David J. Booth

Fluorescence from highly-doped erbium fluorozirconate glasses pumped at 800 nm

Abstract A study of the fluorescence properties, under 800 nm excitation, of new ZBEAN glasses with Er 3+ concentrations up to 18 mol% is reported. This represents the highest reported doping concentration for this type of glass. The fluorescence intensity at 550 nm, 1.53 μm and 2.7 μm did not exhibit the expected strong quenching at these high concentrations and the corresponding decay times were consistent with this observation. Cooperative energy transfer between the relevant levels is discussed as a possible explanation of this behaviour.

Fibre optic distributed temperature sensor with an integrated background correction function

Raman scattering in optical fibres provides a means of measuring continuous temperature distributions over extended distances. However, in many applications it has been found that the background transmission properties of the optical fibre either change after deployment of the fibre or vary over time due to ageing effects. Changes in the fibre transmission can be distinguished from thermal effects by measuring the Rayleigh backscatter, which is relatively insensitive to temperature. The combined use of Raman and Rayleigh data is discussed here in the context of a particularly simple and cost-effective sensor design, where a single, fixed optical filter and a single light source are used for both measurement modes. The Rayleigh backscatter measurement allows the accurate correction of background transmission changes in a probe arrangement that includes several splices between different fibres with different attenuations. In this way, the temperature in a 290 °C test region is accurately recovered from the anti-Stokes Raman signal. However, preliminary measurements of the fibre attenuation as a function of temperature and exposure to an accelerated ageing environment show that these two effects will be difficult to separate in practice. Therefore it remains challenging to perform accurate, unambiguous background corrections in situations where high-temperature ageing occurs.

Multiplexed intrinsic optical fibre Fabry-Pérot temperature and strain sensors addressed using white-light interferometry

The construction and application of low-finesse, intrinsic fibre-optical Fabry-Perot interferometric sensors is presented. These sensors were interrogated using white-light interferometry. Broadband Fabry-Perot cavities were formed by pairs of dielectric mirrors prepared by coating the core region of single-mode fibre with titanium dioxide before fusion splicing. We obtained sensor responses to temperature and strain variations with resolutions of 0.01 °C and 0.07 µ, respectively. Multiplexing of two of these sensors was demonstrated both in parallel and in serial arrangements, the latter of which is readily extended to more than five sensors with little increase in system complexity.

Performance of a Nd:YVO(4) microchip laser with continuous-wave pumping at wavelengths between 741 and 825 nm.

We report the performance of a Nd:YVO(4) laser, which uses cw Ti:sapphire pumping, for a range of pumping wavelengths, polarizations, and crystal temperatures.

High Er(III) content ZBN glasses for microchip laser applications

Abstract The preparation and properties of zirconium/barium/sodium fluoride glasses containing high Er(III) contents are discussed in detail. Glasses containing up to 33×10 20 Er(III) cm −3 (18 mol%) have 1530 nm fluorescence lifetimes in the region of 10 ms and show no evidence of concentration quenching in their emission at various wavelengths in the infra-red. The lack of substantial concentration quenching was an unexpected result and possible reasons for this are discussed.

Intrinsic fibre Fabry-Perot sensors based on co-located Bragg gratings

Abstract An improved low-coherence optical fibre Fabry-Perot sensor, based on multiple co-located pairs of fibre Bragg gratings, is presented. Through the use of two (or more) reflection wavelengths and a compatible broadband source or sources, a sensor output of the form obtained in multiple-wavelength low-coherence interferometry is achieved. This allows easier identification of the centre of the fringe pattern than is possible with just a single pair of Bragg gratings. Modelling of the sensor behaviour with two or three pairs of gratings is discussed, and temperature measurement results with a triple Fabry-Perot are presented.

High erbium content heavy metal fluoride glasses

Abstract Rare earth glasses with high doping concentrations are candidates for the production of eye-safe microchip lasers for use as transmitters and detector amplifiers in laser radar systems and as transmitters in ultrahigh data rate communication systems. Presently only low concentrations of rare earths have been incorporated into glass hosts but microchip lasers will require higher dopant concentrations in order to obtain sufficient absorption of the pump radiation. In this work, glass systems based on ZrF4 were found to be able to support dopant concentrations of ErF3 up to 18 mol%. The thermal, optical and absorption properties of these ZBEAN glasses are examined as a function of concentration.

Fluorescence waveforms and coupled energy levels in Er3+:ZBLAN

Abstract Time-resolved fluorescence data was obtained from a number of levels in Er3+:ZBLAN glasses where the fluorescing level was populated by the decay of a higher level. The waveforms were substantially different from those obtained by direct pumping into the levels and care had to be exercised in the analysis of the data to derive a self-consistent physical interpretation. The fluorescing levels were the 4I13/2, 4I9/2 and 4F9/2 levels which were populated by the decay of the 4I11/2, 4F9/2, and ( 4 S 3/2 + 2 H 11/2 ) levels respectively. A rate-equation analysis was used to explain the observed behaviour. Particularly interesting was the population dynamics of the 4F9/2 level where the lifetime of the populating ( 4 S 3/2 + 2 H 11/2 ) level was strongly dependent on the Er3+ concentration.

Heavy metal oxide glasses as active materials

The solubility of rare earths at a level of 0.5 mol% in traditional heavy metal oxide glasses based on bismuth, lead and gallium is limited to the largest cations Pr, Nd and Sm. Within the families of these oxide glasses, a higher level of doping was achieved in this work with a heavy metal oxide glass containing germanium as a fourth component. Spectroscopic studies on the Nd3+ doped glasses revealed that the fluorescence peak for the 1.3 micrometer transition occurred at a relatively long wavelength of about 1360 nm. Decay time constants for the 4F3/2 level were considerably shorter than in other host materials.

Energy exchange processes in Er3+-doped fluorozirconate glasses

Abstract A comprehensive study has been conducted on the effects of erbium dopant concentration on the fluorescence properties of the three lowest energy levels which are involved in infrared emission in Er3+-doped fluorozirconate glass compositions. Pulsed pump radiation at wavelengths of 800 nm, 980 nm and 1.5 μm was used to measure fluorescence rise and decay waveforms for Er3+ concentrations between 0.2 and 18 mol%. A rate-equation model has been developed for the relevant levels and the fitting of this model to the experimental results has enabled the contribution of various ion–ion energy exchange processes to be identified and quantified. These processes determine, in part, the population dynamics, especially for the larger dopant concentrations used.