Unveiling impacts of PMD on spectral modulations in PM-fiber-based ultrafast amplifiers

In this work, polarization mode dispersion (PMD) in polarization-maintaining (PM) fibers, to the best of our knowledge, is first proposed and experimentally proved to be responsible for severe spectral modulations in ultrafast PM fiber amplifiers, the introduction of which can give reasonable explanation for the dense spectral ripples imposed on the spectra of amplified lasers from the commonly used all-PM-fiber or hybrid “PM-fiber + bulk crystal” amplifiers, including both high-power amplifiers with remarkable nonlinear effects (self-phase modulation, SPM) and even low-power amplifiers with negligible nonlinear effects.