Photonic integrated circuits (PICs) are widely used, but their application in high-precision systems is limited by high phase noise of semiconductor lasers and the difficulty of integrating optical isolators. This paper presents a 3D integration approach that combines III-V gain medium and ultralow-loss silicon nitride waveguides, resulting in ultralow-noise lasers with isolator-free operation. The 3D structure enables ultrahigh-quality-factor cavities, reducing phase noise and enhancing feedback tolerance. This simplifies PIC fabrication and packaging while offering improved scalability and reliability.

Chao Xiang, Warren Jin, Osama Terra, Bozhang Dong, Heming Wang, Lue Wu, Joel Guo, Theodore J. Morin, Eamonn Hughes, Jonathan Peters, Qing-Xin Ji, Avi Feshali, Mario Paniccia, Kerry J. Vahala, John E. Bowers