Optical delay element

• US 20060083472A1
• Filed: 03/23/2005
• Published: 04/20/2006
• Est. Priority Date: 03/24/2004
• Status: Active Grant

• Current Assignee: Ricoh Company Limited, Toshihiko Baba
• Original Assignee: Ricoh Company Limited, Toshihiko Baba
• Inventors: Sakai, Atsushi, Funato, Hiroyoshi, Baba, Toshihiko, Katoh, Ikuo
• Granted Patent: US 7,242,839 B2
• Time in Patent Office: Days
• US Class Current: 385/129
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 6/1225 comprising photonic band-gap structures or photonic lattices

Abstract

An optical delay element including a photonic crystal line defect optical waveguide is disclosed that has a large group refractive index and has small or nearly constant wavelength dispersion of the group refractive index in a wide wavelength region for practical use. The optical delay element includes a line defect optical waveguide formed in a photonic crystal structure, and the volume of the line defect optical waveguide is less than the volume of a single line defect optical waveguide. Thereby, the waveguide band of the line defect optical waveguide has two zero points in the third order dispersion curve of the line defect optical waveguide, and the sign of the third order dispersion curve is inverted near the zero points. Therefore, the waveguide band of the line defect optical waveguide is modified, and this enables expansion of the wavelength region having a large group refractive index, small wavelength dispersion of the group refractive index, and small wavelength dispersion of the speed of optical pulses.

Claims

1. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a volume of the line defect optical waveguide being different from a volume of another line defect optical waveguide formed from a single line defect photonic crystal, a waveguide band of said line defect optical waveguide having a refractive index confinement mode and a photonic bandgap confinement mode, and the line defect optical waveguide guiding light of a frequency higher than a frequency corresponding to the photonic bandgap confinement mode.

9. The optical delay element as claimed in claim 1, wherein

a waveguide band of the line defect optical waveguide has a first zero point and a second zero point in a third order dispersion curve of the line defect optical waveguide, a sign of the third order dispersion curve is inverted near the first zero point and the second zero point, the first zero point corresponds to a first frequency, and the second zero corresponds to a second frequency lower than the first frequency;

and

the line defect optical waveguide guides light having a frequency near the first frequency or the second frequency and lower than the first frequency.

12. The optical delay element as claimed in claim 1, wherein a portion of the line defect optical waveguide has a varying refractive index.

13. The optical delay element as claimed in claim 12, wherein the refractive index of the line defect optical waveguide varies in response to electric field application.

14. The optical delay element as claimed in claim 12, wherein the refractive index of the line defect optical waveguide varies in response to light irradiation.

15. The optical delay element as claimed in claim 12, wherein the refractive index of the line defect optical waveguide varies in response to a temperature change.

16. The optical delay element as claimed in claim 1, wherein the line defect optical waveguide is a photonic crystal slab line defect optical waveguide formed by arranging a two-dimensional photonic crystal structure on a thin film having a thickness approximately equaling a wavelength of the light.

17. The optical delay element as claimed in claim 16, wherein a width of the line defect optical waveguide is varied by moving the photonic crystal structures on two sides of the line defect optical waveguide.

18. The optical delay element as claimed in claim 16, wherein a thickness of the photonic crystal slab line defect optical waveguide is different from a photonic crystal slab constituting the photonic crystal structure.

19. The optical delay element as claimed in claim 16, wherein a refractive index of the line defect optical waveguide is different from a refractive index of the photonic crystal structure portion.

20. The optical delay element as claimed in claim 16, wherein a portion of the line defect optical waveguide has a varying refractive index.

21. The optical delay element as claimed in claim 16, wherein each of an upper cladding portion and a lower cladding portion of the line defect optical waveguide has a refractive index greater than a refractive index of the photonic crystal structure portion.

22. The optical delay element as claimed in claim 1, wherein the line defect optical waveguide is formed from an electro-optical material.

23. The optical delay element as claimed in claim 1, wherein the line defect optical waveguide is formed from a non-linear optical material.

24. The optical delay element as claimed in claim 16, wherein the two-dimensional photonic crystal structure is formed on a thin semiconductor substrate.

25. The optical delay element as claimed in claim 16, wherein the two-dimensional photonic crystal structure is formed on a SOI (silicon-on-insulator) substrate.

26. The optical delay element as claimed in claim 16, wherein the two-dimensional photonic crystal structure is formed on a thin substrate made of an electro-optical material.

27. The optical delay element as claimed in claim 16, wherein the two-dimensional photonic crystal structure is formed on a thin substrate made of a non-linear optical material.

28. The optical delay element as claimed in claim 16, wherein the two-dimensional photonic crystal structure is formed on a composite substrate made of a thin semiconductor film, a thin film made of an electro-optical material, or a non-linear optical material.

2. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a volume of the line defect optical waveguide being less than a volume of another line defect optical waveguide formed from a single line defect photonic crystal, a waveguide band of said line defect optical waveguide having a refractive index confinement mode and a photonic bandgap confinement mode, and the line defect optical waveguide guiding light of a frequency higher than a frequency corresponding to the photonic bandgap confinement mode.

3. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a refractive index of the line defect optical waveguide being different from a refractive index of the photonic crystal structure portion, a waveguide band of said line defect optical waveguide having a refractive index confinement mode and a photonic bandgap confinement mode, and the line defect optical waveguide guiding light having a frequency higher than a frequency corresponding to the photonic bandgap confinement portion of the waveguide band.

4. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a structure different from the photonic crystal structure being provided near the line defect optical waveguide, a waveguide band of said line defect optical waveguide having a refractive index confinement mode and a photonic bandgap confinement mode, and the line defect optical waveguide guiding light having a frequency higher than a frequency corresponding to the photonic bandgap confinement portion of the waveguide band.

5. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a volume of the line defect optical waveguide being different from a volume of another line defect optical waveguide formed from a single line defect photonic crystal, a waveguide band of the line defect optical waveguide having a first zero point and a second zero point in a third order dispersion curve of the line defect optical waveguide of the line defect optical waveguide, a sign of the third order dispersion curve being inverted near the first zero point and the second zero point, the first zero point corresponding to a first frequency, the second zero corresponding to a second frequency lower than the first frequency, and the line defect optical waveguide guiding light having a frequency near the second frequency.

10. The optical delay element as claimed in claim 5, wherein the line defect optical waveguide guides light having a frequency near the first frequency or the second frequency and lower than the first frequency.

11. The optical delay element as claimed in claim 10, wherein

the waveguide band has a refractive index confinement mode and a photonic bandgap confinement mode;

and

the line defect optical waveguide guides light having a frequency higher than a frequency corresponding to the photonic bandgap confinement mode.

6. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a volume of the line defect optical waveguide being less than a volume of another line defect optical waveguide formed from a single line defect photonic crystal, a waveguide band of the line defect optical waveguide having a first zero point and a second zero point in a third order dispersion curve of the line defect optical waveguide, a sign of the third order dispersion curve being inverted near the first zero point and the second zero point, the first zero point corresponding to a first frequency, the second zero corresponding to a second frequency lower than the first frequency, and the line defect optical waveguide guiding light having a frequency near the second frequency.

7. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a refractive index of the line defect optical waveguide being different from a refractive index of the photonic crystal structure portion, a waveguide band of the line defect optical waveguide having a first zero point and a second zero point in a third order dispersion curve of the line defect optical waveguide, a sign of the third order dispersion curve being inverted near the first zero point and the second zero point, the first zero point corresponding to a first frequency, the second zero corresponding to a second frequency lower than the first frequency, and the line defect optical waveguide guiding light having a frequency near the second frequency.

8. An optical delay element, comprising:

a line defect optical waveguide formed in a photonic crystal structure, a structure different from the photonic crystal structure being provided near the line defect optical waveguide, a waveguide band of the line defect optical waveguide having a first zero point and a second zero point in a third order dispersion curve of the line defect optical waveguide, a sign of the third order dispersion curve being inverted near the first zero point and the second zero point, the first zero point corresponding to a first frequency, the second zero corresponding to a second frequency lower than the first frequency, and the line defect optical waveguide guiding light having a frequency near the second frequency.