Mode excitation and supercontinuum generation in a few-mode suspended-core fiber

Abstract

We have studied the excitation of higher-order modes and their role in supercontinuum generation in a three-hole silica suspended-core fiber, both experimentally and numerically. We find that pump coupling optimized to highest transmission can yield substantial excitation of higher order modes. With up to about 40% of the pump power coupled to higher order modes, we have studied supercontinuum generation in this fiber. In agreement with experiments, simulation results based on the multimode generalized nonlinear Schrödinger equation confirm that the spectral width is determined by spectral broadening in the fundamental mode, whereas the numerical analysis reveals that intermodal nonlinear interactions are strongly suppressed.

Multi-milliwatt mid-infrared supercontinuum generation in a suspended core chalcogenide fiber

“…A wavelength dependent Kerr coefficient estimated by Romanova et al [44] was used together with the Raman response measured by Ung and Skorobogatiy [45]. To account for any possible coupling to higher-order modes [46,47] and coupling between the polarization states [48,49] only 2/3 of the peak power was used in the simulations compared to the experiments. When the pump wavelength was shifted from 3.5 to 4.7 μm the solitonic long wavelength edge moved to longer wavelengths in the simulated spectra, and accordingly the short wavelength edge, consisting of group-velocity matched dispersive waves was shifted to shorter wavelengths.…”

“…The absence of a long wavelength extension when pumping at longer wavelengths in the experiments can be explained by coupling instability, e.g. if coupling to the core is slightly off-centered a larger fraction of the power will be coupled to higher-order modes [47] thereby limiting the broadening process. The broadest experimental supercontinuum spectrum spanning from 1.7 to 7.5 μm was obtained when pumping at 4.4 μm, and the average output power was in this case 15.6 mW with a chalcogenide lens at the fiber output and the chopper off.…”

Refractive index dispersion of chalcogenide glasses for ultra-high numerical-aperture fiber for mid-infrared supercontinuum generation

“…However, only very few of these modes will be guided above 5µm and through good coupling the number of excited modes can be significantly reduced. Using short pump pulses to increase intermodal temporal walk-off modal issues can be further reduced, as demonstrated by, e.g., Shavrin et al [22].…”

Mid-infrared supercontinuum generation to 125μm in large NA chalcogenide step-index fibres pumped at 45μm

“…Furthermore, the fibre should preferably be single mode at λ p in order to avoid distributing the pump power into higher order modes [37,38,50,52].…”