Self-mixing interferometer : model and control of the frequency modulation effect

The purpose of this thesis is to discuss the advantages of the Self-Mixing interferometry which is much cheaper and simpler in comparison to traditional interferometers, thanks to the fact that employs laser diodes and no complex optics. More in particular, is focused on how to extract the frequency modulation, by means of a Mach-Zehnder filter, to obtain its many perks. Indeed, thanks to a great signal to noise ratio, it can provide a very good resolution which is furtherly improved by the possibility of avoiding any digital conversion to retrieve the measure. The study includes the creation of a Matlab/Simulink model that grants the possibility of breaking down the complex retroinjection dynamics into more simple scenarios. This eases the process of control design which reflects the multiple applications of the instrument. The most underlined is the employment of the Self-Mixing interferometer in “Ultrasonic Laser” measurements. Under these conditions it possible to obtain, at the same time, good information about nanometric vibrations at very high frequencies in the order of MHz, and also about the mechanical components of the vibrations. To do so, new suggestions for control are introduced while comparing the utility of traditional controllers.