Sub-40 fs Pulses from a Tapered Yb-Doped Fiber Amplifier with Self-Similar Amplification

We extended self-similar amplification to a large-mode-area tapered Yb-doped fiber (LMA T-YDF) with longitudinally decreasing nonlinearity. The theoretical analysis and numerical simulation demonstrate that T-YDFs with different nonlinearity profiles can achieve self-similar evolution, which is confirmed by a self-similar amplifier that employs two kinds of T-YDFs. Further experimental study indicates that the T-YDF with a large core diameter at the thin end can achieve self-similar evolution across a wide range of pump powers and generate 51 W average power, 34 fs nearly transform-limited (TL) pulses with 32 dB gain. To the best of our knowledge, this is the first theoretical and experimental demonstration of self-similar amplification in T-YDFs. The high-gain feature of the T-YDF simplifies the laser system and can be used to build a compact all-fiber high-power femtosecond laser source.