Study On The Self-mixing Interference Displacement Technique Based On Phase Unwrapping Theory

The optical feedback self-mixing interferometric technique is a new measurementtechnique, for the optoelectronic system that makes use of the self-mixing interferometriceffect of semiconductor lasers, the optical feedback self-mixing interferometric (OFSMI)technique has been widely studied and applied in many fields in the measurements field ofgeometric and mechanical quantities for its significant advantages in simplicity,compactness and self-aligning, with its mainly application in geometry sensing parametersmeasurement and semiconductor laser parameters measurement. When a small portion ofthe light emits from a laser diode (LD) is reflected or back scattered by an external objectand re-enter the laser cavity, the light carries the information of external objects and thelaser parameters, and it will interfere with the light inside the cavity, which causes thevariance of the laser output intensity (or called optical output power--OOP) that emitsfrom the LD when the optical path length is varying. This phenomenon is called theoptical feedback self-mixing interferometer effect.Based on the principle of semiconductor laser self-mixing interference effect, thesystem of simple harmonic vibration of measured objects under different optical feedbackis researched in the paper.By using the general theoretical model of self-mixing interference effects thatdeduced according to the three-mirror F-P cavity model, the self-mixing interferencesignals in different feedback levels are numerical simulated, the influence on interferencesignals of the model parameters is analyzed through numerical simulation, which verifythe correctness of the theoretical model.The self-mixing interference signals extraction and processing methods areresearched. A kind of method based on phase unwrapping principle is proposed to recoverthe external cavity displacement information. The method can achieve the displacementsignal reconstruction according to the known relationship between the phase withfeedback and the optical feedback self-mixing interference signals in the weak, moderateand strong feedback mechanisms respectively. Simulation and experimental results are coinciding with each other, which verify the effectiveness of the method.A method based on wavelet analysis data preprocessing is proposed, which is usedfor reducing the noise in the self-mixing interference signals. Simulation results show that,the wavelet analysis method can effectively reduce the noise component in the signals.The displacement measuring system based on self-mixing effect has been designed and setup, the theoretical analysis results are verified through the experimental research.