Spatially coherent surface-emitting, grating coupled quantum cascade laser with unstable resonance cavity

摘要

A surface emitting, unipolar, quantum cascade semiconductor laser is constructed of a multilayer semiconductor structure on a substrate. The laser has doped semiconductor material only of one conductivity type. The laser includes a core region having a larger effective refractive index than cladding regions. The core region includes a plurality of repeat units, each repeat unit having a nominally identical active region and a carrier injection and relaxation region. The repeat units are for quantum cascade generation of a lasing resonance mode within a lasing resonance cavity of the multilayer semiconductor structure. A diffraction grating is fabricated within the multilayer semiconductor structure. The grating resonantly couples diverging counter-propagating traveling wave beams of the laser resonance mode while also diffracting light into an upward direction perpendicular to a grating plane and toward the substrate surface, and also into a downward direction. A mirror reflects the downwardly coupled light toward the upward direction again. The optical distance between reflecting mirror and the grating is selected to combine the reflected light with the upwardly coupled light in-phase as the output beam. A lens-like media structure having an effective refractive index profile that varies quadratically in a direction transverse to the laser resonance cavity is included in the multilayer semiconductor structure. The lowest value of the profile is located at a central portion of the laser. The profile monotonically increases moving away from the central portion. The lens-like media structure interacts with the counter-propagating traveling wave beams to provide single mode output.