Ultrafast tunable lasers using lithium niobate integrated photonics
Viacheslav Snigirev, Annina Riedhauser, Grigory Lihachev, Mikhail Churaev, Johann Riemensberger, Rui Ning Wang, Anat Siddharth, Guanhao Huang, Charles Möhl, Youri Popoff, Ute Drechsler, Daniele Caimi, Simon Hönl, Junqiu Liu, Paul Seidler, Tobias J. Kippenberg
Abstract
Abstract 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 .