Mode-locked microcombs with flat spectral profiles provide the high signal-to-noise ratio and are in high demand for wavelength division multiplexing (WDM)-based applications, particularly in future high-capacity communication and parallel optical computing. Here, we present two solutions to generate local relatively flat spectral profiles. One microcavity with ultra-flat integrated dispersion is pumped to generate one relatively flat single soliton source spanning over 150 nm. Besides, one extraordinary soliton crystal with single vacancy demonstrates the local relatively flat microcomb lines when the inner soliton spacings are slightly irregular. Our work paves a new way for soliton-based applications owing to the relatively flat spectral characteristics.

为了实现粒子的非轴向旋转操控，对圆偏振涡旋光的光致旋转特性进行了研究。理论上，利用T矩阵理论，计算光场作用于微粒的光力和力矩，分析圆偏振涡旋光场中自旋角动量和轨道角动量的取向对非轴向旋转效应的影响。研究结果表明：当轨道角动量和自旋角动量的方向相同时，粒子除受轨道矩和轴向自旋矩作用外，还受一个可观的横向自旋矩作用，可以诱导粒子同时做轨道和非轴向自旋运动；当轨道角动量和自旋角动量方向相反，则粒子受到的横向自旋矩难以驱动其做非轴向自旋运动。实验上，利用全息光镊系统捕获微米尺度的粒子，观察到粒子做轨道运动时的非轴向自旋现象，对理论研究结果进行了初步验证。

We investigate frequency-comb generation in normal dispersion silicon microresonators from the near-infrared to mid-infrared wavelength range in the presence of multiphoton absorption and free-carrier effects. It is found that parametric oscillation is inhibited in the telecom wavelength range resulting from strong two-photon absorption. On the contrary, beyond the wavelength of 2200 nm, where three- and four-photon absorption are less detrimental, a comb can be generated with moderate pump power, or free-carriers are swept out by a positive-intrinsic-negative structure. In the temporal domain, the generated combs correspond to flat-top pulses, and the pulse duration can be easily controlled by varying the laser detuning. The reported comb generation process shows a high conversion efficiency compared with anomalous dispersion regime, which can guide and promote comb formation in materials with normal dispersion. As the comb spectra cover the mid-infrared wavelength range, they can find applications in comb-based radiofrequency photonic filters and mid-infrared spectroscopy.