Fig. 1. Schematics of WGMR principle. (a) Schematic of constructive interference in micro-ring resonator; (b) typical electric field distribution with whispering gallery mode

Fig. 2. Structural diagram of narrow linewidth self-injection locked laser based on WGMR

Fig. 3. Laser self-injection locking bandwidth adjustment based on WGMR

Fig. 4. Structural diagram of 3.4 μm band on-chip laser, reproduced with permission from Ref.[81](©2021 Springer Nature Ltd.)

Fig. 5. Application of WGMR-based nonlinear optics. (a) Optical frequency comb, reproduced with permission from Ref.[90](©2019 Springer Nature Ltd.); (b) integrated Raman laser, reproduced with permission from Ref.[91](©2017 The Optical Society of America); (c) narrow-linewidth Brillouin laser, reproduced with permission from Ref.[89](©2022 Optica); (d) integrated visible light source, reproduced with permission from Ref.[24](©2021 Springer Nature Ltd.)

Fig. 6. Schematic of generating device of self-injection locking optical frequency comb based on WGMR