| Self-mixing Interference(SMI)changing the laser output characteristics according to the feedback light,due to the feedback light carries information about objects outside the laser chamber.This property can be used to measure the physical quantity of the target object.Because of its advantages of simple structure,sensitivity,easy collimation and easy detection,SMI has been widely used in measuring displacement,vibration,morphology,acceleration and micro-angle.However,the SMI detection system has the problem of noise interference in practical application.If effective noise reduction steps are not taken to deal with it,the system stability and detection accuracy will be affected.In this paper,a polarization differential detection technology based on random polarization laser self-mixing interference is proposed.Compared with the existing self-mixing interference differential noise reduction technology,the proposed method has the advantages of low cost and simple structure.This paper also reformed the dual-polarization differential noise reduction measurement on the Surface Plasmon Resonance(SPR)based on the Surface Plasmon Resonance(SPR)sensing system developed earlier by our research group,constructed the SPR differential detection sensor system based on self-mixing interference,and provided a solution for high-precision SPR phase measurement.Firstly,the basic theory of laser self-mixing interferometry is introduced.The laser self-mixing interferometry system based on the modulation of outer cavity length is analyzed.The phase extraction technique of self-mixing interference signal is studied and simulated.Then,the double polarization measurement system based on He-Ne laser interference is built,the interference signal is polarized by polarizing prism and polarizer,detailed observations of double polarization interference signal amplitude and phase relationship by changing light source(linear polarization He-Ne laser and random polarization He-Ne laser)and detection position(to the light side before the laser detection and laser to detect light-leaking end),found the differential interference signals(the same amplitude and opposite phase)and simple method.Based on this,the interference differential measurement system based on external cavity phase modulation by using Piezoelectric-ceramic Transducer(PZT)micro displacement device driver and parallel optical flat rotation driven is constructed.In this paper,the experimental results of the two systems are verified,and the results show that the measurement interference caused by periodic and aperiodic noises can be effectively reduced.Finally,the model of SPR differential measurement based on self-mixing interference phase modulation is analyzed theoretically by simulating,and the intensity and phase change functions of P polarization and S polarized light in SPR effect are derived.Based on this,a dual-polarization differential detection technique of self-mixing interference SPR is proposed.In the optical path,liquid crystal polarization direction rotator is used to control the polarization change of laser beam,detect and obtain the self-mixing interference signal of p-polarized light and s-polarized light,and obtain the phase change of SPR by difference of the phase change of dual-polarization interference signal,so as to achieve the purpose of phase detection.Experiments have proved that this technique can suppress the noise interference in SPR phase detection by experiments and it has a good application prospect in SPR.In this paper,the dual-polarization difference detection technology based on random polarization laser self-mixing interference and the dual-polarization difference detection technology based on self-mixing interference phase type SPR both effectively suppress the influence of noise on the measurement,improve the signal-to-noise ratio and reduce the measurement error.In addition,the method and technique presented in this paper have the advantages of low cost,simple structure and so on.It has good application value in self-mixing interference and surface plasmon resonance. |
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