Surface-emitting 10.1 μm quantum-cascade distributed feedback lasers

We present measurement results on a surface-emitting quantum-cascade distributed feedback laser emitting infrared radiation at 10.1 μm. The use of a second order grating enabled the laser to emit about 25% of its total optical power from the grating. The beam radiated from the grating was at a very low divergence angle of about 1°×14°. As already presented in a previous paper, we simplified the processing by using a lateral current injection scheme avoiding epitaxial regrowth. At 85 K, the laser emitted 210 and 60 mW of pulsed power from facet and grating, respectively; at room temperature, the corresponding numbers were 70 and 18 mW. Threshold current densities of 2.1 ${\mathrm{kA/cm}}^2$ at 85 K and 5.6 ${\mathrm{kA/cm}}^2$ at room temperature were observed. The device showed single mode behavior for the entire temperature range and all investigated power levels. In addition, a constant temperature tuning coefficient of 0.06 ${\mathrm{cm}}^{\mathrm{-1}}\mathrm{/K}$ was seen.