High-power, single-spatial-mode quantum cascade lasers
Single-mode quantum cascade semiconductor lasers are provided. The lasers comprise a laser element, the laser element comprising a quantum cascade active layer; an upper cladding layer over the quantum cascade active layer; and a lower cladding layer under the quantum cascade active layer, wherein the quantum cascade active layer, the upper cladding layer and the lower cladding layer define a guided optical mode. The quantum cascade active layer and the upper and lower cladding layers are shaped in the form of a ridge structure having a front face, a back face opposite the front face, and a lasing face through which laser emission exits the ridge structure, the ridge structure configured such that the laser emission has a single-lobe, far-field beam pattern from the ridge structure comprising certain sections, including tapered sections, collateral sections, or both.
1. A single-mode quantum cascade semiconductor laser comprising a laser element, the laser element comprising:
(a) a quantum cascade active layer;
(b) an upper cladding layer over the quantum cascade active layer; and
(c) a lower cladding layer under the quantum cascade active layer, wherein the quantum cascade active layer, the upper cladding layer and the lower cladding layer define a guided optical mode;
wherein the quantum cascade active layer and the upper and lower cladding layers are shaped in the form of a ridge structure having a front face, a back face opposite the front face, and a lasing face through which laser emission exits the ridge structure, the ridge structure configured such that the laser emission has a single-lobe, far-field beam pattern from the ridge structure comprising:
(1) a tapered section having diverging sides between the front face and the back face which diverge away from one another and towards the back face to define a maximum width w M , wherein the lasing face has a width w m and w M >w m , and the ridge structure is edge-emitting; or
(2) a tapered section having diverging sides between the front face and the back face which diverge away from one another and towards the back face to define a maximum width w M , the ridge structure further comprising a distributed feedback grating and a first face having a width w m between the front face and the back face wherein w M >w m , and the ridge structure is surface-emitting having the lasing face perpendicular to the front, the back, and the first faces; or
(3) a collateral section having parallel sides between the front face and the back face, the ridge structure further comprising a distributed feedback grating configured to suppress one or more symmetric longitudinal modes so as to produce lasing in an antisymmetric longitudinal mode, the distributed feedback grating further configured so that the laser emission from the ridge structure has the single-lobe, far-field beam pattern, wherein the ridge structure is surface-emitting having the lasing face perpendicular to the front and the back faces; or
(4) a collateral section having parallel sides between the front face and the back face and a first connecting portion having outer and inner sides, both of which extend away from the back face and towards the front face, the first connecting portion configured to optically couple the front face to the back face, the ridge structure further comprising a distributed feedback grating configured to suppress an antisymmetric longitudinal mode so as to produce lasing in a symmetric longitudinal mode, the distributed feedback grating further configured so that the laser emission from the ridge structure has the single-lobe, far-field beam pattern, wherein the ridge structure is continuous and surface-emitting having the lasing face perpendicular to the front and the back faces.
2. The laser of claim 1 , wherein the ridge structure comprises (1) or (2) and wherein the width w M is the largest width across the ridge structure.
3. The laser of claim 1 , wherein the ridge structure comprises (1) or (2) and wherein the width w m is the smallest width across the ridge structure.
4. The laser of claim 1 , wherein the ridge structure comprises (1) or (2) and the ridge structure further comprises a collateral section having parallel sides and adjacent to the tapered section.
5. The laser of claim 1 , wherein the ridge structure comprises (1) and wherein the ridge structure is linear and the front face is the lasing face having the width w m .
6. The laser of claim 5 , wherein the tapered section has the lasing face having the width w m and the back face having the width w M .
7. The laser of claim 5 , the linear ridge structure further comprising a collateral section adjacent to the tapered section, the collateral section having the lasing face having the width w m and parallel sides extending from the lasing face to a first face opposite the lasing face,
wherein the diverging sides of the tapered section extend from the first face to a second face having the width w M .
8. The laser of claim 7 , wherein the second face having the width w M is the back face.
9. The laser of claim 7 , the linear ridge structure further comprising a second collateral section having parallel sides extending to a third face opposite the second face.
10. The laser of claim 9 , wherein the parallel sides of the second collateral section extend from the second face having the width w M and the third face is the back face.
11. The laser of claim 7 , wherein the tapered section further comprises additional sides converging to a third face opposite the second face.
12. The laser of claim 11 , the linear ridge structure further comprising a second collateral section having parallel sides extending to a fourth face opposite the third face.
13. The laser of claim 12 , wherein the additional converging sides extend from the second face having the width w M and the parallel sides of the second collateral section extend from the third face and the fourth face is the back face.
14. The laser of claim 13 , wherein the back face has the width w m .
15. The laser of claim 1 , wherein the ridge structure comprises (2) and wherein the ridge structure is linear.
16. The laser of claim 15 , the linear ridge structure further comprising a second tapered section having sides between the front face and the back face and which extend away from the front face and converge towards the back face.
17. The laser of claim 1 , wherein the ridge structure comprises (2) and wherein the ridge structure is continuous.
18. The laser of claim 17 , wherein the tapered section is part of a first central portion having the front face and the back face,
wherein the continuous ridge structure further comprises a first connecting portion having outer and inner sides, both of which extend away from the back face and towards the front face, the first connecting portion configured to optically couple the front face to the back face.
19. The laser of claim 1 , wherein the ridge structure comprises (1) or (2) wherein the diverging sides of the tapered section are curved.
20. The laser of claim 19 , wherein the curve is parabolic.
21. The laser of claim 1 , wherein the ridge structure comprises (3) and is linear.
22. The laser of claim 21 , wherein the laser emission has a wavelength in a range of from 4 μm to 5 μm and the distributed feedback grating is characterized by a duty cycle greater than 0.45.
23. The laser of claim 1 , wherein the ridge structure comprises (1) or (2).
24. The laser of claim 16 , the linear ridge structure further comprising a collateral section having parallel sides, the collateral section extending between the first and second tapered sections.
25. The laser of claim 24 , wherein the second tapered section has the front face and the converging sides extend from the front face to the first face having the width w m opposite the front face; the parallel sides of the collateral section extend from the first face to a second face opposite the first face; and the tapered section has the back face having the width w M and the diverging sides of the tapered section extend from the second face to the back face.
26. The laser of claim 25 , wherein the front face has the width w M .