SPR Sensor Based on Exposed-Core Grapefruit Fiber With Bimetallic Structure

Abstract

A liquid refractive index (RI) sensor based on an exposed-core grapefruit fiber with a bimetallic structure and a central air hole using surface plasmon resonance (SPR) is presented. The asymmetrically SPR region leading to strong birefringence with $x$ -polarized peak provides much higher peak loss and sensitivity than $y$ -polarized. To match with the plasmon and enhance the mode coupling, we introduce a central air hole to lower the effective RI of the core guided mode. We numerically investigate the effects of the central air hole size, silver layer and gold layer thicknesses on the sensor’s performance using wavelength, and amplitude interrogations. A large analyte RI range from 1.33 to 1.42 is evaluated, and the results show that the sensor has a higher sensitivity for high analyte RI change than the low. The extremely high wavelength sensitivity 16 400 nm/RIU at 1.42 is obtained. This letter can provide a reference for developing a high sensitivity, real-time, and distributed SPR sensor.