Research On Surface Plasmon Resonance Sensing Characteristics Of Double Sides Polished Plastic Fiber

Refractive index(RI)measurement plays an important role in many fields such as medical diagnosis,environmental monitoring and food safety.The phenomenon of surface Plasmon resonance(SPR)is extremely sensitive to small RI changes at the interface between dielectric and metal.so it is used for RI sensing.Fiber optic SPR technology has been widely studied depending on the advantages such as strong anti-interference,no marking,real-time monitoring,high sensitivity and rapid response.At present,quartz fiber is applied extensively in preparing fiber SPR sensors.However the fabrication process is time-consuming and the fiber is easy to be damaged due to the physical property of quartz material.In contrast,plastic optical fiber(POF)possesses good toughness,soft texture and easy processing,which is superior to quartz fiber in these respects.In this paper,the SPR detector with double-side-polished structure fabricated with plastic optical fiber is proposed.Such apparatus realizes the enhanced sensing and the SPR sensing of double-parameter measurement.The main research contents in this dissertation are as follows:The enhanced SPR sensor is assembled with the POF which owns double-side-polished structure.The sensor is obtained by axisymmetrical polishing on both sides of the POF along the optical fiber and successive depositing nano gold membrane on each side of the polished areas.Thus SPR can be excited in such membranes.The structure increases numbers of SPR excitation at the same length of fiber device,which leads to an enhanced SPR effect.The experimental results show that the double-side-polished SPR device provides a better spectral contrast,full width at half maximum(FWHM)and a higher quality factor(FOM)compared with the single-side-polished POF device.It performs well even in dealing with the liquid of a high refractive index.When RI of the measured liquid is 1.42,the depth and length of double-side-polished plane are 200 μm and10 mm respectively,the sensitivity of the SPR sensor of the double-side-polished POF reach 4284.8 nm/RIU.Additionally,a two-parameter SPR sensor based on double sides polished POF is studied.In a view of the enhanced probing capability,another SPR sensing channel can be obtained in the transmission spectrum by preparing polydimethylsiloxane(PDMS)layer on one side of the probe.The high thermo-optical coefficient of PDMS ensures possibility of measuring temperature with this sensor.When RI or temperature varies,the two resonance peaks change separately.By virtue of monitoring the wavelength shifts of the two peaks,RI and temperature can therefore be measured simultaneously.Experimental results indicate the sensor gives a RI sensitivity of 1174 nm/RIU in RI range of 1.335 to 1.37 and a temperature sensitivity of –0.7 nm/°C in range of 30 to 80 °C.The results also demonstrate that the crosstalk between the two sensing channels of the sensor is negligible.