GHz-Level Ultrafast Fiber Laser Using a Weakly Polarization Selective Grating

作者：Sheng Zhang, Ying Wan, Chen Jiang, Zhiqin Huang, Fengji Gui, Xuelin Lei, Yunqi Liu, Jianxiang Wen, Zuxing Zhang · 发表于：IEEE Photonics Technology Letters · 年份：2025 · DOI：10.1109/lpt.2025.3623181 · 被引用次数：1 · 研究领域：Advanced Fiber Optic Sensors、Advanced Fiber Laser Technologies、Photonic Crystal and Fiber Optics

We demonstrate an all-fiber harmonic ultrafast fiber laser employing a weakly polarization-dependent long-period fiber grating (WP-LPFG) as a polarization-selective element. The grating was fabricated in standard single-mode fiber using a CO2laser heating technique, exhibiting a maximum polarization-dependent loss (PDL) of only 1.36 dB due to its uniform thermal modulation. Integrated into the laser cavity and combined with a nonlinear polarization rotation (NPR) scheme, the WP-LPFG enables stable harmonic mode-locking. The repetition rate of the laser is tunable from 36.6 MHz to 1.39 GHz by adjusting the pump power, and from 4.428 GHz to 10.573 GHz by varying the intracavity polarization state. A 107th-order harmonic mode-locking state featuring a loosely bound two-soliton structure is also achieved, with a spectral modulation of 1.42 nm, pulse separation of 5.68 ps, and a repetition rate of 1.957 GHz. These results demonstrate that LPFG with a PDL around 1 dB could also acts as mode-locking devices for ultrafast pulse generation. This expands the range of polarization-selective element available for fiber lasers and provides a practical alternative to existing techniques.