| Based on the use of optical feedback that occurs in a semiconductor laser diode when the optical beam is back reflected toward the cavity and then re-introduced inside, the self-mixing interference has been demonstrated to be suitable for non-contact and high-accuracy sensing applications. This is an emerging and promising technique enabling notably displacement, distance, vibration and/or velocity measurements to be performed. The techniques of displacement and velocity measurement based on self-mixing interference in a laser diode have been studied in this thesis.By using the rate equations first derived by Lang and Kobayashi and the model of a three-mirror cavity, the mechanics of the self-mixing interference effect can be analyzed. The general expression of the optical frequency and power emitted by the laser diode are obtained, and then the mathematical model of the common self-mixing can be established. The displacement sensing properties have been numerically simulated and analyzed by using Matlab tools. In order to represent the self-mixing interference phenomenon occurring in different optical feedback regime, a behavioral model of a laser diode described by schematic block diagrams is presented. By virtue of this behavioral model, the simulation of output power of a self-mixing sensor can be performed. The simulated fluctuation waveforms of the power shows that how the parameters associated with the external target movement have influence on the self-mixing interference signal, as well as that the dependence of the self-mixing interference signals on the external cavity vibration modulated by different waveforms.The measuring systems of displacement and velocity base on self-mixing effect have been designed. Correspondingly, the optical path and experimental setups have been established.A simple and compact laser Doppler velocimeter is developed based on self-mixing effect in a vertical-cavity surface-emitting laser (VCSEL). The monitor photodiode mounted on the back facet of the VCSEL acts as a transducer and it generates the self-mixing current signal. The FFT technique is applied to analyze self-mixing interferometric signal. The power spectrum of this signal can be acquired and analyzed to extract the Doppler frequency and the information relative to the velocity measurement. The target velocity component projected along the optical axis of the laser beam is calculated. The experiment results show that the accuracy of velocity measurement is high with relative error of Doppler frequency lower than 2%, while for the velocity higher than 70mm/s.In order to eliminate the output power and wavelength shift of LD caused by temperature instability, A temperature control method of LD with high accuracy is proposed, which adopts thermistor and thermo-electric cooler as temperature sensor and execute component of temperature control respectively. A control algorithm based on fuzzy theory and digital PID control is proposed. The experimental results show that the precision of controlled temperature is better than 0.02℃, and the response characteristic of the system with Fuzzy-PID control is better than that of with general PID control.Although the nonlinear phenomena can govern the global behavior of the laser diode, we concluded that Kalman filtering techniques could also be popular to deal with this problem and increase the measurement precision of self-mixing interferometry. In this paper, a new signal processing method based on Klaman filter is presented for the self-mixing displacement sensor. Based on the approximate linearized model of a LD, the robust Kalman filter is designed for an estimation of the system parameters and the target displacement in the wake feedback regime. The simulation analysis and experiments have been done to illustrate the validity and the effectiveness of the method. These results show that the displacement estimation is good with little noise and the estimated resolution of aboutλ20 is achievable.
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