Multifocal display device and method

1. A multifocal display device, the multifocal display device comprising:

a focus tunable lens;

a controller configured to selectively tune a focus of the focus tunable lens to a plurality of N focal planes during a frame period, the focal planes having indices 1 to N assigned thereto in increasing or decreasing order of the focal planes' focal distances,

a storage storing a plurality of focal plane groups, each group comprising the plurality of focal planes in a different sequence, each of the focal planes appears only once in each of the focal plane groups, an index difference between two adjacent focal planes in the sequence of one of the groups is 0 or 1 or 2,

wherein the controller is configured to select a first group of the focal plane groups, and tune, during a first frame period, the focus of the focus tunable lens to each one of the focal planes in the first group according to the corresponding sequence,

wherein the controller is configured to select a second group from the focal plane groups allowed by a selection rule, and to tune, during a second frame period, the focus of the focus tunable lens to each one of the focal planes in the second group according to the corresponding sequence, and

wherein the selection rule comprises that an index difference between a last focal plane of the focal planes in the sequence of the first group and a first focal plane of the focal planes in the sequence of the second group is 0 or 1 or 2.

2. The multifocal display device according to claim 1 , wherein

the selection rule comprises that the index difference between the last focal plane in the sequence of the first group and the first focal plane in the sequence of the second group is 1 or 2.

3. The multifocal display device according to claim 1 , wherein

the selection rule further comprises that a position distance between two focal planes, of the focal planes, of a same index in the concatenated sequences of the first group and the second group, respectively, is between a predetermined minimum allowed distance and a predetermined maximum allowed distance.

4. The multifocal display device according to claim 3 , wherein

the minimum allowed distance is 2.

5. The multifocal display device according to claim 3 , wherein

the maximum allowed distance is in a range of (2 N fp −2to

(

2

⁢

N

fp

-

⌈

N

fp

2

⌉

)

,

with N fP being a total number of the plurality of focal planes, and ┌ ┐ denoting a ceiling function.

6. The multifocal display device according to claim 1 , wherein

the controller is configured to select the second focal plane group randomly from the focal plane groups allowed by the selection rule.

7. The multifocal display device according to claim 1 , wherein

the controller is configured to select the second focal plane group according to a predefined pattern from the focal plane groups allowed by the selection rule.

8. The multifocal display device according to one of the claim 1 , wherein

the controller is configured to select the second focal plane group from the focal plane groups allowed by the selection rule depending on a number of times the first group was so far selected.

9. The multifocal display device according to claim 1 , wherein

the first focal plane group is included in the focal plane groups allowed by the selection rule, or

the first focal plane group is not included in the focal plane groups allowed by the selection rule.

10. The multifocal display device according to claim 1 , wherein the plurality of focal plane groups comprises one focal plane group for each possible sequence of the plurality of focal planes, for which each individual focal plane of the focal planes appears only once in a focal group of the focal groups and an index difference between two adjacent focal planes of the focal planes in the sequence of the focal plane group is 0 or 1 or 2.

11. The multifocal display device according to claim 1 , wherein the controller is configured to tune the focus of the focus tunable lens by applying a control signal of different values for each focal plane index.

12. The multifocal display device according to claim 1 , wherein

the controller is configured to select the first focal plane group randomly from the plurality of focal plane groups, if no other focal plane group was selected before the first focal plane group.

13. The multifocal display device according to claim 1 , wherein

the controller is configured to select the first focal plane group from the focal plane groups allowed by the selection rule, if another focal plane group was selected before the first focal plane group.

14. A method for providing a multifocal display, the method comprising:

selectively tuning a focus of a focus tunable lens to a plurality of N focal planes during a frame period, the focal planes having indices 1 to N assigned thereto in increasing or decreasing order of the focal planes' focal distances,

storing a plurality of focal plane groups, each focal plane group of the focal plane groups including the plurality of focal planes in a different sequence, each of the focal planes appears only once in each of the focal plane groups, an index difference between two adjacent focal planes in the sequence of one of the groups is 0 or 1 or 2,

wherein the selectively tuning comprises:

selecting a first focal plane group of the focal plane groups, and tuning, during a first frame period, the focus of the focus tunable lens to each one of the focal planes in the first group according to the corresponding sequence, and

selecting a second group from the focal plane groups allowed by a selection rule, and tuning, during a second frame period, the focus of the focus tunable lens to each one of the focal planes in the second group according to the corresponding sequence,

wherein the selection rule comprises that an index difference between a last focal plane of the focal planes in the sequence of the first group and a first focal plane of the focal planes in the sequence of the second group is 0 or 1 or 2.

15. A non-transitory computer-readable medium comprising a program code for controlling a multifocal display device to perform the method of claim 14 .

16. A multifocal display device, the multifocal display device comprising:

a focus tunable lens;

a controller configured to selectively tune a focus of the focus tunable lens to a plurality of N focal planes during a frame period, the focal planes having indices 1 to N assigned thereto in increasing or decreasing order of the focal planes' focal distances,

a storage storing a plurality of focal plane groups, each group comprising the plurality of focal planes in a different sequence,

wherein the controller is configured to select a first group of the focal plane groups, and tune, during a first frame period, the focus of the focus tunable lens to each one of the focal planes in the first group according to the corresponding sequence,

wherein the controller is configured to select a second group from the focal plane groups allowed by a selection rule, and to tune, during a second frame period, the focus of the focus tunable lens to each one of the focal planes in the second group according to the corresponding sequence,

wherein the selection rule comprises that an index difference between a last focal plane of the focal planes in the sequence of the first group and a first focal plane of the focal planes in the sequence of the second group is 0 or 1 or 2, and

wherein the selection rule further comprises that a position distance between two focal planes, of the focal planes, of a same index in the concatenated sequences of the first group and the second group, respectively, is between a predetermined minimum allowed distance and a predetermined maximum allowed distance.