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Proceedings Paper

Measurement of attenuation coefficient of core and cladding modes in Bragg fiber
Author(s): Milan Frank; Michal Jelínek; Václav Kubeček; Vlastimil Matějec; Ondřej Podrazký; Ivan Kašík
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Paper Abstract

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.

Paper Details

Date Published: 1 December 2017
PDF: 7 pages
Proc. SPIE 10603, Photonics, Devices, and Systems VII, 106030Q (1 December 2017); doi: 10.1117/12.2292814
Show Author Affiliations
Milan Frank, Czech Technical Univ. in Prague (Czech Republic)
Michal Jelínek, Czech Technical Univ. in Prague (Czech Republic)
Václav Kubeček, Czech Technical Univ. in Prague (Czech Republic)
Vlastimil Matějec, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic)
Ondřej Podrazký, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic)
Ivan Kašík, Institute of Photonics and Electronics of the ASCR, v.v.i. (Czech Republic)

Published in SPIE Proceedings Vol. 10603:
Photonics, Devices, and Systems VII
Karel Fliegel; Petr Páta, Editor(s)

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