Semiconductor laser dynamics induced by optical feedback for photonic microwave sensing

As one of the most widely used light sources today, semiconductor lasers (SLs) are an important part of many optical systems, especially for sensing, communications, metrology, and storage applications. SLs have the advantages of small size, easy integration, and miniaturization. The massification of electronic devices has furthered this agenda, allowing the creation of portable systems capable of supporting optical sensing systems. Essentially, SLs are inherently nonlinear devices, in nonlinear systems, the folding and stretching behaviors of variables result in di↵erent dynamical routes. It is worth noting that under the conditions of a stable operation, an SL biased by constant current usually emits laser light with a constant intensity. However, with the introduction of external optical feedback (OF), the laser light can become unstable. SL will undergo from steady state, switching status, to period-one (P1) oscillation by crossing Hopf-bifurcation. In the P1 state, the system produces a modulation of the laser optical output power for the generation of microwave photonics (MWP) signals. In this thesis, we operate SL with OF scheme in P1 dynamics, and found that the proposed system has the great capability to achieve both displacement and absolute distance sensing applications with high resolution and wide measurement range, by using time-frequency information, relaxation oscillation information, and nonlinear dynamic characteristics carried in that SLs emit signals. The contributions of each chapter in this thesis are described in the following: In Chapter 3, we propose an SL with OF set at the P1 dynamics to generate the MWP signal for displacement sensing. Di↵erent from the traditional MWP generation method, the designed laser nonlinear dynamics are used by slightly perturbing the SL source with the help of external feedback light to make the system work in the P1 dynamic state, thereby generating regular microwave oscillation. By using the fourth-order Runge-Kutta method to numerically solve the famous Lang-Kobayashi differential equation, the boundary of di↵erent laser dynamic states is delimited, so that the system can generate stable and sustainable MWP signals in P1 dynamics. A set of parameter selection rules for designing an SL based MWP displacement sensing system is obtained. In addition, a measurement algorithm for recovering the displacement from an MWP sensing signal is developed. By making full use of the sensing information carried in both amplitude and frequency of the MWP signal, displacement sensing with high resolution and high sensitivity can be achieved. Both simulations and experiments are conducted to verify the proposed method and show it is capable of realizing high measurement sensitivity, and high resolution for displacement sensing. In Chapter 4, utilizing the rich nonlinear dynamics of an SL with OF, under the proper controllable system parameters, the system enters the P1 dynamics through Hopf-bifurcation. In the P1 state, the detailed relationship between the relaxation oscillation frequency of MWP signals and external cavity length is studied through solving the Lang-Kobayashi delayed di↵erential equations. The displacement measurement formula is thus obtained. In addition, the relevant signal processing algorithm is developed by considering mode-hopping, frequency-hopping, and sawtooth-like phenomena that occurred in the relaxation oscillation. The displacement measurement can be enhanced in a wider sensing range by fully using the relaxation oscillation frequency relationship. Verification results in simulation and experiment show that the proposed MWP displacement sensing system based on SL with OF contributes to designing a prototype of a compact displacement sensor with wide measurement range and high resolution. In Chapter 5, OF induced switching status between two nonlinear dynamic states (stable and P1 states) is observed in the SL with OF system. Without the need for any electronic or optical modulation devices, the laser intensity can be modulated in a square wave form due to the switching via utilizing the inherent SL dynamics near Hopf-bifurcation boundary. The periodicity in the switching enables us to develop a new approach for long-distance sensing compared to other SL with OF based absolute distance measurement systems and lift the relevant restrictions that existed in the systems. Moreover, the impact of system controllable parameters on the duty cycle of the square wave signals generated was investigated as well, aiming to maintain the proposed system robustly operating at the switching status

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

Frequency-Modulated Optical Feedback Interferometry for Nanometric Scale Vibrometry

We demonstrate a novel method that makes an efficient use of laser nonlinear dynamics when subject to optical self-injection for subwavelength displacement sensing purposes. The proposed methodology combines two different phenomena taking place inside the laser cavity: optical self-injection, which results in optical feedback interference, and laser continuous wave frequency modulation, giving rise to a wavelength sweeping effect in the laser's emission. We present a combination of these phenomena to measure vibration amplitudes below lambda/2 with the resolutions of a few nanometers, bandwidth dependent upon the distance of external target, amplitude, and frequency of current modulation. The basic theoretical details and a mathematical model are presented for the developed measurement principle. Experimental results with the system working as a vibrometer to measure a target vibration of amplitude lambda/5 (137.5 nm) with a mean peak-to-peak error of 2.4 nm just by pointing the laser diode onto the target and applying some signal processing are also demonstrated.Postprint (author's final draft

Frequency-domain method for measuring alpha factor by self-mixing interferometry

Linewidth enhancement factor, also known as the alpha factor, is a fundamental characteristic parameter of a laser diode (LD). It characterises the broadening of the laser linewidth, the frequency chirp, the injection lock range and the response to external optical feedback. In the past few decades, extensive researches have been dedicated to the measurement of alpha. Among all the existing approaches, the methods based on selfmixing interferometry (SMI) are considered the most simple and effective. The core components of a SMI consist of an LD, a lens and a moving target. When a portion of laser light backscattered or reflected by the external target and re-enters the laser cavity, a modulated lasing field will be generated. The modulated laser power is also called SMI signal, which carries the information of target movement and LD related parameters, including alpha

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

Simple method for measuring the linewidth enhancement factor of semiconductor lasers

A simple method for measuring the linewidth enhancement factor (LEF) of semiconductor lasers (SLs) is proposed and demonstrated in this paper. This method is based on the self-mixing effect when a small portion of optical signal intensity emitted by the SL reflected by the moving target re-enters the SL cavity, leading to a modulation in the SL\u27s output power intensity, in which the modulated envelope shape depends on the optical feedback strength as well as the LEF. By investigating the relationship between the light phase and power from the well-known Lang and Kobayashi equations, it was found that the LEF can be simply measured from the power value overlapped by two SLs\u27 output power under two different optical feedback strengths. Our proposed method is verified by both simulations and experiments. (C) 2015 Optical Society of Americ

Analysis and implementation of algorithms for embedded self-mixing displacement sensors design

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. ABSTRACT: 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-eective 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

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

Self-Mixing Laser Distance-Sensor Enhanced by Multiple Modulation Waveforms

Optical rangefinders based on Self-Mixing Interferometry are widely described in literature, but not yet on the market as commercial instruments. The main reason is that it is relatively easy to propose new elaboration techniques and get results in controlled conditions, while it is very difficult to develop a reliable instrument. In this paper, we propose a laser distance sensor with improved reliability, realized through a wavelength modulation at a different frequency, able to decorrelate single measurement errors and obtain improvement by averages. A dedicated software is implemented to automatically calculate the modulation pre-emphasis, needed to linearize the wavelength modulation. Finally, data selection algorithms allow to overcome signal fading problems due to the speckle effect. A prototype demonstrates the approach with about 0.1 mm accuracy up to 2 m of distance at 200 measurements per second

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