Self-sustained microcomb lasing in an integrated hybrid oscillator

Abstract

Microcavity optical frequency combs (microcombs) are compact, coherent light sources whose chip-scale integrability is poised to drive advances in metrology, communications, and sensing. Among available microcomb generation methods, hybrid cavities uniquely co-locate gain and Kerr dynamics, where the lasing mode directly resonates in the nonlinear microcavity, simultaneously enabling self-sustained and highly efficient microcomb generation. However, their implementation is often limited by partial integration or the need for external injection, which complicates operation architecture, raises power and hampers system miniaturization. In this work, we present a fully integrated hybrid cavity for self-sustained microcomb generation, relying solely on the co-oscillation of lasing and Kerr nonlinearity without external driving. The system collapses the pump laser, nonlinear resonator and feedback loops into a minimalist on-chip two-element cavity, consisting of a high-Q microresonator with engineered intracavity reflection and a reflective semiconductor optical amplifier (RSOA). The scheme delivers self-starting operation and stable performance without active feedback. The generated coherent microcomb achieves intrinsic linewidths below 1 kHz and integrated linewidths around 100 kHz, with self-sustained operation exceeding 24 hours. This ultra-compact architecture provides a practical path toward scalable, coherent multi-wavelength sources for integrated photonic systems.

Figures (5)

• Figure 1: Principle and basic characterization. a, Comparison of different hybrid cavity schemes of self-injection locking shen2020integratedgil2025high (a1), dual ring filtering stern2018battery (a2) and the one in this manuscript (a3). Top: device structure. Middle: optical responses of different devices, with he black line indicating the gain spectrum. The red, purple and blue curve represent the filter response of the CW laser cavity in a1, dual rings in a2 and the high-Q cavity respectively. Solid and dash lines indicates whether lasing modes can be built up. Bottom: generated spectra from different schemes. b, Photo of a hybrid oscillator. The white and red lines show the photonic circuits on the SiN chip and the RSOA chip respectively. The blue and pink lines denote the propagation directions of the CCW and CW fields, respectively. c, The normalized transmission spectrum of the microresonator. d, The normalized reflection spectrum of the microresonator. e, Integrated dispersion profile. f, The transmission and reflection spectrum of the resonance around 1566.5 nm (191.50 THz). g, Loaded quality factor of resonances.
• Figure 2: Microcomb generation in simulation. a, The concept of the model. b1-3, The simulated temporal field evolution with the phase detuning under saturation powers of 0.02, 2.5 and 10 mW. c, The temporal fields at the marked detuning in Fig. 2b1-3. d, The optical spectra at the marked detuning in Fig. 2b1-3.
• Figure 3: Microcomb generation in experiment. a, Test link. b, The recorded beat spectra with the tuning of the applied voltage on the phase shifter. The optical spectrum of coherent comb state 1 (c1), 2 (c2) and noisy comb state (c3).
• Figure 4: Coherence characterization. a, Test link. b, The optical spectrum of a coherent microcomb state. c, The frequency noise profile of different comblines. d, The measured integrated linewidths (within 1 ms) and intrinsic linewidths of different comblines.
• Figure 5: Turnkey operation and long-term stability. a, Test link. b, The comb power variation with time. c, The spectrogram of the beating signal between the output of the hybrid cavity and the reference laser. d, The optical spectrum during a day. e, The frequency noise profile of one combline. f, The combline power variation during a day. g, The intrinsic linewidth and integrated linewidth (within 1 ms) variation during a day.