Quantum dot comb lasers with external cavity

1. A quantum dot comb laser comprising:

a body defining a lasing cavity; and

an extension wafer-bonded to the body and defining an external cavity, the free spectral range (FSR) of the external cavity being an integer multiple of the lasing cavity FSR; and

at least one mode converter between the lasing cavity and the external cavity;

the quantum dot comb laser emitting, in operation, a comb laser signal comprising light at a plurality of wavelengths with a spacing defined by the FSR of the external cavity.

2. The quantum dot comb laser of claim 1 , further comprising a phase tuner disposed in the external cavity.

3. The quantum dot comb laser of claim 1 , wherein the external cavity includes a ring resonator.

4. The quantum dot comb laser of claim 3 , further comprising a phase tuner disposed in the ring resonator.

5. The quantum dot comb laser of claim 3 , further comprising a dispersion management section disposed within the ring resonator.

6. The quantum dot comb laser of claim 1 , wherein the body further comprises:

a semiconductor optical amplifier defining the lasing cavity bounded on a first end thereof by a fully reflective mirror and on a second end thereof by an internal partially reflective mirror; and

an extension from the semiconductor optical amplifier defining the external cavity bounded on a first end thereof by the internal partially reflective mirror and on a second end thereof by an external partially reflective mirror.

7. The quantum dot comb laser of claim 6 , wherein the external partially reflective mirror is a grating coupler, a multimode interferometer with a loop mirror, or a directional coupler with a loop mirror.

8. A quantum dot comb laser comprising:

a semiconductor optical amplifier defining a lasing cavity having a first free spectral range (FSR), the lasing cavity bounded on a first end thereof by a fuller reflective mirror and on a second end thereof by an internal partially reflective mirror; and

an extension from the semiconductor optical amplifier defining an external cavity having a second FSR, the second FSR being an integer multiple of the first FSR, the external cavity being bounded on a first end thereof by the internal partially reflective mirror and on a second end thereof by an external partially reflective mirror; and

at least one mode converter between the lasing cavity and the external cavity;

the quantum dot comb laser emitting, in operation, a comb laser signal comprising light at a plurality of wavelengths with a spacing defined by the second FSR.

9. The quantum dot comb laser of claim 8 , wherein the external partially reflective mirror is a grating coupler, a multimode interferometer with a loop mirror, or a directional coupler with a loop mirror.

10. The quantum dot comb laser of claim 8 , further comprising a ring resonator disposed within the external cavity.

11. The quantum dot comb laser of claim 8 , further comprising a phase tuner or a dispersion management section disposed within the external cavity.

12. The quantum dot comb laser of claim 8 , further comprising:

a ring resonator included in the external cavity; and

a dispersion management section disposed within the ring resonator.

13. A quantum dot comb laser, comprising:

a semiconductor optical amplifier defining a lasing cavity having a first free spectral range (FSR), the lasing cavity bounded on a first end thereof by a fully reflective mirror and on a second end thereof by an internal partially reflective mirror;

an extension from the semiconductor optical amplifier defining an external cavity having a second FSR, the second FSR being an integer multiple of the first FSR, the external cavity being bounded on a first end thereof by the internal partially reflective mirror and on a second end thereof by an external partially reflective mirror; and

at least one mode converter between the lasing cavity and the external cavity;

the quantum dot comb laser emitting, in operation, a comb laser signal comprising light at a plurality of wavelengths with a spacing defined by the second FSR.

14. The quantum dot comb laser of claim 13 , wherein the external partially reflective mirror is a grating coupler, a multimode interferometer with a loop mirror, or a directional coupler with a loop mirror.

15. The quantum dot comb laser of claim 13 , further comprising a phase tuner disposed within the external cavity.

16. The quantum dot comb laser of claim 13 , further comprising a ring resonator disposed within the external cavity.

17. The quantum dot comb laser of claim 13 , further comprising a dispersion management section disposed within the external cavity.

18. The quantum dot comb laser of claim 1 , wherein:

the body is fabricated from a direct bandgap material; and

the extension is fabricated from an indirect bandgap material.

19. The quantum dot comb laser of claim 8 , wherein:

the body is fabricated from a direct bandgap material; and

the extension is fabricated from an indirect bandgap material.

20. The quantum dot comb laser of claim 13 , wherein:

the semiconductor optical amplifier is fabricated from a direct bandgap material; and

the extension is fabricated from an indirect bandgap material.