Laminated optical element, optical filter, and optical system

Abstract

The present invention addresses the problem of providing a laminated optical element that, when used in a bandpass filter or the like corresponding to a plurality of wavelengths, can suppress fluctuations in the wavelength of light exhibiting a maximum transmittance even when light is incident from an oblique direction, and an optical filter and an optical system that use the same. This laminated optical element comprises a plurality of liquid crystal polarization interference elements each having two or more sets each comprising a first liquid crystal layer and a second liquid crystal layer, each liquid crystal layer having a horizontal alignment layer in which rod-shaped liquid crystal compounds are horizontally aligned and a vertical alignment layer in which rod-shaped liquid crystal compounds are vertically aligned, the first liquid crystal layer and the second liquid crystal layer having in-plane slow axes that cross each other in the respective horizonal alignment layers, and having equal in-plane retardation, and each of the liquid crystal polarization interference elements having a different in-plane retardation of the first liquid crystal layer, thereby solving the above problem.

Description

Multilayer optical element, optical filter and optical system

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

[0002] 2. Description of the Related Art Bandpass filters that transmit light in a specific wavelength range and block light of other wavelengths are used in various optical devices.

[0003] Known bandpass filters include polarization interference filters using a dielectric multilayer film, filters combining a polarizer and a birefringent crystal, etc. Also known is a bandpass filter, as described in Patent Document 1, in which a Solk filter (folded Solk filter) is arranged between polarizers arranged in a crossed Nicol configuration, and the Solk filter is formed by alternately stacking birefringent plates (λ / 2 retardation plates) of equal thickness, in which the angle between the transmission axis direction of the polarizer and the slow axis is +ρ, and birefringent plates in which the angle is −ρ.

[0004] Furthermore, Patent Document 1 proposes an optical filter (solc filter) that can realize a bandpass filter with a small number of parts, which has a structure in which two different types of polarization regions of crystals are periodically arranged, and in which the major axis of an index ellipsoid cut parallel to the interface between the two different types of polarization regions is different in the two different types of polarization regions.

[0005] Japanese Patent Application Laid-Open No. 2004-101577

[0006] However, conventional bandpass filters such as those described in Patent Document 1 have a problem in that when light is incident from an oblique direction, the wavelength of light that exhibits maximum transmittance fluctuates, resulting in a so-called wavelength shift.

[0007] The object of the present invention is to solve the problems of the conventional technology, for example, to provide a laminated optical element that, when used in a bandpass filter compatible with multiple wavelengths, can suppress variation in the wavelength of light that exhibits maximum transmittance when light is incident from an oblique direction, i.e., wavelength shift, as well as an optical filter using this laminated optical element and an optical system using this optical filter.

[0008] In order to solve this problem, the present invention has the following configuration: [1] A laminated optical element having a plurality of liquid crystal polarization interference elements, wherein the liquid crystal polarization interference elements have at least two pairs of liquid crystal layer pairs, each pair consisting of a first liquid crystal layer and a second liquid crystal layer, in a thickness direction, wherein the first liquid crystal layer includes at least one first horizontally aligned liquid crystal layer formed by fixing horizontally aligned rod-shaped liquid crystal compounds and at least one first vertically aligned liquid crystal layer formed by fixing vertically aligned rod-shaped liquid crystal compounds, wherein the second liquid crystal layer includes at least one second horizontally aligned liquid crystal layer formed by fixing horizontally aligned rod-shaped liquid crystal compounds and at least one second vertically aligned liquid crystal layer formed by fixing vertically aligned rod-shaped liquid crystal compounds, wherein the in-plane slow axis of the first horizontally aligned liquid crystal layer intersects with the in-plane slow axis of the second horizontally aligned liquid crystal layer, and the in-plane retardation of the first horizontally aligned liquid crystal layer is equal to that of the second horizontally aligned liquid crystal layer, The plurality of liquid crystal polarization interference elements are laminated optical elements in which the in-plane retardation of the first liquid crystal layers included in the liquid crystal polarization interference elements is different from one another. [2] The liquid crystal polarization interference element is a laminated optical element according to [1], in which the liquid crystal layer pairs arranged on both sides in the thickness direction and the liquid crystal layer pair arranged in the center in the thickness direction have different in-plane slow axis directions of the first horizontally aligned liquid crystal layer and the second horizontally aligned liquid crystal layer. [3] The liquid crystal polarization interference element is a laminated optical element according to [1] or [2], in which the first liquid crystal layer and the second liquid crystal layer contain an infrared absorbing dye. [4] The liquid crystal polarization interference element is a laminated optical element according to any one of [1] to [3], in which the first liquid crystal layer and the second liquid crystal layer contain a liquid crystal elastomer. [5] An optical filter having, in this order, a first polarizer, the laminated optical element according to any one of [1] to [4], and a second polarizer. [6] The optical filter according to [5], wherein the first polarizer and the second polarizer are disposed with their transmission axes perpendicular to each other. [7] The optical filter according to [5], wherein the first polarizer and the second polarizer are disposed with their transmission axes parallel to each other. [8] The optical filter according to any one of [5] to [7], wherein one of the first polarizer and the second polarizer is a reflective polarizer. [9] An optical system comprising a light source unit, the optical filter according to any one of [5] to [8], and a light receiving unit.

[0009] According to the present invention, for example, in a bandpass filter compatible with multiple wavelengths, it is possible to suppress fluctuation in the wavelength of light exhibiting maximum transmittance, that is, wavelength shift, when light is incident from an oblique direction.

[0010] FIG. 1 is a diagram conceptually showing an example of an optical filter of the present invention. FIG. 2 is a diagram conceptually showing an example of a liquid crystal polarization interference element. FIG. 3 is a graph for explaining a conventional optical filter. FIG. 4 is a graph for explaining the optical filter of the present invention. FIG. 5 is a graph for explaining the optical filter of the present invention. FIG. 6 is a diagram conceptually showing an example of an optical system of the present invention. FIG. 7 is a diagram conceptually showing another example of the optical system of the present invention. FIG. 8 is a diagram conceptually showing another example of the optical system of the present invention. FIG. 9 is a diagram conceptually showing another example of the optical system of the present invention. FIG. 10 is a diagram conceptually showing another example of the optical system of the present invention. FIG. 11 is a diagram conceptually showing another example of the optical system of the present invention.

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The laminated optical element, optical filter, and optical system of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0012] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, angles such as "45°," "parallel," "perpendicular," or "orthogonal" mean that the difference from the exact angle is within a range of less than 5°, unless otherwise specified. The difference from the exact angle is preferably less than 3°, and more preferably less than 1°. In this specification, terms such as "same," "equal," and the like include a range of error generally accepted in the relevant technical field.

[0013] In this specification, Re(λ) represents the in-plane retardation at a wavelength λ. In this specification, Re(λ) is a value measured at a wavelength λ using an AxoScan (manufactured by Axometrics). By inputting the average refractive index ((nx+ny+nz) / 3) and film thickness (d (μm)) into AxoScan, the slow axis direction (°) Re(λ) = R0(λ) is calculated. Note that R0(λ) is displayed as a numerical value calculated by AxoScan, but it means Re(λ).

[0014] Furthermore, all of the drawings shown below are conceptual diagrams for explaining the present invention, and the positional relationship, size, thickness, shape, etc. of each component element differ from the actual ones.

[0015] FIG. 1 conceptually illustrates an example of an optical filter of the present invention. The optical filter of the present invention comprises a first polarizer, a laminated optical element of the present invention, and a second polarizer arranged in this order. The optical filter 10 shown in FIG. 1 is a bandpass filter (narrow-band filter) that transmits light in a specific wavelength range and blocks light of other wavelengths. It includes a first polarizer 12, a second polarizer 14, and a laminated optical element 16. The laminated optical element 16 is a laminated optical element of the present invention that includes multiple liquid crystal polarization interference elements. The laminated optical element 16 shown in FIG. 1 includes two liquid crystal polarization interference elements: a first liquid crystal polarization interference element 16a and a second liquid crystal polarization interference element 16b. As will be described later, an optical filter of the present invention that uses a laminated optical element of the present invention becomes a bandpass filter corresponding to multiple wavelength ranges (wavelengths) when used as a bandpass filter, for example. The optical filter 10 of the illustrated example, which uses a laminated optical element 16 having two liquid crystal polarization interference elements, becomes a bandpass filter that transmits light in two wavelength ranges and blocks light of other wavelengths (see FIG. 4).

[0016] The first polarizer 12 and the second polarizer 14 are polarizers (polarizing plates) that transmit linearly polarized light in a predetermined direction, and in the illustrated example, are arranged in a crossed Nicol configuration with their transmission axes orthogonal to each other. There are no limitations on the first polarizer 12 and the second polarizer 14, and various known linear polarizers can be used, such as an iodine-based polarizer, a dye-based polarizer using a dichroic dye, a polyene-based polarizer, and a wire-grid polarizer.

[0017] In the illustrated optical filter 10, a laminated optical element 16 is disposed between the first polarizer 12 and the second polarizer 14. Note that in FIG. 1 , the first polarizer 12 and the second polarizer 14 are spaced apart from the laminated optical element 16. However, the present invention is not limited to this, and the first polarizer 12 and the second polarizer 14 may be laminated in contact with the laminated optical element 16. Furthermore, when the first polarizer 12 and the second polarizer 14 are in contact with the laminated optical element 16, they may be adhered to each other, as necessary, with an adhesive that is transparent to transmitted light, such as an OCA (Optical Clear Adhesive) or an acrylic pressure-sensitive adhesive.

[0018] 1, the first liquid crystal polarization interference element 16a and the second liquid crystal polarization interference element 16b constituting the laminated optical element 16 are stacked in contact with each other, but the present invention is not limited to this. That is, in the laminated optical element of the present invention, the multiple liquid crystal polarization interference elements may be arranged in a spaced-apart state, or a mixture of those arranged in a spaced-apart state and those stacked in contact with each other may be present. Furthermore, when the liquid crystal polarization interference elements are stacked in contact with each other, they may be similarly attached to each other with an adhesive that is transparent to transmitted light, such as an OCA or an acrylic adhesive, if necessary.

[0019] In the optical filter of the present invention, the polarizer is not limited to the above-mentioned form, and various polarizers can be used as long as they limit light to only one-way polarization.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 a polarizer, the form in which polarized light is originally emitted from the light source combined with the optical filter of the present invention, and the form in which the light receiving element (light receiving unit) combined with the optical filter of the present invention has one-way polarization sensitivity characteristics, the polarizers of these optical elements, such as the light source and the light receiving element, are also considered to be the polarizers constituting the optical filter of the present invention.In addition, examples of the form in which polarized light is originally emitted from the light source include polarized light and light reflected from a substrate at Brewster's angle.

[0020] As described above, the laminated optical element of the present invention constituting the optical filter of the present invention includes a plurality of liquid crystal polarization interference elements. The liquid crystal polarization interference element is an optical element that acts as a λ / 2 retardation plate for light in a specific wavelength range (specific wavelength) and does not act as a retardation plate (retardation layer) for other light. Furthermore, as described above, in this example, the first polarizer 12 and the second polarizer 14 are polarizers arranged in a crossed Nicol configuration with their transmission axes orthogonal to each other. Of the light incident on the optical filter 10, only linearly polarized light in a direction corresponding to the transmission axis of the first polarizer 12 is transmitted through the first polarizer 12. The linearly polarized light transmitted through the first polarizer 12 then enters the laminated optical element 16 (liquid crystal polarization interference element). Of the linearly polarized light transmitted through the first polarizer 12, light in a specific wavelength range has its polarization direction rotated by 90° by the liquid crystal polarization interference element and is transmitted through the liquid crystal polarization interference element. On the other hand, light outside the specific wavelength range is transmitted through the liquid crystal polarization interference element in its original polarization direction because the liquid crystal polarization interference element does not function as a retardation plate. The linearly polarized light transmitted through the liquid crystal polarization interference element (laminated optical element 16) then enters the second polarizer 14. In this example, the first polarizer 12 and the second polarizer 14 are arranged in a crossed Nicol configuration with their transmission axes perpendicular to each other. Therefore, light in the specific wavelength range, whose polarization direction has been rotated 90° by the liquid crystal polarization interference element, is transmitted through the second polarizer 14, which is arranged in a crossed Nicol configuration with the first polarizer 12, and is emitted. In contrast, light outside the specific wavelength range, for which the liquid crystal polarization interference element does not function as a retardation plate, remains linearly polarized in the direction of the transmission axis of the first polarizer 12, and is therefore blocked (absorbed) by the second polarizer 14, which is arranged in a crossed Nicol configuration with the first polarizer 12. In this way, the optical filter 10 of the present invention, in which the first polarizer 12 and the second polarizer 14 are arranged in a crossed Nicol configuration, functions as a bandpass filter that transmits only light in a specific wavelength range and blocks other light.

[0021] In the above example, the first polarizer 12 and the second polarizer 14 are arranged in a crossed Nicol state, in which their transmission axes are orthogonal to each other, but the optical filter of the present invention is not limited to this. That is, in the optical filter of the present invention, the first polarizer 12 and the second polarizer 14 may be arranged in a parallel Nicol state, in which their transmission axes are parallel to each other. When the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol state, the optical filter 10 has the opposite effect to when both polarizers are arranged in a crossed Nicol state.

[0022] When the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol configuration, the function of the optical filter 10 is reversed as follows. Similarly, in this example, linearly polarized light transmitted through the first polarizer 12 is incident on the laminated optical element 16 (liquid crystal polarization interference element), and light in a specific wavelength range for which the liquid crystal polarization interference element acts as a λ / 2 retardation plate has its polarization direction changed by 90° and is transmitted through the liquid crystal polarization interference element. In contrast, light outside the specific wavelength range for which the liquid crystal polarization interference element does not act as a retardation plate is transmitted through the liquid crystal polarization interference element as linearly polarized light in the polarization direction of the transmission axis of the first polarizer 12. The linearly polarized light transmitted through the liquid crystal polarization interference element (laminated optical element 16) then enters the second polarizer 14. In this example, the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol configuration with their transmission axes orthogonal to each other. Therefore, linearly polarized light in a specific wavelength range, whose polarization direction has been shifted by 90° when the liquid crystal polarization interference element acts as a λ / 2 retardation plate, is blocked (absorbed) by the second polarizer 14, which is arranged in parallel Nicols with the first polarizer 12. On the other hand, light outside the specific wavelength range, when the liquid crystal polarization interference element does not act as a λ / 2 retardation plate, remains linearly polarized in the direction of the transmission axis of the first polarizer 12, and is incident on the second polarizer 14, which is arranged in parallel Nicols with the first polarizer 12, and is transmitted through the second polarizer before exiting. In other words, the optical filter 10 of the present invention, in which the first polarizer 12 and the second polarizer 14 are arranged in parallel Nicols, functions as a wavelength-selective filter that blocks only light in a specific wavelength range and transmits and exits other light due to this action.

[0023] Here, the laminated optical element of the present invention constituting the optical filter of the present invention has a plurality of liquid crystal polarization interference elements. Furthermore, in the laminated optical element of the present invention, the wavelength ranges in which each liquid crystal polarization interference element acts as a λ / 2 retarder are different from one another. That is, the laminated optical element of the present invention acts as a λ / 2 retarder in response to light in a plurality of wavelength ranges. Therefore, an optical filter using the laminated optical element of the present invention becomes a bandpass filter or wavelength-selective filter corresponding to light in a plurality of wavelength ranges, in which each liquid crystal polarization interference element acts as a λ / 2 retarder. That is, as in the illustrated example, when the laminated optical element 16 has two liquid crystal polarization interference elements, a first liquid crystal polarization interference element 16a and a second liquid crystal polarization interference element 16b, the optical filter becomes a bandpass filter that transmits light in two wavelength ranges: light in the wavelength range in which the first liquid crystal polarization interference element 16a acts as a λ / 2 retarder and light in the wavelength range in which the second liquid crystal polarization interference element 16b acts as a λ / 2 retarder, or a wavelength-selective filter that transmits light other than those in the two wavelength ranges.

[0024] 1, both the first polarizer 12 and the second polarizer 14 are absorptive polarizers. However, in the (optical) filter of the present invention, either the first polarizer 12 or the second polarizer 14, preferably the polarizer on the light exit side, may be a reflective polarizer. This configuration will be described in detail later.

[0025] In the laminated optical element of the present invention, the liquid crystal polarization interference element is an optical element having two or more liquid crystal layer pairs, each consisting of a first liquid crystal layer and a second liquid crystal layer, in the thickness direction; the first liquid crystal layer includes at least one first horizontally aligned liquid crystal layer formed by fixing a horizontally aligned rod-shaped liquid crystal compound, and at least one first vertically aligned liquid crystal layer formed by fixing a vertically aligned rod-shaped liquid crystal compound; the second liquid crystal layer includes at least one second horizontally aligned liquid crystal layer formed by fixing a horizontally aligned rod-shaped liquid crystal compound, and at least one second vertically aligned liquid crystal layer formed by fixing a vertically aligned rod-shaped liquid crystal compound; the in-plane slow axis of the first horizontally aligned liquid crystal layer intersects with the in-plane slow axis of the second horizontally aligned liquid crystal layer; and the in-plane retardation of the first horizontally aligned liquid crystal layer is equal to the in-plane retardation of the second horizontally aligned liquid crystal layer.

[0026] Fig. 2 conceptually shows the configuration of a first liquid crystal polarization interference element 16a as an example of a liquid crystal polarization interference element. In the laminated optical element 16 of the optical filter 10 shown in Fig. 1, the second liquid crystal polarization interference element 16b has the same configuration as the first liquid crystal polarization interference element 16a, except that the wavelength ranges in which they function as λ / 2 phase difference plates are different from each other, specifically, the in-plane retardation of the first liquid crystal layer is different from each other.

[0027] As shown in FIG. 2 , the first liquid crystal polarization interference element 16a (second liquid crystal polarization interference element 16b) has a configuration in which two or more liquid crystal layer pairs 26, each consisting of a combination of a first liquid crystal layer 20 and a second liquid crystal layer 24, are stacked in the thickness direction. Therefore, the total number of first liquid crystal layers 20 and second liquid crystal layers 24 stacked is an even number. That is, the first liquid crystal polarization interference element 16a has a configuration in which the same first liquid crystal layers 20 and second liquid crystal layers 24 are alternately stacked. In the following description, when it is not necessary to distinguish the first liquid crystal polarization interference element 16a (second liquid crystal polarization interference element 16b) from other liquid crystal polarization interference elements, the liquid crystal polarization interference element having the above configuration will also be simply referred to as a "liquid crystal polarization interference element."

[0028] In the liquid crystal polarization interference element, the liquid crystal layer set 26 includes the first liquid crystal layer 20 and the second liquid crystal layer 24 as described above. As shown in FIG. 2 , the first liquid crystal layer 20 includes a first horizontally aligned liquid crystal layer 20H and a first vertically aligned liquid crystal layer 20V. The second liquid crystal layer 24 includes a second horizontally aligned liquid crystal layer 24H and a second vertically aligned liquid crystal layer 24V. The first horizontally aligned liquid crystal layer 20H of the first liquid crystal layer 20 is a liquid crystal layer formed by horizontally aligning and fixing rod-shaped liquid crystal compounds 18. The in-plane slow axis (optical axis) of the rod-shaped liquid crystal compounds is the long axis direction. That is, the first horizontally aligned liquid crystal layer 20H is a layer in which the rod-shaped liquid crystal compounds 18 are aligned so that the in-plane slow axis is parallel to the major surface of the first horizontally aligned liquid crystal layer 20H. Furthermore, as shown in FIG. 2 , within the first horizontally aligned liquid crystal layer 20H, each rod-shaped liquid crystal compound 18 is aligned so that the long axis direction (in-plane slow axis) is aligned in a predetermined direction. That is, such a first horizontally aligned liquid crystal layer 20H is a so-called (positive) A-plate. Note that the main surface is the largest surface of a sheet-like object (layer, plate-like object, film).

[0029] The first vertically aligned liquid crystal layer 20V of the first liquid crystal layer 20 is a liquid crystal layer formed by vertically aligning and fixing rod-shaped liquid crystal compounds 18. That is, the first vertically aligned liquid crystal layer 20V is a layer in which the rod-shaped liquid crystal compounds 18 are aligned so that the in-plane slow axis is perpendicular to the main surface of the first vertically aligned liquid crystal layer 20V. That is, such a first vertically aligned liquid crystal layer 20V is a so-called (positive) C plate.

[0030] Similarly, as shown in Fig. 2, the second horizontally aligned liquid crystal layer 24H of the second liquid crystal layer 24 is a liquid crystal layer formed by horizontally aligning and fixing rod-shaped liquid crystal compounds 18. That is, the second horizontally aligned liquid crystal layer 24H is a layer in which the rod-shaped liquid crystal compounds 18 are aligned so that their in-plane slow axes are parallel to the major surface of the second horizontally aligned liquid crystal layer 24H. Also, as shown in Fig. 2, in the second horizontally aligned liquid crystal layer 24H, each rod-shaped liquid crystal compound 18 is aligned so that its long axis direction (in-plane slow axis) is aligned in a predetermined direction. That is, such a second horizontally aligned liquid crystal layer 24H is a so-called (positive) A-plate.

[0031] The second vertically aligned liquid crystal layer 24V of the second liquid crystal layer 24 is a liquid crystal layer formed by vertically aligning and fixing rod-shaped liquid crystal compounds 18. That is, the second vertically aligned liquid crystal layer 24V is a layer in which the rod-shaped liquid crystal compounds 18 are aligned so that the in-plane slow axis is perpendicular to the main surface of the second vertically aligned liquid crystal layer 24V. That is, such a second vertically aligned liquid crystal layer 24V is a so-called (positive) C plate.

[0032] In the present invention, the in-plane slow axis of the first horizontally aligned liquid crystal layer 20H intersects with the in-plane slow axis of the second horizontally aligned liquid crystal layer. The direction of the in-plane slow axis of the first horizontally aligned liquid crystal layer 20H coincides with the alignment direction of the rod-shaped liquid crystal compounds 18. Similarly, the direction of the in-plane slow axis of the second horizontally aligned liquid crystal layer 24H coincides with the alignment direction of the rod-shaped liquid crystal compounds 18. Here, the direction of the in-plane slow axis of the first liquid crystal layer 20 is mainly due to the direction of the in-plane slow axis of the first horizontally aligned liquid crystal layer 20H. Similarly, the direction of the in-plane slow axis of the second liquid crystal layer 24 is mainly due to the direction of the in-plane slow axis of the second horizontally aligned liquid crystal layer 24H. Therefore, in the present invention, the in-plane slow axis of the first horizontally aligned liquid crystal layer 20H and the in-plane slow axis of the first liquid crystal layer 20 can be said to be synonymous. Furthermore, the in-plane slow axis of the second horizontally aligned liquid crystal layer 24H can be said to be synonymous with the in-plane slow axis of the second liquid crystal layer 24. That is, in the present invention, in the liquid crystal layer set 26 of the liquid crystal polarization interference element, the in-plane slow axis of the first liquid crystal layer 20 and the in-plane slow axis of the second liquid crystal layer 24 intersect.

[0033] As described above, the in-plane slow axis of the first horizontally aligned liquid crystal layer 20H intersects with the in-plane slow axis of the second horizontally aligned liquid crystal layer 24. Therefore, as shown in Fig. 2, the first liquid crystal layer 20 and the second liquid crystal layer 24 are laminated such that the alignment direction (long axis direction) of the rod-shaped liquid crystal compounds 18 in the first horizontally aligned liquid crystal layer 20H intersects with the alignment direction (long axis direction) of the rod-shaped liquid crystal compounds 18 in the second horizontally aligned liquid crystal layer 24H.

[0034] In the liquid crystal layer set 26, the in-plane retardation of the first horizontally aligned liquid crystal layer 20H is equal to the in-plane retardation of the second horizontally aligned liquid crystal layer 24H. Here, the in-plane retardation of the first liquid crystal layer 20 is mainly due to the in-plane retardation of the first horizontally aligned liquid crystal layer 20H. Similarly, the in-plane retardation of the second liquid crystal layer 24 is mainly due to the in-plane retardation of the second horizontally aligned liquid crystal layer 24H. Therefore, in the present invention, the in-plane retardation of the first horizontally aligned liquid crystal layer 20H and the in-plane retardation of the first liquid crystal layer 20 are synonymous. Furthermore, the in-plane retardation of the second horizontally aligned liquid crystal layer 24H and the in-plane retardation of the second liquid crystal layer 24 are also synonymous. That is, in the present invention, the in-plane retardation of the first liquid crystal layer 20 is equal to the in-plane retardation of the second liquid crystal layer 24.

[0035] In the present invention, the term "equal in-plane retardation" does not necessarily mean that the in-plane retardation is completely identical, but may have an error of 10% or less. However, it is preferable that this error is small, and it is preferable that the in-plane retardation of the first horizontally aligned liquid crystal layer 20H and the in-plane retardation of the second horizontally aligned liquid crystal layer 24H are completely identical. The same applies to the sum of the in-plane retardations.

[0036] The liquid crystal layer pair 26 is arranged such that the bisector of the angle between the in-plane slow axis direction of the first liquid crystal layer 20 (first horizontally aligned liquid crystal layer 20H) and the in-plane slow axis direction of the second liquid crystal layer 24 (second horizontally aligned liquid crystal layer 24H) is parallel to one of the transmission axes or absorption axes of the polarizers (first polarizer 12 and second polarizer 14) arranged in a crossed Nicol (or parallel Nicol) configuration. That is, the liquid crystal layer pair 26 and the polarizers are arranged such that the bisector of the angle between the in-plane slow axis direction of the first liquid crystal layer 20 and the in-plane slow axis direction of the second liquid crystal layer 24 is set as a reference line, and this reference line is parallel to one of the transmission axes or absorption axes of the polarizers. For example, a clockwise angle relative to the reference line, i.e., the transmission axis or absorption axis of one polarizer, as viewed from the first polarizer 12 side is defined as positive, and a counterclockwise angle relative to the reference line is defined as negative. In this case, the angle of the in-plane slow axis of the first liquid crystal layer 20 from the reference line and the angle of the in-plane slow axis of the second liquid crystal layer 24 are different in plus and minus but have the same absolute value.

[0037] In the present invention, the liquid crystal polarization interference element has two or more such liquid crystal layer pairs 26. In this case, the plurality of liquid crystal layer pairs 26 are arranged so that the bisectors of the angle between the in-plane slow axis direction of the first liquid crystal layer 20 and the in-plane slow axis direction of the second liquid crystal layer 24 are parallel to each other. That is, in the liquid crystal polarization interference element, the reference lines of all the liquid crystal layer pairs are parallel to each other.

[0038] When measuring the reference line from a completed optical filter, the boundary between the polarizer, the polarization interference element for one wavelength, and the polarization interference element for another wavelength is found from the cross section of the filter, and the polarization interference elements are peeled off from that boundary. When polarization interference elements compatible with multiple wavelengths are stacked, there is an interface where the thickness of the polarization interference element changes depending on the corresponding wavelength. This interface can be detected by observation using a scanning electron microscope (SEM), or by cutting the liquid crystal polarization interference element obliquely and analyzing the liquid crystal compound on the surface of the cross section. When the peeled polarization interference element is measured alone using an AxoScan manufactured by Axometrics, the directions of the slow axes of the odd-numbered liquid crystal layers and the even-numbered liquid crystal layers can be obtained, and the reference line, which is the bisector of the angle between them, can be measured.

[0039] 2, all of the first liquid crystal layers 20 have the same configuration, and all of the second liquid crystal layers 24 also have the same configuration. That is, in the first liquid crystal polarization interference element 16a (second liquid crystal polarization interference element 16b) shown in Fig. 2, all of the first liquid crystal layers 20 (first horizontally aligned liquid crystal layers 20H) have the same in-plane retardation (Δnd) and in-plane slow axis angle, and all of the second liquid crystal layers 24 (second horizontally aligned liquid crystal layers 24H) have the same in-plane retardation (Δnd) and in-plane slow axis angle.

[0040] Light passing through such a liquid crystal polarization interference element is repeatedly and alternately influenced by the in-plane slow axis of the first liquid crystal layer 20 at a certain angle and the in-plane slow axis of the second liquid crystal layer 24 at an angle that has the same absolute value as the angle but a different sign.

[0041] Therefore, in the liquid crystal polarization interference element, by setting the in-plane retardation of the first liquid crystal layer 20 and the second liquid crystal layer 24 according to the wavelength range in which they are intended to act as a retardation layer, and further adjusting the angle of the slow axis in the first liquid crystal layer 20 and the second liquid crystal layer 24 according to the total number of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24, it is possible to form a liquid crystal polarization interference element that acts as a λ / 2 retardation plate for light in a specific wavelength range but does not act as a retardation plate for other light, i.e., does not sense retardation.

[0042] In this way, an optical filter in which a liquid crystal polarization interference element that acts as a λ / 2 retardation plate only for light in a specific wavelength range is arranged between a first polarizer 12 and a second polarizer 14 arranged in a crossed Nicol configuration rotates the polarization direction of light in the specific wavelength range, among the linearly polarized light that has passed through the first polarizer 12, by 90° using the liquid crystal polarization interference element, and transmits the light through the second polarizer 14 arranged in a crossed Nicol configuration with the first polarizer 12. On the other hand, because the liquid crystal polarization interference element does not act as a retardation plate for light outside the specific wavelength range, the linearly polarized light that has passed through the first polarizer 12 passes through the liquid crystal polarization interference element and is blocked by the second polarizer 14. Due to this optical action, an optical filter using a liquid crystal polarization interference element becomes a bandpass filter that transmits only light in a specific wavelength range and blocks other light.

[0043] Furthermore, when the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol configuration, the opposite effect to that of the crossed Nicol configuration is exhibited, as described above. That is, in this case, the optical filter using the liquid crystal polarization interference element functions as a wavelength-selective filter that blocks light in a specific wavelength range and transmits light other than that.

[0044] Here, the laminated optical element of the present invention constituting the optical filter of the present invention has a plurality of liquid crystal polarization interference elements. Furthermore, in the laminated optical element of the present invention, the wavelength ranges in which each liquid crystal polarization interference element acts as a λ / 2 retarder are different from one another. That is, the laminated optical element of the present invention acts as a λ / 2 retarder in response to light in a plurality of wavelength ranges. Therefore, an optical filter using the laminated optical element of the present invention becomes a bandpass filter or wavelength-selective filter corresponding to light in a plurality of wavelength ranges, in which each liquid crystal polarization interference element acts as a λ / 2 retarder. That is, as in the illustrated example, when the laminated optical element 16 has two liquid crystal polarization interference elements, a first liquid crystal polarization interference element 16a and a second liquid crystal polarization interference element 16b, the optical filter becomes a bandpass filter that transmits light in two wavelength ranges: light in the wavelength range in which the first liquid crystal polarization interference element 16a acts as a λ / 2 retarder and light in the wavelength range in which the second liquid crystal polarization interference element 16b acts as a λ / 2 retarder, or a wavelength-selective filter that transmits light other than those in the two wavelength ranges.

[0045] In this way, the liquid crystal polarization interference element acts as a λ / 2 retardation plate only for light in a specific wavelength range. Accordingly, the in-plane retardation (Δnd) of the first liquid crystal layer 20 (first horizontally aligned liquid crystal layer 20H) and the second liquid crystal layer 24 (second horizontally aligned liquid crystal layer 24H) is set to a wavelength at which the liquid crystal polarization interference element is expected to act as a λ / 2 retardation plate. That is, in the case of the optical filter 10 (bandpass filter) shown in FIG. 1 , the in-plane retardation of the first liquid crystal layer 20 and the second liquid crystal layer is set to half the center wavelength (half wavelength) of the wavelength range expected to pass through the optical filter 10.

[0046] For example, assuming that the wavelength at which the liquid crystal polarization interference element functions as a λ / 2 retarder, i.e., one of the central wavelengths of the wavelength range transmitted by the optical filter 10, is 550 nm, Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 may be set to 275 nm. When the first liquid crystal layer 20 is composed of a first horizontally aligned liquid crystal layer 20H and a first vertically aligned liquid crystal layer 20V, the in-plane retardation of the first liquid crystal layer 20 is mainly due to the first horizontally aligned liquid crystal layer 20H, and therefore, Δnd of the first horizontally aligned liquid crystal layer 20H may be set to 275 nm. Similarly, when the second liquid crystal layer 24 is composed of a second horizontally aligned liquid crystal layer 24H and a second vertically aligned liquid crystal layer 24V, the in-plane retardation of the second liquid crystal layer 24 is mainly due to the second horizontally aligned liquid crystal layer 24H, and therefore, Δnd of the second horizontally aligned liquid crystal layer 24H may be set to 275 nm. The Δnd of the first liquid crystal layer 20 and the second liquid crystal layer 24 may have an error of about ±10% with respect to half the central wavelength of the wavelength range transmitted by the optical filter 10 .

[0047] In the present invention, the liquid crystal polarization interference element is such that the absolute value of the sum of the in-plane retardations of the first horizontally aligned liquid crystal layer 20H of the first liquid crystal layer 20 is preferably about 1.33 to 4 times, and more preferably about 2 times, the absolute value of the sum of the thickness direction retardations of the first vertically aligned liquid crystal layer 20V. Also, in the present invention, the liquid crystal polarization interference element is such that the absolute value of the sum of the in-plane retardations of the second horizontally aligned liquid crystal layer 24H of the second liquid crystal layer 24 is preferably about 1.33 to 4 times, and more preferably about 2 times, the absolute value of the sum of the thickness direction retardations of the second vertically aligned liquid crystal layer 24V.

[0048] As described above, conventional bandpass filters have had the problem that when light is incident from an oblique direction, a wavelength shift occurs in which the transmission wavelength range moves toward shorter wavelengths compared to when light is incident from the front, as shown conceptually in Figure 3, from the thick solid line to the thin solid line.

[0049] In contrast, in the liquid crystal polarization interference element of the present invention, the first liquid crystal layer 20 and the second liquid crystal layer 24 have horizontally aligned liquid crystal layers (20H, 24H) and vertically aligned liquid crystal layers (20V, 24V), respectively. This allows the first liquid crystal layer 20 and the second liquid crystal layer 24 to reduce the difference between the phase difference that acts on light when the light is incident vertically and the phase difference that acts on light when the light is incident obliquely. This allows the wavelength shift to be suppressed when light is incident obliquely on the optical filter, as conceptually shown in FIG. 4 . In particular, the wavelength shift reduction effect can be more effectively achieved by setting the absolute value of the sum of the in-plane retardations of the horizontally aligned liquid crystal layers in the first liquid crystal layer 20 and the second liquid crystal layer 24 to about 1.33 to 4 times, more preferably about 2 times, the absolute value of the sum of the retardations in the thickness direction of the vertically aligned liquid crystal layers. In addition, since the optical filter 10 shown in Figure 1 has two liquid crystal polarization interference elements, a first liquid crystal polarization interference element 16a and a second liquid crystal polarization interference element 16b, Figure 4 has peaks in two wavelength ranges.

[0050] The in-plane retardation of the horizontally aligned liquid crystal layer (20H, 24H) can be measured using an Axo Scan (0PMF-1, manufactured by Axometrics).

[0051] The retardation in the thickness direction of the vertically aligned liquid crystal layer (20V, 24V) can be measured using an Axo Scan (0PMF-1, manufactured by Axometrics). The in-plane retardation and the thickness direction retardation can be measured by optical analysis, even when the in-plane periodic structure layer and the thickness direction periodic structure layer are laminated.

[0052] The number of liquid crystal layer pairs 26 in the liquid crystal polarization interference element can be detected by cutting the liquid crystal polarization interference element obliquely and analyzing the orientation direction of the liquid crystal on the surface of the cross section. This method is described in detail in "Depth-Dependent Determination of Molecular Orientation for WV-Film" by Yohei Takahashi et al. (FMC8-3, IDW'04, pp. 651-654).

[0053] Furthermore, the horizontally aligned liquid crystal layer and the vertically aligned liquid crystal layer of each of the first and second liquid crystal layers 20 and 24 in each liquid crystal layer set can be identified by obliquely cutting the liquid crystal polarization interference element and analyzing the alignment direction of the liquid crystal compound on the surface of the cross section. This method is described in detail in the above-mentioned document by Yohei Takahashi et al.

[0054] In each liquid crystal layer pair, the direction of the in-plane slow axis of the first liquid crystal layer 20, i.e., the first horizontally aligned liquid crystal layer 20H, can be detected by obliquely cutting the liquid crystal polarization interference element and analyzing the alignment direction of the liquid crystal compound on the surface of the cross section. Similarly, the direction of the in-plane slow axis of the second liquid crystal layer 24, i.e., the second horizontally aligned liquid crystal layer 24H, can be detected by obliquely cutting the liquid crystal polarization interference element and analyzing the alignment direction of the liquid crystal compound on the surface of the cross section.

[0055] The in-plane retardation of each of the first liquid crystal layer 20 and the second liquid crystal layer 24 can be measured using an AxoScan manufactured by Axometrics, Inc. or the like.

[0056] In the in-plane retardation (Δnd) of the first liquid crystal layer 20 and the second liquid crystal layer 24, Δn is the birefringence of the rod-shaped liquid crystal compound 18 constituting the first liquid crystal layer 20 and the second liquid crystal layer 24. Furthermore, d is the thickness of the first horizontally aligned liquid crystal layer 20H and the second horizontally aligned liquid crystal layer 24H. Therefore, the in-plane retardation may be obtained by measuring the birefringence Δn and the thickness d of the rod-shaped liquid crystal compound 18. The birefringence Δn of the liquid crystal compound can also be measured using an AxoScan manufactured by Axometrics, Inc.

[0057] The angles (angles with respect to the reference line) of the in-plane slow axes of the first liquid crystal layer 20 (first horizontally aligned liquid crystal layer 20H) and the second liquid crystal layer 24 (second horizontally aligned liquid crystal layer 24H) constituting the liquid crystal polarization interference element can be set by simulation to an optimal angle at which the liquid crystal polarization interference element functions as a λ / 2 retardation plate, depending on the center wavelength of the wavelength range in which the liquid crystal polarization interference element is expected to function as a retardation plate and the total number N of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24. In other words, when the liquid crystal polarization interference element is used as a bandpass filter, the optimal angle at which the liquid crystal polarization interference element functions as a λ / 2 retardation plate can be set by simulation depending on the center wavelength of the wavelength range in which it is expected to transmit light as a bandpass filter and the total number N of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24. This simulation can be performed using a general optical simulation tool, or it can be calculated using LCD Master 1D (manufactured by Shintech Co., Ltd., Ver. 9.8.0.0).

[0058] There is no limitation on the thickness d of each of the first horizontally aligned liquid crystal layer 20H and the second horizontally aligned liquid crystal layer 24H, and the thickness may be appropriately set depending on the rod-like liquid crystal compound 18 used so as to make the in-plane retardation (Δnd) of each of the first liquid crystal layer 20 and the second liquid crystal layer 24 equal to half the central wavelength of the wavelength range transmitted by the optical filter 10. As an example, considering that the liquid crystal polarization interference element acts as a retardation plate for visible light, the thickness d of the first horizontally aligned liquid crystal layer 20H and the second horizontally aligned liquid crystal layer 24H is preferably 1 to 5 μm, and more preferably 1 to 3 μm.

[0059] There is no limitation on the thickness of the first vertically aligned liquid crystal layer 20V in the first liquid crystal layer 20 and the thickness of the second vertically aligned liquid crystal layer 24V in the second liquid crystal layer 24, and a thickness that provides a desired retardation in the thickness direction may be appropriately set depending on the rod-shaped liquid crystal compound 18 used. Preferably, a thickness that provides an absolute value of the sum of the in-plane retardations of the horizontally aligned liquid crystal layers (20H, 24H) that is 1.33 to 4 times, more preferably 2 times, the absolute value of the sum of the thickness direction retardations of the vertically aligned liquid crystal layers (20V, 24V) may be appropriately set depending on the liquid crystal compound used, etc.

[0060] As an example, when the first horizontally aligned liquid crystal layer 20H and the first vertically aligned liquid crystal layer 20V in the first liquid crystal layer 20 are formed using the same rod-shaped liquid crystal compound 18, a more preferred embodiment is to make the thickness of the first horizontally aligned liquid crystal layer 20H approximately twice the thickness of the first vertically aligned liquid crystal layer 20V so that the absolute value of the sum of the in-plane retardation of the first horizontally aligned liquid crystal layer 20H is approximately twice the absolute value of the sum of the thickness-wise retardation of the first vertically aligned liquid crystal layer 20V. Similarly, when the second horizontally aligned liquid crystal layer 24H and the second vertically aligned liquid crystal layer 24V in the second liquid crystal layer 24 are formed using the same rod-shaped liquid crystal compound 18, a more preferred embodiment is to make the thickness of the second horizontally aligned liquid crystal layer 24H approximately twice the thickness of the second vertically aligned liquid crystal layer 24V so that the absolute value of the sum of the in-plane retardation of the second horizontally aligned liquid crystal layer 24H is approximately twice the absolute value of the sum of the thickness-wise retardation of the second vertically aligned liquid crystal layer 24V.

[0061] Furthermore, when the first horizontally aligned liquid crystal layer 20H in the first liquid crystal layer 20 and the second horizontally aligned liquid crystal layer 24H in the second liquid crystal layer 24 are formed using the same rod-like liquid crystal compound 18, the thickness of the first horizontally aligned liquid crystal layer 20H and the thickness of the second horizontally aligned liquid crystal layer 24H can be made approximately equal to make the in-plane retardation of the first horizontally aligned liquid crystal layer 20H and the in-plane retardation of the second horizontally aligned liquid crystal layer 24H equal. This makes the in-plane retardation of the first horizontally aligned liquid crystal layer 20H, i.e., the first liquid crystal layer 20, equal to the in-plane retardation of the second horizontally aligned liquid crystal layer 24H, i.e., the second liquid crystal layer 24.

[0062] 2, the first liquid crystal layer 20 includes one first horizontally aligned liquid crystal layer 20H and one first vertically aligned liquid crystal layer 20V, but this is not limiting. That is, the first liquid crystal layer 20 may include multiple first horizontally aligned liquid crystal layers 20H and / or multiple first vertically aligned liquid crystal layers 20V. When the first liquid crystal layer 20 includes multiple first horizontally aligned liquid crystal layers 20H and / or multiple first vertically aligned liquid crystal layers 20V, the sum of the in-plane retardations of the multiple first horizontally aligned liquid crystal layers 20H is preferably 1.33 to 4 times, and more preferably 2 times, the sum of the thickness direction retardations of the multiple first vertically aligned liquid crystal layers 20V.

[0063] 2, the second liquid crystal layer 24 includes one second horizontally aligned liquid crystal layer 24H and one second vertically aligned liquid crystal layer 24V, but this is not limiting. That is, the second liquid crystal layer 24 may include multiple second horizontally aligned liquid crystal layers 24H and / or multiple second vertically aligned liquid crystal layers 24V. When the second liquid crystal layer includes multiple second horizontally aligned liquid crystal layers 24H and / or multiple second vertically aligned liquid crystal layers 24V, the sum of the in-plane retardations of the multiple second horizontally aligned liquid crystal layers 24H is preferably 1.33 to 4 times, and more preferably 2 times, the sum of the thickness direction retardations of the multiple second vertically aligned liquid crystal layers 24V.

[0064] In this case, it is desirable to divide the horizontally aligned liquid crystal layers and vertically aligned liquid crystal layers into thinner layers in one first liquid crystal layer and / or one second liquid crystal layer, thereby increasing the number of horizontally aligned liquid crystal layers and vertically aligned liquid crystal layers, since this reduces the difference between the retardation when viewed from the front (normal direction) and the retardation when viewed from a more oblique direction (a direction with a larger polar angle).

[0065] There are no other limitations on the total number of stacked first and second liquid crystal layers 20 and 24, as long as there are two or more sets of liquid crystal layer pairs 26, i.e., four or more layers, and the number is an even number. The total number of stacked first and second liquid crystal layers 20 and 24 is preferably 6 to 30 layers, more preferably 6 to 20 layers, and even more preferably 6 to 10 layers. That is, the number of liquid crystal layer pairs 26 is preferably 3 to 15 sets, more preferably 3 to 10 sets, and even more preferably 3 to 5 sets.

[0066] In the present invention, the greater the total number of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24, i.e., the greater the number of liquid crystal layer pairs 26, the narrower the wavelength range in which the liquid crystal polarization interference element functions as a λ / 2 retarder. Therefore, in the present invention, the greater the total number of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24, the narrower the half-width of the wavelength range of transmitted light. In other words, the greater the total number of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24, the narrower the bandpass filter with a narrower transmission wavelength range can be achieved by the optical filter. Considering the above, the total number of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24, i.e., the number of liquid crystal layer pairs 26, can be selected appropriately depending on the transmission wavelength range required of the optical filter. If a wide band is desired, a smaller number of layers can be selected, and if a narrow band is required, a larger number of layers can be selected.

[0067] Such a liquid crystal polarization interference element may be produced by a known method, for example, by a coating method using a liquid crystal composition for forming the first and second liquid crystal layers.

[0068] The first and second liquid crystal layers can be formed by laminating a horizontally aligned liquid crystal layer and a vertically aligned liquid crystal layer, respectively, and then bonding them with an adhesive that is transparent to transmitted light, such as an OCA (Optical Clear Adhesive) or an acrylic pressure-sensitive adhesive. Alternatively, a horizontally aligned liquid crystal layer can be formed first and then a vertically aligned liquid crystal layer can be formed on the horizontally aligned liquid crystal layer, or a vertically aligned liquid crystal layer can be formed first and then a horizontally aligned liquid crystal layer can be formed on the vertically aligned liquid crystal layer. These methods are described in detail in Japanese Patent No. 6,276,393.

[0069] The horizontally aligned liquid crystal layer can be produced by a conventionally known method for forming a horizontally aligned liquid crystal layer.

[0070] As an example, first, an alignment film oriented in one direction is formed on an appropriately selected support. The alignment film may be a known alignment film, such as a rubbed film made of an organic compound such as a polymer, an obliquely evaporated film of an inorganic compound, a film having microgrooves, a film formed by accumulating LB (Langmuir-Blodgett) films made of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearate by the Langmuir-Blodgett method, or a film formed by applying an alignment film-forming coating liquid containing a photoalignment material to the surface of a support, drying the coating, and exposing the coating film using a polarizer such as a wire grid polarizer.

[0071] On the other hand, a composition (liquid crystal composition) containing a liquid crystal compound for forming a horizontally aligned liquid crystal layer is prepared.

[0072] The solvent for preparing the composition is not limited and can be appropriately selected depending on the purpose, but organic solvents are preferred.The organic solvent is not limited and can be appropriately selected depending on the purpose, and examples thereof include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers.These may be used alone or in combination of two or more.Among these, ketones are preferred when considering the burden on the environment.

[0073] A composition for forming a horizontally aligned liquid crystal layer is applied to the surface of the formed alignment film to align the liquid crystal compound, and then dried. If necessary, the composition is cured by irradiation with ultraviolet light or the like to form a horizontally aligned liquid crystal layer.

[0074] The vertically aligned liquid crystal layer can be produced by a conventionally known method for forming a vertically aligned liquid crystal layer.

[0075] For details of the manufacturing method of a vertically aligned liquid crystal layer (positive C plate) in which rod-shaped liquid crystal compounds are vertically aligned, see, for example, JP-A-2017-187732, JP-A-2016-053709, and JP-A-2015-200861.

[0076] The horizontally aligned liquid crystal layer and the vertically aligned liquid crystal layer prepared as described above can be attached with an OCA or the like to prepare a first liquid crystal layer and a second liquid crystal layer, respectively.

[0077] Next, the prepared first and second liquid crystal layers are bonded with an OCA or the like so that the angle of the in-plane slow axis of the horizontally aligned liquid crystal layer is a predetermined angle to form a liquid crystal layer pair. A plurality of such liquid crystal layer pairs are prepared, and then the liquid crystal layer pairs are stacked to produce a liquid crystal polarization interference element. The liquid crystal layer pairs can also be laminated together using an OCA or the like. Furthermore, when laminating the liquid crystal layer pairs, the layers are laminated so that the bisector (reference line) of the angle between the in-plane slow axis of the first liquid crystal layer and the in-plane slow axis of the second liquid crystal layer of each liquid crystal layer pair is parallel.

[0078] As described above, the laminated optical element of the present invention has a plurality of such liquid crystal polarization interference elements. Therefore, when producing the laminated optical element of the present invention, a plurality of liquid crystal polarization interference elements having different in-plane retardations of the first liquid crystal layer are produced. Then, the plurality of liquid crystal polarization interference elements are laminated so that the bisector (reference line) of the crossing angle formed by the in-plane slow axes of the first liquid crystal layer (odd-numbered layer) and the second liquid crystal layer (even-numbered layer) coincides when each liquid crystal polarization interference element is produced, thereby forming a laminated optical element.

[0079] The laminated optical element thus prepared is arranged in a crossed Nicol configuration, for example, with the bisector of the crossing angle formed by the in-plane slow axes of the first liquid crystal layer (odd layer) and the second liquid crystal layer (even layer) as the reference line, so that the transmission axis of the first polarizer or the second polarizer is parallel to the reference line. The transmission axis or the light-shielding axis (reflection axis) of the polarizer can also be used as the reference line. In this case, for example, the laminated optical element may be arranged between the first polarizer and the second polarizer arranged in a crossed Nicol configuration so that the transmission axis of the first polarizer or the second polarizer is parallel to the line that bisects the crossing angle formed by the in-plane slow axes of the first liquid crystal layer (odd layer) and the second liquid crystal layer (even layer). As described above, the multiple liquid crystal polarization interference elements, the first polarizer and the laminated optical element, and the second polarizer and the laminated optical element may be attached with a transparent adhesive, if necessary.

[0080] In the liquid crystal polarization interference element constituting the laminated optical element of the present invention, there is no limitation on the rod-shaped liquid crystal compound 18, and various known liquid crystal compounds can be used. As rod-shaped liquid crystal compounds, azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyano-substituted phenylpyrimidines, alkoxy-substituted phenylpyrimidines, phenyldioxanes, tolanes, and alkenylcyclohexylbenzonitriles are preferably used. In addition to the above-mentioned low-molecular-weight liquid crystal molecules, polymeric liquid crystal molecules can also be used.

[0081] It is more preferable to fix the alignment of the rod-shaped liquid crystal compound by polymerization. Examples of polymerizable rod-shaped liquid crystal compounds include those described in Makromol. Chem. , Vol. 190, p. 2255 (1989), Advanced Materials Vol. 5, p. 107 (1993), U.S. Patent Nos. 4,683,327, 5,622,648, 5,770,107, WO 95 / 22586, 95 / 24455, 97 / 00600, 98 / 23580, 98 / 52905, JP-A-1-272551, JP-A-6-16616, JP-A-7-110469, JP-A-11-80081, and compounds described in Japanese Patent Application No. 2001-64627 can be used. Furthermore, as the rod-shaped liquid crystal compound, for example, those described in JP-A-11-513019 and JP-A-2007-279688 can also be preferably used.

[0082] In addition to the liquid crystal compound, the compositions for forming the first liquid crystal layer 20 and the second liquid crystal layer 24 may contain, if necessary, a polymerization initiator, a leveling agent, a crosslinking agent, a surfactant, and the like.

[0083] In the laminated optical element of the present invention, the liquid crystal polarization interference element may have all the first liquid crystal layers that are the same, or all the second liquid crystal layers that are the same, or may have a mixture of first liquid crystal layers that are different in in-plane retardation and / or in-plane slow axis directions, etc., and may also have a mixture of second liquid crystal layers that are different in in-plane retardation and / or in-plane slow axis directions, etc. Furthermore, the liquid crystal polarization interference element may have all the first liquid crystal layers that are different and all the second liquid crystal layers that are different, or may have all the first liquid crystal layers that are the same and a mixture of different second liquid crystal layers, or may have a mixture of different first liquid crystal layers and all the same second liquid crystal layers.

[0084] For example, the first liquid crystal polarization interference element 16a shown in Fig. 2 is formed by alternately stacking the same first liquid crystal layers 20 and the same second liquid crystal layers 24. That is, in the liquid crystal polarization interference element, all the first liquid crystal layers 20 are the same, and all the second liquid crystal layers 24 are the same. Therefore, in the first liquid crystal polarization interference element 16a shown in Fig. 2, all the first liquid crystal layers 20 have the same in-plane retardation, and the in-plane slow axes of the rod-shaped liquid crystal layers are parallel. Similarly, in the first liquid crystal polarization interference element 16a shown in Fig. 2, all the second liquid crystal layers 24 have the same in-plane retardation, and the in-plane slow axes of the rod-shaped liquid crystal layers are parallel.

[0085] However, as described above, in the laminated optical element of the present invention, the liquid crystal polarization interference element is not limited thereto, and may have, for example, a first liquid crystal layer having different in-plane retardation and / or in-plane slow axes that are not parallel to each other. Also, in the present invention, the liquid crystal polarization interference element may have a second liquid crystal layer having different in-plane retardation and / or in-plane slow axes that are not parallel to each other. That is, in the present invention, the liquid crystal polarization interference element has a plurality of liquid crystal layer pairs each consisting of a first liquid crystal layer and a second liquid crystal layer, the first liquid crystal layer and the second liquid crystal layer having a horizontally aligned liquid crystal layer and a vertically aligned liquid crystal layer, the in-plane slow axis of the first horizontally aligned liquid crystal layer (first liquid crystal layer) intersects with the in-plane slow axis of the second horizontally aligned liquid crystal layer (second liquid crystal layer), and further, as long as the in-plane retardation of the first horizontally aligned liquid crystal layer (first liquid crystal layer) is equal to the in-plane retardation of the second horizontally aligned liquid crystal layer (second liquid crystal layer), the liquid crystal layer pairs may differ in in-plane retardation, the angle between the in-plane slow axis of the first horizontally aligned liquid crystal layer and the reference line, and the angle between the in-plane slow axis of the second horizontally aligned liquid crystal layer and the reference line, etc.

[0086] As an example, the liquid crystal polarization interference element may have different in-plane slow axis directions between the first liquid crystal layer (i.e., the first horizontally aligned liquid crystal layer) and the second liquid crystal layer (i.e., the second horizontally aligned liquid crystal layer) in the liquid crystal layer pairs arranged on both sides in the thickness direction and the liquid crystal layer pair arranged in the center of the thickness direction. Specifically, the liquid crystal polarization interference element may have a configuration in which the absolute values ​​of the angles formed between the in-plane slow axis of the first liquid crystal layer and the reference line and the absolute values ​​of the angles formed between the in-plane slow axis of the second liquid crystal layer and the reference line in the liquid crystal layer pairs on both sides in the thickness direction are smaller than those in the liquid crystal layer pair arranged in the center of the thickness direction.

[0087] For example, when the liquid crystal polarization interference element has eight first and second liquid crystal layers, i.e., four liquid crystal layer pairs, in the first liquid crystal layer pair, the angle between the in-plane slow axis of the first liquid crystal layer (first layer) and the reference line is set to φ1, and the angle between the in-plane slow axis of the second liquid crystal layer (second layer) and the reference line is set to -φ1; in the second liquid crystal layer pair, the angle between the in-plane slow axis of the first liquid crystal layer (third layer) and the reference line is set to φ2, which is larger than φ1, and the angle between the in-plane slow axis of the second liquid crystal layer (fourth layer) and the reference line is set to -φ2, which is smaller than -φ1, i.e., has a larger absolute value; in the third liquid crystal layer pair, the angle between the in-plane slow axis of the first liquid crystal layer (fifth layer) and the reference line is set to φ2, and the angle between the in-plane slow axis of the second liquid crystal layer (sixth layer) and the reference line is set to -φ2; In the fourth liquid crystal layer pair, an example configuration is shown in which the angle between the in-plane slow axis of the first liquid crystal layer (seventh layer) and the reference line is φ1, and the angle between the in-plane slow axis of the second liquid crystal layer (eighth layer) and the reference line is −φ1.

[0088] As conceptually shown in Figure 5, a bandpass filter generates unwanted transmission wavelength bands called side lobes, as indicated by arrows S in the figure, at wavelengths shorter and longer than the target transmission wavelength band on either side of the target transmission wavelength band. In contrast, as described above, in a liquid crystal polarization interference element, the absolute value of the angle between the in-plane slow axis of the first liquid crystal layer (first horizontally aligned liquid crystal layer) and the second liquid crystal layer (second horizontally aligned liquid crystal layer) of the liquid crystal layer pairs on both sides in the thickness direction and the reference line is made smaller than that of the liquid crystal layer of the liquid crystal layer pair at the center in the thickness direction, thereby reducing the side lobes when used as a bandpass filter. In other words, in the liquid crystal polarization interference element of the present invention, the angle between the in-plane slow axis of the first liquid crystal layer and the in-plane slow axis of the second liquid crystal layer of the liquid crystal layer pairs on both sides in the thickness direction is made smaller than that of the liquid crystal layer pair at the center in the thickness direction, thereby reducing the side lobes when used as a bandpass filter.

[0089] The angles formed by the in-plane slow axes of the first and second liquid crystal layers and the reference line may be adjusted by a known method. For example, in the above-described manufacturing method, the angles formed by the in-plane slow axes of the first and second liquid crystal layers and the reference line may be adjusted by adjusting the angle of the in-plane slow axis of the horizontally aligned liquid crystal layer, i.e., the alignment direction of the rod-shaped liquid crystal compound, during lamination.

[0090] In this configuration, the absolute value of the angle between the in-plane slow axis of the horizontally aligned liquid crystal layer in each of the liquid crystal layer pairs on both sides in the thickness direction and the reference line is smaller than that of the liquid crystal layer in the central liquid crystal layer pair in the thickness direction. The number of central liquid crystal layer pairs, i.e., the division of the liquid crystal layer pairs into the both sides and the central liquid crystal layer pair, is not limited, and may be appropriately set depending on the number of liquid crystal layers (liquid crystal layer pairs) included in the liquid crystal polarization interference element. Furthermore, the angles between the in-plane slow axes of the first and second liquid crystal layers in the liquid crystal layer pairs on both sides in the thickness direction and the reference line, as well as the angles between the in-plane slow axes of the first and second liquid crystal layers in the central liquid crystal layer pair in the thickness direction and the reference line, are also not limited. That is, these angles may be set, for example, by simulation, to obtain the optimal in-plane retardation and angle that allows the liquid crystal polarization interference element to function as a λ / 2 retarder and reduce side lobes. It is preferable to control the change in the angle between the in-plane slow axes of the first and second liquid crystal layers and the reference line from both sides of the stacking direction (thickness direction) toward the center as smoothly and precisely as possible.

[0091] In the liquid crystal polarization interference element of the present invention described above, the first liquid crystal layer and the second liquid crystal layer may contain an infrared absorbing dye. By containing the infrared absorbing dye in the first liquid crystal layer and the second liquid crystal layer, the liquid crystal wavelength dispersion in the liquid crystal layer can be made to be a strong forward dispersion. As a result, the wavelength range of light in which the liquid crystal polarization interference element acts as a λ / 2 retardation plate (λ / 2 wave plate) can be narrowed. In other words, by adding an infrared absorbing dye to the first liquid crystal layer and the second liquid crystal layer and making the liquid crystal wavelength dispersion in the liquid crystal layer a strong forward dispersion, a bandpass filter with a narrower transmission wavelength range can be obtained.

[0092] As the infrared absorbing dye, various infrared absorbing dyes can be used that can reduce the difference in refractive index between the x and y directions by being oriented in the same direction as the liquid crystal compound. There are no particular limitations on the infrared absorbing dye, as long as it absorbs infrared light (e.g., light with a wavelength of 700 to 900 m). Among these, dichroic dyes are preferred. A dichroic dye refers to a dye that exhibits different absorbance in the long axis direction and the short axis direction of the molecule. Examples of infrared absorbing dyes that can be used include diketopyrrolopyrrole dyes, diimmonium dyes, phthalocyanine dyes, naphthalocyanine dyes, azo dyes, polymethine dyes, anthraquinone dyes, pyrylium dyes, squarylium dyes, triphenylmethane dyes, cyanine dyes, and aminium dyes. Metal complex dyes and boron complex dyes can also be used as the infrared absorbing dye. Infrared absorbing dyes are described in detail in WO 2019 / 044859.

[0093] There is no limitation on the amount of the infrared absorbing dye added to the first and second liquid crystal layers, and it may be set appropriately depending on the width of the transmission wavelength range required for the optical filter (bandpass filter) of the present invention.

[0094] Furthermore, in the liquid crystal polarization interference element of the present invention, the first liquid crystal layer (first horizontally aligned liquid crystal layer) and the second liquid crystal layer (second horizontally aligned liquid crystal layer) may contain a liquid crystal elastomer. The first and second liquid crystal layers containing a liquid crystal elastomer may be formed using a liquid crystal elastomer, or may be liquid crystal layers formed of a normal liquid crystal compound other than an elastomer and containing a liquid crystal elastomer.

[0095] In this way, by including a liquid crystal elastomer in the first and second liquid crystal layers, the first and second liquid crystal layers can be made elastic, and the thickness of the liquid crystal layer can be changed by stretching or shrinking the optical filter in the plane direction. By changing the thickness of the horizontally aligned liquid crystal layer, the in-plane retardation of the liquid crystal layer can be changed. As a result, in the bandpass filter, it is possible to change the wavelength range of light transmitted through the optical filter. In other words, by including a liquid crystal elastomer in the first and second liquid crystal layers, the wavelength range can be changed by stretching and shrinking the horizontally aligned liquid crystal layer, i.e., the filter, enabling active wavelength control in the bandpass filter.

[0096] There are no limitations on the liquid crystal elastomer, and various known ones can be used. As an example of the liquid crystal elastomer, a liquid crystal elastomer prepared from a liquid crystal monomer, a crosslinker, and a plasticizer, as described in JP 2020-131638 A, can be used. This provides the liquid crystal elastomer with mechanical properties and rubber elasticity, enabling it to deform in response to the external force required for active wavelength control.

[0097] In addition, when the horizontally aligned liquid crystal layer is formed from a normal liquid crystal compound that is not an elastomer and a liquid crystal elastomer is added to impart elasticity, there is no restriction on the amount of liquid crystal elastomer added, and it can be set appropriately depending on the required elasticity, i.e., the control range of the transmission wavelength range.

[0098] As described above, the optical filter of the present invention has a configuration in which the laminated optical element of the present invention is disposed between a first polarizer and a second polarizer. Furthermore, the laminated optical element of the present invention has a plurality of the above-described liquid crystal polarization interference elements. The optical filter 10 shown in FIG. 1 has a laminated optical element 16 having two liquid crystal polarization interference elements, a first liquid crystal polarization interference element 16a and a second liquid crystal polarization interference element 16b, disposed between a first polarizer 12 and a second polarizer 14. Here, in the laminated optical element of the present invention, the in-plane retardation of the first liquid crystal layer included in each of the plurality of liquid crystal polarization interference elements, i.e., the in-plane retardation of the first horizontally aligned liquid crystal layer, is different from each other. By having such a configuration, the laminated optical element of the present invention is capable of acting as a λ / 2 retarder for light in a plurality of wavelength ranges.

[0099] As described above, in the liquid crystal polarization interference element constituting the laminated optical element of the present invention, the in-plane retardation of the first horizontally aligned liquid crystal layer, i.e., the first liquid crystal layer, is equal to the in-plane retardation of the second horizontally aligned liquid crystal layer, i.e., the second liquid crystal layer. Furthermore, as described above, the liquid crystal polarization interference element sets the in-plane retardation of the first horizontally aligned liquid crystal layer, i.e., the first liquid crystal layer, and the in-plane retardation of the second horizontally aligned liquid crystal layer, i.e., the second liquid crystal layer, according to the wavelength of light for which it is intended to function as a λ / 2 retarder. Therefore, in the laminated optical element of the present invention, which has multiple liquid crystal polarization interference elements and in which the in-plane retardations of the first liquid crystal layers included in each liquid crystal polarization interference element are different from each other, the wavelength ranges in which each liquid crystal polarization interference element functions as a λ / 2 retarder are different from each other. In other words, the laminated optical element of the present invention has multiple liquid crystal polarization interference elements that function as λ / 2 retarders for different wavelength ranges from each other.

[0100] As described above, in the present invention, the liquid crystal polarization interference element is an optical element that acts as a λ / 2 retardation plate only for light in a specific wavelength range and does not act as a retardation plate for light of other wavelengths. That is, by placing a laminated optical element of the present invention having a liquid crystal polarization interference element that acts as a λ / 2 retardation plate for different wavelength ranges between polarizers and using it as a bandpass filter, a bandpass filter that can accommodate light of multiple wavelength ranges can be obtained. For example, as shown in FIG. 1, by using a laminated optical element 16 having two liquid crystal polarization interference elements as a bandpass filter, only light in the wavelength range λ1, which acts as a λ / 2 retardation plate, is rotated by 90° in the first liquid crystal polarization interference element 16a, while light of other wavelengths is transmitted as is. Furthermore, only light in the wavelength range λ2, which acts as a λ / 2 retardation plate, is rotated by 90° in the second liquid crystal polarization interference element 16b, while light of other wavelengths is transmitted as is. This allows for a bandpass filter that can accommodate light of two wavelength ranges (wavelengths), as shown in FIG. 4. Furthermore, as described above, the liquid crystal polarization interference element constituting the laminated optical element of the present invention can also suppress the wavelength variation of light showing the maximum transmittance when the light is incident from an oblique incident direction, that is, the so-called wavelength shift. That is, when the laminated optical element of the present invention is used in, for example, a bandpass filter, it can realize a bandpass filter that is compatible with light of multiple wavelength ranges and suppresses wavelength shift.

[0101] In the laminated optical element of the present invention, the in-plane retardation of the first liquid crystal layer (second liquid crystal layer) in each liquid crystal polarization interference element may be adjusted by a known method depending on the configuration of the first liquid crystal layer. One example is a method of adjusting the in-plane retardation of the first liquid crystal layer of the liquid crystal polarization interference element by adjusting the thickness of the first horizontally aligned liquid crystal layer. Alternatively, a method of adjusting the in-plane retardation of the first liquid crystal layer of each liquid crystal polarization interference element by selecting the liquid crystal compound used in the first liquid crystal layer (first horizontally aligned liquid crystal layer) may also be used. A plurality of these methods of adjusting the in-plane retardation may be used in combination.

[0102] In the laminated optical element of the present invention, various liquid crystal polarization interference elements can be used in any combination as long as the sums of the in-plane retardations of the first liquid crystal layers are different from each other.

[0103] For example, the laminated optical element of the present invention may have all the liquid crystal polarization interference elements of the same configuration, such as the laminated optical element 16 shown in Figure 1, where all the liquid crystal polarization interference elements are the liquid crystal polarization interference elements shown in Figure 2. Also, the laminated optical element of the present invention may have a configuration in which a certain liquid crystal polarization interference element is, for example, a liquid crystal polarization interference element having the configuration shown in Figure 2, and another liquid crystal polarization interference element is, for example, a first liquid crystal layer and a second liquid crystal layer, each of which is a stack of liquid crystal layer pairs having a plurality of horizontally aligned liquid crystal layers and vertically aligned liquid crystal layers. Note that when the laminated optical element of the present invention has three or more liquid crystal polarization interference elements, all the liquid crystal polarization interference elements may be different, or a mixture of liquid crystal polarization interference elements of the same configuration and liquid crystal polarization interference elements of different configurations may be present, such as a configuration in which there are two liquid crystal polarization interference elements of the same configuration and one liquid crystal polarization interference element of a different configuration.

[0104] In the laminated optical element of the present invention, there is no limitation on the number of liquid crystal polarization interference elements, as long as there is more than one. For example, if it is desired to extract red light, green light, and blue light in response to the display of a color image, it is sufficient to have three liquid crystal polarization interference elements that act as λ / 2 retardation plates according to the desired wavelength ranges of each color. Alternatively, the laminated optical element of the present invention can be configured to have four liquid crystal polarization interference elements, including a liquid crystal polarization interference element that acts as a λ / 2 retardation plate for infrared light in the desired wavelength range. That is, in the laminated optical element of the present invention, the number of liquid crystal polarization interference elements can be appropriately set depending on the number of light in the wavelength range that is desired to be extracted or removed. Note that, in the laminated optical element of the present invention, the number of liquid crystal polarization interference elements is preferably, for example, 2 to 10.

[0105] The optical filter of the present invention comprises a first polarizer, a laminated optical element of the present invention having a plurality of liquid crystal polarization interference elements, and a second polarizer arranged in this order. As described above, in the optical filter 10 of the present invention shown in FIG. 1, in all liquid crystal layer pairs, the angles formed between the in-plane slow axes of the first liquid crystal layer (first horizontally aligned liquid crystal layer) and the second liquid crystal layer (second horizontally aligned liquid crystal layer) and the reference line are equal in the alternating stacking direction. Alternatively, in the liquid crystal polarization interference element, the absolute values ​​of the angles formed between the reference line and the in-plane slow axes of the first liquid crystal layer and the second liquid crystal layer are small on both sides of the stacking direction and large in the central portion. That is, in the above-described example, the angles formed between the in-plane slow axes of the first liquid crystal layer and the second liquid crystal layer and the reference line are uniform in the stacking direction, or increase along the stacking direction and then decrease. The first polarizer 12 and the second polarizer 14 sandwiching a laminated optical element having a plurality of such liquid crystal polarization interference elements in the thickness direction are arranged with their transmission axes in a crossed Nicol configuration, thereby transmitting light in a specific wavelength range in which the liquid crystal polarization interference elements act as a λ / 2 retardation plate and blocking light of other wavelengths. Alternatively, as described above, the first polarizer 12 and the second polarizer 14 sandwiching such a laminated optical element in the thickness direction are arranged with their transmission axes in a parallel Nicol configuration, thereby blocking light in a specific wavelength range in which the liquid crystal polarization interference elements act as a λ / 2 retardation plate and transmitting light of other wavelengths. However, in the optical filter of the present invention, the liquid crystal polarization interference elements constituting the laminated optical element are not limited to this, and various configurations can be used.

[0106] For example, in the laminated optical element of the present invention, the liquid crystal polarization interference element can also be configured such that the angles of the in-plane slow axes of the first liquid crystal layer (first horizontally aligned liquid crystal layer) and the second liquid crystal layer (second horizontally aligned liquid crystal layer) relative to the reference line sequentially increase in the alternating stacking direction of the first liquid crystal layer and the second liquid crystal layer. When using a laminated optical element having such a liquid crystal polarization interference element, when the optical filter (bandpass filter) of the present invention transmits light of a specific wavelength through the second polarizer and emits it, it may be preferable that the polarizers sandwiching the laminated optical element in the thickness direction are arranged with their transmission axes parallel to each other, i.e., in a parallel Nicol configuration. In the following description, the angles of the in-plane slow axes of the first liquid crystal layer and the second liquid crystal layer relative to the reference line are also simply referred to as the "angle of the in-plane slow axes of the liquid crystal layers."

[0107] A liquid crystal polarization interference element having a configuration in which the angle of the in-plane slow axis of the liquid crystal layer with respect to the reference line gradually increases in the stacking direction, contrary to the above-mentioned liquid crystal polarization interference element, does not act as a retardation plate for light in a specific wavelength range, but acts as a λ / 2 retardation plate for light of other wavelengths. Therefore, in the optical filter of the present invention using this liquid crystal polarization interference element, in order to transmit light in a specific wavelength range through the second polarizer and emit it, it is necessary to arrange the first polarizer and the second polarizer in a parallel Nicol state with their transmission axes parallel.

[0108] As with the optical filter 10 shown in Figure 1, in this optical filter, only linearly polarized light in a direction corresponding to the transmission axis of the first polarizer is transmitted through the first polarizer. Of this linearly polarized light, light in a specific wavelength range is transmitted through the liquid crystal polarization interference element in its original polarization direction and enters the second polarizer, because the laminated optical element (liquid crystal polarization interference element) does not function as a retardation plate. Here, the second polarizer and the first polarizer are arranged in a parallel Nicol configuration. Therefore, light in a specific wavelength range that is linearly polarized and remains transmitted through the first polarizer 12 is transmitted through the second polarizer 14 and exits.

[0109] On the other hand, the liquid crystal polarization interference element acts as a half-wave retarder, so that light outside the specific wavelength range has its polarization direction changed by 90° and enters the second polarizer 14. Here, the first polarizer and the second polarizer are arranged in a parallel Nicol state with their transmission axes parallel. Therefore, after passing through the first polarizer 12, light outside the specific wavelength range, whose polarization direction has been changed by 90° by the liquid crystal polarization interference element, is blocked (absorbed) by the second polarizer arranged in a parallel Nicol state with the first polarizer 12.

[0110] As described above, the optical filter of the present invention, which uses a liquid crystal polarization interference element configured such that the angle of the in-plane slow axis of the liquid crystal layer increases sequentially in the stacking direction, arranges the first polarizer and the second polarizer in parallel Nicols, so that, of the incident light, light in a specific wavelength range in which the liquid crystal polarization interference element does not act as a retardation plate is transmitted through the optical filter and exits as transmitted light, while blocking other light. That is, the optical filter of the present invention having this configuration functions as a bandpass filter that transmits light in a specific wavelength range and blocks other light.

[0111] In addition, even in the optical filter of the present invention using a liquid crystal polarization interference element configured such that the angle of the in-plane slow axis of the liquid crystal layer gradually increases in the stacking direction, the first polarizer and the second polarizer may be arranged in a crossed Nicol state. As in the previous example, when the first polarizer and the second polarizer are arranged in a crossed Nicol state, an optical filter having the opposite effect to that when both polarizers are arranged in a parallel Nicol state can be realized.

[0112] In an optical filter using a laminated optical element having this liquid crystal polarization interference element, when the first polarizer and the second polarizer are arranged in a crossed Nicol configuration, the optical filter functions as follows. Even in this case, of the linearly polarized light transmitted through the first polarizer, light in a specific wavelength range for which the laminated optical element (liquid crystal polarization interference element) does not function as a retardation plate does not change its polarization direction in the liquid crystal polarization interference element and enters the second polarizer as linearly polarized light in the direction of the transmission axis of the first polarizer. In contrast, light outside the specific wavelength range for which the liquid crystal polarization interference element functions as a λ / 2 retardation plate has its polarization direction changed by 90° by the liquid crystal polarization interference element and enters the second polarizer. Here, in this example, the first polarizer and the second polarizer are arranged in a crossed Nicol configuration. Therefore, the second polarizer has a transmission axis perpendicular to the transmission axis of the first polarizer. Therefore, light in a specific wavelength range for which the liquid crystal polarization interference element does not function as a retardation plate and is linearly polarized in the direction of the transmission axis of the first polarizer is blocked (absorbed) by the second polarizer. In contrast, after passing through the first polarizer in which the liquid crystal polarization interference element acts as a λ / 2 retardation plate, light outside the specific wavelength range, whose polarization direction has been changed by 90° by the liquid crystal polarization interference element, passes through the second polarizer and is emitted. In other words, in this case, the optical filter of the present invention having this configuration functions as a wavelength selection filter, blocking light in the specific wavelength range in which the liquid crystal polarization interference element does not act as a retardation plate and transmitting light other than that.

[0113] As described above, the laminated optical element of the present invention has a plurality of liquid crystal polarization interference elements. Furthermore, in the laminated optical element of the present invention, the wavelength ranges in which each liquid crystal polarization interference element acts as a λ / 2 retarder are different from one another. That is, the laminated optical element of the present invention acts as a λ / 2 retarder in response to light in a plurality of wavelength ranges. Therefore, an optical filter using the laminated optical element of the present invention becomes a bandpass filter or wavelength-selective filter that corresponds to light in a plurality of wavelength ranges, in which each liquid crystal polarization interference element acts as a λ / 2 retarder. That is, as in the illustrated example, when the laminated optical element 16 has two liquid crystal polarization interference elements, a first liquid crystal polarization interference element 16a and a second liquid crystal polarization interference element 16b, the laminated optical element 16 becomes a bandpass filter that transmits light in two wavelength ranges: light in the wavelength range in which the first liquid crystal polarization interference element 16a acts as a λ / 2 retarder and light in the wavelength range in which the second liquid crystal polarization interference element 16b acts as a λ / 2 retarder, or a wavelength-selective filter that transmits light other than those in the two wavelength ranges.

[0114] When the optical filter of the present invention is used as a bandpass filter, it is preferable to set the transmission axes of the first polarizer and the second polarizer at an appropriate angle in order to obtain desired bandpass characteristics.In particular, when the optical filter of the present invention is used as a bandpass filter, by appropriately adjusting the angles of the transmission axes of the polarizers sandwiching the laminated optical element of the present invention in the thickness direction, the size of the side lobes generated at the wavelengths on both sides (long-wave side and short-wave side) of the main bandpass wavelength can be reduced, and the size of the side lobes on the long-wave side and short-wave side can be adjusted to be equal.

[0115] Furthermore, in the optical filter of the present invention, the shape of the bandpass filter curve can be adjusted by appropriately adjusting the size and angle of the slow axis of the liquid crystal polarization interference element. For example, it can be made into a gentle shape like a Gaussian function or a steep shape like a rectangular function. These can be adjusted to the desired shape depending on the application of the bandpass filter, and can be preferably used for, for example, long-pass and short-pass applications.

[0116] 1 , both the first polarizer 12 and the second polarizer 14 are absorptive polarizers. However, the optical filter of the present invention is not limited to this, and either the first polarizer 12 or the second polarizer 14, preferably the polarizer on the light exit side, may be a reflective polarizer. With such a configuration, the filter of the present invention can be used as a bandpass filter that transmits only light in a specific wavelength range and reflects other wavelengths, thereby separating light into two optical paths according to wavelength, i.e., a so-called dichroic filter.

[0117] In the configuration shown in FIG. 1 , as an example, the first polarizer 12 is on the light incident side, and the second polarizer 14 on the light exit side is a reflective polarizer (reflective linear polarizer). As described above, the liquid crystal polarization interference elements (first liquid crystal polarization interference element 16 a and second liquid crystal polarization interference element 16 b) constituting the laminated optical element 16 are optical elements that act as λ / 2 retardation plates for light in a specific wavelength range (specific wavelength) and do not act as retardation plates for other light. In this example, the first polarizer 12 and the second polarizer 14 are arranged in a crossed Nicol configuration with their transmission axes perpendicular to each other. Of the light incident on the optical filter 10, only linearly polarized light in a direction corresponding to the transmission axis is transmitted through the first polarizer 12. Of this linearly polarized light, light in a specific wavelength range has its polarization direction rotated by 90° by the liquid crystal polarization interference element and enters the second polarizer 14. The second polarizer 14 is a polarizer arranged in a crossed Nicol configuration with the first polarizer 12. Therefore, light in a specific wavelength range, the polarization direction of which has been rotated by 90° by the liquid crystal polarization interference element, passes through the second polarizer 14 and is emitted from the optical filter 10 .

[0118] In contrast, light outside the specific wavelength range, for which the liquid crystal polarization interference element does not function as a retardation plate, enters the second polarizer 14 with its polarization direction intact, i.e., linearly polarized light whose polarization direction is the same as the transmission axis of the first polarizer 12. As described above, the second polarizer 14 is a reflective polarizer. Therefore, it has a reflection axis perpendicular to the transmission axis. The first polarizer 12 and the second polarizer 14 are arranged in a crossed Nicol configuration. That is, the second polarizer 14, which is a reflective polarizer, has a reflection axis in the same direction as the transmission axis of the first polarizer 12. Therefore, light outside the specific wavelength range for which the liquid crystal polarization interference element does not function as a retardation plate is reflected by the second polarizer 14, which is a reflective polarizer, with its polarization direction identical to the transmission axis of the first polarizer 12, passes through the liquid crystal polarization interference element as is, and enters the first polarizer 12. As described above, the polarization direction of the linearly polarized light reflected by the second polarizer 14 is aligned with the transmission axis of the first polarizer 12. Therefore, the linearly polarized light reflected by the second polarizer 14 passes through the first polarizer 12 as it is and is emitted from the optical filter 10 .

[0119] That is, the optical filter 10 of the present invention using a reflective polarizer can extract, from the incident light, light in a specific wavelength range for which the liquid crystal polarization interference element acts as a λ / 2 retardation plate as transmitted light that has passed through the optical filter 10. Furthermore, the optical filter 10 of the present invention using a reflective polarizer can extract, as reflected light that has been reflected by the optical filter 10 (second polarizer 14), light outside the specific wavelength range for which the liquid crystal polarization interference element does not act as a retardation plate. That is, the optical filter of the present invention using a reflective polarizer functions as a dichroic filter that extracts light in other wavelength ranges as reflected light, while functioning as a bandpass filter that extracts light in a predetermined narrowband wavelength as transmitted light.

[0120] In the above example, the first polarizer 12 and the second polarizer 14 are arranged in a crossed Nicol configuration, in which their transmission axes are orthogonal to each other, but the optical filter of the present invention using a reflective polarizer is not limited to this. That is, in the optical filter of the present invention using a reflective polarizer, the first polarizer 12 and the second polarizer 14 may be arranged in a parallel Nicol configuration, in which their transmission axes are parallel to each other. When the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol configuration, the optical filter 10 has the opposite effect to when both polarizers are arranged in a crossed Nicol configuration.

[0121] When the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol configuration, the optical filter 10 using a reflective polarizer functions as follows. Similarly, in this case, of the linearly polarized light transmitted through the first polarizer 12, light in a specific wavelength range for which the liquid crystal polarization interference element acts as a λ / 2 retardation plate has its polarization direction changed by 90° and enters the second polarizer 14. Light with other wavelengths for which the liquid crystal polarization interference element does not act as a retardation plate enters the second polarizer 14 while maintaining the polarization direction of the transmission axis of the first polarizer 12. Here, in this example, the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol configuration. Therefore, light in a specific wavelength range for which the liquid crystal polarization interference element acts as a λ / 2 retardation plate, whose polarization direction has been changed by 90°, is reflected by the second polarizer 14, has its polarization direction restored by the liquid crystal polarization interference element, and enters the first polarizer 12. The polarization direction of this light coincides with the transmission axis of the first polarizer 12, and therefore it is transmitted through the first polarizer 12. On the other hand, the polarization direction of light outside the specific wavelength range in which the liquid crystal polarization interference element does not act as a retardation plate coincides with the transmission axis of the first polarizer 12, and therefore it is transmitted through the second polarizer 14, which is arranged in parallel Nicols with the first polarizer 12, and then emitted. In other words, in this case, the optical filter 10 using a reflective polarizer acts as a dichroic filter that emits light in the specific wavelength range in which the liquid crystal polarization interference element acts as a retardation plate as reflected light and transmits light of other wavelengths.

[0122] Here, the laminated optical element of the present invention constituting the optical filter of the present invention has a plurality of liquid crystal polarization interference elements. Moreover, in the laminated optical element of the present invention, the wavelength ranges in which each liquid crystal polarization interference element acts as a λ / 2 retardation plate are different from one another. That is, the laminated optical element of the present invention acts as a λ / 2 retardation plate in response to light in a plurality of wavelength ranges. Therefore, an optical filter using the laminated optical element of the present invention becomes a dichroic filter in which each liquid crystal polarization interference element acts as a λ / 2 retardation plate and corresponds to light in a plurality of wavelength ranges. That is, as in the illustrated example, when the laminated optical element 16 has two liquid crystal polarization interference elements, a first liquid crystal polarization interference element 16a and a second liquid crystal polarization interference element 16b, the first liquid crystal polarization interference element 16a acts as a λ / 2 retardation plate and the second liquid crystal polarization interference element 16b acts as a λ / 2 retardation plate, the filter becomes a dichroic filter that transmits light in two wavelength ranges and reflects light of other wavelengths, or reflects light in two wavelength ranges and transmits light of other wavelengths.

[0123] In addition, the optical filter of the present invention using a reflective polarizer may also use a laminated optical element having a liquid crystal polarization interference element configured such that the angle of the in-plane slow axis of the liquid crystal layer increases sequentially in the lamination direction. In this case, the effects are reversed between the example in which the polarizers are arranged in a crossed Nicol configuration and the example in which the polarizers are arranged in a parallel Nicol configuration.

[0124] In the present invention, the reflective polarizer is not limited, and various known reflective polarizers can be used. Examples include a reflective polarizer having a selective reflection layer containing at least one cholesteric liquid crystal layer and a λ / 4 retardation plate, a film made of a dielectric multilayer film formed by stretching layers containing two types of polymers as described in JP-A-2011-053705, and a wire grid polarizer as described in JP-A-2015-286656. Commercially available reflective polarizers can also be suitably used. Examples of commercially available reflective polarizers include a reflective polarizer manufactured by 3M (product name: APF), a wire grid polarizer manufactured by THORLABS, and a wire grid polarizer manufactured by Asahi Kasei Corporation (product name: WGF).

[0125] In the optical filter of the present invention, a retarder may be provided between the first polarizer and the laminated optical element (liquid crystal polarization interference element) or between the second polarizer and the laminated optical element (liquid crystal polarization interference element). That is, in the optical filter of the present invention, a retarder may be provided on one or both sides between the laminated optical element and the polarizer. This retarder has the effect of maintaining the orthogonal relationship of the polarization directions of the linear polarizers arranged in a crossed Nicol configuration not only in the front view but also in the off-axis oblique direction of the polarizer. As a result, when the optical filter of the present invention is used as a bandpass filter, good bandpass characteristics similar to those obtained in the front view can be obtained in the oblique view. The in-plane slow axis of the retarder is preferably parallel to the absorption axis of either the first polarizer or the second polarizer arranged in a crossed Nicol configuration. This allows the polarization state to be compensated so as to maintain the orthogonal relationship of the polarization directions in the oblique direction without affecting the front view. Examples of the retardation plate include a positive C plate formed by vertically aligning rod-shaped liquid crystals and a positive A plate formed by horizontally aligning rod-shaped liquid crystals, a negative C plate formed by discotic liquid crystals and a negative A plate formed by discotic liquid crystals, or a combination thereof. Furthermore, a biaxial refractive index B plate (with an Nz factor of 0.1 to 0.9) can also be used as the retardation plate.

[0126] The effect of such a retardation plate is the same even when the first polarizer and the second polarizer are arranged in a parallel Nicol state.

[0127] The laminated optical element and optical filter of the present invention can be used for any wavelength, i.e., the optical filter of the present invention can be used for any electromagnetic wave, such as ultraviolet light, visible light, infrared light, terahertz waves, and millimeter waves.

[0128] The optical system of the present invention includes a light source unit, the 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 little loss of received light can be realized.

[0129] In the optical system of the present invention, there is no limitation on the light source unit, and various known light source units (light source, light-emitting element) that can emit light of a desired wavelength can be used, such as an LED (Light Emitting Diode), an organic EL (OLED organic electro-luminescence) element, a fluorescent lamp, a halogen lamp, a laser light source, a plasma light source, etc. In addition, in the optical system of the present invention, there is no limitation on the light receiving unit, and various known light receiving units (light receiving element, image sensor) can be used, such as a CCD sensor, a photomultiplier, a CMOS sensor, and a photodiode, as long as they can receive light of a target wavelength and measure the light.

[0130] FIG. 6 conceptually illustrates an example of an optical system of the present invention combined with a condensing lens. The optical system shown in FIG. 6 includes a light source unit 90, a condensing lens 92, an optical filter 94 of the present invention, and a light-receiving unit 96. Various known condensing lenses can be used. In this optical system, divergent light emitted by the light source unit 90 is condensed by the condensing lens 92 and received by the light-receiving unit 96 for photometry. In such an optical system, an optical filter 94 (bandpass filter) of the present invention is disposed in the divergent or condensing portion of the light. In the illustrated example, the optical filter 94 of the present invention is disposed in the condensing portion of the light. That is, the light condensed by the condensing lens 92 and transmitted through the optical filter 94 of the present invention is photometrically measured by the light-receiving unit 96.

[0131] As described above, the optical filter of the present invention is compatible with light in multiple wavelength ranges, exhibiting bandpass performance with the same wavelength for both light incident from the front and from oblique directions. This allows light of desired wavelengths over a wide angular range to be collected at the light receiving section. The optical system of the present invention can thereby achieve high light receiving efficiency and minimal light receiving loss. The optical system of the present invention using a condensing lens can be used, for example, in an imaging system. This imaging system achieves high light receiving efficiency when the condensing lens collects light from the light source unit 90, which is the object to be imaged, in various directions and highly focuses the light onto the light receiving unit 96, which is an imaging element. Furthermore, because the optical filter of the present invention exhibits bandpass performance over a wide angle, a thin, compact optical system can be realized by using a condensing lens with a high numerical aperture. Furthermore, the optical system of the present invention can also be used in systems that utilize optical fibers. In this case, a system that achieves high efficiency similar to that described above can be constructed by providing an optical fiber output terminal on the light source unit 90 side and an optical fiber input terminal on the light receiving unit 96 side. Specifically, the light from the output terminal of the optical fiber and / or the light condensed by the lens contain a mixture of light rays from various angles. Therefore, the optical system (optical filter) of the present invention can be used to efficiently select only the desired wavelengths from the light rays from any angle and integrate them into the sensor.

[0132] As shown in FIG. 6 , not only the condensing lens 92 but also the light transmitted through the lens contains light at various angles. In contrast, the liquid crystal polarization interference element constituting the laminated optical element in the optical filter of the present invention, as described above, exhibits very little wavelength shift due to oblique incidence of light. That is, since the optical filter of the present invention has little angle dependency, it functions as a bandpass filter and reflector that acts on the same wavelength range for light incident at various angles, regardless of the angle transmitted and reflected. In other words, the optical filter of the present invention functions as a bandpass filter that acts appropriately on a specific wavelength for light incident at various angles after passing through the lens, as well as for diverging and condensing light. The angle dependency of the optical filter of the present invention is also true for each of the optical systems described below.

[0133] FIG. 7 conceptually illustrates an example of an optical system incorporating a beam splitter according to the present invention. The optical system shown in FIG. 7 includes a light source 90, a beam splitter 98, an optical filter 94 according to the present invention, and a light receiving unit 96. Various known beam splitters can be used. In this optical system, the beam splitter 98 splits the linear light emitted by the light source 90 into multiple (two in the illustrated example) different angular directions. The split light is then received by corresponding light receiving units 96 for photometry. In this optical system, an optical filter 94 (bandpass filter) according to the present invention is disposed in the region after the split light. The optical filter 94 according to the present invention exhibits bandpass performance for the same wavelength for split light traveling in different angular directions. As a result, high light receiving efficiency can be achieved in all of the multiple light receiving units 96 that receive the split light. This optical system using a beam splitter 98 according to the present invention can be applied to various optical systems, such as sensors and lasers. In addition, in systems using optical fibers, the system of the present invention can be used when a straight light beam is split into different angles using a beam splitter and then the connection destination is switched depending on the destination of the optical signal.

[0134] FIG. 8 conceptually illustrates an example of combining a light-guiding element (light guide plate) with the optical system of the present invention. The optical system shown in FIG. 8 includes a light source unit 90, a light-guiding element 100, an optical filter 94 of the present invention, and a light-receiving unit 96. Various known light-guiding elements can be used. In this optical system, light emitted from the light source unit 90 in various angular directions is incident on one end of the light-guiding element 100, and the mixed light propagating through the light-guiding element 100 is emitted from the other end of the light-guiding element 100 and received by the light-receiving unit 96 for photometry. In this optical system, an optical filter 94 (bandpass filter) of the present invention is disposed at the exit position of the propagating light from the light-guiding element 100. The optical filter 94 of the present invention exhibits bandpass performance at the same wavelength for propagating light traveling in different angular directions. As a result, high light-receiving efficiency is achieved for the propagating light emitted from the light-guiding element. The optical system of the present invention using such a light guide element can be used in a sensing system using a light guide element, a display system such as an AR system, and an optical communication system using a waveguide.

[0135] In the optical system of the present invention, an optical filter 94 of the present invention and a light receiving unit 96 may be provided adjacent to each other, as conceptually shown in FIG. 9 . In the optical system shown in FIG. 9 , divergent light emitted from a light source unit 90 reaches an optical filter 94 (bandpass filter) of the present invention from various angular directions. Here, the optical filter 94 of the present invention has wide-angle bandpass performance, allowing light of a desired wavelength to be introduced into the adjacent light receiving unit over a wide angle. As a result, high light receiving efficiency is achieved in the light receiving unit 96. In an optical system in which a light source unit 90 emits divergent light, utilizing an optical system of the present invention that uses the optical filter 94 of the present invention allows the optical filter 94 of the present invention to exhibit the desired bandpass performance over a wide angle, which is effective in reducing the thickness of the system.

[0136] As described above, the optical filter of the present invention, which uses a laminated optical element of the present invention having multiple liquid crystal polarization interference elements, can selectively transmit (block) light in multiple wavelength ranges. Therefore, for example, the optical system of the present invention shown in FIG. 9 can be specifically used as a multispectral sensor. For example, the optical system of the present invention can realize an optical system that senses diffused light from the skin, containing human health information, at different wavelengths with high light receiving efficiency using a thin optical system. In other words, by using the optical filter of the present invention having a laminated optical element of the present invention consisting of multiple liquid crystal polarization interference elements, the optical system of the present invention can realize a thin and compact optical system that can perform highly efficient measurements of light in multiple wavelength ranges, such as multispectral and hyperspectral measurements. This is also true for the optical system of the present invention described below.

[0137] 6 to 9 are examples in which the optical filter 94 of the present invention is used as a bandpass filter. That is, the optical filter 94 is, as an example, an example in which a first polarizer and a second polarizer are arranged in a crossed Nicol configuration in the optical filter of the present invention. Therefore, in this case, of the light emitted by the light source unit 90, light in a specific wavelength range in which the liquid crystal polarization interference element (laminated optical element) acts as a λ / 2 retardation plate is transmitted through the optical filter 94 and enters the light receiving unit 06 for photometry, while other light is blocked by the optical filter 94.

[0138] Alternatively, an optical filter of the present invention in which the first polarizer and the second polarizer are arranged in a parallel Nicol state can be used in the optical systems shown in Figures 6 to 9. When the first polarizer and the second polarizer are arranged in a parallel Nicol state, the function of the optical filter is reversed, as described above. Therefore, in this case, in the optical systems shown in Figures 6 to 9, of the light emitted by the light source unit 90, light in a specific wavelength range in which the liquid crystal polarization interference element (laminated optical element) acts as a λ / 2 retardation plate is blocked by the optical filter 94, and light outside this specific wavelength range passes through the optical filter 94 and enters the light receiving unit 06, where it is measured.

[0139] On the other hand, as described above, the optical filter of the present invention using the laminated optical element of the present invention having a liquid crystal polarization interference element configured such that the angle of the in-plane slow axis of the liquid crystal layer increases sequentially in the lamination direction functions as a bandpass filter when the first polarizer and the second polarizer are arranged in parallel Nicols. Therefore, when this optical filter is used as a bandpass filter in the optical filter 94 in the optical system shown in Figures 6 to 9, light emitted by the light source unit 90, light in a specific wavelength range in which the liquid crystal polarization interference element does not act as a λ / 2 retardation plate, passes through the optical filter 94 and enters the light receiving unit 06 for photometry, while light outside this specific wavelength range is blocked by the optical filter 94.

[0140] Furthermore, an optical filter using the laminated optical element of the present invention having a liquid crystal polarization interference element configured such that the angle of the in-plane slow axis of the liquid crystal layer increases sequentially in the stacking direction, and in which the first and second polarizers are arranged in a crossed Nicol configuration, can also be used in the optical systems shown in Figures 6 to 9. When the first and second polarizers are arranged in a crossed Nicol configuration, the function of the optical filter is reversed, as described above. Therefore, in this case, of the light emitted by the light source unit 90, light in a specific wavelength range in which the liquid crystal polarization interference element does not function as a λ / 2 retardation plate is blocked by the optical filter 94, and light other than this specific wavelength range passes through the optical filter 94 and enters the light receiving unit 06 for photometry.

[0141] 6 to 9, the first and second polarizers of the optical filters are absorptive polarizers (linear absorptive polarizers). However, as described above, in the optical filter of the present invention, one of the first and second polarizers (on the exit side) may be a reflective polarizer.

[0142] FIG. 10 conceptually illustrates an example of an optical system of the present invention that uses an optical filter of the present invention in which one of the first polarizer and the second polarizer is a reflective polarizer, and combines a condensing lens. The optical system shown in FIG. 10 includes a light source unit 90, a condensing lens 92, an optical filter 94 of the present invention, a light receiving unit 96a for transmitted light, and a light receiving unit 96b for reflected light. In this optical system, divergent light emitted from the light source unit 90 is collected by the condensing lens 92. In this optical system, an optical filter 94 of the present invention (a bandpass filter (dichroic filter)) is disposed in the divergent or condensing portion of the light. In the illustrated example, the optical filter 94 of the present invention is disposed in the condensing portion of the light. Furthermore, as shown in FIG. 10, in this optical system, the optical filter 94 is disposed at an angle with respect to the optical axis of the condensing lens 92. The light receiving unit 96a for transmitted light is disposed on the optical axis of the condensing lens 92. On the other hand, the light receiving section 96b for reflected light is disposed on the optical path of the light reflected by the optical filter 94 disposed at an angle.

[0143] As an example, the optical filter 94 shown in the figure has a first polarizer and a second polarizer arranged in a crossed Nicol state with their transmission axes perpendicular to each other. Therefore, in this case, of the light emitted from the light source unit 90, collected by the condensing lens 92, and incident on the optical filter 94, light in a specific wavelength range passes through the optical filter 94 and enters the light-receiving unit 96a for transmitted light, where it is photometered. On the other hand, light outside the specific wavelength range that is collected by the condensing lens 92 and incident on the optical filter 94 is reflected by the optical filter 94 and enters the light-receiving unit 96b for reflected light, where it is photometered. The first polarizer and second polarizer of the optical filter 94 may also be arranged in a parallel Nicol state with their transmission axes parallel to each other. In this case, as described above, of the light that is collected by the collecting lens 92 and enters the optical filter 94, light in a specific wavelength range is reflected by the optical filter 94 and measured by the light receiving unit 96b for reflected light, and light outside the specific wavelength range is transmitted through the optical filter 94 and measured by the light receiving unit 96a for transmitted light.

[0144] 10 can also use an optical filter using a liquid crystal polarization interference element configured such that the angle of the in-plane slow axis of the liquid crystal layer increases sequentially in the stacking direction. In this optical system, when the first and second polarizers of the optical filter are arranged in a parallel Nicol configuration, light of a specific wavelength range, collected by the collecting lens 92 and incident on the optical filter 94, passes through the optical filter and enters the light-receiving unit 96a for transmitted light, where it is photometered. In this optical system, light of a wavelength range other than the specific wavelength range, collected by the collecting lens 92 and incident on the optical filter 94, is reflected by the optical filter and enters the light-receiving unit 96b for reflected light, where it is photometered. On the other hand, when the first and second polarizers of the optical filter are arranged in a crossed Nicol configuration, light of a specific wavelength, collected by the collecting lens 92 and incident on the optical filter 94, is reflected by the optical filter and enters the light-receiving unit 96b for reflected light, where it is photometered. In addition, in this optical system, light outside the specific wavelength range that is collected by the collecting lens 92 and incident on the optical filter 94 passes through the optical filter 94 and enters the light receiving unit 96a for transmitted light, where it is measured.

[0145] As described above, the optical filter (laminated optical element) of the present invention exhibits bandpass performance at the same wavelength for both light incident from the front and from oblique directions, allowing light of desired wavelengths over a wide angular range to be collected at the light receiving section. The optical system of the present invention can thereby achieve high light receiving efficiency and low light receiving loss. The optical system of the present invention using a condensing lens can be used, for example, in an imaging system. This imaging system achieves high light receiving efficiency when light from a light source (the object to be imaged) in various directions is collected by the condensing lens and incident on the light receiving section (the imaging element). Furthermore, because the optical filter of the present invention exhibits bandpass performance over a wide angle, a thin, compact optical system can be realized by using a condensing lens with a high numerical aperture. Furthermore, the optical system of the present invention can also be used in systems that utilize optical fibers. In this case, a system with high efficiency similar to that described above can be constructed by providing an optical fiber output terminal on the light source side and an optical fiber input terminal on the light receiving section side. Specifically, the light from the optical fiber output terminal and / or the light collected by the lens from that light both contain a mixture of light from various angles. Therefore, the optical system (optical filter) of the present invention can be used to efficiently select only the desired wavelengths from light of any angle and integrate them into the sensor.

[0146] As shown in FIG. 10 , not only the condensing lens 92 but also the light transmitted through the lens contains light at various angles. In contrast, as described above, the liquid crystal polarization interference element of the laminated optical element in the optical filter of the present invention exhibits very little wavelength shift due to oblique incidence of light. That is, since the optical filter of the present invention has little angle dependency, it functions as a bandpass filter and reflector that acts on the same wavelength range for light incident at various angles, regardless of the angle transmitted and reflected. In other words, the optical filter of the present invention functions as a bandpass filter (dichroic filter) that acts appropriately on a specific wavelength for light incident at various angles through the lens, as well as for diverging and converging light. The angle dependency of the optical filter of the present invention is also applicable to the optical system shown in FIG. 11 below.

[0147] FIG. 11 conceptually illustrates an example of combining a beam splitter with an optical system of the present invention that uses an optical filter of the present invention in which one of the first polarizer and the second polarizer is a reflective polarizer. The optical system shown in FIG. 11 includes a light source unit 90, a beam splitter 98, an optical filter 94 of the present invention, a light receiving unit 96a for transmitted light, and a light receiving unit 96b for reflected light. In this optical system, the beam splitter 98 splits the linearly traveling light emitted by the light source unit 90 into multiple (two in the figure) different angular directions. Furthermore, in this optical system, an optical filter 94 of the present invention (a bandpass filter (dichroic filter)) is disposed in the region after the splitting of the light. As shown in FIG. 11, in this optical system, the light split by the beam splitter 98 and transmitted through the optical filter 94 is received by the light receiving unit 96a for transmitted light corresponding to each light and photometrically measured. Furthermore, the light split by the beam splitter 98 and reflected by the optical filter 94 is received by the light receiving section 96b for reflected light corresponding to each light and photometry is performed.

[0148] As an example, in the illustrated optical filter 94, the first and second polarizers are arranged in a crossed Nicol configuration with their transmission axes perpendicular to each other. Therefore, in this case, of the light emitted from the light source 90, split by the beam splitter 98, and incident on the optical filter 94, light in a specific wavelength range passes through the optical filter 94 and enters the light-receiving unit 96a for transmitted light corresponding to each light, where it is photometered. On the other hand, light outside the specific wavelength range that is split by the beam splitter 98 and incident on the optical filter 94 is reflected by the optical filter 94 and enters the light-receiving unit 96b for reflected light corresponding to each light, where it is photometered. The first and second polarizers of the optical filter 94 may also be arranged in a parallel Nicol configuration with their transmission axes parallel to each other. In this case, as described above, the light in the specific wavelength range that is split by the beam splitter 98 and incident on the optical filter 94 is reflected by the optical filter 94 and then photometered by the light-receiving unit 96b for reflected light corresponding to each light. On the other hand, light outside the specific wavelength range that is split by the beam splitter 98 and enters the optical filter 94 passes through the optical filter 94 and is measured by the light receiving section 96a for transmitted light that corresponds to each light.

[0149] 11 can also utilize an optical filter using a liquid crystal polarization interference element configured such that the angle of the in-plane slow axis of the liquid crystal layer increases sequentially in the stacking direction. In this optical system, when the first and second polarizers of the optical filter 94 are arranged in parallel Nicols, light emitted from the light source unit 90, split by the beam splitter 98, and incident on the optical filter is split into light of a specific wavelength range. The light is transmitted through the optical filter and incident on the light-receiving unit 96a for transmitted light corresponding to the light, where it is photometered. In this optical system, light of wavelengths other than the specific wavelength range that is split by the beam splitter 98 and incident on the optical filter 94 is reflected by the optical filter 94 and incident on the light-receiving unit 96b for reflected light corresponding to the light, where it is photometered. On the other hand, in this optical system, when the first polarizer and second polarizer of the optical filter 94 are arranged in a crossed Nicol configuration, light of a specific wavelength out of the light split by the beam splitter 98 and incident on the optical filter 94 is reflected by the optical filter 94 and incident on the light receiving unit 96b for reflected light corresponding to each light, where it is photometered. Also, in this optical system, light outside the specific wavelength range that is split by the beam splitter 98 and incident on the optical filter 94 is transmitted through the optical filter 94 and incident on the light receiving unit 96a for transmitted light corresponding to each light, where it is photometered.

[0150] The laminated optical element, optical filter, and optical system of the present invention have been described in detail above, but the present invention is not limited to the above examples, and various improvements and modifications may of course be made within the scope of the present invention.

[0151] It should be noted that the laminated optical element of the present invention has a plurality of liquid crystal polarization interference elements.However, the above-mentioned various liquid crystal polarization interference elements are optical elements that, even if they are a single liquid crystal polarization interference element, act as a retardation plate for light of a specific wavelength range (light outside the specific wavelength range), and do not act as a retardation layer for light of other wavelengths (light of the specific wavelength range).Therefore, the above-mentioned various optical filters and optical systems of the present invention can be configured not only by the laminated optical element of the present invention, but also by using only one of the above-mentioned liquid crystal polarization interference elements.

[0152] The features of the present invention will be explained in more detail below with reference to examples. The materials, reagents, amounts used, amounts of substances, ratios, treatment details, and treatment procedures shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

[0153] [Example 1] <Preparation of first liquid crystal polarization interference element> (Formation of alignment film) A glass substrate was prepared as a support. The following alignment film-forming coating liquid was applied to the support by spin coating. The support on which the coating film of the alignment film-forming coating liquid was formed was dried on a hot plate at 60°C for 60 seconds to form alignment film P-1, which was a photo-alignment film.

[0154] Coating liquid for forming alignment film ----------------------------------- 1.00 parts by mass of the following photoalignment material - Water 16.00 parts by mass - Butoxyethanol 42.00 parts by mass - Propylene glycol monomethyl ether 42.00 parts by mass -----------------------------------

[0155] Material for photo alignment

[0156] (Exposure of Alignment Film) Next, using an ultraviolet exposure device, the alignment film P-1 was irradiated with ultraviolet light that had been linearly polarized by a wire grid polarizer (ProFlux PPL02, manufactured by Moxtek) that was installed so that the angle of the absorption axis was φ1 (=0°). The ultraviolet light had an illuminance of 4.5 mW / cm 2 , cumulative irradiation dose 300 mJ / cm 2 The angle of the absorption axis is the angle with respect to the longitudinal direction of the substrate, and the counterclockwise direction is taken as positive.

[0157] (Formation of Horizontally Aligned Liquid Crystal Layer) The following composition B-1 was prepared as a liquid crystal composition for forming a horizontally aligned liquid crystal layer.

[0158] Composition B-1 --------------------------------------------------- Rod-shaped liquid crystal compound L-1 (shown below) 100.00 parts by mass Polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF) 3.00 parts by mass Photosensitizer (KAYACURE DETX-S, manufactured by Nippon Kayaku) 1.00 part by mass Leveling agent T-1 (shown below) 0.08 part by mass Methyl ethyl ketone 2000.00 parts by mass

[0159] Rod-shaped liquid crystal compound L-1

[0160] Leveling agent T-1

[0161] The horizontally aligned liquid crystal layer was formed by applying composition B-1 onto the alignment film P-2. That is, composition B-1 was first applied onto the alignment film P-2, followed by heating and then ultraviolet curing to form a liquid crystal fixing layer. More specifically, the liquid crystal fixing layer was formed by applying composition B-1 onto the alignment film P-2 to obtain a coating film, heating this coating film to 80°C on a hot plate, and then irradiating the coating film with ultraviolet light of 365 nm at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere at 80°C. 2The coating film was irradiated with light at an irradiation dose of 1.32 μm to fix the alignment of the liquid crystal compound. The thickness of the horizontally aligned liquid crystal layer after fixation was 1.32 μm.

[0162] Twelve similar horizontally aligned liquid crystal layers were formed. The twelve horizontally aligned liquid crystal layers were confirmed to have the following optical properties using an AxoScan (manufactured by Axometrics): thickness: 1.32 μm, Δn: 0.17 (center wavelength: 450 nm), in-plane retardation: 225 nm, and retardation in the thickness direction: 112.5 nm.

[0163] (Formation of Vertically Aligned Liquid Crystal Layer) To prepare a vertically aligned liquid crystal layer, the following composition E-1 was prepared.

[0164] Composition E-1 --------------------------------------------------- Rod-shaped liquid crystal compound L-1 (100.00 parts by mass) 8 parts by mass of polymerizable monomer (M-4) below Polymerization initiator (Irgacure 127, manufactured by BASF) 2 parts by mass Polymerization initiator (Irgacure OXE01, manufactured by BASF) 4 parts by mass Fluorine-based polymer (M-5) 0.4 parts by mass Fluorine-based polymer (M-6) 0.3 parts by mass Onium compound S01 2 parts by mass Polymer compound A107 5 parts by mass Toluene 621 parts by mass Methyl ethyl ketone 69 parts by mass

[0165] Polymerizable Monomer (M-4)

[0166] Fluorine-based polymer (M-5)

[0167] Fluorine-based polymer (M-6)

[0168] Onium salt compound S01

[0169] Polymer compound A107

[0170] Composition E-1 was applied to a support, and then irradiated with ultraviolet light (300 mJ / cm ) at 40° C. under a nitrogen purge and an oxygen concentration of 100 ppm. 2 ) was carried out to form a layer in which the alignment of the liquid crystal compound was fixed. Thereafter, the liquid crystal layer was peeled off from the support to form a vertically aligned liquid crystal layer. The thickness of the vertically aligned liquid crystal layer after fixation was 0.66 μm.

[0171] Twelve similar vertically aligned liquid crystal layers were formed. The twelve vertically aligned liquid crystal layers were confirmed to have the following optical properties using an AxoScan (manufactured by Axometrics): thickness: 0.66 μm, Δn: 0.17 (center wavelength: 450 nm), in-plane retardation: 0 nm, retardation in the thickness direction: −112.5 nm.

[0172] The prepared vertically aligned liquid crystal layer was bonded to a horizontally aligned liquid crystal layer using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) to prepare 12 liquid crystal layers (first and second liquid crystal layers). The sum of the in-plane retardation of this liquid crystal layer having a vertically aligned liquid crystal layer and a horizontally aligned liquid crystal layer was 225 nm. The sum of the retardation in the thickness direction of this liquid crystal layer having a vertically aligned liquid crystal layer and a horizontally aligned liquid crystal layer was 0 nm. Hereinafter, for convenience, this liquid crystal layer having a vertically aligned liquid crystal layer and a horizontally aligned liquid crystal layer will be referred to as a unit layer.

[0173] Two unit layers were bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) so that the angle between the slow axes of the horizontally aligned liquid crystal layers was 7.5°. That is, the angle bisecting the crossing angle between the slow axes on both sides was used as the reference line, and with counterclockwise rotation being positive (+) and clockwise rotation being negative (-), the angle θ of the in-plane slow axis of the horizontally aligned liquid crystal layer of one unit layer was 3.75°, and the angle θ of the in-plane slow axis of the horizontally aligned liquid crystal layer of the other unit layer was -3.75°. Six liquid crystal layer pairs each consisting of a first liquid crystal layer and a second liquid crystal layer were thus prepared.

[0174] Six liquid crystal layer pairs were laminated together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) to prepare a first liquid crystal polarization interference element. The liquid crystal layer pairs were laminated so that the bisectors of the angles between the in-plane slow axes of each liquid crystal layer pair were parallel. Therefore, this first liquid crystal polarization interference element had six liquid crystal layer pairs (12 unit layers), with the in-plane slow axis angle θ of the odd-numbered layers (first liquid crystal layer (first horizontally aligned liquid crystal layer)) being 3.75°, and the in-plane slow axis angle θ of the even-numbered layers (second liquid crystal layer (second horizontally aligned liquid crystal layer)) being -3.75°.

[0175] <Preparation of second liquid crystal polarization interference element> Twelve unit layers were formed in the same manner as in the first liquid crystal polarization interference element, except that the thickness of the horizontally aligned liquid crystal layer in the unit layer was 1.72 μm and the thickness of the vertically aligned liquid crystal layer was 0.86 μm. Furthermore, using these 12 unit layers, a second liquid crystal polarization interference element was prepared in the same manner as in the first liquid crystal polarization interference element. That is, the second liquid crystal polarization interference element also had six liquid crystal layer pairs (12 unit layers) each consisting of a first liquid crystal layer and a second liquid crystal layer, and the angle θ of the in-plane slow axis of the odd-numbered horizontally aligned liquid crystal layers was 3.75°, and the angle θ of the in-plane slow axis of the even-numbered horizontally aligned liquid crystal layers was −3.75°.

[0176] The 12 unit layers thus produced were confirmed to have the following optical properties using an AxoScan (manufactured by Axometrics): Horizontally aligned liquid crystal layer thickness: 1.72 μm, Δn: 0.16 (center wavelength 550 nm), in-plane retardation: 275 nm, thickness direction retardation: 137.5 nm Vertically aligned liquid crystal layer thickness: 0.86 μm, Δn: 0.16 (center wavelength 550 nm), in-plane retardation: 0 nm, thickness direction retardation: −137.5 nm Sum of in-plane retardation: 275 nm Sum of thickness direction retardation: 0 nm

[0177] Also in the second liquid crystal polarization interference element, the angle θ of the in-plane slow axis of the horizontal alignment layer is 3.75° for odd-numbered layers and −3.75° for even-numbered layers.

[0178] <Preparation of Optical Filter> The prepared first liquid crystal polarization interference element and second liquid crystal polarization interference element were bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) so that the line (reference line) bisecting the crossing angle formed by the in-plane slow axes of the odd-numbered and even-numbered layers when the respective liquid crystal polarization interference elements were prepared coincided, thereby preparing a laminated optical element having two liquid crystal polarization interference elements. The prepared liquid crystal polarization interference element was placed between polarizers arranged in a crossed Nicol configuration to prepare a bandpass filter. The bandpass filter was prepared by aligning the line (reference line) bisecting the crossing angle formed by the in-plane slow axes of the odd-numbered and even-numbered layers when the liquid crystal polarization interference element was prepared with the transmission axis of one of the polarizers.

[0179] The wavelength (center wavelength) and half-width showing maximum transmittance, as well as wavelength shift and side lobes, of the fabricated bandpass filters were measured using a spectroradiometer "SR-3" manufactured by Topcon Technohouse Corporation. The wavelength shift (absolute value) was measured when light was incident at a polar angle of 60° relative to when light was incident at a polar angle of 90°. Incident light from a polar angle of 60° was measured from two directions, azimuth angles of 0° and 90°, and the average value was taken as the measured value. The magnitude of the side lobe is the ratio of the side lobe transmittance to the transmittance of the center wavelength. As a result, the fabricated bandpass filter had two peaks in the transmitted light, one with a center wavelength of 450 nm and the other with a center wavelength of 550 nm. Based on the in-plane retardation of the unit layer, it is believed that the peak at a center wavelength of 450 nm is due to the first liquid crystal polarization interference element, and the peak at a center wavelength of 550 nm is due to the second liquid crystal polarization interference element. At the 450 nm peak, the half-width was 65 nm, the wavelength shift was less than 5 nm, and the side lobes were 10%, while at the 550 nm peak, the half-width was 80 nm, the wavelength shift was less than 5 nm, and the side lobes were 10%.

[0180] Example 2 <Preparation of First and Second Liquid Crystal Polarization Interference Elements> In the same manner as in Example 1, a first and second liquid crystal polarization interference element were prepared.

[0181] <Preparation of third liquid crystal polarization interference element> Twelve unit layers were formed in the same manner as in the first liquid crystal polarization interference element, except that the thickness of the horizontally aligned liquid crystal layer in the unit layer was 2.16 μm and the thickness of the vertically aligned liquid crystal layer was 1.08 μm. Furthermore, using these 12 unit layers, a third liquid crystal polarization interference element was prepared in the same manner as in the first liquid crystal polarization interference element. That is, the third liquid crystal polarization interference element also has six liquid crystal layer pairs each consisting of a first liquid crystal layer and a second liquid crystal layer.

[0182] The 12 unit layers thus produced were confirmed to have the following optical properties using an AxoScan (manufactured by Axometrics): Horizontally aligned liquid crystal layer thickness: 2.16 μmμm, Δn: 0.15 (center wavelength 650 nm), in-plane retardation: 325 nm, thickness direction retardation: 162.5 nm Vertically aligned liquid crystal layer thickness: 1.08 μm, Δn: 0.15 (center wavelength 650 nm), in-plane retardation: 0 nm, thickness direction retardation: −162.5 nm Sum of in-plane retardation: 325 nm Sum of thickness direction retardation: 0 nm

[0183] Also in the third liquid crystal polarization interference element, the angle θ of the in-plane slow axis of the horizontally aligned liquid crystal layer is 3.75° for odd-numbered layers and −3.75° for even-numbered layers.

[0184] <Preparation of optical filter> The first liquid crystal polarization interference element, the second liquid crystal polarization interference element and the third liquid crystal polarization interference element that are prepared are bonded together using adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.), so that the line that bisects the cross angle that the in-plane slow axis of odd-numbered layer and even-numbered layer forms when preparing each liquid crystal polarization interference element (reference line) coincides, prepare a laminated optical element that has three liquid crystal polarization interference elements.Furthermore, similar to Example 1, prepare the liquid crystal polarization interference element that is prepared between the polarizers that are arranged in cross Nicol, prepare a bandpass filter.

[0185] The wavelength (center wavelength) and half-width showing the maximum transmittance, as well as the wavelength shift and side lobes, of the fabricated bandpass filter were measured in the same manner as in Example 1. As a result, the fabricated bandpass filter had three peaks in the transmitted light, with center wavelengths of 450 nm, 550 nm, and 650 nm. From the in-plane retardation of the unit layer, it is believed that the peak at the center wavelength of 450 nm is due to the first liquid crystal polarization interference element, the peak at the center wavelength of 550 nm is due to the second liquid crystal polarization interference element, and the peak at the center wavelength of 650 nm is due to the third liquid crystal polarization interference element. Furthermore, at the 450 nm peak, the half-width was 65 nm, the wavelength shift was less than 5 nm, and the side lobe was 10%. Furthermore, at the 550 nm peak, the half-width was 80 nm, the wavelength shift was less than 5 nm, and the side lobe was 10%. Furthermore, at the 650 nm peak, the half-width was 95 nm, the wavelength shift was less than 5 nm, and the side lobe was 10%.

[0186] As shown in Examples 1 and 2, the laminated optical element of the present invention can accommodate multiple wavelength ranges when used, for example, in a bandpass filter, and also exhibits small wavelength shifts when light is incident from an oblique direction.

[0187] [Example 3] In Example 1, the angle θ of the in-plane slow axis of the horizontally aligned liquid crystal layer in the 12 unit layers constituting the first liquid crystal polarization interference element and the second liquid crystal polarization interference element was changed as shown in the following Table 1. Note that the angle θ of the in-plane slow axis of the horizontally aligned liquid crystal layer is the angle between the reference line and the in-plane slow axis of the horizontally aligned liquid crystal layer, as described above.

[0188] Other than this, a bandpass filter was fabricated in the same manner as in Example 1, and the center wavelength, half width, wavelength shift, and side lobes were measured in the same manner as in Example 1. As a result, the fabricated bandpass filter had two peaks in the transmitted light, one with a center wavelength of 450 nm and the other with a center wavelength of 550 nm, similar to Example 1. Furthermore, at the 450 nm peak, the half width was 65 nm, the wavelength shift was less than 5 nm, and the side lobe was less than 3%, and at the 550 nm peak, the half width was 80 nm, the wavelength shift was less than 5 nm, and the side lobe was less than 3%.

[0189] [Example 4] In Example 2, the angles of the in-plane slow axes of the 12 unit layers constituting the first liquid crystal polarization interference element, the second liquid crystal polarization interference element, and the third liquid crystal polarization interference element were changed as shown in Table 1 above. Other than this, a bandpass filter was fabricated in the same manner as in Example 2, and the center wavelength, half-width, wavelength shift, and side lobe were measured in the same manner as in Example 1. As a result, the fabricated bandpass filter had three peaks in the transmitted light, at center wavelengths of 450 nm, 550 nm, and 650 nm, as in Example 2. Furthermore, at the 450 nm peak, the half-width was 65 nm, the wavelength shift was less than 5 nm, and the side lobe was less than 3%; at the 550 nm peak, the half-width was 80 nm, the wavelength shift was less than 5 nm, and the side lobe was less than 3%; and at the 650 nm peak, the half-width was 95 nm, the wavelength shift was less than 5 nm, and the side lobe was less than 3%.

[0190] As described above, when used in, for example, a bandpass filter, the laminated optical element of the present invention can accommodate multiple wavelength ranges and exhibits small wavelength shifts when light is incident from an oblique direction. The side lobes of the bandpass filters in Examples 1 and 2 are 10%. However, as shown in Examples 3 and 4, the side lobes of the bandpass filter can be reduced by reducing the absolute value of the angle between the in-plane slow axis of the rod-shaped liquid crystal layers of the liquid crystal layer pairs on both sides and the reference line compared to the liquid crystal layer of the central liquid crystal layer pair in the thickness direction.

[0191] <<Reference Examples>> As described above, the liquid crystal polarization interference element used in the laminated optical element of the present invention is an optical element that, even in a single layer, acts as a retardation plate for light in a specific wavelength range (light outside the specific wavelength range) and does not act as a retardation layer for light of other wavelengths (light in the specific wavelength range), and like the laminated optical element of the present invention, can be used as a bandpass filter or the like of various configurations. Specific examples are shown below. [Reference Example 1] <Preparation of Liquid Crystal Polarization Interference Element> Eight unit layers similar to the second liquid crystal polarization interference element in Example 1 were prepared. That is, this unit layer was prepared by bonding the horizontally aligned liquid crystal layer and the vertically aligned liquid crystal layer shown below together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.). Horizontally aligned liquid crystal layer thickness: 1.72 μm, Δn: 0.16 (center wavelength 550 nm), in-plane retardation: 275 nm, thickness direction retardation: 137.5 nm Vertically aligned liquid crystal layer thickness: 0.86 μm, Δn: 0.16 (center wavelength 550 nm), in-plane retardation: 0 nm, thickness direction retardation: −137.5 nm Sum of in-plane retardation: 275 nm Sum of thickness direction retardation: 0 nm

[0192] Two unit layers were bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) so that the angle between the slow axes of the horizontally aligned liquid crystal layers was 11.25°. That is, the angle bisecting the crossing angle between the slow axes on both sides was used as the reference (reference line), with counterclockwise rotation being positive (+) and clockwise rotation being negative (-). The two unit layers were bonded together so that the angle θ between the in-plane slow axes of the horizontally aligned liquid crystal layer of one unit layer was 5.625° and the angle θ between the in-plane slow axes of the horizontally aligned liquid crystal layer of the other unit layer was -5.625°. This resulted in four liquid crystal layer pairs each consisting of a first liquid crystal layer and a second liquid crystal layer.

[0193] Four liquid crystal layer pairs were laminated together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) to prepare a liquid crystal polarization interference element. The liquid crystal layer pairs were laminated so that the bisectors of the angles between the in-plane slow axes of each liquid crystal layer pair were parallel. Therefore, this liquid crystal polarization interference element had four liquid crystal layer pairs (eight unit layers), with the in-plane slow axis angle θ of the odd-numbered layer (first liquid crystal layer (first horizontally aligned liquid crystal layer)) being 5.625°, and the in-plane slow axis angle θ of the horizontally aligned liquid crystal layer of the even-numbered layer (second liquid crystal layer (second horizontally aligned liquid crystal layer)) being -5.625°.

[0194] <Preparation of Optical Filter> A bandpass filter was prepared by placing the prepared liquid crystal polarization interference element between polarizers arranged in a crossed Nicol configuration. One of the polarizers was a reflective polarizer (reflective linear polarizer). The bandpass filter was prepared by aligning the transmission axis of one polarizer with the line (reference line) that bisects the crossing angle formed by the in-plane slow axes of the odd-numbered and even-numbered layers when the liquid crystal polarization interference element was prepared.

[0195] As in Example 1, the wavelength (center wavelength) and half-width showing maximum transmittance, as well as wavelength shift and side lobes, of the fabricated bandpass filter were measured using a spectroradiometer "SR-3" manufactured by Topcon Technohouse Corporation. The reflective polarizer side of the bandpass filter was the light exit side of the transmitted light. As a result, the fabricated bandpass filter had a center wavelength of 550 nm, a half-width of 120 nm, a wavelength shift of less than 5 nm, and a side lobe of 10%. Furthermore, in this example, light was also emitted from the polarizer on the incident side. When this exiting light was measured, it was found to have opposite characteristics to the light transmitted through the bandpass filter. As a result, it was confirmed that, with the bandpass filter of this example, light that did not pass through the bandpass filter, i.e., components whose polarization was not changed by the liquid crystal polarization interference element, was reflected by the reflective linear polarizer on the exit side and emitted from the incident side.

[0196] In addition, a similar liquid crystal polarization interference element was fabricated using only a unit layer of horizontally aligned liquid crystal layers without a vertically aligned liquid crystal layer, and a similar bandpass filter was fabricated using this liquid crystal polarization interference element. As a result, the bandpass filter had a center wavelength of 550 nm, a half-width of 120 nm, a wavelength shift of 90 nm, and a side lobe of 10%, which was significantly large in wavelength shift.

[0197] Reference Example 2 An optical filter was prepared in the same manner as in Reference Example 1, except that both polarizers were absorption polarizers (absorption linear polarizers) and the polarizers were arranged in parallel Nicols. The center wavelength, half-width, wavelength shift, and side lobe of the non-transmitting portion of the prepared optical filter were measured. The measurements were performed using a spectroradiometer "SR-3" manufactured by Topcon Technohouse Corporation. As a result, the center wavelength of the non-transmitting portion of the prepared optical filter was 550 nm, the half-width was 120 nm, the wavelength shift was less than 5 nm, and the side lobe was 10%.

[0198] [Reference Example 3] In Reference Example 1, the angle θ of the in-plane slow axis of the horizontally aligned liquid crystal layer in the eight unit layers constituting the liquid crystal polarization interference element was changed as shown in the following Table 2. Note that the angle θ of the in-plane slow axis of the horizontally aligned liquid crystal layer is the angle between the reference line and the in-plane slow axis of the horizontally aligned liquid crystal layer, as described above.

[0199]

[0200] Other than this, a bandpass filter was prepared in the same manner as in Reference Example 1, and the center wavelength, half-width, wavelength shift, and side lobe were measured in the same manner as in Reference Example 1. As a result, the prepared bandpass filter had a center wavelength of 550 nm, a half-width of 120 nm, a wavelength shift of less than 5 nm, and a side lobe of 3% or less. That is, in this example, the side lobe of the transmitted light is reduced compared to Reference Example 1. Furthermore, as described above, the wavelength shift of the bandpass filter using a liquid crystal polarization interference element prepared with a unit layer having only a horizontally aligned liquid crystal layer was 90 nm, but in this example, the wavelength shift was very small, less than 5 nm, as in Reference Example 1. Furthermore, as in Reference Example 1, in this example, light was also emitted from the polarizer on the incident side. When this emitted light was measured, it had the opposite characteristics to the light that passed through the bandpass filter.

[0201] [Reference Example 4] In Reference Example 2, the angles of the in-plane slow axes in the eight unit layers constituting the liquid crystal polarization interference element were changed as shown in Table 2 above. Except for this, an optical filter was prepared in the same manner as in Reference Example 2, and the center wavelength, half-width, wavelength shift, and side lobe were measured in the same manner as in Example 1. As a result, the non-transmitting portion of the prepared optical filter had a center wavelength of 550 nm, a half-width of 120 nm, a wavelength shift of less than 5 nm, and a side lobe of 3% or less. That is, in this example, the side lobe is reduced compared to Reference Example 2.

[0202] Reference Example 5 An optical filter (bandpass filter) was prepared in the same manner as in Reference Example 2, except that the polarizers were arranged in a crossed Nicol configuration. The center wavelength, half-width, wavelength shift, and side lobes of this bandpass filter were measured in the same manner as in Example 1. As a result, the center wavelength, half-width, wavelength shift, and side lobes of the prepared bandpass filter were 550 nm, 120 nm, less than 5 nm, and 10%. Meanwhile, a bandpass filter was prepared in the same manner as in Reference Example 2, except that the angles of the in-plane slow axes of the eight unit layers constituting the liquid crystal polarization interference element were changed as shown in Table 2 above, and the polarizers were arranged in a crossed Nicol configuration. The center wavelength, half-width, wavelength shift, and side lobes of this bandpass filter were measured in the same manner as in Example 1. As a result, the prepared bandpass filter had a center wavelength of 550 nm, a half-width of 120 nm, a wavelength shift of less than 5 nm, and a side lobe of 3% or less, demonstrating reduced side lobes compared to the above-described bandpass filter.

[0203] It can be suitably used as a bandpass filter or the like in various optical devices.

[0204] REFERENCE SIGNS LIST 10 Optical filter 12 First polarizer 14 Second polarizer 16 Laminated optical element 16a First liquid crystal polarization interference element 16b Second liquid crystal polarization interference element 18 Rod-like liquid crystal compound 20 First liquid crystal layer 20H First horizontally aligned liquid crystal layer 20V First vertically aligned liquid crystal layer 24 Second liquid crystal layer 24H Second horizontally aligned liquid crystal layer 24V Second vertically aligned liquid crystal layer 26 Liquid crystal layer set 90 Light source unit 93 Condenser lens 94 Optical filter 96 Light receiving unit 98 Beam splitter 100 Light guide element

Claims

1. A laminated optical element having a plurality of liquid crystal polarization interference elements, wherein the liquid crystal polarization interference elements have at least two pairs of liquid crystal layer pairs, each pair consisting of a first liquid crystal layer and a second liquid crystal layer, in the thickness direction; the first liquid crystal layer includes at least one first horizontally aligned liquid crystal layer formed by fixing horizontally aligned rod-shaped liquid crystal compounds, and at least one first vertically aligned liquid crystal layer formed by fixing vertically aligned rod-shaped liquid crystal compounds; the second liquid crystal layer includes at least one second horizontally aligned liquid crystal layer formed by fixing horizontally aligned rod-shaped liquid crystal compounds, and at least one second vertically aligned liquid crystal layer formed by fixing vertically aligned rod-shaped liquid crystal compounds; the in-plane slow axis of the first horizontally aligned liquid crystal layer intersects with the in-plane slow axis of the second horizontally aligned liquid crystal layer; the in-plane retardation of the first horizontally aligned liquid crystal layer is equal to that of the second horizontally aligned liquid crystal layer; The plurality of liquid crystal polarization interference elements are a laminated optical element in which the first liquid crystal layers included in the liquid crystal polarization interference elements have different in-plane retardations.

2. The laminated optical element of claim 1, wherein the liquid crystal polarization interference element has a liquid crystal layer pair arranged on both sides in the thickness direction and a liquid crystal layer pair arranged in the center in the thickness direction, the liquid crystal layer pair having different in-plane slow axis directions of the first horizontally aligned liquid crystal layer and the second horizontally aligned liquid crystal layer.

3. The laminated optical element according to claim 1, wherein the liquid crystal polarization interference element includes the first liquid crystal layer and the second liquid crystal layer containing an infrared absorbing dye.

4. The laminated optical element according to claim 1, wherein the first liquid crystal layer and the second liquid crystal layer of the liquid crystal polarization interference element contain a liquid crystal elastomer.

5. An optical filter comprising, in this order, a first polarizer, a laminated optical element according to any one of claims 1 to 4, and a second polarizer.

6. The optical filter according to claim 5, wherein the first polarizer and the second polarizer are arranged with their transmission axes orthogonal to each other.

7. The optical filter according to claim 5, wherein the first polarizer and the second polarizer are arranged with their transmission axes parallel to each other.

8. The optical filter according to claim 5, wherein one of the first polarizer and the second polarizer is a reflective polarizer.

9. An optical system comprising a light source section, the optical filter according to claim 5, and a light receiving section.

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