Optica 5, 996–1005 (2018)

When it comes to mid-infrared sources, interband cascade lasers (ICLs) that operate in the mid-infrared band are of interest because they potentially have thresholds for operation that are 1–2 orders of magnitude below quantum cascade lasers (QCLs). Now, scientists in the US have managed to integrate III–V ICLs with silicon waveguides, leading the way to silicon-based photonic integrated circuits for applications in the mid-infrared. The ICLs operate at a wavelength of 3.65 µm and in pulsed mode. The threshold current density of the devices varies with temperature, ranging from ~0.3 kA cm–2 at –100 °C to ~2 kA cm–2 at +50 °C. Output powers are in the range of 1–12 mW. The integration is achieved by using a hydrophilic plasma-assisted bonding process to bond a III–V epilayer that forms the active region of the ICL to silicon. The researchers believe that with further optimization of the design and fabrication, continuous-wave operation should be possible in the future.