[0309] The angle of light was the same as that in Evaluation 1 using the optical element of Example 1.

[0310] Furthermore, light of 550 nm can be split at a high efficiency of 95% or more, light of 400 and 700 nm can be split at a high efficiency of 90% or more, and light of 1000 nm can be split at a high efficiency of 70% or more.

[0311] That is, by using an optically anisotropic layer twisted in a spiral orientation in the thickness direction and stacking optically anisotropic layers with the spiral twisting directions opposite to each other, a higher diffraction efficiency than that of the above-described embodiment can be obtained, and the spectral efficiency can be improved.

[0312] [Evaluation 3]

[0313] A spectroscopic system was produced in the same manner as in Evaluation 1 using the optical element of Example 3.

[0314] The angles of light are shown in Table 2 below.

[0315] Furthermore, the efficiency was the same as that of Evaluation 2 using the optical element of Example 2 having the same liquid crystal diffraction element.

[0316] It can be seen that, unlike the optical elements of Examples 1 and 2 using triangular prisms whose first surface (the bonding surface of the liquid crystal diffraction element) and second surface (the reflection surface) are orthogonal, in the optical element of Example 3 using a prism whose first surface and second surface form an angle of 80°, the angles of φob and φoc do not overlap. That is, in this example, Fig.14 As shown, the ±1st order light separated left and right by the diffraction element, that is, the two diffracted lights separated into different directions according to the polarized light, can be gathered at different focal positions. That is, it can be known that by using the optical element of Example 3, it is possible to perform light splitting according to the polarized light and function as a polarization splitting system.

[0317] [Table 2]

[0318]

[0319] The effects of the present invention are clearly demonstrated from the above results.

[0320] Industrial Applicability

[0321] It can be preferably used in various optical elements such as a spectroscopic element.

[0322] Explanation of symbols

[0323] 10, 10A, 10B-optical element, 12-liquid crystal diffraction element, 14-prism, 16-lens, 18-detector, 20-support, 24-oriented film, 26-optical anisotropic layer, 30-liquid crystal compound, 30A-optical axis, 60-exposure device, 62-laser, 64-light source, 68-beam splitter, 70A, 70B-reflector, 72A, 72B-λ / 4 plate, M-laser beam, MA, MB-light, MP-P polarized light, MS-S polarized light, P0-linearly polarized light, R-right-handed circularly polarized light, L-left-handed circularly polarized light, Q, Q1, Q2-absolute phase, E, E1, E2-equal phase planes.

Claims

1. An optical element comprising a liquid crystal diffraction element and a prism, wherein the prism has a first surface directly in contact with the liquid crystal diffraction element or a first surface in contact with the liquid crystal diffraction element via another layer, The liquid crystal diffraction element includes an optically anisotropic layer having a liquid crystal alignment pattern in which the direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one direction in a plane. The prism has a second surface that reflects one of the lights separated by diffraction of the liquid crystal diffraction element.

2. The optical element according to claim 1, wherein In the optically anisotropic layer, the liquid crystal compound is twisted and aligned in a helical shape along a thickness direction.

3. The optical element according to claim 2, wherein: The liquid crystal diffraction element has at least two layers of the optically anisotropic layers in which the liquid crystal compound is twisted and oriented in a spiral shape along the thickness direction, wherein the twisting directions of the liquid crystal compound along the thickness direction in the two layers of the optically anisotropic layers are opposite.

4. The optical element according to claim 1 or 3, wherein: The angle formed by the first surface and the second surface of the prism is 70 to 110 degrees.

5. The optical element according to claim 1 or 3, wherein: The light separated by the diffraction of the liquid crystal diffraction element and reflected by the second surface and the light not incident on the second surface are emitted from the same surface of the prism.

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