Development of D -type fiber optic sensors for detection of refractive index variation in evanescent wave field /

Güleryüz, Burcu
The purpose of this study is to design, construct, develop and test D-type multimode fiber optic (F/O) sensors based on evanescent wave field sensing. A comprehensive work has been performed both theoretically and experimentally using a geometrical modification approach to improve the sensors response in different manners for detecting the refractive index (RI) variations and bio-molecular interactions in aqueous environment. In this study, the D-type F/O sensors performance was improved utilizing optical waveguide (OWG) and surface plasmon resonance (SPR) modes in evanescent wave field. Development steps of sensors are; fabrication and characterization of silicon V channels (supporting elements), the F/O cable preparation, adhesion, mechanical lapping and polishing, and assembling the Field Assembly Connectors (FC connectors). These steps are explained in detail and sensor performances are demonstrated for RI changes between 1.33 and 1.47. The highest sensitivity is found to be 2x10 5 refractive index unit (RIU) for the zone of 1.44 and 1.46 RIU. In addition, thin gold film is deposited on the D-type F/O sensors to excite surface plasmon (SP) mode. It is shown that the SP mode can amplify the sensors ensitivity between the 1.33 and 1.44 RIU being known as the Dynamic range to monitor the bio-molecular İnteractions. Furthermore, in order to tune thin gold film thickness and roughness for a better sensor response, a novel surface modification approach is introduced with plasma etching process.