Fig. 1. (a) Schematics of two types of lasers (InAs QD laser on GaAs/chirped InAs QD laser on Si) self-injection locked into multiple wavelengths via a PM-fiber-based external cavity. (b) Structure layout of InAs QD laser grown on standard GaAs substrate. (c) Structure layout of chirped InAs QD laser epitaxially grown on Si (001) substrate.

Fig. 2. (a) Optical comb spectrum of free-running InAs/GaAs QDLGS. Inset: measured single-channel optical linewidth. (b) Optical comb spectrum of self-injection locked InAs/GaAs QDLGS with narrowed optical linewidth. Insets: measured optical linewidth of self-injection locked comb lines. Optical spectra of (c) single peak injection locked, (d) second-order injection locked, (e) third-order injection locked, and (f) fifth-order injection locked lasers. Insets: zoom-in spectra of different orders of injection locked conditions, which match the y scale of the main panel.

Fig. 3. (a) Optical comb spectral evolution of InAs/GaAs QDLGS from free-running condition into multi-peak injection locking states (single peak to five peaks). Spectral mapping of FP laser diode under different feedback levels (−35  dB to −10  dB) for (b) dual-peak injection locking state, (c) three-peak injection locking state, and (d) four-peak injection locking state. (e) Spectral mapping of multi-peak injection locking states.

Fig. 4. Self-injection locking of chirped QDLSI. (a) Original optical spectrum of InAs QD laser on Si operated at injection current of 75 mA. (b) The multi-wavelength injection locked comb spectrum with 75 GHz comb spacing. Average optical linewidth of each comb line is approximately 20 kHz (red line). (c) The measured optical linewidth spectra of the original laser modes (top) and self-injection locked comb lines (bottom) via self-heterodyne method. The original optical linewidth of 14.6 MHz is narrowed to 23.93 kHz via the multi-wavelength injection locking technique. (d) The optical spectrum of InAs QD laser on Si operated at higher injection current of 125 mA with merged dual modes. (e) The multi-wavelength injection locked comb spectrum with 50 GHz comb spacing. Optical linewidth of each comb line ranges from 50 to 80 kHz (red line). (f) The measured optical linewidth spectra of original laser modes (top) and self-injection locked comb lines (bottom) both at driving current of 125 mA. The optical linewidths are 19 MHz and 53 kHz, respectively. (g) The optical spectral mapping against varied PMF loop length showing the relationship between FSR and effective PMF length. (h) RIN spectra of injection-locked comb source (blue) and injection-locked SSB up to 25 GHz.

Fig. 5. (a) Optical spectrum, (b) RF spectrum, and (c) wavelength stability diagram of unstable dual-peak injection locked QDLSI. (d) Optical spectrum, (e) RF spectrum, and (f) wavelength stability diagram of stable dual-peak injection locked QDLSI.