Method and controller for operating a variable optical retarder and an array
A method and a controller for operating an array of variable optical retarders are disclosed. Neighboring pixels of the array of variable optical retarders are driven with disordered temporal bit sequences. An optical beam illuminating the pixels tends to integrate time-domain modulation caused by individual pixels driven in a non-coordinated or disordered fashion, which reduces the overall time-domain modulation amplitude of the optical beam.
1. A method comprising:
selecting first and second temporal bit sequences of equal total duration for application to first and second retarders, respectively, for obtaining first and second optical retardation values;
simultaneously applying the first and second temporal bit sequences to the first and second retarders, respectively, to generate a spatial profile of an optical retardation in an optical beam illuminating both the first and the second retarders, based on net amplitudes of the first and second temporal bit sequences, respectively; and
adjusting a bit duration of at least one bit in the first and second temporal bit sequences to lessen a time-domain modulation,
wherein one-bits in the first and second temporal bit sequences are substantially evenly distributed in time.
2. The method of claim 1 , wherein the one-bits in the first and second temporal bit sequences are non-periodic.
3. The method of claim 1 , wherein
a plurality of alternative bit sequences are provided for at least one of the first optical retardation value or the second optical retardation value, and
one of the plurality of the alternative bit sequences is randomly or pseudo-randomly selected for the at least one of the first optical retardation value or the second optical retardation value.
4. The method of claim 1 , wherein the first retardation value is substantially equal to the second retardation value.
5. The method of claim 1 , wherein selecting the first and second temporal bit sequences includes:
selecting, using a look-up table having a plurality of rows that each contains a temporal bit sequence for one of a plurality of optical retardation values including the first and second optical retardation values, the first and second temporal bit sequences.
6. The method of claim 5 , wherein a total quantity of one-bits in a 5×5 bit rectangle centered on a particular bit of a particular row of the look-up table varies by X<3 bits in going from one bit of the particular row to another bit of the particular row, for Y>50% of all bits of the particular row.
7. The method of claim 6 , wherein Y>80% of all bits of the particular row.
8. The method of claim 6 , wherein X<2 bits.
9. The method of claim 5 , wherein probabilities of an nth bit averaged over all temporal bit sequences of the look-up table to be a one bit are within 15% of each other, wherein n is a serial bit number in a temporal bit sequence of the look-up table.
10. The method of claim 7 , wherein the bit duration of the at least one bit in the first and second temporal bit sequences is varied to increase a quantity of attainable values of optical retardation in the first and second retarders.
11. The method of claim 7 , further comprising:
obtaining the time-domain modulation.
12. A controller configured to:
select first and second temporal bit sequences of equal total duration for application to first and second retarders, respectively, for obtaining first and second optical retardation values;
simultaneously apply the first and second temporal bit sequences to the first and second retarders, respectively, to generate a spatial profile of an optical retardation in an optical beam illuminating both the first and the second retarders, based on net amplitudes of the first and second temporal bit sequences, respectively; and
adjust a bit duration of at least one bit in the first and second temporal bit sequences to lessen a time-domain modulation,
wherein one-bits in the first and second temporal bit sequences are substantially evenly distributed in time.
13. The controller of claim 12 , wherein the one-bits in the first and second temporal bit sequences are non-periodic.
14. The controller of claim 12 , wherein
a plurality of alternative bit sequences are provided for at least one of the first optical retardation value or the second optical retardation value, and
one of the plurality of the alternative bit sequences is randomly or pseudo-randomly selected for the at least one of the first optical retardation value or the second optical retardation value.
15. The controller of claim 12 , wherein the first retardation value is substantially equal to the second retardation value.
16. The controller of claim 12 , wherein the controller, when selecting the first and second temporal bit sequences, is configured to:
select, using a look-up table having a plurality of rows that each contains a temporal bit sequence for one of a plurality of optical retardation values including the first and second optical retardation values, the first and second temporal bit sequences.
17. The controller of claim 16 , wherein a total quantity of one-bits in a 5×5 bit rectangle centered on a particular bit of a particular row of the look-up table varies by X<3 bits in going from one bit of the particular row to another bit of the particular row, for Y>50% of all bits of the particular row.
18. The controller of claim 17 , wherein Y>80% of all bits of the particular row and X<2 bits.
19. The controller of claim 16 , wherein probabilities of an nth bit averaged over all temporal bit sequences of the look-up table to be a one bit are within 15% of each other, wherein n is a serial bit number in a temporal bit sequence of the look-up table.
20. The controller of claim 12 , wherein the bit duration of the at least one bit in the first and second temporal bit sequences is varied to increase a quantity of attainable values of optical retardation in the first and second retarders.