Hybrid laser source comprising an integrated waveguide containing an intermediate Bragg grating

1. A laser source, comprising:

a functionalized substrate, comprising an integrated waveguide, said integrated waveguide:

being formed from a stack of a first portion and of a second portion, an upper face of the first portion being at least partially coated with the second portion, and

comprising at least one Bragg grating; and

a semiconductor pad, resting on the functionalized substrate, comprising a gain medium located in an active waveguide, the active waveguide being located perpendicular to the integrated waveguide and oriented parallel thereto, the two waveguides being optically coupled to each other, wherein

the Bragg grating is located in the upper face of the first portion,

the Bragg grating is covered by the second portion,

the second portion does not comprise a Bragg grating, and

the second portion forms a longitudinal rib of a width smaller than that of the first portion.

2. The laser source according to claim 1 , wherein the Bragg grating is formed by a periodic alternation of teeth and troughs, the teeth being filled with a material of low refractive index, the refractive index of which is lower than the refractive index of the first and second portions.

3. The laser source according to claim 1 , wherein the second portion rests on a substantially planar surface.

4. The laser source according to claim 1 , wherein the integrated waveguide is made of silicon and is covered by a silicon oxide, and wherein the Bragg grating comprises troughs filled with a silicon oxide or with a silicon nitride.

5. The laser source according to claim 1 , wherein the first portion of the integrated waveguide is made of crystalline silicon, and the second portion is made of amorphous silicon.

6. The laser source according to claim 1 , wherein the Bragg grating comprises a periodic alternation of teeth and troughs, the second portion making contact with the teeth of the Bragg grating.

7. The laser source according to claim 1 , wherein the Bragg grating comprises a periodic alternation of teeth and troughs, the integrated waveguide comprising a thin continuous layer made of a material of low refractive index that covers the first portion and fills the troughs of the Bragg grating, the second portion being spaced apart from the first portion by the thin continuous layer.

8. A process for fabricating a laser source according to claim 1 , comprising the following steps:

producing a first portion of the integrated waveguide resting on a base layer;

producing at least one Bragg grating in the upper face of the first portion opposite the base layer, the Bragg grating being formed from an alternation of teeth and troughs;

filling the troughs with a material of low refractive index;

producing a second portion of the integrated waveguide on the first portion and covering the Bragg grating;

producing an upper layer covering the second portion; and

producing the semiconductor pad resting on the upper layer.

9. The fabricating process according to claim 8 , wherein the step of producing the first portion is performed by locally etching a layer of crystalline silicon of an SOL substrate, the first portion having a spatially uniform thickness equal to the thickness of the layer of crystalline silicon.

10. The fabricating process according to claim 8 , wherein the step of producing the second portion of the integrated waveguide is performed using a damascene process comprising the following steps:

producing a layer forming a mask and covering the first portion and the Bragg grating;

producing a longitudinal aperture perpendicular to the Bragg grating;

depositing amorphous silicon filling the longitudinal aperture; and

carrying out chemical-mechanical planarization so as to free an upper face of the mask and to preserve the amorphous silicon filling the longitudinal aperture.

11. The fabricating process according to claim 10 , the Bragg grating being formed from a periodic alternation of teeth and troughs, wherein, following the step of producing the longitudinal aperture, a surface of the upper face of the first portion is rendered free, said free surface being formed by teeth made of silicon and by the material of low refractive index filling the troughs of the Bragg grating.

12. The fabricating process according to claim 10 , the Bragg grating being formed from a periodic alternation of teeth and troughs, wherein, following the step of producing the longitudinal aperture, a thin continuous layer of the layer made of silicon oxide covers the teeth made of silicon and fills the troughs of the Bragg grating.

13. The fabricating process according to claim 8 , wherein producing the second portion of the integrated waveguide comprises dishing an upper surface of the second portion.

14. The fabricating process according to claim 8 , wherein the step of producing the second portion of the integrated waveguide is performed using a damascene process comprising the following steps:

producing a layer forming a mask and covering the first portion and the Bragg grating;

producing a longitudinal aperture perpendicular to the Bragg grating;

depositing amorphous silicon filling the longitudinal aperture; and

carrying out chemical-mechanical planarization to expose the mask and create a dished upper surface in the amorphous silicon.

15. The laser source according to claim 1 , comprising the second portion having a dished upper face.

16. The laser source according to claim 1 , wherein:

the Bragg grating comprises a plurality of recesses, and

a depth of the recesses is less than a thickness of the second portion in a depth direction of the recesses.

17. A laser source, comprising:

a functionalized substrate, comprising an integrated waveguide, said integrated waveguide:

being formed from a stack of a first portion and of a second portion, an upper face of the first portion being at least partially coated with the second portion, and

comprising at least one Bragg grating; and

a semiconductor pad, resting on the functionalized substrate, comprising a gain medium located in an active waveguide, the active waveguide being located perpendicular to the integrated waveguide and oriented parallel thereto, the two waveguides being optically coupled to each other,

the Bragg grating being located in the upper face of the first portion, and being covered by the second portion and having a first length in a longitudinal direction,

the semiconductor pad having a second length in the longitudinal direction less than the first length,

the second portion does not comprise a Bragg grating, and

the second portion forms a longitudinal rib of a width smaller than that of the first portion.

18. The laser source according to claim 17 , comprising the upper face of the second portion being dished and having a third length in the longitudinal direction greater than the second length.

19. The laser source according to claim 18 , comprising the third length being substantially the same as the first length.