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.
Highlights
Absorption and emission of electromagnetic radiation are key properties of any laser medium and the subject of continuous and current interest, notably in fibers [1], [2], [3], [4], [5], [6]
∫ ( ) Yb-doped fibers, we used a concentration of 5×1024 = ions/m3, R (r, z) which leads to a peak absorption of 42 dB/m
Simulations as well as measurements show that spectrally overlapping re-emission can lead to unacceptable errors in the characterization of absorption spectra of single-mode fibers doped with erbium and ytterbium
Summary
Absorption and emission of electromagnetic radiation are key properties of any laser medium and the subject of continuous and current interest, notably in fibers [1], [2], [3], [4], [5], [6]. In multimode structures such as double-clad fibers, differences in the small-signal absorption between different modes can modify the absorption spectrum [2], [3] This is not a measurement error but rather a true effect that reduces the absorption in longer fibers due to different overlap of different pump modes with the doped region and imperfect mode mixing. We investigate measurement errors in continuous-wave small-signal absorption spectra in singlemode fibers resulting from spontaneous re-emission of absorbed light at wavelengths that overlap with the absorption line under study. The error becomes more important when a large fraction of the re-emitted light is captured by a fiber with high NA, when the laser medium has a distinct absorption peak on a broad shoulder, and when the required wavelength-selective filtering occurs at either the source or the detector end of the measurement setup, but not at both ends. The increasing use of SC sources with their greater measurement range can lead to even larger errors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
