Electro-optic modulator

• US 20040228565A1
• Filed: 04/19/2004
• Published: 11/18/2004
• Est. Priority Date: 04/24/2003
• Status: Active Grant

• Current Assignee: Seikoh Giken Company Limited
• Original Assignee: NEC Tokin Corporation (Yageo Corporation)
• Inventors: Sato, Masahiro
• Granted Patent: US 7,123,784 B2
• Time in Patent Office: Days
• US Class Current: 385/3
• CPC Class Codes: G02F 1/035 in an optical waveguide structure
• CPC Class Codes: G02F 1/212 Mach-Zehnder type
• CPC Class Codes: G02F 1/225 in an optical waveguide structure
• CPC Class Codes: G02F 2201/07 buffer layer
• CPC Class Codes: G02F 2203/21 Thermal instability, i.e. DC drift, of an optical modulator; Arrangements or methods for the reduction thereof

Abstract

An electro-optic modulator (300) comprises a substrate (310) made of a material which has an electro-optic effect and a pyroelectric effect. In the substrate (310), an optical waveguide (320) is formed to have at least a pair of optical paths. On the substrate (310) and on the optical waveguide (320), a transparent buffer layer (330) is formed to cover the optical waveguide (320). On the buffer layer (330), first and second electrodes (341, 342) are formed so that the first and the second electrodes (341, 342) are arranged to cause refractive index changes in the pair of optical paths in response to electrical fields surrounding the electro-optic modulator (300). The buffer layer (330) is a mutual diffusion layer. The mutual diffusion layer is made from laminated films comprised of at least one transparent insulator film and at least one transparent conductor film but has no clear boundary between the transparent insulator film and the transparent conductor film.

Claims

1. An electro-optic modulator comprising:

a substrate made of a material which has an electro-optic effect;

an optical waveguide which comprises at least a pair of optical paths and is formed in the substrate;

a buffer layer which is transparent and is formed on the substrate and on the optical waveguide, wherein the buffer layer is a mutual diffusion layer made from laminated films which comprise at least one transparent insulator film and at least one transparent conductor film; and

electrodes which are formed on the buffer layer and are arranged to cause refractive index changes in the pair of optical paths in response to electrical fields surrounding the electro-optic modulator.

2. The electro-optic modulator according to claim 1, wherein the buffer layer has a sheet resistance ranging from 10⁶ to 10⁷ ohms per square.

3. The electro-optic modulator according to claim 1, wherein the laminated films comprise a plurality of transparent insulator films and a plurality of transparent conductor films.

4. The electro-optic modulator according to claim 1, wherein the buffer layer has a structure in which there is no clear boundary between the transparent insulator film and the transparent conductor film.

5. The electro-optic modulator according to claim 1, wherein the buffer layer has a distribution of sheet resistances in a thickness direction of the buffer layer.

6. The electro-optic modulator according to claim 1, wherein the buffer layer is a layer obtainable by laminating the transparent insulator film(s) and the transparent conductor film(s) to form laminated films, followed by mutually diffusing the laminated films into each other by means of annealing the laminated films.

7. The electro-optic modulator according to claim 1, wherein the transparent insulator film is made of a transparent insulator oxide.

8. The electro-optic modulator according to claim 7, wherein the transparent insulator oxide is made of at least one of SiO₂, borosilicate glass, Al₂O₃, TiO₂, and ZrO₂.

9. The electro-optic modulator according to claim 1, wherein transparent conductor film is made of a transparent conductor oxide.

10. The electro-optic modulator according to claim 9, wherein the transparent conductor oxide is made of at least one of ITO, SnO₂ and ZnO.

11. An electrical-field sensor comprising:

the electro-optic modulator according to claim 1;

a light source optically coupled to the electro-optic modulator; and

a photodetector optically coupled to the electro-optic modulator.

12. A method of fabricating an electro-optic modulator, comprising steps of:

forming an optical waveguide in a substrate, wherein the substrate is made of a material which has an electro-optic effect, and the optical waveguide comprises at least a pair of optical paths;

laminating at least one transparent insulator film and at least one transparent conductor film to form laminated films on the substrate and on the optical waveguide;

mutually diffusing the laminated films into each other to form a buffer layer on the substrate and on the optical waveguide, wherein the buffer layer is transparent; and

forming electrodes on the buffer layer, wherein the electrodes are arranged to cause refractive index changes in the pair of optical paths in response to electrical fields surrounding the electro-optic modulator.

13. The method according to claim 12, wherein the laminating step comprises steps of:

forming the transparent insulator film; and

forming the transparent conductor film, wherein the forming step of the transparent insulator film and the forming step of the transparent conductor film are carried out separately from each other.

14. The method according to claim 13, wherein the forming step of the transparent insulator film is carried out by means of vacuum deposition, vacuum evaporation, ion plating or sputtering.

15. The method according to claim 13, wherein the forming step of the transparent conductor film is carried out by means of vacuum deposition, vacuum evaporation, ion plating or sputtering.

16. The method according to claim 13, wherein the forming step of the transparent insulator film and the forming step of the transparent conductor film are alternately carried out to form the laminated films.

17. The method according to claim 12, wherein the transparent insulator film and the transparent conductor film each has a thickness of from 20 nm to 200 nm.

18. The method according to claim 12, wherein the mutually diffusing step comprises step of annealing the laminated films.

19. The method according to claim 18, wherein the annealing step is carried out between 500 to 600 degrees centigrade in oxygen atmosphere.

20. The method according to claim 12, wherein the transparent insulator film is made of at least one of SiO₂, borosilicate glass, Al₂O₃, TiO₂, and ZrO₂.

21. The method according to claim 12, wherein the transparent conductor film is made of at least one of ITO, SnO₂ and ZnO.

22. The method according to claim 12, wherein the sheet resistance of the buffer layer is adjusted to lie in a range from 10⁶ to 10⁷ ohms per square, by the number of the transparent insulator films, the number of the transparent conductor films, a thickness of each film, annealing conditions or one of combinations thereof.