Absorption measurement effects in fibres with multimode cores

Abstract

Absorption is a key characteristic of any laser medium and is often the first thing to measure. While this is rather straightforward, several factors can impair the accuracy, e.g., a non-negligible fraction of excited laser ions, nonlinear conversion, and, in multimode structures, differences in absorption between different modes. In multimode structures, mode-coupling is also important. We have previously investigated another error mechanism which had not yet been considered, namely re-emission of radiation into the absorption band of three-level systems [1]. We found that it can induce significant errors in single-mode fibres. Here, we extend those investigations to simulations of Yb-doped fibres with multimode step-index cores, focusing on the case of negligible mode-coupling. As before [1], we use as tandard fibre amplifier model as implemented in RP Fiber Power to simulate white-light absorption measurements. Previously, with a single-mode Er-doped fibre, we found that this approach led to excellent agreement with measured data even for the difficult case of high absorption (up to 60 dB, with errors approaching 50 %).

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Identifiers

ORCID for Yutong Feng: orcid.org/0000-0002-6839-2106

ORCID for Jonathan Price: orcid.org/0000-0003-0256-9172

ORCID for Johan Nilsson: orcid.org/0000-0003-1691-7959

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