Optical Fibre Refractive Index Sensor in a Hybrid Fibre Grating Configuration

A temperature compensated Refractive Index (RI) sensor incorporating a Long Period Grating (LPG) and a Fibre Bragg Grating (FBG) in a series configuration has been developed and evaluated. The LPG was used as a RI sensor allowing it to respond to external RI variations while the FBG was used for temperature compensation. The LPG and FBG wavelengths were chosen to be within suitable spectral bandwidths for efficient interpretation of both RI and temperature. The performance of the hybrid sensor was evaluated for use as a chemical sensor by varying sodium chloride (NaCl) concentrations in water from 0.25 – 2%NaCl and temperature from 10-95 oC and by recording its corresponding attenuation band shifts. The sensitivity of the hybrid sensor to NaCl concentration and temperature is calculated to be 0.61 nm/%NaCl and 8 pm/oC respectively

Use of optical fibres for multi-parameter monitoring in electrical AC machines

This paper describes a new approach to multi-parameter monitoring for electrical AC machines. It is demonstrated that speed, torque and temperature can be measured using optical fibres incorporating sensors in the form of fibre Bragg gratings (FBGs) distributed around the machine. One fibre can incorporate several FBGs and hence provide several measurements. Experimental results showing speed, torque, direction of rotation, stator housing vibration and temperature measured using the FBG method are presented and validated against measurements obtained from conventional sensors. The results show that the optical fibre based approach allows multiple parameters to be monitored accurately and simultaneously with only a fraction of the usual monitoring equipment required. Another advantage of the proposed method is the EMI immunity naturally provided by optical solutions. The presented measurement technique can also offer a new alternative approach to sensorless control

Optical fibre thermometry using ratiometric green emission of an upconverting nanoparticle- polydimethylsiloxane composite

The thermally coupled green band emission from excited Er 3+ ions has been used in the past to create optical thermometers, by doping the material in various types of media, particularly glasses. Glasses are known to be excellent hosts for Er 3+ ions: however, high temperatures (>900 K) are usually required for doping these ions into glasses and a non-linear temperature response is often produced. In this work, the frequently encountered drawbacks of glass-based temperature sensors have been addressed by developing a temperature sensor created at a lower temperature (543 K), by dip-coating chemically synthesized upconverting nanoparticles (UCNP-NaYF4:(18%) Yb 3+ , (2%) Er 3+) embedded in polydimethylsiloxane (PDMS) onto the tip of a 1000 μm optical fibre, to create the actual fibre probe. The sensor shows an excellent linear response (R 2 = 0.991) over a very useful temperature range of 295 K-473 K, with a sensitivity of 2.9 ×10-3 K-1 , a temperature resolution of ± 2.7 K and response time of ~ 5 seconds. Additionally, a probe was investigated 2 where a pure upconverting nanoparticle powder was coated on the tip of optical fibre and its spectral and temperature response was obtained (and cross compared with that of UCNP-PDMS composite). The results obtained from the probe development work show that the UCNP-PDMS-coated optical fibre temperature sensor developed offers a better alternative to more conventional Er 3+ doped glass-based temperature sensors, in terms of the thermal budget, the synthesis process and the ease of coating, creating as a result, a very linear device response

Preparation of novel optical fibre-based Cocaine sensors using a molecular imprinted polymer approach

Novel chemical sensors using fibre optic-based techniques for the detection of Cocaine have been developed, utilising molecularly imprinted polymers (MIPs) containing fluorescein moieties as the signalling groups. The fluorescent MIPs were formed and covalently attached to the distal end of specially chosen optical fibres to create fibre optic probe-based sensors. These sensors exhibited are producible and quantifiable change in the intensity of the fluorescence signal received from the sensor in response to Cocaine in aqueous acetonitrile mixtures. High selectivity for Cocaine over Codeine and a range of known Cocaine interferants has been demonstrated for one of the sensors developed in this work

Wavelength dependent pH optical sensor using the layer-by-layer technique

In this work, the design and characteristics of a wavelength-dependent pH optical sensor have been studied. To create the sensor itself, brilliant yellow (BY) as a pH indicator and poly (allylamine hydrochloride) [PAH] as a cross-linker have been deposited on the end of a bare silica core of an optical fibre by use of a ‘layer-by-layer’ technique. In the experiments carried out to characterize the sensor, it was observed that the value of pKa (the dissociation constant) of the thin film is dependent both on the outer layer and the number of bilayers. A heat treatment process was applied to the sensor to reduce the effect on the deposited layers during the testing of the probe. As a result of these series of experiments, it could be concluded that the probe design on which were deposited structured layers comprising six double layers of (PAH/BY) showed the best sensitivity for a pH range from 6.80 to 9.00 (with an accuracy of ±0.20) and showing an average wavelength shift of 4.65 nm per 0.2 pH units, while the concentration of the BY and the PAH solutions was maintained as 0.25mM and 2.5mM respectively