Characterization of incompletely coated D-shaped PCF-SPR refractive index sensors

Abstract To reduce the complexity of the sensor structure and improve the sensitivity of refractive index (RI) measurement, a D-shaped photonic crystal fiber (PCF) surface plasmon resonance (SPR) RI sensor with incomplete coating of gold-tantalum pentoxide (Au-Ta2O5) on the surface is proposed. When the coating width is 3.1 μm, the sensor can detect RI samples ranging from 1.35 to 1.41 in the ultra-wide near-infrared (NIR) region of 1100–2100 nm wavelength. Its maximum wavelength sensitivity is 20,000 nm RIU−1, maximum amplitude sensitivity is 2817.7 RIU−1, resolution is 5 × 10 − 6 RIU, and figure of merit (FOM) is 333.3 RIU−1. This sensor can be widely used in biological tissue detection. For this type of incomplete coated D-shaped sensor, the coating material and structural parameters not only affect the performance of the sensor, but also change the RI detection range, which has been ignored or not mentioned in previous literature on PCF-SPR sensors. Therefore, the reasons for the change of RI detection interval and negative optimization caused by structural parameters were analyzed, and two different sensors with different coating widths were finally obtained, which can achieve high sensitivity sensing in their respective detection intervals. The detailed research results expand the understanding of the SPR phenomenon in D-shaped PCF and provide theoretical guidance for adjusting and improving the detection performance of PCF-SPR sensors.