Photonic Crystal Fiber Biosensor Based On Birefringence

The composition of biological tissue is very complex,including many substances and structures.Most biomaterials exhibit the characteristics of high scattering and non-transparency to light,which makes it convenient for optical means to study the properties of biomaterials.Optical biosensor has many advantages,such as real-time,non-electromagnetic interference and fast response speed.With the help of waveguide,prism,photonic crystal fiber and other structures,optical biosensor has attracted much attention in the measurement of the refractive index of biomaterials.However,the small amount of biomaterial and small changes in refractive index place high demands on the sensitivity of biosensors.Therefore,researchers improve the sensitivity of biosensor by optimizing the design of the structure and applying different principles.However,the improvement of sensitivity sometimes makes the structure more complicated,which brings difficulty to the actual manufacturing.In this paper,a photonic crystal fiber with an asymmetric single-layer of air holes is designed.The asymmetry of the structure can produce birefringence,so that the target of high linearity,high sensitivity and low loss of the biosensor can be realized by using a simple structure.The Finite Element Method is mainly used for numerical simulation.Based on the finite element simulation software COMSOL Multiphysics,the influence of different geometric parameters and material parameters on the results is studied,so that the loss is the lowest and the detection effect is the best.The simulation results show that the photonic crystal fiber has the properties of high birefringence and wide wavelength single-mode transmission.On the other hand,the application of surface plasmon resonance enables the sensor to form an obvious resonance peak in a specific wavelength range,and the position of resonance wavelength is sensitive to the change of refractive index outside the metal layer.The wavelength shift occurs with the change of refractive index,and the variation of resonant wavelength is the primary physical quantity to analyze the performance of the sensor.The photonic crystal fiber designed in this paper has only one layer of air holes and the metal layer is located outside the photonic crystal fiber cladding,which greatly reduces the complexity of the structure and further reduces the difficulty of fabrication.By analyzing the structure of the sensor without birefringence,it is proved that the birefringence can improve the linearity and sensitivity of the sensor,and only a single resonant peak appears in a certain wavelength range,which improves the accuracy of the detection.The sensor designed in this paper has high sensitivity and good linearity to materials with refractive index change range from 1.4 to 1.44,and can reach a very small resolution,so it is suitable for the detection of biomaterials.