OASLM and a method and apparatus for driving an OASLM

1. A method of controlling the switching of an optically addressable spatial light modulator (OASLM) having a photosensitive layer able to be driven in both a photosensitive direction and non-photosensitive direction, the method comprising:

applying a bipolar switching waveform to control electrodes of the OASLM during a write cycle such that a leading pulse of the waveform applies a voltage across the OASLM which is in the photosensitive direction and a trailing pulse applies a voltage which is not in the photosensitive direction, wherein the trailing pulse causes switching between stable states of the OASLM.

2. The method according to claim 1 , wherein the amplitude of the leading pulse is less than that of the trailing pulse.

3. The method according to claim 1 , wherein the shape and amplitude of the bipolar switching waveform are such that the leading pulse causes substantially no switching between stable states.

4. The method according to claim 1 , wherein the bipolar switching waveform includes no more than two sequential pulses.

5. The method according to claim 1 , wherein the duration of the leading pulse is less than that of the trailing pulse.

6. The method according to claim 1 , wherein the bipolar switching waveform causes unilluminated areas to switch and does not switch illuminated areas.

7. A method of controlling the switching of an optically addressable spatial light modulator (OASLM) having a photosensitive layer able to be driven in both a photosensitive direction and a non-photosensitive direction, the method comprising:

applying a blanking pulse in the photosensitive direction to cause the OASLM to switch to a first state;

applying a bipolar switching waveform to control electrodes of the OASLM during each write cycle, wherein a leading pulse of the switching waveform is also applied in the photosensitive direction, and wherein a trailing pulse of the bipolar waveform is applied in the non-photosensitive direction and causes areas of the OASLM to substantially switch from the first state to an opposite state.

8. The method according to claim 7 , wherein the pulse amplitudes and widths are chosen to lie within that region of pulse amplitude/width space which is substantially bounded by:

a) a line defining between 95% and 100% switching of illuminated areas to the leading pulse of the bipolar waveform; and

b) a line defining between 0% and 5% switching of unilluminated areas to the trailing pulse of the bipolar waveform.

9. The method according to claim 7 , wherein the pulse amplitudes and widths are chosen to lie within that region of pulse amplitude/width space which is substantially bounded by:

a) a line defining between 95% and 100% switching of unilluminated areas to the leading pulse of the bipolar waveform; and

b) a line defining between 0% and 5% switching of illuminated areas to the trailing pulse of the bipolar waveform.

10. The method according to claim 7 , wherein the bipolar switching waveform is preceded by a blanking pulse which switches the entire OASLM to an illuminated state.

11. The method according to claim 7 , wherein the bipolar switching waveform is preceded by a blanking pulse which switches the entire OASLM to a nonilluminated state.

12. The method according to claim 7 , wherein the blanking pulse is completed prior to the leading pulse.

13. An optically addressable spatial light modulator (OASLM) comprising:

a photosensitive layer able to be driven in both a photosensitive direction and a non-photosensitive direction,

wherein switching between stable states is performed by applying an asymmetric bipolar switching waveform to control electrodes of the OASLM during a write cycle, and wherein a switching between stable states is caused by a trailing pulse of the bipolar switching waveform that includes a polarity in the non-photosensitive direction.

14. The OASLM according to claim 13 , wherein the polarity of the leading pulse of the bipolar waveform is in the photosensitive direction.

15. The OASLM according to claim 13 , wherein the pulse width ratio between the leading pulse and the trailing pulse is at least 1:4.

16. The OASLM according to claim 13 , including a liquid crystal having a response time for switching between first and second states which depends upon the voltage across the liquid crystal layer, the response time having a minimum at a given voltage.

17. The OASLM according to claim 13 , wherein the amplitude of the leading pulse is less than that of the trailing pulse.

18. A display system comprising:

an optically addressable spatial light modulator (OASLM) having a photosensitive layer able to be driven in both a photosensitive direction and a non-photosensitive direction;

means for applying a write light signal to a first surface of the OASLM;

means for applying a read light signal to a second surface of the OASLM; and

OASLM control means for applying a bipolar switching waveform to control electrodes of the OASLM during each write cycle such that in use a leading pulse of the waveform applies a voltage across the OASLM which is in the photosensitive direction, and a trailing pulse of the waveform applies a voltage which is not in the photosensitive direction, where the trailing pulse causes the electrodes to switch between stable states.

19. The system according to claim 18 , wherein the amplitude of the leading pulse is less than that of the trailing pulse.

20. The system according to claim 18 , wherein the shape and amplitude of the bipolar switching waveform are such that the leading pulse causes substantially no switching between stable states.

21. The system according to claim 18 , wherein the duration of the leading pulse is less than that of the trailing pulse.