Gamma-shaped long-cavity normal-dispersion mode- locked Er-fiber laser for sub-nanosecond high-energy pulsed generation

We propose the design of a novel γ-shaped fiber laser resonator and apply it to build a long-cavity normal- dispersion mode-locked Er-fiber laser which features enhanced functionalities for management and optimization of pulsed las- ing regimes. We report the generation of sub-nanosecond pulses with the energy of ∼ 0.5 μJ at a kilohertz-scale repetition rate in an all-fiber system based on the new laser design. A combi- nation of special design solutions in the laser, such as polariza- tion instability compensation in the ultra-long arm of the res- onator, intra-cavity spectral selection of radiation with a broad- band fiber Bragg grating, and polarization selection by means of a tilted refractive index grating, ensures low amplified spon- taneous emission (ASE) noise and high stability of the laser system output parameters.