A surface plasmon resonance sensor based on doublesided polished microstructured optical fiber with hollow core is put forward for refractive index sensing. Two gold films parallel to each other attached to the polished surface act as microfluidic sensing channels for the analyte. The artificially introduced air hole can facilitate the phase matching between the core mode and the plasmon mode. The sensitivities of the proposed sensor are investigated by the wavelength, amplitude and phase interrogation methods when the analyte refractive index increases from 1.33 to 1.34. In contrast to the D-shaped design, the double-sided polished structure demonstrates narrower resonance spectral width and greater phase sensitivity. Moreover, the numerical results indicate that the proposed sensor shows a good stability in the fabrication tolerances of ±5% of the thickness of gold film and the depth of polishing, respectively. Index Terms-Fiber optics sensors, surface plasmon resonance, microstructured optical fiber, refractive index sensors. I. INTRODUCTION S URFACE plasmon resonance (SPR) is the excitation of the surface plasmon coupled with the oscillations of free electron density between the metal and dielectric [1]-[5].

We demonstrate a sensitivity-tunable temperature SPR sensor based on side-opening grapefruit fiber. The opening sections of the fiber are coated with gold layer and then filled with a liquid mixture of ethanol and chloroform as the sensing medium. The variation of the temperature will lead to different coupling efficiencies between the core-guided mode and the plasmonic mode, and then resulting in the change of loss spectra of the fiber that will be detected. Simulation results indicate that the temperature sensitivity of the sensor is 19.9 nm/°C at 10°C when the volume fraction of ethanol in the mixture is 0.1. Moreover, by adjusting the volume fraction, the sensitivity of proposed sensor can achieve the upper limit for a certain temperature range without the excitation of higher order plasmonic modes.

We propose a concept of orthogonal-side polished microstructured optical fiber (MOF)-based surface plasmon resonance (SPR) sensor to implement the simultaneous sensing for two parameters. Two feasible structures, L-shaped MOF based and rectangular MOF based SPR sensors are investigated theoretically, which can support x-and y-polarized resonance peaks that can be used to measure and separate variations of the temperature and refractive index (RI). Our results show that the temperature coefficients (K Tx and K Ty ) are 8 pm/°C and 6 pm/°C, and the RI coefficients (K nx and K ny ) are 1470 nm/RIU and 1570 nm/RIU, for the L-shaped MOF-SPR sensor, while the K Tx and the K Ty are 10 pm/°C and 8 pm/°C, the K nx and K ny are 1460 nm/RIU and 1500 nm/RIU, for the rectangular MOF-based SPR sensor. Moreover, these coefficients can be further improved by choosing the appropriate structure parameters. The proposed SPR sensors with the advantages of simultaneously measuring two parameters and no need to be filled with the sensing media are expected to be more competitive in the MOF-based SPR sensor field.

We propose a concept of surface plasmon resonance sensor based on double-sided polished microstructured optical fiber coated with graphene-on-silver layers. The silver films on the polishing planes are covered with multilayer graphene which can prevent the oxidation of silver and enhance the adsorption of biomolecules. The sensing performance of the proposed sensors with polishing planes angle of 0°, 60°and 120°, are investigated by using both wavelength and amplitude interrogations. Our numerical results demonstrate that increasing the size of the air hole in the core area can effectively improve the wavelength and maximum amplitude sensitivities. Moreover, growing number layer of graphene can increase wavelength sensitivity, whereas decrease the maximum amplitude sensitivity.

A novel side-opening grapefruit fiber-based SPR sensor is designed to realize simultaneous measurement of refractive index (RI) and temperature. The open section of the grapefruit fiber is coated with a gold layer, which can support two main resonance peaks. The variations of RI and temperature can influence the coupling efficiency between core-guided mode and plasmon mode, thus lead to the two peaks shifts that can be used to determine the variations of RI and temperature. Simulation results demonstrate that the RI coefficients of Peak I and Peak II are 1400 nm/RIU and 226 nm/RIU, respectively. The temperature coefficients of Peak I and Peak II are 34 pm/°C and 527.2 pm/°C, respectively.