Efficient Beam Self-Cleaning in a Dissipative Double-Clad Fiber

Recent years have seen a resurgence of interest in multimode fibers due to their intriguing physics and applications, with spatial beam self-cleaning (BSC) having received revived attention. In BSC initially multimode light condenses into the fundamental fiber mode at elevated intensities. Nevertheless, BSC found little application as even the best demonstrations so far did not reach more than 75% fundamental mode content. Here we present a method for sufficiently enhancing the beam quality in BSC by employing a dissipative double-clad fiber. Using this fiber, we demonstrate a record-breaking LP₀₁ content of 98%, which constitutes the best demonstrated BSC to date. Concomitantly, transmission reaches 34% for maximum injected powers, which clearly improves over low-power transmission values of less than 10%. Saturable absorption of the erbium-doped fiber core there appears to play a pivotal role in enabling much more efficient BSC.