| Optical Feedback Self-Mixing Interference（OFSMI）effect refers to the phenomenon that the output power of the laser is modulated by the light emitted by the laser being scattered or reflected by the surface of the object,and some of them are coupled to the resonator to produce mixing（interference）with the laser in the cavity.However,the surface of the object to be tested is usually rough,and the OFSMI signal is affected by the speckle effect.Although it has the surface characteristics of the measured object,the presence of speckles will significantly reduce the OFSMI signal and lead to the change of signal amplitude and measurement system parameters（such as the change of optical feedback level C value）,resulting in the reduction of measurement accuracy.To get an accurate displacement,the resulting OFSMI signal needs to be preprocessed.The OFSMI signal affected by speckle reflects the characteristics of the interference signal and the surface characteristics of the measured object when the measured object produces a large displacement.Therefore,the study of the OFSMI signal affected by speckle has certain theoretical significance and application prospects in sensing measurement such as optical feedback self-mixing interference displacement measurement,vibration measurement and surface topography measurement.This paper mainly studies the speckle processing and displacement measurement algorithm,which has the characteristics of simple and effective,large-range displacement measurement and high precision.For the case where the vibration frequency of the measured object may change,this paper uses the normalized LMS algorithm to filter the measured signal whose vibration frequency changes.The main work is as follows:（1）Displacement reconstruction algorithm design of OFSMI signal affected by speckle.In order to obtain higher precision displacement measurement,an envelope conversion detection algorithm is proposed to process the OFSMI signal affected by speckle.The experimental results show that the algorithm can not only deal with the speckle effect in the OFSMI signal,but also recognize the moving direction of the object in the time domain,even under 0（27）C（27）0.2 the condition of weak feedback mechanism.The algorithm provides the measurement accuracy of 62 nm for the OFSMI signal,the speckle-induced modulation depth is 20.33,and the displacement in the range of 10-6m to 10-3m can be restored,and the bit can be improved.The accuracy of displacement measurement can be used for large range displacement measurement.（2）In order to improve the accuracy of the object displacement measurement,the normalized LMS algorithm is used to filter the interference signal.The simulation results show that the weight coefficient of the normalized LMS adaptive filter can be quickly adjusted to a suitable value within a small order of magnitude(10-3)when the vibration frequency of the measured object changes.The filtering effect is almost the same as that of single frequency processing.（3）Hardware design of fringe counting displacement measurement algorithm.Based on the theoretical model of fringe counting algorithm,this paper presents a design scheme of integrated digital signal processing module for fringe counting displacement measurement.The system Generator development tool is used to design the digital signal processing module under Simulink environment,and all the module designs were integrated.The simulation test of the simulation data source and the measured data source proves that the hardware can correctly implement the displacement measurement algorithm based on fringe counting. |
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