Research On U-shaped Plastic Optical Fiber Refractive Index Sensor

The refractive index is an important physical parameter of materials.By detecting the refractive index,we can understand the concentration,purity,temperature and other properties of the material and its changing state.Therefore,the refractive index sensing technology is widely used in medical treatment,biochemistry,and liquid level detection.And other fields.Optical fiber sensing has the advantages of anti-electromagnetic interference,rapid response,sensitivity and convenience,etc.,and can be applied to various complex environments.As the application range of optical fiber sensors increases,cost reduction,process simplification and higher sensitivity continue to require people to make new changes to optical fiber sensors.Among them,the plastic optical fiber sensor has many advantages such as large diameter,simple connection,good flexibility,easy processing,and signal transmission with lasers or LED lights.More and more researchers have begun to conduct research on plastic optical fiber sensors.In the future,plastic optical fiber sensors must have broad development and application space.This paper proposes a U-shaped double-side-throw structure plastic optical fiber refractive index sensor to achieve rapid,low-cost,and high-sensitivity detection of liquid refractive index.The sensing mechanism of the sensor is that the change of the refractive index will cause the change of the output optical power,and the change of the refractive index is proportional to the change of the output optical power.The purpose of detecting the change of the refractive index can be achieved by detecting the output optical power.The U-shaped structure can be made into a probe-type sensor head,and the double-side throw structure can make the light in the optical fiber fully contact with the test substance to achieve the purpose of improving the sensitivity.In this paper,using the geometric optics module of the simulation software,using the ray tracing method,the three-dimensional simulation model of the structure is established through the software,and the simulation analysis of the U-shaped double-side throwing structure is carried out.Compared with the previous theoretical simulation model,the simulation in this article adds a dimension,and I believe that more accurate simulation results can be obtained.This article first introduces the use of the software,simulates the U-shaped bending structure,and establishes the best bending radius.After that,the simulation research on the number and angle of the ray simulation is carried out.After determining these basic parameters,the plastic optical fiber with U-shaped double-side polishing structure is simulated.In the simulation,the side polishing angle and polishing depth will affect the sensitivity of the device.Through the controlled variable method,the optimal polishing angle and polishing depth are determined.The best sensitivity is obtained when the bending radius is 5mm,the side polishing angle is 60°,and the polishing depth is 400 ?m.Pave the way for the following experiments.In this paper,after heating and bending the plastic optical fiber,it is polished and made into a U-shaped double-side polished structure,made into a sensor head,equipped with a refractive index solution and measured.Through experiments,it is found that the polishing angle and polishing depth of the double-side polishing structure will affect the sensitivity of the sensor.Through optimization,when the bending radius is 3 mm,the polishing depth is 400 ? m,and the polishing angle is 60°,a sensitivity of 1541 %/RIU can be obtained in the refractive index range of 1.33 to1.39,and a good linear sensing response is shown.The influence of temperature at the end of this article.Due to the thermo-optical effect of the plastic optical fiber and the measured liquid,the plastic optical fiber refractive index sensor will be affected by temperature changes.The change of ambient temperature will cause the deviation of the sensor's refractive index measurement,which directly affects the temperature of the sensor.stability.Therefore,it is necessary to analyze the influence of temperature response characteristics on the refractive index detection of the U-shaped double-side throw structure plastic optical fiber refractive index sensor.The temperature is controlled by the heating platform,and the response of the sensor temperature is tested in the temperature range of 20 ? to 50 ?.Finally,a temperature compensation method is given.The temperature compensation method can be used to reduce the measurement error caused by the temperature change of the sensor.