Ring Quantum Cascade Lasers
Several sensing applications call for compact coherent light emitters with single-mode operation and a symmetric
low divergent beam profile. Moreover, surface emitting lasers allow for 2D array integrability and on-wafer testing.
Our group was the first who developed the concept of a Ring Cavity Surface Emitting Laser (ring-CSEL). The circular cavity along with
vertical light extraction, given by a surface distributed feedback grating, naturally forms a highly symmetric circularly shaped far
field and the overall large emission area reduces the divergence of the beam. Ring-CSELs provide robust and tunable single-mode operation with a
side-mode-suppression-ratio higher than 25dB. The facetless cavity exhibits reduced threshold currents and enhanced emission as compared to conventional
Modifications of the emission beam facilitates an improved implementation in measurement setups and could even clear the way for completely new applications. The implementation of a grating pi-phase shift or an offcenter grating provides a far field with a central intensity maximum in contrast to the inherent central minimum for standard ring-QCLs. Furthermore, a metamaterial layer etched into the substrate (metasubstrate) can be used to increase the emitting area and collimate the emission beam. A 90um wide metasubstrate produces a peak intensity of over 600% of the initial value without metasubstrate.
A ring quantum cascade laser and corresponding far fields
Metasubstrate on the substrate side of a ring-QCL. The yellow area depicts the location of the ring laser on the surface side. The inset shows the intensity increase due to the metasubstrate.