Highly sensitive externally metal coated plasmonic refractive index sensor based on photonic crystal fiber

A simple configuration of a photonic crystal fiber (PCF) with dual-core is proposed that utilizes surface plasmon resonance (SPR) to work as a refractive index (RI) sensor. The PCF structure is asymmetric; thus, the PCF shows birefringence. A plasmonic metal layer of gold is placed over the fiber sensor to form an analyte channel externally. The sensing range and sensitivity are extended by investigating the best field path that moves from the core throughout the cladding towards the plasmonic layer. The best field path increases the analyte sensing range from 1.33 to 1.43, where the analyte flows through the external channel. The light-guiding properties of the sensor are explored by the finite element method. The optical properties of the sensor are numerically analyzed by the wavelength and amplitude integration methods. The numerical analysis found that the maximum wavelength sensitivity is 44,000 nm/RIU and 50,000 nm/RIU for x- and ypolarization, respectively. Additionally, the maximum amplitude sensitivity for x- and y- polarization is 2244 RIU-1 and 1605 RIU-1, respectively. The highest figure of merit (FOM) of the sensor is 721 and 769 for the x- and y- polarization, respectively. We also investigate the fabrication tolerance of the PCF detector. The sensor can be used for unknown biological or biochemical samples finding because of its wide sensing range with high sensitivity.