Research Of Reflective Intensity Modulated Fiber Optic Micro Displacement And Angular Displacement Sensor

With the development of optical fiber and fiber optic sensing technology, a large number of sensors based on optical fiber have been developed rapidly. Reflective intensity modulated fiber optic sensors is an important part of optical fiber sensor family,and the development of new types of this kind of sensor which can sense different parameters in different occasions, and can meet the needs of different measurements has attracted the attention of researches for a long time. Besides, measurements of linear and angular displacements which are basic parameters in surveying, not only need to be fast, accurate and automatic, but also need to meet the technical requirements like moisture-proof, explosion-proof, passive, low noise and confidentiality. Therefore,studies of new kinds of optical fiber linear and angular displacement sensors is of great importance to the development of surveying and the progress of modern industrial technology.In this paper, a fiber optic micro displacement and angular displacement sensor based on the intensity modulated sensing principle will be designed and studied theoretically and experimentally.Firstly, the basic structure of the sensor will be designed based on the analysis of the sensing principle, and the intensity modulated characteristic functions of micro and angular displacement sensing will be derived. Secondly, theoretical sensing curves will be simulated and draw based on the derived functions. Then, the influence of each parameter on the sensing performance will be analyzed in an attempt to guide the design and construct of this kind of sensor. After that, the sensing performance, reproducibility and hysteresis effect will be measured by experiments, and the results will be compared with the theoretical simulations to verify the consistency. Finally, a special sensing probe structure will be designed to realize intensity compensation, and simulation results will show that the designed structure will improve the stability of the sensing system and the sensing performance at the same time.Some valuable results are obtained, and both theoretical and experimental availability of the designed micro and angular displacement sensor are proved.Therefore, this study has certain innovation significance.1. In the experimental study of micro displacement sensor, a left-right asymmetry bell shaped sensing curve is obtained. Both the left part or called "front slope" and the right part or called "back slope" can be used as linear displacement sensing curve. A linear sensing range of 1.05mm of the front slope from 0.10mm to 1.15mm, and a linear sensing range of 1.60mm of the back slope from 1.30mm to 2.90mm are gained respectively by the least square method on the condition that the linear coefficient is no less than 99%. The sensing range of the back slope is almost 1.5 times of the front slope.The relative sensitivities of the front slope and the back slope are(105.92% × Pmax)mW/mm and (27.51% ×Pmax)mW/ mm respectively, so the sensitivity of the front slope is about 3.85 times of the back slope.2. In the experimental study of angular displacement sensor, the sensing curve is symmetrical to the position of the maximum output (where angular displacement is 0°),and has two linear regions. It is found that the distance between the mirror and the end of the fiber probe corresponds to different angular displacement sensing curves, and the maximum output first increases and then decreases with the increase of this distance.However, before the peak value of the sensing curve reaches its maximum value, the increase of the distance only have an influence on the angular sensing sensitivity. The experiments show that the maximum sensitivity is 13.71%/deg, and the sensing range is[-7.20°,7.20°].The designed reflective intensity modulated fiber optic sensor can not only be used to measure linear or angular displacement separately, but can also be used to measure other parameters like pressure and strain, temperature and magnetic field by the combination with other measurement devices. Therefore, this study has good practical value and research significance.