Direct measurement of current-dependent optical losses in interband cascade lasers

Abstract

Interband cascade lasers (ICLs) are becoming increasingly valuable in mid-infrared applications due to their low power consumption and compatibility with silicon photonic integration, particularly for trace gas sensing. ICLs have demonstrated room-temperature continuous-wave operation in the 3–6 μm range, with excellent performance around 3.3 μm. A key factor limiting ICL performance at longer wavelengths is optical loss, i.e., caused by the intervalence band transitions. These losses increase with hole concentration in the active region, leading to a pronounced current-dependence of the optical losses in ICLs. Conventional methods that infer optical losses from length-dependent variations in parameters such as slope efficiency or threshold current require the assumption of constant optical loss. In this study, we present a direct optical transmission measurement technique to determine waveguide losses. Our experiments confirm strongly increasing waveguide losses with current density, directly impacting the quantum efficiency of ICLs. This approach offers a precise evaluation of optical losses and bears a functional alternative compared to traditional methods, addressing the limitations of assuming constant losses and providing enhanced insight into ICL performance across various wavelengths.