All-fiber mode-locked fiber lasers using femtosecond-direct writing nano-grating polarizers

We demonstrate an all-fiber mode-locked laser employing a femtosecond-laser-inscribed nano-grating polarizer (NGP) as the key intracavity polarization element. This NGP device is fabricated in a single step without the need for precise angular control, offering superior robustness and integration potential compared to conventional tilted fiber gratings. Integrated into a unidirectional ring cavity, the laser generates stable dissipative soliton pulses at 1041.22 nm with a 3-dB bandwidth of 4 nm and a pulse duration of 20.87 ps. The repetition rate is 33.52 MHz. At a pump power of 417 mW, the average output power is 14.73 mW, yielding a high signal-to-noise ratio of 62.12 dB, which confirms excellent stability. The current optical-to-optical conversion efficiency is 4.4%, primarily limited by the NGP's insertion loss (∼8.7 dB). This work establishes the NGP not only as a promising component but as a practical and enabling technology for developing compact, low-cost, and robust integrated ultrafast photonic systems.