Fig. 1. (a) Experimental setup to measure the Q factor and dispersion of Si₃N₄ microresonators: ECDL, external-cavity diode laser; PD, photodetector; PC, polarization controller; OSC, oscilloscope; DUT, the device under test. (b) Measured integrated dispersion of the microresonators. (c) Measured Q factor from 1520 to 1570 nm, including intrinsic Q factor, coupling Q factor, and loaded Q factor.

Fig. 2. (a) Experimental setup of frequency tuning. AWG, arbitrary waveform generator; EDFA, erbium-doped fiber amplifier; OSA, optical spectrum analyzer; MRR, microring resonator; FBG, fiber Bragg grating. (b) Transmission of pump and comb. There is a distinct soliton step with a length on the order of ms. (c)–(h) are experimentally measured comb optical spectra of frequency tuning, representing the primary comb, secondary comb, chaos, multi-soliton, dual-soliton, and single-soliton states, respectively.

Fig. 3. (a) Diagram of self-injection locking. (b) Photograph of a self-injection locking system. (c) Evolutions of power and wavelength parameters of the lens-packed DFB laser versus the injection current.

Fig. 4. (a) Comb power evolution with sweeping laser current (1 s sweep) under varying distances between the DFB laser and microresonator. (b) Single scan power transmission spectrum at a particular phase. (c) Experimentally measured comb optical spectra of SIL by tuning the phase.

Fig. 5. Experimentally measured comb optical spectra of frequency tuning (blue) and SIL (green). (a), (b) represent chaos and single-soliton spectra of 100.44 GHz, respectively. (c) Evolution of comb power by frequency tuning. The orange step is a characteristic feature of soliton formation. (d) Intracavity power curve (blue) of SIL by frequency detuning. The dashed orange line represents the laser tuning curve, and point A indicates soliton formation.

Fig. 6. Intrinsic linewidth comparison between pump frequency tuning (blue) and SIL (red).