Study Of Multi-core Few-mode Fiber Optic Sensor Based On Modal Interference

Bending direction,bending position and lateral force are important physical parameters which should be precisely measured in engineering application,such as composite structures monitoring,MEMS assembly,bone injury rehabilitation and many other fields.There are problems in the present research of bending position,bending direction and lateral force optical fiber sensor,such as complex system,low precision of direction angle measurement and low measurement sensitivity of lateral force.In order to solve above problems,a multi-core few-mode fiber optic sensor for bending direction,bending position,lateral force and lateral force direction measurement were presented in this paper.The advantage of multi-core few-mode fiber optic sensors is that the sensor not only has the characteristics of general fiber optic sensor,such as chemical stability,anti-electromagnetic radiation,low transmission loss,high robustness,harmless to human body and environment and etc.,but also has its unique characteristics,such as multi-parameter measurement and direction angle measurement.Based on the mode interference,the multi-core few-mode fiber optic sensor has the advantages of compact structure and high sensitivity.The main work of this paper:1.Based on single mode-few mode-single mode structure,a multi-core few-mode fiber sensor for bending position measurement was designed.The mode interference theory in multi-core few-mode fiber was analyzed.The sensing principle of bending position sensor was established.And the effect of bending position,bending depth and fiber length on wavelength shift of spectrum was analyzed.The experimental platform of bending position sensor was established,and the sensing experiment was carried out.The sensing experiment result showed that the highest spatial resolution is 0.19 mm and the highest sensitivity is 1066.5pm/cm.2.A multi-core few-mode fiber sensor for bending direction measurement was designed.The Theoretical model of bending direction sensor was established.Based on this theoretical model,the method of bending direction measurement is given.The experimental platform of bending direction sensor was established,and the sensing experiment was carried out.The sensing experiment result showed that the sensor has a high measurement accuracy of bending direction,and its maximum measurement accuracy is about 1°.Based on position sensor and bending direction sensor,the theoretical model to measure both position and direction is proposed and the experiment is carried out.The experiment result showed that the measurement error of position is 0.83 mm and the measurement error of direction is 1.33°.3.Based on multi-core few-mode fiber sensor,a lateral force sensor and a lateral force direction sensor were designed.The theoretical models for lateral force and lateral force direction sensor were established separately.The effect of lateral force,fiber cladding diameter and feature wavelength on spectrum wavelength shift was analyzed.The experimental platform for lateral force and lateral force direction measurement was established,and the sensing experiments were carried out.The sensing experiment result showed that: For a multi-core few-mode fiber with 12 cm,when the lateral force is between 0~0.030 N,the sensitivity of the lateral force sensor is-24.54nm/N.And the maximum measure error of lateral force direction sensor is 1.36°.