Fig. 1. Optical link-budget and resulting performance specifications on optical transmitter (OTX) for 8-λ DWDM^[22]

Fig. 2. Hybrid integrated microring lasers^[11]. (a) Schematic of a multi-channel hybrid microring laser transmitter; (b) SEM image of a fabricated device; (c) cross-sectional schematic of the device with highlighted metal-oxide-semiconductor (MOS) capacitor, (d) an infrared (IR) image of a 5-channel transmitter in operation

Fig. 3. On-chip laser for FMCW LiDAR. (a) Schematic of FMCW LiDAR based on DBR laser^[36]; (b) schematic of FMCW LiDAR based on SGDBR laser^[36]; (c) tunable ECL consists of GaSb gain chip and SOI-based rings^[37]

Fig. 4. Different laser solutions for OCT system. (a) ECL empowered by III‒V/Si RSOA and tunable external cavity^[39]; (b) gain structure of SLD based on excited state broadening effect of quantum dots^[40]; (c) schematic of a thermally tunable VCSEL based SS-OCT applied to retinal scanning^[41]

Fig. 5. Approaches to narrow linewidth lasers. (a) Wavelength tunable laser with silicon photonic-wire waveguide resonators^[52];

Fig. 6. Solutions to couple laser sources to waveguide. (a) Grating coupling between VCSEL and SOI waveguide^[60]; (b) adiabatic coupling between Ge photodetector and Si waveguide^[74]; (c) ultra-low loss adiabatic coupling between III‒V active layer and Si waveguide^[67]; (d) photonic wire bonding between photonic chips^[75]

Fig. 7. Different generation principles of multi-wavelength source. (a) Two sectional mode-locked laser, including forward biased gain section and reverse biased saturable absorber^[79]; (b) optical frequency comb based on Kerr effect (wide-spectral soliton origins from the balance between different nonlinear effects realized in high Q Si₃N₄ micro ring resonator which is pumped by CW DFB laser)^[81]; (c) electro-optic mode-locked laser based on LiNbO₃ modulator^[86]

Fig. 8. Evolution of silicon-based QD on-chip laser. (a) Pulsed lasing 1.3 μm InAs QD laser grown on silicon substrate^[90]; (b) schematic of the layer structure of an InAs/GaAs QD laser on a silicon substrate and its LIV characteristics at room temperature^[91]; (c) life-time of Gen-I, Gen-II, and Gen-III monolithic III‒V lasers on silicon^[92]; (d) schematic of the III‒V materials epitaxially grown on V-shaped silicon substrate^[93]; (e) scanning electron microscopy image of III‒V FP laser using AlGaAs layer to inhibit antiphase domain^[94]; (f) schematic of silicon U-shape patterned substrate for obtaining holes and V-shaped structures through homogeneous epitaxy, followed by insitu heterogeneous epitaxial growth of III‒V materials ^[96]; (g) cross-sectional SEM image of InAs FP laser in situ epitaxially grown GaAs/Si (001) substrate^[97]; (h) III‒V QD DFB laser on silicon^[98]; (i) direct coupling between III‒V laser and silicon waveguide^[100]