Pitch variable optical devices and systems containing the same

1. An optical device, comprising:

an optical grating including two electrodes arranged opposite to each other and a liquid crystal (LC) composition sandwiched between the electrodes, the two electrodes providing a driving voltage to the optical grating,

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.

2. The optical device of claim 1 , wherein the predetermined temperature includes a room temperature.

3. The optical device of claim 1 , wherein a period of the optical grating is continuously variable with an amplitude of the driving voltage.

4. The optical device of claim 1 , further comprising:

an eye-tracking device configured to provide eye tracking information of an eye of a user of the optical device.

5. The optical device of claim 4 , further comprising:

a controller configured to:

receive the eye tracking information from the eye-tracking device;

determine a position of the eye; and

control, based on the position of the eye, an amplitude of the driving voltage of the optical grating to obtain to a desired period of the optical grating.

6. The optical device of claim 5 , further comprising:

a projector configured to generate an image light; and

an image combiner configured to focus the image light received from the projector to one or more spots at an eye-box of the optical device;

wherein the optical grating is optically coupled to the image combiner and configured to steer one of the one or more spots to substantially coincide with the position of the eye.

7. The optical device of claim 6 , wherein the image combiner includes a holographic optical element (HOE).

8. The optical device of claim 5 , further comprising:

a light source configured to emit a light beam towards the optical grating, the optical grating configured to diffract the light beam as diffracted light beams; and

an optical lens optically coupled to the optical grating and configured to focus the diffracted light beams received from the optical grating to one or more spots at an eye-box of the optical device,

wherein one of the one or more spots substantially coincides with the position of the eye.

9. The optical device of claim 8 , further comprising an optical diffuser operatively disposed between the light source and the optical grating, the optical diffuser configured to primarily forwardly diffuse the light beam received from the light source towards the optical grating.

10. The optical device of claim 9 , wherein the optical diffuser is a holographic diffuser.

11. The optical device of claim 9 , wherein the optical lens is a first optical lens, the optical device further comprises:

a second optical lens operatively disposed between the light source and the optical diffuser, the second optical lens configured to collimate the light beam received from the light source.

12. The optical device of claim 1 , wherein the optical grating further includes alignment layers disposed on the two electrodes, respectively, the alignment layers providing anti-parallel alignment directions and the two electrodes being planar electrodes disposed at two substrates, respectively.

13. The optical device of claim 1 , wherein the optical device is a component of a near-eye display (NED).

14. 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.

15. The optical device of claim 14 , wherein the predetermined temperature includes a room temperature.

16. The optical device of claim 14 , wherein an amplitude of the driving voltage applied to the sub-electrodes of the at least one of the two electrodes is progressively decreased from an outermost sub-electrode to an innermost sub-electrode, and an amplitude of the driving voltage applied to the remaining one of the of the two electrodes is uniform.

17. The optical device of claim 14 , further comprising:

an electronic display configured to generate an image light, wherein the diffractive lens is configured to direct the image light towards an eye-box of the optical device.

18. The optical device of claim 17 , further comprising:

an eye-tracking device configured to provide eye tracking information of eyes of a user of the optical device.

19. The optical device of claim 18 , further comprising:

a controller configured to:

receive the eye tracking information from the eye-tracking device;

determine a position of each eye of the user;

determine a vergence distance based on an estimated intersection of gaze lines; and

control, based on the determined vergence distance, an amplitude of the driving voltage applied to the respective sub-electrodes of the diffractive lens to obtain to a desired optical power.

20. The optical device of claim 14 , wherein the optical device is a component of a near-eye display (NED).