Study On The Fiber Sensing Properties With Modal Interferometer Based On Core Diameter Mismatch

There have recently been substantial efforts to develop the practical of fiber sensor. For many years, a great deal of researches have carried out in widening the applications of the fiber sensor and improving its measurement sensitivity. Therefore, the variety of optical fiber sensing technology have made great progress. Optical fiber sensing technology with modal interferometer based on core diameter mismatch was attached importance to domestic and foreign scholars. However, some of optical fiber sensing with core mismatch has many shortcomings such as complicated structure, production difficulties, and lower sensitivity. To improve its sensing structure can enhance the sensitivity of the measurement.This thesis was researched under above ideas.We presented an implementation method for achieving curvature measurement which using modal interference technology of thin core fiber. In this method, thin-core optical fiber was the key device. After a segment of thin-core fiber was inserted into a standard single-mode fiber, curvature and refractive index measurements was realized by modal interference technique. The main work consists of two parts:1. Micro fiber optics curvature sensor with modal interferometer based on core diameter mismatch. Experimental investigations achieve wavelength shift and curvature relationship in the range of0to3.2m"1. The sensitive part of the sensor fix in the middle of the translation stages, and the sensor is based on the buckling effect. At the same time, the Reference light way is also fixed to the same horizontal position with the Measuring light way, it can be used to eliminate the impact of the environment to the Measuring light way. And verify the impact of thin-core optical fiber of different lengths on the experimental results. The sensing principle and related theories of the fiber core mismatch structure are expounded. The experimental results show that the fiber core diameter mismatch structure of the sensor with the good sensitivity in0-3.2m-1range. Experimental results show that this device has good linearity.2. Micro fiber optics refractive index sensor with modal interferometer based on core diameter mismatch. A refractive-index sensor with micro-structured defect is proposed and demonstrated. Its refractive-index characteristics are studied experimentally. With the sensitive parts of the sensor is fixed to the vessel, and then corrode the cladding by HF. Watching the rate of corrosion of the cladding through the microscope at the same time. According to actual needs select different cladding thickness. This refractive index sensing experiment is using different concentrations of sucrose solution. Experimental results show that corroding the sensitive parts of the cladding by HF solution to makes its diameter reduced to improve the sensitivity to external refractive index sensing. The sensitivity coefficient of the sensor before and after corrosion are142.295nm/R.I.U and182.328nm/R.I.U, the linear fit are0.9855and0.9681, so the interference peak wavelength show a good linearity with the external refractive index change.These sensors have a simple structure, small size, stable performance and high resolution, and have good prospects for the development and practical applications. Using the etching craft to reduce the thickness of the cladding have a simple craft, low production cost advantages, and also significantly increase the performance of the sensor.