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Two-mode fibre interferometers have been shown to be well suited as optical fibre strain sensors because (i) they have a higher resolution than do intensity modulation-based strain sensors and (ii) they have a simple geometry since the reference and signal light beams propagate along a single fibre core. This paper discusses a Sagnac ring configuration of polarization-maintaining fibre strain sensor based on frequency-modulation continuous wave technology wherein the basic sensor layout consists of a frequency-modulated single-mode laser, a 100 metre ring of single-mode birefringent fibre and a PIN photodiode detector. By launching light into both ends of the fibre, propagating and counter-propagating beams may be employed to sense the variations in length due to strain. The sensor exhibits good characteristics including temperature insensitivity over a limited temperature range (C), high resolution ( microstrain), large dynamic measurement range ( microstrain), large signal intensity and good signal contrast.

A quasi-distributed pH sensing system was developed to utilize information derived from evanescently excited fluorescence signals originating from sensor sites fabricated on an optical fibre. The sensor sites comprise a section of fibre core exposed by polishing upon which is laid down a sensing film. The film comprises a fluorescent indicator dye immobilized covalently within a hydrogel matrix which is then photopolymerized and attached covalently to the exposed fibre core. Position information is determined from the propagation delay of the returning signals. A system comprising eight sensors spaced at 10 m intervals along an optical fibre has been constructed and characterized. The sensors operate in the region pH 6-pH 8 with a response time of 500 s. The properties of the immobilized indicator dye are found to be similar to those of the dye in aqueous solution. Furthermore, the sensing films so created are found to be resistant to dye leaching.

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Barkcloths, non-woven textiles originating from the Pacific Islands, form part of many museum collections and date back to the 18th and 19th centuries. The ability to determine different plant species which have been used for producing barkcloth is required by art historians to help understand the origin and use of the cloths and by conservators for whom the species type may have an impact on textile durability, deterioration and hence conservation. However, to date the development of a non-destructive, robust analytical technique has been elusive. This article describes the use of Fourier transform infrared spectroscopy with attenuated total reflection (ATR-FTIR) and principal component analysis (PCA) to differentiation between historic barkcloths. Three distinct groups of historic cloths were identified using PCA of the FTIR region between 1200 and 1600 cm-1 where molecular vibrations associated with tannins and lignins are dominant. Analysis of contemporary cloths only identified Pipturus albidus cloth as different and highlighted the difficulties around producing a representative textile sample to mimic the historic cloths. While the methodology does not itself identify species, the use of historically well-provenanced samples allows cloths showing similarities to group together and is a significant aid to identification.