Shaping the light beam is always essential for laser technology and its applications. Among the shaping technologies, shaping the laser in its Fourier domain is a widely used and effective method, such as a pulse shaper, or a 4f system with a phase mask or an iris in between. Orbital angular momentum (OAM) modes spectrum, the Fourier transform of the light field in azimuth, provides a perspective for shaping the light. Here, we propose and experimentally demonstrate a shaping strategy for the azimuthal field by modulating the complex amplitude of the OAM mode spectrum. The scheme utilizes multi-plane light conversion technology and consists only of a spatial light modulator and a mirror. Multiple functions, including beam rotating, beam splitting/combining in azimuth, and OAM mode filtering, are demonstrated. Our work provides a compact and programmable solution for modulating the OAM mode spectrum and shaping beams in azimuth.

激光光束整形技术在现代激光工业领域具有重要作用，为了克服传统激光光束整形自由曲面构造中存在法向矢量偏差的局限性，文中提出一种正交双向迭代的自由曲面设计方法。该方法基于能量守恒和斯涅尔定律建立光源与目标面的能量映射关系，通过正交方向坐标点迭代获得自由曲面数据点，同时利用相邻坐标点的均值进行曲面法向矢量修正，从而提高自由曲面的构造精度。设计实例表明，准直入射的激光光束经自由曲面整形反射镜，在特定目标区域内可形成高均匀度光斑。进一步从自由曲面的连续性、拟合精度与面形误差三个方面，与传统设计方法进行了详细对比分析。结果表明，所提设计方法得到的激光光束整形自由曲面连续性与平滑度更好，拟合精度更高；且在加工误差允许范围内，目标面的辐照度均匀性更稳定。

We develop a method for completely shaping optical vector beams with controllable amplitude, phase, and polarization gradients along three-dimensional freestyle trajectories. We design theoretically and demonstrate experimentally curvilinear Poincaré vector beams that exhibit high intensity gradients and accurate state of polarization prescribed along the beam trajectory.

Experimental generation of stable mode-locked pulses and cylindrical vector beams (CVBs), from an all few-mode fiber (FMF) ring laser is first reported, to the best of our knowledge. In this laser, a section of few-mode erbium-doped fiber (FM-EDF) is used as the gain medium. The FM-EDF is pumped by 976 nm laser with LP₁₁ mode, which is simultaneously converted and multiplexed through a homemade hybrid device, i.e., wavelength division multiplexing-mode selection coupler (WDM-MSC). All the components in our experiment are connected using FMF. The resulted CVB pulses have a spectral width of 0.33 nm with a repetition rate of 30.58 MHz under the pump power of 340 mW. Moreover, both azimuthally and radially polarized CVBs were achieved with a high purity of >95%. This mode-locked CVB fiber laser with an all FMF configuration opens the way to manipulate the transverse mode in mode-locked fiber lasers.