Electro-optic phase-only spatial light modulator

• US 20040008397A1
• Filed: 05/12/2003
• Published: 01/15/2004
• Est. Priority Date: 05/10/2002
• Status: Active Grant

• Current Assignee: Corporation for National Research Initiatives
• Original Assignee: Corporation for National Research Initiatives
• Inventors: Noonan, William A.
• Granted Patent: US 6,819,463 B2
• Time in Patent Office: Days
• US Class Current: 359/245
• CPC Class Codes: G02F 1/21 by interference
• CPC Class Codes: G02F 2203/02 reflective
• CPC Class Codes: G02F 2203/12 spatial light modulator
• CPC Class Codes: G02F 2203/50 Phase-only modulation
• CPC Class Codes: G03H 1/2294 Addressing the hologram to an active spatial light modulator
• CPC Class Codes: G03H 2225/22 Electrically addressed SLM [EA-SLM]
• CPC Class Codes: G03H 2225/32 Phase only
• CPC Class Codes: G03H 2225/34 Amplitude and phase coupled modulation
• CPC Class Codes: G03H 2225/52 Reflective modulator
• CPC Class Codes: G03H 2226/02 Computing or processing means, e.g. digital signal processor [DSP]

Abstract

An electro-optic, phase-only spatial light modulator is disclosed which uses an electro-optic wafer, such as lithium niobate (LiNbO₃) or lead-lanthanum-zirconate-titanate (PLZT). The electro-optic wafer is sandwiched between a transparent top electrode that forms a solid ground plane and a bottom electrode that is segmented into an array of electrode pads. Voltage source circuitry for each electrode is located immediately beneath the electrode. When a voltage is applied across the electrodes, an electrostatic field is generated between the conductors, and the refractive index of the electro-optic wafer changes slightly. The spatial light modulator can also include a totally reflecting dielectric mirror on the bottom face of the electro-optic wafer and a partially reflecting dielectric mirror deposited on the top face. Together, the mirrors and wafer form an asymmetric Fabry-Perot cavity. This resonant cavity enhances the effect that the small changes in the wafer'"'"'s refractive index has, resulting in phase shifts of ±½π in the reflected light.

Because the bottom electrode is segmented, a different voltage can be applied to each electrode. Thus, the refractive index, and therefore the phase of the exiting light wave, can be manipulated to vary with position. In this way, the phase of the outgoing optical wavefront is spatially modulated. The voltage source integrated circuitry for each electrode is located immediately behind the electrode pad. This integrated circuitry is fabricated on a separate silicon wafer that is later bonded to the electro-optic wafer.

Claims

1. A spatial light modulator comprising:

a first wafer that is formed from an electro-optic material,

a partially reflecting dielectric mirror deposited on the top of the first wafer,

a transparent conductor formed on top of the partially reflecting dielectric mirror,

a totally reflecting dielectric mirror formed on the bottom face of the first wafer, wherein the first wafer is sandwiched between the totally reflecting bottom dielectric mirror and the partially reflecting dielectric mirror so as to form an asymmetric Fabry-Perot cavity,

a second wafer,

a metal conductor formed on top of the second wafer, the metal conductor being segmented into a plurality of electrodes, and

a plurality of electronic voltage sources formed in the second wafer, each electronic voltage source being located next to a corresponding electrode and applying a voltage between the corresponding electrode and the transparent conductor,

the first and second wafers being bonded to one another without being aligned with respect to one another in a predetermined manner.

2. The spatial light modulator recited in claim 1, wherein the electro-optic material is a linear electro-optic material.

3. The spatial light modulator recited in claim 1, wherein the electro-optic material is a quadratic electro-optic material.

4. The spatial light modulator recited in claim 1, wherein the electro-optic material is lithium niobate (LiNbO₃).

5. The spatial light modulator recited in claim 1, wherein the electro-optic material is lead-lanthanum-zirconate-titanate (PLZT).

6. The spatial light modulator recited in claim 1, wherein the electro-optic material is selected from the group consisting of lithium tantalate (LiTaO₃) and barium titanate (BaTiO₃).

7. The spatial light modulator recited in claim 1, wherein the electro-optic material is selected from the group consisting of KDP, KD*P, KTA, RTA, and RTP.

8. The spatial light modulator recited in claim 1, wherein each electronic voltage source forms an electrostatic field between its corresponding electrode and the transparent conductor.

9. The spatial light modulator recited in claim 8, wherein the dielectric mirrors are non-conducting so as to not interfere with the electrostatic field between each electrode and the transparent conductor.

10. The spatial light modulator recited in claim 1, wherein the integrated circuit technology used to fabricate the electronic voltage sources is selected from the group consisting of MOS, bipolar and bipolar/MOS hybrid.

11. The spatial light modulator recited in claim 1, wherein the electrostatic field being formed between each electrode and the transparent conductor results in a change in a refractive index of the first wafer.

12. The spatial light modulator recited in claim 1, wherein light incident on the top of the asymmetric Fabry-Perot cavity is reflected with a phase-shift, the size of this phase-shift being a function of the change in the refractive index of the electro-optic wafer induced by a plurality of voltages applied between the electrodes and the transparent conductor.

13. The spatial light modulator recited in claim 1, wherein different voltages are applied between the electrodes and the transparent conductor, whereby the refractive index, and therefore the phase of an exiting light wavefront, can be manipulated to vary with position.

14. The spatial light modulator recited in claim 2, wherein the transparent electrode forms a solid ground plane.

15. The spatial light modulator recited in claim 3, wherein the transparent electrode forms a solid ground plane.

16. The spatial light modulator recited in claim 3, wherein a bias voltage is applied between each of the electrodes and the transparent conductor.

17. The spatial light modulator recited in claim 1, wherein the transparent conductor is indium tin oxide (ITO).

18. An electro-optic spatial light modulator comprising:

an electro-optic wafer,

a partially reflecting dielectric mirror deposited on the top face of the electro-optic wafer,

a transparent electrode formed on top of the partially reflecting dielectric mirror,

a totally reflecting dielectric mirror formed on the bottom face of the electro-optic wafer, wherein the electro-optic wafer is sandwiched between the totally reflecting bottom mirror and the partially reflecting dielectric mirror so as to form an asymmetric Fabry-Perot cavity,

a circuitry wafer,

a metal conductor formed on top of the circuitry wafer, the metal conductor being segmented into an array of electrode pads, and

a plurality of electronic voltage sources formed in the circuitry wafer, each electronic voltage source being located behind a corresponding electrode pad so as to eliminate a need for connection leads between the electrode pads and external voltage sources, each electronic voltage source also applying a voltage between the corresponding electrode pad and the transparent conductor,

wherein the electro-optic wafer and the circuitry wafer are bonded without being aligned with respect to one another in a predetermined manner.

19. The spatial light modulator recited in claim 18, wherein the electro-optic material is a linear electro-optic material.

20. The spatial light modulator recited in claim 18, wherein the electro-optic material is a quadratic electro-optic material.

21. The spatial light modulator recited in claim 18, wherein the electro-optic wafer is lithium niobate (LiNbO₃).

22. The spatial light modulator recited in claim 18, wherein the electro-optic wafer is lead-lanthanum-zirconate-titanate (PLZT).

23. The spatial light modulator recited in claim 18, wherein the electro-optic material is selected from the group consisting of lithium tantalate (LiTaO₃) and barium titanate (BaTiO₃).

24. The spatial light modulator recited in claim 18, wherein the electro-optic material is selected from the group consisting of KDP, KD*P, KTA, RTA, and RTP.

25. The spatial light modulator recited in claim 18, wherein each electronic voltage source forms an electrostatic field between its corresponding electrode pad and the transparent conductor.

26. The spatial light modulator recited in claim 25, wherein the dielectric mirrors are non-conducting so as to not interfere with the electrostatic field between each electrode pad and the transparent conductor.

27. The spatial light modulator recited in claim 18, wherein the integrated circuit technology used to fabricate the electronic voltage sources is selected from the group consisting of MOS, bipolar and bipolar/MOS hybrid.

28. The spatial light modulator recited in claim 25, wherein the electrostatic fields being formed between the electrode pads and the transparent conductor results in a change in the refractive index of the electro-optic wafer.

29. The spatial light modulator recited in claim 18, wherein light incident on the top of the asymmetric Fabry-Perot cavity is reflected with a phase-shift, the size of this phase-shift being a function of the change in the refractive index of the electro-optic wafer induced by a plurality of voltages applied between the electrodes and the transparent conductor.

30. The spatial light modulator recited in claim 18, wherein different voltages are applied between the electrode pads and the transparent conductor, whereby the refractive index, and therefore the phase of an exiting light wavefront, can be manipulated to vary with position.

31. The spatial light modulator recited in claim 19, wherein the transparent electrode forms a solid ground plane.

32. The spatial light modulator recited in claim 20, wherein the transparent electrode forms a solid ground plane.

33. The spatial light modulator recited in claim 18, wherein a bias voltage is applied between each of the electrode pads and the transparent conductor.

34. The spatial light modulator recited in claim 18, wherein the transparent conductor is indium tin oxide (ITO).

35. An electro-optic spatial light modulator comprising:

an electro-optic wafer formed from lead-lanthanum-zirconate-titanate (PLZT),

a transparent electrode formed on top of the electro-optic wafer,

a totally reflecting dielectric mirror formed on the bottom face of the electro-optic wafer,

a silicon wafer,

a metal conductor formed on top of the silicon wafer, the metal conductor being segmented into an array of electrode pads, and

a plurality of electronic voltage sources formed in the silicone wafer, each electronic voltage source being located next to a corresponding electrode pad and being applied between the corresponding electrode pad and the transparent electrode,

wherein the electro-optic wafer and the silicon wafer are bonded together without being aligned with respect to one another in a predetermined manner.

36. The spatial light modulator recited in claim 35, wherein each electronic voltage source forms an electrostatic field between its corresponding electrode pad and the transparent conductor.

37. The spatial light modulator recited in claim 35, wherein the integrated circuit technology used to fabricate the electronic voltage sources is selected from the group consisting of MOS, bipolar and bipolar/hybrid.

38. The spatial light modulator recited in claim 35, wherein the electrostatic fields being formed between the electrode pads and the transparent conductor results in a change in the refractive index of the electro-optic wafer.

39. The spatial light modulator recited in claim 35, wherein different voltages are applied between the electrode pads and the transparent conductor, whereby the refractive index, and therefore the phase of an exiting light wavefront, can be manipulated to vary with position.

40. The spatial light modulator recited in claim 35, wherein a bias voltage is applied between each of the electrode pads and the transparent electrode.

41. The spatial light modulator recited in claim 35, wherein the transparent electrode forms a ground plane.

42. The spatial light modulator recited in claim 35, wherein the transparent conductor is indium tin oxide (ITO).