Guy Plantier

Self-mixing laser diode velocimetry: application to vibration and velocity measurement

A review of recent experimental and theoretical results concerning laser diode self-mixing velocimetry is presented, showing that this technique can be deployed to measure velocity and vibration of solid targets with an extremely simple optical setup. This technique reduces optical alignment problems and achieves results comparable to those obtained by the conventional laser Doppler velocimetry (LDV) approach. It is demonstrated that the self-mixing signal can be processed to recover the target velocity and vibration by applying the same analysis method used for LDV. An optimal signal processing method is then proposed to recover the target velocity with good accuracy, also in the presence of relevant speckle disturbance. Application to the measurement of sub-micron vibrations is also demonstrated, using a self-mixing vibrometer instrument capable of 5-nm accuracy. As an example, the characterization of response and hysteresis of piezoceramic transducers (PZTs) is carried out. These results illustrate the effectiveness of the self-mixing technique in the field of laser velocimetry, opening the way to new applications where compactness and low cost of the measuring apparatus are essential.

Displacement measurements using a self-mixing laser diode under moderate feedback

A semiconductor laser subject to moderate optical feedback has been used to design an interferometric displacement sensor. The autoadaptative signal processing presented in this paper has been computed in order to improve the accuracy of such a sensor. This setup has been successfully tested for both harmonic and aleatory displacements of a remote piezoelectric actuator with a maximum accuracy of 40 nm

Behavioral model of a self-mixing laser diode sensor

The spectral properties of a laser diode are modified when the optical beam is back-scattered into the active cavity of the laser. Based on the use of this optical feedback, the self-mixing effect has been demonstrated to be suitable for sensing applications. This is an emerging technique enabling notably displacement, distance and/or velocity measurements to be performed. However, the self-mixing signal shape is strongly modified by the strength of the back-scattering and by nonlinear phenomena governing the global behavior of the laser diode. This makes signal processing rather challenging. In this paper, a new high-level model is proposed to represent the self-mixing phenomenon and to simplify the solution of nonlinear equations involved in this problem. This model is represented by schematic block diagrams commonly used for the description of complex systems in the domains of nonlinear mechanics, telecommunications, sensors, actuators, etc. This approach will allow the use of powerful and standard simulation tools such as Spice, VHDL-AMS or MATLAB/Simulink to develop new methods for signal processing of optical feedback interferometers, notably in the case of displacements measurements.

A double-laser diode onboard sensor for velocity measurements

In this paper, we validate the feasibility of an onboard velocity sensor using the self-mixing effect. Roughness of the target surface, wet target surface, noncontrolled changes of incident angle, and speed vector vertical components have been considered during this development. A first prototype has been designed with an automotive application so to illustrate this feasibility. This low-cost and low-clutter prototype presents an interesting basic performance (/spl sigma//spl ap/0.22%). In order to improve the accuracy as well as the robustness of the system, a double-laser diode sensor has then been tested successfully (/spl sigma//spl ap/0.038%) by removing the influence of the pitching and the pumping effects.

A Self-Mixing Laser Sensor Design With an Extended Kalman Filter for Optimal Online Structural Analysis and Damping Evaluation

We have developed a new algorithm based on the extended Kalman filter in order to improve the resolution of a self-mixing (SM) optical displacement sensor. This noncontact sensor, which provides vibration measurement with a very high accuracy, can be used for online quality control, for example, measuring the damping of excited mechanical structures. This SM sensor subject to weak feedback has been tested in comparison with a commercial vibrometer in order to measure the frequency response function (FRF) of a plate with a passive damping to be characterized, and to show the efficiency of a damping treatment.

Real-time tracking of time-varying velocity using a self-mixing laser diode

A new method is proposed for estimating the time-varying velocity of a moving target with a low-cost laser sensor using optical feedback interferometry. A new algorithm is proposed to track velocity variations from real-time analysis of the output signal of a self-mixing laser diode. This signal is strongly corrupted by a multiplicative noise caused by the speckle effect, which occurs very often with noncooperative targets used in many industrial applications. The proposed signal processing method is based on a second order adaptive linear predictor filter, which enables us to track the digital instantaneous Doppler frequency, which is proportional to the velocity. A model of the laser diode output signal is proposed, and it is shown that the sensor and its associated algorithm have a global first-order lowpass transfer function with a cutoff frequency expressed as a function of the speckle perturbations, the signal to noise ratio and the mean Doppler frequency. Numerical as well as experimental results illustrate the properties of this sensor.

Real-time parametric estimation of velocity using optical feedback interferometry

A low-cost laser sensor using optical feedback interferometry has been designed to measure velocities. With digital signal processing based on an order two autoregressive model of the optical power, an inaccuracy of about 0.5% can be reached.

Analog sensor design proposal for laser Doppler velocimetry

Laser Doppler velocimetry (LDV) has been widely used for many years in fluid mechanics to measure particle velocity. However, in most applications, i.e., in industrial processes, such a system is often too expensive. This paper discusses a technique based on the use of an analog phase-locked loop and an analog integrator system for processing laser Doppler velocimeter data to infer particle velocity. This method appears to be suitable for designing low-cost integrated LDV sensors. A SIMULINK program has been written in order to validate the method for velocities in the 10-80 mm/s range. Finally, the performance of the estimator is illustrated by Monte-Carlo simulations obtained from synthesized Doppler signal.

Red blood cell velocity estimation in microvessels using the spatiotemporal autocorrelation

This paper deals with the problem of red blood cell velocity measurement in microvessels using dynamic video microscopy. More precisely, the problem of one-dimensional red blood cell velocity estimation is addressed, using algorithms based on the spacetime image obtained when a single line from the video, taken inside and along the vessel axis, is mapped into an image as a function of time. Flowing red blood cells generate an oriented and textured spatiotemporal plane, the orientation of which is related to their velocity. In order to perform space- and time-localized velocity estimations, orientation estimations have to be done locally in the spatiotemporal plane. Therefore, we propose the use of the autocorrelation sequence, the orientation of which is also related to the velocity. The region of interest of the autocorrelation, containing the velocity information, is selected using a watershed algorithm. We finally suggest two different algorithms estimating the spatiotemporal plane orientation upon the aforementioned region. Results and comparisons of these methods are proposed, using a controlled experiment and real-life blood flow video sequences.

Characterization of a self-mixing displacement sensor under moderate feedback

A displacement sensor enabling us to perform measurements under moderate feedback has been designed with a resolution up to 40 nm. Its performance can be optimized by using the wavelet transform when the signal is disturbed by electromagnetic fields, mechanical coupling, or speckle effect. By determining the repeatability and the reproducibility of this sensor, we have also demonstrated that this measuring device is suitable for statistical process control when an interval of tolerance of ±300 nm is required.