Optical fiber strain sensor

• Main Authors: Tan Zhi Sheng, Dickson, Tan, Dickson Zhi Sheng
• Other Authors: Tjin Swee Chuan
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering::Electrical and electronic engineering::Optics, optoelectronics, photonics
• Online Access: http://hdl.handle.net/10356/67941
• Institution: Nanyang Technological University

Application of optical fiber sensor in various industries such as environmental, biological and chemical industry has attracted great attention due to it small physical size, electromagnetic immunity and suitability for harsh environment. Optical fiber is sensitive to changes in temperature and strain, however the main focus of this project is to concentrate on the effect caused solely by strain. The main focus of this study consists of two components, firstly to assess the spectra response of microfibers with different taper under strain, placed under different conditions; open air environment and submerged in deionized water. Secondly, to achieve a negligible spectrum difference for two different infusion cycles. The first experiment was conducted using on tapered microfiber with taper length of 5 mm and 6 mm. While each microfiber of a taper length is produced with a different waist diameter of 4.7 µm, 7.1 µm and 12.6 µm. Microfiber sensitivity towards strain are obtained from the spectrum shift under external strain. The selection of microfiber as a strain sensor is based on its sensitivity towards strain from 0 to 5 mƐ and is able to provide a constant spectrum shift with increasing strain. The selected tapered microfiber to be used as a strain sensor, which has a parameter of 7.1 µm waist diameter and taper length of 6 mm, was used in the second part of the project. The second experiment is the development of different cartridge design to hold the microfiber, while the microfiber that placed in the cartridge will be submerged under DI water. During the course of the experiment, the rate of flow of DI has to be kept constant. Pre-strain of fiber was set at 2 mƐ as this is the minimum pre strain value above which, spectrum shift with increasing strain is constant. Based on the same cartridge, spectrum obtained from the 2nd and 3rd infusion of DI water will be compared and the ideal spectra acceptable difference between spectrums is set to be at 0.1 nm. However, due to the high sensitivity of the tapered microfiber, it is almost impossible to achieve the ideal result. The results showed that the design with an enclosed structure helps to reduce the spectra difference between different infusion cycles compared to the spectra difference obtained from a structure with an opening which expose the microfiber to the surrounding environment. The results also showed that amount of the volume of the DI water infused does not affect spectra difference significantly as long as the microfiber was fully submerged in the DI water.