Dy3+-doped chalcogenide glasses are potential candidates for 1.3-mum optical-fiber amplifiers. We describe spectroscopic characterization of Dy3+-doped gallium lanthanum sulphide glasses with low and high oxide content. The spectroscopic investigations show that small amounts of oxide (similar to1%) in low-oxide-content sulphide glass create a second group of sites with a local environment different than that of the main sulphide sites. Dy3+ ions in the oxide site, which can constitute up to approximately one third of the total number of Dy3+ ions, experience a high-phonon-energy environment and do not show any 1.3-mum emission and hence cannot provide gain for a potential 1.3-mum optical-fiber amplifier in this material. (C) 2001 Optical Society of America.

Gallium lanthanum sulphide (Ga:La:S) glass and fibre have potential use in both active and passive infrared applications. Here we present just some of the steps involved in realising a new compound glass and devices. Importance of raw material synthesis and preparation of preforms through rod-in-tube and extrusion methods is highlighted. With losses close to 1 dB/m and the possibility of devices based on our glass, Ga:La:S will enhance prospects for future generation of sulphide fibre-based devices.

Gallium lanthanum sulphide (GLS) glass and fiber have potential for use in both active and passive infrared applications. In this paper the optical, thermal, and other key properties, which are essential for understanding the applications and crucial in the quest for practical fibres, are discussed. Glass preparation by melt-quenchingand subsequent fibre fabrication is described using both rod-in-tube and extruded preforms. Absorptive and scattering losses are explored as they could represent a fundamental limitation to successful device fabrication. Potential passive and active applications are reported and the prospects for a future generation of sulphide fiber-based devices examined.

Infrared emission at 1.2, 1.25, 1.67, 2.0, 2.2, 2.9, 3.9, and 4.9 mu m is measured in holmium (Ho3+) doped gallium lanthanum sulphide (GLS) glass. Branching ratios, radiative quantum efficiencies, and emission cross-sections are calculated from lifetime, absorption, and emission measurements using Judd-Ofelt analysis and the Fuchtbauer-Ladenburg equation. The fluorescence band at 3.9 mu m coincides with an atmospheric transmission window and the fluorescence band at 4.9 mu m overlaps with the fundamental absorption of carbon monoxide, making the glass a potential fibre laser source for remote sensing and gas sensing applications. This is the first time this latter transition has been reported in any holmium doped host. (C) 1999 Elsevier Science B.V. All rights reserved.

Infrared emission at 0.7, 0.8, 1.2, 1.5, 1.8, 2.3, 3.8, and 4.8 mu m is measured in thulium- (Tm3+) and terbium(Tb3+) doped gallium lanthanum sulfide (GLS) glass. Emission cross sections are calculated from the absorption and emission spectra by use of Judd-Ofelt analysis, the Fuchtbauer-Ladenburg equation, and the theory of McCumber. Fluorescence and lifetime measurements confirm energy transfer from Tm3+ to Tb3+ ions and reveal a number of new cross-relaxation and upconversion processes between Tm3+ ions involving the F-3(2,3) and H-3(5) levels that can be observed only in low-phonon-energy materials. These processes indicate that the most efficient pump wavelength for the 1.2- and 3.8-mu m transitions is 0.7 mu m. The Tm3+ fluorescence at 3.8 mu m coincides with an atmospheric transmission window, and the Tb3+ fluorescence at 4.8 mu m overlaps the fundamental absorption of carbon monoxide, making the glass a potential fiber laser source for remote-sensing and gas-sensing applications. (C) 1999 Optical Society of America [S0740-3224(99)01902-5].

We are currently investigating two infrared glasses for active applications. Gallium lanthanum sulphide (GLS) glass is investigated as a potential host material for rare-earth doped mid-infrared fibre lasers. We have fabricated gallium lanthanum sulphide glass by melt quenching and drawn it into fibres using the rod-in-tube technique. Fluoroaluminate glasses (ALF) are being prepared in planar form by spin coating and clad waveguides have been achieved. The quality of waveguides from both these materials is gradually being improved as methods to eliminate transition metals and other impurities, understand crystallization and reduce the imperfections at the core/clad interface are developed. Although initially motivated by the demand for a practical 1310 nm amplifier, interest has now extended further into the infrared. We describe recent progress in these glasses, their properties and applications.

The wavelength range near 3μm has many applications in medical processes due to an overlap with the absorption spectrum of water. Emission of the Er3+ ion near 2.8μm, which operates on the transition from 4I11/2 to 4I13/2 is especially promising as it can be pumped by either 800nm GaAlAs or 980nm InGaAlAs diodes, paving the way for a compact device with low electrical energy consumption.

Gallium-lanthanum-sulphide (GLS) chalcogenide glass doped with dysprosium (Dy3+) shows promise as 1.3 μm fibre-optic amplifier and mid-infrared laser material. GLS glass has attracted great interest due to its low phonon energy of ~ 425 cm-1, resulting in low non-radiative decay rates of rare-earth ions. Its high refractive index of 2.4 results in high radiative emission rates. Both properties improve the radiative quantum efficiencies for all transitions.

Optical fibres drawn from sulphide-based glasses have been studied now for almost two decades. Initial work began in the 1970s where fibres from glasses based on arsenic sulphide or germanium sulphide rapidly found application as infrared waveguides, providing transmission to beyond 5 microns. In the early 1990s, the demonstration of an optical fibre amplifier for the 1300 nm telecommunications window, motivated again the application of non-silica optical fibres. First, a fluoride fibre device showed amplification with pump efficiencies of only a few percent. In 1993, the first active application of a sulphide glass was demonstrated and measurements on bulk samples of rare-earth doped gallium lanthanum glass showed the possibility of pump efficiencies of over 60%. This lead to a widespread activity to demonstrate a low-loss sulphide glass optical fibre and an 1300 nm optical fibre amplifier. Since that time, research into gallium lanthanum glass and fibre has expanded into several new areas. In this paper, research work at the ORC on sulphide fibres for active applications will be described. Recent progress, including the 1.3 micron amplifier, photonic switching and work extending into the infrared will be reported. Our work is critically depend on the achievement of a low loss single-mode optical fibre. Over the past year, significant improvements have been made in understanding and eliminating the sources of loss in these glasses. The current status of fibre drawing work will be outlined and, together with our spectroscopy and device work, the prospects for a future generation of sulphide-fibre based devices examined.

At Southampton, our work has focused on gallium lanthanum glass and fiber, for both active and passive applications. As part of our ongoing program, optical, thermal and mechanical properties of these glasses are under study. In parallel with this, fiber drawing is being refined in a quest for practical fibers. Over the past year, improvements have been made in understanding and eliminating the sources of loss in these glasses. In this paper, we describe the current specifications of fibers based on this material group. Recent progress in several applications, in particular those extending into the IR will be reported and the prospects for a future generation of sulphide-fiber based devices examined.

Excited-state absorption spectra of erbium and thulium doped gallium lanthanum sulfide glasses reveal transitions whose final 4f states do not appear in the ground state absorption spectra due to resonance with the fundamental absorption of the glass host. The results give direct evidence for the model of isolated rare-earth ions with highly shielded 4f levels showing no noticeable interaction with the host material despite resonance. Only the energy splitting of the 4f levels is relevant for energy transfer processes between rare-earth ions and the host material, whereas the absolute energetic position is unimportant.

Measurements of the fundamental optical absorptions of gallium and lanthanum sulphide based chalcogenide glasses (Ga:La:S, and Ga:La:S:O) in glass and glass fibre forms are presented. Theoretical predictions of the minimum material losses in these glasses are given by calculating the loss from Rayleigh scattering and fitted data from the fundamental glass absorptions. The theoretical minimum loss for Ga:La:S is 0.5 dB km(-1) at 3.5 mu m, for the Ga:La:S:O glass it is 0.1 dB km(-1) at 2.6 mu m. These results show the potential of gallium and lanthanum sulphide based glasses as low loss optical materials. (C) 1998 Elsevier Science B.V. All rights reserved.

Chalcogenide glasses are usually known for their good infrared and poor visible transparency which limit their applications to passive and active devices in the infrared wavelength region. Gallium lanthanum sulphide glasses, however, show visible transparency down to 500nm. The low phonon energy of the glass increases the radiative quantum efficiency of rare-earth energy levels compared to commonly used fluorozirconate glasses and provides long-lived intermediate levels for efficient two-step excitation to visible energy levels. Green and red upconversion emission has been observed in Pr3+, Nd3+, Ho3+, and Er3+ doped glasses under Ti:sapphire pumping in wavelengths regions where diode laser sources are easily available. Lifetime measurements reveal the excitation process is either excited-state absorption or upconversion caused by ion-ion interactions. Modification of the glass with lanthanum oxide or ceasium chloride improves the visible transparency and shifts the UV absorption edge to 450nm and 400nm, respectively, and also improves the fibre drawing of these glasses

We report on laser action in a Neodymium doped Gallium Lanthanum Sulphide glass fibre. Laser action at 1080nm was obtained in a 22mm long multimode glass fibre with a neodymium doped core, fabricated by the rod-in-tube technique. The laser was pumped continuous wave with a Ti:sapphire laser at 815nm and showed a self-pulsing behaviour.

The first laser action in a rare-earth doped chalcogenide glass fibre is reported. Laser action at 1080 nm was obtained in a 22 mm long gallium lanthanum sulphide glass fibre with a neodymium doped core, fabricated by the rod-in-tube technique. The laser was pumped continuous wave with a Ti:sapphire laser at 815 nm and showed a self-pulsing behaviour.