Research Of Micro-structure Fiber Liquid Refractive Index Sensor Based On Surface Plasmon Resonance

Optical fiber sensor has many characteristics,such as strong anti-interference,small size and so on,and is widely used in industrial,medical,military and aerospace fields.When it is transmitted at the interface between metal and dielectric,the light field is easy to excite the surface plasmon resonance effect.Air holes in microstructured optical fibers are used as microfluidic channels in liquid sensing.Combining microstructured optical fiber and surface plasmon resonance technology can obtain a sensor device with high sensitivity,wide detection range,small size and easy integration.Based on the theory of optical waveguide and surface plasma resonance effect,two kinds of microstructure optical fiber sensors with gold wire filled and microfluidic channels are designed.The sensing characteristics of citron type six-hole microstructure optical fiber coated with silver on the surface were experimentally studied.The main research contents are as follows:Firstly,a single-hole microfluidic channel microstructure optical fiber refractive index sensor based on gold wire filled is designed.A large air hole is introduced into the traditional hexagonal structure as a microfluidic channel filled with gold wire and liquid to be measured.The larger air hole is easily filled with liquid.When the surface plasma mode excited by the gold wire on the inner wall of the air hole is coupled with the core mode,the output spectrum corresponding to the core mode will show an obvious loss peak at the resonance wavelength.And the resonance wavelength is very sensitive to the refractive index of the liquid in the microfluidic channel,which effectively improves the sensitivity of the sensor.Through theoretical simulation and analysis,the sensitivities corresponding to the x and y polarization modes are 14306 nm / RIU and 13404 nm / RIU,respectively.Secondly,a three-hole microfluidic channel microstructure fiber refractive index sensor based on gold wire filled is designed.In the traditional regular hexagonal structure,three large air holes are used to replace the small air holes in a specific area to form a symmetrical structure.When filling the gold wire and the liquid to be measured,there is no need to specifically select an air hole.Any one of the three large air holes can be used as a microfluidic channel,which greatly reduces the difficulty of making the sensor.Through numerical research,it is found that the maximum sensitivity of the three-hole microfluidic channel microstructure fiber sensor based on gold wire is 16000 nm / RIU,and the sensor liquid refractive index can reach the detection range of 1.28-1.37.Finally,the refractive index sensing characteristics of citron-type six-hole microstructured optical fiber coated with silver film are experimentally studied.Silver film is deposited on the surface of the fiber by silver mirror reaction.The optical fiber is used as a sensitive element to build an experimental system for liquid refractive index sensor detection.The transmission spectra of sucrose solution with mass percentage from 0% to 45% are measured through experiments.The structural parameters of the microstructured optical fiber are obtained using the digital extraction technology of the microstructured fiber end face.The birefringence,mode field area and dispersion characteristics of the fiber are calculated by the finite element method.Through the analysis of the optical fiber performance and the transmission spectrum,the maximum sensitivity of the sensing system to the refractive index detection of sucrose solution is 11010.5 nm/RIU.It is verified that the silver coating on the surface of the microstructure optical fiber can excite the surface plasmon resonance and enhance the sensitivity of the sensor.