In this paper, a novel non-contact optical measurement method based on the principle of laser self mixing interference for measuring liquid concentration is proposed. The optical path difference caused by changing the concentration of the solution, we found the phenomenon of waveform separation in the laser self-mixing vibration signal. In this system, simulation results of different solution concentrations are obtained based on the feature that each longitudinal mode is independent and do not interfere with each other in the multi-longitudinal mode laser, which successfully verified the corresponding relationship between the degree of waveform separation and the concentration of the solution.
We proposed an all-fiber tunable distributed Bragg reflector (DBR) laser rangefinder, which realized high-accuracy measurement of the absolute distance in the range of 1.88 to 3.33 m based on the self-mixing effect. The theoretical analysis of the all-fiber tunable DBR laser shows that wavelength tuning range and frequency of the laser can influence the measurement range and resolution. In addition, the experimental results indicate that the influence factors of measurement accuracy and sensitivity in absolute distance measurement are modulation response linearity, experimental equipment, and circuit bandwidth, which is in good agreement with theory analysis. Moreover, increasing the linear wavelength tuning range of the tunable DBR laser is an essential method to improve the measurement accuracy and sensitivity of the absolute distance measurement system.
A compact external cavity fiber laser has been proposed by using a silver diaphragm as the end-coupled cavity of Distributed Bragg Reflector. In this paper, structure and performance of the optimized all-fiber laser with external cavity is in good agreement with the theoretical analysis and numerical simulation. Meanwhile, experimental results demonstrate that the external cavity laser based on Distributed Bragg Reflector fiber laser could reduce threshold pump power from 25.6mW to 24.0mW and narrow the linewidth from 28.3kHz to 16.4kHz.
In this paper, we presented a waveform reconstruction method based on the self-mixing interference of DFB fiber laser by phase modulating technique, which is superior to the traditional vibration measurement system due to the wider measurement range and higher accuracy. In our sinusoidal phase modulation technology, the vibration information of the external target is extracted by the Fourier transformation method. For restoring the micro-vibration of the external target effectively with high precision, theoretical analysis and numerical simulations of phase modulation method based on the Distribution Feedback Bragg fiber laser are introduced in detail.
A method for the measurement of the absolute distance based on wavelength tuning technology of DBR fiber laser is presented. Experimental results show that the fringe number of the self-mixing signal and the target distance can reach a good linear relationship which agreed with the simulation results well. This paper demonstrate that DBR fiber laser present a powerful tool for the self-mixing technique and provide measurement of the distance up to 3.33 meters.
The paper introduces the white-light spectral scanning interferometry for surface measurement. This interferometry can
be used to measure the roughness of both smooth surfaces and those with large step heights. This real-time surface
measurement can be achieved using acousto-optic tuneable filtering (AOTF) technique without mechanical scanning. At
first, the structure and principle of this interferometry is introduced. Then the algorithm of the surface roughness
measurement is proposed. What's more, the experiment with standard test piece is conducted. Compared with the
traditional laser-light interferometry, the data shows that the proposed method has a higher accuracy which is proved to
be nano-scale. A conclusion is given at last in which the superiorities and the limitations of the proposed system were
discussed.
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