Linewidth-tunable single-frequency triangle-shaped nanosecond-pulsed fiber laser immune to SPM-induced spectral broadening

In this work, the linewidth performance of triangle-shaped pulsed fiber laser (TPL) with 6.5-ns pulse width was investigated numerically and experimentally. The spectral linewidth of TPL changed with different rising times and fixed pulse width. The minimum spectral linewidth could be obtained when the rising time or falling time is equal to 0. Besides, the self-phase modulation (SPM) could be suppressed when the rising time of TPL is less than 3.25 ns, and the tunable linewidth from 77.73 MHz to 86.69 MHz was obtained at 2.1-kW peak power of pulse. It was found that experimental results are consistent with the theoretical analysis.