High-power, single-spatial-mode quantum cascade lasers

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 wM, wherein the lasing face has a width wm and wM>wm, 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 wM, the ridge structure further comprising a distributed feedback grating and a first face having a width wm between the front face and the back face wherein wM>wm, 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.