Optical element, light guide element, and image display device
Provided are an optical element that can make the brightness of light emitted from a light guide plate uniform, a light guide element, and an image display device. The optical element includes a patterned cholesteric liquid crystal layer that is obtained by immobilizing a cholesteric liquid crystalline phase, in which the patterned cholesteric liquid crystal layer has a liquid crystal alignment pattern in which a direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction, and the patterned cholesteric liquid crystal layer has regions having different pitches of helical structures in a plane.
1. An optical element comprising a plurality of patterned cholesteric liquid crystal layers that are obtained by immobilizing a cholesteric liquid crystalline phase,
wherein the patterned cholesteric liquid crystal layers have different twisted directions of helical structures,
the patterned cholesteric liquid crystal layers have a liquid crystal alignment pattern in which a direction of an optical axis derived from a liquid crystal compound changes while continuously rotating in at least one in-plane direction,
the patterned cholesteric liquid crystal layers have regions having different pitches of helical structures in a plane,
in a case where a length over which the direction of the optical axis derived from the liquid crystal compound rotates by 180° in a plane is set as a single period, the patterned cholesteric liquid crystal layers have regions having different lengths of the single periods,
the patterned cholesteric liquid crystal layers having different twisted directions of the helical structures have the same selective reflection center wavelength, and
in the patterned cholesteric liquid crystal layers having different twisted directions of helical structures, directions in which the direction of the optical axis derived from the liquid crystal compound continuously rotates in the liquid crystal alignment pattern are different from each other.
2. The optical element according to claim 1 ,
wherein in the patterned cholesteric liquid crystal layer, a pitch of a helical structure is larger in a region where the length of the single period is shorter and a reflection angle of reflected light is larger, and the pitch of the helical structure is smaller in a region where the length of the single period is longer and the reflection angle of the reflected light is smaller.
3. The optical element according to claim 1 ,
wherein in the patterned cholesteric liquid crystal layer, 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.
4. The optical element according to claim 1 ,
wherein the liquid crystal alignment pattern 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.
5. The optical element according to claim 1 ,
wherein the length of the single period in the liquid crystal alignment pattern is 50 m or less.