Optical member

Abstract

Provided is an optical member having excellent resistance to heat and humidity. This optical member comprises a light guide member, a λ / 4 plate, a first cholesteric liquid crystal layer, an alignment layer that is in contact with the first cholesteric liquid crystal layer, and a second cholesteric liquid crystal layer that is in contact with the alignment layer. The thickness of the alignment layer is 0.01 μm to 0.5 μm. The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer each have a liquid crystal alignment pattern in which the direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction. The twist directions of helical structures in the first and second cholesteric liquid crystal layers are different from each other, and the respective continuous rotation directions of the directions of the optical axes derived from the liquid crystal compound in the liquid crystal alignment patterns of the first and second cholesteric liquid crystal layers are different from each other.

Description

Optical components

[0001] This invention relates to an optical component.

[0002] In the field of optical communications, the increasing volume of data communication necessitates higher capacity communication devices. To achieve this higher capacity, Wavelength Division Multiplexing (WDM) is employed, and there is a need for improved performance and miniaturization of the Wavelength Selective Switch (WSS) used in WDM. In such optical wavelength selective switches, diffraction elements are used as wavelength separation elements.

[0003] For example, Patent Document 1 describes an optical device comprising: an input port for supplying a multi-wavelength optical signal; a polarization separation element for decomposing the multi-wavelength optical signal into first and second polarization components; a polarization rotation element for rotating the polarization of the second polarization component by approximately 90 degrees; a wavelength disperser for separating the first and second polarization components into sets of first and second light beams according to their wavelengths; an array of optical power sensors positioned to receive sets of first and second light beams; and a modulation assembly configured to modulate sets of first and second light beams before they collide with the array of optical power sensors. The Patent Document 1 describes an optical device in which the wavelength disperser is a diffraction grating or the like.

[0004] Japanese Patent Publication No. 2008-164630

[0005] To further increase the capacity of communication devices, polarization multiplexing (PDC) communication is being considered in addition to wavelength division multiplexing (WDC). However, conventional diffraction elements have polarization-dependent diffraction efficiency, making them difficult to use for polarization multiplexing.

[0006] In response to this, the inventors considered using a liquid crystal diffraction element with low polarization dependence of diffraction efficiency. Specifically, they considered using an optical element as a wavelength dispersion element, which consists of a first cholesteric liquid crystal layer that reflects and diffracts right-circularly polarized light and a second cholesteric liquid crystal layer that reflects and diffracts left-circularly polarized light.

[0007] However, our investigations have revealed that when a laminate of multiple cholesteric liquid crystal layers is used by laminating it onto a light guide member such as a prism, there is a problem in that the diffraction efficiency of one of the polarizations decreases significantly after a humid heat endurance test.

[0008] The object of the present invention is to solve the problems of the prior art and to provide an optical component with excellent resistance to humid heat.

[0009] The inventors have found that the above problem can be solved by the following configuration.

[0010] [1] An optical member comprising: a light guide member; a λ / 4 plate; a first cholesteric liquid crystal layer; an alignment layer in contact with the first cholesteric liquid crystal layer; and a second cholesteric liquid crystal layer in contact with the alignment layer, wherein the thickness of the alignment layer is 0.01 μm to 0.5 μm; the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane; the twisting direction of the helical structure in the first cholesteric liquid crystal layer and the twisting direction of the helical structure in the second cholesteric liquid crystal layer are different from each other; and the continuous rotation direction of the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the first cholesteric liquid crystal layer and the continuous rotation direction of the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the second cholesteric liquid crystal layer are different from each other. [2] The optical member according to [1], wherein the alignment film is a photoalignment film. [3] The optical component described in [1] or [2], used in a wavelength selective switch.

[0011] According to the present invention, it is possible to provide an optical component with excellent resistance to humid heat.

[0012] Figure 1 is a conceptual diagram showing an example of an optical member of the present invention. Figure 2 is a diagram illustrating the first and second cholesteric liquid crystal layers of the optical member shown in Figure 1. Figure 3 is a diagram illustrating the operation of the optical member shown in Figure 1. Figure 4 is a conceptual diagram showing another example of an optical member of the present invention. Figure 5 is a conceptual diagram showing an example of a cholesteric liquid crystal layer of the optical member of the present invention. Figure 6 is a plan view of the cholesteric liquid crystal layer shown in Figure 5. Figure 7 is a conceptual diagram showing an example of an exposure apparatus for exposing an alignment film. Figure 8 is a diagram illustrating the problems of the present invention.

[0013] The optical component of the present invention will be described in detail below based on preferred embodiments shown in the attached drawings.

[0014] The following description of the constituent elements may be based on typical embodiments of the present invention, but the present invention is not limited to such embodiments.

[0015] Furthermore, the following diagrams are all conceptual diagrams intended to explain the present invention. Therefore, the shape, size, thickness, and positional relationships of each component in each diagram do not necessarily correspond to those of actual objects.

[0016] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively.

[0017] In this specification, unless otherwise specified, angles such as "45°", "parallel", "perpendicular", or "orthogonal" mean that the difference from the exact angle is within 5 degrees. Preferably, the difference from the exact angle is less than 3 degrees, and more preferably less than 1 degree.

[0018] In this specification, terms such as “same” and “equal” include a margin of error that is generally accepted in the applicable art.

[0019] [Optical Member] The optical member of the present invention comprises a light guide member, a λ / 4 plate, a first cholesteric liquid crystal layer, an alignment layer in contact with the first cholesteric liquid crystal layer, and a second cholesteric liquid crystal layer in contact with the alignment layer, wherein the thickness of the alignment layer is 0.01 μm to 0.5 μm, the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane, the twisting direction of the helical structure in the first cholesteric liquid crystal layer and the twisting direction of the helical structure in the second cholesteric liquid crystal layer are different from each other, and the continuous rotation direction of the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the first cholesteric liquid crystal layer and the continuous rotation direction of the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the second cholesteric liquid crystal layer are different from each other.

[0020] Figure 1 conceptually shows an example of the optical component of the present invention.

[0021] The optical member 10a shown in Figure 1 comprises, in this order, a light guide member 12, an adhesive layer 13, a λ / 4 plate 14, a second alignment film 15, a first cholesteric liquid crystal layer 16, a first alignment film 18, and a second cholesteric liquid crystal layer 20.

[0022] The optical component 10a can be used, for example, as a wavelength separation element of a wavelength selective switch in an optical communication device.

[0023] In the optical member 10a, the light guide member 12 and the λ / 4 plate 14 are attached by an adhesive layer 13. The λ / 4 plate 14 and the first cholesteric liquid crystal layer 16 are in contact via a second alignment film 15. The first cholesteric liquid crystal layer 16 and the first alignment film 18 are in direct contact. The first alignment film 18 and the second cholesteric liquid crystal layer 20 are in direct contact. The first alignment film 18 is the alignment film in this invention.

[0024] The first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 are formed using a composition containing a liquid crystal compound and have a helical structure in which the liquid crystal compound is spirally stacked in the thickness direction, and have a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction within the plane. The cholesteric liquid crystal layer having a liquid crystal orientation pattern reflects and diffracts one type of circularly polarized light and transmits the other type of circularly polarized light. The configuration of such a cholesteric liquid crystal layer will be described later. Note that in Figures 2 and 5 described later, the vertical direction in the figures is the thickness direction, and in Figure 6, the direction perpendicular to the plane of the paper is the thickness direction.

[0025] In this invention, the twisting direction of the helical structure in the first cholesteric liquid crystal layer 16 and the twisting direction of the helical structure in the second cholesteric liquid crystal layer 20 are different from each other, and the continuous rotational direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the first cholesteric liquid crystal layer 16 and the continuous rotational direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the second cholesteric liquid crystal layer are different from each other. This point will be explained with reference to Figure 2.

[0026] Figure 2 conceptually shows the orientation state of the liquid crystal compounds 30 in the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 of the optical member 10a. In Figure 2, half a pitch of the liquid crystal compounds 30 arranged in the thickness direction of the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 is shown. However, as shown in Figure 5, which will be described later, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 have a structure in which the liquid crystal compounds 30 are stacked in multiple pitches, with each pitch representing one spiral rotation (360° rotation) of the liquid crystal compounds 30.

[0027] As shown in Figure 2, the twisting direction of the helical structure in the first cholesteric liquid crystal layer 16 and the twisting direction of the helical structure in the second cholesteric liquid crystal layer 20 are different. Specifically, in the first cholesteric liquid crystal layer 16, the liquid crystal compound 30 rotates clockwise from top to bottom in the figure. On the other hand, in the second cholesteric liquid crystal layer 20, the liquid crystal compound 30 rotates counterclockwise from top to bottom in the figure.

[0028] As is well known, a cholesteric liquid crystal layer reflects one type of circularly polarized light and transmits the other type of circularly polarized light, depending on the twisting direction of its helical structure. Therefore, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 reflect circularly polarized light with different twisting directions.

[0029] Furthermore, as shown in Figure 2, the rotation direction of the optical axis originating from the liquid crystal compound 30 in the liquid crystal alignment pattern of the first cholesteric liquid crystal layer 16 and the rotation direction of the optical axis originating from the liquid crystal compound 30 in the liquid crystal alignment pattern of the second cholesteric liquid crystal layer 20 are different from each other. Specifically, in the liquid crystal alignment pattern of the first cholesteric liquid crystal layer 16, the liquid crystal compound 30 is arranged to rotate clockwise from left to right when viewed from above in the figure. On the other hand, in the liquid crystal alignment pattern of the second cholesteric liquid crystal layer 20, the liquid crystal compound 30 is arranged to rotate counterclockwise from left to right when viewed from above in the figure.

[0030] In a cholesteric liquid crystal layer having a liquid crystal alignment pattern, the direction of light diffraction depends on the rotation direction of the liquid crystal compound 30 in the liquid crystal alignment pattern, and also on the rotation direction of circularly polarized light. Therefore, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20, whose twisting directions of the helical structure are different from each other, and whose continuous rotation directions of the optical axis orientation originating from the liquid crystal compound 30 in the liquid crystal alignment pattern are different from each other, reflect different circularly polarized light in the same direction.

[0031] For example, in the example shown in Figure 2, if the first cholesteric liquid crystal layer 16 reflects and diffracts right-circularly polarized light incident approximately perpendicular to the main surface in the upper left direction in the figure, then the second cholesteric liquid crystal layer 20 reflects and diffracts left-circularly polarized light incident approximately perpendicular to the main surface in the upper left direction in the figure. The main surface is the largest surface of the sheet-like material (plate-like material, film-like material).

[0032] In such a first cholesteric liquid crystal layer 16 and second cholesteric liquid crystal layer 20, the bright areas 42 and dark areas 44 observed by cross-sectional SEM (Scanning Electron Microscope) are tilted in the same direction and angle (see Figure 2). That is, the first cholesteric liquid crystal layer 16 and second cholesteric liquid crystal layer 20 have the same tilt direction and tilt angle for the bright areas 42 and dark areas 44. In Figure 2, the bright and dark areas are superimposed on a diagram showing the orientation state of the liquid crystal compound.

[0033] Furthermore, the diffraction angle in a cholesteric liquid crystal layer having a liquid crystal alignment pattern depends on the length of one period in the liquid crystal alignment pattern (described later) and the wavelength of the diffracted light. Therefore, a cholesteric liquid crystal layer having a liquid crystal alignment pattern can separate light containing multiple wavelength components according to their respective wavelengths.

[0034] Furthermore, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 have essentially the same helical structure pitch (helical pitch) and the same period length in the liquid crystal alignment pattern. Therefore, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 reflect and diffract different circularly polarized light of the same wavelength in the same direction and at the same angle.

[0035] The operation of the optical component 10a will be explained using Figure 3. In Figure 3, light is indicated by arrows, and only light guided within the light guide member 12 is shown. However, in reality, the light passes through the adhesive layer 13 and the λ / 4 plate 14, etc., is reflected by the first cholesteric liquid crystal layer 16 and / or the second cholesteric liquid crystal layer 20, passes through the λ / 4 plate 14 and the adhesive layer 13, etc., and is guided again within the light guide member 12. The same applies to Figure 4, which will be described later.

[0036] As shown in FIG. 3, when light including P-polarized light and / or S-polarized light of a plurality of wavelengths (indicated by thick solid arrows in FIG. 3) is obliquely incident from the main surface of the light guide member 12 opposite to the λ / 4 plate 14 with respect to the normal to the main surface, the light is diffracted at the air interface of the light guide member 12, and is guided in the light guide member 12 obliquely toward the λ / 4 plate 14 side.

[0037] The light guided through the light guide member 12 is incident on the λ / 4 plate 14 and converted into right-handed circularly polarized light or left-handed circularly polarized light. For example, the following description is given on the assumption that P-polarized light is converted into right-handed circularly polarized light and S-polarized light is converted into left-handed circularly polarized light.

[0038] The right-handed circularly polarized light and / or left-handed circularly polarized light converted by the λ / 4 plate 14 is reflected and diffracted by the first cholesteric liquid crystal layer 16 or the second cholesteric liquid crystal layer 20. At this time, as described above, the light is diffracted at different angles for each wavelength, so that it travels in different directions for each wavelength as indicated by the thin solid arrow, the one-dot chain arrow, and the broken arrow in FIG. 3.

[0039] Further, as described above, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 reflect and diffract different circularly polarized lights of the same wavelength in the same direction. Therefore, for each wavelength, the right-handed circularly polarized light component and the left-handed circularly polarized light component are not separated, but are reflected and diffracted in the same direction. That is, the thin solid arrow in FIG. 3 indicates light including right-handed circularly polarized light and / or left-handed circularly polarized light of a certain wavelength, the one-dot chain arrow indicates light including right-handed circularly polarized light and / or left-handed circularly polarized light of another certain wavelength, and the broken arrow indicates light including right-handed circularly polarized light and / or left-handed circularly polarized light of still another certain wavelength.

[0040] The light of each wavelength reflected and diffracted by the first cholesteric liquid crystal layer 16 or the second cholesteric liquid crystal layer 20 is incident on the λ / 4 plate 14, converted into P-polarized light and / or S-polarized light, then incident on the light guide member 12, guided inside the light guide member 12, and emitted from the light guide member 12 in different directions for each wavelength. In the example shown in FIG. 3, the light is emitted from the end face of the light guide member 12.

[0041] As described above, in the optical member 10a including the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20, the diffraction efficiency does not change depending on the polarization state of incident light, and therefore the optical member 10a can be a wavelength separation element (diffraction element) having no polarization dependence.

[0042] The light of each wavelength wavelength-separated by the optical member 10a is deflected by a deflector such as a micromirror device or LCOS (Liquid Crystal On Silicon), respectively, and output to a predetermined output-side path.

[0043] In addition, the light of each wavelength wavelength-separated by the optical member 10a may be further polarized into P-polarized light and S-polarized light, then deflected by a deflector, and output to a predetermined output-side path.

[0044] Here, according to studies by the present inventors, it has been found that when a laminate of a plurality of cholesteric liquid crystal layers is used by being laminated on a light guide member, there is a problem that the diffraction efficiency of one polarization greatly decreases after a moist heat durability test.

[0045] When the present inventors conducted a more detailed study on this point, it was found that when the distance between the first cholesteric liquid crystal layer 116 and the second cholesteric liquid crystal layer 120 is large, as shown in FIG. 8, the first cholesteric liquid crystal layer 116 on the side closer to the light guide member 112 is constrained by the light guide member 112, so deformation after moist heat durability is small. In contrast, the second cholesteric liquid crystal layer 120 on the side farther from the light guide member 112 is less affected by the light guide member 112, so deformation after moist heat durability becomes large. When the cholesteric liquid crystal layer is deformed, the helical pitch and / or one period of the liquid crystal alignment pattern changes, which results in a decrease in diffraction efficiency. As a result, it was found that the diffraction efficiency of circularly polarized light reflected by the second cholesteric liquid crystal layer 20 greatly decreases. It was also found that after moist heat durability, a difference occurs between the diffraction efficiency of circularly polarized light reflected by the first cholesteric liquid crystal layer 16 and the diffraction efficiency of circularly polarized light reflected by the second cholesteric liquid crystal layer 20, which causes polarization dependence.

[0046] As described above, the first cholesteric liquid crystal layer 116 and the second cholesteric liquid crystal layer 120 have different continuous rotation directions of the optical axes derived from the liquid crystal compound in their liquid crystal alignment patterns. Therefore, when laminating the first cholesteric liquid crystal layer 116 and the second cholesteric liquid crystal layer 120, which have different liquid crystal alignment patterns, it is conceivable to manufacture each layer individually and then laminate them using an adhesive layer in order to properly form each layer. However, according to the inventors' studies, when the first cholesteric liquid crystal layer 116 and the second cholesteric liquid crystal layer 120 are laminated using an adhesive layer and then laminated onto the light guide member 112, the thickness of the adhesive layer is at least several μm, and the distance between the first cholesteric liquid crystal layer 116 and the second cholesteric liquid crystal layer 120 becomes large, resulting in the problem that the cholesteric liquid crystal layer on the side furthest from the light guide member 112 is deformed.

[0047] In contrast, the optical member 10a of the present invention has a first alignment film 18 between a first cholesteric liquid crystal layer 16 and a second cholesteric liquid crystal layer 20, the first cholesteric liquid crystal layer 16 and the first alignment film 18 are in contact, and the first alignment film 18 and the second cholesteric liquid crystal layer 20 are in contact, with the thickness of the first alignment film 18 being 0.01 μm to 0.5 μm. That is, the distance between the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 is 0.01 μm to 0.5 μm.

[0048] The configuration in which the first cholesteric liquid crystal layer 16 and the first alignment film 18 are in contact, and the first alignment film 18 and the second cholesteric liquid crystal layer 20 are in contact, can be fabricated by forming the first alignment film on the surface of one cholesteric liquid crystal layer and forming the other cholesteric liquid crystal layer on top of this first alignment film. In other words, the optical member 10a of the present invention is formed by directly forming the alignment film and the other cholesteric liquid crystal layer on top of one cholesteric liquid crystal layer without using a bonding layer.

[0049] By setting the thickness of the first alignment film 18, that is, the distance between the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20, to 0.5 μm or less, deformation of the second cholesteric liquid crystal layer 20 on the side farther from the light guide member 12 can be suppressed, and a decrease in the diffraction efficiency of circularly polarized light reflected by the second cholesteric liquid crystal layer 20 can be suppressed. From the viewpoint of suppressing a decrease in diffraction efficiency, the thickness of the first alignment film 18 is preferably 0.4 μm or less, and more preferably 0.3 μm or less.

[0050] Furthermore, our own investigations have shown that if the thickness of the first orientation film 18 is too thin, fine delamination occurs at the interface with the first orientation film 18, generating bubbles, and the light is scattered by these bubbles, reducing the diffraction efficiency. From the viewpoint of suppressing such a decrease in diffraction efficiency due to fine delamination, the thickness of the first orientation film 18 is preferably 0.015 μm or more, more preferably 0.02 μm or more.

[0051] In optical communication systems, light in the infrared range with wavelengths of 950 nm to 1650 nm is generally used. Therefore, when the optical component of the present invention is used in a wavelength-selective switch, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 each need to reflect and diffract light in the wavelength range of 950 nm to 1650 nm. In order to increase the reflectivity of the cholesteric liquid crystal layer that reflects light in the infrared range, it is necessary to make it thicker than the cholesteric liquid crystal layer that reflects light in the visible range. On the other hand, as the thickness of the cholesteric liquid crystal layer increases, the orientation of the liquid crystal compound tends to become disordered. Therefore, in order to properly orient the liquid crystal compound even when the thickness of the cholesteric liquid crystal layer is increased, it is desirable to use an alignment film to orient it. In this case, if the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 are manufactured individually, the liquid crystal compounds in each cholesteric liquid crystal layer can be properly aligned. However, as mentioned above, when the two cholesteric liquid crystal layers are laminated using an adhesive layer and then laminated onto a light guide member, the distance between the two cholesteric liquid crystal layers becomes large, resulting in the problem that the cholesteric liquid crystal layer furthest from the light guide member deforms.

[0052] In contrast, by having the first cholesteric liquid crystal layer 16 and the first alignment film 18 in contact, and the first alignment film 18 and the second cholesteric liquid crystal layer 20 in contact, and by having the thickness of the first alignment film 18 within the above range, the liquid crystal compounds in each cholesteric liquid crystal layer can be properly aligned, deformation of the cholesteric liquid crystal layer on the side farther from the light guide member 12 can be suppressed, and a decrease in diffraction efficiency can be suppressed.

[0053] In the example shown in Figure 2, the twisting direction of the helical structure in the first cholesteric liquid crystal layer 16 is clockwise, reflecting right-handed circularly polarized light, and the twisting direction of the helical structure in the second cholesteric liquid crystal layer 20 is counterclockwise, reflecting left-handed circularly polarized light. However, the example is not limited to this, and the twisting direction of the helical structure in the first cholesteric liquid crystal layer 16 may be counterclockwise, reflecting left-handed circularly polarized light, while the twisting direction of the helical structure in the second cholesteric liquid crystal layer 20 may be clockwise, reflecting right-handed circularly polarized light.

[0054] Furthermore, in the example shown in Figure 2, the continuous rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the first cholesteric liquid crystal layer 16, whose helical structure has a clockwise twisting direction, is clockwise from left to right when viewed from above in the figure, and the continuous rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the second cholesteric liquid crystal layer 20, whose helical structure has a counterclockwise twisting direction, is counterclockwise when viewed from left to right in the figure. However, the example is not limited to this, and the continuous rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the cholesteric liquid crystal layer with a clockwise twisting direction may be counterclockwise, and the continuous rotation direction of the optical axis originating from the liquid crystal compound in the liquid crystal alignment pattern of the cholesteric liquid crystal layer with a counterclockwise twisting direction may be clockwise.

[0055] Furthermore, in the example shown in Figure 1, the λ / 4 plate 14 and the first cholesteric liquid crystal layer 16 are laminated via a second alignment film 15, but the invention is not limited to this, and the λ / 4 plate 14 and the first cholesteric liquid crystal layer 16 may be bonded together by an adhesive layer. In the example shown in Figure 1, the second alignment film 15 is formed on the surface of the first cholesteric liquid crystal layer 16, and the λ / 4 plate 14 is formed on this second alignment film 15.

[0056] Furthermore, although the example shown in Figure 1 has two cholesteric liquid crystal layers, a first cholesteric liquid crystal layer 16 and a second cholesteric liquid crystal layer 20, it is not limited to this, and may have one or more cholesteric liquid crystal layers.

[0057] For example, in addition to the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20, there may be a third cholesteric liquid crystal layer having a liquid crystal alignment pattern and a fourth cholesteric liquid crystal layer having a liquid crystal alignment pattern. In this case, the third cholesteric liquid crystal layer and the fourth cholesteric liquid crystal layer may have different selective reflection center wavelengths than the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20, and one of the third cholesteric liquid crystal layer and the other may reflect right-circularly polarized light and the other may reflect left-circularly polarized light, and the continuous rotation directions of the optical axes derived from the liquid crystal compound in the liquid crystal alignment pattern may be different from each other.

[0058] Furthermore, a fourth alignment film is provided between the third cholesteric liquid crystal layer and the fourth cholesteric liquid crystal layer, with the third cholesteric liquid crystal layer and the fourth alignment film in contact, and the fourth alignment film and the fourth cholesteric liquid crystal layer in contact, and the thickness of the fourth alignment film may be 0.01 μm to 0.5 μm. Moreover, for example, when the cholesteric liquid crystal layers are arranged in the order of first to fourth, a third alignment film is provided between the second cholesteric liquid crystal layer and the third cholesteric liquid crystal layer, with the second cholesteric liquid crystal layer and the third alignment film in contact, and the third alignment film and the third cholesteric liquid crystal layer in contact, and the thickness of the third alignment film may be 0.01 μm to 0.5 μm.

[0059] Furthermore, the alignment film (first alignment film) placed between the cholesteric liquid crystal layers is preferably a photoalignment film. By using a photoalignment film, the orientation of the liquid crystal compounds in the cholesteric liquid crystal layer can be increased, and the adhesion to the cholesteric liquid crystal layer and water resistance can be improved.

[0060] In the example shown in Figure 1, the light guide member 12 is a plate-shaped light guide plate, but it is not limited to this. Figure 4 conceptually shows another example of the optical member of the present invention.

[0061] The optical member 10b shown in Figure 4 comprises, in this order, a light guide member 12b, an adhesive layer 13, a λ / 4 plate 14, a second alignment film 15, a first cholesteric liquid crystal layer 16, a first alignment film 18, and a second cholesteric liquid crystal layer 20. Note that the optical member 10b shown in Figure 4 has the same configuration as the optical member 10a shown in Figure 1, except that it has a light guide member 12b instead of the light guide member 12; therefore, the following explanation will mainly focus on the differences.

[0062] The light guide member 12b is a triangular prism in the shape of a triangular prism with a right-angled triangular cross-section. In the illustrated example, a λ / 4 plate 14 is laminated on the two longer sides (hereinafter referred to as the bottom surface) that enclose the right angle of the right-angled triangle cross-section, via an adhesive layer 13.

[0063] As shown in Figure 4, when light containing P-polarized and / or S-polarized light of multiple wavelengths (indicated by the thick solid arrows in Figure 4) is incident on the prism 12b from a side surface (the surface that forms the shorter side of the two sides enclosing the right angle of the right triangle in cross-section) at an oblique angle to the perpendicular to the side surface, the light is diffracted at the air interface of the prism 12b and guided diagonally through the prism 12b toward the λ / 4 plate 14.

[0064] Light guided by the prism 12b is incident on the λ / 4 plate 14 and converted into right-circularly polarized or left-circularly polarized light. For example, let's explain this assuming that P-polarized light is converted into right-circularly polarized light and S-polarized light is converted into left-circularly polarized light.

[0065] The right-circularly polarized and / or left-circularly polarized light converted by the λ / 4 plate 14 is reflected and diffracted by the first cholesteric liquid crystal layer 16 or the second cholesteric liquid crystal layer 20. As described above, the light is diffracted at different angles for each wavelength, and therefore propagates in different directions for each wavelength, as shown by the thin solid arrows, dashed-dotted arrows, and dashed arrows in Figure 4.

[0066] Furthermore, as mentioned above, the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 reflect and diffract different circularly polarized light of the same wavelength in the same direction. Therefore, for each wavelength, the right-circularly polarized component and the left-circularly polarized component are not separated but are reflected and diffracted in the same direction.

[0067] Light of each wavelength reflected and diffracted by the first cholesteric liquid crystal layer 16 or the second cholesteric liquid crystal layer 20 is incident on the λ / 4 plate 14, converted to P-polarized and / or S-polarized light, incident on the prism 12b, guided through the prism 12b, and emitted from the prism 12b in different directions for each wavelength. In the example shown in Figure 4, the light is emitted from the side of the prism 12b.

[0068] Thus, the optical member 10b having the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 can be used as a polarization-independent wavelength separation element (diffractive element) because its diffraction efficiency does not change depending on the polarization state of the incident light.

[0069] Furthermore, by using the prism 12b as a light guide member, the wavelength separation effect of the prism 12b makes it possible to increase the separation angle between light of each wavelength emitted from the optical member 10b.

[0070] In the case of the optical member 10b shown in Figure 4, a first alignment film 18 is present between the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20, with the first cholesteric liquid crystal layer 16 and the first alignment film 18 in contact, and the first alignment film 18 and the second cholesteric liquid crystal layer 20 in contact, and the thickness of the first alignment film 18 is 0.01 μm to 0.5 μm. This suppresses large deformation of the second cholesteric liquid crystal layer 20 after humid heat endurance, and suppresses a decrease in the diffraction efficiency of circularly polarized light reflected by the second cholesteric liquid crystal layer 20.

[0071] In the example shown in Figure 4, light is assumed to enter the prism 12b from the side and the wavelength-separated light is assumed to exit from the side of the prism 12b, but this is not the only option. For example, light may enter the prism 12b from the side and the wavelength-separated light may exit from the slanted surface of the prism 12b (the surface opposite the right angle of the right triangle in the cross-section). Alternatively, light may enter the slanted surface of the prism 12b and the wavelength-separated light may exit from the side of the prism 12b, or light may enter the slanted surface of the prism 12b and the wavelength-separated light may exit from the slanted surface of the prism 12b.

[0072] The components of the optical member of the present invention will be described below.

[0073] <Light Guide Member> The light guide member is used to guide light and cause it to enter the first cholesteric liquid crystal layer and / or the second cholesteric liquid crystal layer. Light guide members can include light guide plates, prisms, lenses, etc.

[0074] (Light guide plate) As a light guide plate, any conventionally known light guide plate can be used as long as it has high transmittance for the target wavelength of light and can guide light. When the optical component is used in an optical communication system, the light guide plate only needs to be able to guide light of wavelengths in the infrared range used in the optical communication system. For example, materials for the light guide plate include glass, synthetic quartz, fused quartz, triacetylcellulose (TAC), polyethylene terephthalate (PET), polycarbonate, polyvinyl chloride, acrylic, and polyolefin.

[0075] The thickness of the light guide plate is not particularly limited, but from the viewpoint of physical strength, smoothness, etc., it is preferably 0.1 mm or more, and more preferably 0.5 mm or more. Furthermore, from the viewpoint of weight reduction, etc., it is preferably 5 mm or less, and more preferably 3 mm or less.

[0076] (Prism) Any conventionally known prism can be used as a prism, as long as it has high transmittance for the target wavelength of light and can guide that light. When the optical component is used in an optical communication system, the prism only needs to be able to guide light of the infrared wavelength range used in the optical communication system. For example, prism materials include glass, synthetic quartz, fused quartz, and acrylic.

[0077] There are no restrictions on the size of the prism; it should be set appropriately according to the prism's forming material, the application of the optical components, the required spectral performance, the spot diameter of the light being spectrally analyzed, etc.

[0078] Furthermore, in the example shown in Figure 4, the shape of the prism is a triangular prism with a right-angled triangular cross-section, but it is not limited to this. The shape of the prism can be any configuration that has a surface on which the cholesteric liquid crystal layer, etc., is arranged, a surface on which light is incident, and a surface on which light is emitted. Also, the surface on which light is incident and the surface on which light is emitted may be the same. For example, the cross-sectional shape of the prism may be a polygon other than a right-angled triangle, such as a triangle, quadrilateral, or pentagon. Also, the prism may have a curved surface.

[0079] <λ / 4 plate> A λ / 4 plate converts incident linearly polarized light into circularly polarized light, and also converts incident circularly polarized light into linearly polarized light. In other words, a λ / 4 plate is a plate in which the in-plane retardation Re at the wavelength λnm of the target light is λ / 4 (or an odd multiple thereof). The in-plane retardation Re(λ) of a λ / 4 plate is centered on the ideal value (λ / 4nm) and may have an error of about 25nm.

[0080] The λ / 4 plate is positioned such that its slow axis makes an angle of approximately 45° with the polarization direction of the incident linearly polarized light.

[0081] The λ / 4 plate used in the present invention may be a single-layer type composed of one optically anisotropic layer, or a multi-layer type composed of stacking two or more optically anisotropic layers, each having multiple different slow phase axes. Examples of multi-layer λ / 4 plates are listed in WO2013 / 137464, WO2016 / 158300, JP 2014-209219, JP 2014-209220, WO2014 / 157079, JP 2019-215416, WO2019 / 160044, and JP 2014-02 Examples include, but are not limited to, Publication No. 6266, WO2022 / 030266, WO2021 / 132624, WO2021 / 033631, WO2022 / 045185, WO2022 / 045185, WO19 / 160016, and WO2020 / 100813.

[0082] There are no restrictions on the λ / 4 plate; various known plates with λ / 4 functionality can be used. Specific examples of λ / 4 plates include those described in U.S. Patent Application Publication 2015 / 0277006.

[0083] Examples of a λ / 4 plate having a single-layer structure include a stretched polymer film and a phase difference film having an optically anisotropic layer on which a liquid crystal compound is oriented to exhibit refractive index anisotropy. Examples of a λ / 4 plate having a multi-layer structure include a broadband λ / 4 plate formed by laminating a λ / 4 plate and a λ / 2 wave plate.

[0084] In the example shown in Figure 1, the λ / 4 plate 14 is an optically anisotropic layer in which a liquid crystal compound is oriented to exhibit refractive index anisotropy, and the second alignment film 15 is an alignment film for oriented the liquid crystal compound. Conventional known alignment films can be appropriately used as the second alignment film 15 for forming the λ / 4 plate 14.

[0085] There are no particular restrictions on the thickness of the λ / 4 plate, but it is preferably 1 to 500 μm, more preferably 1 to 50 μm, and even more preferably 1 to 5 μm.

[0086] <Cholesteric Liquid Crystal Layer> The first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer are formed using a composition containing a liquid crystal compound, and have a helical structure in which the liquid crystal compound is spirally twisted and stacked in the thickness direction, and have a liquid crystal orientation pattern in which the orientation of the optical axis originating from the liquid crystal compound changes while continuously rotating in one direction in the plane. As described above, the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have the same configuration except that the twisting direction of the helical structure is different from that of the second cholesteric liquid crystal layer and the continuous rotation direction of the orientation of the optical axis originating from the liquid crystal compound in the liquid crystal orientation pattern is different from that of the first cholesteric liquid crystal layer. In the following description, when it is not necessary to distinguish between the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer, they will simply be referred to as the cholesteric liquid crystal layer. In this specification, the cholesteric liquid crystal layer on the side closer to the light guide member is referred to as the first cholesteric liquid crystal layer, and the cholesteric liquid crystal layer on the side further away is referred to as the second cholesteric liquid crystal layer 20.

[0087] Figure 5 is a conceptual diagram showing an example of a cholesteric liquid crystal layer. Figure 6 is a plan view of the cholesteric liquid crystal layer shown in Figure 5. A plan view is a view of the cholesteric liquid crystal layer from above in Figure 5, that is, a view of the cholesteric liquid crystal layer from the thickness direction (= stacking direction of each layer (film)). In Figure 6, in order to simplify the drawing and clearly show the structure of the cholesteric liquid crystal layer, only the liquid crystal compound 30 (liquid crystal compound molecules) on the surface of the alignment film is conceptually shown. However, as conceptually shown in Figure 6, the cholesteric liquid crystal layer has a helical structure in which the liquid crystal compound 30 is spirally stacked, similar to a cholesteric liquid crystal layer in which a normal cholesteric liquid crystal phase is fixed. The structure has multiple pitches in which the spirally spiraling liquid crystal compound 30 is stacked, with one spiral rotation (360° rotation) of the liquid crystal compound 30 being considered as one helical pitch.

[0088] In the example shown in Figure 5, a cholesteric liquid crystal layer, an alignment film for aligning the liquid crystal compounds in the cholesteric liquid crystal layer, and a layer having a surface on which the cholesteric liquid crystal layer (alignment film) is formed (hereinafter also referred to as the layer to be formed) are illustrated. Specifically, for example, if the cholesteric liquid crystal layer is a first cholesteric liquid crystal layer 16, the alignment film is a first alignment film 18 and the layer to be formed is a second cholesteric liquid crystal layer 20. Also, if the cholesteric liquid crystal layer is a second cholesteric liquid crystal layer 20, the alignment film is a peelable alignment film 25 after formation, and the layer to be formed is a peelable temporary support 24 after formation.

[0089] As is well known, a cholesteric liquid crystal layer has a helical structure in which liquid crystal compounds are stacked in a spiral in the thickness direction, with one spiral rotation (360° rotation) of the liquid crystal compounds being considered as one spiral pitch (helical pitch), and the layer has a structure in which multiple spiral-rotating liquid crystal compounds are stacked at different pitches.

[0090] A cholesteric liquid crystal layer reflects right-circularly polarized or left-circularly polarized light in a specific wavelength range, while transmitting other light, depending on the length of the helical pitch and the direction of spiral rotation (sense) of the liquid crystal compound. In other words, a cholesteric liquid crystal layer has wavelength-selective reflectivity and polarization selectivity. For example, the cholesteric liquid crystal layer used in the optical component of the present invention has a selective reflection center wavelength in the infrared light range used in optical communication systems, reflecting right-circularly polarized or left-circularly polarized light in this wavelength range and transmitting other circularly polarized light and light in other wavelength ranges.

[0091] Furthermore, since the cholesteric liquid crystal layer is oriented such that the liquid crystal compound 30 continuously rotates and changes in the planar direction, it refracts (diffracts) incident circularly polarized light in the direction in which the optical axis direction continuously rotates and reflects it. In this case, the direction of diffraction differs depending on the rotation direction of the incident circularly polarized light. That is, the cholesteric liquid crystal layer reflects right-circularly polarized or left-circularly polarized light of the selected reflection wavelength and diffracts this reflected light.

[0092] The optical axis 30A derived from the liquid crystal compound 30 is the axis in the liquid crystal compound 30 where the refractive index is highest, the so-called slow axis. For example, if the liquid crystal compound 30 is a rod-shaped liquid crystal compound, the optical axis 30A is aligned along the long axis of the rod shape. If the liquid crystal compound 30 is a disc-shaped liquid crystal compound, the optical axis 30A is aligned in a direction perpendicular to the disc surface. In the following explanation, the optical axis 30A derived from the liquid crystal compound 30 will also be referred to as the "optical axis 30A of the liquid crystal compound 30" or "optical axis 30A".

[0093] As shown in Figure 6, on the surface of the alignment film, the liquid crystal compound 30 constituting the cholesteric liquid crystal layer is arranged two-dimensionally in a predetermined direction indicated by arrow A, and in a direction perpendicular to this direction (arrow A direction), according to the alignment pattern formed on the underlying alignment film.

[0094] In the following explanation, the direction of arrow A will be arbitrarily referred to as the X direction, and the direction perpendicular to the direction of arrow A will be arbitrarily referred to as the Y direction. That is, in Figure 5, the Y direction is the direction perpendicular to the plane of the paper.

[0095] Furthermore, the liquid crystal compound 30 forming the cholesteric liquid crystal layer has a liquid crystal orientation pattern in which the orientation of the optical axis 30A changes while continuously rotating along the direction of arrow A within the plane of the cholesteric liquid crystal layer. In the illustrated example, the liquid crystal compound 30 has a liquid crystal orientation pattern in which the optical axis 30A changes while continuously rotating clockwise along the direction of arrow A. In the following explanation, "the orientation of the optical axis 30A changes" will also simply be referred to as "the optical axis 30A rotates".

[0096] The statement that the orientation of the optical axis 30A of the liquid crystal compound 30 changes while continuously rotating in the direction of arrow A (a predetermined one direction) means that, specifically, the angle between the optical axis 30A of the liquid crystal compounds 30 arranged along the direction of arrow A and the direction of arrow A differs depending on the position in the direction of arrow A, and that the angle between the optical axis 30A and the direction of arrow A changes sequentially from θ to θ+180° or θ-180° along the direction of arrow A. In other words, as shown in Figure 6, the multiple liquid crystal compounds 30 arranged along the direction of arrow A are arranged such that the optical axis 30A changes while rotating in the direction of arrow A by a fixed angle.

[0097] Furthermore, the difference in angle between the optical axes 30A of adjacent liquid crystal compounds 30 in the direction of arrow A is preferably 45° or less, more preferably 15° or less, and even more preferably a smaller angle.

[0098] Furthermore, in the present invention, the rotation direction of the optical axis 30A of the liquid crystal compound 30 in the direction of arrow A is assumed to be such that the liquid crystal compound 30 (optical axis 30A) rotates in a direction that reduces the angle between the optical axes 30A of adjacent liquid crystal compounds 30 in the direction of arrow A. Therefore, in the optically anisotropic layers shown in Figures 5 and 6, the optical axis 30A of the liquid crystal compound 30 rotates clockwise along the direction of arrow A.

[0099] On the other hand, in the liquid crystal compound 30 that forms the cholesteric liquid crystal layer, the orientation of the optical axis 30A is the same in the Y direction, which is perpendicular to the direction of arrow A, that is, in the Y direction, which is perpendicular to the direction in which the optical axis 30A rotates continuously. In other words, in the liquid crystal compound 30 that forms the cholesteric liquid crystal layer, the angle between the optical axis 30A of the liquid crystal compound 30 and the direction of arrow A is the same in the Y direction.

[0100] In such a liquid crystal alignment pattern of liquid crystal compound 30, the length (distance) of a 180° rotation of the optical axis 30A of the liquid crystal compound 30 in the direction of arrow A, where the optical axis 30A rotates continuously within the plane, is defined as the length of one period Λ in the liquid crystal alignment pattern. That is, the distance between the centers of two liquid crystal compounds 30 whose angles with respect to the direction of arrow A are equal, is defined as the length of one period Λ. Specifically, as shown in Figure 6, the distance between the centers of two liquid crystal compounds 30 whose directions of arrow A coincide with the direction of the optical axis 30A is defined as the length of one period Λ. In the following explanation, this length of one period Λ will also be referred to as "period Λ".

[0101] The liquid crystal alignment pattern of the cholesteric liquid crystal layer repeats this one period Λ in one direction, where the direction of arrow A, i.e., the direction of the optical axis 30A, continuously rotates and changes.

[0102] The cholesteric liquid crystal layer has a liquid crystal alignment pattern in which the optical axis 30A continuously rotates and changes along the direction of arrow A (a predetermined direction) within the plane. A cholesteric liquid crystal layer having such a liquid crystal alignment pattern reflects incident light in a direction that is at an angle to the direction of arrow A with respect to specular reflection. For example, the cholesteric liquid crystal layer does not reflect light incident from the normal direction in the normal direction, but rather reflects it at an angle to the direction of arrow A with respect to the normal direction. Light incident from the normal direction is light incident from the front, that is, light incident perpendicular to the principal surface. The principal surface is the largest surface of the sheet-like material.

[0103] The angle of light reflection by a cholesteric liquid crystal layer having a liquid crystal alignment pattern differs depending on the length Λ of one period of the liquid crystal alignment pattern, i.e., the period Λ, in the direction of arrow A, where the optical axis 30A rotates by 180°. Specifically, the shorter the period Λ, the larger the angle of the reflected light (diffraction angle) relative to the reflection direction of specular reflection.

[0104] Furthermore, when reflecting circularly polarized light of the same wavelength and direction of rotation, the direction of reflection of the circularly polarized light can be reversed by reversing the rotation direction of the optical axis 30A of the liquid crystal compound 30 facing the direction of arrow A.

[0105] Furthermore, in cholesteric liquid crystal layers having the same liquid crystal orientation pattern, the reflection direction is reversed depending on the spiral direction of the liquid crystal compound 30, i.e., the spiral direction of the reflected circularly polarized light.

[0106] The diffraction angle of a cholesteric liquid crystal layer with such a liquid crystal orientation pattern varies depending on the wavelength of light. Specifically, the longer the wavelength of light, the larger the angle of reflected light relative to the incident light. Therefore, a cholesteric liquid crystal layer can spectrally separate (wavelength-separate) light by diffracting (reflecting) the incident light at different angles depending on its wavelength.

[0107] Furthermore, the cholesteric liquid crystal layers (first cholesteric liquid crystal layer and second cholesteric liquid crystal layer) only need to have a liquid crystal alignment pattern in at least a portion of their regions, and may have regions that do not have a liquid crystal alignment pattern.

[0108] <<Method for forming a cholesteric liquid crystal layer>> A cholesteric liquid crystal layer can be formed by fixing a liquid crystal phase in which a liquid crystal compound is oriented in a predetermined state.

[0109] The structure in which the cholesteric liquid crystal phase is fixed can be any structure in which the orientation of the liquid crystal compound that constitutes the cholesteric liquid crystal phase is maintained. Typically, a polymerizable liquid crystal compound is placed in the oriented state of the cholesteric liquid crystal phase, and then polymerized and cured by ultraviolet irradiation, heating, etc., to form a non-fluid layer, and at the same time, a structure is preferred in which the orientation form does not change due to an external field or external force.

[0110] In a structure in which the cholesteric liquid crystal phase is fixed, it is sufficient that the optical properties of the cholesteric liquid crystal phase are maintained, and the liquid crystal compound 30 does not need to exhibit liquid crystalline properties in the cholesteric liquid crystal layer. For example, the polymerizable liquid crystal compound may lose its liquid crystalline properties due to its high molecular weight resulting from the curing reaction.

[0111] As an example of a material used to form a cholesteric liquid crystal layer by fixing a cholesteric liquid crystal phase, a liquid crystal composition containing a liquid crystal compound is used. The liquid crystal compound is preferably a polymerizable liquid crystal compound.

[0112] Furthermore, the liquid crystal composition used to form the cholesteric liquid crystal layer may also contain a surfactant and a chiral agent.

[0113] --Polymerizable liquid crystal compounds-- The polymerizable liquid crystal compound may be a rod-shaped liquid crystal compound or a disc-shaped liquid crystal compound.

[0114] Examples of rod-shaped polymerizable liquid crystal compounds that form a cholesteric liquid crystal phase include rod-shaped nematic liquid crystal compounds. Preferred rod-shaped nematic liquid crystal compounds include azomethines, azoxys, cyanobiphenyls, cyanophenyl esters, benzoic acid esters, cyclohexanecarboxylic acid phenyl esters, cyanophenylcyclohexanes, cyanosubstituted phenylpyrimidines, alkoxysubstituted phenylpyrimidines, phenyldioxanes, trans, and alkenylcyclohexylbenzonitriles. Not only low molecular weight liquid crystal compounds but also high molecular weight liquid crystal compounds can be used.

[0115] Polymerizable liquid crystal compounds are obtained by introducing polymerizable groups into liquid crystal compounds. Examples of polymerizable groups include unsaturated polymerizable groups, epoxy groups, and aziridinyl groups, with unsaturated polymerizable groups being preferred and ethylenically unsaturated polymerizable groups being more preferred. Polymerizable groups can be introduced into the molecule of the liquid crystal compound by various methods. The number of polymerizable groups in a polymerizable liquid crystal compound is preferably 1 to 6, more preferably 1 to 3.

[0116] An example of a polymerizable liquid crystal compound is Makromol. Chem. This includes compounds described in Volume 190, page 2255 (1989), Advanced Materials Volume 5, page 107 (1993), U.S. Patent No. 4,683,327, U.S. Patent No. 5,622,648, U.S. Patent No. 5,770,107, International Publication No. 95 / 22586, International Publication No. 95 / 24455, International Publication No. 97 / 00600, International Publication No. 98 / 23580, International Publication No. 98 / 52905, Japanese Patent Publication No. 1-272551, Japanese Patent Publication No. 6-016616, Japanese Patent Publication No. 7-110469, Japanese Patent Publication No. 11-080081, and Japanese Patent Publication No. 2001-328973, etc. Two or more polymerizable liquid crystal compounds may be used in combination. Using two or more polymerizable liquid crystal compounds in combination can lower the orientation temperature.

[0117] Furthermore, as polymerizable liquid crystal compounds other than those mentioned above, cyclic organopolysiloxane compounds having a cholesteric phase, such as those disclosed in Japanese Patent Publication No. 57-165480, can be used. In addition, as the aforementioned polymeric liquid crystal compounds, polymers in which liquid crystal-resisting mesogenic groups are introduced in the main chain, side chains, or both the main chain and side chains, polymeric cholesteric liquid crystals in which cholesteryl groups are introduced in the side chains, liquid crystalline polymers such as those disclosed in Japanese Patent Publication No. 9-133810, and liquid crystalline polymers such as those disclosed in Japanese Patent Publication No. 11-293252 can be used.

[0118] --Disk-shaped liquid crystal compounds-- As disc-shaped liquid crystal compounds, those described in Japanese Patent Publication No. 2007-108732 and Japanese Patent Publication No. 2010-244038 can be preferably used.

[0119] Furthermore, the amount of polymerizable liquid crystal compound added to the liquid crystal composition is preferably 75 to 99.9% by mass, more preferably 80 to 99% by mass, and even more preferably 85 to 90% by mass, based on the solid content mass (mass excluding solvent) of the liquid crystal composition.

[0120] --Surfactants-- The liquid crystal composition used to form the cholesteric liquid crystal layer may contain surfactants.

[0121] The surfactant is preferably a compound that can function as an orientation control agent that contributes stably or rapidly to the orientation of the cholesteric liquid crystal phase. Examples of surfactants include silicate surfactants and fluorine-based surfactants, with fluorine-based surfactants being preferred.

[0122] Specific examples of surfactants include the compounds described in paragraphs

[0082] to

[0090] of Japanese Patent Application Publication No. 2014-119605, the compounds described in paragraphs

[0031] to

[0034] of Japanese Patent Application Publication No. 2012-203237, the compounds exemplified in paragraphs

[0092] and

[0093] of Japanese Patent Application Publication No. 2005-099248, the compounds exemplified in paragraphs

[0076] to

[0078] and paragraphs

[0082] to

[0085] of Japanese Patent Application Publication No. 2002-129162, and fluorine (meth)acrylate polymers described in paragraphs

[0018] to

[0043] of Japanese Patent Application Publication No. 2007-272185, etc.

[0123] Furthermore, a single surfactant may be used alone, or two or more surfactants may be used in combination.

[0124] As a fluorine-based surfactant, the compounds described in paragraphs

[0082] to

[0090] of Japanese Patent Application Publication No. 2014-119605 are preferred.

[0125] The amount of surfactant added to the liquid crystal composition is preferably 0.01 to 10% by mass, more preferably 0.01 to 5% by mass, and even more preferably 0.02 to 1% by mass, relative to the total mass of the liquid crystal compound.

[0126] -- Chiral Agents (Optically Active Compounds) -- Chiral agents have the function of inducing a helical structure in the cholesteric liquid crystal phase. Since different chiral agents induce different helical twist directions or helical pitches, they should be selected according to the purpose.

[0127] There are no particular restrictions on the chiral agent, and known compounds (for example, described in the Liquid Crystal Device Handbook, Chapter 3, Section 4-3, Chiral Agents for TN (twisted nematic) and STN (Super Twisted Nematic), page 199, edited by the 142nd Committee of the Japan Society for the Promotion of Science, 1989), isosorbide, and isomannide derivatives can be used.

[0128] Chiral agents generally contain an asymmetric carbon atom, but axially asymmetric compounds or planar asymmetric compounds that do not contain an asymmetric carbon atom can also be used as chiral agents. Examples of axially asymmetric compounds or planar asymmetric compounds include binaphthyl, helicene, paracyclophane, and their derivatives. Chiral agents may have polymerizable groups. If both the chiral agent and the liquid crystal compound have polymerizable groups, a polymerization reaction between the polymerizable chiral agent and the polymerizable liquid crystal compound can form a polymer having repeating units derived from the polymerizable liquid crystal compound and repeating units derived from the chiral agent. In this embodiment, it is preferable that the polymerizable group of the polymerizable chiral agent is of the same type as the polymerizable group of the polymerizable liquid crystal compound. Therefore, the polymerizable group of the chiral agent is preferably an unsaturated polymerizable group, an epoxy group, or an azilidinyl group, more preferably an unsaturated polymerizable group, and even more preferably an ethylenically unsaturated polymerizable group.

[0129] Furthermore, the chiral agent may be a liquid crystal compound.

[0130] When the chiral agent has a photoisomerizing group, it is preferable because, after coating and orientation, a pattern of the desired reflected wavelength corresponding to the emission wavelength can be formed by photomask irradiation with active light or the like. Preferred photoisomerizing groups are the isomerization site of a photochromic compound, an azo group, an azoxy group, or a cinnamoyl group. Specific compounds that can be used include those described in Japanese Patent Publication No. 2002-080478, 2002-080851, 2002-179668, 2002-179669, 2002-179670, 2002-179681, 2002-179682, 2002-338575, 2002-338668, 2003-313189, and 2003-313292, etc.

[0131] In the liquid crystal composition, the content of the chiral agent is preferably 0.01 to 200 mol%, and more preferably 1 to 30 mol%, relative to the molar amount of the liquid crystal compound.

[0132] --Polymerization Initiator-- If the liquid crystal composition contains a polymerizable compound, it is preferable that it also contains a polymerization initiator. In the embodiment in which the polymerization reaction is carried out by ultraviolet irradiation, it is preferable that the polymerization initiator used is a photopolymerization initiator capable of initiating the polymerization reaction by ultraviolet irradiation.

[0133] Examples of photopolymerization initiators include α-carbonyl compounds (described in U.S. Patent No. 2,367,661 and U.S. Patent No. 2,367,670), acyloin ethers (described in U.S. Patent No. 2,448,828), α-hydrocarbon-substituted aromatic acyloin compounds (described in U.S. Patent No. 2,722,512), polynuclear quinone compounds (described in U.S. Patent No. 3,046,127 and U.S. Patent No. 2,951,758), combinations of triarylimidazole dimers and p-aminophenyl ketones (described in U.S. Patent No. 3,549,367), acridine and phenazine compounds (described in Japanese Patent Publication No. 60-105,667 and U.S. Patent No. 4,239,850), and oxadiazole compounds (described in U.S. Patent No. 4,212,970).

[0134] The content of the photopolymerization initiator in the liquid crystal composition is preferably 0.1 to 20% by mass, and more preferably 0.5 to 12% by mass, relative to the content of the liquid crystal compound.

[0135] --Crosslinking Agent-- The liquid crystal composition may optionally contain a crosslinking agent to improve the strength and durability of the film after curing. Suitable crosslinking agents are those that cure with ultraviolet light, heat, and moisture.

[0136] There are no particular restrictions on the crosslinking agent, and it can be appropriately selected depending on the purpose. Examples include polyfunctional acrylate compounds such as trimethylolpropane tri(meth)acrylate and pentaerythritol tri(meth)acrylate; epoxy compounds such as glycidyl(meth)acrylate and ethylene glycol diglycidyl ether; aziridine compounds such as 2,2-bishydroxymethylbutanol-tris[3-(1-aziridinyl)propionate] and 4,4-bis(ethyleneiminocarbonylamino)diphenylmethane; isocyanate compounds such as hexamethylene diisocyanate and biuret-type isocyanate; polyoxazoline compounds having an oxazoline group in the side chain; and alkoxysilane compounds such as vinyltrimethoxysilane and N-(2-aminoethyl)3-aminopropyltrimethoxysilane. In addition, known catalysts can be used depending on the reactivity of the crosslinking agent, which can improve productivity in addition to improving film strength and durability. These may be used individually or in combination of two or more.

[0137] The crosslinking agent content is preferably 3 to 20% by mass, and more preferably 5 to 15% by mass, relative to the solid content mass of the liquid crystal composition. When the crosslinking agent content is within the above range, the effect of improving the crosslink density is easily obtained, and the stability of the cholesteric liquid crystal phase is further improved.

[0138] --Other Additives-- Polymerization inhibitors, antioxidants, ultraviolet absorbers, light stabilizers, colorants, and metal oxide fine particles may be added to the liquid crystal composition as needed, within limits that do not degrade the optical performance.

[0139] When forming a cholesteric liquid crystal layer, the liquid crystal composition is preferably used as a liquid.

[0140] The liquid crystal composition may contain a solvent. There are no restrictions on the solvent, and it can be appropriately selected depending on the purpose, but organic solvents are preferred.

[0141] There are no restrictions on the organic solvent, and it can be appropriately selected depending on the purpose. Examples include ketones, alkyl halides, amides, sulfoxides, heterocyclic compounds, hydrocarbons, esters, and ethers. These may be used individually or in combination of two or more. Among these, ketones are preferred when considering the environmental impact.

[0142] When forming a cholesteric liquid crystal layer, it is preferable to apply a liquid crystal composition to the surface on which the cholesteric liquid crystal layer is formed, orient the liquid crystal compound into a cholesteric liquid crystal phase, and then cure the liquid crystal compound to form a cholesteric liquid crystal layer.

[0143] In other words, when forming a cholesteric liquid crystal layer on an alignment film, it is preferable to apply a liquid crystal composition to the alignment film to orient the liquid crystal compound into a cholesteric liquid crystal phase, and then cure the liquid crystal compound to fix the cholesteric liquid crystal phase and form a cholesteric liquid crystal layer.

[0144] For coating the liquid crystal composition, all known methods that can uniformly coat a sheet-like material with liquid, such as inkjet and scroll printing, as well as spin coating, bar coating, and spray coating, can be used.

[0145] The coated liquid crystal composition is dried and / or heated as needed, and then cured to form a cholesteric liquid crystal layer. In this drying and / or heating step, the liquid crystal compounds in the liquid crystal composition should be oriented into the cholesteric liquid crystal phase. When heating is performed, the heating temperature is preferably 200°C or lower, and more preferably 130°C or lower.

[0146] The oriented liquid crystal compound is further polymerized as needed. Polymerization may be carried out by thermal polymerization or photopolymerization by light irradiation, but photopolymerization is preferred. Ultraviolet light is preferred for light irradiation. The irradiation energy is 20 mJ / cm². 2 ~50 J / cm 2 Preferably, 50 to 1500 mJ / cm² 2 This is more preferable. To promote the photopolymerization reaction, light irradiation may be carried out under heating conditions or in a nitrogen atmosphere. The wavelength of the ultraviolet light used for irradiation is preferably 250 to 430 nm.

[0147] Furthermore, as a method for forming a cholesteric liquid crystal layer, a method is also suitably used in which a gradient liquid crystal layer is formed using a composition containing a disc-shaped liquid crystal compound, in which the molecular axis of the disc-shaped liquid crystal compound is inclined with respect to the surface, and a cholesteric liquid crystal layer is formed on the gradient liquid crystal layer using a composition containing a liquid crystal compound.

[0148] A method for forming a cholesteric liquid crystal layer using such a gradient liquid crystal layer is described in paragraphs

[0049] to

[0194] of International Publication 2019 / 181247.

[0149] There are no restrictions on the thickness of the cholesteric liquid crystal layer; it can be set appropriately depending on the application of the optical component, the required light reflectivity of the cholesteric liquid crystal layer, and the material used to form the cholesteric liquid crystal layer.

[0150] Furthermore, the cholesteric liquid crystal layer may have a helical pitch that changes in the thickness direction. A cholesteric liquid crystal layer with a helical pitch that changes in the thickness direction can be formed by using a chiral agent that undergoes reverse isomerization, dimerization, and isomerization and dimerization upon irradiation with light, thereby changing the helical twisting power (HTP), and irradiating the liquid crystal composition that forms the cholesteric liquid crystal layer with light of a wavelength that changes the HTP of the chiral agent before curing or during curing of the liquid crystal composition.

[0151] For example, by using a chiral agent whose HTP decreases upon light irradiation, the HTP of the chiral agent decreases upon light irradiation. Here, the irradiated light is absorbed by the forming material of the cholesteric liquid crystal layer. Therefore, for example, when light is irradiated from above, the amount of light irradiation gradually decreases from top to bottom. That is, the amount of decrease in the HTP of the chiral agent gradually decreases from top to bottom. As a result, in the upper part where the HTP has decreased significantly, the induction of helical formation is small, so the helical pitch becomes longer, and in the lower part where the decrease in HTP is small, helical formation is induced by the HTP that the chiral agent inherently possesses, so the helical pitch becomes shorter. This makes it possible to form a cholesteric liquid crystal layer in which the helical pitch changes in the thickness direction.

[0152] Such light irradiation may be performed before exposure for curing the cholesteric liquid crystal layer, or simultaneously with exposure for curing. Furthermore, the wavelength of light used to alter the HTP of the chiral agent and the wavelength of light used to cure the cholesteric liquid crystal layer may be the same or different.

[0153] <Alignment Film (First Alignment Film)> The first alignment film 18 is an alignment film used to align the liquid crystal compound 30 to a predetermined liquid crystal alignment pattern when forming the cholesteric liquid crystal layer. The first alignment film 18 may be an alignment film for forming the first cholesteric liquid crystal layer 16, or an alignment film for forming the second cholesteric liquid crystal layer 20. In the example shown in Figure 1, the first alignment film 18 is an alignment film for forming the first cholesteric liquid crystal layer 16.

[0154] As described above, the cholesteric liquid crystal layer has a liquid crystal alignment pattern in which the orientation of the optical axis 30A (see Figure 6) derived from the liquid crystal compound 30 changes while continuously rotating along one direction in the plane. Therefore, the first alignment film 18 is formed so that the cholesteric liquid crystal layer can form this liquid crystal alignment pattern.

[0155] Various known materials can be used for the first orientation film 18. Examples include rubbing-treated films made of organic compounds such as polymers, obliquely deposited films of inorganic compounds, films having microgrooves, and films obtained by accumulating Langmuir-Blodgett (LB) films of organic compounds such as ω-tricosanoic acid, dioctadecylmethylammonium chloride, and methyl stearylate using the Langmuir-Blodgett method.

[0156] An oriented film formed by rubbing can be created by rubbing the surface of a polymer layer several times in a specific direction with paper or cloth.

[0157] Preferred materials for the orientation film include polyimide, polyvinyl alcohol, polymers having polymerizable groups as described in Japanese Patent Publication No. 9-152509, materials used for forming orientation films as described in Japanese Patent Publication No. 2005-097377, Japanese Patent Publication No. 2005-099228, and Japanese Patent Publication No. 2005-128503.

[0158] As the first orientation film 18, a so-called photo-alignment film is preferably used, which is formed by irradiating a photo-alignable material with polarized or unpolarized light to create an orientation film. That is, as the first orientation film 18, a photo-alignment film formed by coating a photo-alignment material onto a layer to be formed is preferably used.

[0159] Polarized light irradiation can be applied perpendicularly or obliquely to the photo-alignment film, while unpolarized light irradiation can be applied obliquely to the photo-alignment film.

[0160] Examples of photo-alignment materials used in the alignment film applicable to the present invention include those described in Japanese Patent Publication No. 2006-285197, Japanese Patent Publication No. 2007-076839, Japanese Patent Publication No. 2007-138138, Japanese Patent Publication No. 2007-094071, Japanese Patent Publication No. 2007-121721, Japanese Patent Publication No. 2007-140465, Japanese Patent Publication No. 2007-156439, and Japanese Patent Publication No. 20 Azo compounds described in Japanese Patent Publication No. 07-133184, Japanese Patent Publication No. 2009-109831, Japanese Patent No. 3883848 and Japanese Patent No. 4151746, aromatic ester compounds described in Japanese Patent Publication No. 2002-229039, maleimides having photo-orienting units described in Japanese Patent Publication No. 2002-265541 and Japanese Patent Publication No. 2002-317013 Preferred examples include alkenyl-substituted nadiimide compounds, photocrosslinkable silane derivatives described in Japanese Patent No. 4205195 and Japanese Patent No. 4205198, photocrosslinkable polyimides, photocrosslinkable polyamides and photocrosslinkable polyesters described in Japanese Patent Publication No. 2003-520878, Japanese Patent Publication No. 2004-529220 and Japanese Patent No. 4162850, and photodimerizable compounds described in Japanese Patent Publication No. 9-118717, Japanese Patent Publication No. 10-506420, Japanese Patent Publication No. 2003-505561, International Publication No. 2010 / 150748, Japanese Patent Publication No. 2013-177561 and Japanese Patent Publication No. 2014-012823, particularly cinnamate compounds, chalcone compounds and coumarin compounds.

[0161] Among these, azo compounds, photocrosslinkable polyimides, photocrosslinkable polyamides, photocrosslinkable polyesters, cinnamate compounds, and chalcone compounds are particularly suitable for use.

[0162] The following compounds are examples of specific photo-oriented materials.

[0163]

[0164]

[0165] As described above, the thickness of the first orientation film 18 is 0.01 μm to 0.5 μm, preferably 0.015 μm to 0.4 μm, and more preferably 0.02 μm to 0.3 μm.

[0166] There are no limitations on the method for forming the first orientation film 18, and various known methods depending on the material used to form the first orientation film 18 can be used. As an example, one method involves coating the surface of the layer to be formed with the first orientation film 18, drying it, and then exposing the first orientation film 18 with laser light to form an orientation pattern.

[0167] Figure 7 conceptually shows an example of an exposure apparatus for exposing the first alignment film 18 to form an alignment pattern. In the following description, the layer to be formed is assumed to be the second cholesteric liquid crystal layer 20, that is, the first alignment film 18 and the first cholesteric liquid crystal layer 16 are formed on the second cholesteric liquid crystal layer 20.

[0168] The exposure apparatus 60 shown in Figure 7 comprises a light source 64 equipped with a laser 62, a λ / 2 plate 65 that changes the polarization direction of the laser light M emitted by the laser 62, a beam splitter 68 that separates the laser light M emitted by the laser 62 into two beams MA and MB, mirrors 70A and 70B arranged on the optical paths of the two separated beams MA and MB, respectively, and λ / 4 plates 72A and 72B.

[0169] The light source 64 emits linearly polarized light P0. The λ / 4 plate 72A converts the linearly polarized light P0 (ray MA) into right-circularly polarized light P R λ / 4 plate 72B converts linearly polarized light P0 (light ray MB) to left-circularly polarized light P L Convert each of them accordingly.

[0170] A layer to be formed (second cholesteric liquid crystal layer 20) having a first alignment film 18 before the alignment pattern is formed is placed in the exposure area, two light rays MA and MB are made to intersect and interfere on the alignment film 32, and the resulting interference light is irradiated onto the first alignment film 18 to expose it.

[0171] Due to the interference in this process, the polarization state of the light irradiated onto the first orientation film 18 changes periodically in an interference fringe pattern. As a result, an orientation film having an orientation pattern in which the orientation state changes periodically (hereinafter also referred to as a pattern orientation film) is obtained.

[0172] In the exposure apparatus 60, the period of the orientation pattern can be adjusted by changing the intersection angle α of the two light rays MA and MB. That is, in the exposure apparatus 60, by adjusting the intersection angle α, the length Λ of one period in which the optical axis 30A rotates 180° in one direction can be adjusted in an orientation pattern in which the optical axis 30A derived from the liquid crystal compound 30 rotates continuously along one direction.

[0173] By forming a cholesteric liquid crystal layer on a first alignment film 18 having an alignment pattern in which such an alignment state changes periodically, a cholesteric liquid crystal layer (first cholesteric liquid crystal layer 16) can be formed having a liquid crystal alignment pattern in which the optical axis 30A derived from the liquid crystal compound 30 rotates continuously along one direction, as described above.

[0174] Furthermore, by rotating the optical axes of the λ / 4 plates 72A and 72B by 90°, the rotation direction of the optical axis 30A in the liquid crystal alignment pattern can be reversed.

[0175] As described above, the pattern alignment film has an orientation pattern that aligns the liquid crystal compounds such that the orientation of the optical axis of the liquid crystal compounds in the cholesteric liquid crystal layer formed on the pattern alignment film changes while continuously rotating along at least one direction in the plane. If the axis along the direction in which the pattern alignment film aligns the liquid crystal compounds is considered the orientation axis, then the pattern alignment film can be said to have an orientation pattern in which the orientation axis changes while continuously rotating along at least one direction in the plane. The orientation axis of the pattern alignment film can be detected by measuring absorption anisotropy. For example, when linearly polarized light is irradiated onto the pattern alignment film while rotating, and the amount of light transmitted through the pattern alignment film is measured, the direction in which the amount of light is maximum or minimum is observed to gradually change along one direction in the plane.

[0176] Furthermore, the alignment film 25 for forming the second cholesteric liquid crystal layer 20 may be formed in the same manner as the first alignment film 18, except that the layer to be formed and the direction of rotation of the optical axis in the alignment pattern are different.

[0177] For example, an alignment film 25 for forming a second cholesteric liquid crystal layer 20 is applied to a temporary support 24 and exposed to light to form the second cholesteric liquid crystal layer 20, and then the second cholesteric liquid crystal layer 20 is formed using the method described above. Next, a first alignment film 18 is formed on the second cholesteric liquid crystal layer 20 using the method described above, and then the first cholesteric liquid crystal layer 16 is formed using the method described above. This allows for the formation of a first cholesteric liquid crystal layer 16, a first alignment layer 18 in contact with the first cholesteric liquid crystal layer 16, and a second cholesteric liquid crystal layer 20 in contact with the first alignment layer 18. The temporary support 24 and the alignment film 25 may be peeled off after the formation of the second cholesteric liquid crystal layer 20 or after the formation of the first cholesteric liquid crystal layer 16.

[0178] As the temporary support 24, various sheet-like materials (films, plates) can be used, as long as they can support the alignment film 25 and the second cholesteric liquid crystal layer 20.

[0179] As the temporary support 24, a transparent support is preferred, and examples include polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (for example, "Arton" (trade name), manufactured by JSR Corporation; "Zeonor" (trade name), manufactured by Nippon Zeon Co., Ltd.), polyethylene terephthalate (PET), polycarbonate, and polyvinyl chloride. The support is not limited to a flexible film, but may also be a non-flexible substrate such as a glass substrate.

[0180] There are no restrictions on the thickness of the temporary support 24; the thickness can be appropriately set to a level that can hold the alignment film and the second cholesteric liquid crystal layer 20, depending on the material used to form the temporary support 24. The thickness of the temporary support 24 is preferably 1 to 1000 μm, more preferably 3 to 250 μm, and even more preferably 5 to 150 μm.

[0181] <Adhesive Layer> The adhesive layer 13 is used to adhere the light guide member 12 and the λ / 4 plate 14. Known adhesives and tacks can be used as the adhesive layer 13.

[0182] As the adhesive 13, it is preferable to use an acrylic adhesive. As the adhesive, it is preferable to use a water-based adhesive such as polyvinyl alcohol, as well as a curing type adhesive such as an acrylic or epoxy adhesive.

[0183] The adhesive layer is preferably 0.1 μm to 10 μm thick, more preferably 0.3 μm to 8 μm or less, and even more preferably 0.5 μm to 6 μm or less, from the viewpoint of suppressing deformation of the first cholesteric liquid crystal layer 16 and the second cholesteric liquid crystal layer 20 after humid heat endurance, thinning, and reducing the loss of incident light.

[0184] <Manufacturing Method for Optical Components> Next, the manufacturing method for optical components (the order of formation of each layer) will be explained. In the following explanation, the method of forming each layer is as described above.

[0185] As an example, a method for manufacturing the optical component 10a shown in Figure 1 will be described. First, an alignment film 25 is formed on a temporary support 24, and a second cholesteric liquid crystal layer 20 is formed on the alignment film 25. Next, a first alignment film 18 is formed on the second cholesteric liquid crystal layer 20, and a first cholesteric liquid crystal layer 16 is formed on the first alignment film 18. Next, a second alignment film 15 is formed on the first cholesteric liquid crystal layer 16, and a λ / 4 plate 14 is formed on the second alignment film 15.

[0186] Next, the light guide member 12 is laminated onto the λ / 4 plate 14 via the adhesive layer 13. This completes the fabrication of the optical member 10a. Note that the temporary support 24 and the alignment film 25 may be peeled off at any time as needed.

[0187] In the above example, a second alignment film 15 is formed on the first cholesteric liquid crystal layer 16, and a λ / 4 plate 14 is formed on the second alignment film 15. However, the method is not limited to this, and a separately prepared λ / 4 plate 14 may be attached to the first cholesteric liquid crystal layer 16 using an adhesive layer and then laminated.

[0188] Furthermore, in the present invention, the order of formation of the optical elements is not limited to those described above.

[0189] For example, first, an alignment film is formed on a temporary support to form a first cholesteric liquid crystal layer 16, and the first cholesteric liquid crystal layer 16 is formed on this alignment film. Next, a first alignment film 18 is formed on the first cholesteric liquid crystal layer 16, and a second cholesteric liquid crystal layer 20 is formed on the first alignment film 18.

[0190] Next, the temporary support and alignment film are peeled off from the first cholesteric liquid crystal layer 16, and the λ / 4 plate 14 is laminated on the peeled surface of the first cholesteric liquid crystal layer 16. The method for laminating the λ / 4 plate 14 may be to form a second alignment film 15 and then form the λ / 4 plate 14 on the second alignment film 15, or to attach a separately prepared λ / 4 plate 14 using an adhesive layer.

[0191] Next, the light guide member 12 is laminated onto the λ / 4 plate 14 via an adhesive layer 13. This completes the fabrication of the optical member 10a.

[0192] Alternatively, for example, first, an alignment film for forming a first cholesteric liquid crystal layer 16 is formed on the λ / 4 plate 14, and the first cholesteric liquid crystal layer 16 is formed on this alignment film. Next, a first alignment film 18 is formed on the first cholesteric liquid crystal layer 16, and a second cholesteric liquid crystal layer 20 is formed on the first alignment film 18.

[0193] Next, an optical member 10a may be fabricated by laminating a light guide member 12 onto a λ / 4 plate 14 via an adhesive layer 13.

[0194] Alternatively, the λ / 4 plate 14 is first laminated on the light guide member 12. The lamination method for the λ / 4 plate 14 may be to form an alignment film and then form the λ / 4 plate 14 on the alignment film, or to attach a separately prepared λ / 4 plate 14 using an adhesive layer.

[0195] Next, an alignment film for forming the first cholesteric liquid crystal layer 16 is formed on the λ / 4 plate 14, and the first cholesteric liquid crystal layer 16 is formed on this alignment film. Next, a first alignment film 18 is formed on the first cholesteric liquid crystal layer 16, and a second cholesteric liquid crystal layer 20 is formed on the first alignment film 18. By doing so, the optical member 10a can be manufactured.

[0196] [Wavelength Selective Switch] The wavelength selective switch of the present invention uses the optical component described above as a wavelength separation element.

[0197] The wavelength selective switch may have the same configuration as a conventionally known wavelength selective switch, except that it has the optical element of the present invention as the wavelength separation element. For example, in addition to the optical element, the wavelength selective switch may have an optical input port into which light is incident, a deflection unit that variably deflects the light of each wavelength separated by the wavelength separation element (optical element), an optical output port that emits the light of each separated wavelength, and so on.

[0198] Although the optical components of the present invention have been described in detail above, the present invention is not limited to the examples described above, and various improvements and modifications may be made without departing from the spirit of the present invention.

[0199] The features of the present invention will be further described in detail below with reference to examples. The materials, reagents, amounts used, amounts of substance, ratios, processing content, and processing procedures shown in the following examples can be modified as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the specific examples shown below.

[0200] [Example 1] <Formation of substrate-side alignment film> (Application of coating solution for substrate-side alignment film formation) A glass substrate is prepared as a temporary support. The following coating solution P-1 for substrate-side alignment film formation is applied to the temporary support by spin coating. The temporary support on which the coating solution for substrate-side alignment film formation has been applied is dried on a 60°C hot plate for 60 seconds to form a substrate-side alignment film.

[0201] Coating solution P-1 for substrate-side alignment film formation -------------------

[0202] Material for photo alignment 1

[0203] (Exposure of the substrate-side alignment film) The substrate-side alignment film is exposed using the exposure apparatus shown in Figure 7 to form an alignment pattern on the substrate-side alignment film. The exposure apparatus uses a laser that emits laser light with a wavelength of 325 nm. The exposure dose due to interference is 300 mJ / cm². 2 The intersection angle (intersection angle α) of the two laser beams is adjusted so that the period Λ (length of a 180° rotation of the optical axis) of the orientation pattern formed by the interference of the two laser beams is 1.05 μm.

[0204] <Formation of the second cholesteric liquid crystal layer> The following composition B-1 is prepared as the liquid crystal composition for forming the second cholesteric liquid crystal layer.

[0205] Composition B-1 -------------------------------------------------- • Rod-shaped liquid crystal compound L-1 100.00 parts by mass • Polymerization initiator (BASF, Irgacure OXE01) 1.00 parts by mass • Chiral agent C-1 3.00 parts by mass • Leveling agent T-1 0.08 parts by mass • Methyl ethyl ketone 4000.00 parts by mass --------------------------------------------------

[0206] Rod-shaped liquid crystal compound L-1 (contains the following structure in the mass ratio shown on the right)

[0207] Chiral agent C-1

[0208] Leveling agent T-1

[0209] The second cholesteric liquid crystal layer is formed by multilayer coating of composition B-1 onto the substrate-side alignment film. First, the first layer is coated with the first layer of composition B-1 onto the substrate-side alignment film, the coating is heated to 80°C on a hot plate, and then, at 80°C, under a nitrogen atmosphere, ultraviolet light with a wavelength of 365 nm is applied at a rate of 300 mJ / cm using a high-pressure mercury lamp. 2 By irradiating the coating film with a certain irradiation dose, the orientation of the liquid crystal compound is fixed, forming a liquid crystal fixed layer. Subsequent layers are applied by layering them onto the liquid crystal fixed layer, and the process of heating, cooling, and UV curing is repeated to form a second cholesteric liquid crystal layer. In this process, the coating thickness of each layer is adjusted so that the thickness of the liquid crystal layer is approximately 0.2 μm to obtain a good orientation state. The final film thickness of the second cholesteric liquid crystal layer is 8.0 μm. The second cholesteric liquid crystal layer is a cholesteric liquid crystal layer that reflects right-circularly polarized light.

[0210] <Formation of the first orientation film 1> Prepare the following coating solution P-2 for forming the first orientation film 1 as a coating solution for forming the first orientation film.

[0211] Coating solution P-2 for forming the first orientation film 1 -------------------

[0212] Photoalignment material 2 (weight average molecular weight Mw 15,000)

[0213] The first alignment film 1 forming solution P-2 is applied to the second cholesteric liquid crystal layer by spin coating. This is dried on a hot plate at 120°C for 60 seconds, then maintained at 70°C and irradiated with ultraviolet light (300 mJ / cm²) under a nitrogen atmosphere. 2, using an ultra-high pressure mercury lamp) to obtain a first alignment film 1. The film thickness of the first alignment film 1 is 0.5 μm.

[0214] (Exposure of first alignment film 1) The first alignment film 1 is exposed using the exposure apparatus shown in FIG. 7 to form an alignment pattern on the first alignment film 1. At this time, an alignment pattern is formed on the first alignment film 1 in the same manner as for the substrate-side alignment film, except that exposure is performed in an orientation rotated by 180° relative to the orientation of the substrate when the alignment pattern is exposed onto the substrate-side alignment film. As a result, with respect to the alignment pattern of the substrate-side alignment film, the rotation direction of the optical axis of the liquid crystal compound along one in-plane direction is reversed in the alignment pattern of the first alignment film 1.

[0215] <Preparation of First Cholesteric Liquid Crystal Layer> The following composition B-2 is prepared as a liquid crystal composition for forming the first cholesteric liquid crystal layer.

[0216] Composition B-2 ―――――――――――――――――――――――――――――――――― ・Rod-like liquid crystal compound L-1 100.00 parts by mass・Polymerization initiator (manufactured by BASF, Irgacure OXE01) 1.00 part by mass・Chiral agent C-2 3.00 parts by mass・Leveling agent T-1 0.08 part by mass・Methyl ethyl ketone 4000.00 parts by mass ――――――――――――――――――――――――――――――――――

[0217] Chiral agent C-2

[0218] The first cholesteric liquid crystal layer is formed by multilayer-coating composition B-2 on the first alignment film 1. First, for the first layer, the first layer of composition B-2 is coated on the first alignment film 1, the coating film is heated to 80°C on a hot plate, and then, at 80°C under a nitrogen atmosphere, ultraviolet light with a wavelength of 365 nm is applied at 300 mJ / cm 2By irradiating the coating film with a certain irradiation dose, the orientation of the liquid crystal compound is fixed, forming a liquid crystal fixed layer. Subsequent layers are applied by layering them onto the liquid crystal fixed layer, and the process of heating, cooling, and UV curing is repeated to form the first cholesteric liquid crystal layer. At this time, the coating thickness of each layer is set so that the thickness of the liquid crystal layer is about 0.2 μm to obtain a good orientation state. The final film thickness of the cholesteric liquid crystal layer is 7.0 μm. The first cholesteric liquid crystal layer is a cholesteric liquid crystal layer that reflects left-circularly polarized light.

[0219] <Lamination of λ / 4 plate> A λ / 4 plate prepared by the method described in the example of WO2013 / 137464 is attached to the first cholesteric liquid crystal layer using a UV adhesive, and the support portion of the λ / 4 plate is peeled off and the λ / 4 plate is laminated onto the first cholesteric liquid crystal layer. The λ / 4 plate is attached with the angle of its lagging axis adjusted so that P-polarized light incident from the light guide member side is converted to left circular polarized light and S-polarized light is converted to right circular polarized light. That is, in the optical member of Example 1, the left circular polarized light converted from P-polarized light is reflected by the first cholesteric liquid crystal layer, and the right circular polarized light converted from S-polarized light is reflected by the second cholesteric liquid crystal layer.

[0220] <Lamination of light guide member> A 3 mm thick quartz glass is laminated onto a λ / 4 layer using UV adhesive as a light guide member. After lamination, an incision is made between the glass substrate, which is a temporary support, and the substrate-side alignment film, and the glass substrate is peeled off from the substrate-side alignment film to finally obtain the optical member 1 including the light guide member. The optical member 1 has a layer structure of light guide member / λ / 4 plate / first cholesteric liquid crystal layer / first alignment film 1 / second cholesteric liquid crystal layer.

[0221] [Examples 2-3, Comparative Examples 1-2] Optical members 2-5 corresponding to Examples 2-3 and Comparative Examples 1-2 are manufactured in the same manner as in Example 1, except that the spin-coating rotation speed during application of the coating solution for forming the first orientation film 1 and the solid content concentration of the coating solution P-2 for forming the first orientation film 1 are adjusted so that the film thickness of the first orientation film is the value shown in Table 1 below.

[0222] The optical member 2 of Example 2 has a layer configuration of light guide member / λ / 4 plate / first cholesteric liquid crystal layer / first alignment film 2 / second cholesteric liquid crystal layer.

[0223] The optical member 3 of Example 3 has a layer configuration of light guide member / λ / 4 plate / first cholesteric liquid crystal layer / first alignment film 3 / second cholesteric liquid crystal layer.

[0224] The optical member 4 of Comparative Example 1 has a layer configuration of light guide member / λ / 4 plate / first cholesteric liquid crystal layer / first alignment film 4 / second cholesteric liquid crystal layer.

[0225] The optical member 5 of Comparative Example 2 has a layer configuration of light guide member / λ / 4 plate / first cholesteric liquid crystal layer / first alignment film 5 / second cholesteric liquid crystal layer.

[0226] <Measurement of film thickness> From the optical components of each example and comparative example, the laminate of the first cholesteric liquid crystal layer, the first alignment film, and the second cholesteric liquid crystal layer is peeled off and removed. Sections having a cross-section perpendicular to the main surface of the peeled laminate are prepared, and the film thickness of the first alignment film of each layer is measured using a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The arithmetic mean of the thicknesses measured at three locations on the section is taken as the film thickness value.

[0227] [Evaluation] <Change in diffraction efficiency after moist heat endurance test> (Measurement of initial diffraction efficiency) Laser light with a wavelength of 1550 nm is incident on the light guide member side of each optical component after being converted to P-polarized or S-polarized light through a polarizing plate. The intensity of the incident light before it enters the light guide member and the intensity of the diffracted light emitted from the side of the light guide member are measured using a power meter. The incident angle to the light guide member is adjusted appropriately so that the intensity of the diffracted light is highest. The intensity of the incident light and the intensity of the diffracted light are measured for both P-polarized and S-polarized light, and the initial diffraction efficiency is calculated as diffracted light intensity / incident light intensity × 100.

[0228] (Measurement of diffraction efficiency after moist heat endurance test) Next, each optical component is placed in a constant temperature and humidity chamber set to 85°C and 85% RH, and after being left for 2000 hours, the diffraction efficiency after the moist heat endurance test is measured in the same manner as at the beginning.

[0229] The difference between the initial diffraction efficiency and the diffraction efficiency after the moist heat endurance test is defined as the change in diffraction efficiency after the moist heat endurance test, and is evaluated according to the following criteria: • A: Diffraction efficiency change of 0-5% • B: Diffraction efficiency change of 5-10% • C: Diffraction efficiency change of 10% or more

[0230] The results are shown in Table 1.

[0231]

[0232] Table 1 shows that in both the embodiments and comparative examples of the present invention, the change in diffraction efficiency after the moist heat endurance test is small in the case of P-polarized light reflected and diffracted by the first cholesteric liquid crystal layer on the side closer to the light guide member. On the other hand, in the comparative example, the change in diffraction efficiency after the moist heat endurance test is large in the case of S-polarized light reflected and diffracted by the second cholesteric liquid crystal layer on the side farther from the light guide member. In contrast, the embodiments of the present invention show that the change in diffraction efficiency after the moist heat endurance test is kept small even in the case of S-polarized light reflected and diffracted by the second cholesteric liquid crystal layer.

[0233] As in Comparative Example 1, when the thickness of the first alignment film increases, the deformation of the second cholesteric liquid crystal layer increases, and it is thought that the change in diffraction efficiency becomes larger. On the other hand, as in Comparative Example 2, when the thickness of the first alignment film is too thin, minute delamination occurs at the interface with the first and second cholesteric liquid crystal layers, and it is thought that the change in diffraction efficiency in the second cholesteric liquid crystal layer becomes larger due to light scattering caused by the delamination.

[0234] Furthermore, a comparison of Examples 1 to 3 shows that the thickness of the first orientation film is preferably 0.01 μm to 0.5 μm.

[0235] The effects of the present invention are clear from the above.

[0236] 10a-10b Optical components 12 Light guide component (light guide plate) 12b Light guide component (prism) 13 Adhesive layer 14 λ / 4 plate 15 Second alignment layer 16 First cholesteric liquid crystal layer 18 First alignment layer 20 Second cholesteric liquid crystal layer 24 Temporary support 25 Alignment layer 30 Liquid crystal compound 30A Optical axis 60 Exposure apparatus 62 Laser 64 Light source 65 λ / 2 plate 68 Beam splitter 70A, 70B Mirror 72A, 72B λ / 4 plate R Region Λ 1 period P0 Linear polarization P L Left-circular polarization P R Right-circular polarization α, intersection angle M, laser light MA, MB, light ray

Claims

1. An optical member comprising: a light guide member; a λ / 4 plate; a first cholesteric liquid crystal layer; an alignment layer in contact with the first cholesteric liquid crystal layer; and a second cholesteric liquid crystal layer in contact with the alignment layer, wherein the thickness of the alignment layer is 0.01 μm to 0.5 μm; the first cholesteric liquid crystal layer and the second cholesteric liquid crystal layer have a liquid crystal alignment pattern in which the orientation of the optical axis derived from the liquid crystal compound changes while continuously rotating in at least one direction in the plane; the twisting direction of the helical structure in the first cholesteric liquid crystal layer and the twisting direction of the helical structure in the second cholesteric liquid crystal layer are different from each other; and the continuous rotation direction of the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the first cholesteric liquid crystal layer and the continuous rotation direction of the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern of the second cholesteric liquid crystal layer are different from each other.

2. The optical member according to claim 1, wherein the alignment film is a photo-alignment film.

3. The optical member according to claim 1 or 2, used in a wavelength selective switch.

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