1 Department of Photonics Engineering, Technical University of Denmark2 Fiber Sensors and Supercontinuum Generation, Department of Photonics Engineering, Technical University of Denmark3 NKT Photonics A/S
This Ph.D.-project presents numerical simulations of supercontinuum (SC) generation in optical fiber laser systems based on various soft-glass materials. Extensive numerical modeling is performed in order to understand and characterize the generated SC. This includes a review of the generalized nonlinear Schrödinger equation, and a detailed discussion of the implementation. The thesis primarily considers two types of soft-glasses, which are characterized by lower attenuation than conventional silica glasses beyond 2 μm. This low loss enables an extension of the long wavelength edge of existing SC sources. A novel SC system, incorporating a fluor based (ZBLAN) step-index fiber (SIF), has been developed by an industrial collaborator. Numerical simulations show good agreement with measurements of fs-pumped SC generation stretching above 4 μm in a ZBLAN fiber. Furthermore, a design parameter, useful for designing nonlinear laser systems by passive concatenation of optical fibers is proposed. The design parameter quantifies regimes of different soliton dynamics, and predicts either stable soliton redshift for high energy conversion, or soliton fission giving large redshifts but lower energy conversion. Finally, it is predicted numerically how it is possible to design a SC laser spanning the wavelength region between 4 and 12 μm, by pumping a chalcogenide SIF with a praseodymium (Pr) doped fiber laser operating at 4.5 μm.