Research On Optical Feedback Self-mixing Interference Displacement Real-time Tracking Measurement Algorithm

Optical Feedback Self-Mixing Interference(OFSMI)is the phenomenon that a beam of light emitted from a laser source is partially reflected or scattered back into the laser cavity by an external object and interferes with the light in the cavity,causing a modulation of the laser output power.Due to the OFSMI consists of the movement information of the external reflector,such a system is able to be used for the displacement measurement of an target object.The OFSMI replacement measurement system introduces many favorable features e.g.,simple setup,compact hardware structure,and auto collimation capability,without losing sensitivity or resolution,which enables the OFSMI technology to have broad prospects in the sensing measurement field.This paper studies the OFSMI displacement real-time tracking measurement algorithm,which has advantages e.g.,applicable in both weak and moderate feedback regime,real-time,having ability to reconstruct arbitrary displacement waveform,and with high measurement precision.Displacement measurement algorithm includes two parts: integer fringes detection and the corresponding displacement measurement and decimal fringe displacement measurement.The main contents are summarized as follows:1.Two types of integer fringes detection algorithms are proposed.By the research on OFSMI signal singularity,an wavelet-transform-based integer fringes detection algorithm is proposed based on the theory of wavelet transform singularity detection.According to the theory of Hilbert transform and analytic signal,instantaneous phase,the characteristics of the instantaneous phase obtained by Hilbert transform of the OFSMI signal are analyzed,and an integer fringes detection algorithm based on Hilbert transform is proposed.Anti-noise performance is evaluated by comparison between these two types of integer fringe detection algorithms.2.The decimal fringe displacement measurement consists of three parts.According to the relationship between the degree of inclination of interference fringes and the optical feedback regime,judgment algorithm of optical feedback regime is proposed.According to moderate OFSMI signal is sawtooth and hysteresis,moderate OFSMI decimal fringe displacement measurement algorithm is proposed.According to weak OFSMI signal is class sine wave,weak OFSMI decimal fringe displacement measurement algorithm is proposed.3.The OFSMI displacement real-time tracking measurement algorithm is composed of integer fringes detection algorithm based on Hilbert transform and decimal fringe displacement measurement.The effectiveness of the algorithm in the field of displacement reconstruction and amplitude measurement is verified through simulation and experiment.The experimental results show that the absolute error of the proposed algorithm is about 23.2nm,the relative error is about 1.81%,and the measurement accuracy is better than the other two measurement algorithms.