Propagation of light in multimode optical fibers usually gives a spatial and temporal randomization of the transmitted field similar to the propagation through scattering media. Randomization still applies when scattering or multimode propagation occurs in gain media. We demonstrate that appropriate structuration of the input beam wavefront can shape the light amplified by a rare-earth-doped multimode fiber. Profiling of the wavefront was achieved by a deformable mirror in combination with an iterative optimization process. We present experimental results and simulations showing the shaping of a single sharp spot at different places in the output cross-section of an ytterbium-doped fiber amplifier. Cleaning and narrowing of the amplifier far-field pattern was realized as well. Tailoring the wavefront to shape the amplified light can also serve to improve the effective gain. The shaping approach still works under gain saturation
showing the robustness of the method. Modeling and experiments attest that the shaping is effective even with a highly multimode fiber amplifier carrying up to 127 modes.
Wright LG, Wabnitz S, Christodoulides DN, Wise FW. Ultrabroadband dispersive radiation by spatiotemporal oscillation of multimode waves.Phys Rev Lett2015;115: 223902..
Di Leonardo R, Bianchi S. Hologram transmission through multi-mode optical fibers.Opt Express2011;19: 247–254..
Choi Y, Yoon C, Kim M, Yang TD, Fang-Yen Cet al. Scanner-free and wide-field endoscopic imaging by using a single multimode optical fiber.Phys Rev Lett2012;109: 203901..
Čižmár T, Dholakia K. Exploiting multimode waveguides for pure fibre-based imaging.Nat Commun2012;3: 1027..
Papadopoulos IN, Farahi S, Moser C, Psaltis D. Focusing and scanning light through a multimode optical fiber using digital phase conjugation.Opt Express2012;20: 10583–10590..
Mahalati RN, Askarov D, Wilde JP, Kahn JM. Adaptive control of input field to achieve desired output intensity profile in multimode fiber with random mode coupling.Opt Express2012;20: 14321–14337..
Liew SF, Popoff SM, Mosk AP, Vos WL, Cao H. Transmission channels for light in absorbing random media: from diffusive to ballistic-like transport.Phys Rev B2014;89: 224202..
Hao X, Martin-Rouault L, Cui M. A self-adaptive method for creating high efficiency communication channels through random scattering media.Sci Rep2014;4: 5874..
Jung Y, Kang QY, Sahu JK, Corbett B, O'Callagham Jet al. Reconfigurable modal gain control of a few-mode EDFA supporting six spatial modes.IEEE Photon Technol Lett2014;26: 1100–1103..
Mahalati RN, Askarov D, Kahn JM. Adaptive modal gain equalization techniques in multi-mode Erbium-doped fiber amplifiers.J Lightwave Technol2014;32: 2133–2143..
Huang PS, Zhang S. Fast three-step phase-shifting algorithm.Appl Opt2006;45: 5086–5091..
Shen XL, Kahn JM, Horowitz MA. Compensation for multimode fiber dispersion by adaptive optics.Opt Lett2005;30: 2985–2987..
Morales-Delgado EE, Farahi S, Papadopoulos IN, Psaltis D, Moser C. Delivery of focused short pulses through a multimode fiber.Opt Express2015;23: 9109–9120..
Katz O, Small E, Bromberg Y, Silberberg Y. Focusing and compression of ultrashort pulses through scattering media.Nat Photon2011;5: 372–377..