High germanium content waveguide materials

• US 20020154878A1
• Filed: 07/27/2001
• Published: 10/24/2002
• Est. Priority Date: 02/09/2001
• Status: Active Grant

• Current Assignee: Corning Incorporated
• Original Assignee: Corning Incorporated
• Inventors: Akwani, Ikerionwu A., Bellman, Robert A., Simpson, Lynn B.
• Granted Patent: US 6,768,856 B2
• Time in Patent Office: Days
• US Class Current: 385/129
• CPC Class Codes: C03C 3/076 with 40% to 90% silica, by weight C03C3/045 takes precedence
• CPC Class Codes: C03C 3/111 containing nitrogen
• CPC Class Codes: G02B 2006/12145 Switch
• CPC Class Codes: G02B 6/132 by deposition of thin films
• CPC Class Codes: G02F 1/1326 Liquid crystal optical waveguides or liquid crystal cells specially adapted for gating or modulating between optical waveguides

Abstract

Germanium-silicon oxide, germanium-silicon oxynitride and silica-germania-titania materials and oxynitride materials suitable for fabricating optical waveguides for liquid crystal based cross-connect optical switching devices have a refractive index of from about 1.48 to about 1.52 at 1550 nm, and a coefficient of thermal expansion at room temperature of from about 3×10⁻⁶° C.⁻¹ to about 4.4×10⁻⁶° C,⁻¹. The compositions are adjusted so that the refractive index of the germanium-silicon oxide, germanium-silicon oxynitride or silica-germania-titania material is closely matched to the refractive index of a typical liquid crystal material whereby improved optical performance of a liquid crystal based cross-connect optical switching device is achieved. The coefficient of thermal expansion of the germanium-silicon oxide, germanium-silicon oxynitride, or silica-germania-titania material is closely matched to the coefficient of thermal expansion of silicon, whereby strain induced birefringence caused by thermal stresses is reduced or avoided.

Claims

1. A glass composition comprising:

a germanium-silicon oxide or oxynitride having a Ge/(Si+Ge) mole ratio of from about 0.25 to about 0.47 and an N/(N+O) mole ratio of 0 to about 0.1.

2. The glass composition of claim 1, wherein the Ge/(Si+Ge) mole ratio is about 0.35 and the N/(N+O) mole ratio is about 0.05.

3. The glass composition of claim 1 exhibiting a refractive index of from about 1.48 to about 1.52 at 1550 nm, and having a coefficient of thermal expansion at room temperature of from about 3×

10<sup>−

6</sup>°

C.<sup>−

1</sup> to about 4.4×

10<sup>−

6</sup>°

C.<sup>−

1</sup>.

4. The glass composition of claim 1 exhibiting a refractive index of from about 1.48 to about 1.52 at 1550 nm, and having a coefficient of thermal expansion at room temperature of from about 3×

10<sup>−

6</sup>°

C.<sup>−

1</sup> to about 4.4×

10<sup>−

6</sup>°

C.<sup>−

1</sup>.

5. A planar optical device comprising:

a waveguide core and waveguide cladding, wherein at least one of the waveguide core and the waveguide cladding is a germanium-silicon oxide or oxynitride material having a Ge/(Si+Ge) mole ratio of from about 0.25 to about 0.47 and an N/(N+O) mole ratio of from 0 to about 0.1.

6. The planar optical device of claim 5, wherein the Ge/(Si+Ge) mole ratio is about 0.35 and the N/(N+O) mole ratio is about 0.05.

7. The planar optical device of claim 6, wherein the planar optical device is an optical switch having liquid crystal switches located at intersecting waveguides.

8. The planar optical device of claim 7, wherein the planar optical device is a cross-connect optical switching device.

9. A method of forming a planar optical device on a silicon substrate, wherein the device includes a waveguide having a refractive index of from about 1.48 to about 1.52 at 1550 nm, and a coefficient of thermal expansion of from about 3×

10<sup>−

6</sup>°

C.<sup>−

1</sup> to about 4.4×

10<sup>−

6</sup>°

C.<sup>−

1</sup>, comprising;

depositing on a silicon substrate by plasma enhanced chemical vapor deposition a germanium-silicon oxide or oxynitride cladding layer having a Ge/(Si+Ge) mole ratio of from about 0.25 to about 0.47 and an N/(N+O) mole ratio of 0 to about 0. 1;

depositing on the cladding layer by plasma enhanced chemical vapor deposition a germanium-silicon oxide or oxynitride core layer having a Ge/(Si+Ge) mole ratio of from about 0.25 to about 0.47 and an N/(N+O) mole ratio of 0 to about 0. 1, wherein the refractive index of the core layer is higher than the refractive index of the cladding layer.

10. The method of claim 9 further comprising annealing the cladding layer and the core layer to a temperature greater than 1,000°

C. in an oxidizing atmosphere, and cooling the cladding layer and the core layer at a rate greater than 200°

C./hr to a temperature below the strain point of the glass.

11. The method of claim 9 wherein the core layer and the cladding layer are deposited by exposing a substrate to a reaction gas mixture including a silicon precursor, a germanium precursor, a nitrogen source, and optionally including a carrier gas, wherein the plasma is formed by two electrodes driven by separate RF power supplies and a region of the chamber that is grounded, and wherein the substrate is placed on one of the electrodes that is driven with a RF power supply having a frequency less than 1 MHz, and the other electrode is driven with a RF power supply having a frequency greater than 1 MHz.

13. The glass composition of claim 12 having a refractive index of from about 1.48 to about 1.52 at 1550 nm and a coefficient of thermal expansion at room temperature of from about 3×

10<sup>−

6</sup>°

C.<sup>−

1</sup> to about 4.4×

10<sup>−

6</sup>°

C.<sup>−

1</sup>.

15. The planar optical device of claim 14, wherein the planar optical device is an optical switch having liquid crystal switches located at intersecting waveguides.

16. The planar optical device of claim 15, wherein the planar optical device is a cross-connect optical switching device.

12. A glass composition, comprising:

silica-germania-titania having a Ge/(Si+Ge+Ti) mole ratio of from about 0.08 to about 0.17 and a Ti/(Si+Ge+Ti) mole ratio of from 0 to about 0.08.

14. A planar optical device comprising:

a waveguide core and waveguide cladding, wherein at least one of the waveguide core and the waveguide cladding is a silica-germania-titania glass having a Ge/(Si+Ge+Ti) mole ratio of from about 0.08 to about 0.17 and a Ti/(Si+Ge+Ti) mole ratio of from 0 to about 0.08.

17. A method of forming a planar optical device on a silicon substrate, comprising:

depositing on a silicon substrate by plasma enhanced chemical vapor deposition a silica-germania-titania cladding layer having a Ge/(Si+Ge+Ti) mole ratio of from about 0.08 to about 0.17 and a Ti/(Si+Ge+Ti) mole ratio of 0 to about 0.08; and

depositing on the cladding layer by plasma enhanced chemical vapor deposition a silica-germania-titania core layer having a Ge/(Si+Ge+Ti) mole ratio of from about 0.08 to about 0.17 and a Ti/(Si+Ge+Ti) mole ratio of from 0 to about 0.08, wherein the refractive index of the core layer is higher than the refractive index of the cladding layer,

wherein the device includes a waveguide having a refractive index of from about 1.48 to about 1.52 at 1550 nm and a coefficient of thermal expansion of from about 3×

10<sup>−

6</sup>°

C.<sup>−

1</sup> to about 4.4×

10<sup>−

6</sup>°

C.<sup>−

1</sup>.