Abstract
Using femtosecond upconversion we investigate the time and wavelength structure of infrared supercontinuum generation. It is shown that radiation is scattered into higher order spatial modes (HOMs) when generating a supercontinuum using fibers that are not single-moded, such as a step-index ZBLAN fiber. As a consequence of intermodal scattering and the difference in group velocity for the modes, the supercontinuum splits up spatially and temporally. Experimental results indicate that a significant part of the radiation propagates in HOMs. Conventional simulations of super-continuum generation do not include scattering into HOMs, and including this provides an extra degree of freedom for tailoring supercontinuum sources.
Highlights
Supercontinuum generation has been a field of great interest, and the physical processes involved in the generation have been studied vigorously
Numerous applications have emerged since the first supercontinuum in bulk glass was reported by Alfano et al [2], in such diverse fields as spectroscopy [3, 4] and optical metrology [5, 6]
Simulations are carried out using the multi-mode variant of the generalized nonlinear Schrodinger equation (GNLSE) (MM-GNLSE) in [18]
Summary
Supercontinuum generation has been a field of great interest, and the physical processes involved in the generation have been studied vigorously (for a review, see [1]). Supercontinua have been pushed into the mid-infrared, making room for new applications in spectroscopy and microspectroscopy [7,8,9,10], as the molecular fingerprint region can be reached. Novel soft glass fibers such as ZBLAN or chalcogenide are often used to be able to reach into the mid-infrared. ZBLAN fibers are not microstructured and to develop new fibers optimized for supercontinua generation, it is important to consider the generation process correctly. The normalized frequency parameter V determines the number of modes that can propagate through the fiber at a given wavelength, and for step-index fibers, V is defined as [11]
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