Research On Refractive Index Sensing Characteristics Of Dual-core Photonic Crystal Fiber Based On Metal Film Coating

With the rapid development of optical fiber technology,optical fibers are increasingly used in the field of sensors due to their advantages of miniaturization,corrosion resistance and strong anti-interference ability.The flexible structure of photonic crystal fiber provides more freedom to regulate its performance.Metal coating is an effective method to introduce surface plasmon resonance（SPR）in the fiber.At present,the photonic crystal fiber sensor based on SPR has become a hot issue in the research of sensing.In this paper,two kinds of gold-coated dual-core photonic crystal fibers based on the theory of optical waveguide and SPR were designed.The refractive index sensing characteristics of the fiber were ana-lyzed.In addition,the sensing characteristics of a silver-coated photonic crystal fiber with two off-centered core were experimentally studied and the advantages of the off-centered core structure in sensing were analyzed.The main research contents are as follows:Firstly,a dual-core photonic crystal fiber with simple structure was proposed,and the core mode of the fiber is easy to leak to the fiber cladding.SPR was excited by depositing a gold film on the outer surface of the fiber.And the gold-coated fiber was used as a sensing channel for external detection.The finite element method was used to numerically analyze the SPR excitation,mode coupling and its sensitivity to the surrounding liquid refractive in-dex in the gold-coated dual-core photonic crystal fiber.Numerical simulation results show that the sensor based on dual-core photonic crystal fiber can achieve high sensitivity and high resolution detection of liquids with a refractive index ranging from 1.365-1.405.The maxi-mum sensitivity of the sensor can reach 11200 nm/RIU,and the corresponding resolution is8.9×10^-6RIU.Secondly,a symmetrical side-polished dual-core photonic crystal fiber sensor based on SPR was proposed.In order to increase the leakage of core mode,symmetrical polishing was carried out on the outer sides of two cores of the fiber.The detection of liquid refractive index was realized by depositing gold film on two side polishing surfaces to excite SPR.The results of numerical simulation show that the detection range of the liquid refractive index of the dual-core photonic crystal fiber sensor with symmetrical side polishing and gold film coating is larger.It can realize the detection of the large refractive index range of 1.30-1.42.The maximum wavelength sensitivity is 8000 nm/RIU,and the corresponding resolution is1.3×10^-5RIU.Finally,the liquid refractive index sensing characteristics of a silver-coated photonic crystal fiber with two off-centered core were studied.The self-made photonic crystal fiber with two off-centered core was chosen in the experiment.And the silver film was deposit-ed on the outer surface of the fiber through the silver mirror reaction.Because of the off-centered core structure of the optical fiber,the optical energy in the core can easily leak to the fiber cladding without side polishing.And then SPR occurred with the silver film on the outer surface of the fiber,so as to realize the detection of the liquid refractive index.The experimental results show that the sensor based on silver-coated photonic crystal fiber with two off-centered core can detect the refractive index in the range of 1.333-1.385.The maximum wavelength sensitivity is 10907.4 nm/RIU,and the corresponding resolution is1.8×10^-4RIU.