Liquid crystal mixtures for pitch variable optical elements
A liquid crystal (LC) mixture for a pitch variable optical element is provided. The LC mixture includes a host LC and one or more LC dimers dissolved as a guest in the host LC. The host LC and the one or more LC dimers have respective dielectric anisotropies of opposite signs in nematic phase. A net dielectric anisotropy of the LC mixture is substantially neutral.
1. An optical element, comprising:
a liquid crystal (LC) mixture including a plurality of flexoelectric domains; and
a first electrode and a second electrode configured to provide a driving voltage to the flexoelectric domains in the LC mixture,
wherein a pitch of a flexoelectric domain is variable as an amplitude of the driving voltage varies, and
wherein the LC mixture includes:
a host LC; and
one or more LC dimers dissolved as a guest in the host LC, the host LC and the one or more LC dimers having respective dielectric anisotropies of opposite signs in a nematic phase, and a net dielectric anisotropy of the LC mixture being neutral.
2. The optical element of claim 1 , wherein the driving voltage is a direct current (DC) voltage or an ultra-low frequency alternating current (AC) voltage.
3. The optical element of claim 1 , wherein the first electrode and the second electrode are planar electrodes arranged opposite to each other.
4. The optical element of claim 1 , further comprising a first alignment layer and a second alignment layer disposed at the first electrode and the second electrode, respectively, the first alignment layer and the second alignment layer configured to provide anti-parallel alignment directions to LCs in the LC mixture.
5. The optical element of claim 1 , wherein the first electrode and the second electrode are arranged opposite to each other, and at least one of the first electrode and the second electrode includes a plurality of sub-electrodes.
6. The optical element of claim 5 , wherein the driving voltage varies spatially across the sub-electrodes of the at least one of the first electrode and the second electrode.
7. The optical element of claim 5 , wherein the driving voltage is spatially uniform across the remaining one of the first electrode and the second electrode.
8. The optical element of claim 1 , wherein the plurality of flexoelectric domains have a uniform pitch.
9. The optical element of claim 1 , wherein the plurality of flexoelectric domains have different pitches.
10. The optical element of claim 1 , wherein the pitch of the flexoelectric domain decreases as the amplitude of the driving voltage increases.
11. The optical element of claim 1 , wherein the flexoelectric domains are configured to diffract a first light beam with a predetermined polarization as a second light beam, and a diffraction angle of the second light beam is variable as the pitch of the flexoelectric domain varies.
12. The optical element of claim 4 , wherein the pitch of the flexoelectric domain is in a direction perpendicular to an alignment direction provided by the first alignment layer or the second alignment layer.
13. The optical element of claim 5 , wherein the sub-electrodes include a circular center electrode and a plurality of concentric ring electrodes surrounding the circular center electrode.
14. The optical element of claim 1 , wherein at least one of the host LC or the one or more LC dimers has the nematic phase in a temperature range that includes a room temperature.
15. The optical element of claim 1 , wherein the host LC has negative dielectric anisotropy in the nematic phase, and the one or more LC dimers have positive dielectric anisotropy in the nematic phase.
16. The optical element of claim 1 , wherein at least one of the one or more LC dimers has a bent-shaped molecular structure, or a pear-shaped molecular structure.
17. The optical element of claim 1 , wherein a weight percentage of the host LC in the LC mixture is larger than 50%.