Electro-optical devices using dynamic reconfiguration of effective electrode structures
Variable liquid crystal devices for controlling the propagation of light through a liquid crystal layer use a frequency dependent material to dynamically reconfigure effective electrode structures in the device. The drive signal source uses pulse-width modulation to set a frequency and an amplitude of the drive signal.
1. A variable optical device for controlling the propagation of light passing through the device using a dynamically-configured effective electrode geometry, said optical device comprising:
a liquid crystal layer having an aperture through which said light passes, said liquid crystal layer comprising a low angle pre-tilt alignment layer on a substrate containing liquid crystal material, wherein optical properties of the liquid crystal material are able to control said light propagation using a spatial variation of liquid crystal molecule orientation;
an electrode system arranged to generate an electric field acting on said liquid crystal layer, the electrode system comprising at least one electrode having a gap or hole and including a weakly conductive material near the gap or hole for providing an electric field profile over the aperture;
an electrical signal generator for generating a drive signal at a plurality of different frequencies and applying the drive signal to the electrode system,
wherein said generator is configured to provide a first drive signal at which said spatial profile is substantially uniform, with said liquid crystal being able to be reoriented from a ground state defined by the alignment layer into a state substantially without disclinations, and a second drive signal having a frequency different from a frequency of the first drive signal at which said spatial profile is not spatially uniform to achieve a desired control over light propagation.
2. The device as claimed in claim 1 , wherein said drive signal comprises substantially a single frequency signal that is changed to change said light propagation.
3. The device as claimed in claim 1 , wherein said signal generator controls said light propagation without substantive voltage variation of said drive signal.
4. The device as claimed in claim 2 , wherein said signal generator controls said light propagation using a plurality of voltages of said drive signal.
5. The device as claimed in claim 1 , wherein said drive signal comprises a plurality of frequencies that combine to create said spatial profile.
6. The device as claimed in claim 1 , wherein said signal generator changes an amplitude of said drive signal to adjust said light propagation.
7. The device as claimed in claims 1 , wherein said device is a lens, said signal generator is operative to control an optical power of the lens.
8. The device as claimed in claim 7 , wherein said device comprises at least two liquid crystal layers having a different direction of liquid crystal orientation to reduce polarization sensitivity of said device.
9. The device as claimed in claim 8 , wherein said electrode system comprises a middle ring electrode positioned between at least one upper liquid crystal layer and at least one lower liquid crystal layer, an upper transparent electrode and a lower transparent electrode, said weakly conductive material comprises a layer of material located near said middle ring electrode, said spatial profile modulated by said weakly conductive material being thus the same for said at least one upper liquid crystal layer between the middle ring electrode and the upper transparent electrode and for said at least one lower liquid crystal layer between the middle ring electrode and the lower transparent electrode.
10. The device as claimed in claims 8 , wherein said lens is a circular lens and said electrode system comprises at least one circular hole patterned electrode.
11. The device as claimed in claims 10 , wherein said liquid crystal layer is substantially planar, and said device is a gradient index lens (GRIN).
12. The device as claimed in claim 11 , wherein said lens has a tunable variable optical power over a range of more than 3 diopters.
13. The device as claimed in claims 1 , wherein said signal generator comprises a pulse-width modulation circuit for varying an effective voltage across electrodes and a corresponding electric field across the liquid crystal material.
14. The device as claimed in claim 13 , wherein said pulse-width modulation circuit provides a plurality of pulse amplitudes, and said amplitude is changed with a corresponding change in duty cycle to deliver substantially a same effective PWM voltage when a frequency content in said waveform contains too much energy away from a central frequency.
15. The device as claimed in claim 1 , wherein said frequency dependent material comprises a semiconductor material.