Thulium environment in a silica doped optical fibre

TL;DR

This paper investigates how adding aluminium to silica-based optical fibres affects the thulium environment and potentially improves the efficiency of thulium-doped fibre amplifiers in the S-band.

Contribution

It explores the impact of aluminium addition on the local environment of thulium in silica, using fluorescence decay analysis across different core compositions.

Findings

Aluminium modifies the thulium local environment.

Fluorescence decay curves indicate environmental changes due to aluminium.

Different core compositions show varied effects on thulium fluorescence.

Abstract

Thulium-doped optical fibre amplifiers (TDFA) are developed to extend the optical telecommunication wavelength division multiplexing (WDM) bandwidth in the so-called S-band (1460-1530 nm). The radiative transition at 1.47 lm (3H4 -> 3F4) competes with a non-radiative multi-phonon de-excitation (3H4 -> 3H5). The quantum efficiency of the transition of interest is then highly affected by the phonon energy (Ep) of the material. For reliability reasons, oxide glasses are preferred but suffer from high phonon energy. In the case of silica glass, Ep is around 1100 cm-1 and quantum efficiency is as low as 2%. To improve it, phonon energy in the thulium environment must be lowered. For that reason, aluminium is added and we explore three different core compositions: pure silica, and silica slightly modified with germanium or phosphorus. The role of aluminium is studied through fluorescence decay curves, fitted according to the continuous function decay analysis. From this analysis, modification of the thulium local environment due to aluminium is evidenced.