Ultrafast tunable lasers using lithium niobate integrated photonics

• Published in: Nature (London) 2023-03, Vol.615 (7952), p.411-417
• Main Authors: Snigirev, Viacheslav, Riedhauser, Annina, Lihachev, Grigory, Churaev, Mikhail, Riemensberger, Johann, Wang, Rui Ning, Siddharth, Anat, Huang, Guanhao, Möhl, Charles, Popoff, Youri, Drechsler, Ute, Caimi, Daniele, Hönl, Simon, Liu, Junqiu, Seidler, Paul, Kippenberg, Tobias J.
• Format: Article
• Language: English
• Subjects: 639/624/1020/1085; 639/624/1075/401; Decibels; Etching; Humanities and Social Sciences; Hybrid modes; Integrated circuits; Laser ranging; Lasers; Lidar; Lithium; Lithium niobates; Microwave photonics; Modulators; multidisciplinary; Optics; Photonics; Propagation; Science; Science (multidisciplinary); Semiconductor lasers; Semiconductors; Silicon; Silicon nitride; Thin films; Tunable lasers; Tuning
• ISSN: 0028-0836; 1476-4687
• DOI: 10.1038/s41586-023-05724-2

Early works 1 and recent advances in thin-film lithium niobate (LiNbO 3 ) on insulator have enabled low-loss photonic integrated circuits 2 , 3 , modulators with improved half-wave voltage 4 , 5 , electro-optic frequency combs 6 and on-chip electro-optic devices, with applications ranging from microwave photonics to microwave-to-optical quantum interfaces 7 . Although recent advances have demonstrated tunable integrated lasers based on LiNbO 3 (refs. 8 , 9 ), the full potential of this platform to demonstrate frequency-agile, narrow-linewidth integrated lasers has not been achieved. Here we report such a laser with a fast tuning rate based on a hybrid silicon nitride (Si 3 N 4 )–LiNbO 3 photonic platform and demonstrate its use for coherent laser ranging. Our platform is based on heterogeneous integration of ultralow-loss Si 3 N 4 photonic integrated circuits with thin-film LiNbO 3 through direct bonding at the wafer level, in contrast to previously demonstrated chiplet-level integration 10 , featuring low propagation loss of 8.5 decibels per metre, enabling narrow-linewidth lasing (intrinsic linewidth of 3 kilohertz) by self-injection locking to a laser diode. The hybrid mode of the resonator allows electro-optic laser frequency tuning at a speed of 12 × 10 15  hertz per second with high linearity and low hysteresis while retaining the narrow linewidth. Using a hybrid integrated laser, we perform a proof-of-concept coherent optical ranging (FMCW LiDAR) experiment. Endowing Si 3 N 4 photonic integrated circuits with LiNbO 3 creates a platform that combines the individual advantages of thin-film LiNbO 3 with those of Si 3 N 4 , which show precise lithographic control, mature manufacturing and ultralow loss 11 , 12 . A frequency-tunable laser based on a hybrid silicon nitride and lithium niobate integrated photonic platform has a fast tuning rate and could be used for optical ranging applications.