Top Grating, Surface-Emitting DFB Quantum Cascade Lasers in Continuous-Wave Operation

We demonstrate room temperature, continuous-wave operation of top grating based surface-emitting distributed feedback quantum cascade lasers at lambda similar to 4.8 gm. The secondorder metal/semiconductor grating structure allows efficient surface emission for the transverse-magnetic-polarized light. The CW output power from the substrate facet reached 94 mW at 25 degrees C, with a low threshold current density of 1.21 kA/cm(2). Single-mode emission with a side-mode suppression ratio about 30 dB is continuously tunable by the heat sink temperature or injection current. A far-field radiation pattern with a small divergence angle of 0.58 x 16.2 is obtained. Our work may contribute to the fabrication approach for substrateemitting distributed feedback lasers based on a very simple processing.