Research Of High Sensitivity Long Period Grating Sensor Based On Photonic Crystal Fiber

Photonic crystal fiber has attracted many scientists' attention for several years since it was invented due to its flexible structure,fillable cladding,large mode field area,endless single mode,high birefringence and other characteristics.Currently,various optical fiber sensors have been developed based on photonic crystal fiber,so it has great research value and application potential.Compared with traditional long period fiber grating sensor,the long period fiber grating based on photonic crystal fiber has combined the advantages of photonic crystal fiber and long period fiber grating,it has high refractive index sensitivity,flexible structure design,and temperature insensitive property which can eliminate temperature cross-sensitivity problem in actual measurement.In addition,the cladding air holes of photonic crystal fiber provide a novel optical micro channel sensing platform.Therefore,long period grating based on photonic crystal fiber can be designed into a variety of new sensors by combining with nanometer functional materials.In this paper,the research content mainly focus on photonic crystal fiber long grating sensing technology to solve the problem of traditional long period fiber grating sensor can't satisfy the high sensitivity measurement request in biochemistry fields.And the sensor structure parameters have been constantly optimized to explore high sensitivity solutions by theoretical simulation.The completed distinctive and innovative research work includes:1.The dispersion characteristics of photonic crystal fiber were adjusted by optimizing the structural parameters to ensure photonic crystal fiber long period grating work near dispersion turning point,which has greatly improved its measurement sensitivity in low refractive index region(1.334?1.344).The obtained sensitivity indicator is 20490 nm/RIU,which has provided a solution for high sensitivity biosensor.2.The coupled cladding mode was limited in mode transition region by coating a high refractive index film on fiber surface for the first time based on the proposed dual-peak resonance photonic crystal fiber long period grating,and the refractive index sensitivity was further increased by more than two times(as high as 67600 nm/RIU).This sensitivity indicator has exceeded that of the currently reported photonic crystal fiber long period grating sensor.3.A highly sensitive electronically tunable photonic crystal fiber long period grating temperature sensor has been proposed based on electro-optical and thermo-optical effects of nematic liquid crystal E7.And the fluor crown FK51A was adopted to act as the background material of photonic crystal fiber.Research results show that the obtained highest sensitivity of 481.9 nm/? has exceed the liquid-crystal-filled optical fiber temperature sensor near dispersion clear point temperature(58?).In addition,the proposed sensor is tunable and reusable,and it has great potential to be used as thermo-optical switch,filter and voltage sensor.