Lasers

Homogeneous broadening in the spectrum of a broadband erbium-doped fibre light source

S. K. Morshnev, N. I. Starostin, Ya. V. Przhiyalkovskiy, A. I. Sazonov

Kotelnikov Institute of Radioengineering and Electronics, Fryazino Branch, Russian Academy of Sciences

Abstract: Interference of wave trains separated out in an inhomogeneous emission spectrum of a superluminescent erbium-doped fibre source has been studied by scanning the wavelength of a spectrum analyser. The results demonstrate that, as the spectral resolution of the spectrum analyser decreases to a level corresponding to a sharp drop in interference fringe visibility relative to its original level, near 100%, fringe visibility becomes dependent on the wavelength in the inhomogeneous spectrum of the source. The reason for this is that, at some characteristic resolution σλ (σλ > 0.5 nm in our case), the coherence time of wave trains is not limited by the spectral resolution of the spectrum analyser and is related to the inhomogeneous spectrum of the source, whose limiting width can be thought of as the homogeneous linewidth in the spectrum of the source. This feature can be used for evaluating homogeneous line broadening.

Keywords: homogeneous broadening, interference visibility, coherence time.

Received: 10.04.2020
Revised: 19.06.2020

 English version: Quantum Electronics, 2020, 50:10, 904–909

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