| With the rapid development of economy and science,it is important·to develop new practical and high-performance sensors in all industries.Among all kinds of optical sensors,the tapered sensor based on mode interference has become a hot research direction.Tapered fiber with a mature theoretical basis and preparation technology,can reduces the size of the sensor to millimeter or even micron and can realize high sensitivity and high reliability.Based on the principle of mode interference,two kinds of sensor structures with tapered fiber are proposed,which are S-tapered fiber sensor with larger core diameter and micro fiber sensor near the dispersion turning point with smaller core diameter.The advantages of the two structures are verified by comparing with traditional devices.The research contents of this paper are as follows:First of all,the application requirements of sensing devices in recent years are investigated,and different types of optical fiber sensors based on mode interference are introduced.Among these optical fiber sensors,the historical developme nt,frontier design and existing problems of S-type fiber,straight taper fiber and micro nano fiber based on dispersion turning point are introduced in detail.Secondly,the principle simulation,theoretical analysis and Simulation of tapered fiber are carried out.The transmission model of S-tapered fiber is constructed by using differential theory.The mode interference and energy coupling of S-tapered fiber are analyzed by beam propagation method.For micro fiber,the waveguide equation is given and the evanescent field energy ratio of micro fiber with different waist diameter is calculated to verify the sensing feasibility.Next,the preparation,analysis and performance testing of the fiber sensors are introduced.Firstly,the fabrication process of S-cone fiber is explored,and the influence factors of structure parameters are analyzed.A micro-channel sensing system for low concentration liquid environment is built.Sodium chloride solution with different concentration gradient is used to detect the refractive index sensing performance of S-tapered fiber.In order to study the influence of sensors'structural parameters on the refractive index sensitivity,the experiment is carried out on S-tapered fiber with different waist diameter and axial offset.What's more,choose the sensor with higher sensitivity and explore its temperature response characteristics.Further,the surface of the sensor was functionalized and used in the biosensor experiment to realize the specific recognition of ultra-low concentration of Ig G biomolecules.At last,in order to achieve a higher sensitivity in the environment with a low refractive index,the fiber sensor near the dispersion turning point is prepared.Firstly,the principle of dispersion turning point is introduced.Due to the strict conditions for the occurrence of dispersion turning point,it is necessary to have a systematical simulation on occurrence conditions of dispersion turning point.The main influencing factors of different fiber diameter,incident wavelength and external environment refractive index are analyzed.Based on the calculation of the micro fiber near the dispersion turning point,the refractive index sensitivity is up to 10~4nm/RIU.According to the theoretical simulation,ultra-high performance of this micro fiber structure based on dispersion turning point is fabricated experimentally.The sensitivity of the micro fiber at the dispersion turning point in the liquid environment is 3957.1 nm/RIU,which verifies its high sensitivity. |
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