This thesis describes the development of silicon planar micro-calorimetric gas sensors employing a nanostructured palladium (Pd) catalyst. Present commercial, bead-type calorimetric sensors have been manufactured for nearly forty years and are used in many applications, such as mining, water treatment and emergency services, with an estimated European market value of €221M by 2004. However, recent advances in both silicon micro-machining and nano materials have created the technologies necessary to transform the present labour-intensive fabrication process in to a new low-cost batch production. In addition, a reduction in power consumption, improved sensitivity and increased poisoning resistance of the sensor can also be achieved. Here, two generations of micro-calorimeter have been designed and fabricated comprising a silicon membrane structured micro-hotplate that can reach up to a temperature of 870'C without failure and an ultra-high surface area nanoporous Pd catalyst (about 20 m2/g), typically 25 run thick, deposited electrochemically on top of a gold electrode above the micro-heater. The exothermic reaction caused by the target gas (e.g. methane) interacting with the Pd catalyst results in an increase in the temperature and so resistance of the micro-heater. A Wheatstone bridge interface circuit is normally used to detect and measure the fractional resistance change. Full 3-D thermo-mechanical simulations have been performed employing experimental data in order to establish a simulation database for future developments. The differences between simulated and experimental results were found to be as low as 4.6%. The response of the sensors has been characterised in both continuous powering mode and pulse modulation powering mode. Device power consumption is only 50mW at 500'C in continuous mode, which is up to 100mW lower than that for commercial sensors. Typical response times of 2ms have been measured and so further power saving can be achieved when the sensors are operated in a pulse mode, e.g. 50% duty-cycle at 10Hz. Hence, an overall power saving of 75% could be achieved compared to commercial product. Infrared thermography revealed that a centre hot spot, commonly found with meander style micro-heaters, has been eliminated by the new drive-wheel micro-heater design. The sensitivity of the sensors has also been improved, up to a factor of 4 at 500'C ((60 mV/mm2)/%CH4), by the nanoporous catalyst and by heating it more isothermally. Furthermore, improvements have also been found on the poisoning resistance. Therefore, the potential commercialisation of the micro-calorimeter is very promising.

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Dans le cadre de la thématique de recherche du Département Chimie-Environnement de l’Ecole des Mines de Douai portant sur le développement de capteurs de polluants gazeux, de précédents travaux de thèse avaient permis la mise au point d’un capteur chimique d’ammoniac présentant une teneur minimale détectable de 10 ppm, une réponse réversible et une durée de vie supérieure à 3 ans, répondant ainsi au défaut majeur des cellules électrochimiques du marché. La surface sensible du capteur synthétisée de manière propre pour l’environnement, se compose principalement d’un polymère conducteur intrinsèque dont la résistance électrique varie proportionnellement à la concentration en gaz. L’objectif visé dans cette thèse est double : d’une part améliorer les performances métrologiques du capteur d’ammoniac, d’autre part modifier sa surface sensible par une méthode appropriée à la détection spécifique du formaldéhyde. Pour le premier objectif, différents paramètres d’influence tels que la température, l’humidité relative, la vitesse de vent et les composés gazeux interférents ont tout d’abord été évalués, puis le seuil de détection a été réduit d’un facteur 100 par la réalisation de couches minces sur peignes interdigités. Les performances des différentes synthèses ont été comparées et enfin, la robustesse de ces capteurs a été testée lors de campagnes terrains en élevages porcins, qui sont parmi les contributeurs majeurs des émissions d’ammoniac. Pour le second objectif, plusieurs composés sensibles et sélectifs au formaldéhyde ont été introduits dans la surface sensible du capteur et testés. Le fluoral-p a finalement été retenu. Les premiers résultats obtenus ont montré une sensibilité au formaldéhyde proportionnelle à sa concentration, avec une limite de détection de quelques ppm et un temps de réponse inférieur à la minute. Le concept utilisé ici est innovant et montre la faisabilité de la détection du formaldéhyde basé sur la mesure simple des variations de la résistance électrique du film réalisé. La limite de détection reste cependant à diminuer afin de répondre à la problématique de la mesure du formaldéhyde en air intérieur. / As part of the research topic of the Department of Chemistry and Environment at Ecole des Mines de Douai on the development of sensors for gaseous pollutants, previous thesis had enabled the development of a chemical sensor of ammonia with a minimum detectable concentration of 10 ppm, a reversible response and a lifetime of more than 3 years, responding to the major flaw of the electrochemical cells of the market. The sensitive surface of the sensor synthesized in a clean way for the environment, consists mainly of an intrinsically conductive polymer whose electrical resistance varies in proportion to gas concentration.The objective in this thesis is double: on the one hand improve the metrological performance of the ammonia sensor, on the other hand change its sensitive surface by an appropriate method for the specific detection of formaldehyde.For the first objective, different influence parameters such as temperature, relative humidity, wind speed and interfering gases were first evaluated, then the detection threshold was reduced by a factor of 100 by the realization of thin films on interdigitated electrodes. The performances of different syntheses were compared and finally, the robustness of these sensors has been tested in piggeries, which are among the major contributors of ammonia emissions. For the second objective, more sensitive and selective compounds to formaldehyde were introduced into the sensitive surface of the sensor and tested. The fluoral p was finally selected. The first results showed sensitivity to formaldehyde proportional to its concentration, with a detection limit of a few ppm and a response time less than one minute. The concept used here is innovative and demonstrates the feasibility of formaldehyde detection based on the simple measure of changes in electrical resistance of the sensitive film made. The detection limit must still be decreased to respond to the problem of measuring formaldehyde indoor.

Measuring fine track widths with optical instruments has become increasingly difficult as the dimensions of the features of interest have become smaller than the traditional optical resolution limit. This has caused a move to non-optical methods such as scanning electron and atomic force microscopy techniques, or novel optical methods combined with signal processing techniques to provide measurements of these samples. This thesis presents one method to increase the measurement capabilities of an optical system. This is achieved by combining an optical profiler such as a scanning interferometer, with an artificial neural network (ANN). Once trained the ANN can calculate the object parameter for other tracks not contained in the training set. This process works extremely well; with experimental results showing that a 60nm track width can be calculated with a 2nm error using an optical system with a spot size of 2.6 microns. The technique can be extended to obtain other parameters such as height, sidewall slope and for other structures such as double tracks. Various aspects of the ANNs have been investigated, such as the training range, the size of network and the impact of noise etc. These studies show that the technique is extremely robust, and has huge potential for general usage.

The work presented in this thesis reports on four novel techniques for fabricating speciality silica preforms and optical fibres. The project aims were to conceive new fabrication methods by adapting conventional Modified Chemical Vapour Deposition (MCVD) and optical fibre drawing equipment, and to demonstrate fibre devices for ytterbium (Yb)-doped high-power fibre lasers (HPFL) and optical sensing applications. Firstly, a new in-situ solution doping technique is presented for fabricating actively-doped fibre-preforms of complex design. The fabrication and characterisation of several multilayered rare-earth (RE)-doped fibres suitable for HPFL applications are reported, including an Yb-doped (>18,000ppm, by weight) fibre with a low effective-NA, which incorporates a pedestal refractive index profile and a unique aluminosilcate (Al:Si) inner-cladding. The vapour-phase deposition of RE ions in fibre-preforms has also been demonstrated using a novel chemical-in-crucible process that is intended for use with precursors of low volatility. Modifications to the standard MCVD setup were made which allows the dopant source to be placed within the substrate glassware and in close proximity to the reaction zone. Preforms with dopant concentrations of up to 25,000 ppm (by weight) of Yb3+ ions have been attained using an organometallic precursor, whilst passive Al:Si preforms containing >16mol% of Al have been achieved using gaseous aluminium chloride. A straightforward fabrication technique for producing silica suspended-core holey fibre (SC-HF) is also presented. The drawn fibre exhibits a relatively low optical loss (of 0.3 dB.m-1 at λ = 1550nm), and the high air-filling fraction, which was predicted as ~30% (for a core size of 0.8μm), is believed to the highest reported value at the time the work was undertaken. The sensing capability of SC-HF has been demonstrated by constructing an all-fibre acetylene-filled gas cell. The final experimental chapter describes the first example of a novel flat fibre concept. Extended lengths of low-loss planar glass substrates were produced using MCVD and conventional fibre drawing equipment. In combination with direct UV-writing, multifunctional planar waveguiding devices can be fabricated that are mechanically flexible. The potential of the flat fibre platform for sensing applications is discussed. The reported fabrication techniques have been implemented through the successful demonstration of several fibre devices suitable for Yb-doped HPFLs and optical sensing applications. The developed techniques have future potential in industry and manufacturing, and it is anticipated that the work presented will enable fibres with novel properties and glass compositions to be researched.

Στην παρούσα διδακτορική διατριβή παρουσιάζεται η δυνατότητα ανάπτυξης νέων αισθητήρων με χρήση μιας καινοτόμας οπτικής ίνας, γνωστή ως Ίνα Φωτονικών Κρυστάλλων (ΙΦΚ) - (Photonic crystal fiber) σε συνδυασμό με νέα και λειτουργικά υλικά. Η ΙΦΚ αποτελείται από μια περιοδική συνήθως εξαγωνική δομή οπών που δρα ως τον μανδύα της ίνας και τις περισσότερες φορές κατασκευάζεται από γυαλί (SiO2) ή πολυμερές (PMMA, TOPAS, κτλ). Η αλλαγή στην διάμετρο των οπών και της απόστασης μεταξύ τους δίνει πολύ μεγάλη ευελιξία για διαχείριση των οπτικών ιδιοτήτων της. Εδώ παρουσιάζεται πώς η διήθηση νέων υλικών στις οπές της ΙΦΚ είναι μια αποδοτική μέθοδος για ενεργοποίηση της ΙΦΚ σε εξωτερικές παρεμβολές χωρίς να απαιτείται η κατασκευή μιας νέας ίνας από την αρχή. / This PhD thesis presents the possibility of development of new sensors using a novel optical fiber, called as photonic crystal fiber (PCF) in combination with new functional materials. PCF is consisted by a periodical, usually hexagonal structure of holes which acts as the cladding of the fiber and most of the times this fiber is made of glass (SiO2) or polymer (PMMA, TOPAS, etc.). The hole diameter and the pitch size of these fibers provides great flexibility for manipulation of their optical properties. Here, it is presented how the infiltration of new materials inside the holes of PCF constitutes an efficient method to sensitize the fiber to external perturbations without the need of a new fiber.

Το θέμα το οποίο πραγματεύεται η παρούσα διπλωματική είναι οι αισθητήρες οπτικών ινών με φράγματα Bragg προσδιορίζοντας τον δείκτη διάθλασης του περιβάλλοντος υγρού κατά τη βύθιση του οπτικού αισθητήρα μέσα σε αυτό. Στο πρώτο κεφάλαιο θα γίνει αρχικά μια ανάλυση των οπτικών ινών αφού θα αναφερθούν ο τρόπος λειτουργίας τους, οι τύποι οπτικών ινών που υπάρχουν, πλεονεκτήματα και μειονεκτήματα που παρουσιάζουν αλλά και ο λόγος που οδηγήθηκε η τεχνολογία στην κατασκευή τους. Στο δεύτερο κεφάλαιο περιγράφονται τα γενικά χαρακτηριστικά, δηλαδή ο τρόπος κατασκευής καθώς επίσης και ο τρόπος λειτουργίας των φραγμάτων Bragg. Αναφέρονται τα διάφορα είδη φραγμάτων Bragg που υπάρχουν και οι μηχανισμοί φωτοευαισθησίας τους. Στο τρίτο κεφάλαιο δίνεται έμφαση στη χρήση των φραγμάτων Bragg σαν αισθητήρες ταυτοποίησης της φύσης των υγρών στα οποία εισάγονται οι αισθητήρες αλλά και σαν αισθητήρες μέτρησης στάθμης υγρών. Τα φράγματα Bragg χρησιμοποιούνται ευρέως και σαν αισθητήρες πίεσης, θερμοκρασίας, ροής, μετατόπισης στάθμης υγρών, χημικής ταυτοποίησης, PH, ηλεκτρικών πεδίων, μαγνητικών πεδίων καθώς και άλλων φυσικών μεγεθών. Ακόμα γίνεται μια περιγραφή της διαδικασίας χημικής απογύμνωσης (etching), καθώς επίσης και τα τεχνικά χαρακτηριστικά και τρόπους λειτουργίας της πηγής φωτός που χρησιμοποιήθηκε, η οποία είναι ένας ενισχυτής Erbium Doped Fiber Amplifier –EDFA. Το τέταρτο κεφάλαιο πραγματεύεται τα αποτελέσματα των προσομοιώσεων που έγιναν με τη χρήση του προγράμματος COMSOL Multiphysics 4.2. Οι προσομοιώσεις έγιναν για διαφορετικές τιμές δεικτών διάθλασης μιας ποικιλίας υγρών. Στο πέμπτο κεφάλαιο αναλύεται το πειραματικό μέρος της ειδικής ερευνητικής εργασίας. Παρουσιάζονται η πειραματική διάταξη και τα πειραματικά δεδομένα που ελήφθησαν στο εργαστήριο Laser, καθώς επίσης και τα σχετικά σχόλια σύγκρισης με τα αποτελέσματα των αντίστοιχων προσομοιώσεων που έγιναν. / -

The study of an optical correlation spectroscopy gas detection system is presented in this thesis. The correlation spectroscopy method uses a sample of reference gas as a filter to identify the concentration of the target gas in a measurement gas cell. containing reference gas cell was also investigated by simulation and experiment. It was found by experiment and simulation, that by the pressurisation of the reference gas cell to 6 bar, the modulation index could by increased by up to a factor of 2. However, it was shown that the cross-sensitivity to a contaminant gas also increased.

Distributed fibre sensors have been successfully demonstrated and used in various industries for performing continuous measurements of the physical parameters such as temperature and strain. However, the measurement range and the performance of such sensors are limited by the intrinsic attenuation of the signal in the sensing fibre. This thesis investigates using optical amplification within the sensing fibre to enhance the range and the performance of the distributed Brillouin based sensors. To extend the range beyond this, remote amplification was also investigated using CW Raman amplification in which a Raman pump is injected at the midpoint of a 100km sensing fibre and a remotely pumped Erbium doped fibre amplifier is also situated at the midpoint. The performance achieved using each technique was measured and the relative advantages of each configuration were identified and discussed