Two octave supercontinuum generation in a non-silica graded-index multimode fiber

TL;DR

This paper reports the generation of a two-octave supercontinuum from visible to mid-infrared in a specially designed non-silica graded-index multimode fiber, demonstrating broad spectral coverage and beam self-cleaning effects.

Contribution

It introduces a novel non-silica graded-index multimode fiber with enhanced nonlinearity and extended transmission, enabling efficient supercontinuum generation across two octaves with experimental and numerical validation.

Findings

Successful generation of a two-octave supercontinuum (700-2800 nm).

Observation of beam self-cleaning in high power regimes.

Excellent agreement between experimental spectra and 3+1D numerical simulations.

Abstract

The generation of a two-octave supercontinuum from the visible to mid-infrared (700 - 2800 nm) in a non-silica graded-index multimode fiber is reported. The fiber design is based on a nanostructured core comprised of two types of drawn lead-bismuth-gallate glass rods with different refractive indices. This structure yields an effective parabolic index profile, an extended transmission window, and ten times increased nonlinearity when compared to silica fibers. Using femtosecond pulse pumping at wavelengths in both normal and anomalous dispersion regimes, a detailed study is carried out into the supercontinuum generating mechanisms and instabilities seeded by periodic self imaging. Significantly, suitable injection conditions in the high power regime are found to result in the output beam profile showing clear signatures of beam self-cleaning from nonlinear mode mixing. Experimental observations are interpreted using spatio-temporal 3+1D numerical simulations of the generalized nonlinear Schr\"odinger equation, and simulated spectra are in excellent agreement with experiment over the full two-octave spectral bandwidth. These results demonstrate a new pathway towards the generation of bright, ultrabroadband light sources in the mid-infrared.