Research On Optical Fiber Sensor Based On Surface Plasmon Resonance

A surface plasmon resonance(SPR)sensor based on optical fiber has the advantage of both optical fiber sensing technology and SPR technology,which means it has the features of SPR sensors,such as label-free detection,high sensitivity and real-time measurement,at the same time,it has abilities of resistance to electromagnetic interference,miniaturization and long-range measurement,just like an optical fiber sensor does.In this paper,a four-layer Kretschmann SPR modeling has been builded based on Maxwell electromagnetic waveguide and Fresnel multilayer reflection theory,with the help of MATLAB,structure parameters of the sensor such as the material and thickness of metal coating,thickness of bonding layer,incident angel,core diameter and the length of sensing area are obtained.According to the theory analysis,the phase difference of P and S polarized components in the reflected wave is almost linearly changing with the refractive index in its section of 1.333?1.336,thus the measurement formulae of the sensor is derived.By using a dual-frequency He-Ne laser head,an optical fiber SPR sensing system with common optical path structure based on heterodyne interferometry is presented,which can achieve higher measurement solution by means of phase detection method.Two sensors with the core diameter of 300?m and 400?m are manufactured by fixed-wheel polishing method,besides,three types of solutions including glycerin,saccharose and sodium chloride whose refractive index within 1.333?1.336 are prepared,therefore 6 calibration experiments are designed to verify the measurement repeatability.Comparison analysis of the experimental data reveals that the measurement results are consistent with the theoretical analysis,and the maximum error between this system and another measuring method is less than 1.3×10^-4.The proposed optical fiber SPR sensing system has a high measurement resolution of 10^-5level,which can be applied in many fields such as environment detection,food safety,drug screen,clinical medicine and so on.