Abstract

Antiresonant hollow core fibers (ARHCF) have low propagation loss, broad transparency windows from ultraviolet to mid-infrared regime in fundamental mode propagation and can be easily fabricated [1,2]. In these fibers, geometrically-induced strand resonances are given by ${\lambda }_m=2t\sqrt{n^2-1}/m$, where t is the strand thickness, n is the refractive index of the material and 𝑚 is the integer resonance. The strand resonances influence the effective refractive index and hence the dispersion of the fiber resulting in a complex group velocity dispersion (GVD) profile. ARHCF shown in Fig. 1a (inset) exhibits abrupt GVD variation over hundreds of fs²⁄cm in magnitude at resonance in both anomalous and normal dispersion regime passing through multiple zero dispersion wavelengths, which constitutes an increased fidelity in dispersion design in contrast to a Kagome-type PCF that typically exhibits one zero-GVD wavelength [3]. The strand thickness can be varied in order to position the fundamental resonance wavelength close to available ultra-short laser central wavelength triggering immediate soliton dynamics. This possibility of positioning of resonances with unique dispersion profile in ARHCF opens a new interesting platform for nonlinear optics and supercontinuum generation (SCG) [4,5]. In the experiment an 80 fs, 800 nm pulse is coupled into the differentially pumped ARHCF where the input is maintained in vacuum and the output is maintained at high pressure of inert gas (Kr at 6 bar) or Raman-active gas (N₂ at 4.5 bar). By tuning the input energy, a sudden spectral broadening over three octaves is observed. We attribute this sudden spectral broadening to a novel soliton explosion mechanism, becoming effective once the onset of the initially SPM-broadened spectrum reaches the position of the strand resonance [4]. This effect is studied in both inert and Raman-active gases and the output spectrum (Fig. 1a) extends from UV to SWIR. Fundamental output mode profiles (Fig. 1b) are observed across the complete supercontinuum bandwidth. Dispersion control in fiber design through strand resonances opens a new platform for nonlinear laser matter interaction by specially positioning the modified GVD profile. We intend to present comprehensive experiment results along with simulations at the conference. As outlook, these developments may lead to a new class of ultra-compact high energy supercontinuum sources, with applications in spectroscopy, microscopy and biophotonics.

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