Stable Mode-Locked Nanosecond Chirp-Free Pulse Generation With Ultra-Narrow Bandwidth

A stable nanosecond chirp-free pulse generation with ultra-narrow bandwidth is established from a passively mode-locked erbium-doped fiber laser with a homemade fiber Bragg grating as the intra-cavity filter and careful intra-cavity dispersion management introduced. The laser generates nearly chirp-free pulse that is close to the Fourier transform-limited condition. The measured pulsewidth is 2 ns and the spectral width is only 192 MHz. The measured time jitter is below 1%. The pulse repetition rate is 982 kHz, which reveals there are only 195 oscillating longitudinal modes. This is the longest duration of single stable chirp-free pulse in passively continuous-wave mode-locked fiber lasers to our best knowledge.