Dissipative Kerr solitons formed in high-Q optical microresonators provide a route to miniaturized optical frequency combs that can revolutionize precision measurements, spectroscopy, sensing, and communication. In the last decade, a myriad of integrated material platforms have been extensively studied and developed to create photonic-chip-based soliton combs. However, the photo-thermal effect in integrated optical microresonators has been a major issue preventing simple and reliable soliton generation. Several sophisticated techniques to circumvent the photo-thermal effect have been developed. In addition, instead of the single-soliton state, emerging applications in microwave photonics and frequency metrology prefer multi-soliton states. Here we demonstrate an approach to manage the photo-thermal effect and facilitate soliton generation. The approach is based on a single phase-modulated pump, where the generated blue-detuned sideband synergizes with the carrier and thermally stabilizes the microresonator. We apply this technique and demonstrate deterministic soliton generation of 19.97 GHz repetition rate in an integrated silicon nitride microresonator. Furthermore, we develop a program to automatically address to target N−soliton state, in addition to the single-soliton state, with near 100% success rate and as short as 10 s time consumption. Our method is valuable for soliton generation in essentially any platforms even with strong photo-thermal effect, and can promote wider applications of soliton frequency comb systems for microwave photonics, telecommunication and frequency metrology.
Figure 1. Principle and numerical simulation of soliton generation in optical microresonators assisted with sideband heating. (a). Comparison of soliton step length without (top row) and with (bottom row) sideband heating. Left column shows the photos of the same Si3N4 microresonator of 19.97 GHz FSR. Red and blue arc arrows represent the CW carrier pump and the blue-detuned sideband. Middle column show the intra-cavity power dynamics (solid black line) and the “cold” resonance (dashed black line). Right column shows the intra-cavity temperature dynamics. If the scanning pump (red line) stops on the soliton step, a soliton state is formed (red spot). Such a process can be facilitated by the blue-detuned sideband (blue line), which locks the “hot” resonance, avoid its shift, and extend the soliton step. (b). Numerical simulation of the intra-cavity power (blue) and temperature(red), without (left) and with (right) the blue-detuned sideband. The simulation reveals soliton step extension due to the blue-detuned sideband.
