Optical element and light guide element
An object is to provide an optical element in which a wavelength dependence of refraction of transmitted light is small, and a light guide element including the optical element. The optical element includes: plurality of optically-anisotropic layers that are formed using a composition including a liquid crystal compound and have a liquid crystal alignment pattern in which a direction of an optical axis derived from the liquid crystal compound continuously rotates in one in-plane direction; and a wavelength selective phase difference layer that is disposed between two optically-anisotropic layers and converts circularly polarized light in a specific wavelength range into circularly polarized light having an opposite turning direction, in which, in a case where, in the liquid crystal alignment pattern, a length over which the direction of the optical axis rotates by 180° in the in-plane direction in which the direction of the optical axis changes is set as a single period, a length of the single period in at least one optically-anisotropic layer is different from that of another optically-anisotropic layer.
1. An optical element comprising:
a plurality of optically-anisotropic layers, each of the optically-anisotropic layers being formed using a composition including a liquid crystal compound and having a liquid crystal alignment pattern in which a direction of an optical axis derived from the liquid crystal compound changes while continuously rotating in at least one in-plane direction; and
a wavelength selective phase difference layer that is disposed between at least one pair of two optically-anisotropic layers adjacent to each other among the plurality of optically-anisotropic layers and converts circularly polarized light in a specific wavelength range into circularly polarized light having an opposite turning direction,
wherein, in a case where, in the liquid crystal alignment pattern of each of the plurality of optically-anisotropic layers, a length over which the direction of the optical axis derived from the liquid crystal compound rotates by 180° in the in-plane direction in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating is set as a single period, a length of the single period in at least one optically-anisotropic layer is different from that of another optically-anisotropic layer.
2. The optical element according to claim 1 , comprising
plural pairs of two optically-anisotropic layers, each pair of which being the one pair of two adjacent optically-anisotropic layers, and
a plurality of wavelength selective phase difference layers, each of which being the wavelength selective phase difference layer and disposed between the one pair of two adjacent optically-anisotropic layers,
wherein a specific wavelength range in which circularly polarized light is converted by the wavelength selective phase difference layer gradually decreases among the wavelength selective phase difference layers in an arrangement direction of the optically-anisotropic layer.
3. The optical element according to claim 1 ,
wherein the length of the single period in the liquid crystal alignment patterns of the optically-anisotropic layers varies depending on all the optically-anisotropic layers.
4. The optical element according to claim 1 , comprising a plurality of wavelength selective phase difference layers, each of which being the wavelength selective phase difference layer,
wherein each of the optically-anisotropic layers and the wavelength selective phase difference layers are alternately disposed.
5. The optical element according to claim 1 ,
wherein in the optically-anisotropic layer positioned at one end in an arrangement direction of the optically-anisotropic layers, the length of the single period in the liquid crystal alignment pattern is the shortest.
6. The optical element according to claim 1 ,
wherein at least one of the optically-anisotropic layers has in-plane regions having different lengths of the single periods in the liquid crystal alignment pattern.
7. The optical element according to claim 6 ,
wherein the length of the single period in the liquid crystal alignment pattern gradually decreases in the in-plane direction in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating in the liquid crystal alignment pattern.
8. The optical element according to claim 1 ,
wherein the liquid crystal alignment pattern of each of the optically-anisotropic layer is a concentric circular pattern having a concentric circular shape where the in-plane direction in which the direction of the optical axis derived from the liquid crystal compound changes while continuously rotating moves from an inside toward an outside.
9. The optical element according to claim 1 , comprising:
three or more optically-anisotropic layers; and
two or more wavelength selective phase difference layers.
10. The optical element according to claim 9 ,
wherein one wavelength selective phase difference layer converts circularly polarized light of red light into circularly polarized light having an opposite turning direction, and
another wavelength selective phase difference layer converts circularly polarized light of green light into circularly polarized light having an opposite turning direction.
11. The optical element according to claim 1 , comprising a plurality of wavelength selective phase difference layers, each of which being the wavelength selective phase difference layer,
wherein the number of the wavelength selective phase difference layers is less than the number of the optically-anisotropic layers by one.
12. The optical element according to claim 1 ,
wherein the wavelength selective phase difference layer is consisting of a plurality of phase difference layers, and
an in-plane slow axis direction of at least one phase difference layer is different from that of another phase difference layer.
13. The optical element according to claim 12 ,
wherein at least one phase difference layer in the wavelength selective phase difference layer is a λ/4 plate.
14. The optical element according to claim 13 ,
wherein the λ/4 plate in the wavelength selective phase difference layer has reverse wavelength dispersibility, and
at least one other phase difference layer has forward wavelength dispersibility.
15. A light guide element comprising:
the optical element according to claim 1 ; and
a light guide plate.
16. The light guide element according to claim 15 ,
wherein two optical elements spaced from each other are provided in the light guide.