Utilizing magneto-optical short-range surface plasmon resonance to enhance the performance of optical fiber sensor

Although the short-range surface plasmon resonance (SRSPR) has larger sensitivity than the long-range surface plasmon resonance (LRSPR) excited simultaneously, SRSPR is usually ignored in previous studies of the LRSPR sensors due to its much larger peak width. However, since the resonance peaks of both SRSPR and LRSPR narrow vastly when combined with the magneto-optical (MO) effect, SRSPR has the potential to reach much higher figure-of-merit (FOM) than LRSPR due to its higher sensitivity. In this work, the feasibility of utilizing magnetooptical short-range surface plasmon resonance (MOSRSPR), which is the combination of SRSPR and MO effect, to enhance FOM was verified first by analyzing the prism-based structure sensor with the transfer matrix method (TMM). Then a novel optical fiber sensor based on MOSRSPR was proposed. The structure of the proposed sensor is a D-shaped optical fiber coated with an MgF2 film, a thin silver film, and a MO material film of cerium-doped yttrium-iron garnet (CeYIG). The influence of the structural parameters including the MgF2, silver, and CeYIG film thicknesses was analyzed theoretically by the finite element method (FEM). With the optimal parameters, the FOM of the optical fiber MOSRSPR sensor is greatly enhanced to 10,750 RIU- 1 in maximum and 2888 RIU- 1 in average, which surpasses all reported optical fiber LRSPR sensors vastly. The miniaturized and simple design of the D-shaped fiber MOSRSPR sensor, coupled with its high performance, offers a significant reference for the study of optical fiber sensors with ultra-high FOM.