Photonic crystal fiber modal interferometer for biosensing applications

We fabricate and demonstrate a refractometer based on photonic crystal fiber (PCF) modal interferometer. The streptavidin and biotin are used as analyte and receptor in the experiment. The fabrication of the sensor is carried out via micro-hole collapsing with straightforward fusion arc splicing technique. Both sides of a short length of PCF (∼3 mm) are spliced to conventional single mode fibers (SMF). The voids of the PCF are completely collapsed in the splice region, acting as mode splitter and combiner for the PCF modal interferometer. The bulk liquid sensitivity is about 70.2 nm/RIU (refractive index unit) based on the linear curve fit for refractive index ranging from 1.33 to 1.35. The transmission spectrum of the biotin modified PCF modal interferometer exhibits 0.8 nm wavelength shift after streptavidin and biotin binding occurs.