Design Of SPR Refractive Index Sensor Based On Photonic Quasicrystal Fiber

Surface plasmon resonance（SPR）is an optical phenomenon,which refers to the process of free electron oscillation coupling of electromagnetic wave at the interface between metal and medium.SPR refractive index sensor based on this principle is widely used in the field of refractive index detection.Among them,the SPR refractive index sensor based on photonic quasi-crystal fiber（PQF）is a new kind of micro-structure optical fiber sensor in recent years.Photonic quasi-crystal fiber has a unique two-dimensional quasi-crystal structure,which has rotational symmetry,but does not have translation periodicity,many defect modes and large degrees of freedom,which makes photonic quasi-crystal fiber have many unique excellent characteristics in dispersion Birefringence and mode field area show excellent properties superior to other optical fibers,which can be used to design high-sensitivity refractive index sensors.In this paper,three kinds of PQF-SPR refractive index sensors are designed based on the photonic quasi-crystal structure.The loss spectrum and structural parameters of the refractive index sensor are calculated and analyzed by using the finite element method and spectral analysis method,and the best performance index of the sensor is optimized,which provides a new idea for the Research of micro-structure optical fiber sensor in the future.Firstly,a new type of U-channel octal PQF-SPR sensor is proposed.The unique U-shaped structure significantly shortens the distance between the metal layer and the fiber core,achieves the effect of enhancing surface plasmon resonance,and improves the sensing performance of the sensor.In order to produce higher plasma frequency in the near infrared region,indium tin oxide（ITO）was coated on the bottom of the channel.The parameters of the sensor are optimized,including the thickness and width of the plasma coating material and the diameter of the air hole.In the range of refractive index of the medium to be measured from 1.306 to 1.386,the sensor has average wavelength sensitivity of12750nm/RIU,maximum wavelength sensitivity of 42000nm/RIU and amplitude sensitivity of 436.23RIU^-1.At the same time,the sensor shows excellent refractive index resolution,and its wavelength resolution is 2.38×10^-6RIU.Secondly,a partial core D-shaped ten fold PQF-SPR sensor is proposed.The partial core D-shaped structure shortens the distance between the metal layer and the fiber core and enhances the coupling effect between the core mode and SPP mode on the premise of retaining the original structure of the optical fiber to the greatest extent.Indium tin oxide is also selected as the surface plasmon material.By optimizing the structural parameters of the sensor,the sensor has an average wavelength sensitivity of 17800nm/RIU and a maximum wavelength sensitivity of 60000nm/RIU in the refractive index range of 1.35～1.40.The wavelength resolution of 1.67×10^-6RIU and the amplitude sensitivity of 594.241RIU^-1.The sensor has higher refractive index measurement accuracy.Finally,a PQF-SPR sensor with low refractive index region and wide refractive index measurement range is proposed.The sensor adopts D-shaped PQF structure and indium tin oxide as surface plasma material.Through the optimization of the sensor structure,it has good sensitivity in the range of low refractive index 1.1～1.38,which is far higher than the refractive index measurement range of other similar sensors.The average wavelength sensitivity in the measurement range can reach 3414nm/RIU,with the maximum wavelength sensitivity of 54000nm/RIU and The wavelength resolution of 1.85×10^-6RIU and the wide measurement range of the sensor will further expand its application field and have better application prospects.