J.R. Williams

Fluoride fibres for optical transmission

Optical fibres made from heavy metal fluorides have been under development for much of the past decade. There have been significant advances in understanding the fundamental characteristics of these materials. Progress towards achieving low optical losses and in optimizing the design of fluoride fibres for use in long transmission systems is reviewed.

A review of fluoride fibres for optical amplification

Abstract This paper reviews the current world-wide status of fibres based on the fluoride glass system for optical amplification, with particular emphasis on telecom applications. The key feature of fluorozirconate glasses, with the very long wavelength multiphonon edge, is the accompanying relatively low non-radiative decay rate of excited rare-earth dopant ions. This gives unique opportunities compared with the better known oxide glass systems. Amplifiers with high gains have been demonstrated at important wavelengths such as 0.8, 1.3 and 1.5 μm. Improvements to allow the fabrication of more efficient fibres are also discussed.

Ultimate Realistic Losses Of ZrF 4 Based Ir Fibres

An estimation has been made of the minimum loss that might be expected in ZrF. based IR fibre taking into account extrinsic absorption losses as well as the intrinsic loss mechanisms associated with the IR edge and Rayleigh scattering. The results suggest that an overall loss of approximately 0.03 dB/ km might be expected at 2.56 μm, a factor of three higher than the intrinsic loss and a factor of seven lower than overall loss in a typical silica fibre.

Loss Mechanisms in Zrf4 Based IR Fibres

Loss mechanisms in ZrF4 — based infrared fibres are reviewed with particular emphasis on intrinsic losses, extrinsic absorption losses and extrinsic scattering. This information is then used to evaluate the status of low-loss fibres (0.9 – 4 dB/km) that are currently being reported from several laboratories, and a breakdown of losses and impurity concentrations is given. Finally an estimate is made of the likely eventual impurity concentrations in the starting materials and the information is used to estimate the potential realistic losses that might be expected in infrared fibres made by melting techiques.

Overview Of Fluoride Glass Fibre Optics

The characteristics of glasses and fibres based on zirconium fluoride are reviewed. The fundamental limits to attenuation due to intrinsic processes in these materials are surveyed, leading to a predicted minimum loss approaching 0.01 dB/km at the likely operating wavelength of 2.55 μm. Current limitations due to extrinsic scattering and absorption are analysed, showing that most of the excess loss comes from wavelength-independent scattering due to small bubbles, crystallites and other small particles. These extrinsic mechanisms limit the attenuation to around 1dB/km in the best current fibres. Design criteria for single mode fibres are also reviewed, taking into account dispersion and mode field effects to optimise microbending and splicing characteristics.

Origins of scattering centres in ZrF4-based infrared fibres, and reduction of loss

Abstract The minimum loss of current fluoride fibres is dominated by wavelength independent scatter, and it is of great importance to identify its origin. Techniques have been developed to locate and analyse scattering centres, and over twenty different types of defect have been characterised. By improved processing, many types of centres, including the most serious, crystals and bubbles, have greatly reduced in frequency. As a result, the minimum fibre loss has been decreased to 0.65 dB/km, due mainly to decrease in extrinsic scatter loss to only 0.3 dB/km.

Prospects for ultra-low-loss fluoride fibres at BTRL

Abstract An evaluation of the loss mechanisms operating in fluoride fibres indicates that a minimum loss of 0.035 dB/km could be achieved. However, the current minimum loss reached at BTRL is 0.65 dB/km, measured over 110 m of fibre. The paper concentrates on three stages involved in fibre fabrication, including raw materials, purification, and preform fabrication. In each case, particular attention is paid to the influence on absorption and scatter loss. In addition, the prospects for scaling up to produce long lengths of monomode fibre is discussed.

Properties Of Fluorozirconate Fibres For Applications In The 0.5 To 4.5 Um Region

The primary objective for the development of infrared fibres based on fluorozirconate glasses has been the that of long distance repeaterless telecommunications, and sufficient progress has been made to suggest that this target should be reached in the not too distant future. The quality of the fibre has improved dramatically over the past two years, to the extent that moderate losses ( 3 - 5 dB/km ) are possible over lengths in excess of 200 m, and although not yet suitable for telecommunications, this type of fibre has many other commercial uses. In this work we will review the progress that has been made in reducing losses and improving reproducibility and mechanical properties. We will discuss the types of fibre that it is now possible to fabricate and finally descibe some preliminary applications that these fibres are already able to meet.

Infrared fiber applications

The main advantage of using infrared fibres in a number of applications is the delivery of radiation to a remote point of application. Fluorozirconate (O.3-5tm) and chalcogenide glass fibres (2-12gm) are receiving most attention, particularly in remote spectroscopy, laser power delivery, fibre lasers and thermal imaging.

Synthesis and Characterisation of Heavy Metal Fluoride Glasses and Fibres

The fabrication of optical fibres based on fluoride glasses has required the development of novel preparation techniques. Some of these techniques are based on methods used to prepare multicomponent oxide glass fibres although some have been developed specially for fluoride glasses. This paper will review such processes as glove-box melting, reactive atmosphere processing, and rapid quenching; show how these have been used to prepare fluoride glass fibres with losses down to 2.6 dB/km at 2.6 μm; and discuss remaining problems with the glass.