Extreme nonlinear optics in optical fibers

TL;DR

This review surveys extreme nonlinear optics in optical fibers, detailing MPI-driven material modification, plasma dynamics, filamentation, and rainbow spiral emission in multimode and hollow-core fibers. It highlights space-time wavepackets and MM-UPPE modeling as tools to understand and design ultrabroadband frequency conversion near self-focusing, with experimental demonstrations of discretized conical waves and optimized supercontinua. The hollow-core photonic crystal fiber platform emerges as a versatile bridge to gas-phase nonlinearities, enabling SRS, SC across UV-to-mid-IR, ultrashort pulse compression, high-harmonic generation, guided plasma formation, and nonclassical light generation. The article outlines a forward-looking agenda toward spatiotemporal helicon waves, ultrafast pulse propagation, mid-IR to vacuum-UV continua, and fiber technologies that can impact telecommunications, sensing, and quantum science.

Abstract

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.

Figures (18)

• Figure 1: Deterioration of the fiber material because of MPI. a) Transmission quenching vs. time. The dashed horizontal line represents the steady value of transmission reached, once that the deterioration process is over. b) Optical microscope image of the damage formed in the vicinity of the input GRIN fiber tip. The white bar corresponds to 100 $\mu$m. Details are available in Ref. Ferraro2022.
• Figure 2: a) A sketch of the experimental setup used for generating UL in silica fibers using 5-photon absorption Mangini2020. b-d) Digital microscope images of the luminescence scattered from GRIN with 62.5 $\mu$m (b) and 50.0 $\mu$m (c), core diameter, and 50.0 $\mu$m step-index fibers (d). The dashed lines denote the cladding-air interface, while the scale bar corresponds to 1 mm. Further details are available in Ref. Mangini2020.
• Figure 3: Helical plasma filaments in optical fibers. a) Geometry of beam injection and propagation. b) Comparison between the UL generated at power below self-channeling (top) and the helical plasma filament (bottom). The values of the left indicate the beam peak power. c) Intensity profile of the scattered light, obtained as the integral of corresponding images in b). For additional information see Ref. Mangini2022-helical.
• Figure 4: Rainbow spiral emission. a) SCG spectra at different input peak powers. b) Dependence of the far-field patterns (bottom row) on the input beam position (red dot in the upper row). c) Rainbow spiral emission at different fiber lengths. Additional information are available in Ref. Mangini2021-spiral.
• Figure 5: Example of helicon wavepacket constructed from phase-matching of spatiotemporal components in a commercial MMF with core radius $R=$ 52.5 $\mu$m and numerical aperture $NA=$ 0.22. (a) Quadric surfaces obtained by using parameters of simulations in Sec. \ref{['self-focus']}. Green dots indicate discretized conic sections for each p coordinate. Black circles correspond to the selected modes used for the linear construction of helicon wavepacket. (b) Corresponding total spectrum of the selected modes. (c) Calculated iso-surface at half-maximum of the corresponding spatiotemporal intensity pattern of the constructed helicon wavepacket. The dashed black line indicates the origin $(x=0,y=0)$. Projections on planes (shadow plots) are also provided for a clear observation of rotating field pattern.