IN-LINE OPTICAL FIBER STRUCTURES FOR ENVIRONMENTAL SENSING

Surface plasmon and evanescent wave sensors are attractive for chemical and biological sensing applications. They can work in aqueous media and when used in conjunction with the appropriate surface chemistry they can have high specificity and high sensitivity. However, most surface plasmon sensors are relatively complex as they are based on the use of attenuated total internal reflection to excite surface plasmon resonance in a thin gold film and require light to be incident at the appropriate angle and polarization. Other surface plasmon and optical affinity sensors have used the evanescent waves in planar waveguides to interact with the environment. These devices are sensitive but, have strict optical coupling requirements and are difficult to fabricate. In optical fiber evanescent wave sensors the interaction with the surrounding environment is usually obtained by tapering an optical fiber, which significantly weakens the structure, or by just utilizing the end of the optical fiber. In this paper, in-line optical fiber structures are presented that are mechanically robust, and provide a large interaction length for high sensitivity. They are compatible with standard chemistries for optical affinity sensing of biological compounds.