Controllable orbital angular momentum generation based on polarization-maintaining broadband long-period fiber grating

• Non-degenerate LP 11 modes can be generated by polarization-maintaining broadband long-period fiber gratings (PM-BLPFGs). • Orbital angular momentum (OAM) with the high purity based on PM-BLPFG is generated. • OAM mode-locked (ML) pulses are generated by combining the OAM mode converter and a ML fiber laser. Orbital angular momentum (OAM) exhibits broad application prospects due to its unique special polarization distribution and spatial field distribution. In this letter, controllable OAM generation based on polarization-maintaining broadband long-period fiber grating (PM-BLPFG) is demonstrated. The 3-dB bandwidth of the grating based on the dispersion turning point (DTP) is more than 100 nm and the mode conversion efficiency is higher than 98 %, which is satisfied with the group velocity matching condition, so that the pulse walk-off effect can be effectively suppressed. And all the non-degenerated first high-order modes can be generated by the PM-BLPFGs with clear intensity distributions. Not only can not the polarization state of the incident light be changed through the grating, but also the spatial field distributions of the output higher-order modes also remain unaffected. The stable generation of OAM ±1 can be realized by splicing a segment of PM fiber (PMF) at a specific angle at the end of grating and adjusting the phase difference between the vector modes. Additionally, we demonstrate the high purity of the OAM based on the deep learning–based stochastic parallel gradient descent (DL-SPGD) algorithm. Finally, OAM mode-locked (ML) pulses are successfully generated by combining the OAM mode converter and a ML fiber laser. This study provides a controllable method for the generation of OAM and a new technique for ML fiber laser, which drives further advancements in the field of optics.