Continuous-wave Operation of GaSb-based Interband Cascade Lasers beyond $\boldsymbol{6\mu \mathrm{m}}$

GaSb-based Fabry-Pérot interband cascade lasers with a center emission wavelength of 6.12
$\mu \mathrm{m}$
, showing the lowest reported threshold current density of 612 A/cm2 at this wavelength at room temperature are presented. An epi-side-down mounted device showed over 25 mW cw-output power at
$20^{\mathrm{o}}\mathrm{C}$
.