Ultrafast nonlinear optics in gas-filled hollow-core photonic crystal fibers [Invited]
Spotlight summary: The capability to engineer the core-cladding characteristics of optical fibers in the micron scale has allowed the fabrication of fibers with precise control over their dispersive and nonlinear properties. Microstructure fiber designs that tightly confine the light in the glass region of the core have been seminal for the demonstration of several nonlinear fiber optics applications. However, even more curious designs are those that guide light in a hollow core surrounded by a holey glass cladding. Amongst this class of fibers, those with a kagome cladding microstructure are particularly interesting. The Japanese word kagome refers to the familiar woven pattern one finds in traditional baskets made of straw or bamboo, but when formed by microscopic strands of glass in the cross-section of the cladding of an optical fiber, they can facilitate light transmission in the hollow core over a broad spectral window, with very low chromatic dispersion and relatively low loss.
An exciting attraction of kagome fibers draws from the possibility to fill the hollow regions of the fiber with gases under certain pressure. The chromatic dispersion of the gas can then be counter-balanced by the dispersion of the waveguide structure and yield optical fibers with a relatively flat dispersion profile over a broadband region, and importantly with a zero-dispersion wavelength which is tunable with the gas pressure. These attributes make such fiber systems particularly well suited to nonlinear applications with intense ultra-short pulses, leading for example to extreme spectral broadening or the generation of light at obscure wavelengths.
Beyond conventional nonlinear effects, the interaction of ultra-short pulses with a gas can lead to the ionization of the latter under certain conditions, thereby giving rise to light-plasma interactions in an environment that forms in effect an anomalously dispersive single-mode waveguide. This is an exciting prospect, leading to the observation of physical phenomena which have not been possible before in dielectric optical fibers, such as the soliton self-frequency blue shift or the generation of a large number of high harmonics.
The paper by J.C. Travers et al. is an excellent review of this area of research. The unique benefits of gas-filled kagome fibers are analyzed and some of the key results achieved so far are presented. The paper benefits from a number of numerical simulations summarizing in a clear manner the advantages of kagome fiber-based systems, while the reader is immersed gradually from the more common to the ever more unusual nonlinear effects enabled by gas-filled hollow-core fibers.
|OCIS Codes:||(190.4370) Nonlinear optics : Nonlinear optics, fibers|
|(190.7110) Nonlinear optics : Ultrafast nonlinear optics|
|(260.5210) Physical optics : Photoionization|
|(060.5295) Fiber optics and optical communications : Photonic crystal fibers|
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