Continuous-wave single-mode interband cascade lasers emitting at 3.5 µm

Type-II quantum well (QW) interband cascade lasers (ICLs) have become the most efficient laser source in the mid-infrared spectral range spanning 3 - 6 µm. In order to use ICLs for gas sensing applications, they must be fabricated for single-mode emission. Distributed feedback (DFB) ICLs are commercially available single-mode lasers and offer low threshold currents for these types of applications but this technology is expensive and time consuming to fabricate since they require e-beam lithography. Slotted waveguides are explored in this work as an inexpensive alternative to electron beam (e-beam) lithography since standard UV photolithography can be used to fabricate the larger, reflective defects (slots) in the waveguide. The geometry of the slot pattern must be simulated beforehand in order to design a photolithography mask for the ICL growth so limitations and behavior of key design parameters will be presented. For 8 µm narrow ridge slotted ICLs emitting near 3.5 µm around 20 °C, single-mode emission was achieved with threshold currents in the range of 60 - 80 mA and output power of 2+ mW/facet. Single-mode emission was only reached for certain temperatures and injected current values, but for all operating conditions the number of longitudinal cavity modes supported was suppressed with respect to a Fabry-Pérot ICL; thus, validating the success of the first Sb based slotted laser.