Stress tuned blazed grating light valve

• US 20030035189A1
• Filed: 08/15/2001
• Published: 02/20/2003
• Est. Priority Date: 08/15/2001
• Status: Active Grant

• Current Assignee: Silicon Light Machines Corporation (SCREEN Holdings Co., Ltd.)
• Original Assignee: Silicon Light Machines Corporation (SCREEN Holdings Co., Ltd.)
• Inventors: Amm, David T., Hunter, James, Gudeman, Christopher
• Granted Patent: US 6,639,722 B2
• Time in Patent Office: Days
• US Class Current: 359/254
• CPC Class Codes: G02B 26/0808 by means of one or more diffracting elements

Abstract

A light modulator includes elongated elements arranged parallel to each other and suspended above a substrate. The light modulator operates in a first diffraction mode and in a second diffraction mode. In the first diffraction mode, an incident light diffracts into at least two diffraction orders. In the second diffraction mode, the incident light diffracts into a single diffraction order. Each of the elongated elements comprises a central blazed portion, a first outer blaze transition, and a second outer blaze transition. The central blaze portion couples the first outer blaze transition to the second outer blaze transition. Each of the central blazed portions comprises a reflective surface. Selected ones of the central blazed portions comprise a first conductive element. The first outer blaze transition and the second outer blaze transition are coupled to the substrate. The substrate comprises a second conductive element. The elongated elements produce the first diffraction when a first electrical bias, preferably a zero electrical bias, is applied between the first conductive elements of the selected ones of the elongated elements and the second conductive element. A relative height of the blazed portions are adjusted to produce the second diffraction when a second electrical bias is applied between the first conductive elements of the selected ones of the elongated elements and the second conductive element.

Claims

1. A light modulator comprising:

a. elongated elements arranged parallel to each other and configured in a grating plane, each elongated element comprising a central blazed portion, a first outer blaze transition, and a second outer blaze transition, the central blaze portion coupling the first outer blaze transition to the second outer blaze transition, each central blazed portion comprising a reflective surface such that in operation an incident light illuminating the central blazed portions diffracts into at least two diffraction orders; and

b. means for adjusting a height of selected ones of the elongated elements relative to the grating plane such that in operation the incident light diffracts into a single diffraction order.

2. The light modulator of claim 1 wherein the means for adjusting the height of the selected ones of the elongated elements comprise:

a. a first conductive element along the central blazed portion of each of the selected ones of the elongated elements; and

b. a substrate coupled to the elongated elements, the substrate comprising a second conductive element such that an electrical bias applied between the first conductive elements and the second conductive element adjusts the height of the selected ones of the elongated elements.

3. The light modulator of claim 2 further comprising first and second posts, the first post coupling each of the elongated elements along the first outer blaze transition to the substrate, the second post coupling each of the elongated elements along the second outer blaze transition to the substrate.

4. The light modulator of claim 1 wherein the selected ones of the elongated elements comprise every other ones of the elongated elements.

5. The light modulator of claim 4 wherein the incident light illuminates the central blaze portions of the elongated elements normal to the grating plane such that the at least two diffraction orders comprise a zeroth diffraction order normal to the grating plane and a second diffraction order at a second order blaze angle of about an arcsin of one quarter of a light wavelength divided by a pitch of the elongated elements

6. The light modulator of claim 5 wherein the incident light illuminates the central blaze portions of the elongated elements normal to the grating plane such that the single diffraction order comprises a first order diffraction at a first order angle given by the arcsin of one quarter of the light wavelength divided by twice the pitch.

7. The light modulator of claim 1 wherein the central blazed portion comprises a rectangular cross section.

8. The light modulator of claim 7 wherein the rectangular cross section of the central blaze portion has been rotated to a blaze angle by a combination of a residual stress within the elongated element and a rigidity of the first and second outer blaze transitions.

9. A light modulator comprising:

a. elongated elements arranged parallel to each other and configured in a grating plane, each elongated element comprising a central blazed portion, a first outer blaze transition, and a second outer blaze transition, the central blaze portion coupling the first outer blaze transition to the second outer blaze transition, selected ones of the central blazed portions comprising a first conductive element, each of the central blazed portions comprising a reflective surface such that in operation an incident light illuminating the central blazed portions diffracts into at least two diffraction orders; and

b. a substrate coupled to the elongated elements, the substrate comprising a second conductive element such that in operation an electrical bias applied between the first conductive elements and the second conductive element adjusts a height of the selected ones of the elongated elements and further such that in operation the incident light diffracts into a single diffraction order.

10. A light modulator comprising:

a. elongated elements arranged parallel to each other and configured in a grating plane, each elongated element having a rectangular cross section and configured with a blaze angle, each of selected ones of the elongated elements comprising a first conductive element, each elongated element comprising a reflective surface such that in operation an incident light diffracts into at least two diffraction orders; and

b. a substrate coupled to the elongated elements, the substrate comprising a second conductive element such that in operation an electrical bias applied between the first conductive elements and the second conductive element adjusts a height of the selected ones of the elongated elements and further such that in operation the incident light diffracts into a single diffraction order.

11. A light modulator comprising:

a. means for stress inducing a blaze angle into elongated elements arranged parallel to each other and configured in a grating plane such that in operation an incident light diffracts into at least two diffraction orders; and

b. means for adjusting a height of selected ones of the elongated elements relative to the grating plane such that in operation the incident light diffracts into a single diffraction order.

12. A method of fabricating a light modulator comprising the steps of:

a. depositing a sacrificial layer on a substrate;

b. etching first outer blaze transition producing features and second outer blaze transition producing features into the sacrificial layer;

c. depositing a resilient material on the sacrificial layer;

d. etching the resilient material to form elongated elements supported by the sacrificial layer; and

e. etching the sacrificial layer to completion leaving the elongated elements coupled to the substrate, each of the elongated elements comprising a central blazed portion, a first outer blaze transition, and a second outer blaze transition, the first outer blaze transition coupled to the second outer blaze transition by the central blazed portion.

13. The method of claim 12 further comprising the steps of:

a. forming an oxide layer on the substrate between the substrate and the sacrificial layer prior to depositing the sacrificial layer; and

b. depositing a first conducting layer on the substrate between the oxide layer and the sacrificial layer prior to depositing the sacrificial layer.

14. The method of claim 13 wherein the substrate comprises silicon and further wherein the oxide layer comprises a field oxide layer of silicon dioxide.

15. The method of claim 13 wherein the first conducting layer comprises doped poly-silicon.

16. The method of claim 15 further comprising the step of depositing an etch stop on the doped poly-silicon between the doped poly-silicon and the sacrificial layer.

17. The method of claim 16 further comprising the step of etching first post holes and second post holes through the sacrificial layer.

18. The method of claim 17 wherein sacrificial layer comprises poly-silicon.

19. The method of claim 18 wherein the step of etching the sacrificial layer to completion comprises a xenon difluoride dry etch.

20. The method of claim 17 wherein the step of depositing the resilient material further comprises depositing the resilient material within the first and second post holes, thereby forming first and second posts.

21. The method of claim 20 wherein the resilient material comprises silicon nitride.

22. The method of claim 21 further comprising the step of depositing a reflective material on the resilient material.

23. The method of claim 22 wherein the reflective material comprises aluminum.

24. The method of claim 22 wherein the step of etching the resilient material further comprises etching the reflective material.

25. The method of claim 20 wherein each of the elongated elements are supported by one of the first posts and by one of the second posts, the first post supporting the first outer blaze transition, the second post supporting the second outer blaze transition.