Measurement of attenuation coefficient of core and cladding modes in Bragg fiber

0485707 - ÚFE 2018 RIV US eng C - Conference Paper (international conference)
Frank, M. - Jelínek, M. - Kubeček, V. - Matějec, Vlastimil - Podrazký, Ondřej - Kašík, Ivan
Measurement of attenuation coefficient of core and cladding modes in Bragg fiber.
Proceedings of SPIE - The International Society for Optical Engineering 2017. Vol. 10603. Bellingham: SPIE: The Society of Photo-Optical Instrumentation Engineers, 2017 - (Fliegel, K.; Páta, P.), č. článku 106030Q. SPIE. ISBN 978-1-5106-1702-5. ISSN 0277-786X.
[Photonics, Devices, and Systems VII 2017. Prague (CZ), 28.08.2017-30.08.2017]
R&D Projects: GA ČR GA16-10019S
Institutional support: RVO:67985882
Keywords : delivery radiation * bragg fiber * core mode
OECD category: Electrical and electronic engineering

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
Permanent Link: http://hdl.handle.net/11104/0280665