Absorption measurement errors in single-mode fibers resulting from re-emission of radiation

Abstract

We investigate errors in small-signal absorption spectra that result from re-emission in single-mode fibers with overlapping absorption and emission spectra. Experiments on Er-doped fibers and simulations of Er- and Yb-doped fibers show that the re-emission can severely distort the spectrum, especially the peak, under common measurement conditions, and underestimate the absorption by well over 10% already at 30-dB peak absorption, if only the source or the detector is spectrally filtered. Re-emission can then be the dominant source of errors. The error increases for higher absorption and higher fiber-NA. For sufficiently high NA, a significant error remains even in the limit of zero absorption and reaches 5% at the peak of a 0.46-NA Yb-doped fiber. Furthermore, in contrast to the high-absorption case, the error is larger at longer wavelengths than at the peak. Simultaneous filtering of both source and detector with 0.1-nm bandwidth reduces the re-emission error to ~1% or less up to 90-dB absorption. Then, detector noise or saturation errors are likely to dominate and render re-emission errors insignificant. A standard amplifier model is well suited to the simulations of the rich physics of single-mode-fiber absorption measurements.

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Identifiers

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

ORCID for Sheng Zhu: orcid.org/0000-0002-4256-6307

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

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

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