Direct Generation and Amplification of Ultra-Broadband Noise-Like Pulse in an All-PM Tm-Doped Fiber Laser System

An ultra-broadband noise-like pulse (NLP) directly emitted from an all polarization-maintaining (all-PM) fiber laser is reported, for the first time. The fiber laser is designed as a figure-of-eight cavity and relies on nonlinear amplifying loop mirror for mode-locking. A phase shifter is used to ensure the self-starting capability of the fiber laser. By enhancing the intracavity positive feedback and nonlinear response, a linearly polarized ultra-broadband NLP is obtained with spectral coverage of 1900.2 nm to 2367.3 nm, corresponding to a 30 dB spectral width of 418.2 nm. The average power and pulse energy of the achieved NLP are 90.4 mW and 16.86 nJ, respectively. Then, an all-PM single-stage cladding-pumped amplifier is utilized to boost the power to 14.4 W and broaden the spectrum to >2400 nm, the corresponding pulse energy is 2.68 μJ. Such μJ-levels, all-PM, cost-effective and easy-to-integrate fiber laser system is an excellent pump source for linearly polarized optical coherence tomography and supercontinuum generation.