The paper "A Ge-on-Si laser operating at room temperature" by Jifeng Liu, Xiaochen Sun, Rodolfo Camacho-Aguilera, Lionel Kimerling, and Jurgen Michel reports the first experimental observation of lasing from the direct gap transition of Ge-on-Si at room temperature using an edge-emitting waveguide device. The authors demonstrate a monolithic laser on Si, which is ideal for high-volume and large-scale electronic-photonic integration. By using tensile strain and n-type doping, they engineered the band structure of Ge to behave like a direct gap material. The laser exhibits a gain spectrum in the 1590-1610 nm range, line narrowing, and polarization evolution from mixed TE/TM to predominantly TE with increasing gain. The threshold behavior is clearly observed, marking the onset of transparency. The study also confirms the presence of multiple guided modes in the Ge waveguide, supporting the coexistence of lasing modes under high excitation. This work highlights the potential of Ge-on-Si lasers for monolithic electronic-photonic integrated circuits.The paper "A Ge-on-Si laser operating at room temperature" by Jifeng Liu, Xiaochen Sun, Rodolfo Camacho-Aguilera, Lionel Kimerling, and Jurgen Michel reports the first experimental observation of lasing from the direct gap transition of Ge-on-Si at room temperature using an edge-emitting waveguide device. The authors demonstrate a monolithic laser on Si, which is ideal for high-volume and large-scale electronic-photonic integration. By using tensile strain and n-type doping, they engineered the band structure of Ge to behave like a direct gap material. The laser exhibits a gain spectrum in the 1590-1610 nm range, line narrowing, and polarization evolution from mixed TE/TM to predominantly TE with increasing gain. The threshold behavior is clearly observed, marking the onset of transparency. The study also confirms the presence of multiple guided modes in the Ge waveguide, supporting the coexistence of lasing modes under high excitation. This work highlights the potential of Ge-on-Si lasers for monolithic electronic-photonic integrated circuits.