Optical waveguide element and method of fabrication thereof

• US 6,816,660 B2
• Filed: 05/16/2002
• Issued: 11/09/2004
• Est. Priority Date: 05/22/2001
• Status: Expired due to Fees

• Current Assignee: EpiPhotonics Corp.
• Original Assignee: Nozomi Photonics Co., Ltd.
• Inventors: Nashimoto, Keiichi
• Primary Examiner(s): Ullah, Akm Enayet
• Assistant Examiner(s): Rahll, Jerry T
• Application Number:
  US10/146,062
• Publication Number:
  US 20020176679A1
• Time in Patent Office: 908 Days
• Field of Search: 385/43, 385/129-132, 385/49
• US Class Current: 385/131
• CPC Class Codes: G02B 2006/12097 Ridge, rib or the like
• CPC Class Codes: G02B 2006/12195 Tapering
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/131 by using epitaxial growth epitaxial growth for semiconductors H01L21/02365
• CPC Class Codes: G02B 6/305 and having an integrated mode-size expanding section, e.g. tapered waveguide

Abstract

A ridge type channel optical waveguide is formed in an optical waveguide layer. A cladding layer having a refractive index smaller than that of the optical waveguide layer and having a width substantially the same as that of the channel optical waveguide and having a thickness which increases in a tapered manner toward an end surface, is formed above both of a light entering end portion and a light exiting end portion of the channel optical waveguide. By the cladding layer, a mode field diameter in a direction orthogonal to a substrate surface can be enlarged, and a coupling loss with an optical fiber can be greatly reduced. Further, loss due to mode mismatching can be prevented by a light confining effect.

Claims

1. An optical waveguide element comprising:

an optical waveguide layer having a ridge type channel optical waveguide; and

a cladding layer provided above at least one of a light entering end portion and a light exiting end portion of the channel optical waveguide of a surface of the optical waveguide layer, the cladding layer having substantially the same width as the channel optical waveguide, and having a refractive index which is smaller than a refractive index of the optical waveguide layer, and having a tapered configuration in which a thickness of the cladding layer increases toward an end surface and the width of the channel optical waveguide is increasing at the end surface.

2. The optical waveguide element of claim 1, wherein a difference in refractive indices of the optical waveguide layer and the cladding layer is from 0.001 or more to 0.05 or less.

3. The optical waveguide element of claim 1, wherein a width, of the channel optical waveguide, at at least one of the light entering end portion and the light exiting end portion increases toward the end surface.

4. The optical waveguide element of claim 3, wherein a width, of the channel optical waveguide, at an end portion is 5 μ

m or more.

5. The optical waveguide element of claim 1, wherein a thickness, of the cladding layer, at an end portion is 1 μ

m or more.

6. The optical waveguide element of claim 1, wherein a length of a taper-shaped section of the cladding layer is from 50 μ

m or more to 5000 μ

m or less.

7. The optical waveguide element of claim 1, wherein at least one of the optical waveguide layer and the cladding layer is formed of an oxide which has been epitaxially grown.

8. The optical waveguide element of claim 1, wherein at least one of the optical waveguide layer and the cladding layer is formed of a ferroelectric having an electro-optical effect.

9. The optical waveguide element of claim 1, wherein at least one of the optical waveguide layer and the cladding layer is formed from Pb_1-xLa_x(Zr_yTi_1-y)_1-x/4O₃ (0<

x<

0.3, 0<

y<

0).

10. The optical waveguide element of claim 1, wherein the optical waveguide layer is formed on a single crystal substrate via a buffer layer having a refractive index which is smaller than a refractive index of the optical waveguide layer.

11. The optical waveguide element of claim 10, wherein the single crystal substrate is formed by an SrTiO₃ substrate doped with an impurity element.

12. A method of fabricating an optical waveguide element, comprising the steps of:

(a) forming, on a surface of an optical waveguide layer having a ridge type channel optical waveguide and formed by epitaxial growth, an amorphous thin film whose refractive index after epitaxial growth is smaller than a refractive index of the optical waveguide layer;

(b) reshaping the amorphous thin film such that a taper-shaped portion, which has substantially the same width as a width of a channel optical waveguide and has a thickness which increases toward an end surface, remains above at least one of a light entering end portion and a light exiting end portion of the channel optical waveguide; and

(c) forming a taper type cladding layer by solid phase epitaxially growing the reshaped amorphous thin film by heating the reshaped amorphous thin film.

13. The method of claim 12, wherein the step (b) of reshaping includes the sub-steps of:

(i) forming a resist film having a specific opening pattern, on the amorphous thin film; and

(ii) etching the amorphous thin film by using the resist film.

14. The method of claim 13, wherein the sub-step (ii) of etching is carried out in a state in which a taper formation promoting layer, whose speed of being etched is greater than a speed of being etched of the amorphous thin film, is provided between the amorphous thin film and the resist film.

15. The method of claim 13, wherein the etching is carried out by a wet etching method.

16. A method of fabricating an optical waveguide element, comprising the steps of:

(a) forming, by epitaxial growth and on a surface of a slab type optical waveguide layer formed by epitaxial growth, a slab type cladding layer whose refractive index is smaller than a refractive index of the optical waveguide layer;

(b) forming a taper type cladding layer by reshaping the slab type cladding layer such that a taper-shaped portion, which has substantially the same width as a width of a channel optical waveguide and has a thickness which increases toward an end surface, remains above at least one of a light entering end portion and a light exiting end portion at which the channel optical waveguide is to be formed; and

(c) forming a ridge type channel optical waveguide by reshaping the slab type optical waveguide layer into a predetermined channel pattern having a width that is increasing at the end surface.

17. The method of claim 16, wherein the step (b) of forming the cladding layer includes the sub-steps of:

(i) forming, on the slab type cladding layer, a resist film which has a specific opening pattern and whose film thickness varies gradually; and

(ii) etching the slab type cladding layer by using the resist film.

18. The method of claim 16, wherein the etching is carried out by using a dry etching method.

19. An optical waveguide element comprising:

an optical waveguide layer having a ridge type channel optical waveguide; and

a cladding layer provided above at least one of a light entering end portion and a light exiting end portion of the channel optical waveguide of a surface of the optical waveguide layer, the cladding layer having substantially the same width as the channel optical waveguide, and having a refractive index which is smaller than a refractive index of the optical waveguide layer, and having a tapered configuration in which a thickness of the cladding layer increases toward an end surface,

wherein a difference in refractive indices of the optical waveguide layer and the cladding layer is from 0.001 or more to 0.05 or less.

20. An optical waveguide element comprising:

an optical waveguide layer having a ridge type channel optical waveguide; and

a cladding layer provided above at least one of a light entering end portion and a light exiting end portion of the channel optical waveguide of a surface of the optical waveguide layer, the cladding layer having substantially the same width as the channel optical waveguide, and having a refractive index which is smaller than a refractive index of the optical waveguide layer, and having a tapered configuration in which a thickness of the cladding layer increases toward an end surface,

wherein at least one of the optical waveguide layer and the cladding layer is formed of a ferroelectric having an electro-optical effect.

21. An optical waveguide element comprising:

an optical waveguide layer having a ridge type channel optical waveguide; and

a cladding layer provided above at least one of a light entering end portion and a light exiting end portion of the channel optical waveguide of a surface of the optical waveguide layer, the cladding layer having substantially the same width as the channel optical waveguide, and having a refractive index which is smaller than a refractive index of the optical waveguide layer, and having a tapered configuration in which a thickness of the cladding layer increases toward an end surface,

wherein at least one of the optical waveguide layer and the cladding layer is formed from Pb_1-xLa_x(Zr_yTi_1-y)_1-x/4O₃ (0<

x<

0.3, 0<

y<

0).

22. An optical waveguide element comprising:

an optical waveguide layer having a ridge type channel optical waveguide; and

a cladding layer provided above at least one of a light entering end portion and a light exiting end portion of the channel optical waveguide of a surface of the optical waveguide layer, the cladding layer having substantially the same width as the channel optical waveguide, and having a refractive index which is smaller than a refractive index of the optical waveguide layer, and having a tapered configuration in which a thickness of the cladding layer increases toward an end surface,

wherein the optical waveguide layer is formed on a single crystal substrate via a buffer layer having a refractive index which is smaller than a refractive index of the optical waveguide layer, and

wherein the single crystal substrate is formed by an SrTiO₃ substrate doped with an impurity element.