High-power ultra-broadband supercontinuum generation in tapered multimode glass rods

Abstract

Simultaneously increasing the spectral bandwidth and average output power of mid-infrared supercontinuum sources remains a major challenge for their practical application. We address this issue through experimental developments of short tapered rods made from distinct glasses (silica, tellurite and chalcogenide families) for covering distinct spectral regions by means of supercontinuum generation in the femtosecond regime. We demonstrate that ultra-broadband spectral broadenings over the entire glass transmission window can be achieved in few-cm-long segments of tapered rods by a fine adjustment of input modal excitation. As the most significant example, our simple post-processing of glass rods unlocks the high-power regime for fiber-based supercontinuum sources beyond the 10 micron waveband. By using a 5-cm-long tapered Ge-Se-Te rod pumped at 6 micron, a supercontinuum spanning from 2 to 15 micron (3 to 14 micron) with an average output power of 93 mW (170 mW) is obtained for 500-kHz (1-MHz) repetition rate. Spectral coverages from the visible to 5 micron, and from the visible to 2.7 micron, are also reported with tapered rods made of tellurite and silica glasses, respectively. Numerical simulations are used to confirm the main contribution of the fundamental mode in the ultrafast nonlinear dynamics, as well as the possible preservation of coherence features. Our study opens a new route towards the power scaling of high-repetition-rate fiber supercontinuum sources over the full molecular fingerprint region.