Laser device and process for fabricating such a laser device

1. A III-V heterostructure laser device located in and/or on silicon, comprising

a III-V heterostructure gain medium, and

a rib optical waveguide, located facing the gain medium and comprising a strip waveguide equipped with a longitudinal rib, the rib optical waveguide being located in the silicon,

two sets of Bragg gratings formed in the rib optical waveguide and located on either side of the III-V heterostructure gain medium,

each set of Bragg gratings comprising a first Bragg grating having a first pitch and formed in the rib and a second Bragg grating having a second pitch different from the first pitch and formed on that side of the rib waveguide which is opposite the rib.

2. The laser device as claimed in claim 1 , wherein the rib optical waveguide is oriented so that the rib is located on that side of the strip waveguide that is distal with respect to the gain medium.

3. The laser device as claimed in claim 2 , wherein the first pitch of the first Bragg gratings formed in the rib is larger than the second pitch of the second grating formed on that side of the rib waveguide which is opposite the rib.

4. The laser device as claimed in claim 1 , wherein one of the sets of Bragg gratings possesses a length comprised between 700 μm and 1000 μm, limits inclusive, and a reflectivity higher than 90%, and in that the other of the sets of Bragg gratings possesses a length comprised between 300 μm and 600 μm, limits inclusive, and a reflectivity comprised between 30% and 80%, limits inclusive.

5. The laser device as claimed in claim 1 , wherein the first Bragg gratings are formed by narrow sections and wider sections of the rib.

6. The laser device as claimed in claim 5 , wherein the width of the rib in the narrow sections is comprised between 0%-80% of the width of the wider sections of the rib.

7. The laser device as claimed in claim 5 , wherein the second Bragg gratings are only formed at the level of the first Bragg gratings in the location of the wider sections of the rib.

8. The laser device as claimed in claim 5 , wherein the second Bragg gratings are only formed at the level of the first Bragg gratings in the location of the narrow sections of the rib.

9. The laser device as claimed claim 5 , wherein the transition between the narrow sections and the wide sections defines transitional flanks that are oriented perpendicularly to the propagation direction of the light.

10. The laser device as claimed in claim 5 , wherein the transition between the narrow sections and the wide sections defines transitional flanks that are inclined with respect to a direction that is perpendicular to the propagation direction of the light.

11. The laser device as claimed in claim 5 , wherein the etching depth of the two gratings of a set of Bragg gratings is different.

12. The laser device as claimed in claim 3 , wherein the etching depth of the first gratings is larger than the etching depth of the second gratings.

13. The laser device as claimed in claim 1 , wherein the width of the second gratings of the sets of Bragg gratings is larger than that of the rib.

14. The laser device as claimed in claim 1 , wherein the width of the second gratings of the sets of Bragg gratings is substantially equal to the width of the strip waveguide.

15. The laser device as claimed in claim 1 , wherein the strip waveguide and the longitudinal rib are each formed from crystalline silicon or one is made of crystalline silicon and the other of amorphous silicon.

16. The laser device as claimed in claim 1 , wherein the longitudinal rib is made of crystalline silicon and the strip waveguide is formed by two layers, the layer making contact with the longitudinal rib also being made of crystalline silicon and the other layer proximal to the gain medium being made of amorphous silicon.

17. A process for fabricating a laser device as claimed in claim 1 , comprising the following steps:

producing a rib waveguide comprising a strip waveguide equipped with a longitudinal rib in a silicon layer that is located above a buried insulating layer, which itself is located above a carrier substrate;

producing by etching in the rib first gratings of the sets of Bragg gratings;

encapsulating in a first insulating layer the rib waveguide;

flipping the assembly;

removing the carrier substrate and the first buried insulating layer so as to uncover a side of the strip waveguide;

producing by etching the second gratings of the sets of Bragg gratings in the side of the strip waveguide;

depositing a second insulating layer and carrying out chemical-mechanical polishing of the second insulating layer;

depositing a heterostructure formed from III-V semiconductor; and

carrying out selective chemical etching of the heterostructure to obtain a gain medium.