Study Of Reflection-type Fiber-optic Biosensor Based On Multimode Interference

Compared with traditional electrochemical biosensor, fiber-optic biosensor can avoid the impacts of electromagnetic interference and acid corrosion. In addition sensor structure can be miniaturized and can work without a reference electrode. Therefore, the fiber-optic biosensor is attracting more and more attention all over the world.The fiber-optic biosensor based on multimode interference (MMI) has more advantages than other types of fiber-optic biosensors. The features of the multimode interference-based fiber-optic biosensor include an extremely simple structure, easy fabrication, low cost and wavelength encoding. The research on this type of fiber-optic biosensor will greatly promote the development of bio-sensing technology.A reflection-type fiber-optic biosensor based on multimode interference is reported in this paper. It is fabricated by connecting a segment of coreless silica fiber (CSF) with a reflective film to a single mode fiber (SMF). This structure has been demonstrated to be a simple and effective way to realize multimode interference in optical fiber. And by utilizing the interference of the higher order modes excited in the CSF, the fiber sensor can measure the refractive index of the surrounding solution. The reflection-type fiber-optic sensor based on multimode interference is studied by numerical simulation and experimentation. The results show that the wavelength of the interference trough on the output spectrum goes with the increase of surrounding solution's refractive index, and when the refractive index is less than 1.4 there is an approximately linear relationship between the wavelength of interference trough and the refractive index. When the refractive index is higher than 1.4, the sensitivity significantly improves. The minimum resolution can reach to 10-6.Based on the research work of the refractive index sensing, the application in biological sensing of the fiber-optic sensor based on MMI is studied. By modifying the goat anti-rabbit IgG antibodies onto the fiber sensor probe, a reflection-type fiber-optic biosensor based on MMI can be constructed. Experimental results show that the output spectrum of this fiber-optic biosensor can reflect the modification process and the immune responses between sheep anti-rabbit IgG and rabbit IgG.