Pitch variable optical devices and systems containing the same

An optical device, comprising:

• a diffractive lens including two electrodes arranged opposite to each other, and a liquid crystal (LC) composition sandwiched between the two electrodes, the two electrodes providing a driving voltage to the diffractive lens, and at least one of the two electrodes including a plurality of sub-electrodes,
• wherein the LC composition 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 nematic phase, and a net dielectric anisotropy of the LC composition being substantially neutral at a predetermined temperature.