1 December 2017 Measurement of attenuation coefficient of core and cladding modes in Bragg fiber
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Proceedings Volume 10603, Photonics, Devices, and Systems VII; 106030Q (2017) https://doi.org/10.1117/12.2292814
Event: Photonics Prague 2017, 2017, Prague, Czech Republic
In this contribution a new method for determination of transmission characteristics and mechanism of optical radiation propagation in Bragg fibers is described. The investigated Bragg fibers are designed for high-power laser radiation delivery. Attenuation coefficient and coupling efficiency are usually measured using simple cutback method for optimum mode matching of the incident radiation to the fiber mode. Our current approach is based on the cut-back technique but we also investigate the dependence of the mentioned parameters on radial position of the excitation mode from the fiber axis. In addition, using the imaging of the measured fiber output face on a CCD camera, the spatial profile of the propagated beam can be obtained. For this reason this method is suitable for delivered laser mode control.

The investigated Bragg fiber consisted of the 26um diameter silica core surrounded by three pairs of circular Bragg layers. Each pair is composed of one layer with a high and one layer with a low refractive index being characterized by a refractive-index contrast up to ~0.03. The 1064nm laser beam was focused by a telescope onto the fiber input face. The beam radius in the focal plane was 5um. The Bragg fiber output face was imaged by a 1:6 optical telescope on the CCD camera. The transmitted power and spatial beam profile were registered simultaneously for various offset from the fiber axis. After the fiber shortening, the measurement was repeated and the cut-back was performed. The lowest attenuation coefficient of 0.17dB/m corresponded to a core mode of the delivered laser radiation. In general, the attenuation was higher with a shift from the radial axis of the fiber symmetry. In the case of cladding mode excitation, the attenuation parameter shows a local minimum. This phenomenon was consistent with the refractive index profile of the tested Bragg fiber.
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Milan Frank, Milan Frank, Michal Jelínek, Michal Jelínek, Václav Kubeček, Václav Kubeček, Vlastimil Matějec, Vlastimil Matějec, Ondřej Podrazký, Ondřej Podrazký, Ivan Kašík, Ivan Kašík, } "Measurement of attenuation coefficient of core and cladding modes in Bragg fiber", Proc. SPIE 10603, Photonics, Devices, and Systems VII, 106030Q (1 December 2017); doi: 10.1117/12.2292814; https://doi.org/10.1117/12.2292814


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