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We report on a tapered large-core Yb fiber laser operating at 976 nm emission wavelength. It was realized using a high-numerical aperture large-core fiber with 126 µm core diameter, which was fabricated by powder-sinter technology and shows a very homogeneous step-index profile. The end of the fiber is tapered down to match a single-mode fiber containing a fiber Bragg grating. Using the benefits of core-pumping and the feedback of the spliced fiber Bragg grating, we achieved efficient pump light absorption and wavelength stable 976 nm lasing with single-mode performance. We could demonstrate 10 W laser power out of a 10 µm fiber core with a slope efficiency of 31% with respect to the launched pump power. The presented device is well-suited for fiber-coupled pumping of amplifiers for high peak power.

In this paper we present a method for the selective blocking and subsequent filling of metals into photonic crystal fibers. We derive a model which can predict the necessary duration of the filling process. With a melt and pump procedure we obtain single micron sized metal wires adjacent to the PCF core with aspect ratios of about 10 5 . We will present a semi-analytical solution of the dispersion relation of a cylindrical metal wire in a dielectric and discuss the results with respect to surface plasmon polaritons. By comparision with finite element simulations of an unfilled photonic crystal fiber we will show that a coupling between a core mode and surface mode is possible at specific phase matching wavelengths. Furthermore, measurements of transmission spectra will be presented to confirm the mode coupling between the fundamental core mode and the surface plasmon polariton of order m = 3.

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