Polarization interference element, optical filter, and optical system

Abstract

Provided are a polarization interference element capable of transmitting or shielding light with a small number of optically anisotropic layers when used in a bandpass filter for light in a plurality of wavelength regions, an optical filter using the polarization interference element, and an optical system using the optical filter. The present invention comprises at least one optically anisotropic layer, the optically anisotropic layer satisfying the relationships of formula (1): Re(535) > 600 nm, formula (2): 0.79 + 4.5×105 / Re(535)2 – 1.2×1011 / Re(535)4 < Re(450 / 535) < 1.16 + 4.5×105 / Re(535)2 – 1.2×1011 / Re(535)4, and formula (3): 0.74 – 3.6×105 / Re(535)2 – 6.0×108 / Re(535)4 < Re(630 / 535) < 1.16 – 3.5×105 / Re(535)2 – 2.2×109 / Re(535)4.

Description

Polarizing interference elements, optical filters, and optical systems

[0001] The present invention relates to a polarizing interference element, an optical filter using this polarizing interference element, and an optical system using this optical filter.

[0002] Bandpass filters, which transmit light within a specific wavelength range while blocking light of other wavelengths, are used in various optical devices.

[0003] Known bandpass filters include polarization interference filters using dielectric multilayer films and filters combining polarizers and birefringent crystals. Also known are Solk filters (folded Solk filters) in which a Solk filter is constructed by alternately stacking birefringent plates (λ / 2 phase difference plates) of equal thickness and with an angle of +ρ between the polarizer's transmission axis and its slow axis, and birefringent plates with an angle of -ρ, between polarizers arranged in crossed nicols.

[0004] Furthermore, Patent Document 1 describes how using a birefringent plate made by alternately stacking optical anisotropic layers consisting of rod-shaped liquid crystals and optical anisotropic layers consisting of disc-shaped liquid crystals can suppress wavelength shift when light is incident from an oblique direction when placed in a bandpass filter.

[0005] International Publication No. 2024-185846

[0006] Patent Document 1 describes a bandpass filter that transmits or blocks light of a single wavelength. On the other hand, it does not describe a bandpass filter that transmits or blocks light of multiple wavelength ranges (for example, λ = 450 nm, 535 nm, 630 nm).

[0007] The object of the present invention is to provide a polarization interference element that can transmit or block light with a small number of optical anisotropy layers when used in a bandpass filter for light in multiple wavelength ranges, an optical filter using this polarization interference element, and an optical system using this optical filter.

[0008] The present inventor has found that the above problems can be solved by the following configuration.

[0009] 〔1〕A polarization interference element having at least one layer of an optically anisotropic layer, wherein the optically anisotropic layer satisfies the following formulas (1), (2), and (3). Formula (1): Re(535) > 600 nm Formula (2): 0.79 + 4.5×10 ５ / Re(535) ２ −1.2×10 １１ / Re(535) ４ < Re(450 / 535) < 1.16 + 4.5×10 ５ / Re(535) ２ −1.2×10 １１ / Re(535) ４ Formula (3): 0.74 − 3.6×10 ５ / Re(535) ２ −6.0×10 ８ / Re(535) ４ < Re(630 / 535) < 1.16 − 3.5×10 ５ / Re(535) ２ −2.2×10 ９ / Re(535) ４However, in the formula, Re(535) represents the in-plane retardation at a wavelength of 535 nm, Re(450 / 535) represents the ratio of the in-plane retardation at a wavelength of 450 nm to the in-plane retardation at a wavelength of 535 nm, and Re(630 / 535) represents the ratio of the in-plane retardation at a wavelength of 630 nm to the in-plane retardation at a wavelength of 535 nm. [2] The polarization interference element according to [1], wherein the optical anisotropy layer includes a layer on which a liquid crystal compound is fixed. [3] The polarization interference element according to [1] or [2], wherein the optical anisotropy layer satisfies the following formula (4): Formula (4) 600 nm < Re(535) < 2000 nm [4] The polarization interference element according to any one of [1] to [3], having two or more of the optical anisotropy layers. [5] The polarization interference element according to any one of [1] to [4], wherein the optical anisotropy layer is a laminate of a layer in which horizontally oriented rod-shaped liquid crystal compounds are fixed and a layer in which vertically oriented disc-shaped liquid crystal compounds are fixed. [6] The polarization interference element according to any one of [1] to [4], wherein the optical anisotropy layer is a laminate of a layer in which horizontally oriented rod-shaped liquid crystal compounds are fixed and a layer in which vertically oriented rod-shaped liquid crystal compounds are fixed. [7] The polarization interference element according to any one of [1] to [4], wherein the optical anisotropy layer is a laminate of a layer in which vertically oriented disc-shaped liquid crystal compounds are fixed and a layer in which horizontally oriented disc-shaped liquid crystal compounds are fixed. [8] The polarization interference element according to any one of [1] to [7], wherein the optical anisotropy layer is a layer in which torsion-oriented liquid crystal compounds with the thickness direction as the helical axis are fixed. [9] The polarization interference element according to any one of [1] to [8], wherein the optical anisotropy layer contains an infrared absorbing dye.

[10] A polarization interference element according to any one of [1] to [9], wherein the optical anisotropy layer includes a liquid crystal elastomer.

[11] An optical filter comprising a first polarizer, a polarization interference element according to any one of [1] to

[10] , and a second polarizer, arranged in this order, wherein the transmission axis of the first polarizer and the transmission axis of the second polarizer are parallel or orthogonal.

[12] An optical system comprising a light source, the optical filter according to

[11] , and a light receiving unit.

[13] The optical system according to

[12] , comprising a condensing lens.

[14] The optical system according to

[12] , comprising a beam splitter.

[15] The optical system according to

[12] , comprising a light guide element.

[16] The optical system according to any one of

[12] to

[15] , wherein the optical filter and the light receiving unit are facing each other.

[17] The optical system according to any one of

[12] to

[16] , comprising a plurality of optical filters with different wavelengths of transmitted light.

[0010] According to the present invention, in a bandpass filter for light in multiple wavelength ranges, it is possible to reduce the number of optical anisotropy layers required, reduce the thickness, suppress the decrease in transmittance, and further provide a polarization interference element that can transmit or block light only in a desired wavelength range, an optical filter using this polarization interference element, and an optical system using this optical filter.

[0011] Figure 1 is a diagram showing an example of the configuration of an optical filter of the present invention using the polarization interference element of the present invention. Figure 2 is a conceptual graph showing the preferred optical characteristic range of the optical anisotropy layer included in the polarization interference element of the present invention. Figure 3 is a conceptual graph showing the preferred optical characteristic range of the optical anisotropy layer included in the polarization interference element of the present invention. Figure 4 is a graph for explaining the optical filter of the present invention. Figure 5 is a diagram conceptually showing an example of an optical filter of the present invention using the polarization interference element of the present invention. Figure 6 is a conceptual diagram for explaining another example of the polarization interference element of the present invention. Figure 7 is a conceptual diagram for explaining another example of the polarization interference element of the present invention. Figure 8 is a graph for explaining the optical filter of the present invention. Figure 9 is a conceptual diagram for explaining another example of the polarization interference element of the present invention. Figure 10 is a conceptual diagram for explaining another example of the polarization interference element of the present invention. Figure 11 is a conceptual diagram for explaining another example of the polarization interference element of the present invention. Figure 12 is a conceptual diagram for explaining another example of the polarization interference element of the present invention. Figure 13 is a conceptual diagram for explaining another example of the polarization interference element of the present invention. Figure 14 is a diagram conceptually showing an example of an optical system of the present invention. Figure 15 is a conceptual diagram illustrating another example of the optical system of the present invention. Figure 16 is a conceptual diagram illustrating another example of the optical system of the present invention. Figure 17 is a conceptual diagram illustrating another example of the optical system of the present invention. Figure 18 is a conceptual diagram illustrating another example of the optical system of the present invention.

[0012] The polarization interference element, optical filter, and optical system of the present invention will be described in detail below based on preferred embodiments shown in the attached drawings.

[0013] In this specification, numerical ranges expressed using "~" mean a range that includes the numbers before and after "~" as the lower and upper limits. Furthermore, the following figures are all conceptual diagrams for explaining the present invention, and the positional relationships, sizes, thicknesses, and shapes of each component differ from those of actual objects. In this specification, terms such as "same," "match," and "equal" include error ranges that are generally accepted in the art. Also, in this specification, when terms such as "all," "all," and "perfectly" are used, they include not only 100% but also error ranges that are generally accepted in the art, such as 99% or more, 95% or more, or 90% or more. Furthermore, with respect to angles, "orthogonal" or "perpendicular" means a range of 90° ± 5°, and "parallel" means a range of 0° ± 5°. Similarly, with respect to angles, unless otherwise specified, it means that the difference from the exact angle is within 5 degrees. The above angle difference is preferably within 4 degrees, and more preferably within 3 degrees.

[0014] In this specification, "lamination" may refer to layers being directly laminated together, or layers being laminated together via other layers. Furthermore, a laminated structure may be created by bonding.

[0015] Figure 1 shows an example of the configuration of the optical filter of the present invention. In the following description, the optical filter will also be simply referred to as a filter. The optical filter of the present invention has a first polarizer, a polarization interference element of the present invention, and a second polarizer arranged in this order. The filter 10 shown in Figure 1 is a bandpass filter (narrowband filter) that transmits light in a plurality of specific wavelength ranges and blocks light of other wavelengths, and has a first polarizer 12, a second polarizer 14, and a polarization interference element 16. The polarization interference element 16 has at least one optical anisotropy layer, and the optical anisotropy layer satisfies the following formulas (1), (2), and (3).

[0016] Figures 2 and 3 conceptually show the range of preferred optical properties of the optical anisotropy layer included in the polarization interference element 16.

[0017] Figure 2 conceptually illustrates equation (2). The preferred value of Re(450 / 535) varies depending on the value of Re(535), and is preferably within the range between dashed line 18 and dashed line 20 (for example, solid line 22). Equation (2) 0.79 + 4.5 × 10 ５ / Re(535) ２ -1.2 × 10 １１ / Re(535) ４ <Re(450 / 535) <1.16+4.5×10 ５ / Re(535) ２ -1.2 × 10 １１ / Re(535) ４

[0018] Figure 3 conceptually illustrates equation (3). The preferred value of Re(630 / 535) varies depending on the value of Re(535), and is preferably within the range between dashed lines 24 and 26 (for example, solid line 28). Equation (3) 0.74 - 3.6 × 10 ５ / Re(535) ２ -6.0 x 10 ８ / Re(535) ４ < Re (630 / 535) < 1.16-3.5×10 ５ / Re(535) ２ -2.2 × 10 ９ / Re(535) ４

[0019] In the formula, Re(535) represents the in-plane retardation of the optically anisotropic layer at a wavelength of 535 nm, Re(450 / 535) represents the ratio of the in-plane retardation of the optically anisotropic layer at a wavelength of 450 nm to the in-plane retardation of the optically anisotropic layer at a wavelength of 535 nm, and Re(630 / 535) represents the ratio of the in-plane retardation of the optically anisotropic layer at a wavelength of 630 nm to the in-plane retardation of the optically anisotropic layer at a wavelength of 535 nm.

[0020] ​​The in-plane retardation of the optically anisotropic layer can be measured by known methods, such as using an AxoScan manufactured by Axometrics. Alternatively, as will be described later, if the optically anisotropic layer is a liquid crystal layer, the in-plane retardation of the liquid crystal layer may be calculated using Δnd. In Δnd, Δn is the birefringence of the liquid crystal compound 30R constituting the optically anisotropic layer, and d is the thickness of the optically anisotropic layer.

[0021] As shown in formula (1), the value of Re(535) is preferably greater than 600 nm. Formula (1) Re(535) > 600 nm From the viewpoint of reducing thickness, it is more preferable that it is greater than 600 nm and less than 2000 nm (see formula (4) below), more preferably greater than 600 nm and less than 1500 nm, and even more preferably greater than 600 nm and less than 1000 nm. Formula (4) 600 nm < Re(535) < 2000 nm

[0022] By adjusting the optical properties of the optical anisotropy layer contained in the polarization interference element 16 within the range that satisfies equations (1) to (3), multiple specific wavelengths (λ) can be controlled. １ , λ ２ , λ ３ ..λ n This optical element can be configured to act as a λ / 2 phase difference plate ((2n+1)λ / 2 phase difference plate, where n is a non-negative integer) for light of type 0, but not as a λ / 2 phase difference plate for other types of light.

[0023] Specifically, for example, the polarization interference element 16 has a wavelength λ １ , λ ２ , λ ３ If it acts as a λ / 2 phase difference plate for light, then λ １ <λ ２ <λ ３ Therefore, the optical anisotropy layer of the polarization interference element 16 is λ １ It acts as a λ / 2 phase difference plate for light, λ ２ It acts as a 3λ / 2 phase difference plate for light, λ ３ By acting as a 5λ / 2 phase difference plate, the wavelength λ １ , λ ２ , λ ３For light, it effectively acts as a λ / 2 phase difference plate, and for light of other wavelengths (wavelength λ １ Light in the wavelength range shorter than λ １ and λ ２ Light in the wavelength range between and λ ２ and λ ３ Light in the wavelength range between wavelengths λ ３ For light with wavelengths longer than λ, it acts as a phase difference plate shifted from λ / 2.

[0024] Note that the wavelength λ １ , λ ２ , λ ３ The action of the polarization interference element 16 on light is not limited to the above example, λ １ It acts as a (2i+1)λ / 2 phase difference plate for light, λ ２ It acts as a (2(i+1)+1)λ / 2 phase difference plate for light, λ ３ It may also act as a (2(i+2)+1)λ / 2 phase difference plate, where i is a non-negative integer. Furthermore, when a specific wavelength is 4 or greater, the polarization interference element 16 can act as a phase difference plate shifted by λ for each wavelength.

[0025] An optical filter 10 in which such a polarization interference element 16 is placed between a first polarizer 12 and a second polarizer 14 arranged in crossed nicols with orthogonal transmission axes, allows for the detection of multiple specific wavelengths (λ １ , λ ２ , λ ３ ..λ n It acts as a bandpass filter (narrowband filter) that selectively transmits light of a certain wavelength and blocks light of other wavelengths.

[0026] Specifically, of the light incident on the filter 10, only linearly polarized light in the direction corresponding to the transmission axis is transmitted through the first polarizer 12. Of this linearly polarized light, a specific wavelength (λ) １ , λ ２ , λ ３ ..λ nThe light from (λ) is subjected to a phase difference of λ / 2 (a phase difference of (2n+1)λ / 2) by the polarization interference element 16, so its polarization direction is rotated by 90° and incident on the second polarizer 14, which is arranged in crossed nicols with the first polarizer 12, and is transmitted. In contrast, the specific (λ １ , λ ２ , λ ３ ..λ n Light outside the specified wavelength range does not have the polarization interference element 16 acting as a λ / 2 phase difference plate, so its polarization direction is offset from the direction of the transmission axis of the first polarizer 12 and the second polarizer 14 which is arranged in crossed nicols. As a result, light outside the specific wavelength range is incident on the second polarizer 14 and blocked. Through this optical action, the filter 10 becomes a bandpass filter that transmits only light in multiple specific wavelength ranges and blocks all other light (see Figure 4).

[0027] Here, in equations (2) and (3) above, Re(450 / 535) and Re(630 / 535) represent the wavelength dispersibility of the optical anisotropy layer. A higher Re(450 / 535) indicates higher forward wavelength dispersibility of the optical anisotropy layer, and a lower Re(630 / 535) indicates higher forward wavelength dispersibility of the optical anisotropy layer. Therefore, equations (2) and (3) indicate that the higher the forward wavelength dispersibility of the optical anisotropy layer, the smaller the in-plane retardation Re(535) of the optical anisotropy layer at a wavelength of 535 nm can be in the range above 600 nm.

[0028] The higher the forward wavelength dispersion, the greater the difference in in-plane retardation due to wavelength differences. Therefore, the in-plane retardation Re(535) required to create the aforementioned phase shift of λ between multiple specific wavelengths can be reduced.

[0029] Furthermore, equations (1) to (3) above use blue wavelength light (450 nm), green wavelength light (535 nm), and red wavelength light (630 nm) to determine a specific wavelength (λ). １ , λ ２ , λ ３This represents the appropriate range of wavelength dispersion and in-plane retardation (optical properties) for the optical anisotropy layer to act as a (2n+1)λ / 2 phase difference plate for light of these wavelengths when set to ).

[0030] Note that a specific wavelength λ １ , λ ２ , λ ３ The optical anisotropy layer is not limited to 450 nm, 535 nm, and 630 nm, but can be set to have wavelength dispersion and in-plane retardation so that it acts as a (2n+1)λ / 2 phase difference plate for light in the blue wavelength range, green wavelength range, and red wavelength range, respectively. Although not limited to these, light in the 420-490 nm wavelength range is blue light, light in the 495-570 nm wavelength range is green light, and light in the 620-700 nm wavelength range is red light.

[0031] Furthermore, in addition to light in the blue wavelength range, light in the green wavelength range, and light in the red wavelength range, or by substituting any one of them, light in the infrared wavelength range and / or light in the ultraviolet wavelength range may also be included as specific wavelengths.

[0032] Furthermore, the specific wavelength may include, for example, two different wavelengths of light within the red wavelength range.

[0033] Thus, by adjusting the optical properties of the optical anisotropy layer included in the polarization interference element within the range satisfying equations (1) to (3), the polarization interference element of the present invention can realize an optical filter that acts as a bandpass filter for light in multiple wavelength ranges with a small number of layers. Furthermore, because the number of layers can be reduced, the thickness of the optical filter can be reduced.

[0034] Furthermore, from the viewpoint of enabling thinner layers, etc., it is preferable that Re(450 / 535) be large and Re(630 / 535) be small. Specifically, Re(450 / 535) is preferably 0.80 or higher, more preferably 0.90 to 1.60, and even more preferably 1.00 to 1.40. Also, Re(630 / 535) is preferably 1.20 or lower, more preferably 0.20 to 1.10, and even more preferably 0.30 to 1.00.

[0035] Figure 4 conceptually shows an example of the transmission spectrum of the optical filter of the present invention. By adjusting the optical properties of the optical anisotropy layer included in the polarization interference element 16 within the range that satisfies the above-mentioned equations (1) to (3), multiple specific wavelengths (λ) can be obtained. １ , λ ２ , λ ３ ..λ n This realizes a bandpass filter (narrowband filter) that selectively transmits light of a certain wavelength and blocks light of other wavelengths.

[0036] The wavelength of light transmitted or blocked (λ) １ , λ ２ , λ ３ ..λ n The λ can be adjusted as needed. For example, a bandpass filter adjusted to selectively transmit wavelengths of λ = 450 nm, 535 nm, and 630 nm can be used to expand the color gamut of a display.

[0037] Figure 5 conceptually shows an example of an optical filter, polarization interference element, and optical anisotropy layer according to the present invention. The optical filter 10 shown in Figure 5 has the same configuration as in Figure 1. The polarization interference element 16 is a polarization interference element according to a first embodiment of the present invention, and is arranged between the first polarizer 12 and the second polarizer 14.

[0038] The first polarizer 12 and the second polarizer 14 are polarizers (polarizing plates) that transmit linearly polarized light in a predetermined direction, and are arranged in a crossed nicol configuration with the transmission axis perpendicular to it. There are no restrictions on the first polarizer 12 and the second polarizer 14; various known linear polarizers can be used, such as iodine-based polarizers, dye-based polarizers using dichroic dyes, and polyene-based polarizers.

[0039] The first polarizer 12 described above is not limited to an absorption-type linear polarizer as described above, but a reflection-type linear polarizer may also be used. Various known linear polarizers can be used as reflection-type linear polarizers, such as wire grid polarizers, those made of dielectric multilayer films, and those having a selective reflection layer including at least one cholesteric liquid crystal layer and a λ / 4 phase difference plate.

[0040] In the illustrated example of the filter 10, a polarization interference element 16 is positioned between the first polarizer 12 and the second polarizer 14. In Figures 1 and 5, the first polarizer 12 and the second polarizer 14 are spaced apart from the polarization interference element 16. However, the present invention is not limited thereto, and the first polarizer 12 and the second polarizer 14 and the polarization interference element 16 may be stacked in contact with each other. Furthermore, if the first polarizer 12 and the second polarizer 14 and the polarization interference element 16 are stacked, they may be bonded together with an adhesive that is transparent to transmitted light, such as OCA (Optical Clear Adhesive) and acrylic adhesives, as needed. In the filter (optical filter) of the present invention, the polarizer is not limited to the above configuration and various types can be used, as long as they limit the function of light to polarization in only one direction. For example, when optical elements such as a light source (light source unit) and a light-receiving element (light-receiving unit) combined with the optical filter of the present invention have polarizers, the form in which the light source combined with the optical filter of the present invention originally emits polarization, and the form in which the light-receiving element (light-receiving unit) combined with the optical filter of the present invention has a unidirectional polarization sensitivity characteristic, the polarizers of these optical elements, such light sources and light-receiving units, are also considered as polarizers constituting the optical filter of the present invention. Examples of forms in which the light source originally emits polarization include polarized light sources and reflected light from a Brewster angle substrate.

[0041] The polarization interference element 16 is an optical element that acts as a (2n+1)λ / 2 phase difference plate for light in a specific wavelength range (specific wavelength), but does not act as a (2n+1)λ / 2 phase difference plate (phase difference layer) for other light. As described above, the first polarizer 12 and the second polarizer 14 are polarizers arranged in a crossed nicol configuration with the transmission axis perpendicular to it. Of the light incident on the filter 10, only linearly polarized light in the direction corresponding to the transmission axis is transmitted through the first polarizer 12. Of this linearly polarized light, light of a specific wavelength has its polarization direction rotated by 90° by the polarization interference element 16 and is incident on the second polarizer 14, which is arranged in a crossed nicol configuration with the first polarizer 12, and is transmitted. In contrast, light outside the specific wavelength range is blocked when it is incident on the second polarizer 14, which is arranged in a crossed nicol configuration with the first polarizer 12, because the polarization interference element 16 does not act as a (2n+1)λ / 2 phase difference plate. Through this optical action, filter 10 becomes a bandpass filter that transmits only light in a specific wavelength range and blocks other light.

[0042] The polarization interference element 16 is an optically anisotropic layer (hereinafter also referred to as the rod-shaped liquid crystal layer) formed by fixing rod-shaped liquid crystal compounds 30R in a horizontal orientation. The angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the optically anisotropic layer corresponding to the polarization interference element 16 is set to 45°.

[0043] Furthermore, when a rod-shaped liquid crystal compound is described as horizontally oriented, it means that the direction of the molecular axis of the rod-shaped liquid crystal compound is oriented parallel to the main plane of the optically anisotropic layer. The direction of the molecular axis of a rod-shaped liquid crystal compound is the direction of the long axis of the rod-shaped liquid crystal compound. Also, when a rod-shaped liquid crystal compound is described as vertically oriented, it means that the direction of the molecular axis of the rod-shaped liquid crystal compound is oriented perpendicular to the main plane of the optically anisotropic layer. Furthermore, when a disc-shaped liquid crystal compound is described as horizontally oriented, it means that the disc surface of the disc-shaped liquid crystal compound is oriented parallel to the main plane of the optically anisotropic layer. Also, when a disc-shaped liquid crystal compound is described as vertically oriented, it means that the disc surface of the disc-shaped liquid crystal compound is oriented perpendicular to the main plane of the optically anisotropic layer. The main plane is the largest surface in a sheet-like material (film-like material, plate-like material).

[0044] Such a polarization interference element 16 having an optically anisotropic layer can be fabricated by known methods. For example, it can be fabricated by a coating method using a liquid crystal composition for forming a rod-shaped liquid crystal layer.

[0045] First, an orientation film oriented in one direction is formed on a suitably selected support. The orientation film can be any known orientation film, such as a rubbing-treated film made of organic compounds like polymers, an obliquely vapor-deposited film of an inorganic compound, a film having microgrooves, or a film formed by accumulating Langmuir-Blodgett (LB) films of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearylate using the Langmuir-Blodgett method, or a film obtained by coating the surface of a support with an orientation film-forming solution containing a photo-orientation material, drying it, and then exposing the coating film using a polarizer such as a wire grid polarizer.

[0046] On the other hand, a liquid crystal composition for forming a rod-shaped liquid crystal layer containing rod-shaped liquid crystal compound 30R is prepared. There are no restrictions on the solvent used to prepare the composition, and it can be appropriately selected depending on the purpose, but organic solvents are preferred. Organic solvents are not limited and can be appropriately selected depending on the purpose, and examples include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used individually or in combination of two or more. Among these, ketones are preferred when considering the environmental impact.

[0047] After preparing the liquid crystal composition, the liquid crystal composition for forming the rod-shaped liquid crystal compound is applied to the alignment film to orient the rod-shaped liquid crystal compound 30R, and then dried. If necessary, the composition is cured by ultraviolet irradiation or the like to form a rod-shaped liquid crystal layer, thereby forming the polarization interference element 16.

[0048] Once the polarization interference element 16 is fabricated in this manner, the first polarizer 12 and the second polarizer 14 are arranged in a cross-nicol configuration with the polarization interference element 16 in between, such that the angle between the transmission axis of the first polarizer 12 and the slow axis of the optical anisotropy layer in the polarization interference element 16 is 45°. This allows the fabrication of a filter 10 (bandpass filter) as shown in Figure 5.

[0049] In the polarization interference element 16 of the present invention, there are no limitations on the rod-shaped liquid crystal compound 30R, and various known liquid crystal compounds can be used. Preferably used rod-shaped liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. Not only low-molecular-weight liquid crystal molecules as described above, but also high-molecular-weight liquid crystal molecules can be used.

[0050] It is more preferable to fix the orientation of the rod-shaped liquid crystal compound by polymerization, and as a polymerizable rod-shaped liquid crystal compound, Makromol. Chem. Compounds described in Volume 190, page 2255 (1989), Advanced Materials Volume 5, page 107 (1993), U.S. Patent No. 4683327, No. 5622648, No. 5770107, International Publication Nos. 95 / 22586, 95 / 24455, 97 / 00600, 98 / 23580, 98 / 52905, Japanese Patent Publication No. 1-272551, 6-16616, 7-110469, 11-80081, and Japanese Patent Application No. 2001-64627 can be used. Furthermore, as rod-shaped liquid crystal compounds, those described in Japanese Patent Publication No. 11-513019 and Japanese Patent Application Publication No. 2007-279688 can also be preferably used.

[0051] Figure 6 conceptually shows the configuration of an optical filter including a polarization interference element according to a second embodiment of the present invention.

[0052] The polarization interference element 16 shown in Figure 6 has a structure in which one or more optical anisotropy layer sets 36 are stacked in the thickness direction, with each set consisting of a first optical anisotropy layer 32 and a second optical anisotropy layer 34, each formed by fixing a rod-shaped liquid crystal compound 30R in a horizontal orientation, forming one optical anisotropy layer set 36. Therefore, the total number of optical anisotropy layers is even.

[0053] Furthermore, in the polarization interference element 16 shown in Figure 6, the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the second optical anisotropy layer 34 intersect. Specifically, the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the second optical anisotropy layer 34 are tilted in opposite directions at the same angle with respect to a certain reference line. More specifically, the direction of the in-plane slow axis of the liquid crystal layer is such that, for example, with the direction of the reference line as 0°, counterclockwise as positive (+), and clockwise as negative (-), if the angle between the reference line and the in-plane slow axis of the first optical anisotropy layer 32 is 'φ[°]', then the angle between the reference line and the in-plane slow axis of the second optical anisotropy layer 34 will be '-φ[°]'. In other words, the absolute value of the angle formed by the reference line and the in-plane slow axis of the first optical anisotropy layer 32 is equal to the absolute value of the angle formed by the reference line and the in-plane slow axis of the second optical anisotropy layer 34.

[0054] In the example filter 10 shown in Figure 6, the transmission axis of the first polarizer 12 is used as the reference line, and the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the first optical anisotropy layer 32 of the polarization interference element 16 is φ[°], and the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the second optical anisotropy layer 34 of the polarization interference element 16 is -φ[°]. In other words, the filter 10 is configured such that the angle bisector of the angle between the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the first optical anisotropy layer 34 of the polarization interference element 16 coincides with the transmission axis (reference line) of the first polarizer 12.

[0055] In the filter 10 of the present invention, the reference line is not limited to the transmission axis of the first polarizer 12. For example, in the filter 10 of the present invention, the reference line may be the absorption axis of the first polarizer 12, the transmission axis of the second polarizer 14, or the absorption axis of the second polarizer 14.

[0056] In a polarization interference element 16, such as the one shown in Figure 6, in which the same first optical anisotropy layer 32 and second optical anisotropy layer 34 are alternately stacked, the absolute value [°] of the angle between the reference line and the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the first optical anisotropy layer 34 can be determined by the following formula, depending on the rotation angle (optical rotation angle) of the linearly polarized light that the polarization interference element 16 is intended for, and the number of layers of the first optical anisotropy layer 32 and second optical anisotropy layer 34 that the polarization interference element 16 has. In other words, since the rotation angle of linearly polarized light targeted by the polarization interference element 16 is usually 90°, the absolute value of the angle between the reference line and the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the first optical anisotropy layer 34 can be calculated using the following formula: 90 ÷ (number of layers of the first optical anisotropy layer 32 and the second optical anisotropy layer 34) ÷ 2.

[0057] For example, if the number of layers of the first optical anisotropy layer 32 and the second optical anisotropy layer 34 is four, that is, if there are two sets of liquid crystal layer assemblies 36, then "90 ÷ 4 ÷ 2 = 11.25". Therefore, in the above example, the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the first optical anisotropy layer 32 is 11.25°, and the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the second optical anisotropy layer 34 is -11.25°.

[0058] The number of first optical anisotropy layers 32 and second optical anisotropy layers 34 in the polarization interference element 16, that is, the number of optical anisotropy layer sets 36, can be detected by methods such as observation using a scanning electron microscope (SEM) and analysis of liquid crystal compounds on the surface of the cross-section of the polarization interference element 16 after oblique cutting. The method of analyzing each liquid crystal layer by oblique cutting of the polarization interference element 16 is described in detail in "Depth-Dependent Determination of Molecular Orientation for WV-Film" by Yohei Takahashi et al. (FMC8-3, IDW'04, 651-654).

[0059] In the polarization interference element 16 of the present invention, the absolute values ​​of the angle between the reference line and the in-plane slow axis of the first optical anisotropy layer 32, and the angle between the reference line and the in-plane slow axis of the second optical anisotropy layer 34, are not limited to perfectly matching, and may have an error of ±10° or less. However, it is preferable that this error be small, for example, ±8° or less is preferable, ±5° or less is more preferable, and ±3° or less is even more preferable. It is most preferable that the absolute values ​​of the angle between the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the second optical anisotropy layer 34 match.

[0060] Furthermore, in the polarization interference element 16 of the present invention, it is preferable that the in-plane retardation of the first optical anisotropy layer 32 and the in-plane retardation of the second optical anisotropy layer 34 are equal.

[0061] In this invention, the term "equal in-plane retardation" is not limited to "perfectly matching in-plane retardation," and may have an error of 10% or less. However, a smaller error is preferable, for example, 8% or less is preferable, 5% or less is more preferable, and 3% or less is even more preferable. It is most preferable that the in-plane retardations of the first optical anisotropy layer 32 and the second optical anisotropy layer 34 are perfectly matching.

[0062] Furthermore, the polarization interference element of the present invention is not limited to a configuration in which the in-plane retardation of the first optical anisotropy layer and the in-plane retardation of the second optical anisotropy layer are equal. For example, if the sum of the in-plane retardations of the first optical anisotropy layer and the second optical anisotropy layer satisfies the desired retardation value of the present invention, the in-plane retardation of the first optical anisotropy layer and the in-plane retardation of the second optical anisotropy layer may be different.

[0063] Here, the first optical anisotropy layer 32 and the second optical anisotropy layer 34 satisfy the above-described equations (1), (2), and (3).

[0064] The polarization interference element 16 shown in FIG. 6, by having such a configuration, acts as a (2n + 1)λ / 2 retardation plate for light in a plurality of specific wavelength ranges. As described above, the polarization interference element 16 has an optically anisotropic layer made of the rod-like liquid crystal compound 30R, and has a configuration in which a first optically anisotropic layer 32 and a second optically anisotropic layer 34 in which the in-plane slow axis directions are opposite to each other with respect to the reference line are alternately laminated. That is, the polarization interference element 16 has a configuration in which a first optically anisotropic layer 32 and a second optically anisotropic layer 34 in which the angles of the in-plane slow axes with respect to the reference line are 'φ' and '-φ' are alternately laminated. Light passing through such a polarization interference element 16 alternately and repeatedly receives the influence of the in-plane slow axis having an angle of 'φ' with respect to the reference line and the influence of the in-plane slow axis having an angle of '-φ' with respect to the reference line. For example, when the absolute value of the angle with respect to the reference line is 11.25°, the light passing through the polarization interference element 16 is alternately and repeatedly rotated by the in-plane slow axis having an angle of 11.25° with respect to the reference line and then rotated by the in-plane slow axis having an angle of -11.25° with respect to the reference line. Therefore, according to the wavelength of the light for which the polarization interference element 16 is intended to act as a (2n + 1)λ / 2 retardation plate, the in-plane retardation of the first optically anisotropic layer 32 and the second optically anisotropic layer 34 is set as described above, and further, according to the number of layers of the first optically anisotropic layer 32 and the second optically anisotropic layer 34, the angles of the in-plane slow axes in the first optically anisotropic layer 32 and the second optically anisotropic layer 34 are adjusted. Thereby, a polarization interference element 16 that acts as a (2n + 1)λ / 2 retardation plate for light in a specific wavelength range and does not act as a (2n + 1)λ / 2 retardation plate for other light can be formed.

[0065] Here, the first optically anisotropic layer 32 and the second optically anisotropic layer 34 each satisfy the above-described formulas (1), (2), and (3). Therefore, the polarization interference element 16 shown in FIG. 6 can be made an optical element that acts as a λ / 2 retardation plate ((2n + 1)λ / 2 retardation plate) for light of a plurality of specific wavelengths (λ １ , λ ２ , λ ３ ··· λ n ) and does not act as a λ / 2 retardation plate for other light.

[0066] Therefore, by arranging the polarization interference element 16 shown in Figure 6 between two polarizers arranged in crossed nicols, such that the transmission axis or absorption axis of one polarizer coincides with the angle bisector of the angle formed by the in-plane slow axis of the first optical anisotropy layer 32 and the second optical anisotropy layer 34, a bandpass filter can be obtained that acts as (2n+1)λ / 2 only on linearly polarized light in multiple specific wavelength ranges that has passed through one polarizer, causing its polarization direction to rotate by 90° (optical rotation) and be emitted from the other polarizer, while blocking light in other wavelength ranges.

[0067] In the present invention, there are no restrictions on the thickness of the first optical anisotropy layer 32 and the second optical anisotropy layer 34. The thickness can be appropriately set to obtain the desired in-plane retardation depending on the rod-shaped liquid crystal compound 30R used. The first optical anisotropy layer 32 and the second optical anisotropy layer 34 are usually formed using the same liquid crystal compound. However, the present invention is not limited to this, and they may be formed using different liquid crystal compounds. Furthermore, as described above, the in-plane retardation of the first optical anisotropy layer 32 and the second optical anisotropy layer 34 is equal. Therefore, the thickness of the first optical anisotropy layer 32 and the second optical anisotropy layer 34 is usually equal.

[0068] Here, the thickness of the first optical anisotropy layer 32 and the second optical anisotropy layer 34 is preferably 1 to 100 μm, more preferably 1 to 80 μm, and even more preferably 1 to 50 μm.

[0069] The total number of layers of the first optical anisotropy layer 32 and the second optical anisotropy layer 34 is not limited as long as there is one or more optical anisotropy layer sets 36, i.e., two or more layers, and the number is even. The total number of layers of the first optical anisotropy layer 32 and the second optical anisotropy layer 34 is preferably 2 to 10 layers, more preferably 2 to 8 layers, and even more preferably 2 to 6 layers.

[0070] In the polarization interference element of the second aspect of the present invention, the greater the total number of layers of the first optical anisotropy layer 32 and the second optical anisotropy layer 34, that is, the greater the number of optical anisotropy layer sets 36, the narrower the wavelength range in which the polarization interference element 16 acts as a (2n+1)λ / 2 phase difference plate. Therefore, in an optical filter having the polarization interference element of the second aspect of the present invention, the greater the total number of layers of the first optical anisotropy layer 32 and the second optical anisotropy layer 34, the narrower the full width at half maximum of the transmitted light wavelength range. In other words, the greater the total number of layers N of the first optical anisotropy layer 32 and the second optical anisotropy layer 34, the more the filter 10 can be made into a bandpass filter with a narrower transmission wavelength range. Therefore, the total number of layers N of the first optical anisotropy layer 32 and the second optical anisotropy layer 34, that is, the number of optical anisotropy layer sets 36, can be appropriately selected according to the required transmission wavelength range of the filter 10. A smaller number of layers is preferred if a broadband is desired, and a larger number of layers is preferred if a narrowband is required.

[0071] A polarization interference element 16 having such a first optical anisotropy layer 32 and a second optical anisotropy layer 34 can be manufactured by known methods. For example, it can be manufactured by a coating method using a liquid crystal composition for forming a rod-shaped liquid crystal layer.

[0072] Similar to the first aspect of the present invention, a liquid crystal composition for forming a rod-shaped liquid crystal layer is applied to the alignment film to form a first optical anisotropy layer 32 and a second optical anisotropy layer 34, respectively. The second optical anisotropy layer 34 is attached to the first optical anisotropy layer 32 using OCA or the like.

[0073] In this process, the layers are stacked such that the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the second optical anisotropy layer 34 are at a predetermined angle. For example, as described above, if the angle between the in-plane slow axis of the first optical anisotropy layer 32 and the reference line is 11.25°, and the angle between the in-plane slow axis of the second optical anisotropy layer 34 and the reference line is -11.25°, the second optical anisotropy layer 34 is stacked on top of the first optical anisotropy layer 32 such that the angle between the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the second optical anisotropy layer 34 is 22.5°. This forms an optical anisotropy layer assembly 36 consisting of the first optical anisotropy layer 32 and the second optical anisotropy layer 34.

[0074] Furthermore, similarly, a liquid crystal composition for forming a rod-shaped liquid crystal layer is applied to the alignment film to form an optically anisotropic layer. Then, the rod-shaped liquid crystal layer is peeled off from the alignment film and, as before, the angle of the in-plane slow axis is aligned and it is laminated and attached to the second optically anisotropic layer 34. By repeating this lamination of laminates for the number of layers of the first optically anisotropic layer 32 and the second optically anisotropic layer 34 to be laminated, that is, the number of optically anisotropic layer sets 36 to be laminated, a polarization interference element 16 as shown in Figure 6 can be fabricated.

[0075] Once the polarization interference element 16 is fabricated in this manner, the first polarizer 12 and the second polarizer 14 are positioned in a cross-nicol configuration with the polarization interference element 16 in between, such that the bisector of the angle formed by the in-plane slow axis of the first optical anisotropy layer 32 and the in-plane slow axis of the second optical anisotropy layer 34 coincides with, for example, the transmission axis of the first polarizer 12. This allows the fabrication of a filter 10 (bandpass filter) as shown in Figure 6.

[0076] In the polarization interference element of the present invention, the method for producing the first optical anisotropy layer and the second optical anisotropy layer is not limited to this method. For example, in the polarization interference element of the present invention, the first optical anisotropy layer and the second optical anisotropy layer may be formed by a coating method and directly laminated. Alternatively, in the polarization interference element of the present invention, the first optical anisotropy layer and the second optical anisotropy layer may be made in sheet form, and these may be alternately laminated and bonded with an optical bonding layer that is transparent to transmitted light, such as OCA, an acrylic adhesive, an adhesive, and a polymer layer. In this case, it is preferable from the viewpoint of improving transmittance that the refractive index of the optical bonding layer is close to the refractive index of the liquid crystal layer (optical anisotropy layer). Specifically, it is preferable that the difference between the refractive index of the optical bonding layer and the refractive index of the liquid crystal layer is 0.3 or less. Furthermore, it is preferable that the refractive index of the optical bonding layer is a value between the two birefringences of the liquid crystal layer, because the difference in refractive index from either of the two refractive indices is small. Furthermore, in terms of the transmittance of transmitted light passing through the liquid crystal polarization interference element, the first and second optical anisotropic layers, which are directly laminated by a coating method and do not have adhesive layers, are preferable.

[0077] Furthermore, in the polarization interference element of the present invention, it is preferable that the in-plane retardation of the first optical anisotropy layer 32 and the in-plane retardation of the second optical anisotropy layer 34 are equal.

[0078] The polarization interference element 16 shown in Figure 6 is constructed by alternately stacking the same first optical anisotropy layer 32 and the same second optical anisotropy layer 34. That is, in the polarization interference element 16, all the first optical anisotropy layers 32 are the same, and all the second optical anisotropy layers 34 are also the same. Therefore, in the polarization interference element 16 shown in Figure 6, the in-plane retardation of all the first optical anisotropy layers 32 is equal, and the in-plane retardation of all the second optical anisotropy layers 34 is equal.

[0079] However, the polarization interference element of the present invention is not limited thereto and may have a first optical anisotropy layer 32 having different in-plane retardations and in-plane slow axes that are not parallel to each other. Furthermore, the polarization interference element of the present invention may have a second optical anisotropy layer 34 having different in-plane retardations and in-plane slow axes that are not parallel to each other. In other words, in the polarization interference element of the present invention, the in-plane slow axes of the first optical anisotropy layer and the second optical anisotropy layer intersect, and in addition, if the in-plane retardations of the first optical anisotropy layer and the second optical anisotropy layer are equal, there may be optical anisotropy layer sets that have different in-plane retardations, as well as different angles between the in-plane slow axis of the first optical anisotropy layer and the reference line, and different angles between the in-plane slow axis of the second optical anisotropy layer and the reference line.

[0080] As an example, a configuration is provided in which the in-plane retardation of the first and second optical anisotropic layers of the optical anisotropic layer sets on both sides of the thickness direction is increased compared to the optical anisotropic layer set in the center of the thickness direction, and the absolute values ​​of the angle between the in-plane slow axis of the first optical anisotropic layer and the reference line, and the angle between the in-plane slow axis of the second optical anisotropic layer and the reference line are reduced. As an example, when the polarization interference element has eight layers of first and second optical anisotropic layers, that is, when it has four sets of optical anisotropic layer sets, in the first set of optical anisotropic layer sets, the in-plane retardation of the first optical anisotropic layer (1st layer) is set to Re1, the angle between the in-plane slow axis and the reference line is set to φ1, the in-plane retardation of the second optical anisotropic layer (2nd layer) is set to Re1, and the angle between the in-plane slow axis and the reference line is set to -φ1. In the second set of optically anisotropic layers, the in-plane retardation of the first optically anisotropic layer (third layer) is set to Re2, which is less than Re1, and the angle between the in-plane slow axis and the reference line is set to φ2, which is greater than φ1. The in-plane retardation of the second optically anisotropic layer (fourth layer) is set to Re2, which is less than Re1, and the angle between the in-plane slow axis and the reference line is set to -φ2, which is greater than -φ1. In the third set of optically anisotropic layers, the in-plane retardation of the first optically anisotropic layer (fifth layer) is set to Re2, and the angle between the in-plane slow axis and the reference line is set to φ2. The in-plane retardation of the second optically anisotropic layer (sixth layer) is set to Re2, and the angle between the in-plane slow axis and the reference line is set to -φ2. In the fourth set of optically anisotropic layers, an example configuration is given in which the in-plane retardation of the first optically anisotropic layer (7th layer) is Re1, the angle between the in-plane slow axis and the reference line is φ1, and the in-plane retardation of the second optically anisotropic layer (8th layer) is Re1, the angle between the in-plane slow axis and the reference line is -φ1.

[0081] In a bandpass filter, as conceptually shown in Figure 4, unwanted transmission wavelength ranges called side lobes are generated at positions shorter and longer than the target transmission wavelength range, on either side of the target transmission wavelength range, as indicated by arrows S in the figure. In contrast, as described above, in a polarization interference element, by increasing the in-plane retardation of the first and second optical anisotropy layers of the optical anisotropy layer set on both sides of the thickness direction compared to the first and second optical anisotropy layers of the optical anisotropy layer set in the center of the thickness direction, and by decreasing the absolute value of the angle between the in-plane slow axis and the reference line, these side lobes can be reduced when used as a bandpass filter. In other words, in the polarization interference element of the present invention, the in-plane retardation of the first and second optical anisotropy layers of the optical anisotropy layer assembly on both sides in the thickness direction is increased compared to the first and second optical anisotropy layers of the optical anisotropy layer assembly in the central part in the thickness direction, and the angle between the in-plane slow axis of the first optical anisotropy layer and the in-plane slow axis of the second optical anisotropy layer is reduced, thereby reducing side lobes when used as a bandpass filter.

[0082] The in-plane retardation of the first and second optical anisotropic layers can be adjusted by changing the thickness of the first and second optical anisotropic layers. Alternatively, the in-plane retardation can be adjusted by changing the liquid crystal compound used. Furthermore, the angle between the in-plane slow axis and the reference line can be adjusted, for example, by adjusting the angle of the in-plane slow axis of the rod-shaped liquid crystal layer during lamination in the manufacturing method described above.

[0083] In a configuration in which the in-plane retardation of the first and second optical anisotropic layers is increased in the liquid crystal layer sets on both sides in the thickness direction compared to the liquid crystal layer set in the center in the thickness direction, and the absolute value of the angle between the in-plane slow axis and the reference line is decreased, there are no restrictions on the number of central optical anisotropic layer sets that increase the in-plane retardation of the optical anisotropic layers and decrease the absolute value of the angle between the in-plane slow axis and the reference line compared to the sides, that is, the way in which the optical anisotropic layer sets are divided between the sides and the center, and it can be set appropriately according to the number of optical anisotropic layers (optical anisotropic layer sets) that the polarization interference element has. Furthermore, there are no restrictions on the in-plane retardation of the first and second optical anisotropic layers and the angle between the in-plane slow axis and the reference line in the optical anisotropic layer sets on both sides in the thickness direction, nor on the in-plane retardation of the first and second optical anisotropic layers and the angle between the in-plane slow axis and the reference line in the optical anisotropic layer set in the center in the thickness direction. In other words, these angles can be set, for example, by simulation, to the optimal in-plane retardation and angle that allows the liquid crystal polarization interference element to act as a (2n+1)λ / 2 phase difference plate and reduce side lobes. It is preferable to control the changes in the in-plane retardation of the first and second optical anisotropic layers and the changes in the angle between the in-plane slow axis and the reference line from both sides toward the center in the stacking direction (thickness direction) as smoothly and precisely as possible.

[0084] Furthermore, the configuration of the filter using the polarization interference element of the present invention is not limited to a configuration in which the polarization interference element is placed between two polarizers arranged in crossed nicols. For example, the filter of the present invention may have a configuration in which the polarization interference element of the present invention is placed between two polarizers arranged in parallel nicols. That is, the filter of the present invention may have a configuration in which the polarization interference element is placed between two polarizers whose transmission axes are parallel to each other. In this case, it is preferable that the polarization interference element has a configuration in which optical anisotropic layers are stacked, with equal thickness and the angles between the direction of the transmission axis of the polarizer and the slow axis being ρ, 3ρ, 5ρ, ... Filters with such a configuration are also called Fansoluk filters.

[0085] Figure 7 conceptually shows the configuration of an optical filter including a polarization interference element according to a third embodiment of the present invention.

[0086] The polarization interference element 16 shown in Figure 7 is an optically anisotropic layer consisting of a rod-shaped liquid crystal layer 38R formed by fixing a rod-shaped liquid crystal compound 30R in a horizontal orientation, and a disc-shaped liquid crystal layer 38D formed by fixing a disc-shaped liquid crystal compound 30D in a vertical orientation. The angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the optically anisotropic layer corresponding to the polarization interference element 16 is set to 45°.

[0087] In this invention, the boundary between the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D can be detected by the method of observation using a SEM described above, and by the method of analyzing the polarization interference element 16 by oblique cutting.

[0088] The in-plane slow axis of the rod-shaped liquid crystal layer 38R and the in-plane slow axis of the disc-shaped liquid crystal layer 38D are parallel.

[0089] The in-plane slow-phase axes of the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D can be detected by the method described above, which involves observation using a SEM, and by the method of analyzing the polarization interference element 16 by oblique cutting.

[0090] Here, the optically anisotropic layer formed by stacking the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D satisfies the above-described equations (1), (2), and (3). As a result, the optically anisotropic layer formed by stacking the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D has multiple specific wavelengths (λ １ , λ ２ , λ ３ ..λ n This optical element can be configured to act as a (2n+1)λ / 2 phase difference plate for light of type 1, but not as a (2n+1)λ / 2 phase difference plate for other types of light.

[0091] Therefore, by placing the polarization interference element 16 shown in Figure 6 between two polarizers arranged in crossed nicols, a bandpass filter can be obtained that acts as a (2n+1)λ / 2 phase difference plate to rotate the polarization direction by 90° (optical rotation) only the linearly polarized light in multiple specific wavelength ranges that has passed through one polarizer, causing it to exit from the other polarizer, while blocking light in other wavelength ranges.

[0092] In the polarization interference element 16 shown in Figure 7, it is preferable that the in-plane retardation (Re) of the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D are equal. The polarization interference element 16 in the example shown in Figure 7 has one rod-shaped liquid crystal layer and one disc-shaped liquid crystal layer. However, the present invention is not limited thereto, and the polarization interference element 16 (optical anisotropy layer) may have multiple rod-shaped liquid crystal layers and multiple disc-shaped liquid crystal layers. In this case, the polarization interference element 16 (optical anisotropy layer) is configured such that the sum of the in-plane retardations of the multiple rod-shaped liquid crystal layers is equal to the sum of the in-plane retardations of the multiple disc-shaped liquid crystal layers. In this case, it is preferable to further subdivide the region consisting of the rod-shaped liquid crystal compound 38R (rod-shaped liquid crystal layer) and the region consisting of the disc-shaped liquid crystal compound 38D (disc-shaped liquid crystal layer) to increase the number of liquid crystal layers. This reduces the difference between the retardance of the front (normal) and the retardance at the polar angle for wider oblique directions.

[0093] In a bandpass filter having a polarization interference element composed solely of an optical anisotropy layer formed by horizontally oriented and fixed rod-shaped liquid crystal compounds, there is a problem in that when light is incident from an oblique direction, the wavelength of light exhibiting maximum transmittance fluctuates, resulting in a so-called wavelength shift, as conceptually shown in Figure 8.

[0094] In contrast, the polarization interference element 16 (optical anisotropic layer) shown in Figure 7 has a rod-shaped liquid crystal layer 38R made of a rod-shaped liquid crystal compound 30R whose in-plane slow axis is parallel, and a disc-shaped liquid crystal layer 38D made of a disc-shaped liquid crystal compound 30D, and the in-plane retardation of the rod-shaped liquid crystal layer and the in-plane retardation of the disc-shaped liquid crystal layer are equal. Therefore, the retardation in the thickness direction (Rth) due to the rod-shaped liquid crystal layer 38R can be canceled out by the retardation in the thickness direction due to the disc-shaped liquid crystal layer 38D. As a result, by using the polarization interference element 16 shown in Figure 7 as a bandpass filter, wavelength shift, which causes fluctuations in the wavelength of light that shows maximum transmittance, can be suppressed even when light is incident from an oblique direction.

[0095] Furthermore, there are no restrictions on the thickness of the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D in the polarization interference element 16. That is, the thickness of the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D can be appropriately set to obtain the desired in-plane retardation depending on the liquid crystal compound used. Here, it is preferable that the rod-shaped liquid crystal compound 30R forming the rod-shaped liquid crystal layer and the disc-shaped liquid crystal compound 30D forming the disc-shaped liquid crystal layer have similar Δn values, and more preferably equal Δn values. Therefore, it is preferable that the thicknesses of the rod-shaped liquid crystal layer and the disc-shaped liquid crystal layer be equal.

[0096] In the example shown in Figure 7, the thickness of the polarization interference element 16 is corresponding to the thickness of the rod-shaped liquid crystal layer and the disc-shaped liquid crystal layer described above.

[0097] In the example shown in Figure 7, the thickness of the polarization interference element 16 is preferably 1 to 100 μm, and more preferably 1 to 80 μm. Therefore, the thickness of the rod-shaped liquid crystal layer and the disc-shaped liquid crystal layer in the polarization interference element 16 shown in Figure 7 is preferably 0.5 to 50 μm, and more preferably 0.5 to 40 μm.

[0098] Such a polarizing interference element 16, including a rod-shaped liquid crystal layer and a disc-shaped liquid crystal layer, can be manufactured by known methods. For example, there are coating methods (sequential coating), methods of bonding with an adhesive, and methods of separating into upper and lower layers by one-component coating (layer phase separation). As an example, it can be manufactured by a coating method using a liquid crystal composition for forming the rod-shaped liquid crystal layer and the disc-shaped liquid crystal layer.

[0099] As an example, a liquid crystal composition for forming a rod-shaped liquid crystal layer containing a rod-shaped liquid crystal compound 30R and a liquid crystal composition for forming a disc-shaped liquid crystal layer containing a disc-shaped liquid crystal compound 30D are prepared. The liquid crystal composition for forming the disc-shaped liquid crystal layer is applied to the alignment film prepared by the above method to orient the disc-shaped liquid crystal compound 30D, and then dried. If necessary, the composition is cured by ultraviolet irradiation or the like to form a disc-shaped liquid crystal layer 38D. Next, the liquid crystal composition for forming the rod-shaped liquid crystal compound is applied on the disc-shaped liquid crystal layer 38D to orient the rod-shaped liquid crystal compound 30R, and then dried. If necessary, the composition is cured by ultraviolet irradiation or the like to form a rod-shaped liquid crystal layer 38R, thereby forming a depolarization element 16. Here, when a liquid crystal layer is formed on a liquid crystal layer by a coating method, the orientation of the liquid crystal compound in the upper liquid crystal layer is the same as that of the liquid crystal compound on the surface of the lower liquid crystal layer. The orientation direction of the liquid crystal compound in the disc-shaped liquid crystal layer 38D and the rod-shaped liquid crystal layer 38R coincides, that is, their in-plane slow axis is parallel.

[0100] Once the polarization interference element 16 is fabricated in this manner, the first polarizer 12 and the second polarizer 14 are arranged in crossed nicols, flanking the polarization interference element 16, such that the angle between the in-plane slow axis of the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D and, for example, the transmission axis of the first polarizer 12 is 45°. This allows the fabrication of a filter 10 (bandpass filter) as shown in Figure 7.

[0101] In the polarization interference element 16 of the present invention, there are no limitations on the disc-shaped liquid crystal compound 30D, and various known liquid crystal compounds can be used. As the disc-shaped liquid crystal compound 30D, for example, those described in Japanese Patent Application Publication No. 2007-108732 and Japanese Patent Application Publication No. 2010-244038 can be preferably used. It is preferable to fix the orientation of the disc-shaped liquid crystal compound 30D by polymerization.

[0102] Figure 9 conceptually shows the configuration of an optical filter including a polarization interference element according to a fourth embodiment of the present invention.

[0103] The polarization interference element 16 shown in Figure 9 has a structure in which one or more optical anisotropy layer sets 48 are stacked in the thickness direction, with a first optical anisotropy layer 44 and a second optical anisotropy layer 46 forming one optical anisotropy layer set 48. Therefore, the total number of optical anisotropy layers is even.

[0104] The first optical anisotropic layer 44 has a rod-shaped liquid crystal layer 40R1 and a disc-shaped liquid crystal layer 40D1. The second optical anisotropic layer 46 has a rod-shaped liquid crystal layer 42R2 and a disc-shaped liquid crystal layer 42D2.

[0105] The rod-shaped liquid crystal layer 40R1 and the rod-shaped liquid crystal layer 42R2 are both liquid crystal layers formed by fixing rod-shaped liquid crystal compounds 30R in a horizontal orientation. The disc-shaped liquid crystal layer 40D1 and the disc-shaped liquid crystal layer 42D2 are both liquid crystal layers formed by fixing disc-shaped liquid crystal compounds 30D in a vertical orientation. In the following description, when it is not necessary to distinguish between the rod-shaped liquid crystal layer 40R1 and the rod-shaped liquid crystal layer 42R2, both will be collectively referred to as the "rod-shaped liquid crystal layer." Also, in the following description, when it is not necessary to distinguish between the disc-shaped liquid crystal layer 40D1 and the disc-shaped liquid crystal layer 42D2, both will be collectively referred to as the "disc-shaped liquid crystal layer."

[0106] In the polarization interference element 16 shown in Figure 9, the relationship between the in-plane phase-lagging axis and in-plane retardation between the first optical anisotropy layer 44 and the second optical anisotropy layer 46 is the same as the relationship between the in-plane phase-lagging axis and in-plane retardation between the first optical anisotropy layer 32 and the second optical anisotropy layer 34 in the second embodiment shown in Figure 6.

[0107] Furthermore, the relationship between the in-plane phase-lagging axis and in-plane retardation between the rod-shaped liquid crystal layer 40R1 and the disc-shaped liquid crystal layer 40D1 in the first optical anisotropic layer 44, and the relationship between the in-plane phase-lagging axis and in-plane retardation between the rod-shaped liquid crystal layer 42R2 and the disc-shaped liquid crystal layer 42D2 in the second optical anisotropic layer 46, are the same as the relationship between the in-plane phase-lagging axis and in-plane retardation between the rod-shaped liquid crystal layer 38R and the disc-shaped liquid crystal layer 38D in the third embodiment shown in Figure 7.

[0108] Here, the first optical anisotropic layer 44 and the second optical anisotropic layer 46 each satisfy the above-described formulas (1), (2), and (3). That is, the first optical anisotropic layer 44 formed by laminating the rod-like liquid crystal layer 40R1 and the disc-like liquid crystal layer 40D1, and the second optical anisotropic layer 46 formed by laminating the rod-like liquid crystal layer 42R2 and the disc-like liquid crystal layer 42D2 each satisfy the above-described formulas (1), (2), and (3). As a result, the polarization interference element having a plurality of optical anisotropic layers can be an optical element that acts as a (2n + 1)λ / 2 retardation plate for light of a plurality of specific wavelengths (λ １ , λ ２ , λ ３ ··· λ n ), and does not act as a (2n + 1)λ / 2 retardation plate for other light.

[0109] Therefore, by disposing the polarization interference element 16 shown in FIG. 9 between two polarizers arranged in a cross Nicol, among the linearly polarized light transmitted through one polarizer, only the light in a plurality of specific wavelength ranges acts as a (2n + 1)λ / 2 retardation plate to rotate (optical rotation) the polarization direction by 90°, and is emitted from the other polarizer, and the light in other wavelength ranges is blocked, thereby obtaining a band-pass filter.

[0110] The polarization interference element 16 having such a first optical anisotropic layer 44 and a second optical anisotropic layer 46 may be manufactured by a known method. As an example, it is manufactured by a coating method using a liquid crystal composition for forming a rod-like liquid crystal layer and a disc-like liquid crystal layer.

[0111] As an example, a liquid crystal composition for forming a rod-shaped liquid crystal layer containing a rod-shaped liquid crystal compound 30R and a liquid crystal composition for forming a disc-shaped liquid crystal layer containing a disc-shaped liquid crystal compound 30D are prepared. The liquid crystal composition for forming the disc-shaped liquid crystal layer is applied to the alignment film prepared by the above method to orient the disc-shaped liquid crystal compound 30D, and the film is further dried and, if necessary, the composition is cured by ultraviolet irradiation or the like to form a disc-shaped liquid crystal layer 40D1. Next, the liquid crystal composition for forming the rod-shaped liquid crystal compound is applied on the disc-shaped liquid crystal layer 40D1 to orient the rod-shaped liquid crystal compound 30R, and the film is further dried and, if necessary, the composition is cured by ultraviolet irradiation or the like to form a rod-shaped liquid crystal layer 40R1, thereby forming a first optical anisotropy layer 44. Here, when a liquid crystal layer is formed on a liquid crystal layer by a coating method, the orientation of the liquid crystal compound on the surface of the upper liquid crystal layer is the same as that of the liquid crystal compound on the surface of the lower liquid crystal layer. The orientation direction of the liquid crystal compounds in the disc-shaped liquid crystal layer 40D1 and the rod-shaped liquid crystal layer 40R1 coincides, meaning that their in-plane slow phase axes are parallel.

[0112] Furthermore, in a similar manner, a liquid crystal composition is applied to the alignment film to form a disc-shaped liquid crystal layer, and then a liquid crystal composition for forming a rod-shaped liquid crystal compound is applied on top of it to form a rod-shaped liquid crystal layer. This laminate of two liquid crystal layers (second optical anisotropy layer) is peeled off from the alignment film, and the laminate is laminated onto the previously formed first optical anisotropy layer 44 (rod-shaped liquid crystal layer 40R1) and attached using OCA or the like.

[0113] In this process, the laminate is stacked on the first optical anisotropy layer 44 such that the in-plane slow axis of the rod-shaped liquid crystal layer 40R1 of the first optical anisotropy layer 44 and the in-plane slow axis of the rod-shaped liquid crystal layer in the stacked laminate form a predetermined angle. For example, as described above, if the angle between the in-plane slow axis of the rod-shaped liquid crystal layer 40R1 of the first optical anisotropy layer 44 and the reference line is 11.25°, and the angle between the in-plane slow axis of the rod-shaped liquid crystal layer 42R2 of the second optical anisotropy layer 46 and the reference line is -11.25°, the laminate is stacked on the first optical anisotropy layer 44 such that the angle between the in-plane slow axis of the rod-shaped liquid crystal layer 40R1 of the first optical anisotropy layer 44 and the in-plane slow axis of the rod-shaped liquid crystal layer in the stacked laminate forms a predetermined angle. This allows for the formation of an optical anisotropy layer assembly 48, which consists of a first optical anisotropy layer 44 having a rod-shaped liquid crystal layer 40R1 and a disc-shaped liquid crystal layer 40D1, and a second optical anisotropy layer 46 having a rod-shaped liquid crystal layer 42R2 and a disc-shaped liquid crystal layer 42D2.

[0114] Furthermore, similarly, a liquid crystal composition is applied to the alignment film to form a disc-shaped liquid crystal layer, and then a liquid crystal composition for forming a rod-shaped liquid crystal compound is applied on top of it to form a rod-shaped liquid crystal layer. After that, the laminate of these two liquid crystal layers is peeled off from the alignment film and, as before, the angle of the in-plane slow axis of the rod-shaped liquid crystal layer is aligned and it is laminated and attached to the second optical anisotropy layer 46 (rod-shaped liquid crystal layer 42R2). By repeating this lamination of laminates for the number of layers of the first optical anisotropy layer 44 and the second optical anisotropy layer 46 to be laminated, that is, the number of optical anisotropy layer sets 48 to be laminated, a polarization interference element 16 as shown in Figure 9 can be fabricated.

[0115] Once the polarization interference element 16 is fabricated in this manner, the first polarizer 12 and the second polarizer 14 are positioned in a cross-nicol configuration with the polarization interference element 16 in between, such that the bisector of the angle formed by the in-plane slow axis in the rod-shaped liquid crystal layer 40R1 of the first optical anisotropy layer 44 and the in-plane slow axis in the rod-shaped liquid crystal layer 42R2 of the second optical anisotropy layer 46 coincides with, for example, the transmission axis of the first polarizer 12. This allows the fabrication of a filter 10 (bandpass filter) as shown in Figure 9.

[0116] Figure 10 conceptually shows the configuration of an optical filter including a polarization interference element according to a fifth aspect of the present invention.

[0117] The polarization interference element 16 shown in Figure 10 is an optically anisotropic layer consisting of a rod-shaped liquid crystal layer 50R1 formed by fixing rod-shaped liquid crystal compounds 30R in a horizontal orientation, and a rod-shaped liquid crystal layer 50R2 formed by fixing rod-shaped liquid crystal compounds 30R in a vertical orientation. The angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the rod-shaped liquid crystal layer 50R1 in the polarization interference element 16 is set to 45°.

[0118] In this invention, the boundary between the rod-shaped liquid crystal layer 50R1 and the rod-shaped liquid crystal layer 50R2 can be detected by the method of observation using a SEM described above, and by the method of analyzing the polarization interference element 16 by oblique cutting.

[0119] Here, the optical anisotropic layer formed by stacking the rod-shaped liquid crystal layer 50R1 and the rod-shaped liquid crystal layer 50R2 satisfies the above-described equations (1), (2), and (3). As a result, the optical anisotropic layer formed by stacking the rod-shaped liquid crystal layer 50R1 and the rod-shaped liquid crystal layer 50R2 has multiple specific wavelengths (λ １ , λ ２ , λ ３ ..λ n This optical element can be configured to act as a (2n+1)λ / 2 phase difference plate for light of type 1, but not as a (2n+1)λ / 2 phase difference plate for other types of light.

[0120] Therefore, by placing the polarization interference element 16 shown in Figure 10 between two polarizers arranged in crossed nicols, a bandpass filter can be obtained that acts as a (2n+1)λ / 2 phase difference plate to rotate the polarization direction by 90° (optical rotation) only for linearly polarized light in multiple specific wavelength ranges that has passed through one polarizer, causing it to exit from the other polarizer, while blocking light in other wavelength ranges.

[0121] In the polarization interference element 16 (optical anisotropic layer) shown in Figure 10, it is preferable that half of the in-plane retardation (Re) of the rod-shaped liquid crystal layer 50R1 is equal to the retardation (Rth) in the thickness direction of the rod-shaped liquid crystal layer 50R2. Note that the polarization interference element 16 in the example shown in Figure 10 has one rod-shaped liquid crystal layer 50R1 and one rod-shaped liquid crystal layer 50R2. However, the present invention is not limited thereto, and the polarization interference element 16 may have multiple rod-shaped liquid crystal layers 50R1 and multiple rod-shaped liquid crystal layers 50R2. In this case, each polarization interference element 16 has half of the sum of the in-plane retardations of the multiple rod-shaped liquid crystal layers 50R1 equal to the sum of the retardations in the thickness direction of the multiple rod-shaped liquid crystal layers 50R2. In this case, it is preferable to further subdivide the region consisting of the rod-shaped liquid crystal layer 50R1 and the region consisting of the rod-shaped liquid crystal layer 50R2 to increase the number of liquid crystal layers. This reduces the difference between the retardance of the front (normal) and the retardance at the polar angle for wider oblique directions.

[0122] The polarization interference element 16 shown in Figure 10 has a rod-shaped liquid crystal layer 50R1 and a rod-shaped liquid crystal layer 50R2 made of a rod-shaped liquid crystal compound 30R, and half of the in-plane retardation of the rod-shaped liquid crystal layer 50R1 is equal to the retardation in the thickness direction of the rod-shaped liquid crystal layer 50R2. Therefore, the retardation in the thickness direction (Rth) due to the rod-shaped liquid crystal layer 50R1 can be canceled out by the retardation in the thickness direction due to the rod-shaped liquid crystal layer 50R2. As a result, by using the polarization interference element 16 of the present invention in a bandpass filter, wavelength shift, which causes fluctuations in the wavelength of light that shows maximum transmittance, can be suppressed even when light is incident from an oblique direction.

[0123] Such a polarizing interference element 16, including the rod-shaped liquid crystal layer 50R1 and the rod-shaped liquid crystal layer 50R2, can be manufactured by known methods. For example, a rod-shaped liquid crystal layer 50R2 in which the rod-shaped liquid crystal compound 30R is vertically oriented can be manufactured by adding a vertical alignment agent to a liquid crystal composition for forming the rod-shaped liquid crystal layer 50R2.

[0124] Figure 11 conceptually shows the configuration of an optical filter including a polarization interference element according to a sixth aspect of the present invention.

[0125] The polarization interference element 16 shown in Figure 11 has a structure in which one or more optical anisotropy layer sets 60 are stacked in the thickness direction, with a first optical anisotropy layer 56 and a second optical anisotropy layer 58 forming one optical anisotropy layer set 60. Therefore, the total number of optical anisotropy layers is even.

[0126] The first optical anisotropic layer 56 has a rod-shaped liquid crystal layer 52R1 and a rod-shaped liquid crystal layer 52R2. The second optical anisotropic layer 58 has a rod-shaped liquid crystal layer 54R1 and a rod-shaped liquid crystal layer 54R2.

[0127] Both the rod-shaped liquid crystal layer 52R1 and the rod-shaped liquid crystal layer 54R1 are liquid crystal layers formed by fixing rod-shaped liquid crystal compounds 30R in a horizontal orientation. Both the rod-shaped liquid crystal layer 52R2 and the rod-shaped liquid crystal layer 54R2 are liquid crystal layers formed by fixing rod-shaped liquid crystal compounds 30R in a vertical orientation.

[0128] In the polarization interference element 16 shown in Figure 11, the relationship between the in-plane slow axis and in-plane retardation between the first optical anisotropy layer 56 and the second optical anisotropy layer 58 is the same as the relationship between the in-plane slow axis and in-plane retardation between the first optical anisotropy layer 32 and the second optical anisotropy layer 34 in the second embodiment shown in Figure 6.

[0129] Furthermore, the relationship between the in-plane retardation of the rod-shaped liquid crystal layer 52R1 and the thickness direction retardation of the rod-shaped liquid crystal layer 52R2 in the first optical anisotropy layer 56, and the relationship between the in-plane retardation of the rod-shaped liquid crystal layer 54R1 and the thickness direction retardation of the rod-shaped liquid crystal layer 54R2 in the second optical anisotropy layer 58, are the same as the relationship between the in-plane retardation of the rod-shaped liquid crystal layer 50R1 and the thickness direction retardation of the rod-shaped liquid crystal layer 50R2 in the fifth embodiment shown in Figure 10.

[0130] Here, the first optical anisotropy layer 56 and the second optical anisotropy layer 58 satisfy the above-described equations (1), (2), and (3). That is, the first optical anisotropy layer 56, which is formed by laminating a rod-shaped liquid crystal layer 52R1 and a rod-shaped liquid crystal layer 52R2, and the second optical anisotropy layer 58, which is formed by laminating a rod-shaped liquid crystal layer 54R1 and a rod-shaped liquid crystal layer 54R2, satisfy the above-described equations (1), (2), and (3). As a result, the polarization interference element 16 having multiple optical anisotropy layers can react to multiple specific wavelengths (λ １ , λ２ , λ ３ ..λ n This optical element can be configured to act as a (2n+1)λ / 2 phase difference plate for light of type 1, but not as a (2n+1)λ / 2 phase difference plate for other types of light.

[0131] Therefore, by placing the polarization interference element 16 shown in Figure 11 between two polarizers arranged in crossed nicols, a bandpass filter can be obtained that acts as a (2n+1)λ / 2 phase difference plate to rotate the polarization direction by 90° (optical rotation) only for linearly polarized light in multiple specific wavelength ranges that has passed through one polarizer, causing it to exit from the other polarizer, while blocking light in other wavelength ranges.

[0132] A polarization interference element 16 including such a first optical anisotropy layer 56 and a second optical anisotropy layer 58 can be fabricated by known methods.

[0133] Figure 12 conceptually shows the configuration of an optical filter including a polarization interference element according to a seventh aspect of the present invention.

[0134] The polarization interference element 16 shown in Figure 12 is an optically anisotropic layer consisting of a disc-shaped liquid crystal layer 62D1 formed by fixing a disc-shaped liquid crystal compound 30D in a vertical orientation, and a disc-shaped liquid crystal layer 62D2 formed by fixing a disc-shaped liquid crystal compound 30D in a horizontal orientation. The angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the disc-shaped liquid crystal layer 62D1 in the polarization interference element 16 is set to 45°.

[0135] In this invention, the boundary between the disc-shaped liquid crystal layer 62D1 and the disc-shaped liquid crystal layer 62D2 can be detected by the method of observation using a SEM described above, and by the method of analyzing the polarization interference element 16 by oblique cutting.

[0136] Here, the optical anisotropic layer formed by stacking the disc-shaped liquid crystal layer 62D1 and the disc-shaped liquid crystal layer 62D2 satisfies the above-described equations (1), (2), and (3). As a result, the optical anisotropic layer formed by stacking the disc-shaped liquid crystal layer 62D1 and the disc-shaped liquid crystal layer 62D2 has multiple specific wavelengths (λ １ , λ ２ , λ ３ ..λ nThis optical element can be configured to act as a (2n+1)λ / 2 phase difference plate for light of type 1, but not as a (2n+1)λ / 2 phase difference plate for other types of light.

[0137] Therefore, by placing the polarization interference element 16 shown in Figure 12 between two polarizers arranged in crossed nicols, a bandpass filter can be obtained that acts as a (2n+1)λ / 2 phase difference plate to rotate the polarization direction by 90° (optical rotation) only for linearly polarized light in multiple specific wavelength ranges that has passed through one polarizer, causing it to exit from the other polarizer, while blocking light in other wavelength ranges.

[0138] In the polarization interference element 16 shown in Figure 12, it is preferable that half of the in-plane retardation (Re) of the disc-shaped liquid crystal layer 62D1 is equal to the retardation (Rth) in the thickness direction of the disc-shaped liquid crystal layer 62D2. The polarization interference element 16 in the example shown in Figure 12 has one disc-shaped liquid crystal layer 62D1 and one disc-shaped liquid crystal layer 62D2. However, the present invention is not limited thereto, and the polarization interference element 16 may have multiple disc-shaped liquid crystal layers 62D1 and multiple disc-shaped liquid crystal layers 62D2. In this case, each polarization interference element 16 has half of the sum of the in-plane retardations of the multiple disc-shaped liquid crystal layers 62D1 equal to the sum of the retardations in the thickness direction of the multiple disc-shaped liquid crystal layers 62D2. In this case, it is preferable to further subdivide the region consisting of the disc-shaped liquid crystal layer 62D1 and the region consisting of the disc-shaped liquid crystal layer 62D2 to increase the number of liquid crystal layers. This reduces the difference between the retardance of the front (normal) and the retardance at the polar angle for wider oblique directions.

[0139] The polarization interference element 16 shown in Figure 12 has a disc-shaped liquid crystal layer 62D1 and a disc-shaped liquid crystal layer 62D2 made of a disc-shaped liquid crystal compound 30D, and half of the in-plane retardation of the disc-shaped liquid crystal layer 62D1 is equal to the retardation in the thickness direction of the disc-shaped liquid crystal layer 62D2. Therefore, the retardation in the thickness direction (Rth) due to the disc-shaped liquid crystal layer 62D1 can be canceled out by the retardation in the thickness direction due to the disc-shaped liquid crystal layer 62D2. As a result, by using the polarization interference element 16 of the present invention in a bandpass filter, wavelength shifts that cause fluctuations in the wavelength of light exhibiting maximum transmittance can be suppressed even when light is incident from an oblique direction.

[0140] A polarization interference element 16 including such disc-shaped liquid crystal layers 62D1 and 62D2 can be manufactured by known methods.

[0141] Figure 13 conceptually shows the configuration of an optical filter including a polarization interference element according to the eighth aspect of the present invention.

[0142] The polarization interference element 16 shown in Figure 13 has a structure in which one or more optical anisotropy layer sets 72 are stacked in the thickness direction, with a first optical anisotropy layer 68 and a second optical anisotropy layer 70 forming one optical anisotropy layer set 72. Therefore, the total number of optical anisotropy layers is even.

[0143] The first optical anisotropic layer 68 has a disc-shaped liquid crystal layer 64D1 and a disc-shaped liquid crystal layer 64D2. The second optical anisotropic layer 70 has a disc-shaped liquid crystal layer 66D1 and a disc-shaped liquid crystal layer 66D2.

[0144] The disc-shaped liquid crystal layer 64D1 and the disc-shaped liquid crystal layer 66D1 are both liquid crystal layers formed by fixing disc-shaped liquid crystal compounds 30D in a vertically oriented manner. The disc-shaped liquid crystal layer 64D2 and the disc-shaped liquid crystal layer 66D2 are both liquid crystal layers formed by fixing disc-shaped liquid crystal compounds 30D in a horizontally oriented manner.

[0145] In the polarization interference element 16 shown in Figure 13, the relationship between the in-plane phase-lagging axis and in-plane retardation between the first optical anisotropy layer 68 and the second optical anisotropy layer 70 is the same as the relationship between the in-plane phase-lagging axis and in-plane retardation between the first optical anisotropy layer 32 and the second optical anisotropy layer 34 in the second embodiment shown in Figure 6.

[0146] Furthermore, the relationship between the in-plane retardation of the disc-shaped liquid crystal layer 64D1 and the thickness direction retardation of the disc-shaped liquid crystal layer 64D2 in the first optical anisotropy layer 68, and the relationship between the in-plane retardation of the disc-shaped liquid crystal layer 66D1 and the thickness direction retardation of the disc-shaped liquid crystal layer 66D2 in the second optical anisotropy layer 70, are the same as the relationship between the in-plane retardation of the disc-shaped liquid crystal layer 62D1 and the thickness direction retardation of the disc-shaped liquid crystal layer 62D2 in the seventh embodiment shown in Figure 12.

[0147] Here, the first optical anisotropy layer 68 and the second optical anisotropy layer 70 satisfy the above-described equations (1), (2), and (3). That is, the first optical anisotropy layer 68, which is formed by laminating a disc-shaped liquid crystal layer 64D1 and a disc-shaped liquid crystal layer 64D2, and the second optical anisotropy layer 70, which is formed by laminating a disc-shaped liquid crystal layer 66D1 and a disc-shaped liquid crystal layer 66D2, satisfy the above-described equations (1), (2), and (3). As a result, the polarization interference element 16 having multiple optical anisotropy layers can react to multiple specific wavelengths (λ １ , λ ２ , λ ３ ..λ n This optical element can be configured to act as a (2n+1)λ / 2 phase difference plate for light of type 1, but not as a (2n+1)λ / 2 phase difference plate for other types of light.

[0148] Therefore, by placing the polarization interference element 16 shown in Figure 13 between two polarizers arranged in crossed nicols, a bandpass filter can be obtained that acts as a (2n+1)λ / 2 phase difference plate to rotate the polarization direction by 90° (optical rotation) only for linearly polarized light in multiple specific wavelength ranges that has passed through one polarizer, causing it to exit from the other polarizer, while blocking light in other wavelength ranges.

[0149] Such a polarization interference element 16, including the first optical anisotropy layer 68 and the second optical anisotropy layer 70, can be fabricated by known methods.

[0150] In the polarization interference element of the present invention described above, a layer may be used as the optical anisotropy layer, in which the orientation state of a liquid crystal compound is fixed in a torsion orientation along a helical axis extending along the thickness direction (with the thickness direction as the helical axis). The orientation of the liquid crystal compound may be left-handed (counterclockwise twist) or right-handed (clockwise twist).

[0151] The twist angle is determined by simulation to find the optimal twist angle for the polarization interference element to act as a (2n+1)λ / 2 phase difference plate, depending on the central wavelength of the wavelength range that is expected to pass through the filter 10 and the total number of optical anisotropy layers.

[0152] The torsion angle of the optically anisotropic layer can be detected by obliquely cutting a polarization interference element and analyzing the orientation direction of the liquid crystal on the surface of the cross-section. This method is described in detail in the aforementioned literature by Yohei Takahashi et al. Furthermore, this torsion angle can also be measured using an AxoScan (manufactured by Axometrics) by employing a separation measurement method that assumes a model with input parameters.

[0153] The twist direction and twist angle of the optically anisotropic layer can be arbitrarily adjusted by adjusting the type and amount of chiral agent (chiral compound) that has the function of inducing the twist orientation of the liquid crystal compound. There are no particular restrictions on the chiral agent, and known compounds, isosorbide, and isomannide derivatives can be used. Examples of known compounds include those described in "Liquid Crystal Device Handbook, Chapter 3, Section 4-3, Chiral Agents for TN (twisted nematic) and STN (Super Twisted Nematic), p. 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989". Specifically, isosorbide refers to a chiral agent having an isosorbide structure. Furthermore, chiral agents that undergo re-isomerization, dimerization, and decrease in helical twisting power (HTP) upon irradiation with light can also be suitably used.

[0154] Chiral agents generally contain an asymmetric carbon atom, but axially asymmetric compounds or planar asymmetric compounds that do not contain an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric compounds or planar asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. Chiral agents may have polymerizable groups. If both the chiral agent and the liquid crystal compound have polymerizable groups, a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound can form a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral agent. In this embodiment, it is preferable that the polymerizable group of the polymerizable chiral agent is of the same type as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is preferably an unsaturated polymerizable group, an epoxy group, or an azilidinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group. The chiral agent may also be a liquid crystal compound.

[0155] When the chiral agent has a photoisomerizing group, it is preferable because, after coating and orientation, a pattern of the desired reflected wavelength corresponding to the emission wavelength can be formed by photomask irradiation with active light or the like. Preferred photoisomerizing groups are the isomerization site of a photochromic compound, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in Japanese Patent Publication No. 2002-080478, 2002-080851, 2002-179668, 2002-179669, 2002-179670, 2002-179681, 2002-179682, 2002-338575, 2002-338668, 2003-313189, and 2003-313292, etc.

[0156] In the polarization interference element of the present invention described above, a biaxial refractive index material, such as a B plate (with an Nz factor of 0.1 to 0.9), may be used for the optical anisotropy layer.

[0157] A phase difference film that is a biaxial refractive index material, such as a B plate (Nz factor of 0.1 to 0.9), can be obtained, for example, by controlling the refractive index in the thickness direction by stretching a polymer film biaxially in the planar direction, or by stretching it uniaxially or biaxially in the planar direction and also stretching it in the thickness direction. Alternatively, the above phase difference film can be obtained by bonding a heat-shrinkable film to a polymer film and stretching and / or shrinking the polymer film under the action of the shrinkage force caused by heating to cause a tilted orientation. Furthermore, the phase difference film may be an orientation film of a liquid crystal polymer or an orientation film of a low-molecular-weight liquid crystal.

[0158] In the polarization interference element of the present invention described above, an in-plane periodic structure layer may be used for the optical anisotropy layer, which has a periodic structure in which two types of unit layers with different refractive indices are stacked alternately adjacent to each other in the in-plane direction.

[0159] The in-plane periodic structure layer has a periodic structure in which two types of unit layers with different refractive indices are stacked alternately adjacent to each other in the in-plane direction, and there are no particular restrictions as long as it can transmit light in the target wavelength range.

[0160] An in-plane periodic structure layer results in a birefringent layer, but the material itself does not necessarily have to exhibit birefringence. Therefore, a birefringent structure layer can also be used by using an optically isotropic material and adjusting its periodic structure to exhibit birefringence.

[0161] An example of an in-plane periodic structure layer is a component having a surface with a surface irregular structure with a period shorter than the design wavelength. In this case, the protrusions correspond to a high refractive index layer, and the air layers in the recesses correspond to a low refractive index layer. Alternatively, a low refractive index layer may be formed by filling the recesses with a material having a lower refractive index than the material forming the protrusions.

[0162] As the in-plane periodic structure layer having an uneven structure, various in-plane periodic structure layers described in Japanese Patent Publication No. 2018-180112, Japanese Patent Publication No. 2007-101856, etc., can be used as appropriate.

[0163] Furthermore, an optical phase difference element is provided, which has an in-plane periodic structure layer comprising a substrate having a surface with an uneven structure portion having a period shorter than the design wavelength, as described in Japanese Patent Application Publication No. 2007-101856; a first coating film having a higher refractive index than the material of the convex portion of the uneven structure portion and formed on the convex portion of the uneven structure portion; and a second coating film formed to cover the recess of the uneven structure portion and the first coating film, with an air layer formed in the recess. In this optical phase difference element, the first coating film and the convex portion correspond to a high refractive index layer, and the air layer in the recess and the third coating film correspond to a low refractive index layer.

[0164] There are no particular restrictions on the material used for the high refractive index layer, but various high refractive index polymers such as acrylics (for example, described in Japanese Patent No. 5463170, Japanese Patent Application Publication No. 2013-095833, etc.), inorganic materials such as quartz glass (SiO2), TiO2, Ta2O5, HfO2, Si3N4, Zn2SnO4, Nb2O5, etc. can be used.

[0165] There are no particular restrictions on the material used for the low refractive index layer, but it can be air, resin materials such as polymer nanocomposites (for example, as described in Japanese Patent No. 6121204), or inorganic materials such as quartz glass (SiO2), TiO2, Ta2O5, HfO2, Si3N4, Zn2SnO4, Nb2O5, etc.

[0166] In an in-plane periodic structure layer, the difference between the refractive index of the high refractive index layer and the refractive index of the low refractive index layer can be appropriately set according to the required in-plane retardation (Δnd), etc. The refractive index difference between the high refractive index layer and the low refractive index layer is preferably 0.1 or more, and more preferably 0.5 or more.

[0167] Such in-plane periodic structure layers can be fabricated using known methods.

[0168] Furthermore, in the polarization interference element of the present invention described above, a thickness-direction periodic structure layer may be used for the optical anisotropy layer, which has a periodic structure in which two types of unit layers with different refractive indices are stacked alternately adjacent to each other in the thickness direction.

[0169] The thickness-direction periodic structure layer has a periodic structure in which two types of unit layers with different refractive indices are stacked alternately adjacent to each other in the thickness direction, and there are no particular restrictions as long as it can transmit light in the target wavelength range.

[0170] The thickness-direction periodic structure layer is a known multilayer film in which high-refractive-index layers and low-refractive-index layers, each with a thickness sufficiently smaller than the design wavelength, are alternately stacked. Such multilayer films are described in Japanese Patent Application Publication No. 2004-102200, among others.

[0171] The materials for the high refractive index layer and the low refractive index layer can be the same materials as those used for the high refractive index layer and the low refractive index layer of the in-plane periodic structure layer.

[0172] In a periodic structure layer in the thickness direction, the difference between the refractive index of the high refractive index layer and the refractive index of the low refractive index layer can be appropriately set according to the required in-plane retardation (Δnd), etc. The refractive index difference between the high refractive index layer and the low refractive index layer is preferably 0.1 or more, and more preferably 0.5 or more.

[0173] Such a thickness-direction periodic structure layer can be fabricated using known methods.

[0174] In the polarization interference element of the present invention described above, the rod-shaped liquid crystal layer and / or disc-shaped liquid crystal layer included in the optical anisotropy layer may contain an infrared absorbing dye. By including an infrared absorbing dye in the rod-shaped liquid crystal layer and the disc-shaped liquid crystal layer, the chromatic dispersion of liquid crystals in the liquid crystal layer can be made into a strong forward dispersion. That is, the value of Re(450 / 535) in Figure 2 is increased, and the value of Re(630 / 535) in Figure 3 is decreased. As a result, the required value of Re(535) for the purpose of transmitting or blocking light in multiple wavelength ranges (for example, λ = 450 nm, 535 nm, 630 nm) becomes smaller, and a thinner bandpass filter can be obtained.

[0175] Various infrared absorbing dyes can be used as infrared absorbing dyes, provided they are oriented in the same direction as the liquid crystal compound, thereby reducing the difference in refractive index between the x and y directions. The infrared absorbing dye is not particularly limited as long as it absorbs infrared light (for example, light with a wavelength of 700 to 1000 m). Among these, dichroic dyes are preferred. A dichroic dye is a dye that has different absorbances in the long axis direction and the short axis direction of the molecule. Examples of infrared absorbing dyes include diketopyrrolopyrrole dyes, diimmonium dyes, phthalocyanine dyes, naphthalocyanine dyes, azo dyes, polymethine dyes, anthraquinone dyes, pyryllium dyes, squarylium dyes, triphenylmethane dyes, cyanine dyes, and aminium dyes. Metal complex dyes and boron complex dyes can also be used as infrared absorbing dyes. Regarding infrared absorbing dyes, details are provided in International Publication No. 2019 / 044859.

[0176] There are no restrictions on the amount of infrared absorbing dye added to the rod-shaped liquid crystal layer and / or disc-shaped liquid crystal layer; it can be set appropriately according to the required transmission wavelength range for the bandpass filter.

[0177] Furthermore, in the polarization interference element of the present invention, the rod-shaped liquid crystal layer and / or disc-shaped liquid crystal layer included in the optical anisotropy layer may contain a liquid crystal elastomer. The rod-shaped liquid crystal layer and disc-shaped liquid crystal layer containing the liquid crystal elastomer may be formed using a liquid crystal elastomer, or the liquid crystal layer may be formed using a conventional liquid crystal compound that is not an elastomer and contains a liquid crystal elastomer.

[0178] Thus, by including a liquid crystal elastomer in the rod-shaped and disc-shaped liquid crystal layers, the optical anisotropy layer can be made elastic, and the thickness of the liquid crystal layer can be changed by stretching or contracting the filter in the planar direction. By changing the thickness of the liquid crystal layer, the in-plane retardation of the liquid crystal layer can be changed. As a result, in a bandpass filter, it becomes possible to change the wavelength range of light transmitted through the filter. In other words, by including a liquid crystal elastomer in the rod-shaped and disc-shaped liquid crystal layers, the wavelength range can be varied by stretching and contracting the liquid crystal layer, i.e., the filter, enabling active wavelength control in a bandpass filter.

[0179] There are no restrictions on the liquid crystal elastomer; various known types can be used. As an example, a liquid crystal elastomer prepared from a liquid crystal monomer, a crosslinking agent, and a plasticizer, as described in Japanese Patent Application Publication No. 2020-131638, can be used. This imparts mechanical properties to the liquid crystal elastomer, giving it rubber elasticity and enabling deformation in response to external forces necessary for active wavelength control.

[0180] Furthermore, when forming rod-shaped and disc-shaped liquid crystal layers with ordinary liquid crystal compounds other than elastomers, and then adding liquid crystal elastomers to impart elasticity, there are no restrictions on the amount of liquid crystal elastomer added. It can be set appropriately according to the required elasticity, i.e., the control range of the transmission wavelength range.

[0181] The optical filter of the present invention has a first polarizer, a polarization interference element of the present invention (the first to eighth embodiments), and a second polarizer arranged in this order. In the optical filter of the present invention shown in Figures 5, 6, 7, 9, 10, 11, 12, and 13, the first polarizer 12 and the second polarizer 14, which sandwich the polarization interference element of the present invention in the thickness direction, are arranged with their transmission axes orthogonal (crossed nicols). However, the optical filter of the present invention using the liquid crystal polarization interference element of the present invention is not limited to this, and various configurations are available. For example, the polarization interference element of the present invention (the second, fourth, sixth, and eighth embodiments) can also be configured such that the angle of the in-plane slow axis with respect to the reference line increases sequentially in the alternating stacking direction of the first liquid crystal layer and the second liquid crystal layer. When using such a polarization interference element of the present invention, it is preferable that the polarizers sandwiching the polarization interference element of the present invention in the thickness direction have their transmission axes parallel to each other.

[0182] When using the optical filter of the present invention as a bandpass filter, it is preferable to set the transmission axes of the first and second polarizers to an appropriate angle in order to obtain the desired bandpass characteristics. In particular, when using the optical filter of the present invention as a bandpass filter, by appropriately adjusting the angle of the transmission axes of the polarizers that sandwich the polarization interference element of the present invention in the thickness direction, it is possible to reduce the size of the side lobes generated on both sides of the main bandpass wavelength (long wave side and short wave side), and to make the size of the side lobes on the long wave side and short wave side equal.

[0183] In the optical filter of the present invention, a phase difference layer may be provided between the first polarizer and the polarization interference element, and between the second polarizer and the polarization interference element, at least one of the two. That is, in the optical filter of the present invention, a phase difference layer can be provided on one or both sides between the polarization interference element and the polarizer. This phase difference layer has the effect of maintaining the orthogonal relationship of the polarization direction by the linear polarizers arranged in crossed nicols, not only in the front but also in the oblique direction off-axis of the polarizers. As a result, when the optical filter of the present invention is used as a bandpass filter, good bandpass characteristics similar to those in the front can be obtained even at oblique angles. Preferably, the slow axis in the plane of the phase difference layer is parallel to the absorption axis of either the first polarizer or the second polarizer arranged in crossed nicols. This makes it possible to compensate the polarization state so as to maintain the orthogonal relationship of the polarization direction in the oblique direction without affecting the front. Examples of the phase difference layer include a positive C plate by vertical orientation of rod-shaped liquid crystals and a positive A plate by horizontal orientation of rod-shaped liquid crystals, or a negative C plate by disc-shaped liquid crystals and a negative A plate by disc-shaped liquid crystals, or a combination thereof. Furthermore, a B-plate (with an Nz factor of 0.1 to 0.9), which is a biaxial refractive index material, can also be used as the phase difference layer.

[0184] Such liquid crystal polarization interference elements and optical filters of the present invention can be used at any wavelength. That is, the optical filters of the present invention can be used for any electromagnetic wave, including ultraviolet light, visible light, infrared light, terahertz waves, and millimeter waves.

[0185] The optical system of the present invention comprises a light source, an optical filter of the present invention, and a light receiving unit. In such an optical system of the present invention, for example, by using the optical filter of the present invention as a bandpass filter, an optical system with low light receiving loss can be realized.

[0186] Furthermore, in the optical system of the present invention, there are no restrictions on the light source, and various known light sources (light sources, light-emitting elements) that can emit light of a desired wavelength can be used, such as LEDs (Light Emitting Diodes), organic EL (OLED organic electro-luminescence) elements, fluorescent lamps, halogen lamps, laser light sources, and plasma light sources. Also, in the optical system of the present invention, there are no restrictions on the light-receiving unit, and various known light-receiving units (light-receiving elements, image sensors) that can receive light of a target wavelength and measure it can be used, such as CCD sensors, photomultipliers, CMOS sensors, and photodiodes.

[0187] Figure 14 conceptually shows an example of combining a focusing lens with the optical system of the present invention. The optical system shown in Figure 14 includes a light source 74, a focusing lens 76, an optical filter 78 of the present invention, and a light receiving unit 80. Various known focusing lenses can be used. In this optical system, divergent light emitted from the light source 74 is focused by the focusing lens 76, received by the light receiving unit 80, and photometric measurement is performed. In such an optical system, the optical filter 78 (bandpass filter) of the present invention is placed in the divergent part of the light (between the light source 74 and the focusing lens 76) or the focusing part (between the focusing lens 76 and the light receiving unit 80). In the illustrated example, the optical filter 78 of the present invention is placed in the focusing part of the light. As described above, the optical filter of the present invention exhibits the same wavelength bandpass performance for both light in the forward direction and light in the oblique direction, so that light of a desired wavelength over a wide angular range can be focused on the light receiving unit. The optical system of the present invention enables an optical system that achieves high light reception efficiency and low light reception loss. The optical system of the present invention, which uses a condensing lens in this way, can be used, for example, in an imaging system. In this imaging system, a system with high light reception efficiency can be realized when the condensing lens collects light from various directions from the light source unit 74, which is the object to be imaged, and concentrates it at high intensity on the light receiving unit 80, which is the image sensor. Furthermore, because the optical filter of the present invention has bandpass performance over a wide angle, a thin and compact optical system can be realized by using a condensing lens with a high numerical aperture. Moreover, the optical system of the present invention can also be used in a system that utilizes optical fibers, for example. In this case, at the connection point between optical fibers, the output terminal of one optical fiber is made into the light source unit 74, and the input terminal of the other optical fiber is made into the light receiving unit 80, and the condensing lens 76 and optical filter 78 are placed between them to configure a system that achieves high efficiency in the same way as described above. Specifically, the light from the output terminal of the optical fiber, and / or the light collected by the lens, both contain light from various angles. Therefore, the optical system (optical filter) of the present invention can be used to efficiently select only the desired wavelengths of light from any angle and integrate them into the sensor.

[0188] Figure 15 conceptually shows an example of combining a beam splitter with the optical system of the present invention. The optical system shown in Figure 15 includes a light source 74, a beam splitter 82, an optical filter 78 of the present invention, and a light receiving unit 80. Various known beam splitters can be used. In this optical system, the straight-traveling light emitted from the light source 74 is split into multiple (two in the figure) different angular directions by the beam splitter 82, and the split light is received by two corresponding light receiving units 80 for photometry. In such an optical system, the optical filter 78 (bandpass filter) of the present invention is placed in the region after the light has been split (between the beam splitter 82 and the light receiving unit 80). The optical filter 78 of the present invention exhibits bandpass performance of the same wavelength with a single optical filter 78 for light after splitting that travels in different angular directions. As a result, high light reception efficiency can be obtained in any of the multiple light receiving units 80 that receive the light after splitting. The optical system of the present invention, which uses the beam splitter 82 in this way, can be applied to various optical systems such as sensors and lasers. Furthermore, in systems using optical fibers, the system of the present invention can be used when a straight-traveling light ray is split at different angles by the beam splitter, and then the connection destination is switched according to the destination of the optical signal.

[0189] Figure 16 conceptually shows an example of combining a light guide element (light guide plate) with the optical system of the present invention. The optical system shown in Figure 16 includes a light source unit 74, a light guide element 84, an optical filter 78 of the present invention, and a light receiving unit 80. Various known light guide elements can be used. In this optical system, light emitted from the light source unit 74 in various angular directions is incident on one end of the light guide element 84, and the light that propagates while mixing inside the light guide element 84 is emitted from the other end of the light guide element 84, received by the light receiving unit 80, and photometric measurement is performed. In such an optical system, the optical filter 78 (bandpass filter) of the present invention is placed at the emission position of the propagating light from the light guide element 84. The optical filter 78 of the present invention exhibits the same bandpass performance for the same wavelength to propagating light traveling in different angular directions. As a result, high light reception efficiency can be obtained for propagating light emitted from the light guide element. The optical system of the present invention, which uses such a light guide element, can be used in sensing systems using light guide elements, display systems such as augmented reality (AR), and optical communication systems using waveguides.

[0190] In the optical system of the present invention, as conceptually shown in Figure 17, the optical filter 78 and the light-receiving unit 80 may be arranged facing each other (with the opposing surfaces of the optical filter and the light-receiving unit aligned). Furthermore, on the surfaces facing each other, the surfaces of the optical filter 78 and the light-receiving unit 80 may be aligned, or the surface of the light-receiving unit 80 may be larger than the surface of the optical filter 78; however, it is preferable that the opposing surfaces of the optical filter 78 and the light-receiving unit 80 are aligned. Here, "the opposing surfaces are aligned" means that, when viewed from the direction of the light source unit 74, the opposing surfaces of the optical filter 78 and the light-receiving unit 80 completely overlap. Also, the light-receiving unit 80 may be larger than the optical filter 78. In the optical system shown in Figure 17, divergent light emitted from the light source unit 74 reaches the optical filter 78 (bandpass filter) of the present invention from various angular directions. Here, the optical filter 78 of the present invention, with its wide-angle bandpass performance, can capture light of a desired wavelength at a wide angle to the light-receiving section facing it. As a result, high light-receiving efficiency can be obtained in the light-receiving section 80. In an optical system in which the light source section 74 emits divergent light, using the optical system of the present invention that utilizes the optical filter 78 of the present invention allows the optical filter 78 to exhibit the desired bandpass performance at a wide angle, which is effective in making the system thinner.

[0191] Furthermore, in the optical system of the present invention in which the optical filter and the light receiving unit face each other, a plurality of optical filters with different central wavelengths of transmitted light may be arranged. An example of this is shown in Figure 18. In the optical system shown in Figure 18, the optical filter (bandpass filter) of the present invention can obtain high light reception efficiency with wide-angle bandpass performance for divergent light emitted from the light source unit 74, just as in the example shown in Figure 17. Here, in the example shown in Figure 18, there are optical filters 78a and 78b of the present invention with different central wavelengths of transmitted light, and a plurality of light receiving units 80a and 80b corresponding to each optical filter. The optical system shown in Figure 18 can thus simultaneously receive light of different wavelengths. Note that in Figure 18, since a plurality of optical filters with different central wavelengths of transmitted light are used, it is preferable that the positions of the faces of the optical filter 78a and the light receiving unit 80a, and the faces of the optical filter 78b and the light receiving unit 80b are aligned. "The positions of the facing faces are aligned" is the same as above. The optical system of the present invention shown in Figure 18 can specifically be used as a multispectral sensor. For example, the optical system of the present invention makes it possible to realize an optical system that senses diffuse light from the skin containing human health information at different wavelengths with high light reception efficiency using a thin optical system. In the example shown in Figure 18, two optical filters with different central wavelengths of transmitted light are used, but the optical system of the present invention is not limited to this. For example, the optical system of the present invention makes it possible to realize a thin and compact optical system that can efficiently measure multispectral, hyperspectral, etc., by increasing the number of optical filters with different central wavelengths of transmitted light, i.e., the number of wavelengths to be measured. Furthermore, the optical filter of the present invention may be a single optical filter that can handle multiple wavelengths by patterning multiple liquid crystal polarization interference elements with different central wavelengths of transmission in the plane. In that case, patterning is performed so that the retardation value differs in location, but this can be achieved by changing either the film thickness of the liquid crystal layer or the birefringence in the plane. The patterning may be discrete or continuous.

[0192] Although the polarization interference element, optical filter, and optical system of the present invention have been described in detail above, the present invention is not limited to the examples described above, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0193] The features of the present invention will be further described in detail below with reference to examples. The materials, reagents, amounts used, amounts of substance, ratios, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0194] [Comparative Example 1] (Formation of Alignment Film) A glass substrate was prepared as a support. The following alignment film forming coating solution was applied to the support by spin coating. The support on which the alignment film forming coating solution was applied was dried on a 60°C hot plate for 60 seconds to form an alignment film P-1, which is a photo-alignment film.

[0195] Coating solution for forming an alignment film -------------------

[0196] Material for photo alignment

[0197]

[0198] (Exposure of the alignment film) Next, using an ultraviolet exposure apparatus, the alignment film P-1 was irradiated with linearly polarized ultraviolet light produced by a wire grid polarizer (Moxtek ProFlux PPL02) set up so that the angle of the absorption axis was φ1 (=0°). The ultraviolet light intensity was 4.5 mW / cm². 2 The cumulative irradiation dose was 300 mJ / cm². 2 This was determined. The angle of the absorption axis is the angle with respect to the longitudinal direction of the substrate, with counterclockwise rotation being considered positive.

[0199] (Formation of a disc-shaped liquid crystal layer) The following composition D-1 was prepared as a liquid crystal composition for forming a disc-shaped liquid crystal layer. Composition D-1 -------------------------------------------------- ・Disc-shaped liquid crystal compound L-1 80.00 parts by mass ・Disc-shaped liquid crystal compound L-2 20.00 parts by mass ・Polymerization initiator (BASF, Irgacure® 907) 5.00 parts by mass ・Megafac F444 (DIC) 0.50 parts by mass ・Methyl ethyl ketone 300.00 parts by mass --------------------------------------------------

[0200] Disc-shaped liquid crystal compound L-1

[0201]

[0202] Disc-shaped liquid crystal compound L-2

[0203]

[0204] The disc-shaped liquid crystal layer was formed by coating composition D-1 onto alignment film P-1. Specifically, composition D-1 was first coated onto alignment film P-1, then heated, and then ultraviolet curing was performed to form a disc-shaped liquid crystal layer (thickness 0.86 μm), which is the liquid crystal immobilization layer. More specifically, the disc-shaped liquid crystal layer was formed by coating composition D-1 onto alignment film P-1 to obtain a coating film, heating this coating film to 80°C on a hot plate, and then, at 80°C, using a high-pressure mercury lamp, ultraviolet light with a wavelength of 365 nm was applied at 300 mJ / cm² under a nitrogen atmosphere. 2 The disc-shaped liquid crystal compound was formed by irradiating the coating film with a specified irradiation dose to fix its orientation.

[0205] (Formation of rod-shaped liquid crystal layer) Composition B-1 was prepared as a liquid crystal composition for forming a rod-shaped liquid crystal layer.

[0206] Composition B-1 -------------------------------------------------- • Rod-shaped liquid crystal compound L-3 100.00 parts by mass • Polymerization initiator (BASF, Irgacure® 907) 3.00 parts by mass • Photosensitizer (Nippon Kayaku, KAYACURE DETX-S) 1.00 parts by mass • Leveling agent T-1 0.08 parts by mass • Methyl ethyl ketone 2000.00 parts by mass --------------------------------------------------

[0207] Rod-shaped liquid crystal compound L-3

[0208]

[0209] Leveling agent T-1

[0210]

[0211] The prepared composition B-1 was applied onto the disc-shaped liquid crystal layer prepared above, then heated, and subsequently cured with ultraviolet light to form a rod-shaped liquid crystal layer (thickness 0.86 μm) which is a liquid crystal immobilization layer containing a rod-shaped liquid crystal compound.

[0212] Hereinafter, the liquid crystal layer having this disc-shaped liquid crystal layer and rod-shaped liquid crystal layer will also be referred to as a "unit layer" for convenience. The thickness of the fabricated unit layer 1 was confirmed by cutting and observing it from the cross-sectional direction with an SEM. Furthermore, by inputting the average refractive index ((nx + ny + nz) / 3) and film thickness (d (μm)) using AxoScan (manufactured by Axometrics), it was confirmed that it has the following optical properties. The refractive indices nx, ny, and nz were measured using an Abbe refractometer (NAR-4T, manufactured by Atago Co., Ltd.) with a sodium lamp (λ = 589 nm) as the light source. The wavelength dependence was measured using a multi-wavelength Abbe refractometer DR-M2 (manufactured by Atago Co., Ltd.) in combination with an interference filter. Unit layer 1 Thickness: 1.7 μm Re(535): 267.5 nm Re(450 / 535): 1.07 Re(630 / 535): 0.94 where Re(535) represents the in-plane retardation at a wavelength of 535 nm, Re(450 / 535) represents the ratio of the in-plane retardation at a wavelength of 450 nm to the in-plane retardation at a wavelength of 535 nm, and Re(630 / 535) represents the ratio of the in-plane retardation at a wavelength of 630 nm to the in-plane retardation at a wavelength of 535 nm.

[0213] The formed unit layer 1 was peeled off from the alignment film and bonded using an adhesive (SK Dyne 2057, manufactured by Soken Chemical Co., Ltd., 20 μm thick), and 24 layers were stacked to fabricate a polarization interference element 1. In this process, the in-plane slow axis of the rod-shaped liquid crystal layer of the odd-numbered layers (first liquid crystal layer) of the stacked unit layer 1 was made to intersect with the in-plane slow axis of the rod-shaped liquid crystal layer of the even-numbered layers (second liquid crystal layer). Specifically, the angle that bisects the intersection angle formed by the in-plane slow axis of both sides was used as the reference (reference line), with counterclockwise rotation being positive (+) and clockwise rotation being negative (-), and the 24 units of unit layer 1 were stacked and bonded so that the angle θ of the in-plane slow axis of the rod-shaped liquid crystal layer of the odd-numbered layers was 1.875° and the angle θ of the in-plane slow axis of the rod-shaped liquid crystal layer of the even-numbered layers was -1.875°. In other words, the fabricated polarization interference element 1 has 12 sets of liquid crystal layer assemblies, each consisting of a first liquid crystal layer and a second liquid crystal layer. As described above, when a liquid crystal layer is formed on top of a liquid crystal layer by a coating method, the orientation of the liquid crystal compound in the upper liquid crystal layer is the same as the orientation of the liquid crystal compound in the lower layer. Therefore, in this example, the angle θ of the in-plane slow axis for the rod-shaped liquid crystal layer is 1.875° for odd-numbered layers and -1.875° for even-numbered layers, and the angle θ of the in-plane slow axis for the disc-shaped liquid crystal layer is 1.875° for odd-numbered layers and -1.875° for even-numbered layers.

[0214] Polarization interference element 1 acts as a λ / 2 phase difference plate for light with a wavelength of 535 nm. In polarization interference element 1, the first liquid crystal layer corresponds to the first optical anisotropy layer, and the second liquid crystal layer corresponds to the second optical anisotropy layer. Neither the first nor the second optical anisotropy layer satisfies equation (1).

[0215] Furthermore, in order to obtain polarization interference elements corresponding to light of different wavelengths, unit layers 2 and 3 were fabricated by changing the coating thickness of the disc-shaped liquid crystal and rod-shaped liquid crystal layers using the same method as described above. The fabricated unit layers 2 and 3 were measured using AxoScan (manufactured by Axometrics Corporation) in the same manner as described above, and it was confirmed that they have the following optical properties. Unit layer 2 Thickness: 1.33 μm Re(535): 210 nm Re(450 / 535): 1.07 Re(630 / 535): 0.94 Unit layer 3 Thickness: 3.38 μm Re(535): 335 nm Re(450 / 535): 1.07 Re(630 / 535): 0.94

[0216] The formed unit layers 2 and 3 were stacked 24 times each using the same method as for unit layer 1 to fabricate polarization interference elements 2 and 3.

[0217] Polarizing interference element 2 acts as a λ / 2 phase difference plate for light with a wavelength of 450 nm, and polarizing interference element 3 acts as a λ / 2 phase difference plate for light with a wavelength of 630 nm. In polarizing interference element 2, the unit layer 2 corresponds to an optically anisotropic layer, and the optically anisotropic layer does not satisfy equation (1). Similarly, in polarizing interference element 3, the unit layer 3 corresponds to an optically anisotropic layer, and the optically anisotropic layer does not satisfy equation (1).

[0218] A bandpass filter was fabricated by placing the fabricated polarization interference elements 1 to 3 between polarizers arranged in a crossed nicol configuration. The bandpass filter was fabricated by aligning the line that bisects the intersection angle between the in-plane slow axes of the odd-numbered and even-numbered layers when the laminate was stacked with the transmission axis of one of the polarizers. For the fabricated bandpass filter, the thickness, and the polarization transmittance, full width at half maximum, and side lobes at wavelengths of 450 nm, 535 nm, and 630 nm were measured using a Topcon Techno House SR-3 spectroradiometer. Polarization transmittance is calculated as the ratio of light transmitted through one polarizer (incident light side) to light transmitted through the other polarizer (outgoing light side) in the bandpass filter.

[0219] As a result, the fabricated bandpass filter had a thickness of 1619 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 87%, 88%, and 88%, respectively. The full width at half maximum at each wavelength was 20 nm, 28 nm, and 36 nm, and the side lobes at each wavelength were 17%, 28%, and 25%. The size of the side lobes is the ratio of the transmittance of the side lobes to the transmittance of the center wavelength.

[0220] [Example 1] Composition B-2 was prepared as a liquid crystal composition for forming a rod-shaped liquid crystal layer. Composition B-2 -------------------------------------------------- Rod-shaped liquid crystal compound L-4 65.00 parts by mass Rod-shaped liquid crystal compound L-3 35.00 parts by mass Polymerization initiator I-1 0.50 parts by mass Leveling agent T-2 0.06 parts by mass Cyclopentanone 231.00 parts by mass Methyl ethyl ketone 69.00 parts by mass --------------------------------------------------

[0221] Rod-shaped liquid crystal compound L-4

[0222]

[0223] Polymerization initiator I-1

[0224]

[0225] Leveling agent T-2

[0226]

[0227] After applying the prepared composition B-2 to an alignment film P-1 similar to that in Comparative Example 1, the film was heated and then cured with ultraviolet light to form a rod-shaped liquid crystal layer (30 μm thick), which is a liquid crystal immobilization layer containing rod-shaped liquid crystal compounds. Hereinafter, this rod-shaped liquid crystal layer will be referred to as unit layer 4.

[0228] The fabricated unit layer 4 was measured using AxoScan (manufactured by Axometrics) in the same manner as described above, and the following optical properties were confirmed. Unit layer 4 Thickness: 60 μm Re(535): 3478 nm Re(450 / 535): 0.97 Re(630 / 535): 1.00

[0229] The formed unit layer 4 was peeled off from the alignment film to form a polarization interference element 4. In the polarization interference element 4, the unit layer 4 corresponds to the optical anisotropy layer, and the optical anisotropy layer satisfies equation (1). Furthermore, when the values ​​of the left and right sides of equation (2) were calculated, the left side of equation (2) was found to be 0.83 and the right side was found to be 1.20, thus satisfying equation (2). Furthermore, when the values ​​of the left and right sides of equation (3) were calculated, the left side of equation (3) was found to be 0.71 and the right side was found to be 1.13, thus satisfying equation (3).

[0230] A bandpass filter was fabricated by placing the fabricated polarization interference element 4 between polarizers arranged in a crossed nicol configuration. In this process, the lagging axis of the polarization interference element 4 was fabricated so that the angle it made with the transmission axis of one of the polarizers was 45°. The thickness, polarization transmittance, full width at half maximum, and side lobes of the fabricated bandpass filter were measured in the same manner as in Comparative Example 1.

[0231] As a result, the thickness of the fabricated bandpass filter was 104 μm, the polarization transmittance at wavelengths of 450 nm, 535 nm, and 630 nm was 100%, 100%, and 100%, the full width at half maximum at each wavelength was 50 nm, 45 nm, and 55 nm, and the side lobes at each wavelength were 0%, 0%, and 0%. Thus, compared to the bandpass filter of Comparative Example 1, which had a thickness of 1619 μm, the bandpass filter of Example 1, which includes the polarization interference element of the present invention fabricated by adjusting the optical properties of the optical anisotropy layer to within the optical range defined in the present invention, can significantly reduce its thickness. Furthermore, while the side lobes of Comparative Example 1 were 17-25%, the side lobes of Example 1 were 0%, confirming a significant reduction effect.

[0232] [Example 2] Four unit layers 4 prepared in Example 1 were made, peeled off from the alignment film, and bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical Co., Ltd., 20 μm thick) to create a polarization interference element 5 by stacking the four layers. In this process, the in-plane slow axis of the odd-numbered layers (first liquid crystal layer) and the in-plane slow axis of the even-numbered layers (second liquid crystal layer) of the stacked unit layers 4 were made to intersect. Specifically, the angle that bisects the intersection angle formed by the in-plane slow axes of both sides was used as the reference (reference line), with counterclockwise being positive (+) and clockwise being negative (-), and the four unit layers 4 were stacked and bonded so that the angle θ of the in-plane slow axis of the odd-numbered layers was 11.25° and the angle θ of the in-plane slow axis of the even-numbered layers was -11.25°. In other words, the fabricated polarization interference element 5 has two sets of liquid crystal layer assemblies, each consisting of a first liquid crystal layer and a second liquid crystal layer.

[0233] In the polarization interference element 5, the first liquid crystal layer corresponds to the first optical anisotropy layer, and the second liquid crystal layer corresponds to the second optical anisotropy layer. The first optical anisotropy layer and the second optical anisotropy layer satisfy equations (1) to (3).

[0234] A bandpass filter was fabricated by placing the fabricated polarization interference element 5 between polarizers arranged in crossed nicols. The bandpass filter was fabricated by aligning the transmission axis of one of the polarizers with the line that bisects the intersection angle between the in-plane slow axes of the odd-numbered and even-numbered layers when the laminate was stacked. For the fabricated bandpass filter, the thickness, polarization transmittance and full width at half maximum at wavelengths of 450 nm, 535 nm, and 630 nm, as well as the side lobes, were measured using the Topcon Techno House SR-3 spectroradiometer.

[0235] As a result, the fabricated bandpass filter had a thickness of 342 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 98%, 98%, and 98%, respectively. The full width at half maximum at each wavelength was 18 nm, 17 nm, and 21 nm, and the side lobes at each wavelength were 5%, 5%, and 5%.

[0236] [Example 3] Composition B-3 was prepared as a liquid crystal composition for forming a rod-shaped liquid crystal layer. Composition B-3 -------------------------------------------------- ・Rod-shaped liquid crystal compound L-4 45.36 parts by mass ・Rod-shaped liquid crystal compound L-5 21.84 parts by mass ・Rod-shaped liquid crystal compound L-6 20.00 parts by mass ・Rod-shaped liquid crystal compound L-3 7.80 parts by mass ・Rod-shaped liquid crystal compound L-7 5.00 parts by mass ・The above polymerization initiator I-1 0.50 parts by mass ・Leveling agent T-2 0.06 parts by mass ・Cyclopentanone 180.73 parts by mass ・Methyl ethyl ketone 53.98 parts by mass --------------------------------------------------

[0237] Rod-shaped liquid crystal compound L-5

[0238]

[0239] Rod-shaped liquid crystal compound L-6

[0240]

[0241] Rod-shaped liquid crystal compound L-7

[0242]

[0243] A disc-shaped liquid crystal layer (thickness 11 μm) was prepared using the same procedure as in Comparative Example 1, but with only the coating thickness of the disc-shaped liquid crystal layer changed. The prepared composition B-3 was applied onto this disc-shaped liquid crystal layer, then heated, and subsequently cured with ultraviolet light to form a rod-shaped liquid crystal layer (thickness 36 μm), which is a liquid crystal immobilization layer containing a rod-shaped liquid crystal compound. Hereinafter, this laminate of the disc-shaped liquid crystal layer and the rod-shaped liquid crystal layer will be referred to as unit layer 5.

[0244] The fabricated unit layer 5 was measured using AxoScan (manufactured by Axometrics) in the same manner as described above, and the following optical properties were confirmed: Unit layer 5 Thickness: 47 μm Re(535): 3478 nm Re(450 / 535): 0.97 Re(630 / 535): 1.00

[0245] The formed unit layer 5 was peeled off from the alignment film to form a polarization interference element 6.

[0246] In the polarization interference element 6, the unit layer 5 corresponds to the optical anisotropy layer. The optical anisotropy layer satisfies equations (1) to (3).

[0247] A bandpass filter was fabricated by placing the fabricated polarization interference element 6 between polarizers arranged in a crossed nicol configuration. In this process, the lagging axis of the polarization interference element 6 was fabricated so that the angle it made with the transmission axis of one of the polarizers was 45°. The thickness, polarization transmittance, full width at half maximum, and side lobes of the fabricated bandpass filter were measured in the same manner as in Comparative Example 1.

[0248] As a result, the fabricated bandpass filter had a thickness of 92 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 100%, 100%, and 100%, respectively. The full width at half maximum at each wavelength was 50 nm, 45 nm, and 55 nm, and the side lobes at each wavelength were 0%, 0%, and 0%.

[0249] [Example 4] Four unit layers 5 prepared in Example 3 were made, peeled off from the alignment film, and bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical Co., Ltd., 20 μm thick) to create a polarization interference element 7 by stacking four layers. In this process, the in-plane slow axis of the odd-numbered layers (first liquid crystal layer) and the in-plane slow axis of the even-numbered layers (second liquid crystal layer) of the stacked unit layers 5 were made to intersect. Specifically, the angle that bisects the intersection angle formed by the in-plane slow axes of both sides was used as the reference (reference line), with counterclockwise being positive (+) and clockwise being negative (-), and the four unit layers 5 were stacked and bonded so that the angle θ of the in-plane slow axis of the odd-numbered layers was 11.25° and the angle θ of the in-plane slow axis of the even-numbered layers was -11.25°. In other words, the fabricated polarization interference element 7 has two sets of liquid crystal layer assemblies, each consisting of a first liquid crystal layer and a second liquid crystal layer.

[0250] In the polarization interference element 7, the first liquid crystal layer corresponds to the first optical anisotropy layer, and the second liquid crystal layer corresponds to the second optical anisotropy layer. The first optical anisotropy layer and the second optical anisotropy layer satisfy equations (1) to (3).

[0251] A bandpass filter was fabricated by placing the fabricated polarization interference element 7 between polarizers arranged in crossed nicols. The bandpass filter was fabricated by aligning the transmission axis of one of the polarizers with the line that bisects the intersection angle between the in-plane slow axes of the odd-numbered and even-numbered layers when the laminate is stacked. The thickness of the fabricated bandpass filter, as well as the polarization transmittance, full width at half maximum, and side lobes at wavelengths of 450 nm, 535 nm, and 630 nm, were measured using the Topcon Techno House SR-3 spectroradiometer.

[0252] As a result, the fabricated bandpass filter had a thickness of 293 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 98%, 98%, and 98%, respectively. The full width at half maximum at each wavelength was 18 nm, 17 nm, and 21 nm, and the side lobes at each wavelength were 5%, 5%, and 5%.

[0253] [Example 5] Composition B-4 was prepared as a liquid crystal composition for forming a rod-shaped liquid crystal layer. Composition B-4 -------------------------------------------------- ・Rod-shaped liquid crystal compound L-3 100.00 parts by mass ・Ethylene oxide-modified trimethylolpropane triacrylate (V#360, manufactured by Osaka Organic Chemical Co., Ltd.) 8.00 parts by mass ・Polymerization initiator (Irgacure 127, manufactured by BASF) 2.00 parts by mass ・Polymerization initiator (Irgacure OXE01, manufactured by BASF) 4.00 parts by mass ・The following onium salt compound 2.00 parts by mass ・Megafac F444 (manufactured by DIC) 0.30 parts by mass ・Leveling agent T-3 0.40 parts by mass ・Substrate-side biased polymer P-1 5.00 parts by mass ・Toluene 621.00 parts by mass ・Methyl ethyl ketone 69.00 parts by mass --------------------------------------------------

[0254] Onium salt compounds

[0255]

[0256] Leveling agent T-3

[0257]

[0258] Base material side polymer P-1

[0259]

[0260] Composition B-4 was applied to a rod-shaped liquid crystal layer (30 μm thick) prepared using the same procedure as in Example 1. After heating and then UV curing, a rod-shaped liquid crystal layer (15 μm thick), which is a liquid crystal immobilization layer containing rod-shaped liquid crystal compounds, was formed. Hereinafter, this laminate of rod-shaped liquid crystal layers will be referred to as unit layer 6. The rod-shaped liquid crystal layer prepared with composition B-4 is a liquid crystal layer in which rod-shaped liquid crystal compounds are vertically oriented.

[0261] The fabricated unit layer 6 was measured using AxoScan (manufactured by Axometrics) in the same manner as described above, and the following optical properties were confirmed: Unit layer 6 Thickness: 45 μm Re(535): 3478 nm Re(450 / 535): 0.97 Re(630 / 535): 1.00

[0262] The formed unit layer 6 was peeled off from the alignment film to form a polarization interference element 8.

[0263] In the polarization interference element 8, the unit layer 6 corresponds to the optical anisotropy layer. The optical anisotropy layer satisfies equations (1) to (3).

[0264] A bandpass filter was fabricated by placing the fabricated polarization interference element 8 between polarizers arranged in crossed nicols. In this process, the slow axis of the polarization interference element 8 was fabricated so that the angle it made with the transmission axis of one of the polarizers was 45°. The thickness, polarization transmittance, full width at half maximum, and side lobes of the fabricated bandpass filter were measured in the same manner as in Comparative Example 1.

[0265] As a result, the fabricated bandpass filter had a thickness of 134 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 100%, 100%, and 100%, respectively. The full width at half maximum at each wavelength was 50 nm, 45 nm, and 55 nm, and the side lobes at each wavelength were 0%, 0%, and 0%.

[0266] [Example 6] Four unit layers 6 prepared in Example 5 were made, peeled off from the alignment film, and bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical Co., Ltd., 20 μm thick) to create a polarization interference element 9 by stacking the four layers. In this process, the in-plane slow axis of the odd-numbered layers (first liquid crystal layer) and the in-plane slow axis of the even-numbered layers (second liquid crystal layer) of the stacked unit layers 6 were made to intersect. Specifically, the angle that bisects the intersection angle formed by the in-plane slow axes of both sides was used as the reference (reference line), with counterclockwise being positive (+) and clockwise being negative (-), and the four unit layers 6 were stacked and bonded so that the angle θ of the in-plane slow axis of the odd-numbered layers was 11.25° and the angle θ of the in-plane slow axis of the even-numbered layers was -11.25°. In other words, the fabricated polarization interference element 9 has two sets of liquid crystal layer assemblies, each consisting of a first liquid crystal layer and a second liquid crystal layer.

[0267] In the polarization interference element 9, the first liquid crystal layer corresponds to the first optical anisotropy layer, and the second liquid crystal layer corresponds to the second optical anisotropy layer. The first optical anisotropy layer and the second optical anisotropy layer satisfy equations (1) to (3).

[0268] A bandpass filter was fabricated by placing the fabricated polarization interference element 9 between polarizers arranged in crossed nicols. The bandpass filter was fabricated by aligning the transmission axis of one of the polarizers with the line that bisects the intersection angle between the in-plane slow axes of the odd-numbered and even-numbered layers when the laminate was stacked. The thickness of the fabricated bandpass filter, as well as the polarization transmittance, full width at half maximum, and side lobes at wavelengths of 450 nm, 535 nm, and 630 nm, were measured using the Topcon Techno House SR-3 spectroradiometer.

[0269] As a result, the fabricated bandpass filter had a thickness of 461 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 98%, 98%, and 98%, respectively. The full width at half maximum at each wavelength was 18 nm, 17 nm, and 21 nm, and the side lobes at each wavelength were 5%, 5%, and 5%.

[0270] [Example 7] Composition D-2 was prepared as a liquid crystal composition for forming a disc-shaped liquid crystal layer. Composition D-2 -------------------------------------------------- ・Disc-shaped liquid crystal compound L-1 80.00 parts by mass ・Disc-shaped liquid crystal compound L-2 20.00 parts by mass ・Ethylene oxide modified trimethylolpropane triacrylate (V#360, manufactured by Osaka Organic Chemical Co., Ltd.) 12.00 parts by mass ・Polymerization initiator S-1 (oxime type) 3.00 parts by mass ・Leveling agent T-4 0.60 parts by mass ・Substrate-side biased polymer P-2 0.60 parts by mass ・Methyl isobutyl ketone 360.00 parts by mass ・Ethyl propionate 90.00 parts by mass ・Methyl ethyl ketone 25.00 parts by mass --------------------------------------------------

[0271] Polymerization initiator S-1

[0272]

[0273] Leveling agent T-4

[0274]

[0275] Base material side unevenly distributed polymer P-2 (weight average molecular weight: 7800)

[0276]

[0277] A disc-shaped liquid crystal layer (22 μm thick) was prepared using the same procedure as in Comparative Example 1, but with only the coating thickness of the disc-shaped liquid crystal layer changed. The prepared composition D-2 was applied onto this disc-shaped liquid crystal layer, then heated, and subsequently cured with ultraviolet light to form a disc-shaped liquid crystal layer (11 μm thick) which is a liquid crystal immobilization layer containing the disc-shaped liquid crystal compound. Hereinafter, this laminate of disc-shaped liquid crystal layers will be referred to as unit layer 7. The disc-shaped liquid crystal layer prepared with composition D-4 is a liquid crystal layer in which the disc-shaped liquid crystal compound is horizontally oriented.

[0278] The fabricated unit layer 7 was measured using AxoScan (manufactured by Axometrics) in the same manner as described above, and the following optical properties were confirmed. Unit layer 7 Thickness: 33 μm Re(535): 3478 nm Re(450 / 535): 1.08 Re(630 / 535): 0.94

[0279] The formed unit layer 7 was peeled off from the alignment film to form a polarization interference element 10.

[0280] In the polarization interference element 10, the unit layer 7 corresponds to the optical anisotropy layer. The optical anisotropy layer satisfies equations (1) to (3).

[0281] A bandpass filter was fabricated by placing the fabricated polarization interference element 10 between polarizers arranged in a crossed nicol configuration. In this process, the slow axis of the polarization interference element 10 was fabricated so that the angle it made with the transmission axis of one of the polarizers was 45°. The thickness, polarization transmittance, full width at half maximum, and side lobes of the fabricated bandpass filter were measured in the same manner as in Comparative Example 1.

[0282] As a result, the fabricated bandpass filter had a thickness of 78 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 100%, 100%, and 100%, respectively. The full width at half maximum at each wavelength was 50 nm, 45 nm, and 55 nm, and the side lobes at each wavelength were 0%, 0%, and 0%.

[0283] [Example 8] Four unit layers 7 prepared in Example 7 were made, peeled off from the alignment film, and bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical Co., Ltd., 20 μm thick) to create a polarization interference element 11 by stacking the four layers. In this process, the in-plane slow axis of the odd-numbered layers (first liquid crystal layer) and the in-plane slow axis of the even-numbered layers (second liquid crystal layer) of the stacked unit layers 7 were made to intersect. Specifically, the angle that bisects the intersection angle formed by the in-plane slow axes of both sides was used as the reference (reference line), with counterclockwise being positive (+) and clockwise being negative (-), and the four unit layers 7 were stacked and bonded so that the angle θ of the in-plane slow axis of the odd-numbered layers was 11.25° and the angle θ of the in-plane slow axis of the even-numbered layers was -11.25°. In other words, the fabricated polarization interference element 11 has two sets of liquid crystal layer assemblies, each consisting of a first liquid crystal layer and a second liquid crystal layer.

[0284] In the polarization interference element 11, the first liquid crystal layer corresponds to the first optical anisotropy layer, and the second liquid crystal layer corresponds to the second optical anisotropy layer. The first optical anisotropy layer and the second optical anisotropy layer satisfy equations (1) to (3).

[0285] A bandpass filter was fabricated by placing the fabricated polarization interference element 11 between polarizers arranged in crossed nicols. The bandpass filter was fabricated by aligning the transmission axis of one of the polarizers with the line that bisects the intersection angle between the in-plane slow axes of the odd-numbered and even-numbered layers when the laminate was stacked. The thickness of the fabricated bandpass filter, as well as the polarization transmittance and full width at half maximum, and the side lobes at wavelengths of 450 nm, 535 nm, and 630 nm, were measured using the Topcon Techno House SR-3 spectroradiometer.

[0286] As a result, the fabricated bandpass filter had a thickness of 236 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 98%, 98%, and 98%, respectively. The full width at half maximum at each wavelength was 18 nm, 17 nm, and 21 nm, and the side lobes at each wavelength were 5%, 5%, and 5%.

[0287] [Example 9] To evaluate the optical performance of a birefringent media laminate, a bandpass filter was fabricated in the same manner as in Example 1, using a polarization interference element in which an infrared absorbing dye was added to the rod-shaped liquid crystal layer of each unit layer, as in Example 1. The optical simulation was performed using "Optical Waves in Layered Media 2nd Edition," by Pochi Yeh, Wiley-Interscience (March 3, 2005). The infrared absorbing dye was specified to have dichroic absorption in the near-infrared and to orient as a guest dye in the host liquid crystal compound. The optical properties of the fabricated unit layer 8 are as follows: Unit layer 8 Thickness: 6 μm Re(535): 803 nm Re(450 / 535): 1.40 Re(630 / 535): 0.39

[0288] The formed unit layer 8 is used as a polarization interference element 12, and the fabricated polarization interference element 12 is placed between polarizers arranged in crossed nicols to create a bandpass filter. In this process, the slow axis of the polarization interference element 12 is fabricated such that the angle it makes with the transmission axis of one of the polarizers is 45°.

[0289] In the polarization interference element 12, the unit layer 8 corresponds to the optical anisotropy layer. The optical anisotropy layer satisfies equation (1). Furthermore, when the values ​​of the left and right sides of equation (2) were calculated, the left side of equation (2) was 1.20 and the right side was 1.57, thus satisfying equation (2). Furthermore, when the values ​​of the left and right sides of equation (3) were calculated, the left side of equation (3) was 0.18 and the right side was 0.61, thus satisfying equation (3).

[0290] The fabricated bandpass filter has a thickness of 50 μm, and its polarization transmittance at wavelengths of 450 nm, 535 nm, and 630 nm is 100%, 100%, and 100%, respectively. The full width at half maximum at each wavelength is 50 nm, 45 nm, and 55 nm, and the side lobes at each wavelength are 0%, 0%, and 0%.

[0291] [Example 10] A polarization interference element 13 is fabricated by laminating the unit layers 8 prepared in Example 9 and stacking four layers. In this case, the in-plane slow axis of the odd-numbered layers (first liquid crystal layer) and the in-plane slow axis of the even-numbered layers (second liquid crystal layer) of the stacked unit layers 8 are made to intersect. Specifically, the angle that bisects the intersection angle formed by the in-plane slow axes of both sides is used as the reference (reference line), with counterclockwise being positive (+) and clockwise being negative (-), and the four unit layers 8 are stacked and bonded so that the angle θ of the in-plane slow axis of the odd-numbered layers is 11.25° and the angle θ of the in-plane slow axis of the even-numbered layers is -11.25°. That is, the polarization interference element 13 to be fabricated has two sets of liquid crystal layer sets consisting of a first liquid crystal layer and a second liquid crystal layer.

[0292] In the polarization interference element 13, the first liquid crystal layer corresponds to the first optical anisotropy layer, and the second liquid crystal layer corresponds to the second optical anisotropy layer. The first optical anisotropy layer and the second optical anisotropy layer satisfy equations (1) to (3).

[0293] A bandpass filter is fabricated by placing the fabricated polarization interference element 13 between polarizers arranged in crossed nicols. The bandpass filter is fabricated by aligning the line that bisects the intersection angle between the in-plane slow axes of the odd-numbered and even-numbered layers when the laminate is stacked with the transmission axis of one of the polarizers.

[0294] The fabricated bandpass filter has a thickness of 125 μm, and its polarization transmittance at wavelengths of 450 nm, 535 nm, and 630 nm is 98%, 98%, and 98%, respectively. The full width at half maximum at each wavelength is 18 nm, 17 nm, and 21 nm, and the side lobes at each wavelength are 5%, 5%, and 5%.

[0295] [Example 11] Four unit layers 4 prepared in Example 1 were made, peeled off from the alignment film, and bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical Co., Ltd., 20 μm thick). The four layers were stacked to create a polarization interference element 14. Furthermore, the fabricated polarization interference element 14 was placed between polarizers arranged in a paranicol configuration to create a bandpass filter. In this case, the angle θ of the in-plane slow axis of the stacked unit layers 4 was set with the transmission axis of one polarizer as the reference (reference line), with counterclockwise being positive (+) and clockwise being negative (-), so that the angles from the end were 11.25°, 33.75°, 56.25°, and 78.75°, respectively, when the four unit layers 4 were stacked and bonded. For the fabricated bandpass filter, the thickness, and the polarization transmittance, full width at half maximum, and side lobes at wavelengths of 450 nm, 535 nm, and 630 nm were measured using the Topcon Techno House SR-3 spectroradiometer.

[0296] As a result, the fabricated bandpass filter had a thickness of 342 μm, and the polarization transmittances at wavelengths of 450 nm, 535 nm, and 630 nm were 98%, 98%, and 98%, respectively. The full width at half maximum at each wavelength was 18 nm, 17 nm, and 21 nm, and the side lobes at each wavelength were 5%, 5%, and 5%.

[0297] [Comparative Example 2] A bandpass filter is fabricated in the same manner as in Example 1, using a polarization interference element in which the optical properties of each unit layer are outside the range of equations (2) and (3) in the present invention, as determined by optical simulation. The optical properties of the fabricated unit layer 9 are as follows: Unit layer 9 Thickness: 45 μm Re(535): 3478 nm Re(450 / 535): 1.40 Re(630 / 535): 0.39

[0298] The formed unit layer 9 is used as a polarization interference element 15, and the fabricated polarization interference element 15 is placed between polarizers arranged in crossed nicols to create a bandpass filter. In this process, the slow axis of the polarization interference element 15 is fabricated such that the angle it makes with the transmission axis of one of the polarizers is 45°.

[0299] In the polarization interference element 15, the unit layer 9 corresponds to the optical anisotropy layer. The optical anisotropy layer satisfies equation (1). However, it does not satisfy equations (2) and (3).

[0300] The fabricated bandpass filter had a thickness of 50 μm, and its polarization transmittance at wavelengths of 450 nm, 535 nm, and 630 nm was 6%, 21%, and 87%, respectively.

[0301] Table 1 shows the configurations of the polarization interference elements fabricated in Comparative Examples 1 and 2 and Examples 1 to 11, and Table 2 shows the performance evaluation results of the bandpass filters. In Table 1, the number of optical anisotropy layers for Comparative Example 1 is the total number of optical anisotropy layers for polarization interference elements 1 to 3. The bandpass filter of the present invention requires fewer optical anisotropy layers than conventional products and exhibits superior characteristics in terms of thickness and polarization transmittance. Furthermore, compared to the bandpass filter of Comparative Example 1, which has a large number of optical anisotropy layers, the bandpass filter of the embodiment of the present invention has fewer optical anisotropy layers, thus reducing side lobes.

[0302] Furthermore, comparisons between Examples 1 and 2, Examples 3 and 4, Examples 5 and 6, Examples 7 and 8, and Examples 9 and 10 show that a filter having a polarization interference element with multiple stacked optical anisotropic layers can narrow the transmission bandwidth.

[0303]

[0304]

[0305] 10 (Optical) filter 12 First polarizer 14 Second polarizer 16 Polarization interference element 18, 20, 22 Curves in the graph conceptually showing the optical characteristic range 22, 24, 26 Curves in the graph conceptually showing the optical characteristic range 30R Rod-shaped liquid crystal compound 30D Disc-shaped liquid crystal compound 32, 44, 56, 68 First optical anisotropy layer 34, 46, 58, 70 Second optical anisotropy layer 36, 48, 60, 72 Optical anisotropy layer combination 38R, 40R1, 42R2, 50R1, 52R1, 54R1 Rod-shaped liquid crystal layer (horizontal orientation) 38D, 40D1, 42D2, 62D1, 64D1, 66D1 Disc-shaped liquid crystal layer (vertical orientation) 50R2, 52R2, 54R2 Rod-shaped liquid crystal layer (vertical orientation) 62D2, 64D2, 66D2 Disc-shaped liquid crystal layer (horizontal alignment) 74 Light source section 76 Focusing lens 78, 78a, 78b Optical filter 80, 80a, 80b Light receiving section 82 Beam splitter 84 Light guide element

Claims

A polarization interference element having at least one optical anisotropic layer, wherein the optical anisotropic layer satisfies the following equations (1), (2), and (3). Formula (1) Re(535) > 600nm Equation (2) 0.79 + 4.5×10 ５ / Re(535) ２ −1.2×10 １１ / Re(535) ４ < Re(450 / 535) < 1.16 + 4.5×10 ５ / Re(535) ２ −1.2×10 １１ / Re(535) ４ Equation (3) 0.74 - 3.6×10 ５ / Re(535) ２ -6.0×10 ８ / Re(535) ４ < Re(630 / 535) < 1.16 - 3.5×10 ５ / Re(535) ２ -2.2×10 ９ / Re(535) ４ However, in the formula, Re(535) represents the in-plane retardation at a wavelength of 535 nm, Re(450 / 535) represents the ratio of the in-plane retardation at a wavelength of 450 nm to the in-plane retardation at a wavelength of 535 nm, and Re(630 / 535) represents the ratio of the in-plane retardation at a wavelength of 630 nm to the in-plane retardation at a wavelength of 535 nm. 　 The polarization interference element according to claim 1, wherein the optical anisotropy layer includes a layer on which a liquid crystal compound is fixed. 　 The polarization interference element according to claim 1, wherein the optical anisotropy layer satisfies the following formula (4). Formula (4) 600nm < Re(535) < 2000nm The polarization interference element according to claim 1, having two or more optical anisotropic layers. 　 The polarization interference element according to claim 1, wherein the optical anisotropy layer is a laminate of a layer on which horizontally oriented rod-shaped liquid crystal compounds are fixed and a layer on which vertically oriented disc-shaped liquid crystal compounds are fixed. 　 The polarization interference element according to claim 1, wherein the optical anisotropy layer is a laminate of a layer on which horizontally oriented rod-shaped liquid crystal compounds are fixed and a layer on which vertically oriented rod-shaped liquid crystal compounds are fixed. 　 The polarization interference element according to claim 1, wherein the optical anisotropy layer is a laminate of a layer in which vertically oriented disc-shaped liquid crystal compounds are fixed and a layer in which horizontally oriented disc-shaped liquid crystal compounds are fixed. 　 The polarization interference element according to claim 1, wherein the optical anisotropic layer is a layer in which a liquid crystal compound is fixed in a torsion orientation with the thickness direction as the helical axis. 　 The polarization interference element according to claim 1, wherein the optical anisotropy layer includes an infrared absorbing dye. 　 The polarization interference element according to claim 1, wherein the optical anisotropy layer includes a liquid crystal elastomer. 　 An optical filter comprising a first polarizer, a polarization interference element according to any one of claims 1 to 10, and a second polarizer, arranged in this order, wherein the transmission axis of the first polarizer and the transmission axis of the second polarizer are parallel or orthogonal. 　 An optical system comprising a light source unit, an optical filter as described in claim 11, and a light receiving unit. 　 The optical system according to claim 12, comprising a light-gathering lens. 　 The optical system according to claim 12, comprising a beam splitter. 　 The optical system according to claim 12, comprising a light guide element. 　 The optical system according to claim 12, wherein the optical filter and the light receiving unit are facing each other. 　 The optical system according to claim 12, comprising a plurality of optical filters with different wavelengths of transmitted light.

Images