Separation And Vibration Measurement Of Self-mixing Interference Signals With Two-external-cavity Structure

The phenomenon of Self-Mixing Interference(SMI)refers to that the laser light emitted by the laser irradiates the external vibration target,and after reflection or scattering,a part of the laser light carrying the target vibration information is fed back to the laser cavity and mixed with the laser in the cavity,Making the laser output optical power change,thereby forming laser self-mixing interference.Since the feedback laser carries the motion state information of external vibration objects,self-mixing interference technology is widely used in vibration measurement.At present,the research on self-mixing signals has been extended to the double external cavity structure,and a self-mixing interference model with two feedback external cavity structures has been constructed.Because the two external cavity self-mixing signals are aliased in the frequency domain,it is difficult for the spectrum analysis method to completely separate the two signals,so the existing single-channel self-mixing interference signal microdisplacement measurement method cannot be directly applied to the vibration information of the two signals extract.In order to achieve the separation of the two laser self-mixed signals to achieve the purpose of simultaneous measurement,the research of this topic mainly includes the following aspects.First,according to the three-mirror cavity theoretical model,the theory of double external cavity self-mixing is derived to obtain the power and frequency equations.The theoretical derivation of the principle of Butterworth low-pass filter lays the foundation for the separation part later.Because the optical fiber has superior reliability and anti-electromagnetic interference capability.All-fiber self-mixing interferometer is used to study self-mixing interference.Second,complete the theoretical derivation of the EMD algorithm.Simulate the dual external cavity laser self-mixing signal,and use the EMD algorithm to separate the two self-mixing simulation signals.Butterworth low-pass filter is used to pre-denoise the self-mixed signal of dual external cavity laser,and then separated by EMD algorithm.Then,the pre-denoising dual-cavity laser self-mixing interference signal is enveloped multiple times.Separate the dual external cavity signals according to the formula.The maximum vibration of the vibrating object is obtained by the main frequency order judgment method.The experimental results show that the two self-mixing signals have been separated.Finally,using the improved trip point detection algorithm and multiple Hilbert transform phase extraction methods to process the two separate single-channel laser self-mixing vibration signals to reconstruct the micro-vibration of the two-way vibrating objects.The simulation and experimental results show that the dual external cavity self-mixing interference signal can be separated and used for vibration measurement.