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The effectiveness of self-mixing interferometry has been demonstrated across the electromagnetic spectrum, from visible to microwave frequencies, in a plethora of sensing applications, ranging from distance measurement to material analysis, microscopy and coherent imaging. Owing to their intrinsic stability to optical feedback, quantum cascade lasers (QCLs) represent a source that offers unique and versatile characteristics to further improve the self-mixing functionality at mid infrared and terahertz (THz) frequencies. Here, we show the feasibility of detecting with nanometer precision deeply subwalength (< {\lambda}/6000) mechanical vibrations of a suspended Si3N4-membrane used as the external element of a THz QCL feedback interferometric apparatus. Besides representing a platform for the characterization of small displacements, our self-mixing configuration can be exploited for the realization of optomechanical systems, where several laser sources can be linked together through a common mechanical microresonator actuated by radiation pressure., Comment: 5 pages, 4 figures

Recent progress of interferometric sensors based on the optical feedback in a laser diode have demonstrated possibility for measurement of flow rates and flow-profiles at the micro-scale. That type of compact and embedded sensors is very promising for a research and industrial field –microfluidics – that is a growing domain of activities, at the frontiers of the physics, the chemical science, the biology and the biomedical. However, the acquisition of flow rate or local velocity at high resolution remains a very challenging issue, and the sensors that have been proposed so far did not have been giving sufficient information on the nature of the particles flowing. The present thesis is driven to the implementation, validation and evaluation of the sensing performances of the optical feedback interferometry technology in both chemical and biomedical fields of applications. The elaboration of a new generation of sensors that will provide both a high spatial resolution for 2D Doppler imaging is presented, as well as a methodology that gives further information on the flowing particles concentration and/or dimensions. Then, a new embedded optical feedback interferometry imager for flowmetry has been realized using a 2-axis beamsteering mirror mounted on Micro-Electro-Mechanical Systems (MEMS) thus taking the full advantage of the compactness offered by the optical feedback interferometry sensing scheme. While previous works on optical feedback interferometry flowmetry have been limited to high particle densities fluids in single or multiple scattering regimes, we present also a sensing technique based on the optical feedback interferometry scheme in a laser diode that enables single particle detection at micro and nanoscales through the Doppler-Fizeau effect. Thanks to the proposed signal processing, this sensing technique can detect the presence of single spherical polystyrene micro/nanospheres seeded in watery suspensions, and measure their flow velocity, even when their diameter is below half the laser wavelength. It discriminates particle by their diameter up to a ratio of 5 between large and small ones while most of the technologies for particle characterization is bulk and requires manipulation of the fluid with small volume handling, precise flow and concentration control. Altogether, the results presented in this thesis realize a major improvement for the use of optical feedback interferometry in the chemical engineering or biomedical applications involving micro-scale flows.; Les progrès récents des capteurs interférométriques basés sur la réinjection optique dans une diode laser ont démontré la possibilité de mesurer des débits d’écoulements et des profils de vitesses d’écoulement à l'échelle micrométrique. Ce type de capteurs compacts et intégrés est très prometteur pour un domaine - la microfluidique - qui est en expansion, aux frontières de la physique, de la chimie, de la biologie et du biomédical. Cependant, la mesure du débit ou de la vitesse locale en haute résolution reste un problème très complexe et les capteurs proposés jusqu’à présent n’ont pas fourni d’informations sur la nature des particules qui s’écoulent. La présente thèse porte sur la mise en œuvre, la validation et l'évaluation des performances de détection de la technologie OFI dans les domaines d'applications chimiques et biomédicaux. L'élaboration d'une nouvelle génération de capteurs qui fourniront à la fois une haute résolution spatiale pour l’imagerie Doppler 2D est présentée ainsi qu’une approche novatrice permettant de fournir des informations supplémentaires sur la concentration et / ou les dimensions des particules en mouvement. Ensuite, un imageur Doppler par réinjection optique, embarqué dans un système compact pour la débitmétrie a été réalisé à l'aide d'un micro-miroir monté sur des systèmes microélectromécaniques (MEMS), tirant ainsi pleinement parti de la compacité offerte par le système de détection par réinjection optique. Alors que les travaux précédents sur la débitmétrie par réinjection optique ont été limités aux fluides à haute densité de particules dans des régimes de diffusion simples ou multiples, nous présentons également une technique permettant la détection de particules uniques de dimensions micro et nanométriques à travers l'effet Doppler-Fizeau. Grâce au traitement du signal proposé, cette technique de détection peut détecter la présence de micro/nanosphères de polystyrène sphériques uniques ensemencées dans des suspensions aqueuses et mesurer leur vitesse d'écoulement, même lorsque leur diamètre est inférieur à la moitié de la longueur d'onde du laser. Cette méthode présente de nombreux avantages par rapport aux méthodes habituelles qui nécessitent une manipulation du fluide, dans des volumes toujours plus petits avec un contrôle précis du débit et de la concentration. L’ensemble des aspects traités dans cette thèse représente une avancée majeure pour l’utilisation des capteurs par réinjection dans les applications d’ingénierie chimique ou biomédicale implicant des écoulements à micro-échelle

International audience; The fringes disappearance phenomenon in the self-mixing interferometry occurs whenever the external round-trip phase at free-running state is modulated by either external modulation such as external cavity length changes or internal modulation when the laser injection current is modulated with a high back-scattered light power. This phenomenon has been observed by many authors for harmonic motion or vibration application, and more recently in the case of the absolute distance measurement scheme when the laser injection current is modulated in the triangle waveform. However, there are no clear explanations on the fringes disappearance phenomenon and its dependence on the self-mixing's regimes. In this paper, a novel approach that depicts the mechanism of interferometric fringes disappearance is proposed that highlight with a new perspective the impact of the coupling strength between the laser and the external cavity on the number of missing fringes. The proposed modelling is validated by a set of measurements using the optical feedback interferometry absolute distance measurement scheme.

At the mirrors of a laser diode self-mixing interferometer, the output beams carry anti-correlated (i.e., in phase opposition) interferometric signals, whereas the superposed noise fluctuations are (partially) correlated. Therefore, by using an instrumental output of the interferometer as the difference of the two, we double the amplitude of the self-mixing useful signal, while the superposed noise is reduced. To validate the idea, we first calculate the noise reduction by means of a second-quantization model, finding that in a laser diode the signal-to-noise ratio (SNR) can be improved by 8.2 dB, typically. Then, we also carry out an experimental measurement of SNR and find very good agreement with the theoretical result.

It is established in the optical feedback interferometry (OFI) theory that the shape of the interferometric fringe has an impact on the detector’s response to very small displacement measurements. In this paper, we validate—for the first time, to the best of our knowledge, based on experimental results—this statement by comparing experiments to an established model implementation. Through these experiments, we show that the amplitude of the signals induced by sub- λ / 2 optical path variations is linearly dependent on the slope of the underlying fringe. Thus, careful control of the phase allows us to maximize the detection amplitude of very small displacements by positioning the phase where the fringe slope is the steepest. These results are directly applicable to established OFI applications that measure sub- λ / 2 optical path variations, such as OFI vibrometers or acoustic imaging though the acousto-optic effect.

Co-auteur étranger; International audience; Magma recharge into a differentiated reservoir is one of the main triggering mechanisms for explosive eruptions. Here wedescribe the petrology of the eruptive products of the last explosive eruption of Tutupaca volcano (southern Peru) in order toconstrain the pre-eruptive physical conditions (P-T-XH2O) of the Tutupaca dacitic reservoir. We demonstrate that prior to theparoxysm, magma in the Tutupaca dacitic reservoir was at low temperature and high viscosity (735 ± 23 °C), with a mineralassemblage of plagioclase, low-Al amphibole, biotite, titanite, and Fe-Ti oxides, located at 8.8 ± 1.6 km depth (233 ± 43 MPa).The phenocrysts of the Tutupaca dacites show frequent disequilibrium textures such as reverse zonation, resorption zones, andovergrowth rims. These disequilibrium textures suggest a heating process induced by the recharge of a hotter magma into thedacitic reservoir. As a result, high-Al amphibole and relatively high-Ca plagioclase phenocryst rims and microlites were formedand record high temperatures from just before the eruption (840 ± 45 °C). Based on these data, we propose that the recent eruptionof Tutupaca was triggered by the recharge of a hotter magma into a highly crystallized dacitic magma reservoir. As a result, theresident dacitic magma was reheated and remobilized by a self-mixing process. These magmatic processes induced an enhancedphase of dome growth that provoked destabilization of the NE flank, producing a debris avalanche and its accompanyingpyroclastic density currents.

We report on a new detection method for real-time molecular spectroscopy with a terahertz quantum-cascade laser. The self-mixing effect is exploited to tune the lasing frequency across molecular absorption lines of D 2 O and CH 3 OD and for the detection of the self-mixing signal. The method allows for realtime monitoring of gas mixtures in an absorption cell.

A self-mixing (SM) micro-interferometer laser displacement sensor coupled with an adaptive liquid lens (ALL) system is proposed and implemented. This has been made possible by a new method of real-time estimation of the optical feedback coupling factor $C$ . It is shown that such an estimation of $C$ combined with an appropriate amplification of the SM signal $Gain$ allows the ALL system to seek and maintain the SM signal in the moderate optical feedback regime in spite of variations in the optical feedback. The ALL system thus enables robust real-time displacement sensing in an unmanned autonomous manner. The implemented system has provided measurement precision better than 90 nm for different target surfaces and distances. The paper also investigates the impact of the weighting attributed to $C$ and $Gain$ on the retrieved displacement precision. As this autofocus is presently only performed once during the sensor initialization, so maximum displacement span after achieving optical feedback regime locking has also been investigated and tabulated. This proof of concept, thus paves the way for the deployment of autonomous SM sensors.

International audience; Self-Mixing (SM) is a promising technique for sensing vibration, distance, velocity etc. To retrieve accurate metric measurements from an acquired SM signal, it is necessary to correctly detect all interferometric fringes. Traditionally, SM fringes are detected by a derivative based threshold(DBT) scheme. However, such a scheme gives correct results only for SM signals with high signal- to-noise ratio (SNR) and moderate optical feedback regime. So, in this paper, a better fringe detection method, based on Matched Filter (MF), is proposed which has provided correct SM fringedetection even in case of low SNR and weak optical feedback regime. The proposed approach has resulted in fringe detection accuracy of 100% for a low SNR SM signal belonging to the weak feedback regime.

International audience; Absolute distance measurement by means of a self-mixing interferometer (SMI) can be obtained by modulating the laser frequency. This modulation is typically achieved through the modulation of the laser injection current with a triangle waveform. Various strategies have been proposed to increase the performances and recent researches have shown real-time performance of SMI with resolution reaching 100 μm for distances up to 2 m. In the present paper, we demonstrate for the first time, both experimentally and by modeling, that with high coupling factors between the laser and the target, disappearance of interferometric fringes occurs that can strongly affect the measurement reliability.

In this paper, we present a method of velocity measurement using of a novel self-mixing velocimeter with orthogonal-beam incident system (OSMV), which enables the velocity measurement without knowing the incident angle information. The fiber ring laser used could provide a stable and narrow-width laser light source, which could enhance the stability and the signal-to-noise ratio of the novel self-mixing fiber ring laser velocimeter. The result indicates a much better linearity of our novel velocimeter than the traditional one in the turntable experiment due to the use of the orthogonal-beam incident system and fiber ring laser source. The relative error rates of our novel velocimeter system are up to 1.258% in contrast with the 13.720% result of the traditional one.

Trabalho de Projeto do Mestrado Integrado em Engenharia Biomédica apresentado à Faculdade de Ciências e Tecnologia A onda de pulso arterial (OPA) gerada pelo coração durante a sístole causa a dilatação das artérias do sistema circulatório sistémico. A energia cinética desta dilatação é propagada para a vizinhança e pode ser detetada sob a forma de vibração da pele sobre artérias periféricas como a carótida. A velocidade da vibração é proporcional à velocidade de onda de pulso (VOP) que por sua vez, está intrinsecamente relacionada com a elasticidade da parede arterial. VOP é assim um índice da rigidez arterial, sendo esta por sua vez um indicador de doença cardiovascular (DCV), uma das maiores causas de mortalidade no Ocidente.Este trabalho tem como objetivo demonstrar que um sistema ótico simples baseado em self-mixing (SM) é capaz de extrair a VOP por meios não invasivos. SM é uma técnica de interferometria em que parte da luz refletida por um objeto em movimento provoca a modulação da frequência (FM) na luz captada pelo fotodíodo (PD) na cavidade de um díodo laser (LD). A FM contém informação sobre a frequência Doppler e consequentemente sobre a VOP. Posteriormente um algoritmo baseado na transformada rápida de Fourier (FFT) extrai essa informação, no entanto, este projeto também tem como propósito extrair essa informação analogicamente, sem necessitar de pós-processamento digital, o que habilita esta instrumentação a revelação da VOP em tempo real.____________________________________________________________________________________________________________________________________________________________________________________________________ The arterial pulse wave (APW) generated by the heart during systole causes the arteries in the systemic cardiovascular system to distend. The kinetic energy of this distention is propagated thought the vicinity and it can be detected in the form of vibration on top of the skin over peripheral arteries like the carotid. The velocity of the skin vibration is proportional to the pulse wave velocity (VOP) underneath it and this parameter is intrinsic related to the arterial wall elasticity. VOP is then an index of the arterial stiffness and hence an indicator of cardiovascular disease (CVD), one of the leading causes of mortality in the West.This project aims to demonstrate that a simple optical system based on self-mixing (SM) is capable of detecting VOP in a non-invasive way. SM is an interferometry technique in which part of the light reflected by an object in motion induces a frequency modulation (FM) in the light perceived by the photodiode (PD) in the laser diode (LD) cavity. The FM contains information regarding the Doppler frequency and so information about the VOP. An algorithm based on fast Fourier transform then extracts that information, but another purpose of this project is to extract this information analogically, without the need of software processing, enabling this instrumentation of detecting PW in real time.____________________________________________________________________________________________________________________________________________________________________________________________________

The selfmixer properties of a laser compound cavity are investigated and experimentally exploited to couple the mechanical fluctuations of a silicon nitride membrane to the laser photons and electronical states, producing an active optomechanical system.

International audience; Self-mixing interferometry (SMI) has been widely used for sensing of diverse vibration, velocity, displacement, biomedical and flow applications. The simplicity of the SMI configuration enables the design of a low-cost, self-aligned and compact sensor with a small optical component count. SMI occurs when a small portion of emitted coherent optical beam is backscattered by the remote target and re-enters the laser cavity, causing interference. Under SMI, the employed laser diode simultaneously acts as a laser source, coherent detector, as well as micro-interferometer. This simple sensor design configuration, however, comes at a price of complex signal processing algorithms, because the SMI signals have rich characteristics as a function of optical feedback level. The purpose of this research work is to implement two of these algorithms, time-frequency signal processing (TFSP) and Consecutive samples based Unwrapping (CSU) in hardware so that real-time displacement and vibration measurements with nanometric precision can be retrieved from the SM sensor in an embedded, autonomous manner. We implemented and tested both algorithms on a Xilinx ZYBO Zynq 7000 development board using VHDL. Results show that our design of CSU algorithm is capable of operating at 432 MHZ minimum clock frequency and latency of 3 clock cycles. Our CSU design consumes 159 slice registers and 215 LUT's, and draws 0.70 watts of onboard power. While the design of TFSP algorithm is capable of operating at 363.3 MHZ clock frequency and latency of 570k clock cycles. TFSP design consumes 5056 slice registers and 5192 LUT's, and draws 0.8 watts of onboard power.

The optical feedback interferometry phenomenon occurs when a portion of the output optical power is back-scattered from a remote target and coupled into the laser cavity to vary the laser’s emission properties (frequency and power mostly). Thus, this scheme results in a compact, self-aligned and contact-less interferometric sensor. Recent applications of optical feedback interferometer in the domains of microfluidics or acoustics have shown promising results and open new fields of researches. However in these applications, the amplitude of the sensing signal is extremely small due to the weakness of the backscattered power changes that are measured. In this thesis, an analytical model that describes the laser injection current and temperature dependence of the optical feedback interferometry signal strength for a single-mode laser diode has been derived from the Lang and Kobayashi rate equations. The model has been developed for all the known signal acquisition methods of the optical feedback interferometry scheme: from the package included monitoring photodiode, by collection of the laser power with an external photodetector and by amplification of the variations in the laser junction voltage. The model shows that both the photodiodes and the voltage signals strengths are related to the laser slope efficiency, which itself is a function of the laser injection current and of the temperature. Moreover, the model predicts different behaviors of the photodiodes and the voltage signal strengths with the change of the laser injection current and the temperature; an important result that has been proven by conducting measurements on all three signals for a wide range of injection current and temperature. Therefore, this simple model provides important insights into the radically different biasing strategies required to achieve optimal sensor sensitivity for the different interferometric signal acquisition schemes. In addition, the phase and amplitude relationships between the external and the in-package photodiode signals have been investigated theoretically and experimentally demonstrating unexpected results. Based on our model and on experimental observations, a critical study has been performed on the impact of the combination of the three signals in the signal processing strategy in order to improve the sensor sensibility to low amplitude optical feedback.

National audience; The optical feedback interferometry phenomenon occurs when a portion of the output optical power is back-scattered from a remote target and coupled into the laser cavity to vary the laser’s emission properties (frequency and power mostly). Thus, this scheme results in a compact, self-aligned and contact-less interferometric sensor. Recent applications of optical feedback interferometer in the domains of microfluidics or acoustics have shown promising results and open new fields of researches. However in these applications, the amplitude of the sensing signal is extremely small due to the weakness of the backscattered power changes that are measured. In this thesis, an analytical model that describes the laser injection current and temperature dependence of the optical feedback interferometry signal strength for a single-mode laser diode has been derived from the Lang and Kobayashi rate equations. The model has been developed for all the known signal acquisition methods of the optical feedback interferometry scheme: from the package included monitoring photodiode, by collection of the laser power with an external photodetector and by amplification of the variations in the laser junction voltage. The model shows that both the photodiodes and the voltage signals strengths are related to the laser slope efficiency, which itself is a function of the laser injection current and of the temperature. Moreover, the model predicts different behaviors of the photodiodes and the voltage signal strengths with the change of the laser injection current and the temperature; an important result that has been proven by conducting measurements on all three signals for a wide range of injection current and temperature. Therefore, this simple model provides important insights into the radically different biasing strategies required to achieve optimal sensor sensitivity for the different interferometric signal acquisition schemes. In addition, the phase and amplitude relationships between the external and the in-package photodiode signals have been investigated theoretically and experimentally demonstrating unexpected results. Based on our model and experimental observations, a critical study has been performed on the impact of the combination of the three signals in the signal processing strategy in order to improve the sensor sensibility to low amplitude optical feedback.; Le phénomène d’interférométrie par réinjection optique se produit lorsqu’une portion de la puissance optique du laser est rétrodiffusée par une cible distante puis réinjectée dans la cavité laser ce qui affecte les propriétés d’émission du laser (fréquence et puissance en particulier).Ce principe résulte alors en un capteur interférométrique compact, auto-aligné et sans contact. Des applications récentes des capteurs par réinjection optique dans les domaines de la microfluidique et de l’acoustique ont montré des résultats prometteurs et ouvert de nouveaux domaines de recherche. Pourtant, dans le cadre de ces applications, l’amplitude du signal est extrêmement faible à cause de la faible amplitude des variations de la puissance rétrodiffusée qui est mesurée. Dans cette thèse, un modèle analytique décrivant la dépendance de l’amplitude du signal issu d’une diode laser monomode au courant d’injection et à la température est développé à partir des équations d’évolution de Lang et Kobayashi. Le modèle a été développé pour toutes les méthodes connues d’acquisition du signal interférométrique par réinjection optique : par la photodiode de monitoring incluse dans le boîtier de la diode laser, par la captation de la puissance optique au moyen d’un photodétecteur externe et par l’amplification de la tension aux bornes de la diode laser elle-même. Le modèle démontre que les signaux des photodiodes et de la tension sont liés à l’efficacité externe de la diode laser, qui elle-même est fonction du courant injecté et de la température. Qui plus est, le modèle prédit une évolutiontrès différente de l’amplitude de ces différents signaux en fonction du courant d’injection ou de la température. Un résultat remarquable,confirmé par une campagne de mesures pour ces trois types de signaux sur une large plage de courants d’injection etde températures. Ainsi ce modèle simple permet une compréhension nouvelle des stratégies de polarisation très différentes de la diode laser permettant d’obtenir une sensibilité optimale du capteur dans les différents schémas d’acquisition du signal. Par ailleurs, les relations entre la phase et l’amplitude des signaux issus des photodiodes externes et de monitoring ont été étudiées sur le plan théorique et expérimental ce qui a permis de révéler des résultats inattendus. À partir du modèle et basé sur des observations expérimentales, une étude critique a été menée sur l’impact de la combinaison des trois signaux dans la stratégie de traitement du signal afin d’améliorer la sensibilité du capteur aux réinjections optiques de faible amplitude.

We report on the development of an all-interferometric optomechatronic sensor for the detection of multi-degrees-of-freedom displacements of a remote target. The prototype system exploits the self-mixing technique and consists only of a laser head, equipped with six laser sources, and a suitably designed reflective target. The feasibility of the system was validated experimentally for both single or multi-degrees-of-freedom measurements, thus demonstrating a simple and inexpensive alternative to costly and bulky existing systems.

International audience; This paper presents a general displacement reconstruction algorithm for sensors based on self-mixing (SM) interferometry suitable to work at different optical feedback conditions. The approach relies on a robust phase observation through analytic signals for the fringe detection stage, while the motion of the pointed target is retrieved by a self-adapting filter in a piece-wise basis. The implementation for real-time calculations demonstrates the feasibility of robust SM sensors for different usage conditions without the need of modifying the base device configuration.

We report on a fast self-mixing approach for real-time, coherent terahertz imaging based on a quantum-cascade laser and a scanning mirror. Due to a fast deflection of the terahertz beam, images with frame rates up to several Hz are obtained, eventually limited by the mechanical inertia of the employed scanning mirror. A phase modulation technique allows for the separation of the amplitude and phase information without the necessity of parameter fitting routines. We further demonstrate the potential for transmission imaging.

This paper describes and addresses the challenges that are encountered while designing a 900 GHz antenna for FET detectors using a standard submicron CMOS technology. The reduced metal stack, the problem of surface waves and technology-related rules are taken into account in order to properly design an efficient antenna, with the objective to couple it to field-effect transistor (FET) detectors in a focal-plane array configuration. Simulations on a 0.15-μm standard CMOS technology show that up to 58% efficiency with responsivity in the several kV/W range can be achieved.

This paper describes and addresses the challenges that are encountered while designing a 900 GHz antenna for FET detectors using a standard submicron CMOS technology. The reduced metal stack, the problem of surface waves and technology-related rules are taken into account in order to properly design an efficient antenna, with the objective to couple it to field-effect transistor (FET) detectors in a focal-plane array configuration. Simulations on a 0.15-μm standard CMOS technology show that up to 58% efficiency with responsivity in the several kV/W range can be achieved.

International audience; We present a simple analytical model that describes the injection current and temperature dependence of optical feedback interferometry signal strength for a single-mode laser diode. The model is derived from the Lang and Kobayashi rate equations, and is developed both for signals acquired from the monitoring photodiode (proportional to the variations in optical power) and for those obtained by amplification of the corresponding variations in laser voltage. The model shows that both the photodiode and the voltage signal strengths are dependent on the laser slope efficiency, which itself is a function of the injection current and the temperature. Moreover, the model predicts that photodiode and voltage signal strengths depend differently on injection current and temperature. This important model prediction was proven experimentally for a near-infrared distributed feedback laser by measuring both types of signals over a wide range of injection currents and temperatures. Therefore, this simple model provides important insight into the radically different biasing strategies required to achieve optimal sensor sensitivity for both interferometric signal acquisition schemes. 1. Introduction Optical feedback interferometry (OFI) is a promising sensing technique for both industrial and laboratory environments due to its simple optical setup relative to other interferometric techniques. Typical sensing applications of OFI are the measurement of displacement, distance, and velocity [1]. OFI signals can be acquired by two different means: (i) by observing power fluctuations in the light emitted by the rear facet of the laser diode with a monitoring photodiode (denoted here as the PD signal), or (ii) by amplifying voltage variations across the laser terminals (denoted here as the LV signal) [2]. The latter is the only viable measurement approach when a monitoring photodiode is not included in the laser diode package, for example when an array of laser diodes is used [3]. For both methods of signal acquisition , in order to achieve the best performance of the OFI sensor it is essential to maintain the signal-to-noise ratio (SNR) at a maximum. The dependence of OFI signal strength on bias current has been investigated previously in experiment [4–6], with earlier models providing important insight into the genesis of the interferometric signal [2, 7, 8]. Experimental results reported to date suggest that the relationship between OFI signal strength and bias current depends

The interaction between an emitted laser beam and a small portion of backscattered light from a pointed target that re-enters the laser's cavity, is at the origin of optical feedback phenomenon or self-mixing. Exploiting these unconventional interferometric fringes for non-contact sensors is attractive due to its minimal optical part-count and self-aligned nature. In this thesis we approach its development as a cost-e ective embedded implementation for displacement measurement. To this end we explored signal processing methods for fringe detection and target's movement reconstruction, avoiding the usage of external components. We first identified some incompatibilities in prior algorithms from our research center, and then proposed further solutions. Based on interpolation theory, a simplified but proved real-time algorithm resulted for displacement reconstruction. Relying on analytical signal elaboration, an improved approach for phase calculation allowed us to provide a fringe detection algorithm robust to amplitude variations, disregarding the feedback regime and thus, allowing a seemly usage over an increased variety of applications.; L'interaction entre un faisceau laser émis avec une partie de la lumière réfléchi depuis une cible qui rentre dans la cavité active du laser, est à l'origine du phénomène de rétro-injection optique ou self-mixing. L'utilisation de ces franges interférométriques non conventionnelles, semble attractive du au faible nombre des composant optiques et son caractère auto-aligné. Dans cette thèse nous approchons leur développement en tant qu'implémentation embarqué rentable pour la mesure du déplacement. A cette fin, nous avons exploré des méthodes du traitement du signal pour la détection des franges et la reconstruction du mouvement de la cible, en évitant l'usage de composant externes. Premièrement, nous avons identifié quelques incompatibilités dans des algorithmes précédentes établis dans notre centre de recherche, puis nous avons avancé des solutions. Fondé sur la théorie d'interpolation, an algorithme simplifié mais démontré convenable en temps-réel à été proposé pour la reconstruction du déplacement. En s'appuyant sur l'élaboration d'un signal analytique, il à été proposé une version amélioré pour le calcul de phase. Celle-ci nous à permit de fournir un algorithme pour la détection de franges, robuste aux variations d'amplitude, sans tenir compte du régime de rétro-injection, impliquant une convenable utilisation pour une variété d'applications.

The interaction between an emitted laser beam and a small portion of backscattered light from a pointed target that re-enters the laser's cavity, is at the origin of optical feedback phenomenon or self-mixing. Exploiting these unconventional interferometric fringes for non-contact sensors is attractive due to its minimal optical part-count and self-aligned nature. In this thesis we approach its development as a cost-e ective embedded implementation for displacement measurement. To this end we explored signal processing methods for fringe detection and target's movement reconstruction, avoiding the usage of external components. We first identified some incompatibilities in prior algorithms from our research center, and then proposed further solutions. Based on interpolation theory, a simplified but proved real-time algorithm resulted for displacement reconstruction. Relying on analytical signal elaboration, an improved approach for phase calculation allowed us to provide a fringe detection algorithm robust to amplitude variations, disregarding the feedback regime and thus, allowing a seemly usage over an increased variety of applications.; L'interaction entre un faisceau laser émis avec une partie de la lumière réfléchi depuis une cible qui rentre dans la cavité active du laser, est à l'origine du phénomène de rétro-injection optique ou self-mixing. L'utilisation de ces franges interférométriques non conventionnelles, semble attractive du au faible nombre des composant optiques et son caractère auto-aligné. Dans cette thèse nous approchons leur développement en tant qu'implémentation embarqué rentable pour la mesure du déplacement. A cette fin, nous avons exploré des méthodes du traitement du signal pour la détection des franges et la reconstruction du mouvement de la cible, en évitant l'usage de composant externes. Premièrement, nous avons identifié quelques incompatibilités dans des algorithmes précédentes établis dans notre centre de recherche, puis nous avons avancé des solutions. Fondé sur la théorie d'interpolation, an algorithme simplifié mais démontré convenable en temps-réel à été proposé pour la reconstruction du déplacement. En s'appuyant sur l'élaboration d'un signal analytique, il à été proposé une version amélioré pour le calcul de phase. Celle-ci nous à permit de fournir un algorithme pour la détection de franges, robuste aux variations d'amplitude, sans tenir compte du régime de rétro-injection, impliquant une convenable utilisation pour une variété d'applications.

Velocity measurements contactless mobile targets such as mechanical structures are often used in various industrial applications for non-destructive testing and quality control. In addition, the process of measuring speed can be critical if it is one of the parameters that govern the safety and performance of a system as in transportation. Accurate measurement and non-contact speed fluid flowing in microchannels is a major challenge for the chemical industry producing pharmaceuticals. In medicine, the knowledge of the velocity of blood flow in the vessels can help to anticipate cardiovascular disease.Such non-contact measurement can be performed by ultrasonic or microwave but these methods have a relatively low spatial resolution. On the other hand , the conventional optical sensors are often costly. For example , the conventional laser Doppler velocimetry ( LDV or for Laser Doppler Velocimetry) is a technique for high-precision measurements of the speed , but the use of a large number of optical components involves a high price. The rétroinjection optical interferometry is an attractive solution that allows us to design low-cost laser with high precision sensors . With optical non-contact sensors using just a diode laser subject to optical rétroinjection come to measure speeds , the objective of this thesis is to develop devices suitable for this type of measurement and operating in real time. In optical interferometry rétroinjection ( OFI or Interferometry for Optical Feedback ) , commonly called self -mixing , interference occurs in the active laser cavity between the existing field in the cavity and the one backscattered by a target located outside in front of the diode laser inducing changes in optical power output due mainly to the Doppler effect.By measuring the Doppler frequency of the optical power , the speed of the target can be determined. In this thesis , we study the main technical signal processing to provide real-time measurements of Doppler frequency of acceptable accuracy. The first technique is based on a conventional spectral analysis and requires the calculation of a fast Fourier transform (FFT ) . This technique is robust but requires a complex and expensive resource for signal processing in real time electronics. The second is based on a 2 -order autoregressive ( AR2) of the self -mixing signal by a linear prediction filter . The Doppler frequency corresponding to the resonance frequency of this filter.This technique is more accurate , faster and less resource intensive than the FFT . By cons , it presents a risk of divergence and requires calibration at startup. The third is an original technique for processing real - time signal has improved sensor performance in terms of range of measurable velocities. This technique is not as resource-intensive FFT and does not require calibration as AR2 . This technique has been implemented and validated experimentally in real configurations. It has provided good accuracy of measurements , similar to that of the FFT . We then apply the methods of signal processing on signals from the self -mixing passage of particles carried by a fluid in the beam of the laser diode used . In fact, in this case, the self -mixing signal no longer exhibits a Doppler peak but a distribution of Doppler frequencies for the particles passing through the beam are of different speeds from zero canal jusqu'une maximum value at the center . Another phenomenon that can contribute to the spectral broadening is multicast particles . The AR2 and technology have developed to obtain reliable measurements of the fluid flow rate in a channel on a microscopic scale .On the other hand , we study the optical configurations of the measuring device . We show that the device using a single laser diode is sensitive to changes in angle of incidence with the target. This angle must be known to calculate the speed . We then propose a system using two laser diodes and show its robustness to variations of angles of incidence and its ability to calculate the speed of the target without knowing the angles of incidence. We analyze this system to determine the optimum configuration to ensure the best performance. Simulations and experimental results validate the performance of this device in terms of accuracy and robustness. Finally, we apply the laser device and the double-headed processing technique developed in this thesis for measuring the flow rate of a gas injected into a macroscopic channel by a peristaltic pump in non -flow liquid . This thesis has helped develop a robust low cost to measure the speed in real - time using optical rétroinjection optical sensor.; Les mesures de vitesse sans contact des cibles mobiles comme les structures mécaniques sont souvent utilisés dans diverses applications industrielles pour le contrôle non destructif et le contrôle qualité. En outre, les processus de mesure de vitesse peuvent devenir cruciaux si elle est l'un des paramètres qui régissent la sécurité et la performance d'un système comme dans le transport. La mesure précise et sans contact de vitesse de fluide circulant dans des micro-canaux est un enjeu majeur pour l’industrie chimique fabriquant des produits pharmaceutiques. En médecine, la connaissance de la vitesse du flux sanguin dans les vaisseaux peut permettre d’anticiper sur des maladies cardiovasculaires. De telles mesures sans contact peuvent être réalisées par ultrasons ou par micro-ondes mais ces deux méthodes ont une résolution spatiale relativement faible. D’autre part, les capteurs optiques usuels sont souvent de coût élevé. Par exemple, la vélocimétrie laser Doppler conventionnelle (ou LDV pour Laser Doppler Velocimetry) est une technique de haute précision pour des mesures de vitesse, mais l'utilisation d'un grand nombre de composants optiques implique un prix élevé. L’interférométrie à rétroinjection optique est une solution attrayante qui nous permet de concevoir des capteurs laser à faible coût présentant une bonne précision. Disposant de capteurs optiques sans contact utilisant juste une diode Laser soumise à la rétroinjection optique pour venir mesurer des vitesses, l’objectif de cette thèse est de développer des dispositifs adaptés à ce type de mesure et opérant en temps réel. En interférométrie à rétroinjection optique (ou OFI pour Optical Feedback Interferometry), couramment appelée self-mixing, une interférence se produit dans la cavité active du laser entre le champ existant dans la cavité et celui rétrodiffusé par une cible extérieure située en face de la diode laser induisant des variations de la puissance optique de sortie dues notamment à l'effet Doppler. Par mesure de la fréquence Doppler de la puissance optique, la vitesse de la cible peut être déterminée. Dans cette thèse, nous étudions les principales techniques de traitement du signal permettant d’offrir en temps réel des mesures de fréquence Doppler de précision acceptable. La première technique est basée sur une analyse spectrale classique et requiert le calcul d’une transformée de Fourier rapide (FFT). Cette technique est robuste mais nécessite un matériel électronique complexe et coûteux en ressources pour le traitement du signal en temps réel. La seconde est basée sur une modélisation autorégressive d’ordre 2 (AR2) du signal de self-mixing par un filtre de prédiction linéaire. La fréquence Doppler correspond à la fréquence de résonnance de ce filtre. Cette technique est plus précise, plus rapide et moins gourmande en ressources que la FFT. Par contre, elle présente un risque de divergence et nécessite un calibrage au démarrage. La troisième est une technique originale de traitement du signal temps-réel qui a permis d’améliorer les performances du capteur en termes de gamme de vitesses mesurables. Cette technique n’est pas gourmande en ressources comme la FFT et ne nécessite pas de calibrage comme l’AR2. Cette technique a été implémentée et validée expérimentalement en configurations réelles. Elle a permis de fournir des mesures de bonne précision, comparable à celle de la FFT. Nous appliquons ensuite ces méthodes de traitement du signal sur des signaux de self-mixing issus du passage de particules portées par un liquide dans le faisceau de la diode laser utilisée. En fait, dans ce cas, le signal de self-mixing ne présente plus un pic Doppler mais une distribution de fréquences Doppler car les particules traversant le faisceau sont de vitesses différentes allant de zéro au bord du canal jusqu’une valeur maximale au centre. Un autre phénomène qui peut contribuer à l’élargissement spectral est la diffusion multiple des particules. L’AR2 et la technique développée ont permis d’obtenir des mesures fiables de la vitesse d’écoulement fluidique dans un canal à l’échelle microscopique. D’autre part, nous étudions les configurations optiques du dispositif de mesure. Nous montrons que le dispositif employant une seule diode laser est sensible aux variations d’angle d’incidence avec la cible. Cet angle doit être connu pour calculer la vitesse. Nous proposons ensuite un dispositif employant deux diodes laser et nous montrons sa robustesse face aux variations d’angles d’incidence et sa capacité de calculer la vitesse de la cible sans connaitre les angles d’incidence. Nous analysons ce dispositif afin de déterminer la configuration optimale permettant de garantir les meilleures performances. Des simulations et des résultats expérimentaux permettent de valider les performances de ce dispositif en termes de précision et de robustesse. Enfin, nous appliquons ce dispositif à double-tête laser et la technique de traitement développée dans cette thèse pour mesurer la vitesse d’écoulement d’un liquide injecté dans un canal macroscopique par une pompe péristaltique à débit non continu. Cette thèse a donc permis de développer un capteur optique robuste à faible coût permettant de mesurer la vitesse en temps-réel en utilisant la rétroinjection optique.

The phenomenon of optical feedback interferometry (OFI) or self-mixing effect in a laser is used to design non-invasive and self-aligned sensors, requiring only few optical elements and simple to implement. This type of sensor is used to measure the displacement, velocity or position of cooperative targets (reflective or strongly scattering targets). In this study, this phenomenom is applied to the measurement of fluid flow profile in microchannels. The low cost and versatility of optical feedback sensors are of great interest in biomedical and chemical industry as well as research in fluid mechanics. Based on studies in macro-channels, we proposed first a theoretical model of OFI in a laser diode when the target consists of moving particles suspended in a liquid. Based on this model, we then studied experimentally the impact of the sensor's sensing volume and the type of particles (size and concentration) on the OFI signal. We then proposed signal processing methods for calculating the fluid flow rate, as well as the local velocity at any point in a microchannel. These preliminary studies allowed us to reconstruct the flow profile of different liquids flowing in a circular channel of 320μm diameter. Finally, we compared the performance of the sensor developed in this thesis with a sensor based on the Dual-Slit technique, which has been already validated for microchannels, by measuring the flow profile in a rectangular shaped channel (100x20µm).; Le phénomène d'interférométrie par réinjection optique, ou effet self-mixing dans un laser permet de concevoir des capteurs non-invasifs, auto-alignés, ne nécessitant que peu d'éléments optiques et simples à implémenter. Ce type de capteur permet de mesurer avec la précision propre à l'interférométrie laser le déplacement, la vitesse ou la position de cibles dite coopératives (cibles réfléchissantes ou fortement diffusantes). Dans cette étude, ce type de capteurs est appliqué à la mesure de profil d'écoulement des fluides dans des microcanaux. Le faible coût et la polyvalence des capteurs à réinjection optique sont d'un grand intérêt dans l'industrie biomédicale et chimique, ainsi que pour la recherche en mécanique des fluides. Dans un premier temps, et en se basant sur les études réalisées dans des macro-canaux, nous avons proposé un modèle d'interferométrie par réinjection optique dans une diode laser lorsque la cible est constitué de particules en mouvement, en suspension dans un liquide. A partir de ce modèle, nous avons étudié expérimentalement l'impact du volume de mesure ainsi que du type de particules (taille et concentration) sur le signal mesuré. Nous avons ensuite proposé des méthodes de traitement du signal permettant de calculer le calcul du débit du fluide, ainsi que sous certaines conditions identifiées, la vitesse locale en tout point d'un microcanal. Ces études préliminaires nous ont permis de reconstruire le profil d'écoulement de différents liquides dans des canaux de 320µm de diamètre. Enfin, nous avons comparé les performances du capteur développé dans cette thèse avec un capteur basé sur la technique du Dual-Slit, technique déjà validée pour la microfluidique, en mesurant le profil d'écoulement dans un canal à section rectangulaire de 100x20µm.

9 pages; International audience; In this paper, we present a self-mixing double-head laser diode velocimeter. Analyzes are performed to evaluate the sensitivity to misalignment for this setup and calculate errors due to this misalignment. The analyses and calculations are verified by experimental results.

National audience; Le phénomène de rétro-injection optique (interférences de deux ondes dans le milieu actif d'une diode laser) est utilisé pour des applications métrologiques telles que la mesure de vitesse ou de distance. Dans le cadre de ce projet, cette technologie est appliquée à la mesure de profil d'écoulement dans des puces microfluidiques. L'évolution du signal en fonction de la taille et de la forme du canal microfluidique, du volume de mesure, de la concentration et de la taille des particules est étudiée. Une nouvelle classe de capteurs non invasifs, faible coût et intégrable, est présentée pour la mesure de la microcirculation sanguine in-vivo.

International audience; In this paper, we present a self-mixing double-head laser diode velocimeter. Several analyzes are performed to determine the optimal architecture of the double laser diode in terms of accuracy. We demonstrate that the double-head laser diode is insensitive to angle variation contrary to the single laser diode. The accuracy of the double-head laser diode sensor is verified by simulations and experiments.