| At present,the combination of taper fiber structure and functional materials with special physical properties to improve the performance of optical fiber devices is one of the hot research directions of optical fiber devices.The tapered fiber,with its unique tapered "leakage window",the light interact with external environment can be greatly heightened,and has the characteristics of strong evanescent wave,small size and high sensitivity to changes in the external environment.As a kind of special functional material,liquid crystal is widely used in the field of electronic display and new optical waveguide devices due to its strong electro-optic effect,high dielectric anisotropy and unique optical properties.The transmission characteristics and sensing characteristics of the taper fiber and the liquid crystal are studied,which has guiding significance for the research of the structure miniaturization,function diversification and integration of the new fiber devices.In this paper,the taper fiber is placed in a traditional liquid crystal cell filled with nematic liquid crystal,and the output light power of the liquid crystal tapered fiber is controlled by changing the magnitude of the applied voltage on the liquid crystal cell.This electronically controlled optical fiber device has potential value in sensing and optical switch applications.The main research contents of this paper are as follows:1.Experimental material selection and device preparation.First,the material selection,preparation process and device packaging of the experiment are introduced,and the related technologies and precautions in the preparation process of the device are analyzed.The tapering technology of the tapered fiber is introduced emphatically.The size of the tapered fiber is measured with a microscope,and the relationship between the speed of the stepping motor,the hydrogen quantity and the diameter of the tapered fiber waist and the length of the tapered fiber are obtained.2.Simulation and experimental research on the switching characteristics of liquid crystal tapered fiber.Geometric modeling and simulation of tapered fiber with the Beam Prop module of the waveguide simulation software Rsoft.The relationship between the output light energy and the geometric size of the tapered fiber is solved with the beam propagation method,and the structure parameters of the tapered fiber required for the optical switch experiment were selected and optimized.Then,by building a liquid crystal tapered fiber switch test platform,the device has a certain extinction ratio measured by the experiment,and the relationship between the extinction ratio and the magnitude of the applied voltage,frequency,the diameter and the length of the tapered fiber waist is studied.Theoretically analyzed and calculated the switching time of the device.Point out the improvement direction of the experiment by comparing the simulation results with the experimental results.3.Simulation and experimental research on the sensing characteristics of liquid crystal tapered optical fiber.Firstly,through geometric modeling and simulation,the sensitivity of tapered fibers with different structure sizes to changes in the external environment is analyzed,and the structure size of tapered fibers required for the experiment is selected and optimized.Then the experiment proved the electrical control output optical power characteristics of the tapered fiber,and the linear fitting equation of the applied voltage and the output optical power of the device was obtained.Analyzed the repeatability of the device by boosting and stepping down.The influence of factors such as the diameter of the waist of the tapered fiber,the length of the waist,the input light power and the voltage frequency on the sensing characteristics of the device is analyzed.It is proposed to calibrate the output optical power with a standard refractive index liquid to achieve the purpose of refractive index sensing. |
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