Simultaneous measurement of refractive index and temperature of seawater based on surface plasmon resonance in a dual D-type photonic crystal fiber

A dual D-type photonic crystal fiber (PCF) was proposed in this work to measure the refractive index and temperature of seawater. Two golden layers were designed to be coated on the two polished planes in the dual D-type PCF. Two confinement loss peaks in the transmission spectrum appeared due to the surface plasmon resonances which were inspired on the two golden layers. In order to achieve two-parameter sensing, one of the two polished planes was further coated with a polydimethylsiloxane (PDMS) layer which was temperature-sensitive. Seawater was assumed to be coated on the outer surface of the PCF. Numerical results by using the finite element method showed that the measurement sensitivity of the refractive index of seawater reached 1371 and 1228 nm/RIU, while the measurement sensitivity of temperature reached −0.3 and −1.06 nm/ °C, respectively. Finally, we obtained the transfer matrix expression which could be used to measure the refractive index and temperature of seawater simultaneously. The designed dual D-type PCF, which is simple in structure, highly sensitive and two-parameter measuring, could be a promising candidate for the monitoring of seawater.