The Sensing Characteristics Of Hetero-core Fiber And Its Applications In Human Health Monitoring

As an application of optical fiber,optical fiber sensor is widely used in national defense,aerospace,environmental protection,biomedicine and other fields because of its small volume,anti-disturbance of electromagnetism,easy combination with clothing and strong affinity with organisms.In recent years,optical fiber sensors gradually come into people's lives and begin to emerge in the field of life and health monitoring.In this paper,the structure of hetero-core optical fiber is fabricated by fusing common single-mode fiber at both ends of a thin core fiber.The optical fiber with this structure has the advantages of low cost,simple structure,without complex demodulation technology,easy to manufacture,etc.The refractive index,static strain and dynamic strain sensing characteristics of the hetero-core optical fiber are explored,the sensing principle is analyzed theoretically,and verified by experiments;the pulse wave shape of the radial artery of the wrist and the respiratory rate during sleep were obtained and analyzed by using the micro-bending effect of the hetero-core fiber.The main contents are as follows:(1)This paper analyzes and summarizes the research background,dynamics and development trend of optical fiber sensors at home and abroad,as well as the application of optical fiber sensors in human health monitoring in recent years.the principle of refractive index sensor with different core fiber is introduced,and the experimental research is carried out.A reflective fiber sensor based on Michael interference is constructed by cascading a Faraday mirror at one end of the hetero-core fiber.In the glycerine solution with refractive index range of 1.3436-1.4015 and sensitivity of 155.148 nm / RIU;in the glucose solution of 0 g/dl~34 g/dl,the output spectrum changes linearly with the increase of concentration,and the linear correlation can reach 0.996;in the temperature range of0?~100?,the sensor is insensitive to temperature,which eliminates the problem of temperature crosstalk in the actual measurement process.(2)The static strain characteristics of hetero-core fiber are measured by using cantilever structure.In the experiment,the displacement of cantilever beam is controlled to produce different strain,and the strain is obtained by demodulating FBG signal.With the increase of strain,the transmission loss of different core fiber increases linearly.It is found that the dynamic strain frequency range of hetero-core fiber structure is 0 Hz~200 Hz.The measurement of dynamic signal lays a foundation for the application of different core fiberin pulse and breath monitoring.Meanwhile,the demodulation of static and dynamic signal strength greatly reduces the difficulty and cost of demodulation.(3)Based on the microbend effect,the application of hetero-core fiber in pulse and breath monitoring was explored.For pulse monitoring,a sensitization package structure is designed,and the influence of thin-core fiber with different length and core diameter on the sensor is studied.The experimental results show that when the sensor is fused into a thin core fiber with a diameter of 2.5 ?m and a length of 2 mm,the test effect is better.By comparing the commercial pulse sensor with the optical fiber sensor,the practicability of the optical fiber pulse sensor is verified.For respiratory monitoring,the characteristics of optical fiber transmission loss under different pressure are studied.The experimental results show that the output optical loss increases monotonously with the increase of pressure.A test system was set up to collect and analyze the respiratory signals of people during sleep,which proved the potential of hetero-core optical fiber in respiratory monitoring and its important significance in preventing a variety of diseases.