Long-Period Fiber-Grating-Based Filter for Generation of Picosecond and Subpicosecond Transform-Limited Flat-Top Pulses

We suggest and demonstrate an all-fiber pulse shaper for synthesizing transform-limited flat-top waveforms. The proposed scheme can be easily scaled down to the (sub-)picosecond regime while offering low polarization dependence and extremely low insertion loss. It is based on a cascade of two long-period fiber gratings. As a proof-of-concept experiment, we report the generation of transform-limited flat-top pulses with full-width at half- maximum duration of 2 ps, which is over two times faster than the shortest transform-limited flat-top pulse ever generated with an all-fiber filter.