A high linearity refractive index sensor based on D-shaped photonic-crystal fiber with built-in metal wires

We proposed a D-shaped photonic crystal fiber refractive index sensor based on surface plasmon resonance for the detection of refractive-index (RI) liquid analytes between 1.27 and 1.37. In contrast to the common D-shaped structure photonic crystal fiber, three metal wires were added between the D-surface and top level air holes in our design, which prevent the analytes from contacting the metal. It is particularly suitable for detecting some analytes which are easy to react with metal. The sensing performance of D-shaped photonic crystal fiber was studied by the finite element method. Simulation result shows that the sensor has a very good linearity. The adjusted R2 values of resonance wavelengths fitting lines are 0.9996 in 1.27−1.32. The sensitivity of the designed sensor can be as high as 11,500 nm/RIU, and a high resolution of 8.7 × 10−6 RIU is achieved when na = 1.36.An average sensitivity of 8,846.67 nm/RIU in the sensing range 1.27−1.32, and 10,812 nm/RIU in 1.33−1.37 with high linearity is obtained. The D-shaped optical fiber usually realizes the sensing function by coating a metal film, but the method of adding metal wires has rarely been reported before. Owing to the high linearity, high resonance intensity and sensitivity, the proposed sensor can find important applications in environmental, biological and biochemical analytes detection.