US-12619113-B2 - Transmissive liquid crystal diffraction element

US12619113B2US 12619113 B2US12619113 B2US 12619113B2US-12619113-B2

Abstract

Provided is a transmissive liquid crystal diffraction element that can diffract different polarized light components in the same direction and can maintain a polarization state during incidence. The transmissive liquid crystal diffraction element includes: first and second optically-anisotropic layers each of which has a liquid crystal alignment pattern in which an orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction; and two retardation layers that are disposed on a side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer and between the first optically-anisotropic layer and the second optically-anisotropic layer, respectively, in which a rotation direction of the optical axis in the liquid crystal alignment pattern of the first optically-anisotropic layer is opposite to that of the second optically-anisotropic layer, a single period of the liquid crystal alignment pattern of the first optically-anisotropic layer is the same as that of the second optically-anisotropic layer, the retardation layer is a positive C-plate or an O-plate, and the positive C-plate satisfies Expression (1). 0.12 ≤ ❘ "\[LeftBracketingBar]" Rth ⁡ ( λ ) / λ ❘ "\[RightBracketingBar]" ≤ 0.66 ( 1 )

Inventors

Kazuya HISANAGA
Yukito Saitoh
Yujiro YANAI

Assignees

FUJIFILM CORPORATION

Dates

Publication Date: 20260505
Application Date: 20240517
Priority Date: 20211118

Claims (20)

1 . A transmissive liquid crystal diffraction element comprising: a first optically-anisotropic layer and a second optically-anisotropic layer each of which has a liquid crystal alignment pattern in which an orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction; and two retardation layers that are disposed on a side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer and between the first optically-anisotropic layer and the second optically-anisotropic layer, respectively, wherein a rotation direction of the optical axis in the liquid crystal alignment pattern of the first optically-anisotropic layer and a rotation direction of the optical axis in the liquid crystal alignment pattern of the second optically-anisotropic layer are opposite to each other; wherein a length over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern rotates by 180° in a plane is set as a single period, a single period of the liquid crystal alignment pattern in the first optically-anisotropic layer and a single period of the liquid crystal alignment pattern in the second optically-anisotropic layer are the same, the retardation layer is a positive C-plate or an O-plate, and the positive C-plate satisfies Expression (1), 0.12≤|Rth(λ)/λ|≤0.66 . . . (1), where λ represents a wavelength (nm) of incidence light, and Rth(λ) represents a retardation (nm) in a thickness direction at the wavelength λ nm of the retardation layer.
2 . The transmissive liquid crystal diffraction element according to claim 1 , wherein the liquid crystal compound in each of the first optically-anisotropic layer and the second optically-anisotropic layer is twisted and aligned in the thickness direction, a twisted angle of the twisted alignment is less than 360°, and a twisted direction of the liquid crystal compound in the first optically-anisotropic layer and a twisted direction of the liquid crystal compound in the second optically-anisotropic layer are opposite to each other.
3 . The transmissive liquid crystal diffraction element according to claim 2 , wherein the liquid crystal compound is a rod-like liquid crystal compound.
4 . The transmissive liquid crystal diffraction element according to claim 2 , wherein a difference Δn in a refractive index of the rod-like liquid crystal compound is 0.2 to 1.
5 . The transmissive liquid crystal diffraction element according to claim 2 , wherein among the two retardation layers, the retardation layer on an incidence side is an O-plate and the retardation layer on an emission side is a positive C-plate.
6 . The transmissive liquid crystal diffraction element according to claim 2 , further comprising: a λ/4 plate that is disposed on at least one of a side of the first optically-anisotropic layer opposite to the second optically-anisotropic layer or a side of the retardation layer opposite to the first optically-anisotropic layer, the retardation layer being disposed on the side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer.
7 . The transmissive liquid crystal diffraction element according to claim 1 , wherein the liquid crystal compound is a rod-like liquid crystal compound.
8 . The transmissive liquid crystal diffraction element according to claim 7 , wherein a difference Δn in a refractive index of the rod-like liquid crystal compound is 0.2 to 1.
9 . The transmissive liquid crystal diffraction element according to claim 7 , wherein among the two retardation layers, the retardation layer on an incidence side is an O-plate and the retardation layer on an emission side is a positive C-plate.
10 . The transmissive liquid crystal diffraction element according to claim 7 , further comprising: a λ/4 plate that is disposed on at least one of a side of the first optically-anisotropic layer opposite to the second optically-anisotropic layer or a side of the retardation layer opposite to the first optically-anisotropic layer, the retardation layer being disposed on the side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer.
11 . The transmissive liquid crystal diffraction element according to claim 1 , wherein a difference Δn in a refractive index of the rod-like liquid crystal compound is 0.2 to 1.
12 . The transmissive liquid crystal diffraction element according to claim 11 , wherein among the two retardation layers, the retardation layer on an incidence side is an O-plate and the retardation layer on an emission side is a positive C-plate.
13 . The transmissive liquid crystal diffraction element according to claim 1 , wherein among the two retardation layers, the retardation layer on an incidence side is an O-plate and the retardation layer on an emission side is a positive C-plate.
14 . The transmissive liquid crystal diffraction element according to claim 1 , further comprising: a λ/4 plate that is disposed on at least one of a side of the first optically-anisotropic layer opposite to the second optically-anisotropic layer or a side of the retardation layer opposite to the first optically-anisotropic layer, the retardation layer being disposed on the side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer.
15 . A transmissive liquid crystal diffraction element comprising: a first optically-anisotropic layer and a second optically-anisotropic layer each of which has a liquid crystal alignment pattern in which an orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction; and two retardation layers that are disposed on a side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer and between the first optically-anisotropic layer and the second optically-anisotropic layer, respectively, wherein a rotation direction of the optical axis in the liquid crystal alignment pattern of the first optically-anisotropic layer and a rotation direction of the optical axis in the liquid crystal alignment pattern of the second optically-anisotropic layer are opposite to each other; wherein a length over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern rotates by 180° in a plane is set as a single period, a single period Λ 1 of the liquid crystal alignment pattern in the first optically-anisotropic layer and a single period Λ 2 of the liquid crystal alignment pattern in the second optically-anisotropic layer satisfy Λ 1 /Λ 2 =0.2 to 5, the retardation layer is a positive C-plate or an O-plate, and the positive C-plate satisfies Expression (1), 0.12≤|Rth(λ)/λ|≤0.66 . . . (1), where λ represents a wavelength (nm) of incidence light, and Rth(λ) represents a retardation (nm) in a thickness direction at the wavelength λ nm of the retardation layer).
16 . The transmissive liquid crystal diffraction element according to claim 15 , wherein the liquid crystal compound in each of the first optically-anisotropic layer and the second optically-anisotropic layer is twisted and aligned in the thickness direction, a twisted angle of the twisted alignment is less than 360°, and a twisted direction of the liquid crystal compound in the first optically-anisotropic layer and a twisted direction of the liquid crystal compound in the second optically-anisotropic layer are opposite to each other.
17 . The transmissive liquid crystal diffraction element according to claim 15 , wherein the liquid crystal compound is a rod-like liquid crystal compound.
18 . The transmissive liquid crystal diffraction element according to claim 15 , wherein a difference Δn in a refractive index of the rod-like liquid crystal compound is 0.2 to 1.
19 . The transmissive liquid crystal diffraction element according to claim 15 , wherein among the two retardation layers, the retardation layer on an incidence side is an O-plate and the retardation layer on an emission side is a positive C-plate.
20 . The transmissive liquid crystal diffraction element according to claim 15 , further comprising: a λ/4 plate that is disposed on at least one of a side of the first optically-anisotropic layer opposite to the second optically-anisotropic layer or a side of the retardation layer opposite to the first optically-anisotropic layer, the retardation layer being disposed on the side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation of PCT International Application No. PCT/JP2022/042692 filed on Nov. 17, 2022, which claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2021-187851 filed on Nov. 18, 2021. The above applications are hereby expressly incorporated by reference, in their entirety, into the present application. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive liquid crystal diffraction element that diffracts incident light. 2. Description of the Related Art As an optical element that bends light to control a traveling direction of the light, a diffraction element is used in many optical devices or optical systems. As this diffraction element, a liquid crystal diffraction element formed of a liquid crystal compound is disclosed. For example, JP2014-089476A discloses a polarization diffraction grating including a first polarization diffraction grating layer and a second polarization diffraction grating layer disposed on the first polarization diffraction grating layer. The first polarization diffraction grating layer includes a molecular structure that is twisted according to a first twist sense such that respective relative alignments of molecules of the first polarization diffraction grating layer are rotated by a first twisted angle over a first thickness defined between opposing faces of the first polarization diffraction grating layer. The second polarization diffraction grating layer includes a molecular structure that is twisted according to a second twist sense opposite to the first twist sense such that respective relative alignments of molecules of the second polarization diffraction grating layer are rotated by a second twisted angle over a second thickness defined between opposing faces of the second polarization diffraction grating layer. SUMMARY OF THE INVENTION In a polarization diffraction element formed of a liquid crystal compound, a direction in which light is bent varies depending on polarized light. Specifically, left circularly polarized light and right circularly polarized light incident into the polarization diffraction element are bent in opposite directions and separated. Therefore, light cannot be diffracted in a predetermined direction irrespective of polarized light. In addition, particularly in a case where polarized light is obliquely incident, there is a problem in that light that is bent by the polarization diffraction element using a liquid crystal compound enters a polarization state different from that during the incidence. An object of the present invention is to provide a transmissive liquid crystal diffraction element that can diffract different polarized light components in the same direction and can maintain a polarization state during incidence. In order to achieve the object, the present invention has the following configurations. [1] A transmissive liquid crystal diffraction element comprising: a first optically-anisotropic layer and a second optically-anisotropic layer each of which has a liquid crystal alignment pattern in which an orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction; andtwo retardation layers that are disposed on a side of the second optically-anisotropic layer opposite to the first optically-anisotropic layer and between the first optically-anisotropic layer and the second optically-anisotropic layer, respectively,in which a rotation direction of the optical axis in the liquid crystal alignment pattern of the first optically-anisotropic layer and a rotation direction of the optical axis in the liquid crystal alignment pattern of the second optically-anisotropic layer are opposite to each other,in a case where a length over which the orientation of the optical axis derived from the liquid crystal compound in the liquid crystal alignment pattern rotates by 180° in a plane is set as a single period, a single period of the liquid crystal alignment pattern in the first optically-anisotropic layer and a single period of the liquid crystal alignment pattern in the second optically-anisotropic layer are the same,the retardation layer is a positive C-plate or an O-plate, andthe positive C-plate satisfies Expression (1), 0.12≤❘"\[LeftBracketingBar]"Rth⁡(λ)/λ❘"\[RightBracketingBar]"≤0.66,(1)(in the expression, λ represents a wavelength (nm) of incidence light, and Rth(λ) represents a retardation (nm) in a thickness direction at the wavelength λ nm of the retardation layer). [2] A transmissive liquid crystal diffraction element comprising: a first optically-anisotropic layer and a second optically-anisotropic layer each of which has a liquid crystal alignment pattern in which an orientation of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction; andtwo retardation laye