Research On Laser Self-mixing Grating Interference Micro/nano Sensing Technology

By controlling the light feedback to the laser,the internal properties of the laser will be affected by external feedback.This phenomenon was summarized as the laser Self-Mixing Interference(SMI)theory.Various novel sensors have been developed with the maturity of laser SMI technology.In SMI systems,the lasers play parts in output and input simultaneously.Comparing with the traditional two-beam interference system,SMI systems have the same fringe resolution,more compact system structure and higher sensitivity,which can replace the traditional laser interferometer in many fields.By introducing a diffraction grating in SMI,a novel Self-Mixing Grating Interferometry(SMGI)was developed.SMGI adopts the grating pitch rather than the wavelength as the measuring standard,removing the measurement error caused by the wavelength undulation and providing better immunity against environmental disturbances.The paper analyzes the theoretical model of SMGI and designs several micro-nanometer displacement sensing systems.The main works of this thesis are summarized as follows:A SMGI system with multiple-diffraction is proposed to measure the one-dimensional displacement of the grating.Based on Fourier optics theory and three-mirror cavity model,the mathematical model of SMGI is derived.And the relationship between each SMGI fringe and the displacement of the grating along the grating vector direction is obtained.The SMGI system with multiple-diffraction is designed,which multiplying the resolution of SMGI fringes.Sinusoidal phase modulation and orthogonal phase demodulation algorithm are introduced to realize one-dimensional micro-displacement reconstruction.Experimental results shows the measurement accuracy of the system with five-times-diffraction reached nano level.An orthogonal polarization SMGI system for simultaneous in-plane and out-of-plane displacement measurement is proposed.The influence of out-of-plane displacement of grating on the feedback light is analyzed.A scheme is designed to demodulate the two-dimensional displacement simultaneously by using optical feedback of different diffraction orders.The out-of-plane displacement has no effect on the optical path structure.Based on Lamb's semi-classical theory,the output behavior of birefringent dual-frequency He-Ne laser under weak feedback is explained.The polarization of two feedback light is orthogonal,and then the information aliasing between different feedback light paths can be avoided.Based on the sinusoidal phase modulation technique with frequency division multiplexing,information in different feedback light is separated in frequency domain,so only one photodetector is needed for practical detection.Various Lissajous movement were reconstructed by proposed system.Experimental results show that the accuracy of the system is in the sub-micron level.A multiple SMI system for fiber ring laser is proposed.Based on Dragic's erbium-doped fiber ring laser(FRL)model and the equivalent reflectivity theory,the SMI model of erbium-doped FRL is established.The density of self-mixing interference fringes doubled by introducing an optical circular.The surface reflection of optical collimator will influence the shape of SMI fringes,which is analyzed and verified by adjusting external cavity loss experimentally.Based on the short-time Fourier transform(STFT),the time-frequency analysis of the signal is realized.In addition,a double-peak frequency identify algorithm is proposed to extract the time-domain Doppler frequency of the signal.The velocity measurement is carried out by servo motor translation stage.With more precise requirements,the translation stage is replaced by a piezoelectric ceramic actuator.The results show that the system has high reliability and the accuracy of velocity measurement is better than 0.1 mm/s.