Quantum cascade superluminescent light emitters with high power and compact structure

Quantum cascade(QC) superluminescent light emitters(SLEs) have emerged as desirable broadband mid-infrared(MIR) light sources for growing number of applications in areas like medical imaging, gas sensing and national defense.However, it is challenging to obtain a practical high-power device due to the very low efficiency of spontaneous emission in the intersubband transitions in QC structures. Herein a design of ～5 μm SLEs is demonstrated with a two-phonon resonancebased QC active structure coupled with a compact combinatorial waveguide structure which comprises a short straight part adjacent to a tilted stripe and to a J-shaped waveguide. The as-fabricated SLEs achieve a high output power of 1.8 mW, exhibiting the potential to be integrated into array devices without taking up too much chip space. These results may facilitate the realization of SLE arrays to attain larger output power and pave the pathway towards the practical applications of broadband MIR light sources.