Optical waveguide and method for producing same

• US 20040047539A1
• Filed: 11/21/2002
• Published: 03/11/2004
• Est. Priority Date: 10/27/1998
• Status: Active Grant

• Current Assignee: Akihiko Okubora, Tsuyoshi Ogawa
• Original Assignee: Akihiko Okubora, Tsuyoshi Ogawa
• Inventors: Ogawa, Tsuyoshi, Okubora, Akihiko
• Granted Patent: US 7,163,598 B2
• Time in Patent Office: Days
• US Class Current: 385/14
• CPC Class Codes: G02B 6/13 Integrated optical circuits characterised by the manufacturing method
• CPC Class Codes: Y10T 428/24868 Translucent outer layer
• CPC Class Codes: Y10T 428/2804 Next to metal

Abstract

An optical waveguide having a optical waveguide path capable of securing a high light propagation characteristic regardless of the type of a supporting base, provided with a multilayer circuit board, an optical waveguide path arranged on the multilayer circuit board, a light receiving element, IC chips, and a light emitting element, the optical waveguide path formed on a transparent substrate excellent in flatness and transferred to the multilayer circuit board. The light propagation loss becomes small, and a signal to be transmitted at a high speed being transmitted as a light signal and a signal which can be transmitted at a relatively low speed being transmitted as an electrical signal, whereby the signal propagation delay which becomes the problem when a signal is transmitted by only electrical wiring is overcome, and the influence of electromagnetic noise becomes small.

Claims

1. An optical waveguide comprising:

a substrate; and

an optical waveguide path which is separately formed so that the light signal is propagated inside it and is arranged on and secured to the substrate.

2. An optical waveguide as set forth in claim 1, further comprising electrical wiring formed on the substrate.

3. An optical waveguide as set forth in claim 1, further comprising on said substrate

at least one of a light emitting element for converting an electrical signal to a light signal and

a light receiving element for converting a light signal to an electrical signal.

4. An optical waveguide as set forth in claim 3, further comprising on said substrate an integrated circuit for transferring an electrical signal with said at least one of the light emitting element and light receiving element.

5. An optical waveguide as set forth in claim 1, wherein said optical waveguide path is formed on another substrate different from said substrate and transferred from that other substrate to said substrate.

6. An optical waveguide as set forth in claim 1, wherein said optical waveguide path comprises at least at one end with a light reflecting portion having at least one of a function of reflecting a light signal from the outside into the optical waveguide path and has a function of reflecting a light signal propagated through said optical waveguide path out of the optical waveguide path.

7. An optical waveguide as set forth in claim 6, wherein the optical waveguide path comprises a core layer and a cladding layer and

wherein the light reflecting portion has at least at one end of the core layer.

8. An optical waveguide as set forth in claim 2, further comprising on said substrate:

at least one of a light emitting element for converting an electrical signal to a light signal;

at least one of a light receiving element for converting a light signal to an electrical signal; and

an integrated circuit for transferring an electrical signal with said at least one of the light emitting element and light receiving element,

said optical waveguide path being formed at least at one end with a light reflecting portion for inputting or outputting a light signal.

9. An optical waveguide as set forth in claim 8, wherein the electrical wiring on the substrate transfers electric power to said at least one of a light emitting element and light receiving element and the integrated circuit.

10. An optical waveguide as set forth in claim 8, wherein the electrical wiring on the substrate is for electrically connecting said at least one of a light emitting element and light receiving element and the integrated circuit.

11. An optical waveguide as set forth in claim 8, wherein said substrate comprises a multilayer circuit board having a plurality of electrical wiring layers stacked via insulators.

12. An optical waveguide as set forth in claim 8, wherein said optical waveguide path comprises a first cladding layer formed on said substrate, a core layer stacked on said first cladding layer, and a second cladding layer stacked on said core layer.

13. An optical waveguide as set forth in claim 12, wherein said first cladding layer functions as said bonding layer.

14. An optical waveguide as set forth in claim 8, wherein said bonding layer comprises a photo-curing resin.

15. An optical waveguide as set forth in claim 8, wherein said bonding layer comprises a heat-curing resin.

16. An optical waveguide as set forth in claim 8, wherein said at least one of a light emitting element and light receiving element and the integrated circuit are connected by connection electrodes to the electrical wiring on the substrate.

17. An optical waveguide as set forth in claim 16, wherein the connection electrodes comprise spherical bodies made of an electroconductive material coated with a solder.

18. An optical waveguide as set forth in claim 16, wherein said connection electrodes comprise a solder mainly of lead (Pb) and tin (Sn).

19. An optical waveguide as set forth in claim 8, wherein said optical waveguide path is one which transmits a transmitted signal at a first rate and the electrical wiring of the substrate is one which transmits a transmitted signal at a second rate slower than the first rate.

20. An optical waveguide as set forth in claim 8, wherein said light emitting element, light receiving element, and integrated circuit are arranged on said substrate using said optical waveguide path as a spacer interposed between it and the substrate.

21. An optical waveguide as set forth in claim 8, wherein said light reflecting portion

comprises of an inclined surface formed at least at one end of said optical waveguide path and

has at least one of a function of reflecting a light signal from the outside into the optical waveguide path and a function of reflecting a light signal propagated through said optical waveguide path outside of said optical waveguide path.

22. An optical waveguide as set forth in claim 21, wherein said inclined surface is inclined approximately 45°

with respect to a direction of light propagation in said optical waveguide path.

23. An optical waveguide as set forth in claim 11, wherein said insulator of said multilayer circuit board comprises an inorganic material including at least one material selected from the group comprising alumina (Al₂O₃), a glass ceramic, aluminum nitride (AlN), and mullite.

24. An optical waveguide as set forth in claim 11, wherein the insulator of said multilayer circuit board comprises an organic material including at least one material selected from the group comprising a glass epoxy resin, a polyimide, BT resin, polyphenyl ether (PPE) resin, phenol resin, and polyolefin resin.

25. A method of producing an optical waveguide including the steps of:

forming an optical waveguide path using a first substrate as a supporting base;

securing the optical waveguide path supported by the first substrate and a second substrate; and

removing the first substrate so as to transfer the optical waveguide path to the second substrate.

26. A method of producing an optical waveguide as set forth in claim 25, wherein the step of securing the optical waveguide path and the second substrate uses an adhesive.

27. A method of producing an optical waveguide as set forth in claim 26, wherein a photo-curing resin is used as the adhesive.

28. A method of producing an optical waveguide as set forth in claim 27, wherein a substrate comprised of a light transmitting material is used as the first substrate and the photo-curing resin is cured by irradiating light through the first substrate.

29. A method of producing an optical waveguide as set forth in claim 26, wherein the step of forming the optical waveguide path and the step of securing the optical waveguide path and the second substrate include:

a step of forming a core layer,

a step of forming a resin layer serving as a cladding layer so as to surround the core layer,

a step of using the resin layer in the uncured state as the adhesive and bonding together the optical waveguide path supported by the first substrate and the second substrate, and

a step of curing the resin layer to form the cladding layer and simultaneously completing the securing of the optical waveguide path to the second substrate.

30. A method of producing an optical waveguide as set forth in claim 25, wherein said step of forming the optical waveguide path includes a step of forming a substrate separation layer between said first substrate and said optical waveguide path so as to enable the first substrate to be separated from said optical waveguide path in a later step and

wherein, in the step of transferring the optical waveguide path to the second substrate, the substrate separation layer is removed to remove the first substrate.

31. A method of producing an optical waveguide as set forth in claim 30, wherein said substrate separation layer is formed by silicon dioxide (SiO₂).

32. A method of producing an optical waveguide as set forth in claim 25, wherein

a substrate comprised of a material which is dissolved by a predetermined solution is used as the first substrate and

in the step of transferring the optical waveguide path to the second substrate, the first substrate is dissolved so as to remove it.

33. A method of producing an optical waveguide as set forth in claim 32, wherein the solution is a not more than 5 volt hydrofluoric acid (HF) solution and the dissolvable material is a photosensitive glass.

34. A method of producing an optical waveguide as set forth in claim 25, wherein the step of forming the optical waveguide path on the first substrate includes a step of forming a plurality of optical waveguide paths spaced from each other and

wherein the step of securing the optical waveguide path and the second substrate includes:

a step of bonding the second substate to the optical waveguide paths through an adhesive comprised of a photo-curing resin,

a step of irradiating light to the bonding layer through the first substrate to selectively expose and cure only regions of the bonding layer corresponding to the optical waveguide paths, and

a step of removing the uncured photo-curing resin on the second substrate.

35. A method of producing an optical waveguide as set forth in claim 34, wherein before the step of bonding the second substrate to the optical waveguide paths, the following step is carried out:

a step of forming a light blocking film at the regions of the first substrate other than the regions where the optical waveguide paths are formed and the side surfaces of the optical waveguide paths,

the light blocking film being used as a mask for selective exposure.

37. A method of producing an optical waveguide as set forth in claim 25, further comprising a step of forming on said second substrate at least one of a light emitting element for converting an electrical signal to a light signal and a light receiving element for converting a light signal to an electrical signal.

38. A method of producing an optical waveguide as set forth in claim 37, further comprising a step of forming on said second substrate an integrated circuit for transferring an electrical signal with said at least one of the light emitting element and light receiving element.

39. A method of producing an optical waveguide as set forth in claim 25, wherein said second substrate comprises an electrical circuit board formed with electrical wiring.

40. A method of producing an optical waveguide as set forth in claim 39, further comprising:

a step of forming on said second substrate at least one of a light emitting element for converting an electrical signal to a light signal and a light receiving element for converting a light signal to an electrical signal; and

a step of forming on said second substrate an integrated circuit for transferring an electrical signal with said at least one of the light emitting element and light receiving element.

41. A method of producing an optical waveguide as set forth in claim 40, further comprising a step of sealing said at least one of a light emitting element and light receiving element and said integrated circuit by a sealing resin material.

42. A method of producing an optical waveguide as set forth in claim 40, wherein said step of forming an optical waveguide path using said first substrate as a supporting base includes:

a step of forming a substrate separation layer on said first substrate so as to enable the first substrate and the optical waveguide path to be separated,

a step of forming an optical waveguide path on said substrate separation layer, and

a step of forming at inclined surface at least at one end of the optical waveguide path.

43. A method of producing an optical waveguide as set forth in claim 42, wherein said step of forming said optical waveguide path includes:

a step of forming a first cladding layer on said substrate separation layer,

a step of forming a core layer on said first cladding layer, and

a step of forming a second cladding layer on said core layer.

44. A method of producing an optical waveguide as set forth in claim 40, wherein a multilayer circuit board is used as said second substrate, the multilayer circuit containing at least one type of inorganic material selected from the group comprising alumina (Al₂O₃), a glass ceramic, aluminum nitride (AIN), and mullite.

45. A method of producing an optical waveguide as set forth in claim 40, wherein a multilayer circuit board is used as said second substrate, the multilayer circuit containing at least one type of organic material selected from the group comprising a glass epoxy resin, a polyimide, BT resin, polyphenyl ether (PPE) resin, phenol resin, and polyolefin resin.

46. A method of producing an optical waveguide as set forth in claim 40, wherein said second substrate comprises a core substrate and a printed substrate formed on at least one surface of the core substrate and printed with electrical wiring patterns.

47. A method of producing an optical waveguide as set forth in claim 43, wherein the material for forming the first and second cladding layers, has a refractive index of light smaller than that of the material forming the core layer.

48. A method of producing an optical waveguide as set forth in claim 43, wherein the material forming the first and second cladding layers includes as a main ingredient at least one material selected from the group comprising a polyimide, epoxy resin, acryl resin, polyolefin resin, and synthetic rubber.

49. A method of producing an optical waveguide as set forth in claim 42, wherein the material forming the substrate separation layer includes silicon dioxide (SiO₂) .

50. A method of producing an optical waveguide as set forth in claim 42, wherein the material forming the substrate separation layer includes an etchable metal material.

51. A method of producing an optical waveguide as set forth in claim 42, wherein said step of forming an inclined surface at least at one end of the optical waveguide path includes:

a step of coating the optical waveguide path with a photoresist and exposing and developing the photoresist so as to form a desired photoresist pattern,

a step of inclining an edge region of the photoresist pattern,

a step of using the photoresist pattern as a mask and anistropically etching the portion of the optical waveguide path exposed from the edge region of the photoresist pattern to make the end of the optical waveguide path a tapered inclined surface, and

a step of removing the photoresist pattern.

52. A method of producing an optical waveguide as set forth in claim 42, wherein said step of forming an inclined surface at least at one end of the optical waveguide path includes:

a step of vapor depositing on the optical waveguide path a metal film,

a step of coating the metal film with a photoresist and exposing and developing the photoresist so as to form a desired photoresist pattern,

a step of using the photoresist pattern as a mask and etching the metal film to form a desired pattern,

a step of using the metal film as a mask and irradiating a laser beam on a predetermined region of the optical waveguide path from a predetermined angle to cut the optical waveguide path, and

a step of removing the metal film by etching and cleaning the processed product as a whole.

53. A method of producing an optical waveguide as set forth in claim 42, wherein said step of forming an inclined surface at least at one end of the optical waveguide path includes:

a step of heating a heat tool having an inclined surface at its tip and pressing the tip of the heat tool into the optical waveguide path so as to form said inclined surface in the optical waveguide path and

a step of removing the heat tool and then polishing off scum produced at the melted portion of the optical waveguide path.

54. A method of producing an optical waveguide as set forth in claim 42, wherein said step of forming an inclined surface at least at one end of the optical waveguide path includes:

a step of cutting the first substrate at a predetermined angle and

a step of polishing an end surface formed by the cutting of the first substrate so as to form the end surface of the optical waveguide path into an inclined surface.

55. A method of producing an optical waveguide as set forth in claim 40, wherein,

a substrate comprised of a light transmitting material able to pass light is used as the first substrate, and

wherein said step of securing the second substrate to the optical waveguide path includes:

a step of forming at a predetermined position on the second substrate a bonding layer comprised of a photo-curing resin which cures by irradiation of light,

a step of bringing the bonding layer of the second substrate into close contact with the optical waveguide path formed on the first substrate, and

a step of irradiating light from the back of the first substrate toward the second substrate to cure the bonding layer.

56. A method of producing an optical waveguide as set forth in claim 40, wherein said step of securing the second substrate to the optical waveguide path includes:

a step of forming at a predetermined position on the second substrate a bonding layer comprised of a heat-curing resin,

a step of bringing the bonding layer of the second substrate into close contact with the optical waveguide path formed on the first substrate, and

a step of heating the first substrate and the second substrate as a whole to cure the bonding layer.

57. A method of producing an optical waveguide as set forth in claim 42, wherein, in the step of removing the first substrate to transfer the optical waveguide path to the second substrate, a solvent is supplied between the bonded first substrate and second substrate to remove the substrate separation layer and then the first substrate is separated from the optical waveguide path.

58. A method of producing an optical waveguide as set forth in claim 42, wherein, in the step of removing the first substrate to transfer the optical waveguide path to the second substrate, a solvent is supplied between the bonded first substrate and second substrate to separate the boundary between the substrate separation layer and the optical waveguide path.

59. A method of producing an optical waveguide as set forth in claim 40, wherein said at least one of the light emitting element and light receiving element and said integrated circuit have connection electrodes, and

wherein, in said step of forming the at least one of the light emitting element and light receiving element and said step of forming said integrated circuit, at least one of the light emitting element and light receiving element and the integrated circuit are mounted on the second substrate by flip chip bonding using said connection electrodes.

60. A method of producing an optical waveguide as set forth in claim 59, wherein in said step of forming the at least one of the light emitting element and light receiving element and said step of forming said integrated circuit, the optical waveguide path is used as a spacer interposed between the at least one of the light emitting element and light receiving element and the integrated circuit and the second substrate

61. A method of producing an optical waveguide as set forth in claim 59, wherein spherical portions formed on tips of fine gold wires are pressed against electrodes of the at least one of the light emitting element and light receiving element and said integrated circuit, then the spherical portions and the fine gold wires are pulled apart to cut them and thereby form the connection electrodes.

36. A method of producing an optical waveguide as set forth in claim 36, wherein said step of forming a light blocking film includes:

a step of forming a peeling layer at a surface of the optical waveguide paths to which the second substrate is secured,

a step of forming a light blocking film over the entire exposed surface of the first substrate, optical waveguide paths, and peeling layer, and

a step of removing the peeling layer so as to selectively remove the light blocking layer in contact with the peeling layer.