Mid-infrared Supercontinuum Generation in Multimode Optical Fibers

Abstract

The generation of broadband supercontinuum (SC) via a cascade of nonlinear effects is one of the most significant development in laser technology over the past two decades. These unique sources of light combines both the advantages of coherent laser sources and the bandwidth of light bulbs. While now routinely generated in single-mode fibers in various spectral regions, their development in the context of multimode fibers has recently gained major interest with the possibility of power-scaling due to the larger core size that increases the damage threshold. Furthermore, increased design flexibility and the possibility to structure light in multimode fiber systems both in the spatial and temporal domain have opened up new prospects with many potential breakthrough applications in sensing and imaging.

Supercontinuum generation in multimode fibers has been essentially limited to the visible and near-infrared and there can be important benefits if their regime of operation can be extended to other regions of the electromagnetic spectrum. A region of particular interest is the mid-infrared which is central to spectroscopy, sensing, and biomedical imaging as it contains characteristic spectral signatures of many important molecules. The research presented in this thesis demonstrates the experimental generation of broadband SC in multimode step-index and graded-index fibers made of different transparent soft glasses in the mid-infrared range. Detailed systematic studies are conducted to analyze the underlying spatio-temporal dynamics and properties of the generated broadband light. The research reported in this thesis contribute to our understanding of the nonlinear physics of complex multimode systems and provides novel technological avenues towards the development of coherent high-power broadband mid-infrared light sources.