Laminated optical element, optical filter, and optical system

Abstract

The objective of the present invention is to solve the problem of providing: a laminated optical element that, when used in a bandpass filter or the like that supports multiple wavelengths, can suppress fluctuations in the wavelength of light exhibiting maximum transmittance, even in cases where the light is incident from an oblique direction; an optical filter using said laminated optical element; and an optical system using said laminated optical element. The problem is solved by including two or more pairs each comprising a first liquid crystal layer and a second liquid crystal layer, the first and / or second liquid crystal layer including a liquid crystal layer in which a rod-like liquid crystal compound is fixed in place and / or a liquid crystal layer in which a discotic liquid crystal compound is fixed in place, the first and second liquid crystal layers having a plurality of liquid crystal polarization interference elements with intersecting in-plane slow phase axes and equal in-plane retardation, and furthermore, the liquid crystal polarization interference elements having mutually different total in-plane retardations in the first liquid crystal layer.

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 two or more 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, wherein the first or second liquid crystal layer includes at least one liquid crystal layer R containing a rod-shaped liquid crystal compound, and the first or second liquid crystal layer includes at least one liquid crystal layer D containing a discotic liquid crystal compound, wherein the in-plane slow axis of the first liquid crystal layer intersects with the in-plane slow axis of the second liquid crystal layer, and the sum of the in-plane retardations of the first liquid crystal layer and the second liquid crystal layer is equal, and the plurality of liquid crystal polarization interference elements are a laminated optical element in which the sums of the in-plane retardations of the first liquid crystal layers included in the liquid crystal polarization interference elements are 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 liquid crystal layer and the second liquid crystal layer. [3] The liquid crystal polarization interference element is a laminated optical element according to [1] or [2], in which the liquid crystal layer R and the liquid crystal layer D 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 liquid crystal layer R and the liquid crystal layer D 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], in which the first polarizer and the second polarizer are arranged with their transmission axes perpendicular to each other. [7] The optical filter according to [5], in which the first polarizer and the second polarizer are arranged with their transmission axes parallel to each other. [8] The optical filter according to any one of [5] to [7], wherein either the first polarizer or 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 conceptual diagram showing an example of an optical filter of the present invention. FIG. 2 is a conceptual diagram 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 conceptual diagram for explaining another example of a liquid crystal polarization interference element. FIG. 6 is a conceptual diagram for explaining another example of a liquid crystal polarization interference element. FIG. 7 is a conceptual diagram for explaining another example of a liquid crystal polarization interference element. FIG. 8 is a graph for explaining the optical filter of the present invention. FIG. 9 is a conceptual diagram for explaining another example of a liquid crystal polarization interference element. FIG. 10 is a conceptual diagram showing an example of an optical system of the present invention. FIG. 11 is a conceptual diagram showing another example of an optical system of the present invention. FIG. 12 is a conceptual diagram showing another example of an optical system of the present invention. FIG. 13 is a conceptual diagram showing another example of an optical system of the present invention. FIG. 14 is a conceptual diagram showing another example of an optical system of the present invention. FIG. 15 is a conceptual diagram showing another example of an 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 addition, 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 may differ from the actual ones.

[0013] 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, and 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 is a bandpass filter that corresponds to multiple wavelength ranges (wavelengths). The illustrated optical filter 10, which uses a laminated optical element 16 having two liquid crystal polarization interference elements, is a bandpass filter that transmits light in two wavelength ranges and blocks light of other wavelengths (see FIG. 4).

[0014] 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. In the present invention, orthogonal does not necessarily have to be completely orthogonal (90°), and may have an error of ±10° or less. There are no limitations on the first polarizer 12 and the second polarizer 14, and various known linear polarizers can be used, such as iodine-based polarizers, dye-based polarizers using dichroic dyes, polyene-based polarizers, and wire-grid polarizers.

[0015] 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.

[0016] 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.

[0017] 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.

[0018] 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 liquid crystal polarization interference element (laminated optical element 16). 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.

[0019] 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.

[0020] When the first polarizer 12 and the second polarizer 14 are arranged in a parallel Nicol configuration, the optical filter 10 functions as follows. Similarly, in this example, linearly polarized light transmitted through the first polarizer 12 is incident on the liquid crystal polarization interference element (laminated optical element 16), 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.

[0021] 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.

[0022] 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.

[0023] 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, wherein the first liquid crystal layer or the second liquid crystal layer includes at least one liquid crystal layer R containing a rod-shaped liquid crystal compound, the first liquid crystal layer or the second liquid crystal layer includes at least one liquid crystal layer D containing a discotic liquid crystal compound, the in-plane slow axis of the first liquid crystal layer intersects with the in-plane slow axis of the second liquid crystal layer, and the sum of the in-plane retardations of the first liquid crystal layer and the second liquid crystal layer is equal.

[0024] As an example of a liquid crystal polarization interference element, the structure of the first liquid crystal polarization interference element 16a is conceptually shown in Fig. 2. 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 structure 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 sums of the in-plane retardations of the first liquid crystal layers are different from each other.

[0025] 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 are stacked in the thickness direction, each pair consisting of a first liquid crystal layer 20 and a second liquid crystal layer 24. Therefore, the total number of stacked first liquid crystal layers 20 and second liquid crystal layers 24 is an even number. In other words, the liquid crystal polarization interference element has a configuration in which the same first liquid crystal layers 20 and second liquid crystal layers 24 are stacked alternately.

[0026] The first liquid crystal polarization interference element 16a shown in FIG. 2 has, as an example, the following: the first liquid crystal layer includes at least one liquid crystal layer R1 formed by fixing horizontally aligned rod-shaped liquid crystal compounds and at least one liquid crystal layer D1 formed by fixing vertically aligned discotic liquid crystal compounds; the second liquid crystal layer includes at least one liquid crystal layer R2 formed by fixing horizontally aligned rod-shaped liquid crystal compounds and at least one liquid crystal layer D2 formed by fixing vertically aligned discotic liquid crystal compounds; the in-plane slow axis of the liquid crystal layer R1 is parallel to the in-plane slow axis of the liquid crystal layer D1, and the in-plane slow axis of the liquid crystal layer R2 is parallel to the in-plane slow axis of the liquid crystal layer D2; the in-plane slow axis of the liquid crystal layer R1 intersects with the in-plane slow axis of the liquid crystal layer R2; Furthermore, the total in-plane retardation of the liquid crystal layer R1 is equal to the total in-plane retardation of the liquid crystal layer D1, and the total in-plane retardation of the liquid crystal layer R2 is equal to the total in-plane retardation of the liquid crystal layer D2.

[0027] The first liquid crystal layer 20 includes a rod-shaped liquid crystal layer 20R1 and a discotic liquid crystal layer 20D1. The rod-shaped liquid crystal layer 20R1 corresponds to the above-mentioned liquid crystal layer R1, and the discotic liquid crystal layer 20D1 corresponds to the above-mentioned liquid crystal layer D1. The second liquid crystal layer 24 includes a rod-shaped liquid crystal layer 24R2 and a discotic liquid crystal layer 24D2. The rod-shaped liquid crystal layer 24R2 corresponds to the above-mentioned liquid crystal layer R2, and the discotic liquid crystal layer 24D2 corresponds to the above-mentioned liquid crystal layer D2.

[0028] As described above, the rod-shaped liquid crystal layer 20R1 and the rod-shaped liquid crystal layer 24R2 are both liquid crystal layers formed by horizontally aligning and fixing the rod-shaped liquid crystal compound 18R. The discotic liquid crystal layer 20D1 and the discotic liquid crystal layer 24D2 are both liquid crystal layers formed by vertically aligning and fixing the discotic liquid crystal compound 18D. In the following description, when it is not necessary to distinguish between the rod-shaped liquid crystal layer 20R1 and the rod-shaped liquid crystal layer 24R2, they will also be collectively referred to as "rod-shaped liquid crystal layers." In the following description, when it is not necessary to distinguish between the discotic liquid crystal layer 20D1 and the discotic liquid crystal layer 24D2, they will also be collectively referred to as "disctic liquid crystal layers."

[0029] The boundaries between the rod-shaped liquid crystal layer and the discotic liquid crystal layer in the first liquid crystal layer 20 and the second liquid crystal layer 24 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. The method of cutting the liquid crystal polarization interference element obliquely and analyzing each liquid crystal layer 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).

[0030] In the first liquid crystal layer 20, the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 is parallel to the in-plane slow axis of the discotic liquid crystal layer 20D1. In the second liquid crystal layer 24, the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 is parallel to the in-plane slow axis of the discotic liquid crystal layer 24D2. In the present invention, "parallel" does not only mean completely parallel, but also includes a case where the angle between the two axes is greater than 0° and less than or equal to 10°.

[0031] The in-plane slow axes of the rod-shaped liquid crystal layer and the discotic liquid crystal layer can be detected by the above-mentioned method of observation using an SEM and the method of obliquely cutting and analyzing the liquid crystal polarization interference element.

[0032] Furthermore, in the liquid crystal polarization interference element, the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 of the first liquid crystal layer 20 intersects with the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 of the second liquid crystal layer 24. Specifically, the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 are tilted in opposite directions at the same angle with respect to a certain reference line. More specifically, the direction of the in-plane slow axis of the liquid crystal layer is, for example, defined as 0° with the direction of the reference line being positive (+) counterclockwise and negative (-) clockwise. For example, if the angle between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 is φ [°], the angle between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 is −φ [°]. That is, the angle formed between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the angle formed between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 have the same absolute value.

[0033] The optical filter 10 shown in the figure is configured, for example, such that, with the transmission axis of the first polarizer 12 as a reference line, the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 in the first liquid crystal layer 20 of the liquid crystal polarization interference element is "φ [°]," and the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 in the second liquid crystal layer 24 of the liquid crystal polarization interference element is "-φ [°]." In other words, the optical filter 10 is configured such that the transmission axis (reference line) of the first polarizer 12 coincides with the bisector of the angle between the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 of the liquid crystal polarization interference element.

[0034] In the optical filter 10 of the present invention, the reference line is not limited to the transmission axis of the first polarizer 12. As an example, in the optical filter 10 of the present invention, the reference line may be any one of the absorption axis of the first polarizer 12, the transmission axis of the second polarizer 14, and the absorption axis of the second polarizer 14.

[0035] 2, in a liquid crystal polarization interference element in which the same first liquid crystal layer 20 and second liquid crystal layer 24 are alternately laminated, the absolute value [°] of the angle between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 can be calculated by the following formula depending on the rotation angle (optical rotation angle) of linearly polarized light intended by the liquid crystal polarization interference element and the number of first liquid crystal layers 20 and second liquid crystal layers 24 included in the liquid crystal polarization interference element. That is, since the rotation angle of linearly polarized light intended by the liquid crystal polarization interference element is usually 90°, the absolute value of the angle between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 can be calculated by the following formula: 90 ÷ (number of layers of the first liquid crystal layer 20 and second liquid crystal layer 24) ÷ 2

[0036] For example, if the first liquid crystal layer 20 and the second liquid crystal layer 24 each have eight layers, i.e., if there are four liquid crystal layer pairs 26, then 90 / 8 / 2=5.625. Therefore, in this example, the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 of the first liquid crystal layer 20 is 5.625°, and the angle between the transmission axis of the first polarizer 12 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 of the second liquid crystal layer 24 is −5.625°.

[0037] The number of first liquid crystal layers 20 and second liquid crystal layers 24 in the liquid crystal polarization interference element, i.e., the number of liquid crystal layer pairs 26, can be detected by the above-mentioned SEM observation method and by cutting the liquid crystal polarization interference element at an angle.

[0038] In the present invention, the liquid crystal polarization interference element is not limited to perfect agreement between the angle between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the absolute value of the angle between the reference line and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2, and may have an error of ±10° or less. However, it is preferable that this error is small, and it is most preferable that the absolute values ​​of the angles between the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 are identical. This also applies to the agreement of other angles.

[0039] 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 optical 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 methods such as observation using an 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.

[0040] In the first liquid crystal polarization interference element 16a, the rod-shaped liquid crystal layer 20R1 and the discotic liquid crystal layer 20D1 of the first liquid crystal layer 20 have the same in-plane retardation (Re). Also, in the first liquid crystal polarization interference element 16a, the rod-shaped liquid crystal layer 24R2 and the discotic liquid crystal layer 24D2 of the second liquid crystal layer 24 have the same in-plane retardation. In the illustrated example, the first liquid crystal layer 20 and the second liquid crystal layer 24 each include one rod-shaped liquid crystal layer and one discotic liquid crystal layer. However, as will be described later, the present invention is not limited to this, and the first liquid crystal layer and the second liquid crystal layer may each include multiple rod-shaped liquid crystal layers and multiple discotic liquid crystal layers. In this case, in the first liquid crystal layer 20 and the second liquid crystal layer 24, the sum of the in-plane retardations of the multiple rod-shaped liquid crystal layers is set to be equal to the sum of the in-plane retardations of the multiple discotic liquid crystal layers. In this case, it is preferable to increase the number of liquid crystal layers by dividing each liquid crystal layer into smaller regions (rod-shaped liquid crystal layers) composed of rod-shaped liquid crystal compound 18R and regions (disk-shaped liquid crystal layers) composed of discotic liquid crystal compound 18D, thereby reducing the difference between the front (normal) retardation and the retardation at polar angles for a wider range of oblique directions.

[0041] Furthermore, in the present invention, it is preferable that the in-plane retardation of the first liquid crystal layer 20 and the in-plane retardation of the second liquid crystal layer 24 are equal to each other.

[0042] In the present invention, "equal in-plane retardation" does not necessarily mean that the in-plane retardations are completely identical, and may have an error of 10% or less. However, it is preferable that this difference is small, and it is preferable that the in-plane retardations of the rod-shaped liquid crystal layer and the discotic liquid crystal layer in the first liquid crystal layer 20 and the second liquid crystal layer 24, as well as the in-plane retardation of the first liquid crystal layer 20 and the second liquid crystal layer 24, are completely identical. This also applies to the sum of the in-plane retardations.

[0043] In the present invention, the liquid crystal polarization interference element is not limited to a configuration in which the in-plane retardation of the first liquid crystal layer is equal to the in-plane retardation of the second liquid crystal layer. For example, as long as the sum of the in-plane retardations of the first and second liquid crystal layers satisfies the desired retardation value, the in-plane retardation of the first liquid crystal layer may be different from the in-plane retardation of the second liquid crystal layer. The desired retardation value of the present invention may be, for example, a half-wave retardation value.

[0044] In a liquid crystal polarization interference element, the measurement wavelength for in-plane retardation is determined, for example, as follows: Two polarizers are arranged in a crossed Nicol configuration, and a liquid crystal polarization interference element is placed between them. In this case, the transmission axis or absorption axis of one of the polarizers arranged in a crossed Nicol configuration is aligned with the bisector of the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2. In this state, the transmittance is measured at each wavelength, and the wavelength with the highest transmittance is determined as the measurement wavelength for in-plane retardation.

[0045] The in-plane retardation of each liquid crystal layer may be measured by a known method, such as a method using an AxoScan manufactured by Axometrics. Alternatively, the in-plane retardation of each liquid crystal layer may be calculated using Δnd, where Δn is the birefringence of the liquid crystal compound 18 constituting the liquid crystal layer, and d is the thickness of the liquid crystal layer.

[0046] In the liquid crystal polarization interference element, the in-plane retardation of the rod-shaped liquid crystal layer and the discotic liquid crystal layer is preferably half the wavelength of the light at which the liquid crystal polarization interference element is assumed to function as a λ / 2 retarder. That is, the in-plane retardation of the first liquid crystal layer 20 and the second liquid crystal layer 24 is preferably half the wavelength of the light at which the liquid crystal polarization interference element is assumed to function as a λ / 2 retarder. For example, when the wavelength of the light at which the liquid crystal polarization interference element is assumed to mainly function as a λ / 2 retarder is 550 nm, the in-plane retardation of the rod-shaped liquid crystal layer and the discotic liquid crystal layer is preferably 137.5 nm. Therefore, in this case, the in-plane retardation of the first liquid crystal layer 20 and the second liquid crystal layer 24 is preferably 275 nm.

[0047] With this configuration, the liquid crystal polarization interference element functions as a λ / 2 retarder for light in a specific wavelength range. As described above, the first liquid crystal polarization interference element 16a has a rod-shaped liquid crystal layer made of rod-shaped liquid crystal compound 18R and a discotic liquid crystal layer made of discotic liquid crystal compound 18D, and is configured such that first liquid crystal layers 20 and second liquid crystal layers 24, whose in-plane slow axes have opposite directions relative to the reference line and whose absolute values ​​of the in-plane slow axes angles relative to the reference line are equal, are alternately stacked. That is, the first liquid crystal polarization interference element 16a has a rod-shaped liquid crystal layer and a discotic liquid crystal layer, and is configured such that first liquid crystal layers 20 and second liquid crystal layers 24, whose in-plane slow axes have angles of "φ" and "-φ" relative to the reference line, are alternately stacked. Light passing through such a liquid crystal polarization interference element is alternately and repeatedly influenced by the in-plane slow axis having an angle of "φ" relative to the reference line and the in-plane slow axis having an angle of "-φ" relative to the reference line. For example, when the absolute value of the angle relative to the reference line is 5.625°, the light passing through the liquid crystal polarization interference element is rotated by the in-plane slow axis having an angle of 5.625° relative to the reference line, and then rotated by the in-plane slow axis having an angle of -5.625° relative to the reference line. Therefore, the in-plane retardation of the first liquid crystal layer 20 and the second liquid crystal layer 24 is set as described above depending on the wavelength of light for which the liquid crystal polarization interference element is intended to function as a λ / 2 retarder. Furthermore, the angle of the in-plane slow axis in the first liquid crystal layer 20 and the second liquid crystal layer 24 is adjusted depending on the number of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24. This allows the formation of a liquid crystal polarization interference element that acts as a λ / 2 retardation plate for light in a specific wavelength range and does not act as a retardation plate for light other than that, i.e., does not sense in-plane retardation. The function of such a liquid crystal polarization interference element as a retardation plate is the same for various liquid crystal polarization interference elements described later.

[0048] Therefore, by arranging a liquid crystal polarization interference element between two polarizers arranged in a crossed Nicol configuration so that the transmission axis or absorption axis of one polarizer coincides with the bisector of the angle formed by the in-plane slow axes of the first liquid crystal layer 20 and the second liquid crystal layer 24, it is possible to obtain a bandpass filter that rotates (optical rotation) only light in a specific wavelength range, of the linearly polarized light that has passed through one polarizer, by λ / 2 and emits it from the other polarizer. Here, as mentioned above, conventional bandpass filters have the problem that when light is incident from an oblique direction, the wavelength of light that exhibits maximum transmittance varies, as conceptually shown in Figure 3, resulting in a so-called wavelength shift.

[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 both have a rod-shaped liquid crystal layer made of rod-shaped liquid crystal compound 18R and a discotic liquid crystal layer made of discotic liquid crystal compound 18D, with their in-plane slow axes parallel to each other, and the in-plane retardation of the rod-shaped liquid crystal layer is equal to the in-plane retardation of the discotic liquid crystal layer. Therefore, in the first liquid crystal layer 20 and the second liquid crystal layer 24, the thickness direction retardation (Rth) of the rod-shaped liquid crystal layer can be offset by the thickness direction retardation of the discotic liquid crystal layer. As a result, by using such a laminated optical element of the present invention using a liquid crystal polarization interference element as a bandpass filter, it is possible to suppress wavelength shift, which is a change in the wavelength of light exhibiting maximum transmittance, even when light is incident from an oblique direction, as conceptually shown in FIG. 4 . As described above, the laminated optical element of the present invention has a plurality of such liquid crystal polarization interference elements. Therefore, the optical filter of the present invention acts as a bandpass filter for light in a plurality of wavelength ranges, as shown in the example of the laminated optical element of the present invention having two liquid crystal polarization interference elements in Fig. 4. The effect of suppressing such wavelength shift is similar to that of various liquid crystal polarization interference elements described later.

[0050] In the present invention, there are no limitations on the thickness of the first liquid crystal layer 20 and the second liquid crystal layer 24, and thicknesses that provide the desired in-plane retardation may be appropriately set depending on the rod-shaped liquid crystal compound 18R and the discotic liquid crystal compound 18D used. The first liquid crystal layer 20 and the second liquid crystal layer 24 are typically formed using the same liquid crystal compound. As described above, in the example shown in FIG. 2 , the first liquid crystal layer 20 and the second liquid crystal layer 24 have the same in-plane retardation. Therefore, the thicknesses of the first liquid crystal layer 20 and the second liquid crystal layer 24 are typically the same.

[0051] Furthermore, there are no limitations on the thicknesses of the rod-shaped liquid crystal layer 20R1 and the discotic liquid crystal layer 20D1 in the first liquid crystal layer 20 and the rod-shaped liquid crystal layer 24R2 and the discotic liquid crystal layer 24D2 in the second liquid crystal layer 24. That is, the thicknesses of the rod-shaped liquid crystal layer and the discotic liquid crystal layer in the first liquid crystal layer 20 and the second liquid crystal layer 24 may be appropriately set so as to obtain the desired in-plane retardation depending on the liquid crystal compound used. Here, it is preferable that the rod-shaped liquid crystal compound 18R forming the rod-shaped liquid crystal layer and the discotic liquid crystal compound 18D forming the discotic liquid crystal layer have similar Δn values, and more preferably, the same Δn values. Therefore, it is preferable that the thicknesses of the rod-shaped liquid crystal layer and the discotic liquid crystal layer in the first liquid crystal layer 20 and the second liquid crystal layer 24 are the same.

[0052] In the first liquid crystal polarization interference element 16a shown in Figure 2, the thicknesses of the first liquid crystal layer 20 and the second liquid crystal layer 24 correspond to the thicknesses of the rod-shaped liquid crystal layer and the discotic liquid crystal layer described above. The first liquid crystal layer 20 and the second liquid crystal layer 24 are usually formed using the same liquid crystal compound. As described above, the in-plane retardation of the first liquid crystal layer 20 and the second liquid crystal layer 24 is equal. Therefore, the thicknesses of the first liquid crystal layer 20 and the second liquid crystal layer 24 are usually equal.

[0053] In the liquid crystal polarization interference element used in the laminated optical element of the present invention, there is no limitation on the thickness of the first liquid crystal layer 20 and the second liquid crystal layer 24. Here, the thickness of the first liquid crystal layer 20 and the second liquid crystal layer 24 is preferably set so that the product of the birefringence (Δn) of the liquid crystal compound and the thickness of the liquid crystal layer (in-plane retardation (Δnd)) is approximately half the center wavelength at which it acts as a retardation plate, depending on the liquid crystal compound used. As an example, considering that the liquid crystal polarization interference element acts as a retardation plate for visible light, the thickness of the first liquid crystal layer 20 and the second liquid crystal layer 24 is preferably 1 to 5 μm, more preferably 1 to 3 μm. Therefore, in the first liquid crystal polarization interference element 16a shown in FIG. 2, the thickness of the rod-shaped liquid crystal layer and the discotic liquid crystal layer in the first liquid crystal layer 20 and the second liquid crystal layer 24 is preferably 0.5 to 2.5 μm, more preferably 0.5 to 1.5 μm.

[0054] In the laminated optical element of the present invention, the total number of stacked first and second liquid crystal layers 20 and 24 of the liquid crystal polarization interference element is not limited other than that, so long as there are two or more liquid crystal layer sets 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.

[0055] In the laminated optical element of 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 of the liquid crystal polarization interference element, the narrower the half-width of the wavelength range of transmitted light. In other words, the greater the total number N 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 made by the optical filter 10. The total number N of layers of the first liquid crystal layer 20 and the second liquid crystal layer 24 in the liquid crystal polarization interference element, i.e., the number of liquid crystal layer pairs 26, can be appropriately selected depending on the width of the transmission wavelength range required for the optical filter 10. 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.

[0056] The liquid crystal polarization interference element having such a first liquid crystal layer 20 and a second liquid crystal layer 24 may be fabricated by a known method, such as a coating method using a liquid crystal composition for forming a rod-shaped liquid crystal layer and a discotic liquid crystal layer.

[0057] 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 a microgroove, 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 using a polarizer such as a wire grid polarizer.

[0058] Separately, a liquid crystal composition for forming a rod-shaped liquid crystal layer containing rod-shaped liquid crystal compound 18R and a liquid crystal composition for forming a discotic liquid crystal layer containing discotic liquid crystal compound 18D are prepared. The solvent for preparing the compositions is not limited and can be selected appropriately depending on the purpose, but organic solvents are preferred. The organic solvent is not limited and can be selected appropriately depending on the purpose, and examples 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 environmental impact is taken into consideration.

[0059] After preparing the liquid crystal composition, the liquid crystal composition is applied to an alignment film to form a discotic liquid crystal layer, aligning the discotic liquid crystal compound 18D, followed by drying and, if necessary, curing the composition by UV irradiation or the like to form discotic liquid crystal layer 20D1. Next, a liquid crystal composition for forming a rod-shaped liquid crystal compound is applied to the discotic liquid crystal layer 20D1 to align the rod-shaped liquid crystal compound 18R, followed by drying and, if necessary, curing the composition by UV irradiation or the like to form rod-shaped liquid crystal layer 20R1, thereby forming the first liquid crystal layer 20. When a liquid crystal layer is formed on top of the liquid crystal layer by a coating method, the upper liquid crystal layer follows the alignment of the liquid crystal compound on the surface of the lower liquid crystal layer. The alignment directions of the liquid crystal compounds in the discotic liquid crystal layer 20D1 and the rod-shaped liquid crystal layer 20R1 are the same, i.e., their in-plane slow axes are parallel.

[0060] Similarly, a liquid crystal composition for forming a discotic liquid crystal layer is applied to the alignment film to form a discotic liquid crystal layer, and a liquid crystal composition for forming rod-shaped liquid crystal compounds is applied thereon to form a rod-shaped liquid crystal layer. The laminate of these two liquid crystal layers is peeled off from the alignment film, and the laminate is laminated on the previously formed first liquid crystal layer 20 (rod-shaped liquid crystal layer 20R1), and is attached using an OCA or the like.

[0061] In this case, the laminate is laminated on the first liquid crystal layer 20 so that the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 of the first liquid crystal layer 20 and the in-plane slow axis of the rod-shaped liquid crystal layer in the laminate to be laminated form a predetermined angle. For example, as described above, if the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 of the first liquid crystal layer 20 and the reference line is 5.625° and the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 of the second liquid crystal layer 24 and the reference line is −5.625°, the laminate is laminated on the first liquid crystal layer 20 so that the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 of the first liquid crystal layer 20 and the in-plane slow axis of the rod-shaped liquid crystal layer in the laminate becomes 11.25°. This forms a liquid crystal layer set 26 in which the first liquid crystal layer 20 having the rod-shaped liquid crystal layer 20R1 and the discotic liquid crystal layer 20D1 and the second liquid crystal layer 24 having the rod-shaped liquid crystal layer 24R2 and the discotic liquid crystal layer 24D2 are stacked.

[0062] Similarly, a liquid crystal composition for forming a discotic liquid crystal layer is applied to the alignment film to form a discotic liquid crystal layer, and a liquid crystal composition for forming rod-shaped liquid crystal compounds is applied thereon to form a rod-shaped liquid crystal layer. The two-layer liquid crystal layer stack is then peeled off from the alignment film, and, as before, the rod-shaped liquid crystal layer is laminated and attached to a second liquid crystal layer 24 (rod-shaped liquid crystal layer 24R2) with the in-plane slow axis angle of the rod-shaped liquid crystal layer aligned. By repeating this laminate stacking process for the number of first and second liquid crystal layers 20 and 24 to be laminated, i.e., the number of liquid crystal layer pairs 26 to be laminated, a liquid crystal polarization interference element as shown in FIG. 2 can be fabricated.

[0063] After the liquid crystal polarization interference element is fabricated in this manner, the first polarizer 12 and the second polarizer 14 are arranged in a crossed Nicol configuration with the liquid crystal polarization interference element sandwiched therebetween so that the bisector of the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer 20R1 of the first liquid crystal layer 20 and the in-plane slow axis of the rod-shaped liquid crystal layer 24R2 of the second liquid crystal layer 24 coincides with, for example, the transmission axis of the first polarizer 12. This makes it possible to fabricate an optical filter 10 (bandpass filter) as shown in FIG.

[0064] In the liquid crystal polarization interference element of the present invention, the method for producing the first and second liquid crystal layers is not limited to this method. For example, in the liquid crystal polarization interference element of the present invention, the first and second liquid crystal layers may be formed by a coating method and directly laminated. Alternatively, in the liquid crystal polarization interference element of the present invention, sheet-like first and second liquid crystal layers may be prepared, alternately laminated, and bonded with an optical bonding layer that is transparent to transmitted light, such as OCA, an acrylic pressure-sensitive adhesive, an adhesive, or a polymer layer. In this case, from the perspective of improving transmittance, it is preferable that the refractive index of the optical bonding layer be close to the refractive index of the liquid crystal. Specifically, the difference between the refractive index of the optical bonding layer and the refractive index of the liquid crystal is preferably 0.3 or less. Furthermore, it is preferable that the refractive index of the optical bonding layer be a value between the two birefringences of the liquid crystal, because this reduces the difference in refractive index from either of the two refractive indices. Furthermore, in terms of the transmittance of transmitted light passing through the liquid crystal polarization interference element, the first and second liquid crystal layers are preferably directly laminated by a coating method without an adhesive layer or the like.

[0065] Various liquid crystal polarization interference elements, which will be described later, may also be produced in accordance with the method for producing the liquid crystal polarization interference element described above.

[0066] In the laminated optical element of the present invention, the rod-shaped liquid crystal compound 18R constituting the liquid crystal polarization interference element is not limited, and various known liquid crystal compounds can be used.As the rod-shaped liquid crystal compound, 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.

[0067] 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.

[0068] The discotic liquid crystal compound 18D is also not limited, and various known compounds can be used. As the discotic liquid crystal compound 18D, for example, compounds described in JP-A-2007-108732 and JP-A-2010-244038 can be preferably used. It is preferable to fix the alignment of the discotic liquid crystal compound 18D by polymerization.

[0069] In the first liquid crystal polarization interference element 16a shown in Fig. 2, the first liquid crystal layer 20 and the second liquid crystal layer 24 each include one rod-shaped liquid crystal layer and one discotic liquid crystal layer. However, the present invention is not limited to this. For example, the first liquid crystal layer 20 and the second liquid crystal layer 24 may include multiple rod-shaped liquid crystal layers and multiple discotic liquid crystal layers, such as a configuration of rod-shaped liquid crystal layer / discotic liquid crystal layer / rod-shaped liquid crystal layer / discotic liquid crystal layer.

[0070] As described above, when the first liquid crystal layer 20 and the second liquid crystal layer 24 each include a plurality of rod-shaped and discotic liquid crystal layers, there is no limit to the number of each layer. When the first liquid crystal layer 20 and / or the second liquid crystal layer 24 each include a plurality of rod-shaped and discotic liquid crystal layers, as in the example shown in FIG. 2 , optically, it is preferable that the number of rod-shaped and discotic liquid crystal layers constituting the first liquid crystal layer 20 and the second liquid crystal layer 24 is large. The larger the number of rod-shaped and discotic liquid crystal layers constituting the first liquid crystal layer 20 and the second liquid crystal layer 24, the more precisely the discotic and rod-shaped liquid crystals can complement each other (optical compensation) in smaller regions. As a result, the thickness direction can be made more uniform with less bias, thereby reducing wavelength shift when light is incident from an oblique direction.

[0071] In the liquid crystal polarization interference element, when the first liquid crystal layer 20 and the second liquid crystal layer 24 each include a plurality of rod-shaped liquid crystal layers and discotic liquid crystal layers, the sum of the in-plane retardations of the rod-shaped liquid crystal layers is equal to the sum of the in-plane retardations of the discotic liquid crystal layers. Here, as long as the sum of the in-plane retardations of the rod-shaped liquid crystal layers is equal to the sum of the in-plane retardations of the discotic liquid crystal layers, the first liquid crystal layer 20 and the second liquid crystal layer 24 may have different numbers of rod-shaped liquid crystal layers and discotic liquid crystal layers. However, it is preferable that the number of rod-shaped liquid crystal layers and the number of discotic liquid crystal layers are equal to each other in the first liquid crystal layer 20 and the second liquid crystal layer 24.

[0072] In the present invention, the liquid crystal polarization interference element preferably has an in-plane retardation equal to that of the first liquid crystal layer 20 and the second liquid crystal layer 24. When the first liquid crystal layer 20 and the second liquid crystal layer 24 include a discotic liquid crystal layer and a rod-shaped liquid crystal layer, the number of rod-shaped liquid crystal layers 20R1 and the number of discotic liquid crystal layers 20D1 in the first liquid crystal layer 20 may be different from the number of rod-shaped liquid crystal layers 24R2 and the number of discotic liquid crystal layers 24D2 in the second liquid crystal layer 24, as long as the in-plane retardation of the first liquid crystal layer 20 and the in-plane retardation of the second liquid crystal layer 24 are equal to each other. However, it is preferable that the number of rod-shaped liquid crystal layers 20R1 and the number of discotic liquid crystal layers 20D1 in the first liquid crystal layer 20 be the same as the number of rod-shaped liquid crystal layers 24R2 and the number of discotic liquid crystal layers 24D2 in the second liquid crystal layer 24. Furthermore, when the first liquid crystal layer 20 and the second liquid crystal layer 24 have rod-shaped liquid crystal layers and discotic liquid crystal layers, the number of rod-shaped liquid crystal layers and the number of discotic liquid crystal layers may be different as long as the sum of the in-plane retardations of the rod-shaped liquid crystal layers and the discotic liquid crystal layers is equal in the first liquid crystal layer 20 and the second liquid crystal layer 24. However, it is preferable that the number of rod-shaped liquid crystal layers and the number of discotic liquid crystal layers are the same in the first liquid crystal layer 20 and the second liquid crystal layer 24.

[0073] As described above, the first liquid crystal polarization interference element 16a shown in FIG. 2 has 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 liquid crystal layer R1 formed by fixing horizontally aligned rod-shaped liquid crystal compounds and at least one liquid crystal layer D1 formed by fixing vertically aligned discotic liquid crystal compounds; the second liquid crystal layer includes at least one liquid crystal layer R2 formed by fixing horizontally aligned rod-shaped liquid crystal compounds and at least one liquid crystal layer D2 formed by fixing vertically aligned discotic liquid crystal compounds; the in-plane slow axis of the liquid crystal layer R1 is parallel to the in-plane slow axis of the liquid crystal layer D1, and the in-plane slow axis of the liquid crystal layer R2 is parallel to the in-plane slow axis of the liquid crystal layer D2; the in-plane slow axis of the liquid crystal layer R1 intersects with the in-plane slow axis of the liquid crystal layer R2; The total in-plane retardation of the liquid crystal layer R1 is equal to the total in-plane retardation of the liquid crystal layer D1, and the total in-plane retardation of the liquid crystal layer R2 is equal to the total in-plane retardation of the liquid crystal layer D2.

[0074] However, in the laminated optical element of the present invention, the liquid crystal polarization interference element is not limited thereto. That is, in the laminated optical element of the present invention, the liquid crystal polarization interference element has 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 or the second liquid crystal layer includes at least one liquid crystal layer R (rod-shaped liquid crystal layer) containing a rod-shaped liquid crystal compound, the first liquid crystal layer or the second liquid crystal layer includes at least one liquid crystal layer D (disctic liquid crystal layer) containing a discotic liquid crystal compound, the in-plane slow axis of the first liquid crystal layer and the in-plane slow axis of the second liquid crystal layer intersect, and the sum of the in-plane retardations of the first liquid crystal layer and the second liquid crystal layer is equal to each other, and various configurations can be used. In the laminated optical element of the present invention, the liquid crystal polarization interference element has such a configuration, and as described above, it acts as a λ / 2 retarder for light in a specific wavelength range, and the liquid crystal layer set has a discotic liquid crystal layer and a rod-shaped liquid crystal layer, so that when it is used as a bandpass filter in combination with a polarizer as shown in Figure 1, it can suppress the fluctuation of the wavelength of light that shows the maximum transmittance when light is incident from an oblique direction, that is, wavelength shift. Note that the description of the first liquid crystal polarization interference element 16a shown in Figure 2 above also applies to the liquid crystal polarization interference element shown below with respect to corresponding parts (for example, parts, members, configuration and structure, etc.).

[0075] As described above, in the laminated optical element of the present invention, the first or second liquid crystal layer of the liquid crystal polarization interference element includes at least one rod-shaped liquid crystal layer, and the first or second liquid crystal layer includes at least one discotic liquid crystal layer. Therefore, in the present invention, the liquid crystal polarization interference element may have two or more liquid crystal layer pairs 54, each of which includes a first liquid crystal layer 50 having only a rod-shaped liquid crystal layer composed of rod-shaped liquid crystal compound 18R and a second liquid crystal layer 52 having only a discotic liquid crystal layer composed of discotic liquid crystal compound 18D, as conceptually shown in FIG. 5 . Alternatively, in the present invention, the liquid crystal polarization interference element may have two or more liquid crystal layer pairs 54, each of which includes a first liquid crystal layer (second liquid crystal layer) having only a rod-shaped liquid crystal layer and a second liquid crystal layer (first liquid crystal layer) having both a rod-shaped liquid crystal layer and a discotic liquid crystal layer. Alternatively, in the present invention, the liquid crystal polarization interference element may have two or more liquid crystal layer sets 54, each set consisting of a first liquid crystal layer (second liquid crystal layer) having only a discotic liquid crystal layer and a second liquid crystal layer (first liquid crystal layer) having a rod-shaped liquid crystal layer and a discotic liquid crystal layer. Furthermore, in the present invention, the liquid crystal polarization interference element may have two or more liquid crystal layer sets, each set consisting of a first liquid crystal layer having a rod-shaped liquid crystal layer and a discotic liquid crystal layer and a second liquid crystal layer having a rod-shaped liquid crystal layer and a discotic liquid crystal layer, similar to the first liquid crystal polarization interference element 16a shown in FIG. 2 described above. However, in either configuration, in the liquid crystal polarization interference element of the present invention, the in-plane slow axis of the first liquid crystal layer intersects with the in-plane slow axis of the second liquid crystal layer, and the sum of the in-plane retardations of the first liquid crystal layer and the second liquid crystal layer is equal to each other.

[0076] In the present invention, the liquid crystal polarization interference element may have different in-plane retardations between the rod-shaped liquid crystal layer and the discotic liquid crystal layer in at least one of the first and second liquid crystal layers, as long as the sum of the in-plane retardations of the first and second liquid crystal layers is equal to each other. As an example, as conceptually shown in FIG. 6 , the liquid crystal polarization interference element may have a configuration including a plurality of liquid crystal layer pairs 70, each of which includes a first liquid crystal layer 60 having a rod-shaped liquid crystal layer 56R made of rod-shaped liquid crystal compound 18R and a discotic liquid crystal layer 56D made of discotic liquid crystal compound 18D, and a second liquid crystal layer 68 having a rod-shaped liquid crystal layer 62R made of rod-shaped liquid crystal compound 18R and a discotic liquid crystal layer 62D made of discotic liquid crystal compound 18D. In this case, as long as the sum of the in-plane retardations of the first liquid crystal layer 60 and the second liquid crystal layer 68 is equal to each other, the rod-shaped liquid crystal layer may be made thicker than the discotic liquid crystal layer, as shown in Fig. 6, so that the in-plane retardation of the rod-shaped liquid crystal layer is greater than that of the discotic liquid crystal layer in both the first liquid crystal layer 60 and the second liquid crystal layer 68. Alternatively, when the liquid crystal polarization interference element includes both the first and second liquid crystal layers each having a rod-shaped liquid crystal layer and a discotic liquid crystal layer, as long as the sum of the in-plane retardations of the first and second liquid crystal layers is equal to each other, the in-plane retardation of the discotic liquid crystal layer in both the first and second liquid crystal layers may be greater than that of the rod-shaped liquid crystal layer. Furthermore, in the liquid crystal polarization interference element, when the first and second liquid crystal layers both have a rod-shaped liquid crystal layer and a discotic liquid crystal layer, as long as the sum of the in-plane retardations of the first and second liquid crystal layers is equal, the first liquid crystal layer (second liquid crystal layer) may have a larger in-plane retardation of the rod-shaped liquid crystal layer, and the second liquid crystal layer (first liquid crystal layer) may have a larger in-plane retardation of the discotic liquid crystal layer.

[0077] In this configuration, as long as the sum of the in-plane retardation of the first liquid crystal layer and the in-plane retardation of the second liquid crystal layer is equal, the liquid crystal polarization interference element of the present invention can be used even if either the first liquid crystal layer or the second liquid crystal layer has only a rod-shaped liquid crystal layer or a discotic liquid crystal layer. However, regardless of the configuration, in the liquid crystal polarization interference element of the present invention, the in-plane slow axis of the first liquid crystal layer and the in-plane slow axis of the second liquid crystal layer intersect.

[0078] That is, in the laminated optical element of 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 / or the second liquid crystal layer has a rod-shaped liquid crystal layer and the first liquid crystal layer and / or the second liquid crystal layer has a discotic liquid crystal layer, the in-plane slow axis of the first liquid crystal layer intersects with the in-plane slow axis of the second liquid crystal layer, and further, the sum of the in-plane retardations of the first liquid crystal layer and the second liquid crystal layer is equal to each other, so long as these various configurations are available.

[0079] In the above examples, when the first and second liquid crystal layers each include a rod-shaped liquid crystal layer and a discotic liquid crystal layer, each of the first and second liquid crystal layers includes one rod-shaped liquid crystal layer and one discotic liquid crystal layer. However, the liquid crystal polarization interference element of the present invention is not limited to this, and at least one of the first and second liquid crystal layers may include multiple rod-shaped liquid crystal layers and / or multiple discotic liquid crystal layers. As an example, as conceptually shown in Figure 7, the liquid crystal polarization interference element may include two or more liquid crystal layer sets 78, each of which includes a first liquid crystal layer 74 having two alternating rod-shaped liquid crystal layers 80R and two alternating discotic liquid crystal layers 80D, and a second liquid crystal layer 76 having two alternating rod-shaped liquid crystal layers 82R and two alternating discotic liquid crystal layers 82D.

[0080] In the present invention, when at least one of the first and second liquid crystal layers of the liquid crystal polarization interference element has a configuration in which the first and second liquid crystal layers have a plurality of rod-shaped liquid crystal layers and discotic liquid crystal layers, the number of at least one of the rod-shaped liquid crystal layers and discotic liquid crystal layers may be different between the first and second liquid crystal layers. Furthermore, the liquid crystal polarization interference element may be configured such that either the first or second liquid crystal layer has two or more layers of at least one of the rod-shaped liquid crystal layer and the discotic liquid crystal layer, and the other has one rod-shaped liquid crystal layer and one discotic liquid crystal layer. Alternatively, the liquid crystal polarization interference element may be configured such that either the first or second liquid crystal layer has two or more layers of at least one of the rod-shaped liquid crystal layer and the discotic liquid crystal layer, and the other has only rod-shaped liquid crystal layers or only discotic liquid crystal layers.

[0081] 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.

[0082] 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 and the discotic 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 and the discotic liquid crystal layers are parallel.

[0083] 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, wherein the first liquid crystal layer and / or the second liquid crystal layer has a rod-shaped liquid crystal layer and the first liquid crystal layer and / or the second liquid crystal layer has a discotic liquid crystal layer, the in-plane slow axis of the first liquid crystal layer intersects with the in-plane slow axis of the second liquid crystal layer, and further, as long as the sum of the in-plane retardations of the first liquid crystal layer and the second liquid crystal layer are equal, the liquid crystal layer pairs may differ in in-plane retardation, the angle between the in-plane slow axis of the first liquid crystal layer and the reference line, the angle between the in-plane slow axis of the second liquid crystal layer and the reference line, etc.

[0084] For example, the orientations of the in-plane slow axes of the first and second liquid crystal layers may be different between 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 be configured such that the absolute values ​​of the angles formed between the in-plane slow axes of the first and second liquid crystal layers 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. For example, in the first liquid crystal polarization interference element 16a shown in FIG. 2 , if the first liquid crystal layer and the second liquid crystal layer have eight layers, i.e., four sets of liquid crystal layer pairs, in the first set of liquid crystal layer pairs, the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer of the first liquid crystal layer (first layer) and the reference line is set to φ1, and the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer of the second liquid crystal layer (second layer) and the reference line is set to −φ1, in the second set of liquid crystal layer pairs, the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer of the first liquid crystal layer (third layer) and the reference line is set to φ2, which is larger than φ1, and the angle formed by the in-plane slow axis of the rod-shaped liquid crystal layer 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 formed between the in-plane slow axis of the rod-shaped liquid crystal layer of the first liquid crystal layer (fifth layer) and the reference line is φ2, and the angle formed between the in-plane slow axis of the rod-shaped liquid crystal layer of the second liquid crystal layer (sixth layer) and the reference line is −φ2; and in the fourth liquid crystal layer pair, the angle formed between the in-plane slow axis of the rod-shaped liquid crystal layer of the first liquid crystal layer (seventh layer) and the reference line is φ1, and the angle formed between the in-plane slow axis of the rod-shaped liquid crystal layer of the second liquid crystal layer (eighth layer) and the reference line is −φ1.

[0085] As conceptually shown in Figure 8, 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, by reducing the absolute value of the angle between the in-plane slow axes of the first and second liquid crystal layers of the liquid crystal layer pair on both sides in the thickness direction and the reference line, compared to the liquid crystal layer of the liquid crystal layer pair at the center in the thickness direction, the side lobes can be reduced when used as a bandpass filter. In other words, in the liquid crystal polarization interference element of the present invention, by reducing the angle between the in-plane slow axes of the first and second liquid crystal layers on both sides in the thickness direction and the in-plane slow axes of the second liquid crystal layer, compared to the liquid crystal layer of the liquid crystal layer pair at the center in the thickness direction, the side lobes can be reduced when used as a bandpass filter.

[0086] In addition, in the manufacturing method described above, the angle between the in-plane slow axis of the first and second liquid crystal layers and the reference line can be adjusted by adjusting the angle of the in-plane slow axis of the rod-shaped liquid crystal layer when stacked.

[0087] In this configuration, the absolute value of the angle between the in-plane slow axis and the reference line is smaller in the liquid crystal layer pairs on both sides in the thickness direction than in the liquid crystal layer pair at the center 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 center, 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 liquid crystal layer pair at the center in the thickness direction and the reference line, are also not limited. That is, these angles may be set, for example, by simulation, to optimal in-plane retardation and angle that allow 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.

[0088] In the first and second liquid crystal layers described above, the liquid crystal compounds are aligned with the direction of their slow axes in the thickness direction. However, the present invention is not limited thereto, and the liquid crystal compounds may be aligned in a helical twisted manner in the thickness direction in the first and second liquid crystal layers. Specifically, as an example, the liquid crystal polarization interference element constituting the laminated optical element of the present invention may be configured such that the in-plane slow axes (orientation directions of the liquid crystal compounds) of the liquid crystal compounds are aligned at the interface between the first liquid crystal layer 20a and the second liquid crystal layer 24a, as conceptually shown in FIG. 9 , and the rod-shaped liquid crystal compound 18R and the discotic liquid crystal compound 18D are aligned in a helical twisted manner in opposite directions in the thickness direction in the first and second liquid crystal layers. That is, in the present invention, by aligning the liquid crystal compounds in a helical twisted manner in opposite directions in the first and second liquid crystal layers, the in-plane slow axis of the first liquid crystal layer and the in-plane slow axis of the second liquid crystal layer may intersect.

[0089] In this case, there is no limitation on the twist angle of the liquid crystal compound. However, when the total number of layers of the first and second liquid crystal layers is N and the twist angle of the liquid crystal compound in the first and second liquid crystal layers is ±φ [°], the twist angle can be calculated by the following formula: 0.9×(129.05×N -0.961 )≦|φ|≦1.1×(129.05×N -0.961 It is preferable to set the twist angles of the liquid crystal compounds in the first and second liquid crystal layers so as to satisfy the following condition: 1) the twist angles of the liquid crystal compounds in the first and second liquid crystal layers are equal to each other.

[0090] In the liquid crystal polarization interference element of the present invention described above, the rod-shaped liquid crystal layer and the discotic liquid crystal layer of the first and second liquid crystal layers may contain an infrared absorbing dye. By containing the infrared absorbing dye in the rod-shaped liquid crystal layer and the discotic 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 rod-shaped liquid crystal layer and the discotic liquid crystal layer to make 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.

[0091] 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.

[0092] There is no limitation on the amount of the infrared absorbing dye added to the rod-like liquid crystal layer and the discotic liquid crystal layer, 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.

[0093] Furthermore, in the liquid crystal polarization interference element of the present invention, the rod-shaped liquid crystal layer and the discotic liquid crystal layer of the first liquid crystal layer and the second liquid crystal layer may contain a liquid crystal elastomer. The rod-shaped liquid crystal layer and the discotic liquid crystal layer containing a liquid crystal elastomer may be formed using a liquid crystal elastomer, or a liquid crystal layer formed from a normal liquid crystal compound other than an elastomer and containing a liquid crystal elastomer.

[0094] In this way, by including a liquid crystal elastomer in the rod-shaped liquid crystal layer and the discotic liquid crystal layer, the first liquid crystal layer and the second liquid crystal layer can be made elastic, and the thickness of the liquid crystal layer can be changed by stretching or shrinking the filter in the plane direction. By changing the thickness of the liquid crystal layer, the in-plane retardation of the liquid crystal layer can be changed. As a result, in a bandpass filter, it is possible to change the wavelength range of light transmitted through the filter. In other words, by including a liquid crystal elastomer in the rod-shaped liquid crystal layer and the discotic liquid crystal layer, the wavelength range can be changed by stretching and shrinking the liquid crystal layer, i.e., the filter, enabling active wavelength control in the bandpass filter.

[0095] 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.

[0096] When the rod-shaped liquid crystal layer and the discotic liquid crystal layer are 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 may be set appropriately depending on the required elasticity, i.e., the control range of the transmission wavelength range.

[0097] 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 sums of the in-plane retardations of the first liquid crystal layers included in each liquid crystal polarization interference element are 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 retardation plate for light in a plurality of wavelength ranges.

[0098] As described above, in the liquid crystal polarization interference element constituting the laminated optical element of the present invention, the sum of the in-plane retardation of the first liquid crystal layer is equal to the sum of the in-plane retardation of the second liquid crystal layer. Furthermore, as described above, the liquid crystal polarization interference element sets the in-plane retardation of the first liquid crystal layer and 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 a plurality of liquid crystal polarization interference elements and in which the sums of 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 a plurality of liquid crystal polarization interference elements that function as λ / 2 retarders for different wavelength ranges from each other.

[0099] 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 the 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 corresponding to light of multiple wavelength ranges can be obtained. For example, as shown in FIG. 1, by using a laminated optical element having two liquid crystal polarization interference elements as a bandpass filter, only the light in the wavelength range λ1 that acts as a λ / 2 retardation plate in the first liquid crystal polarization interference element 16a is rotated by 90°, and light of other wavelengths is transmitted as it is, and further, only the light in the wavelength range λ2 that acts as a λ / 2 retardation plate in the second liquid crystal polarization interference element 16b is rotated by 90°, and light of other wavelengths is transmitted as it is, so that a bandpass filter corresponding to light of two wavelength ranges (wavelengths) can be realized, as shown in FIG. 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.

[0100] In the laminated optical element of the present invention, the sum of the in-plane retardations of the first liquid crystal layers in each liquid crystal polarization interference element (the in-plane retardation of the first liquid crystal layer) may be adjusted by a known method depending on the configuration of the first liquid crystal layer, etc. One example is a method of adjusting the sum of the in-plane retardations of the first liquid crystal layers of the liquid crystal polarization interference element by adjusting the thickness of the first liquid crystal layer (second liquid crystal layer). It is also possible to use a method of adjusting the sum of the in-plane retardations of the first liquid crystal layers of each liquid crystal polarization interference element by selecting the liquid crystal compound used in the first liquid crystal layer. A plurality of these methods of adjusting the in-plane retardation may be used in combination.

[0101] In the laminated optical element of the present invention, various liquid crystal polarization interference elements having the above-described configurations 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.

[0102] For example, the laminated optical element of the present invention may have all liquid crystal polarization interference elements of the same configuration, such as the laminated optical element 16 shown in Fig. 1, where all the liquid crystal polarization interference elements are liquid crystal polarization interference elements shown in Fig. 2. Furthermore, the laminated optical element of the present invention may have liquid crystal polarization interference elements of different configurations, such as a configuration in which one liquid crystal polarization interference element is a liquid crystal polarization interference element of the configuration shown in Fig. 2, and another liquid crystal polarization interference element is a liquid crystal polarization interference element formed by stacking a liquid crystal layer set 54 consisting of a first liquid crystal layer 50 that is a rod-shaped liquid crystal layer (liquid crystal layer R) and a second liquid crystal layer 52 that is a discotic liquid crystal layer (liquid crystal layer D) as shown in Fig. 5. 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 two liquid crystal polarization interference elements of the same configuration and one liquid crystal polarization interference element of a different configuration are present.

[0103] 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.

[0104] 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 (optical filter 10) of the present invention shown in FIG. 1, the angles formed between the in-plane slow axes of the first and second liquid crystal layers and the reference line are equal in the alternating stacking direction in all liquid crystal layer pairs. 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 and second liquid crystal layers 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 and second liquid crystal layers 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.

[0105] For example, in the optical laminated element of the present invention, the liquid crystal polarization interference element can also be configured such that the angle of the in-plane slow axis with respect to the reference line increases sequentially in the alternate lamination 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 so that their transmission axes are parallel to each other, i.e., in a parallel Nicol state.

[0106] A liquid crystal polarization interference element having a configuration in which the angle of the in-plane slow axis increases sequentially 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, which is an absorptive polarizer (absorptive linear polarizer), and the second polarizer, which is a reflective polarizer (reflective linear polarizer), in a parallel Nicol state with their transmission axes parallel.

[0107] 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.

[0108] 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.

[0109] 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 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 function 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.

[0110] In the optical filter of the present invention, which uses a liquid crystal polarization interference element having a configuration in which the angle of the in-plane slow axis increases sequentially in the stacking direction, the first polarizer and the second polarizer may be arranged in a crossed Nicol state, as a matter of course. 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.

[0111] In an optical filter using a laminated optical element having this liquid crystal polarization diffraction 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 that has passed 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 have its polarization direction changed by the liquid crystal polarization interference element and remains linearly polarized in the direction of the transmission axis of the first polarizer and enters the second 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 that is linearly polarized in the direction of the transmission axis of the first polarizer and for which the liquid crystal polarization interference element does not function as a retardation plate 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.

[0112] 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.

[0113] 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.

[0114] 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.

[0115] 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.

[0116] 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 .

[0117] 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 .

[0118] 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.

[0119] 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.

[0120] 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.

[0121] 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.

[0122] 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 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.

[0123] 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).

[0124] In the optical filter of the present invention, a retarder may be provided between the first polarizer and the liquid crystal polarization interference element, or between the second polarizer, the first polarizer, and the 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 liquid crystal polarization interference 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 a frontal view but also in an oblique direction off-axis of the polarizer. As a result, when the optical filter of the present invention is used as a bandpass filter, excellent bandpass characteristics similar to those obtained in a frontal view are obtained in an 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 an oblique direction without affecting the frontal 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.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] FIG. 10 conceptually illustrates an example of an optical system of the present invention combined with a condensing lens. The optical system illustrated in FIG. 10 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.

[0130] 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 focuses it on the light receiving unit 96, which is an imaging element. Furthermore, because the optical filter of the present invention has 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.

[0131] 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, 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.

[0132] FIG. 11 conceptually illustrates an example of an optical system incorporating a beam splitter according to the present invention. The optical system shown in FIG. 11 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 linearly traveling 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.

[0133] FIG. 12 conceptually illustrates an example of combining a light-guiding element (light guide plate) with an optical system of the present invention. The optical system shown in FIG. 12 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.

[0134] 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. 13 . In the optical system shown in FIG. 13 , 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.

[0135] 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. 13 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 efficiently measure light in multiple wavelength ranges, such as multispectral and hyperspectral. This point is also true for the optical system of the present invention described below.

[0136] 10 to 13 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.

[0137] Alternatively, an optical filter according to 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 10 to 13. 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 10 to 13, 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 96, where it is measured.

[0138] 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 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 10 to 13, light emitted by the light source unit 90 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 96 for photometry, while light outside this specific wavelength range is blocked by the optical filter 94.

[0139] 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 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 10 to 13. 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, where it is measured.

[0140] 10 to 13, the first polarizer and the second polarizer of the optical filter are absorptive polarizers (linear absorptive polarizers). However, as described above, in the optical filter of the present invention, one of the first polarizer and the second polarizer (on the exit side) may be a reflective polarizer.

[0141] FIG. 14 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 with the optical system of the present invention. The optical system shown in FIG. 14 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. 14, 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.

[0142] 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.

[0143] The optical system shown in FIG. 14 can also utilize an optical filter using a liquid crystal polarization interference element in which the angle of the in-plane slow axis 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 in a specific wavelength range, which is 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 outside the specific wavelength range, which is 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, in this optical system, when the first and second polarizers of the optical filter are arranged in a crossed Nicol configuration, light in a specific wavelength range, which is 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 and enters the light receiving unit 96a for transmitted light, where it is measured.

[0144] 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 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 various directions from the light source unit 90, which is the object to be imaged, and focuses the light on the light receiving units 96a and 96b, which are imaging elements. 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, an optical fiber output terminal can be provided on the light source unit 90 side and an optical fiber input terminal on the light receiving units 96a and 96b side, thereby achieving a system with high efficiency similar to that described above. 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.

[0145] As shown in FIG. 14 , 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. 15 below.

[0146] FIG. 15 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. 15 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. 15, 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.

[0147] 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.

[0148] 15 can also utilize an optical filter using a liquid crystal polarization interference element in which the angle of the in-plane slow axis 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 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 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.

[0149] 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 be made within the scope of the present invention.

[0150] 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.

[0151] [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.

[0152] 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

[0153] Material for photo alignment

[0154] (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.

[0155] (Formation of discotic liquid crystal layer) The following composition D-1 was prepared as a liquid crystal composition for forming a discotic liquid crystal layer. Composition D-1: 80.00 parts by mass of discotic liquid crystal compound L-2 below; 20.00 parts by mass of discotic liquid crystal compound L-3 below; 5.00 parts by mass of polymerization initiator (Irgacure (registered trademark) 907, manufactured by BASF); 0.50 parts by mass of Megafac F444 (manufactured by DIC); 300.00 parts by mass of methyl ethyl ketone.

[0156] Discotic liquid crystal compound L-2 Discotic liquid crystal compound L-3

[0157] The discotic liquid crystal layer was formed by applying composition D-1 onto the alignment film P-1. That is, composition D-1 was first applied onto the alignment film P-1, followed by heating and then ultraviolet curing to form a discotic liquid crystal layer (thickness 0.66 μm) which was a liquid crystal fixed layer containing a discotic liquid crystal compound. More specifically, the discotic liquid crystal layer was formed by applying composition D-1 onto the alignment film P-1 to obtain a coating film, heating this coating film to 80°C on a hot plate, and then irradiating ultraviolet light of 365 nm wavelength at 300 mJ / cm using a high-pressure mercury lamp in a nitrogen atmosphere at 80°C. 2 The coating film was irradiated with an irradiation dose of 1000 .mu.m to fix the alignment of the discotic liquid crystal compound.

[0158] (Formation of Rod-Shaped Liquid Crystal Layer) The following composition B-1 was prepared as a liquid crystal composition for forming a rod-shaped liquid crystal layer.

[0159] 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

[0160] Rod-shaped liquid crystal compound L-1

[0161] Leveling agent T-1

[0162] Composition B-1 was applied onto the formed discotic liquid crystal layer, followed by heating and UV curing to form a rod-shaped liquid crystal layer (thickness: 0.66 μm) which was a liquid crystal fixed layer containing a rod-shaped liquid crystal compound. The temperature, heating, and curing conditions for forming the rod-shaped liquid crystal layer were the same as those for forming the discotic liquid crystal layer.

[0163] Twelve liquid crystal layers each having the same discotic liquid crystal layer and rod-shaped liquid crystal layer were formed. Hereinafter, for convenience, these liquid crystal layers each having a discotic liquid crystal layer and a rod-shaped liquid crystal layer will also be referred to as a "unit layer." The twelve unit layers thus formed were confirmed to have the following optical properties using an AxoScan (manufactured by Axometrics): rod-shaped liquid crystal layer thickness: 0.66 μm, Δn: 0.17 (center wavelength 450 nm), in-plane retardation: 112.5 nm; discotic liquid crystal layer thickness: 0.66 μm, Δn: 0.17 (center wavelength 450 nm), in-plane retardation: 112.5 nm; and total in-plane retardation: 225 nm.

[0164] The formed unit layers were peeled from the alignment film and bonded together using an adhesive (SK Dyne 2057, manufactured by Soken Chemical & Engineering Co., Ltd.) to form a first liquid crystal polarization interference element. The 12 unit layers were laminated together, with the in-plane slow axes of the rod-shaped liquid crystal layers of the odd-numbered layers (first liquid crystal layers) of the laminated unit layers intersecting with the in-plane slow axes of the rod-shaped liquid crystal layers of the even-numbered layers (second liquid crystal layers). Specifically, the angle bisecting the crossing angle formed by the in-plane slow axes of both layers was used as the reference (reference line), with the counterclockwise direction being positive (+) and the clockwise direction being negative (-). The 12 unit layers were laminated and bonded together so that the angle θ of the in-plane slow axes of the rod-shaped liquid crystal layers of the odd-numbered layers was 3.75° and the angle θ of the in-plane slow axes of the rod-shaped liquid crystal layers of the even-numbered layers was −3.75°. That is, the fabricated first liquid crystal polarization interference element had six liquid crystal layer pairs, each consisting of a first liquid crystal layer and a second liquid crystal layer. As described above, when a liquid crystal layer is formed on a liquid crystal layer by coating, the orientation of the liquid crystal compound in the upper liquid crystal layer follows the orientation of the liquid crystal compound in the lower layer. Therefore, in the first liquid crystal polarization interference element, the angle θ of the in-plane slow axis of the rod-shaped liquid crystal layer is 3.75° for the odd-numbered layers and −3.75° for the even-numbered layers, and the angle θ of the in-plane slow axis of the discotic liquid crystal layer is 3.75° for the odd-numbered layers and −3.75° for the even-numbered layers.

[0165] <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 rod-shaped liquid crystal layer in the unit layer was 0.86 μm and the thickness of the discotic 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 has six liquid crystal layer pairs each consisting of a first liquid crystal layer and a second liquid crystal layer.

[0166] The 12 unit layers thus fabricated were confirmed to have the following optical properties using an AxoScan (manufactured by Axometrics): rod-shaped liquid crystal layer thickness: 0.86 μm, Δn: 0.16 (center wavelength 550 nm), in-plane retardation: 137.5 nm; discotic liquid crystal layer thickness: 0.86 μm, Δn: 0.16 (center wavelength 550 nm), in-plane retardation: 137.5 nm; total in-plane retardation: 275 nm.

[0167] Also in the second liquid crystal polarization interference element, the angle θ of the in-plane slow axis of the rod-shaped liquid crystal layers is 3.75° for odd-numbered layers and −3.75° for even-numbered layers, and the angle θ of the in-plane slow axis of the discotic liquid crystal layers is 3.75° for odd-numbered layers and −3.75° for even-numbered layers.

[0168] <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.

[0169] 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 wavelength shift (absolute value) was measured when light was incident from a polar angle of 60° relative to when light was incident from a polar angle of 90°. Incident light from a polar angle of 60° was also incident from two directions, azimuth angles of 0° and 90°, and the average value was taken as the measured value. 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, the peak with a center wavelength of 450 nm is believed to be due to the first liquid crystal polarization interference element, and the peak with a center wavelength of 550 nm is believed to be due to the second 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%. On the other hand, 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%.

[0170] 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.

[0171] <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 rod-shaped liquid crystal layer in the unit layer was 1.08 μm and the thickness of the discotic 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.

[0172] The 12 unit layers thus fabricated were confirmed to have the following optical properties using an AxoScan (manufactured by Axometrics): Rod-shaped liquid crystal layer thickness: 1.08 μm, Δn: 0.15 (center wavelength 650 nm), in-plane retardation: 162.5 nm Discotic liquid crystal layer thickness: 1.08 μm, Δn: 0.15 (center wavelength 650 nm), in-plane retardation: 162.5 nm Total in-plane retardation: 325 nm

[0173] Also in the third liquid crystal polarization interference element, the angle θ of the in-plane slow axis of the rod-shaped liquid crystal layers is 3.75° for odd-numbered layers and −3.75° for even-numbered layers, and the angle θ of the in-plane slow axis of the discotic liquid crystal layers is 3.75° for odd-numbered layers and −3.75° for even-numbered layers.

[0174] <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 (reference line) that bisects the cross angle that the in-plane slow axis of odd-numbered layer and even-numbered layer make when preparing each liquid crystal polarization interference element 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.

[0175] 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%.

[0176] As shown in Examples 1 and 2, when used in, for example, a bandpass filter, the laminated optical element of the present invention can accommodate multiple wavelength ranges, and also exhibits small wavelength shifts when light is incident from an oblique direction.

[0177] In Example 1, the angle θ of the in-plane slow axis in each of 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 is the angle between the reference line and the in-plane slow axis, as described above.

[0178] 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%.

[0179] [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%.

[0180] 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.

[0181] It can be suitably used as a bandpass filter or the like in various optical devices.

[0182] 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 18R Rod-shaped liquid crystal compound 18D Discotic liquid crystal compound 20, 50, 60, 74 First liquid crystal layer 20R1, 24R2, 56R, 62R, 80R, 82R Rod-shaped liquid crystal layer 20D1, 24D2, 56D, 62D, 80D, 82D Discotic liquid crystal layer 24, 52, 68, 76 Second liquid crystal layer 26, 54, 70, 78 Liquid crystal layer set 90 Light source unit 93 Condenser lens 94, 94a, 94b Optical filter 96 Light receiving unit 98 Beam splitter 100 Light guide element

Claims

A laminated optical element having a plurality of liquid crystal polarization interference elements, The liquid crystal polarization interference element is The liquid crystal display device has two or more liquid crystal layer pairs each consisting of a first liquid crystal layer and a second liquid crystal layer in a thickness direction, the first liquid crystal layer or the second liquid crystal layer includes at least one liquid crystal layer R containing a rod-like liquid crystal compound; the first liquid crystal layer or the second liquid crystal layer includes at least one liquid crystal layer D containing a discotic liquid crystal compound; an in-plane slow axis of the first liquid crystal layer and an in-plane slow axis of the second liquid crystal layer intersect with each other; a sum of in-plane retardations of the first liquid crystal layer and the second liquid crystal layer is equal to each other; The plurality of liquid crystal polarization interference elements are laminated optical elements in which the sums of the in-plane retardations of the first liquid crystal layers included in the liquid crystal polarization interference elements are different from one another. 　 The liquid crystal polarization interference element is a laminated optical element as described in claim 1, wherein 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 liquid crystal layer and the second liquid crystal layer. 　 The laminated optical element according to claim 1 , wherein the liquid crystal polarization interference element includes the liquid crystal layer R and the liquid crystal layer D each containing an infrared absorbing dye. 　 The laminated optical element according to claim 1 , wherein the liquid crystal polarization interference element includes the liquid crystal layer R and the liquid crystal layer D each containing a liquid crystal elastomer. 　 An optical filter comprising, in this order, a first polarizer, the laminated optical element according to any one of claims 1 to 4, and a second polarizer. 　 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. 　 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. 　 The optical filter according to claim 5 , wherein one of the first polarizer and the second polarizer is a reflective polarizer. 　 An optical system comprising a light source unit, the optical filter according to claim 5, and a light receiving unit.

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