Extreme nonlinear optics in optical fibers
This paper reviews the field of extreme nonlinear optics in optical fibers, highlighting key phenomena and advancements. It discusses multiple ionization effects caused by femtosecond laser pulses that generate plasma and induce permanent material modifications, as well as plasma luminescence and its dependence on material imperfections. The formation and dynamics of plasma filaments, including helical structures, are explored, along with the rainbow spiral emission pattern useful in communications and particle manipulation. The review covers the generation of spatial-temporal waves, supercontinuum broadening, and advanced modeling techniques, such as multimode unidirectional pulse propagation equations for describing optical pulse evolution. Experimental demonstrations involving discretized conical waves and supercontinuum generation optimization are detailed. The paper emphasizes the unique capabilities of photonic crystal fibers, especially hollow-core variants, in achieving broad supercontinua and Raman frequency combs, ultrashort pulse compression, high-harmonic generation, plasma formation, and nonclassical light production. Our outlook highlights ongoing research into spatiotemporal helicon waves, ultrashort pulse propagation, vacuum ultraviolet and mid-infrared supercontinuum generation, and innovative fiber technologies. Future directions focus on enhancing fiber performance, understanding multimodal wave dynamics, and expanding applications in telecommunications, sensing, and quantum science.