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

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 mu m range, with excellent performance around 3.3 mu m. 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. (C) 2024 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/)