Temperature dependence of reversible photodarkening in Ga:La:S and Ga:La:S:O glass fibres

Abstract

I. Introduction
Glasses based on gallium and lanthanum sulphides have been investigated because of their properties, such as low phonon energy, high rare-earth solubility and high nonlinearity, which make them attractive for the fabrication of active waveguide devices for photonic applications, such as fibre lasers, amplifiers and all-optical switches (1,2).

It is well known that glassy chalcogenides exhibit a number of modifications to their physical properties under the action of light or temperature (3). Reversible photodarkening (PD) is a red-shift of the position of the electronic edge, induced by bandgap or sub-bandgap illumination (4). We have investigated PD in unclad glass fibres with nominal composition 65Ga₂S₃:32La₂S₃:3La₂O₃ (Ga:La:S) and 72.5Ga₂S₃:27.5La₂O₃ (Ga:La:S:O) respectively. Both fundamental and practical reasons justify the interest in the PD effect in these materials. From a fundamental point of view, one is interested in understanding the phenomena underlying the absorption edge in these amorphous semiconducting materials. A more practical aspect is that PD also affects their transparency in the near IR region, which is relevant to most photonic applications. Here we report for the first time the existence of PD effect in these oxysulphide glasses and we present a description of its dependence on temperature, in the range 77-563 K.

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Identifiers

ORCID for M. Petrovich: orcid.org/0000-0002-3905-5901

ORCID for D.W. Hewak: orcid.org/0000-0002-2093-5773

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