OPTICAL DEVICE HAVING A STEPWISE OR TAPERED LIGHT INPUT/OUTPUT PART AND MANUFACTURING METHOD THEREFOR

• US 20150086153A1
• Filed: 09/10/2014
• Published: 03/26/2015
• Est. Priority Date: 09/20/2013
• Status: Active Grant

• Current Assignee: National Institute of Advanced Industrial Science and Technology (Government of Japan), OKI Electric Industry Company Limited
• Original Assignee: National Institute of Advanced Industrial Science and Technology (Government of Japan), OKI Electric Industry Company Limited, Photonics Electronics Technology Research Association
• Inventors: ONO, Hideki, HORIKAWA, Tsuyoshi, HIRAYAMA, Naoki
• Granted Patent: US 9,335,475 B2
• Time in Patent Office: Days
• US Class Current: 385/11
• CPC Class Codes: G02B 2006/12061 Silicon
• CPC Class Codes: G02B 2006/12147 Coupler
• CPC Class Codes: G02B 6/12002 Three-dimensional structures
• CPC Class Codes: G02B 6/1228 Tapered waveguides, e.g. integrated spot-size transformers for coupling with fibres G02B6/305
• CPC Class Codes: G02B 6/124 Geodesic lenses or integrated gratings
• CPC Class Codes: G02B 6/126 using polarisation effects G02B6/1226 takes precedence
• CPC Class Codes: G02B 6/136 by etching
• CPC Class Codes: G02B 6/305 and having an integrated mode-size expanding section, e.g. tapered waveguide
• CPC Class Codes: G02B 6/34 utilising prism or grating G02B6/293 takes precedence

Abstract

In a method of manufacturing an optical device including an optical waveguide having a core, a cladding and a light input/output part through which a light beam is input or output, a substrate is prepared which is provided with a uniform thickness of single-crystalline film having its constituent atoms forming a diamond lattice structure and its surface being neither the (111) plane nor its equivalent planes. In the single-crystalline film, a precursor structure is formed which has a precursor of light input/output part. A mask is formed such as to expose the precursor with the remaining part covered. The structure is immersed into an alkaline solution for wet etching with the (111) planes used as etch-stop planes.

Claims

1. A method of manufacturing an optical device comprising an optical waveguide, the optical waveguide comprising a core, a cladding provided around the core, and a light input/output part through which a light beam is input or output, said method comprising:

preparing a substrate having a principal on which a substantially uniform thickness of single-crystalline film is formed, the film having constituent atoms substantially forming a diamond lattice structure and having a surface being of neither a (111) plane nor an equivalent plane to the (111) plane; and

subjecting the single-crystalline film to etching showing anisotropy depending on plane orientation to form the film into a terraced or tapered pattern so as to expose the (111) plane and the equivalent plane.

2. A method of manufacturing an optical device comprising an optical waveguide, the optical waveguide comprising a core, a cladding provided around the core, and a light input/output part through which a light beam is input or output, said method comprising:

preparing a substrate having a principal surface on which a substantially uniform thickness of single-crystalline film is formed, the film having constituent atoms substantially forming a diamond lattice structure and having a surface being neither a (111) plane nor an equivalent plane to the (111) plane;

subjecting the single-crystalline film to etching showing anisotropy depending on plane orientation while increasing gradually a length of the single-crystalline film which is to be exposed from the etching mask so as to form the film into a terraced shape;

applying to the terraced shape a photoresist for covering a section where a width is substantially constant and a tapered section where the width changes gradually;

conducting etching with the photoresist used as an etching mask to pattern the single-crystalline film; and

removing the photoresist, followed by forming a cladding for covering the single-crystalline film,

the terraced shape being formed by a riser having a face on which the (111) plane or the equivalent plane is exposed.

3. The method according to claim 2, wherein the single-crystalline film is made of Si.

4. The method according to claim 2, wherein the cladding is configured by a substance having a refractive index smaller than 71.4% of the refractive index of the core.

5. The method according to claim 2, wherein the cladding is configured by a substance selected from a group consisting of SiO₂, SiOx, where x represents a real number, 0<

x<

2, SiON, and optical resin.

6. The method according to claim 2, wherein the cladding comprises an upper cladding which resides above the core;

and a lower cladding which resides below the core, and is composed of a substance different from the upper cladding,

the substance composing each of the upper and lower claddings being selected from a group consisting of SiO₂, SiOx, where x represents a real number, 0<

x<

2, SiON, and optical resin.

7. The method according to claim 2, wherein the anisotropic etching is conducted by using as etchant an alkaline solution, which is selected from a group consisting of aqueous KOH solution, aqueous NaOH solution, aqueous CsOH solution, aqueous tetramethylammonium hydrate ((CH₂)₄NOH) solution, aqueous ethylenediamine (C₂H₈N₂) solution, aqueous ethylenediamine pyrocatechol solution, aqueous hydrazine hydrate (N₂H₄.H₂O) solution, and aqueous ammonium hydroxide (NH₄OH) solution, or a mixture of them.

8. A method of manufacturing an optical device comprising an optical waveguide, the optical waveguide comprising a core, a first cladding provided around the core, and a light input/output part through which a light beam is input or output, said method comprising:

a first step of preparing a substrate having a principal surface on which a substantially uniform thickness of single-crystalline film is formed, the film having constituent atoms substantially forming a diamond lattice structure and having a surface being neither a (111) plane nor an equivalent plane to the (111) plane;

a second step of patterning the single-crystalline film to form a substantially uniform thickness of precursor structure having a precursor of light input/output part;

a third step of fabricating a structure having a mask formed thereon, the mask exposing the precursor of light input/output part and covering remaining part of the precursor structure;

a fourth step of subjecting the precursor to etching showing anisotropy depending on plane orientation with the (111) plane and the equivalent plane used as etch-stop planes to thereby form the core in the precursor of the light input/output part;

a fifth step of removing the mask; and

a sixth step of covering the core with the first cladding to obtain the optical device.

9. The method according to claim 8, wherein, said fourth step comprises exposing two of the (111) plane and the equivalent plane on the precursor as the etch-stop planes, the two planes being substantially non-parallel to each other.

10. The method according to claim 8, wherein the substrate to be prepared has the single-crystalline film with a (100) plane exposed to the surface,

in said second step, the precursor is patterned into a substantially right rectangular cylinder having an isosceles trapezoidal planar shape tapered in width in a direction of light propagation, where the width is defined by a length measured in a direction substantially parallel with the principal surface of the substrate and in a direction substantially perpendicular to the direction of light propagation,

said fourth step comprising exposing two (111) planes arranged substantially symmetrically about a center line of an isosceles trapezoid, and one (111) plane at an end portion of the isosceles-trapezoidal substantially right rectangular cylinder as the etch-stop planes.

11. The method according to claim 8, wherein the substrate to be prepared has the single-crystalline film with the (110) plane exposed to the surface,

in said second step, the precursor is patterned into a substantially right rectangular cylinder having an isosceles trapezoidal planar shape tapered in width in the direction of light propagation, where the width is defined by a length measured in a direction substantially parallel with the principal surface of the substrate and in a direction substantially perpendicular to the direction of light propagation,

said fourth step comprising exposing two (111) planes arranged substantially symmetrically about a center line of an isosceles trapezoid, and one (111) plane at an end portion of the isosceles-trapezoidal substantially right rectangular cylinder as the etch-stop planes.

12. The method according to claim 8, wherein the substrate to be prepared has the single-crystalline film with the (112) plane exposed to the surface,

in said second step, the precursor is patterned into a substantially right rectangular cylinder having an isosceles trapezoidal planar shape tapered in width in the direction of light propagation, where the width is defined by a length measured in a direction substantially parallel with the principal surface of the substrate and in a direction substantially perpendicular to the direction of light propagation,

said fourth step comprising exposing the (111) plane on a top face of the substantially right rectangular cylinder connected to the (112) plane which configures the surface of the single-crystalline film, and exposing the equivalent plane to the (111) plane as the etch-stop plane on both side faces connected to the top face,

the (111) plane being exposed as the etch-stop plane at the end portion of the isosceles-trapezoidal substantially right rectangular cylinder.

13. The method according to claim 10, wherein said third to fifth steps are repeated while increasing stepwise a portion of the precursor which exposes from the mask.

14. The method according to claim 10, further comprising, after said fourth step, truncating the end portion formed in said fourth step so as to expose the (111) plane substantially perpendicularly to the direction of light propagation.

15. The method according to claim 10, wherein said sixth step further comprises:

covering the structure, obtained after said fifth step, with a second cladding having a refractive index substantially larger than that of the first cladding, and substantially smaller than that of the core; and

covering the second cladding with the first cladding.

16. The method according to claim 8, wherein the substrate to be prepared has the single-crystalline film with a (kjj) plane exposed to the surface, where k and j are an integer of 0 or larger and not equal to each other.

17. An optical device comprising an optical waveguide provided on a principal surface of a substrate, said optical waveguide comprising a core and a cladding provided around the core, the cladding being configured by a substance having a refractive index smaller than 71.4% of the refractive index of the core, the core having constituent atoms substantially forming a diamond lattice structure,

said optical waveguide comprising a light input/output part through which alight beam is input and/or output,

the light input/output part decreasing stepwise in thickness towards an output end while tapering down in its width,

the core being provided in the light input/output part to have a (111) plane or an equivalent plane to the (111) plane exposed on a face of a riser of the stepwise thickness of the light input/output part.

18. The optical device according to claim 17, wherein the core comprises Si as a constituent element.

19. An optical device comprising an optical waveguide provided on a principal surface of a substrate, said optical waveguide comprising a core and a cladding provided around the core, the cladding being configured by a substance having a refractive index smaller than 71.4% of the refractive index of the core, the core having constituent atoms substantially forming a diamond lattice structure,

said optical waveguide further comprising a light input/output part through which alight beam is input and/or output,

the light input/output part having two or more planes selected from a (111) plane and an equivalent plane to the (111) plane, and the core having two planes substantially non-parallel to each other among the (111) plane and the equivalent plane.

20. The optical device according to claim 19, wherein the light input/output part is connected to a body of the core and has an end portion,

the body of the core having a top face opposed to the principal surface and being a (100) plane or an equivalent plane of the (100) plane,

the light input/output part comprising a connective part and a functional part,

the functional part having a transverse cross section which is taken substantially perpendicularly to a direction of light propagation and connected to the body of the core while placing the connective part in between being at least either one of an isosceles triangle with two equal sides configured by the (111) planes and an isosceles trapezoid with two equal legs configured by the (111) planes, and being tapered towards the end portion so that the transverse cross section monotonously shrinks while keeping similarity,

the connective part being surrounded by connective planes configured by a (110) plane and an equivalent plane to the (110) plane,

the functional part thereby functioning as a spot-size converter.

21. The optical device according to claim 19, wherein the light input/output part is connected to a body of the core and has an end portion,

the body of the core having a top face opposed to the principal surface being a (110) plane or an equivalent plane to the (110) plane,

the light input/output part having a connective part and a functional part,

the functional part having a transverse cross section which is taken substantially perpendicularly to a direction of light propagation and connected to the body of the core while placing the connective part in between being at least either one of an isosceles triangle with two equal sides configured by the (111) planes and an isosceles trapezoid with two equal legs configured by the (111) planes, and being tapered towards the end portion so that the transverse cross section monotonously shrinks while keeping similarity,

the connective part being surrounded by connective planes configured by the (111) plane and the equivalent plane to the (111) plane,

the functional part thereby functioning as a spot-size converter.

22. The optical device according to claim 19, wherein the light input/output part is connected to a body of the core and has an end portion,

the body of the core having a top face opposed to the principal surface being a (112) plane or an equivalent plane to the (112) plane,

the light input/output part having a connective part and a functional part, each of which has a generally rectangular transverse cross section taken substantially perpendicularly to the direction of light propagation, and is monotonously tapered in width towards the end portion, the width being defined a length measured in a direction that is substantially parallel with the principal surface of the substrate and perpendicular to the direction of light propagation,

the connective part being surrounded by connective planes configured by the (111) plane connected to the top face, and an equivalent plane that is equivalent to the (111) plane and connected to a side face of the body of the core, and has a generally rectangular transverse cross section taken substantially perpendicularly to the direction of light propagation,

the functional part having a flat part configured by a (112) plane, the end portion being connected to the flat part and being configured by the (111) plane,

the functional part thereby functioning as a spot-size converter.

23. The optical device according to claim 19, wherein the light input/output part has a plurality of cores arranged so as to cross a direction of light propagation, and substantially in parallel to each other with a predetermined period,

each of the cores which has a transverse cross section taken in a direction crossing substantially perpendicularly to all of the plurality of cores and to the principal surface being at least either one of an isosceles triangle with two equal sides configured by the (111) planes and an isosceles trapezoid with two equal legs configured by the (111) planes,

the light input/output part thereby functioning as a grating coupler.

24. An optical device comprising an optical waveguide provided on a principal surface of a substrate, said optical waveguide comprising:

a core formed by patterning a single-crystalline film which has constituent atoms substantially forming a diamond lattice structure and has a surface being neither a (111) plane nor an equivalent plane to the (111) plane;

a first cladding formed by covering the core with a substance having a refractive index smaller than 71.4% of the refractive index of the core; and

a light input/output part through which a light beam is input or output,

the light input/output part having two or more planes selected from a (111) plane and an equivalent plane to the (111) plane, which expose as etch-stop planes when a precursor of the light input/output part is wet etched using an alkaline solution, and the core having two planes substantially non-parallel to each other among the (111) plane and the equivalent plane.

25. The optical device according to claim 24, wherein the connective part has a plurality of sub-connective parts arrayed in series in a direction of light propagation,

each of the sub-connective parts having a sub-connective plane as a slope, and a sub-plane connected to the sub-connective plane and having a same plane orientation as a top face of the core,

the sub-connective planes having the same plane orientation for all of the plurality of sub-connective parts, and being configured to shrink stepwise in area in the direction of light propagation.

26. The optical device according to claim 24, wherein the light input/output part has an end portion truncated substantially perpendicularly to a direction of light propagation, ensuring a size of cross section capable of allowing both of TE wave and TM wave to propagate therethrough.

27. The optical device according to claim 24, wherein the light input/output part has provided therearound with a second cladding having a refractive index substantially larger than that of the first cladding and substantially smaller than that of the core,

the first cladding extending around the second cladding.

28. An optical device comprising an optical waveguide provided on the principal surface of a substrate, said optical waveguide comprising:

a core;

a cladding provided around the core,

the cladding being configured by a substance having a refractive index smaller than 71.4% of the refractive index of the core,

the core having constituent atoms substantially forming a diamond lattice structure; and

a polarization conversion part which takes part in polarization conversion of light to be propagated,

the polarization conversion part having a transverse cross section which is taken substantially perpendicularly to a direction of light propagation, and is at least either one of an isosceles triangle with two equal sides configured by (111) planes and an isosceles trapezoid with two equal legs configured by the (111) planes,

said optical waveguide thereby functioning as a polarization converter.

29. An optical device comprising an optical waveguide provided on a principal surface of a substrate, said optical waveguide comprising:

a core formed by patterning a single-crystalline film which has constituent atoms substantially forming a diamond lattice structure and has a surface being neither a (111) plane nor an equivalent plane to the (111) plane;

a cladding formed by covering the core with a substance having a refractive index smaller than 71.4% of the refractive index of the core; and

a polarization conversion part which takes part in polarization conversion of light to be propagated,

the polarization conversion part having two or more planes selected from the (111) plane and the equivalent plane, which expose as etch-stop planes when a precursor of the polarization conversion part is wet etched using an alkaline solution,

the polarization conversion part having a transverse cross section which is taken substantially perpendicularly to a direction of light propagation, and is at least either one of an isosceles triangle with two equal sides configured by the (111) planes and an isosceles trapezoid with two equal legs configured by the (111) planes,

said optical waveguide thereby functioning as a polarization converter.