Fig. 1. Principle of microcavity optical frequency comb. (a) Optical propagation process of microcavity; (b) principle of FWM; (c) principle of primary comb generation based on degenerate FWM; (d) principle of comb extension based on cascaded FWM; (e) principle of sub-comb generation based on cascaded FWM

Fig. 2. Silicon nitride microcavity optical frequency comb test system

Fig. 3. Wavelength scanning transmission test and detuning analysis of silicon nitride microcavity. (a) Microcavity transmission spectrum during forward scanning(inset: transmission spectrum of microcavity with 50 μW pump); (b) resonance state in the process of power increase in microcavity; (c) non-resonant state of microcavity after power jump

Fig. 4. Optical frequency comb spectral characterizations in silicon nitride microcavity. (a) Spectrogram without sideband; (b) primary sideband spectrogram; (c) spectrum of “Turing Ring” states produced in the late second stage; (d) spectrum of “Turing Ring” states produced in the third stage; (e) spectral diagram of chaotic states generated by high power pumping

Fig. 5. Distribution and resonant states of equilibrium solutions. (a) Distribution of three equilibrium solutions; (b), (c), and (d) are the cavity real-time resonant states corresponding to the warm cavity stable solution, warm cavity unstable solution, and cold cavity stable solution, respectively.

Fig. 6. Disturbance test of thermal self-stability of microcavity