Study On The Self-mixing Interference Micro-displacement Measurement Based On Frequency Spectrum Analysis

The optical feedback self-mixing interferometric (OFSMI) technique is a newinterferometric measurement technique, which rises in recent years and has been widelyapplied in many fields. When part of the light emitted from a laser diode (LD) is reflectedor scattered back to the laser active cavity by an external object, the light that re-enters thecavity is mixing with the light inside the laser, causing the the modulation of the laseroutput frequency and intensity. The feedback light carries the information of externalobjects and the laser own parameters, and the measurement system based on OFSMI isnon-contact,simple, compact, self-aligning and high accuracy, so it is widely used in avariety of sensor measurements.By using the general theoretical model of self-mixing interference effect opticalfeedback, the measurement of object displacement and the feedback level C areresearched in this paper.Based on the principle of semiconductor laser self-mixing interference effect, theself-mixing signals under different feedback are numerical simulated and the influence oninterference signals of every model parameter is analyzed.A kind of method based on Fourier transform of the phase measurement principle ofself-mixing interference is presented. Fourier transform is used to extract phaseinformation, and then recover the displacement. Simulation studies are carried out toverify the validity of the displacement reconstruction algorithm. The applicability of thealgorithm and detection limit of the measuring system are researched.The results showthat this algorithm the article presented can achieve a high precision under the condition ofweak feedback without any external optics component.A measurement algorithm based on the optical feedback phase frequency spectrumcharacteristics is proposed. Based on phase unwrapping operations, phase information wasacquired from the laser self-mixing interference (SMI) signal. Then the phase informationwas converted to the frequency domain to analyze their spectrum characteristics. Thefeedback level C can be acquired by the spectrum characteristics. This method is simple and convenient to operate and the algorithm can be used in all the three kinds of feedbackmechanism. And the simulation results verified the algorithm’s validity and accuracy.In order to verify the method’s precision in practice, the self-mixing interferencemeasurement system of feedback level C is constructed. In this measurement system, itshows that the proposed parameter C measurement accuracy of the algorithm acquireshigh precision in the actual data processing.