Design and optimization of multimode fiber sensor based on surface plasmon resonance

Using finite element method (FEM), a D-shaped multimode fiber sensor (MFS) based on surface plasmon resonance (SPR) was designed and optimized. Here the core radius of multimode fiber is 52.5μm. The simulations show that the resonant wavelengths of 45th~50th propagation modes and their wavelength redshifts due to the ambient refractive index change are all the same. Among the SPR spectrums for different modes, higher order mode will induce deeper notch and larger extinction ratio. By tracing the wavelength shift of the 45th mode, the MFS was optimized. The optimized MFS has 75μm residual fiber thickness and gold film coated on D-shaped multimode fiber. Its average sensitivity of 4989nm/RIU can be attained, which is much higher than 3150nm/RIU of the single mode fiber SPR sensor in the ref. [1].