Sensitivity Improvement of an Optical Fiber Sensor Based on Surface Plasmon Resonance with Pure Higher-Order Modes.

Featured Application: We propose an SPR sensor with high sensitivity and resolution based on the higher-order modes, which can be applied in the measurement of the refractive index. In this paper, we propose an approach to improve the sensitivity of an optical fiber surface plasmon resonance (SPR) sensor with a pure higher-order mode excited by a designed mode selective coupler (MSC). We calculate the proportion of the power of the higher-order mode in the cladding. Compared to the LP 01 mode, the power proportion of the LP 11 mode ( LP 21 mode) in the cladding theoretically improves by 100% (150%). To generate a relatively pure LP 11 mode or LP 21 mode, a mode selective coupler (MSC, 430–580 nm) is designed. The coupling efficiency of the LP 01 – LP 11 mode coupler is over 80%, and that of the LP 01 – LP 21 mode coupler is over 50%. The simulation results show that the sensitivity of the LP 11   mode and the LP 21 mode increases by approximately 330% and 360%, respectively, using the intensity modulation (n = 1.33–1.38, 430–580 nm); the resolution of the refractive indices of our sensor, using the LP 11 mode ( LP 21 mode), is 2.6 × 10 − 4 RIU ( 2.4 × 10 − 4 RIU). The higher sensitivity and resolution of our presented fiber SPR sensor containing a visible MSC make it a promising candidate for the measurement of refractive indices. [ABSTRACT FROM AUTHOR]