Kerr Beam Self-Cleaning in the Telecom Band

Multimode graded index (GRIN) fibers received a renewed interest in recent years, in particular for the development of new laser sources [1]. In many cases, the use of GRIN fibers is limited by multimodal propagation, leading to a spatially modulated intensity distribution (speckles) at the fiber output. Recent studies have found that quasi-single mode propagation can be recovered in GRIN fibers by the so-called Kerr self-cleaning effect [2]. It consists in the spontaneous recovery of the spatial beam quality, without any frequency shift [2] (as opposed to, e.g., Raman beam self-cleaning [3]). This nonlinear process was only observed so far at laser wavelengths around 1 μm, for peak power levels above a certain threshold value. In this communication, we show that Kerr beam self-cleaning also occurs in a GRIN fiber pumped with chirped pulses in the telecom band (1562 nm). At these wavelengths, the power threshold of the self-cleaning process is decreased by one order of magnitude with respect to pumping at 1 μm.