Mode-locked large-mode-area Er/Yb-doped fiber oscillator via nonlinear polarization evolution with enhanced mode suppression

Abstract

We report a mode-locked Er/Yb-doped large-mode-area (LMA) fiber oscillator based on nonlinear polarization evolution (NPE), which utilizes a linear cavity primarily composed of polarization-maintaining (PM) fibers. The oscillator operates at 1.56 µm with a fundamental repetition rate of 34.47 MHz and has two output ports. One port can deliver high-quality soliton-like pulses with a pulse duration of 325 fs and an average power of 39.5 mW (corresponding to a pulse energy of 1.15 nJ). In contrast, the other port not only generates lower-quality complex pulses but also exhibits poorer short-term and long-term stability, likely due to cross-phase modulation effects. To the best of our knowledge, this is the first implementation of the NPE mode-locked technology in a PM-LMA Er/Yb-doped fiber oscillator at 1.55 µm which often suffers from poor self-starting mode-locking capabilities. This achievement is primarily attributed to the use of endlessly single-mode photonic crystal fibers, which effectively suppress higher-order modes in PM-LMA fibers.