Method and apparatus for curvature-resistant micro-mirror structures to reduce light beam loss in free-space micro-machined optical switches

• US 6,271,958 B1
• Filed: 10/29/1999
• Issued: 08/07/2001
• Est. Priority Date: 12/15/1998
• Status: Expired due to Term

• Current Assignee: AT&T Corporation (AT&T, Inc.)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Lin, Lih Yuan, Goldstein, Evan Lee, Tkach, Robert William
• Primary Examiner(s): Sugarman, Scott J.
• Assistant Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US09/429,789
• Time in Patent Office: 648 Days
• Field of Search: 359/298, 359/273, 359/267, 359/846, 359/848, 359/883
• US Class Current: 359/298
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 6/3518 the reflective optical element being an intrinsic part of a MEMS device, i.e. fabricated together with the MEMS device MEMS devices in general B81B; manufacture of MEM devices in general B81C; micromechanical devices controlling the direction of light G02B26/0833
• CPC Class Codes: G02B 6/3584 constructional details of an associated actuator having a MEMS construction, i.e. constructed using semiconductor technology such as etching MEMS per se B81B, B81C

Abstract

A method and apparatus for curvature-resistant micro-mirror structures to reduce light beam coupling loss due to mirror curvature in free-space micro-machined optical switches is presented. As a significant contributor to light beam coupling loss is the curvature of the micro-mirrors in these cross-connect systems, an improved thick mirror slab utilizing a phosopho-silicate glass (PSG) core is constructed. The PSG core is sandwiched between two poly-silicon layers, thus providing an enhanced, bending-resistant structure which protects the PSG core from the release etchant used in surface micro-machining and substantially reduces mirror curvature. The reflective layer is laid down on top of the enhanced, bending-resistant structure.

Claims

1. A micro-mirror apparatus for use in a free-space micro-machined optical switch, the micro-mirror apparatus comprising:

a first poly-silicon layer, which first layer acts as a base;

a phosopho-silicate glass (PSG) core, which core is laid down on top of the base;

a second poly-silicon layer, which second layer is laid down on top of the first poly-silicon layer and the phosopho-silicate glass core thereby creating an enhanced bending-resistant structure; and

a reflective surface layer, which layer is laid down on top of the enhanced bending-resistant structure.

2. The apparatus according to claim 1, wherein the reflective surface layer can have a thickness of less than 5000 Å

and greater than 500 Å

without causing curvature of the micro-mirror apparatus due to the enhanced bending-resistant structure.

3. The apparatus according to claim 1, wherein the reflective surface layer is gold.

4. The apparatus according to claim 1, wherein the enhanced bending-resistant structure has a thickness of 4.25 μ

m.

5. The apparatus according to claim 1, wherein the PSG core is less than or the same length as each of the first and second poly-silicon layers.

6. An apparatus for a micro-mirror, the apparatus comprising:

an enhanced bending-resistant structure, the structure comprising;

a bottom poly-silicon layer;

a phosopho-silicate glass core; and

a top poly-silicon layer,

wherein the phosopho-silicate glass core is sandwiched between the bottom and top poly-silicon layers; and

a reflective surface layer, which layer is laid down on top of the enhanced bending-resistant structure.

7. The apparatus according to claim 6, wherein the reflective surface layer can have a thickness of less than 5000 Å

and greater than 500 Å

without causing the curvature of the micro-mirror due to the sandwiching of the glass core between the bottom and top layers.

8. The apparatus according to claim 6, wherein the reflective surface layer is gold.

9. The apparatus according to claim 6, wherein the sandwiching of the glass core between the bottom and top layers has a thickness of 0.75 μ

m.

10. The apparatus according to claim 6, wherein the phosoph-silicate glass core is less than or the same length as each of the first and second poly-silicon layers.

11. A method of creating a micro-mirror with an enhanced bending-resistant structure for use in a free-space micro-machined optical switch, the method comprising the steps of:

laying down a first poly-silicate layer as a base;

placing a phosopho-silicate glass (PSG) core on top of the base;

laying down a second poly-silicate layer on top of the PSG core and base; and

laying down a reflective surface on top of the second poly-silicate layer.

12. The method according to claim 11, wherein the reflective surface layer can have a thickness of less than 5000 Å

and greater than 500 Å

without causing curvature of the micro-mirror due to the sandwiching of the glass core between the two poly-silicate layers.

13. The method according to claim 11, wherein the reflective surface layer is gold.

14. The method according to claim 11, wherein the glass core and the two poly-silicate layers create a sandwich having a thickness of 4.25 μ

m.

15. The method according to claim 11, wherein the phosopho-silicate glass core is less than or the same length as each of the first and second poly-silicon layers.