TY - GEN

T1 - Spatial Instability of Fundamental Mode in Step-Index Multimode Fiber

AU - Boni, S.

AU - Ciorra, A.

AU - Gemechu, W. A.

AU - Sparapani, A.

AU - Mangini, F.

AU - Ferraro, M.

AU - Sun, Y.

AU - Gervaziev, M.

AU - Kharenko, D.

AU - Babin, S.

AU - Wabnitz, S.

N1 - S. Boni et al., "Spatial Instability of Fundamental Mode in Step-Index Multimode Fiber," 2025 Photonics & Electromagnetics Research Symposium - Spring (PIERS-Spring), Abu Dhabi, United Arab Emirates, 2025, pp. 1-4, doi: 10.1109/PIERS-Spring66516.2025.11276557. W. A. G. acknowledges M. Zitelli for insightful discussions during the simulation and V. Couderc for index profile measurement. This work was supported by the European Innovation Council (101185664), the Marie Sklodowska-Curie Actions (101064614,101149506), the EU — Next Generation EU under the Italian National Recovery and Resilience Plan (NRRP), Mission 4, CUP B53C22004050001, partnership on “Telecommunications of the Future” (PE00000001 — program “RESTART”, the Italian Ministerial grant PRIN2022 “SAFE” (2022ESAC3K), and the Russian Science Foundation (No. 21-72-30024-Π).

PY - 2025/12/15

Y1 - 2025/12/15

N2 - Research on nonlinear optics in multimode optical fibers is a hot emerging field, motivated by applications to spatial division multiplexing in long distance communications, novel high energy laser sources, as well as for the fundamental interest in complex physical systems. A spectacular nonlinear effect which has been recently revealed in highly multimode graded-index fibers is beam self-cleaning, whereby a speckled beam transforms into a bell-shaped beam, typically dominated by the fundamental mode of the fiber. This transition is driven by the Kerr effects, and it occurs as the input power is increased above a certain value. In this paper we discuss a new type of spatial beam instability in few-mode step-index fibers, whereby a femtosecond laser beam coupled to the fiber's fundamental mode loses its stability at high peak powers. As a result, the fundamental beam becomes fully depleted, in favor of the higher-order modes of the fiber. The resulting multimode beam pattern is now dominated by the modes of highest order, and it remains remarkably stable even in the presence of external fiber perturbations. In this respect, the fundamental mode instability has a strong similarity with beam self-cleaning, but it acts in reverse.

AB - Research on nonlinear optics in multimode optical fibers is a hot emerging field, motivated by applications to spatial division multiplexing in long distance communications, novel high energy laser sources, as well as for the fundamental interest in complex physical systems. A spectacular nonlinear effect which has been recently revealed in highly multimode graded-index fibers is beam self-cleaning, whereby a speckled beam transforms into a bell-shaped beam, typically dominated by the fundamental mode of the fiber. This transition is driven by the Kerr effects, and it occurs as the input power is increased above a certain value. In this paper we discuss a new type of spatial beam instability in few-mode step-index fibers, whereby a femtosecond laser beam coupled to the fiber's fundamental mode loses its stability at high peak powers. As a result, the fundamental beam becomes fully depleted, in favor of the higher-order modes of the fiber. The resulting multimode beam pattern is now dominated by the modes of highest order, and it remains remarkably stable even in the presence of external fiber perturbations. In this respect, the fundamental mode instability has a strong similarity with beam self-cleaning, but it acts in reverse.

UR - https://www.scopus.com/pages/publications/105031910725

UR - https://www.mendeley.com/catalogue/18ab0122-d902-3afa-b257-15979c53e313/

U2 - 10.1109/piers-spring66516.2025.11276557

DO - 10.1109/piers-spring66516.2025.11276557

M3 - Conference contribution

SN - 979-8-3315-9915-7

SP - 1

EP - 4

BT - 2025 Photonics & Electromagnetics Research Symposium - Spring (PIERS-Spring)

PB - Institute of Electrical and Electronics Engineers Inc.

T2 - 2025 Photonics & Electromagnetics Research Symposium - Spring

Y2 - 4 May 2025 through 8 May 2025

ER -