22 June 2015 Experimental measurement of group velocity dispersion during operation in cladding-pumped large-mode-area Yb-doped fibers
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Abstract
Ever higher output power of fiber lasers leads to growing requirements on the fibers used. The increasing intensity of light in the fiber core is compensated by enlargement of the area of the doped core. The guiding properties of the optical fiber are significantly affected and must be very accurately defined. This high intensity leads to significant deviations of the guiding properties of the optical fiber during laser operation due to absorption and thermal effects. In particular, information about the change in group-velocity dispersion(GVD) during operation is important for the development of high power fiber laser systems. In an effort to gather such knowledge, this paper presents the results of dispersion characterization measurements using ytterbium-doped large-mode-area double-clad fibers which are cladding pumped at a wavelength of 975 nm. The direct measurement of the GVD in the emission range of the ytterbium-doped fibers (1000 nm to 1150 nm) is shown.

GVD characteristics of two different large-mode-area double-clad fibers with defined launching pump laser power level were systematically analyzed. The dispersion parameters for different fiber designs and various doping levels are investigated over a broad spectral range in the emission area of Yb-doped fiber samples for controlled sets of operating parameters. The experiment utilizes a supercontinuum source developed within this laboratory as well as a Mach-Zehnder interferometer with a dual-channel spectral-detection system sensitive to wavelengths from 0.95 μm to 1.75 μm. Temporally resolved spectrograms recorded at distinct delay positions enable the detection of interference fringes for the equalization wavelength. By applying a Sellmeier polynomial fit to the wavelength dependent differential group-delay function, the GVD can be derived. The measured Yb-doped large-mode-area fibers show a variation of the doping concentration between 0.7 mass percent to 3 mass percent of ytterbium. The measurement of the Yb-doped large-mode-area fiber with or without optical load on the sample during the measurement was examined.
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Tobias Baselt, Tobias Baselt, Christopher Taudt, Christopher Taudt, Andrés-Fabián Lasagni, Andrés-Fabián Lasagni, Peter Hartmann, Peter Hartmann, } "Experimental measurement of group velocity dispersion during operation in cladding-pumped large-mode-area Yb-doped fibers", Proc. SPIE 9525, Optical Measurement Systems for Industrial Inspection IX, 95253Z (22 June 2015); doi: 10.1117/12.2184803; https://doi.org/10.1117/12.2184803
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