Characterisation Of Photonic Crystal Fibre Optic Sensors Based On The Vernier Effect

Compared with conventional optical fiber,photonic crystal optical fiber has the advantages of adjustable dispersion,low loss,good nonlinearity,and adjustable structure,which can be used as sensors for temperature,strain,refractive index,curvature,acceleration,etc.,and is widely used in aerospace,communication,and medical detection.When using photonic crystal fiber optic sensors for measurement of various parameters,high requirements are made on the sensor sensitivity,and this paper improves the sensitivity of the sensors by the vernier effect.The proposed vernier effect-based photonic crystal fiber sensor has higher sensitivity compared to the general sensor consisting of a single photonic crystal fiber.This article investigates the sensing properties of three photonic crystal fiber sensors with vernier effect,which can achieve accurate measurement of refractive index,pressure,and strain,respectively,The primary objective of the research is summarized as shown below:1.The characteristics of microstructured optical fibres are introduced,and the energy coupling principle of the dual-core photonic crystal fibre,the interference principle of the fibre Sagnac interferometer and the measurement principle of the vernier effect are investigated.2.Based on the vernier effect,a cascaded dual-coremicrostructured optical fiber refractive index sensor is proposed,three double-core photonic crystal fiber structures with different air hole diameters are designed,and the refractive index sensor sensitivity is investigated using beam propagation method and full vector finite element method.The results show that the structure with the smallest air hole diameter among the three structures has the highest sensitivity,and the closer the lengths of the dual-core photonic crystal fibers in the reference and sensing zones,the greater the sensitivity amplification of the sensor.3.Based on the vernier effect,a parallel type double Sagnac ring type Polarization-maintaining microstructured fibre optic pressure sensor is proposed,firstly,two Sagnac rings are made by fusing a single-mode fiber with a polarization-preserving photonic crystal fiber and encapsulated,then the two are connected in parallel to form a pressure sensor,the pressure properties of this sensor are verified,and the impact of temperature on the pressure sensor is investigated,the test results show that the sensor temperature-insensitive pressure measurements are possible.4.Based on the vernier effect,a Sagnac cascaded Fabry-Perot type Polarization-maintaining microstructured fiber optic strain sensor is proposed.The strain sensing test was also conducted,and the test results showed that the transmissiont spectrum of the sensor has both red-shift and blue-shift characteristics with the change of strain,which further improves the strain sensitivity of the sensor.