Characterization Speckle Effect on Measurement of Blood Flow Using Sensor Based on Self-Mixing Interferometry

The applications of Self-Mixing Interferometry (SMI) have been popular in many fields, including biomedical signals. The self-mixing effect occurs from the coherent back-coupling of the reflected or scattered lights from a target surface. The reflected lights will be detected by a photodiode which has been integrated in one device with the laser. That's why the SMI sensor is quite practical, affordable and simple. However, SMI has the serious problem with the presence of speckle effect in measured signal. The speckle effect produced by the human tissue is called “biospeckles.” The biospeckles observed from the skin tissues contain information about the blood flow in dermal capillarities, heartbeat, and others. These biospeckle patterns cause random modulations that will be detected as random amplitude and spectrum by photodiode. In this paper we present a technique to characterize speckle effect on measurement of blood flow in fingertip using sensor based on Self-Mixing Interferometry (SMI). We used a laser diode 785 nm as a light source and a constant current of 70 mA as a current source which is irradiated on the skin tissue in the fingertip. Then, the backscattered light reenters the laser cavity and it will be detected by photodiode. The SMI signal with speckle effect will be processed by Continuous Wavelet Transform for reconstruction and detection fringe. Signal processing results show that the number of detected speckle fringes depends largely on determining the number of wavelet waves and the scale used. The fringe pattern resulting from the reconstruction of the signal can be used to determine the frequency of speckles due to object movement. The average speckle frequency of fingertip is 0,5-0,7 H

Evaluation of Self-Mixing Interferometry Performance in the Measurement of Ablation Depth

This paper studies self-mixing interferometry (SMI) for measuring ablation depth during laser percussion drilling of TiAlN ceramic coating. The measurement performance of SMI was investigated in a large processing range producing blind microholes with depths below and beyond the average coating thickness. Signal characteristics of the measurement system were evaluated indicating sources of disturbance. The SMI measurements were compared with a conventional measurement device based on focus variation microscopy to evaluate the measurement error. The measurement error classes were defined, as well as defining the related error sources. The results depict that the measurement error was independent of the processing condition, hence the hole geometry and ablation rate. For 76% of cases, measurement error was below the intrinsic device resolution obtainable by simple fringe counting of half a wavelength (λ/2 = 0.393 μm)

Implementation of a high resolution optical feedback interferometer for microfluidics applications

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

Self-Mixing Diode Laser Interferometry

Self-mixing interferometry in a laser diode is a very powerful tool in measurement science. The Self-mixing interferometer is a very robust and low cost interferometer with extreme simplicity in alignment and setup. In this thesis, a self-mixing interferometer is analysed and developed. The measurements of the self-mixing interferometer are verified using a Michelson interferometer. It is then followed by the signal processing of the detected signal. Three different methods are developed to retrieve the movement of the target. Results obtained by applying these methods to different experimental data sets are presented. In the later part of the thesis, a phase locked self-mixing interferometer is developed. This slightly modified interferometer follows the target movement. As a result no additional circuitry or signal processing is necessary for the recovery of the target movement. Phase locked interferometer developed in this thesis was able to measure down to 1 nm of vibration. It is then followed by a novel method to detect cracks in eggshells using the phase locked vibrometer. The proposed method is tested and proved to be capable of differentiating between the intact and cracked eggs

The application of laser doppler technique to vibration measurement and position control.

The laser Doppler interferometer reported here was developed to investigate the possibilities of remote vibration and motion measurements. The method is noncontacting and operates with unprepared targets, using the diffusely scattered light to measure the axial component of the motion. A full description of the motion requires both magnitude and direction of the target motion. The magnitude was found by standard heterodyning techniques, mixing light scattered from the target with a part of the original laser output in a controlled manner. A phase quadrature method was used to identify the direction of the target. This differs from the more usual method of frequency offsetting in requiring only passive optical components and therefore being considerably cheaper. This feature is believed to be novel to the LDI reported here. Measurements were recorded for target motions over the range 100 mm. to (c. ) 1 um. Because unprepared and therefore optically rough targets were used the light received by the detectors was not well behaved. This resulted in instability of the sense of motion signal due to loss of either of the detector signals for displacements above 500 um. However this should not be considered an upper limit to the range of the LDI, as serious loss of the sense signal was rare up to (c. ) 25 mm. and measurements were made up to a peak displacement of 200 mm. Correlations with an accelerometer and an LVDT show that the LDI can reliably measure displacement up to a range of 25 mm. with a maximum target velocity of 32 mm/s limited currently be the signal processing. Theoretical resolution with this device is better than 0.08 um. if full use is made of both detected signals

Optimisation of a self-mixing laser displacement sensor

Optical Feedback Interferometry, also known as Self-Mixing, results in compact, selfaligned and contact-less sensors. In this phenomenon, a portion of the laser beam is back reflected from the target and enters the active laser cavity to vary its spectral properties. The laser diode then simultaneously acts as a light source, a micro- nterferometer as well as a light detector. In this thesis, a self-mixing displacement sensor has been optimised so that precise measurement can be obtained in real-time. The sensor is robust to the disappearance of self-mixing fringes for harmonic vibrations. It is also able to auto-adapt itself to a change in the optical feedback regime and so can extract displacement from the weak as well as moderate feedback regime signals. The use of adaptive optics, in the form of a liquid lens, has also been demonstrated for this sensor, which has allowed us to maintain the sensor in a fringe-loss less regime. The influence of speckle has also been reduced so that the sensor can now measure up to the centimetric range for non-cooperative targets. A novel technique has also been presented that makes the sensor insensitive to parasitic mechanical vibrations that would falsify the measurement under industrial conditions

Implementation of optical feedback interferometry for sensing applications in fluidic systems

Optical feedback interferometry is a sensing technique with relative recent implementation for the interrogation of fluidic systems. The sensing principle is based on the perturbation of the laser emission parameters induced by the reinjection in the laser cavity of light back-scattered from a distant target. The technique allows for the development of compact and noninvasive sensors that measure various parameters related to the motion of moving targets. In particular, optical feedback interferometers take advantage of the Doppler effect to measure the velocity of tracers in flowing liquids. These important features of the optical feedback interferometry technique make it wellsuited for a variety of applications in chemical engineering and biomedical fields, where accurate monitoring of the flows is needed. This thesis presents the implementation of optical feedback interferometry based sensors in multiple fluidic systems where local velocity or flow rate are directly measured. We present an application-centered study of the optical feedback sensing technique used for flow measurement at the microscale with focus on the reliability of the signal processing methods for flows in the single and the multiple scattering regimes. Further, we present experimental results of ex vivo measurements where the optical feedback sensor is proposed as an alternative system for myography. In addition we present a real-time implementation for the assessment of non-steady flows in a millifluidic configuration. A semi-automatized system for single particle detection in a microchannel is proposed and demonstrated. Finally, an optical feedback based laser sensor is implemented for the characterization of the interactions between two immiscible liquid-liquid flowing at the microscale, and the measurement is compared to a theoretical model developed to describe the hydrodynamics of both fluids in a chemical microreactor. The present manuscript describes an important contribution to the implementation of optical feedback sensors for fluidic and microfluidic applications. It also presents remarkable experimental results that open new horizons to the optical feedback interferometry

Implementation of differential self-mixing interferometry systems for the detection of nanometric vibrations

In this Thesis, we explore Self-mixing interferometry (SMI ), a method capable of producing high resolution optical path related measurements in a simple, compact and cost-effective way. Even with a notably less complex setup than traditional interferometric methods, SMI can produce measurements with a resolution well below the micrometric scale (N'2) which is sufficient for most industrial applications. The SMI effect is produced when a small part of the laser power impacting a target is back-scattered and re-injected into the laser cavity. As a result, the phase and amplitude of the laser wave is modified generating a signature beat, which can be "easily" related to different optical path-related dynamics. The main advantage of this method in relation to other interferometric methods is the simple setup consisting mainly of a single mode laser diode (LO) equipped with a simple electronic system readout a simple optical system may be used to collimate/focus the beam allowing measurements at larger distances. Because of the small amount of reflected optical power required to allow the effect, the technique can produce high resolution measurements even with diffusive targets. While the SMI method has been largely studied in the last three decades, there are still several topics worth the development of further research. One of those topics, how to increase the resolution on displacement measurements, is one of the main topics covered in this work. Classical SMI methods allow the reconstruction of displacement measurement with a resolution of N'2. The use of special processing algorithms can push further this limit reaching values in the order of e.g. N32. In this work, we propose a method to increase even further this limit reach values better than N100.The idea discussed, differential self-mixing interferometry (OSMI) proposes the use of a reference modulation (mechanical or electrical) to be used as a reference for the measurement. Simulated results have shown that under ideal conditions, it may be possible to reach resolutions in the order of N1000. In practice, however, this limit is much smaller (N100) because of LO dynamics, and different practical limitations present in the amplification and readout electronics. Experiments and measurements are presented along the second chapter of this work to present proof of the proposed method. After exploring the basics of OSMI, possible applications for classic SMI and DSMI were pursued. The obtained results are presented in the following sections. First, a review on potential biomedical measurements using SMI is discussed. The obtained results suggest that it is possible to obtain some key values related to biomedical constants (e.g. P.PW) using a displacement SMI measurement. The method, however, may not be reliable enough especially on long time measurements. Moreover, the use of certain wavelengths must be avoided during long exposures as they may prove harmful to the soft tissue due to the requirements of a small laser spot. lt is observed that SNR may lead to difficulties during the signal processing stage which may impact the results of the reconstructed signal. Next, the DSMI method was tested in an AFM-like cantilever system. The results suggest that is possible to follow the motion of a micrometric size cantilever oscillating at low frequencies with a high resolution. Higher frequencies may be achieved by using an electronic reference modulation configuration. The proposed system was able to detect some artefacts on the motion which maybe attributed to possible deflections on the cantilever surface. Possible enhancements to the method are suggested for any researcher who wants to expand the topic.En esta Tesis, se explora la interferometría auto-mezclante, mejor conocida por su nombre en inglés Self-m ixing interferometry (SMI), un método capaz de producir mediciones relativas al cambio del camino óptico en un haz laser. La técnica está caracterizada por su tamaño compacto, bajo coste y alta resolución. Pese a su simplicidad, la resolución alcanzada por sistemas basados en SMI se encuentra por debajo de la escala micrométrica (N2), lo cual es suficiente para la mayoría de las aplicaciones industriales. El efecto SMI se genera cuando una pequeña parte de la potencia óptica del láser es retro reflectada por un blanco y reinyectada en la cavidad láser. Como resultado, se genera una modulación de la amplitud y fase del láser, la cual puede ser "fácilmente" relacionada con diferentes efectos relativos al camino óptico del láser. La principal ventaja del método SMI es la simplicidad del sistema de medición el cual está compuesto de un diodo láser (LO) equipado con una tarjeta de procesamiento electrónico. una lente de enfoque o colimación puede ser utilizada con el fin de regular la reinyección de potencia y la distancia al blanco. Debido a que el SMI se genera con una pequeña cantidad de potencia es posible realizar mediciones incluso en blancos con reflexión difusa. . Si bien el método SMI ha sido estudiado ampliamente durante las 3 últimas décadas, aún existen diversos puntos de interés en su estudio. Uno de estos puntos corresponde a la mejora de resolución en la medida de desplazamiento, el cuál es uno de los temas abordados en el presente trabajo. Los métodos clásicos SMI para la medición de desplazamiento permiten alcanzar una resolución en el orden de A/2. El uso de algoritmos de procesamiento especializados puede permitir mejorar el límite de la técnica alcanzando resoluciones (por ejemplo) en el orden de N32. En este trabajo proponemos un método que teóricamente permitiría alcanzar resoluciones mejores que N1OO. La discusión en este punto se sitúa sobre la técnica differential self-mixing interferometry (DSMI), la cual hace uso de una modulación de referencia (mecánica o electrónica) para realizar la medición. Los resultados de diversas simulaciones sugieren que, en condiciones ideales, la técnica es capaz de producir una resolución superior a N1000. En la práctica, el límite encontrado es menor (N100), lo cual puede ser atribuido a condiciones de ruido y efectos de no linealidad en el láser. Para apoyar la idea propuesta diversas medidas simuladas y experimentales son presentadas a lo largo de esta Tesis. Después de explorar las ideas básicas de DSMI, un grupo de posibles aplicaciones para SMI y DSMI fueron exploradas en este trabajo. Una revisión de posibles aplicaciones biomédicas utilizando SMI fue explorada. Los resultados obtenidos sugieren que es posible obtener valores relacionados con constantes biomédicas de interés (p.e. APW) utilizando medidas de desplazamiento basadas en SMI. El método, sin embargo, no es lo suficientemente fiable como para producir medidas estables en un uso prolongado. El SNR de la señal puede introducir complicaciones durante el procesado SMI que puede derivar en errores de reconstrucción de la señal original. . El método DSMI fue probado en un prototipo de sistema AFM equipado con un cantiléver. Los resultados obtenidos sugieren que la técnica es capaz de medir movimientos producidos por un cantiléver de dimensiones micrométricas con alta resolución en bajas frecuencias. La medición de oscilaciones de mayor frecuencia podría ser alcanzada utilizando una configuración basada en modulación electrónica. El sistema propuesto fue capaz de detectar artefactos en el movimiento que podrían ser atribuidos a deflexiones en el cantiléver. Algunas posibles mejoras a esta implementación son sugeridas como puntos para futuras investigaciones alrededor de este tema.Postprint (published version

Optical feedback interferometry sensing technique for flow measurements in microchannels

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. ABSTRACT : 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)