Photonic-integrated circuits (PICs) are a key enabler for the ultimate miniaturization of various disruptive technologies such as LiDAR for autonomous vehicles, bio-chemical sensors and chip-level optical communications. However, the realization of fully functional PICs is currently limited by the absence of an efficient laser source on silicon (Si), thus making a practical Si-compatible laser the Holy Grail. It has been thus far considered close to impossible to create a practical on-chip laser using Si-compatible group IV semiconductor materials (e.g. germanium (Ge)) owing to their indirect bandgap nature.
In the quest for practical group IV lasers, researchers have proposed a few innovative ideas such as strain engineering of Ge and alloying of tin (Sn) into Ge. The strain engineering of Ge holds a clear advantage over the Sn alloying since it bypasses the formidable task of the material growth. Over the past few years, various creative platforms for strain engineering have been experimentally demonstrated (Nature Photon. 6, 398–405 (2012) / Nature Photon. 7, 466–472 (2013)). However, despite several years of attempts, there has been no successful demonstration of lasing in highly strained Ge. Our group recently reported the first experimental observation of low-threshold lasing in highly strained Ge nanowire at 83 K. The lasing threshold is nearly two orders of magnitude lower than the state-of-the-art GeSn laser. This striking achievement is strongly supported by a rigorous theoretical simulation, which predicts a large optical net gain in strained Ge. By presenting unambiguous quantitative evidence of low-threshold, multimode lasing action in a fully CMOS-compatible material system, our results pave the way towards a truly monolithic realization of PICs.