Fig. 1. Comparison of process flow for several laser integration methods with Si PICs^[19]

Fig. 2. Ⅲ-Ⅴ/Si/SiN multilayer heterogeneously integrated laser^[48]. (a) Process flow of multilayer heterogeneous integration; (b) schematic of the structure; (c) comparison of temperature stability; (d) noise performance

Fig. 3. Ⅲ-Ⅴ/Si/SiN fully heterogeneous integrated E-DBR laser^[49]. (a) Process flow of fully heterogeneous integration; (b) top-view schematic illustration of the E-DBR laser; (c) three different operating states of Ⅲ-Ⅴ/Si/SiN fully integrated laser

Fig. 4. Heterogeneously integrated tunable lasers. (a) Schematic of integrated coherent tunable laser with ultra-wideband wavelength tuning and sub-100 Hz Lorentzian linewidth (left), various high-resolution integrated coherent tunable laser spectra (right)^[73]; (b) broadband tunable laser array construction including entire low-loss fiber telecommunication window (left), optical spectra of the E-band laser tuned from 1350 nm to 1408 nm with SMSR greater than 50 dB (right) ^[74]; (c) schematic of the integrated mode-hop-free tunable heterogeneously integrated laser (left), calibration results of the mode-hop-free tuning algorithm (right) ^[75]

Fig. 4. 3D integration enables ultralow-noise isolator-free lasers in silicon photonics^[27]. (a) Concept of 3D photonic integration (top left) and physical diagram of fabricated 3D PIC (bottom left), cross-section of the demonstrated 3D PIC, and expected additional EIC integration to be achieved in future work (right); (b)frequency noise of the laser output taken from the through port and drop port of the ring resonator; (c) frequency noise of the drop port at the self-injection locking condition under different on-chip feedback levels

Fig. 6. Laser soliton microcombs are heterogeneously integrated on silicon^[81]. (a) Schematic of laser soliton microcomb devices consisting of DFB lasers, phase tuners, and high-Q microring resonators; (b) optical spectra of different soliton states

Fig. 7. Microwave signal generation based on heterogeneously integrated lasers. (a) Schematic of widely tunable microwave-signal generation^[27]; (b) schematic design of a photonic microwave oscillator on a single chip with ultra-low phase noise^[113]

Fig. 8. Electronic-photonic integrated circuits based on heterogeneously integrated laser. (a) Schematic of 3D electronic-photonic heterogeneous integration^[27]; (b) interconnect distances and electrical wiring length dependence for connectivity solutions^[95]