Microcombs have enabled a host of cutting-edge applications from metrology to communications that have garnered significant attention in the last decade. Nevertheless, due to the thermal instability of the microresonator, additional control devices like auxiliary lasers are indispensable for single-soliton generation in some scenarios. Specifically, the increased system complexity would be too overwhelming for dual-microcomb generation. Here, we put forward a novel approach to mitigate the thermal instability and generate the dual-microcomb using a compact system. This process is akin to mode-division multiplexing, as the dual-microcombs are generated by pumping the dual-mode of a single Si3N4 microresonator with a continuous-wave laser. Both numerical simulations and experimental measurements indicate that this innovative technique could offer a straightforward way to enlarge the soliton existence range, allowing entry into the multistability regime and triggering another microcomb alongside the main soliton pulse. This outcome not only shines new light on the interaction mechanism of microresonator modes but also provides an avenue for the development of dual-microcomb-based ranging and low phase noise microwave generation.

Dissipative Kerr solitons (DKSs) with mode-locked pulse trains in high-Q optical microresonators possess low-noise and broadband parallelized comb lines, having already found plentiful cutting-edge applications. However, thermal bistability and thermal noise caused by the high microresonator power and large temperature exchange between microresonator and the environment would prevent soliton microcomb formation and deteriorate the phase and frequency noise. Here, a novel method that combines rapid frequency sweep with optical sideband thermal compensation is presented, providing a simple and reliable way to get into the single-soliton state. Meanwhile, it is shown that the phase and frequency noises of the generated soliton are greatly reduced. Moreover, by closing the locking loop, an in-loop repetition rate fractional instability of 5.5×10-15 at 1 s integration time and a triangular linear repetition rate sweep with 2.5 MHz could be realized. This demonstration provides a means for the generation, locking, and tuning of a soliton microcomb, paving the way for the application of single-soliton microcombs in low-phase-noise microwave generation and laser ranging.

The year 2019 marks the 10th anniversary of the first report of ultrafast fiber laser mode-locked by graphene. This result has had an important impact on ultrafast laser optics and continues to offer new horizons. Herein, we mainly review the linear and nonlinear photonic properties of two-dimensional (2D) materials, as well as their nonlinear applications in efficient passive mode-locking devices and ultrafast fiber lasers. Initial works and significant progress in this field, as well as new insights and challenges of 2D materials for ultrafast fiber lasers, are reviewed and analyzed.

Here, we used the micro P-scan method to investigate the saturated absorption (SA) of different layered Bi2Se3 continuous films. Through resonance excitation, first, we studied the influence of the second surface state (SS) on SA. The second SS resonance excitation (～2.07eV) resulted in a free carrier cross section that was 4 orders of magnitude larger than usual. At the same time, we found that the fast relaxation process of the massless Dirac electrons is much shorter than that of electrons in bulk states. Moreover, the second SS excitation resonance reduced the saturation intensity. Second, we studied the effect of the thickness on the SA properties of materials. The results showed that the saturation intensity was positively correlated to the thickness, the same as the modulation depth, and the thicker the Bi2Se3 film was, the less the second SS would influence it. This work demonstrated that by using Bi2Se3 as a saturable absorber through changing the thickness or excitation wavelength, a controllable SA could be achieved.