Optical linewidth of soliton microcombs

Parametric interaction of laser cavity-solitons with an external CW pump

We study the interaction of a laser cavity-soliton microcomb with an externally coupled, co-propagating tunable CW pump, observing parametric Kerr interactions which lead to the formation of both a cross-phase modulation and a four-wave mixing replica of the laser cavity-soliton. We compare and explain the dependence of the microcomb spectra from both the cavity-soliton and pump parameters, demonstrating the ability to adjust the microcomb externally without breaking or interfering with the soliton state. The parametric nature of the process agrees with numerical simulations. The parametric extended state maintains the typical robustness of laser-cavity solitons.

Fabrication of an ultra-high quality MgF2 micro-resonator for a single soliton comb generation

Crystalline micro-resonators are attractive for a wide range of applications due to their extremely high quality (Q) factor. In this paper, we develop a semi-automatic method for fabricating ultra-high Q-factor MgF₂ crystalline micro-resonators. By utilizing a force feedback sensor and corresponding control, we made a semi-automatic precision grind-and-polishing machine, and successfully fabricated trapezoid MgF₂ resonators with diameter of 9.5 mm and a root mean square surface roughness of 0.26 nm. The maximum difference of peaks and valleys is about 1.5 nm. The Q-factor was characterized to be 9.24 × 10⁹at 1550 nm by the cavity ring-down spectroscopy. A single soliton optical frequency comb was generated by pumping the microcavity with 150 mW optical power.

Synthesized spatiotemporal mode-locking and photonic flywheel in multimode mesoresonators

Dissipative Kerr soliton (DKS) frequency combs—also known as microcombs—have arguably created a new field in cavity nonlinear photonics, with a strong cross-fertilization between theoretical, experimental, and technological research. Spatiotemporal mode-locking (STML) not only adds new degrees of freedom to ultrafast laser technology, but also provides new insights for implementing analogue computers and heuristic optimizers with photonics. Here, we combine the principles of DKS and STML to demonstrate the STML DKS by developing an unexplored ultrahigh-quality-factor Fabry–Pérot (FP) mesoresonator based on graded index multimode fiber (GRIN-MMF). Complementing the two-step pumping scheme with a cavity stress tuning method, we can selectively excite either the eigenmode DKS or the STML DKS. Furthermore, we demonstrate an ultralow noise microcomb that enhances the photonic flywheel performance in both the fundamental comb linewidth and DKS timing jitter. The demonstrated fundamental comb linewidth of 400 mHz and DKS timing jitter of 500 attosecond (averaging times up to 25 μs) represent improvements of 25× and 2.5×, respectively, from the state-of-the-art. Our results show the potential of GRIN-MMF FP mesoresonators as an ideal testbed for high-dimensional nonlinear cavity dynamics and photonic flywheel with ultrahigh coherence and ultralow timing jitter.

Here the authors demonstrate spatiotemporal mode-locked dissipative Kerr soliton and enhanced photonic flywheel performances in both the fundamental comb linewidth and DKS timing jitter.