Refractive index sensor based on an abrupt biconical fiber taper
Date of Issue2016-05-18
School of Electrical and Electronic Engineering
Tapered fiber sensor, also known as biconical fiber is widely used in sensing application because of its small size, light weight and the insensitive to electromagnetic interference. In this report, we will study the sensing principle of tapered fiber sensor and how different taper profile of the fiber can affect its sensing ability. Tapering structure include parameters like the taper length, taper waist diameter and different type of tapering method. Sensitivity is a crucial element of a sensor. The sensitivity of a tapered fiber sensor is strongly correlated to the penetration depth of the evanescence field and the number of modes in the tapered fiber. Both the evanescence field and the modes are related to the refractive index (RI). Therefore by measuring the RI indices, the sensitivity of the tapered fiber sensor can be studied. The characteristic and sensitivity of the microfiber is appropriate for use in heavy metal detection to reduce human exposure to metal ions, since high exposure to these metal ions can cause adverse effect to human’s health. In this study, the microfiber sensor underwent surface functionalization, followed by the functionalization of the chelating agent compound onto the surface. Each type of chelating agent has higher affinities toward specific metal ion type, thus, this could be an advantage to increase the specificity of our microfiber sensor. Functionalization of various chelating agents can specific the types of metal ions to be detected. Through the chelation process, metal ions are bind by the chelating agent to form a stable metal chelates. Results from various experiments have justified the principal behind the characteristic of the tapered optical fiber. For instance, tapered optical fiber of different taper waist diameter showed distinct level of sensitivity toward RI change. The outcome of this study was validated through the changes in the amount of resonant wavelength shift as observed in optical spectrum analyzer. The resonant wavelength shift was found to increase exponentially with increasing RI of sample metal solutions. Next, a chelating agent-functionalized microfiber is found to have higher sensitivity compared to a non-functionalized microfiber. On top of this, A DPA-functionalized microfiber was found to be more effective than EDTA-functionalized microfiber due their respective chelative properties. In addition, experiment to investigate effect of pH value of the metal solutions also showed optimal of EDTA chelation process was found to be pH5.
Final Year Project (FYP)
Nanyang Technological University