Composite substrate for electro-optic element and method for manufacturing the same

Patent metadata

Field	Value
Publication number	US-12025864-B2
Application number	US-202117480870-A
Country	US
Kind code	B2
Filing date	Sep 21, 2021
Priority date	Nov 8, 2018
Publication date	Jul 2, 2024
Grant date	Jul 2, 2024

Abstract

A composite substrate for an electro-optic element is disclosed. The composite substrate includes: an electro-optic crystal substrate having an electro-optic effect; a low-refractive-index layer being in contact with the electro-optic crystal substrate and having a lower refractive index than the electro-optical crystal substrate; and a support substrate bonded to the low-refractive-index layer at least via a bonding layer. A plurality of interfaces located between the low-refractive-index layer and the support substrate includes at least one rough interface having a roughness that is larger than a roughness of an interface between the electro-optic crystal substrate and the low-refractive-index layer.

First claim

The invention claimed is:

1. A composite substrate for an electro-optic element, the composite substrate comprising:
an electro-optic crystal substrate having an electro-optic effect and being an offset substrate having a c-axis that is not parallel with the electro-optic substrate, the c-axis forming an angle less than 10 degrees with a plane parallel with the electro-optic crystal substrate;
a low-refractive-index layer in contact with the electro-optic crystal substrate and having a lower refractive index than the electro-optic crystal substrate; and
a support substrate bonded to the low-refractive-index layer at least via a bonding layer,
wherein a plurality of interfaces located between the low-refractive-index layer and the support substrate includes at least one rough interface having a roughness that is larger than a roughness of an interface between the electro-optic crystal substrate and the low-refractive-index layer,
wherein an arithmetic roughness average Ra of the at least one rough interface is in a range from 0.5 nm to 10 nm.

2. The composite substrate according to claim 1 , wherein a thickness of the low-refractive-index layer is in a range from 0.1 μm to 10 μm.

3. The composite substrate according to claim 1 , wherein a thickness of the electro-optic crystal substrate is in a range from 0.1 μm to 10 μm.

4. The composite substrate according to claim 1 , wherein the roughness of the at least one rough interface is at least three times the roughness of the interface between the electro-optic crystal substrate and the low-refractive-index layer.

5. The composite substrate according to claim 1 , wherein the roughness of the at least one rough interface is at least five times the roughness of the interface between the electro-optic crystal substrate and the low-refractive-index layer.

6. The composite substrate according to claim 1 , wherein
an arithmetic roughness average Ra of the interface between the electro-optic crystal substrate and the low-refractive-index layer is in a range from 0.03 nm to 0.5 nm.

7. The composite substrate according to claim 1 , wherein the at least one rough interface is an interface between the low-refractive-index layer and the bonding layer.

8. The composite substrate according to claim 7 , wherein an arithmetic roughness average Ra of the interface between the low-refractive-index layer and the bonding layer is at least one thousandth of a thickness of the low-refractive-index layer.

9. The composite substrate according to claim 7 , wherein
a thickness of the low-refractive-index layer is at least 0.5 μm.

10. The composite substrate according to claim 1 , wherein the at least one rough interface is an interface between the bonding layer and the support substrate.

11. The composite substrate according to claim 1 , further comprising an intermediate layer located between the low-refractive-index layer and the bonding layer, wherein the at least one rough interface is an interface between the intermediate layer and the bonding layer.

12. The composite substrate according to claim 1 , further comprising an intermediate layer located between the bonding layer and the support layer, wherein the at least one rough interface is an interface between the intermediate layer and the support layer.

13. The composite substrate according to claim 1 , further comprising a conductive layer comprising an electric conductor,
wherein the at least one rough interface includes one or more interfaces located between the electro-optic crystal substrate and the conductive layer.

14. The composite substrate according to claim 13 , wherein the conductive layer is at least a part of either the bonding layer or the intermediate layer.

15. The composite substrate according to claim 1 , wherein the electro-optic crystal substrate is a substrate of lithium niobate, lithium tantalate, potassium titanyl phosphate, potassium lithium niobate, potassium niobate, potassium tantalate niobate, or a solid solution of lithium niobate and lithium tantalate.

16. The composite substrate according to claim 1 , wherein the low-refractive-index layer comprises at least one substance selected from a group consisting of silicon oxide, tantalum oxide, aluminum oxide, magnesium fluoride, and calcium fluoride.

17. The composite substrate according to claim 1 , wherein the bonding layer comprises at least one substance selected from a group consisting of tantalum oxide, niobium oxide, silicon, aluminum oxide, titanium oxide, gold, silver, copper, aluminum, platinum, and an alloy containing at least two of the aforementioned metal elements.

18. The composite substrate according to claim 1 , wherein the support layer is a substrate comprising lithium niobate, lithium tantalate, silicon, glass, sialon, mullite, aluminum nitride, silicon nitride, magnesium oxide, sapphire, quartz, crystal, gallium nitride, silicon carbide, or gallium oxide.

19. The composite substrate according to claim 1 , wherein a reverse polarized portion is formed in the electro-optic crystal substrate.

20. A method of manufacturing a composite substrate for an electro-optic element, comprising:
forming a low-refractive-index layer on a surface of an electro-optic crystal substrate having an electro-optic effect, the low-refractive-index layer having a lower refractive index than the electro-optic crystal substrate, the electro-optic crystal substrate being an offset substrate having a c-axis that is not parallel with the electro-optic crystal substrate, the c-axis forming an angle less than 10 degrees with a plane parallel with the electro-optic crystal substrate;
forming a bonding layer on a surface of the low-refractive-index layer formed on the electro-optic crystal substrate; and
bonding a support substrate on a surface of the bonding layer formed on the low-refractive-index layer,
wherein a roughness of the surface of the low-refractive-index layer before the forming of the bonding layer is larger than a roughness of the surface of the electro-optic crystal substrate before the forming of the low-refractive-index layer,
wherein an arithmetic roughness average Ra of the surface of the low-refractive-index layer before the forming of the bonding layer is in a range from 0.5 nm to 10 nm.

21. The method according to claim 20 , further comprising smoothing the surface of the bonding layer between the forming of the bonding layer and the bonding of the support substrate.

22. The method according to claim 20 , wherein the forming of the low-refractive-index layer comprises forming the low-refractive-index layer by sputter deposition.

23. The method according to claim 20 , further comprising forming a bonding layer on a surface of the support substrate before the bonding of the support substrate.

Assignees

• Ngk Insulators Ltd

Inventors

• UNO Yudai
• Tai Tomoyoshi
• Kondo Jungo

Classifications

• G02B2006/12142

  Modulator · CPC title

• G02F1/03 Primary

  based on ceramics or electro-optical crystals, e.g. exhibiting Pockels effect or Kerr effect (G02F1/061 takes precedence) · CPC title

• G02B6/122

  Basic optical elements, e.g. light-guiding paths · CPC title

• G02B6/134

  by substitution by dopant atoms · CPC title

• G02B6/12

  of the integrated circuit kind (electric integrated circuits H10B, H10D84/00 - H10D89/00, H10F19/00, H10F39/00, H10H29/00, H10K19/00, H10K39/00, H10K59/00, H10N19/00, H10N39/00, H10N59/00, H10N69/00, H10N79/00, H10N89/00) · CPC title