Michèle Ude

Thulium environment in a silica doped optical fibre

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 μm ( 3 H 4 → 3F 4 ) competes with a non-radiative multi-phonon de-excitation ( 3 H 4 → 3 H 5 ). 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.

Design and fabrication of an asymmetric twin-core fiber directional coupler for gain-flattened EDFA

Fiber directional couplers made of highly asymmetric twin-cores (ATC), one of which is doped with erbium, are designed to achieve an inherently gain flattened erbium doped fiber amplifier (EDFA). The refractive index profiles of the fibers as well as the spacing between the two cores were carefully designed to achieve a targeted gain with low gain excursions across the C-band. One of the designs yielded a theoretical median gain ∼ 38 dB with an excursion within ±1 dB. In order to suite fabrication of such an inherently gain flattened EDFA by the MCVD fiber preform fabrication process, the design had to be modified and a more modest target of about 20 dB was set with excursion below ± 1.5 dB for metro-centric applications. It involved preparation of two independent preforms, which required selective polishing of the cladding from one side by a certain amount to meet the required nominal separation between the two cores set at the design stage of the fiber. Several intricate operations were required to implement the fiber drawing step from the two assembled preforms. Preliminary characterization of the fabricated fiber shows filtering of ASE peak through selective wavelength coupling from Er-doped core to un-doped core.

Impact of aluminium codoping on the 1.47 μm emission efficiency in a thulium-doped silica fibre

Silica glass is generally set aside to realize a TDFA because of its high phonon energy. From decay curves analysis, Tm3+ ions with a five times increased emission efficiency are evidenced in rich Al-environment.

Erbium- and Magnesium-codoped Silica-Based Transparent Glass Ceramic Core Fiber Made by FCVD and Flash Vaporization

A fiber made by Furnace CVD was codoped with Erbium and Magnesium using a Flash Vaporization System for the first time. The fiber core is spontaneously formed as a Transparent Glass Ceramic (TGC). Due to the small nanoparticle size (<50 nm) and high volumetric density (1020~1021 m−3), the optical loss due to scattering is as low as < 0,6 dB/m. Erbium ions are highly concentrated within phase-separated nanoparticles. We study the absorption and emission properties of Erbium around 1.55 µm in this TGC-core fiber.

Characterization of erbium-doped nanoparticles in transparent glass ceramic optical fibres

We report on using nanometric mass spectroscopy and molecular dynamics modelling to characterize the composition and structure of self-grown erbium-doped nanoparticles in transparent glass ceramic optical fibres fabricated by modified chemical vapour deposition without post-ceramming.