Laser Self-mixing Interferometer Research Articles

Analysis and measurement of vibration characteristics of a hollowing defect based on a laser self-mixing interferometer

Abstract To solve the problems with the existing methods for detecting hollowing defects, such as inconvenient operation, low efficiency and intense subjectivity, and to improve the efficiency of the acoustic-optic fusion method for detecting hollowing defects, in this paper the vibration characteristics of hollowing defects are measured and analyzed using a laser self-mixing interferometer. The ceramic tile above the hollowing defect is equivalent to a thin circular plate with peripheral fixed support. According to Kirchhoff’s classical circular plate theory and the circular plate displacement function based on the improved Fourier series, a theoretical model of a circular plate is established. By solving the characteristic equation, the theoretical modal parameters of hollowing defects are obtained. Subsequently, an experimental system based on a laser self-mixing interferometer is built, and modal experiments are carried out using the hammering method. The experimental modal parameters are obtained with a professional modal analysis software. Through comparative analysis between the theoretical and experimental modal parameters, the error of the natural frequency results is found to be tiny and the mode shapes are consistent. These results provide theoretical guidance for a practical non-destructive acoustic-optic fusion method for detecting hollowing defects.

Collimated beam formation in 3D acoustic sonic crystals

We demonstrate strongly collimated beam formation, at audible frequencies, in a three-dimensional acoustic phononic crystal where the wavelength is commensurate with the crystal elements; the crystal is a seemingly simple rectangular cuboid constructed from closely-spaced spheres, and yet demonstrates rich wave phenomena acting as a canonical three-dimensional metamaterial. We employ theory, numerical simulation and experiments to design and interpret this collimated beam phenomenon and use a crystal consisting of a finite rectangular cuboid array of 4×10×10 polymer spheres 1.38 cm in diameter in air, arranged in a primitive cubic cell with the centre-to-centre spacing of the spheres, i.e. the pitch, as 1.5 cm. Collimation effects are observed in the time domain for chirps with central frequencies at 14.2 kHz and 18 kHz, and we deployed a laser feedback interferometer or Self-Mixing Interferometer – a recently proposed technique to observe complex acoustic fields—that enables experimental visualisation of the pressure field both within the crystal and outside of the crystal. Numerical exploration using a higher-order multi-scale finite element method designed for the rapid and detailed simulation of 3D wave physics further confirms these collimation effects and cross-validates with the experiments. Interpretation follows using High Frequency Homogenization and Bloch analysis whereby the different origin of the collimation at these two frequencies is revealed by markedly different isofrequency surfaces of the sonic crystal.

Quadrature phase detection based on a laser self-mixing interferometer with a wedge for displacement measurement

We report a novel and simple method to generate a pair of self-mixing signals with quadrature phase difference in He-Ne laser by introducing a wedge into the external cavity. A wedge phase-shift laser self-mixing effect theory is developed to explain the phase-shift phenomenon, and the relationship between the phase difference and the distance from the center of the iris diaphragm to the center of the spot is given. Then a simple and effective wedge-quadrature laser self-mixing interferometer is established for displacement measurement by the quadrature phase detection method. Experimental results show that the max error is 182 nm for a target displacement of 20 μm. This structure provides a useful exploration for phase-shift signal generation and simplifies the self-mixing signal demodulation process with only a single four-quadrant inverse tangent operation, which has potential application in real-time displacement measurement.

Quadrature Phase Detection Based on a Laser Self-Mixing Interferometer with a Wedge for Displacement Measurement

Quadrature Phase Detection Based on a Laser Self-Mixing Interferometer with a Wedge for Displacement Measurement

Laser self-mixing interferometer with scalable fringe precision based on phase multiplication algorithm

Laser self-mixing interferometer with scalable fringe precision based on phase multiplication algorithm

Laser Self-Mixing Interferometer for Three-Dimensional Dynamic Displacement Sensing

In this letter, we proposed an innovative laser self-mixing interferometer (SMI) with a reflection-type two-dimensional (2D) grating for three-dimensional (3D) dynamic displacement sensing. When the beams emitted by three lasers are incident on a reflective 2D grating with auto-collimation diffraction angles, the diffracted beams will return into the lasers along the original path, thus generating self-mixing interference effect in each laser. In order to obtain higher measurement resolution, phase-modulation technique is applied to the proposed interferometer. The operating principle for the proposed system has been demonstrated in detail. Measurement results show that our method is capable of sensing 3D dynamic displacement with resolution of nanometer level. The SMI presented in this letter has the merits of high resolution, compact system configuration and straightforward operation.

Non-invasive human extremely weak pulse wave measurement based on a high-precision laser self-mixing interferometer

In this paper, a technique based on laser self-mixing effect for acquiring pulse wave profile is proposed and demonstrated. For the characteristics of extremely weak vibration in human pulse waves, a method of multiple reflections with external cavity is designed to improve the measurement accuracy to λ/4. Based on the fringe counting algorithm, one period of pulse wave is successfully reconstructed. The measurement results show that the root mean square error (RMSE) of the reconstructed pulse wave is 0.912 μm at sampling rate of 8 kHz. Besides, the correlation coefficients and heart beats of this method and the traditional photoplethysmography (PPG) measurement are analyzed.

Semiconductor laser self-mixing micro-vibration measuring technology based on Hilbert transform

A signal-processing synthesizing Wavelet transform and Hilbert transform is employed to measurement of uniform or non-uniform vibrations in self-mixing interferometer on semiconductor laser diode with quantum well. Background noise and fringe inclination are solved by decomposing effect, fringe counting is adopted to automatic determine decomposing level, a couple of exact quadrature signals are produced by Hilbert transform to extract vibration. The tempting potential of real-time measuring micro vibration with high accuracy and wide dynamic response bandwidth using proposed method is proven by both simulation and experiment. Advantages and error sources are presented as well. Main features of proposed semiconductor laser self-mixing interferometer are constant current supply, high resolution, simplest optical path and much higher tolerance to feedback level than existing self-mixing interferometers, which is competitive for non-contact vibration measurement.

Simultaneous measurement of vibration amplitude and rotation angle based on a single-channel laser self-mixing interferometer

Based on a single-channel laser self-mixing interferometer, we present a new simultaneous measurement of the vibration amplitude and the rotation angle of objects that both affect the power spectrum containing two peaks of the interferometer signals. The fitted results indicate that the curve of the peak frequency versus the vibration amplitude follows a linear distribution, and the curve of the difference of the two-peak power values versus the angle follows a Gaussian distribution. A vibration amplitude with an error less than 3.0% and a rotation angle with an error less than 11.7% are calculated from the fitted results.

Implementation of the reflection phase-shift laser self-mixing interferometer for large-scale displacement measurement

Beginning with introducing π/2 phase-shift on the laser self-mixing front output signal reflected by the metal–dielectric film, the new measurement technique of laser self-mixing interferometer is studied. Through the glass substrate coated by metal film attenuating the laser intensity while introducing π/2 phase-shift on the reflection self-mixing interference front signal in the electronic domain, it is easy to make the laser self-mixing interferometer system work under weak feedback conditions and to produce two orthogonal interference signals which are used to measure the displacement. The simulation result indicates high measurement accuracy. In order to improve the measurement accuracy and resolution of interferometer in 100mm level displacement, the collected self-mixing interference signal is dealt with electronics subdivision in the digital domain, improving the noise performance and measurement reliability. Calibration experiments with high precision guide shows that 0.4μm resolution in 100mm displacement measurement process is achieved. As the self-mixing interference signals are acquired directly, the system measurement speed can be high. But subject to sampling rate of the data collection and processing system, the speed can reach close to 100mm/s in 100mm range displacement measurement theoretically.

A Novel Phase Modulation Accelerometer

A novel phase modulation accelerometer based on self-mixing effect is presented. A quartz pendulous reed suspended by dual flexible beam is used as the first step sensing unit, which translates the acceleration signal to the displacement of quartz pendulous reed. The laser self-mixing interferometer reads out the displacement of quartz pendulous reed while the sensor experience acceleration. All-phase spectrum analysis is applied to detect the phase of self-mixing interference signals to reconstruct the acceleration. Finally, performances of the novel phase modulation accelerometer are measured by experiments. Experimental results indicate that the resolution of the acceleration sensor based on laser self-mixing interference can achieve sub micro-g. The phase modulation accelerometer has the potential to achieve high-precision, compact accelerometers.

Self-mixing vibration measurement using emission frequency sinusoidal modulation

In this paper, a simplified phase demodulation scheme is applied to recover vibration trail on a laser self-mixing interferometer for noncontact vibration measurement. The emission of semiconductor laser diode is modulated by injecting sinusoidal wave, and corresponding interference signal is a quasi-sinusoid wave. The vibration mathematical model for semiconductor laser diode is theoretically educed from basic self-mixing theory, the variation of target is converted into phase information. The simulation of demodulation algorithm and standard deviation are presented and the reconstructed waveform displays a desirable consistence with various moving trails. Following the principle, a minimum experimental system is established and position variation of the target mirror driven by voltage signal is translated into phase shifts, feedback is controlled at weak level during experiment, Fourier transform is implemented to analyze phase information. The comparisons of both amplitude and velocity with a Germany Doppler vibrometer are performed to testify vibration model, the error of proposed demodulation method is less than 30nm and achieve a high accuracy in vibration frequency. The experimental results indicate the traditional phase technology can be applied on complex optical power signal after adaption providing a feasible application prospects in industrial and scientific situation with an inexpensive semiconductor laser.

Laser self-mixing interferometer for MEMS dynamic measurement

Laser self-mixing interferometer has the advantages of simple architecture, compact size, naturally self-aligned optical characteristics, and low cost. It is promising to replace conventional interferometers for physical measurements, such as displacement, distance, velocity, vibration, and so on. In this paper, this interferometer was tried to be used for micro-electromechanical system (MEMS) dynamic measurement. Firstly, its measurement principle based on a three-mirror cavity model was presented, and then the laser self-mixing interferometer for MEMS dynamic measurement was designed, experiments were finally performed as target moves with different forms. Experimental results suggest that self-mixing interferometer is available for MEMS dynamic measurement, and may have wider applications in the future.

相位调制型激光自混合干涉仪的动态特性分析及测试

相位调制型激光自混合干涉仪的动态特性分析及测试