Abstract
We experimentally demonstrate that spatial beam self-cleaning can be highly efficient when obtained with a few-mode excitation in graded-index multimode optical fibers. By using 160 ps long, highly chirped (6 nm bandwidth at -3dB) optical pulses at 1562 nm, we demonstrate a one-decade reduction of the power threshold for spatial beam self-cleaning, with respect to previous experiments using pulses with laser wavelengths at 1030-1064 nm. Self-cleaned beams remain spatio-temporally stable for more than a decade of their peak power variation. The impact of input pulse temporal duration is also studied.
Highlights
Nonlinear beam propagation in multimode optical fibers (MMFs) is currently being extensively investigated as a test-bed of fundamental wave propagation effects, and for a variety of different applications [1]
We experimentally demonstrate that spatial beam self-cleaning can be highly efficient when obtained with a few-mode excitation in graded-index multimode optical fibers
We experimentally investigate the process of beam self-cleaning in GRIN-MMFs under the condition of few-mode coherent excitation
Summary
Nonlinear beam propagation in multimode optical fibers (MMFs) is currently being extensively investigated as a test-bed of fundamental wave propagation effects, and for a variety of different applications [1]. As a matter of fact, an experimental validation of the condensation theory was carried out, by controlling the wave front launched into a GRIN MMF with a diffuser This permits to change the number of excited modes, while keeping constant the input power [15]. Depending on the specific input spatial coupling conditions (i.e., the incidence angle of the beam), a beam self-cleaning in the odd low-order LP11 mode can be obtained at the fiber output. This effect, as we shall explain later in the text, may be interpreted as the generation of transient beam, before its eventual decay into the fundamental mode at longer distances. The power threshold for self-cleaning is reduced by one order of magnitude with respect to previous experiments carried out in the normal GVD regime, and based on highly multimode excitation
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