A self-mixing laser sensor design with an extended kalman filter for optimal online structure analysis and damping evaluation

We have developed a new algorithm based on the extended Kalman filter, in order to improve the resolution of an optical displacement sensor. This new non contact sensor which provides vibration measurement with a very good accuracy might be used for online quality control by measuring the damping of excited mechanical structure. This self-mixing sensor subject to weak feedback has been tested in comparison with a commercial vibrometer, to measure the frequency response function of a plate with a passive damping to be characterized, in order to show the efficiency of a damping treatment

Research and Application of Measurement System Base on Laser Self-Mixing Interference

激光自混合干涉效应是指由于外部物体反射或者散射，而导致光反馈回激光腔内引起光功率波动的现象。该技术不仅保证了传统干涉的测量精度，还具备单光路、结构紧凑、易准直等优点，解决了传统干涉中存在的问题，因此受到了研究人员的关注，被广泛应用于速度、位移和振动、生物医学等领域的测量。 本文介绍了激光自混合干涉效应的发展历程和研究现状。通过三种不同的数学模型，详细阐述了自混合效应的机理，并对自混合干涉系统进行数值仿真，进而分析研究了系统模型中各参数对自混合干涉信号的影响。在此基础上，搭建半导体激光器自混合干涉测量系统，通过观察和研究实验现象，验证了理论仿真的结果。此外，本文还根据自混合基本数学模型，研究了...As a new laser technique called, self-mixing interference (SMI), which is based on the interaction of cavity field with the field backscatter from the remote target, has increasingly garnered intense attention. The SMI has advantages of simple and compact system structure and easy collimated light path. Therefore, the applications of the SMI have been popularized in many fields, including metrolog...学位：工学硕士院系专业：信息科学与技术学院_光学工程学号：2312013115309

Analysis of Self-Mixing Moderate and Strong Feedback Regimes for Mechatronics Applications

L'utilisation des lasers est répandue dans le domaine de l'instrumentation. Cependant, le fonctionnement de tels dispositifs peut être perturbé par le phénomène de rétro-injection optique (ou self-mixing) auquel est soumis la diode laser. Cette sensibilité du laser à la rétro-injection optique offre de nombreux avantages, notamment pour la mesure de déplacements, de vitesse ou de distance. Dans ce travail, nous introduisons le phénomène de self-mixing avant d'effectuer un état de l'art des différentes applications de ce type de capteurs. Le régime de fonctionnement de rétro-injection optique modérée est d'abord étudié en détails en introduisant la notion de perte de pics; en l'interprétant et en étudiant son effet sur différentes méthodes de mesure de déplacement. Nous étudions ensuite le régime de forte rétro-injection optique en analysant son aspect statistique et l'effet des différents paramètres sur cet aspect. Un capteur de déplacement relatif opérant dans ce régime est alors conçu et réalisé. Après l'avoir caractérisé, l'application de ce capteur était étendue à l'analyse modale où il avait l'avantage majeur de donner une image très fidèle du déplacement en temps réel sans traitement de signal complexe. Ce capteur est alors utilisé pour caractériser une plaque encastrée et pour détecter les impacts dans des poutres en fibre de carbone. ABSTRACT : Lasers have been widely used in different types of applications such as telecommunications, CD/DVD readers or for sensing purposes. A major drawback in their use is the optical feedback caused by an obstacle in their direction of propagation. This light reinjected in the active area modifies the emission properties of laser diodes and obliges the developers to consider adding isolators increasing thereby the complexity and the price of such systems. However this optical feedback induces a variation in the emission power and frequency in function with the distance to the reflector. This phenomenon, more commonly known as self-mixing, is used in different types of displacement, velocity and vibration sensors. In this work, the physical theory of the self-mixing effect is introduced and then a state of the art of its main applications in the different fields of instrumentation is accomplished. A detailed study of the self-mixing signal in the moderate feedback regime is achieved introducing the effect of "loss of peaks", its physical interpretation, mechanisms and effect on different types of displacement measurement. Afterwards, the discrepancy concerning the strong feedback regime was cleared out showing that it may be used for relative displacement measurement. A detailed study of this regime covers its statistical aspect and the influence of different parameters on this aspect. Finally, the self-mixing sensor under strong feedback was introduced in modal analysis applications after being characterized. It was applied to study a clamped plate or to detect damage in carbon fiber CFBs. This type of sensors proved its major advantage of simplicity providing a direct image of the displacement without the need of any advanced signal processing. This facilitates its duplication where an array of sensors was used in different experiments

Versatile multimodality imaging system based on detectorless and scanless optical feedback interferometry—a retrospective overview for a prospective vision

In this retrospective compendium, we attempt to draw a “fil rouge” along fifteen years of our research in the field of optical feedback interferometry aimed at guiding the readers to the verge of new developments in the field. The general reader will be moved at appreciating the versatility and the still largely uncovered potential of the optical feedback interferometry, for both sensing and imaging applications. By discovering the broad range of available wavelengths (0.4–120 μm), the different types of suitable semiconductor lasers (Fabry–Perot, distributed feedback, vertical-cavity, quantum-cascade), and a number of unconventional tenders in multi-axis displacement, ablation front progression, self-referenced measurements, multispectral, structured light feedback imaging and compressive sensing, the specialist also could find inspirational suggestions to expand his field of research

FPGA-Based Smart Sensor for Online Displacement Measurements Using a Heterodyne Interferometer

The measurement of small displacements on the nanometric scale demands metrological systems of high accuracy and precision. In this context, interferometer-based displacement measurements have become the main tools used for traceable dimensional metrology. The different industrial applications in which small displacement measurements are employed requires the use of online measurements, high speed processes, open architecture control systems, as well as good adaptability to specific process conditions. The main contribution of this work is the development of a smart sensor for large displacement measurement based on phase measurement which achieves high accuracy and resolution, designed to be used with a commercial heterodyne interferometer. The system is based on a low-cost Field Programmable Gate Array (FPGA) allowing the integration of several functions in a single portable device. This system is optimal for high speed applications where online measurement is needed and the reconfigurability feature allows the addition of different modules for error compensation, as might be required by a specific application

Robust Detection of Non-Regular Interferometric Fringes From a Self-Mixing Displacement Sensor Using Bi-Wavelet Transform

An innovative signal processing method based on custom-made wavelet transform (WT) is presented for robust detection of fringes contained in the interferometric signal of self-mixing (SM) laser diode sensors. It enables the measurement of arbitrarily-shaped vibrations even in the corruptive presence of speckle. Our algorithm is based on the pattern recognition capability of bespoke WTs for detecting SM fringes. Once the fringes have been correctly detected, phase unwrapping methods can be applied to retrieve the complete instantaneous phase of the SM signals. Here, the novelty consists in using two distinct mother wavelets Ψr(t) and Ψd(t) specifically designed to distinguish SM patterns as well as the displacement direction. The peaks, i.e. the maxima modulus of WT, then allow the detection of the fringes

Suppression of Air Refractive Index Variations in High-Resolution Interferometry

The influence of the refractive index of air has proven to be a major problem on the road to improvement of the uncertainty in interferometric displacement measurements. We propose an approach with two counter-measuring interferometers acting as a combination of tracking refractometer and a displacement interferometer referencing the wavelength of the laser source to a mechanical standard made of a material with ultra-low thermal expansion. This technique combines length measurement within a specified range with measurement of the refractive index fluctuations in one axis. Errors caused by different position of the interferometer laser beam and air sensors are thus eliminated. The method has been experimentally tested in comparison with the indirect measurement of the refractive index of air in a thermal controlled environment. Over a 1 K temperature range an agreement on the level of 5 × 10−8 has been achieved

Sensitivity Enhancement of a Self-Mixing Laser Diode Sensor by Using a Dual-cavity Configuration

When a part of light emitted by a laser is back-reflected or back- scattered from an external target and re-enters the laser cavity, the laser output power will be modulated. This is called Self-Mixing Effect (SME), which is a universal phenomenon occurring in lasers regardless of type. For SME based laser sensing system, a laser diode is usually employed to make a compact sensing system due to its small size. The laser diode in this case is also called Self-Mixing Laser Diode (SMLD). In some practical cases, a target surface has a very low reflectivity and thus not able to provide enough high feedback light to the laser diode. In this case, the observed sensing signal from the SMLD sensor is blurred and sensing sensitivity is degraded. To improve the sensing ability, we propose to apply a pre-feedback to the SMLD sensor. Investigation from both simulation and experiments are conducted to verify the proposed design. The results show that a proper pre-feedback can greatly enhance the sensing performance for a SMLD sensor

Adaptive self-mixing interferometry for metrology applications

Among the laser based techniques proposed for metrology applications, classical interferometers offer the highest precision measurements. However, the cost of some of the elements involved and the number of optical components used in the setup complicates using them in several industrial applications. Apart from cost, the complexities due to optical alignment and the required quality of the environmental conditions can be quite restrictive for those systems. Within the category of optical interferometers, optical feedback interferometry (OFI), also called self-mixing interferometry (SMI) has the potential to overcome some of the complexities of classical interferometry. It is compact in size, cost effective, robust, self-aligned, and it doesn't require a large number of optical components in the experimental configuration. In OFI, a portion of the emitted laser beam re-enters to the laser cavity after backreflection from the target, causing the wavelength of the laser to change, modifying the power spectrum and consequently the emitted output power, which can be detected for measurement purposes. Thus, the laser operates simultaneously as the light source, the light detector, and as the ultra-sensitive coherent sensor for optical path changes. The present PhD pursued improving the performance of OFI-based sensors using a novel and compact optical system. A solution using an adaptive optical element in the form of a voltage programmable liquid lens was proposed for automated focus adjustments. The amount of backreflected light re-entering the laser cavity could be controlled, and the laser feedback level was adjusted to the best condition in different situations, enabling the power signal to be adjusted to the best possible conditions for measurement. Feedback control enabled the proposal of a novel solution called differential OFI, which improved the measurement resolution down to the nanometre order, even if the displacements were below half-wavelength of the laser, for first time in OFI sensors. Another relevant part of the PhD was devoted to the analysis of speckle-affected optical power signals in feedback interferometers. Speckle effect appears when the displacements of the target are large, and introduces an undesired modulation of the amplitude of the signal. After an analysis of the speckle-affected signal and the main factors contributing to it, two novel solutions were proposed for the control of speckle noise. The adaptive optical head developed previously was used in a real time setup to control the presence of speckle effect, by tracking the signal to noise ratio of the emitted power, and modifying the spot size on the target when required using a feedback loop. Besides, a sensor diversity solution was proposed to enable enhancements in signal detection in fast targets, when real time control could not be applied. Finally, two industrial applications of the technique with the presence of different levels of speckle noise have been presented. A complete measurement methodology for the control of motor shaft runout in permanent magnet electrical motors, enabling complete monitoring of the displacement of the shaft has been developed and implemented in practice. Results here are validated with those obtained using a commercial laser Doppler vibrometer, an equipment with a much higher cost. A second application in the monitoring the displacement of polymer-reinforced beams used in civil engineering under dynamic loading was also demonstrated. Results here are validated using a conventional contact probe (a Linear Vertical Differential Transducer, LVDT). Both applications show that with controlled speckle features OFI performs adequately in industrial environments as a non-contact proximity probe with resolution limited by the constraints defined by the setu