Fabrication of D-type Fiber Optic Sensors with a Long Interaction Length and Studying Effects of Critical Parameters on Sensor Response

Today evanescent wave based fiber optic (F/O) platforms are in favor of the use for monitoring molecular interactions since they are practical, economic and easy to operate which make them ideal turnkey systems for clinical, pharmaceutical, environmental and security applications. The side polishing is one of techniques for reshaping the geometry of the waveguide to make the F/O sensor more sensitive to surrounding refractive index (RI) in evanescent field. In this study D-type F/O sensors with a 25 mm-long interaction lengths are fabricated. In addition to that, effects of the critical parameters such as the polishing depth, the wavelength, and the temperature on the sensor response are determined for the RI in the range of 1.33 - 1.47. The developing key of these F/O sensors is reaching high strength and penetration depth of evanescent wave in varying RI of the surrounding bio-layer. Development steps of D-type F/O sensors are; fabrication of supporting elements - silicon V channels, F/O cable preparation, adhesion, lapping and polishing, fusing the FC connectors, construction of the optical system, and RI measurements. Details of these steps are explained and the general characteristics of the D-type F/O sensor are presented. Results indicate that the sensor's responses in three different RI ranges can be improved by the polishing depth. A maximum sensitivity of around 2x10(5) for the D-type F/O sensors is demonstrated in the RI range of 1.44-1.46.