Electrostatic actuation for diffractive optical devices
An optical device includes first and second planar substrates having respective first and second faces and including first and second diffractive structure disposed respectively on the first and second faces. First and second planar electrodes are disposed respectively on the first and second faces. A mount holds the second planar substrate parallel to the first planar substrate, with the second face adjacent to the first face and with the first and second planar electrodes in mutual proximity, while permitting the second planar substrate to move transversely relative to the first planar substrate. A control circuit is coupled to apply an electrical potential between the first and second planar electrodes with a voltage sufficient to shift the second diffractive structure transversely relative to the first diffractive structure.
1. An optical device, comprising:
a first planar substrate having a first face and comprising a first diffractive structure disposed on the first face;
a second planar substrate having a second face and comprising a second diffractive structure disposed on the second face;
a first planar electrode disposed on the first face;
a second planar electrode disposed on the second face;
a mount holding the second planar substrate parallel to the first planar substrate, with the second face adjacent to the first face and with the first and second planar electrodes in mutual proximity, while permitting the second planar substrate to move transversely relative to the first planar substrate; and
a control circuit, which is coupled to apply an electrical potential between the first and second planar electrodes with a voltage sufficient to shift the second diffractive structure transversely relative to the first diffractive structure.
2. The device according to claim 1 , wherein the mount comprises a set of flexible beams connecting the second planar substrate to a frame to which the first planar substrate is fixed.
3. The device according to claim 2 , wherein the flexible beams comprise silicon.
4. The device according to claim 1 , and comprising third and fourth planar electrodes disposed in mutual proximity on the first and second faces, respectively,
wherein the control circuit is configured to apply a first electrical potential between the first and second planar electrodes in order to shift the second diffractive structure relative to the first diffractive structure in a first transverse direction and to apply a second electrical potential between the third and fourth planar electrodes in order to shift the second diffractive structure relative to the first diffractive structure in a second transverse direction, different from the first transverse direction.
5. The device according to claim 1 , wherein the first and second planar electrodes are interleaved respectively in the first and second diffractive structures.
6. The device according to claim 5 , wherein the first and second planar electrodes are disposed in respective serpentine patterns within the first and second diffractive structures.
7. The device according to claim 1 , wherein the second planar substrate has a third face opposite the second face, and wherein the device comprises;
a planar cover, which has a fourth face and is mounted with the fourth face parallel to and in proximity to the third face; and
third and fourth planar electrodes disposed in mutual proximity on the third and fourth faces, respectively, and
wherein the control circuit is configured to apply simultaneously a first electrical potential between the first and second planar electrodes and a second electrical potential between the third and fourth planar electrodes in order to shift the second diffractive structure relative to the first diffractive structure.
8. The device according to claim 1 , and comprising an actuator, which is controllable by the control circuit to apply a first transverse shift to the second diffractive structure relative to the first diffractive structure, wherein application of the electrical potential between the first and second planar electrodes applies a second transverse shift to the second diffractive structure in addition to the first transverse shift.
9. The device according to claim 1 , and comprising a spacer, which is disposed between the first and second faces and is configured to maintain a predefined distance between the first and second faces while permitting the second planar substrate to move transversely relative to the first planar substrate.
10. The device according to claim 9 , wherein the spacer comprises a liquid enclosed between the first and second faces.
11. The device according to claim 9 , wherein the spacer comprises one or more spherical particles, which roll between the first and second faces as the second planar substrate moves transversely relative to the first planar substrate.
12. An optical system, comprising:
the device according to claim 1 ; and
a radiation source, which is configured to direct a beam of optical radiation toward the device,
wherein shifting the second diffractive structure transversely relative to the first diffractive structure modifies an optical property of the beam.
13. The system according to claim 12 , wherein the first and second planar substrates are transparent to the optical radiation, and the device is configured to modify the optical property as the beam is transmitted through the device.
14. The system according to claim 12 , wherein the device is configured to modify the optical property as the beam is reflected from the device.
15. A method for controlling a beam of optical radiation, the method comprising:
directing the beam of optical radiation toward a device comprising:
a first planar substrate having a first face and comprising a first diffractive structure disposed on the first face;
a second planar substrate having a second face and comprising a second diffractive structure disposed on the second face;
a first planar electrode disposed on the first face;
a second planar electrode disposed on the second face; and
a mount holding the second planar substrate parallel to the first planar substrate, with the second face adjacent to the first face and with the first and second planar electrodes in mutual proximity, while permitting the second planar substrate to move transversely relative to the first planar substrate; and
applying an electrical potential between the first and second planar electrodes with a voltage sufficient to shift the second diffractive structure transversely relative to the first diffractive structure, thereby modifying an optical property of the beam.
16. The method according to claim 15 , wherein the first and second planar substrates are transparent to the optical radiation, and wherein modifying the optical property comprises modifying the beam as the beam is transmitted through the device.
17. A method for fabricating an optical device, comprising:
forming a first diffractive structure on a first face of a first planar substrate;
forming a second diffractive structure on a second face of a second planar substrate;
depositing a first planar electrode on the first face;
depositing a second planar electrode on the second face;
mounting the second planar substrate parallel to the first planar substrate, with the second face adjacent to the first face and with the first and second planar electrodes in mutual proximity, while permitting the second planar substrate to move transversely relative to the first planar substrate; and
coupling a control circuit to apply an electrical potential so as to shift the second diffractive structure transversely relative to the first diffractive structure.
18. The method according to claim 17 , wherein forming the first diffractive structure and the second diffractive structure comprises applying at least one of an etching process and a nano-imprint process to the first face and the second face to create diffractive elements.
19. The method according to claim 17 , wherein depositing the first planar electrode and the second planar electrode comprises interleaving at least one of the first and second planar electrodes with at least one of the first and second diffractive structures.
20. The method according to claim 17 , wherein depositing the first planar electrode and the second planar electrode comprises depositing at least one of the first and second planar electrodes on at least one of the first face and the second face before forming the diffractive structure on the at least one of the first face and the second face.