Research On Key Technologies Of Micro-nano Vibration Measurement Based On Laser Self-mixing

Self-mixing effect (SMI) means optical sources playing double roles of emitting and receiving laser beam. Optical intensity, phase and frequency spectrum varies due to back-scattered light or applied-driven parameters (such as pump current, high power electron beam or light beam) changing, where laser oscillates in a steady-statue microwave-photonic wave carrying measured information. By analyzing fluctuating optical intensity, kinematic quantities of moving external targets can be figured out.Since emitted light and back-scattered light share same optical propagation path in absence of reference components, SMI systems often feature with compact and easy-alignment. External cavity inserted an acoustic-optic or electro-optic crystal manipulating optical frequency or phase shift has brought significant performance improvement in terms of accuracy to SMI systems, therefore, SMI with manipulated external cavities has been expected as a competitive alternative metrological tool in precision non-contact measurement fields. This paper elucidates dynamical laser behavior in single-mode and dual-mode SMI respectively modelled on the dynamical compounded-cavity theory. The devised novel SMI configuration was demonstrated in non-contact measuring one-dimension, ultra-sound and two-dimension micron vibrations. Comparison to a commercial laser Doppler velocity meter (LDV) will be found as well to show feasibility of established optical systems. Main works of this paper are classified into four charpters as follows:Firstly, in search of smart technology for non-contact sensing, we investigated a simplified semiconductor (AlGaInP) diode self-mixing. Fringe shape within moderate and weak feedback regime was analyzed to conclude the effect of incline factor. Then,we deployed continuous wavelet decomposition and Hilbert transform for phase extraction to retrieve micro scale vibration with automatic direction discrimination.Further, we found the multi-quantum well (MQW) structure help to decrease the threshold value of driven current and provide high current-power slope. During measurement in laboratory environment, the diode directly projected laser beam on measured surface and obtained a resolution better than ?/12. This no-attentuation system promised a wider feedback regime, a simpler structure than traddtional diode system with a desirable restraining ability against the random and speckle noises,therefore, it was potential to develop as an embedded laser technique with a bendable ESD-protection line.Secondly, a novel half-rad phase shifting SMI for online vibration reconstruction was performed with high computational efficiency. The special half-rad phase shifting depth enables a pure time-domain data processing directly extract quadrature phases through multiplying and filtering based on simple algebraic operations. Avoiding complicated FFT or inverse FFT calculation, this system demodulats out the transient vibration spending less than 100 milli-seconds, meanwhile, results show an accuracy improvement about one magnitude than semiconductor laser self-mixing. Using the established configuration, some non-uniform vibration such as nano-scale, damping or burst vibrations were reconstructed. Moreover, error sources and systematic noise of this optical system were discussed briefly.Then, we demonstrated a resonant phase-shifting self-mixing interferometer for improving the measured velocity limitation. Radio frequency (12MHz) phase shifting was introduced through a resonant electro-optic crystal, this SMI combined with a high-speed data transferring technology to mirror the frequency-to-amplitude curve of an ultra-sound transducer. Experimentation shown magnesium oxide-doped lithium niobate crystal resonated easily with low driven voltages in radio frequency zone.12MHz phase shifting offered the self-mixing microwave-photonic light a better immunity to frequency aliasing and a nanometer resolution of 40nm in measuring ultra-sound (>30kHz) vibration. Meanwhile, small diffusive angle of linear-polarized light allowed a far target-to-laser distance in measurement.Subsequently, we established a two-dimeisonal self-mixing system by means of integrating polarization-multiplexing and phase shifting on a dual-longitudinal mode He-Ne laser. Due to the orthogonality of polarizations, microwave-photonic band SMI optical power was a two-dimensional vector without optical cross-talk between two paths. The dynamic laser behavior was explained by semi-classical Lamb's gas laser theory associated with compounded cavity theory. Beneficially, experiment proved no mode competition phenomenon or polarization hopping happen within weak feedback regime. The outputted optical intensities were in reversely-duplicated waveforms fluctuating as superimposition of sinusoid-likes curves. Fortunately, multi-harmonics contained in laser intensity were distinguishable due to sufficient adjacent spacing by the photonic phase manipulaton at different polariations. Theoretically, by changing applied driven voltages to crystals flexibly, any possible frequency aliasing could be eliminated and resolutions (<10nm) of simultaneous dual-targets measurement was adjustable to meet various requirements. In addtion, the two independent measuring paths of this system can work simultaneously or individually.At last, fiber-pigtail semiconductor laser diode self-mixing vibrometer utilizing a waveguide phase modulator was experimentally observed,where near-infrared single mode laser beam was coupled into a polarization-maintaining fiber for improving the immunity to electromagnetic interference in bendable optical path. As demonstraged,the proposed configuration solved diffusion problem of Guassian beam propagation.