Growth and characterisation of single-crystal fibres for sensing applications

The laser heated pedestal growth technique has been successfully employed to grow pure and doped sapphire crystal fibres for characterisation as suitable sensor materials. Source materials used were polycrystalline and crystalline sapphire rods while fibres with typical diameters in the range 80 - 170 mm were grown. Pure sapphire fibres, both a- and c-axis, were found to grow easily with no complications such as melt instability. C-axis fibre growth was readily initiated while a-axis fibres required an appropriate a-axis oriented seed crystal. Dip-coating has been used to prepare suitably coated sapphire source rods for growth into doped fibres. Doped fibres grown included Cr3+:, Er3+:, Er3+:Yb3+: and Yb3+:Er3+:Al2O3. Er3+:Yb3+:Al2O3 fibres have been prepared with approximately equal concentration of both dopants while a 10:1 Yb3+ to Er3+ concentration ratio was used for preparing Yb3+:Er3+:Al2O3 fibres. Ruby fibres were also found to grow easily although brownish-green deposits have been observed on some of these fibres. Large transmission losses have been found in fibres with these deposits. Acid cleaning was not effective in removing these deposits, suggesting that they have diffused beneath the surface of the fibres. This was attributed to the condensation of chromium oxide on the fibre surface during growth. Growth of rare earth-doped fibres was initially problematic due to the constant breaking-off of the crystallising fibres from the melt. This was thought to be due to the flexibility of the small diameter source fibres used as well as the high concentration levels of doping. Replacing these small fibres with larger source rods thus permitted RE-doped fibres with relatively good optical quality to be grown. Fibres were grown with typical growth rates of 0.5 - 1 mm/min

Low-Pressure Measurement using an Extrinsic Fiber-Based Fabry-Perot Interferometer for Industrial Applications

The development of an extrinsic fiber-based Fabry-Perot interferometer (EFFPI) for low-pressure measurement in the industry applications has been studied in this work. Monochromatic light from a laser diode with a wavelength of 1310 nm is operated as a source for illuminating the EFFPI sensor. A 30 mm diameter PVC pipe is utilized as a target, of which one end is sealed with a rubber balloon and the end is connected to the air pressure flow controlling system. Furthermore, the center point of the balloon is secured with a reflective thin film, which has a reflectance of ~55%. For the performance validation of the fiber sensor, a low-pressure range from 5 to 50 mBar is released onto the target. With 12 rounds repeatability, the experimental results reported that the average measured pressure values from the EFFPI sensor are 4.915 – 50.988 mBar. When compared to the reference instrument, the maximum and average errors in percentage terms are, however, 3.77% and 1.45%, respectively. In addition, results showed that the measured pressure value is directly proportional to the number of interference fringes, giving a sensitivity in the pressure measurement of the EFFPI sensor of 0.248 mBar/fringe

Estimation of Transition Metal Nitride Surface Plasmon Refractometer Sensitivity

We numerically investigate the sensitivity of surface plasmon sensors using transition metal nitrides instead of noble metals, such as silver and gold. These alternative metals present improved thermal and mechanical properties that support the design of better sensors for harsh environment. The results show that titanium nitride and zirconium nitride are viable alternatives to silver as the sensitivity of sensors using these metals is better than sensors using silver

Analysis and design of a hybrid optical fiber refractometer for large dynamic range measurements

A fiber refractometer with large dynamic range from 1.316 to 1.61 RIU has been realized using a hybrid configuration of a single-mode fiber (SMF) coupled to a stripped-cladding multimode fiber (MMF) as sensing element. An extended analysis of the diffraction principle of a Gaussian beam is specifically developed for this sensor configuration to determine the injected power density into the MMF which, when subsequently combined with ray optics, analytical wave optics and Fresnel equations, enables the sensor response to be comprehensively estimated. Simulation results have been experimentally corroborated to very high agreement for a 2-cm and a 5-cm decladded section of multimode fiber used as the sensing element. The results show, for the shorter sensor (2 cm), a very high sensitivity of ~ -250 a.u./RIU being achieved in the Zone II operating regime, i.e. for indices between the cladding and core indices together with a resolution of 2.76 × 10 -6 RIU being attained. In addition, the developed models have been used to accurately predict the response of sensing elements of various lengths, hence demonstrating the potential capability of this research to be exploited for optimizing bespoke design of fiber refractometers of any arbitrary sensing lengths or dimensions. As an example, we present the design of a refractometer achieving a maximum sensitivity of 300 a.u./RIU with a potential resolution of 2.26 × 10 -6 RIU

Fiber optic sensors for metrology, geophysics and strain measurements

This HDR manuscript principally describes the research activities in which I have been involved since my appointment in August 2003 to my current laboratory, the Optoelectronics for Embedded Systems Group of the Laboratory for Analysis and Architecture Systems (LAAS-OSE). Before detailing these activities, I have also added a brief description of research work carried out during my PhD. This has been willingly added to this manuscript to demonstrate the evolution of my research activities over the past decade. Chapter 1 is a very brief introduction to my early career as a researcher in optics and fiber optics, basically describing work carried out on ruby crystal fiber-based sensors for harsh environments during my PhD at the University of Glasgow. Results show that c-axis ruby crystal fibers are uniquely sensitive to temperature effects while being insensitive to high levels of strains. Chapter 2 concerns an extrinsic-type fiber Fabry-Perot (EFFPI) interferometer which I initially developed during my post-doctoral fellowship at the Ecole des Mines de Nantes where I was responsible for setting up and leading the fiber optic sensing branch of the Instrumentation and Sensor Group. The proof-of-concept of the fiber interferometer was demonstrated before my departure to ENSEEIHT–INPT in Toulouse where I continue to work on its improvement at my current laboratory, LAAS–OSE, for metrology purposes. The initial polarization-based EFFPI which was developed earlier is thus described in the first half of Chapter 2 where a quadrature signal pair is obtained, hence the optical dual-cavity nature of the instrument. This is followed by its evolution into a modulation-based instrument, in the second half of the chapter, where, effectively, the introduction of a double-modulation scheme to the laser drive current enables a quadrature pair as well as the capability for detecting displacement amplitudes smaller than λ/4 to be achieved. This latter sensor has been conceived for applications in optical metrology and, more specifically, in geophysics under the ANR RISKNAT-sponsored LINES project. Three optical fiber-based geophysics instruments have been developed during the course of this project, namely, an EFFPI-based long baseline tiltmeter (or hydrostatic leveling system, HLS), an EFFPI-based borehole tiltmeter and an EFFPI-based seismometer. The modulation-based EFFPI is currently undergoing further development as a key component of the HLS for accelerator alignment at the CERN. A TRL 7 (technology readiness level) maturity state is envisaged at the outcome of this project. The final ambitions are to attain TRL 8 and TRL 9 before production and commercialization of the instrument for geophysics and industrial applications. Chapter 3 describes the second research activity which I lead at LAAS-OSE. This essentially involves the development of a novel technique for interrogating fiber Bragg grating-based (FBG) strain sensors based on optical feedback or self-mixing interferometry. The reflections off an FBG are retro-injected into the cavity of a laser diode, perturbing the internal fields. These result in a series of sawtooth fringes being detected by an internal photodiode and which are a function of the strength as well as frequency of the external strains applied on the FBG. This sensor has been demonstrated for dynamic strain measurements under a cantilever set-up. Further, a proof-of-concept is also experimentally demonstrated for extending the dynamic strain measurement range by 50% of the current limit via a low-frequency modulation scheme to the laser diode current. Chapter 4 is a summary of all the administrative tasks throughout my research career. It is organized around my supervision of PhD students including post-doctoral fellows, the various research projects that I have led and a selected list of my publications. Included is also a short discussion on the perspectives for leading further research as well as my services to my research community. I have also summarized my teaching duties and, to conclude this manuscript, my Curriculum Vitae is enclosed for perusal

Capteurs à fibres optiques pour la métrologie, la géophysique et les déformations mécaniques

This HDR manuscript principally describes the research activities in which I have been involved since my appointment in August 2003 to my current laboratory, the Optoelectronics for Embedded Systems Group of the Laboratory for Analysis and Architecture Systems (LAAS-OSE). Before detailing these activities, I have also added a brief description of research work carried out during my PhD. This has been willingly added to this manuscript to demonstrate the evolution of my research activities over the past decade. Chapter 1 is a very brief introduction to my early career as a researcher in optics and fiber optics, basically describing work carried out on ruby crystal fiber-based sensors for harsh environments during my PhD at the University of Glasgow. Results show that c-axis ruby crystal fibers are uniquely sensitive to temperature effects while being insensitive to high levels of strains. Chapter 2 concerns an extrinsic-type fiber Fabry-Perot (EFFPI) interferometer which I initially developed during my post-doctoral fellowship at the Ecole des Mines de Nantes where I was responsible for setting up and leading the fiber optic sensing branch of the Instrumentation and Sensor Group. The proof-of-concept of the fiber interferometer was demonstrated before my departure to ENSEEIHT-INPT in Toulouse where I continue to work on its improvement at my current laboratory, LAAS-OSE, for metrology purposes. The initial polarization-based EFFPI which was developed earlier is thus described in the first half of Chapter 2 where a quadrature signal pair is obtained, hence the optical dual-cavity nature of the instrument. This is followed by its evolution into a modulation-based instrument, in the second half of the chapter, where, effectively, the introduction of a double-modulation scheme to the laser drive current enables a quadrature pair as well as the capability for detecting displacement amplitudes smaller than /4 to be achieved. This latter sensor has been conceived for applications in optical metrology and, more specifically, in geophysics under the ANR RISKNAT-sponsored LINES project. Three optical fiber-based geophysics instruments have been developed during the course of this project, namely, an EFFPI-based long baseline tiltmeter (or hydrostatic leveling system, HLS), an EFFPI-based borehole tiltmeter and an EFFPI-based seismometer. The modulation-based EFFPI is currently undergoing further development as a key component of the HLS for accelerator alignment at the CERN. A TRL 7 (technology readiness level) maturity state is envisaged at the outcome of this project. The final ambitions are to attain TRL 8 and TRL 9 before production and commercialization of the instrument for geophysics and industrial applications. Chapter 3 describes the second research activity which I lead at LAAS-OSE. This essentially involves the development of a novel technique for interrogating fiber Bragg grating-based (FBG) strain sensors based on optical feedback or self-mixing interferometry. The reflections off an FBG are retro-injected into the cavity of a laser diode, perturbing the internal fields. These result in a series of sawtooth fringes being detected by an internal photodiode and which are a function of the strength as well as frequency of the external strains applied on the FBG. This sensor has been demonstrated for dynamic strain measurements under a cantilever set-up. Further, a proof-of-concept is also experimentally demonstrated for extending the dynamic strain measurement range by 50% of the current limit via a low-frequency modulation scheme to the laser diode current. Chapter 4 is a summary of all the administrative tasks throughout my research career. It is organized around my supervision of PhD students including post-doctoral fellows, the various research projects that I have led and a selected list of my publications. Included is also a short discussion on the perspectives for leading further research as well as my services to my research community. I have also summarized my teaching duties and, to conclude this manuscript, my Curriculum Vitae is enclosed for perusal.Ce manuscrit d'Habilitation décrit les principales activités de recherche que je mène au sein du groupe Optoélectronique pour les Systèmes Embarqués du LAAS depuis 2003. Dans un premier temps, les travaux porteront sur le développement des capteurs à fibres optiques à base de fibres cristallines de rubis pour des environnements hostiles à savoir température élevée et déformations mécaniques très importantes. Il est à noter que ces capteurs sont insensibles aux dernières perturbations, et par conséquence, ne mesurent que la grandeur physique ciblée. Une deuxième partie concerne le développement initial d'un interféromètre fibré de Fabry-Pérot extrinsèque (EFFPI). Ce premier dispositif est basé sur la décomposition du mode fondamental injecté dans l'interféromètre en deux signaux intrinsèques interférométriques déphasés en quadrature, d'où l'EFFPI à double-cavité optiques. L'EFFPI à double-cavité se montre cependant sensible aux effets de polarisation lors des perturbations induites (variations de température et vibration parasites). Pour éliminer ces difficultés, un EFFPI à modulation est développé. Ce travail est effectué dans le cadre d'un projet ANR qui a pour objectif de développer des nouveaux instruments pour les applications en géophysique. En effet, une double modulation du courant de la diode laser est appliquée, ce qui équivaut une modulation sur la longueur d'onde du laser. Ainsi, nous obtenons une condition de quadrature où l'amplitude du déplacement ainsi que sa direction peuvent être précisément déterminées sans aucune ambiguïté. Par ailleurs, grâce a cette double modulation, l'EFFPI est aussi capable de mesurer des très faibles déplacements, inférieurs à lambda/4 (< 327.50 nm pour lambda = 1310 nm). Trois instruments opto-géophysiques ont ainsi été développés à savoir un inclinomètre longue base à fibre optique, un inclinomètre de forage à fibre optique et un sismomètre à fibre optique. La troisième partie taitera le développement des capteurs à fibres optiques à réseaux de Bragg pour la mesure de déformations mécaniques. Pour ce travail, une nouvelle technique d'interrogation des fibres à réseaux de Bragg basée sur la rétro-injection optique (ou "self-mixing") est exploitée pour réaliser des capteurs de contraintes (déformations mécaniques) avec une bonne précision

Real-time demodulation of a field interferometer by an inverse problem algorithm

National audienc

Real-time demodulation of a field interferometer by an inverse problem algorithm

National audienc

Development of an extrinsic dual-cavity fiber Fabry-Perot interferometer (applications to periodic and non-periodic vibration measurements)

Le travail présenté dans cette thèse concerne le développement et la caractérisation d un interféromètre extrinsèque à double cavités de type Fabry-Pérot (EFFPI) en vue de l'analyse de vibrations périodiques et non périodiques. Le système comprend une cavité virtuelle pseudo-duale obtenue par l'introduction d'une optique de polarisation dans le chemin optique de la cavité de mesure. Cette configuration permet d'obtenir deux signaux d'interférence en quadrature. Deux techniques de démodulation, comptage de frange de type passage à zéro modifiée et poursuite de phase, ont été développées pour démoduler les signaux interférométriques déplacement. Les résultats expérimentaux montrent le potentiel du capteur pour résoudre l'ambiguïté directionnelle du mouvement de la cible, doublant ainsi son résolution par rapport à un interféromètre classique.TOULOUSE-ENSEEIHT (315552331) / SudocSudocFranceF

Validation of Fiber Optic-based Fabry-Perot Interferometer for Simultaneous Heart Rate and Pulse Pressure Measurements

International audienceIn this work, a fiber optic-based Fabry-Perot interferometer (FFPI) developed for simultaneous heart rate (HR) and pulse pressure (PP) measurement was investigated. Particularly, the FFPI was designed with simplicity in configuration for highly precise and non-invasive arterial distension measurement whose output was then demodulated via fringe counting to simultaneously obtain both HR and PP information through fringe pattern analysis and Kirchhoff-Love’s plate theory, respectively. The sensitivity was then characterized by linear fitting of measured PP inducing a number of interference fringes, whose slope represented the FFPI sensitivity. Experiments were conducted both on a simulating device and healthy subjects, each measurement carried out at least 10 times. Obtained results demonstrated the FFPI sensitivity for PP measurement in both experiments to be ~1.916 mmHg/fringe. For HR measurements, an average difference of 1.24% was found when compared to a digital sphygmomanometer employed as reference. Analysis of the FFPI resolution revealed the impact of the fringe counting technique, interrogating wavelength, and sensing material properties on measurement accuracy. Consequently, the thickness of the transducing thin film was found to have the most impact on PP demodulation. Therefore, optimization of the aforementioned parameters could lead to the development of a more accurate FFPI for PP measurement