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This work focuses on the development of sensitive elements incorporating bacteriorhodopsin thin films for fibre optic sensors. The sensing principle is based on monitoring optical properties of the bacteriorhodopsin thin films during changes of environmental conditions. The photochromic properties of the bR films change in response to the presence of different chemical species and this effect can be employed for the development of sensitive elements for optical sensors. For practical sensing applications, one can monitor changes (in the presence of chemical species) of the spectral and kinetic parameters of bR films incorporated into a matrix. The main topic of this thesis is to study the possibility of using bacteriorhodopsin thin films for the construction of fibre-optic sensors for monitoring ammonia and humidity. The possibility to control sensitivity and selectivity of the sensor to the presence of ammonia and humidity by adding chemicals to the bR film and by employing different materials as a matrix for the creation of bR films is reported. The examples based on ammonia and relative humidity are used to show how using a broad range of different chemical additives bR can be sensitized to a wide spectrum of species, and thus possesses the potential to be a universal film material for optical sensors.

A review of non-contact rotation measurement techniques has been undertaken. A non-contact sensor utilising optical fibres for the measurement of angular frequency and torsional strain in rotating shafts has been devised and tested. Initially a system was developed capable of measuring angular frequency over a range from 5 Hz to 1000 Hz to a resolution of 1Hz by monitoring variations in the intensity of the reflected light produced by the surface profile of the rotating shaft. Signal processing techniques such as windowing and auto-correlation were investigated in detail and proved beneficial in the reduction of noise thus enhancing the visibility of the peaks in the Fast Fourier Transform (FFT) spectrum. It was found that the best results were obtained using a Hamming window. In order to identify automatically the peak in the Fourier spectrum representing the rotation rate an algorithm was devised that enabled this to be determined when the peak containing the greatest energy was not necessarily that with the lowest frequency. The addition of a second identical channel enabling data to be collected at a different point along the axis of the shaft allowed the two signals to be cross-correlated and hence changes in the relative phase of the two points deduced. A digital cross-correlation technique was implemented on a PC. From this information torques up to 0.12 Nm have been measured, with a system resolution of 0.02 Nm and a response time of 1.5 seconds.

The development of sensing devices is one of the instrumentation fields that has grown rapidly in the last decade. Corresponding to the swift advance in the development of microelectronic sensors, optical fibre sensors are widely investigated because of their advantageous properties over the electronics sensors such as their wavelength multiplexing capability and high sensitivity to temperature, pressure, strain, vibration and acoustic emission. Moreover, optical fibre sensors are more attractive than the electronics sensors as they can perform distributed sensing, in terms of covering a reasonably large area using a single piece of fibre. Apart from being a responsive element in the sensing field, optical fibre possesses good assets in generating, distributing, processing and transmitting signals in the future broadband information network. These assets include wide bandwidth, high capacity and low loss that grant mobility and flexibility for wireless access systems. Among these core technologies, the fibre optic signal processing and transmission of optical and radio frequency signals have been the subjects of study in this thesis. Based on the intrinsic properties of single-mode optical fibre, this thesis aims to exploit the fibre characteristics such as thermal sensitivity, birefringence, dispersion and nonlinearity, in the applications of temperature sensing and radio-over-fibre systems. By exploiting the fibre thermal sensitivity, a fully distributed temperature sensing system consisting of an apodised chirped fibre Bragg grating has been implemented. The proposed system has proven to be efficient in characterising grating and providing the information of temperature variation, location and width of the heat source applied in the area under test.To exploit the fibre birefringence, a fibre delay line filter using a single high-birefringence optical fibre structure has been presented. The proposed filter can be reconfigured and programmed by adjusting the input azimuth of launched light, as well as the strength and direction of the applied coupling, to meet the requirements of signal processing for different purposes in microwave photonic and optical filtering applications. To exploit the fibre dispersion and nonlinearity, experimental investigations have been carried out to study their joint effect in high power double-sideband and single-sideband modulated links with the presence of fibre loss. The experimental results have been theoretically verified based on the in-house implementation of the split-step Fourier method applied to the generalised nonlinear Schrödinger equation. Further simulation study on the inter-modulation distortion in two-tone signal transmission has also been presented so as to show the effect of nonlinearity of one channel on the other. In addition to the experimental work, numerical simulations have also been carried out in all the proposed systems, to ensure that all the aspects concerned are comprehensively investigated.

This thesis describes novel developments in the fabrication and understanding of type IA fibre Bragg gratings, the uses of said gratings as optical sensors and the interrogation of optical sensors using tilted fibre Bragg gratings. This thesis presents the most detailed study of type IA gratings performed to date and provides the basis of a dual grating optical sensor capable of independently measuring strain and temperature. Until this work it was not known how to reliably fabricate type IA gratings or how they would react to high ambient temperatures, nor was it known what effect external parameters such as fibre type, dopant levels, inscription laser intensity, or hydrogenation levels would have on the physical properties of the grating. This comprehensive study has yielded answers to all of these unknowns and produced several unexpected uses for type IA gratings, such as the use of the previously unreported strong loss band at 1400nm to locally heat fibres by optical absorption and thereby fabricate optically tuneable gratings which do not affect directly adjacent standard gratings. Blazed fibre Bragg gratings have been studied in detail and used to produce several high quality prototype sensor interrogation systems yielding stability an accuracy values unsurpassed by similar devices reported in literature. An accurate distribution map of light radiated by blazed gratings is shown for the first time and has been studied in respect of polarisation state showing that for certain easily achievable conditions a blazed grating spectrometer may be deemed to be polarisation insensitive. In a novel implementation of the system, it is shown that the dynamic wavelength range of a blazed grating spectrometer may be at least doubled by superimposing blazed gratings.

This thesis presents the fabrication of fibre gratings in novel optical fibres for sensing applications. Long period gratings have been inscribed into photonic crystal fibre using the electric-arc technique. The resulting sensing characteristics were found to depend on the air-hole geometry of the particular fibre. This provides the potential of designing a fibre to have enhanced sensitivity to a particular measure and whilst removing unwanted cross sensitivities. Fibre Bragg gratings have been fabricated in a variety of polymer optical fibres, including microstructured polymer optical fibre, using a continuous wave helium cadmium laser. The thermal response of the gratings have been characterised and found to have enhanced sensitivity compared to fibre Bragg gratings in silica optical fibre. The increased sensitivity has been harnessed to achieve a grating based device in single mode step index polymer optical fibre by fabricating an electrically tunable fibre Bragg grating. This was accomplished by coating the grating region in a thin layer of copper, which upon application of a direct current, causes a temperature induced Bragg wavelength shift.

Through the application of novel signal processing techniques we are able to measure physical measurands with both high accuracy and low noise susceptibility. The first interrogation scheme is based upon a CCD spectrometer. We compare different algorithms for resolving the Bragg wavelength from a low resolution discrete representation of the reflected spectrum, and present optimal processing methods for providing a high integrity measurement from the reflection image. Our second sensing scheme uses a novel network of sensors to measure the distributive strain response of a mechanical system. Using neural network processing methods we demonstrate the measurement capabilities of a scalable low-cost fibre Bragg grating sensor network. This network has been shown to be comparable with the performance of existing fibre Bragg grating sensing techniques, at a greatly reduced implementation cost.

This thesis presents a novel high-performance approach to time-division-multiplexing (TDM) fibre Bragg grating (FBG) optical sensors, known as the resonant cavity architecture. A background theory of FBG optical sensing includes several techniques for multiplexing sensors. The limitations of current wavelength-division-multiplexing (WDM) schemes are contrasted against the technological and commercial advantage of TDM. The author’s hypothesis that ‘it should be possible to achieve TDM FBG sensor interrogation using an electrically switched semiconductor optical amplifier (SOA)’ is then explained. Research and development of a commercially viable optical sensor interrogator based on the resonant cavity architecture forms the remainder of this thesis. A fully programmable SOA drive system allows interrogation of sensor arrays 10km long with a spatial resolution of 8cm and a variable gain system provides dynamic compensation for fluctuating system losses. Ratiometric filter- and diffractive-element spectrometer-based wavelength measurement systems are developed and analysed for different commercial applications. The ratiometric design provides a low-cost solution that has picometre resolution and low noise using 4% reflective sensors, but is less tolerant to variation in system loss. The spectrometer design is more expensive, but delivers exceptional performance with picometre resolution, low noise and tolerance to 13dB system loss variation. Finally, this thesis details the interrogator’s peripheral components, its compliance for operation in harsh industrial environments and several examples of commercial applications where it has been deployed. Applications include laboratory instruments, temperature monitoring systems for oil production, dynamic control for wind-energy and battery powered, self-contained sub-sea strain monitoring.

Glasses systems based on TeO2-ZnO-Na2O (TZN), TeO2-WO3, and TeO2-Na2O-ZnF2 are reported here, with a number of other components added (PbO, GeO2, Nb2O5, Bi2O3, Er2O3, Yb2O3, PbF2, and ErF3). Glass formation was shown for the first time, to this author's knowledge, in the ternary system (90-x)TeO2-10Na2O-xZnF2 for x = 5 to 30 mol. %. Glass stability (Tx-Tg) was found to increase with ZnF2 addition, reaching a plateau of around 161oC at x = 25 mol. %. This could be due to competition of various phases to crystallise (NaZnF3 and Zn2Te3O8) as the eutectic is approached, with fluoride addition. These glasses are the most stable ZnF2 containing tellurite compositions reported to date, to the author's knowledge. As-received ZnF2 batch material was shown to contain a significant proportion of Zn(OH)F, identified by XRD. The as-received ZnF2 was fluorinated with (NH4)HF2, which produced a substantially more phase pure powder, with oxygen levels reduced from around 13.2 to 3.1 at. % from XPS spectra. By calculation from the O1s XPS peaks, the proportion of Zn(OH)F was reduced in the powders from 39.7 to 9.4 mol. %. A number of absorption bands in the infrared were identified by FTIR for the TeO2 -ZnO-Na2O glasses due to intrinsic lattice vibrations (visible in a 0.2 mm sample), and extrinsic impurity absorption, including: free OH (around 3.0 microns, 3300 cm-1), weakly hydrogen-bonded OH (around 3.3 microns, 3060 cm-1), and strongly hydrogen-bonded OH (around 4.8 microns, 2090 cm-1). For the series (90-x)TeO2-10Na2O-xZnF2, mol. %, x = 5 to 30 mol. % melted for 2 hours as bulk glasses, OH bands at 2900 cm-1 were reduced in intensity with ZnF2 addition due to self drying of the melt, from around 0.12 cm-1 (120 dB.m-1) for x = 5 mol. %, to around 0.02 cm-1 (20 dB.m-1) for x > 15 mol. %. Melting time also had a significant effect on drying of this series, with the loss at 2900 cm-1 reduced by two orders of magnitude when increased from 1 hour (around 705 cm-1, 705 dB.m-1) to 2 hours (0.01 cm-1, 10 dB.m-1). Refractive index of the series (90-x)TeO2-10Na2O-xZnF2, mol. %, x = 5 to 30 mol. % decreased linearly with ZnF2 addition, from 2.02 (x = 5 mol. %) to 1.85 (x = 30 mol. %), as the fluoride and zinc are less polarisable than oxygen and tellurium. Cohen-Grest viscosity modelling was used to predict the fibre drawing temperature (around 330oC, corresponding to a viscosity of 10^4.5 Pa.s), and fragility of the fluorotellurite core / clad pair (20 / 25 mol. % ZnF2), occurring at least 60oC < Tx. Fragility of these glasses was predicted to lie between oxide tellurite glasses (stronger) and fluorozirconate glasses (more fragile). Increasing melting time and fluorination resulted in a significant decrease in OH bands in the 700 nm to 2.5 micron region for unstructured 70TeO2-10Na2O-20ZnF2 mol. % fibre, from around 40 to 4 dB.m-1 at 2.5 microns as melting time was increased from 3 to 10 hours. Fibre optical loss for the 10 hour melt was relatively flat (around 5 dB.m-1) over the entire 700 nm to 2.5 micron region.