Fig. 3.

Heterogeneous integration technology. a A schematic illustration of the bonding process. b A fully integrated Si3N4-based laser through multiple wafer bonding. Adapted with permission from [58], copyright 2020, OPG. c A heterogeneously-integrated QCL with the longest wavelength at 4.8 μm. Adapted with permission from [63], copyright 2016, OPG. d Compact low-threshold micro-ring lasers with heterogeneously integrated QD epitaxial material as an active layer. Adapted with permission from [65], copyright 2019, OPG. e Heterogeneously integrated QD-DFB lasers with efficient light coupling to the silicon waveguide. Adapted with permission from [66], copyright 2021, WILEY. f Widely tunable lasers using a coupled-triple ring structure. Adapted with permission from [69], copyright 2019, IEEE. g Laser soliton microcombs. Adapted with permission from [21], copyright 2021, AAAS